778 research outputs found
Hubble Space Telescope Near-IR Transmission Spectroscopy of the Super-Earth HD 97658b
Recent results from the Kepler mission indicate that super-Earths (planets
with masses between 1-10 times that of the Earth) are the most common kind of
planet around nearby Sun-like stars. These planets have no direct solar system
analogue, and are currently one of the least well-understood classes of
extrasolar planets. Many super-Earths have average densities that are
consistent with a broad range of bulk compositions, including both
water-dominated worlds and rocky planets covered by a thick hydrogen and helium
atmosphere. Measurements of the transmission spectra of these planets offer the
opportunity to resolve this degeneracy by directly constraining the scale
heights and corresponding mean molecular weights of their atmospheres. We
present Hubble Space Telescope near-infrared spectroscopy of two transits of
the newly discovered transiting super-Earth HD 97658b. We use the Wide Field
Camera 3's scanning mode to measure the wavelength-dependent transit depth in
thirty individual bandpasses. Our averaged differential transmission spectrum
has a median 1 sigma uncertainty of 23 ppm in individual bins, making this the
most precise observation of an exoplanetary transmission spectrum obtained with
WFC3 to date. Our data are inconsistent with a cloud-free solar metallicity
atmosphere at the 10 sigma level. They are consistent at the 0.4 sigma level
with a flat line model, as well as effectively flat models corresponding to a
metal-rich atmosphere or a solar metallicity atmosphere with a cloud or haze
layer located at pressures of 10 mbar or higher.Comment: ApJ in press; revised version includes an updated orbital ephemeris
for the plane
Detection of Helium in the Atmosphere of the Exo-Neptune HAT-P-11b
The helium absorption triplet at a wavelength of 10,833 \AA\ has been
proposed as a way to probe the escaping atmospheres of exoplanets. Recently
this feature was detected for the first time using Hubble Space Telescope (HST)
WFC3 observations of the hot Jupiter WASP-107b. We use similar HST/WFC3
observations to detect helium in the atmosphere of the hot Neptune HAT-P-11b at
the confidence level. We compare our observations to a grid of 1D
models of hydrodynamic escape to constrain the thermospheric temperatures and
mass loss rate. We find that our data are best fit by models with high mass
loss rates of - g s. Although we do
not detect the planetary wind directly, our data are consistent with the
prediction that HAT-P-11b is experiencing hydrodynamic atmospheric escape.
Nevertheless, the mass loss rate is low enough that the planet has only lost up
to a few percent of its mass over its history, leaving its bulk composition
largely unaffected. This matches the expectation from population statistics,
which indicate that close-in planets with radii greater than 2 R
form and retain H/He-dominated atmospheres. We also confirm the independent
detection of helium in HAT-P-11b obtained with the CARMENES instrument, making
this the first exoplanet with the detection of the same signature of
photoevaporation from both ground- and space-based facilities.Comment: 12 pages, 9 figures, accepted for publication in ApJ
A Precise Water Abundance Measurement for the Hot Jupiter WASP-43b
The water abundance in a planetary atmosphere provides a key constraint on
the planet's primordial origins because water ice is expected to play an
important role in the core accretion model of planet formation. However, the
water content of the Solar System giant planets is not well known because water
is sequestered in clouds deep in their atmospheres. By contrast, short-period
exoplanets have such high temperatures that their atmospheres have water in the
gas phase, making it possible to measure the water abundance for these objects.
We present a precise determination of the water abundance in the atmosphere of
the 2 short-period exoplanet WASP-43b based on thermal
emission and transmission spectroscopy measurements obtained with the Hubble
Space Telescope. We find the water content is consistent with the value
expected in a solar composition gas at planetary temperatures (0.4-3.5x solar
at 1 confidence). The metallicity of WASP-43b's atmosphere suggested
by this result extends the trend observed in the Solar System of lower metal
enrichment for higher planet masses.Comment: Accepted to ApJL; this version contains three supplemental figures
that are not included in the published paper. See also our companion paper
"Thermal structure of an exoplanet atmosphere from phase-resolved emission
spectroscopy" by Stevenson et a
Hubble Space Telescope transmission spectroscopy for the temperate sub-Neptune TOI-270d: a possible hydrogen-rich atmosphere containing water vapour
TOI-270d is a temperate sub-Neptune discovered by the Transiting Exoplanet
Survey Satellite (TESS) around a bright (J=9.1mag) M3V host star. With an
approximate radius of 2RE and equilibrium temperature of 350K, TOI-270d is one
of the most promising small exoplanets for atmospheric characterisation using
transit spectroscopy. Here we present a primary transit observation of TOI-270d
made with the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3)
spectrograph across the 1.126-1.644 micron wavelength range, and a 95% credible
upper limit of erg s cm A
arcsec for the stellar Ly-alpha emission obtained using the Space
Telescope Imaging Spectrograph (STIS). The transmission spectrum derived from
the TESS and WFC3 data provides evidence for molecular absorption by a
hydrogen-rich atmosphere at 4-sigma significance relative to a featureless
spectrum. The strongest evidence for any individual absorber is obtained for
H2O, which is favoured at 3-sigma significance. When retrieving on the WFC3
data alone and allowing for the possibility of a heterogeneous stellar
brightness profile, the detection significance of H2O is reduced to 2.8-sigma.
Further observations are therefore required to robustly determine the
atmospheric composition of TOI-270d and assess the impact of stellar
heterogeneity. If confirmed, our findings would make TOI-270d one of the
smallest and coolest exoplanets to date with detected atmospheric spectral
features.Comment: Accepted for publication in AAS journals on November 22, 2022
(received July 5, 2022; revised October 30, 2022
Climate of an Ultra hot Jupiter: Spectroscopic phase curve of WASP-18b with HST/WFC3
We present the analysis of a full-orbit, spectroscopic phase curve of the
ultra hot Jupiter WASP-18b, obtained with the Wide Field Camera 3 aboard the
Hubble Space Telescope. We measure the planet's normalized day-night contrast
as >0.96 in luminosity: the disk-integrated dayside emission from the planet is
at 964+-25 ppm, corresponding to 2894+-30 K, and we place an upper limit on the
nightside emission of <32ppm or 1430K at the 3-sigma level. We also find that
the peak of the phase curve exhibits a small, but significant offset in
brightness of 4.5+-0.5 degrees eastward.
We compare the extracted phase curve and phase resolved spectra to 3D Global
Circulation Models and find that broadly the data can be well reproduced by
some of these models. We find from this comparison several constraints on the
atmospheric properties of the planet. Firstly we find that we need efficient
drag to explain the very inefficient day-night re-circulation observed. We
demonstrate that this drag could be due to Lorentz-force drag by a magnetic
field as weak as 10 Gauss. Secondly, we show that a high metallicity is not
required to match the large day-night temperature contrast. In fact, the effect
of metallicity on the phase curve is different from cooler gas-giant
counterparts, due to the high-temperature chemistry in WASP-18b's atmosphere.
Additionally, we compare the current UHJ spectroscopic phase curves, WASP-18b
and WASP-103b, and show that these two planets provide a consistent picture
with remarkable similarities in their measured and inferred properties.
However, key differences in these properties, such as their brightness offsets
and radius anomalies, suggest that UHJ could be used to separate between
competing theories for the inflation of gas-giant planets.Comment: Accepted for publication in A&
A HST/WFC3 Thermal Emission Spectrum of the Hot Jupiter HAT-P-7b
Secondary eclipse observations of several of the hottest hot Jupiters show
featureless, blackbody-like spectra or molecular emission features, which are
consistent with thermal inversions being present in those atmospheres. Theory
predicts a transition between warmer atmospheres with thermal inversions and
cooler atmospheres without inversions, but the exact transition point is
unknown. In order to further investigate this issue, we observed two secondary
eclipses of the hot Jupiter HAT-P-7b with the Hubble Space Telescope (HST) WFC3
instrument and combined these data with previous Spitzer and Kepler secondary
eclipse observations. The HST and Spitzer data can be well fit by a blackbody
with K, and the Kepler data point constrains the geometric
albedo to . We modeled these data with a 3D GCM and 1D
self-consistent forward models. The 1D models indicate that the atmosphere has
a thermal inversion, weak heat redistribution, and water dissociation that
limits the range of pressures probed. This result suggests that WFC3
observations of HAT-P-7b and possibly some other ultra-hot Jupiters appear
blackbody-like because they probe a region near the tropopause where the
atmospheric temperature changes slowly with pressure. Additionally, the 1D
models constrain the atmospheric metallicity
() and the carbon-to-oxygen ratio (C/O
at 99 % confidence). The solar composition 3D GCM matches the Spitzer data but
generally underpredicts the flux in the WFC3 bandpass and cannot reproduce its
featureless shape. This discrepancy could be explained by high atmospheric drag
or nightside clouds, and may be better understood through further observation
with the James Webb Space Telescope (JWST).Comment: 14 pages, 10 figures, submitted to AAS Journal
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