CCD photometry of GRO JO422+32 during activity and quiescence

Details CCD photometry of GRO JO422+32 during activity and quiescence CCD photometry of GRO JO422+32 during activity and quiescence

May 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...297..103c&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 297, no. 1, p. 103-114

Astronomy and Astrophysics

Astronomy

41

Accretion Disks, Binary Stars, Stellar Color, Stellar Radiation, X Ray Astronomy, Astronomical Photometry, Color-Magnitude Diagram, Light Curve, Starburst Galaxies, Stellar Activity

Scientific paper

We present CCD photometry of the optical counterpart of the X-ray transient GRO JO422+32 obtained with the 1.2-m telescope at Haute-Provence on 79 nights from September 1992 through March 1994. During this interval the source underwent several outbursts. Oe double event of large amplitude (7 mag in V), lasting 250 days, coincided with the major X-ray outbursts and its secondary maximum, and had an e-folding time three times longer than in X-rays, while two other outbursts were shorter-lived (1 month), lower amplitude (5.5 mag in V) events with subsequent smaller after-events. Our BVI data are consistent with a power-law energy distribution (flambda approximately lambda-alpha) over the 4000-9000 A range whose index alpha varies from 2.8 to 2.0 as the source spectrum changes from being disk-dominated to one where the companion becomes progressively visible, first in I, then in V. Adopting a visual absorption of AV = 1.25 mag, and assuming alpha = 2 during quiescence, we derive for the companion a probable spectral type of MOV at approximately 2 kpc with the disk contributing approximately 40% of the total light in V. Time analysis of the high state data for January, February and December 1993 shows a dominant period of 5.1 hours. The amplitude and shape of this light curve are highly variable with several occurences of nights with no detectable modulation. Analysis of low state data for February and March 1994 reveals an identical period but with an even more complex and changing light curve, and although the disk contribution is still not negligeable in this state, part of the variability and complexity of the light curve may be due to the companion star itself.

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