Spectroscopic and Photometric Observations of a Z Cam-Type Dwarf Nova, AT Cancri, in Standstill
Abstract
We performed quasi-simultaneous spectroscopic and photometric observations of a Z Cam star, AT Cnc, in standstill in 1997 February. V-band time-resolved photometry marginally revealed small-amplitude ( ~ 0.01 mag) oscillations with period candidates of 0.132 d, 0.124 d, 0.142 d, and 0.249 d. Low-resolution spectra show Balmer lines in emission and absorption, and Na D absorption. From the radial-velocity variation of Hα , we deduced the system parameters: the orbital period = 0.2011 (+/- 0.0006) d, the semi-amplitude = 80 (+/- 4) km s^{{-1}} , the systemic velocity = 11 (+/- 3) km s^{{-1}} , the primary mass = 0.9 (+/- 0.5) MO . The phase of the velocity variation of Hα is very close to that of Na D. There are two possibilities: the Hα emission line radiated (a) from the secondary star, or (b) from the accretion disk. The inclination is estimated to be 17^° (+/- 5^° ) and 36^° (+/- 12^° ) based on the respective possibilities. Doppler map drawn under possibility (a) revealed on a broadly extended component in the (-V_x, -V_y) region. In the Doppler map drawn under the possibility (b), the peak exists on the irradiated side of the Doppler position of the secondary and the (+V_x, +V_y) region. We discovered an absorption component in the blue wing at Hα . The P Cyg profile appeared during a limited period in its orbital phase, which is interpreted to be caused by transient mass ejection episodes.
- Publication:
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Publications of the Astronomical Society of Japan
- Pub Date:
- February 1999
- DOI:
- 10.1093/pasj/51.1.115
- Bibcode:
- 1999PASJ...51..115N
- Keywords:
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- ACCRETION;
- ACCRETION DISKS;
- STARS: CATACLYSMIC;
- STARS: DWARF NOVAE;
- STARS: INDIVIDUAL (AT CANCRI)