764 research outputs found
The Rossiter-McLaughlin effect and analytic radial velocity curves for transiting extrasolar planetary systems
A transiting extrasolar planet sequentially blocks off the light coming from
the different parts of the disk of the host star in a time dependent manner.
Due to the spin of the star, this produces an asymmetric distortion in the line
profiles of the stellar spectrum, leading to an apparent anomaly of the radial
velocity curves, known as the Rossiter - McLaughlin effect. Here, we derive
approximate but accurate analytic formulae for the anomaly of radial velocity
curves taking account of the stellar limb darkening. The formulae are
particularly useful in extracting information of the projected angle between
the planetary orbit axis and the stellar spin axis, \lambda, and the projected
stellar spin velocity, V sin I_s. We create mock samples for the radial curves
for the transiting extrasolar system HD209458, and demonstrate that constraints
on the spin parameters (V sin I_s, \lambda) may be significantly improved by
combining our analytic template formulae and the precision velocity curves from
high-resolution spectroscopic observations with 8-10 m class telescopes. Thus
future observational exploration of transiting systems using the Rossiter -
McLaughlin effect is one of the most important probes to better understanding
of the origin of extrasolar planetary systems, especially the origin of their
angular momentum.Comment: 39 pages, 16 figures, Accepted to ApJ. To match the published version
(ApJ 623, April 10 issue
On stellar limb darkening and exoplanetary transits
This paper examines how to compare stellar limb-darkening coefficients
evaluated from model atmospheres with those derived from photometry. Different
characterizations of a given model atmosphere can give quite different
numerical results (even for a given limb-darkening `law'), while light-curve
analyses yield limb-darkening coefficients that are dependent on system
geometry, and that are not directly comparable to any model-atmosphere
representation. These issues are examined in the context of exoplanetary
transits, which offer significant advantages over traditional binary-star
eclipsing systems in the study of stellar limb darkening. `Like for like'
comparisons between light-curve analyses and new model-atmosphere results,
mediated by synthetic photometry, are conducted for a small sample of stars.
Agreement between the resulting synthetic-photometry/atmosphere-model (SPAM)
limb-darkening coefficients and empirical values ranges from very good to quite
poor, even though the targets investigated show only a small dispersion in
fundamental stellar parameters.Comment: Accepted, MNRAS, 4/8/201
Two New Tidally Distorted White Dwarfs
We identify two new tidally distorted white dwarfs (WDs), SDSS
J174140.49+652638.7 and J211921.96-001825.8 (hereafter J1741 and J2119). Both
stars are extremely low mass (ELM, < 0.2 Msun) WDs in short-period, detached
binary systems. High-speed photometric observations obtained at the McDonald
Observatory reveal ellipsoidal variations and Doppler beaming in both systems;
J1741, with a minimum companion mass of 1.1 Msun, has one of the strongest
Doppler beaming signals ever observed in a binary system (0.59 \pm 0.06%
amplitude). We use the observed ellipsoidal variations to constrain the radius
of each WD. For J1741, the star's radius must exceed 0.074 Rsun. For J2119, the
radius exceeds 0.10 Rsun. These indirect radius measurements are comparable to
the radius measurements for the bloated WD companions to A-stars found by the
Kepler spacecraft, and they constitute some of the largest radii inferred for
any WD. Surprisingly, J1741 also appears to show a 0.23 \pm 0.06% reflection
effect, and we discuss possible sources for this excess heating. Both J1741 and
J2119 are strong gravitational wave sources, and the time-of-minimum of the
ellipsoidal variations can be used to detect the orbital period decay. This may
be possible on a timescale of a decade or less.Comment: 6 pages, 4 figures, accepted for publication in the Astrophysical
Journa
Abrupt appearance of the domain pattern and fatigue of thin ferroelectric films
We study the domain structure in ferroelectric thin films with a `passive'
layer (material with damaged ferroelectric properties) at the interface between
the film and electrodes within a continuous medium approximation. An abrupt
transition from a monodomain to a polydomain state has been found with the
increase of the `passive' layer thickness . The domain width changes very
quickly at the transition (exponentially with ). We have estimated the
dielectric response (the slope of the hysteresis loop) in the
`fatigued' multidomain state and found that it is in agreement with experiment,
assuming realistic parameters of the layer. We derive a simple universal
relation for the dielectric response, which scales as , involving only the
properties of the passive layer. This relation qualitatively reproduces the
evolution of the hysteresis loop in fatigued samples and it could be tested
with controlled experiments. It is expected that the coercive field should
increase with decreasing lateral size of the film. We believe that specific
properties of the domain structure under bias voltage in ferroelectrics with a
passive layer can resolve the long-standing `paradox of the coercive field'.Comment: 5 pages, REVTeX 3.1 with two eps-figures. Minor amendments. To appear
in Phys. Rev. Letter
The EBLM Project I-Physical and orbital parameters, including spin-orbit angles, of two low-mass eclipsing binaries on opposite sides of the Brown Dwarf limit
This paper introduces a series of papers aiming to study the dozens of low
mass eclipsing binaries (EBLM), with F, G, K primaries, that have been
discovered in the course of the WASP survey. Our objects are mostly single-line
binaries whose eclipses have been detected by WASP and were initially followed
up as potential planetary transit candidates. These have bright primaries,
which facilitates spectroscopic observations during transit and allows the
study of the spin-orbit distribution of F, G, K+M eclipsing binaries through
the Rossiter-McLaughlin effect. Here we report on the spin-orbit angle of
WASP-30b, a transiting brown dwarf, and improve its orbital parameters. We also
present the mass, radius, spin-orbit angle and orbital parameters of a new
eclipsing binary, J1219-39b (1SWAPJ121921.03-395125.6, TYC 7760-484-1), which,
with a mass of 95 +/- 2 Mjup, is close to the limit between brown dwarfs and
stars. We find that both objects orbit in planes that appear aligned with their
primaries' equatorial planes. Neither primaries are synchronous. J1219-39b has
a modestly eccentric orbit and is in agreement with the theoretical
mass--radius relationship, whereas WASP-30b lies above it.Comment: 12 pages, 7 figures, data in appendices, submitted to A&A (taking in
account 1st referee report
Taming the Invisible Monster: System Parameter Constraints for Epsilon Aurigae from the Far-Ultraviolet to the Mid-Infrared
We have assembled new Spitzer Space Telescope Infrared Array Camera
observations of the mysterious binary star Epsilon Aurigae, along with archival
far-ultraviolet to mid-infrared data, to form an unprecedented spectral energy
distribution spanning three orders of magnitude in wavelength from 0.1 microns
to 100 microns. The observed spectral energy distribution can be reproduced
using a three component model consisting of a 2.2+0.9/-0.8 Msun F type
post-asymptotic giant branch star, and a 5.9+/-0.8 Msun B5+/-1 type main
sequence star that is surrounded by a geometrically thick, but partially
transparent, disk of gas and dust. At the nominal HIPPARCOS parallax distance
of 625 pc, the model normalization yields a radius of 135+/-5 Rsun for the F
star, consistent with published interferometric observations. The dusty disk is
constrained to be viewed at an inclination of i > 87 deg, and has effective
temperature of 550+/-50 K with an outer radius of 3.8 AU and a thickness of
0.95 AU. The dust content of the disk must be largely confined to grains larger
than ~10 microns in order to produce the observed gray optical-infrared
eclipses and the lack of broad dust emission features in the archival Spitzer
mid-infrared spectra. The total mass of the disk, even considering a potential
gaseous contribution in addition to the dust that produces the observed
infrared excess, is << 1 Msun. We discuss evolutionary scenarios for this
system that could lead to the current status of the stellar components and
suggests possibilities for its future evolution, as well as potential
observational tests of our model.Comment: 13 pages, 3 figures. Accepted for publication in The Astrophysical
Journal
Absolute properties of the low-mass eclipsing binary CM Draconis
Spectroscopic and eclipsing binary systems offer the best means for
determining accurate physical properties of stars, including their masses and
radii. The data available for low-mass stars have yielded firm evidence that
stellar structure models predict smaller radii and higher effective
temperatures than observed, but the number of systems with detailed analyses is
still small. In this paper we present a complete reanalysis of one of such
eclipsing systems, CM Dra, composed of two dM4.5 stars. New and existing light
curves as well as a radial velocity curve are modeled to measure the physical
properties of both components. The masses and radii determined for the
components of CM Dra are M1=0.2310+/-0.0009 Msun, M2=0.2141+/-0.0010 Msun,
R1=0.2534+/-0.0019 Rsun, and R2=0.2396+/-0.0015 Rsun. With relative
uncertainties well below the 1% level, these values constitute the most
accurate properties to date for fully convective stars. This makes CM Dra a
valuable benchmark for testing theoretical models. In comparing our
measurements with theory, we confirm the discrepancies reported previously for
other low-mass eclipsing binaries. These discrepancies seem likely to be due to
the effects of magnetic activity. We find that the orbit of this system is
slightly eccentric, and we have made use of eclipse timings spanning three
decades to infer the apsidal motion and other related properties.Comment: 19 pages, 9 figures. Accepted for publication in Ap
Blue Straggler Stars: Early Observations that Failed to Solve the Problem
In this chapter, I describe early ideas on blue stragglers, and various
observations (some published, some not) that promised but failed to resolve the
question of their origin. I review the data and ideas that were circulating
from Allan Sandage's original discovery in 1953 of "anomalous blue stars" in
the globular cluster M3, up until about 1992, when what seems to have been the
only previous meeting devoted to Blue Straggler Stars (BSSs) was held at the
Space Telescope Science Institute.Comment: Chapter 2, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G.
Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe
Optical Observations of GRO J1655-40 in Quiescence I: A Precise Mass for the Black Hole Primary
We report photometric and spectroscopic observations of the black hole binary
GRO J1655-40 in complete quiescence. In contrast to the 1995 photometry, the
light curves from 1996 are almost completely dominated by ellipsoidal
modulations from the secondary star. Model fits to the light curves, which take
into account the temperature profile of the accretion disk and eclipse effects,
yield an inclination of i=69.50 +/- 0.08 degrees and a mass ratio of Q=2.99 +/-
0.08. The precision of our determinations of i and Q allow us to determine the
black hole mass to an accuracy of approximately 4% (7.02 +/- 0.22 solar
masses). The secondary star's mass is 2.34 +/- 0.12 solar masses. The position
of the secondary on the Hertzsprung-Russell diagram is consistent with that of
a 2.3 solar mass star which has evolved off the main sequence and is halfway to
the start of the giant branch. Using the new spectra we present an improved
value of the spectroscopic period (2.62157 +/- 0.00015 days), radial velocity
semiamplitude (228.2 +/- 2.2 km/sec), and mass function (3.24 +/- 0.09 solar
masses). Evolutionary models suggest an average mass transfer rate for such a
system of 3.4E-9 solar masses per year (2.16E+17 grams per second), which is
much larger than the average mass transfer rates implied in the other six
transient black hole systems, but still barely below the critical mass transfer
rate required for stability.Comment: 30 pages, 12 figures, LaTeX (uses orosztwo.sty), to appear in ApJ,
vol. 474 (March 10, 1997
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