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Title: The secondary eclipses of WASP-19b as seen by the ASTEP 400 telescope from Antarctica
Authors: L. Abe, I. Gonçalves, A. Agabi, A. Alapini, T. Guillot, D. Mékarnia, J.-P. Rivet, F.-X. Schmider, N. Crouzet, J. Fortney, F. Pont, M. Barbieri, J.-B. Daban, Y. Fanteď-Caujolle, C. Gouvret, Y. Bresson, A. Roussel, S. Bonhomme, A. Robini, M. Dugué, E. Bondoux, S. Péron, P.-Y. Petit, J. Szulágyi, T. Fruth, A. Erikson, H. Rauer, F. Fressin, F. Valbousquet, P.-E. Blanc, A. Le van Suu, S. Aigrain

The ASTEP (Antarctica Search for Transiting ExoPlanets) program was originally aimed at probing the quality of the Dome C, Antarctica for the discovery and characterization of exoplanets by photometry. In the first year of operation of the 40 cm ASTEP 400 telescope (austral winter 2010), we targeted the known transiting planet WASP-19b in order to try to detect its secondary transits in the visible. This is made possible by the excellent sub-millimagnitude precision of the binned data. The WASP-19 system was observed during 24 nights in May 2010. The photometric variability level due to starspots is about 1.8% (peak-to-peak), in line with the SuperWASP data from 2007 (1.4%) and larger than in 2008 (0.07%). We find a rotation period of WASP-19 of 10.7 ± 0.5 days, in agreement with the SuperWASP determination of 10.5 ± 0.2 days. Theoretical models show that this can only be explained if tidal dissipation in the star is weak, i.e. the tidal dissipation factor Q'star > 3.10^7. Separately, we find evidence for a secondary eclipse of depth 390 ± 190 ppm with a 2.0 sigma significance, a phase consistent with a circular orbit and a 3% false positive probability. Given the wavelength range of the observations (420 to 950 nm), the secondary transit depth translates into a day side brightness temperature of 2690(-220/+150) K, in line with measurements in the z' and K bands. The day side emission observed in the visible could be due either to thermal emission of an extremely hot day side with very little redistribution of heat to the night side, or to direct reflection of stellar light with a maximum geometrical albedo Ag=0.27 ± 0.13. We also report a low-frequency oscillation well in phase at the planet orbital period, but with a lower-limit amplitude that could not be attributed to the planet phase alone, and possibly contaminated with residual lightcurve trends.

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Title: Ground-based Transit Spectroscopy of the Hot-Jupiter WASP-19b in the Near-Infrared
Authors: Jacob L. Bean, Jean-Michel Désert, Andreas Seifahrt, Nikku Madhusudhan, Igor Chilingarian, Derek Homeier, Andrew Szentgyorgyi

We present ground-based measurements of the transmission and emission spectra of the hot-Jupiter WASP-19b in nine spectroscopic channels from 1.25 to 2.35 microns. The measurements are based on the combined analysis of time-series spectroscopy obtained during two complete transits and two complete secondary eclipses of the planet. The observations were performed with the MMIRS instrument on the Magellan II telescope using the technique of multi-object spectroscopy with wide slits. We compare the transmission and emission data to theoretical models to constrain the composition and thermal structure of the planet's atmosphere. Our measured transmission spectrum exhibits a scatter that corresponds to 1.3 scale heights of the planet's atmosphere, which is consistent with the size of spectral features predicted by theoretical models for a clear atmosphere. We detected the secondary eclipses of the planet at significances ranging from 2.2 to 14.4 sigma. The secondary eclipse depths, and the significances of the detections increase towards longer wavelengths. Our measured emission spectrum is consistent with a 2250 K effectively isothermal 1-D model for the planet's dayside atmosphere. This model also matches previously published photometric measurements from the Spitzer Space Telescope and ground-based telescopes. These results demonstrate the important role that ground-based observations using multi-object spectroscopy can play in constraining the properties of exoplanet atmospheres, and they also emphasize the need for high-precision measurements based on observations of multiple transits and eclipses.

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Title: z'-band Ground-Based Detection of the Secondary Eclipse of WASP-19b
Authors: John Burton, Christopher Watson, Stuart Littlefair, Vikram Singh Dhillon, Neale Gibson, Thomas Marsh, Don Louis Pollacco

We present the ground-based detection of the secondary eclipse of the transiting exoplanet WASP-19b. The observations were made in the Sloan z'-band using the ULTRACAM triple-beam CCD camera mounted on the NTT. The measurement shows a 0.088 ±0.019% eclipse depth, matching previous predictions based on H- and K-band measurements. We discuss in detail our approach to the removal of errors arising due to systematics in the data set, in addition to fitting a model transit to our data. This fit returns an eclipse centre, T0, of 2455578.7676 HJD, consistent with a circular orbit. Our measurement of the secondary eclipse depth is also compared to model atmospheres of WASP-19b, and is found to be consistent with previous measurements at longer wavelengths for the model atmospheres we investigated.

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Title: Thermal emission at 3.6-8 micron from WASP-19b: a hot Jupiter without a stratosphere orbiting an active star
Authors: D. R. Anderson, A. M. S. Smith, N. Madhusudhan, P. J. Wheatley, A. Collier Cameron, C. Hellier, C. Campo, M. Gillon, J. Harrington, P. F. L. Maxted, D. Pollacco, D. Queloz, B. Smalley, A. H. M. J. Triaud, R. G. West

We report detection of thermal emission from the exoplanet WASP-19b at 3.6, 4.5, 5.8 and 8.0 micron. We used the InfraRed Array Camera on the Spitzer Space Telescope to observe two occultations of WASP-19b by its host star. We combine our new detections with previous measurements of WASP-19b's emission at 1.6 and 2.09 micron to construct a spectral energy distribution of the planet's dayside atmosphere. By comparing this with model-atmosphere spectra, we find that the dayside atmosphere of WASP-19b lacks a strong temperature inversion. As WASP-19 is an active star (log RHK = -4.50 ±0.03), this finding supports the hypothesis of Knutson, Howard & Isaacson (2010) that inversions are suppressed in hot Jupiters orbiting active stars. The available data are unable to differentiate between a carbon-rich and an oxygen-rich atmosphere.

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Title: On the orbit of the short-period exoplanet WASP-19b
Authors: Coel Hellier (Keele), D.R. Anderson, A. Collier Cameron, G.R.M. Miller, D. Queloz, B. Smalley, J. Southworth, A.H.M.J. Triaud
(Version v2)

WASP-19b has the shortest orbital period of any known exoplanet, orbiting at only 1.2 times the Roche tidal radius. By observing the Rossiter-McLaughlin effect we show that WASP-19b's orbit is aligned, with lambda = 4.6 ±5.2 degrees. Using, in addition, a spectroscopic vsini and the observed rotation period we conclude that the obliquity, psi, is less than 20 degrees. Further, the eccentricity of the orbit is less than 0.02. We argue that hot Jupiters with orbital periods as short as that of WASP-19b are two orders of magnitude less common than hot Jupiters at the 3-4-d 'pileup'. We discuss the evolution of WASP-19b's orbit and argue that most likely it was first moved to near twice the Roche limit by third-body interactions, and has since spiralled inwards to its current location under tidal decay. This is compatible with a stellar tidal-dissipation quality factor, Qs, of order 10^7.

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Title: WASP-19b: the shortest period transiting exoplanet yet discovered
Authors: Leslie Hebb, A.Collier-Cameron, A.H.M.J. Triaud, T.A. Lister, B. Smalley, P.F.L. Maxted, C. Hellier, D.R. Anderson, D. Pollacco, M. Gillon, D. Queloz, R.G. West, S. Bentley, B. Enoch, C.A. Haswell, K. Horne, M. Mayor, F. Pepe, D. Segransan, I. Skillen, S. Udry, P.J. Wheatley

We report on the discovery of a new extremely short period transiting extrasolar planet, WASP-19b. The planet has mass Mpl = 1.15 ±0.08 MJ, radius Rpl = 1.31 ±0.06 RJ, and orbital period P = 0.7888399 ±0.0000008 days. Through spectroscopic analysis, we determine the host star to be a slightly super-solar metallicity ([M/H] = 0.1 ±0.1 dex) G-dwarf with Teff = 5500 ±100 K. In addition, we detect periodic, sinusoidal flux variations in the light curve which are used to derive a rotation period for the star of Prot = 10.5 ±0.2 days. The relatively short stellar rotation period suggests that either WASP-19 is somewhat young (~ 600 Myr old) or tidal interactions between the two bodies have caused the planet to spiral inward over its lifetime resulting in the spin-up of the star. Due to the detection of the rotation period, this system has the potential to place strong constraints on the stellar tidal quality factor, Q's, if a more precise age is determined.

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