- ID:
- ivo://CDS.VizieR/J/A+A/538/A142
- Title:
- OB stars in NGC 6334 and NGC 6357
- Short Name:
- J/A+A/538/A142
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Star-forming complexes are large structures exhibiting massive star-formation at different stages of evolution, from dense cores to well-developed HII regions. They are very interesting for the study of the formation and evolution of stars. NGC 6334 and NGC 6357 are two active and relatively nearby star-forming complexes. From the extinction map and the sub-mm cold dust emission, and because they have similar velocities, these regions are most likely connected. However, located in the direction of the Galactic center their radial velocity is not representative of their distance. An alternative is then to determine the distance of NGC 6334 and NGC 6357 from their stellar content. Our aim is to perform a census of O-B3 ionising stars in NGC 6334 and NGC 6357, to determine the extinction coefficient, and the distance of both regions. A census of O-B3 stars is an essential basis for estimating the statistical lifetime of the earliest massive star-forming phases.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/657/A62
- Title:
- OB stars spectral classification automated tool
- Short Name:
- J/A+A/657/A62
- Date:
- 17 Mar 2022 14:50:02
- Publisher:
- CDS
- Description:
- As an increasing number of spectroscopic surveys become available, an automated approach to spectral classification becomes necessary. Due to the significance of the massive stars, it is of great importance to identify the phenomenological parameters of these stars (e.g., the spectral type), which can be used as proxies to their physical parameters (e.g., mass and temperature). In this work, we aim to use the random forest (RF) algorithm to develop a tool for the automated spectral classification of OB-type stars according to their sub-types. We used the regular RF algorithm, the probabilistic RF (PRF), which is an extension of RF that incorporates uncertainties, and we introduced the KDE-RF method which is a combination of the kernel-density estimation and the RF algorithm. We trained the algorithms on the equivalent width (EW) of characteristic absorption lines measured in high-quality spectra (Signal-to-Noise (S/N)>50) from large Galactic (LAMOST, GOSSS) and extragalactic surveys (2dF, VFTS) with available spectral types and luminosity classes. By following an adaptive binning approach, we grouped the labels of these data in 11 spectral classes within the O2-B9 range. We examined which of the characteristic spectral lines (features) are more important for the classification based on a number of feature selection methods, and we searched for the optimal hyperparameters of the classifiers to achieve the best performance. From the feature-screening process, we find that the full set of 17 spectral lines is needed to reach the maximum performance per spectral class. We find that the overall accuracy score is ~70%, with similar results across all approaches. We apply our model in other observational data sets providing examples of the potential application of our classifier to real science cases. We find that it performs well for both single massive stars and for the companion massive stars in Be X-ray binaries, especially for data of similar quality to the training sample. In addition, we propose a reduced ten-features scheme that can be applied to large data sets with lower S/N~20-50. The similarity in the performances of our models indicates the robustness and the reliability of the RF algorithm when it is used for the spectral classification of early-type stars. The score of ~70% is high if we consider (a) the complexity of such multiclass classification problems (i.e., 11 classes), (b) the intrinsic scatter of the EW distributions within the examined spectral classes, and (c) the diversity of the training set since we use data obtained from different surveys with different observing strategies. In addition, the approach presented in this work is applicable to products from different surveys in terms of quality (e.g., different resolution) and different formats (e.g., absolute or normalized flux), while our classifier is agnostic to the luminosity class of a star, and, as much as possible, it is metallicity independent.
- ID:
- ivo://CDS.VizieR/J/A+A/352/600
- Title:
- O & B stars uvby-Hbeta photometry. I.
- Short Name:
- J/A+A/352/600
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stroemgren and H{beta} photometry of OB-stars generally brighter than 9.5mag in the Canis Major - Puppis - Vela region of Milky Way is reported. The observations are based on the Milky Way luminous-star (LS) identifications and are designed to create a complete, magnitude-limited sample of LS for this field. We present new uvby photometry for 127 LS and H{beta} photometry for 25 of them. These observations are part of an ongoing effort to improve the completeness of the existing uvby{beta} data-base for the bright OB-type stars in the Milky Way, with the aim to investigate the structure of selected star-forming regions.
- ID:
- ivo://CDS.VizieR/J/A+A/352/605
- Title:
- O & B stars uvby-Hbeta photometry. II.
- Short Name:
- J/A+A/352/605
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stroemgren and H{beta} photometry of O and B type stars, generally brighter than 10mag is presented for the fields of the galactic OB associations Monoceros OB2, Canis Major OB1 and Collinder 121. The observations are based on the PPM catalogue identifications and are designed to improve the completeness of the existing uvby{beta} data for the bright early-type stars in these fields. We present new uvby photometry for 343 stars and H{beta} photometry for 213 of them. These observations are part of our effort to study the structure of selected star-forming regions in the Milky Way, utilizing uvby{beta} photometry.
- ID:
- ivo://CDS.VizieR/J/AJ/106/591
- Title:
- OP Survey of Halo early-type stars
- Short Name:
- J/AJ/106/591
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results are reported of an objective-prism survey of stars, mostly earlier than spectral type F5, for two fields at (l;b) = (90 deg and 270 deg; -45 deg). The fields, each of approximately 70 square degrees, are examined on plates taken with the Schmidt Telescope of the Anglo-Australian Observatory. The brightness range of the stars classified is 10 < V < 15. The prism combination used provides a dispersion of 600 A/mm at Hgamma. The spectral classification presented is defined by the equality of equivalent widths of Ca II K and Hdelta at type "F0" and the absence of Ca II K in stars with significant Balmer lines at type "A0". Positions listed in the catalog were measured on the Stromlo PDS microdensitometer. Most stars were subsequently identified with objects in the ST ScI-NASA-ESO Hubble Space Telescope Guide Star Catalog in which positions have an accuracy of near +/- 1.0 arcsec.
- ID:
- ivo://CDS.VizieR/J/MNRAS/485/2312
- Title:
- Outer Galactic disk A and F stars space motions
- Short Name:
- J/MNRAS/485/2312
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A and F stars can be used as probes of outer Galactic disk kinematics: here we extend the work of Harris et al. (2018, Cat. J/MNRAS/475/1680) by crossmatching their A/F sample with Gaia DR2 to bring in proper motions. These are combined with the already measured radial velocities and spectro-photometric distances to obtain full space motions. We use this sample of 1173 stars, located in two pencil-beam sightlines (l=178{deg} and l=118{deg}), to sample the Galactocentric velocity field out to almost R_G_=15kpc. We find there are significant differences in all three (radial, azimuthal and vertical) kinematic components between the two directions. The rotation curve is roughly flat in the anticentre direction, confirming and extending the result of Kawata et al. (2018MNRAS.479L.108K) thanks to the greater reach of our spectro-photometric distance scale. However at l=118{deg} the circular velocity rises outwards from R_G_=10.5kpc and there is a more pronounced gradient in radial motion than is seen at l=178{deg}. Furthermore, the A star radial motion differs from the F stars by ~10km/s. We discuss our findings in the context of perturbers potentially responsible for the trends, such as the central bar, spiral arms, the warp and external satellites. Our results at l=178{deg} are broadly consistent with previous work on K giants in the anticentre, but the kinematics at l=118{deg} in the Perseus region do not yet reconcile easily with bar or spiral arm perturbation.
- ID:
- ivo://CDS.VizieR/J/MNRAS/466/546
- Title:
- Parameters for the 172 {lambda} Boo stars
- Short Name:
- J/MNRAS/466/546
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The evolutionary status of the chemically peculiar class of {lambda} Boo stars has been intensely debated. It is now agreed that the {lambda} Boo phenomenon affects A stars of all ages, from star formation to the terminal age main sequence, but the cause of the chemical peculiarity is still a puzzle. We revisit the debate of their ages and temperatures in order to shed light on the phenomenon, using the new parallaxes in Gaia Data Release 1 with existing Hipparcos parallaxes and multicolour photometry. We find that no single formation mechanism is able to explain all the observations, and suggest that there are multiple channels producing {lambda} Boo spectra. The relative importance of these channels varies with age, temperature and environment.
- ID:
- ivo://CDS.VizieR/J/MNRAS/475/1680
- Title:
- Parameters of 1183 A and F stars
- Short Name:
- J/MNRAS/475/1680
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Previous studies of the rotation law in the outer Galactic disc have mainly used gas tracers or clump giants. Here, we explore A and F stars as alternatives: these provide a much denser sampling in the outer disc than gas tracers and have experienced significantly less velocity scattering than older clump giants. This first investigation confirms the suitability of A stars in this role. Our work is based on spectroscopy of roughly 1300 photometrically selected stars in the red calcium-triplet region, chosen to mitigate against the effects of interstellar extinction. The stars are located in two low Galactic latitude sightlines, at longitudes l=118{deg}, sampling strong Galactic rotation shear, and l=178{deg}, near the anticentre. With the use of Markov Chain Monte Carlo parameter fitting, stellar parameters and radial velocities are measured, and distances computed. The obtained trend of radial velocity with distance is inconsistent with existing flat or slowly rising rotation laws from gas tracers (Brand & Blitz, 1993A&A...275...67B, Cat J/A+A/275/67; Reid et al., 2014ApJ...783..130R, Cat. J/ApJ/783/130). Instead, our results fit in with those obtained by Huang et al. (2016MNRAS.463.2623H) from disc clump giants that favoured rising circular speeds. An alternative interpretation in terms of spiral arm perturbation is not straight forward. We assess the role that undetected binaries in the sample and distance error may have in introducing bias, and show that the former is a minor factor. The random errors in our trend of circular velocity are within +/-5km/s.
- ID:
- ivo://CDS.VizieR/J/AJ/158/73
- Title:
- Parameters of OB stars & their bow shock nebulae
- Short Name:
- J/AJ/158/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Second only to initial mass, the rate of wind-driven mass loss determines the final mass of a massive star and the nature of its remnant. Motivated by the need to reconcile observational values and theory, we use a recently vetted technique to analyze the mass-loss rates in a sample of OB stars that generate bow shock nebulae. We measure peculiar velocities from new Gaia parallax and proper motion data and their spectral types from new optical and infrared spectroscopy. For our sample of 70 central stars in morphologically selected bow shock nebulae, 67 are OB stars. The median peculiar velocity is 11 km/s, significantly smaller than classical "runaway star" velocities. Mass-loss rates for these O and early B stars agree with recently lowered theoretical predictions, ranging from ~10^-7^ M_{sun}_/yr for mid-O dwarfs to 10^-9^ M_{sun}_/yr for late O dwarfs - a factor of about 2.7 lower than the often-used Vink et al. (2000A&A...362..295V, 2001A&A...369..574V) formulation. Our results provide the first observational mass-loss rates for B0-B3 dwarfs and giants - 10^-9^ to 10^-8^ M_{sun}_/yr. We find evidence for an increase in the mass-loss rates below a critical effective temperature, consistent with predictions of the bistability phenomenon in the range T_eff_=19000-27000 K. The sample exhibits a correlation between modified wind momentum and luminosity, consistent in slope but lower by 0.43 dex in magnitude compared to canonical wind-luminosity relations. We identify a small subset of objects deviating most significantly from theoretical expectations as probable radiation-driven bow wave nebulae by virtue of their low stellar-to-nebular luminosity ratios. For these, the inferred mass-loss rates must be regarded as upper limits.
- ID:
- ivo://CDS.VizieR/J/AJ/135/564
- Title:
- Photometry and spectroscopy of BHB candidates
- Short Name:
- J/AJ/135/564
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a complete spectroscopic survey of 2414 2MASS-selected blue horizontal branch (BHB) candidates selected over 4300{deg}^2^ of the sky. We identify 655 BHB stars in this non-kinematically selected sample. We calculate the luminosity function of field BHB stars, and find evidence for very few hot BHB stars in the field.
