ORBITAL PARAMETERS OF THE CANDIDATE BLACK HOLE BINARY GRO J0422 + 32

摘要

We present optical observations of the black hole candidate GRO J0422 + 32 in quiescence. CCD imaging over a period of two nights reveals ellipsoidal variations with an amplitude of ≈0.15 mag in / and a period of 0.2107d ± 0.0012d. This period is consistent with periods found during the decay from outburst. The optical spectra show strong double-peaked Balmer emission lines (characteristic of emission from an accretion disk) with a separation of ～910 km s~(-1), implying that the projected velocity of the outer edge of the accretion disk is 455 ± 15 km s~(-1), which in turn implies a velocity semiamplitude for the secondary star of approx < 400 km s~(-1). The spectra also show TiO absorption bands indicative of early M-type dwarfs. The signal-to-noise ratios in the individual spectra are too low to extract reliable velocities. However, analyzing the full data set, we find that the most probable range of values of the secondary star velocity semiamplitude is 300 ≤ K_2 ≤ 400 km s~(-1). The implied range of mass functions is then 0.5 ≤ f(M) ≤ 1.4 solar mass. The primary mass will then be greater than 3 solar mass if the orbital inclination is less than 59° and the secondary star mass is less than 0.5 solar mass.