2,955 research outputs found
Modelling of the 10-micrometer natural laser emission from the mesospheres of Mars and Venus
The NLTE radiative transfer problem is solved to obtain the 00 deg 1 vibrational state population. This model successfully reproduces the existing center-to-limb observations, although higher spatial resolution observations are needed for a definitive test. The model also predicts total fluxes which are close to the observed values. The strength of the emission is predicted to be closely related to the instantaneous near-IR solar heating rate
Marginalising instrument systematics in HST WFC3 transit lightcurves
Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) infrared observations
at 1.1-1.7m probe primarily the HO absorption band at 1.4m, and
has provided low resolution transmission spectra for a wide range of
exoplanets. We present the application of marginalisation based on Gibson
(2014) to analyse exoplanet transit lightcurves obtained from HST WFC3, to
better determine important transit parameters such as R/R, important
for accurate detections of HO. We approximate the evidence, often referred
to as the marginal likelihood, for a grid of systematic models using the Akaike
Information Criterion (AIC). We then calculate the evidence-based weight
assigned to each systematic model and use the information from all tested
models to calculate the final marginalised transit parameters for both the
band-integrated, and spectroscopic lightcurves to construct the transmission
spectrum. We find that a majority of the highest weight models contain a
correction for a linear trend in time, as well as corrections related to HST
orbital phase. We additionally test the dependence on the shift in spectral
wavelength position over the course of the observations and find that
spectroscopic wavelength shifts , best describe the
associated systematic in the spectroscopic lightcurves for most targets, while
fast scan rate observations of bright targets require an additional level of
processing to produce a robust transmission spectrum. The use of
marginalisation allows for transparent interpretation and understanding of the
instrument and the impact of each systematic evaluated statistically for each
dataset, expanding the ability to make true and comprehensive comparisons
between exoplanet atmospheres.Comment: 19 pages, 13 figures, 8 tables, Accepted to Ap
Sorption of Perfluorochemicals to Granular Activated Carbon in the Presence of Ultrasound
Perfluorochemicals (PFCs) are emerging pollutants of increasing public health and environmental concern due to their worldwide distribution, environmental persistence, and bioaccumulation potential. Activated carbon adsorption is an effective method to remove PFCs from water. Herein, we report on the sorption of four PFCs: perfluorooctane sulfonate (PFOS), perfluorooctanoate (PFOA), perfluorobutane sulfonate (PFBS), and perfluorobutanoate (PFBA), from deionized water (MQ) and landfill groundwater (GW) by granular activated carbon (GAC) in the absence and presence of 20 kHz ultrasound. In all cases, the adsorption kinetics were found to be well-represented by a pseudosecond-order model, with maximum monolayer sorption capacity and initial sorption rate values following the orders q_(e)^(PFOS) > q_(e)^(PFOA) > q_(e)^(PFBS) > q_(e)^(PFBA) and v_(0)^(PFOS) > v_(0)^(PFBS) > v_(0)^(PFOA) > v_(0)^(PFBA), respectively. The equilibrium adsorption was quantified by the BET multilayer absorption isotherm, and the monolayer sorption capacity increased with increasing PFC chain length: q_(m)^(PFOS) > q_(m)^(PFOA) > q_(m)^(PFBS) > q_(m)^(PFBA). The equilibrium PFC sorption constants, q_e and q_m, and the sorption kinetic constants, v_0 and k_2, were greater in Milli-Q water than in landfill groundwater with or without pretreatment, indicating competition for sorption sites by natural and cocontaminant groundwater organics. Ultrasonic irradiation significantly increased the PFC−GAC sorption kinetics, 250−900%, and slightly increased the extent of PFC equilibrium adsorption, 5−50%. The ultrasonic PFC−GAC sorption kinetics enhancement increased with increasing PFC chain length, suggesting ultrasound acts to increase the PFC diffusion rate into GAC nanopores
Detecting Water on Super-Earths Using JAVST
Nearby lower train sequence stars host a class of planets known as Super-Earths, that have no analog in our own solar system. Super-Earths are rocky and/or icy planets with masses up to about 10 Earth masses, They are expected to host atmospheres generated by a number of processes including accretion of chondritic material. Water vapor should be a common constituent of super-Earth atmospheres, and may be detectable in transiting super-Earths using transmission spectroscopy during primar y eclipse, and emission spectroscopy at secondary eclipse. I will discuss the prospects for super-Earth atmospheric measurements using JWST
Theoretical Spectral Models of the Planet HD 209458b with a Thermal Inversion and Water Emission Bands
We find that a theoretical fit to all the HD 209458b data at secondary
eclipse requires that the dayside atmosphere of HD 209458b have a thermal
inversion and a stratosphere. This inversion is caused by the capture of
optical stellar flux by an absorber of uncertain origin that resides at
altitude. One consequence of stratospheric heating and temperature inversion is
the flipping of water absorption features into emission features from the near-
to the mid-infrared and we see evidence of such a water emission feature in the
recent HD 209458b IRAC data of Knutson et al. In addition, an upper-atmosphere
optical absorber may help explain both the weaker-than-expected Na D feature
seen in transit and the fact that the transit radius at 24 m is smaller
than the corresponding radius in the optical. Moreover, it may be a factor in
why HD 209458b's optical transit radius is as large as it is. We speculate on
the nature of this absorber and the planets whose atmospheres may, or may not,
be affected by its presence.Comment: Accepted to the Astrophysical Journal Letters on August 28, 2007, six
pages in emulateapj forma
On the Method to Infer an Atmosphere on a Tidally-Locked Super Earth Exoplanet and Upper limits to GJ 876d
We develop a method to infer or rule out the presence of an atmosphere on a
tidally-locked hot super Earth. The question of atmosphere retention is a
fundamental one, especially for planets orbiting M stars due to the star's
long-duration active phase and corresponding potential for stellar-induced
planetary atmospheric escape and erosion. Tidally-locked planets with no
atmosphere are expected to show a Lambertian-like thermal phase curve, causing
the combined light of the planet-star system to vary with planet orbital phase.
We report Spitzer 8 micron IRAC observations of GJ 876 taken over 32
continuous hours and reaching a relative photometric precision of 3.9e-04 per
point for 25.6 s time sampling. This translates to a 3 sigma limit of 5.13e-05
on a planet thermal phase curve amplitude. Despite the almost photon-noise
limited data, we are unable to conclusively infer the presence of an atmosphere
or rule one out on the non-transiting short-period super Earth GJ 876d. The
limiting factor in our observations was the miniscule, monotonic photometric
variation of the slightly active host M star, because the partial sine wave due
to the planet has a component in common with the stellar linear trend. The
proposed method is nevertheless very promising for transiting hot super Earths
with the James Webb Space Telescope and is critical for establishing
observational constraints for atmospheric escape.Comment: Published in Ap
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