Orbital Parameters for the Soft X-ray Transient 4U 1543-47: Evidence for a Black Hole

Spectroscopic observations of the soft X-ray transient 4U 1543-47 reveal a radial velocity curve with a period of P = 1.123 ± 0.008 days and a semi-amplitude of K2 = 124± 4 km s. The resulting mass function is f(M) = 0.22± 0.02M⊙. We classify the secondary star as A2V, in agreement with previous work, and measure Teff = 9000±500 K and E(B − V ) = 0.50 ± 0.05 from fits to synthetic spectra. We derive a distance of d = 9.1 ± 1.1 kpc if the secondary is on the main sequence. We see no emission lines from the accretion disk, and the measured fraction of disk light in the B and V bands is 10% and 21% respectively. The V and I light curves exhibit two waves per orbital cycle with amplitudes ≈ 0.08 mag. We modeled the light curves as ellipsoidal variations in the secondary star and derive extreme inclination limits of 20 ≤ i ≤ 40◦. The formal 3σ limits on the inclination from a simultaneous fit to the V and I light curves are 24 ≤ i ≤ 36◦ for a mass ratio Q ≡ M1/M2 ≥ 1. However, there are systematic effects in Visiting Astronomer at Cerro Tololo Inter-American Observatory (CTIO), which is operated by the Association of Universities for Research in Astronomy Inc., under contract with the National Science Foundation. Also Department of Physics, Yale University National Young Investigator