Stars and brown dwarfs in the sigma Orionis cluster. II. A proper motion study - Astrophysics > Solar and Stellar AstrophysicsReport as inadecuate




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Abstract: Aims: I seek to fully know the stellar and substellar populations in theyoung sigma Orionis open cluster, which is a benchmark for star-formingstudies. Because of the very low proper motion of the cluster, late-type dwarfswith appreciable proper motion in the foreground of sigma Orionis can be easilydiscarded for expensive spectroscopic follow-up. Methods: I use the Aladin skyatlas, USNO-B1, public astrometric catalogues, and photographic platedigitisations to identify stars with proper motions inconsistent with clustermembership in a circular area of radius 30 arcmin centred on the early-typemultiple system sigma Ori. Mostly due to the long time baseline, of more thanhalf a century, the errors in the measured proper motions are lower than 2mas-a. Results: Of the 42 stars selected for astrometric follow-up, 37 of themare proper-motion cluster interlopers. Some USNO-B1 measurements were affectedby partially resolved visual multiplicity and target faintness. Because oftheir late spectral types and, hence, red colours, 24 contaminants had beenconsidered as sigma Orionis members at some moment. I discuss how contaminationmay have affected previous works especially related to disc frequencies andthe curious presence of lithium absorption in three M-dwarf proper-motioncontaminants. Finally, I classify the bright star HD 294297 as a late-F fielddwarf unrelated to the cluster based on a new proper motion measurement.Conclusions: Although proper motions cannot be used to confirm membership insigma Orionis, they can be used instead to discard a number of cluster membercandidates without spectroscopy.



Author: Jose A. Caballero

Source: https://arxiv.org/







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