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Optical studies of transient low-mass X-ray binaries in quiescence. I - Centaurus X-4: Orbital period, light curve, spectrum and models for the system
The results of CCD photometry of the Centaurus X-4 soft X-ray transientsource are presented. Analysis of the observations shows that thebrightness of the system in the quiescent state is modulated with aperiod of 15.1 hours. The mean brightness of the system is variablebetween V of about 18.5 and V = 18.35. In April 1986 an active state wasfound where the object was bluer, brighter by about 0.5 mag in V, andvarying rapidly in an erratic fashion, the quiescent light curve havingdisappeared even in the I-band. The amplitude and general shape of thequiescent light curve seem to be independent of the mean brightness. Arather stable minimum appears at phi of about 0.4, but significantvariability is seen in the phi interval from about 0.4 to 0.8.Low-dispersion spectra taken in the quiescent state reveal that the coolcompanion is a dwarf of spectral type close to K7V. A classicalinterpretation of the system involving a Roche lobe-filling K star isdiscussed.
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Observation and Astrometry data
| Constellation: | Πρύμνη |
| Right ascension: | 08h09m36.90s |
| Declination: | -40°17'00.7" |
| Apparent magnitude: | 8.837 |
| Distance: | 649.351 parsecs |
| Proper motion RA: | 5.8 |
| Proper motion Dec: | -16.3 |
| B-T magnitude: | 11.01 |
| V-T magnitude: | 9.017 |
Catalogs and designations:
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