New Luminous ON Spectra from the Galactic O-Star Spectroscopic Survey

Abstract

Two new ON supergiant spectra (bringing the total known to seven) and one new ONn giant (total of this class now eight) are presented; they have been discovered by the Galactic O-Star Spectroscopic Survey. These rare objects represent extremes in the mixing of CNO-cycled material to the surfaces of evolved, late-O stars, by uncertain mechanisms in the first category but likely by rotation in the second. The two supergiants are at the hot edge of the class, which is a selection effect from the behavior of defining N III and C III absorption blends, related to the tendency toward emission (Of effect) in the former. An additional N/C criterion first proposed by Bisiacchi et al. is discussed as a means to alleviate that effect, and it is relevant to the two new objects. The entire ON supergiant class is discussed; they display a fascinating diversity of detail undoubtedly related to the complexities of their extended atmospheres and winds that are sensitive to small differences in physical parameters, as well as to binary effects in some cases. Serendipitously, we have found significant variability in the spectrum of a little-known hypergiant with normal N, C spectra selected as a comparison for the anomalous objects. In contrast to the supergiants, the ONn spectra are virtual (nitrogen)-carbon copies of one another except for the degrees of line broadening, which emphasizes their probable unique origin and hence amenability to definitive astrophysical interpretation.

arXiv comment14 pages, 2 figures, 1 table; Accepted by AJ

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Cited by in corpus (4)

• The Galactic O-Star Spectroscopic Survey (GOSSS). III. 142 additional O-type systems
• MONOS.II. Orbit review and analysis for 35 single-lined spectroscopic binary systems and candidates
• Ultraviolet extinction properties of the 30 Dor Nebula and interpreting observations of starburst clusters
• Two New Rapidly-Rotating ON Stars Found With LAMOST