426 research outputs found
A Ground-Based Search for Thermal Emission from the Exoplanet TrES-1
Eclipsing planetary systems give us an important window on extrasolar planet
atmospheres. By measuring the depth of the secondary eclipse, when the planet
moves behind the star, we can estimate the strength of the thermal emission
from the day side of the planet. Attaining a ground-based detection of one of
these eclipses has proven to be a significant challenge, as time-dependent
variations in instrument throughput and atmospheric seeing and absorption
overwhelm the small signal of the eclipse at infrared wavelengths. We gathered
a series of simultaneous L grism spectra of the transiting planet system TrES-1
and a nearby comparison star of comparable brightness, allowing us to correct
for these effects in principle. Combining the data from two eclipses, we
demonstrate a detection sensitivity of 0.15% in the eclipse depth relative to
the stellar flux. This approaches the sensitivity required to detect the
planetary emission, which theoretical models predict should lie between
0.05-0.1% of the stellar flux in our 2.9-4.3 micron bandpass. We explore the
factors that ultimately limit the precision of this technique, and discuss
potential avenues for future improvements.Comment: 10 pages, 1 table, four figures, accepted for publication in PAS
Discovery and Atmospheric Characterization of Giant Planet Kepler-12b: An Inflated Radius Outlier
We report the discovery of planet Kepler-12b (KOI-20), which at 1.695 Ā± 0.030 R_J is among the handful of planets with super-inflated radii above 1.65 R_J. Orbiting its slightly evolved G0 host with a 4.438 day period, this 0.431 Ā± 0.041 M_J planet is the least irradiated within this largest-planet-radius group, which has important implications for planetary physics. The planet's inflated radius and low mass lead to a very low density of 0.111 Ā± 0.010 g cm^(ā3). We detect the occultation of the planet at a significance of 3.7Ļ in the Kepler bandpass. This yields a geometric albedo of 0.14 Ā± 0.04; the planetary flux is due to a combination of scattered light and emitted thermal flux. We use multiple observations with Warm Spitzer to detect the occultation at 7Ļ and 4Ļ in the 3.6 and 4.5 Ī¼m bandpasses, respectively. The occultation photometry timing is consistent with a circular orbit at e < 0.01 (1Ļ) and e < 0.09 (3Ļ). The occultation detections across the three bands favor an atmospheric model with no dayside temperature inversion. The Kepler occultation detection provides significant leverage, but conclusions regarding temperature structure are preliminary, given our ignorance of opacity sources at optical wavelengths in hot Jupiter atmospheres. If Kepler-12b and HD 209458b, which intercept similar incident stellar fluxes, have the same heavy-element masses, the interior energy source needed to explain the large radius of Kepler-12b is three times larger than that of HD 209458b. This may suggest that more than one radius-inflation mechanism is at work for Kepler-12b or that it is less heavy-element rich than other transiting planets
Spitzer Secondary Eclipses of Qatar-1b
Previous secondary eclipse observations of the hot Jupiter Qatar-1b in the Ks
band suggest that it may have an unusually high day side temperature,
indicative of minimal heat redistribution. There have also been indications
that the orbit may be slightly eccentric, possibly forced by another planet in
the system. We investigate the day side temperature and orbital eccentricity
using secondary eclipse observations with Spitzer. We observed the secondary
eclipse with Spitzer/IRAC in subarray mode, in both 3.6 and 4.5 micron
wavelengths. We used pixel-level decorrelation to correct for Spitzer's
intra-pixel sensitivity variations and thereby obtain accurate eclipse depths
and central phases. Our 3.6 micron eclipse depth is 0.149 +/- 0.051% and the
4.5 micron depth is 0.273 +/- 0.049%. Fitting a blackbody planet to our data
and two recent Ks band eclipse depths indicates a brightness temperature of
1506 +/- 71K. Comparison to model atmospheres for the planet indicates that its
degree of longitudinal heat redistribution is intermediate between fully
uniform and day side only. The day side temperature of the planet is unlikely
to be as high (1885K) as indicated by the ground-based eclipses in the Ks band,
unless the planet's emergent spectrum deviates strongly from model atmosphere
predictions. The average central phase for our Spitzer eclipses is 0.4984 +/-
0.0017, yielding e cos(omega) = -0.0028 +/- 0.0027. Our results are consistent
with a circular orbit, and we constrain e cos(omega) much more strongly than
has been possible with previous observations
Constraints on the Spin Evolution of Young Planetary-Mass Companions
Surveys of young star-forming regions have discovered a growing population of
planetary-mass (<13 M_Jup) companions around young stars. There is an ongoing
debate as to whether these companions formed like planets (that is, from the
circumstellar disk), or if they represent the low-mass tail of the star
formation process. In this study we utilize high-resolution spectroscopy to
measure rotation rates of three young (2-300 Myr) planetary-mass companions and
combine these measurements with published rotation rates for two additional
companions to provide a look at the spin distribution of these objects. We
compare this distribution to complementary rotation rate measurements for six
brown dwarfs with masses <20 M_Jup, and show that these distributions are
indistinguishable. This suggests that either that these two populations formed
via the same mechanism, or that processes regulating rotation rates are
independent of formation mechanism. We find that rotation rates for both
populations are well below their break-up velocities and do not evolve
significantly during the first few hundred million years after the end of
accretion. This suggests that rotation rates are set during late stages of
accretion, possibly by interactions with a circumplanetary disk. This result
has important implications for our understanding of the processes regulating
the angular momentum evolution of young planetary-mass objects, and of the
physics of gas accretion and disk coupling in the planetary-mass regime.Comment: 31 pages, 10 figures, published in Nature Astronomy,
DOI:10.1038/s41550-017-0325-
Kepler-18b,c, and d: A System of Three Planets Confirmed by Transit Timing Variations, Light Curve Validation, Warm-Spitzer Photometry, and Radial Velocity Measurements
We report the detection of three transiting planets around a Sun-like star, which we designate Kepler-18. The transit signals were detected in photometric data from the Kepler satellite, and were confirmed to arise from planets using a combination of large transit-timing variations (TTVs), radial velocity variations, Warm-Spitzer observations, and statistical analysis of false-positive probabilities. The Kepler-18 star has a mass of 0.97 M_ā, a radius of 1.1 R_ā, an effective temperature of 5345 K, and an iron abundance of [Fe/H] = +0.19. The planets have orbital periods of approximately 3.5, 7.6, and 14.9 days. The innermost planet "b" is a "super-Earth" with a mass of 6.9 Ā± 3.4 M_ā, a radius of 2.00 Ā± 0.10 R_ā, and a mean density of 4.9 Ā± 2.4 g cm^3. The two outer planets "c" and "d" are both low-density Neptune-mass planets. Kepler-18c has a mass of 17.3 Ā± 1.9 M_ā, a radius of 5.49 Ā± 0.26 R_ā, and a mean density of 0.59 Ā± 0.07 g cm^3, while Kepler-18d has a mass of 16.4 Ā± 1.4 M_ā, a radius of 6.98 Ā± 0.33 R_ā and a mean density of 0.27 Ā± 0.03 g cm^3. Kepler-18c and Kepler-18d have orbital periods near a 2:1 mean-motion resonance, leading to large and readily detected TTVs
Exoplanet atmospheres
Twenty years ago planets orbiting
faraway stars were the stuff of science
fiction. Now their atmospheric
composition and even their weather
are being revealed by sensitive
spectral measurements
Characterizing the Atmospheres of Hot Jupiters: From Spectra to Multi-Color Maps
We present new observations of the emission spectrum of the hot Jupiter TrES-4 designed
to test the theory that the presence of temperature inversions in the atmospheres of these
planets are correlated with the amount of radiation received by the planet. Our observations
reveal that TrES-4 has an emission spectrum similar to that of HD 209458b, which requires
the presence of an inversion layer high in the atmosphere and water emission bands in order to
explain the observed features, providing additional support for that theory. We also present new
observations of the thermal phase curve of HD 189733b at 24 Ī¼m, which we combine with our
previous observations at 8 Ī¼m to examine how circulation in this planetās atmosphere varies as a
function of depth. We discuss the relationship between the strength of the day-night circulation
on both planets and their other observable properties, in particular their emission spectra
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