Orbital period analysis of eclipsing dwarf novae: U Geminorum

Details Orbital period analysis of eclipsing dwarf novae: U Geminorum Orbital period analysis of eclipsing dwarf novae: U Geminorum

May 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009ap%26ss.321...91d&link_type=abstract

Astrophysics and Space Science, Volume 321, Issue 2, pp.91-100

Astronomy and Astrophysics

Astrophysics

1

Stars: Cataclysmic Variables, Stars: Binaries: Eclipsing, Stars: Individual U Geminorum

Scientific paper

A new orbital period analysis for U Geminorum is made by means of the standard O-C technique based on 187 times of light minima including the three newest CCD data from our observation. Although there are large scatter near 70,000 cycles in its O-C diagram, there is strong evidence (>99.9% confidence level) to show the secular increase of orbital period with a rate dot{P}=7.8(1)× 10^{-12} s-1. Using the physical parameters recently derived by Echevarría et al. (Astron. J. 134:262, 2007), the range of mass transfer rate for U Geminorum is estimated as from -3.5(5)×10-9 M &sun; yr-1 to -1.30(6)×10-8 M &sun; yr-1. Moreover, the data before 60,000 cycles shows the obvious quasi-period variations. The least square estimation of a ˜17.4 yr quasi-periodic variation superimposed on secular orbital period increase is derived. Considering the possibility that solar-type magnetic activity cycles in the secondary star of U Geminorum may produce the quasi-period variations of the orbital period, Applegate’s mechanism is discussed and the results indicate such mechanism has difficulty explaining the quasi-period variation for U Geminorum. Hence, we attempted to apply the light-travel time effect to interpret the quasi-period variation and found the perturbation of ˜17.4 yr quasi-period may result from a brown dwarf. If the orbital inclination is assumed as i˜15°, corresponding to the upper limit of mass of a brown dwarf, then its orbital radii is ˜7.7 AU.

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