Independent Confirmation and Refined Parameters of the Hot Jupiter XO-5b

We present HATNet observations of XO-5b, confirming its planetary nature based on evidence beyond that described in the announcement of Burke et al., namely, the lack of significant correlation between spectral bisector variations and orbital phase. In addition, using extensive spectroscopic measurements spanning multiple seasons, we investigate the relatively large scatter in the spectral line bisectors. We also examine possible blended stellar configurations (hierarchical triples, chance alignments) that can mimic the planet signals, and we are able to show that none are consistent with the sum of all the data. The analysis of the S activity index shows no significant stellar activity. Our results for the planet parameters are consistent with values in Burke et al., and we refine both the stellar and the planetary parameters using our data. XO-5b orbits a slightly evolved, late G type star with mass M _sstarf = 0.88 ± 0.03 M _sun, radius R _sstarf = 1.08 ± 0.04 R _sun, and metallicity close to solar. The planetary mass and radius are 1.059 ± 0.028 M _J and 1.109 ± 0.050 R _J, respectively, corresponding to a mean density of 0.96_{-0.11}^{+0.14} g cm^{-3}. The ephemeris for the orbit is P = 4.187757 ± 0.000011 days, E = 2454552.67168 ± 0.00029 (BJD) with transit duration of 0.1307 ± 0.0013 days. By measuring four individual transit centers, we found no signs for transit timing variations. The planet XO-5b is notable for its anomalously high Safronov number and has a high surface gravity when compared to other transiting exoplanets with similar period.

Based in part on observations obtained at the W. M. Keck Observatory, which is operated by the University of California and the California Institute of Technology. Keck time has been granted by NOAO and NASA (programs N162Hr, N128Hr, and A264Hr).