1999/08/02 by Gibor Basri, Eduardo L. Martín, Eduardo Martin · 1 citation
Physics and Astronomy · Social Sciences · #Astronomy and Astrophysical Research #Binary number #Binary system #Brown dwarf #Diagram #Eccentricity (behavior) #Educational Leadership and Practices #Luminosity #Pleiades #Proper motion #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/301079
published as Astron.J.118:2460-2465,1999 · Latex, 18 pages, 4 figures, submitted to Astron.J
arxiv created 1999/08/02 · openalex publication_date 1999/11/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
PPl 15 is the first object to have been confirmed as a brown dwarf by the lithium test (in 1995), though its inferred mass was very close to the substellar limit. It is a member of the Pleiades open cluster. Its position in a cluster color-magnitude diagram suggested that it might be binary, and preliminary indications that it is a double-lined spectroscopic binary were reported by us in 1997. Here we report on the results of a consecutive week of Keck HIRES observations of this system, which yield its orbit. It has a period of about 5.8 days, and an eccentricity of 0.4 ± 0.05. The rotation of the stars is slow for this class of objects. Because the system luminosity is divided between two objects with a mass ratio of 0.85, each of them is rendered an incontrovertible brown dwarf, with masses between 60 and 70 M J . We show that component B is a little redder than A by studying their wavelength-dependent line ratios and that this variation is compatible with the mass ratio. We confirm that the system has lithium but cannot support the original conclusion that it is depleted (which would be surprising, given the new masses). This is a system of very close objects, which, if they had combined, would have produced a low-mass star. We discuss the implications of this discovery for the theories of binary formation and formation of very low mass objects.