1,274 research outputs found
Eclipsing binaries observed with the WIRE satellite. II, β Aurigae and non-linear limb darkening in light curves
Aims. We present the most precise light curve ever obtained of a detached eclipsing binary star and use it investigate the inclusion of non-linear limb darkening laws in light curve models of eclipsing binaries. This light curve, of the bright eclipsing system β Aurigae, was obtained using the star tracker aboard the wire satellite and contains 30 000 datapoints with a point-to-point scatter of 0.3mmag.
Methods. We analyse the wire light curve using a version of the ebop code modified to include non-linear limb darkening laws and to directly incorporate observed times of minimum light and spectroscopic light ratios into the photometric solution as individual observations. We also analyse the dataset with the Wilson-Devinney code to ensure that the two models give consistent results.
Results. ebop is able to provide an excellent fit to the high-precision wire data.Whilst the fractional radii of the stars are only defined to a precision of 5% by this light curve, including an accurate published spectroscopic light ratio improves this dramatically to 0.5%. Using non-linear limb darkening improves the quality of the fit significantly compared to the linear law and causes the measured radii to increase by 0.4%. It is possible to derive all of the limb darkening coefficients from the light curve, although they are strongly correlated with each other. The fitted coefficients agree with theoretical predictions to within their fairly large error estimates. We
were able to obtain a reasonably good fit to the data using the Wilson-Devinney code, but only using the highest available integration accuracy and by iterating for a long time. Bolometric albedos of 0.6 were found, which are appropriate to convective rather than radiative envelopes.
Conclusions. The radii and masses of the components of β Aur are RA = 2.762 ± 0.017 R, RB = 2.568 ± 0.017 R, MA = 2.376 ±0.027 M and MB = 2.291 ± 0.027 M, where A and B denote the primary and secondary star, respectively. Theoretical stellar evolutionary models can match these parameters for a solarmetal abundance and an age of 450−500 Myr. The Hipparcos trigonometric parallax and an interferometrically-derived orbital parallax give distances to β Aur which are in excellent agreement with each other
and with distances derived using surface brightness relations and several sets of empirical and theoretical bolometric corrections
The biology of phrynosoma
Thesis (M.A.)--Boston University, 1935. This item was digitized by the Internet Archive
KIC 4247791: A SB4 system with two eclipsing binaries (2EBs)
KIC 4247791 is an eclipsing binary observed by the Kepler satellite mission.
We wish to determine the nature of its components and in particular the origin
of a shallow dip in its Kepler light curve that previous investigations have
been unable to explain in a unique way. We analyze newly obtained
high-resolution spectra of the star using synthetic spectra based on atmosphere
models, derive the radial velocities of the stellar components from
cross-correlation with a synthetic template, and calculate the orbital
solution. We use the JKTEBOP program to model the Kepler light curve of KIC
4247791. We find KIC 4247791 to be a SB4 star. The radial velocity variations
of its four components can be explained by two separate eclipsing binaries. In
contradiction to previous photometric findings, we show that the observed
composite spectrum as well as the derived masses of all four of its components
correspond to spectral type F. The observed small dip in the light curve is not
caused by a transit-like phenomenon but by the eclipses of the second binary
system. We find evidence that KIC 4247791 might belong to the very rare
hierarchical SB4 systems with two eclipsing binaries.Comment: 6 pages, 8 figures, 2 table
Limb darkening in spherical stellar atmospheres
(Abridged) Context. Stellar limb darkening, I({\mu} = cos{\theta}), is an
important constraint for microlensing, eclipsing binary, planetary transit, and
interferometric observations, but is generally treated as a parameterized
curve, such as a linear-plus-square-root law. Many analyses assume
limb-darkening coefficients computed from model stellar atmospheres. However,
previous studies, using I({\mu}) from plane- parallel models, have found that
fits to the flux-normalized curves pass through a fixed point, a common {\mu}
location on the stellar disk, for all values of T eff, log g and wavelength.
Aims. We study this fixed {\mu}-point to determine if it is a property of the
model stellar atmospheres or a property of the limb-darkening laws.
Furthermore, we use this limb-darkening law as a tool to probe properties of
stellar atmospheres for comparison to limb- darkening observations. Methods.
Intensities computed with plane-parallel and spherically-symmetric Atlas models
(characterized by the three fundamental parameters L\star, M\star and R\star)
are used to reexamine the existence of the fixed {\mu}-point for the
parametrized curves. Results. We find that the intensities from our spherical
models do not have a fixed point, although the curves do have a minimum spread
at a {\mu}-value similar to the parametrized curves. We also find that the
parametrized curves have two fixed points, {\mu}1 and {\mu}2, although {\mu}2
is so close to the edge of the disk that it is missed using plane-parallel
atmospheres. We also find that the spherically- symmetric models appear to
agree better with published microlensing observations relative to
plane-parallel models.Comment: 8 pages, 8 figures, figures 4 and 6 have lower resolution. A&A in
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Master\u27s Liability for Injuries to Servants Resulting from Negligence of Co-Employes
Prepared for Degree of LL. M
Physical properties of the eclipsing Delta Sct star KIC 10661783
KIC 10661783 is an eclipsing binary that shows Delta Sct-like oscillations.
More than 60 pulsation frequencies have been detected in its light curve as
observed by the Kepler satellite. We want to determine the fundamental stellar
and system parameters of the eclipsing binary as a precondition for
asteroseismic modelling of the pulsating component and to establish whether the
star is a semi-detached Algol-type system. We measured the radial velocities of
both components from new high-resolution spectra using TODCOR and compute the
orbit using PHOEBE. We used the KOREL program to decompose the observed spectra
into its components, and analysed the decomposed spectra to determine the
atmospheric parameters. For this, we developed a new computer program for the
normalisation of the KOREL output spectra. Fundamental stellar parameters are
determined by combining the spectroscopic results with those from the analysis
of the Kepler light curve. We obtain Teff, logg, vsini, and the absolute masses
and radii of the components, together with their flux ratio and separation.
Whereas the secondary star rotates synchronously with the orbital motion, the
primary star rotates subsynchronously by a factor of 0.75. The newly determined
mass ratio of 0.0911 is higher than previously thought and means a detached
configuration is required to fit the light curve. With its low orbital period
and very low mass ratio, the system shows characteristics of the R CMa-type
stars but differs from this group by being detached. Its current state is
assumed to be that of a detached post-Algol binary system with a pulsating
primary component.Comment: 13 pages, 8 tables, 17 figure
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