A TiO study of the black hole binary GRO J0422+32 in a very low state |
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| Authors: | N A Webb T Naylor Z Ioannou P A Charles T Shahbaz |
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| Institution: | Department of Physics, Keele University, Keele, Staffordshire ST5 5BG;Department of Astrophysics, Nuclear Physics Laboratory, Keble Road, Oxford OX1 3RH |
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| Abstract: | We present 53 simultaneous photometric ( I band) and spectroscopic (69009500 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±16 km s1, which yields f ( M )=1.191±0.021 M and 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 0002 E .
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 M45 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 69508400 Å. From this we calculate the distance to the system to be 1.39±0.15 kpc. |
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| Keywords: | accretion accretion discs black hole physics binaries: close stars: fundamental parameters stars: individual: GRO J0422+32 stars: late-type |
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