- ID:
- ivo://CDS.VizieR/J/AJ/160/115
- Title:
- JHK observation of 75 OB stars in Cyg OB2
- Short Name:
- J/AJ/160/115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of a high angular resolution survey of massive OB stars in the Cygnus OB2 association that we conducted with the Near-Infrared Imager camera and ALTAIR adaptive optics system of the Gemini North telescope. We observed 74 O- and early-B-type stars in Cyg OB2 in the JHK infrared bands in order to detect binary and multiple companions. The observations are sensitive to equal-brightness pairs at separations as small as 0.08", and progressively fainter companions are detectable out to {Delta}K=9mag at a separation of 2". This faint contrast limit due to read noise continues out to 10" near the edge of the detector. We assigned a simple probability of chance alignment to each companion based upon its separation and magnitude difference from the central target star and upon areal star counts for the general star field of Cyg OB2. Companion stars with a field membership probability of less than 1% are assumed to be physical companions. This assessment indicates that 47% of the targets have at least one resolved companion that is probably gravitationally bound. Including known spectroscopic binaries, our sample includes 27 binary, 12 triple, and 9 systems with 4 or more components. These results confirm studies of high-mass stars in other environments that find that massive stars are born with a high-multiplicity fraction. The results are important for the placement of the stars in the Hertzsprung-Russell diagram, the interpretation of their spectroscopic analyses, and for future mass determinations through measurement of orbital motion.
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- ID:
- ivo://CDS.VizieR/J/other/ApSS/365.112
- Title:
- Kinematic data for high luminosity stars
- Short Name:
- J/other/ApSS/365
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We calculated the median parallaxes for 47 OB associations including at least 10 stars with known Gaia DR2 parallaxes. A comparison between trigonometric and photometric parallaxes of OB associations reveals a zero-point offset of {Delta}_{pi}_=-0.11+/-0.04mas indicating that Gaia DR2 parallaxes are, on average, underestimated and the distances derived from them are overestimated. The correction of {Delta}_{pi}=-0.11 mas is consistent with the estimate that Arenou et al. (2018A&A...616A..17A) obtained for bright stars. An analysis of parallaxes of OB associations and high-luminosity field stars confirms our previous conclusion (Dambis et al., 2001AstL...27...58D) that the distance scale for OB stars established by Blaha and Humphreys (1989AJ.....98.1598B) must be reduced by 10-20%. Spurious systematic motions of 10-20km/s at the distances of 2-3kpc from the Sun are found to arise from the use of the uncorrected Gaia DR2 parallaxes.
- ID:
- ivo://CDS.VizieR/V/31A
- Title:
- Kinematic data for O-B5 stars
- Short Name:
- V/31A
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This document describes the magnetic tape version of a catalog of 1440 O-B5 star with radial velocities accurate to within 5 km/sec, located within 3 kpc of the sun and within 10 degrees of the galactic equator. Radial velocities, luminosities and spectral classifications have been included from the literature; proper motions have been compiled for 898 of the stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/472/3887
- Title:
- Kinematic data for stars in OB-associations
- Short Name:
- J/MNRAS/472/3887
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use stellar proper motions from the catalog TGAS (2016, Cat. I/337) to study the kinematics of OB-associations identified by Blaha and Humphreys (1989AJ.....98.1598B). The TGAS proper motions of OB-associations generally agree well with the Hipparcos proper motions. The parameters of the Galactic rotation curve obtained with TGAS and Hipparcos proper motions agree within the errors. The average internal velocity dispersion calculated for 18 OB-associations with more than 10 TGAS stars is sigma_v_=3.9km/s, which is considerably smaller, by a factor of 0.4, than the velocity dispersions derived from Hipparcos data. The effective contribution from binary OB-stars into the velocity dispersion sigma_v inside OB-associations is sigma_b_=1.2km/s. The median virial and stellar masses of OB-associations are equal to 7.1x10^5^ and 9.0x10^3^M_{sun}_, respectively. Thus OB-associations must be unbound objects provided they do not include a lot of dense gas. The median star-formation efficiency is epsilon=2.1%. Nearly one third of stars of OB-associations must lie outside their tidal radius. We found that the Per OB1 and Car OB1 associations are expanding with the expansion started in a small region of 11-27pc 7-10Myr ago. The average expansion velocity is 6.3km/s.
- ID:
- ivo://CDS.VizieR/J/ApJS/253/22
- Title:
- Ks absolute magnitudes from LAMOST for OB stars
- Short Name:
- J/ApJS/253/22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a data-driven method to estimate absolute magnitudes for O- and B-type stars from the LAMOST spectra, which we combine with Gaia DR2 parallaxes to infer distance and binarity. The method applies a neural network model trained on stars with precise Gaia parallax to the spectra and predicts K_s_-band absolute magnitudes M_Ks_ with a precision of 0.25mag, which corresponds to a precision of 12% in spectroscopic distance. For distant stars (e.g., >5kpc), the inclusion of constraints from spectroscopic M_Ks_ significantly improves the distance estimates compared to inferences from Gaia parallax alone. Our method accommodates for emission-line stars by first identifying them via principal component analysis reconstructions and then treating them separately for the M_Ks_ estimation. We also take into account unresolved binary/multiple stars, which we identify through deviations in the spectroscopic M_Ks_ from the geometric M_Ks_ inferred from Gaia parallax. This method of binary identification is particularly efficient for unresolved binaries with near equal-mass components and thus provides a useful supplementary way to identify unresolved binary or multiple-star systems. We present a catalog of spectroscopic M_Ks_, extinction, distance, flags for emission lines, and binary classification for 16002 OB stars from LAMOST DR5. As an illustration, we investigate the M_Ks_ of the enigmatic LB-1 system, which Liu et al. 2019Natur.575..618L had argued consists of a B star and a massive stellar-mass black hole. Our results suggest that LB-1 is a binary system that contains two luminous stars with comparable brightness, and the result is further supported by parallax from the Gaia eDR3.
- ID:
- ivo://CDS.VizieR/J/A+A/650/A112
- Title:
- Mapping hot luminous stars in the Galaxy
- Short Name:
- J/A+A/650/A112
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Luminous hot stars (M_Ks_<~0mag and Teff>~8000K) dominate the stellar energy input to the interstellar medium (ISM) throughout cosmological time, are used as laboratories to test theories of stellar evolution and multiplicity, and serve as luminous tracers of star formation in the Milky Way and other galaxies. Massive stars occupy well-defined loci in colour-colour and colour-magnitude spaces, enabling selection based on the combination of Gaia EDR3 astrometry and photometry and 2MASS photometry, even in the presence of substantive dust extinction. In this paper we devise an all-sky sample of such luminous OBA-type stars, which was designed to be complete rather than very pure, providing targets for spectroscopic follow-up with the SDSS-V survey. To estimate the purity and completeness of our catalogue, we derive stellar parameters for the stars in common with LAMOST DR6 and we compare the sample to other O and B-type star catalogues. We estimate `astro-kinematic' distances by combining parallaxes and proper motions with a model for the expected velocity and density distribution of young stars; we show that this adds useful constraints on the distances and therefore luminosities of the stars. With these distances we map the spatial distribution of a more stringently selected subsample across the Galactic disc, and find it to be highly structured, with distinct over- and under-densities. The most evident over-densities can be associated with the presumed spiral arms of the Milky Way, in particular the Sagittarius-Carina and Scutum-Centaurus arms. Yet, the spatial picture of the Milky Way's young disc structure emerging in this study is complex, and suggests that most young stars in our Galaxy (t_age_<t_dyn_) are not neatly organised into distinct spiral arms. The combination of the comprehensive spectroscopy to come from SDSS-V (yielding velocities, ages, etc.) with future Gaia data releases will be crucial in order to reveal the dynamical nature of the spiral arms themselves.
- ID:
- ivo://CDS.VizieR/J/ApJ/763/101
- Title:
- Massive field OB stars in the SMC
- Short Name:
- J/ApJ/763/101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Some theories of star formation suggest massive stars may only form in clustered environments, which would create a deficit of massive stars in low-density environments. Observationally, Massey (2002, Cat. II/236) finds such a deficit in samples of the field population in the Small and Large Magellanic Clouds, with an initial mass function (IMF) slope of {Gamma}_IMF_~4. These IMF measurements represent some of the largest known deviations from the standard Salpeter IMF slope of {Gamma}_IMF_=1.35. Here, we carry out a comprehensive investigation of the mass function above 20M_{sun}_ for the entire field population of the Small Magellanic Cloud (SMC), based on data from the Runaways and Isolated O Type Star Spectroscopic Survey of the SMC (RIOTS4). This is a spatially complete census of the entire field OB star population of the SMC obtained with the IMACS multi-object spectrograph and MIKE echelle spectrograph on the Magellan telescopes. Based on Monte Carlo simulations of the evolved present-day mass function, we find the slope of the field IMF above 20M_{sun}_ is {Gamma}_IMF_=2.3+/-0.4. We extend our IMF measurement to lower masses using BV photometry from the OGLE II survey. We use a statistical approach to generate a probability distribution for the mass of each star from the OGLE photometry, and we again find {Gamma}_IMF_=2.3+/-0.6 for stellar masses from 7M_{sun}_ to 20M_{sun}_. The discovery and removal of ten runaways in our RIOTS4 sample steepens the field IMF slope to {Gamma}_IMF_=2.8+/-0.5. We discuss the possible effects of binarity and star formation history on our results, and conclude that the steep field massive star IMF is most likely a real effect.
- ID:
- ivo://CDS.VizieR/J/A+A/550/A21
- Title:
- Massive star-forming regions radio lines
- Short Name:
- J/A+A/550/A21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Australia Telescope Compact Array (ATCA) observations of the H_2_O maser line and radio continuum at 18.0GHz and 22.8GHz toward a sample of 192 massive star-forming regions containing several clumps already imaged at 1.2mm. The main aim of this study is to investigate the water maser and centimeter continuum emission (that likely traces thermal free-free emission) in sources at different evolutionary stages, using evolutionary classifications previously published. We used the recently comissioned Compact Array Broadband Backend (CABB) at ATCA that obtains images with 20arcsec resolution in the 1.3cm continuum and H_2_O maser emission in all targets. For the evolutionary analysis of the sources we used millimeter continuum emission from the literature and the infrared emission from the MSX Point Source Catalog. We detect centimeter continuum emission in 88% of the observed fields with a typical rms noise level of 0.45mJy/beam. Most of the fields show a single radio continuum source, while in 20% of them we identify multiple components. A total of 214 centimeter continuum sources have been identified, that likely trace optically thin HII regions, with physical parameters typical of both extended and compact HII regions. Water maser emission was detected in 41% of the regions, resulting in a total of 85 distinct components. The low angular (20arcsec) and spectral (14km/s) resolutions do not allow a proper analysis of the water maser emission, but suffice to investigate its association with the continuum sources. We have also studied the detection rate of HII regions in the two types of IRAS sources defined in the literature on the basis of the IRAS colors: High and Low. No significant differences are found, with high detection rates (>90%) for both High and Low sources. We classify the millimeter and infrared sources in our fields in three evolutionary stages following the scheme presented previously: (Type 1) millimeter-only sources, (Type 2) millimeter plus infrared sources, (Type 3) infrared-only sources. We find that HII regions are mainly associated with Type 2 and Type 3 objects, confirming that these are more evolved than Type 1 sources. The HII regions associated with Type 3 sources are slightly less dense and larger in size than those associated with Type 2 sources, as expected if the HII region expands as it evolves, and Type 3 objects are older than Type 2 objects. The maser emission is mostly found to be associated with Type 1 and Type 2 sources, with a higher detection rate toward Type 2, consistent with the results of the literature. Finally, our results on HII region and H_2_O maser association with different evolutionary types confirm the evolutionary classification proposed previously.
- ID:
- ivo://CDS.VizieR/J/ApJS/247/17
- Title:
- Massive stars in APOGEE2 Survey. III.
- Short Name:
- J/ApJS/247/17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have applied the semi-empirical spectral analysis, developed by the Sloan Digital Sky Survey (SDSS)-IV/Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE2) Massive Star Team, to a large sample of new O- and B-type stars identified along the Sagittarius spiral arm, in the direction of the southern star clusters NGC3603 and NGC3576. We obtained H-band spectra for 265 point sources, using the APOGEE2-S spectrograph at the du Pont Telescope at the Las Campanas Observatory. We analyzed the associated spectral features deriving spectral types, as well as the massive star distribution along the line of sight. From a total of 265 science targets, 95 are classified as mid- to late-O-type stars (for which only 10 O-type stars are previously known in the literature), 38 are found to be early- to mid-B-type stars, and 32 are classified as either yellow or blue supergiants, completing a total of 165 massive stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/873/66
- Title:
- Massive stars in SDSS/APOGEE-2. II. W3-W4-W5
- Short Name:
- J/ApJ/873/66
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we have applied a semi-empirical spectral classification method for OB-stars using the APOGEE spectrograph to a sample of candidates in the W3-W4-W5 (W345) complexes. These massive star-forming regions span over 200pc across the Perseus arm and have a notorious population of massive stars, from which a large fraction are members of various embedded and young open clusters. From 288 APOGEE spectra showing H-band spectral features typical of O- and B-type sources, 46 probably correspond to previously unknown O-type stars. Therefore, we confirm that Br11-Br13 together with HeII {lambda}16923 (7-12) and HeII {lambda}15723 (7-13) lines contained in the APOGEE spectral bands are useful in providing spectral classification down to one spectral sub-class for massive stars in regions as distant as d~2kpc. The large number of newly found O-type stars as well as the numerous intermediate-mass population confirm that W345 is a very efficient massive star factory, with an integral stellar population probably amounting several thousand solar masses.
