3,244 research outputs found
Toward a homogeneous set of transiting planet parameters
With 40 or more transiting exoplanets now known, the time is ripe to seek
patterns and correlations among their observed properties, which may give
important insights into planet formation, structure, and evolution. This task
is made difficult by the widely different methodologies that have been applied
to measure their properties in individual cases. Furthermore, in many systems
our knowledge of the planet properties is limited by the knowledge of the
properties of the parent stars. To address these difficulties we have
undertaken the first comprehensive analysis of the data for 23 transiting
planets using a uniform methodology. We revisit several of the recently
proposed correlations, and find new ones involving the metallicity of the
parent stars.Comment: 4 pages including figures. To appear in Proceedings of IAU Symposium
253, "Transiting Planets", May 2008, Cambridge, M
Conceptual design study of a six-man solid electrolyte system for oxygen reclamation
A six-man solid electrolyte oxygen regeneration system (SEORS) that will produce 12.5 lbs/day of oxygen has been designed. The SEORS will simultaneously electrolyze both carbon dioxide and water vapor and be suitable for coupling with a carbon dioxide concentration system of either molecular sieve, solid amine or hydrogen depolarized electrochemical type. The total system will occupy approximately 19 cu ft (34.5 in. x .26 in. x 36 in. high) and will weigh approximately 500 pounds. It is estimated that the total electrical power required will be 1783 watts. The system consists of three major components; electrolyzer, hydrogen diffuser, and carbon deposition reactor. There are 108 electrolysis stacks of 12 cells each in the electrolyzer. Only 2/3 of the 108 stacks will be operated at a time; the remainder will be held in reserve. The design calls for 96 palladium membranes for hydrogen removal to give 60 percent redundancy. Four carbon deposition reactors are employed. The iron catalyst tube in each reactor weighs 7.1 lb and 100 percent redundancy is allowed
The Apparently Decaying Orbit of WASP-12
We present new transit and occultation times for the hot Jupiter WASP-12b.
The data are compatible with a constant period derivative:
ms yr and Myr. However, it is difficult to tell whether
we have observed orbital decay, or a portion of a 14-year apsidal precession
cycle. If interpreted as decay, the star's tidal quality parameter is
about . If interpreted as precession, the planet's Love number is
. Orbital decay appears to be the more parsimonious model: it is
favored by despite having two fewer free parameters than the
precession model. The decay model implies that WASP-12 was discovered within
the final 0.2% of its existence, which is an unlikely coincidence but
harmonizes with independent evidence that the planet is nearing disruption.
Precession does not invoke any temporal coincidence, but does require some
mechanism to maintain an eccentricity of 0.002 in the face of rapid
tidal circularization. To distinguish unequivocally between decay and
precession will probably require a few more years of monitoring. Particularly
helpful will be occultation timing in 2019 and thereafter.Comment: 10 pages [AAS journals, in press, note added in proof
A Precise Estimate of the Radius of HD 149026b
We present Spitzer 8 micron transit observations of the extrasolar planet
system HD 149026. At this wavelength, transit light curves are weakly affected
by stellar limb-darkening, allowing for a simpler and more accurate
determination of planetary parameters. We measure a planet-star radius ratio of
R_p/R_s = 0.05158 +/- 0.00077, and in combination with ground-based data and
independent constraints on the stellar mass and radius, we derive an orbital
inclination of i = 85.4 +0.9/-0.8 deg. and a planet radius of 0.755 +/- 0.040
Jupiter radii. These measurements further support models in which the planet is
greatly enriched in heavy elements.Comment: To appear in the Proceedings of the 253rd IAU Symposium: "Transiting
Planets", May 2008, Cambridge, M
The Transit Light Curve project. XIV. Confirmation of Anomalous Radii for the Exoplanets TrES-4b, HAT-P-3b, and WASP-12b
We present transit photometry of three exoplanets, TrES-4b, HAT-P-3b, and
WASP-12b, allowing for refined estimates of the systems' parameters. TrES-4b
and WASP-12b were confirmed to be "bloated" planets, with radii of 1.706 +/-
0.056 R_Jup and 1.736 +/- 0.092 R_Jup, respectively. These planets are too
large to be explained with standard models of gas giant planets. In contrast,
HAT-P-3b has a radius of 0.827 +/- 0.055 R_Jup, smaller than a pure
hydrogen-helium planet and indicative of a highly metal-enriched composition.
Analyses of the transit timings revealed no significant departures from strict
periodicity. For TrES-4, our relatively recent observations allow for
improvement in the orbital ephemerides, which is useful for planning future
observations.Comment: AJ, in press [11 pages]; corrected error in distance to WASP-1
HAT-P-7: A Retrograde or Polar Orbit, and a Third Body
We show that the exoplanet HAT-P-7b has an extremely tilted orbit, with a
true angle of at least 86 degrees with respect to its parent star's equatorial
plane, and a strong possibility of retrograde motion. We also report evidence
for an additional planet or companion star. The evidence for the unparalleled
orbit and the third body is based on precise observations of the star's
apparent radial velocity. The anomalous radial velocity due to rotation (the
Rossiter-McLaughlin effect) was found to be a blueshift during the first half
of the transit and a redshift during the second half, an inversion of the usual
pattern, implying that the angle between the sky-projected orbital and stellar
angular momentum vectors is 182.5 +/- 9.4 degreees. The third body is
implicated by excess radial-velocity variation of the host star over 2 yr. Some
possible explanations for the tilted orbit are a close encounter with another
planet, the Kozai effect, and resonant capture by an inward-migrating outer
planet.Comment: ApJ Letters, in press [7 pages
Obliquity Tides on Hot Jupiters
Obliquity tides are a potentially important source of heat for extrasolar
planets on close-in orbits. Although tidal dissipation will usually reduce the
obliquity to zero, a nonzero obliquity can persist if the planet is in a
Cassini state, a resonance between spin precession and orbital precession.
Obliquity tides might be the cause of the anomalously large size of the
transiting planet HD 209458b.Comment: To appear in ApJ Letters [9 pages, 2 figures
Five New Transits of the Super-Neptune HD 149026
We present new photometry of HD 149026 spanning five transits of its
"super-Neptune" planet. In combination with previous data, we improve upon the
determination of the planet-to-star radius ratio: R_p/R_star =
0.0491^{+0.0018}_{-0.0005}. We find the planetary radius to be 0.71 +/- 0.05
R_Jup, in accordance with previous theoretical models invoking a high metal
abundance for the planet. The limiting error is the uncertainty in the stellar
radius. Although we find agreement among four different ways of estimating the
stellar radius, the uncertainty remains at 7%. We also present a refined
transit ephemeris and a constraint on the orbital eccentricity and argument of
pericenter, e cos(omega) = -0.0014 +/- 0.0012, based on the measured interval
between primary and secondary transits.Comment: To appear in ApJ [19 pages
Relative photometry of HAT-P-1b occultations
We present HST STIS observations of two occultations of the transiting
exoplanet HAT-P-1b. By measuring the planet to star flux ratio near opposition,
we constrain the geometric albedo of the planet, which is strongly linked to
its atmospheric temperature gradient. An advantage of HAT-P-1 as a target is
its binary companion ADS 16402 A, which provides an excellent photometric
reference, simplifying the usual steps in removing instrumental artifacts from
HST time-series photometry. We find that without this reference star, we would
need to detrend the lightcurve with the time of the exposures as well as the
first three powers of HST orbital phase, and this would introduce a strong bias
in the results for the albedo. However, with this reference star, we only need
to detrend the data with the time of the exposures to achieve the same
per-point scatter, therefore we can avoid most of the bias associated with
detrending. Our final result is a 2 sigma upper limit of 0.64 for the geometric
albedo of HAT-P-1b between 577 and 947 nm.Comment: 8 pages, 2 figures, 3 table
The Transit Light Curve Project. XII. Six Transits of the Exoplanet XO-2b
We present photometry of six transits of the exoplanet XO-2b. By combining
the light-curve analysis with theoretical isochrones to determine the stellar
properties, we find the planetary radius to be 0.996 +0.031/-0.018 rjup and the
planetary mass to be 0.565 +/- 0.054 mjup. These results are consistent with
those reported previously, and are also consistent with theoretical models for
gas giant planets. The mid-transit times are accurate to within 1 min and are
consistent with a constant period. However, the period we derive differs by 2.5
sigma from the previously published period. More data are needed to tell
whether the period is actually variable (as it would be in the presence of an
additional body) or if the timing errors have been underestimated.Comment: Accepted for publication in AJ. 20 pages, 3 tables, 4 figure
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