HAT-P-25b: a Hot-Jupiter Transiting a Moderately Faint G Star

We report the discovery of HAT-P-25b, a transiting extrasolar planet orbiting the V = 13.19 G5 dwarf star GSC 1788-01237, with a period P = 3.652836 +/- 0.000019 days, transit epoch Tc = 2455176.85173 +/- 0.00047 (BJD), and transit duration 0.1174 +/- 0.0017 days. The host star has mass of 1.01 +/- 0.03 M(Sun), radius of 0.96 +(0.05)-(0.04) R(Sun), effective temperature 5500 +/- 80 K, and metallicity [Fe/H] = +0.31 +/- 0.08. The planetary companion has a mass of 0.567 +/- 0.022 M(Jup), and radius of 1.190 +(0.081)-(0.056) R(Jup) yielding a mean density of 0.42 +/- 0.07 g cm-3. Comparing these observations with recent theoretical models, we find that HAT-P-25b is consistent with a hydrogen-helium dominated gas giant planet with negligible core mass and age 3.2 +/- 2.3 Gyr. The properties of HAT-P-25b support several previously observed correlations for planets in the mass range 0.4 < M < 0.7 M(Jup), including those of core mass vs. metallicity, planet radius vs. equilibrium temperature, and orbital period vs. planet mass. We also note that HAT-P-25b orbits the faintest star found by HATNet to have a transiting planet to date, and is one of only a very few number of planets discovered from the ground orbiting a star fainter than V = 13.0.Comment: 11 pages, 8 figures, 5 tables, submitted to Ap

Constraining planet structure from stellar chemistry: the cases of CoRoT-7, Kepler-10, and Kepler-93

We explore the possibility that the stellar relative abundances of different species can be used to constrain the bulk abundances of known transiting rocky planets. We use high resolution spectra to derive stellar parameters and chemical abundances for Fe, Si, Mg, O, and C in three stars hosting low mass, rocky planets: CoRoT-7, Kepler-10, and Kepler-93. These planets follow the same line along the mass-radius diagram, pointing toward a similar composition. The derived abundance ratios are compared with the solar values. With a simple stoichiometric model, we estimate the iron mass fraction in each planet, assuming stellar composition. We show that in all cases, the iron mass fraction inferred from the mass-radius relationship seems to be in good agreement with the iron abundance derived from the host star's photospheric composition. The results suggest that stellar abundances can be used to add constraints on the composition of orbiting rocky planets.Comment: A&A Letters, in pres

Self-Enhancement of Dynamic Gratings in Photogalvanic Crystals

We have developed a compact closed-form solution of the band transport model for high-contrast gratings in photogalvanic crystals. Our solution predicts the effect of the photoconductivity and the electric field grating enhancement due to the photogalvanic effect. We predict a pronounced dependence of the steady-state photogalvanic current on the contrast of the interference pattern and an increase of holographic storage time due to the enhancement of the photoconductivity grating contrast. In the high contrast limit and a large photogalvanic effect the refractive index grating will be shifted from the position of the intensity modulation pattern, contrary to the usually adopted model of unshifted gratings

HAT-P-27b: A hot Jupiter transiting a G star on a 3 day orbit

We report the discovery of HAT-P-27b, an exoplanet transiting the moderately bright G8 dwarf star GSC 0333-00351 (V=12.214). The orbital period is 3.039586 +/- 0.000012 d, the reference epoch of transit is 2455186.01879 +/- 0.00054 (BJD), and the transit duration is 0.0705 +/- 0.0019 d. The host star with its effective temperature 5300 +/- 90 K is somewhat cooler than the Sun, and is more metal-rich with a metallicity of +0.29 +/- 0.10. Its mass is 0.94 +/- 0.04 Msun and radius is 0.90 +/- 0.04 Rsun. For the planetary companion we determine a mass of 0.660 +/- 0.033 MJ and radius of 1.038 +0.077 -0.058 RJ. For the 30 known transiting exoplanets between 0.3 MJ and 0.8 MJ, a negative correlation between host star metallicity and planetary radius, and an additional dependence of planetary radius on equilibrium temperature are confirmed at a high level of statistical significance.Comment: Submitted to ApJ on 2011-01-18. 12 pages, 7 figures, 7 table

Two 'b's in the Beehive: The Discovery of the First Hot Jupiters in an Open Cluster

We present the discovery of two giant planets orbiting stars in Praesepe (also known as the Beehive Cluster). These are the first known hot Jupiters in an open cluster and the only planets known to orbit Sun-like, main-sequence stars in a cluster. The planets are detected from Doppler shifted radial velocities; line bisector spans and activity indices show no correlation with orbital phase, confirming the variations are caused by planetary companions. Pr0201b orbits a V=10.52 late F dwarf with a period of 4.4264 +/- 0.0070 days and has a minimum mass of 0.540 +/- 0.039 Mjup, and Pr0211b orbits a V=12.06 late G dwarf with a period of 2.1451 +/- 0.0012 days and has a minimum mass of 1.844 +/- 0.064 Mjup. The detection of 2 planets among 53 single members surveyed establishes a lower limit on the hot Jupiter frequency of 3.8 (+5.0)(-2.4) % in this metal-rich open cluster. Given the precisely known age of the cluster, this discovery also demonstrates that, in at least 2 cases, giant planet migration occurred within 600 Myr after formation. As we endeavor to learn more about the frequency and formation history of planets, environments with well-determined properties -- such as open clusters like Praesepe -- may provide essential clues to this end.Comment: 5 pages, 3 tables, 2 figures. Published in ApJ Letter