88 research outputs found
On the properties of contact binary stars
A catalogue of light curve solutions of contact binary stars has been
compiled. It contains the results of 159 light curve solutions. Properties of
contact binary stars were studied by using the catalogue data.
As it is well known since Lucy's (1968a,b) and Mochnacki's (1981) works,
primary components transfer their own energy to the secondary star via the
common envelope around the two stars. This transfer was parameterized by a
transfer parameter (ratio of the observed and intrinsic luminosities of the
primary star). We proved that this transfer parameter is a simple function of
the mass and luminosity ratio. This newly found relation is valid for all
systems except H type systems which have a different relation.
We introduced a new type of contact binary stars: H subtype systems which
have a large mass ratio (). These systems show highly different
behaviour on the luminosity ratio - transfer parameter diagram from other
systems and according to our results the energy transfer rate is less efficient
in them than in other type of contact binary stars. We also show that different
types of contact binaries have well defined locations on the mass ratio -
luminosity ratio diagram. All contact binary systems do not follow Lucy's
relation (). No strict mass ratio - luminosity
ratio relation of contact binary stars exists.Comment: 5 pages, 4 figures, accepted for publication in A&
A CCD photometric study of the late type contact binary EK Comae Berenices
We present CCD photometric observations of the W UMa type contact binary EK
Comae Berenices using the 2 metre telescope of Girawali Observatory,
India. The star was classified as a W UMa type binary of subtype-W by
\citet{sam1996}. The new V band photometric observations of the star reveal
that shape of the light curve has changed significantly from the one observed
by \citet{sam1996}. A detailed analysis of the light curve obtained from the
high-precision CCD photometric observations of the star indicates that EK Comae
Berenices is not a W-type but an A-type totally eclipsing W UMa contact binary.
The photometric mass ratio is determined to be 0.349 0.005. A temperature
difference of K between the components and an orbital
inclination of were obtained for the binary
system. Absolute values of masses, radii and luminosities are estimated by
means of the standard mass-luminosity relation for zero age main-sequence
stars. The star shows O'Connell effect, asymmetries in the light curve shape
around the primary and secondary maximum. The observed O'Connell effect is
explained by the presence of a hot spot on the primary component.Comment: 26 pages, 9 figures, 5 tables. Accepted for publication in New
Astronom
IV.3 The wealth of stellar variability
This book is dedicated to all the people interested in the CoRoT mission and the beautiful data that were delivered during its six year duration. Either amateurs, professional, young or senior researchers, they will find treasures not only at the time of this publication but also in the future twenty or thirty years. It presents the data in their final version, explains how they have been obtained, how to handle them, describes the tools necessary to understand them, and where to find them. It also highlights the most striking first results obtained up to now. CoRoT has opened several unexpected directions of research and certainly new ones still to be discovered
GSC 2314-0530: the shortest-period eclipsing system with dMe components
CCD photometric observations in VRI colors and spectroscopic observations of
the newly discovered eclipsing binary GSC 2314-0530 (NSVS 6550671) with dMe
components and very short period of P=0.192636 days are presented. The
simultaneous light-curve solution and radial velocity solution allows to
determine the global parameters of GSC 2314-0530: T_{1}=3735 K; T_{2}=3106 K;
M_{1}=0.51 M_sun; M_{2}=0.26 M_sun; R_{1}=0.55 R_sun; R_{2}=0.29 R_sun;
L_{1}=0.053 L_sun; L_{2}=0.007 L_sun; i=72.5 degr; a=1.28 R_sun; d=59 pc. The
chromospheric activity of its components is revealed by strong emission in the
H_alpha line (with mean EW=5 A) and observed several flares. Empirical
relations mass-M_{bol}, mass-radius and mass-temperature are derived on the
basis of the parameters of known binaries with low-mass dM components.Comment: 10 pages, 11 figures, MNRAS (accepted
Eclipsing Binaries in the OGLE Variable Star Catalogs.V. Long-Period Beta Lyrae-type Systems in the Small Magellanic Cloud and the PLC-beta Relation
Thirty eight long-period (P>10 days), apparently contact binary stars
discovered by the OGLE-II project in the SMC appear to be Beta Lyrae-type
systems with ellipsoidal variations of the cool components dominating over
eclipse effects in the systemic light variations and in the total luminosity. A
new period-luminosity- color (PLC) relation has been established for these
systems; we call it the PLC-beta relation, to distinguish it from the Cepheid
relation. Two versions of the PLC-beta relation - based on the (B-V)0 or (V-I)0
color indices - have been calibrated for 33 systems with (V-I)0>0.25 spanning
the orbital period range of 11 to 181 days. The relations can provide
maximum-light, absolute-magnitude estimates accurate to epsilon-M_V~0.35 mag.
within the approximate range -3<M_V<+1. In terms of their number in the SMC,
the long-period Beta Lyrae-type binaries are about 50 times less common than
the Cepheids. Nevertheless, their large luminosities coupled with continuous
light variations make these binaries very easy to spot in nearby galaxies, so
that the PLC-beta relation can offer an auxiliary and entirely independent
method of distance determination to nearby stellar systems rich in massive
stars. The sample of the long-period Beta Lyrae systems in the SMC analyzed in
this paper is currently the best defined and uniform known sequence of such
binaries.Comment: submitted for publication in Astronomical Journal; 8 PS figures, 2
table
CoRoT 105906206: a short-period and totally eclipsing binary with a Delta Scuti type pulsator
Eclipsing binary systems with pulsating components allow the determination of
several physical parameters of the stars, such as mass and radius, that, when
combined with the pulsation properties, can be used to constrain the modeling
of stellar interiors and evolution. Hereby, we present the results of the study
of CoRoT 105906206, an eclipsing binary system with a pulsating component
located in the CoRoT LRc02 field. The analysis of the CoRoT light curve was
complemented by high-resolution spectra from the Sandiford at McDonald
Observatory and FEROS at ESO spectrographs, which revealed a double-lined
spectroscopic binary. We used an iterative procedure to separate the
pulsation-induced photometric variations from the eclipse signals. First, a
Fourier analysis was used to identify the significant frequencies and
amplitudes due to pulsations. Second, after removing the contribution of the
pulsations from the light curve we applied the PIKAIA genetic-algorithm
approach to derive the best parameters that describe the orbital properties of
the system. The light curve cleaned for pulsations contains the partial eclipse
of the primary and the total eclipse of the secondary. The system has an
orbital period of about 3.694 days and is formed by a primary star with mass M1
= 2.25 +/- 0.04 solar masses, radius R1 = 4.24 +/- 0.02 solar radii, and
effective temperature Teff1 = 6750 +/- 150 K, and a secondary with M2 = 1.29
+/- 0.03 solar masses, R2 = 1.34 +/- 0.01 solar radii, and Teff2 = 6152 +/- 162
K. The best solution for the parameters was obtained by taking into account the
asymmetric modulation observed in the light curve, known as the O'Connell
effect, presumably caused by Doppler beaming. The analysis of the Fourier
spectrum revealed that the primary component has p-mode pulsations in the range
5-13 c/d, which are typical of Delta Scuti type stars.Comment: 11 pages, 8 figures, 3 table
Radial Velocity Studies of Close Binary Stars.VIII
Radial-velocity measurements and sine-curve fits to the orbital velocity
variations are presented for the seventh set of ten close binary systems: V410
Aur, V523 Cas, QW Gem, V921 Her, V2357 Oph, V1130 Tau, HN UMa, HX UMa, HD
93917, NSV 223. All systems, but three (V523 Cas, HD 93917, NSV 223), were
discovered photometrically by the Hipparcos mission. All systems are
double-lined (SB2) binaries and all, but the detached, very close system V1130
Tau, are contact binaries. The broadening-function permitted improvement of the
orbital elements for V523 Cas, which was the only system observed before for
radial velocity variations. Spectroscopic/visual companions were detected for
V410 Aur and HX UMa.Comment: AASTeX5, 4 figures, 3 tables, to appear AJ, June 200
Periodic variable stars in CoRoT field LRa02 observed with BEST II
The Berlin Exoplanet Search Telescope II (BEST II) is a small wide
field-of-view photometric survey telescope system located at the Observatorio
Cerro Armazones, Chile. The high duty cycle combined with excellent observing
conditions and millimagnitude photometric precision makes this instrument
suitable for ground based support observations for the CoRoT space mission.
Photometric data of the CoRoT LRa02 target field collected between November
2008 and March 2009 were analysed for stellar variability. The presented
results will help in the future analysis of the CoRoT data, particularly in
additional science programs related to variable stars. BEST II observes
selected CoRoT target fields ahead of the space mission. The photometric data
acquired are searched for stellar variability, periodic variable stars are
identified with time series analysis of the obtained stellar light curves. We
obtained the light curves of 104335 stars in the CoRoT LRa02 field over 41
nights. Variability was detected in light curves of 3726 stars of which 350
showed a regular period. These stars are, with the exception of 5 previously
known variable stars, new discoveries.Comment: The figures with light curves can be find in the A&A journal as
online onl
The asteroseismic ground-based observational counterpart of CoRoT
We present different aspects of the ground-based observational counterpart of
the CoRoT satellite mission. We give an overview of the selected asteroseismic
targets, the numerous instruments and observatories involved, and the first
scientific results.Comment: 3 pages, 2 tables, 1 figure, to be published in the conference
proceedings 'Stellar Pulsation: Challenges for Theory and Observation' (31
May - 5 June, Santa Fe, New Mexico, US), publishers: American Institute of
Physic
Genetic-Algorithm-based Light Curve Optimization Applied to Observations of the W UMa star BH Cas
I have developed a procedure utilizing a Genetic-Algorithm-based optimization
scheme to fit the observed light curves of an eclipsing binary star with a
model produced by the Wilson-Devinney code. The principal advantages of this
approach are the global search capability and the objectivity of the final
result. Although this method can be more efficient than some other comparably
global search techniques, the computational requirements of the code are still
considerable. I have applied this fitting procedure to my observations of the W
UMa type eclipsing binary BH Cassiopeiae. An analysis of V-band CCD data
obtained in 1994/95 from Steward Observatory and U- and B-band photoelectric
data obtained in 1996 from McDonald Observatory provided three complete light
curves to constrain the fit. In addition, radial velocity curves obtained in
1997 from McDonald Observatory provided a direct measurement of the system mass
ratio to restrict the search. The results of the GA-based fit are in excellent
agreement with the final orbital solution obtained with the standard
differential corrections procedure in the Wilson-Devinney code.Comment: 9 pages, 2 figures, 2 tables, uses emulateapj.st
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