ALBERT

Description: Dusty, star-forming galaxies have a critical role in the formation and evolution of massive galaxies in the Universe. Using deep far-infrared imaging in the range 100–500 μm obtained with the Herschel telescope, we investigate the dust-obscured star formation (SF) in the galaxy cluster XDCP J0044.0-2033 at z  = 1.58, the most massive cluster at z  〉 1.5, with a measured mass M 200  = 4.7 $^{+1.4}_{-0.9}$  10 14  M . We perform an analysis of the spectral energy distributions (SEDs) of 12 cluster members (5 spectroscopically confirmed) detected with ≥3 significance in the PACS maps, all ultraluminous infrared galaxies. The individual star formation rates (SFRs) lie in the range 155–824 M yr –1 , with dust temperatures of 24–35 K. We measure a strikingly high amount of SF in the cluster core, SFR (〈250 kpc) ≥ 1875 ± 158 M yr –1 , four times higher than the amount of SF in the cluster outskirts. This scenario is unprecedented in a galaxy cluster, showing for the first time a reversal of the SF–density relation at z ~ 1.6 in a massive cluster.

Description: Radiation fields emitted by O- and B-type stars or young stellar populations (SPs) are generally considered as significant central ionizing sources (CISs) of classic H  ii regions. In our previous studies, we showed that the inclusion of binary interactions in stellar population synthesis models can significantly increase the ultraviolet spectrum hardness and the number of ionizing photons of intermediate-age (IA) SPs (7 log( t /yr) 8). In this work, we present photoionization models of H  ii regions ionized by radiation fields emitted by IA SPs, including binary systems, and show that these fields are in theory possible candidates for significant CISs of classic H  ii regions. When radiation fields of IA SPs comprising binary systems are used as the CISs of classic H  ii regions, the theoretical strengths of a number of lines (such as [O  iii ] 4959 ' , [S  ii ] 6716 ' , etc.), which are weaker than observations, are increased; the border or selection-criterion lines between star-forming galaxies and active galactic nuclei (AGNs) in the diagnostic diagrams (for example, [N  ii ] 6583/Hα versus [O  iii ] 5007/Hβ), move into the region occupied originally by AGNs; and the He  ii 1640 line, observed in Lyman break and high-redshift gravitationally lensed galaxies, also can be produced.

Description: We reformulate rotation measure (RM) synthesis for data sets with discrete frequency channels and an arbitrary channel response function. The most commonly used version of the formalism by Brentjens & De Bruyn assumes a top-hat response function in wavelength squared, while real data sets can often be approximated better with a top-hat in frequency. We simulate mock data sets for various source geometries, using a top-hat response function in frequency, and we compare the quality of the RM spectra that are found with both formalisms. We include the response function of the simulated data to calculate exact RM spectra using our formalism. We show that the formalism by Brentjens & De Bruyn produces accurate results even if depolarization at the lowest frequencies in the observing band is severe. If RMs are large, our formalism reconstructs the emitted signal more accurately, with a higher amplitude and (in most cases) a narrower RM spread function. Our formalism can also detect sources with larger (absolute) RMs for a given sensitivity level of the observations.

Description: We present the results of an analysis of archival 21 cm (H i ) data of the blue compact dwarf galaxy Haro 11 (ESO 350-IG038). Observations were obtained at the Very Large Array, and the presence of a compact absorption feature near the optical centre of the galaxy has been detected. The central location of the absorption feature coincides with the centre of the continuum background of the galaxy, as well as with the location of knot B. The absorption feature yields an H i mass in the range of 3–10 x 10 8 M , corresponding to spin temperatures from 91 K to 200 K, respectively. The absence of H i seen in emission places an upper limit of 1.7 10 9 M on the mass. To our knowledge this is the first example of a dwarf galaxy that shows H i absorption from its own background continuum. The continuum emission from the galaxy is also used to determine star formation rates, namely 6.85 ± 0.05 M yr –1 (for a stellar mass range of 5 M 〈 M 〈 100 M ), or 32.8 ± 0.2 M yr –1 (for an extended range of 0.1 M 〈 M 〈 100 M ).

Description: We have shown analytically that shapes of incompressible stars could be prolate if appropriate meridional flows exist. Although this result is strictly valid only if either the meridional flow or the rotation is absent and the vorticity is associated uniformly with meridional flow, this implies that perpendicular forces against centrifugal and/or magnetic forces might play important roles within stars. A consequence of the presence of meridional flows might be to decrease stellar oblateness due to centrifugal and/or magnetic fields.

Description: ‘Conspiracy’ between the dark and the baryonic matter prohibits an unambiguous decomposition of disc galaxy rotation curves into the corresponding components. Several methods have been proposed to counter this difficulty, but their results are widely discrepant. In this paper, I revisit one of these methods, which relies on the relation between the halo density and the decrease of the bar pattern speed. The latter is routinely characterized by the ratio ${\cal R}$ of the corotation radius R CR to the bar length L b , ${\cal R} = R_{\rm CR}/L_{\rm b}$ . I use a set of N -body+SPH simulations, including subgrid physics, whose initial conditions cover a range of gas fractions and halo shapes. The models, by construction, have roughly the same azimuthally averaged circular velocity curve and halo density and they are all submaximal, i.e. according to previous works, they are expected to have all roughly the same ${\cal R}$ value, well outside the fast bar range (1.2 ± 0.2). Contrary to these expectations, however, these simulations end up having widely different ${\cal R}$ values, either within the fast bar range or well outside it. This shows that the ${\cal R}$ value cannot constrain the halo density, nor determine whether galactic discs are maximal or submaximal. I argue that this is true even for early-type discs (S0s and Sas).

Description: Stellar differential rotation can be separated into two main regimes: solar-like when the equator rotates faster than the poles and antisolar when the polar regions rotate faster than the equator. We investigate the transition between these two regimes with 3D numerical simulations of rotating spherical shells. We conduct a systematic parameter study which also includes models from different research groups. We find that the direction of the differential rotation is governed by the contribution of the Coriolis force in the force balance, independently of the model setup (presence of a magnetic field, thickness of the convective layer, density stratification). Rapidly rotating cases with a small Rossby number yield solar-like differential rotation, while weakly rotating models sustain antisolar differential rotation. Close to the transition, the two kinds of differential rotation are two possible bistable states. This study provides theoretical support for the existence of antisolar differential rotation in cool stars with large Rossby numbers.

Description: Millisecond pulsars (MSPs) are believed to be old neutron stars, formed via Type Ib/c core-collapse supernovae, which have subsequently been spun up to high rotation rates via accretion from a companion star in a highly circularized low-mass X-ray binary. The recent discoveries of Galactic field binary MSPs in eccentric orbits, and mass functions compatible with that expected for helium white dwarf companions, PSR J2234+06 and PSR J1946+3417, therefore challenge this picture. Here, we present a hypothesis for producing this new class of systems, where the MSPs are formed directly from a rotationally delayed accretion-induced collapse of a super-Chandrasekhar mass white dwarf. We compute the orbital properties of the MSPs formed in such events and demonstrate that our hypothesis can reproduce the observed eccentricities, masses and orbital periods of the white dwarfs, as well as forecasting the pulsar masses and velocities. Finally, we compare this hypothesis to a triple-star scenario.

Description: Sungrazing comets have always captured a lot of interest and curiosity among the general public as well as scientists since ancient times. The perihelion passage of comet C/2012 S1 (ISON) at the end of this year (on 2013 November 28) is an eagerly awaited event. In this work, we do a mathematical study to check whether meteoroids ejected from this comet during its journey around the Sun can produce spectacular meteor phenomena on Earth. Our calculations show that although the orbital elements of this comet are much more favourable than for most sungrazers to have its descending node near the Earth's orbit, even ejection velocities as high as 1 km s –1 do not induce sufficient nodal dispersion to bring meteoroids to Earth intersection during present times. A similar result applies to Newton's comet C/1680 V1 which has surprisingly similar orbital elements, although it is known to be a distinct comet from C/2012 S1. Our analysis also shows that for meteoroids ejected from all known sungrazing groups during recent epochs, only the Marsden family (with required ejection velocities of some hundreds of m s –1 ) can produce meteor phenomena during present times. In a broader sense, we indicate why we do not observe visually brilliant meteor showers from frequently observed sungrazers.

Description: We study the spatial distribution of the Fe 6.4 and 6.7 keV lines in the nuclear region of M82 using the Chandra archival data with a total exposure time of 500 ks. The deep exposure provides a significant detection of the Fe 6.4 keV line. Both the Fe 6.4 and 6.7 keV lines are diffuse emissions with similar spatial extent, but their morphology do not exactly follow each other. Assuming a thermal collisional-ionization-equilibrium (CIE) model, the fitted temperatures are around 5–6 keV and the Fe abundances are about 0.4–0.6 solar value. We also report the spectrum of a point source, which shows a strong Fe 6.7 keV line and is likely a supernova remnant or a superbubble. The fitted Fe abundance of the point source is 1.7 solar value. It implies that part of the iron may be depleted from the X-ray emitting gases as the predicted Fe abundance is about 5 times solar value if assuming a complete mixing. If this is a representative case of the Fe enrichment, a mild mass-loading of a factor of 3 will make the Fe abundance of the point source in agreement with that of the hot gas, which then implies that most of the hard X-ray continuum (2–8 keV) of M82 has a thermal origin. In addition, the Fe 6.4 keV line is consistent with the fluorescence emission irradiated by the hard photons from nuclear point sources.

Description: We consider how the radiation pressure of an accreting supermassive black hole (SMBH) affects the interstellar medium around it. Much of the gas originally surrounding the hole is swept into a shell with a characteristic radius somewhat larger than the black hole's radius of influence (~1–100 pc). The shell has a mass directly comparable to the ( M -) mass that the hole will eventually reach, and may have a complex topology. We suggest that outflows from the central SMBHs are halted by collisions with the shell, and that this is the origin of the warm absorber components frequently seen in active galactic nucleus (AGN) spectra. The shell may absorb and reradiate some of the black hole accretion luminosity at long wavelengths, implying both that the bolometric luminosities of some known AGN may have been underestimated, and that some accreting SMBH may have escaped detection entirely.

Description: The recently discovered asteroid 2013 LX 28 is in 1:1 resonance with Earth, but has large eccentricity and inclination. These lead to unusual dynamics in which the Kozai resonance plays a large role on long time-scales, while interaction with the terrestrial planets causes shorter term orbital changes. For the nominal orbit, an interaction with Venus changed the nature of the Kozai resonance and injected the asteroid into resonance with Earth. Despite frequent planetary encounters, the nominal orbit shows remarkable stability. Recovery prospects for this object are excellent, so that investigation of its remarkable properties should be able to proceed on a firmer observational base in future.

Description: While the deflection of light is achromatic in General Relativity, it is not always so in several new-physics models (e.g. certain quantum-gravity and string-inspired models, models with non-minimal photon–gravity coupling or with massive photon, etc.). We discuss how parameters of these models may be constrained by precise astrometry at different wavelengths. From published observations of the gravitational lens MG J2016+112, we obtain world-best limits on chromatic gravitational deflection of light (and the unique limit on the photon mass relevant for distance scales 〉Mpc). We also outline prospects for further improvement of these limits.

Description: The presence of silicon at the surface of the two Hyades DA white dwarfs WD 0421+162 and WD 0431+126 requires mechanisms that counteract the effects of the downward diffusion. Radiative levitation calculations indicate that the silicon abundance observed in WD 0431+126 corresponds to the abundance supported by radiative levitation. Detailed time-dependent diffusion calculations that take into account radiative levitation and accretion indicate that accretion with rates of $\dot{M}_{\rm {Si}} \lesssim 10^4$  g s –1 could also be present without disrupting the abundance supported by radiative levitation. In the case of WD 0421+162, accretion with a rate of $\dot{M}_{\rm {Si}} = 10^{5.1}$  g s –1 must be invoked, because its observed silicon abundance is larger than the abundance supported by radiative levitation. This accretion rate is lower than the accretion rate given by the accretion–diffusion model, because the radiative levitation slows down the downward diffusion of silicon. The silicon abundances observed in the two Hyades white dwarfs cannot be interpreted solely in terms of accretion. The interpretation of the silicon abundances must take into account the interplay between radiative levitation and accretion.

Description: Optical spectroscopy is used to confirm membership for eight low-mass candidates in the young Beta Pic moving group (BPMG) via their radial velocities, chromospheric activity and kinematic parallaxes. We searched for the presence of the Li i 6708 Å resonance feature and combined the results with literature measurements of other BPMG members to find the age-dependent lithium depletion boundary (LDB) – the luminosity at which Li remains unburned in a coeval group. The LDB age of the BPMG is 21 ± 4 Myr and insensitive to the choice of low-mass evolutionary models. This age is more precise, likely to be more accurate, and much older than that commonly assumed for the BPMG. As a result, substellar and planetary companions of BPMG members will be more massive than previously thought.

Description: We present a new programme for placing constraints on radial inhomogeneity in a dark-energy-dominated universe. We introduce a new measure to quantify violations of the Copernican principle. Any violation of this principle would interfere with our interpretation of any dark-energy evolution. In particular, we find that current observations place reasonably tight constraints on possible late-time violations of the Copernican principle: the allowed area in the parameter space of amplitude and scale of a spherical inhomogeneity around the observer has to be reduced by a factor of 3 so as to confirm the Copernican principle. Then, by marginalizing over possible radial inhomogeneity we provide the first constraints on the cosmological constant which are free of the homogeneity prior prevalent in cosmology.

Description: We present optical and X-ray observations of two tidally distorted, extremely low-mass white dwarfs (WDs) with massive companions. There is no evidence of neutron stars in our Chandra and XMM observations of these objects. SDSS J075141.18–014120.9 (J0751) is an eclipsing double WD binary containing a 0.19 M WD with a 0.97 M companion in a 1.9 h orbit. J0751 becomes the fifth eclipsing double WD system currently known. SDSS J174140.49+652638.7 (J1741) is another binary containing a 0.17 M WD with an unseen M  ≥ 1.11 M WD companion in a 1.5-h orbit. With a mass ratio of 0.1, J1741 will have stable mass transfer through an accretion disc and turn into an interacting AM Canum Venaticorum (AM CVn) system in the next 160 Myr. With a mass ratio of 0.2, J0751 is likely to follow a similar evolutionary path. These are the first known AM CVn progenitor binary systems and they provide important constraints on the initial conditions for AM CVn. Theoretical studies suggest that both J0751 and J1741 may create thermonuclear supernovae in ~10 8  yr, either .Ia or Ia. Such explosions can account for ~1 per cent of the Type Ia supernova rate.

Description: The X-ray spectrum of the Galactic X-ray binary V4641 Sgr in outburst has been found to exhibit a remarkably broad emission feature above 4 keV, with inferred equivalent widths up to 2 keV. Such a feature was first detected during the X-ray flaring activity associated with the giant outburst that the source experienced in 1999 September. The extraordinarily large equivalent width line was then ascribed to reflection/reprocessing of fluorescent Fe emission within an extended optically thick outflow enshrouding the binary system as a result of a short-lived, super-Eddington accretion episode. Making use of new and archival X-ray observations, we show here that a similar feature persists over four orders of magnitude in luminosity, down to Eddington ratios as low as log ( L X / L Edd ) ~= –4.5, where the existence of an optically thick envelope appears at odds with any viable accretion flow model. Possible interpretations for this highly unusual X-ray spectrum include a blend of Doppler-shifted/boosted Fe lines from unresolved X-ray jets (a la SS433), or, the first Galactic analogue of a blazar spectrum, where the 〉4 keV emission would correspond to the onset of the inverse Compton hump. This either requires a low-inclination angle of the jet with respect to the line of sight, in agreement with the estimates for the 1999 superluminal jet ( i jet  〈 10°). The fast variability of the feature, combined with the high orbital axis inclination (60° 〈  i orb  〈 71°), argue for a rapidly precessing accretion flow around V4641 Sgr, possibly leading to a transient microblazar behaviour.

Description: Modified Newtonian Dynamics (MOND) represents a phenomenological alternative to dark matter (DM) for the missing mass problem in galaxies and clusters of galaxies. We analyse the central regions of a local sample of ~220 early-type galaxies from the ATLAS 3D survey, to see if the data can be reproduced without recourse to DM. We estimate dynamical masses in the MOND context through Jeans analysis and compare to ATLAS 3D stellar masses from stellar population synthesis. We find that the observed stellar mass–velocity dispersion relation is steeper than expected assuming MOND with a fixed stellar initial mass function (IMF) and a standard value for the acceleration parameter a 0 . Turning from the space of observables to model space (a) fixing the IMF, a universal value for a 0 cannot be fitted, while, (b) fixing a 0 and leaving the IMF free to vary, we find that it is ‘lighter’ (Chabrier like) for low-dispersion galaxies and ‘heavier’ (Salpeter like) for high dispersions. This MOND-based trend matches inferences from Newtonian dynamics with DM and from the detailed analysis of spectral absorption lines, adding to the converging lines of evidence for a systematically varying IMF.

Description: An earlier study of the complex jet of 3C 380 by Papageorgiou et al. revealed total intensity and polarization structure associated with a bright knot K1 about 0.7 arcsec from the core that was reminiscent of that expected for a conical shock wave. In this new study, 1.42, 1.66 and 4.99 GHz total intensity, polarization and Faraday rotation images are presented and analysed. These images were derived from observations with the Very Long Baseline Array plus one antenna of the Very Large Array, obtained in 2006 March. These new images confirm the overall magnetic field structure of the knot K1 indicated in the earlier observations. In addition, a clear Faraday rotation gradient has been detected across the jet, extending roughly from 10 to 30 mas (70–200 pc) along the jet from the core (a radial distance of approximately two beamwidths). The gradient spans roughly 3.5 beamwidths in the transverse direction, and the difference in the rotation measures on either side of the jet is 4–5, demonstrating that the detection of the gradient is firm. We interpret this transverse Faraday rotation gradient as reflecting systematic variation of the line-of-sight component of a helical or toroidal magnetic field ( B ) associated with the jet of 3C 380. These results provide evidence that the helical field arising due to the joint action of the rotation of the central black hole and its accretion disc and the jet outflow can survive to distances of hundreds of parsecs from the central engine.

Description: The tidal disruption event (TDE) PS1-10jh lacked strong Balmer lines but showed strong, broad He ii emission both before maximum light and for at least eight months thereafter. Gezari et al. interpreted this as evidence for the disruption of a rare hydrogen-deficient star. However, Guillochon et al. have argued instead that the disrupted star was a normal main-sequence star and that the strength of the He ii emission compared with the Balmer lines is a result the emission being similar to the broad-line region (BLR) of an active galactic nucleus (AGN), but lacking the outer, lower ionization BLR gas. We show that the profile of He ii 4686 in PS1-10jh is similar to the blueshifted profiles of high-ionization lines in AGNs. We find an He ii 4686/Hα ratio for PS1-10jh of ~3.7. We show that both the high-velocity gas of the inner BLR of normal AGNs and the spectra of Type II-P supernovae right after shock break out also produce very high He ii 4686/Hα ratios. A high He ii 4686/Hα ratio can thus be produced with a solar H/He abundance ratio. We demonstrate from photoionization modelling that the estimated He ii 4686/Hα ratio can be produced with a BLR truncated before the He ++ Strömgren length if the density is ~10 11 cm –3 . The similarity of the He ii 4686 emission in PS1-10jh to the emission from the inner BLRs of AGNs supports the idea that the emission after a TDE event is similar to that of normal AGNs.

Description: Many nearby main-sequence stars have been searched for debris using the far-infrared Herschel satellite, within the DEBRIS, DUNES and Guaranteed-Time Key Projects. We discuss here 11 stars of spectral types A–M where the stellar inclination is known and can be compared to that of the spatially resolved dust belts. The discs are found to be well aligned with the stellar equators, as in the case of the Sun's Kuiper belt, and unlike many close-in planets seen in transit surveys. The ensemble of stars here can be fitted with a star–disc tilt of 10°. These results suggest that proposed mechanisms for tilting the star or disc in fact operate rarely. A few systems also host imaged planets, whose orbits at tens of au are aligned with the debris discs, contrary to what might be expected in models where external perturbers induce tilts.

Description: Pulsar glitches are sudden increases in the spin frequency of an otherwise steadily spinning down neutron star. These events are thought to represent a direct probe of the dynamics of the superfluid interior of the star. However glitches can differ significantly from one another, not only in size and frequency, but also in the post-glitch response of the star. Some appear as simple steps in frequency, while others also display an increase in spin-down rate after the glitch. Others still show several exponentially relaxing components in the post-glitch recovery. We show that if glitches are indeed due to large-scale unpinning of superfluid vortices, the different regions in which this occurs and respective time-scales on which they recouple can lead to the various observed signatures. Furthermore, we show that this framework naturally accounts for the peculiar relaxations of glitches in Anomalous X-ray Pulsars.

Description: We present new 10.4 m-GTC/OSIRIS spectroscopic observations of the black hole X-ray binary XTE J1118+480 that confirm the orbital period decay at $\dot{P}=-1.90\pm 0.57$ ms yr –1 . This corresponds to a period change of –0.88 ± 0.27 μs per orbital cycle. We have also collected observations of the black hole X-ray binary A0620–00 to derive an orbital period derivative of $\dot{P}=-0.60\pm 0.08$ ms yr –1 (–0.53 ± 0.07 μs/cycle). Angular momentum losses due to gravitational radiation are unable to explain these large orbital decays in these two short-period black hole binaries. The orbital period decay measured in A0620–00 is very marginally consistent with the predictions of conventional models including magnetic braking, although significant mass-loss ( $\dot{M}_{\rm BH} / \dot{M}_2 \le 20$  per cent) from the system is required. The fast spiral-in of the star in XTE J1118+480, however, does not fit any standard model and may be driven by magnetic braking under extremely high magnetic fields and/or may require an unknown process or non-standard theories of gravity. This result may suggest an evolutionary sequence in which the orbital period decay begins to speed up as the orbital period decreases. This scenario may have an impact on the evolution and lifetime of black hole X-ray binaries.

Description: Fomalhaut is one of the most interesting and well-studied nearby stars, hosting at least one planet, a spectacular debris ring and two distant low-mass stellar companions (TW PsA and LP 876–10, a.k.a. Fomalhaut B and C). We observed both companions with Herschel , and while no disc was detected around the secondary, TW PsA, we have discovered the second debris disc in the Fomalhaut system, around LP 876–10. This detection is only the second case of two debris discs seen in a multiple system, both of which are relatively wide (3000 au for HD 223352/40 and 158 kau [0.77 pc] for Fomalhaut/LP 876–10). The disc is cool (24 K) and relatively bright, with a fractional luminosity L disc / L *  = 1.2 10 –4 , and represents the rare observation of a debris disc around an M dwarf. Further work should attempt to find if the presence of two discs in the Fomalhaut system is coincidental, perhaps simply due to the relatively young system age of 440 Myr, or if the stellar components have dynamically interacted and the system is even more complex than it currently appears.

Description: Recently, general relations among the quadrupole moment ( Q ), the moment of inertia ( I ) and the tidal deformability (Love number) of a neutron star were shown to exist. They are nearly independent of the nuclear matter equation of state and would be of great aid in extracting parameters from observed gravitational waves and in testing general relativity. These relations, however, do not account for strong magnetic fields. We consider this problem by studying the effect of a strong magnetic field on slowly rotating relativistic neutron stars and show that, for simple magnetic field configurations that are purely poloidal or purely toroidal, the relation between Q and I is again nearly universal. However, different magnetic field geometries lead to different I – Q relations, and, in the case of a more realistic twisted-torus magnetic field configuration, the relation depends significantly on the equation of state, losing its universality. I –Love– Q relations must thus be used with very great care, since universality is lost for stars with long spin periods, i.e. P 10 s, and strong magnetic fields, i.e. B 10 12 G.

Description: The luminosities of ultraluminous X-ray sources (ULXs) require an exotic solution with either supercritical accretion modes on to stellar-mass black holes or subcritical accretion on to intermediate-mass black holes (IMBHs) being invoked. Discriminating between the two is non-trivial due to the present lack of a direct mass measurement. A key expectation of the supercritical mode of accretion is the presence of powerful radiatively driven winds. Here we analyse XMM–Newton data from NGC 5408 X-1 and NGC 6946 X-1 and find that strong soft residuals present in the X-ray spectra can be reconciled with broadened, blueshifted absorption by a partially ionized, optically thin phase of this wind. We derive initial values for the physical parameters of the wind; we also discuss other possible origins for the observed features.

Description: We present early photometric and spectroscopic observations of SN 2013ej, a bright Type IIP supernova (SN) in M74. SN 2013ej is one of the closest SNe ever discovered. The available archive images and the early discovery help to constrain the nature of its progenitor. The earliest detection of this explosion was on 2013 July 24.125 ut and our spectroscopic monitoring with the FLOYDS spectrographs began on July 27.7 ut , continuing almost daily for two weeks. Daily optical photometric monitoring was achieved with the 1 m telescopes of the Las Cumbres Observatory Global Telescope (LCOGT) network, and was complemented by UV data from Swift and near-infrared spectra from Public ESO Spectroscopic Survey of Transient Objects and Infrared Telescope Facility. The data from our monitoring campaign show that SN 2013ej experienced a 10 d rise before entering into a well-defined plateau phase. This unusually long rise time for a Type IIP has been seen previously in SN 2006bp and SN 2009bw. A relatively rare strong absorption blueward of Hα is present since our earliest spectrum. We identify this feature as Si ii , rather than high-velocity Hα as sometimes reported in the literature.

Description: Atoms and molecules, and in particular CO, are important coolants during the evolution of interstellar star-forming gas clouds. The presence of dust grains, which allow many chemical reactions to occur on their surfaces, strongly impacts the chemical composition of a cloud. At low temperatures, dust grains can lock up species from the gas phase which freeze out and form ices. In this sense, dust can deplete important coolants. Our aim is to understand the effects of freeze-out on the thermal balance and the evolution of a gravitationally bound molecular cloud. For this purpose, we perform 3D hydrodynamical simulations with the adaptive mesh code flash . We simulate a gravitationally unstable cloud under two different conditions, with and without grain surface chemistry. We let the cloud evolve until one free-fall time is reached and track the thermal evolution and the abundances of species during this time. We see that at a number density of 10 4  cm –3 most of the CO molecules are frozen on dust grains in the run with grain surface chemistry, thereby depriving the most important coolant. As a consequence, we find that the temperature of the gas rises up to ~25 K. The temperature drops once again due to gas–grain collisional cooling when the density reaches a few 10 4  cm –3 . We conclude that grain surface chemistry not only affects the chemical abundances in the gas phase, but also leaves a distinct imprint in the thermal evolution that impacts the fragmentation of a star-forming cloud. As a final step, we present the equation of state of a collapsing molecular cloud that has grain surface chemistry included.

Description: The eclipsing white dwarf plus main-sequence binary NN Serpentis provides one of the most convincing cases for the existence of circumbinary planets around evolved binaries. The exquisite timing precision provided by the deep eclipse of the white dwarf has revealed complex variations in the eclipse arrival times over the last few decades. These variations have been interpreted as the influence of two planets in orbit around the binary. Recent studies have proved that such a system is dynamically stable over the current lifetime of the binary. However, the existence of such planets is by no means proven and several alternative mechanisms have been proposed that could drive similar variations. One of these is apsidal precession, which causes the eclipse times of eccentric binaries to vary sinusoidally on many year time-scales. In this Letter, we present timing data for the secondary eclipse of NN Ser and show that they follow the same trend seen in the primary eclipse times, ruling out apsidal precession as a possible cause for the variations. This result leaves no alternatives to the planetary interpretation for the observed period variations, although we still do not consider their existence as proven. Our data limit the eccentricity of NN Ser to e  〈 10 –3 . We also detect a 3.3 ± 1.0 s delay in the arrival times of the secondary eclipses relative to the best planetary model. This delay is consistent with the expected 2.84 ± 0.04 s Rømer delay of the binary, and is the first time this effect has been detected in a white dwarf plus M dwarf system.

Description: We present Hα images of an ionized nebula surrounding the M2-5Ia red supergiant (RSG) W26 in the massive star cluster Westerlund 1. The nebula consists of a circumstellar shell or ring ~0.1 pc in diameter and a triangular nebula ~0.2 pc from the star that in high-resolution Hubble Space Telescope images shows a complex filamentary structure. The excitation mechanism of both regions is unclear since RSGs are too cool to produce ionizing photons and we consider various possibilities. The presence of the nebula, high stellar luminosity and spectral variability suggests that W26 is a highly evolved RSG experiencing extreme levels of mass-loss. As the only known example of an ionized nebula surrounding an RSG W26 deserves further attention to improve our understanding of the final evolutionary stages of massive stars.

Description: We propose a possibility of ultrarelativistic electromagnetic counterparts to gravitational waves from binary neutron star mergers at nearly all the viewing angles. Our proposed mechanism relies on the merger-shock propagation accelerating a smaller mass in the outer parts of the neutron star crust to a larger Lorentz factor with smaller energy ~10 47 –1 erg. This mechanism is difficult to resolve by current 3D numerical simulations. The outflows emit synchrotron flares for seconds to days by shocking the ambient medium. Ultrarelativistic flares shine at an early time and in high-energy bands, potentially detectable by current X-ray to radio instruments, such as Swift XRT and Pan-STARRS, and even in low ambient density ~10 –2 cm –3 by EVLA. The flares probe the merger position and time, and the merger types as black hole–neutron star outflows would be non-/mildly relativistic.

Description: We present Herschel photometry and spectroscopy, carried out as part of the Herschel ultraluminous infrared galaxy (ULIRG) survey, and a model for the infrared to submillimetre emission of the ULIRG IRAS 08572+3915. This source shows one of the deepest known silicate absorption features and no polycyclic aromatic hydrocarbon emission. The model suggests that this object is powered by an active galactic nucleus (AGN) with a fairly smooth torus viewed almost edge-on and a very young starburst. According to our model, the AGN contributes about 90 per cent of the total luminosity of 1.1 x 10 13 L , which is about a factor of 5 higher than previous estimates. The large correction of the luminosity is due to the anisotropy of the emission of the best-fitting torus. Similar corrections may be necessary for other local and high- z analogues. This correction implies that IRAS 08572+3915 at a redshift of 0.058 35 may be the nearest hyperluminous infrared galaxy and probably the most luminous infrared galaxy in the local ( z  〈 0.2) Universe. IRAS 08572+3915 shows a low ratio of [C ii ] to IR luminosity (log L [C ii ] / L IR 〈 –3.8) and a [O i ]63 μm to [C ii ]158 μm line ratio of about 1 that supports the model presented in this Letter.

Description: We estimate the potential contribution of M  〈 10 9 M dwarf galaxies to the reionization and early metal enrichment of the Milky Way environment, or circum-Galactic medium. Our approach is to use the observed properties of ancient stars (12 Gyr old) measured in nearby dwarf galaxies to characterize the star formation at high z . We use a merger-tree model for the build-up of the Milky Way, which self-consistently accounts for feedback processes, and which is calibrated to match the present-day properties of the Galaxy and its dwarf satellites. We show that the high- z analogues of nearby dwarf galaxies can produce the bulk of ionizing radiation (〉80 per cent) required to reionize the Milky Way environment. Our fiducial model shows that the gaseous environment can be 50 per cent reionized at z 8 by galaxies with 10 7 M  ≤  M  〈 10 8 M . At later times, radiative feedback stops the star formation in these small systems, and reionization is completed by more massive dwarf galaxies by z rei = 6.4 ± 0.5. The metals ejected by supernova-driven outflows from M  〈 10 9 M dwarf galaxies almost uniformly fill the Milky Way environment by z 5, enriching it to Z 2 10 –2 Z . At z 2, these early metals are still found to represent the 50 per cent of the total mass of heavy elements in the circum-Galactic medium.

Description: We propose that the abundance anomalies of proton-capture elements in globular clusters, such as the C-N, Na-O, Mg-Al and Na-F anticorrelations, were produced by supermassive stars with M ~ 10 4 M . Such stars could form in the runaway collisions of massive stars that sank to the cluster centre as a result of dynamical friction, or via the direct monolithic collapse of the low-metallicity gas cloud from which the cluster formed. To explain the observed abundance anomalies, we assume that the supermassive stars had lost significant parts of their initial masses when only a small mass fraction of hydrogen, X ~ 0.15, was transformed into helium. We speculate that the required mass-loss might be caused by the super-Eddington radiation continuum-driven stellar wind or by the diffusive mode of the Jeans instability.

Description: We estimate an empirical lower limit for the fraction of cosmic star formation that is triggered by minor mergers in the local Universe. Splitting the star formation budget by galaxy morphology, we find that early-type galaxies (ETGs) host ~14 per cent of the budget, while Sb/Sc galaxies host the bulk (~53 per cent) of the local star formation activity. Recent work indicates that star formation in nearby ETGs is driven by minor mergers, implying that at least ~14 per cent of local star formation is triggered by this process. A more accurate estimate can be derived by noting that an infalling satellite likely induces a larger starburst in a galaxy of ‘later’ morphological type, both due to higher availability of gas in the accreting galaxy and also because a bigger bulge better stabilizes the disc against star formation. This enables us to use the star formation in ETGs to estimate a lower limit for the fraction of star formation in late-type galaxies (LTGs) that is minor-merger-driven. Using a subsample of ETGs that is mass- and environment-matched to the LTGs (implying a similar infalling satellite population), we estimate this limit to be ~24 per cent. Thus, a lower limit for the fraction of cosmic star formation that is induced by minor mergers is ~35 per cent [14 per cent (ETGs) + 0.24 86 per cent (LTGs)]. The observed positive correlation between black hole and galaxy mass further implies that a similar fraction of black hole accretion may also be triggered by minor mergers. Detailed studies of minor-merger remnants are therefore essential, to quantify the role of this important process in driving stellar mass and black hole growth in the local Universe.

Description: We propose that star formation (SF) is delayed relative to the inflow rate in rapidly accreting galaxies at very high redshift ( z  〉 2) because of the energy conveyed by the accreting gas. Accreting gas streams provide fuel for SF, but they stir the disc and increase turbulence above the usual levels compatible with gravitational instability, reducing the SF efficiency in the available gas. After the specific inflow rate has sufficiently decreased – typically at z  〈 3 – galaxies settle in a self-regulated regime with efficient SF. An analytic model shows that this interaction between infalling gas and young galaxies can significantly delay SF and maintain high gas fractions (〉40 per cent) down to z 2, in contrast to other galaxy formation models. Idealized hydrodynamic simulations of infalling gas streams on to primordial galaxies confirm the efficient energetic coupling at z  〉 2 and suggest that this effect is largely under-resolved in existing cosmological simulations.

Description: We estimate the parameters of the Kennicutt–Schmidt (KS) relationship, linking the star formation rate ( SFR ) to the molecular gas surface density ( mol ), in the Survey Toward Infrared-Bright Nearby Galaxies sample of nearby disc galaxies using a hierarchical Bayesian method. This method rigorously treats measurement uncertainties, and provides accurate parameter estimates for both individual galaxies and the entire population. Assuming standard conversion factors to estimate SFR and mol from the observations, we find that the KS parameters vary between galaxies, indicating that no universal relationship holds for all galaxies. The KS slope of the whole population is 0.76, with the 2 range extending from 0.58 to 0.94. These results imply that the molecular gas depletion time is not constant, but varies from galaxy-to-galaxy, and increases with the molecular gas surface density. Therefore, other galactic properties besides just mol affect SFR , such as the gas fraction or stellar mass. The non-universality of the KS relationship indicates that a comprehensive theory of star formation must take into account additional physical processes that may vary from galaxy to galaxy.

Description: We argue that the properties of the Type Ia supernova (SN Ia) SN 2011fe can be best explained within the frame of the core-degenerate (CD) scenario. In the CD scenario, a white dwarf (WD) merges with the core of an asymptotic giant branch (AGB) star and forms a rapidly rotating WD, with a mass close to and above the critical mass for explosion. Rapid rotation prevents immediate collapse and/or explosion. Spinning down over a time of 0-10 10 yr brings the WD to explosion. A very long delayed explosion to post-crystallization phase, which lasts for about 2 10 9 yr, leads to the formation of a highly carbon-enriched outer layer. This can account for the carbon-rich composition of the fastest-moving ejecta of SN 2011fe. In reaching the conclusion that the CD scenario best explains the observed properties of SN 2011fe, we consider both its specific properties, like a very compact exploding object and carbon-rich composition of the fastest-moving ejecta, and the general properties of SNe Ia.

Description: We discuss the effects of destruction of wide binaries in the nuclei of the lower mass giant elliptical galaxies. We show that the numbers of barium stars and extrinsic S stars should be dramatically reduced in these galaxies compared to what is seen in the largest elliptical galaxies. Given that the extrinsic S stars show strong Wing–Ford band and Na i D absorption, we argue that the recent claims of different initial mass functions from the most massive elliptical galaxies versus lower mass ellipticals may be the result of extrinsic S stars, rather than bottom-heavy initial mass function.

Description: Bursts of millisecond duration were recently discovered in the 1 GHz band. There is a strong evidence that they come from ~1 Gpc distances, which implies extraordinary high-brightness temperature. I propose that these bursts could be attributed to synchrotron maser emission from relativistic, magnetized shocks. At the onset of the magnetar flare, a strongly magnetized pulse is formed, which propagates away through the relativistic magnetar wind and eventually reaches the nebula inflated by the wind within the surrounding medium. I show that the observed radio bursts could be generated at shocks formed via the interaction of the magnetic pulse with the plasma within the nebula. The model predicts strong millisecond bursts in the TeV band, which could be observed even from distant galaxies.

Description: Over the last decade, warm dark matter (WDM) has been repeatedly proposed as an alternative scenario to the standard cold dark matter (CDM) one, potentially resolving several disagreements between the CDM model and observations on small scales. Here, we reconsider the most important CDM small-scale discrepancies in the light of recent observational constraints on WDM. As a result, we find that a conventional thermal (or thermal-like) WDM cosmology with a particle mass in agreement with Lyman α is nearly indistinguishable from CDM on the relevant scales and therefore fails to alleviate any of the small-scale problems. The reason for this failure is that the power spectrum of conventional WDM falls off too rapidly. To maintain WDM as a significantly different alternative to CDM, more evolved production mechanisms leading to multiple dark matter components or a gradually decreasing small-scale power spectrum have to be considered.

Description: Galactic open clusters do not survive long in the high-density regions of the inner Galactic disc. Inside the solar ring only 11 open clusters are known with ages older than 1 Gyr. We show here, basing on deep, high-quality photometry, that NGC 4337, contrary to earlier findings, is indeed an old open cluster. The cluster is located very close to the conspicuous star cluster Trumpler 20, as well misclassified in the past, and that has received so much attention in recent years. NGC 4337 shows a significant clump of He-burning stars which was not detected previously. Its beautiful colour–magnitude diagram is strikingly similar to the one of the classical old open clusters IC 4651, NGC 752, and NGC 3680, and this suggests similar age and composition. A spectroscopic study is much needed to confirm our findings. This, in turn, would also allow us to better define the inner disc radial abundance gradient and its temporal evolution. To this aim, a list of clump star candidates is provided.

Description: M-dwarfs demonstrate two types of activity: (1) strong (kilogauss) almost axisymmetric poloidal magnetic fields; and (2) considerably weaker non-axisymmetric fields, sometimes including a substantial toroidal component. Dynamo bistability has been proposed as an explanation. However, it is not straightforward to obtain such a bistability in dynamo models. On the other hand, the solar magnetic dipole at times of magnetic field inversion becomes transverse to the rotation axis, while the magnetic field becomes weaker at times far from that of inversion. Thus, the Sun resembles a star with the second type of activity. We suggest that M-dwarfs can have magnetic cycles, and that M-dwarfs with the second type of activity can just be stars observed at times of magnetic field inversion. Then the relative number of M-dwarfs with the second type of activity can be used in the framework of this model to determine parameters of stellar convection near the surface.

Description: Using parsec-resolution simulations of a typical galaxy merger, we study the triggering of starbursts by connecting the (inter-)galactic dynamics to the structure of the interstellar medium. The gravitational encounter between two galaxies enhances tidal compression over large volumes, which increases and modifies the turbulence, in particular its compressive mode with respect to the solenoidal one. This generates an excess of dense gas leading to intense star formation activity. Along the interaction, the compressive turbulence modifies the efficiency of gas-to-star conversion which, in the Schmidt–Kennicutt diagram, drives the galaxies from the sequence of discs to that of starbursts.

Description: We present Hubble Space Telescope ( HST ) imaging observations of the site of the Type-Ia supernova SN2011fe in the nearby galaxy M101, obtained about 1 yr prior to the event, in a narrow band centred on the He ii 4686 Å emission line. In a ‘single-degenerate’ progenitor scenario, the hard photon flux from an accreting white dwarf (WD), burning hydrogen on its surface over ~1 Myr should, in principle, create a He iii Strömgren sphere or shell surrounding the WD. Depending on the WD luminosity, the interstellar density, and the velocity of an outflow from the WD, the He iii region could appear unresolved, extended, or as a ring, with a range of possible surface brightnesses. We find no trace of He ii 4686 Å line emission in the HST data. Using simulations, we set 2 upper limits on the He ii 4686 Å luminosity of L He ii 〈 3.4 x 10 34 erg s –1 for a point source, corresponding to an emission region of radius r  〈 1.8 pc. The upper limit for an extended source is L He ii 〈 1.7 x 10 35  erg s –1 , corresponding to an extended region with r  ~ 11 pc. The largest detectable shell, given an interstellar-medium density of 1 cm –3 , has a radius of ~6 pc. Our results argue against the presence, within the ~10 5  yr prior to the explosion, of a supersoft X-ray source of luminosity L bol 3 x 10 37  erg s –1 , or of a super-Eddington accreting WD that produces an outflowing wind capable of producing cavities with radii of 2–6 pc.

Description: We trace the full evolution of low- and intermediate-mass stars (1 ≤ M ≤ 8 M ) during the asymptotic giant branch (AGB) phase in the Spitzer two-colour and colour–magnitude diagrams. We follow the formation and growth of dust particles in the circumstellar envelope with an isotropically expanding wind, in which gas molecules impinge upon pre-existing seed nuclei, favour their growth. These models are the first able to identify the main regions in the Spitzer data occupied by AGB stars in the Large Magellanic Cloud (LMC). The main diagonal sequence traced by LMC extreme stars in the [3.6] – [4.5] versus [5.8] – [8.0] and [3.6] – [8.0] versus [8.0] planes is nicely fit by carbon stars models; it results to be an evolutionary sequence with the reddest objects being at the final stages of their AGB evolution. The most extreme stars, with [3.6] – [4.5] 〉 1.5 and [3.6] – [8.0] 〉 3, are 2.5–3 M stars surrounded by solid carbon grains. In higher mass (〉3 M ) models dust formation is driven by the extent of hot bottom burning (HBB) – most of the dust formed is in the form of silicates and the maximum obscuration phase by dust particles occurs when the HBB experienced is strongest, before the mass of the envelope is considerably reduced.

Description: We present the analysis of the extraordinarily bright gamma-ray burst (GRB) 130427A under the hypothesis that the GRB central engine is an accretion-powered magnetar. In this framework, initially proposed to explain GRBs with precursor activity, the prompt emission is produced by accretion of matter on to a newly born magnetar, and the observed power is related to the accretion rate. The emission is eventually halted if the centrifugal forces are able to pause accretion. We show that the X-ray and optical afterglow is well explained as the forward shock emission with a jet break plus a contribution from the spin-down of the magnetar. Our modelling does not require any contribution from the reverse shock, that may still influence the afterglow light curve at radio and mm frequencies, or in the optical at early times. We derive the magnetic field ( B  ~ 10 16  G) and the spin period ( P  ~ 20 ms) of the magnetar and obtain an independent estimate of the minimum luminosity for accretion. This minimum luminosity results well below the prompt emission luminosity of GRB 130427A, providing a strong consistency check for the scenario where the entire prompt emission is the result of continuous accretion on to the magnetar. This is in agreement with the relatively long spin period of the magnetar. GRB 130427A was a well-monitored GRB showing a very standard behaviour and, thus, is a well-suited benchmark to show that an accretion-powered magnetar gives a unique view of the properties of long GRBs.

Description: We use high-resolution Eulerian simulations to study the stability of cold gas flows in a galaxy size dark matter halo (10 12 M ) at redshift z = 2. Our simulations show that a cold stream penetrating a hot gaseous halo is stable against thermal convection and Kelvin–Helmholtz instability. We then investigate the effect of a satellite orbiting the main halo in the plane of the stream. The satellite is able to perturb the stream and to inhibit cold gas accretion towards the centre of the halo for 0.5 Gyr. However, if the supply of cold gas at large distances is kept constant, the cold stream is able to re-establish itself after 0.3 Gyr. We conclude that cold streams are very stable against a large variety of internal and external perturbations.

Description: Barbarians, so named after the prototype of this class (234) Barbara, are a rare class of asteroids exhibiting anomalous polarimetric properties. Their very distinctive feature is that they show negative polarization at relatively large phase angles, where all ‘normal’ asteroids show positive polarization. The origin of the Barbarian phenomenon is unclear, but it seems to be correlated with the presence of anomalous abundances of spinel, a mineral usually associated with the so-called calcium–aluminium-rich inclusions (CAIs) on meteorites. Since CAIs are samples of the oldest solid matter identified in our Solar system, Barbarians are very interesting targets for investigations. Inspired by the fact that some of the few known Barbarians are members of, or very close to, the dynamical family of Watsonia, we have checked whether this family is a major repository of Barbarians, in order to obtain some hints about their possible collisional origin. We have measured the linear polarization of a sample of nine asteroids which are members of the Watsonia family within the phase-angle range 17°–21°. We found that seven of them exhibit the peculiar Barbarian polarization signature, and we conclude that the Watsonia family is a repository of Barbarian asteroids. The new Barbarians identified in our analysis will be important to confirm the possible link between the Barbarian phenomenon and the presence of spinel on the surface.

Description: The size distribution of small asteroids in the Main Belt is assumed to be determined by an equilibrium between the creation of new bodies out of the impact debris of larger asteroids and the destruction of small asteroids by collisions with smaller projectiles. However, for a diameter less than 6 km, we find that YORP-induced rotational disruption significantly contributes to the erosion even exceeding the effects of collisional fragmentation. Including this additional grinding mechanism in a collision evolution model for the asteroid belt, we generate size–frequency distributions from either an accretional or an ‘Asteroids were born big’ initial size–frequency distribution that are consistent with observations reported in Gladman et al. Rotational disruption is a new mechanism that must be included in all future collisional evolution models of asteroids.

Description: We present an analysis of X-Shooter spectra of the polluted hydrogen-rich white dwarfs (DAZ) NLTT 888 and NLTT 53908. The spectra of NLTT 53908 show strong, Zeeman-split calcium lines (Ca ii H&K and Ca i 4226) and the star appears to be a close relative of the polluted magnetic white dwarf (DAZH) NLTT 10480, while the spectra of NLTT 888 show narrow lines of calcium and iron. A comparison of the DAZ NLTT 888 and the DAZH NLTT 53908 with other class members illustrates the diversity of environment and formation circumstances surrounding these objects. In particular, we find that the incidence of magnetism in old, polluted white dwarfs significantly exceeds that found in the general white dwarf population which suggests a hypothetical link between a crowded planetary system and magnetic field generation.

Description: We present the first lensing total mass estimate of a galaxy, at redshift 2.207, that acts as a gravitational deflector and damped Lyman α absorber on the background QSO SDSS J1135–0010, at redshift 2.888. The remarkably small projected distance, or impact parameter, between the lens and the source has been estimated to be 0.8 ± 0.1 kpc in a recent work. By exploiting the Sloan Digital Sky Survey data base, we establish a likely lensing magnification signal in the photometry of the QSO. This is determined to be 2.2 mag brighter (or eight times more luminous) than the median QSO at comparable redshifts. We describe the total mass distribution of the lens galaxy with a one-component singular isothermal sphere model and contrast the values of the observed and model-predicted magnification factors. For the former, we use conservatively the photometric data of the 95 per cent of the available distant QSO population. We estimate that the values of the lens effective velocity dispersion and two-dimensional total mass, projected within a cylinder with radius equal to the impact parameter, are included between 60 and 170 km s –1 and 2.1 10 9 and 1.8 10 10 M , respectively. We conclude by remarking that analyses of this kind are crucial to exploring the relation between the luminous and dark-matter components of galaxies in the high-redshift Universe.

Description: Type 1a supernova magnitudes are used to fit cosmological parameters under the assumption that the model will fit the observed redshift dependence. We test this assumption with the Union 2.1 compilation of 580 sources. Several independent tests find that the existing model fails to account for a significant correlation of supernova colour and redshift. The correlation of magnitude residuals relative to the CDM model and colour   redshift has a significance equivalent to 13 standard deviations, as evaluated by randomly shuffling the data. Extending the existing B  –  V colour correction to a relation linear in redshift improves the goodness of fit 2 by more than 50 units, an equivalent 7 significance, while adding only one parameter. The colour – redshift correlation is quite robust, cannot be attributed to outliers and passes several tests of consistency. We review previous hints of redshift dependence in colour parameters found in bin-by-bin fits interpreted as parameter bias. We show that neither the bias nor the change 2 of our study can be explained by those effects. The previously known relation that bluer supernovae have larger absolute luminosity tends to empirically flatten out with increasing redshift. The best-fitting cosmological dark energy density parameter is revised from  = 0.71 ± 0.02 to  = 0.74 ± 0.02 assuming a flat universe. One possible physical interpretation is that supernovae or their environments evolve significantly with increasing redshift.

Description: Broad-band flux measurements centred around [3.6 μm] and [4.5 μm] obtained with Spitzer during the occultation of seven extrasolar planets by their host stars have been combined with parallax measurements to compute the absolute magnitudes of these planets. Those measurements are arranged in two colour–magnitude diagrams. Because most of the targets have sizes and temperatures similar to brown dwarfs, they can be compared to one another. In principle, this should permit inferences about exoatmospheres based on knowledge acquired by decades of observations of field brown dwarfs and ultracool stars’ atmospheres. Such diagrams can assemble all measurements gathered so far and will provide help in the preparation of new observational programmes. In most cases, planets and brown dwarfs follow similar sequences. HD 2094589b and GJ 436b are found to be outliers, so is the night side of HD 189733b. The photometric variability associated with the orbital phase of HD 189733b is particularly revealing. The planet exhibits what appears like a spectral type and chemical transition between its day and night sides: HD 189733b straddles the L–T spectral class transition, which would imply different cloud coverage on each hemisphere. Methane absorption could be absent at its hotspot but present over the rest of the planet.

Description: We report on a robust constraint on the possible variation of the fine-structure constant, α e 2 / c , obtained using O iii 4959,5007 nebular emission lines from quasi-stellar objects (QSOs). We find α/α = –(2.1 ± 1.6) 10 –5 , based on a well-selected sample of 2347 QSOs from the Sloan Digital Sky Survey Data Release 7 with 0.02 〈 z 〈 0.74. Our result is consistent with a non-varying α at a level of 2 10 –5 over approximately 7 Gyr. This is the largest sample of extragalactic objects yet used to constrain the variation of α. While this constraint is not as stringent as those determined using the many-multiplet method, it is free from various systematic effects. A factor of ~4 improvement in α/α achieved here compared to a previous study is consistent with what is expected based on the sample used here, which is a factor of 14 times larger. This suggests that errors are mainly dominated by statistical uncertainty. We also find that the ratio of transition probabilities corresponding to the O iii 5007 and 4959 lines is 2.933 ± 0.002, in good agreement with the measurements of the National Institute of Standards and Technology.

Description: Reverberation mapping (RM) is an important technique in studies of active galactic nuclei (AGN). The key idea of RM is to measure the time lag between variations in the continuum emission from the accretion disc and subsequent response of the broad-line region (BLR). The measurement of is typically used to estimate the physical size of the BLR and is combined with other measurements to estimate the black hole mass M BH . A major difficulty with RM campaigns is the large amount of data needed to measure . Recently, Fine et al. introduced a new approach to RM where the BLR light curve is sparsely sampled, but this is counteracted by observing a large sample of AGN, rather than a single system. The results are combined to infer properties of the sample of AGN. In this Letter, we implement this method using a hierarchical Bayesian model and contrast this with the results from the previous stacked cross-correlation technique. We find that our inferences are more precise and allow for more straightforward interpretation than the stacked cross-correlation results.

Description: Recent stellar evolution computations show that the blue supergiant (BSG) stars could come from two distinct populations: a first group arising from massive stars that just left the main sequence and are crossing the Hertzsprung–Russell diagram (HRD) towards the red supergiant (RSG) branch, and a second group coming from stars that have lost considerable amount of mass during the RSG stage and are crossing the HRD for a second time towards the blue region. Due to very different luminosity-to-mass ratio, only stars from the second group are expected to have excited pulsations observable at the surface. In a previous work, we have shown that our models were able to reproduce the pulsational properties of BSGs. However, these models failed to reproduce the surface chemical composition of stars evolving back from an RSG phase. In this Letter, we show how the use of the Ledoux criterion instead of the Schwarzschild one for convection allows us to significantly improve the agreement with the observed chemical composition, while keeping the agreement with the pulsation periods. This gives some support to the Ledoux criterion.

Description: We present Herschel and XMM–Newton observations of ULASJ1234+0907 ( z  = 2.503), the reddest broad-line type 1 quasar currently known with ( i  –  K ) AB  〉 7.1. Herschel observations indicate that the quasar host is a hyperluminous infrared galaxy with a total infrared luminosity of log 10 ( L IR /L ) = 13.90 ± 0.02. A greybody fit gives a dust temperature of T d  = 60 ± 3 K assuming an emissivity index of β = 1.5, considerably higher than in submillimeter bright galaxies observed at similar redshifts. The star formation rate is estimated to be 〉2000 M yr –1 even accounting for a significant contribution from an active galactic nucleus (AGN) component to the total infrared luminosity or requiring that only the far-infrared luminosity is powered by a starburst. XMM–Newton observations constrain the hard X-ray luminosity to be L 2-10 keV = 1.3 x 10 45 erg s –1 , putting ULASJ1234+0907 among the brightest X-ray quasars known. Through very deep optical and near-infrared imaging of the field at subarcsecond seeing, we demonstrate that despite its extreme luminosity, it is highly unlikely that ULASJ1234+0907 is being lensed. We measure a neutral hydrogen column density of N H  = 9.0 10 21 cm –2 corresponding to A V ~ 6. The observed properties of ULASJ1234+0907 – high luminosity and Eddington ratio, broad lines, moderate column densities and significant infrared emission from reprocessed dust – are similar to those predicted by galaxy formation simulations for the AGN blowout phase. The high Eddington ratio, combined with the presence of significant amounts of dust, is expected to drive strong outflows due to the effects of radiation pressure on dust.

Description: We present a systematic analysis of the complete set of observations of the black hole (BH) binary XTE J1550-564 obtained by the Rossi X-ray Timing Explorer . We study the fast time variability properties of the source and determine the spin of the BH through the relativistic precession model. Similarly to what is observed in the BH binary GRO J1655-40, the frequencies of the QPOs and broad-band noise components match the general relativistic frequencies of particle motion close to the compact object predicted by the relativistic precession model. The combination of two simultaneously observed quasi-periodic oscillation (QPO) frequencies together with the dynamical BH mass from optical/infrared observations yields a spin equal to a = 0.34 ± 0.01, consistent with previous determinations from X-ray spectroscopy. Based on the derived BH parameters, the low-frequency QPO emission radii vary from ~30 gravitational radii ( R g ) to the innermost stable orbit for this spin (~5 R g ), where they sharply disappear as observed for the case of GRO J1655-40.

Description: The large-scale structure of the Universe is characterized by a web-like structure made of voids, sheets, filaments and knots. The structure of this so-called cosmic web is dictated by the local velocity shear tensor. In particular, the local direction of a filament should be strongly aligned with $\hat{e}_3$ , the eigenvector associated with the smallest eigenvalue of the tensor. That conjecture is tested here on the basis of a cosmological simulation. The cosmic web delineated by the halo distribution is probed by a marked point process with interactions (the Bisous model), detecting filaments directly from the halo distribution (P-web). The detected P-web filaments are found to be strongly aligned with the local $\hat{e}_3$ : the alignment is within 30° for ~80 per cent of the elements. This indicates that large-scale filaments defined purely from the distribution of haloes carry more than just morphological information, although the Bisous model does not make any prior assumption on the underlying shear tensor. The P-web filaments are also compared to the structure revealed from the velocity shear tensor itself (V-web). In the densest regions, the P- and V-web filaments overlap well (90 per cent), whereas in lower density regions, the P-web filaments preferentially mark sheets in the V-web.

Description: We present the first complete calculation of the history of the inhomogeneous 21 cm signal from neutral hydrogen during the era of the first stars. We use hybrid computational methods to capture the large-scale distribution of the first stars, whose radiation couples to the neutral hydrogen emission, and to evaluate the 21 cm signal from z ~ 15–35. In our realistic picture, large-scale fluctuations in the 21 cm signal are sourced by the inhomogeneous density field and by the Lyα and X-ray radiative backgrounds. The star formation is suppressed by two spatially varying effects: negative feedback provided by the Lyman–Werner radiative background, and supersonic relative velocities between the gas and dark matter. Our conclusions are quite promising: we find that the fluctuations imprinted by the inhomogeneous Lyα background in the 21 cm signal at z ~ 25 should be detectable with the Square Kilometre Array.

Description: In this Letter, we analyse the distributions of stellar ages in giant molecular clouds (GMCs) in spiral arms, interarm spurs and at large galactic radii, where the spiral arms are relatively weak. We use the results of numerical simulations of galaxies, which follow the evolution of GMCs and include star particles where star formation events occur. We find that GMCs in spiral arms tend to have predominantly young (〈10 Myr) stars. By contrast, clouds which are the remainders of spiral arm giant molecular asssociations that have been sheared into interarm GMCs contain fewer young (〈10 Myr) stars and more ~20 Myr stars. We also show that clouds which form in the absence of spiral arms, due to local gravitational and thermal instabilities, contain preferentially young stars. We propose that the age distributions of stars in GMCs will be a useful diagnostic to test different cloud evolution scenarios, the origin of spiral arms and the success of numerical models of galactic star formation. We discuss the implications of our results in the context of Galactic and extragalactic molecular clouds.

Description: Despite the recent rapid progress in numerical relativity, a convergence order less than the second has so far plagued codes solving the Einstein–Euler system of equations. We report simulations of the inspiral of binary neutron stars in quasi-circular orbits computed with a new code employing high-order, high-resolution shock-capturing, finite-differencing schemes that, for the first time, go beyond the second-order barrier. In particular, without any tuning or alignment, we measure a convergence order above three both in the phase and in the amplitude of the gravitational waves. Because the new code is already able to calculate waveforms with very small phase errors at modest resolutions, we are able to obtain accurate estimates of tidal effects in the inspiral that are essentially free from the large numerical viscosity typical of lower order methods, and even for the challenging large compactness and small-deformability binary considered here. We find a remarkable agreement between our Richardson-extrapolated waveform and the one from the tidally corrected post-Newtonian (PN) Taylor-T4 model, with a de-phasing smaller than 0.4 rad during the seven orbits of the inspiral and up to the contact point. Because our results can be used reliably to assess the validity of the PN or other approximations at frequencies significantly larger than those considered so far in the literature, at these compactnesses, they seem to exclude significant tidal amplifications from next to next-to-leading-order terms in the PN expansion.

Description: We report optical and near-infrared observations of SN2012ca with the Public ESO Spectroscopy Survey of Transient Objects (PESSTO), spread over one year since discovery. The supernova (SN) bears many similarities to SN1997cy and to other events classified as Type IIn but which have been suggested to have a thermonuclear origin with narrow hydrogen lines produced when the ejecta impact a hydrogen-rich circumstellar medium (CSM). Our analysis, especially in the nebular phase, reveals the presence of oxygen, magnesium and carbon features. This suggests a core-collapse explanation for SN2012ca, in contrast to the thermonuclear interpretation proposed for some members of this group. We suggest that the data can be explained with a hydrogen- and helium-deficient SN ejecta (Type I) interacting with a hydrogen-rich CSM, but that the explosion was more likely a Type Ic core-collapse explosion than a Type Ia thermonuclear one. This suggests that two channels (both thermonuclear and stripped envelope core-collapse) may be responsible for these SN 1997cy-like events.

Description: Recently, we performed a complete study of the SB2 system HD 161701 with an orbital period of 12.5 d, consisting of an HgMn primary and a classical Ap secondary. Since this is the first system identified with this particular combination of peculiar stars, a study of the presence of a magnetic field in both components is of considerable interest to astronomers studying stellar magnetism and the impact of the presence of a magnetic field in binary systems. Apart from HD 161701, only one other close binary systems with a magnetic Ap component, the system HD 98088, is currently known. Using high accuracy radial velocity planet searcher (HARPS) polarimetric spectra obtained on six consecutive nights, we detect in the Ap component a mean longitudinal magnetic field of up to 200 G varying in strength over the orbital/rotational period. The magnetic field behaviour in this component is closely related to the position of the primary component, exhibiting negative polarity. There was no detection of any longitudinal magnetic field with an upper limit of ~90 G in the primary.

Description: It has been proposed that the observed systems of hot super-Earths formed in situ from high-mass discs. By fitting a disc profile to the entire population of Kepler planet candidates, Chiang & Laughlin constructed a ‘minimum-mass extrasolar nebula’ with surface density profile   r –1.6 . Here, we use multiple-planet systems to show that it is inconsistent to assume a universal disc profile. Systems with 3–6 low-mass planets (or planet candidates) produce a diversity of minimum-mass discs with surface density profiles ranging from   r –3.2 to   r 0.5 (5th–95th percentile). By simulating the transit detection of populations of synthetic planetary systems designed to match the properties of observed super-Earth systems, we show that a universal disc profile is statistically excluded at high confidence. Rather, the underlying distribution of minimum-mass discs is characterized by a broad range of surface density slopes. Models of gaseous discs can only explain a narrow range of slopes (roughly between r 0 and r –1.5 ). Yet accretion of terrestrial planets in a gas-free environment preserves the initial radial distribution of building blocks. The known systems of hot super-Earths must therefore not represent the structure of their parent gas discs and cannot have predominantly formed in situ . We instead interpret the diversity of disc slopes as the imprint of a process that re-arranged the solids relative to the gas in the inner parts of protoplanetary discs. A plausible mechanism is inward type 1 migration of Mars- to Earth-mass planetary embryos, perhaps followed by a final assembly phase.

Description: We consider the most commonly occurring circumstances which apply to galaxies, namely membership in galaxy groups of about 10 13 h –1 M total mass, and estimate the accompanying physical conditions of intergalactic medium (IGM) density and the relative galaxy–IGM space velocity. We then investigate the dynamical consequences of such a typical galaxy–IGM interaction on a rotating gaseous disc within the galaxy potential. We find that the rotating outer disc is systematically distorted into a characteristic ‘warp’ morphology, of the type that has been well-documented in the majority of well-studied nearby systems. The distortion is established rapidly, within 2 rotation periods, and is long-lived, surviving for at least 10. A second consequence of the interaction is the formation of a one-arm retrograde spiral wave pattern that propagates in the disc. We suggest that the ubiquity of the warp phenomenon might be used to reconstruct both the IGM density profile and individual member orbits within galaxy groups.

Description: We use very long baseline interferometry (VLBI) imaging of the interstellar scattering speckle pattern associated with the pulsar PSR 0834+06 to measure the astrometric motion of its emission. The D ~ 5 au interstellar baselines, provided by interference between speckles spanning the scattering disc, enable us to detect motions with subnanoarcsecond accuracy. We measure a small pulse deflection of ~18 ± 2 km (not including geometric uncertainties), which is 100 times smaller than the characteristic resolution (/ D ) of this interstellar interferometer. This implies that the emission region is small, and at an altitude of a few hundred km, with the exact value depending on field geometry. This is substantially closer to the star than to the light cylinder. Future VLBI measurements can improve on this finding. This new regime of ultraprecise astrometry may enable precision parallax distance determination of pulsar binary displacements.

Description: High-mass X-ray binaries (HMXBs) may have had a significant impact on the heating of the intergalactic medium in the early Universe. Study of HMXBs in nearby, low-metallicity galaxies that are local analogues to early galaxies can help us understand early HMXBs. The total luminosity of HMXB populations is dominated by sources at high luminosities. These sources exhibit X-ray spectra that show curvature above 2 keV and the same is likely true of HMXB populations at high redshifts. The spectral curvature changes the K -correction for X-rays from HMXBs in a manner that weakens the constraints on X-ray emission of early HMXBs obtained from the soft X-ray background. Applied to deep X-ray surveys of star-forming galaxies, the modified K -correction suggests a moderate increase in the ratio of X-ray luminosity to star formation rate at intermediate redshifts, z  = 3–5, and is consistent with a large enhancement at high redshifts, z  = 6–7.

Description: Dark matter haloes in cosmological filaments and walls have (in average) their spin vector aligned with their host structure. While haloes in walls are aligned with the plane of the wall independently of their mass, haloes in filaments present a mass-dependent two-regime orientation. Here, we show that the transition mass determining the change in the alignment regime (from parallel to perpendicular) depends on the hierarchical level in which the halo is located, reflecting the hierarchical nature of the Cosmic Web. By explicitly exposing the hierarchical structure of the Cosmic Web, we are able to identify the contributions of different components of the filament network to the alignment signal. We propose a unifying picture of angular momentum acquisition that is based on the results presented here and previous results found by other authors. In order to do a hierarchical characterization of the Cosmic Web, we introduce a new implementation of the multiscale morphology filter, the MMF-2, that significantly improves the identification of structures and explicitly describes their hierarchy.

Description: We present a detailed comparison between the photometric properties of the bulges of two simulated galaxies and those of a uniform sample of observed galaxies. This analysis shows that the simulated galaxies have bulges with realistic surface brightnesses for their sizes and magnitude. These two field disc galaxies have rotational velocities ~100 km s –1 and were integrated to a redshift of zero in a fully cosmological cold dark matter context as part of high-resolution smoothed particle hydrodynamic simulations. We performed bulge–disc decompositions of the galaxies using artificial observations, in order to conduct a fair comparison to observations. We also dynamically decomposed the galaxies and compared the star formation histories of the bulges to those of the entire galaxies. These star formation histories showed that the bulges were primarily formed before z = 1 and during periods of rapid star formation. Both galaxies have large amounts of early star formation, which is likely related to the relatively high bulge-to-disc ratios also measured for them. Unlike almost all previous cosmological simulations, the realistically concentrated bulges of these galaxies do not lead to unphysically high rotational velocities, causing them to naturally lie along the observed Tully–Fisher relation.

Description: Some combination of binary interactions and accretion plausibly conspire to produce the ubiquitous collimated outflows from planetary nebulae (PN) and their presumed pre-PN (PPN) precursors. But which accretion engines are viable? The difficulty in observationally resolving the engines warrants the pursuit of indirect constraints. We show how kinematic outflow data for 19 PPN can be used to determine the minimum required accretion rates. We consider main-sequence (MS) and white dwarf (WD) accretors and five example accretion rates inferred from published models to compare with the minima derived from outflow momentum conservation. While our primary goal is to show the method in anticipation of more data and better theoretical constraints, taking the present results at face value already rules out modes of accretion: Bondi–Hoyle–Lyttleton (BHL) wind accretion and wind Roche lobe overflow (M-WRLOF, based on Mira parameters) are too feeble for all 19/19 objects for an MS accretor. For a WD accretor, BHL is ruled out for 18/19 objects and M-WRLOF for 15/19 objects. RLOF from the primary at the Red Rectangle level can accommodate 7/19 objects, though RLOF modes with higher accretion rates are not yet ruled out. Accretion modes operating from within common envelope evolution can accommodate all 19 objects, if jet collimation can be maintained. Overall, sub-Eddington rates for an MS accretor are acceptable but 8/19 would require super-Eddington rates for a WD.

Description: We re-analyse the recently published High-Accuracy Radial velocity Planet Searcher (HARPS) and Planet Finder Spectrograph (PFS) velocities of the nearby K dwarf GJ 221 that have been reported to contain the signatures of two planets orbiting the star. Our goal is to see whether the earlier studies discussing the system fell victims of false negative detections. We perform the analyses by using an independent statistical method based on posterior samplings and model comparisons in the Bayesian framework that is known to be more sensitive to weak signals of low-mass planets. According to our analyses, we find strong evidence in favour of a third candidate planet in the system corresponding to a cold sub-Saturnian planet with an orbital period of 500 d and a minimum mass of 29 M . Application of sub-optimal signal detection methods can leave low-amplitude signals undetected in radial velocity time series. Our results suggest that the estimated statistical properties of low-mass planets can thus be biased because several signals corresponding to low-mass candidate planets may have gone unnoticed. This also suggests that the occurrence rates of such planets based on radial velocity surveys might be underestimated.

Description: While it is well recognized that interstellar grains are made of amorphous silicates and some form of carbonaceous materials, it remains debated regarding what exact chemical and physical form the carbonaceous component takes. Contemporary grain models assume that the silicate and carbon components are either physically separated or they form a core–mantle structure, or they agglomerate to form porous composites. The core–mantle model posits that the mantle is made of some sort of aliphatic hydrocarbon materials and is responsible for the 3.4 μm absorption feature ubiquitously seen in the diffuse interstellar medium (ISM) of the Milky Way and external galaxies. This model is challenged by the non-detection of polarization in the 3.4 μm absorption feature as the 9.7 μm silicate feature is observed to be polarized. To alleviate this challenge, we calculate the degree of polarization of the 3.4 μm feature for spheroidal silicate dust coated by a layer of spherical aliphatic hydrocarbon. It is found that the 3.4 μm feature polarization still exceeds the observational upper limit, even though spherical aliphatic hydrocarbon mantles are expected to cause much less polarization than non-spherical (e.g. spheroidal) mantles. We have also shown that the composite grain model which consists of amorphous silicate, aliphatic hydrocarbon and vacuum also predicts the 3.4 μm feature polarization to well exceed what is observed. These results support the earlier arguments that the aliphatic hydrocarbon component is physically separated from the silicate component unless the 3.4 μm absorption feature is just a minor carbon sink in the ISM.

Description: We report the detection of molecular CO(1–0) gas in F00183-7111, one of the most extreme ultraluminous infrared galaxies (ULIRGs) known, with the Australia Telescope Compact Array. We measure a redshift of 0.3292 for F00183-7111 from the CO(1–0) line and estimate the mass of the molecular gas in 00183 to be 1 10 10 M . We find that F00183-7111 is predominately powered by the active galactic nucleus (AGN) and only ~14 per cent of the total luminosity is contributed by star formation (SFR ~220 M  yr –1 ). We also present an optical image of F00183-7111, which shows an extension to the east. We searched for star formation in this extension using radio continuum observations but do not detect any. This suggests that the star formation is likely to be predominately nuclear. These observations provide additional support for a model in which the radio emission from ULIRGs is powered by an intense burst of star formation and by a radio-loud AGN embedded in its nucleus, both triggered by a merger of gas-rich galaxies.

Description: Observations have revealed interesting universal properties of dark matter (DM) haloes especially around low-mass galaxies. Strigari et al. showed that DM haloes have common enclosed masses within 300 pc (Strigari relation). Kormendy & Freeman reported DM haloes having almost identical central surface densities (the μ 0D relation). In addition, there exists a core–cusp problem, a discrepancy of the central density distribution between simulated haloes and observations. We investigate whether a scenario where cuspy haloes transform into cores by some dynamical processes can also explain their universal structural properties. It is shown that a cusp-to-core transformation model naturally reproduces the μ 0D relation and that Strigari relation follows from the μ 0D relation for dwarf galaxies. We also show that the central densities of cored dark haloes provide valuable information about their formation redshifts.

Description: We simulate the formation of a metal-poor (10 –2 Z ) stellar cluster in one of the first galaxies to form in the early Universe, specifically a high-redshift atomic cooling halo ( z  ~ 14). This is the first calculation that resolves the formation of individual metal-enriched stars in simulations starting from realistic cosmological initial conditions. We follow the evolution of a single dense clump among several in the parent halo. The clump forms a cluster of ~40 stars and sub-stellar objects within 7000 yr and could continue forming stars ~5 times longer. Protostellar dust heating has a negligible effect on the star formation efficiency, at least during the early evolutionary stages, but it moderately suppresses gaseous fragmentation and brown dwarf formation. We observe fragmentation in thin gaseous filaments and sustained accretion in larger, rotating structures as well as ejections by binary interactions. The stellar initial mass function above 0.1 M , evaluated after ~10 4 yr of fragmentation and accretion, seems in agreement with the recent measurement in ultrafaint dwarf spheroidal Galactic satellites of Geha et al.

Description: We present the first kinematic study of an α-dynamo in the general relativistic magnetohydrodynamics regime, applied to thick discs orbiting around Kerr black holes and using a fully covariant mean-field dynamo closure for the Ohm law. We show that the α-dynamo mechanism leads to a continuous exponential growth of the magnetic field within the disc and to the formation of dynamo waves drifting away or towards the equatorial plane. Since the evolution of the magnetic field occurs qualitatively in the same fashion as in the Sun, we present also butterfly diagrams that characterize our models and show the establishment of an additional time-scale, which depends on the microscopic properties of the turbulent motions, possibly providing an alternative explanation to periodicities observed in many high-energy astrophysical sources where accretion on to a rotating black hole is believed to operate.

Description: The relation between the stellar mass and size of a galaxy's structural subcomponents, such as discs and spheroids, is a powerful way to understand the processes involved in their formation. Using very large catalogues of photometric bulge+disc structural decompositions and stellar masses from the Sloan Digital Sky Survey Data Release Seven, we carefully define two large subsamples of spheroids in a quantitative manner such that both samples share similar characteristics with one important exception: the ‘bulges’ are embedded in a disc and the ‘pure spheroids’ are galaxies with a single structural component. Our bulge and pure spheroid subsample sizes are 76 012 and 171 243, respectively. Above a stellar mass of ~10 10 M , the mass–size relations of both subsamples are parallel to one another and are close to lines of constant surface mass density. However, the relations are offset by a factor of 1.4, which may be explained by the dominance of dissipation in their formation processes. Whereas the size–mass relation of bulges in discs is consistent with gas-rich mergers, pure spheroids appear to have been formed via a combination of ‘dry’ and ‘wet’ mergers.

Description: A recent determination of the distance to the HDE 226868/Cyg X-1 binary system and a more precise determination of the effective temperature of HDE 226868 allow for a more accurate estimate of the masses of both components. Using up-to-date evolutionary models, I obtain a mass range of between 25 and 35 M for the mass of the supergiant and between 13 and 23 M for the mass of the black hole. By accepting more liberal estimates of uncertainties in both the distance and the effective temperature, it is possible to extend these ranges to 21–35 and 10–23 M for both masses, respectively. The most likely values within these ranges are 27 and 16 M , respectively. The mass obtained for the black hole agrees with the value of 15 ± 1 M suggested by Orosz et al. However, their value of 19 ± 2 M suggested for the mass of the supergiant should not be used because such a star violates the mass–luminosity relation for the massive core hydrogen-burning stars. This consideration was not incorporated into the iterative process of Orosz et al. To resolve this violation, I consider the possibility that the hydrogen content of HDE 226868 might be lowered as a result of the mass transfer and the induced fast rotation of the mass gainer. I have analysed the evolutionary effects of such a situation and have found that, while important, these do not invalidate the conclusions listed above. If, as a result of the rotation-induced mixing, the present hydrogen content of HDE 226868 is equal to about 0.6 (as suggested by some observational data), then its present mass might be lower: ~24 M rather than ~27 M .

Description: We explore the utility of C i as an alternative high-fidelity gas-mass tracer for galactic molecular clouds. We evaluate the ‘ X C i -factor’ for the 609 μm carbon line, the analogue of the CO ‘ X -factor’, which is the ratio of the H 2 column density to the integrated 12 CO(1–0) line intensity. We use 3d-pdr to post-process hydrodynamic simulations of turbulent, star-forming clouds. We compare the emission of C i and CO for model clouds irradiated by 1 and 10 times the average background and demonstrate that C i is a comparable or superior tracer of the molecular gas distribution for column densities up to 6 x 10 23  cm –2 . Our results hold for both reduced and full chemical networks. For our fiducial Galactic cloud, we derive an average X CO of 3.0 x 10 20  cm –2  K –1  km –1  s and X C i of 1.1 x 10 21  cm –2  K –1  km –1  s.

Description: Based on data from the Galaxy and Mass Assembly (GAMA) survey, we report on the discovery of structures that we refer to as ‘tendrils’ of galaxies: coherent, thin chains of galaxies that are rooted in filaments and terminate in neighbouring filaments or voids. On average, tendrils contain six galaxies and span 10 h –1 Mpc. We use the so-called line correlation function to prove that tendrils represent real structures rather than accidental alignments. We show that voids found in the Sloan Digital Sky Survey, 7th data release survey that overlap with GAMA regions contain a large number of galaxies, primarily belonging to tendrils. This implies that void sizes are strongly dependent on the number density and sensitivity limits of a survey. We caution that galaxies in low-density regions, which may be defined as ‘void galaxies,’ will have local galaxy number densities that depend on such observational limits and are likely higher than those can be directly measured.

Description: The radio-loud quasar SDSS J114657.79+403708.6 at a redshift z  = 5.0 is one of the most distant radio-loud objects. The IR-optical luminosity and spectrum suggest that its black hole has a very large mass: M  = (5 ± 1) 10 9 M . The radio-loudness (ratio of the radio to optical flux) of the source is large (around 100), suggesting that the source is viewed at small angles from the jet axis, and could be a blazar. The X-ray observations fully confirm this hypothesis, due to the high level and hardness of the flux. This makes SDSS J114657.79+403708.6 the third most distant blazar known, after Q0906+693 ( z  = 5.47) and B2 1023+25 ( z  = 5.3). Among those, SDSS J114657.79+403708.6 has the largest black hole mass, setting interesting constraints on the mass function of heavy (〉10 9 M ) black holes at high redshifts.

Description: Spectral and temporal properties of black hole candidates can be explained reasonably well using Chakrabarti–Titarchuk solution of two-component advective flow (TCAF). This model requires two accretion rates, namely the Keplerian disc accretion rate and the halo accretion rate, the latter being composed of a sub-Keplerian, low-angular-momentum flow which may or may not develop a shock. In this solution, the relevant parameter is the relative importance of the halo (which creates the Compton cloud region) rate with respect to the Keplerian disc rate (soft photon source). Though this model has been used earlier to manually fit data of several black hole candidates quite satisfactorily, for the first time, we made it user friendly by implementing it into xspec software of Goddard Space Flight Center (GSFC)/NASA. This enables any user to extract physical parameters of the accretion flows, such as two accretion rates, the shock location, the shock strength, etc., for any black hole candidate. We provide some examples of fitting a few cases using this model. Most importantly, unlike any other model, we show that TCAF is capable of predicting timing properties from the spectral fits, since in TCAF, a shock is responsible for deciding spectral slopes as well as quasi-periodic oscillation frequencies.

Description: We present X-ray imaging and spectroscopy of the redshift z  = 7.084 radio-quiet quasar ULAS J112001.48+064124.3 obtained with Chandra and XMM–Newton . The quasar is detected as a point source with both observatories. The Chandra observation provides a precise position, confirming the association of the X-ray source and the quasar, while a sufficient number of photons is detected in the XMM–Newton observation to yield a meaningful X-ray spectrum. In the XMM–Newton observation, the quasar has a 2–10 keV luminosity of 4.7 ± 0.9 x 10 44  erg s –1 and a spectral slope $\alpha = 1.6^{+0.4}_{-0.3}$ (where f    –α ). The quasar appears to have dimmed in the 15 months between the two observations, with a 2–10 keV luminosity of $1.8^{+1.0}_{-0.7}\times 10^{45}$  erg s –1 during the Chandra observation. We derive optical-to-X-ray spectral slopes α OX of 1.76 ± 0.07 and $1.54^{+0.09}_{-0.08}$ at the times of the XMM–Newton and Chandra observations, respectively, consistent with the range of α OX found in other quasars of comparable ultraviolet luminosity. The very soft X-ray spectrum suggests that the quasar is accreting above the Eddington rate, $L/L_{\rm Edd} = 5^{+15}_{-4}$ , compared to $L/L_{\rm Edd} = 1.2^{+0.6}_{-0.5}$ derived from the rest-frame ultraviolet. Super-Eddington accretion would help to reduce the discrepancy between the age of the quasar implied by the small size of the ionized near-zone in which it sits (〈10 7  yr) and the characteristic e-folding time (2.5 10 7  yr if L / L Edd  = 2). Such super-Eddington accretion would also alleviate the challenging constraints on the seed black hole mass provided that the quasar has been rapidly accreting throughout its history. The remnant of an individual Population III star is a plausible progenitor if an average L / L Edd  〉 1.46 has been maintained over the quasar's lifetime.

Description: The recent discovery of a magnetar in the Galactic Centre region has allowed Spitler et al. to characterize the interstellar scattering in that direction. They find that the temporal broadening of the pulse profile of the magnetar is substantially less than that predicted by models of the electron density of that region. This raises the question of what the plausible limits for the number of potentially observable pulsars – i.e. the number of pulsars beaming towards the Earth – in the Galactic Centre are. In this Letter, using reasonable assumptions – namely (i) the luminosity function of pulsars in the Galactic Centre region is the same as that in the field, (ii) the region has had a constant pulsar formation rate, (iii) the spin and luminosity evolution of magnetars and pulsars are similar and (iv) the scattering in the direction of the Galactic Centre magnetar is representative of the entire inner parsec – we show that the potentially observable population of pulsars in the inner parsec has a conservative upper limit of ~200 and that it is premature to conclude that the number of pulsars in this region is small. We also show that the observational results so far are consistent with this number and make predictions for future radio pulsar surveys of the Galactic Centre.

Description: The double-detonation explosion scenario of Type Ia supernovae (SNe Ia) has gained increased support from the SN Ia community as a viable progenitor model, making it a promising candidate alongside the well-known single degenerate and double degenerate scenarios. We present delay times of double-detonation SNe, in which a sub-Chandrasekhar mass carbon–oxygen white dwarf (WD) accretes non-dynamically from a helium-rich companion. One of the main uncertainties in quantifying SN rates from double detonations is the (assumed) retention efficiency of He-rich matter. Therefore, we implement a new prescription for the treatment of accretion/accumulation of He-rich matter on WDs. In addition, we test how the results change depending on which criteria are assumed to lead to a detonation in the helium shell. In comparing the results to our standard case (Ruiter et al.), we find that regardless of the adopted He accretion prescription, the SN rates are reduced by only ~25 per cent if low-mass He shells (0.05 M ) are sufficient to trigger the detonations. If more massive (0.1 M ) shells are needed, the rates decrease by 85 per cent and the delay time distribution is significantly changed in the new accretion model – only SNe with prompt (〈500 Myr) delay times are produced. Since theoretical arguments favour low-mass He shells for normal double-detonation SNe, we conclude that the rates from double detonations are likely to be high, and should not critically depend on the adopted prescription for accretion of He.

Description: In order to empirically determine the time-scale and environmental dependence of stellar cluster disruption, we have undertaken an analysis of the unprecedented multipointing (seven), multiwavelength ( U , B , V , Hα, and I ) Hubble Space Telescope imaging survey of the nearby, face-on spiral galaxy M83. The images are used to locate stellar clusters and stellar associations throughout the galaxy. Estimation of cluster properties (age, mass, and extinction) was done through a comparison of their spectral energy distributions with simple stellar population models. We constructed the largest catalogue of stellar clusters and associations in this galaxy to-date, with ~1800 sources with masses above ~5000 M and ages younger than ~300 Myr. In this Letter, we focus on the age distribution of the resulting clusters and associations. In particular, we explicitly test whether the age distributions are related with the ambient environment. Our results are in excellent agreement with previous studies of age distributions in the centre of the galaxy, which gives us confidence to expand out to search for similarities or differences in the other fields which sample different environments. We find that the age distribution of the clusters inside M83 varies strongly as a function of position within the galaxy, indicating a strong correlation with the galactic environment. If the age distributions are approximated as a power law of the form ${\frac{\mathrm{d} N}{\mathrm{d}t}}\propto t^{\zeta }$ , we find values between 0 and –0.62 ( ~ –0.40 for the whole galaxy), in good agreement with previous results and theoretical predictions.

Description: We use photometry from the recent AllWISE Data Release of the Wide-field Infrared Survey Explorer ( WISE ) of 129 calibration stars, combined with prior distances obtained from the established M V –[Fe/H] relation and Hubble Space Telescope trigonometric parallax, to derive mid-infrared period–luminosity relations for RR Lyrae pulsating variable stars. We derive relations in the W 1, W 2 and W 3 wavebands (3.4, 4.6 and 12 μm, respectively), and for each of the two main RR Lyrae sub-types (RRab and RRc). We report an error on the period–luminosity relation slope for RRab stars of 0.2. We also fit posterior distances for the calibration catalogue and find a median fractional distance error of 0.8 per cent.

Description: RX J1713.7–3946 is a key object to check the supernova remnant paradigm of the origin of Galactic cosmic rays. While the origin of its gamma-ray emission (hadronic versus leptonic) is still debated, the hard spectrum at GeV energies reported by the Fermi collaboration is generally interpreted as a strong argument in favour of a leptonic scenario. On the contrary, we show that hadronic interactions can naturally explain the gamma-ray spectrum if gas clumps are present in the supernova remnant shell. The absence of thermal X-rays from the remnant fits well within this scenario.

Description: Cloud collision has been proposed as a way to link the small-scale star formation process with the observed global relation between the surface star formation rate and gas surface density. We suggest that this model can be improved further by allowing the productivity of such collisions to depend on the relative velocity of the two clouds. Our adjustment implements a simple step function that results in the most successful collisions being at the observed velocities for triggered star formation. By applying this to a high-resolution simulation of a barred galaxy, we successfully reproduce the observational result that the star formation efficiency (SFE) in the bar is lower than that in the spiral arms. This is not possible when we use an efficiency dependent on the internal turbulence properties of the clouds. Our results suggest that high-velocity collisions driven by the gravitational pull of the clouds are responsible for the low bar SFE.

Description: We explore the use of spectropolarimetry as a remote sensing tool for asteroids in addition to traditional reflectance measurements. In particular, we are interested in possible relationships between the wavelength-dependent variation of linear polarization and the properties of the surfaces, including albedo and composition. We have obtained optical spectropolarimetric measurements of a dozen asteroids of different albedo and taxonomic classes and of two small regions at the limb of the Moon. We found that objects with marginally different relative reflectance spectra (in the optical) may have totally different polarization spectra. This suggests that spectropolarimetry may be used to refine the classification of asteroids. We also found that in some cases the Umov law may be violated, that is, in contrast to what is expected from basic physical considerations, the fraction of linear polarization and the reflectance may be positively correlated. In agreement with a few previous studies based on multicolour broad-band polarimetry, we found that the variation of linear polarization with wavelength and with phase-angle is correlated with the albedo and taxonomic class of the objects. Finally, we have serendipitously discovered that spinel-rich asteroid (599) Luisa, located very close to the Watsonia family, is a member of the rare class of Barbarian asteroids. We suggest that future modelling attempts of the surface structure of asteroids should be aimed at explaining both reflectance and polarization spectra.

Description: We present new observations of the lensing cluster SMACSJ2031.8-4036 obtained with the Multi Unit Spectroscopic Explorer (MUSE) integral field spectrograph as part of its commissioning on the Very Large Telescope. By providing medium-resolution spectroscopy over the full 4750–9350 Å domain and a 1 1 arcmin 2 field of view, MUSE is ideally suited for identifying lensed galaxies in the cluster core, in particular multiple-imaged systems. We perform a redshift analysis of all sources in the data cube and identify a total of 12 systems ranging from z  = 1.46 to 6.4, with all images of each system confirmed by a spectroscopic redshift. This allows us to accurately constrain the cluster mass profile in this region. We foresee that future MUSE observations of cluster cores should help us discover very faint Lyman α emitters thanks to the strong magnification and the high sensitivity of this instrument.

Description: We report the discovery of the first millisecond pulsar with a pulsating white dwarf (WD) companion. Following the recent discoveries of pulsations in extremely low-mass (ELM, ≤0.3 M ) WDs, we targeted ELM WD companions to two millisecond pulsars with high-speed Gemini photometry. We find significant optical variability in PSR J1738+0333 with periods between roughly 1790–3060 s, consistent in time-scale with theoretical and empirical observations of pulsations in 0.17 M He-core ELM WDs. We additionally put stringent limits on a lack of variability in PSR J1909–3744, showing this ELM WD is not variable to 〈0.1 per cent amplitude. Thanks to the accurate distance and radius estimates from radio timing measurements, PSR J1738+0333 becomes a benchmark for low-mass, pulsating WDs. Future, more extensive time series photometry of this system offers an unprecedented opportunity to constrain the physical parameters (including the cooling age) and interior structure of this ELM WD, and in turn, the mass and spin-down age of its pulsar companion.

Description: We use a high-resolution hydrodynamic simulation that tracks the non-equilibrium abundance of molecular hydrogen within a massive high-redshift galaxy to produce mock Atacama Large Millimeter Array (ALMA) maps of the fine-structure lines of atomic carbon, C  i 1–0 and C  i 2–1. Inspired by recent observational and theoretical work, we assume that C  i is thoroughly mixed within giant molecular clouds and demonstrate that its emission is an excellent proxy for H 2 . Nearly all of the H 2 associated with the galaxy can be detected at redshifts z  〈 4 using a compact interferometric configuration with a large synthesized beam (that does not resolve the target galaxy) in less than 4 h of integration time. Low-resolution imaging of the C  i lines (in which the target galaxy is resolved into three to four beams) will detect ~80 per cent of the H 2 in less than 12 h of aperture synthesis. In this case, the resulting data cube also provides the crucial information necessary for determining the dynamical state of the galaxy. We conclude that ALMA observations of the C  i 1–0 and 2–1 emission are well-suited for extending the interval of cosmic look-back time over which the H 2 distributions, the dynamical masses, and the Tully–Fisher relation of galaxies can be robustly probed.

Description: It is customarily assumed that Earth-striking meteoroids are completely random, and that all the impacts must be interpreted as uncorrelated events distributed according to Poisson statistics. If this is correct, their impact dates must be uniformly spread throughout the year and their impact coordinates must be evenly scattered on the surface of our planet. Here, we use a time- and yield-limited sample of Earth-impacting superbolides detected since 2000 to explore statistically this critical though frequently overlooked topic. We show that the cadence of these multi-kiloton impact events is incompatible with a random fall pattern at the 0.05 significance level or better. This result is statistically robust and consistent with the observed distribution of the longitudes of the ascending nodes of near-Earth objects (NEOs). This lack of randomness is induced by planetary perturbations, in particular Jupiter's, and suggests that some of the recent, most powerful Earth impacts may be associated with resonant groups of NEOs and/or very young meteoroid streams. An intriguing consequence of this scenario is that the impact hazard of Chelyabinsk-like objects should peak at certain times in the year.

Description: Among the interstellar molecules, the CN radical is of particular interest since it is a good probe of cold dark molecular clouds, and especially prestellar cores. Modelling of CN emission spectra from these dense molecular clouds requires the calculation of rate coefficients for excitation by collisions with the most abundant species. We calculate fine- and hyperfine-structure-resolved excitation rate coefficients of CN(X 2 + ) by para- and ortho-H 2 . The calculations are based on a new potential energy surface obtained recently from highly correlated ab initio calculations. State-to-state rate coefficients between fine and hyperfine levels of CN were calculated for low temperatures ranging from 5 to 100 K. The new results are compared to available CN rate coefficients. Significant differences are found between the different sets of rate coefficients. This comparison shows that the new CN–H 2 rate coefficients have to be used for observations interpretations. We expect that their use will help significantly to have a new insight into the physical conditions of prestellar cores.

Description: Using N -body simulations, we study the origin of prolate rotation observed in the kinematic data for Andromeda II (And II), a dwarf spheroidal satellite of M31. We propose an evolutionary model for the origin of And II involving a merger between two discy dwarf galaxies with different disc scalelengths. The dwarfs are placed on a radial orbit towards each other with their angular momenta inclined by 90 deg. The merger remnant forms a stable triaxial galaxy with rotation only around the longest axis whose origin is naturally explained as due to the symmetry of the initial configuration and the conservation of angular momentum components along the direction of the merger. The stars originating from the two dwarfs show significantly different surface density profiles while having very similar kinematics as required by the data. We also study an alternative scenario for the formation of And II, via tidal stirring of a discy dwarf. While intrinsic rotation occurs naturally in this model as a remnant of the initial rotation of the disc, it is mostly around the shortest axis of the stellar component. We conclude that the velocity distribution in And II is much more naturally explained by a scenario involving a past merger.

Description: The mechanism behind the launching of gamma-ray burst (GRB) jets remains debated resulting in large uncertainty over the jet composition. Both magnetohydrodynamical and neutrino annihilation models have been proposed for the energy extraction in a black hole/accretion-disc central engine. In particular, for the extreme accretion rates $\dot{M}\sim 0.1\hbox{--}1$ M s –1 expected for bursts of duration T   100 s, the disc can be an efficient neutrino emitter. Neutrino–antineutrino annihilation results in an energy deposition rate at the jet that can, in principle, account for the burst's energetics. Recent discoveries of X-ray flares hours after the burst and of ultra-long GRBs suggest that GRB activity can last for ~10 4 s or longer. These long-lived events have fluence similar to that of classical GRBs. In view of these findings, we re-evaluate the neutrino annihilation model. We derive the maximum possible energy of a neutrino-powered jet as a function of the burst duration and show that the available energy drops fast for longer bursts. For a standard choice of the parameters, the model falls short by three to four orders of magnitude in explaining the observed energetics of events that last longer than ~10 3 s.