162 research outputs found
Directly Determined Linear Radii and Effective Temperatures of Exoplanet Host Stars
We present interferometric angular sizes for 12 stars with known planetary
companions, for comparison with 28 additional main-sequence stars not known to
host planets. For all objects we estimate bolometric fluxes and reddenings
through spectral energy distribution fits, and in conjunction with the angular
sizes, measurements of effective temperature. The angular sizes of these stars
are sufficiently small that the fundamental resolution limits of our primary
instrument, the Palomar Testbed Interferometer, are investigated at the
sub-milliarcsecond level and empirically established based upon known
performance limits. We demonstrate that the effective temperature scale as a
function of dereddened color is statistically identical for stars
with and without planets. A useful byproduct of this investigation is a direct
calibration of the scale for solar-like stars, as a function of
both spectral type and color, with an precision of K over the range and K for the range F6V -- G5V. Additionally, we provide in
an appendix spectral energy distribution fits for the 166 stars with known
planets which have sufficient photometry available in the literature for such
fits; this derived "{\tt XO-Rad}" database includes homogenous estimates of
bolometric flux, reddening, and angular size.Comment: Accepted for publication in Ap
The PTI Carbon Star Angular Size Survey: Effective Temperatures and Non-Sphericity
We report new interferometric angular diameter observations of 41 carbon
stars observed with the Palomar Testbed Interferometer (PTI). Two of these
stars are CH carbon stars and represent the first such measurements for this
subtype. Of these, 39 have Yamashita (1972,1975) spectral classes and are of
sufficiently high quality that we may determine the dependence of effective
temperature on spectral type. We find that there is a tendency for the
effective temperature to increase with increasing temperature index by ~120K
per step, starting at T_EFF ~= 2500K for C3,y, although there is a large amount
of scatter about this relationship. Overall, the median effective temperature
for the carbon star sample is found to be 2800 +- 270K, and the median linear
radius is 360 +- 100 R_SUN. We also find agreement on average within 15K with
the T_EFF determinations of Bergeat (2001,2002a,b), and a refinement of carbon
star angular size prediction based on V & K magnitudes is presented that is
good to an rms of 12%. A subsample of our stars have sufficient {u,v} coverage
to permit non-spherical modeling of their photospheres, and a general tendency
for detection of statistically significant departures from sphericity with
increasing signal-to-noise of the interferometric data is seen. The
implications of most - and potentially all - carbon stars being non-spherical
is considered in the context of surface inhomogeneities and a rotation-mass
loss connection.Comment: 59 pages, 15 figures, 6 tables; accepted for publication in Ap
The Spitzer 24μm Photometric Light Curve of the Eclipsing M-dwarf Binary GU Boötis
We present a carefully controlled set of Spitzer 24 μm MIPS time series observations of the low mass eclipsing binary star GU Boötis (GU Boo). Our data cover three secondary eclipses of the system: two consecutive events and an additional eclipse six weeks later. The study’s main purpose is the long wavelength characterization of GU Boo’s light curve, independent of limb darkening and less sensitive to surface features such as spots. Its analysis allows for independent verification of the results of optical studies of GU Boo. Our mid-infrared results show good agreement with previously obtained system parameters. In addition, the analysis of light curves of other objects in the field of view serves to characterize the photometric stability and repeatability of Spitzer’s MIPS-24 at flux densities between approximately 300–2,000μJy. We find that the light curve root mean square about the median level falls into the 1–4% range for flux densities higher than 1 mJy
Stellar diameters and temperatures. IV. Predicting stellar angular diameters
The number of stellar angular diameter measurements has greatly increased over the past few years due to innovations and developments in the field of long baseline optical interferometry. We use a collection of high-precision angular diameter measurements for nearby, main-sequence stars to develop empirical relations that allow the prediction of stellar angular sizes as a function of observed photometric color. These relations are presented for a combination of 48 broadband color indices. We empirically show for the first time a dependence on metallicity of these relations using Johnson (B-V) and Sloan (g-r) colors. Our relations are capable of predicting diameters with a random error of less than 5% and represent the most robust and empirical determinations of stellar angular sizes to date. © 2014. The American Astronomical Society. All rights reserved.
Establishing Visible Interferometer System Responses: Resolved and Unresolved Calibrators
The propagation of errors through the uniform disk visibility function is
examined. Implications of those errors upon measures of absolute visibility
through optical and near-infrared interferometers are considered within the
context of using calibration stars to establish system visibilities for these
instruments. We suggest a simple ratio test to establish empirically whether or
not the measured visibilities produced by such an instrument are relative
(errors dominated by calibrator angular size prediction error) or absolute
(errors dominated by measurement error).Comment: 20 pages, 7 figures, to be published in the PAS
Direct imaging of planet transit events
Exoplanet transit events are attractive targets for the ultrahigh-resolution capabilities afforded by optical interferometers. The intersection of two developments in astronomy enable direct imaging of exoplanet transits: first, improvements in sensitivity and precision of interferometric instrumentation; and second, identification of ever-brighter host stars. Efforts are underway for the first direct high-precision detection of closure phase signatures with the CHARA Array and Navy Precision Optical Interferometer. When successful, these measurements will enable recovery of the transit position angle on the sky, along with characterization of other system parameters, such as stellar radius, planet radius, and other parameters of the transit event. This technique can directly determine the planet\u27s radius independent of any outside observations, and appears able to improve substantially upon other determinations of that radius; it will be possible to extract wavelength dependence of that radius determination, for connection to characterization of planetary atmospheric composition & structure. Additional directly observed parameters - also not dependent on transit photometry or spectroscopy - include impact parameter, transit ingress time, and transit velocity. Copyright © International Astronomical Union 2014
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