Massive stars in the Sloan Digital Sky Survey V: New O2 stars in the Large Magellanic Cloud

Abstract

O2 stars define the hottest end of the normal O-star sequence, but their identification requires blue-optical nitrogen diagnostics, which are absent in many surveys. We reassess three luminous Large Magellanic Cloud (LMC) sources with multi-epoch Sloan Digital Sky Survey V spectroscopy obtained with the Baryon Oscillation Spectroscopic Survey (BOSS) spectrographs: łh, and We measured visit-resolved radial velocities and H, He, and N equivalent widths (EWs); compared robust combinations with LMC O2 templates at a common effective resolution; and used OSTAR2002 spectral energy distribution fits and a Gaia colour--magnitude diagram (CMD) as broadband checks. The weighted łog| ̊m EW (∋v łambda4058)/ ̊m EW (∋ii łambda4640)| values are 0.64 0.48 and 0.34 for łh, and The detection of łambdałambda4604,4620 supports the O2 If* and O2 V--III classifications adopted for and łh, respectively. For the uncertain ∋v/∋ii ratio and non-detection of motivate O2--3 V--III. Weak łambda4471 may indicate unresolved later-type contamination in and The radial velocities of show suggestive but non-significant variability. OSTAR2002 fits over 45--55 kK and the Gaia CMD place all three sources in the luminous very early O regime; shows a strong mid-infrared excess, łh is nearly photospheric, and shows only a modest 3--8,μm excess. The BOSS spectra place and łh in the LMC very early O population and identify as an additional O2--3 source. These cases show how incomplete blue coverage and ambiguous catalogue associations can conceal the hottest massive stars.