The Mass of the Probable Black Hole in the X-Ray Nova GRO J0422+32

view Abstract Citations (89) References (67) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Mass of the Probable Black Hole in the X-Ray Nova GRO J0422+32 Filippenko, Alexei V. ; Matheson, Thomas ; Ho, Luis C. Abstract A series of 21 moderate-resolution (∼2.4 Å) spectra of the now quiescent Galactic X-ray nova GRO J0422+32, obtained in 1994 November and 1995 January with the W. M. Keck 10 m telescope, is used to derive the physical parameters of the binary system. The Hα emission-line profile exhibits large variations in consecutive half-hour exposures taken in 1994 November, but smaller variations in 1995 January. Cross-correlation of the 6000-6500 Å spectral region with that of late-type dwarf stars yields reliable absorption-line radial velocities for the secondary star. The orbital period is found to be 0d.21159±0d.00057, with a semiamplitude of 380.6±6.5 km s-1; the implied mass function is 1.21±0.06 Msun. Inspection of the averaged spectrum of GRO J0422+32 in the rest frame of the secondary star suggests that the secondary is an M2 V star, but the accretion disk contributes 30%-60% of the light at ∼6300 Å. Fits to the wings of the strong, double-peaked Hα emission line yield approximate radial velocities for the compact primary; the velocity curve has a semi-amplitude of 41.6±3.2 km s-1, but with a phase offset by 253° (rather than 180°) from that of the secondary star. The offset, which is similar to that of several other X-ray novae and many dwarf novae, may be indicative of geometric distortions or additional emission components on the accretion disk; hence, the observed semi-amplitude does not necessarily reflect the true motion of the compact primary. Under the assumption that it does, however, we find q = 0.1093±0.0086, the mass ratio of the secondary to the primary. If the secondary star is a normal M2 dwarf (M = 0.39±0.02 M0), as suggested by its spectrum and (independently) by the requirement that it fill its Roche lobe, the mass of the primary is 3.57±0.34 Msun, somewhat higher than the theoretical upper limit (∼3.2 Msun) for a slowly rotating neutron star with an extremely stiff equation of state, and considerably above the measured masses of neutron stars. We conclude that the compact object is probably a black hole, as suggested by its hard X-ray spectrum during outburst. The derived inclination angle of the system (48±3° ) is consistent with the apparent absence of eclipses of the accretion disk. Publication: The Astrophysical Journal Pub Date: December 1995 DOI: 10.1086/176609 Bibcode: 1995ApJ...455..614F Keywords: STARS: BINARIES: CLOSE; BLACK HOLE PHYSICS; X-RAYS: STARS; STARS: INDIVIDUAL ALPHANUMERIC: GRO J0422+32; STARS: NOVAE; CATACLYSMIC VARIABLES full text sources ADS | data products SIMBAD (7)