2,967 research outputs found
Warm Ice Giant GJ 3470b. I. A Flat Transmission Spectrum Indicates a Hazy, Low-methane, and/or Metal-rich Atmosphere
We report our spectroscopic investigation of the transiting ice giant GJ
3470b's atmospheric transmission, and the first results of extrasolar planet
observations from the new Keck/MOSFIRE spectrograph. We measure a planet/star
radius ratio of Rp/Rs = 0.0789 +/- 0.0020 in a bandpass from 2.09-2.36 micron
and in six narrower bands across this wavelength range. When combined with
existing broadband photometry, these measurements rule out cloud-free
atmospheres in chemical equilibrium assuming either solar abundances (5.4 sigma
confidence) or a moderate level of metal enrichment (50x solar abundances, 3.8
sigma), confirming previous results that such models are not representative for
cool, low-mass, externally irradiated extrasolar planets. Current measurements
are consistent with a flat transmission spectrum, which suggests that the
atmosphere is explained by high-altitude clouds and haze, disequilibrium
chemistry, unexpected abundance patterns, or the atmosphere is extremely
metal-rich (>200x solar). Because GJ 3470b's low bulk density sets an upper
limit on the planet's atmospheric enrichment of <300x solar, the atmospheric
mean molecular weight must be <9. Thus, if the atmosphere is cloud-free its
spectral features should be detectable with future observations. Transit
observations at shorter wavelengths will provide the best opportunity to
discriminate between plausible scenarios. We obtained optical spectroscopy with
the GMOS spectrograph, but these observations exhibit large systematic
uncertainties owing to thin, persistent cirrus conditions. Finally, we also
provide the first detailed look at the steps necessary for well-calibrated
MOSFIRE observations, and provide advice for future observations with this
instrument.Comment: Accepted to A&A. Light curves will be available at CDS (or download
arXiv tarball
Re-evaluating Hot Jupiter WASP-12b: An Update
The hot Jupiter WASP-12b is one of the largest, hottest, and best-studied
extrasolar planets. We revisit our recent analysis of WASP-12b's emission
spectrum in light of near-infrared spectroscopic measurements which have been
claimed to support either a hydride-dominated or carbon-rich atmospheric
composition. We show that this new spectrum is still consistent with a
featureless blackbody, indicating a nearly isothermal photosphere on the
planet's day side. Thus the ensemble of occultation measurements for WASP-12b
is still insufficient to constrain the planet's atmospheric composition.Comment: 4 pages, 2 figures. Submitted as Proceedings to the ROPACS meeting
"Hot Planets and Cool Stars" (Nov. 2012, Garching),
http://www.mpe.mpg.de/events/ropacs-2012/Home.htm
Acute aortic dissection in a young healthy athlete with androgenic anabolic steroid use: A case report
Background: Acute aortic dissection can occur at the time of intense physical exertion in strength-trained athletes like weight lifters, bodybuilders, throwers, and wrestlers. Rapid rise in blood pressure and history of hypertension are the most common causes of aortic dissection in athletes. It is a very tragic event because of its high mortality rate of about 32% in young patients. We report a case of aortic dissection in a young weightlifter with a history of anabolic steroid usage with an extensive intimal tear of the aorta at Sino tubular junction and arch. All athletes must be assessed for predisposing factors for aortic dissection, and all patients should be encouraged to undergo appropriate diagnostic studies, like echocardiography and blood pressure monitoring while weightlifting to recognize possible predisposing factors for aortic dissection. Athletes who do have a problem should be encouraged to avoid or limit their exercise or activity by their cardiologist. It is vital that this disastrous event be prevented in young people. In conclusion, although a rare occurrence, AD should be considered in symptomatic patients with any family history of early cardiac deaths, a history suggestive of a connective tissue disorder (that is, multiple joint surgeries) or who practice weightlifting
High Resolution, Differential, Near-infrared Transmission Spectroscopy of GJ 1214b
The nearby star GJ 1214 hosts a planet intermediate in radius and mass
between Earth and Neptune, resulting in some uncertainty as to its nature. We
have observed this planet, GJ 1214b, during transit with the high-resolution,
near-infrared NIRSPEC spectrograph on the Keck II telescope, in order to
characterize the planet's atmosphere. By cross-correlating the spectral changes
through transit with a suite of theoretical atmosphere models, we search for
variations associated with absorption in the planet atmosphere. Our
observations are sufficient to rule out tested model atmospheres with
wavelength-dependent transit depth variations >5e-4 over the wavelength range
2.1 - 2.4 micron. Our sensitivity is limited by variable slit loss and telluric
transmission effects.
We find no positive signatures but successfully rule out a number of
plausible atmospheric models, including the default assumption of a gaseous,
H-dominated atmosphere in chemical equilibrium. Such an atmosphere can be made
consistent if the absorption due to methane is reduced. Clouds can also render
such an atmosphere consistent with our observations, but only if they lie
higher in the atmosphere than indicated by recent optical and infrared
measurements.
When taken in concert with constraints from other groups, our results support
a consensus model in which the atmosphere of GJ 1214b contains significant H
and He, but where methane is depleted. If this depletion is the result of
photochemical processes, it may also produce a haze that suppresses spectral
features in the optical.Comment: 32 pages, 15 figures, preprint, accepted to ApJ, responded to
referee's comments. Comments welcom
A Review on Different Control Techniques Used for Pitch Control of Horizontal Axis Wind Turbine
In wind turbine technology, the pitch control mechanism of blades is a very important factor for the efficient power output of a wind turbine. Various control techniques can be implemented for pitch control. This paper deals with the study and review of different control methodologies used by the researchers and engineers to control the pitch angle of the blades of a horizontal axis wind turbine to optimize the power in low rated wind speed. This paper involves the study of PI, PID, Fuzzy logic control, Sliding mode control and Adaptive control methodologies
Grain Physics and Rosseland Mean Opacities
Tables of mean opacities are often used to compute the transfer of radiation
in a variety of astrophysical simulations from stellar evolution models to
proto-planetary disks. Often tables, such as Ferguson et al. (2005), are
computed with a predetermined set of physical assumptions that may or may not
be valid for a specific application. This paper explores the effects of several
assumptions of grain physics on the Rosseland mean opacity in an oxygen rich
environment. We find that changing the distribution of grain sizes, either the
power-law exponent or the shape of the distribution, has a marginal effect on
the total mean opacity. We also explore the difference in the mean opacity
between solid homogenous grains and grains that are porous or conglomorations
of several species. Changing the amount of grain opacity included in the mean
by assuming a grain-to-gas ratio significantly affects the mean opacity, but in
a predictable way.Comment: 19 pages, 6 figures, accepted for publication in Ap
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