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|WASP-1: a lithium- and metal-rich star with an oversized planet|
In this paper, we present our results of a comprehensive spectroscopicanalysis of WASP-1, the host star to the exoplanet WASP-1b. We deriveTeff = 6110 +/- 45 K, log g = 4.28 +/- 0.15 and [M/H] = 0.23+/- 0.08, and also a high abundance of lithium, logn(Li) = 2.91 +/-0.05. These parameters suggest an age for the system of 1-3 Gyr and astellar mass of 1.25 -1.35 Msolar. This means that WASP-1 hasproperties very similar to those of HD 149026, the host star for thehighest density planet yet detected. Moreover, their planets orbit atcomparable distances and receive comparable irradiating fluxes fromtheir host stars. However, despite the similarity of WASP-1 with HD149026, their planets have strongly different densities. This suggeststhat gas giant planet density is not a simple function of host-starmetallicity or of radiation environment at ages of ~2 Gyr.Based on observations made with the Nordic Optical Telescope.E-mail: Eric.Stempels@st-andrews.ac.uk
|Possible Solutions to the Radius Anomalies of Transiting Giant Planets|
We calculate the theoretical evolution of the radii of all 14 of theknown transiting extrasolar giant planets (EGPs) for a variety ofassumptions concerning atmospheric opacity, dense inner core masses, andpossible internal power sources. We incorporate the effects of stellarirradiation and customize such effects for each EGP and star. Lookingcollectively at the family as a whole, we find that there are in facttwo radius anomalies to be explained. Not only are the radii of a subsetof the known transiting EGPs larger than expected from previous theory,but many of the other objects are smaller than the default theory wouldallow. We suggest that the larger EGPs can be explained by invokingenhanced atmospheric opacities that naturally retain internal heat. Thisexplanation might obviate the necessity for an extra internal powersource. We explain the smaller radii by the presence in perhaps all theknown transiting EGPs of dense cores, such as have been inferred forSaturn and Jupiter. Importantly, we derive a rough correlation betweenthe masses of our ``best-fit'' cores and the stellar metallicity thatseems to buttress the core-accretion model of their formation. Althoughmany caveats and uncertainties remain, the resulting comprehensivetheory that incorporates enhanced-opacity atmospheres and dense cores isin reasonable accord with all the current structural data for the knowntransiting giant planets.
|Millimagnitude Photometry for Transiting Extrasolar Planetary Candidates. II. Transits of OGLE-TR-113-b in the Optical and Near-IR|
We present precise V- and Ks-band transit photometry for theplanetary host star OGLE-TR-113. Using the Ks-bandphotometry, we confirm the dwarf nature of OGLE-TR-113 and obtain newestimates for its effective temperature, distance, and reddening. Weemploy the V-band photometry to obtain planetary and orbit parametersfrom the transit fit, a=0.0232+/-0.0038 AU, orbital periodP=1.4324752+/-0.0000015 day, i=86.7-90, and Rp=1.09+/-0.09RJ. These values are in excellent agreement with previousworks. Assuming a mass Mp=1.32+/-0.19 MJ for theplanet, we obtain its mean density ρ=1.26+/-0.50 g cm-3,also in agreement with previous works. The transit observed in theKs band has a larger scatter, and we find its amplitude to beconsistent with that in the V band. In this way, we find an independentconfirmation of the planetary nature of OGLE-TR-113b.Based on observations collected with the Very Large Telescope at ParanalObservatory (J. M. F. and D. M. visiting observers) and at the ESO NewTechnology Telescope at La Silla Observatory (S. R., F. P., and D. M.visiting observers) for the ESO Programs 075.C-0427, 075.B-0414, and076.C-0122.
|Photometric follow-up of the transiting planet WASP-1b|
We report on photometric follow-up of the recently discovered transitingplanet WASP-1b. We observed two transits with the Wise Observatory 1-mtelescope, and used a variant of the Eclipsing Binary Orbit Program(EBOP) code together with the Sys-Rem detrending approach to fit thelight curve. Assuming a stellar mass of 1.15Msolar, wederived a planetary radius of Rp = 1.40 +/- 0.06RJand mass of Mp = 0.87 +/- 0.07MJ. An uncertaintyof 15 per cent in the stellar mass results in an additional systematicuncertainty of 5 per cent in the planetary radius and of 10 per cent inplanetary mass. Our observations yielded a slightly better ephemeris forthe centre of the transit: Tc[HJD] = (2454013.3127 +/-0.0004) + Ntr(2.51996 +/- 0.00002). The new planet is aninflated, low-density planet, similar to HAT-P-1b and HD209458b.
|Precise Radius Estimates for the Exoplanets WASP-1b and WASP-2b|
We present precise z-band photometric time series spanning times oftransit of the two exoplanets recently discovered by the SuperWASPcollaboration. We find planetary radii of 1.44+/-0.08 and 1.04+/-0.06RJ for WASP-1b and WASP-2b, respectively. These errorestimates include both random errors in the photometry and also theuncertainty in the stellar masses. Our results are 5 times more precisethan the values derived from the discovery data alone. Our measurementof the radius of WASP-2b agrees with previously published models of hotJupiters that include both a 20 M⊕ core of solidmaterial and the effects of stellar insolation. In contrast, we findthat the models cannot account for the large size of WASP-1b, even ifthe planet has no core. Thus, we add WASP-1b to the growing list of hotJupiters that are larger than expected. This suggests that ``inflated''hot Jupiters are more common than previously thought and that anypurported explanations involving highly unusual circumstances aredisfavored.
|WASP-1b and WASP-2b: two new transiting exoplanets detected with SuperWASP and SOPHIE|
We have detected low-amplitude radial-velocity variations in two stars,USNO-B1.0 1219-0005465 (GSC 02265-00107 = WASP-1) and USNO-B1.00964-0543604 (GSC 00522-01199 = WASP-2). Both stars were identified asbeing likely host stars of transiting exoplanets in the 2004 SuperWASPwide-field transit survey. Using the newly commissioned radial-velocityspectrograph SOPHIE at the Observatoire de Haute-Provence, we found thatboth objects exhibit reflex orbital radial-velocity variations withamplitudes characteristic of planetary-mass companions and in-phase withthe photometric orbits. Line-bisector studies rule out faint blendedbinaries as the cause of either the radial-velocity variations or thetransits. We perform preliminary spectral analyses of the host stars,which together with their radial-velocity variations and fits to thetransit light curves yield estimates of the planetary masses and radii.WASP-1b and WASP-2b have orbital periods of 2.52 and 2.15 d,respectively. Given mass estimates for their F7V and K1V primaries, wederive planet masses 0.80-0.98 and 0.81-0.95 times that of Jupiter,respectively. WASP-1b appears to have an inflated radius of at least1.33 RJup, whereas WASP-2b has a radius in the range0.65-1.26 RJup.
|The Transit Light Curve Project. III. Tres Transits of TrES-1|
We present z-band photometry of three consecutive transits of theexoplanet TrES-1, with an accuracy of 0.15% and a cadence of 40 s. Weimprove on estimates of the system parameters, finding in particularthat the planetary radius is 1.081+/-0.029 RJup and thestellar radius is 0.811+/-0.020 Rsolar. The uncertaintiesinclude both the statistical error and the systematic error arising fromthe uncertainty in the stellar mass. The transit times are determined towithin about 15 s and allow us to refine the estimate of the meanorbital period: P=3.0300737+/-0.0000026 days. We find no evidence forstarspots or other irregularities that have been previously reported.
|The SuperWASP wide-field exoplanetary transit survey: candidates from fields 23 h < RA < 03 h|
Photometric transit surveys promise to complement the currently knownsample of extra-solar planets (ESPs) by providing additional informationon the planets and especially their radii. Here, we present ESPcandidates from one such survey called, the Wide Angle Search forPlanets (WASP) obtained with the SuperWASP wide-field imaging system.Observations were taken with SuperWASP North located in La Palma duringthe 2004 April to October observing season. The data cover fieldsbetween 23 and 03 h in RA at declinations above +12. This amounts toover ~400000 stars with V magnitudes 8-13.5. For the stars brighter than12.5, we achieve better than 1 per cent photometric precision. Here, wepresent 41 sources with low-amplitude variability between ~1 and 10mmag, from which we select 12 with periods between 1.2 and 4.4 d as themost promising ESP candidates. We discuss the properties of these ESPcandidates, the expected fraction of transits recovered for our sampleand implications for the frequency and detection of hot-Jupiters.
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