Li, G-W; Howarth, ID; (2020) Two New Rapidly Rotating ON Stars Found with LAMOST. The Astrophysical Journal , 888 (2) , Article 81. 10.3847/1538-4357/ab5b01.

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Abstract

The ON stars are a rare subtype of O stars, of uncertain origin. We report two new, rapidlyrotating ON stars found in data acquired with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, LAMOST. LS I +61 28 is an ON8.5 Vn dwarf with a projected equatorial rotational velocity of ve sin i ≃ 298 km s−1 , while HDE 236672 is an ON9 IVn subgiant with ve sin i ≃ 253 km s−1 . The former is the first rapidly-rotating ON dwarf to be found, and the latter is only the third ON subgiant. The luminosity classes of non-supergiant ON stars appear to be influenced by the axial inclination angle i: the rapidly-rotating giants are close to equator-on, while ON dwarfs with lower ve sin i values are viewed more nearly pole-on. Combining parallaxes and proper motions from Gaia DR2 with radial-velocity measurements, we investigate the kinematics of non-supergiant ON stars, and infer that the dynamics, rapid rotation, and surface-nitrogen characteristics may all be consequences of binary interaction.

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