Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002a%26a...396..609q&link_type=abstract
Astronomy and Astrophysics, v.396, p.609-613 (2002)
Astronomy and Astrophysics
Astrophysics
12
Stars: Binaries: Close, Stars: Individual: Sw Cyg, Stars: Individual: Rr Dra, Stars: Evolution
Scientific paper
SW Cyg and DD Dra are two Algol-type eclipsing binary systems. Both contain an A2-type main-sequence primary and a K0-type secondary component with a rather deep primary light minimum in their light curves (2fm 6 and 3fm 8, respectively). In the present paper, orbital period changes of these stars are studied based on the analyses of their century-long times of light minimum. Several period jumps are found to superimpose on a rapid secular increase (dP/dt=+4.71x10-6 and +4.24x10-6 days/year, respectively). Since the period increases are rather rapid, the mass exchange between the components would be dynamical. SW Cyg is a low-mass ratio system (q=0.20) and it is expected that the mass ratio of RR Dra may also be very low because of the rather deep primary eclipse minimum. The rapid period increases suggest that a rapid mass transfer also occurs in a low-mass ratio Alogl-type close binary which is opposite to the theoretically evolutionary scheme of the binary star. The period jumps superimposed on the long-term increases are caused by the structura variation of the cool mass-loser via instabilities in the convective outer layer (COL) or via cyclic magnetic activity of the K0-type components. As the period jumps do not occur in a short-term alternating way, the structura change caused by instabilities in the COL via a dynamical mass loss from the cool subgiant may be more plausible.
Boonrucksar Soonthornthum
Qian Sheng Bang
Zhu Li Ying
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