849 research outputs found
ELLC - a fast, flexible light curve model for detached eclipsing binary stars and transiting exoplanets
Very high quality light curves are now available for thousands of detached
eclipsing binary stars and transiting exoplanet systems as a result of surveys
for transiting exoplanets and other large-scale photometric surveys. I have
developed a binary star model (ELLC) that can be used to analyse the light
curves of detached eclipsing binary stars and transiting exoplanet systems that
is fast and accurate, and that can include the effects of star spots, Doppler
boosting and light-travel time within binaries with eccentric orbits. The model
represents the stars as triaxial ellipsoids. The apparent flux from the binary
is calculated using Gauss-Legendre integration over the ellipses that are the
projection of these ellipsoids on the sky. The model can also be used to
calculate the flux-weighted radial velocity of the stars during an eclipse
(Rossiter-McLaughlin effect). The main features of the model have been tested
by comparison to observed data and other light curve models. The model is found
to be accurate enough to analyse the very high quality photometry that is now
available from space-spaced instruments, flexible enough to model a wide range
of eclipsing binary stars and extrasolar planetary systems, and fast enough to
enable the use of modern Monte Carlo methods for data analysis and model
testing.Comment: Accepted for publication in A&A. Source code available from
pypi.python.org/pypi/ellc. Definition of "third-light" changed from version
ellc-1.0.0 to ellc-1.1.0 - this preprint describes the definition used in the
later versio
Photometry of the Magnetic White Dwarf SDSS 121209.31+013627.7
The results of 27 hours of time series photometry of SDSS 121209.31+013627.7
are presented. The binary period established from spectroscopy is confirmed and
refined to 0.061412 d (88.43 minutes). The photometric variations are dominated
by a brightening of about 16 mmag, lasting a little less than half a binary
cycle. The amplitude is approximately the same in V, R and white light. A
secondary small brightness increase during each cycle may also be present. We
speculate that SDSS 121209.31+013627.7 may be a polar in a low state.Comment: Accepted for publication in MNRA
On the frequency of close binary systems among very low-mass stars and brown dwarfs
We have used Monte Carlo simulation techniques and published radial velocity
surveys to constrain the frequency of very low-mass star (VLMS) and brown dwarf
(BD) binary systems and their separation (a) distribution. Gaussian models for
the separation distribution with a peak at a = 4 au and 0.6 =< sigma(log(a/au))
=< 1.0 correctly predict the number of observed binaries, yielding a close
(a<2.6 au) binary frequency of 17-30 per cent and an overall VLMS/BD binary
frequency of 32-45 per cent. We find that the available N-body models of
VLMS/BD formation from dynamically decaying protostellar multiple systems are
excluded at >99 per cent confidence because they predict too few close binary
VLMS/BDs. The large number of close binaries and high overall binary frequency
are also very inconsistent with recent smoothed particle hydrodynamical
modelling and argue against a dynamical origin for VLMS/BDs.Comment: Accepted for publication in MNRAS letters. 5 pages, 2 figure
Projected rotational velocities of WD1614+136 and WD1353+409 - implications for the rate of galactic Type Ia supernovae
The white dwarf stars WD1614+136 and WD1353+409 are not sufficiently massive
to have formed through single star evolution. However, observations to date
have not yet found any evidence for binarity. It has therefore been suggested
that these stars are the result of a merger. In this paper we place an upper
limit of approximately 50kms on the projected rotational velocities of both
stars. This suggests that, if these stars are the results of a merger,
efficient angular momentum loss with accompanying mass loss must have occurred.
If the same process occurs following the merging of more massive white dwarf
stars, the predicted rate of Type Ia supernovae due to merging white dwarfs may
have been greatly over-estimated. Further observations to determine binarity in
WD1614+136 and WD1353+409 are therefore encouraged.Comment: 3 pages. 1 figur
Eclipsing binaries in open clusters
Accurate physical parameters have been determined for two early-type detached
eclipsing binaries in the open cluster h Persei (NGC 869). Masses accurate to
1.5% are derived from high-resolution spectroscopy and radii accurate to 4--6%
have been obtained from fitting the existing light curves. The four stars are
placed in the mass radius plane and compared to the theoretical stellar models
of the Granada Group. The best-fitting models have a low metallicity of
approximately Z=0.01 and a high helium abundance of Y=0.34. This is the first
determination of the bulk metallicity of the Perseus Double Cluster. Recent
studies have assumed a solar metallicity so their results should be reviewed.Comment: 4 pages, 5 figures. To appear in Spectroscopically and Spatially
Resolving the Components of Close Binary Stars, ASP Conf. Series, 200
Fundamental effective temperature measurements for eclipsing binary stars -- IV. Selection of new benchmark stars and first results for HD 22064
I describe the selection and initial characterisation of 20 eclipsing binary
stars that are suitable for calibration and testing of stellar models and data
analysis algorithms used by the PLATO mission and spectroscopic surveys. The
binary stars selected are F-/G-type dwarf stars with M-type dwarf companions
that contribute less than 2% of the flux at optical wavelengths. The light
curves typically show well-defined total eclipses with very little variability
between the eclipses. I have used near-infrared spectra obtained by the APOGEE
survey to measure the spectroscopic orbit for both stars in HD22064. Combined
with an analysis of the TESS light curve, I derive the following masses and
radii: , , , . Using and
the parallax from Gaia EDR3, I find that the primary star's angular diameter is
mas. The apparent bolometric flux of the primary
star is erg cm
s. Hence, this F2V star has an effective temperature . HD22064 is an ideal benchmark star that can be
used for ``end-to-end'' tests of the stellar parameters measured by large-scale
spectroscopic surveys, or stellar parameters derived from asteroseismology with
PLATO. The techniques described here for HD22064 can be applied to the other
eclipsing binaries in the sample in order to create an all-sky network of such
benchmark stars.Comment: 12 pages, 9 figures. Submitted to MNRAS. arXiv admin note: text
overlap with arXiv:2205.0146
Bayesian mass and age estimates for transiting exoplanet host stars
The mean density of a star transited by a planet, brown dwarf or low mass
star can be accurately measured from its light curve. This measurement can be
combined with other observations to estimate its mass and age by comparison
with stellar models. Our aim is to calculate the posterior probability
distributions for the mass and age of a star given its density, effective
temperature, metallicity and luminosity. We computed a large grid of stellar
models that densely sample the appropriate mass and metallicity range. The
posterior probability distributions are calculated using a Markov-chain
Monte-Carlo method. The method has been validated by comparison to the results
of other stellar models and by applying the method to stars in eclipsing binary
systems with accurately measured masses and radii. We have explored the
sensitivity of our results to the assumed values of the mixing-length
parameter, , and initial helium mass fraction, Y. For a star
with a mass of 0.9 solar masses and an age of 4 Gyr our method recovers the
mass of the star with a precision of 2% and the age to within 25% based on the
density, effective temperature and metallicity predicted by a range of
different stellar models. The masses of stars in eclipsing binaries are
recovered to within the calculated uncertainties (typically 5%) in about 90% of
cases. There is a tendency for the masses to be underestimated by about 0.1
solar masses for some stars with rotation periods Pd. Our method
makes it straightforward to determine accurately the joint posterior
probability distribution for the mass and age of a star eclipsed by a planet or
other dark body based on its observed properties and a state-of-the art set of
stellar models.Comment: Accepted for publication in A&A. 9 pages, 4 figures. Source code for
the software described is available from
http://sourceforge.net/projects/bagemas
KPD1930+2752 - a candidate Type Ia supernova progenitor
We present spectra of the pulsating sdB star KPD1930+2752 which confirm that
this star is a binary. The radial velocities measured from the H-alpha and
HeI6678 spectral lines vary sinusoidally with the same period (2h 17m) as the
ellipsoidal variability seen by Billeres et al. (2000). The amplitude of the
orbital motion (349.3+-2.7 km/s) combined with the canonical mass for sdB stars
(0.5 solar masses) implies a total mass for the binary of 1.47+-0.01 solar
masses The unseen companion star is almost certainly a white dwarf star. The
binary will merge within about 200 million years due to gravitational wave
radiation. The accretion of helium and other elements heavier than hydrogen
onto the white dwarf which then exceeds the Chandrasekhar mass (1.4 solar
masses) is a viable model for the cause of Type Ia supernovae. KPD1930+2752 is
the first star to be discovered which is a good candidate for the progenitor of
a Type Ia supernova of this type which will merge on an astrophysically
interesting timescale.Comment: Accepted for publication in MNRAS. 4 pages, 2 figures. Added
Institutio
WD1953-011 - a magnetic white dwarf with peculiar field structure
We present H-alpha spectra of the magnetic white dwarf star WD1953-011 which
confirm the presence of the broad Zeeman components corresponding to a field
strength of about 500kG found by Maxted & Marsh (1999). We also find that the
line profile is variable over a timescale of a day or less. The core of the
H-alpha line also shows a narrow Zeeman triplet corresponding to a field
strength of of about 100kG which appears to be almost constant in shape. These
observations suggest that the magnetic field on WD1953-011 has a complex
structure and that the star has a rotational period of hours or days which
causes the observed variability of the spectra. We argue that neither an offset
dipole model nor a double-dipole model are sufficient to explain our
observations. Instead, we propose a two component model consisting of a high
field region of magnetic field strength of about 500kG covering about 10% of
the surface area of the star superimposed on an underlying dipolar field of
mean field strength of about 70kG. Radial velocity measurements of the narrow
Zeeman triplet show that the radial velocity is constant to within a few km/s
so this star is unlikely to be a close binary.Comment: Accpeted for publication in MNRAS. 4 pages, 2 figure
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