J. M. Fernandez

HAT-P-11b: A super-neptune planet transiting a bright K star in the kepler field

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 (RV) 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 (17 M_⊕, 3.8 R_⊕) 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 = 355o.2 ± 17o.3, causing a reflex motion of its parent star with amplitude 11.6 ± 1.2 ms^(–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 days, and secondary eclipse epoch of 2454608.96 ± 0.15 days (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 Keplers field. We also present a blend analysis, that for the first time treats the case of a blended transiting hot Jupiter mimicking a transiting hot Neptune, and proves that HAT-P-11b is not such a blend.

HD 147506b: A supermassive planet in an eccentric orbit transiting a bright star

We report the discovery of a massive (M_p = 9.04 ± 0.50 M_J) planet transiting the bright (V = 8.7) F8 star HD 147506, with an orbital period of 5.63341 ± 0.00013 days and an eccentricity of e = 0.520 ± 0.010. From the transit light curve we determine that the radius of the planet is R_p = 0.982^(+0.038)_(-0.105) 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 ρp ≈ 12 g cm^(-3), 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 (≳100 M_⊕) 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) = 2,454,212.8559 ± 0.0007 (HJD) and the transit duration is 0.177 ± 0.002 days.

A NEW SPECTROSCOPIC AND PHOTOMETRIC ANALYSIS OF THE TRANSITING PLANET SYSTEMS TrES-3 AND TrES-4

We report new spectroscopic and photometric observations of the parent stars of the recently discovered transiting planets TrES-3 and TrES-4. A detailed abundance analysis based on high-resolution spectra yields [Fe/H] = –0.19 ± 0.08, T_(eff) = 5650 ± 75 K, and log g = 4.4 ± 0.1 for TrES-3, and [Fe/H] = +0.14 ± 0.09, T_(eff) = 6200 ± 75 K, and log g = 4.0 ± 0.1 for TrES-4. The accuracy of the effective temperatures is supported by a number of independent consistency checks. The spectroscopic orbital solution for TrES-3 is improved with our new radial velocity measurements of that system, as are the light-curve parameters for both systems based on newly acquired photometry for TrES-3 and a reanalysis of existing photometry for TrES-4. We have redetermined the stellar parameters taking advantage of the strong constraint provided by the light curves in the form of the normalized separation a/R_* (related to the stellar density) in conjunction with our new temperatures and metallicities. The masses and radii we derive are M_* = 0.928^(+0.028)_(–0.048) M_⊙, R_* = 0.829^(+0.015)_(–0.022) R_⊙, and M_* = 1.404^(+0.066)_(–0.134) M_⊙, R_* = 1.846^(+0.096)_(–0.087) R_⊙ for TrES-3 and TrES-4, respectively. With these revised stellar parameters, we obtain improved values for the planetary masses and radii. We find M_p = 1.910^(+0.075)_(–0.080) M_(Jup), R_p = 1.336^(+0.031)_(–0.036) R_(Jup) for TrES-3, and M_p = 0.925 ± 0.082 M_(Jup), R_p = 1.783^(+0.093)_(–0.086) R_(Jup) for TrES-4. We confirm TrES-4 as the planet with the largest radius among the currently known transiting hot Jupiters.

HAT-P-12b: A Low-Density Sub-Saturn Mass Planet Transiting a Metal-Poor K Dwarf

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 ± 0.0000021 d, transit epoch T_c = 2454419.19556 ± 0.00020 (BJD), and transit duration 0.0974 ± 0.0006 d. The host star has a mass of 0.73 ± 0.02 M_☉, radius of 0.70^(+0.02)_(–0.01) R_☉, effective temperature 4650 ± 60 K, and metallicity [Fe/H] = –0.29 ± 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.

HAT-P-3b: A Heavy-Element-rich Planet Transiting a K Dwarf Star

We report the discovery of a Jupiter-size planet transiting a relatively bright (V = 11.56) and metal-rich early K dwarf star with a period of ~2.9 days. On the basis of follow-up photometry and spectroscopy we determine the mass and radius of the planet, HAT-P-3b, to be Mp = 0.599 ± 0.026 MJup and Rp = 0.890 ± 0.046 RJup. The relatively small size of the object for its mass implies the presence of about 75 M⊕ worth of heavy elements (~ of the total mass) based on current theories of irradiated extrasolar giant planets, similar to the mass of the core inferred for the transiting planet HD 149026b. The bulk density of HAT-P-3b is found to be ρp = 1.06 ± 0.17 g cm-3, and the planet orbits the star at a distance of 0.03894 AU. Ephemerides for the transit centers are Tc = 2,454,218.7594 ± 0.0029 + N × (2.899703 ± 0.000054) (HJD).

TrES-4: A Transiting Hot Jupiter of Very Low Density

We report the discovery of TrES-4, a hot Jupiter that transits the star GSC 02620-00648 every 3.55 days. From high-resolution spectroscopy of the star, we estimate a stellar effective temperature of K, and T p 6100 150 eff from high-precision z and B photometry of the transit we constrain the ratio of the semimajor axis a and the stellar radius to be . We compare these values to model stellar isochrones to constrain the stellar Ra /R p 6.03 0.13 ∗∗ mass to be . Based on this estimate and the photometric time series, we constrain the stellar M p 1.22 0.17 M ∗ , radius to be and the planet radius to be . We model our radial R p 1.738 0.092 RR p 1.674 0.094 R ∗ , p Jup velocity data assuming a circular orbit and find a planetary mass of . Our radial velocity observations 0.84 0.10 MJup rule out line-bisector variations that would indicate a specious detection resulting from a blend of an eclipsing binary system. TrES-4 has the largest radius and lowest density of any of the known transiting planets. It presents a challenge to current models of the physical structure of hot Jupiters and indicates that the diversity of physical properties among the members of this class of exoplanets has yet to be fully explored. Subject headings: planetary systems — techniques: photometric — techniques: radial velocities — techniques: spectroscopic

THE TRANSIT LIGHT CURVE (TLC) PROJECT. VI. THREE TRANSITS OF THE EXOPLANET TrES-2

Of the nearby transiting exoplanets that are amenable to detailed study, TrES-2 is both the most massive and the one with the largest impact parameter. We present z-band photometry of three transits of TrES-2. We improve on the estimates of the planetary, stellar, and orbital parameters, in conjunction with the spectroscopic analysis of the host star by Sozzetti and coworkers. We find the planetary radius to be Rp = 1.222 ± 0.038 RJup and the stellar radius to be R* = 1.003 ± 0.027 R☉. The quoted uncertainties include the systematic error due to the uncertainty in the stellar mass (M* = 0.980 ± 0.062 M☉). The timings of the transits have an accuracy of 25 s and are consistent with a uniform period, thus providing a baseline for future observations with the NASA Kepler satellite, whose field of view will include TrES-2.

The Mass and Radius of the Unseen M Dwarf Companion in the Single-Lined Eclipsing Binary HAT-TR-205-013

We derive masses and radii for both components in the single-lined eclipsing binary HAT-TR-205-013, which consists of an F7 V primary and a late M dwarf secondary. The systems period is short, P = 2.230736 ± 0.000010 days, with an orbit indistinguishable from circular, e = 0.012 ± 0.021. We demonstrate generally that the surface gravity of the secondary star in a single-lined binary undergoing total eclipses can be derived from characteristics of the light curve and spectroscopic orbit. This constrains the secondary to a unique line in the mass-radius diagram, with M/R2 = constant. For HAT-TR-205-013, we assume the orbit has been tidally circularized and that the primarys rotation has been synchronized and aligned with the orbital axis. Our observed line broadening, Vrot sin irot = 28.9 ± 1.0 km s-1, gives a primary radius of RA = 1.28 ± 0.04 R☉. Our light-curve analysis leads to the radius of the secondary, RB = 0.167 ± 0.006 R☉, and the semimajor axis of the orbit, a = 7.54 ± 0.30 R☉ = 0.0351 ± 0.0014 AU. Our single-lined spectroscopic orbit and the semimajor axis then yield the individual masses MB = 0.124 ± 0.010 M☉ and MA = 1.04 ± 0.13 M☉. Our result for HAT-TR-205-013 B lies above the theoretical mass-radius models from the Lyon group, consistent with results from double-lined eclipsing binaries. The method we describe offers the opportunity to study the very low end of the stellar mass-radius relation.

HAT-P-4b: A METAL-RICH LOW-DENSITY TRANSITING HOT JUPITER †

We describe the discovery of HAT-P-4b, a low-density extrasolar planet transiting BD+36 2593, a V = 11.2mag slightly evolved metal-rich late F star. The planet’s orbital period is 3.056536 ± 0.000057d with a mid-transit epoch of 2,454,245.8154±0.0003 (HJD). Based on high-precision photometric and spectroscopic data, and by using transit light curve modeling, spectrum analysis and evolutionary models, we derive the following planet parameters: Mp= 0.68±0.04MJ, Rp= 1.27±0.05RJ, �p= 0.41±0.06gcm −3 and a = 0.0446±0.0012AU. Because of its relatively large radius, together with its assumed high metallicity of that of its parent star, this planet adds to the theoretical challenges to explain inflated extrasolar planets. Subject headings: planetary systems: individual: HAT-P-4b — stars: individual: BD+36 2593 — techniques: photometric — techniques: spectroscopic

HAT-P-6b: A hot jupiter transiting a bright F star

In the ongoing HATNet survey we have detected a giant planet, with radius 1.33 ± 0.06 RJup and mass -->1.06 ± 0.12 MJup, transiting the bright ( -->V = 10.5) star GSC 03239–00992. The planet is in a circular orbit with period -->3.852985 ± 0.000005 days and midtransit epoch 2,454,035.67575 ± 0.00028 (HJD). The parent star is a late F star with mass -->1.29 ± 0.06 M☉, radius -->1.46 ± 0.06 R☉, Teff ~ 6570 ± 80 K , -->[ Fe/H ] = − 0.13 ± 0.08, and age ~ -->2.3+ 0.5−0.7 Gyr. With this radius and mass, HAT-P-6b has somewhat larger radius than theoretically expected. We describe the observations and their analysis to determine physical properties of the HAT-P-6 system, and briefly discuss some implications of this finding.