391 research outputs found
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 ± 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 ± 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 ± 0.010 g cm^(–3). We detect the occultation of the planet at a significance of 3.7σ in the Kepler bandpass. This yields a geometric albedo of 0.14 ± 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 7σ and 4σ in the 3.6 and 4.5 μm bandpasses, respectively. The occultation photometry timing is consistent with a circular orbit at e < 0.01 (1σ) and e < 0.09 (3σ). 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
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_☉, a radius of 1.1 R_☉, 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 ± 3.4 M_⊕, a radius of 2.00 ± 0.10 R_⊕, and a mean density of 4.9 ± 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 ± 1.9 M_⊕, a radius of 5.49 ± 0.26 R_⊕, and a mean density of 0.59 ± 0.07 g cm^3, while Kepler-18d has a mass of 16.4 ± 1.4 M_⊕, a radius of 6.98 ± 0.33 R_⊕ and a mean density of 0.27 ± 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
Moduli of elliptic curves via twisted stable maps
Abramovich, Corti and Vistoli have studied modular compactifications of
stacks of curves equipped with abelian level structures arising as substacks of
the stack of twisted stable maps into the classifying stack of a finite group,
provided the order of the group is invertible on the base scheme. Recently
Abramovich, Olsson and Vistoli extended the notion of twisted stable maps to
allow arbitrary base schemes, where the target is a tame stack, not necessarily
Deligne-Mumford. We use this to extend the results of Abramovich, Corti and
Vistoli to the case of elliptic curves with level structures over arbitrary
base schemes; we prove that we recover the compactified Katz-Mazur regular
models, with a natural moduli interpretation in terms of level structures on
Picard schemes of twisted curves. Additionally, we study the interactions of
the different such moduli stacks contained in a stack of twisted stable maps in
characteristics dividing the level.Comment: 46 pages; to appear in Algebra & Number Theor
The Young Substellar Companion ROXs 12 B: Near-Infrared Spectrum, System Architecture, and Spin-Orbit Misalignment
ROXs 12 (2MASS J16262803-2526477) is a young star hosting a directly imaged
companion near the deuterium-burning limit. We present a suite of
spectroscopic, imaging, and time-series observations to characterize the
physical and environmental properties of this system. Moderate-resolution
near-infrared spectroscopy of ROXs 12 B from Gemini-North/NIFS and Keck/OSIRIS
reveals signatures of low surface gravity including weak alkali absorption
lines and a triangular -band pseudo-continuum shape. No signs of Pa
emission are evident. As a population, however, we find that about half (46
14\%) of young (15 Myr) companions with masses 20
possess actively accreting subdisks detected via Pa
line emission, which represents a lower limit on the prevalence of
circumplanetary disks in general as some are expected to be in a quiescent
phase of accretion. The bolometric luminosity of the companion and age of the
host star (6 Myr) imply a mass of 17.5 1.5
for ROXs 12 B based on hot-start evolutionary models. We identify a wide (5100
AU) tertiary companion to this system, 2MASS J16262774-2527247, which is
heavily accreting and exhibits stochastic variability in its light curve.
By combining sin measurements with rotation periods from , we
constrain the line-of-sight inclinations of ROXs 12 A and 2MASS
J16262774-2527247 and find that they are misaligned by
60. In addition, the orbital axis of ROXs 12 B is likely
misaligned from the spin axis of its host star ROXs 12 A, suggesting that ROXs
12 B formed akin to fragmenting binary stars or in an equatorial disk that was
torqued by the wide stellar tertiary.Comment: AJ, accepte
The California Legacy Survey IV. Lonely, Poor, and Eccentric: A Comparison Between Solitary and Neighborly Gas Giants
We compare systems with single giant planets to systems with multiple giant
planets using a catalog of planets from a high-precision radial velocity survey
of FGKM stars. Our comparison focuses on orbital properties, planet masses, and
host star properties. We use hierarchical methods to model the orbital
eccentricity distributions of giant singles and giant multis, and find that the
distributions are distinct. The multiple giant planets typically have moderate
eccentricities and their eccentricity distribution extends to (90th
percentile), while the single giant planets have a pile-up of nearly circular
orbits and a long tail that extends to . We determine that stellar
hosts of multiple giants are distinctly more metal-rich than hosts of solitary
giants, with respective mean metallicities vs.
dex. We measure the distinct occurrence distributions of single and multiple
giants with respect to orbital separation, and find that single gas giants have
a 2.3 significant hot () Jupiter pile-up not seen among
multi giant systems. We find that the median mass (\msini ) of giants in
multiples is nearly double that of single giants (1.71 \mjup vs. 0.92 \mjup
). We find that giant planets in the same system have correlated masses,
analogous to the `peas in a pod' effect seen among less massive planets
Kepler-1656b: a Dense Sub-Saturn With an Extreme Eccentricity
Kepler-1656b is a 5 planet with an orbital period of 32 days initially
detected by the prime Kepler mission. We obtained precision radial velocities
of Kepler-1656 with Keck/HIRES in order to confirm the planet and to
characterize its mass and orbital eccentricity. With a mass of ,
Kepler-1656b is more massive than most planets of comparable size. Its high
mass implies that a significant fraction, roughly 80%, of the planet's total
mass is in high density material such as rock/iron, with the remaining mass in
a low density H/He envelope. The planet also has a high eccentricity of , the largest measured eccentricity for any planet less than 100
. The planet's high density and high eccentricity may be the result of one
or more scattering and merger events during or after the dispersal of the
protoplanetary disk.Comment: 10 pages, 6 figures, published in The Astronomical Journa
A Correlation Between Stellar Activity and Hot Jupiter Emission Spectra
We present evidence for a correlation between the observed properties of hot
Jupiter emission spectra and the activity levels of the host stars measured
using Ca II H & K emission lines. We find that planets with dayside emission
spectra that are well-described by standard 1D atmosphere models with water in
absorption (HD 189733, TrES-1, TrES-3, WASP-4) orbit chromospherically active
stars, while planets with emission spectra that are consistent with the
presence of a strong high-altitude temperature inversion and water in emission
orbit quieter stars. We estimate that active G and K stars have Lyman alpha
fluxes that are typically a factor of 4-7 times higher than quiet stars with
analogous spectral types, and propose that the increased UV flux received by
planets orbiting active stars destroys the compounds responsible for the
formation of the observed temperature inversions. In this paper we also derive
a model-independent method for differentiating between these two atmosphere
types using the secondary eclipse depths measured in the 3.6 and 4.5 micron
bands on the Spitzer Space Telescope, and argue that the observed correlation
is independent of the inverted/non-inverted paradigm for classifying hot
Jupiter atmospheres.Comment: 9 pages, 5 figures, accepted for publication in ApJ. The updated
paper includes spectra for ten additional systems and a new section
discussing the connection between chromospheric activity and UV flu
Friends of Hot Jupiters II: No Correspondence Between Hot-Jupiter Spin-Orbit Misalignment and the Incidence of Directly Imaged Stellar Companions
Multi-star systems are common, yet little is known about a stellar
companion's influence on the formation and evolution of planetary systems. For
instance, stellar companions may have facilitated the inward migration of hot
Jupiters towards to their present day positions. Many observed short period gas
giant planets also have orbits that are misaligned with respect to their star's
spin axis, which has also been attributed to the presence of a massive outer
companion on a non-coplanar orbit. We present the results of a multi-band
direct imaging survey using Keck NIRC2 to measure the fraction of short period
gas giant planets found in multi-star systems. Over three years, we completed a
survey of 50 targets ("Friends of Hot Jupiters") with 27 targets showing some
signature of multi-body interaction (misaligned or eccentric orbits) and 23
targets in a control sample (well-aligned and circular orbits). We report the
masses, projected separations, and confirmed common proper motion for the 19
stellar companions found around 17 stars. Correcting for survey incompleteness,
we report companion fractions of , , and
in our total, misaligned/eccentric, and control samples, respectively. This
total stellar companion fraction is larger than the fraction of
field stars with companions approximately AU. We observe no
correlation between misaligned/eccentric hot Jupiter systems and the incidence
of stellar companions. Combining this result with our previous radial velocity
survey, we determine that of hot Jupiters are part of
multi-planet and/or multi-star systems.Comment: typos and references updated; 25 pages, 7 figures and 10 tables,
accepted for publication in Ap
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
No difference in orbital parameters of RV-detected giant planets between 0.1 and 5 au in single vs multi-stellar systems
Our Keck/NIRC2 imaging survey searches for stellar companions around 144
systems with radial velocity (RV) detected giant planets to determine whether
stellar binaries influence the planets' orbital parameters. This survey, the
largest of its kind to date, finds eight confirmed binary systems and three
confirmed triple systems. These include three new multi-stellar systems (HD
30856, HD 86081, and HD 207832) and three multi-stellar systems with newly
confirmed common proper motion (HD 43691, HD 116029, and HD 164509). We combine
these systems with seven RV planet-hosting multi-stellar systems from the
literature in order to test for differences in the properties of planets with
semimajor axes ranging between 0.1-5 au in single vs multi-stellar systems. We
find no evidence that the presence or absence of stellar companions alters the
distribution of planet properties in these systems. Although the observed
stellar companions might influence the orbits of more distant planetary
companions in these systems, our RV observations currently provide only weak
constraints on the masses and orbital properties of planets beyond 5 au. In
order to aid future efforts to characterize long period RV companions in these
systems, we publish our contrast curves for all 144 targets. Using four years
of astrometry for six hierarchical triple star systems hosting giant planets,
we fit the orbits of the stellar companions in order to characterize the
orbital architecture in these systems. We find that the orbital plane of the
secondary and tertiary companions are inconsistent with an edge-on orbit in
four out of six cases.Comment: 34 pages, 10 figures, 16 tables, including 4 tables in machine
readable format and 7 tables with online supplemental dat
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