arXiv subjects

J. Puls

Publications and source records attributed to J. Puls.

At least 55 records · Page 3Linked to original sources

arXiv2018

The IACOB project. V. Spectroscopic parameters of the O-type stars in the modern grid of standards for spectral classification

The IACOB and OWN surveys are two ambitious complementary observational projects which have made available a large multi-epoch spectroscopic database of optical high resolution spectra of Galactic massive O-type stars. As a first step in the study of the full sample of (more than 350) O stars surveyed by the IACOB/OWN projects, we have performed the quantitative spectroscopic analysis of a subsample of 128 stars included in the modern grid of O-type standards for spectral classification. We use semi-automatized tools to determine the set of spectroscopic parameters that can be obtained from the optical spectrum of O-type stars. We also benefit from the multi-epoch character of the surveys to perform a spectroscopic variability study of the sample, accounting for spectroscopic binarity and variability of the main wind diagnostic lines. We provide a general overview of the stellar and wind parameters of this reference sample, and updated recipes for the SpT\,--\,Teff/log g calibrations for Galactic O-type stars. We evaluate our semi-automatized analysis strategy with $\sim$40 stars from the literature, and find a good agreement. The agreement between the synthetic spectra associated with fastwind best fitting models and the observed spectra is good for most targets, but 46 stars present a particular behavior of the wind diagnostic lines that cannot be reproduced by our grid of spherically symmetric unclumped models. These are potential targets of interest for more detailed investigations of clumpy winds and/or the existence of additional circumstellar components. Last, our variability study has led to the detection of signatures of spectroscopic binarity in 27\% of the stars and small amplitude radial velocity variations in the photospheric lines of another 30\%. Additionally, 31\% of the investigated stars show variability in the wind diagnostic lines.

astro-ph.SR↗

arXiv2018

Atmospheric NLTE-models for the spectroscopic analysis of blue stars with winds. IV. Porosity in physical and velocity space

[Abridged] Clumping in the radiation-driven winds of hot, massive stars affects the derivation of synthetic observables across the electromagnetic spectrum. We implement a formalism for treating wind clumping - in particular the light-leakage effects associated with a medium that is porous in physical and velocity space - into the global (photosphere+wind) NLTE model atmosphere code FASTWIND. We assume a stochastic, two-component wind consisting of a mixture of optically thick and thin clumps embedded in a rarefied inter-clump medium. We account fully for the reductions in opacity associated with porosity in physical and velocity-space, and for the well-known effect that opacities depending on rho^2 are higher in clumpy winds than in smooth ones of equal mass-loss rate. By formulating our method in terms of suitable mean and effective opacities for the clumpy wind, we are able to compute models with the same speed (~15 min. on a modern laptop) as in previous code-generations. Some first, generic results of the new models include: i) Confirming earlier results that velocity-space porosity is critical for analysis of UV wind lines in O-stars; ii) for the optical Halpha line, optically thick clumping effects are small for O-stars, but potentially very important for late B and A-supergiants; iii) spatial porosity is a marginal effect for absorption of high-energy X-rays in O-stars, as long as the mean-free path between clumps are kept at realistic values; iv) porosity is negligible at typical O-star radio-photosphere radii; v) regarding the wind ionization balance, a general trend is that increased rates of recombination in simulations with optically thin clumps lead to overall lower degrees of ionization than in corresponding smooth models, but that this effect now is counteracted by the increased levels of light-leakage associated with porosity in physical and velocity space.

astro-ph.SR↗

arXiv2018

Coherent dynamics of localized excitons and trions in ZnO/(Zn,Mg)O quantum wells studied by photon echoes

We study optically the coherent evolution of trions and excitons in a $δ$-doped 3.5 nm-thick ZnO/Zn$_{0.91}$Mg$_{0.09}$O multiple quantum well by means of time-resolved four-wave mixing at temperature of 1.5~K. Employing spectrally narrow picosecond laser pulses in the $χ^{(3)}$ regime allows us to address differently localized trion and exciton states, thereby avoiding many-body interactions and excitation-induced dephasing. The signal in the form of photon echoes from the negatively charged A excitons (T$_\text{A}$, trions) decays with coherence times varying from 8 up to 60~ps, depending on the trion energy: more strongly localized trions reveal longer coherence dynamics. The localized neutral excitons decay on the picosecond timescale with coherence times up to $T_2=4.5$~ps. The coherent dynamics of the X$_\text{B}$ exciton and T$_\text{B}$ trion are very short ($T_2<1$~ps), which is attributed to the fast energy relaxation from the trion and exciton B states to the respective A states. The trion population dynamics is characterized by the decay time $T_1$, rising from 30~ps to 100~ps with decreasing trion energy.

cond-mat.mes-hall↗

arXiv2018

The VLT-FLAMES Tarantula Survey XXIV. Stellar properties of the O-type giants and supergiants in 30 Doradus

The Tarantula region in the Large Magellanic Cloud contains the richest population of spatially resolved massive O-type stars known so far. This unmatched sample offers an opportunity to test models describing their main-sequence evolution and mass-loss properties. Using ground-based optical spectroscopy obtained in the framework of the VLT-FLAMES Tarantula Survey (VFTS), we aim to determine stellar, photospheric and wind properties of 72 presumably single O-type giants, bright giants and supergiants and to confront them with predictions of stellar evolution and of line-driven mass-loss theories. We apply an automated method for quantitative spectroscopic analysis of O stars combining the non-LTE stellar atmosphere model {\sc fastwind} with the genetic fitting algorithm {\sc pikaia} to determine the following stellar properties: effective temperature, surface gravity, mass-loss rate, helium abundance, and projected rotational velocity. We present empirical effective temperature versus spectral subtype calibrations at LMC-metallicity for giants and supergiants. In the spectroscopic and classical Hertzsprung-Russell diagrams, our sample O stars are found to occupy the region predicted to be the core hydrogen-burning phase by Brott et al. (2011) and Köhler et al. (2015). Except for five stars, the helium abundance of our sample stars is in agreement with the initial LMC composition. The aforementioned five stars present moderate projected rotational velocities (i.e., $v_{\mathrm{e}}\,\sin\,i\,<\,200\,\mathrm{km\,s^{-1}}$) and hence do not agree with current predictions of rotational mixing in main-sequence stars. Adopting theoretical results for the wind velocity law, we find modified wind momenta for LMC stars that are $\sim$0.3 dex higher than earlier results. [Due to the limitation of characters, the abstract appearing here is slightly shorter than that in the PDF file.]

astro-ph.SR↗

arXiv2018

An excess of massive stars in the local 30 Doradus starburst

The 30 Doradus star-forming region in the Large Magellanic Cloud is a nearby analogue of large star-formation events in the distant Universe. We determine the recent formation history and the initial mass function (IMF) of massive stars in 30 Doradus based on spectroscopic observations of 247 stars more massive than 15 solar masses ($\mathrm{M}_\odot$). The main episode of massive star formation started about $8\,\mathrm{Myr}$ ago and the star-formation rate seems to have declined in the last $1\,\mathrm{Myr}$. The IMF is densely sampled up to $200\,\mathrm{M}_\odot$ and contains $32\pm12\%$ more stars above $30\,\mathrm{M}_\odot$ than predicted by a standard Salpeter IMF. In the mass range $15-200\,\mathrm{M}_\odot$, the IMF power-law exponent is $1.90^{+0.37}_{-0.26}$, shallower than the Salpeter value of 2.35.

astro-ph.SR↗

arXiv2017

2D wind clumping in hot, massive stars from hydrodynamical line-driven instability simulations using a pseudo-planar approach

Context: Clumping in the radiation-driven winds of hot, massive stars arises naturally due to the strong, intrinsic instability of line-driving (the `LDI'). But LDI wind models have so far mostly been limited to 1D, mainly because of severe computational challenges regarding calculation of the multi-dimensional radiation force. Aims: To simulate and examine the dynamics and multi-dimensional nature of wind structure resulting from the LDI. Methods: We introduce a `pseudo-planar', `box-in-a-wind' method that allows us to efficiently compute the line-force in the radial and lateral directions, and then use this approach to carry out 2D radiation-hydrodynamical simulations of the time-dependent wind. Results: Our 2D simulations show that the LDI first manifests itself by mimicking the typical shell-structure seen in 1D models, but how these shells then quickly break up into complex 2D density and velocity structures, characterized by small-scale density `clumps' embedded in larger regions of fast and rarefied gas. Key results of the simulations are that density-variations in the well-developed wind statistically are quite isotropic and that characteristic length-scales are small; a typical clump size is ~0.01R at 2R, thus resulting also in rather low typical clump-masses ~10^17 g. Overall, our results agree well with the theoretical expectation that the characteristic scale for LDI-generated wind-structure is of order the Sobolev length. We further confirm some earlier results that lateral `filling-in' of radially compressed gas leads to somewhat lower clumping factors in 2D simulations than in comparable 1D models. We conclude by discussing an extension of our method toward rotating LDI wind models that exhibit an intriguing combination of large- and small-scale structure extending down to the wind base.

astro-ph.SR↗

arXiv2017

Carbon line formation and spectroscopy in O-type stars

The determination of chemical abundances constitutes a fundamental requirement for obtaining a complete picture of a star. Particularly in massive stars, CNO abundances are of prime interest, due to the nuclear CNO-cycle and various mixing processes which bring these elements to the surface. We aim at enabling a reliable carbon spectroscopy for our unified NLTE atmosphere code FASTWIND. We develop a new carbon model atom including CII/III/IV/V, and discuss problems related to carbon spectroscopy in O-type stars. We describe different tests to examine the reliability of our implementation, and investigate which mechanisms influence the carbon ionization balance. By comparing with high-resolution spectra from six O-type stars, we check in how far observational constraints can be reproduced by our new carbon line synthesis. Carbon lines are even more sensitive to a variation of temperature, gravity, and mass-loss rate, than hydrogen/helium lines. We are able to reproduce most of the observed lines from our stellar sample, and to estimate those specific carbon abundances which bring the lines from different ions into agreement. For hot dwarfs and supergiants earlier than O7, X-rays from wind-embedded shocks can impact the synthesized line strengths, particularly for CIV, potentially affecting the abundance determination. We have demonstrated our capability to derive realistic carbon abundances by means of FASTWIND, using our recently developed model atom. We found that complex effects can have a strong influence on the carbon ionization balance in hot stars. For a further understanding, the UV range needs to be explored as well. By means of detailed nitrogen and oxygen model atoms available to use, we will be able to perform a complete CNO abundance analysis for larger samples of massive stars, and to provide constraints on corresponding evolutionary models and aspects.

astro-ph.SR↗

arXiv2017

Transient photon echoes from donor-bound excitons in ZnO epitaxial layers

The coherent optical response from 140~nm and 65~nm thick ZnO epitaxial layers is studied using transient four-wave-mixing spectroscopy with picosecond temporal resolution. Resonant excitation of neutral donor-bound excitons results in two-pulse and three-pulse photon echoes. For the donor-bound A exciton (D$^0$X$_\text{A}$) at temperature of 1.8~K we evaluate optical coherence times $T_2=33-50$~ps corresponding to homogeneous linewidths of $13-19~μ$eV, about two orders of magnitude smaller as compared with the inhomogeneous broadening of the optical transitions. The coherent dynamics is determined mainly by the population decay with time $T_1=30-40$~ps, while pure dephasing is negligible in the studied high quality samples even for strong optical excitation. Temperature increase leads to a significant shortening of $T_2$ due to interaction with acoustic phonons. In contrast, the loss of coherence of the donor-bound B exciton (D$^0$X$_\text{B}$) is significantly faster ($T_2=3.6$~ps) and governed by pure dephasing processes.

cond-mat.mtrl-sci↗

arXiv2017

The VLT-FLAMES Tarantula Survey XXVI: Properties of the O-dwarf population in 30 Doradus

The VLT-FLAMES Tarantula Survey has observed hundreds of O-type stars in the 30 Doradus region of the Large Magellanic Cloud (LMC). We study the properties of 105 apparently single O-type dwarfs. To determine stellar and wind parameters, we used the IACOB-GBAT package, an automatic procedure based on a large grid of atmospheric models calculated with the FASTWIND code. In addition to classical techniques, we applied the Bayesian BONNSAI tool to estimate evolutionary masses. We provide a new calibration of effective temperature vs. spectral type for O-type dwarfs in the LMC, based on our homogeneous analysis of the largest sample of such objects to date and including all spectral subtypes. Good agreement with previous results is found, although the sampling at the earliest subtypes could be improved. Rotation rates and helium abundances are studied in an evolutionary context. We find that most of the rapid rotators (vsini higher than 300 km/s ) in our sample have masses below 25 MSun and intermediate rotation-corrected gravities (log gc between 3.9 and 4.1). Such rapid rotators are scarce at higher gravities (i.e. younger ages) and absent at lower gravities (larger ages). This is not expected from theoretical evolutionary models, and does not appear to be due to a selection bias in our sample. We compare the estimated evolutionary and spectroscopic masses, finding a trend that the former is higher for masses below 20 MSun. This can be explained as a consequence of limiting our sample to the O-type stars, and we see no compelling evidence for a systematic mass discrepancy. For most of the stars in the sample we were unable to estimate the wind-strength parameter (hence mass-loss rates) reliably, particularly for objects with luminosity lower than logL/LSun about 5.1. Ultraviolet spectroscopy is needed to undertake a detailed investigation of the wind properties of these dwarfs.

astro-ph.SR↗

arXiv2016

Magnetic massive stars as progenitors of "heavy" stellar-mass black holes

The groundbreaking detection of gravitational waves produced by the inspiralling and coalescence of the black hole (BH) binary GW150914 confirms the existence of "heavy" stellar-mass BHs with masses >25 Msun. Initial modelling of the system by Abbott et al. (2016a) supposes that the formation of black holes with such large masses from the evolution of single massive stars is only feasible if the wind mass-loss rates of the progenitors were greatly reduced relative to the mass-loss rates of massive stars in the Galaxy, concluding that heavy BHs must form in low-metallicity (Z < 0.25-0.5 Zsun) environments. However, strong surface magnetic fields also provide a powerful mechanism for modifying mass loss and rotation of massive stars, independent of environmental metallicity (ud-Doula & Owocki 2002; ud-Doula et al. 2008). In this paper we explore the hypothesis that some heavy BHs, with masses >25 Msun such as those inferred to compose GW150914, could be the natural end-point of evolution of magnetic massive stars in a solar-metallicity environment. Using the MESA code, we developed a new grid of single, non-rotating, solar metallicity evolutionary models for initial ZAMS masses from 40-80 Msun that include, for the first time, the quenching of the mass loss due to a realistic dipolar surface magnetic field. The new models predict TAMS masses that are significantly greater than those from equivalent non-magnetic models, reducing the total mass lost by a strongly magnetized 80 Msun star during its main sequence evolution by 20 Msun. This corresponds approximately to the mass loss reduction expected from an environment with metallicity Z = 1/30 Zsun.

astro-ph.SR↗

arXiv2016

The VLT-FLAMES Tarantula Survey XXV. Surface nitrogen abundances of O-type giants and supergiants

Theoretically, rotation-induced chemical mixing in massive stars has far reaching evolutionary consequences, affecting the sequence of morphological phases, lifetimes, nucleosynthesis, and supernova characteristics. Using a sample of 72 presumably single O-type giants to supergiants observed in the context of the VLT-FLAMES Tarantula Survey (VFTS), we aim to investigate rotational mixing in evolved core-hydrogen burning stars initially more massive than $15\,M_\odot$ by analysing their surface nitrogen abundances. Using stellar and wind properties derived in a previous VFTS study, we constrained the nitrogen abundance by fitting the equivalent widths of relatively strong lines that are sensitive to changes in the abundance of this element. Given the quality of the data, we constrained the nitrogen abundance in 38 cases; for 34 stars only upper limits could be derived, which includes almost all stars rotating at $v_\mathrm{e}\sin i >200\,\mathrm{km s^{-1}}$. We analysed the nitrogen abundance as a function of projected rotation rate $v_\mathrm{e}\sin i$ and confronted it with predictions of rotational mixing. The upper limits on the nitrogen abundance of the rapidly rotating stars are not in apparent violation with theoretical expectations. However, we found a group of N-enhanced slowly-spinning stars that is not in accordance with predictions of rotational mixing in single stars. Among O-type stars with (rotation-corrected) gravities less than $\log\,g_c = 3.75$ this group constitutes 30$-$40 percent of the population. We found a correlation between nitrogen and helium abundance which is consistent with expectations, suggesting that, whatever the mechanism that brings N to the surface, it displays CNO-processed material.

astro-ph.SR↗

arXiv2016

The IACOB project: III. New observational clues to understand macroturbulent broadening in massive O- and B-type stars

We aim to provide new empirical clues about macroturbulent spectral line broadening in O- and B-type stars to evaluate its physical origin. We use high-resolution spectra of ~430 stars with spectral types in the range O4-B9 (all luminosity classes). We characterize the line-broadening of adequate diagnostic metal lines using a combined FT and GOF technique. We perform a quantitative spectroscopic analysis of the whole sample using automatic tools coupled with a huge grid of FASTWIND models. We also incorporate quantitative information about line asymmetries to our observational description of the characteristics of the line-profiles, and present a comparison of the shape and type of line-profile variability found in a small sample of O stars and B supergiants with still undefined pulsational properties and B main sequence stars with variable line-profiles. We present a homogeneous and statistically significant overview of the (single snapshot) line-broadening properties of stars in the whole O and B star domain. We find empirical evidence of the existence of various types of non-rotational broadening agents acting in the realm of massive stars. Even though all of them could be quoted and quantified as a macroturbulent broadening from a practical point of view, their physical origin can be different. Contrarily to the early- to late-B dwarfs/giants, which present a mixture of cases in terms of line-profile shape and variability, the whole O-type and B supergiant domain (or, roughly speaking, stars with M_ZAMS > 15 M_sol) is fully dominated by stars with a remarkable non-rotational broadening component and very similar profiles (including type of variability). We provide some examples illustrating how this observational dataset can be used to evaluate scenarios aimed at explaining the existence of sources of non-rotational broadening in massive stars.

astro-ph.SR↗

arXiv2016

The SILCC project: III. Regulation of star formation and outflows by stellar winds and supernovae

We study the impact of stellar winds and supernovae on the multi-phase interstellar medium using three-dimensional hydrodynamical simulations carried out with FLASH. The selected galactic disc region has a size of (500 pc)$^2$ x $\pm$ 5 kpc and a gas surface density of 10 M$_{\odot}$/pc$^2$. The simulations include an external stellar potential and gas self-gravity, radiative cooling and diffuse heating, sink particles representing star clusters, stellar winds from these clusters which combine the winds from indi- vidual massive stars by following their evolution tracks, and subsequent supernova explosions. Dust and gas (self-)shielding is followed to compute the chemical state of the gas with a chemical network. We find that stellar winds can regulate star (cluster) formation. Since the winds suppress the accretion of fresh gas soon after the cluster has formed, they lead to clusters which have lower average masses (10$^2$ - 10$^{4.3}$ M$_{\odot}$) and form on shorter timescales (10$^{-3}$ - 10 Myr). In particular we find an anti-correlation of cluster mass and accretion time scale. Without winds the star clusters easily grow to larger masses for ~5 Myr until the first supernova explodes. Overall the most massive stars provide the most wind energy input, while objects beginning their evolution as B-type stars contribute most of the supernova energy input. A significant outflow from the disk (mass loading $\gtrsim$ 1 at 1 kpc) can be launched by thermal gas pressure if more than 50% of the volume near the disc mid-plane can be heated to T > 3x10$^5$ K. Stellar winds alone cannot create a hot volume-filling phase. The models which are in best agreement with observed star formation rates drive either no outflows or weak outflows.

astro-ph.GA↗

arXiv2016

The R136 star cluster dissected with Hubble Space Telescope/STIS. I. Far-ultraviolet spectroscopic census and the origin of HeII 1640 in young star clusters

We introduce a HST/STIS stellar census of R136a, the central ionizing star cluster of 30 Doradus. We present low resolution far-ultraviolet STIS/MAMA spectroscopy of R136 using 17 contiguous 52x0.2 arcsec slits which together provide complete coverage of the central 0.85 parsec (3.4 arcsec). We provide spectral types of 90% of the 57 sources brighter than m_F555W = 16.0 mag within a radius of 0.5 parsec of R136a1, plus 8 additional nearby sources including R136b (O4\,If/WN8). We measure wind velocities for 52 early-type stars from CIV 1548-51, including 16 O2-3 stars. For the first time we spectroscopically classify all Weigelt & Baier members of R136a, which comprise three WN5 stars (a1-a3), two O supergiants (a5-a6) and three early O dwarfs (a4, a7, a8). A complete Hertzsprung-Russell diagram for the most massive O stars in R136 is provided, from which we obtain a cluster age of 1.5+0.3_-0.7 Myr. In addition, we discuss the integrated ultraviolet spectrum of R136, and highlight the central role played by the most luminous stars in producing the prominent HeII 1640 emission line. This emission is totally dominated by very massive stars with initial masses above ~100 Msun. The presence of strong HeII 1640 emission in the integrated light of very young star clusters (e.g A1 in NGC 3125) favours an initial mass function extending well beyond a conventional upper limit of 100 Msun. We include montages of ultraviolet spectroscopy for LMC O stars in the Appendix. Future studies in this series will focus on optical STIS/CCD medium resolution observations.

astro-ph.SR↗

arXiv2016

Atmospheric NLTE-Models for the Spectroscopic Analysis of Blue Stars with Winds. III. X-ray emission from wind-embedded shocks

X-rays/EUV radiation emitted from wind-embedded shocks in hot, massive stars can affect the ionization balance in their outer atmospheres, and can be the mechanism responsible for the production of highly ionized species. To allow for these processes in the context of spectral analysis, we have implemented such emission into our unified, NLTE model atmosphere/spectrum synthesis code FASTWIND. The shock structure and corresponding emission is calculated as a function of user-supplied parameters. We account for a temperature and density stratification inside the post-shock cooling zones, calculated for radiative and adiabatic cooling in the inner and outer wind, respectively. The high-energy absorption of the cool wind is considered by adding important K-shell opacities, and corresponding Auger ionization rates have been included into the NLTE network. We tested and verified our implementation carefully against corresponding results from various alternative model atmosphere codes, and studied the effects from shock emission for important ions from He, C, N, O, Si, and P. Surprisingly, dielectronic recombination turned out to play an essential role for the ionization balance of OIV/OV around Teff = 45,000 K. Finally, we investigated the behavior of the mass absorption coefficient, kappa_nu(r), important in the context of X-ray line formation in massive star winds. In almost all considered cases, direct ionization is of major influence, and Auger ionization significantly affects only NVI and OVI. The approximation of a radially constant kappa_nu is justified for r > 1.2 Rstar and lambda < 18 A, and also for many models at longer wavelengths. To estimate the actual value of this quantity, however, the HeII opacities need to be calculated from detailed NLTE modeling, at least for wavelengths longer than 18 to 20 A, and information on the individual CNO abundances has to be present.

astro-ph.SR↗

arXiv2015

The ephemeris, orbital decay, and masses of 10 eclipsing HMXBs

We take advantage of more than 10 years of monitoring of the eclipsing HMXB systems LMC X-4, Cen X-3, 4U 1700-377, 4U 1538-522, SMC X-1, IGR J18027-2016, Vela X-1, IGR J17252-3616, XTE J1855-026, and OAO 1657-415 with the ASM on-board RXTE and ISGRI on-board INTEGRAL to update their ephemeris. These results are used to refine previous measurements of the orbital period decay of all sources (where available) and provide the first accurate values of the apsidal advance in Vela X-1 and 4U 1538-522. Updated values for the masses of the neutron stars hosted in the ten HMXBs are also provided, as well as the long-term lightcurves folded on the sources best determined orbital parameters. These lightcurves reveal complex eclipse ingresses and egresses, that are understood mostly as being due to the presence of accretion wakes. The results reported in this paper constitute a database to be used for population and evolutionary studies of HMXBs, as well as theoretical modelling of long-term accretion in wind-fed X-ray binaries.

astro-ph.HE↗

arXiv2015

The VLT-FLAMES Tarantula Survey XIX. B-type Supergiants - Atmospheric parameters and nitrogen abundances to investigate the role of binarity and the width of the main sequence

TLUSTY non-LTE model atmosphere calculations have been used to determine atmospheric parameters and nitrogen (N) abundances for 34 single and 18 binary B-type supergiants (BSGs). The effects of flux contribution from an unseen secondary were considered for the binary sample. We present the first systematic study of the incidence of binarity for a sample of BSGs across the theoretical terminal age main sequence (TAMS). To account for the distribution of effective temperatures of the BSGs it may be necessary to extend the TAMS to lower temperatures. This is consistent with the derived distribution of mass discrepancies, projected rotational velocities (vsini) and N abundances, provided that stars cooler than this temperature are post RSG objects. For the BSGs in the Tarantula and previous FLAMES surveys, most have small vsini. About 10% have larger vsini (>100 km/s) but surprisingly these show little or no N enhancement. All the cooler BSGs have low vsini of <70km/s and high N abundance estimates, implying that either bi-stability braking or evolution on a blue loop may be important. A lack of cool binaries, possibly reflects the small sample size. Single star evolutionary models, which include rotation, can account for the N enhancement in both the single and binary samples. The detailed distribution of N abundances in the single and binary samples may be different, possibly reflecting differences in their evolutionary history. The first comparative study of single and binary BSGs has revealed that the main sequence may be significantly wider than previously assumed, extending to Teff=20000K. Some marginal differences in single and binary atmospheric parameters and abundances have been identified, possibly implying non-standard evolution for some of the sample. This sample as a whole has implications for several aspects of our understanding of the evolution of BSGs. Full abstract in paper

astro-ph.SR↗

arXiv2014

The mass discrepancy problem in O stars of solar metallicity. Does it still exist?

Using own and literature data for a large sample of O stars in the Milky Way, we investigate the correspondence between their spectroscopic and evolutionary masses, and try to put constraints on various parameters that might influence the estimates of these two quantities.

astro-ph.SR↗