New Astronomy 15 (2010) 380–384
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New Astronomy
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Orbital period analysis of eclipsing post-novae T Aurigae: Evidence of magnetic braking and an unseen companion
Zhibin Dai a,b,c,*, Shengbang Qian a,b a National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, P.O. Box 110, 650011 Kunming, PR China b Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, PR China c Graduate School of the CAS, Beijing, PR China article info abstract
Article history: Four new CCD times of light minimum of T Aurigae are presented. The orbital period variation is analyzed Received 20 March 2009 by means of the standard O–C technique. The new times of light minimum indicate that a 24 yr sine- Received in revised form 8 October 2009 like period variation superimposed on a secular orbital period decrease is obviously seen in the O–C dia- Accepted 7 November 2009 gram. However, the orbital period should increase because of mass transfer between components. In Available online 14 November 2009 order to solve this apparent paradox, three possibilities including magnetic braking mechanism, which Communicated by E.P.J. van den Heuvel plays an important role in angular moment loss of binary, are proposed. The mass loss rate M_ ¼ 10 10:4M yr 1 is derived by assuming that the Alfvén radius of secondary is the same as that of Keywords: the sun (i.e. R 15R ). Using the observational relationship of M_ P h (McDermott and Taam, Stars: cataclysmic variables A ’ mb orbð Þ Stars: binaries: eclipsing 1989; Rappaport et al., 1983), the Alfvén radius of secondary is estimated as RA ’ 1:9R , which only Stars: individual (T Aurigae) requires a weak magnetic field in secondary. Since the brightness variations of T Aurigae caused by App- Stars: magnetic braking legate’s mechanism need large energy beyond the total radiant energy in the time interval of 24 yr, the third body light travel-time effect is the most likely explanation for the 24-yr variation. The third body may be a brown-dwarf star in case of the high orbital inclination. Ó 2009 Elsevier B.V. All rights reserved.