62 research outputs found
Eclipsing Binary Stars from Space
We have begun a programme to obtain high-precision photometry of bright
detached eclipsing binary (dEB) stars with the Wide field InfraRed Explorer
(WIRE) satellite. Due to the small aperture of WIRE only stars brighter than
V=6 can be observed. We are collecting data for about a dozen dEB targets and
here we present preliminary results for three of them. We have chosen dEBs with
primary components of B and early A type. One of our aims is to combine the
information from the light curve analyses of the eclipses with asteroseismic
information from the analysis of the pulsation of the primary component.Comment: 4 pages, 3 figures. To appear in conference proceedings for IAU
Symposium No. 240: Binary Stars as Critical Tools & Tests in Contemporary
Astrophysics, eds. W. Hartkopf, E. Guinan & P. Harmane
Accurate Fundamental Stellar Parameters
We combine results from interferometry, asteroseismology and spectroscopic
analyses to determine accurate fundamental parameters (mass, radius and
effective temperature) of 10 bright solar-type stars covering the H-R diagram
from spectral type F5 to K1. Using ``direct'' techniques that are only weakly
model-dependent we determine the mass, radius and effective temperature. We
demonstrate that model-dependent or ``indirect'' methods can be reliably used
even for relatively faint single stars for which direct methods are not
applicable. This is important for the characterization of the targets of the
CoRoT and Kepler space missions.Comment: 2 pages. To appear in the proceedings of IAU Symp. 265: Chemical
Abundances in the Universe: Connecting First Stars to Planet
Testing convection in stellar models using detached eclipsing binaries
The fundamental properties of detached eclipsing binary stars can be measured
very accurately, which could make them important objects for constraining the
treatment of convection in theoretical stellar models. However, only four or
five pieces of information can be found for the average system, which is not
enough. We discuss studies of more interesting and useful objects: eclipsing
binaries in clusters and eclipsing binaries with pulsating components.Comment: 3 pages, 2 figures, poster proceedings for IAUS 239 (Convection in
Astrophysics). The actual poster, and other resources, can be downloaded from
http://www.astro.keele.ac.uk/~jkt
A Revised Effective Temperature Scale for the Kepler Input Catalog
We present a catalog of revised effective temperatures for stars observed in
long-cadence mode in the Kepler Input Catalog (KIC). We use SDSS griz filters
tied to the fundamental temperature scale. Polynomials for griz
color-temperature relations are presented, along with correction terms for
surface gravity effects, metallicity, and statistical corrections for binary
companions or blending. We compare our temperature scale to the published
infrared flux method (IRFM) scale for VJKs in both open clusters and the Kepler
fields. We find good agreement overall, with some deviations between (J -
Ks)-based temperatures from the IRFM and both SDSS filter and other diagnostic
IRFM color-temperature relationships above 6000 K. For field dwarfs we find a
mean shift towards hotter temperatures relative to the KIC, of order 215 K, in
the regime where the IRFM scale is well-defined (4000 K to 6500 K). This change
is of comparable magnitude in both color systems and in spectroscopy for stars
with Teff below 6000 K. Systematic differences between temperature estimators
appear for hotter stars, and we define corrections to put the SDSS temperatures
on the IRFM scale for them. When the theoretical dependence on gravity is
accounted for we find a similar temperature scale offset between the
fundamental and KIC scales for giants. We demonstrate that statistical
corrections to color-based temperatures from binaries are significant. Typical
errors, mostly from uncertainties in extinction, are of order 100 K.
Implications for other applications of the KIC are discussed.Comment: Corrected for sign flip errors in the gravity corrections. Erratum to
this paper is attached in Appendix. Full version of revised Table 7 can be
found at http://home.ewha.ac.kr/~deokkeun/kic/sdssteff_v2.dat.g
Metal Abundances, Radial Velocities, and Other Physical Characteristics for the RR Lyrae Stars in The Kepler Field
Spectroscopic iron-to-hydrogen ratios, radial velocities, atmospheric parameters, and new photometric analyses are presented for 41 RR Lyrae stars (and one probable high-amplitude δ Sct star) located in the field-of-view of the Kepler space telescope. Thirty-seven of the RR Lyrae stars are fundamental-mode pulsators (i.e., RRab stars) of which sixteen exhibit the Blazhko effect. Four of the stars are multiperiodic RRc pulsators oscillating primarily in the first-overtone mode. Spectroscopic [Fe/H] values for the 34 stars for which we were able to derive estimates range from –2.54 ± 0.13 (NR Lyr) to –0.05 ± 0.13 dex (V784 Cyg), and for the 19 Kepler-field non-Blazhko stars studied by Nemec et al. the abundances agree will with their photometric [Fe/H] values. Four non-Blazhko RR Lyrae stars that they identified as metal-rich (KIC 6100702, V2470 Cyg, V782 Cyg and V784 Cyg) are confirmed as such, and four additional stars (V839 Cyg, KIC 5520878, KIC 8832417, KIC 3868420) are also shown here to be metal-rich. Five of the non-Blazhko RRab stars are found to be more metal-rich than [Fe/H] ~–0.9 dex while all of the 16 Blazhko stars are more metal-poor than this value. New P-Ø_(31)^s-[Fe/H] relationships are derived based on ~970 days of quasi-continuous high-precision Q0-Q11 long- and short-cadence Kepler photometry. With the exception of some Blazhko stars, the spectroscopic and photometric [Fe/H] values are in good agreement. Several stars with unique photometric characteristics are identified, including a Blazhko variable with the smallest known amplitude and frequency modulations (V838 Cyg)
Calibrating Convective properties of Solar-like Stars in the Kepler Field of View
Stellar models generally use simple parametrizations to treat convection. The
most widely used parametrization is the so-called "Mixing Length Theory" where
the convective eddy sizes are described using a single number, \alpha, the
mixing-length parameter. This is a free parameter, and the general practice is
to calibrate \alpha using the known properties of the Sun and apply that to all
stars. Using data from NASA's Kepler mission we show that using the
solar-calibrated \alpha is not always appropriate, and that in many cases it
would lead to estimates of initial helium abundances that are lower than the
primordial helium abundance. Kepler data allow us to calibrate \alpha for many
other stars and we show that for the sample of stars we have studied, the
mixing-length parameter is generally lower than the solar value. We studied the
correlation between \alpha and stellar properties, and we find that \alpha
increases with metallicity. We therefore conclude that results obtained by
fitting stellar models or by using population-synthesis models constructed with
solar values of \alpha are likely to have large systematic errors. Our results
also confirm theoretical expectations that the mixing-length parameter should
vary with stellar properties.Comment: 16 pages, 4 figures, accepted for publication in ApJ
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