Issue |
A&A
Volume 371, Number 1, May III 2001
|
|
---|---|---|
Page(s) | 174 - 185 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20010324 | |
Published online | 15 May 2001 |
On the determination of the light curve parameters of detached active binaries
I. The prototype RS Canum Venaticorum
1
Dipartimento di Fisica e Astronomia dell'Università degli Studi di Catania, Italy
2
Osservatorio Astrofisico di Catania, Via Santa Sofia, 78, Città Universitaria, 95125 Catania, Italy e-mail: mro@sunct.ct.astro.it, nla@sunct.ct.astro.it, ube@sunct.ct.astro.it
Corresponding author: A. F. Lanza, nla@sunct.ct.astro.it
Received:
5
January
2001
Accepted:
1
March
2001
Photospheric cool spots are responsible for wave-like distortions
observed in the wide-band light curves of close active binaries. They
affect the determination of the photometric parameters in eclipsing systems
making it necessary to accurately model the spot effects in order to
estimate the true luminosity ratio, the fractionary radii and the inclination
of the orbital plane in a consistent way. We address such a problem for the prototype
active binary RS Canum Venaticorum, for which the availability of a long-term and accurate
series of light curves allows us to minimize the starspot
effects on the estimation of the quoted parameters. We have analysed
the available light curve sequence by using a new parallel code
we specifically designed for such an
application by solving simultaneously for the system parameters and
spot configuration. The uniqueness and stability problems related to the
spot mapping are solved by means of a regularization approach, following the
method described by Lanza et al. ([CITE]).
We evaluate the best set of photometric parameters and their confidence
levels by using a statistical method based on the total
criterion applied to the solution of the entire light
curve sequence. The advantages offered by our approach
include simplicity and generality with
respect to other commonly used methods based on the covariance matrix. We discuss the quantitative effects of the starspots on the estimation of
the parameters and compare our method and results with those of
other authors.
As an application of the derived results, we study the position
of the components of RS CVn on the H-R diagram and compare them with computed evolutionary tracks. We find that the
position of the primary component is compatible only by assuming a trigonometric
parallax of ~8.2 mas, i.e., at the lower boundary of the confidence interval
given by Hipparcos. Conversely,
the effective temperature of the cooler component turns out to be
~5%
smaller than expected on the basis of its radius.
The comparison with evolutionary tracks also yields an estimate of
years for the age of the system.
Moreover, we address
the high precision with which the inclination of the orbital plane can be
estimated in eclipsing systems, despite the presence of an intense starspot activity. This
opens the interesting possibility of detecting precessional motions in young RS CVn binaries, the spin angular momenta of which are not yet aligned with that of the orbital motion.
Key words: binaries: close / binaries: eclipsing / stars: activity / starspots / stars: fundamental parameters / methods: statistical
© ESO, 2001
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