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Stars can produce steady-state winds through radiative driving as long as the mechanical luminosity of the wind does not exceed the radiative luminosity at its base. This upper bound on the mass loss rate is known as the photon-tiring limit. Once above this limit, the radiation field is unable to lift all the material out of the gravitational potential of the star, such that only part of it can escape and reach infinity. The rest stalls and falls back toward the stellar surface, making a steady-state wind impossible. Photon-tiring is not an issue for line-driven winds since they cannot achieve sufficiently high mass loss rates. It can however become important if the star exceeds the Eddington limit and continuum interaction becomes the dominant driving mechanism. This paper investigates the time-dependent behaviour of stellar winds that exceed the photon-tiring limit, using 1-D numerical simulations of a porosity moderated, continuum-driven stellar wind. We find that the regions close to the star show a hierarchical pattern of high density shells moving back and forth, unable to escape the gravitational potential of the star. At larger distances, the flow eventually becomes uniformly outward, though still quite variable. Typically, these winds have a very high density but a terminal flow speed well below the escape speed at the stellar surface. Since most of the radiative luminosity of the star is used to drive the stellar wind, such stars would appear much dimmer than expected from the super-Eddington energy generation at their core. The visible luminosity typically constitutes less then half of the total energy flow and can become as low as ten percent or less for those stars that exceed the photon-tiring limit by a large margin., Comment: Accepted for publication in MNRAS

Massive stars with strong stellar winds are expected to have a huge impact on their interstellar surroundings, an effect which, in a surprisingly large number of cases, is not observed. This work is part of a concerted effort to obtain a better and more homogeneous observational data base with which to test the predictions of theoretical models. Analysis of the interstellar medium around the Of star HD 229196 shows that it coincides (in projection) with a region of lower radio continuum emission. This suggests that the star has shaped the surrounding interstellar medium via its ionizing flux and stellar wind. However, we find no clear evidence of the star's action in atomic hydrogen images. The radio continuum morphology and absence of a clear expanding H i shell are consistent with the possibility that the star, which is travelling supersonically at ∼30 km s-1 with respect to its local interstellar medium, is creating a weak bow shock. We cannot however rule out the possibility that the observed asymmetry is due to an inhomogeneous interstellar density distribution. We use data from the Canadian Galactic Plane Survey to carry out this study., Facultad de Ciencias Astronómicas y Geofísicas, Instituto Argentino de Radioastronomía

Context. R Coronae Borealis (R CrB) variable stars are suspected to sporadically eject optically thick dust clouds causing, when one of them lies on the line-of-sight, a huge brightness decline in visible light. Direct detections with 8-m class adaptive optics of such clouds located at about 0.2–0.3 arcsec from the center (∼1000 stellar radii) were recently reported for RY Sgr, the brightest R CrB of the southern hemisphere. Aims. Mid-infrared interferometric observations of RY Sgr allowed us to explore the circumstellar regions much closer to the central star (∼20–40 mas) to look for the signature of any heterogeneities and to characterize them. Methods. Using the VLTI/MIDI instrument, five dispersed visibility curves in the N-band were recorded in May and June 2005 with different projected baselines oriented towards two roughly perpendicular directions. The large spatial frequencies’ visibility curves exhibit a sinusoidal shape, whereas, at shorter spatial frequencies’ visibility curves follow a Gaussian decrease. These observations are well interpreted with a geometrical model consisting of a central star surrounded by an extended circumstellar envelope in which one bright cloud is embedded. Results. Within this simple geometrical scheme, the inner 110 AU dusty environment of RY Sgr is dominated at the time of observations by a single dusty cloud, which at 10 µm represents ∼10% of the total flux of the whole system, slightly less that the star flux. The cloud is located at about 100 stellar radii (or ∼30 AU) from the center toward the East-North-East direction (or the symmetric direction with respect to center) within a circumstellar envelope whose FWHM is about 120 stellar radii. This first detection of a cloud so close to the central star supports the classical scenario of the R CrB brightness variations in the optical spectral domain and demonstrates the feasibility of a temporal monitoring of the dusty environment of this star on a monthly scale.

ALMA observations show a non-detection of carbon monoxide around the four most luminous asymptotic giant branch (AGB) stars in the globular cluster 47 Tucanae. Stellar evolution models and star counts show that the mass-loss rates from these stars should be ~1.2-3.5 x 10^-7 solar masses per year. We would naively expect such stars to be detectable at this distance (4.5 kpc). By modelling the ultraviolet radiation field from post-AGB stars and white dwarfs in 47 Tuc, we conclude CO should be dissociated abnormally close to the stars. We estimate that the CO envelopes will be truncated at a few hundred stellar radii from their host stars and that the line intensities are about two orders of magnitude below our current detection limits. The truncation of CO envelopes should be important for AGB stars in dense clusters. Observing the CO (3-2) and higher transitions and targeting stars far from the centres of clusters should result in the detections needed to measure the outflow velocities from these stars., Comment: 14 pages, 4 figures, accepted MNRAS

We present our findings on a supernova (SN) impostor, SNHunt248, based on optical and near-IR data spanning $\sim$15 yrs before discovery, to $\sim$1 yr post-discovery. The light curve displays three distinct peaks, the brightest of which is at $M_{R} \sim -15.0$ mag. The post-discovery evolution is consistent with the ejecta from the outburst interacting with two distinct regions of circumstellar material. The 0.5 - 2.2 $\mu$m spectral energy distribution at -740 d is well-matched by a single 6700 K blackbody with $\log(L/L_\odot) \sim 6.1$. This temperature and luminosity support previous suggestions of a yellow hypergiant progenitor; however, we find it to be brighter than the brightest and most massive Galactic late-F to early-G spectral type hypergiants. Overall the historical light curve displays variability of up to $\sim \pm1$ mag. At current epochs ($\sim$1 yr post-outburst), the absolute magnitude ($M_{R} \sim -9$ mag) is just below the faintest observed historical absolute magnitude $\sim$10 yrs before discovery., Comment: 7 pages, 3 figures, accepted for A&A Letters

Titanium dioxide, TiO$_2$, is a refractory species that could play a crucial role in the dust-condensation sequence around oxygen-rich evolved stars. To date, gas phase TiO$_2$ has been detected only in the complex environment of the red supergiant VY CMa. We aim to constrain the distribution and excitation of TiO$_2$ around VY CMa in order to clarify its role in dust formation. We analyse spectra and channel maps for TiO$_2$ extracted from ALMA science verification data. We detect 15 transitions of TiO$_2$, and spatially resolve the emission for the first time. The maps demonstrate a highly clumpy, anisotropic outflow in which the TiO$_2$ emission likely traces gas exposed to the stellar radiation field. A roughly east-west oriented, accelerating bipolar-like structure is found, of which the blue component runs into and breaks up around a solid continuum component. A distinct tail to the south-west is seen for some transitions, consistent with features seen in the optical and near-infrared. We find that a significant fraction of TiO$_2$ remains in the gas phase outside the dust-formation zone and suggest that this species might play only a minor role in the dust-condensation process around extreme oxygen-rich evolved stars like VY CMa., Accepted for publication in Astronomy & Astrophysics, 25 pages, 20 figures

We report the late-time evolution of Type IIb supernova (SN IIb) 2013df. SN 2013df showed a dramatic change in its spectral features at ∼1 yr after the explosion. Early on it showed typical characteristics shared by SNe IIb/Ib/Ic dominated by metal emission lines, while later on it was dominated by broad and flat-topped H and He i emissions. The late-time spectra are strikingly similar to SN IIb 1993J, which is the only previous example clearly showing the same transition. This late-time evolution is fully explained by a change in the energy input from the 56Co decay to the interaction between the SN ejecta and dense circumstellar matter (CSM). The mass-loss rate is derived to be ~ (5.4 ± 3.2) 10-5 M⊙ yr-1 (for the wind velocity of ∼20 km s-1), similar to SN 1993J but larger than SN IIb 2011dh by an order of magnitude. The striking similarity between SNe IIb 2013df and 1993J in the (candidate) progenitors and the CSM environments and the contrast in these natures to SN 2011dh infer that there is a link between the natures of the progenitor and the mass loss: SNe IIb with a more extended progenitor have experienced a much stronger mass loss in the final centuries toward the explosion. It might indicate that SNe IIb from a more extended progenitor are the explosions during a strong binary interaction phase, while those from a less extended progenitor have a delay between the strong binary interaction and the explosion., La lista completa de autores que integran el documento puede consultarse en el archivo., Facultad de Ciencias Astronómicas y Geofísicas, Instituto de Astrofísica de La Plata

Spatially resolved multi-wavelength centimeter continuum observations of cool evolved stars can not only constrain the morphology of the radio emitting regions, but can also directly probe the mean gas temperature at various depths of the star's extended atmosphere. Here, we use the Very Large Array (VLA) in the A configuration with the Pie Town (PT) Very Long Baseline Array (VLBA) antenna to spatially resolve the extended atmosphere of Betelgeuse over multiple epochs at 0.7, 1.3, 2.0, 3.5, and 6.1 cm. The extended atmosphere deviates from circular symmetry at all wavelengths while at some epochs we find possible evidence for small pockets of gas significantly cooler than the mean global temperature. We find no evidence for the recently reported e-MERLIN radio hotspots in any of our multi-epoch VLA/PT data, despite having sufficient spatial resolution and sensitivity at short wavelengths, and conclude that these radio hotspots are most likely interferometric artefacts. The mean gas temperature of the extended atmosphere has a typical value of 3000 K at 2 R∗ and decreases to 1800 K at 6 R∗, in broad agreement with the findings of the single epoch study from Lim et al. (1998, Nature, 392, 575). The overall temperature profile of the extended atmosphere between 2 R∗ ≲ r ≲ 6 R∗ can be described by a power law of the form Tgas(r) ∝ r-0.6, with temporal variability of a few 100 K evident at some epochs. Finally, we present over 12 yr of V band photometry, part of which overlaps our multi-epoch radio data. We find a correlation between the fractional flux density variability at V band with most radio wavelengths. This correlation is likely due to shock waves induced by stellar pulsations, which heat the inner atmosphere and ionize the more extended atmosphere through radiative means. Stellar pulsations may play an important role in exciting Betelgeuse's extended atmosphere.

OH 231.8+4.2, a bipolar outflow around a Mira-type variable star, displays a unique molecular richness amongst circumstellar envelopes (CSEs) around O-rich AGB and post-AGB stars. We report line observations of the HCO+ and H13CO+ molecular ions and the first detection of SO+, N2H+, and (tentatively) H3O+ in this source. SO+ and H3O+ have not been detected before in CSEs around evolved stars. These data have been obtained as part of a full mm-wave and far-IR spectral line survey carried out with the IRAM 30 m radio telescope and with Herschel/HIFI. Except for H3O+, all the molecular ions detected in this work display emission lines with broad profiles (FWHM ~ 50−90 km s-1), which indicates that these ions are abundant in the fast bipolar outflow of OH 231.8. The narrow profile (FWHM ~ 14 km s-1) and high critical densities (>106 cm-3) of the H3O+ transitions observed are consistent with this ion arising from denser, inner (and presumably warmer) layers of the fossil remnant of the slow AGB CSE at the core of the nebula. From rotational diagram analysis, we deduce excitation temperatures of Tex~ 10−20 K for all ions except for H3O+, which is most consistent with Tex≈ 100 K. Although uncertain, the higher excitation temperature suspected for H3O+ is similar to that recently found for H2O and a few other molecules, which selectively trace a previously unidentified, warm nebular component. The column densities of the molecular ions reported here are in the range Ntot≈ [1−8] × 1013 cm-2, leading to beam-averaged fractional abundances relative to H2 of X(HCO+) ≈ 10-8, X(H13CO+) ≈2 × 10-9, X(SO+) ≈4 × 10-9, X(N2H+) ≈2 × 10-9, and X(H3O+) ≈7 × 10-9 cm-2. We have performed chemical kinetics models to investigate the formation of these ions in OH 231.8 as the result of standard gas phase reactions initiated by cosmic-ray and UV-photon ionization. The model predicts that HCO+, SO+, and H3O+ can form with abundances comparable to the observed average values in the external layers of the slow central core (at ~[3−8] × 1016 cm); H3O+ would also form quite abundantly in regions closer to the center (X(H3O+) ~ 10-9 at ~1016 cm). For N2H+, the model abundance is lower than the observed value by more than two orders of magnitude. The model fails to reproduce the abundance enrichment of HCO+, SO+, and N2H+ in the lobes, which is directly inferred from the broad emission profiles of these ions. Also, in disagreement with the narrow H3O+ spectra, the model predicts that this ion should form in relatively large, detectable amounts (≈10-9) in the external layers of the slow central core and in the high-velocity lobes. Some of the model-data discrepancies are reduced, but not suppressed, by lowering the water content and enhancing the elemental nitrogen abundance in the envelope. The remarkable chemistry of OH 231.8 probably reflects the molecular regeneration process within its envelope after the passage of fast shocks that accelerated and dissociated molecules in the AGB wind ~800 yr ago., This work has been partially supported by the Spanish MINECO through grants CSD2009-00038, AYA2009-07304, and AYA2012-32032.

4U 1538-52, an absorbed high mass X-ray binary with an orbital period of 3.73 days, shows moderate orbital intensity modulations with a low level of counts during the eclipse. Several models have been proposed to explain the accretion at different orbital phases by a spherically symmetric stellar wind from the companion. The aim of this work is to study both the light curve and orbital phase spectroscopy of this source in the long term. Particularly, the folded light curve and the changes of the spectral parameters with orbital phase to analyse the stellar wind of QV Nor, the mass donor of this binary system. We used all the observations made from the Gas Slit Camera on board MAXI of 4U 1538-52 covering many orbits continuously. We obtained the good interval times for every orbital phase range which were the input to extract our data. We estimated the orbital period of the system and then folded the light curves and we fitted the X-ray spectra with the same model for every orbital phase spectrum. We also extracted the averaged spectrum of all the MAXI data available. The MAXI spectra in the 2-20 keV energy range were fitted with an absorbed Comptonization of cool photons on hot electrons. We found a strong orbital dependence of the absorption column density but neither the fluorescence iron emission line nor low energy excess were needed to fit the MAXI spectra. The variation of the spectral parameters over the binary orbit were used to examine the mode of accretion onto the neutron star in 4U 1538-52. We deduce a best value of $\dot{M}/v_\infty=0.65\times 10^{-9}$ $M_{\odot} \, yr^{-1}/(km \, s^{-1})$ for QV Nor., 12 pages, 5 figures, accepted to be published by A&A, corrected typos (changing bold font to normal one)

The progenitor stars of several Type IIb supernovae (SNe) show indications for extended hydrogen envelopes. These envelopes might be the outcome of luminous energetic pre-explosion events, so-called precursor eruptions. We use the Palomar Transient Factory (PTF) pre-explosion observations of a sample of 27 nearby Type IIb SNe to look for such precursors during the final years prior to the SN explosion. No precursors are found when combining the observations in 15-day bins, and we calculate the absolute-magnitude-dependent upper limit on the precursor rate. At the 90% confidence level, Type IIb SNe have on average $, 16 pages, 10 figures

We report on both high-precision photometry from the Microvariability and Oscillations of Stars (MOST) space telescope and ground-based spectroscopy of the triple system δ Ori A, consisting of a binary O9.5II+early-B (Aa1 and Aa2) with P = 5.7 days, and a more distant tertiary (O9 IV years). This data was collected in concert with X-ray spectroscopy from the Chandra X-ray Observatory. Thanks to continuous coverage for three weeks, the MOST light curve reveals clear eclipses between Aa1 and Aa2 for the first time in non-phased data. From the spectroscopy, we have a well-constrained radial velocity (RV) curve of Aa1. While we are unable to recover RV variations of the secondary star, we are able to constrain several fundamental parameters of this system and determine an approximate mass of the primary using apsidal motion. We also detected second order modulations at 12 separate frequencies with spacings indicative of tidally influenced oscillations. These spacings have never been seen in a massive binary, making this system one of only a handful of such binaries that show evidence for tidally induced pulsations., La lista completa de autores que integran el documento puede consultarse en el archivo., Facultad de Ciencias Astronómicas y Geofísicas, Instituto de Astrofísica de La Plata

Aim: The late stages of stellar evolution are mainly governed by the mass of the stars. Low- and intermediate-mass stars lose copious amounts of mass during the asymptotic giant branch (AGB) which obscure the central star making it difficult to study the stellar spectra and determine the stellar mass. In this study, we present observational data that can be used to determine lower limits to the stellar mass. Method: Spectra of nine heavily reddened AGB stars taken by the Herschel Space Observatory display numerous molecular emission lines. The strongest emission lines are due to H2O. We search for the presence of isotopologues of H2O in these objects. Result: We detected the 16O and 17O isotopologues of water in these stars, but lines due to H2^{18}O are absent. The lack of 18O is predicted by a scenario where the star has undergone hot-bottom burning which preferentially destroys 18O relative to 16O and 17O. From stellar evolution calculations, this process is thought to occur when the stellar mass is above 5 Msun for solar metallicity. Hence, observations of different isotopologues of H2O can be used to help determine the lower limit to the initial stellar mass. Conclusion: From our observations, we deduce that these extreme OH/IR stars are intermediate-mass stars with masses of >= 5 Msun. Their high mass-loss rates of ~ 1.0e-4 Msun/yr may affect the enrichment of the interstellar medium and the overall chemical evolution of our Galaxy., Accepted for publication in A&A. 50 pages including online material (28 figures)

Through CO mm-line and optical spectroscopy, we investigate the properties of the Fried Egg nebula IRAS 17163-3907, which has recently been proposed to be one of the rare members of the yellow hypergiant class. The CO J=2-1 and J=3-2 emission arises from a region within 20" of the star and is clearly associated with the circumstellar material. The CO lines show a multi-component asymmetrical profile, and an unexpected velocity gradient is resolved in the east-west direction, suggesting a bipolar outflow. This is in contrast with the apparent symmetry of the dust envelope as observed in the infrared. The optical spectrum of IRAS 17163-3907 between 5100 and 9000 {\AA} was compared with that of the archetypal yellow hypergiant IRC+10420 and was found to be very similar. These results build on previous evidence that IRAS 17163-3907 is a yellow hypergiant., Comment: 14 pages including appendix, accepted for publication in A&A

CONTEXT: Spectroscopic analysis remains the most common method to derive masses of massive stars, the most fundamental stellar parameter. While binary orbits and stellar pulsations can provide much sharper constraints on the stellar mass, these methods are only rarely applicable to massive stars. Unfortunately, spectroscopic masses of massive stars heavily depend on the detailed physics of model atmospheres. AIMS: We demonstrate the impact of a consistent treatment of the radiative pressure on inferred gravities and spectroscopic masses of massive stars. Specifically, we investigate the contribution of line and continuum transitions to the photospheric radiative pressure. We further explore the effect of model parameters, e.g., abundances, on the deduced spectroscopic mass. Lastly, we compare our results with the plane-parallel TLUSTY code, commonly used for the analysis of massive stars with photospheric spectra. METHODS: We calculate a small set of O-star models with the Potsdam Wolf-Rayet (PoWR) code using different approaches for the quasi-hydrostatic part. These models allow us to quantify the effect of accounting for the radiative pressure consistently. We further use PoWR models to show how the Doppler widths of line profiles and abundances of elements such as iron affect the radiative pressure, and, as a consequence, the derived spectroscopic masses. RESULTS: Our study implies that errors on the order of a factor of two in the inferred spectroscopic mass are to be expected when neglecting the contribution of line and continuum transitions to the radiative acceleration in the photosphere. Usage of implausible microturbulent velocities, or the neglect of important opacity sources such as Fe, may result in errors of approximately 50% in the spectroscopic mass. A comparison with TLUSTY model atmospheres reveals a very good agreement with PoWR at the limit of low mass-loss rates., 13 pages, 10 figures, accepted for publication in A&A

We study the circumstellar evolution of the binary HD101584, consisting of a post-AGB star and a low-mass companion, which is most likely a post-common-envelope-evolution system. We used ALMA observations of the 12CO, 13CO, and C18O J=2-1 lines and the 1.3mm continuum to determine the morphology, kinematics, masses, and energetics of the circumstellar environment. The circumstellar medium has a bipolar hour-glass structure, seen almost pole-on, formed by an energetic jet, about 150 km/s. We conjecture that the circumstellar morphology is related to an event that took place about 500 year ago, possibly a capture event where the companion spiraled in towards the AGB star. However, the kinetic energy of the accelerated gas exceeds the released orbital energy, and, taking into account the expected energy transfer efficiency of the process, the observed phenomenon does not match current common-envelope scenarios. This suggests that another process must augment, or even dominate, the ejection process. A significant amount of material resides in an unresolved region, presumably in the equatorial plane of the binary system., Comment: A&A Letter, accepted

Aims. They are the interpretation of the emission line formation regions in CI Cygni. Methods. They involve the examination of radial velocities and fluxes of ultraviolet emission lines at different epochs, deduced from archival IUE and GRHS/HST spectra. Results. The line fluxes give electron densities and were in addition used to calculate emission measures, suggesting line formation in regions rather smaller than the binary separation. Examination of the radial velocities led to us to find a systematic redshift of the high ionization resonance lines with respect to the intercombination, and He ii lines. Possible explanations of the redshift and the high resolution GHRS C iv profile are discussed. We favour that involving resonance line absorption by a circum-binary region most probably in an asymmetric wind interaction shell or in a wind from the accretion disk., Facultad de Ciencias Astronómicas y Geofísicas

Aims.Analysis of the innermost regions of the carbon-rich star IRC+10216 and of the outer layers of its circumstellar envelope have been performed in order to constrain its mass-loss history. Methods: .We analyzed the high dynamic range of near-infrared adaptive optics and the deep V-band images of the circumstellar envelope of IRC+10216 using high angular resolution, collected with the VLT/NACO and FORS1 instruments. Results: .From the near-infrared observations, we present maps of the sub-arcsecond structures, or clumps, in the innermost regions. The morphology of these clumps is found to strongly vary from J- to L-band. Their relative motion appears to be more complex than proposed in earlier works: they can be weakly accelerated, have a constant velocity, or even be motionless with respect to one another. From V-band imaging, we present a high spatial resolution map of the shell distribution in the outer layers of IRC+10216. Shells are resolved well up to a distance of about 90'' to the core of the nebula and most of them appear to be composed of thinner elongated shells. Finally, by combining the NACO and FORS1 images, a global view is present to show both the extended layers and the bipolar core of the nebula together with the real size of the inner clumps. Conclusions: .This study confirms the rather complex nature of the IRC+10216 circumstellar environment. In particular, the coexistence at different spatial scales of structures with very different morphologies (clumps, bipolarity, and almost spherical external layers) is very puzzling. This confirms that the formation of AGB winds is far more complex than usually assumed in current models., Comment: Published in Astronomy & Astrophysics, 2006, 455, 187

We present the first spectroscopic data for a sample of the recently discovered blue double-periodic variables in the Magellanic Clouds. The optical spectrum of these objects is dominated by Balmer and helium absorption lines and a continuum with a blue or sometimes flat slope. Spectral classification yields B spectral types and luminosity classes mostly of type III. However, the Hβ absorption line is weaker than expected for the spectral classification in most objects. For two objects, OGLE 05060009-6855025 and OGLE 05195898-6917013 we obtained time-resolved spectroscopy, finding radial velocity variations consistent with binarity. Phasing the short-term photometric variability of these two systems with their spectroscopic ephemeris, we find that they can be interpreted as ellipsoidal variations of the brighter component in a close binary system. From the analysis of their short-term light curves and radial velocities, we estimate that the cooler component could be a B-type dwarf. Our findings support the hypothesis that double-periodic variables are close binary systems consisting of two B-type stars. The shorter periodicity in non-eclipsing systems should be the ellipsoidal variation of the more evolved component. Regarding the long-term periodicity, we find their origin in or around the brighter star, as the oscillations virtually disappear at primary eclipse. Their nature remains unknown, at the present time. We also report the discovery of three (two of them eclipsing) new double-periodic variables in the Large Magellanic Cloud. One of them shows a shortening of the long-term period by approximately 20 per cent in a couple of cycles, which coincides with an increase of the maximum oscillation brightness., Facultad de Ciencias Astronómicas y Geofísicas

We investigate the effect of rotation on the maximum mass-loss rate due to an optically-thin radiatively-driven wind according to a formalism which takes into account the possible presence of any instability at the base of the wind that might increase the mass-loss rate. We include the Von Zeipel effect and the oblateness of the star in our calculations. We determine the maximum surface-integrated mass that can be lost from a star by line driving as a function of rotation for a number of relevant stellar models of massive OB stars with luminosities in the range of 5.0 < log (L/L-&ODOT;) < 6.0. We also determine the corresponding maximum loss of angular momentum. We find that rotation increases the maximum mass-loss rate by a moderate factor for stars far from the Eddington limit as long as the ratio of equatorial to critical velocity remains below 0.7. For higher ratios, however, the temperature, flux and Eddington factor distributions change considerably over the stellar surface such that extreme mass loss is induced. Stars close to the Eddington-Gamma limit suffer extreme mass loss already for a low equatorial rotation velocity. We compare the maximum mass-loss rates as a function of rotation velocity with other predicted relations available in the literature which do not take into account possible instabilities at the stellar surface and we find that the inclusion thereof leads to extreme mass loss at much lower rotation rates. We present a scaling law to predict maximum mass-loss rates. Finally, we provide a mass-loss model for the LBVeta Carinae that is able to explain the large observed current mass-loss rate of similar to10(-3) M-circle dot yr(-1) but that leads to too low wind velocities compared to those derived from observations. ispartof: Astronomy & astrophysics vol:418 issue:2 pages:639-648 status: published

18 pags., 17 figs., 4 tabs., We present interferometric and single-dish molecular line observations of the interstellar bullet-outflow source IRAS 05506+2414, whose wide-angle bullet spray is similar to the Orion BN/KL explosive outflow and likely arises from an entirely different mechanism than the classical accretion-disk-driven bipolar flows in young stellar objects. The bullet-outflow source is associated with a large pseudo-disk and three molecular outflows - a high-velocity outflow (HVO), a medium-velocity outflow (MVO), and a slow, extended outflow (SEO). The size (mass) of the pseudo-disk is 10,350 au ×6400 au (0.64-0.17 M ); from a model-fit assuming infall and rotation, we derive a central stellar mass of 8-19 M . The HVO (MVO) has an angular size ∼5180 (∼3330) au and a projected outflow velocity of ∼140 km s (∼30 km s). The SEO size (outflow speed) is ∼0.9 pc (∼6 km s). The HVO's axis is aligned with (orthogonal to) that of the SEO (pseudo-disk). The velocity structure of the MVO is unresolved. The scalar momenta in the HVO and SEO are very similar, suggesting that the SEO has resulted from the HVO interacting with ambient-cloud material. The bullet spray shares a common axis with the pseudo-disk and has an age comparable to that of MVO (few hundred years), suggesting that these three structures are intimately linked. We discuss several models for the outflows in IRAS 05506+2414 (including dynamical decay of a stellar cluster, chance encounter of a runaway star with a dense cloud, and close passage of two protostars), and conclude that second-epoch imaging to derive proper motions of the bullets and nearby stars can help to discriminate between them., R.S.’s contribution to the research described here was carried out at the Jet Propulsion Laboratory (JPL), California Institute of Technology, under a contract with NASA. Financial support was provided by NASA, in part from HST/GO awards (nos. GO-09463.01-A and GO-09801.01-A) from the Space Telescope Science Institute (operated by the Association of Universities for Research in Astronomy, under NASA contract NAS5–26555). C.S.C. is supported by the Spanish MINECO through grants AYA2016-75066-C2-1-P and AYA2012-32032, and by the European Research Council through grant ERC-2013-SyG 610256. C.-F.L. acknowledges grants from the Ministry of Science and Technology of Taiwan (MoST 104-2119-M-001-015-MY3) and the Academia Sinica (Career Development Award). The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Infrared observations of the dusty, massive Homunculus Nebula around the luminous blue variable $\eta$ Carinae are crucial to characterize the mass-loss history and help constrain the mechanisms leading to the Great Eruption. We present the 2.4 - 670 $\mu$m spectral energy distribution, constructed from legacy ISO observations and new spectroscopy obtained with the {\em{Herschel Space Observatory}}. Using radiative transfer modeling, we find that the two best-fit dust models yield compositions which are consistent with CNO-processed material, with iron, pyroxene and other metal-rich silicates, corundum, and magnesium-iron sulfide in common. Spherical corundum grains are supported by the good match to a narrow 20.2 $\mu$m feature. Our preferred model contains nitrides AlN and Si$_3$N$_4$ in low abundances. Dust masses range from 0.25 to 0.44 $M_\odot$ but $M_{\rm{tot}} \ge$ 45 $M_\odot$ in both cases due to an expected high Fe gas-to-dust ratio. The bulk of dust is within a 5$"$ $\times$ 7$"$ central region. An additional compact feature is detected at 390 $\mu$m. We obtain $L_{\rm{IR}}$ = 2.96 $\times$ 10$^6$ $L_\odot$, a 25\% decline from an average of mid-IR photometric levels observed in 1971-1977. This indicates a reduction in circumstellar extinction in conjunction with an increase in visual brightness, allowing 25-40\% of optical and UV radiation to escape from the central source. We also present an analysis of $^{12}$CO and $^{13}$CO $J = 5-4$ through $9-8$ lines, showing that the abundances are consistent with expectations for CNO-processed material. The [$^{12}$C~{\sc{ii}}] line is detected in absorption, which we suspect originates in foreground material at very low excitation temperatures., Comment: Accepted in ApJ

[Context] M 2-9 is a young planetary nebula (PN) that shows the characteristics of its last ejections in unprecedented detail. These last ejections are thought to trigger the post-asymptotic giant branch evolution., [Aims] To assemble an overall picture of how M 2-9 was shaped, we analyzed the characteristics of the different molecular gas components and their relation with the warmer parts of the nebula that are visible in the optical domain., [Methods] CO and CO J = 3-2 line emission maps were obtained with the Atacama Large Millimeter/submillimeter Array with high angular-resolution and sensitivity., [Results] Two equatorial rings are found to host most of the cold molecular gas in M 2-9, as has been described for previous CO J = 2-1 emission observations. In addition, we have detected a double crown-shaped structure that is symmetric with respect to the main nebular axis, which is located 1.5′′ away from both sides of the equatorial plane. Their distribution and kinematics show a very close relationship with the inner molecular ring: Both are part of the same small hourglass structure formed ∼900 yr ago. Two clearly distinct ejections with a remarkable axial symmetry are found to have shaped the molecular gas distribution in M 2-9, in agreement with the ejection processes that were probably responsible for the optical lobes. For the first time, the physical conditions of the different molecular components in M 2-9 are comprehensively analyzed with a radiative transfer model. They are found to follow standard laws, like those obtained in other young PN, with densities and temperatures decreasing with radius and ballistic expansion. A total mass of ∼5 × 10M was derived for the detected molecular component, the larger and older equatorial ring hosting most (∼90%) of this gas., This work has also been supported by the Spanish MINECO, grants AYA2016-78994-P and FIS2012-32096, and by the European Research Council (ERC) Grant 610256: NANOCOSMOS.

We report observations of $\eta$ Carinae obtained with ALMA in the continuum of 100, 230, 280 and 660 GHz in 2012 November, with a resolution that varied from 2.88" to 0.45" for the lower and higher frequencies respectively. The source is not resolved, even at the highest frequency; its spectrum is characteristic of thermal bremsstrahlung of a compact source, but different from the spectrum of optically thin wind. The recombination lines H42$\alpha$, He42$\alpha$, H40$\alpha$, He40$\alpha$, H50$\beta$, H28$\alpha$, He28$\alpha$, H21$\alpha$ and He21$\alpha$ were also detected and their intensities reveal non local thermodynamic equilibrium (NLTE) effects. We found that the line profiles could only be fit by an expanding shell of dense and ionized gas, which produces a slow shock in the surroundings of $\eta$ Carinae. Combined with fittings to the continuum, we were able to constrain the shell size, radius, density, temperature and velocity. The detection of the He recombination lines is compatible with the high temperature gas and requires a high energy ionizing photon flux, which must be provided by the companion star. The mass loss rate and wind velocity, necessary to explain the formation of the shell, are compatible with a LBV eruption. The position, velocity and physical parameters of the shell coincide with those of the Weigelt blobs. The dynamics found for the expanding shell corresponds to matter ejected by $\eta$ Carinae in 1941, in an event similar to that which formed the Little Homunculus ; for that reason we called the new ejecta the "Baby Homunculus"., Comment: 15 pages, 10 figures, accepted, Astrophysical Journal

There is a growing number of supernovae (SNe), mainly of Type IIn, which present an outburst prior to their presumably final explosion. These precursors may affect the SN display, and are likely related to some poorly charted phenomena in the final stages of stellar evolution. Here we present a sample of 16 SNe IIn for which we have Palomar Transient Factory (PTF) observations obtained prior to the SN explosion. By coadding these images taken prior to the explosion in time bins, we search for precursor events. We find five Type IIn SNe that likely have at least one possible precursor event, three of which are reported here for the first time. For each SN we calculate the control time. Based on this analysis we find that precursor events among SNe IIn are common: at the one-sided 99% confidence level, more than 50% of SNe IIn have at least one pre-explosion outburst that is brighter than absolute magnitude -14, taking place up to 1/3 yr prior to the SN explosion. The average rate of such precursor events during the year prior to the SN explosion is likely larger than one per year, and fainter precursors are possibly even more common. We also find possible correlations between the integrated luminosity of the precursor, and the SN total radiated energy, peak luminosity, and rise time. These correlations are expected if the precursors are mass-ejection events, and the early-time light curve of these SNe is powered by interaction of the SN shock and ejecta with optically thick circumstellar material., 15 pages, 20 figures, submitted to ApJ

Interaction of supernova (SN) ejecta with the optically thick circumstellar medium (CSM) of a progenitor star can result in a bright, long-lived shock breakout event. Candidates for such SNe include Type IIn and superluminous SNe. If some of these SNe are powered by interaction, then there should be a relation between their peak luminosity, bolometric light-curve rise time, and shock-breakout velocity. Given that the shock velocity during shock breakout is not measured, we expect a correlation, with a significant spread, between the rise time and the peak luminosity of these SNe. Here, we present a sample of 15 SNe IIn for which we have good constraints on their rise time and peak luminosity from observations obtained using the Palomar Transient Factory. We report on a possible correlation between the R-band rise time and peak luminosity of these SNe, with a false-alarm probability of 3%. Assuming that these SNe are powered by interaction, combining these observables and theory allows us to deduce lower limits on the shock-breakout velocity. The lower limits on the shock velocity we find are consistent with what is expected for SNe (i.e., ~10^4 km/s). This supports the suggestion that the early-time light curves of SNe IIn are caused by shock breakout in a dense CSM. We note that such a correlation can arise from other physical mechanisms. Performing such a test on other classes of SNe (e.g., superluminous SNe) can be used to rule out the interaction model for a class of events., Accepted to ApJ, 6 pages

Massive stars likely played an important role in the reionization of the Universe, and the formation of the first black holes. Massive stars in low-metallicity environments in the local Universe are reminiscent of their high redshift counterparts. In a previous paper, we reported on indications that the stellar winds of low-metallicity O stars may be stronger than predicted, which would challenge the current paradigm of massive star evolution. In this paper, we aim to extend our initial sample of six O stars in low-metallicity environments by four. We aim to derive their stellar and wind parameters, and compare these to radiation-driven wind theory and stellar evolution models. We have obtained intermediate-resolution VLT/X-Shooter spectra of our sample of stars. We derive the stellar parameters by fitting synthetic fastwind line profiles to the VLT/X-Shooter spectra using a genetic fitting algoritm. We compare our parameters to evolutionary tracks and obtain evolutionary masses and ages. We also investigate the effective temperature versus spectral type calibration for SMC and lower metallicities. Finally, we reassess the wind momentum versus luminosity diagram. The derived parameters of our target stars indicate stellar masses that reach values of up to 50 $M_{\odot}$. The wind strengths of our stars are, on average, stronger than predicted from radiation-driven wind theory and reminiscent of stars with an LMC metallicity. We discuss indications that the iron content of the host galaxies is higher than originally thought and is instead SMC-like. We find that the discrepancy with theory is lessened, but remains significant for this higher metallicity. This may imply that our current understanding of the wind properties of massive stars, both in the local universe as well as at cosmic distances, remains incomplete., Accepted for publication in Astronomy and Astrophysics. 10 pages, 8 figures

(Abridged) Some supernovae (SNe) may be powered by the interaction of the SN ejecta with a large amount of circumstellar matter (CSM). Here we outline a method to measure the mass of the optically thick CSM around such SNe. We present observations of SN2010jl, including the first detection of a SN using NuSTAR. The total radiated luminosity of SN2010jl is extreme, at least 9e50 erg. By modeling the visible-light data, we robustly show that the mass of the circumstellar material within ~1e16 cm of the progenitor was in excess of 10 solar masses, likely ejected tens of years prior to the SN explosion. Our modeling suggests that the shock velocity during shock breakout was ~6000 km/s, decelerating to ~2600 km/s about two years after maximum light. Our late-time NuSTAR+XMM spectra of the SN presumably provide the first direct measurement of SN shock velocity two years after the SN maximum light -- measured to be in the range of 2000 to 4500 km/s if the ions and electrons are in equilibrium, and >~2000 km/s if they are not in equilibrium. This measurement is in agreement with the shock velocity predicted by our modeling of the optical data. We also show that the mean radial density distribution of the CSM roughly follows an r^-2 law. A possible explanation for the massive CSM with a wind-like profile is that they are the result of multiple pulsational pair instability events prior to the SN explosion, separated from each other by years., Submitted to ApJ, 17 pages, 13 figures

We present follow-up optical imaging and spectroscopy of one of the light echoes of $\eta$ Carinae's 19th-century Great Eruption discovered by Rest et al. (2012). By obtaining images and spectra at the same light echo position between 2011 and 2014, we follow the evolution of the Great Eruption on a three-year timescale. We find remarkable changes in the photometric and spectroscopic evolution of the echo light. The $i$-band light curve shows a decline of $\sim 0.9$ mag in $\sim 1$ year after the peak observed in early 2011 and a flattening at later times. The spectra show a pure-absorption early G-type stellar spectrum at peak, but a few months after peak the lines of the [Ca II] triplet develop strong P-Cygni profiles and we see the appearance of [Ca II] 7291,7324 doublet in emission. These emission features and their evolution in time resemble those observed in the spectra of some Type IIn supernovae and supernova impostors. Most surprisingly, starting $\sim 300$ days after peak brightness, the spectra show strong molecular transitions of CN at $\gtrsim 6800$ \AA. The appearance of these CN features can be explained if the ejecta are strongly Nitrogen enhanced, as it is observed in modern spectroscopic studies of the bipolar Homunculus nebula. Given the spectroscopic evolution of the light echo, velocities of the main features, and detection of strong CN, we are likely seeing ejecta that contributes directly to the Homunculus nebula., Comment: accepted in ApJL

We present measurements of the star formation rate (SFR) in the early-type galaxies (ETGs) of the ATLAS3D sample, based on Wide-field Infrared Survey Explorer (WISE) 22um and Galaxy Evolution Explorer (GALEX) far-ultraviolet emission. We combine these with gas masses estimated from 12CO and HI data in order to investigate the star formation efficiency (SFE) in a larger sample of ETGs than previously available. We first recalibrate (based on WISE data) the relation between old stellar populations (traced at Ks-band) and 22um luminosity, allowing us to remove the contribution of 22um emission from circumstellar dust. We then go on to investigate the position of ETGs on the Kennicutt-Schmidt (KS) relation. Molecular gas-rich ETGs have comparable star formation surface densities to normal spiral galaxy centres, but they lie systematically offset from the KS relation, having lower star formation efficiencies by a factor of ~2.5 (in agreement with other authors). This effect is driven by galaxies where a substantial fraction of the molecular material is in the rising part of the rotation curve, and shear is high. We show here for the first time that although the number of stars formed per unit gas mass per unit time is lower in ETGs, it seems that the amount of stars formed per free-fall time is approximately constant. The scatter around this dynamical relation still correlates with galaxy properties such as the shape of the potential in the inner regions. This leads us to suggest that dynamical properties (such as shear or the global stability of the gas) may be important second parameters that regulate star formation and cause much of the scatter around star-formation relations., Comment: 16 (+4) pages, 10 figures, accepted for publication in MNRAS

We initiated long-term optical interferometry monitoring of the diameters of unstable yellow hypergiants (YHG) with the goal of detecting both the long-term evolution of their radius and shorter term formation related to large mass-loss events. We observed HR5171 A with AMBER/VLTI. We also examined archival photometric data in the visual and near-IR spanning more than 60 years, as well as sparse spectroscopic data. HR5171A exhibits a complex appearance. Our AMBER data reveal a surprisingly large star for a YHG R*=1315+/-260Rsun\ (~6.1AU) at the distance of 3.6+/-0.5kpc. The source is surrounded by an extended nebulosity, and these data also show a large level of asymmetry in the brightness distribution of the system, which we attribute to a newly discovered companion star located in front of the primary star. The companion's signature is also detected in the visual photometry, which indicates an orbital period of Porb=1304+/-6d. Modeling the light curve with the NIGHTFALL program provides clear evidence that the system is a contact or possibly over-contact eclipsing binary. A total current system mass of 39^{+40}_{-22} solar mass and a high mass ratio q>10 is inferred for the system. The low-mass companion of HR5171 A is very close to the primary star that is embedded within its dense wind. Tight constraints on the inclination and vsini of the primary are lacking, which prevents us from determining its influence precisely on the mass-loss phenomenon, but the system is probably experiencing a wind Roche-Lobe overflow. Depending on the amount of angular momentum that can be transferred to the stellar envelope, HR5171 A may become a fast-rotating B[e]/Luminous Blue Variable (LBV)/Wolf-Rayet star. In any case, HR5171 A highlights the possible importance of binaries for interpreting the unstable YHGs and for massive star evolution in general., Accepted in Astronomy & Astrophysics (Jan 2014)

We present an analysis of the far-infrared and submillimetre molecular emission line spectrum of the luminous M-supergiant VY CMa, observed with the SPIRE and PACS spectrometers aboard the Herschel Space Observatory. Over 260 emission lines were detected in the 190-650-micron SPIRE FTS spectra, with one-third of the observed lines being attributable to H2O. Other detected species include CO, 13CO, H2^18O, SiO, HCN, SO, SO2, CS, H2S, and NH3. Our model fits to the observed 12CO and 13CO line intensities yield a 12C/13C ratio of 5.6+-1.8, consistent with measurements of this ratio for other M supergiants, but significantly lower than previously estimated for VY CMa from observations of lower-J lines. The spectral line energy distribution for twenty SiO rotational lines shows two temperature components: a hot component at 1000 K, which we attribute to the stellar atmosphere and inner wind, plus a cooler ~200 K component, which we attribute to an origin in the outer circumstellar envelope. We fit the line fluxes of 12CO, 13CO, H2O and SiO, using the SMMOL non-LTE line transfer code, with a mass-loss rate of 1.85x10^-4 Msun yr^-1 between 9 R* and 350 R*. To fit the observed line fluxes of 12CO, 13CO, H2O and SiO with SMMOL non-LTE line radiative transfer code, along with a mass-loss rate of 1.85x10^-4 Msun yr^-1. To fit the high rotational lines of CO and H2O, the model required a rather flat temperature distribution inside the dust condensation radius, attributed to the high H2O opacity. Beyond the dust condensation radius the gas temperature is fitted best by an r^-0.5 radial dependence, consistent with the coolant lines becoming optically thin. Our H2O emission line fits are consistent with an ortho:para ratio of 3 in the outflow., Accepted for publication in MNRAS, 24 pages, 9 figures and 7 tables

Accurate massloss rate estimates are crucial keys to study wind properties of massive stars and test different evolutionary scenarios. From a theoretical point of view, this implies to solve a complex set of differential equations in which the radiation field and the hydrodynamics are strong coupled. The use of analytical expression to represent the radiation force and the solution of the equation of motion have many advantages over numerical integrations. Therefore, in this work, we present an analytical expression as solution of the equation of motion for radiation driven winds, in terms of the force multipliers parameters. This analytical expression is obtained by employing the line acceleration expression given by Villata (1992) and the methodology proposed by Mueller and Vink (2008). On the other hand, we find useful relationships to determine the parameters for the line acceleration given by Mueller and Vink (2008) in terms of the force multiplier parameters., Comment: Accepted for publication in ApJ (2014 November 1) 27 pages 9 figs

Context. Recent studies of O-type stars have demonstrated that discrepant mass-loss rates are obtained when different diagnostic methods are employed. Fitting the unsaturated UV resonance lines (e.g., P v) gives drastically lower values than obtained from the Hα emission. Wind inhomogeneity (so-called "clumping") may be the main cause of this discrepancy. Aims. In a previous paper, we presented 3D Monte-Carlo calculations for the formation of scattering lines in a clumped stellar wind. In the present paper we select five O-type supergiants (from O4 to O7) and test whether the reported discrepancies can be resolved this way. Methods. In the first step, the analyses started with simulating the observed spectra with Potsdam Wolf-Rayet (PoWR) non-LTE model atmospheres. The mass-loss rates are adjusted to fit to the observed Hα emission lines best. For the unsaturated UV resonance lines (i.e., P v) we then applied our 3D Monte-Carlo code, which can account for wind clumps of any optical depths ("macroclumping"), a non-void interclump medium, and a velocity dispersion inside the clumps. The ionization stratifications and underlying photospheric spectra were adopted from the PoWR models. The properties of the wind clumps were constrained by fitting the observed resonance line profiles. Results. Our results show that with the mass-loss rates that fit Hα (and other Balmer and He ii lines), the UV resonance lines (especially the unsaturated doublet of P v) can also be reproduced with no problem when macroclumping is taken into account. There is no need to artificially reduce the mass-loss rates or to assume a subsolar phosphorus abundance or an extremely high clumping factor, unlike what was claimed by other authors. These consistent mass-loss rates are lower by a factor of 1.3 to 2.6, compared to the mass-loss rate recipe from Vink et al. Conclusions. Macroclumping resolves the previously reported discrepancy between Hα and P v mass-loss diagnostics., Facultad de Ciencias Astronómicas y Geofísicas, Instituto de Astrofísica de La Plata

[Context] During the transition from the asymptotic giant branch (AGB) to the planetary nebulae phase the circumstellar envelopes of most low- and intermediate-mass stars experience a dramatic change in morphology. CRL 618 exhibits characteristics of both an AGB and post-AGB star. It also displays a spectacular array of bipolar lobes with a dense equatorial region, which makes it an excellent object for studying the development of asymmetries in evolved stars. In recent decades, an elliptical compact HII region located in the center of the nebula has been seen to be increasing in size and flux. This seems to be due to the ionization of the circumstellar envelope by the central star, and it probably indicates the beginning of the planetary nebula phase for CRL 618., [Aims] We aim to determine the physical conditions under which the ionization of the circumstellar envelope of CRL 618 began to take place as well as the subsequent propagation of the ionization front., [Methods] We analyzed interferometric radio continuum data at ~5 and 22 GHz from observations carried out at seven epochs with the VLA. We traced the flux increase of the ionized region over a period of ~26 years. We measured the dimensions of the HII region directly from the brightness distribution images to determine the increase of its size over time. For one of the epochs we analyzed observations at six frequencies from which we estimated the electron density distribution. We carried out model calculations of the spectral energy distribution at two different epochs to corroborate our observational results., [Results] We found that the radio continuum flux and the size of the ionized region have been increasing monotonically in the past three decades. The size of the major axis of the HII region shows a dependance on frequency, which has been interpreted as a result of the gradient of the electron density in this direction. The growth of the HII region is due to the expansion of an ionized wind whose mass-loss rate increased continuously for a period of ~100 years until a few decades ago, when the mass-loss rate experienced a sudden decline. Our results indicate that the circumstellar envelope began to be ionized around 1971, which marks the start of the planetary nebula phase of CRL 618., This research was supported by the Deutsche Forschungsgemeinschaft (DFG; through the Emmy Noether Research grant VL 61/3-1). L.L. acknowledges the financial support of DGAPA, UNAM and CONACyT, México. J.P.F. acknowledges the Spanish Ministerio de Educación y Ciencia for funding support through grants ESP 2004-665 and AYA 2003-2785 and the “Comunidad de Madrid” government under PRICIT project S-0505/ESP-0237 (ASTROCAM). This study has been supported in part by the UNAM through a postdoctoral fellowship and the European Community’s Human Potential Program under contract MCRTN-CT-2004-51230, “Molecular Universe”.

Aims. We obtained Herschel/PACS imaging and spectroscopic observations of the nebula surrounding the candidate LBV HD168625. By combining these data with optical spectra of the star, we want to constrain the abundances in the nebula and in the star and compare them to trace back its evolution. Methods. We use CMFGEN to determine the fundamental parameters and the CNO abundances of the central star whilst the abundances of the nebula are derived from the emission lines present in the Herschel/PACS spectrum. Result. The FIR images show a nebula composed of an elliptical ring/torus of ejecta with a ESE-WNW axis and of a second perpendicular bipolar structure composed of empty caps/rings. We detect equatorial shells composed of dust and ionized material with different sizes when observed at different wavelengths, and bipolar caps more of less separated from the central star in H$\alpha$ and mid-IR images. This complex global structure seems to show 2 different inclinations: 40{\deg} for the equatorial torus and 60{\deg} for the bipolar ejections. From the Herschel/PACS spectrum, we determine nebular abundances of $\mathrm{N/H} = 4.1 \pm 0.8 \times~10^{-4}$ and $\mathrm{C/H} \sim 1.6_{-0.35}^{+1.16} \times~10^{-4}$, as well as a mass of ionized gas of $0.17\pm 0.04$M$_{\odot}$ and a neutral hydrogen mass of about $1.0\pm 0.3$M$_{\odot}$ which dominates. Analysis of the central star reveals Teff = 14000K, log g = 1.74 and log (L/L$_{\odot}$) = 5.58. We derive stellar abundances of about $\mathrm{N/H} = 5.0 \pm 1.5 \times~10^{-4}$, $\mathrm{C/H} = 1.4 \pm 0.5 \times~10^{-4}$ and $\mathrm{O/H} = 3.5 \pm 1.0\times~10^{-4}$. All these measurements taken together are compatible with the evolutionary tracks of a star with an initial mass between $28$ and $33$M$_{\odot}$ and with a crit. rotational rate between 0.3 and 0.4 that has lost its material during or just after the BSG phase., Comment: 14 pages, 16 figures, A&A, in press

Thermal pulses are fundamental to the chemical evolution of AGB stars and their circumstellar envelopes. A further consequence of thermal pulses is the formation of detached shells of gas and dust around the star. We aim to determine the physical properties of the detached gas shell around R Sculptoris, in particular the shell mass and temperature, and to constrain the evolution of the mass-loss rate during and after a thermal pulse. We analyse CO(1-0), CO(2-1), and CO(3-2) emission, observed by. The spatial resolution of the ALMA data allows us to separate the detached shell emission from the extended emission inside the shell. We perform radiative transfer modelling of both components to determine the shell properties and the post-pulse mass-loss properties. The ALMA data show a gas shell with a radius of 19.5" expanding at 14.3km/s. The different scales probed by the ALMA Cycle 0 array show that the shell must be entirely filled with gas, contrary to the idea of a detached shell. The comparison to single-dish spectra and radiative transfer modelling confirms this. We derive a shell mass of 4.5e-3 Msun with a temperature of 50K. Typical timescales for thermal pulses imply a pulse mass-loss rate of 2.3e-5 Msun/yr. For the post-pulse mass-loss rate, we find evidence for a gradual decline of the mass-loss rate, with an average value of 1.6e-5 Msun/yr. The total amount of mass lost since the last thermal pulse is 0.03 Msun, a factor four higher compared to classical models, with a sharp decline in mass-loss rate immediately after the pulse. We find that the mass-loss rate after a thermal pulse has to decline more slowly than generally expected from models of thermal pulses. This may cause the star to lose significantly more mass during a thermal pulse cycle, which affects the chemical evolution of the star and the interstellar medium., Comment: 12 pages, 7 figures, accepted by A&A

Context. The formation and evolution of gas and dust environments around B[e] supergiants are still open issues. Aims. We intend to study the geometry, kinematics and physical structure of the circumstellar environment (CE) of the B[e] supergiant CPD-52 9243 to provide further insights into the underlying mechanism causing the B[e] phenomenon. Methods. The influence of the different physical mechanisms acting on the CE (radiation pressure, rotation, bi-stability or tidal forces) is somehow reflected in the shape and kinematic properties of the gas and dust regions (flaring, Keplerian, accretion or outflowing disks). To investigate these processes we mainly used quasi-simultaneous observations taken with high spatial resolution optical long-baseline interferometry (VLTI/MIDI), near-IR spectroscopy of CO bandhead features (Gemini/Phoenix and VLT/CRIRES) and optical spectra (CASLEO/REOSC). Results. High angular resolution interferometric measurements obtained with VLTI/MIDI provide strong support for the presence of a dusty disk(ring)-like structure around CPD-52 9243, with an upper limit for its inner edge of ~8 mas (~27.5 AU, considering a distance of 3.44 kpc to the star). The disk has an inclination angle with respect to the line of sight of 46 ± 7°. The study of CO first overtone bandhead evidences a disk structure in Keplerian rotation. The optical spectrum indicates a rapid outflow in the polar direction. Conclusions. The IR emission (CO and warm dust) indicates Keplerian rotation in a circumstellar disk while the optical line transitions of various species are consistent with a polar wind. Both structures appear simultaneously and provide further evidence for the proposed paradigms of the mass-loss in supergiant B[e] stars. The presence of a detached cold CO ring around CPD-52 9243 could be due to a truncation of the inner disk caused by a companion, located possibly interior to the disk rim, clearing the center of the system. More spectroscopic and interferometric data are necessary to determine a possible binary nature of the star., Facultad de Ciencias Astronómicas y Geofísicas

We calculated the influence of the limb-darkened finite-disk correction factor in the theory of radiation-driven winds from massive stars. We solved the one-dimensional m-CAK hydrodynamical equation of rotating radiation-driven winds for all three known solutions, i.e., fast, Ω-slow, and δ-slow. We found that for the fast solution, the mass-loss rate is increased by a factor of 10%, while the terminal velocity is reduced about 10%, when compared with the solution using a finite-disk correction factor from a uniformly bright star. For the other two slow solutions, the changes are almost negligible. Although we found that the limb darkening has no effects on the wind-momentum-luminosity relationship, it would affect the calculation of synthetic line profiles and the derivation of accurate wind parameters., Facultad de Ciencias Astronómicas y Geofísicas, Instituto de Astrofísica de La Plata

We have analyzed the available spectra of WW And and for the first time obtained a reasonably well defined radial velocity curve of the primary star. Combined with the available radial velocity curve of the secondary component, these data led to the first determination of the spectroscopic mass ratio of the system at q-spec = 0.16 +/- 0.03. We also determined the radius of the accretion disc from analysis of the double-peaked H-alpha emission lines. Our new, high-precision, Johnson VRI and the previously available Stromgren vby light curves were modelled with stellar and accretion disc models. A consistent model for WW And - a semidetached system harbouring an accretion disc which is optically thick in its inner region, but optically thin in the outer parts - agrees well with both spectroscopic and photometric data., Comment: Accepted by New Astronomy

Gamma-ray binaries are systems containing a massive star and a compact object that have been detected up to TeV energies. The high energy emission could result from particle acceleration in the region where the stellar wind from the massive star interacts with the relativistic wind from a young pulsar. LS 5039 has the most compact orbit amongst gamma-ray binaries and its X-ray lightcurve shows a stable modulation synchronized with the orbital period. Photoelectric absorption of X-rays in the O star wind and occultation of the X-ray emitting region by the massive star can alter the X-ray lightcurve and spectrum along the orbit. Yet, the X-ray spectrum and lightcurve of LS 5039 do not show intrinsic absorption or X-ray eclipses. We study these effects in the framework of the pulsar wind scenario as a function of the binary inclination angle, the stellar wind mass-loss rate and the size of the X-ray emitter. An extended X-ray emission region >~ 3R_star appears necessary to reconcile the pulsar wind scenario with observations., Accepted for publication in MNRAS, 8 pages, 5 figures

It has been known since the 1950s that the observed gas content of Galactic globular clusters (GCs) is two to three orders of magnitude less than the mass lost by stars between Galactic disc crossings. In this work, we address the question: what happens to this stellar gas?Using an Eulerian nested grid code, we present 3D simulations to determine how stellar wind material evolves within the GC environment. We expand upon work done in the 1970s and move a single-mass King-model GC through the Galactic halo medium, stripping a 10(5) M-circle dot GC of its intracluster medium but predicting a detectable medium for a 10(6) M-circle dot cluster. We find from new multi-mass King-model simulations, the first to incorporate empirical mass-loss formulae, that the single-mass King model underestimates the retention of intracluster gas in the cluster. Lastly, we present a simple discretized multi-mass GC model, which yields lower levels of intracluster medium compared to the continuous single-and multi-mass King models.Our results show that there is still an issue with the predicted intracluster gas content of massive GCs. We conclude that by modelling GC systems more accurately, in particular the stellar structure and description of mass loss, we will be able to work towards resolving this issue and begin to fill in some of the gaps in our understanding of the evolution of GCs.

We present observations of the embedded massive young stellar object (YSO) candidate 08576nr292, obtained with X-shooter and SINFONI on the ESO Very Large Telescope (VLT). The flux-calibrated, medium-resolution X-shooter spectrum (300 - 2500 nm) includes over 300 emission lines, but no (photospheric) absorption lines and is consistent with a reddened disk spectrum. Among the emission lines are three hydrogen series and helium lines, both permitted and forbidden metal lines, and CO first-overtone emission. A representative sample of lines with different morphologies is presented. The H alpha and Ca II triplet lines are very strong, with profiles indicative of outflow and - possibly - infall, usually observed in accreting stars. These lines include a blue-shifted absorption component at ~ -125 km/s. The He I and metal-line profiles are double-peaked, with a likely origin in a circumstellar disk. The forbidden lines, associated with outflow, have a single blue-shifted emission component centered at -125 km/s, coinciding with the absorption components in H alpha and Ca II. SINFONI H- and K-band integral-field spectroscopy of the cluster environment demonstrates that the [Fe II] emission is produced by a jet originating at the location of 08576nr292. Because the spectral type of the central object cannot be determined, its mass remains uncertain. We argue that 08576nr292 is an intermediate-mass YSO with a high accretion rate Mdot_acc ~ 10^-5 - 10^-6 Msun/yr. These observations demonstrate the potential of X-shooter and SINFONI to study in great detail an accretion disk-jet system, rarely seen around the more massive YSOs., Comment: 6 pages, 4 figures, 1 appendix (11 pages), accepted for publication in ApJ Letters

VFTS 682 is located in an active star-forming region, at a projected distance of 29 pc from the young massive cluster R136 in the Tarantula Nebula of the Large Magellanic Cloud. It was previously reported as a candidate young stellar object, and more recently spectroscopically revealed as a hydrogen-rich Wolf-Rayet (WN5h) star. Our aim is to obtain the stellar properties, such as its intrinsic luminosity, and to investigate the origin of VFTS 682. To this purpose, we model optical spectra from the VLT-FLAMES Tarantula Survey with the non-LTE stellar atmosphere code CMFGEN, as well as the spectral energy distribution from complementary optical and infrared photometry. We find the extinction properties to be highly peculiar (RV ~4.7), and obtain a surprisingly high luminosity log(L/Lsun) = 6.5 \pm 0.2, corresponding to a present-day mass of ~150Msun. The high effective temperature of 52.2 \pm 2.5kK might be explained by chemically homogeneous evolution - suggested to be the key process in the path towards long gamma-ray bursts. Lightcurves of the object show variability at the 10% level on a timescale of years. Such changes are unprecedented for classical Wolf-Rayet stars, and are more reminiscent of Luminous Blue Variables. Finally, we discuss two possibilities for the origin of VFTS 682: (i) the star either formed in situ, which would have profound implications for the formation mechanism of massive stars, or (ii) VFTS 682 is a slow runaway star that originated from the dense cluster R136, which would make it the most massive runaway known to date., Comment: 5 pages, 5 figures, accepted by A&A Letters

We present a spectroscopic analysis of VLT/X-Shooter observations of six O-type stars in the low-metallicity (Z ~ 1/7 Z\odot) galaxies IC 1613, WLM and NGC 3109. The stellar and wind parameters of these sources allow us, for the first time, to probe the mass-loss versus metallicity dependence of stellar winds below that of the Small Magellanic Cloud (at Z ~ 1/5Z\odot) by means of a modified wind momentum versus luminosity diagram. The wind strengths that we obtain for the objects in WLM and NGC 3109 are unexpectedly high and do not agree with theoretical predictions. The objects in IC 1613 tend towards a higher than expected mass-loss rate, but remain consistent with predictions within their error bars. We discuss potential systematic uncertainties in the mass-loss determinations to explain our results. However, if further scrutinization of these findings point towards an intrinsic cause for this unexpected sub-SMC mass-loss behavior, implications would include a higher than anticipated number of Wolf-Rayet stars and Ib/Ic supernovae in low-metallicity environments, but a reduced number of long-duration gamma-ray bursts produced through a single-star evolutionary channel., Comment: 9 pages, 3 figures; accepted for publication in The Astrophysical Journal Letters

The theory of radiation-driven winds succeeded in describing terminal velocities and mass-loss rates of massive stars. However, for A-type supergiants the standard m-CAK solution predicts values of mass loss and terminal velocity higher than the observed values. Based on the existence of a slow wind solution in fast rotating massive stars, we explore numerically the parameter space of radiation-driven flows to search for new wind solutions in slowly rotating stars that could explain the origin of these discrepancies. We solve the one-dimensional hydrodynamical equation of rotating radiation-driven winds at different stellar latitudes and explore the influence of ionization changes throughout the wind in the velocity profile. We have found that for particular sets of stellar and line-force parameters, a new slow solution exists over the entire star when the rotational speed is slow or even zero. In the case of slow rotating A-type supergiant stars, the presence of this novel slow solution at all latitudes leads to mass losses and wind terminal velocities which are in agreement with the observed values. The theoretical wind-momentum-luminosity relationship derived with these slow solutions shows very good agreement with the empirical relationship. In addition, the ratio between the terminal and escape velocities, which provides a simple way to predict stellar wind energy and momentum input into the interstellar medium, is also properly traced., Facultad de Ciencias Astronómicas y Geofísicas

We present the first ultraviolet (UV) and multi-epoch optical spectroscopy of 30 Dor 016, a massive O2-type star on the periphery of 30 Doradus in the Large Magellanic Cloud. The UV data were obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope as part of the Servicing Mission Observatory Verification program after Servicing Mission 4, and reveal #016 to have one of the fastest stellar winds known. From analysis of the CIV 1548-51 doublet we find a terminal velocity, v_infty=3450 +/- 50km/s. Optical spectroscopy is from the VLT-FLAMES Tarantula Survey, from which we rule out a massive companion (with 2d, Comment: 6 pages, ApJL, in press

Publicado en línea el 22 de marzo de 2010., Aiming to perform a study of the warm dust and gas in the luminous blue variable star G79.29+0.46 and its associated nebula, we present infrared Spitzer imaging and spectroscopy, and new CO J=2-->1 and 4-->3 maps obtained with the IRAM 30m radio telescope and with the Submillimeter Telescope, respectively. We have analyzed the nebula detecting multiple shells of dust and gas connected to the star. Using Infrared Spectrograph-Spitzer spectra, we have compared the properties of the central object, the nebula, and their surroundings. These spectra show a rich variety of solid-state features (amorphous silicates, polycyclic aromatic hydrocarbons, and CO2 ices) and narrow emission lines, superimposed on a thermal continuum. We have also analyzed the physical conditions of the nebula, which point to the existence of a photo-dissociation region.

Aims: Little information exists on the circumstellar molecular abundance stratifications of many molecules. The aim is to study the circumstellar chemical abundance pattern of 11 molecules and isotopologs ($^{12}$CO, $^{13}$CO, SiS, $^{28}$SiO, $^{29}$SiO, $^{30}$SiO, HCN, CN, CS, SO, SO$_2$) in the oxygen-rich evolved star IK~Tau. Methods: We have performed an in-depth analysis of a large number of molecular emission lines excited in the circumstellar envelope around IK~Tau. The analysis is done based on a non-local thermodynamic equilibrium (non-LTE) radiative transfer analysis, which calculates the temperature and velocity structure in a self-consistent way. The chemical abundance pattern is coupled to theoretical outer wind model predictions including photodestruction and cosmic ray ionization. Not only the integrated line intensities, but also the line shapes, are used as diagnostic tool to study the envelope structure. Results: The deduced wind acceleration is much slower than predicted from classical theories. SiO and SiS are depleted in the envelope, possibly due to the adsorption onto dust grains. For HCN and CS a clear difference with respect to inner wind non-equilibrium predictions is found, either indicating uncertainties in the inner wind theoretical modeling or the possibility that HCN and CS (or the radical CN) participate in the dust formation. The low signal-to-noise profiles of SO and CN prohibit an accurate abundance determination; the modeling of high-excitation SO$_2$ lines is cumbersome, possibly related to line misidentifications or problems with the collisional rates. The SiO isotopic ratios ($^{29}$SiO/$^{28}$SiO and $^{30}$SiO/$^{28}$SiO) point toward an enhancement in $^{28}$SiO compared to results of classical stellar evolution codes. Predictions for H$_2$O lines in the spectral range of the Herschel/HIFI mission are performed. [abbreviated], Comment: 24 pagees, accepted for publication in Astronomy & Astrophysics

Aims. We aim to study the physical conditions, particularly the excitation state, of the intermediate-temperature gas components in the protoplanetary nebula CRL 618. These components are particularly important for understanding the evolution of the nebula. Methods. We performed Herschel/HIFI observations of several CO lines in the far-infrared/sub-mm in the protoplanetary nebula CRL 618. The high spectral resolution provided by HIFI allows measurement of the line profiles. Since the dynamics and structure of the nebula is well known from mm-wave interferometric maps, it is possible to identify the contributions of the different nebular components (fast bipolar outflows, double shells, compact slow shell) to the line profiles. The observation of these relatively high-energy transitions allows an accurate study of the excitation conditions in these components, particularly in the warm ones, which cannot be properly studied from the low-energy lines. Results. The 12CO J = 16−15, 10−9, and 6−5 lines are easily detected in this source. Both 13CO J = 10−9 and 6−5 are also detected.Wide profiles showing spectacular line wings have been found, particularly in 12CO J = 16−15. Other lines observed simultaneously with CO are also shown. Our analysis of the CO high-J transitions, when compared with the existing models, confirms the very low expansion velocity of the central, dense component, which probably indicates that the shells ejected during the last AGB phases were driven by radiation pressure under a regime of maximum transfer of momentum. No contribution of the diffuse halo found from mm-wave data is identified in our spectra, because of its low temperature. We find that the fast bipolar outflow is quite hot, much hotter than previously estimated; for instance, gas flowing at 100 km s−1 must have a temperature higher than ∼200 K. Probably, this very fast outflow, with a kinematic age