摘要：Context. AI Phe is a double-lined, detached eclipsing binary, in which a
K-type sub-giant star totally eclipses its main-sequence companion every 24.6 days. This
configuration makes AI Phe ideal for testing stellar evolutionary models. Difficulties in
obtaining a complete lightcurve mean the precision of existing radii measurements could be
improved.
Aims. Our aim is to improve the precision of the radius measurements for
the stars in AI Phe using high-precision photometry from the Wide Angle Search for Planets
(WASP), and use these improved radius measurements together with estimates of the masses,
temperatures and composition of the stars to place constraints on the mixing length,
helium abundance and age of the system.
Methods. A best-fit ebop model is used to obtain lightcurve
parameters, with their standard errors calculated using a prayer-bead algorithm. These
were combined with previously published spectroscopic orbit results, to obtain masses and
radii. A Bayesian method is used to estimate the age of the system for model grids with
different mixing lengths and helium abundances.
Results. The radii are found to be R1 = 1.835 ± 0.014
R⊙, R2 = 2.912 ± 0.014
R⊙ and the masses M1 = 1.1973 ± 0.0037
M⊙, M2 = 1.2473 ± 0.0039
M⊙. From the best-fit stellar models we
infer a mixing length of 1.78, a helium abundance of YAI = 0.26
+0.02-0.01 and an age of 4.39 ± 0.32 Gyr. Times of primary minimum
show the period of AI Phe is not constant. Currently, there are insufficient data to
determine the cause of this variation.
Conclusions. Improved precision in the masses and radii have improved
the age estimate, and allowed the mixing length and helium abundance to be constrained.
The eccentricity is now the largest source of uncertainty in calculating the masses.
Further work is needed to characterise the orbit of AI Phe. Obtaining more binaries with
parameters measured to a similar level of precision would allow us to test for
relationships between helium abundance and mixing length.
关键词：stars: solar-type;stars: evolution;stars: fundamental
parameters;binaries: eclipsing
