2dF-AAOmega spectroscopy of massive stars in the Magellanic Clouds

Abstract

We present spectral classifications from optical spectroscopy of 263 massive stars in the north-eastern region of the Large Magellanic Cloud. The observed two-degree field includes the massive 30 Doradus star-forming region, the environs of SN1987A, and a number of star-forming complexes to the south of 30 Dor. These are the first classifications for the majority (203) of the stars and include eleven double-lined spectroscopic binaries. The sample also includes the first examples of early OC-type spectra (AAΩ 30 Dor 248 and 280), distinguished by the weakness of their nitrogen spectra and by C IV λ4658 emission. We propose that these stars have relatively unprocessed CNO abundances compared to morphologically normal O-type stars, indicative of an earlier evolutionary phase. From analysis of observations obtained on two consecutive nights, we present radial-velocity estimates for 233 stars, finding one apparent single-lined binary and nine (>3σ) outliers compared to the systemic velocity; the latter objects could be runaway stars or large-amplitude binary systems and further spectroscopy is required to investigate their nature.

Massive stars in the Small Magellanic Cloud

“…When we extrapolate this to environments with lower metallicities such as the MCs, where stronger and faster chemical processing is expected, the OC phenomenon may appear in earlier evolutionary stages and spectral type such as giants and even dwarfs. This is supported by the identification of two LMC early-type stars as OC stars by Evans et al (2015), or by MPG 113, which is an SMC OC dwarf (Bouret et al 2003(Bouret et al , 2013.…”

Surface abundances of OC supergiants

“…OC stars may be seen among giants (Hillier et al 2003). A recent study by Evans et al (2015) assigns a spectral type OC to two early type O giants in the LMC, based on the weakness of nitrogen lines.…”

Evolved massive stars at low-metallicity

“…The following additional classifications were also retrieved from the literature with a search radius of 1 , including: 113 matches from Whitney et al (2008), for which ∼1000 young stellar objects (YSOs) and also some evolved stars were identified in the LMC based on their IR color and spectral energy distribution (SED); 143,447 matches from Boyer et al (2011), who investigated the IR properties of cool, evolved stars in the MCs using observations from Spitzer; 124 matches from Jones et al (2017), where nearly 800 point sources observed by the Spitzer Infrared Spectrograph (IRS; Houck et al 2004) were classified using a decision tree method based on their infrared spectral features, continuum and SED shape, bolometric luminosity, cluster membership, and variability information; 98 matches from Massey & Olsen (2003), who used optical spectra to identify hundreds of RSGs in the MCs based on photometric data from Massey 2002; 620 matches from Bonanos et al (2009), which is a catalog for 1,750 massive stars in the LMC from the literature with accurate spectral types, and a multiwavelength photometric catalog for a subset of 1,268 of these stars, with the goal of exploring their infrared properties; 63 matches from Neugent et al 2012, who investigated the evolution of YSGs and RSGs in the LMC by identifying them based on the optical spectroscopy and comparing them with the new Geneva evolutionary models of the CMD; 108 matches from Evans et al (2015), for which 263 massive stars in the northeastern region of the LMC were spectrally classified; 156 matches from González-Fernández et al (2015), for which the physical properties of about 500 RSGs in the LMC and SMC were studied by using NIR/MIR photometry and optical spectroscopy; 31,919 matches from Simbad (Wenger et al 2000). We retrieved RVs, optical spectral classifications, main object types, and auxiliary object types.…”