52,094 research outputs found
Thermodynamics of an attractive 2D Fermi gas
Thermodynamic properties of matter are conveniently expressed as functional
relations between variables known as equations of state. Here we experimentally
determine the compressibility, density and pressure equations of state for an
attractive 2D Fermi gas in the normal phase as a function of temperature and
interaction strength. In 2D, interacting gases exhibit qualitatively different
features to those found in 3D. This is evident in the normalized density
equation of state, which peaks at intermediate densities corresponding to the
crossover from classical to quantum behaviour.Comment: Contains minor revision
Strict Upper Limits on the Carbon-to-Oxygen Ratios of Eight Hot Jupiters from Self-Consistent Atmospheric Retrieval
The elemental compositions of hot Jupiters are informative relics of planet
formation that can help us answer long-standing questions regarding the origin
and formation of giant planets. Here, I present the main conclusions from a
comprehensive atmospheric retrieval survey of eight hot Jupiters with
detectable molecular absorption in their near-infrared transmission spectra. I
analyze the eight transmission spectra using the newly-developed,
self-consistent atmospheric retrieval framework, SCARLET. Unlike previous
methods, SCARLET combines the physical and chemical consistency of complex
atmospheric models with the statistical treatment of observational
uncertainties known from atmospheric retrieval techniques. I find that all
eight hot Jupiters consistently require carbon-to-oxygen ratios (C/O) below
0.9. The finding of C/O<0.9 is highly robust for HD209458b, WASP-12b, WASP-19b,
HAT-P-1b, and XO-1b. For HD189733b, WASP-17b, and WASP-43b, I find that the
published WFC3 transmission spectra favor C/O<0.9 at greater than 95%
confidence. I further show that the water abundances on all eight hot Jupiters
are consistent with solar composition. The relatively small depth of the
detected water absorption features is due to the presence of clouds, not due to
a low water abundance as previously suggested for HD209458b. The presence of a
thick cloud deck is inferred for HD209458b and WASP-12b. HD189733b may host a
similar cloud deck, rather than the previously suggested Rayleigh hazes, if
star spots affect the observed spectrum. The approach taken in SCARLET can be
regarded as a new pathway to interpreting spectral observations of planetary
atmospheres. In this work, including our prior knowledge of H-C-N-O chemistry
enables me to constrain the C/O ratio without detecting a single carbon-bearing
molecule.Comment: under review at ApJ; updated to account for recently announced
observations of WASP-12b and HD 209458
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