Orbital period changes of the nova-like cataclysmic variable AC Cancri: evidence of magnetic braking and an unseen companion

Details Orbital period changes of the nova-like cataclysmic variable AC Cancri: evidence of magnetic braking and an unseen companion Orbital period changes of the nova-like cataclysmic variable AC Cancri: evidence of magnetic braking and an unseen companion

May 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007a%26a...466..589q&link_type=abstract

Astronomy and Astrophysics, Volume 466, Issue 2, May I 2007, pp.589-594

Astronomy and Astrophysics

Astrophysics

6

Stars: Novae, Cataclysmic Variables, Stars: Binaries: Eclipsing, Stars: Individual: Ac Cnc, Stars: Evolution, Stars: Mass-Loss, Stars: Binaries: Close

Scientific paper

Aims:The source AC Cnc is a nova-like cataclysmic variable containing a white-dwarf primary with a mass of 0.76 M&sun; and a K2-type secondary with a mass of 0.77 M&sun;. 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 M&sun;) 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 R&sun;), the mass-loss rate should be dot{M_2}=-1.65×{10-10} M&sun;/year. By using the enhanced mass loss proposed by Tout & Eggleton (1988), the mass-loss rate should be dot{M_2}=-1.18×{10-9} M&sun;/year. In this case, the Alfén radius is determined to be RA = 5.2 R&sun;. 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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