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17091. VLT-FLAMES survey of massive stars
ID:
ivo://CDS.VizieR/J/A+A/466/277
Title:
VLT-FLAMES survey of massive stars
Short Name:
J/A+A/466/277
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an analysis of high-resolution FLAMES spectra of approximately 50 early B-type stars in three young clusters at different metallicities, NGC 6611 in the Galaxy, N 11 in the Large Magellanic Cloud (LMC) and NGC 346 in the Small Magellanic Cloud (SMC). Using the TLUSTY non-LTE model atmospheres code, atmospheric parameters and photospheric abundances (C, N, O, Mg and Si) of each star have been determined. These results represent a significant improvement on the number of Magellanic Cloud B-type stars with detailed and homogeneous estimates of their atmospheric parameters and chemical compositions. The relationships between effective temperature and spectral type are discussed for all three metallicity regimes, with the effective temperature for a given spectral type increasing as one moves to a lower metallicity regime. Additionally the difficulties in estimating the microturbulent velocity and the anomalous values obtained, particularly in the lowest metallicity regime, are discussed. Our chemical composition estimates are compared with previous studies, both stellar and interstellar with, in general, encouraging agreement being found.
17092. VLT-FLAMES survey of massive stars
ID:
ivo://CDS.VizieR/J/A+A/479/541
Title:
VLT-FLAMES survey of massive stars
Short Name:
J/A+A/479/541
Date:
21 Oct 2021
Publisher:
CDS
Description:
We aim to provide the atmospheric parameters and rotational velocities for a large sample of O- and early B-type stars, analysed in a homogeneous and consistent manner, for use in constraining theoretical models. Atmospheric parameters, stellar masses, and rotational velocities have been estimated for approximately 250 early B-type stars in the Large (LMC) and Small (SMC) Magellanic Clouds from high-resolution VLT-FLAMES data using the non-LTE TLUSTY model atmosphere code. This data set has been supplemented with our previous analyses of some 50 O-type stars (Mokiem et al., 2006A&A...456.1131M, 2007A&A...465.1003M) and 100 narrow-lined early B-type stars (Hunter et al., 2006, Cat. <J/A+A/466/277>, Trundle et al., 2007, Cat. <J/A+A/471/625>) from the same survey, providing a sample of ~400 early-type objects.
17093. VLT-FLAMES survey of massive stars
ID:
ivo://CDS.VizieR/J/A+A/471/625
Title:
VLT-FLAMES survey of massive stars
Short Name:
J/A+A/471/625
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an analysis of high resolution VLT-FLAMES spectra of 61 B-type stars with relatively narrow-lined spectra located in 4 fields centered on the Milky Way clusters; NGC3293 and NGC4755 and the Large and Small Magellanic cloud clusters; NGC2004 and NGC330. For each object a quantitative analysis was carried out using the non-LTE model atmosphere code TLUSTY; resulting in the determination of their atmospheric parameters and photospheric abundances of the dominant metal species (C, N, O, Mg, Si, Fe). The results are discussed in relation to our earlier work on 3 younger clusters in these galaxies; NGC6611, N11 and NGC346 paying particular attention to the nitrogen abundances which are an important probe of the role of rotation in the evolution of stars. This work along with that of the younger clusters provides a consistent dataset of abundances and atmospheric parameters for over 100 B-type stars in the three galaxies. We provide effective temperature scales for B-type dwarfs in all three galaxies and for giants and supergiants in the SMC and LMC. In each galaxy a dependence on luminosity is found between the three classes with the unevolved dwarf objects having significantly higher effective temperatures. A metallicity dependence is present between the SMC and Galactic dwarf objects, and whilst the LMC stars are only slightly cooler than the SMC stars, they are significantly hotter than their Galactic counterparts.
17094. VLT-FLAMES survey of massive stars
ID:
ivo://CDS.VizieR/J/A+A/496/841
Title:
VLT-FLAMES survey of massive stars
Short Name:
J/A+A/496/841
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have previously analysed the spectra of 135 early B-type stars in the Large Magellanic Cloud (LMC) and found several groups of stars that have chemical compositions that conflict with the theory of rotational mixing. Here we extend this study to Galactic and Small Magellanic Cloud (SMC) metallicities. We provide chemical compositions for ~50 Galactic and ~100 SMC early B-type stars and compare these to the LMC results. These samples cover a range of projected rotational velocities up to ~300km/s and hence are well suited to testing rotational mixing models. The surface nitrogen abundances are utilised as a probe of the mixing process since nitrogen is synthesized in the core of the stars and mixed to the surface.
17095. VLT-FLAMES Tarantula Survey
ID:
ivo://CDS.VizieR/J/A+A/530/A108
Title:
VLT-FLAMES Tarantula Survey
Short Name:
J/A+A/530/A108
Date:
21 Oct 2021
Publisher:
CDS
Description:
The VLT-FLAMES Tarantula Survey (VFTS) is an ESO Large Programme that has obtained multi-epoch optical spectroscopy of over 800 massive stars in the 30 Doradus region of the Large Magellanic Cloud (LMC). Here we introduce our scientific motivations and give an overview of the survey targets, including optical and near-infrared photometry and comprehensive details of the data reduction. One of the principal objectives was to detect massive binary systems via variations in their radial velocities, thus shaping the multi-epoch observing strategy. Spectral classifications are given for the massive emission-line stars observed by the survey, including the discovery of a new Wolf-Rayet star (VFTS 682, classified as WN5h), 2' to the northeast of R136. To illustrate the diversity of objects encompassed by the survey, we investigate the spectral properties of sixteen targets identified by Gruendl & Chu (2009, Cat. J/ApJS/184/172) from Spitzer photometry as candidate young stellar objects or stars with notable mid-infrared excesses. Detailed spectral classification and quantitative analysis of the O- and B-type stars in the VFTS sample, paying particular attention to the effects of rotational mixing and binarity, will be presented in a series of future articles to address fundamental questions in both stellar and cluster evolution.
17096. VLT-FLAMES Tarantula Survey: B supergiants
ID:
ivo://CDS.VizieR/J/A+A/575/A70
Title:
VLT-FLAMES Tarantula Survey: B supergiants
Short Name:
J/A+A/575/A70
Date:
21 Oct 2021
Publisher:
CDS
Description:
Model atmosphere analyses have been previously undertaken for both Galactic and extragalactic B-type supergiants. By contrast, little attention has been given to a comparison of the properties of single supergiants and those that are members of multiple systems. Atmospheric parameters and nitrogen abundances have been estimated for all the B-type supergiants identified in the VLT-FLAMES Tarantula survey. These include both single targets and binary candidates. The results have been analysed to investigate the role of binarity in the evolutionary history of supergiants. TLUSTY non-local thermodynamic equilibrium (LTE) model atmosphere calculations have been used to determine atmospheric parameters and nitrogen abundances for 34 single and 18 binary supergiants. Effective temperatures were deduced using the silicon balance technique, complemented by the helium ionisation in the hotter spectra. Surface gravities were estimated using Balmer line profiles and microturbulent velocities deduced using the silicon spectrum. Nitrogen abundances or upper limits were estimated from the NII spectrum. The effects of a 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 B-type supergiants across the theoretical terminal age main sequence (TAMS).
17097. VLT-FLAMES Tarantula Survey. 30 Dor luminous stars
ID:
ivo://CDS.VizieR/J/A+A/558/A134
Title:
VLT-FLAMES Tarantula Survey. 30 Dor luminous stars
Short Name:
J/A+A/558/A134
Date:
21 Oct 2021
Publisher:
CDS
Description:
The VLT-FLAMES Tarantula Survey has an extensive view of the copious number of massive stars in the 30 Doradus (30 Dor) star forming region of the Large Magellanic Cloud. These stars play a crucial role in our understanding of the stellar feedback in more distant, unresolved star forming regions.
17098. VLT-FLAMES Tarantula Survey: vsini measures
ID:
ivo://CDS.VizieR/J/A+A/550/A109
Title:
VLT-FLAMES Tarantula Survey: vsini measures
Short Name:
J/A+A/550/A109
Date:
21 Oct 2021
Publisher:
CDS
Description:
Projected rotational velocities (vsini) have been estimated for 334 targets in the VLT-FLAMES Tarantula survey that do not manifest significant radial velocity variations and are not supergiants. They have spectral types from approximately O9.5 to B3. The estimates have been analysed to infer the underlying rotational velocity distribution, which is critical for understanding the evolution of massive stars. Projected rotational velocities were deduced from the Fourier transforms of spectral lines, with upper limits also being obtained from profile fitting. For the narrower lined stars, metal and non-diffuse helium lines were adopted, and for the broader lined stars, both non-diffuse and diffuse helium lines; the estimates obtained using the different sets of lines are in good agreement. The uncertainty in the mean estimates is typically 4% for most targets. The iterative deconvolution procedure of Lucy has been used to deduce the probability density distribution of the rotational velocities. Projected rotational velocities range up to approximately 450km/s and show a bi-modal structure. This is also present in the inferred rotational velocity distribution with 25% of the sample having 0>=v_e_>=100km/s and the high velocity component having v_e_~250km/s. There is no evidence from the spatial and radial velocity distributions of the two components that they represent either field and cluster populations or different episodes of star formation. Be-type stars have also been identified.
17099. VLTI/MIDI AGN Large Program observations
ID:
ivo://CDS.VizieR/J/A+A/558/A149
Title:
VLTI/MIDI AGN Large Program observations
Short Name:
J/A+A/558/A149
Date:
21 Oct 2021
Publisher:
CDS
Description:
The AGN-heated dust distribution (the "torus") is increasingly recognized not only as the absorber required in unifying models, but as a tracer for the reservoir that feeds the nuclear Super-Massive Black Hole. Yet, even its most basic structural properties (such as its extent, geometry and elongation) are unknown for all but a few archetypal objects. In order to understand how the properties of AGN tori are related to feeding and obscuration, we need to resolve the matter distribution on parsec scales. Since most AGNs are unresolved in the mid-infrared, even with the largest telescopes, we utilize the MID-infrared interferometric Instrument (MIDI) at the Very Large Telescope Interferometer (VLTI) that is sensitive to structures as small as a few milli-arcseconds (mas). We present here an extensive amount of new interferometric observations from the MIDI AGN Large Program (2009-2011) and add data from the archive to give a complete view of the existing MIDI observations of AGNs. Additionally, we have obtained high-quality mid-infrared spectra from VLT/VISIR to provide a precise total flux reference for the interferometric data. We present correlated and total fluxes for 23 AGNs (16 of which with new data) and derive flux and size estimates at 12m using simple axisymmetric geometrical models.
17100. VLTI/PIONIER images of 15 Herbig Ae/Be stars
ID:
ivo://CDS.VizieR/J/A+A/636/A116
Title:
VLTI/PIONIER images of 15 Herbig Ae/Be stars
Short Name:
J/A+A/636/A116
Date:
21 Oct 2021
Publisher:
CDS
Description:
The innermost astronomical unit (au) in protoplanetary disks is a key region for stellar and planet formation, as exoplanet searches have shown a large occurrence of close-in planets, located within the first au around their host star. We aim to reveal the morphology of the disk inner rim using near-infrared interferometric observations with milli-arcsecond resolution provided by near-infrared multi-telescope interferometry. Methods: We provide model-independent reconstructed images of 15 objects selected from the Herbig AeBe survey carried out with VLTI/PIONIER, using the semi-parametric approach for image reconstruction of chromatic objects (SPARCO). We propose a set of methods to reconstruct and analyze the images in a consistent way. 40% of the systems (6/15) are found to be centro-symmetric at the angular resolution of the observations. For the rest of the objects, we find evidence for asymmetric emission due to moderate-to-strong inclination of a disk-like structure for ~30% of the objects (5/15), and non-centro-symmetric morphology due to an non-axisymmetric and possible variable environment (4/15, ~27%). Among the systems with disk-like structure, 20% (3/15) show a resolved dust-free cavity. Finally, we do not detect extended emission beyond the inner rim. The image reconstruction process is a powerful tool to reveal complex disk inner rim morphologies which is complementary to the fit of geometrical models. At the angular resolution reached by near-infrared interferometric observations most of the images are compatible with a centrally peaked emission (no cavity). For the most resolved targets, image reconstruction reveals morphologies that cannot be reproduced by generic parametric models (e.g., perturbed inner rims, complex brightness distributions). Moreover, the non-axisymmetric disks show that the spatial resolution probed by optical interferometers makes the observations of the near-infrared emission (inside a few au) sensitive to temporal evolution with a time-scale down to few weeks. The evidence of non-axisymmetric emission that cannot be explained by simple inclination and radiative transfer effects requires for alternative explanations such as a warping of the inner disks. Interferometric observations can therefore be used to follow the evolution of the asymmetry of those disks at an au or sub-au scale.

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