1,051 research outputs found
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
High-precision photometry by telescope defocussing. III. The transiting planetary system WASP-2
We present high-precision photometry of three transits of the extrasolar
planetary system WASP-2, obtained by defocussing the telescope, and achieving
point-to-point scatters of between 0.42 and 0.73 mmag. These data are modelled
using the JKTEBOP code, and taking into account the light from the
recently-discovered faint star close to the system. The physical properties of
the WASP-2 system are derived using tabulated predictions from five different
sets of stellar evolutionary models, allowing both statistical and systematic
errorbars to be specified. We find the mass and radius of the planet to be M_b
= 0.847 +/- 0.038 +/- 0.024 Mjup and R_b = 1.044 +/- 0.029 +/- 0.015 Rjup. It
has a low equilibrium temperature of 1280 +/- 21 K, in agreement with a recent
finding that it does not have an atmospheric temperature inversion. The first
of our transit datasets has a scatter of only 0.42 mmag with respect to the
best-fitting light curve model, which to our knowledge is a record for
ground-based observations of a transiting extrasolar planet.Comment: Accepted for publication in MNRAS. 9 pages, 3 figures, 10 table
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
Absolute dimensions of detached eclipsing binaries. I. The metallic-lined system WW Aurigae
WW Aurigae is a detached eclipsing binary composed of two metallic-lined
A-type stars orbiting each other every 2.5 days. We have determined the masses
and radii of both components to accuracies of 0.4 and 0.6 percent,
respectively. From a cross-correlation analysis of high-resolution spectra we
find masses of 1.964 +/- 0.007 Msun for the primary star and 1.814 +/- 0.007
Msun for the secondary star. From an analysis of photoelectric uvby and UBV
light curves we find the radii of the stars to be 1.927 +/- 0.011 Rsun and
1.841 +/- 0.011 Rsun, where the uncertainties have been calculated using a
Monte Carlo algorithm. Fundamental effective temperatures of the two stars have
been derived, using the Hipparcos parallax of WW Aur and published ultraviolet,
optical and infrared fluxes, and are 7960 +/- 420 and 7670 +/- 410 K. The
masses, radii and effective temperatures of WW Aur are only matched by
theoretical evolutionary models for a fractional initial metal abundance, Z, of
approximately 0.06 and an age of roughly 90 Myr. This seems to be the highest
metal abundance inferred for a well-studied detached eclipsing binary, but we
find no evidence that it is related to the metallic-lined nature of the stars.
The circular orbit of WW Aur is in conflict with the circularization timescales
of both the Tassoul and the Zahn tidal theories and we suggest that this is due
to pre-main-sequence evolution or the presence of a circular orbit when the
stars were formed.Comment: Accepted for publication in MNRAS (14 pages, 8 figures). Photometric
data will be made available at the CDS once the final version appear
Exoplanet Catalogues
One of the most exciting developments in the field of exoplanets has been the
progression from 'stamp-collecting' to demography, from discovery to
characterisation, from exoplanets to comparative exoplanetology. There is an
exhilaration when a prediction is confirmed, a trend is observed, or a new
population appears. This transition has been driven by the rise in the sheer
number of known exoplanets, which has been rising exponentially for two decades
(Mamajek 2016). However, the careful collection, scrutiny and organisation of
these exoplanets is necessary for drawing robust, scientific conclusions that
are sensitive to the biases and caveats that have gone into their discovery.
The purpose of this chapter is to discuss and demonstrate important
considerations to keep in mind when examining or constructing a catalogue of
exoplanets. First, we introduce the value of exoplanetary catalogues. There are
a handful of large, online databases that aggregate the available exoplanet
literature and render it digestible and navigable - an ever more complex task
with the growing number and diversity of exoplanet discoveries. We compare and
contrast three of the most up-to-date general catalogues, including the data
and tools that are available. We then describe exoplanet catalogues that were
constructed to address specific science questions or exoplanet discovery space.
Although we do not attempt to list or summarise all the published lists of
exoplanets in the literature in this chapter, we explore the case study of the
NASA Kepler mission planet catalogues in some detail. Finally, we lay out some
of the best practices to adopt when constructing or utilising an exoplanet
catalogue.Comment: 14 pages, 6 figures. Invited review chapter, to appear in "Handbook
of Exoplanets", edited by H.J. Deeg and J.A. Belmonte, section editor N.
Batalh
Combined observations of meteors by image-orthicon television camera and multi-station radar
Observations from multiple sites of a radar network and by television of 29 individual meteors from February 1969 through June 1970 are reported. Only 12 of the meteors did not appear to fragment over all the observed portion of their trajectories. From these 12, the relation for the radar magnitude to the panchromatic absolute magnitude was found in terms of velocity of the meteor. A very tentative fit to the data on the duration of long enduring echoes versus visual absolute magnitude is made. The exponential decay characteristics of the later parts of several of the light curves are pointed out as possible evidence of mutual coalescence of droplets into which the meteoroid has completely broken
Physical properties and radius variations in the HAT-P-5 planetary system from simultaneous four-colour photometry
The radii of giant planets, as measured from transit observations, may vary
with wavelength due to Rayleigh scattering or variations in opacity. Such an
effect is predicted to be large enough to detect using ground-based
observations at multiple wavelengths. We present defocussed photometry of a
transit in the HAT-P-5 system, obtained simultaneously through Stromgren u,
Gunn g and r, and Johnson I filters. Two more transit events were observed
through a Gunn r filter. We detect a substantially larger planetary radius in
u, but the effect is greater than predicted using theoretical model atmospheres
of gaseous planets. This phenomenon is most likely to be due to systematic
errors present in the u-band photometry, stemming from variations in the
transparency of Earth's atmosphere at these short wavelengths. We use our data
to calculate an improved orbital ephemeris and to refine the measured physical
properties of the system. The planet HAT-P-5b has a mass of 1.06 +/- 0.11 +/-
0.01 Mjup and a radius of 1.252 +/- 0.042 +/- 0.008 Rjup (statistical and
systematic errors respectively), making it slightly larger than expected
according to standard models of coreless gas-giant planets. Its equilibrium
temperature of 1517 +/- 29 K is within 60K of that of the extensively-studied
planet HD 209458b.Comment: Version 2 corrects the accidental omission of one author in the arXiv
metadata. Accepted for publication in MNRAS. 9 pages, 4 figures, 7 tables.
The properties of HAT-P-5 have been added to the Transiting Extrasolar Planet
Catalogue at http://www.astro.keele.ac.uk/~jkt/tepcat
Eclipsing binaries in open clusters - III. V621 Per in χ Persei
V621 Persei is a detached eclipsing binary in the open cluster χ Persei, which is composed of an early B-type giant star and a main-sequence secondary component. From high-resolution spectroscopic observations and radial velocities from the literature, we determine the orbital period to be 25.5 d and the primary velocity semi-amplitude to be K= 64.5 ± 0.4 km s−1. No trace of the secondary star has been found in the spectrum. We solve the discovery light curves of this totally eclipsing binary and find that the surface gravity of the secondary star is log gB= 4.244 ± 0.054. We compare the absolute masses and radii of the two stars in the mass-radius diagram, for different possible values of the primary surface gravity, with the predictions of stellar models. We find that log gA≈ 3.55, in agreement with values found from fitting Balmer lines with synthetic profiles. The expected masses of the two stars are 12 and 6 M⊙ and the expected radii are 10 and 3 R⊙. The primary component is near the blue loop stage in its evolutio
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