394 research outputs found
Search for Variable Stars in the Globular Cluster M3
We describe here results of a photometric time-sequence survey of the
globular cluster M3 (NGC 5272), in a search for contact and detached eclipsing
binary stars. We have discovered only one likely eclipsing binary and one SX
Phe type star in spite of monitoring 4077 stars with and observing 25
blue stragglers. The newly identified SX Phe star, V237, shows a light curve
with a variable amplitude. Variable V238 shows variability either with a period
of 0.49 d or with a period of 0.25 d. On the cluster colour-magnitude diagram,
the variable occupies a position a few hundredths of magnitude to the blue of
the base of the red giant branch. V238 is a likely descendent of a binary blue
straggler. As a side result we obtained high quality data for 42 of the
previously known RR Lyrae variables, including 33 of Bailey type ab, 7 type c
and 2 double-mode pulsators. We used equations that relate the physical
properties of RRc stars to their pulsation periods and Fourier parameters to
derive masses, luminosities, temperatures and helium parameters for five of the
RRc stars. One of the RRd stars (V79) has switched modes. In previous studies,
it was classified as RRab, but our observations show that it is an RRd star
with the first overtone mode dominating. This indicates blueward evolution on
the horizontal branch.Comment: 21 pages including 14 figures, Latex, requires mn.sty, psfig.sty.
Submitted, MNRA
Evolution of Horizontal Branch Stars in Globular Clusters: The Interesting Case of V79 in M3
New observations of variable stars in the globular cluster M3 reveal that the
RR Lyrae variable V79 is a double-mode (RRd) variable with the first overtone
mode dominating. In all previous studies, V79 was found to be a fundamental
mode (RRab) pulsator with an irregular light curve. This is the first observed
mode switch for an RR Lyrae variable and it is direct observational evidence
for blueward evolution of horizontal branch stars in the Oosterhoff type I
cluster M3. It also demonstrates that there is a connection between the Blazhko
effect and pulsational mode mixing in RR Lyrae variables. These new
observations also show that the strength of the overtone oscillations in the
RRd star V68 in M3 may have increased in the last 70 years, thus indicating
blueward evolution for V68 as well. A survey of previously published
investigations of RRd stars in Oosterhoff type II systems indicates that there
is marginal evidence for an increase in the strength of fundamental mode
oscillations in two stars: V30 in M15 and AQ Leo. If these increases are
confirmed by future observations, it will indicate redward evolution for RRd
stars in type II systems.Comment: 10 pages including 3 figures, Latex, requires aaspp4.sty. Accepted by
ApJ
Equipotential Surfaces and Lagrangian points in Non-synchronous, Eccentric Binary and Planetary Systems
We investigate the existence and properties of equipotential surfaces and
Lagrangian points in non-synchronous, eccentric binary star and planetary
systems under the assumption of quasi-static equilibrium. We adopt a binary
potential that accounts for non-synchronous rotation and eccentric orbits, and
calculate the positions of the Lagrangian points as functions of the mass
ratio, the degree of asynchronism, the orbital eccentricity, and the position
of the stars or planets in their relative orbit. We find that the geometry of
the equipotential surfaces may facilitate non-conservative mass transfer in
non-synchronous, eccentric binary star and planetary systems, especially if the
component stars or planets are rotating super-synchronously at the periastron
of their relative orbit. We also calculate the volume-equivalent radius of the
Roche lobe as a function of the four parameters mentioned above. Contrary to
common practice, we find that replacing the radius of a circular orbit in the
fitting formula of Eggleton (1983) with the instantaneous distance between the
components of eccentric binary or planetary systems does not always lead to a
good approximation to the volume-equivalent radius of the Roche-lobe. We
therefore provide generalized analytic fitting formulae for the
volume-equivalent Roche lobe radius appropriate for non-synchronous, eccentric
binary star and planetary systems. These formulae are accurate to better than
1% throughout the relevant 2-dimensional parameter space that covers a dynamic
range of 16 and 6 orders of magnitude in the two dimensions.Comment: 12 pages, 10 figures, 2 Tables, Accepted by the Astrophysical Journa
A photometric and spectroscopic study of NSVS 14256825: the second sdOB+dM eclipsing binary
We present an analysis of UBVRIJH photometry and
phase-resolved optical spectroscopy of NSVS 14256825, an HW Vir type binary.
The members of this class consist of a hot subdwarf and a main-sequence
low-mass star in a close orbit ( d). Using the
primary-eclipse timings, we refine the ephemeris for the system, which has an
orbital period of 0.11037 d. From the spectroscopic data analysis, we derive
the effective temperature, K, the surface gravity, , and the helium abundance, , for the hot component. Simultaneously modelling the
photometric and spectroscopic data using the Wilson-Devinney code, we obtain
the geometrical and physical parameters of NSVS 14256825. Using the fitted
orbital inclination and mass ratio (i = 82\fdg5\pm0\fdg3 and , respectively), the components of the system have , , , and . From its spectral
characteristics, the hot star is classified as an sdOB star.Comment: 8 pages, 7 figures, accepted for publication in MNRA
Tomographic Separation of Composite Spectra. IX. The Massive Close Binary HD 115071
We present the first orbital elements for the massive close binary, HD
115071, a double-lined spectroscopic binary in a circular orbit with a period
of 2.73135 +/- 0.00003 days. The orbital semiamplitudes indicate a mass ratio
of M_2/M_1 = 0.58 +/- 0.02 and yet the stars have similar luminosities. We used
a Doppler tomography algorithm to reconstruct the individual component optical
spectra, and we applied well known criteria to arrive at classifications of
O9.5 V and B0.2 III for the primary and secondary, respectively. We present
models of the Hipparcos light curve of the ellipsoidal variations caused by the
tidal distortion of the secondary, and the best fit model for a Roche-filling
secondary occurs for an inclination of i = 48.7 +/- 2.1 degrees. The resulting
masses are 11.6 +/- 1.1 and 6.7 +/- 0.7 solar masses for the primary and
secondary, respectively, so that both stars are very overluminous for their
mass. The system is one of only a few known semi-detached, Algol-type binaries
that contain O-stars. We suggest that the binary has recently emerged from
extensive mass transfer (possibly through a delayed contact and common envelope
process).Comment: Submitted to Ap
Contact Discontinuities in Models of Contact Binaries Undergoing Thermal Relaxation Oscillations
In this paper we pursue the suggestion by Shu, Lubow & Anderson (1979) and
Wang (1995) that contact discontinuity (DSC) may exist in the secondary in the
expansion TRO (thermal relaxation oscillation) state. It is demonstrated that
there is a mass exchange instability in some range of mass ratio for the two
components. We show that the assumption of {\it constant} volume of the
secondary should be relaxed in DSC model. For {\it all} mass ratio the
secondary alway satisfies the condition that no mass flow returns to the
primary through the inner Lagrangian point. The secondary will expand in order
to equilibrate the interaction between the common convective envelope and the
secondary. The contact discontinuity in contact binary undergoing thermal
relaxation does not violate the second law of thermodynamics. The maintaining
condition of contact discontinuity is derived in the time-dependent model. It
is desired to improve the TRO model with the advanced contact discontinuity
layer in future detailed calculations.Comment: 5 pages in emulateapj, 1 figur
Mining of Topographic Feature from Heterogeneous Imagery and Its Application to Lunar Craters
Abstract. In this study, a crater detection system for a large-scale image database is proposed. The original images are grouped according to spatial frequency patterns and both optimized parameter sets and noise reduction techniques used to identify candidate craters. False candidates are excluded using a self-organizing map (SOM) approach. The results show that despite the fact that a accurate classification is achievable using the proposed technique, future improvements in detection process of the system are needed.
The Post-Common Envelope and Pre-Cataclysmic Binary PG 1224+309
We have made extensive spectroscopic and photometric observations of PG
1224+309, a close binary containing a DA white dwarf primary and an M4+
secondary. The H alpha line is in emission due to irradiation of the M-star by
the hot white dwarf and is seen to vary around the orbit. From the radial
velocities of the H alpha line we derive a period of P = 0.258689 +/- 0.000004
days and a semi-amplitude of K_Halpha = 160 +/- 8 km/s. We estimate a
correction Delta_K = 21 +/- 2 km/s, where K_M = K_Halpha + Delta_K. Radial
velocity variations of the white dwarf reveal a semi-amplitude of K_WD = 112
+/- 14 km/s. The blue spectrum of the white dwarf is well fit by a synthetic
spectrum having T_eff = 29,300 K and log(g) = 7.38. The white dwarf contributes
97% of the light at 4500 Angstroms and virtually all of the light blueward of
3800 Angstroms. No eclipses are observed. The mass inferred for the white dwarf
depends on the assumed mass of the thin residual hydrogen envelope: 0.40 < M_WD
< 0.45 solar masses for hydrogen envelope masses of 0 < M_H < 4.0E-4 solar
masses. We argue that the mass of the white dwarf is closer to 0.45 solar
masses, hence it appears that the white dwarf has a relatively large residual
hydrogen envelope. The mass of the M-star is then M_M = 0.28 +/- 0.05 solar
masses, and the inclination is i = 77 +/- 7 degrees. We discuss briefly how PG
1224+309 may be used to constrain theories of close binary star evolution, and
the past and future histories of PG 1224+309 itself. The star is both a
``post-common envelope'' star and a ``pre-cataclysmic binary'' star. Mass
transfer by Roche-lobe overflow should commence in about 10 Gyr.Comment: 17 pages, 8 figures, AAS LaTeX, to appear in AJ, March 199
A Search for Nitrogen-Enhanced Metal-Poor Stars
Theoretical models of very metal-poor intermediate-mass Asymptotic Giant
Branch (AGB) stars predict a large overabundance of primary nitrogen. The very
metal-poor, carbon-enhanced, s-process-rich stars, which are thought to be the
polluted companions of now-extinct AGB stars, provide direct tests of the
predictions of these models. Recent studies of the carbon and nitrogen
abundances in metal-poor stars have focused on the most carbon-rich stars,
leading to a potential selection bias against stars that have been polluted by
AGB stars that produced large amounts of nitrogen, and hence have small [C/N]
ratios. We call these stars Nitrogen-Enhanced Metal-Poor (NEMP) stars, and
define them as having [N/Fe] > +0.5 and [C/N] < -0.5. In this paper, we report
on the [C/N] abundances of a sample of 21 carbon-enhanced stars, all but three
of which have [C/Fe] < +2.0. If NEMP stars were made as easily as
Carbon-Enhanced Metal-Poor (CEMP) stars, then we expected to find between two
and seven NEMP stars. Instead, we found no NEMP stars in our sample. Therefore,
this observational bias is not an important contributor to the apparent dearth
of N-rich stars. Our [C/N] values are in the same range as values reported
previously in the literature (-0.5 to +2.0), and all stars are in disagreement
with the predicted [C/N] ratios for both low-mass and high-mass AGB stars. We
suggest that the decrease in [C/N] from the low-mass AGB models is due to
enhanced extra-mixing, while the lack of NEMP stars may be caused by
unfavorable mass ratios in binaries or the difficulty of mass transfer in
binary systems with large mass ratios.Comment: 14 pages, 7 figures, to be published in Ap
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