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Register a new userOGLE2-TR-L9: An extrasolar planet transiting a fast-rotating F3 star
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Context: Photometric observations for the OGLE-II microlens monitoring campaign have been taken in the period 1997-2000. All light curves of this campaign have recently been made public. Our analysis of these data has revealed 13 low-amplitude transiting objects among ~15700 stars in three Carina fields towards the galactic disk. One of these objects, OGLE2-TR-L9 (P~2.5 days), turned out to be an excellent transiting planet candidate. Aims: In this paper we report on our investigation of the true nature of OGLE2-TR-L9, by re-observing the photometric transit with the aim to determine the transit parameters at high precision, and by spectroscopic observations, to estimate the properties of the host star, and to determine the mass of the transiting object through radial velocity measurements. Methods: High precision photometric observations have been obtained in g, r, i, and z band simultaneously, using the new GROND detector, mounted on the MPI/ESO 2.2m telescope at La Silla. Eight epochs of high-dispersion spectroscopic observations were obtained using the fiber-fed FLAMES/UVES Echelle spectrograph, mounted on ESOs Very Large Telescope at Paranal. Results: The photometric transit, now more than 7 years after the last OGLE-II observations, was re-discovered only ~8 minutes from its predicted time. The primary object is a fast rotating F3 star, with vsini=39.33+-0.38 km/s, T=6933+-58 K, log g = 4.25+-0.01, and [Fe/H] = -0.05+-0.20. The transiting object is an extrasolar planet with M_p=4.5+-1.5 M_Jup and R_p=1.61+-0.04 R_Jup. The rejection of possible blend scenarios was based on a quantitative analysis of the multi-color photometric data [abridged].
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Context: Repeated observations of exoplanet transits allow us to refine the planetary parameters and probe them for any time dependent variations. In particular deviations of the period from a strictly linear ephemeris, transit timing variations (TTVs), can indicate the presence of additional bodies in the planetary system. Aims: Our goal was to reexamine the largely unstudied OGLE2-TR-L9 system with high cadence, multi-color photometry in order to refine the planetary parameters and probe the system for TTVs. Methods: We observed five full transits of OGLE2-TR-L9 with the GROND instrument at the ESO/MPG 2.2 m telescope at La Silla Observatory. GROND is a multichannel imager that allowed us to gather simultaneous light curves in the g, r, i, and z filters. Results: From our analysis we find that the semi-major axis and the inclination differ from the previously published values. With the newly observed transits, we were able to refine the ephemeris to 2454492.80008(+/- 0.00014) + 2.48553417(+/- 6.4) x 10^-7 E. The newly derived parameters are a=0.0418 (+/- 0.0015) AU, r_p =1.67 (+/- 0.05) R_j, and inc=82.47{deg} (+/- 0.12), differing significantly in a and inc from the previously published values. Within our data, we find indications for TTVs.
We report the discovery of the planet XO-4b, which transits the star XO-4 (GSC 03793-01994, V=10.7, F5V). Transits are 1.0% deep and 4.4 hours in duration. The star XO-4 has a mass of 1.32 M_sun.... The planet XO-4b has a mass of 1.72 M_Jup....radius of 1.34 R_Jup...orbital period 4.125 days. We analyze scintillation-limited differential R-band photometry of XO-4b in transit made with a 1.8-m telescope under photometric conditions, yielding photometric precision of 0.6 to 2.0 millimag per one-minute interval. The declination of XO-4 places it within the continuous viewing zone of the Hubble Space Telescope (HST), which permits observation without interruption caused by occultation by the Earth. Because the stellar rotation periods of the three hottest stars orbited by transiting gas-giant planets are 2.0, 1.1, and 2.0 times the planetary orbital periods, we note the possibility of resonant interaction.
Two consecutive transits of planetary companion OGLE-TR-111b were observed in the I band. Combining these observations with data from the literature, we find that the timing of the transits cannot be explained by a constant period, and that the observed variations cannot be originated by the presence of a satellite. However, a perturbing planet with the mass of the Earth in an exterior orbit could explain the observations if the orbit of OGLE-TR-111b is eccentric. We also show that the eccentricity needed to explain the observations is not ruled out by the radial velocity data found in the literature.
We report the discovery of HATS-2b, the second transiting extrasolar planet detected by the HATSouth survey. HATS-2b is moving on a circular orbit around a V=13.6 mag, K-type dwarf star (GSC 6665-00236), at a separation of 0.0230 pm 0.0003 AU and with a period of 1.3541 days. The planetary parameters have been robustly determined using a simultaneous fit of the HATSouth, MPG/ESO~2.2,m/GROND, Faulkes Telescope South/Spectral transit photometry and MPG/ESO~2.2,m/FEROS, Euler~1.2,m/CORALIE, AAT~3.9,m/CYCLOPS radial-velocity measurements. HATS-2b has a mass of 1.37 pm 0.16 M_J, a radius of 1.14 pm 0.03 R_J and an equilibrium temperature of 1567 pm 30 K. The host star has a mass of 0.88 pm 0.04 M_Sun, radius of 0.89 pm 0.02 R_Sun and shows starspot activity. We characterized the stellar activity by analysing two photometric follow-up transit light curves taken with the GROND instrument, both obtained simultaneously in four optical bands (covering the wavelength range of 3860-9520 AA). The two light curves contain anomalies compatible with starspots on the photosphere of the parent star along the same transit chord.
Only a few hot Jupiters are known to orbit around fast rotating stars. These exoplanets are harder to detect and characterize and may be less common than around slow rotators. Here, we report the discovery of the transiting hot Jupiter XO-6b, which orbits a bright, hot, and fast rotating star: V = 10.25, Teff = 6720 +/- 100 K, v sin i = 48 +/- 3 km/s. We detected the planet from its transits using the XO instruments and conducted a follow-up campaign. Because of the fast stellar rotation, radial velocities taken along the orbit do not yield the planets mass with a high confidence level, but we secure a 3-sigma upper limit Mp < 4.4 MJup. We also obtain high resolution spectroscopic observations of the transit with the SOPHIE spectrograph at the 193-cm telescope of the Observatoire de Haute-Provence and analyze the stellar lines profile by Doppler tomography. The transit is clearly detected in the spectra. The radii measured independently from the tomographic analysis and from the photometric lightcurves are consistent, showing that the object detected by both methods is the same and indeed transits in front of XO-6. We find that XO-6b lies on a prograde and misaligned orbit with a sky-projected obliquity lambda = -20.7 +/- 2.3 deg. The rotation period of the star is shorter than the orbital period of the planet: Prot < 2.12 days, Porb = 3.77 days. Thus, this system stands in a largely unexplored regime of dynamical interactions between close-in giant planets and their host stars.
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