ALBERT

Description: We present spectroscopic and photometric solutions for three spotted systems with red giant components. Absolute physical and orbital parameters for these double-lined detached eclipsing binary stars are presented for the first time. These were derived from the V -, and I -band ASAS and WASP photometry, and new radial velocities calculated from high quality optical spectra we obtained with a wide range of spectrographs and using the two-dimensional cross-correlation technique (TODCOR). All of the investigated systems (ASAS J184949-1518.7, BQ Aqr, and V1207 Cen) show the differential evolutionary phase of their components consisting of a main-sequence star or a subgiant and a red giant, and thus constitute very informative objects in terms of testing stellar evolution models. Additionally, the systems show significant chromospheric activity of both components. They can be also classified as classical RS CVn-type stars. Besides the standard analysis of radial velocities and photometry, we applied spectral disentangling to obtain separate spectra for both components of each analysed system which allowed for a more detailed spectroscopic study. We also compared the properties of red giant stars in binaries that show spots, with those that do not, and found that the activity phenomenon is substantially suppressed for stars with Rossby number higher than ~1 and radii larger than ~20 R .

Description: Limb darkening is fundamental in determining transit light-curve shapes, and is typically modelled by a variety of laws that parametrize the intensity profile of the star that is being transited. Confronted with a transit light curve, some authors fix the parameters of these laws, the so-called limb darkening coefficients (LDCs), while others prefer to let them float in the light-curve fitting procedure. Which of these is the best strategy, however, is still unclear, as well as how and by how much each of these can bias the retrieved transit parameters. In this work we attempt to clarify those points by first recalculating these LDCs, comparing them to measured values from Kepler transit light curves using an algorithm that takes into account uncertainties in both the geometry of the transit and the parameters of the stellar host. We show there are significant departures from predicted model values, suggesting that our understanding of limb darkening still needs to improve. Then, we show through simulations that if one uses the quadratic limb darkening law to parametrize limb darkening, fixing and fitting the LDCs can lead to significant biases – up to ~3 and ~1 per cent in R p / R * , respectively – which are important for several confirmed and candidate exoplanets. We conclude that, in this case, the best approach is to let the LDCs be free in the fitting procedure. Strategies to avoid biases in data from present and future missions involving high precision measurements of transit parameters are described.

Description: We report the discovery and characterization of a new M-dwarf binary, with component masses and radii of $M_1 = 0.244_{-0.003}^{+0.003} \, \mathrm{M}_{\odot }$ , $R_1 = 0.261_{-0.009}^{+0.006} \, \mathrm{R}_{\odot }$ , $M_2 = 0.179_{-0.001}^{+0.002} \, \mathrm{M}_{\odot }$ , $R_2 = 0.218 _{-0.011}^{+0.007} \, \mathrm{R}_{\odot }$ , and orbital period of ~4.1 d. The M-dwarf binary HATS551–027 (LP 837–20) was identified as an eclipsing binary by the HATSouth survey, and characterized by a series of high-precision photometric observations of the eclipse events, and spectroscopic determinations of the atmospheric parameters and radial velocity orbits. HATS551–027 is one of few systems with both stellar components lying in the fully convective regime of very low mass stars, and can serve as a test for stellar interior models. The radius of HATS551–027A is consistent with models to 1, whilst HATS551–027B is inflated by 9 per cent at 2 significance. We measure the effective temperatures for the two stellar components to be T eff, 1  = 3190 ± 100 K and T eff, 2  = 2990 ± 110 K; both are slightly cooler than theoretical models predict, but consistent with other M-dwarfs of similar masses that have previously been studied. We also measure significant H α emission from both components of the binary system, and discuss this in the context of the correlation between stellar activity and the discrepancies between the observed and model temperatures.

Description: We report the discovery of an extremely close white dwarf plus F dwarf main-sequence star in a 12 h binary identified by combining data from the Radial Velocity Experiment survey and the Galaxy Evolution Explorer survey. A combination of spectral energy distribution fitting and optical and Hubble Space Telescope ultraviolet spectroscopy allowed us to place fairly precise constraints on the physical parameters of the binary. The system, TYC 6760-497-1, consists of a hot T eff  ~ 20 000 K, $M_\rm{WD}\sim 0.6 {\rm{M_{{\odot }}}}$ white dwarf and an F8 star ( $M_\rm{MS}\sim 1.23{\rm M_{\odot }}$ , $R_\rm{MS}\sim 1.3\,{\rm R_{\odot }}$ ) seen at a low inclination ( i  ~ 37°). The system is likely the descendant of a binary that contained the F star and an ~2 M A-type star that filled its Roche lobe on the thermally pulsating asymptotic giant branch, initiating a common envelope phase. The F star is extremely close to Roche lobe filling and there is likely to be a short phase of thermal time-scale mass transfer on to the white dwarf during which stable hydrogen burning occurs. During this phase, it will grow in mass by up to 20 per cent, until the mass ratio reaches close to unity, at which point it will appear as a standard cataclysmic variable star. Therefore, TYC 6760-497-1 is the first known progenitor of a supersoft source system, but will not undergo a Type Ia supernova explosion. Once an accurate distance to the system is determined by Gaia , we will be able to place very tight constraints on the stellar and binary parameters.

Description: Accurate measurements of the physical characteristics of a large number of exoplanets are useful to strongly constrain theoretical models of planet formation and evolution, which lead to the large variety of exoplanets and planetary-system configurations that have been observed. We present a study of the planetary systems WASP-45 and WASP-46, both composed of a main-sequence star and a close-in hot Jupiter, based on 29 new high-quality light curves of transits events. In particular, one transit of WASP-45 b and four of WASP-46 b were simultaneously observed in four optical filters, while one transit of WASP-46 b was observed with the NTT obtaining a precision of 0.30 mmag with a cadence of roughly 3 min. We also obtained five new spectra of WASP-45 with the FEROS spectrograph. We improved by a factor of 4 the measurement of the radius of the planet WASP-45 b, and found that WASP-46 b is slightly less massive and smaller than previously reported. Both planets now have a more accurate measurement of the density (0.959 ± 0.077 Jup instead of 0.64 ± 0.30 Jup for WASP-45 b, and 1.103 ± 0.052 Jup instead of 0.94 ± 0.11 Jup for WASP-46 b). We tentatively detected radius variations with wavelength for both planets, in particular in the case of WASP-45 b we found a slightly larger absorption in the redder bands than in the bluer ones. No hints for the presence of an additional planetary companion in the two systems were found either from the photometric or radial velocity measurements.

Description: Very precise measurements of exoplanet transit light curves both from ground- and space-based observatories make it now possible to fit the limb-darkening coefficients in the transit-fitting procedure rather than fix them to theoretical values. This strategy has been shown to give better results, as fixing the coefficients to theoretical values can give rise to important systematic errors which directly impact the physical properties of the system derived from such light curves such as the planetary radius. However, studies of the effect of limb-darkening assumptions on the retrieved parameters have mostly focused on the widely used quadratic limb-darkening law, leaving out other proposed laws that are either simpler or better descriptions of model intensity profiles. In this work, we show that laws such as the logarithmic, square-root and three-parameter law do a better job that the quadratic and linear laws when deriving parameters from transit light curves, both in terms of bias and precision, for a wide range of situations. We therefore recommend to study which law to use on a case-by-case basis. We provide code to guide the decision of when to use each of these laws and select the optimal one in a mean-square error sense, which we note has a dependence on both stellar and transit parameters. Finally, we demonstrate that the so-called exponential law is non-physical as it typically produces negative intensities close to the limb and should therefore not be used.

Description: We present radial velocity measurements of a sample of M5V–M9V stars from our Red-Optical Planet Survey, operating at 0.652–1.025 μm. Radial velocities for 15 stars, with rms precision down to 2.5 m s –1 over a week-long time-scale, are achieved using thorium–argon reference spectra. We are sensitive to planets with m p sin i ≥ 1.5 M (3 M at 2) in the classical habitable zone, and our observations currently rule out planets with m p sin i 〉 0.5 M J at 0.03 au for all our targets. A total of 9 of the 15 targets exhibit rms 〈 16 m s –1 , which enables us to rule out the presence of planets with m p sin i 〉 10 M in 0.03 au orbits. Since the mean rotation velocity is of the order of 8 km s –1 for an M6V star and 15 km s –1 for M9V, we avoid observing only slow rotators that would introduce a bias towards low axial inclination ( i 〈〈 90°) systems, which are unfavourable for planet detection. Our targets with the highest v sin  i values exhibit radial velocities significantly above the photon-noise-limited precision, even after accounting for v sin  i . We have therefore monitored stellar activity via chromospheric emission from the Hα and Ca ii infrared triplet lines. A clear trend of log 10 ( L Hα / L bol ) with radial velocity rms is seen, implying that significant starspot activity is responsible for the observed radial velocity precision floor. The implication that most late M dwarfs are significantly spotted, and hence exhibit time varying line distortions, indicates that observations to detect orbiting planets need strategies to reliably mitigate against the effects of activity-induced radial velocity variations.

Description: We present the orbital and physical parameters of the detached eclipsing binary V1200 Centauri (ASAS J135218–3837.3) from the analysis of spectroscopic observations and light curves from the All-Sky Automated Survey (ASAS) and SuperWASP (Wide Angle Search for Planets) data base. The radial velocities were computed from the high-resolution spectra obtained with the OUC (Observatorio Universidad Católica) 50-cm telescope and PUCHEROS (Pontificia Universidad Católica High Echelle Resolution Optical Spectrograph) spectrograph and with 1.2-m Euler telescope and CORALIE spectrograph using the cross-correlation technique todcor . We found that the absolute parameters of the system are M 1  = 1.394 ± 0.030 M , M 2  = 0.866 ± 0.015 M , R 1  = 1.39 ± 0.15 R , R 2  = 1.10 ± 0.25 R . We investigated the evolutionary status and kinematics of the binary and our results indicate that V1200 Centauri is likely a member of the Hyades moving group, but the largely inflated secondary's radius may suggest that the system may be even younger, around 30 Myr. We also found that the eclipsing pair is orbited by another, stellar-mass object on a 351-d orbit, which is unusually short for hierarchical triples. This makes V1200 Cen a potentially interesting target for testing the formation models of multiple stars.

Description: Seven linker histone H1 variants are present in human somatic cells with distinct prevalence across cell types. Despite being key structural components of chromatin, it is not known whether the different variants have specific roles in the regulation of nuclear processes or are differentially distributed throughout the genome. Using variant-specific antibodies to H1 and hemagglutinin (HA)-tagged recombinant H1 variants expressed in breast cancer cells, we have investigated the distribution of six H1 variants in promoters and genome-wide. H1 is depleted at promoters depending on its transcriptional status and differs between variants. Notably, H1.2 is less abundant than other variants at the transcription start sites of inactive genes, and promoters enriched in H1.2 are different from those enriched in other variants and tend to be repressed. Additionally, H1.2 is enriched at chromosomal domains characterized by low guanine–cytosine (GC) content and is associated with lamina-associated domains. Meanwhile, other variants are associated with higher GC content, CpG islands and gene-rich domains. For instance, H1.0 and H1X are enriched at gene-rich chromosomes, whereas H1.2 is depleted. In short, histone H1 is not uniformly distributed along the genome and there are differences between variants, H1.2 being the one showing the most specific pattern and strongest correlation with low gene expression.

Description: The star HR 8799 hosts one of the largest known debris discs and at least four giant planets. Previous observations have found evidence for a warm belt within the orbits of the planets, a cold planetesimal belt beyond their orbits and a halo of small grains. With the infrared data, it is hard to distinguish the planetesimal belt emission from that of the grains in the halo. With this in mind, the system has been observed with ALMA in band 6 (1.34 mm) using a compact array format. These observations allow the inner edge of the planetesimal belt to be resolved for the first time. A radial distribution of dust grains is fitted to the data using an MCMC method. The disc is best fitted by a broad ring between $145^{+12}_{-12}$ au and $429^{+37}_{-32}$ au at an inclination of $40^{+5}_{-6}{^{\circ }}$ and a position angle of $51^{+8}_{-8}{^{\circ }}$ . A disc edge at ~145 au is too far out to be explained simply by interactions with planet b, requiring either a more complicated dynamical history or an extra planet beyond the orbit of planet b.