1,051 research outputs found
The Solar-Type Contact Binary BX Pegasi Revisited
We present the results of new CCD photometry for the contact binary BX Peg,
made during three successive months beginning on September 2008. As do
historical light curves, our observations display an O'Connell effect and the
November data by themselves indicate clear evidence for very short-time
brightness disturbance. For these variations, model spots are applied
separately to the two data set of Group I (Sep.--Oct.) and Group II (Nov.). The
former is described by a single cool spot on the secondary photosphere and the
latter by a two-spot model with a cool spot on the cool star and a hot one on
either star. These are generalized manifestations of the magnetic activity of
the binary system. Twenty light-curve timings calculated from Wilson-Devinney
code were used for a period study, together with all other minimum epochs. The
complex period changes of BX Peg can be sorted into a secular period decrease
caused dominantly by angular momentum loss due to magnetic stellar wind
braking, a light-travel-time (LTT) effect due to the orbit of a low-mass third
companion, and a previously unknown short-term oscillation. This last period
modulation could be produced either by a second LTT orbit with a period of
about 16 yr due to the existence of a fourth body or by the effect of magnetic
activity with a cycle length of about 12 yr.Comment: 23 pages, including 6 figures and 8 tables, accepted for publication
in PAS
The Light and Period Variations of the Eclipsing Binary BX Draconis
New CCD photometric observations of BX Dra were obtained for 26 nights from
2009 April to 2010 June. The long-term photometric behaviors of the system are
presented from detailed studies of the period and light variations, based on
the historical data and our new observations. All available light curves
display total eclipses at secondary minima and inverse O'Connell effects with
Max I fainter than Max II, which are satisfactorily modeled by adding the
slightly time-varying hot spot on the primary star. A total of 87 times of
minimum light spanning over about 74 yrs, including our 22 timing measurements,
were used for ephemeris computations. Detailed analysis of the O-C diagram
showed that the orbital period has changed in combinations with an upward
parabola and a sinusoidal variation. The continuous period increase with a rate
of +5.65 \times 10^-7 d yr^-1 is consistent with that calculated from the
Wilson-Devinney synthesis code. It can be interpreted as a mass transfer from
the secondary to the primary star at a rate of 2.74 \times 10^-7 M\odot yr^-1,
which is one of the largest rates for contact systems. The most likely
explanation of the sinusoidal variation with a period of 30.2 yrs and a
semi-amplitude of 0.0062 d is a light-traveltime effect due to the existence of
a circumbinary object. We suggest that BX Dra is probably a triple system,
consisting of a primary star with a spectral type of F0, its secondary
component of spectral type F1-2, and an unseen circumbinary object with a
minimum mass of M3 = 0.23 M\odot.Comment: 24 pages, including 5 figures and 9 tables, accepted for publication
in PAS
Physical Properties of the Transiting Planetary System TrES-3
We present four new transits of the planetary system TrES-3 observed between
2009 May and 2010 June. Among these, the third transit by itself indicates
possible evidence for brightness disturbance, which might be the result of the
planet blocking a cool starspot on the stellar surface. A total of 109 transit
times, including our measurements, were used to determine the improved
ephemeris with a transit epoch of 2454185.9109440.000072 HJED and an
orbital period of 1.306187000.00000015 d. We analyzed the transit light
curves using the JKTEBOP code and adopting the quadratic limb-darkening law. In
order to derive the physical properties of the TrES-3 system, the transit
parameters are combined with the empirical relations from eclipsing binary
stars and stellar evolutionary models. The stellar mass and radius obtained
from a calibration using , log and [Fe/H] are consistent
with those from the isochrone analysis. We found that the exoplanet TrES-3b has
a mass of 1.930.07 M, a radius of 1.300.04 R,
a surface gravity of log =3.450.02, a density of 0.820.06
, and an equilibrium temperature of 164123 K. The results
are in good agreement with theoretical models for gas giant planets.Comment: 15 pages, including 4 figures and 4 tables, accepted for publication
in PAS
The Light and Period Variations of the Eclipsing Binary AA Ursae Majoris
We present new multiband CCD photometry for AA UMa made on 8 nights between
January and March 2009; the light curves are the first ever compiled.
Historical light curves, as well as ours, display partial eclipses and inverse
O'Connell effects with Max I fainter than Max II. Among possible spot models, a
cool spot on either of the component stars and its variability with time permit
good light-curve representations for the system. A total of 194 eclipse timings
over 81 yrs, including our five timings, were used for ephemeris computations.
We found that the orbital period of the system has varied due to a periodic
oscillation overlaid on an upward parabolic variation. The continuous period
increase at a fractional rate of 1.310 is consistent with
that calculated from the W-D code and can be interpreted as a thermal mass
transfer from the less to the more massive secondary star at a rate of
6.610 M yr. The periodic component is in
satisfactory accord with a light-time effect due to an unseen companion with a
period of 28.2 yrs, a semi-amplitude of 0.007 d, and a minimum mass of =0.25 but this period variation could also arise from
magnetic activity.Comment: 23 pages, including 5 figures and 8 tables, accepted for publication
in PAS
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