962 research outputs found
The Detectability of Rocky Planet Surface and Atmosphere Composition with JWST: The Case of LHS 3844b
The spectroscopic characterization of terrestrial exoplanets will be made
possible for the first time with JWST. One challenge to characterizing such
planets is that it is not known a priori whether they possess optically thick
atmospheres or even any atmospheres altogether. But this challenge also
presents an opportunity - the potential to detect the surface of an extrasolar
world. This study explores the feasibility of characterizing the atmosphere and
surface of a terrestrial exoplanet with JWST, taking LHS 3844b as a test case
because it is the highest signal-to-noise rocky thermal emission target among
planets that are cool enough to have non-molten surfaces. We model the
planetary emission, including the spectral signal of both atmosphere and
surface, and we explore all scenarios that are consistent with the existing
Spitzer 4.5 m measurement of LHS 3844b from Kreidberg et al. (2019). In
summary, we find a range of plausible surfaces and atmospheres that are within
3 of the observation - less reflective metal-rich, iron oxidized and
basaltic compositions are allowed, and atmospheres are restricted to a maximum
thickness of 1 bar, if near-infrared absorbers at 100 ppm are
included. We further make predictions on the observability of surfaces and
atmospheres, perform a Bayesian retrieval analysis on simulated JWST data and
find that a small number, ~3, of eclipse observations should suffice to
differentiate between surface and atmospheric features. However, the surface
signal may make it harder to place precise constraints on the abundance of
atmospheric species and may even falsely induce a weak HO detection.Comment: 33 pages, 20 figure
Bethe-Salpeter equation and a nonperturbative quark-gluon vertex
A Ward-Takahashi identity preserving Bethe-Salpeter kernel can always be
calculated explicitly from a dressed-quark-gluon vertex whose diagrammatic
content is enumerable. We illustrate that fact using a vertex obtained via the
complete resummation of dressed-gluon ladders. While this vertex is planar, the
vertex-consistent kernel is nonplanar and that is true for any dressed vertex.
In an exemplifying model the rainbow-ladder truncation of the gap and
Bethe-Salpeter equations yields many results; e.g., pi- and rho-meson masses,
that are changed little by including higher-order corrections. Repulsion
generated by nonplanar diagrams in the vertex-consistent Bethe-Salpeter kernel
for quark-quark scattering is sufficient to guarantee that diquark bound states
do not exist.Comment: 16 pages, 12 figures, REVTEX
Determinants of the Use of a Diabetes Risk-Screening Test
A study was designed to investigate why people do or do not make use of a diabetes risk test developed to facilitate the timely diagnosis of diabetes. Data were collected using a web-based questionnaire, which was based on the Health Belief Model, the Theory of Planned Behavior, and the Threatening Medical Situations Inventory. People who had and had not used the risk test were recruited to complete the survey. The sample consisted of 205 respondents: 44% who had used the test and 56% who had not. The hypothesized relationships between the dependent variable (diabetes risk test use) and the determinants used in this study were tested using logistic regression analysis. Only two significant predictors of diabetes risk test use were found: gender and barriers. More women than men use the test. Furthermore, people who experience more barriers will be less inclined to use the test. The contribution of diabetes screening tests fully depends on people’s willingness to use them. To optimize the usage of such test, it is especially important to address the barriers as perceived by the public. Two types of barriers must be addressed: practical barriers (time to take the test, fear of complexity of the test), and consequential barriers (fear of the disease and treatment, uncertainties about where to go in the case of an increased risk of diabetes)
Effects of morphine and nalorphine upon tooth pulp thresholds of dogs in the alert and drowsy state
The alteration of tooth pulp thresholds of dogs with chronically implanted electrodes was determined in the awake and drowsy states after morphine and nalorphine. The elevation in tooth pulp threshold was significantly greater after morphine than during the alert or drowsy state of the animal. Nalorphine antagonized this effect of morphine.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46329/1/213_2004_Article_BF00441191.pd
A rocky planet transiting a nearby low-mass star
M-dwarf stars -- hydrogen-burning stars that are smaller than 60 per cent of
the size of the Sun -- are the most common class of star in our Galaxy and
outnumber Sun-like stars by a ratio of 12:1. Recent results have shown that M
dwarfs host Earth-sized planets in great numbers: the average number of M-dwarf
planets that are between 0.5 to 1.5 times the size of Earth is at least 1.4 per
star. The nearest such planets known to transit their star are 39 parsecs away,
too distant for detailed follow-up observations to measure the planetary masses
or to study their atmospheres. Here we report observations of GJ 1132b, a
planet with a size of 1.2 Earth radii that is transiting a small star 12
parsecs away. Our Doppler mass measurement of GJ 1132b yields a density
consistent with an Earth-like bulk composition, similar to the compositions of
the six known exoplanets with masses less than six times that of the Earth and
precisely measured densities. Receiving 19 times more stellar radiation than
the Earth, the planet is too hot to be habitable but is cool enough to support
a substantial atmosphere, one that has probably been considerably depleted of
hydrogen. Because the host star is nearby and only 21 per cent the radius of
the Sun, existing and upcoming telescopes will be able to observe the
composition and dynamics of the planetary atmosphere.Comment: Published in Nature on 12 November 2015, available at
http://dx.doi.org/10.1038/nature15762. This is the authors' version of the
manuscrip
Exoplanet phase curves: observations and theory
Phase curves are the best technique to probe the three dimensional structure
of exoplanets' atmospheres. In this chapter we first review current exoplanets
phase curve observations and the particular challenges they face. We then
describe the different physical mechanisms shaping the atmospheric phase curves
of highly irradiated tidally locked exoplanets. Finally, we discuss the
potential for future missions to further advance our understanding of these new
worlds.Comment: Fig.5 has been updated. Table 1 and corresponding figures have been
updated with new values for WASP-103b and WASP-18b. Contains a table
sumarizing phase curve observation
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