6,920 research outputs found
Thermal Processes Governing Hot-Jupiter Radii
There have been many proposed explanations for the larger-than-expected radii
of some transiting hot Jupiters, including either stellar or orbital energy
deposition deep in the atmosphere or deep in the interior. In this paper, we
explore the important influences on hot-Jupiter radius evolution of (i)
additional heat sources in the high atmosphere, the deep atmosphere, and deep
in the convective interior; (ii) consistent cooling of the deep interior
through the planetary dayside, nightside, and poles; (iii) the degree of heat
redistribution to the nightside; and (iv) the presence of an upper atmosphere
absorber inferred to produce anomalously hot upper atmospheres and inversions
in some close-in giant planets. In particular, we compare the radius expansion
effects of atmospheric and deep-interior heating at the same power levels and
derive the power required to achieve a given radius increase when night-side
cooling is incorporated. We find that models that include consistent day/night
cooling are more similar to isotropically irradiated models when there is more
heat redistributed from the dayside to the nightside. In addition, we consider
the efficacy of ohmic heating in the atmosphere and/or convective interior in
inflating hot Jupiters. Among our conclusions are that (i) the most highly
irradiated planets cannot stably have uB > (10 km/s Gauss) over a large
fraction of their daysides, where u is the zonal wind speed and B is the
dipolar magnetic field strength in the atmosphere, and (ii) that ohmic heating
cannot in and of itself lead to a runaway in planet radius.Comment: Accepted by ApJ., 20 pages, 11 figure
Signatures of X-rays in the early Universe
[abridged] With their long mean free paths and efficient heating of the
intergalactic medium (IGM), X-rays could have a dramatic impact on the thermal
and ionization history of the Universe. We explore this in various signals: (i)
Reionization history: including X-rays results in an earlier, more extended
reionization. Efficient thermal feedback from X-ray heating could yield an
extended, ~10% ionized epoch. (ii) Reionization morphology: a sizable (~10%)
contribution of X-rays to reionization results in a more uniform morphology,
though the impact is modest when compared at the same global neutral fraction,
xH. However, changes in morphology cannot be countered by increasing the bias
of the ionizing sources, making them a robust signature. (iii) The kinetic
Sunyaev-Zel'dovich (kSZ) effect: at a fixed reionization history, X-rays
decrease the kSZ power at l=3000 by ~0.5 microK^2. Our extreme model in which
X-rays dominate reionization is the only one that is marginally consistent with
upper limits from the South Pole Telescope, assuming no thermal
Sunyaev-Zel'dovich (tSZ) - dusty galaxy correlation. Since this extreme model
is unlikely, we conclude that there should be a sizable tSZ-dusty galaxy
signal. (iv) The cosmic 21cm signal: the impact of X-rays on the 21cm power
spectrum during the advanced stages of reionization (xH<0.7) is modest, except
in extreme, X-ray dominated models. The largest impact of X-rays is to govern
IGM heating. In fact, unless thermal feedback is efficient, the epoch of X-ray
heating likely overlaps with the beginning of reionization (xH>0.9). This
results in a 21cm power spectrum which is ~ 10-100 times higher than obtained
from naive estimates ignoring this overlap. However, if thermal feedback is
efficient, the resulting extended epoch between X-ray heating and reionization
could provide a clean probe of the matter power spectrum in emission.Comment: 17 pages, 12 figures, MNRAS in-pres
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