G. Á. Bakos

Obliquities of hot Jupiter host stars: Evidence for tidal interactions and primordial misalignments

We provide evidence that the obliquities of stars with close-in giant planets were initially nearly random, and that the low obliquities that are often observed are a consequence of star-planet tidal interactions. The evidence is based on 14 new measurements of the Rossiter-McLaughlin effect (for the systems HAT-P-6, HAT-P-7, HAT-P-16, HAT-P-24, HAT-P-32, HAT-P-34, WASP-12, WASP-16, WASP-18, WASP-19, WASP-26, WASP-31, Gl 436, and Kepler-8), as well as a critical review of previous observations. The low-obliquity (well-aligned) systems are those for which the expected tidal timescale is short, and likewise the high-obliquity (misaligned and retrograde) systems are those for which the expected timescale is long. At face value, this finding indicates that the origin of hot Jupiters involves dynamical interactions like planet-planet interactions or the Kozai effect that tilt their orbits rather than inspiraling due to interaction with a protoplanetary disk. We discuss the status of this hypothesis and the observations that are needed for a more definitive conclusion.

Wide‐Field Millimagnitude Photometry with the HAT: A Tool for Extrasolar Planet Detection

ABSTRACT We discuss the system requirements for obtaining millimagnitude photometric precision over a wide field using small‐aperture, short focal length telescope systems such as those being developed by a number of research groups to search for transiting extrasolar planets. We describe a Hungarian Automated Telescope (HAT) system, which attempts to meet these requirements. The attainable precision of HAT has been significantly improved by a technique in which the telescope is made to execute small pointing steps during each exposure so as to broaden the effective point‐spread function (PSF) of the system to a value more compatible with the pixel size of our CCD detector. Experiments during a preliminary survey (spring 2003) of two star fields with the HAT‐5 instrument allowed us to optimize the HAT photometric precision using this method of PSF broadening; in this way we have been able to achieve a precision as good as 2 mmag on brighter stars. We briefly describe development of a network of longitudin...

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.

Transiting Exoplanet Survey Satellite (TESS)

The Transiting Exoplanet Survey Satellite (TESS ) will search for planets transiting bright and nearby stars. TESS has been selected by NASA for launch in 2017 as an Astrophysics Explorer mission. The spacecraft will be placed into a highly elliptical 13.7-day orbit around the Earth. During its two-year mission, TESS will employ four wide-field optical CCD cameras to monitor at least 200,000 main-sequence dwarf stars with IC (approximately less than) 13 for temporary drops in brightness caused by planetary transits. Each star will be observed for an interval ranging from one month to one year, depending mainly on the stars ecliptic latitude. The longest observing intervals will be for stars near the ecliptic poles, which are the optimal locations for follow-up observations with the James Webb Space Telescope. Brightness measurements of preselected target stars will be recorded every 2 min, and full frame images will be recorded every 30 min. TESS stars will be 10-100 times brighter than those surveyed by the pioneering Kepler mission. This will make TESS planets easier to characterize with follow-up observations. TESS is expected to find more than a thousand planets smaller than Neptune, including dozens that are comparable in size to the Earth. Public data releases will occur every four months, inviting immediate community-wide efforts to study the new planets. The TESS legacy will be a catalog of the nearest and brightest stars hosting transiting planets, which will endure as highly favorable targets for detailed investigations.

Transiting Exoplanet Survey Satellite

Abstract. The Transiting Exoplanet Survey Satellite (TESS) will search for planets transiting bright and nearby stars. TESS has been selected by NASA for launch in 2017 as an Astrophysics Explorer mission. The spacecraft will be placed into a highly elliptical 13.7-day orbit around the Earth. During its 2-year mission, TESS will employ four wide-field optical charge-coupled device cameras to monitor at least 200,000 main-sequence dwarf stars with IC≈4−13 for temporary drops in brightness caused by planetary transits. Each star will be observed for an interval ranging from 1 month to 1 year, depending mainly on the star’s ecliptic latitude. The longest observing intervals will be for stars near the ecliptic poles, which are the optimal locations for follow-up observations with the James Webb Space Telescope. Brightness measurements of preselected target stars will be recorded every 2 min, and full frame images will be recorded every 30 min. TESS stars will be 10 to 100 times brighter than those surveyed by the pioneering Kepler mission. This will make TESS planets easier to characterize with follow-up observations. TESS is expected to find more than a thousand planets smaller than Neptune, including dozens that are comparable in size to the Earth. Public data releases will occur every 4 months, inviting immediate community-wide efforts to study the new planets. The TESS legacy will be a catalog of the nearest and brightest stars hosting transiting planets, which will endure as highly favorable targets for detailed investigations.

A trend filtering algorithm for wide-field variability surveys

We show that various systematics related to certain instrumental effects and data reduction anomalies in wide-field variability surveys can be efficiently corrected by a trend filtering algorithm (TFA) applied to the photometric time-series produced by standard data pipelines. Statistical tests, performed on the data base of the HAT Network project, show that by the application of this filtering method the cumulative detection probability of periodic transits increases by up to 0.4 for variables brighter than 11 mag, with a trend of increasing efficiency toward brighter magnitudes. We also show that the TFA can be used for the reconstruction of periodic signals by iteratively filtering out systematic distortions.

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-16b: A 4 MJ planet transiting a bright star on an eccentric orbit

We report the discovery of HAT-P-16b, a transiting extrasolar planet orbiting the V = 10.8 mag F8 dwarf GSC 2792-01700, with a period P = 2.775960 ± 0.000003 days, transit epoch T_c = 2455027.59293 ± 0.00031 (BJD^(10)), and transit duration 0.1276 ± 0.0013 days. The host star has a mass of 1.22 ± 0.04 M ⊙, radius of 1.24 ± 0.05 R ⊙ , effective temperature 6158 ± 80 K, and metallicity [Fe/H] = +0.17 ± 0.08. The planetary companion has a mass of 4.193 ± 0.094 M _J and radius of 1.289 ± 0.066 R _J, yielding a mean density of 2.42 ± 0.35 g cm^(–3). Comparing these observed characteristics with recent theoretical models, we find that HAT-P-16b is consistent with a 1 Gyr H/He-dominated gas giant planet. HAT-P-16b resides in a sparsely populated region of the mass-radius diagram and has a non-zero eccentricity of e = 0.036 with a significance of 10σ.