A Catalog of OB Stars from LAMOST Spectroscopic Survey

Abstract

We present 22 901 OB spectra of 16 032 stars identified from LAMOST DR5 dataset. A larger sample of OB candidates are firstly selected from the distributions in the spectral line indices space. Then all 22 901 OB spectra are identified by manual inspection. Based on a sub-sample validation, we find that the completeness of the OB spectra reaches about 89 ± 22% for the stars with spectral type earlier than B7, while around 57 ± 16% B8-B9 stars are identified. The smaller completeness for late B stars is lead to the difficulty to discriminate them from A0-A1 type stars. The sub-classes of the OB samples are determined using the software package MKCLASS. With a careful validation using 646 sub-samples, we find that MKCLASS can give fairly reliable sub-types and luminosity class for most of the OB stars. The uncertainty of the spectral sub-type is around 1 sub-type and the uncertainty of the luminosity class is around 1 level. However, about 40% of the OB stars are failed to be assigned to any class by MKCLASS and a few spectra are significantly misclassified by MKCLASS. This is likely because that 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 metallicity. The rotation of the OB stars may also be responsible for the mis-classifications. 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 latitude smaller than 20 • , which may either due to the observational selection effect or hint a different origin of the high Galactic latitude OB stars.

Mapping luminous hot stars in the Galaxy

“…which we derived by noticing that, for the spectroscopically confirmed O-and B-type stars selected by Liu et al (2019), the (J − K s ) and (G − K s ) colours are linearly correlated (see Fig. 1, left), and by assuming that the difference between the J and K s magnitudes for such stars is close to zero (see e.g.…”

Intrinsic Color Indices of Early-type Dwarf Stars

“…LAMOST (Large Sky Area Multi-Object Fiber Spectroscopy Telescope; ) is a reflective Schmidt telescope at the Xinglong Station of the National Astronomical Observatory of China. We used two catalogs from the LAMOST survey, one of the A-type stars from Xiang et al (2017) and the other of the OB stars from Liu et al (2019). They both contain the basic stellar parameters: effective temperature T eff and surface gravity log g. The A-type catalog is selected from the LAMOST DR5 value-added catalog (Xiang et al 2017) with T eff from 8000 K to 10000 K including 205,068 high-temperature A-type stars.…”

“…Altogether, 2898 objects are removed from the A-type catalog of Xiang et al (2017) for mis-classification. The OB star catalog is also based on the DR5 but resulted from a dedicated study of the spectral line indices, containing 8582 OB stars (Liu et al 2019), with T eff ranging within 10000-32000 K (Liu et al in prep). In addition to T eff and log g, the stellar metallicity [Fe/H] and its error are available as well for the A-type stars, while not for the OB stars.…”

“…The LAMOST sample includes supergiant stars in addition to dwarfs from which Liu et al (2019) determined the luminosity class and spectral type for more than 8000 OB stars. The Liu et al (2019) catalog contains no star in Class I or I-II, 208 stars in Class II, and 498 stars in Class II-III. We only take the 208 Class II stars as supergiants since Class III may be dwarf stars or mis-classified.…”

“…Although identifying OB stars is not very difficult, deriving the stellar parameters is hard due to the scarcity of spectral lines and the fact that LAMOST survey makes no absolute flux calibration. Liu et al (2019) identified about 16,000 OB stars from the data release 5 (DR5) of LAMOST survey 1 , ever the largest reliable catalog of the OB stars. Furthermore, Liu et al (in prep) determined the basic stellar parameters, i.e.…”