Absolute Properties of the Eclipsing Binary Star V459
Cassiopeiae
C. H. S. Lacy1, A. Claret2 and J. A. Sabby1
Department of Physics - University of Arkansas – Fayetteville – USA1
Instituto de Astrofísica de Andalucía-Granada-Spain2
Abstract
We present 5064 differential observations in the V filter measured by a robotic telescope, as well as 30 pairs of radial velocities from high-resolution spectroscopic observations
of the detached EA-type, 8.46 day period, double-lined eclipsing binary star V459 Cas. Absolute dimensions of the components are determined with good precision (better than
1.6% in the masses and radii) for the purpose of testing various aspects of theoretical modeling. We obtain 2.02±0.03 solar masses and 2.009 ± 0.013 solar radii for the
hotter, larger, more massive and more luminous photometric primary (star A), and 1.96 ± 0.03 solar masses and 1.965 ± 0.013 solar radii for the cooler, smaller,
less massive and less luminous photometric secondary (star B). The effective temperatures and interstellar reddening of the stars are accurately determined from uvby
photometry: 9140 ± 300 K for the primary, 9100 ± 300 K for the secondary, corresponding to spectral types of A1, and 0.186 mag for Eb-y. The orbits are eccentric, and spectral
line widths give observed rotational velocities that are much faster than synchronous for both components. The components of V459 Cas are main-sequence stars with an age
of about 525 Myr according to models.
Figure 1. Ephemeris curve data (points with error bars)
and fitted model (solid curves). Open circles with error
bars correspond to dates of primary eclipse; those with
filled circles correspond to dates of secondary eclipse.
Photoelectric and CCD observations on the right side of the
diagram are much more accurate than the older
photographic observations on the left side.
Figure 2. Spectrogram of V459 Cas in the 4500 Å
region. The Mg II 4481 Å lines are much stronger
than the others.
Figure 4. Theoretical evolutionary tracks (solid curves) for the
components of V459 Cas and the observed values of log g and log
Teff (shown with error bars). The dashed curves on either side of
the tracks correspond to varying the assumed masses by one
standard deviation. The best fit occurs at an age of about 525
million years for both components.
Figure 5. Theoretical evolutionary tracks (solid curves) for
radii of the components of V459 Cas. The pairs of horizontal
lines represent the range of radii actually measured (±1
sigma). The upper pair of horizontal lines corresponds to the
hotter, more massive star which evolves more quickly. The
best fit for both components occurs in an overlap region at a
log age of about 8.72 (525 Myr).
Conclusions
Figure 3. Radial velocity measurements (points) and
fitted model (solid curves) based on absorption lines
in the 4500 Å region. Open circles correspond to
radial velocities of the primary (hotter, more
massive) star; filled circles correspond to radial
velocities of the secondary star.
New photometric and spectroscopic observations of the eccentric
eclipsing binary V459 Cas combined with a reanalysis of data
from the literature have allowed us toderive definitive orbital
parameters and physical properties of the component stars. Our
determinations have formal errors smaller than 1.6% in the
masses and radii. V459 Cas thus joins the elite of stars with
well- measured absolute properties. At an age of about 525 Myr
according to models, the system is a middle-aged main sequence
pair of stars with a somewhat higher surface abundance of heavy
elements compared to the solar composition. The two currently
favored mechanisms that describe the tidal evolution of binary
star properties disagree in their prediction of whether the
rotations of the V459 Cas stars should be synchronous with their
orbits,but agree that the stars’ orbits should be eccentric.