982 research outputs found
Understanding WASP-12b
The orbital period of the hot Jupiter WASP-12b is apparently changing. We
study whether this reflects orbital decay due to tidal dissipation in the star,
or apsidal precession of a slightly eccentric orbit. In the latter case, a
third body or other perturbation would be needed to sustain the eccentricity
against tidal dissipation in the planet itself. We have analyzed several such
perturbative scenarios, but none is satisfactory. Most likely therefore, the
orbit really is decaying. If this is due to a dynamical tide, then WASP-12
should be a subgiant without a convective core as Weinberg et al. (2017) have
suggested. We have modeled the star with the MESA code. While no model fits all
of the observational constraints, including the luminosity implied by the GAIA
DR2 distance, main-sequence models are less discrepant than subgiant ones.Comment: 12 pages, 4 figure, submitted to MNRA
Observations of the D/H ratio in Methane in the atmosphere of Saturn's moon, Titan - where did the Saturnian system form?
The details of the Solar system's formation are still heavily debated.
Questions remain about the formation locations of the giant planets, and the
degree to which volatile material was mixed throughout the proto-planetary
system. One diagnostic which offers great promise in helping to unravel the
history of planet formation is the study of the level of deuteration in various
Solar system bodies. For example, the D/H ratio of methane in the atmosphere of
Titan can be used as a diagnostic of the initial conditions of the solar nebula
within the region of giant planet formation, and can help us to determine where
Titan (and, by extension, the Saturnian system) accreted its volatile material.
The level of Titanian deuteration also has implications for both the sources
and long term evolution of Titan's atmospheric composition. We present the
results of observations taken in the 1.58 microns window using the NIFS
spectrometer on the Gemini telescope, and model our data using the VSTAR
line--by--line transfer model, which yields a D/H ratio for Titan's atmosphere
of 143+/-16) x 10^{-6} [1]. We are currently in the process of modeling the
Gemini high resolution GNIRS spectra using new sets of line parameters derived
for methane in the region between 1.2-1.7 microns [2].Comment: 12 pages, 4 figures, Accepted for publication in proceedings of the
Australian Space Science Conference 201
It\u27s the War Power, Again
Reviewing Fred I. Greenstein, Presidents and the Dissolution of the Union: Leadership Style from Polk to Lincoln; Stephen M. Griffin, Long Wars and the Constitution; Andrew J. Polsky, Elusive Victories: The American Presidency at War; and Mariah Zeisberg, War Powers: The Politics of Constitutional Authority
Empirical line lists and absorption cross sections for methane at high temperature
Hot methane is found in many "cool" sub-stellar astronomical sources
including brown dwarfs and exoplanets, as well as in combustion environments on
Earth. We report on the first high-resolution laboratory absorption spectra of
hot methane at temperatures up to 1200 K. Our observations are compared to the
latest theoretical spectral predictions and recent brown dwarf spectra. The
expectation that millions of weak absorption lines combine to form a continuum,
not seen at room temperature, is confirmed. Our high-resolution transmittance
spectra account for both the emission and absorption of methane at elevated
temperatures. From these spectra, we obtain an empirical line list and
continuum that is able to account for the absorption of methane in high
temperature environments at both high and low resolution. Great advances have
recently been made in the theoretical prediction of hot methane, and our
experimental measurements highlight the progress made and the problems that
still remain.Comment: 9 pages, 5 figures and 3 tables. For associated online data see
http://dx.doi.org/10.1088/0004-637X/813/1/1
Examining the broadband emission spectrum of WASP-19b: A new z band eclipse detection
WASP-19b is one of the most irradiated hot-Jupiters known. Its secondary
eclipse is the deepest of all transiting planets, and has been measured in
multiple optical and infrared bands. We obtained a z band eclipse observation,
with measured depth of 0.080 +/- 0.029 %, using the 2m Faulkes Telescope South,
that is consistent with the results of previous observations. We combine our
measurement of the z band eclipse with previous observations to explore
atmosphere models of WASP-19b that are consistent with the its broadband
spectrum. We use the VSTAR radiative transfer code to examine the effect of
varying pressure-temperature profiles and C/O abundance ratios on the emission
spectrum of the planet. We find models with super-solar carbon enrichment best
match the observations, consistent with previous model retrieval studies. We
also include upper atmosphere haze as another dimension in the interpretation
of exoplanet emission spectra, and find that particles <0.5 micron in size are
unlikely to be present in WASP-19b.Comment: 10 pages, 8 figures, 2 tables, accepted for publication in Ap
In deciding how to exercise power via Executive Orders, US Presidents appeal to Congress only if it can be united
Recent months have seen Republican attacks on President Obama, accusing him of presiding over an ‘imperial presidency’, but to what extent do presidents actually operate completely outside of Congress’ powers? By looking at 5,000 executive orders issued by presidents over the last 80 years Jeremy D. Bailey and Brandon Rottinghaus find that when issuing these orders, presidents tend to appeal back to Congress when the majority party is strong, and act unilaterally when the majority is weak and divided
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