A TiO study of the black hole binary GRO J0422+32 in a very low state

N. A. Webb*, T. Naylor, Z. Ioannou, P. A. Charles, T. Shahbaz

*Corresponding author for this work

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37 Citations (SciVal)


We present 53 simultaneous photometric (I band) and spectroscopic (6900-9500 Å) observations of GRO J0422+32, taken during 1997 December. From these we determine that J0422+32 was in its lowest state yet observed, at I = 20.44 ± 0.08. Using relative spectrophotometry, we show that it is possible to correct very accurately for telluric absorption. Following this, we use the TiO bands at 7055 and 7589 Å for a radial velocity study and thereby obtain a semi-amplitude of 378 ± 16km s-1, which yields f(M) = 1.191 ± 0.021 M and q = 9.0+2.2-2.7, consistent with previous observations. We further demonstrate that this little-explored method is very powerful for such systems. We also determine a new orbital ephemeris of HJD = 245 0274.4156 ± 0.0009 + 0.212 1600 ± 0.000 0002E. We see some evidence for an ellipsoidal modulation, from which we determine the orbital inclination of J0422 + 32 to be less than 45°. We therefore calculate a minimum mass for the primary of 2.22 M, consistent with a black hole, but not necessarily the supermassive one proposed recently (1997) by Beekman et al. We obtain an M4-5 spectral type for the secondary star, and determine that the secondary contributes 38 ± 2 per cent of the flux that we observe from J0422+32 over the range 6950-8400 Å. From this we calculate the distance to the system to be 1.39 ± 0.15 kpc.

Original languageEnglish
Pages (from-to)528-534
Number of pages7
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Publication statusPublished - Sept 21 2000
Externally publishedYes


  • Accretion, accretion discs
  • Binaries: close
  • Black hole physics
  • Stars: fundamental parameters
  • Stars: individual: GRO J0422 + 32
  • Stars: late-type

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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