Orbital period changes of the nova-like cataclysmic variable AC Cancri: evidence of magnetic braking and an unseen companion
| Authors | |
|---|---|
| Year of publication | 2007 |
| Type | Article in Periodical |
| Magazine / Source | Astronomy and Astrophysics |
| MU Faculty or unit | |
| Citation | |
| Web | http://adsabs.harvard.edu/abs/2007A%26A...466..589Q |
| Field | Astronomy and astrophysics |
| Keywords | nova; cataclysmic variables; eclipsing binaries;AC Cnc; evolution; mass loss |
| Description | Aims.The source AC Cnc is a nova-like cataclysmic variable containing a white-dwarf primary with a mass of 0.76 Mo and a K2-type secondary with a mass of 0.77 Mo. We intend to study its period changes and search for evidence of magnetic braking and unseen third body. Methods: The period changes were investigated based on the analysis of the O-C curve, which is formed by one new eclipse time together with the others compiled from the literature. Results: A cyclic change with a period of 16.2 yr was found to be superimposed on a long-term period decrease at a rate of dot{P}=-1.24(0.44).{10-8} days/year. Conclusions: It is shown that the mechanism of magnetic activity-driven changes in the quadrupole momentum of the secondary star (Applegate's mechanism) does not explain it easily. This period oscillation was plausibly interpreted by a light-travel time effect caused by the presence of a cool M-type dwarf companion (M_3<0.097 Mo) in a long orbit (16.2 yr) around the binary. Since the masses of both components are nearly the same, the mass transfer from the lobe-filling secondary to the primary is not efficient to cause the continuous period decrease. It may be strong evidence of an enhanced magnetic stellar wind from the K2-type component. If the Alfén radius of the cool secondary is the same as that of the Sun (i.e., RA = 15 Ro), the mass-loss rate should be dot{M_2}=-1.65.{10-10} Mo/year. By using the enhanced mass loss proposed by Tout and Eggleton (1988), the mass-loss rate should be dot{M_2}=-1.18.{10-9} Mo/year. In this case, the Alfén radius is determined to be RA = 5.2 Ro. However, the long-term decrease of the period may be only a part of a long-period (<100 yr) oscillation caused by the presence of an additional body. To check the conclusions, new precise times of light minimum will be required. |
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