- ID:
- ivo://CDS.VizieR/J/A+A/384/473
- Title:
- O, B and Be stars equivalent widths
- Short Name:
- J/A+A/384/473
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an atlas of spectra of O- and B-type stars, obtained with the Short Wavelength Spectrometer (SWS) during the Post-Helium program of the Infrared Space Observatory (ISO). This program is aimed at extending the Morgan & Keenan (1973ARA&A..11...29M) classification scheme into the near-infrared. Later type stars will be discussed in a separate publication. The observations consist of 57 SWS Post-Helium spectra from 2.4 to 4.1{mu}m, supplemented with 10 spectra acquired during the nominal mission with a similar observational setting. For B-type stars, this sample provides ample spectral coverage in terms of subtype and luminosity class. For O-type stars, the ISO sample is coarse and therefore is complemented with 8 UKIRT L'-band observations. In terms of the presence of diagnostic lines, the L'-band is likely the most promising of the near-infrared atmospheric windows for the study of the physical properties of B stars. Specifically, this wavelength interval contains the Br{alpha}, Pf{gamma}, and other Pfund lines which are probes of spectral type, luminosity class and mass loss. Here, we present simple empirical methods based on the lines present in the 2.4 to 4.1{mu}m interval that allow the determination of i) the spectral type of B dwarfs and giants to within two subtypes; ii) the luminosity class of B stars to within two classes; iii) the mass-loss rate of O stars and B supergiants to within 0.25dex.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/454/151
- Title:
- OB Associations of the Northern Milky Way
- Short Name:
- J/ApJ/454/151
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the massive star content of Milky Way clusters and OB associations in order to answer three questions: (1) How coeval is star formation? (2) How constant is the initial mass function (IMF)? (3) What is the progenitor mass of Wolf-Rayet stars? Our sample includes NGC 6823/Vul OB1, NGC 6871/Cyg OB3, Berkeley 86/Cyg OB1, NGC 6913/Cyg OB1, NGC 7235, NGC 7380/Cep OB1, Cep OB5, IC 1805/Cas OB6, NGC 1893/Aur OB2, and NGC 2244/Mon OB2. Large-field CCD imaging and multiobject, fiber spectroscopy has resulted in UBV photometry for >10,000 stars and new spectral types for ~200 stars. These data are used to redetermine distances and reddenings for these regions and to help exclude probable nonmembers in constructing the H-R diagrams. We reanalyze comparable data previously published on Cyg OB2, Tr 14/16, and NGC 6611 and use all of these to paint a picture of star formation and to measure the IMFs. We find the following: (1) Most of the massive stars are born during a period Delta(Tau) < 3 Myr in each association. Some star formation has clearly preceded this event, as evidenced by the occasional presence of evolved (Tau ~ 10 Myr) 15 Msun stars despite a typical age Tau ~ 2 Myr for the more massive population. However, all these regions also show evidence of 5-10 Msun pre-main-sequence stars (Tau < 1 Myr), demonstrating that some star formation at lower masses does continue for at least 1 Myr after the formation of high-mass stars. (2) There is no statistically significant difference in IMF slopes among these clusters, and the average value is found to be Gamma = -1.1 +/- 0.1 for stars with masses > 7 Msun. A comparison with similarly studied OB associations in the Magellanic Clouds reveals no difference in IMF slope, and hence we conclude that star formation of massive stars in clusters proceeds independently of metallicity, at least between z = 0.02 and z = 0.002. The masses of the highest mass stars are approximately equal in the Milky Way, LMC, and SMC associations, contrary to the expectation that this value should vary by a factor of 3 over this metallicity range. We conclude that radiation pressure on grains must not limit the mass of the highest mass star that can form, in accord with the suggestion of Wolfire & Cassinelli that the mere existence of massive stars suggests that shocks or other mechanisms have disrupted grains in star-forming events. (3) The four Wolf-Rayet stars in our sample have come from stars more massive than 40 Msun; one WC star and one late-type WN star each appear to have come from very massive (~100 Msun) progenitors.
- ID:
- ivo://CDS.VizieR/J/A+A/423/919
- Title:
- Objects in LHA 115-N83-84-85 SMC region
- Short Name:
- J/A+A/423/919
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this article we study the N83-84-85 region of the inner wing of the SMC. Direct and low-dispersion objective prism plates taken with the 1.2m UK Schmidt Telescope have been digitized by the SuperCOSMOS machine. Star counts have been performed for our region in selected luminosity slices in the U filter and isodensity contours have been used to identify the structures with enhanced stellar number density. We find evidence of triggered star formation from massive stars of older to more recent OB associations. Circular arcs constructed by O and B stars have been detected. A study of the population places stars with more recent ages in the groups of the arcs than of their centers. These effects can be explained by supernova explosions. A catalogue of the non-saturated detected OB stars in this region is given.
- ID:
- ivo://CDS.VizieR/J/AcA/43/209
- Title:
- OB stars extinction based in IR photometry
- Short Name:
- J/AcA/43/209
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The paper presents an extensive survey of interstellar extinction curves derived from the near IR photometric measurements of early type stars belonging to our Galaxy. This survey is more extensive and deeper than any other one, based on spectral data. The IR magnitudes of about 500 O and B type stars with E(B-V)>=0.05 were selected from literature. The IR color excesses are determined with the aid of "artificial standards". The results indicate that the extinction law changes from place to place. The mean galactic extinction curve in the near IR is very similar in different directions and changes very little from the value R=3.10+/-0.05 obtained in this paper.
- 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.
- 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/A+AS/146/365
- Title:
- O & B stars uvby-Hbeta photometry. III.
- Short Name:
- J/A+AS/146/365
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stroemgren and H{beta} photometry of O and B type stars, generally brighter than 9.5 mag is reported for the field of the Carina Spiral Feature. The observations are based on the PPM (Cat. <I/193>) catalogue identifications and are designed to improve the completeness of the existing uvby{beta} data for the bright early-type stars in the field. We present new uvby photometry for 283 stars and H{beta} photometry for 225 of them. These observations are part of an ongoing effort to study the structure of selected star-forming regions in the Milky Way by means of uvby{beta} photometry. A comparison of the new data to other uvby{beta} data sets for this field is presented.
- 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.
