A. Pál

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.

The Transit Light Curve Project. I. Four Consecutive Transits of the Exoplanet XO-1b

We present RIz photometry of four consecutive transits of the newly discovered exoplanet XO-1b. We improve on the estimates of the transit parameters, finding the planetary radius to be RP = 1.184 +0.028 -0.018 RJ, and the stellar radius to be R* = 0.928 +0.018 -0.013 R☉, assuming a stellar mass of M* = (1.00 ± 0.03) M☉. The uncertainties in the planetary and stellar radii are dominated by the uncertainty in the stellar mass. These uncertainties increase by a factor of 2-3 if a more conservative uncertainty of 0.10 M☉ is assumed for the stellar mass. Our estimate of the planetary radius is smaller than that reported by McCullough and coworkers, and the resulting estimate for the mean density of XO-1b is intermediate between that of the low-density planet HD 209458b and the higher density planets TrES-1 and HD 189733b. The timings of the transits have an accuracy ranging from 0.2 to 2.5 minutes and are marginally consistent with a uniform period.

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.

HAT-P-7b: An extremely hot massive planet transiting a bright star in the Kepler field

We report on the latest discovery of the HATNet project: a very hot giant planet orbiting a bright ( -->V = 10.5) star with a small semimajor axis of -->a = 0.0377 ± 0.0005 AU. Ephemeris for the system is -->P = 2.2047299 ± 0.0000040 days, midtransit time -->E = 2,453,790.2593 ± 0.0010 (BJD). Based on the available spectroscopic data on the host star and photometry of the system, the planet has a mass of -->Mp = 1.78+ 0.08−0.05 MJ and radius of -->Rp = 1.36+ 0.20−0.09 RJ. The parent star is a slightly evolved F6 star with -->M = 1.47+ 0.08−0.05 M☉, R = 1.84+ 0.23−0.11 R☉, -->Teff = 6350 ± 80 K, and metallicity -->[ Fe/H ] = + 0.26 ± 0.08. The relatively hot and large host star, combined with the close orbit of the planet, yield a very high planetary irradiance of -->4.71+ 1.44−0.05 × 109 erg cm -->−2 s -->−1, which places the planet near the top of the pM class of irradiated planets as defined by Fortney et al. If as predicted by Fortney et al. the planet reradiates its absorbed energy before distributing it to the night side, the day-side temperature should be about -->2730+ 150−100 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.

HAT-P-13b,c: A transiting hot jupiter with a massive outer companion on an eccentric orbit

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 days. The outer planet HAT-P-13c orbits the star every P_2 = 428.5 ± 3.0 days with a 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 of 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.

A PHOTOMETRIC VARIABILITY SURVEY OF FIELD K AND M DWARF STARS WITH HATNet

Using light curves from the HATNet survey for transiting extrasolar planets we investigate the optical broadband photometric variability of a sample of 27, 560 field K and M dwarfs selected by color and proper motion (V – K 3.0, μ > 30 mas yr–1, plus additional cuts in J – H versus H – KS and on the reduced proper motion). We search the light curves for periodic variations and for large-amplitude, long-duration flare events. A total of 2120 stars exhibit potential variability, including 95 stars with eclipses and 60 stars with flares. Based on a visual inspection of these light curves and an automated blending classification, we select 1568 stars, including 78 eclipsing binaries (EBs), as secure variable star detections that are not obvious blends. We estimate that a further ~26% of these stars may be blends with fainter variables, though most of these blends are likely to be among the hotter stars in our sample. We find that only 38 of the 1568 stars, including five of the EBs, have previously been identified as variables or are blended with previously identified variables. One of the newly identified EBs is 1RXS J154727.5+450803, a known P = 3.55 day, late M-dwarf SB2 system, for which we derive preliminary estimates for the component masses and radii of M 1 = M 2 = 0.258 ± 0.008 M ☉ and R 1 = R 2 = 0.289 ± 0.007 R ☉. The radii of the component stars are larger than theoretical expectations if the system is older than ~200 Myr. The majority of the variables are heavily spotted BY Dra-type stars for which we determine rotation periods. Using this sample, we investigate the relations between period, color, age, and activity measures, including optical flaring, for K and M dwarfs, finding that many of the well-established relations for F, G, and K dwarfs continue into the M dwarf regime. We find that the fraction of stars that is variable with peak-to-peak amplitudes greater than 0.01 mag increases exponentially with the V – KS color such that approximately half of field dwarfs in the solar neighborhood with M 0.2 M ☉ are variable at this level. Our data hint at a change in the rotation-activity-age connection for stars with M 0.25 M ☉.

“TNOs are Cool”: a survey of the trans-Neptunian region - VI. Herschel/PACS observations and thermal modeling of 19 classical Kuiper belt objects

Trans-Neptunian objects (TNO) represent the leftovers of the formation of the Solar System. Their physical properties provide constraints to the models of formation and evolution of the various dynamical classes of objects in the outer Solar System. Based on a sample of 19 classical TNOs we determine radiometric sizes, geometric albedos and beaming parameters. Our sample is composed of both dynamically hot and cold classicals. We study the correlations of diameter and albedo of these two subsamples with each other and with orbital parameters, spectral slopes and colors. We have done three-band photometric observations with Herschel/PACS and we use a consistent method for data reduction and aperture photometry of this sample to obtain monochromatic flux densities at 70.0, 100.0 and 160.0 \mu m. Additionally, we use Spitzer/MIPS flux densities at 23.68 and 71.42 \mu m when available, and we present new Spitzer flux densities of eight targets. We derive diameters and albedos with the near-Earth asteroid thermal model (NEATM). As auxiliary data we use reexamined absolute visual magnitudes from the literature and data bases, part of which have been obtained by ground based programs in support of our Herschel key program. We have determined for the first time radiometric sizes and albedos of eight classical TNOs, and refined previous size and albedo estimates or limits of 11 other classicals. The new size estimates of 2002 MS4 and 120347 Salacia indicate that they are among the 10 largest TNOs known. Our new results confirm the recent findings that there are very diverse albedos among the classical TNOs and that cold classicals possess a high average albedo (0.17 +/- 0.04). Diameters of classical TNOs strongly correlate with orbital inclination in our sample. We also determine the bulk densities of six binary TNOs.

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.

DISCOVERY OF A TRANSITING PLANET AND EIGHT ECLIPSING BINARIES IN HATNet FIELD G205

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 v sin i = 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 MJ, radius Rp = 1.50 +0.08 −0.06 RJ, 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 M⊙ and R⋆ = 1.58 −0.06R⊙. Subject headings: planetary systems — stars: individual (HAT-P-8, GSC 02757-01152) techniques: spectroscopic

Properties of analytic transit light-curve models

In this paper a set of analytic formulae are presented with which the partial derivatives of the flux obscuration function can be evaluated – for planetary transits and eclipsing binaries – under the assumption of quadratic limb darkening. The knowledge of these partial derivatives is crucial for many of the data modeling algorithms and estimates of the light curve variations directly from the changes in the orbital elements. These derivatives can also be utilized to speed up some of the fitting methods. A gain of ∼ 8 in computing time can be achieved in the implementation of the Levenberg-Marquardt algorithm, relative to using numerical derivatives.