Dynamical Evidence for a Black Hole in X-Ray Nova Ophiuchi 1977

Details Dynamical Evidence for a Black Hole in X-Ray Nova Ophiuchi 1977 Dynamical Evidence for a Black Hole in X-Ray Nova Ophiuchi 1977

Mar 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...459..226r&link_type=abstract

Astrophysical Journal v.459, p.226

Physics

55

Stars: Binaries: Spectroscopic, Black Hole Physics, Stars: Novae, Cataclysmic Variables, Stars: Individual Constellation Name: Nova Ophiuchi 1977, X-Rays: Stars

Scientific paper

We have conducted spectral and photometric observations of the quiescent optical counterpart of X-ray Nova Ophiuchi 1977 (H1705-250; V2107 Oph) at CTIO. Fifty hours of photometry during 1994 July reveal a typical double-wave modulation of + 0.2 mag with a period of 12.51 + 0.03 hr. The mean brightness was V 21.5. Forty spectra (2000 s exposures) were obtained in 1994 July and 13 similar spectra were obtained in 1993 May. We derived the absorption-line radial velocities using two conventional cross-correlation techniques. Both of them suggest a velocity semiamplitude (K) in excess of 400 km S 1, but only half or less of the spectra could be utilized because the signal-to-noise ratio is so low. Consequently, we devised a new and powerful "restframe search" technique that uses all of the available data. For each of several million binary ephemerides, we summed all of the spectra in a trial restframe of the secondary star, and each restframe spectrum was cross-correlated against a template spectrum with a well-known velocity. We then searched for the set of orbital parameters that produced the strongest cross-correlation value. The results confirmed the photometric period and the best restframe spectrum has a highly significant correlation (r 6) against a broad range of K star templates. The best value for the velocity amplitude is K = 420 + 30 km - 1 The corresponding mass function is f(M) = 4.0 + 0.8 M0. The probability is high that the compact object exceeds the maximum mass ( 3 M0) for a neutron star. Furthermore, this nova is very similar in many respects to the dynamical black hole binaries, A0620-00 and X-ray Nova Muscae 1991. We conclude that X-ray Nova Oph 1977 is the sixth confirmed example of an X-ray binary with a black hole primary. The estimated magnitude of the secondary star is V 22.0. This distance to the binary system is 6 kpc, if the companion is a K3 star near the main sequence. Double-peaked Hα emission suggests low levels of accretion 17 yr after outburst, similar to the behavior seen in A0620 -00. Unusual structure in the Hα line profile was observed during 1994 July, and its cause remains unexplained. The most straightforward interpretations of the light curves confine the binary inclination angle to the range of 600 80 . In that case, the mass of the black hole primary is 6 + 1 M0, if the companion is a K3 star on the main sequence.

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