Issue |
A&A
Volume 503, Number 3, September I 2009
|
|
---|---|---|
Page(s) | 883 - 888 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361/200810909 | |
Published online | 23 June 2009 |
Plausible explanations for the variations of orbital period in the old nova DQ Herculis*
1
National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, PR China e-mail: zhibin_dai@ynao.ac.cn
2
United Laboratory of Optical Astronomy, Chinese Academy of Science (ULOAC), 100012 Beijing, PR China
3
Graduate School of the CAS, Beijing, PR China
Received:
4
September
2008
Accepted:
28
April
2009
Aims. Several mechanisms are presented to explain the observed small variation in the orbital period of the old nova DQ Herculis.
Methods. We have combined two new CCD times of light minimum of DQ Herculis with all 226 available times of light minimum, including 79 visual observations, for the new orbital period analysis.
Results. Based on this analysis, the best-fit of the O–C diagram for
DQ Herculis is a quadratic-plus-sinusoidal fit. A secular
orbital period increase with a rate of is confirmed, which corresponds to a lower limit of the
mass transfer rate of
. We
investigate three plausible mechanisms (direct change of the red
dwarf's radius, Applegate's mechanism and the light travel-time
effect) to explain the quasi-periodic variation shown in the O–C
diagram. Although previous works have suggested that solar-type
magnetic cycles in the red dwarf can explain the quasi-periodic
variation in the orbital period, we were not able to reproduce this
finding. Accordingly, a light trave-time effect is proposed, with a
brown dwarf as a tertiary component with a significance level of
orbiting around nova DQ Herculis. In order
to interpret the small departure from the best-fit near
60 000 cycles, we assume an eccentric orbit of the third body with a small
eccentricity. However, a satisfying result was obtained because the
eccentricity
is close to zero. The parameters of this
elliptical orbit are similar to that of a circular orbit.
Key words: stars: novae, cataclysmic variables / stars: binaries: eclipsing / stars: individual: DQ Herculis
© ESO, 2009
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