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Title: A lower radius and mass for the transiting extrasolar planet HAT-P-8b
Authors: L. Mancini, J. Southworth, S. Ciceri, J. J. Fortney, C. V. Morley, J. A. Dittmann, J. Tregloan-Reed, I. Bruni, M. Barbieri, D. F. Evans, G. D'Ago, N. Nikolov, Th. Henning

Context. The extrasolar planet HAT-P-8 b was thought to be one of the more inflated transiting hot Jupiters. Aims. By using new and existing photometric data, we computed precise estimates of the physical properties of the system. Methods. We present photometric observations comprising eleven light curves covering six transit events, obtained using five medium-class telescopes and telescope-defocusing technique. One transit was simultaneously obtained through four optical filters, and two transits were followed contemporaneously from two observatories. We modelled these and seven published datasets using the jktebop code. The physical parameters of the system were obtained from these results and from published spectroscopic measurements. In addition, we investigated the theoretically-predicted variation of the apparent planetary radius as a function of wavelength, covering the range 330-960 nm. Results. We find that HAT-P-8 b has a significantly lower radius (1.321 Jupiter radii) and mass (1.275 Jupiter masses) compared to previous estimates (1.50 Jupiter radii and 1.52 Jupiter masses respectively). We also detect a radius variation in the optical bands that, when compared with synthetic spectra of the planet, may indicate the presence of a strong optical absorber, perhaps TiO and VO gases, near the terminator of HAT-P-8 b. Conclusions. These new results imply that HAT-P-8 b is not significantly inflated, and that its position in the planetary mass-radius diagram is congruent with those of many other transiting extrasolar planets.

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Title: HATNet Field G205: Follow-Up Observations of 28 Transiting-Planet candidates and Confirmation of the Planet HAT-P-8b
Authors: David W. Latham (1), Gáspár A. Bakos (1,2), Guillermo Torres (1), Robert P. Stefanik (1), Robert W. Noyes (1), Géza Kovács (3), András Pál (1,4), Geoffrey W. Marcy (5), Debra A. Fischer (6), R. Paul Butler (7), Brigitta Sip\H{o)cz (4, 1), Dimitar D. Sasselov (1), Gilbert A. Esquerdo (1), Steven S. Vogt (8), Joel D. Hartman (1), Gábor Kovács (1), József Lázár (9), István Papp (9), Pál Sári (9) ( (1)CfA, (2) NSF Fellow, (3) Konkoly Observatory, (4) ELTE, (5) UC Berkeley, (6) SFSU, (7) Carnegie, (8) UC Santa Cruz, (9) Hungarian Astronomical Association)

We report the identification of 32 transiting-planet candidates in HATNet field G205. We describe the procedures that we have used to follow up these candidates with spectroscopic and photometric observations, and we present a status report on our interpretation of the 28 candidates for which we have follow-up observations. Eight are eclipsing binaries with orbital solutions whose periods are consistent with their photometric ephemerides; two of these spectroscopic orbits are singled-lined and six are double-lined. For one of the candidates, a nearby but fainter eclipsing binary proved to be the source for the HATNet light curve, due to blending in the HATNet images. Four of the candidates were found to be rotating more rapidly than vsini = 50 km/s and were not pursued further. Thirteen of the candidates showed no significant velocity variation at the level of 0.5 to 1.0 km/s . Seven of these were eventually withdrawn as photometric false alarms based on an independent reanalysis using more sophisticated tools. Of the remaining six, one was put aside because a close visual companion proved to be a spectroscopic binary, and two were not followed up because the host stars were judged to be too large. Two of the remaining candidates are members of a visual binary, one of which was previously confirmed as the first HATNet transiting planet, HAT-P-1b. In this paper we confirm that the last of this set of candidates is also a a transiting planet, which we designate HAT-P-8b, with mass Mp = 1.52 ±0.18/0.16 Mjup, radius Rp = 1.50 ±0.08/0.06 Rjup, and photometric period P = 3.076320 ±0.000004 days. HAT-P-8b has an inflated radius for its mass, and a large mass for its period. The host star is a solar-metallicity F dwarf, with mass M* = 1.28 ±0.04 Msun and Rp = 1.58 ±0.08/0.06 Rsun.

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