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Post Info TOPIC: Exoplanet host stars
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Title: Spectroscopy of Faint Kepler Mission Exoplanet Candidate Host Stars
Authors: Mark E. Everett, Steve B. Howell, David R. Silva, Paula Szkody

Stellar properties are measured for a large set of Kepler Mission exoplanet candidate host stars. Most of these stars are fainter than 14th magnitude, in contrast to other spectroscopic follow-up studies. This sample includes many high-priority Earth-sized candidate planets. A set of model spectra are fitted to R~3000 optical spectra of 268 stars to improve estimates of Teff, log(g), and [Fe/H] for the dwarfs in the range 4750K<Teff<7200K. These stellar properties are used to find new stellar radii and, in turn, new radius estimates for the candidate planets. The result of improved stellar characteristics is a more accurate representation of this Kepler exoplanet sample and identification of promising candidates for more detailed study. This stellar sample, particularly among stars with Teff>5200K, includes a greater number of relatively evolved stars with larger radii than assumed by the mission on the basis of multi-colour broadband photometry. About 26% of the modelled stars require radii to be revised upwards by a factor of 1.35 or greater, and modelling of 87% of the stars suggest some increase in radius. The sample presented here also exhibits a change in the incidence of planets larger than 3-4 Earth radii as a function of metallicity. Once [Fe/H] increases to >=-0.05, large planets suddenly appear in the sample while smaller planets are found orbiting stars with a wider range of metallicity. The modelled stellar spectra, as well as an additional 84 stars of mostly lower effective temperatures, are made available to the community.

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Blobrana


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Title: A new interferometric study of four exoplanet host stars : Theta Cygni, 14 Andromedae, upsilon Andromedae and 42 Draconis 
Authors: R. Ligi, D. Mourard, A.M. Lagrange, K. Perraut, T. Boyajian, Ph. Bério, N. Nardetto, I. Tallon-Bosc, H. McAlister, T. ten Brummelaar, S. Ridgway, J. Sturmann, L. Sturmann, N. Turner, C. Farrington, P.J. Goldfinger 

Studying exoplanet host stars is of the utmost importance to establish the link between the presence of exoplanets around various types of stars and to understand the respective evolution of stars and exoplanets. 
Using the limb-darkened diameter (LDD) obtained from interferometric data, we determine the fundamental parameters of four exoplanet host stars. We are particularly interested in the F4 main-sequence star, theta Cyg, for which Kepler has recently revealed solar-like oscillations that are unexpected for this type of star. Furthermore, recent photometric and spectroscopic measurements with SOPHIE and ELODIE (OHP) show evidence of a quasi-periodic radial velocity of \sim150 days. Models of this periodic change in radial velocity predict either a complex planetary system orbiting the star, or a new and unidentified stellar pulsation mode. 
We performed interferometric observations of theta Cyg, 14 Andromedae, upsilon Andromedae and 42 Draconis for two years with VEGA/CHARA (Mount Wilson, California) in several three-telescope configurations. We measured accurate limb darkened diameters and derived their radius, mass and temperature using empirical laws. 
We obtain new accurate fundamental parameters for stars 14 And, upsilon And and 42 Dra. We also obtained limb darkened diameters with a minimum precision of \sim 1.3%, leading to minimum planet masses of Msini=5.33 ±0.57, 0.62 ±0.09 and 3.79 ±0.29 Jupiter masses for 14 And b, upsilon And b and 42 Dra b, respectively. The interferometric measurements of theta Cyg show a significant diameter variability that remains unexplained up to now. We propose that the presence of these discrepancies in the interferometric data is caused by either an intrinsic variation of the star or an unknown close companion orbiting around it. 

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Title: Rotation periods of exoplanet host stars
Authors: Elaine Simpson (1,2,3), Sallie Baliunas (1), Greg Henry (4), Chris Watson (3) ((1) Harvard-Smithsonian Centre for Astrophysics, (2) University of Southampton, (3) Queen's University Belfast, (4) Tennessee State University)

The stellar rotation periods of ten exoplanet host stars have been determined using newly analysed Ca II H & K flux records from Mount Wilson Observatory and Stromgren b, y photometric measurements from Tennessee State University's automatic photometric telescopes (APTs) at Fairborn Observatory. Five of the rotation periods have not previously been reported, with that of HD 130322 very strongly detected at Prot = 26.1 ±3.5 d. The rotation periods of five other stars have been updated using new data. We use the rotation periods to derive the line-of-sight inclinations of the stellar rotation axes, which may be used to probe theories of planet formation and evolution when combined with the planetary orbital inclination found from other methods. Finally, we estimate the masses of fourteen exoplanets under the assumption that the stellar rotation axis is aligned with the orbital axis. We calculate the mass of HD 92788 b (28 MJ) to be within the low-mass brown dwarf regime and suggest that this object warrants further investigation to confirm its true nature.

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