OB Spectra Research Articles

A Catalog of OB Stars from LAMOST Spectroscopic Survey

Abstract We present 22,901 OB spectra of 16,032 stars identified from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope data release 5 data set. A larger sample of OB candidates are first selected from the distributions in the spectral line indices’ space. Then, all 22,901 OB spectra are identified by manual inspection. Based on a subsample validation, we find that the completeness of the OB spectra reaches about 89 ± 22% for the stars with spectral types earlier than B7, while around 57 ± 16% B8–B9 stars are identified. The smaller completeness for late B stars will lead to the difficulty in discriminating them from A0–A1-type stars. The subclasses of the OB samples are determined using the software package MKCLASS. With a careful validation using 646 subsamples, we find that MKCLASS can give fairly reliable subtypes and luminosity classes for most of the OB stars. The uncertainty of the spectral subtype is around 1 subtype, and the uncertainty of the luminosity class is around 1 level. However, about 40% of the OB stars fail to be assigned to any class by MKCLASS, and a few spectra are significantly misclassified by MKCLASS. This is likely because the template spectra of MKCLASS are selected from nearby stars in the solar neighborhood, while the OB stars in this work are mostly located in the outer disk and may have lower metallicities. The rotation of the OB stars may also be responsible for the misclassifications. Moreover, we find that the spectral and luminosity classes of the OB stars located in the Galactic latitude larger than 20° are substantially different with those located in the latitude smaller than 20°, which may either be due to the observational selection effect or may hint a different origin of the high Galactic latitude OB stars.

The earliest O-type stars

High-quality, blue-violet digital spectroscopy has been assembled of most previously known (and one new) members of the O3 class that exhibit N iv emission and N v absorption lines, with the collaboration of most specialists in the field. A detailed comparative study has led to the introduction of new spectral types O2 and O3.5 to describe the range of classification criteria present. Primary reliance has been placed on the N iv/N iii selective emission-line ratio, because of various difficulties affecting the interpretation of weak He i absorption lines in some of these spectra, which are discussed. Some representative spectra defining the new types are shown. The majority of the O2 - O3 class members reside in the LMC. Their large ranges of luminosities and masses suggest a close evolutionary connection to the WN class, as do several spectroscopic and spatial relationships. The salient characteristics of O2-O3 spectra in the ultraviolet longward of 1200 Å have been established for some time by IUE and HST data. Recently, the rich 900-1200 Å range has been well covered for the first time by FUSE; in a collaboration with its hot-star team, a comprehensive atlas of OB spectra in the Magellanic Clouds has been prepared. Several O2 stars are included, one of which is newly discovered, and some examples of these data are also shown.

The OB Zoo: A Digital Atlas of Peculiar Spectra

ABSTRACTA digital atlas of 20 high‐luminosity, peculiar OB spectra in the 3800–4900 Å range is presented. The atlas is organized and discussed in terms of the following four categories: WN‐A or WNL stars, OB Iape or very late WN (WNVL) stars, iron stars, and B‐supergiant luminous blue variables (LBVs). Several objects in the earlier categories are also active or quiescent LBVs. Some (but not all) of these objects have been well studied, and extensive references are provided, as are comprehensive spectral‐line identifications. Several new morphological relationships among the objects have been recognized through this presentation. In particular, attention is drawn to the occurrence of spatial pairing between nearly identical, unusual spectra, which may have implications for a particular mode of massive‐star formation. This small sample includes one or both members of at least five such pairs. Physical explanations of these peculiar, likely transitional spectra and the relationships among them are essential for a complete understanding of massive stellar evolution.

CONTEMPORARY OPTICAL SPECTRAL CLASSIFICATION OF THE OB STARS: A DIGITAL ATLAS

ABSTRACT Some recent developments in the optical classification of OB spectra are reviewed in terms of a comprehensive atlas of new blue-violet digital data from the CTIO 1-meter photon-counting system. These developments include the O3 spectral type; luminosity criteria for the O stars; OBN/OBC anomalies; and refined, interpolated late-O/early-B types. Examples of these phenomena are included among extensive spectral- and luminosity-class sequences, comprising 75 standard objects arranged into 27 montages and covering the wavelength range 3950-4750 A for types O3-B3 (-B8 at Ia). It is intended that this atlas serve a reference function analogous to that of the printed MK atlases, for morphological investigations of OB spectra based on digital data, which will supersede photographic techniques in most future applications.

On the Observational Determination of OB Standards

Observational evaluation of intrinsic energy distributions in OB spectra is difficult as these stars are usually reddened and any dereddening procedure may change from place to place in the Galaxy. We compare two-color diagrams (UV vs. visual) from two stellar complexes of the same Sp/L class. The observed differences may be caused by additional far-UV reddening of distant objects as well as by intrinsic differences between stars belonging to different complexes. We argue in favor of the first possibility which would allow one to use the same standards in all of the Galaxy.

An Atlas of yellow-red OB spectra

An Atlas of yellow-red OB spectra

The OBn and OBc stars.

view Abstract Citations (238) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The OBN and OBC stars. Walborn, N. R. Abstract A review of present knowledge concerning nitrogen and carbon anomalies in absorption-line OB spectra is presented, from the observational point of view. The procedure whereby such anomalies are discovered and described is explained, and its capabilities as well as limitations are discussed. A list of all presently known OBN and OBC stars is given, which includes several newly discovered examples. In addition, the problem of more moderate CNO anomalies in OB spectra is examined; an important conclusion is that all of the 09.5-BO. 7 supergiants in the Orion Belt and in NGC 6231 (the nucleus of Scorpius OBi) are systematically nitrogen-deficient, relative to the majority of supergiants with the same spectral types. Since the members of these associations have often been used as standards, an extensive list of O9-B 1 supergiants with normal CNO spectra is also given. Finally, the significance and possible origins of these anomalies are discussed. Subject headings: clusters: associations - stars: abundances - stars: early-type - stars: spectral classification Publication: The Astrophysical Journal Pub Date: April 1976 DOI: 10.1086/154292 Bibcode: 1976ApJ...205..419W full text sources ADS | data products SIMBAD (92)

Nitrogen and Carbon Anomalies in OB Spectra

The following new OBN and OBC stars have been found: HD 75860, BC 2 Iab; HD 104565, OC 9.7 Ia; HD 123008, ON 9.7 Iab; and HD 150574, ON 9 III(n). Examples of morphologically more moderate CNO anomalies in OB spectra are also discussed; it is concluded that the O9-B0 7 supergiants of the Orion Belt and NGC 6231 (the nuclear cluster of Scorpius OB1) are systematically nitrogen-deficient. One possible explanation of these nitrogen-deficient supergiants in sub-associations is that they may have formed from nitrogen-deficient clouds; another could be that the more numerous morphologically normal supergiants show the effects of mixing in their spectra, while the nitrogen-deficient ones are relatively younger or have not yet been red supergiants. No red supergiants are found in Sco OB1, whereas NGC 3293 contains two B0 supergiants with normal CNO spectra together with a red supergiant. The paper will appear in the Astrophysical Journal, April 15, 1976.

On the Existence of OB Stars with Anomalous Nitrogen and Carbon Spectra

view Abstract Citations (62) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Existence of OB Stars with Anomalous Nitrogen and Carbon Spectra Walborn, Nolan R. Abstract It has been fomid that there are absorption-line OB spectra showing anomalies analogous to those among the WoIf-Rayet stars. A new spectralclassilication notation is proposed for these stars, and several ezamples are briefly described. Publication: The Astrophysical Journal Pub Date: March 1971 DOI: 10.1086/180693 Bibcode: 1971ApJ...164L..67W full text sources ADS | data products SIMBAD (8)