THE GALACTIC O-STAR SPECTROSCOPIC SURVEY. I. CLASSIFICATION SYSTEM AND BRIGHT NORTHERN STARS IN THE BLUE-VIOLET AT R ∼ 2500

Abstract

We present the first installment of a massive spectroscopic survey of Galactic O stars, based on new, high signal-to-noise ratio, R ∼ 2500 digital observations from both hemispheres selected from the Galactic O-Star Catalog of Maíz and Sota et al. (2008). The spectral classification system is rediscussed and a new atlas is presented, which supersedes previous versions. Extensive sequences of exceptional objects are given, including types Ofc, ON/OC, Onfp, Of?p, Oe, and double-lined spectroscopic binaries. The remaining normal spectra bring this first sample to 184 stars, which is close to complete to B = 8 and north of δ = −20 • and includes all of the northern objects in Maíz that are still classified as O stars. The systematic and random accuracies of these classifications are substantially higher than previously attainable, because of the quality, quantity, and homogeneity of the data and analysis procedures. These results will enhance subsequent investigations in Galactic astronomy and stellar astrophysics. In the future we will publish the rest of the survey, beginning with a second paper that will include most of the southern stars in Maíz Apellániz et al. (2004).

A Constraint on the Formation Timescale of the Young Open Cluster NGC 2264: Lithium Abundance of Pre-Main Sequence Stars

“…In addition, a low stellar density region (halo) surrounds these subclusters (Sung et al 2008). The largest subcluster S Mon contains not only the high-mass multiple system S Mon (O7V + early B + ?- Sota et al 2011) but also a large number of Class II objects. However, the number of Class I objects is much smaller than that of the other embedded or partially embedded subclusters, the Spokes and Cone nebula regions.…”

Surface abundances of OC supergiants

“…CMGFEN computed non-LTE, spherically extended atmosphere models that include line-blanketing. Synthetic spectra calculated from Sota et al (2011Sota et al ( , 2014. (2) Star analyzed by Martins et al (2015a).…”

The discovery of a shell-like event in the O-type star HD 120678

“…On the other hand, absorption lines of He ii (λ4200, λ4542, λ4686, and λ5411), C iii (λ4070, λ4650), O iii (λ5592), N iii (λλ4511, 4515, λ4535), and Si iv λ4089, can be also identified. It is important to note that the traditional spectral-classification criteria for OB stars (Walborn & Fitzpatrick 1990;Sota et al 2011), cannot be applied here, since the He i lines which are included in the temperature-sensitive ratios are filled-in by emission. However, the He ii lines suggest a spectral type of O9-B0 according to the strength of the He ii λ4542 line.…”