We present direct radii measurements of the well-known transiting exoplanet host stars HD 189733 and HD 209458 using the CHARA Array interferometer. We find the limb-darkened angular diameters to be ...θLD = 0.3848 ± 0.0055 and 0.2254 ± 0.0072 mas for HD 189733 and HD 209458, respectively. HD 189733 and HD 209458 are currently the only two transiting exoplanet systems where detection of the respective planetary companion's orbital motion from high-resolution spectroscopy has revealed absolute masses for both star and planet. We use our new measurements together with the orbital information from radial velocity and photometric time series data, Hipparcos distances, and newly measured bolometric fluxes to determine the stellar effective temperatures (T
eff = 4875 ± 43, 6092 ± 103 K), stellar linear radii (R
* = 0.805 ± 0.016, 1.203 ± 0.061 R⊙), mean stellar densities (ρ* = 1.62 ± 0.11, 0.58 ± 0.14 ρ⊙), planetary radii (R
p = 1.216 ± 0.024, 1.451 ± 0.074 R
Jup), and mean planetary densities (ρp = 0.605 ± 0.029, 0.196 ± 0.033 ρJup) for HD 189733b and HD 209458b, respectively. The stellar parameters for HD 209458, an F9 dwarf, are consistent with indirect estimates derived from spectroscopic and evolutionary modelling. However, we find that models are unable to reproduce the observational results for the K2 dwarf, HD 189733. We show that, for stellar evolutionary models to match the observed stellar properties of HD 189733, adjustments lowering the solar-calibrated mixing-length parameter to αMLT =1.34 need to be employed.
Based on CHARA Array measurements, we present the angular diameters of 23 nearby, main-sequence stars, ranging from spectral types A7 to K0, 5 of which are exoplanet host stars. We derive linear ...radii, effective temperatures, and absolute luminosities of the stars using Hipparcos parallaxes and measured bolometric fluxes. The new data are combined with previously published values to create an Angular Diameter Anthology of measured angular diameters to main-sequence stars (luminosity classes V and IV). This compilation consists of 125 stars with diameter uncertainties of less than 5%, ranging in spectral types from A to M. The large quantity of empirical data is used to derive color-temperature relations to an assortment of color indices in the Johnson (BVR sub(J)I sub(J)JHK), Cousins (R sub(C)I sub(C)), Kron (R sub(K)I sub(K)), Sloan (griz), and WISE (W sub(3)W sub(4)) photometric systems. These relations have an average standard deviation of ~3% and are valid for stars with spectral types A0-M4. To derive even more accurate relations for Sun-like stars, we also determined these temperature relations omitting early-type stars (T sub(eff) > 6750 K) that may have biased luminosity estimates because of rapid rotation; for this subset the dispersion is only ~2.5%. We find effective temperatures in agreement within a couple of percent for the interferometrically characterized sample of main-sequence stars compared to those derived via the infrared flux method and spectroscopic analysis.
We use near-infrared interferometric data coupled with trigonometric parallax values and spectral energy distribution fitting to directly determine stellar radii, effective temperatures and ...luminosities for the exoplanet host stars 61 Vir, ρ CrB, GJ 176, GJ 614, GJ 649, GJ 876, HD 1461, HD 7924, HD 33564, HD 107383 and HD 210702. Three of these targets are M dwarfs. Statistical uncertainties in the stellar radii and effective temperatures range from 0.5 to 5 per cent and from 0.2 to 2 per cent, respectively. For eight of these targets, this work presents the first directly determined values of radius and temperature; for the other three, we provide updates to their properties. The stellar fundamental parameters are used to estimate stellar mass and calculate the location and extent of each system's circumstellar habitable zone. Two of these systems have planets that spend at least parts of their respective orbits in the system habitable zone: two of GJ 876's four planets and the planet that orbits HD 33564. We find that our value for GJ 876's stellar radius is more than 20 per cent larger than previous estimates and frequently used values in the astronomical literature.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted) The late-type dwarf GJ 436 is known to host a transiting Neptune-mass planet in a 2.6 day orbit. We present results of our ...interferometric measurements to directly determine the stellar diameter (Rlow * = 0.455 + or - 0.018 R sub(middot in circle)) and effective temperature (T sub(EFF) = 3416 + or - 54 K). We combine our stellar parameters with literature time-series data, which allows us to calculate physical and orbital system parameters, including GJ 436's stellar mass (...), stellar density (...), planetary radius (...), and planetary mass (...), implying a mean planetary density of ... These values are generally in good agreement with previous literature estimates based on assumed stellar mass and photometric light curve fitting. Finally, we examine the expected phase curves of the hot Neptune GJ 436b, based on various assumptions concerning the efficiency of energy redistribution in the planetary atmosphere, and find that it could be constrained with Spitzer monitoring observations.
The bright star 55 Cancri is known to host five planets, including a transiting super-Earth. The study presented here yields directly determined values for 55 Cnc's stellar astrophysical parameters ...based on improved interferometry: R = 0.943 ? 0.010 R , T EFF = 5196 ? 24 K. We use isochrone fitting to determine 55 Cnc's age to be 10.2 ? 2.5 Gyr, implying a stellar mass of 0.905 ? 0.015 M . Our analysis of the location and extent of the system's habitable zone (HZ; 0.67-1.32 AU) shows that planet f, with period ~260 days and Msin i = 0.155 M Jupiter, spends the majority of the duration of its elliptical orbit in the circumstellar HZ. Though planet f is too massive to harbor liquid water on any planetary surface, we elaborate on the potential of alternative low-mass objects in planet f's vicinity: a large moon and a low-mass planet on a dynamically stable orbit within the HZ. Finally, our direct value for 55 Cancri's stellar radius allows for a model-independent calculation of the physical diameter of the transiting super-Earth 55 Cnc e (~2.05 ? 0.15 R {circled plus}), which, depending on the planetary mass assumed, implies a bulk density of 0.76 Delta *r{circled plus} or 1.07 Delta *r{circled plus}.
HR 8799 is an hF0 mA5 gamma Doradus-, lambdaBootis-, Vega-type star best known for hosting four directly imaged candidate planetary companions. Using the CHARA Array interferometer, we measure HR ...8799's limb-darkened angular diameter to be 0.342 + or - 0.008 mas (an error of only 2%). By combining our measurement with the star's parallax and photometry from the literature, we greatly improve upon previous estimates of its fundamental parameters, including stellar radius (1.44 + or - 0.06 R sub(middot in circle)), effective temperature (7193 + or - 87 K, consistent with F0), luminosity (5.05 + or - 0.29 L sub(middot in circle)), and the extent of the habitable zone (HZ; 1.62-3.32 AU). These improved stellar properties permit much more precise comparisons with stellar evolutionary models, from which a mass and age can be determined, once the metallicity of the star is known. Considering the observational properties of other lambda Bootis stars and the indirect evidence for youth of HR 8799, we argue that the internal abundance, and what we refer to as the effective abundance, is most likely near solar. Finally, using the Yonsei-Yale evolutionary models with uniformly scaled solar-like abundances, we estimate HR 8799's mass and age considering two possibilities: 1.516 super(+0.038) sub(+0.024) M sub(middot in circle) and 33 super(+7) sub(-13.2) Myr if the star is contracting toward the zero-age main sequence or 1.513 super(+0.023) sub(-0.024) M sub(middot in circle) and 90 super(381) sub(-50) Myr if it is expanding from it. This improved estimate of HR 8799's age with realistic uncertainties provides the best constraints to date on the masses of its orbiting companions, and strongly suggests they are indeed planets. They nevertheless all appear to orbit well outside the HZ of this young star.
GJ 581 is an M dwarf host of a multiplanet system. We use long-baseline interferometric measurements from the CHARA Array, coupled with trigonometric parallax information, to directly determine its ...physical radius to be 0.299 ? 0.010 R . Literature photometry data are used to perform spectral energy distribution fitting in order to determine GJ 581's effective surface temperature T EFF = 3498 ? 56 K and its luminosity L = 0.01205 ? 0.00024 L . From these measurements, we recompute the location and extent of the system's habitable zone and conclude that two of the planets orbiting GJ 581, planets d and g, spend all or part of their orbit within or just on the edge of the habitable zone.
We have measured the angular diameters for a sample of 24 exoplanet host stars using Georgia State University's CHARA Array interferometer. We use these improved angular diameters together with ...Hipparcos parallax measurements to derive linear radii and to estimate the stars' evolutionary states.
A study of the host stars to exoplanets is important for understanding their environment. To that end, we report new speckle observations of a sample of exoplanet host primaries. The bright exoplanet ...host HD 8673 (= HIP 6702) is revealed to have a companion, although at this time we cannot definitively establish the companion as physical or optical. The observing lists for planet searches and for these observations have for the most part been pre-screened for known duplicity, so the detected binary fraction is lower than what would otherwise be expected. Therefore, a large number of double stars were observed contemporaneously for verification and quality control purposes, to ensure that the lack of detection of companions for exoplanet hosts was valid. In these additional observations, 10 pairs are resolved for the first time and 60 pairs are confirmed. These observations were obtained with the USNO speckle camera on the NOAO 4 m telescopes at both KPNO and CTIO from 2001 to 2010.
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