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.
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).
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.
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.
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.
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.
Red supergiant stars represent one of the latest stages of the evolution of massive stars. Their photospheric convection may play an important role in the launching mechanism of their mass loss. Yet, its characteristics and dynamics are poorly constrained. By observing red supergiant stars with near infrared interferometry at different epochs, we expect to unveil the evolution of bright convective features on their stellar surface. We observed the M2Iab-Ib red supergiant star CE Tau with the VLTI/PIONIER instrument in the H band at two different epochs separated by one month. We derive the angular diameter of the star, basic stellar parameters and reconstruct two reliable images of its H band photosphere. The contrast of the convective pattern of the reconstructed images is 5+/-1% and 6+/-1 % for our two epochs of observation. The stellar photosphere shows few changes between the two epochs. The contrast of the convective pattern is below the average contrast variations obtained on 30 randomly chosen snapshots of the best matching 3D radiative hydrodynamics simulation: 23+/-1% for the original simulation images, and 16+/-1% for the maps degraded to the reconstruction resolution. We offer two hypotheses to explain this observation: CE Tau may be experiencing a quiet convective activity episode or it could be a consequence of its warmer effective temperature (hence its smaller radius) compared to the simulation.
We present the results of high angular resolution adaptive optics (AO) near-infrared (JHKs) observations of the deeply embedded massive cluster RCW 38 using NACO on the Very Large Telescope. Narrowband AO observations centered at wavelengths of 1.28um, 2.12um, and 2.17um were also obtained. The area covered by these observations is about 0.5pc^2^, centered on the O-star RCW 38 IRS 2. We use the JHKs colors to identify young stars with infrared (IR) excess in this region.
We present a catalogue of 2135 galaxy redshifts from the VLT LBG Redshift Survey (VLRS), a spectroscopic survey of z~3 galaxies in wide fields centred on background quasi-stellar objects. We have used deep optical imaging to select galaxies via the Lyman-break technique. Spectroscopy of the Lyman-break galaxies (LBGs) was then made using the Very Large Telescope (VLT) Visible Multi-Object Spectrograph (VIMOS) instrument, giving a mean redshift of z=2.79. We analyse the clustering properties of the VLRS sample and also of the VLRS sample combined with the smaller area Keck-based survey of Steidel et al. (2003, Cat. J/ApJ/592/728).
We have measured redshifts for 243 z~~3 quasars in nine Very Large Telescope (VLT) Visible Imaging and Multi-Object Spectrograph (VIMOS) Lyman-break galaxy (LBG) redshift survey areas, each of which is centred on a known bright quasar. Using the spectra of these quasars, we measure the cross-correlation between neutral hydrogen gas causing the Ly{alpha} forest and 1020 LBGs at z~~3.
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