On the Nature of the Dwarf Carbon Star G77-61
Liebert, James; Dahn, Conard C.; Mould, Jeremy; Dearborn, D. S. P.; Aaronson, Marc; Harrington, Robert; Greenstein, Jesse L.
United States
Abstract
A variety of new astrometric, photometric, and spectrophotometric data are presented for the low-luminosity carbon star G77-61. The improved parallax yields Mv = +10.08±0.43, while the revised temperature estimate from infrared, optical, and ultraviolet fluxes in 4100 (+200, -300)K, yielding logL/L_sun; = -1.75±0.16. Most importantly, radial velocity variations have been detected, with the binary period 245 days. The unseen companion probably is a cool white dwarf of much higher mass than the visible object. Both the spectrum and the H-R diagram position below the main sequence require G77-61 to be either extremely metal poor, or helium enriched and at least moderately metal poor.