- ID:
- ivo://CDS.VizieR/J/A+A/411/361
- Title:
- VI photometry of extra-galactic Cepheids
- Short Name:
- J/A+A/411/361
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we recalibrate the Cepheid distance to some nearby galaxies observed by the HST Key Project and the Sandage-Tammann-Saha group. We use much of the Key Project methodology in our analysis but apply new techniques, based on Fourier methods to estimate the mean of a sparsely sampled Cepheid light curve, to published extra-galactic Cepheid data. We also apply different calibrating PL relations to estimate Cepheid distances, and investigate the sensitivity of the distance moduli to the adopted calibrating PL relation. We re-determine the OGLE LMC PL relations using a more conservative approach and also study the effect of using Galactic PL relations on the distance scale.
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- ID:
- ivo://CDS.VizieR/J/MNRAS/424/1807
- Title:
- VISTA Magellanic Cloud Survey. V. Cepheids
- Short Name:
- J/MNRAS/424/1807
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The VISTA Magellanic Cloud (VMC; PI: M.-R. L. Cioni) survey is collecting deep K_s_-band time series photometry of the pulsating variable stars hosted by the system formed by the two Magellanic Clouds (MCs) and the bridge connecting them. In this paper, we present the first results for classical Cepheids, from the VMC observations of two fields in the Large Magellanic Cloud (LMC), centred on the South Ecliptic Pole and the 30 Doradus star-forming regions, respectively. The VMC K_s_-band light curves of the Cepheids are well sampled (12 epochs) and of excellent precision (typical errors of ~0.01mag). We were able to measure for the first time the K_s_magnitude of the faintest classical Cepheids in the LMC (K_s_~17.5mag), which are mostly pulsating in the first overtone (FO) mode, and to obtain FO period--luminosity (PL), period-Wesenheit (PW) and period-luminosity-colour (PLC) relations, spanning the full period range from 0.25 to 6d. Since the longest period Cepheid in our data set has a variability period of 23d, we have complemented our sample with literature data for brighter F Cepheids. On this basis, we have built a PL relation in the K_s_ band that, for the first time, includes short-period - hence low-luminosity - pulsators, and spans the full range from 1.6 to 100 d in period.We also provide the first ever empirical PW and PLC relations using the (V-K_s_) colour and time series K_s_photometry. The very small dispersion (~0.07mag) of these relations makes them very well suited to study the three-dimensional geometry of the Magellanic system. The use of 'direct' (parallax- and Baade--Wesselink-based) distance measurements to both Galactic and LMC Cepheids allowed us to calibrate the zero-points of the PL, PW and PLC relations obtained in this paper, and in turn to estimate an absolute distance modulus of (m-M)_0_=18.46+/-0.03mag for the LMC. This result is in agreement with most of the latest literature determinations based on classical Cepheids.
- ID:
- ivo://CDS.VizieR/II/351
- Title:
- VISTA Magellanic Survey (VMC) catalog
- Short Name:
- II/351
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The new VISual and Infrared Telescope for Astronomy (VISTA) has started operations in 2009. Over its first five years it collected data for six public surveys, one of which is the near-infrared YJKs VISTA survey of the Magellanic Clouds system (VMC). This survey comprises the Large Magellanic Cloud (LMC), the Small Magellanic Cloud, the Magellanic Bridge connecting the two galaxies and two fields in the Magellanic Stream. The main goals of the VMC survey are the determination of the spatially-resolved star-formation history and the three-dimensional structure of the Magellanic system. The VMC survey is therefore designed to reach stars as faint as the oldest main sequence turn-off point and to constrain the mean magnitude of pulsating variables such as RR Lyrae stars and Cepheids. The VMC data are comprised of multi-epoch observations which are executed following specific time constraints. The first science results, aimed at assessing the scientific quality of the VMC data, include an overview of the distribution of stars in colour-magnitude and colour-colour diagrams, the detection of planetary nebulae and stellar clusters, and the Ks band light-curves of variable stars. The VMC survey represents a tremendous improvement, in spatial resolution and sensitivity, on previous panoramic observations of the Magellanic system in the near-infrared, providing a powerful complement to deep observations at other wavelengths.
- ID:
- ivo://CDS.VizieR/J/A+A/456/623
- Title:
- VLT-FLAMES survey of massive stars
- Short Name:
- J/A+A/456/623
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new observations of 470 stars using the Fibre Large Array Multi-Element Spectrograph (FLAMES) instrument in fields centered on the clusters NGC 330 and NGC 346 in the Small Magellanic Cloud (SMC), and NGC 2004 and the N11 region in the Large Magellanic Cloud (LMC). A further 14 stars were observed in the N11 and NGC 330 fields using the Ultraviolet and Visual Echelle Spectrograph (UVES) for a separate programme. Spectral classifications and stellar radial velocities are given for each target, with careful attention to checks for binarity. In particular, we have investigated previously unexplored regions around the central LH9/LH10 complex of N11, finding ~25 new O-type stars from our spectroscopy. We have observed a relatively large number of Be-type stars that display permitted Fe II emission lines. These are primarily not in the cluster cores and appear to be associated with classical Be-type stars, rather than pre main-sequence objects. The presence of the Fe II emission, as compared to the equivalent width of H{alpha}, is not obviously dependent on metallicity. We have also explored the relative fraction of Be- to normal B-type stars in the field-regions near to NGC 330 and NGC 2004, finding no strong evidence of a trend with metallicity when compared to Galactic results. A consequence of service observations is that we have reasonable time-sampling in three of our FLAMES fields. We find lower limits to the binary fraction of O- and early B-type stars of 23 to 36%. One of our targets (NGC 346-013) is especially interesting with a massive, apparently hotter, less luminous secondary component.
- 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.
- 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.
- 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.
- 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.
- ID:
- ivo://CDS.VizieR/J/A+A/580/A93
- Title:
- VLTS. B stars multiplicity
- Short Name:
- J/A+A/580/A93
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the multiplicity properties of 408 B-type stars observed in the 30 Doradus region of the Large Magellanic Cloud with multi-epoch spectroscopy from the VLT-FLAMES Tarantula Survey (VFTS). We use a cross-correlation method to estimate relative radial velocities from the helium and metal absorption lines for each of our targets. Objects with significant radial-velocity variations (and with an amplitude larger than 16km/s) are classified as spectroscopic binaries. We find an observed spectroscopic binary fraction (defined by periods of <10^3.5^d and mass ratios >0.1) for the B-type stars, f_B_(obs)=0.25+/-0.02, which appears constant across the field of view, except for the two older clusters (Hodge 301 and SL 639). These two clusters have significantly lower binary fractions of 0.08+/-0.08 and 0.10+/-0.09, respectively. Using synthetic populations and a model of our observed epochs and their potential biases, we constrain the intrinsic multiplicity properties of the dwarf and giant (i.e. relatively unevolved) B-type stars in 30 Dor. We obtain a present-day binary fraction f_B_(true)=0.58+/-0.11, with a flat period distribution. Within the uncertainties, the multiplicity properties of the B-type stars agree with those for the O stars in 30 Dor from the VFTS.
- ID:
- ivo://CDS.VizieR/J/A+A/603/A91
- Title:
- VLTS. B-type main-sequence binary systems
- Short Name:
- J/A+A/603/A91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A spectroscopic analysis has been undertaken for the B-type multiple systems (excluding those with supergiant primaries) in the VLT-FLAMES Tarantula Survey (VFTS). Projected rotational velocities, vsini, for the primaries have been estimated using a Fourier Transform technique and confirmed by fitting rotationally broadened profiles. A subset of 33 systems with vsini<=80km/s have been analysed using a TLUSTY grid of model atmospheres to estimate stellar parameters and surface abundances for the primaries. The effects of a potential flux contribution from an unseen secondary have also been considered. For 20 targets it was possible to reliably estimate their effective temperatures (Teff) but for the other 13 objects it was only possible to provide a constraint of 20000<=Teff<=26000K - the other parameters estimated for these targets will be consequently less reliable. The estimated stellar properties are compared with evolutionary models and are generally consistent with their membership of 30 Doradus, while the nature of the secondaries of 3 SB2 system is discussed. A comparison with a sample of single stars with vsini<=80km/s obtained from the VFTS and analysed with the same techniques implies that the atmospheric parameters and nitrogen abundances of the two samples are similar. However, the binary sample may have a lack of primaries with significant nitrogen enhancements, which would be consistent with them having low rotational velocities and having effectively evolved as single stars without significant rotational mixing. This result, which may be actually a consequence of the limitations of the pathfinder investigation presented in this paper, should be considered as a motivation for spectroscopic abundance analysis of large samples of binary stars, with high quality observational data.
