183 research outputs found
The Transit Light Curve Project. X. A Christmas Transit of HD 17156b
Photometry is presented of the Dec. 25, 2007 transit of HD 17156b, which has
the longest orbital period and highest orbital eccentricity of all the known
transiting exoplanets. New measurements of the stellar radial velocity are also
presented. All the data are combined and integrated with stellar-evolutionary
modeling to derive refined system parameters. The planet's mass and radius are
found to be 3.212_{-0.082}^{+0.069} Jupiter masses and 1.023_{-0.055}^{+0.070}
Jupiter radii. The corresponding stellar properties are 1.263_{-0.047}^{+0.035}
solar masses and 1.446_{-0.067}^{+0.099} solar radii. The planet is smaller by
1 sigma than a theoretical solar-composition gas giant with the same mass and
equilibrium temperature, a possible indication of heavy-element enrichment. The
midtransit time is measured to within 1 min, and shows no deviation from a
linear ephemeris (and therefore no evidence for orbital perturbations from
other planets). We provide ephemerides for future transits and superior
conjunctions. There is an 18% chance that the orbital plane is oriented close
enough to edge-on for secondary eclipses to occur at superior conjunction.
Observations of secondary eclipses would reveal the thermal emission spectrum
of a planet that experiences unusually large tidal heating and insolation
variations.Comment: To appear in ApJ [26 pages
Photometric Follow-up Observations of the Transiting Neptune-Mass Planet GJ 436b
This paper presents multi-band photometric follow-up observations of the
Neptune-mass transiting planet GJ 436b, consisting of 5 new ground-based
transit light curves obtained in May 2007. Together with one already published
light curve we have at hand a total of 6 light curves, spanning 29 days. The
analysis of the data yields an orbital period P = 2.64386+-0.00003 days,
mid-transit time T_c [HJD] =2454235.8355+-0.0001, planet mass M_p = 23.1+-0.9
M_{\earth} = 0.073+-0.003 M_{Jup}, planet radius R_p = 4.2+-0.2 R_{\earth} =
0.37+-0.01 R_{Jup} and stellar radius R_s = 0.45+-0.02 R_{\sun}. Our typical
precision for the mid transit timing for each transit is about 30 seconds. We
searched the data for a possible signature of a second planet in the system
through transit timing variations (TTV) and variation of the impact parameter.
The analysis could not rule out a small, of the order of a minute, TTV and a
long-term modulation of the impact parameter, of the order of +0.2 year^{-1}.Comment: V2: Replaced with accepted versio
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
Kepler Eclipsing Binary Stars. VI. Identification of Eclipsing Binaries in the K2 Campaign 0 Data-set
The original {\it Kepler} mission observed and characterized over 2400
eclipsing binaries in addition to its prolific exoplanet detections. Despite
the mechanical malfunction and subsequent non-recovery of two reaction wheels
used to stabilize the instrument, the {\it Kepler} satellite continues
collecting data in its repurposed {\it K2} mission surveying a series of fields
along the ecliptic plane. Here we present an analysis of the first full
baseline {\it K2} data release: the Campaign 0 data-set. In the 7761 light
curves, we have identified a total of 207 eclipsing binaries. Of these, 97 are
new discoveries that were not previously identified. Our pixel-level analysis
of these objects has also resulted in identification of several false positives
(observed targets contaminated by neighboring eclipsing binaries), as well as
the serendipitous discovery of two short period exoplanet candidates. We
provide catalog cross-matched source identifications, orbital periods,
morphologies and ephemerides for these eclipsing systems. We also describe the
incorporation of the K2 sample into the Kepler Eclipsing Binary
Catalog\footnote{\url{keplerebs.villanova.edu/k2}}, present spectroscopic
follow-up observations for a limited selection of nine systems, and discuss
prospects for upcoming {\it K2} campaigns.Comment: Accepted for publication in MNRAS. 51 pages [20 figures, 8 tables].
Results available online in the Kepler Eclipsing Binary Star Catalog
http://keplerebs.villanova.edu/k
Superior Vena Cava Defibrillator Coils Make Transvenous Lead Extraction More Challenging and Riskier
Kepler-16: A Transiting Circumbinary Planet
We report the detection of a planet whose orbit surrounds a pair of low-mass
stars. Data from the Kepler spacecraft reveal transits of the planet across
both stars, in addition to the mutual eclipses of the stars, giving precise
constraints on the absolute dimensions of all three bodies. The planet is
comparable to Saturn in mass and size, and is on a nearly circular 229-day
orbit around its two parent stars. The eclipsing stars are 20% and 69% as
massive as the sun, and have an eccentric 41-day orbit. The motions of all
three bodies are confined to within 0.5 degree of a single plane, suggesting
that the planet formed within a circumbinary disk.Comment: Science, in press; for supplemental material see
http://www.sciencemag.org/content/suppl/2011/09/14/333.6049.1602.DC1/1210923.Doyle.SOM.pd
Transit Timing Observations from Kepler: III. Confirmation of 4 Multiple Planet Systems by a Fourier-Domain Study of Anti-correlated Transit Timing Variations
We present a method to confirm the planetary nature of objects in systems
with multiple transiting exoplanet candidates. This method involves a
Fourier-Domain analysis of the deviations in the transit times from a constant
period that result from dynamical interactions within the system. The
combination of observed anti-correlations in the transit times and mass
constraints from dynamical stability allow us to claim the discovery of four
planetary systems Kepler-25, Kepler-26, Kepler-27, and Kepler-28, containing
eight planets and one additional planet candidate.Comment: Accepted to MNRA
Planet Occurrence within 0.25 AU of Solar-type Stars from Kepler
We report the distribution of planets as a function of planet radius (R_p),
orbital period (P), and stellar effective temperature (Teff) for P < 50 day
orbits around GK stars. These results are based on the 1,235 planets (formally
"planet candidates") from the Kepler mission that include a nearly complete set
of detected planets as small as 2 Earth radii (Re). For each of the 156,000
target stars we assess the detectability of planets as a function of R_p and P.
We also correct for the geometric probability of transit, R*/a. We consider
first stars within the "solar subset" having Teff = 4100-6100 K, logg =
4.0-4.9, and Kepler magnitude Kp < 15 mag. We include only those stars having
noise low enough to permit detection of planets down to 2 Re. We count planets
in small domains of R_p and P and divide by the included target stars to
calculate planet occurrence in each domain. Occurrence of planets varies by
more than three orders of magnitude and increases substantially down to the
smallest radius (2 Re) and out to the longest orbital period (50 days, ~0.25
AU) in our study. For P < 50 days, the radius distribution is given by a power
law, df/dlogR= k R^\alpha. This rapid increase in planet occurrence with
decreasing planet size agrees with core-accretion, but disagrees with
population synthesis models. We fit occurrence as a function of P to a power
law model with an exponential cutoff below a critical period P_0. For smaller
planets, P_0 has larger values, suggesting that the "parking distance" for
migrating planets moves outward with decreasing planet size. We also measured
planet occurrence over Teff = 3600-7100 K, spanning M0 to F2 dwarfs. The
occurrence of 2-4 Re planets in the Kepler field increases with decreasing
Teff, making these small planets seven times more abundant around cool stars
than the hottest stars in our sample. [abridged]Comment: Submitted to ApJ, 22 pages, 10 figure
Accretion of Planetary Material onto Host Stars
Accretion of planetary material onto host stars may occur throughout a star's
life. Especially prone to accretion, extrasolar planets in short-period orbits,
while relatively rare, constitute a significant fraction of the known
population, and these planets are subject to dynamical and atmospheric
influences that can drive significant mass loss. Theoretical models frame
expectations regarding the rates and extent of this planetary accretion. For
instance, tidal interactions between planets and stars may drive complete
orbital decay during the main sequence. Many planets that survive their stars'
main sequence lifetime will still be engulfed when the host stars become red
giant stars. There is some observational evidence supporting these predictions,
such as a dearth of close-in planets around fast stellar rotators, which is
consistent with tidal spin-up and planet accretion. There remains no clear
chemical evidence for pollution of the atmospheres of main sequence or red
giant stars by planetary materials, but a wealth of evidence points to active
accretion by white dwarfs. In this article, we review the current understanding
of accretion of planetary material, from the pre- to the post-main sequence and
beyond. The review begins with the astrophysical framework for that process and
then considers accretion during various phases of a host star's life, during
which the details of accretion vary, and the observational evidence for
accretion during these phases.Comment: 18 pages, 5 figures (with some redacted), invited revie
Masses, radii, and orbits of small Kepler planets : The transition from gaseous to rocky planets
We report on the masses, sizes, and orbits of the planets orbiting 22 Kepler stars. There are 49 planet candidates around these stars, including 42 detected through transits and 7 revealed by precise Doppler measurements of the host stars. Based on an analysis of the Kepler brightness measurements, along with high-resolution imaging and spectroscopy, Doppler spectroscopy, and (for 11 stars) asteroseismology, we establish low false-positive probabilities (FPPs) for all of the transiting planets (41 of 42 have an FPP under 1%), and we constrain their sizes and masses. Most of the transiting planets are smaller than three times the size of Earth. For 16 planets, the Doppler signal was securely detected, providing a direct measurement of the planet's mass. For the other 26 planets we provide either marginal mass measurements or upper limits to their masses and densities; in many cases we can rule out a rocky composition. We identify six planets with densities above 5 g cm-3, suggesting a mostly rocky interior for them. Indeed, the only planets that are compatible with a purely rocky composition are smaller than 2 R ⊕. Larger planets evidently contain a larger fraction of low-density material (H, He, and H2O).Peer reviewedFinal Accepted Versio
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