ALBERT

Description: We report the results of spectrophotometric observations of the massive star MN18 revealed via discovery of a bipolar nebula around it with the Spitzer Space Telescope . Using the optical spectrum obtained with the Southern African Large Telescope, we classify this star as B1 Ia. The evolved status of MN18 is supported by the detection of nitrogen overabundance in the nebula, which implies that it is composed of processed material ejected by the star. We analysed the spectrum of MN18 by using the code cmfgen , obtaining a stellar effective temperature of 21 kK. The star is highly reddened, E ( B – V )  2 mag. Adopting an absolute visual magnitude of M V  = –6.8 ± 0.5 (typical of B1 supergiants), MN18 has a luminosity of log L /L   5.42 ± 0.30, a mass-loss rate of (2.8-4.5) x 10 – 7 M yr – 1 , and resides at a distance of 5.6 $^{+1.5} _{-1.2}$  kpc. We discuss the origin of the nebula around MN18 and compare it with similar nebulae produced by other blue supergiants in the Galaxy (Sher 25, HD 168625, [SBW2007] 1) and the Large Magellanic Cloud (Sk–69 $\deg$ 202). The nitrogen abundances in these nebulae imply that blue supergiants can produce them from the main-sequence stage up to the pre-supernova stage. We also present a K -band spectrum of the candidate luminous blue variable MN56 (encircled by a ring-like nebula) and report the discovery of an OB star at 17 arcsec from MN18. The possible membership of MN18 and the OB star of the star cluster Lynga 3 is discussed.

Description: We present the first reported case of the simultaneous metallicity determination of a gamma-ray burst (GRB) host galaxy, from both afterglow absorption lines as well as strong emission-line diagnostics. Using spectroscopic and imaging observations of the afterglow and host of the long-duration Swift GRB 121024A at z  = 2.30, we give one of the most complete views of a GRB host/environment to date. We observe a strong damped Lyα absorber (DLA) with a hydrogen column density of log  $N({\rm H\,{\small I}})\,=\,21.88\pm 0.10$ , H 2 absorption in the Lyman–Werner bands (molecular fraction of log( f ) –1.4; fourth solid detection of molecular hydrogen in a GRB-DLA), the nebular emission lines Hα, Hβ, [O ii ], [O iii ] and [N ii ], as well as metal absorption lines. We find a GRB host galaxy that is highly star forming (SFR ~ 40 M  yr –1 ), with a dust-corrected metallicity along the line of sight of [Zn/H] corr  = –0.6 ± 0.2 ([O/H] ~ –0.3 from emission lines), and a depletion factor [Zn/Fe] = 0.85 ± 0.04. The molecular gas is separated by 400 km s –1 (and 1–3 kpc) from the gas that is photoexcited by the GRB. This implies a fairly massive host, in agreement with the derived stellar mass of log( M * /M ) =  $9.9^{+0.2}_{-0.3}$ . We dissect the host galaxy by characterizing its molecular component, the excited gas, and the line-emitting star-forming regions. The extinction curve for the line of sight is found to be unusually flat ( R V  ~ 15). We discuss the possibility of an anomalous grain size distributions. We furthermore discuss the different metallicity determinations from both absorption and emission lines, which gives consistent results for the line of sight to GRB 121024A.

Description: We present optical observations of the peculiar Type Ibn supernova (SN Ibn) OGLE-2012-SN-006, discovered and monitored by the Optical Gravitational Lensing Experiment-IV survey, and spectroscopically followed by Public ESO Spectroscopic Survey of Transient Objects (PESSTO) at late phases. Stringent pre-discovery limits constrain the explosion epoch with fair precision to JD = 245 6203.8 ± 4.0. The rise time to the I -band light-curve maximum is about two weeks. The object reaches the peak absolute magnitude M I  = –19.65 ± 0.19 on JD = 245 6218.1 ± 1.8. After maximum, the light curve declines for about 25 d with a rate of 4 mag (100 d) –1 . The symmetric I -band peak resembles that of canonical Type Ib/c supernovae (SNe), whereas SNe Ibn usually exhibit asymmetric and narrower early-time light curves. Since 25 d past maximum, the light curve flattens with a decline rate slower than that of the 56 Co– 56 Fe decay, although at very late phases it steepens to approach that rate. However, other observables suggest that the match with the 56 Co decay rate is a mere coincidence, and the radioactive decay is not the main mechanism powering the light curve of OGLE-2012-SN-006. An early-time spectrum is dominated by a blue continuum, with only a marginal evidence for the presence of He i lines marking this SN type. This spectrum shows broad absorptions bluewards than 5000 Å, likely O ii lines, which are similar to spectral features observed in superluminous SNe at early epochs. The object has been spectroscopically monitored by PESSTO from 90 to 180 d after peak, and these spectra show the typical features observed in a number of SN 2006jc-like events, including a blue spectral energy distribution and prominent and narrow ( v FWHM   1900 km s –1 ) He i emission lines. This suggests that the ejecta are interacting with He-rich circumstellar material. The detection of broad (10 4 km s –1 ) O i and Ca ii features likely produced in the SN ejecta (including the [O i ] 6300,6364 doublet in the latest spectra) lends support to the interpretation of OGLE-2012-SN-006 as a core-collapse event.

Description: We present the first reported case of the simultaneous metallicity determination of a gamma-ray burst (GRB) host galaxy, from both afterglow absorption lines as well as strong emission-line diagnostics. Using spectroscopic and imaging observations of the afterglow and host of the long-duration Swift GRB 121024A at z  = 2.30, we give one of the most complete views of a GRB host/environment to date. We observe a strong damped Lyα absorber (DLA) with a hydrogen column density of log  $N({\rm H\,{\small I}})\,=\,21.88\pm 0.10$ , H 2 absorption in the Lyman–Werner bands (molecular fraction of log( f ) –1.4; fourth solid detection of molecular hydrogen in a GRB-DLA), the nebular emission lines Hα, Hβ, [O ii ], [O iii ] and [N ii ], as well as metal absorption lines. We find a GRB host galaxy that is highly star forming (SFR ~ 40 M  yr –1 ), with a dust-corrected metallicity along the line of sight of [Zn/H] corr  = –0.6 ± 0.2 ([O/H] ~ –0.3 from emission lines), and a depletion factor [Zn/Fe] = 0.85 ± 0.04. The molecular gas is separated by 400 km s –1 (and 1–3 kpc) from the gas that is photoexcited by the GRB. This implies a fairly massive host, in agreement with the derived stellar mass of log( M * /M ) =  $9.9^{+0.2}_{-0.3}$ . We dissect the host galaxy by characterizing its molecular component, the excited gas, and the line-emitting star-forming regions. The extinction curve for the line of sight is found to be unusually flat ( R V  ~ 15). We discuss the possibility of an anomalous grain size distributions. We furthermore discuss the different metallicity determinations from both absorption and emission lines, which gives consistent results for the line of sight to GRB 121024A.

Description: We report the results of spectrophotometric observations of the massive star MN18 revealed via discovery of a bipolar nebula around it with the Spitzer Space Telescope . Using the optical spectrum obtained with the Southern African Large Telescope, we classify this star as B1 Ia. The evolved status of MN18 is supported by the detection of nitrogen overabundance in the nebula, which implies that it is composed of processed material ejected by the star. We analysed the spectrum of MN18 by using the code cmfgen , obtaining a stellar effective temperature of 21 kK. The star is highly reddened, E ( B – V )  2 mag. Adopting an absolute visual magnitude of M V  = –6.8 ± 0.5 (typical of B1 supergiants), MN18 has a luminosity of log L /L   5.42 ± 0.30, a mass-loss rate of (2.8-4.5) x 10 – 7 M yr – 1 , and resides at a distance of 5.6 $^{+1.5} _{-1.2}$  kpc. We discuss the origin of the nebula around MN18 and compare it with similar nebulae produced by other blue supergiants in the Galaxy (Sher 25, HD 168625, [SBW2007] 1) and the Large Magellanic Cloud (Sk–69 $\deg$ 202). The nitrogen abundances in these nebulae imply that blue supergiants can produce them from the main-sequence stage up to the pre-supernova stage. We also present a K -band spectrum of the candidate luminous blue variable MN56 (encircled by a ring-like nebula) and report the discovery of an OB star at 17 arcsec from MN18. The possible membership of MN18 and the OB star of the star cluster Lynga 3 is discussed.

Description: We describe the pre-OmegaTranS project, a deep survey for transiting extra-solar planets in the Carina region of the Galactic disc. In 2006–2008, we observed a single dense stellar field with a very high cadence of ~2 min using the European Southern Observatory Wide Field Imager at the La Silla Observatory. Using the Astronomical Wide-field Imaging System for Europe environment and the Munich Difference Imaging Analysis pipeline, a module that has been developed for this project, we created the light curves of 16 000 stars with more than 4000 data points which we searched for periodic transit signals using a box-fitting least-squares detection algorithm. All light curves are publicly available. In the course of the pre-OmegaTranS project, we identified two planet candidates – POTS-1b and POTS-C2b – which we present in this work. With extensive follow-up observations we were able to confirm one of them, POTS-1b, a hot Jupiter transiting a mid-K dwarf. The planet has a mass of 2.31 ± 0.77  M Jup , a radius of 0.94 ± 0.04  R Jup and a period of P  = 3.16 d. The host star POTS-1 has a radius of 0.59 ± 0.02 R and a mass of 0.70 ± 0.05 M . Due to its low apparent brightness of I  = 16.1 mag, the follow-up and confirmation of POTS-1b was particularly challenging and costly.

Description: We identify a new candidate for a Be/X-ray binary in the XMM–Newton slew survey and archival Swift observations that is located in the transition region of the Wing of the Small Magellanic Cloud and the Magellanic Bridge. We investigated and classified this source with follow-up XMM–Newton and optical observations. We model the X-ray spectra and search for periodicities and variability in the X-ray observations and the Optical Gravitational Lensing Experiment I -band light curve. The optical counterpart has been classified spectroscopically, with data obtained at the South African Astronomical Observatory 1.9 m telescope, and photometrically, with data obtained using the Gamma-ray Burst Optical Near-ir Detector at the MPG 2.2 m telescope. The X-ray spectrum is typical of a high-mass X-ray binary with an accreting neutron star. We detect X-ray pulsations, which reveal a neutron-star spin period of P s  = (264.516 ± 0.014) s. The source likely shows a persistent X-ray luminosity of a few 10 35 erg s –1 and in addition type-I outbursts that indicate an orbital period of ~146 d. A periodicity of 0.867 d, found in the optical light curve, can be explained by non-radial pulsations of the Be star. We identify the optical counterpart and classify it as a B1-2II-IVe star. This confirms SXP 265 as a new Be/X-ray binary pulsar originating in the tidal structure between the Magellanic Clouds.

Description: Long gamma-ray burst's (LGRB's) association with the death of massive stars suggests that they could be used to probe the cosmic star formation history (CSFH) with high accuracy, due to their high luminosities. We utilize cosmological simulations from the First Billion Years project to investigate the biases between the CSFH and the LGRB rate at z  〉 5, assuming various different models and constraints on the progenitors of LGRBs. We populate LGRBs using a selection based on environmental properties and demonstrate that the LGRB rate should trace the CSFH to high redshifts. The measured LGRB rate suggests that LGRBs have opening angles of jet  = 0 $_{.}^{\circ}$ 1, although the degeneracy with the progenitor model cannot rule out an underlying bias. We demonstrate that proxies that relate the LGRB rate with global LGRB host properties do not reflect the underlying LGRB environment, and are in fact a result of the host galaxy's spatial properties, such that LGRBs can exist in galaxies of solar metallicity. However, we find a class of host galaxies that have low stellar mass and are metal rich, and that their metallicity dispersions would not allow low-metallicity environments. Detection of hosts with this set of properties would directly reflect the progenitor's environment. We predict that 10 per cent of LGRBs per year are associated with this set of galaxies that would have forbidden line emission that could be detected by instruments on the James Webb Space Telescope . Such a discovery would place strong constraints on the collapsar model and suggests other avenues to be investigated.

Description: The near-maximum spectra of most superluminous supernovae (SLSNe) that are not dominated by interaction with a H-rich circum-stellar medium (SLSN-I) are characterized by a blue spectral peak and a series of absorption lines which have been identified as O ii . SN 2011kl, associated with the ultra-long gamma-ray burst GRB111209A, also had a blue peak but a featureless optical/ultraviolet (UV) spectrum. Radiation transport methods are used to show that the spectra (not including SN 2007bi, which has a redder spectrum at peak, like ordinary SNe Ic) can be explained by a rather steep density distribution of the ejecta, whose composition appears to be typical of carbon–oxygen cores of massive stars which can have low metal content. If the photospheric velocity is ~10 000–15 000 km s –1 , several lines form in the UV. O ii lines, however, arise from very highly excited lower levels, which require significant departures from local thermodynamic equilibrium to be populated. These SLSNe are not thought to be powered primarily by 56 Ni decay. An appealing scenario is that they are energized by X-rays from the shock driven by a magnetar wind into the SN ejecta. The apparent lack of evolution of line velocity with time that characterizes SLSNe up to about maximum is another argument in favour of the magnetar scenario. The smooth UV continuum of SN 2011kl requires higher ejecta velocities (~20 000 km s –1 ): line blanketing leads to an almost featureless spectrum. Helium is observed in some SLSNe after maximum. The high-ionization near-maximum implies that both He and H may be present but not observed at early times. The spectroscopic classification of SLSNe should probably reflect that of SNe Ib/c. Extensive time coverage is required for an accurate classification.

Description: The nature of the ultraluminous X-ray sources (ULXs) in the nearby galaxies is a matter of debates. One of the popular hypothesis associates them with accretion at a sub-Eddington rate on to intermediate-mass black holes. Another possibility is a stellar-mass black hole in a high-mass X-ray binary accreting at super-Eddington rates. In this paper, we find a highly significant association between brightest X-ray sources in the Antennae galaxies and stellar clusters. On the other hand, we show that most of the X-ray sources are located outside of these clusters. We study clusters associated with the ULXs using the ESO Very Large Telescope spectra and the Hubble Space Telescope data together with the theoretical evolutionary tracks and determine their ages to be below 6 Myr. This implies that the ULX progenitor masses certainly exceed 30 and for some objects are closer to 100 M . We also estimate the ages of clusters situated close to the less luminous X-ray sources (with luminosity in the range 3  x 10 38   L X   10 39 erg s –1 ) and find that most of them are younger than 10 Myr, because they are surrounded by strong Hα emission. These findings are consistent with the idea that majority of ULXs are massive X-ray binaries that have been ejected in the process of formation of stellar clusters by a few-body encounters and at the same time rule out the proposal that most of the ULXs are intermediate-mass black holes.