We report on the discovery of HAT-P-11b, the smallest radius transiting extrasolar planet (TEP) discovered from the ground, and the first hot Neptune discovered to date by transit searches. HAT-P-11b orbits the bright (V=9.587) and metal rich ([Fe/H] = +0.31 ± 0.05) K4 dwarf star GSC 03561-02092 with P = 4.8878162 ± 0.0000071 days and produces a transit signal with depth of 4.2 mmag; the shallowest found by transit searches that is due to a confirmed planet. We present a global analysis of the available photometric and radial-velocity data that result in stellar and planetary parameters, with simultaneous treatment of systematic variations. The planet, like its near-twin GJ 436b, is somewhat larger than Neptune (17M ⊕ , 3.8R ⊕ ) both in mass M p = 0.081 ± 0.009 M J (25.8 ± 2.9 M ⊕ ) and radius R p = 0.422 ± 0.014 R J (4.73 ± 0.16 R ⊕ ). HAT-P-11b orbits in an eccentric orbit with e = 0.198 ± 0.046 and ω = 355.2 ± 17.3 • , causing a reflex motion of its parent star with amplitude 11.6 ± 1.2 m s −1 , a challenging detection due to the high level of chromospheric activity of the parent star. Our ephemeris for the transit events is T c = 2454605.89132 ± 0.00032 (BJD), with duration 0.0957 ± 0.0012 d, and secondary eclipse epoch of 2454608.96 ± 0.15 d (BJD). The basic stellar parameters of the host star are M ⋆ = 0.809 +0.020 −0.027 M ⊙ , R ⋆ = 0.752 ± 0.021 R ⊙ and T eff⋆ = 4780 ± 50 K. Importantly, HAT-P-11 will lie on one of the detectors of the forthcoming Kepler mission; this should make possible fruitful investigations of the detailed physical characteristic of both the planet and its parent star at unprecedented precision. We discuss an interesting constraint on the eccentricity of the system by the transit light curve and stellar parameters. This will be particularly useful for eccentric TEPs with low amplitude RV variations in Kepler's field. We also present a blend analysis, that for the first time treats the case of a blended transiting hot Jupiter mimicing a transiting hot Neptune, and proves that HAT-P-11b is not such a blend.

We report on the latest discovery of the HATNet project: a very hot giant planet orbiting a bright (V ¼ 10:5) star with a small semimajor axis of a ¼ 0:0377 AE 0:0005 AU. Ephemeris for the system is P ¼ 2:2047299 AE 0:0000040 days, midtransit time E ¼ 2;453;790:2593 AE 0:0010 (BJD). Based on the available spectroscopic data on the host star and photometry of the system, the planet has a mass of M p ¼ 1:78 K. Because the host star is quite bright, measurement of the secondary eclipse should be feasible for ground-based telescopes, providing a good opportunity to compare the predictions of current hot Jupiter atmospheric models with the observations. Moreover, the host star falls in the field of the upcoming Kepler mission; hence extensive space-borne follow-up, including not only primary transit and secondary eclipse observations but also asteroseismology, will be possible.

We report the discovery of a massive ( M p ¼ 9:04 AE 0:50 M J ) planet transiting the bright (V ¼ 8:7) F8 star HD 147506, with an orbital period of 5:63341 AE 0:00013 days and an eccentricity of e ¼ 0:520 AE 0:010. From the transit light curve we determine that the radius of the planet is R p ¼ 0:982 þ0:038 À0:105 R J . HD 147506b (also coined HAT-P-2b) has a mass about 9 times the average mass of previously known transiting exoplanets and a density of p % 12 g cm À3 , greater than that of rocky planets like the Earth. Its mass and radius are marginally consistent with theories of structure of massive giant planets composed of pure H and He, and accounting for them may require a large (k100 M È ) core. The high eccentricity causes a ninefold variation of insolation of the planet between peri-and apastron. Using follow-up photometry, we find that the center of transit is T mid ¼ 2;454;212:8559 AE 0:0007 ( HJD) and the transit duration is 0:177 AE 0:002 days.

We report on the discovery of a planetary system with a close-in transiting hot Jupiter on a near circular orbit and a massive outer planet on a highly eccentric orbit. The inner planet, HAT-P-13b, transits the bright V=10.622 G4 dwarf star GSC 3416-00543 every P = 2.916260±0.000010 days, with transit epoch T c = 2454779.92979 ± 0.00038 (BJD) and duration 0.1345 ± 0.0017 d. The outer planet, HAT-P-13c orbits the star with P 2 = 428.5±3.0 days and nominal transit center (assuming zero impact parameter) of T 2c = 2454870.4 ± 1.8 (BJD) or time of periastron passage T 2,peri = 2454890.05 ± 0.48 (BJD). Transits of the outer planet have not been observed, and may not be present. The host star has a mass of 1.22 +0.05 −0.10 M ⊙ , radius of 1.56 ± 0.08 R ⊙ , effective temperature 5653 ± 90 K, and is rather metal rich with [Fe/H] = +0.41 ± 0.08. The inner planetary companion has a mass of 0.853 +0.029 −0.046 M J , and radius of 1.281±0.079 R J yielding a mean density of 0.498 +0.103 −0.069 g cm −3 . The outer companion has m 2 sin i 2 = 15.2 ± 1.0 M J , and orbits on a highly eccentric orbit of e 2 = 0.691 ± 0.018. While we have not detected significant transit timing variations of HAT-P-13b, due to gravitational and light-travel time effects, future observations will constrain the orbital inclination of HAT-P-13c, along with its mutual inclination to HAT-P-13b. The HAT-P-13 (b,c) double-planet system may prove extremely valuable for theoretical studies of the formation and dynamics of planetary systems.

We report on the discovery of HAT-P-12b, a transiting extrasolar planet orbiting the moderately bright V ≈ 12.8 K4 dwarf GSC 03033−00706, with a period P = 3.2130598 ± 0. 05. We find a slight correlation between the observed spectral line bisector spans and the radial velocity, so we consider, and rule out, various blend configurations including a blend with a background eclipsing binary, and hierarchical triple systems where the eclipsing body is a star or a planet. We conclude that a model consisting of a single star with a transiting planet best fits the observations, and show that a likely explanation for the apparent correlation is contamination from scattered moonlight. Based on this model, the planetary companion has a mass of 0.211 ± 0.012 M J and radius of 0.959 +0.029 −0.021 R J yielding a mean density of 0.295 ± 0.025 g cm −3 . Comparing these observations with recent theoretical models, we find that HAT-P-12b is consistent with a ∼1-4.5 Gyr, mildly irradiated, H/He-dominated planet with a core mass M C 10 M ⊕ . HAT-P-12b is thus the least massive H/He-dominated gas giant planet found to date. This record was previously held by Saturn.

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Context. HD 15082 (WASP-33) is the hottest and fastest rotating star known to harbor a transiting extrasolar planet (WASP-33b). The lack of high precision radial velocity (RV) data stresses the need for precise light curve analysis and gathering further RV data. Aims. By using available photometric and RV data, we perform a blend analysis, compute more accurate system parameters, confine the planetary mass, and, attempt to cast light on the observed transit anomalies. Methods. We combined the original HATNet observations and various followup data to jointly analyze the signal content and extract the transit component and used our RV data to aid the global parameter determination.Results. The blend analysis of the combination of multicolor light curves yields the first independent confirmation of the planetary nature of WASP-33b. We clearly identify three frequency components in the 15-21 d −1 regime with amplitudes 7-5 mmag. These frequencies correspond to the δ Scuti-type pulsation of the host star. None of these pulsation frequencies or their low-order linear combinations are in close resonance with the orbital frequency. We show that these pulsation components explain some but not all of the observed transit anomalies. The grand-averaged transit light curve shows that there is a ∼1.5 mmag brightening shortly after the planet passes the mid-transit phase. Although the duration and amplitude of this brightening varies, it is visible even through the direct inspections of the individual transit events (some 40-60% of the followup light curves show this phenomenon). We suggest that the most likely explanation of this feature is the presence of a well-populated spot belt which is highly inclined to the orbital plane. This geometry is consistent with the inference from the spectroscopic anomalies. Finally, we constrain the planetary mass to M p = 3.27 ± 0.73 M J by using our RV data collected by the TRES spectrograph.

We report the discovery of 16 detached M dwarf eclipsing binaries with J < 16 mag and provide a detailed characterization of three of them, using high-precision infrared light curves from the WFCAM Transit Survey (WTS). Such systems provide the most accurate and modelindependent method for measuring the fundamental parameters of these poorly understood yet numerous stars, which currently lack sufficient observations to precisely calibrate stellar evolution models. We fully solve for the masses and radii of three of the systems, finding orbital periods in the range 1.5 < P < 4.9 d, with masses spanning 0.35-0.50 M and radii between 0.38 and 0.50 R , with uncertainties of ∼3.5-6.4 per cent in mass and ∼2.7-5.5 per cent in radius. Close companions in short-period binaries are expected to be tidally locked into fast rotational velocities, resulting in high levels of magnetic activity. This is predicted to inflate their radii by inhibiting convective flow and increasing starspot coverage. The radii of the WTS systems are inflated above model predictions by ∼3-12 per cent, in agreement with the observed trend, despite an expected lower systematic contribution from starspot signals at infrared wavelengths. We searched for correlation between the orbital period and radius inflation by combining our results with all existing M dwarf radius measurements of comparable precision, but we found no statistically significant evidence for a decrease in radius inflation for longer period, less active systems. Radius inflation continues to exists in non-synchronized systems, indicating that the problem remains even for very low activity M dwarfs. Resolving this issue is vital not only for understanding the most populous stars in the Universe, but also for characterizing their planetary companions, which hold the best prospects for finding Earth-like planets in the traditional habitable zone.