1,405 research outputs found
Exoplanet albedo spectra and colors as a function of planet phase, separation, and metallicity
First generation optical coronagraphic telescopes will obtain images of cool
gas and ice giant exoplanets around nearby stars. The albedo spectra of
exoplanets at planet-star separations larger than about 1 AU are dominated by
reflected light to beyond 1 {\mu}m and are punctuated by molecular absorption
features. We consider how exoplanet albedo spectra and colors vary as a
function of planet-star separation, metallicity, mass, and observed phase for
Jupiter and Neptune analogs from 0.35 to 1 {\mu}m. We model Jupiter analogs
with 1x and 3x the solar abundance of heavy elements, and Neptune analogs with
10x and 30x. Our model planets orbit a solar analog parent star at separations
of 0.8 AU, 2 AU, 5 AU, and 10 AU. We use a radiative-convective model to
compute temperature-pressure profiles. The giant exoplanets are cloud-free at
0.8 AU, have H2O clouds at 2 AU, and have both NH3 and H2O clouds at 5 AU and
10 AU. For each model planet we compute moderate resolution spectra as a
function of phase. The presence and structure of clouds strongly influence the
spectra. Since the planet images will be unresolved, their phase may not be
obvious, and multiple observations will be needed to discriminate between the
effects of planet-star separation, metallicity, and phase. We consider the
range of these combined effects on spectra and colors. For example, we find
that the spectral influence of clouds depends more on planet-star separation
and hence temperature than metallicity, and it is easier to discriminate
between cloudy 1x and 3x Jupiters than between 10x and 30x Neptunes. In
addition to alkalis and methane, our Jupiter models show H2O absorption
features near 0.94 {\mu}m. We also predict that giant exoplanets receiving
greater insolation than Jupiter will exhibit higher equator to pole temperature
gradients than are found on Jupiter and thus may have differing atmospheric
dynamics.Comment: 62 pages, 19 figures, 6 tables Accepted for publication in Ap
Transmission spectroscopy of the sodium 'D' doublet in WASP-17b with the VLT
The detection of increased sodium absorption during primary transit implies
the presence of an atmosphere around an extrasolar planet, and enables us to
infer the structure of this atmosphere. Sodium has only been detected in the
atmospheres of two planets to date - HD189733b and HD209458b. WASP-17b is the
least dense planet currently known. It has a radius approximately twice that of
Jupiter and orbits an F6-type star. The transit signal is expected to be about
five times larger than that observed in HD209458b. We obtained 24 spectra with
the GIRAFFE spectrograph on the VLT, eight during transit. The integrated flux
in the sodium doublet at wavelengths 5889.95 and 5895.92 {\AA} was measured at
bandwidths 0.75, 1.5, 3.0, 4.0, 5.0, and 6.0 {\AA}. We find a transit depth of
0.55 \pm 0.13 per cent at 1.5 {\AA}. This suggests that, like HD209458b,
WASP-17b has an atmosphere depleted in sodium compared to models for a
cloud-free atmosphere with solar sodium abundance. We observe a sharp cut-off
in sodium absorption between 3.0 and 4.0 {\AA} which may indicate a layer of
clouds high in the atmosphere.Comment: Amended for typographic conventions following publicatio
High Temperature Photochemistry in the Atmosphere of HD189733b
Recent infrared spectroscopy of hot exoplanets is beginning to reveal their
atmospheric composition. Deep with in the planetary atmosphere, the composition
is controlled by thermochemical equilibrium. Photochemistry becomes important
higher in the atmosphere, at levels above ~1 bar. These two chemistries compete
between ~1-10 bars in hot Jupiter-like atmospheres, depending on the strength
of the eddy mixing and temperature. HD189733b provides an excellent laboratory
in which to study the consequences of chemistry of hot atmospheres. The recent
spectra of HD189733b and HD209458b contain signatures of CH4, CO2, CO and H2O.
Here we identify the primary chemical pathways that govern the abundances of
CH4, CO2, CO and H2O in the cases of thermochemical equilibrium chemistry,
photochemistry, and their combination. Our results suggest that the abundance
of these species can be photochemically enhanced above or below the
thermochemical equilibrium value, so some caution must be taken when assuming
that an atmosphere is in strict thermochemical equilibrium
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
Refined physical properties and g',r',i',z',J,H,K transmission spectrum of WASP-23b from the ground
Multi-band observations of planetary transits using the telescope defocus
technique may yield high-quality light curves suitable for refining the
physical properties of exoplanets even with small or medium size telescopes.
Such observations can be used to construct a broad-band transmission spectrum
of transiting planets and search for the presence of strong absorbers. We have
thoroughly characterised the orbital ephemeris and physical properties of the
transiting planet and host star in the WASP-23b system, constructed a
broad-band transmission spectrum of WASP-23b and performed a comparative
analysis with theoretical models of hot Jupiters. We observed a complete
transit of WASP-23b in seven bands simultaneously, using the GROND instrument
on the MPG/ESO 2.2m telescope at La Silla Observatory and telescope
defocussing. The optical data were taken in the Sloan g',r',i' and z' bands.
The resulting light curves are of high quality, with a root-mean-square scatter
of the residual as low as 330ppm in the z'-band, with a cadence of 90s.
Near-infrared data were obtained in the JHK bands. We performed MCMC analysis
of our photometry plus existing radial velocity data to refine measurements of
the ephemeris and physical properties of the WASP-23. We constructed a
broad-band transmission spectrum of WASP-23b and compared it with a theoretical
transmission spectrum of a Hot Jupiter. We measured the central transit time
with a precision about 8s. From this and earlier observations we obtain an
orbital period of P=2.9444300+/-0.0000011d. Our analysis also yielded a larger
radius and mass for the planet (Rp=1.067+0.045-0.038 RJup and,
Mp=0.917+0.040-0.039MJup). The transmission spectrum is marginally flat, given
the limited precision of the measurements for the planet radius and poor
spectral resolution of the data.Comment: 8 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
The TRAPPIST survey of southern transiting planets. I. Thirty eclipses of the ultra-short period planet WASP-43 b
We present twenty-three transit light curves and seven occultation light
curves for the ultra-short period planet WASP-43 b, in addition to eight new
measurements of the radial velocity of the star. Thanks to this extensive data
set, we improve significantly the parameters of the system. Notably, the
largely improved precision on the stellar density (2.41+-0.08 rho_sun) combined
with constraining the age to be younger than a Hubble time allows us to break
the degeneracy of the stellar solution mentioned in the discovery paper. The
resulting stellar mass and size are 0.717+-0.025 M_sun and 0.667+-0.011 R_sun.
Our deduced physical parameters for the planet are 2.034+-0.052 M_jup and
1.036+-0.019 R_jup. Taking into account its level of irradiation, the high
density of the planet favors an old age and a massive core. Our deduced orbital
eccentricity, 0.0035(-0.0025,+0.0060), is consistent with a fully circularized
orbit. We detect the emission of the planet at 2.09 microns at better than
11-sigma, the deduced occultation depth being 1560+-140 ppm. Our detection of
the occultation at 1.19 microns is marginal (790+-320 ppm) and more
observations are needed to confirm it. We place a 3-sigma upper limit of 850
ppm on the depth of the occultation at ~0.9 microns. Together, these results
strongly favor a poor redistribution of the heat to the night-side of the
planet, and marginally favor a model with no day-side temperature inversion.Comment: 14 pages, 6 tables, 11 figures. Accepted for publication in A&
Gemini/GMOS Transmission Spectral Survey: Complete Optical Transmission Spectrum of the hot Jupiter WASP-4b
We present the complete optical transmission spectrum of the hot Jupiter
WASP-4b from 440-940 nm at R ~ 400-1500 obtained with the Gemini Multi-Object
Spectrometers (GMOS); this is the first result from a comparative
exoplanetology survey program of close-in gas giants conducted with GMOS.
WASP-4b has an equilibrium temperature of 1700 K and is favorable to study in
transmission due to a large scale height (370 km). We derive the transmission
spectrum of WASP-4b using 4 transits observed with the MOS technique. We
demonstrate repeatable results across multiple epochs with GMOS, and derive a
combined transmission spectrum at a precision about twice above photon noise,
which is roughly equal to to one atmospheric scale height. The transmission
spectrum is well fitted with a uniform opacity as a function of wavelength. The
uniform opacity and absence of a Rayleigh slope from molecular hydrogen suggest
that the atmosphere is dominated by clouds with condensate grain size of ~1 um.
This result is consistent with previous observations of hot Jupiters since
clouds have been seen in planets with similar equilibrium temperatures to
WASP-4b. We describe a custom pipeline that we have written to reduce GMOS
time-series data of exoplanet transits, and present a thorough analysis of the
dominant noise sources in GMOS, which primarily consist of wavelength- and
time- dependent displacements of the spectra on the detector, mainly due to a
lack of atmospheric dispersion correction.Comment: 23 pages, 12 figures, accepted for publication in AJ, 2017 July
Thermal Emission and Tidal Heating of the Heavy and Eccentric Planet XO-3b
We determined the flux ratios of the heavy and eccentric planet XO-3b to its
parent star in the four IRAC bands of the Spitzer Space Telescope: 0.101% +-
0.004% at 3.6 micron; 0.143% +- 0.006% at 4.5 micron; 0.134% +- 0.049% at 5.8
micron and 0.150% +- 0.036% at 8.0 micron. The flux ratios are within
[-2.2,0.3, -0.8, -1.7]-sigma of the model of XO-3b with a thermally inverted
stratosphere in the 3.6 micron, 4.5 micron, 5.8 micron and 8.0 micron channels,
respectively. XO-3b has a high illumination from its parent star (Fp ~(1.9 -
4.2) x 10^9 ergs cm^-2 s^-1) and is thus expected to have a thermal inversion,
which we indeed observe. When combined with existing data for other planets,
the correlation between the presence of an atmospheric temperature inversion
and the substellar flux is insufficient to explain why some high insolation
planets like TrES-3 do not have stratospheric inversions and some low
insolation planets like XO-1b do have inversions. Secondary factors such as
sulfur chemistry, atmospheric metallicity, amounts of macroscopic mixing in the
stratosphere or even dynamical weather effects likely play a role. Using the
secondary eclipse timing centroids we determined the orbital eccentricity of
XO-3b as e = 0.277 +- 0.009. The model radius-age trajectories for XO-3b imply
that at least some amount of tidal-heating is required to inflate the radius of
XO-3b, and the tidal heating parameter of the planet is constrained to Qp <
10^6 .Comment: Accepted for publications in The Astrophysical Journa
Oral Contraceptives and Reproductive Cancers: Weighing the Risks and Benefits
The hypothetical incidence of reproductive cancers resulting from oral contraceptive use was estimated in several models comparing the cumulative lifetime incidence of cancer of the breast, cervix, ovary and endometrium expected in pill users with the incidence expected in nonusers. The potential number of cancer-free days that would be gained or lost by pill users was com- pared with similar estimates among nonusers. If five years or more of pill use were associated with a 20% increase in the risk of breast cancerbeing diagnosed before age 50, a 20% increase in cervical cancer risk and a 50% reduction in the risks of ovarian and endometrial cancers, then every 100,000 pill users would experience 44 fewer reproductive cancers during their lifetime than would nonusers, and would gain one more day free of cancer. If higher estimates of the five-yearpill-associated risks of breast and cervical cancer are used-a 50% increased risk of each, for example-then pill users would experience more reproductive cancers than nonusers and would have 11 fewer cancer-free days of life
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
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