3,238 research outputs found
A Framework for Quantifying the Degeneracies of Exoplanet Interior Compositions
Several transiting super-Earths are expected to be discovered in the coming
few years. While tools to model the interior structure of transiting planets
exist, inferences about the composition are fraught with ambiguities. We
present a framework to quantify how much we can robustly infer about
super-Earth and Neptune-size exoplanet interiors from radius and mass
measurements. We introduce quaternary diagrams to illustrate the range of
possible interior compositions for planets with four layers (iron core,
silicate mantles, water layers, and H/He envelopes). We apply our model to
CoRoT-7b, GJ 436b, and HAT-P-11b. Interpretation of planets with H/He envelopes
is limited by the model uncertainty in the interior temperature, while for
CoRoT-7b observational uncertainties dominate. We further find that our planet
interior model sharpens the observational constraints on CoRoT-7b's mass and
radius, assuming the planet does not contain significant amounts of water or
gas. We show that the strength of the limits that can be placed on a
super-Earth's composition depends on the planet's density; for similar
observational uncertainties, high-density super-Mercuries allow the tightest
composition constraints. Finally, we describe how techniques from Bayesian
statistics can be used to take into account in a formal way the combined
contributions of both theoretical and observational uncertainties to
ambiguities in a planet's interior composition. On the whole, with only a mass
and radius measurement an exact interior composition cannot be inferred for an
exoplanet because the problem is highly underconstrained. Detailed quantitative
ranges of plausible compositions, however, can be found.Comment: 20 pages, 10 figures, published in Ap
On the Unique Solution of Planet and Star Parameters from an Extrasolar Planet Transit Light Curve
There is a unique solution of the planet and star parameters from a planet
transit light curve with two or more transits if the planet has a circular
orbit and the light curve is observed in a band pass where limb darkening is
negligible. The existence of this unique solution is very useful for current
planet transit surveys for several reasons. First, there is an analytic
solution that allows a quick parameter estimate, in particular of Rp. Second,
the stellar density can be uniquely derived from the transit light curve alone.
The stellar density can be used to immediately rule out a giant star (and hence
a much larger than planetary companion) and can also be used to put an upper
limit on the stellar and planet radius even considering slightly evolved stars.
Third, the presence of an additional fully blended star that contaminates an
eclipsing system to mimic a planet transit can be largely ruled out from the
transit light curve given a spectral type for the central star. Fourth, the
period can be estimated from a single-transit light curve and a measured
spectral type. All of these applications can be used to select the best planet
transit candidates for mass determination by radial velocity follow-up. To use
these applications in practice, the photometric precision and time sampling of
the light curve must be high (better than 0.005 mag precision and 5 minute time
sampling).Comment: 26 pages incl. 11 figs, submitted to Ap
Investigating the role of SUMOylation of Mitochondrial Fission Factor in Mitochondrial Dynamics
Induced two-photon decay of the 2s level and the rate of cosmological hydrogen recombination
Induced emission due to the presence of soft CMB photons slightly increases
the two-photon decay rate of the 2s level of hydrogen defining the rate of
cosmological recombination. This correspondingly changes the degree of
ionization, the visibility function and the resulting primordial temperature
anisotropies and polarization of the CMB on the percent level. These changes
exceed the precision of the widely used CMBFAST and CAMB codes by more than one
order of magnitude and can be easily taken into account.Comment: 5 pages, 5 figure, accepted by Astronomy and Astrophysic
On the Period Distribution of Close-In Extrasolar Giant Planets
Transit (TR) surveys for extrasolar planets have recently uncovered a
population of ``very hot Jupiters,'' planets with orbital periods of P< 3 d. At
first sight this may seem surprising, given that radial velocity (RV) surveys
have found a dearth of such planets, despite the fact that their sensitivity
increases with decreasing P. We examine the confrontation between RV and TR
survey results, paying particular attention to selection biases that favor
short-period planets in transit surveys. We demonstrate that, when such biases
and small-number statistics are properly taken into account, the period
distribution of planets found by RV and TR surveys are consistent at better
than the 1-sigma level. This consistency holds for a large range of reasonable
assumptions. In other words, there are not enough planets detected to robustly
conclude that the RV and TR short-period planet results are inconsistent.
Assuming a logarithmic distribution of periods, we find that the relative
frequency of very hot Jupiters (VHJ: P=1-3 d) to hot Jupiters (HJ: P=3-9 d) is
10-20%. Given an absolute frequency of HJ of ~1%, this implies that
approximately one star in ~500-1000 has a VHJ. We also note that VHJ and HJ
appear to be distinct in terms of their upper mass limit. We discuss the
implications of our results for planetary migration theories, as well as
present and future TR and RV surveys.Comment: 11 pages, 4 figures, 2 tables. Minor changes. Accepted to ApJ, to
appear in the April 20, 2005 issue (v623
Infrared Observations During the Secondary Eclipse of HD 209458 b II. Strong Limits on the Infrared Spectrum Near 2.2 Microns
We report observations of the transiting extrasolar planet, HD 209458 b,
designed to detect the secondary eclipse. We employ the method of `occultation
spectroscopy', which searches in combined light (star and planet) for the
disappearance and reappearance of weak infrared spectral features due to the
planet as it passes behind the star and reappears. Our observations cover two
predicted secondary eclipse events, and we obtained 1036 individual spectra of
the HD 209458 system using the SpeX instrument at the NASA IRTF in September
2001. Our spectra extend from 1.9 to 4.2 microns with a spectral resolution of
1500. We have searched for a continuum peak near 2.2 microns (caused by CO and
water absorption bands), as predicted by some models of the planetary
atmosphere to be approximately 6E-4 of the stellar flux, but no such peak is
detected at a level of about 3E-4 of the stellar flux. Our results represent
the strongest limits on the infrared spectrum of the planet to date and carry
significant implications for understanding the planetary atmosphere. In
particular, some models that assume the stellar irradiation is re-radiated
entirely on the sub-stellar hemisphere predict a flux peak inconsistent with
our observations. Several physical mechanisms can improve agreement with our
observations, including the re-distribution of heat by global circulation, a
nearly isothermal atmosphere, and/or the presence of a high cloud.Comment: Accepted to the Astrophysical Journal 17 pages, 6 figure
Cosmological hydrogen recombination: Lyn line feedback and continuum escape
We compute the corrections to the cosmological hydrogen recombination history
due to delayed feedback of Lyman-series photons and the escape in the
Lyman-continuum. The former process is expected to slightly delay
recombination, while the latter should allow the medium to recombine a bit
faster. It is shown that the subsequent feedback of released Lyman-n photons on
the lower lying Lyman-(n-1) transitions yields a maximal correction of DN_e/N_e
0.22% at z~ 1050. Including only Lyman-\beta feedback onto the Lyman-\alpha
transition, accounts for most of the effect. We find corrections to the cosmic
microwave background TT and EE power spectra \change{with typical peak to peak
amplitude |DC^{TT}_l/C^{TT}_l|~0.15% and |\Delta C^{EE}_l/C^{EE}_l|~0.36% at
l<~3000. The escape in the Lyman-continuum and feedback of Lyman-\alpha photons
on the photoionization rate of the second shell lead to modifications of the
ionization history which are very small (less than |DN_e/N_e|~few x 10^{-6}).Comment: 5+epsilon pages, 7 figures, accepted versio
Pacific Ocean Forcing and Atmospheric Variability are the Dominant Causes of Spatially Widespread Droughts in the Contiguous United States
The contributions of oceanic and atmospheric variability to spatially widespread summer droughts in the contiguous United States (hereafter, pan-CONUS droughts) are investigated using 16-member ensembles of the Community Climate Model version 3 (CCM3) forced with observed sea surface temperatures (SSTs) from 1856 to 2012. The employed SST forcing fields are either (i) global or restricted to the (ii) tropical Pacific or (iii) tropical Atlantic to isolate the impacts of these two ocean regions on pan-CONUS droughts. Model results show that SST forcing of pan-CONUS droughts originates almost entirely from the tropical Pacific because of atmospheric highs from the northern Pacific to eastern North America established by La Nia conditions, with little contribution from the tropical Atlantic. Notably, in all three model configurations, internal atmospheric variability influences pan-CONUS drought occurrence by as much or more than the ocean forcing and can alone cause pan-CONUS droughts by establishing a dominant high centered over the US montane West. Similar results are found for the Community Atmosphere Model version 5 (CAM5). Model results are compared to the observational record, which supports model-inferred contributions to pan-CONUS droughts from La Nias and internal atmospheric variability. While there may be an additional association with warm Atlantic SSTs in the observational record, this association is ambiguous due to the limited number of observed pan-CONUS. The ambiguity thus opens the possibility that the observational results are limited by sampling over the 20th-century and not at odds with the suggested dominance of Pacific Ocean forcing in the model ensembles
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