627 research outputs found
New Analysis Indicates No Thermal Inversion in the Atmosphere of HD 209458b
An important focus of exoplanet research is the determination of the
atmospheric temperature structure of strongly irradiated gas giant planets, or
hot Jupiters. HD 209458b is the prototypical exoplanet for atmospheric thermal
inversions, but this assertion does not take into account recently obtained
data or newer data reduction techniques. We re-examine this claim by
investigating all publicly available Spitzer Space Telescope secondary-eclipse
photometric data of HD 209458b and performing a self-consistent analysis. We
employ data reduction techniques that minimize stellar centroid variations,
apply sophisticated models to known Spitzer systematics, and account for
time-correlated noise in the data. We derive new secondary-eclipse depths of
0.119 +/- 0.007%, 0.123 +/- 0.006%, 0.134 +/- 0.035%, and 0.215 +/- 0.008% in
the 3.6, 4.5, 5.8, and 8.0 micron bandpasses, respectively. We feed these
results into a Bayesian atmospheric retrieval analysis and determine that it is
unnecessary to invoke a thermal inversion to explain our secondary-eclipse
depths. The data are well-fitted by a temperature model that decreases
monotonically between pressure levels of 1 and 0.01 bars. We conclude that
there is no evidence for a thermal inversion in the atmosphere of HD 209458b.Comment: 8 pages, 5 figures; accepted for publication in Ap
A Search for Water in the Atmosphere of HAT-P-26b Using LDSS-3C
The characterization of a physically-diverse set of transiting exoplanets is
an important and necessary step towards establishing the physical properties
linked to the production of obscuring clouds or hazes. It is those planets with
identifiable spectroscopic features that can most effectively enhance our
understanding of atmospheric chemistry and metallicity. The newly-commissioned
LDSS-3C instrument on Magellan provides enhanced sensitivity and suppressed
fringing in the red optical, thus advancing the search for the spectroscopic
signature of water in exoplanetary atmospheres from the ground. Using data
acquired by LDSS-3C and the Spitzer Space Telescope, we search for evidence of
water vapor in the transmission spectrum of the Neptune-mass planet HAT-P-26b.
Our measured spectrum is best explained by the presence of water vapor, a lack
of potassium, and either a high-metallicity, cloud-free atmosphere or a
solar-metallicity atmosphere with a cloud deck at ~10 mbar. The emergence of
multi-scale-height spectral features in our data suggests that future
observations at higher precision could break this degeneracy and reveal the
planet's atmospheric chemical abundances. We also update HAT-P-26b's transit
ephemeris, t_0 = 2455304.65218(25) BJD_TDB, and orbital period, p =
4.2345023(7) days.Comment: 9 pages, 8 figures, Accepted for publication in Ap
Thermal Emission and Albedo Spectra of Super Earths with Flat Transmission Spectra
Planets larger than Earth and smaller than Neptune are some of the most
numerous in the galaxy, but observational efforts to understand this population
have proved challenging because optically thick clouds or hazes at high
altitudes obscure molecular features (Kreidberg et al. 2014b). We present
models of super Earths that include thick clouds and hazes and predict their
transmission, thermal emission, and reflected light spectra. Very thick, lofted
clouds of salts or sulfides in high metallicity (1000x solar) atmospheres
create featureless transmission spectra in the near-infrared. Photochemical
hazes with a range of particle sizes also create featureless transmission
spectra at lower metallicities. Cloudy thermal emission spectra have muted
features more like blackbodies, and hazy thermal emission spectra have emission
features caused by an inversion layer at altitudes where the haze forms. Close
analysis of reflected light from warm (~400-800 K) planets can distinguish
cloudy spectra, which have moderate albedos (0.05-0.20), from hazy models,
which are very dark (0.0-0.03). Reflected light spectra of cold planets (~200
K) accessible to a space-based visible light coronagraph will have high albedos
and large molecular features that will allow them to be more easily
characterized than the warmer transiting planets. We suggest a number of
complementary observations to characterize this population of planets,
including transmission spectra of hot (>1000 K) targets, thermal emission
spectra of warm targets using the James Webb Space Telescope (JWST), high
spectral resolution (R~10^5) observations of cloudy targets, and reflected
light spectral observations of directly-imaged cold targets. Despite the dearth
of features observed in super Earth transmission spectra to date, different
observations will provide rich diagnostics of their atmospheres.Comment: 23 pages, 23 figures. Revised for publication in The Astrophysical
Journa
Forward and Inverse Modeling of the Emission and Transmission Spectrum of GJ 436b: Investigating Metal Enrichment, Tidal Heating, and Clouds
The Neptune-mass GJ 436b is one of the most-studied transiting exoplanets
with repeated measurements of both its thermal emission and transmission
spectra. We build on previous studies to answer outstanding questions about
this planet, including its potentially high metallicity and tidal heating of
its interior. We present new observations of GJ 436b's thermal emission at 3.6
and 4.5 micron, which reduce uncertainties in estimates of GJ 436b's flux at
those wavelengths and demonstrate consistency between Spitzer observations
spanning more than 7 years. We analyze the Spitzer thermal emission photometry
and Hubble WFC3 transmission spectrum in tandem. We use a powerful dual-pronged
modeling approach, comparing these data to both self-consistent and retrieval
models. We vary the metallicity, intrinsic luminosity from tidal heating,
disequilibrium chemistry, and heat redistribution. We also study the effect of
clouds and photochemical hazes on the spectra, but do not find strong evidence
for either. The self-consistent and retrieval modeling combine to suggest that
GJ 436b has a high atmospheric metallicity, with best fits at or above several
hundred times solar metallicity, tidal heating warming its interior with
best-fit intrinsic effective effective temperatures around 300--350 K, and
disequilibrium chemistry. High metal-enrichments (>600x solar) can only occur
from the accretion of rocky, rather than icy, material. Assuming Tint~300--350
K, we find that Q'~2x10^5--10^6, larger than Neptune's Q', and implying a long
tidal circularization timescale for the planet's orbit. We suggest that
Neptune-mass planets may be a more diverse class than previously imagined, with
metal-enhancements potentially spanning several orders of magnitude, to perhaps
over 1000x solar metallicity. High fidelity observations with instruments like
JWST will be critical for characterizing this diversity.Comment: 15 pages, 18 figures. Revised for publication in Ap
Catastrophic thinking about pain: A critical appraisal highlighting the importance of the social context and balance
Numerous research studies have shown that endorsing a catastrophic interpretation about pain is associated with deleterious outcomes, such as higher levels of distress, pain intensity and disability for the person in pain. The fear-avoidance model has been found to be useful in explaining these associations by stressing that heightened feelings of distress and behaviour aimed at reducing or avoiding pain might be adaptive in an acute pain context but can become maladaptive when the pain becomes chronic. Pain is rarely a private event and the communal coping model underscores that the heightened pain expression in people endorsing catastrophic thoughts about pain could have a social, communicative function of eliciting empathic responses in others. However, these models are not all-encompassing. In particular, neither of the models takes into account the growing evidence indicating that catastrophic thinking in observers can also impact their emotional experience and behaviour in response to the other’s pain. Moreover, the context of multiple goals in which pain and pain behaviour occurs is largely ignored in both models. In this article we present an integrative perspective on catastrophic thinking that takes into account the social system and interplay between different goals people in pain and observers might pursue (e.g., school/work performance, leisure, social engagement). Specifically, this integrative perspective stresses the importance of considering the bidirectional influence between catastrophic thoughts in the person experiencing pain and observers. Furthermore, the importance of balance between pain-relief and other important goals as well as in the level of catastrophic thoughts in understanding the maladaptive influence of catastrophic thinking will be underlined. Clinical implications and future research directions of this integrated perspective are discussed
Brown Dwarf Retrievals on FIRE!: Atmospheric Constraints and Lessons Learned from High Signal-to-Noise Medium Resolution Spectroscopy of a T9 Dwarf
Brown dwarf spectra offer vital testbeds for our understanding of the
chemical and physical processes that sculpt substellar atmospheres. Recently,
atmospheric retrieval approaches have been applied to a number of
low-resolution (R~100) spectra of brown dwarfs, yielding constraints on the
abundances of chemical species and temperature structures of these atmospheres.
Medium-resolution (R~1e3) spectra of brown dwarfs offer significant additional
insight, as molecular features are more easily disentangled from one another
and the thermal structure of the upper atmosphere is more readily probed. We
present results from a GPU-based retrieval analysis of a high signal-to-noise,
medium-resolution (R~6000) FIRE spectrum from 0.85-2.5 microns of a T9 dwarf.
At 60x higher spectral resolution than previous brown dwarf retrievals, a
number of novel challenges arise. We examine the strong effect of different
opacity sources on our retrieved constraints, in particular for CH4.
Furthermore, we find that flaws in the data such as errors from order stitching
can greatly bias our results. We compare these results to those obtained for a
R~100 spectrum of the same object, revealing how constraints on atmospheric
abundances and temperatures improve by an order of magnitude or more (depending
on the species) with increased spectral resolution. In particular, we precisely
constrain the abundance of H2S, which is undetectable at lower spectral
resolution. While these medium-resolution retrievals offer the potential of
precise, stellar-like constraints on atmospheric abundances (~0.02 dex), our
retrieved radius is unphysically small (R~0.50 R), indicating lingering
shortcomings with our modeling framework. This work is an initial investigation
into brown dwarf retrievals at medium spectral resolution, offering guidance
for future ground-based studies and JWST observations of substellar objects.Comment: 28 pages, 28 figures, 4 tables. Accepted to Ap
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