70 research outputs found
The High Eccentricity of the Planet Around 16 Cyg B
We consider the high eccentricity, 0.66, of the newly discovered planet
around 16 Cyg B, using the fact that the parent star is part of a wide binary.
We show that the high eccentricity of the planet could be the result of tidal
forces exerted on 16 Cyg B and its planet by 16 Cyg A, the distant companion in
the system. By following stellar triple systems with parameters similar to
those of 16 Cyg, we have established that the orbital eccentricity of the
planet could have gone through strong modulation, with an amplitude of 0.8 or
even larger, with typical timescale of tens of millions years. The amplitude of
the planet eccentricity strongly depends on the relative inclination between
the plane of motion of the planet and that of the wide binary 16 Cyg AB. To
account for the present eccentricity of the planet we have to assume that the
angle between the two planes of motion is large, at least 60 deg. We argue that
this assumption is reasonable for wide binaries like 16 Cyg AB.Comment: 2 Figures, Latex, submitted for publication to ApJ
Did the ancient egyptians record the period of the eclipsing binary Algol - the Raging one?
The eclipses in binary stars give precise information of orbital period
changes. Goodricke discovered the 2.867 days period in the eclipses of Algol in
the year 1783. The irregular orbital period changes of this longest known
eclipsing binary continue to puzzle astronomers. The mass transfer between the
two members of this binary should cause a long-term increase of the orbital
period, but observations over two centuries have not confirmed this effect.
Here, we present evidence indicating that the period of Algol was 2.850 days
three millenia ago. For religious reasons, the ancient Egyptians have recorded
this period into the Cairo Calendar, which describes the repetitive changes of
the Raging one. Cairo Calendar may be the oldest preserved historical document
of the discovery of a variable star.Comment: 26 pages, 5 figures, 11 table
Evolution in Binary and Triple Stars, with an application to SS Lac
We present equations governing the way in which both the orbit and the
intrinsic spins of stars in a close binary should evolve subject to a number of
perturbing forces, including the effect of a third body in a possibly inclined
wider orbit. We illustrate the solutions in some binary-star and triple-star
situations: tidal friction in a wide but eccentric orbit of a radio pulsar
about a B star, the Darwin and eccentricity instabilities in a more massive but
shorter-period massive X-ray binary, and the interaction of tidal friction with
Kozai cycles in a triple such as Algol (beta-Per), at an early stage in that
star's life when all 3 components were ZAMS stars. We also attempt to model in
some detail the interesting triple system SS Lac, which stopped eclipsing in
about 1950. We find that our model of SS Lac is quite constrained by the
relatively good observational data of this system, and leads to a specific
inclination (29 deg) of the outer orbit relative to the inner orbit at epoch
zero (1912). Although the intrinsic spins of the stars have little effect on
the orbit, the converse is not true: the spin axes can vary their orientation
relative to the close binary by up to 120 deg on a timescale of about a
century.Comment: 30 pages, 6 figure
VW LMi: tightest quadruple system known. Light-time effect and possible secular changes of orbits
Tightest known quadruple systems VW LMi consists of contact eclipsing binary
with P_12 = 0.477551 days and detached binary with P_34 = 7.93063 days
revolving in rather tight, 355.0-days orbit. This paper presents new
photometric and spectroscopic observations yielding 69 times of minima and 36
disentangled radial velocities for the component stars. All available radial
velocities and minima times are combined to better characterize the orbits and
to derive absolute parameters of components. The total mass of the quadruple
system was estimated at 4.56 M_sun. The detached, non-eclipsing binary with
orbital period P = 7.93 days is found to show apsidal motion with U
approximately 80 years. Precession period in this binary, caused by the
gravitational perturbation of the contact binary, is estimated to be about 120
years. The wide mutual orbit and orbit of the non-eclipsing pair are found to
be close to coplanarity, preventing any changes of the inclination angle of the
non-eclipsing orbit and excluding occurrence of the second system of eclipses
in future. Possibilities of astrometric solution and direct resolving of the
wide, mutual orbit are discussed. Nearby star, HD95606, was found to form loose
binary with quadruple system VW LMi.Comment: 4 figures. accepted to MNRAS on July 31, 200
From the Heart of The Ghoul: C and N Abundances in the Corona of Algol B
Chandra Low Energy Transmission Grating Spectrograph observations of Algol
have been used to determine the abundances of C and N in the secondary star for
the first time. The analysis was performed relative to similar observations of
an adopted "standard" star HR 1099. It is demonstrated that HR 1099 and Algol
are coronal twins in many respects and that their X-ray spectra are very
similar in nearly all details, except for the observed strengths of C and N
lines. The H-like transitions of C and N in the coronae of Algol and HR 1099
demonstrate that the surface abundances of Algol B have been strongly modified
by CN-processing, as shown earlier by Schmitt & Ness (2002). It is found that N
is enhanced in Algol B by a factor of 3 compared to HR 1099. No C lines are
detected in the Algol spectrum, indicating a C depletion relative to HR 1099 by
a factor of 10 or more. These C and N abundances indicate that Algol B must
have lost at least half of its initial mass, and are consistent with
predictions of evolutionary models that include non-conservative mass transfer
and angular momentum loss through magnetic activity. Little or no dredge-up of
material subjected to CN-processing has occurred on the subgiant component of
HR 1099. It is concluded that Fe is very likely depleted in the coronae of both
Algol and HR 1099 relative to their photospheres by 0.5 dex, and C, N and O by
0.3 dex. Instead, Ne is enhanced by up to 0.5 dex.Comment: 17 pages, 4 figures, ApJ accepte
The Solar Neighborhood X: New Nearby Stars in the Southern Sky and Accurate Photometric Distance Estimates for Red Dwarfs
Photometric VRI and spectroscopic (6000-9500 A) observations of high proper
motion stars discovered during the first phase of the SuperCOSMOS RECONS (SCR)
search are used to estimate accurate distances to eight new nearby red dwarfs,
including probable 10 pc sample members SCR 1845-6357 (M8.5V at 4.6 pc), the
binary SCR 0630-7643AB (M6.0VJ at 7.0 pc), and SCR 1138-7721 (M5.0V at 9.4 pc).
Distance estimates are determined using a suite of new photometric color-Mk
relations defined using a robust set of nearby stars with accurate VRIJHK
photometry and trigonometric parallaxes.
These relations are utilized, with optical and infrared photometry, to
estimate distances on a uniform system (generally good to 15%) for two
additional samples of red nearby star candidates: several recently discovered
members of the solar neighborhood, and known faint stars with proper motions in
excess of 1.0"/yr south of DEC = -57.5. Of those without accurate trigonometric
parallax measurements, there are five stars in the first sample and three in
the second that are likely to be within 10 pc. The two nearest are SO 0253+1652
(M7.0V at 3.7 pc) and DEN 1048-3956 (M8.5V at 4.5 pc). When combined with SCR
1845-6357, these three stars together represent the largest increase in the 5
pc sample in several decades.
Red spectra are presented for the red dwarfs and types are given on the
RECONS standard spectral system. Red spectra are also given for two new nearby
white dwarfs for which we estimate distances from the photometry of less than
20 pc -- WD 0141-675 (LHS 145, 9.3 pc) and SCR 2012-5956 (17.4 pc). WD 0141-675
brings the total number of systems nearer than 10 pc discussed in this paper to
12.Comment: accepted to The Astronomical Journal (scheduled for November 2004
issue
Nearby low-mass triple system GJ795
We report the results of our optical speckle-interferometric observations of
the nearby triple system GJ795 performed with the 6-m BTA telescope with
diffraction-limited angular resolution. The three components of the system were
optically resolved for the first time. Position measurements allowed us to
determine the elements of the inner orbit of the triple system. We use the
measured magnitude differences to estimate the absolute magnitudes and spectral
types of the components of the triple: =7.310.08,
=8.660.10, =8.420.10, K5,
K9, K8. The total mass of the system is
equal to =1.69. We show
GJ795 to be a hierarchical triple system which satisfies the empirical
stability criteria.Comment: 6 pages, 2 figures, published in Astrophysical Bulleti
Photometric Monitoring of Open Clusters I. The Survey
Open clusters, which have age, abundance, and extinction information from
studies of main-sequence turn off stars, are the ideal location in which to
determine the mass-luminosity-radius relation for low-mass stars. We have
undertaken a photometric monitoring survey of open clusters in the Galaxy
designed to detect low-mass eclipsing binary systems through variations in
their relative light curves. Our aim is to provide an improved calibration of
the mass-luminosity-radius relation for low-mass stars and brown dwarfs, to
test stellar structure and evolution models, and to help quantify the
contribution of low-mass stars to the global mass census in the Galaxy. In this
paper we present our survey, describing the data and outlining the analysis
techniques. We study six nearby open clusters, with a range of ages from to 4 Gyr and metallicities from approximately solar to -0.2dex. We monitor
a field-of-view of > 1 square degree per target cluster, well beyond the
characteristic cluster radius, over timescales of hours, days, and months with
a sampling rate optimised for the detection of eclipsing binaries with periods
of hours to days. Our survey depth is designed to detect eclipse events in a
binary with a primary star of \lesssim 0.3~M_{\sun}. Our data have a
photometric precision of mmag at .Comment: 50 pages, 18 figures, accepted for publication in A
PHASES High Precision Differential Astrometry of delta Equulei
delta Equulei is among the most well-studied nearby binary star systems.
Results of its observation have been applied to a wide range of fundamental
studies of binary systems and stellar astrophysics. It is widely used to
calibrate and constrain theoretical models of the physics of stars. We report
27 high precision differential astrometry measurements of delta Equulei from
the Palomar High-precision Astrometric Search for Exoplanet Systems (PHASES).
The median size of the minor axes of the uncertainty ellipses for these
measurements is 26 micro-arcseconds. These data are combined with previously
published radial velocity data and other previously published differential
astrometry measurements using other techniques to produce a combined model for
the system orbit. The distance to the system is determined to within a
twentieth of a parsec and the component masses are determined at the level of a
percent. The constraints on masses and distance are limited by the precisions
of the radial velocity data; we outline plans improve this deficiency and
discuss the outlook for further study of this binary.Comment: Accepted by AJ. Complete versions of tables 2-7 now available at
http://stuff.mit.edu/~matthew1/deltaEquTables/ (removed from astroph server
Mining the Metal-Rich Stars for Planets
We examine the correlation between stellar metallicity and short period
planets. It appears that approximately 1% of dwarf stars in the solar
neighborhood harbor short-period planets characterized by near-circular orbits
and orbital periods P<20 days. However, among the most metal-rich stars
(defined as having [Fe/H]>0.2 dex), it appears that the fraction increases to
10%. Using the Hipparcos database and the Hauck & Mermilliod (1998) compilation
of Stromgren uvby photometry, we identify a sample of 206 metal-rich stars of
spectral type K, G, and F which have an enhanced probability of harboring
short-period planets. Many of these stars would be excellent candidates for
addition to radial velocity surveys. We have searched the Hipparcos epoch
photometry for transiting planets within our 206 star catalog. We find that the
quality of the Hipparcos data is not high enough to permit unambiguous transit
detections. It is, however, possible to identify candidate transit periods. We
then discuss various ramifications of the stellar metallicity - planet
connection. First, we show that there is preliminary evidence for increasing
metallicity with increasing stellar mass among known planet-bearing stars. This
trend can be explained by a scenario in which planet-bearing stars accrete an
average of 30 Earth Masses of rocky material after the gaseous protoplanetary
disk phase has ended. We present dynamical calculation which suggest that a
survey of metallicities of spectroscopic binary stars can be used to understand
the root cause of the stellar metallicity - planet connection.Comment: 36 pages, 8 figures, 2 tables, accepted by Astrophysical Journa
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