236 research outputs found
94 GHz Radar Backscatter Characteristics of Alpine Glacier Ice
Acknowledgments William D. Harcourt would like to thank PhD studentship funding from SAGES and EP281 SRC (grant number: EP/R513337/1). Funding for this study was obtained from the Scot282 tish Alliance for Geoscience, Environment and Society (SAGES) Small Grant Scheme. We would like to thank the staff at the Rhˆonegletscher Eisgrotte Cafe for enabling en284 trance to the field site and supporting the field activities, as well as the VAW Glaciol285 ogy Group and Glacier Monitoring in Switzerland groups for providing aerial photogram metry data over Rhˆonegletscher. Thanks also to Josu´e Gehring, Alexis Berne and Etienne Vignon for assisting with collection and delivery of our equipment at Ecole Polytechnique D´ed´erale de Lausanne (EPFL).Peer reviewedPublisher PD
All Six Planets Known to Orbit Kepler-11 Have Low Densities
The Kepler-11 planetary system contains six transiting planets ranging in
size from 1.8 to 4.2 times the radius of Earth. Five of these planets orbit in
a tightly-packed configuration with periods between 10 and 47 days. We perform
a dynamical analysis of the system based upon transit timing variations
observed in more than three years of \ik photometric data. Stellar parameters
are derived using a combination of spectral classification and constraints on
the star's density derived from transit profiles together with planetary
eccentricity vectors provided by our dynamical study. Combining masses of the
planets relative to the star from our dynamical study and radii of the planets
relative to the star from transit depths together with deduced stellar
properties yields measurements of the radii of all six planets, masses of the
five inner planets, and an upper bound to the mass of the outermost planet,
whose orbital period is 118 days. We find mass-radius combinations for all six
planets that imply that substantial fractions of their volumes are occupied by
constituents that are less dense than rock. The Kepler-11 system contains the
lowest mass exoplanets for which both mass and radius have been measured.Comment: 39 pages, 10 figure
Superhumps in Cataclysmic Binaries. XXIII. V442 Ophiuchi and RX J1643.7+3402
We report the results of long observing campaigns on two novalike variables:
V442 Ophiuchi and RX J1643.7+3402. These stars have high-excitation spectra,
complex line profiles signifying mass loss at particular orbital phases, and
similar orbital periods (respectively 0.12433 and 0.12056 d). They are
well-credentialed members of the SW Sex class of cataclysmic variables. Their
light curves are also quite complex. V442 Oph shows periodic signals with
periods of 0.12090(8) and 4.37(15) days, and RX J1643.7+3402 shows similar
signals at 0.11696(8) d and 4.05(12) d. We interpret these short and long
periods respectively as a "negative superhump" and the wobble period of the
accretion disk. The superhump could then possibly arise from the heating of the
secondary (and structures fixed in the orbital frame) by inner-disk radiation,
which reaches the secondary relatively unimpeded since the disk is not
coplanar.
At higher frequencies, both stars show another type of variability:
quasi-periodic oscillations (QPOs) with a period near 1000 seconds. Underlying
these strong signals of low stability may be weak signals of higher stability.
Similar QPOs, and negative superhumps, are quite common features in SW Sex
stars. Both can in principle be explained by ascribing strong magnetism to the
white dwarf member of the binary; and we suggest that SW Sex stars are
borderline AM Herculis binaries, usually drowned by a high accretion rate. This
would provide an ancestor channel for AM Hers, whose origin is still
mysterious.Comment: PDF, 41 pages, 4 tables, 16 figures; accepted, in press, to appear
December 2002, PASP; more info at http://cba.phys.columbia.edu
Validation of Twelve Small Kepler Transiting Planets in the Habitable Zone
We present an investigation of twelve candidate transiting planets from
Kepler with orbital periods ranging from 34 to 207 days, selected from initial
indications that they are small and potentially in the habitable zone (HZ) of
their parent stars. Few of these objects are known. The expected Doppler
signals are too small to confirm them by demonstrating that their masses are in
the planetary regime. Here we verify their planetary nature by validating them
statistically using the BLENDER technique, which simulates large numbers of
false positives and compares the resulting light curves with the Kepler
photometry. This analysis was supplemented with new follow-up observations
(high-resolution optical and near-infrared spectroscopy, adaptive optics
imaging, and speckle interferometry), as well as an analysis of the flux
centroids. For eleven of them (KOI-0571.05, 1422.04, 1422.05, 2529.02, 3255.01,
3284.01, 4005.01, 4087.01, 4622.01, 4742.01, and 4745.01) we show that the
likelihood they are true planets is far greater than that of a false positive,
to a confidence level of 99.73% (3 sigma) or higher. For KOI-4427.01 the
confidence level is about 99.2% (2.6 sigma). With our accurate characterization
of the GKM host stars, the derived planetary radii range from 1.1 to 2.7
R_Earth. All twelve objects are confirmed to be in the HZ, and nine are small
enough to be rocky. Excluding three of them that have been previously validated
by others, our study doubles the number of known rocky planets in the HZ.
KOI-3284.01 (Kepler-438b) and KOI-4742.01 (Kepler-442b) are the planets most
similar to the Earth discovered to date when considering their size and
incident flux jointly.Comment: 27 pages in emulateapj format, including tables and figures. To
appear in The Astrophysical Journa
An Unusual Transmission Spectrum for the Sub-Saturn KELT-11b Suggestive of a Sub-Solar Water Abundance
We present an optical-to-infrared transmission spectrum of the inflated
sub-Saturn KELT-11b measured with the Transiting Exoplanet Survey Satellite
(TESS), the Hubble Space Telescope (HST) Wide Field Camera 3 G141 spectroscopic
grism, and the Spitzer Space Telescope (Spitzer) at 3.6 m, in addition to
a Spitzer 4.5 m secondary eclipse. The precise HST transmission spectrum
notably reveals a low-amplitude water feature with an unusual shape. Based on
free retrieval analyses with varying molecular abundances, we find strong
evidence for water absorption. Depending on model assumptions, we also find
tentative evidence for other absorbers (HCN, TiO, and AlO). The retrieved water
abundance is generally solar (0.001--0.7 solar
over a range of model assumptions), several orders of magnitude lower than
expected from planet formation models based on the solar system metallicity
trend. We also consider chemical equilibrium and self-consistent 1D
radiative-convective equilibrium model fits and find they too prefer low
metallicities (, consistent with the free retrieval
results). However, all the retrievals should be interpreted with some caution
since they either require additional absorbers that are far out of chemical
equilibrium to explain the shape of the spectrum or are simply poor fits to the
data. Finally, we find the Spitzer secondary eclipse is indicative of full heat
redistribution from KELT-11b's dayside to nightside, assuming a clear dayside.
These potentially unusual results for KELT-11b's composition are suggestive of
new challenges on the horizon for atmosphere and formation models in the face
of increasingly precise measurements of exoplanet spectra.Comment: Accepted to The Astronomical Journal. 31 pages, 20 figures, 7 table
Masses, radii, and orbits of small Kepler planets : The transition from gaseous to rocky planets
We report on the masses, sizes, and orbits of the planets orbiting 22 Kepler stars. There are 49 planet candidates around these stars, including 42 detected through transits and 7 revealed by precise Doppler measurements of the host stars. Based on an analysis of the Kepler brightness measurements, along with high-resolution imaging and spectroscopy, Doppler spectroscopy, and (for 11 stars) asteroseismology, we establish low false-positive probabilities (FPPs) for all of the transiting planets (41 of 42 have an FPP under 1%), and we constrain their sizes and masses. Most of the transiting planets are smaller than three times the size of Earth. For 16 planets, the Doppler signal was securely detected, providing a direct measurement of the planet's mass. For the other 26 planets we provide either marginal mass measurements or upper limits to their masses and densities; in many cases we can rule out a rocky composition. We identify six planets with densities above 5 g cm-3, suggesting a mostly rocky interior for them. Indeed, the only planets that are compatible with a purely rocky composition are smaller than 2 R ⊕. Larger planets evidently contain a larger fraction of low-density material (H, He, and H2O).Peer reviewedFinal Accepted Versio
Geometric Metasurfaces for Ultrathin Optical Devices
Alces alces, Asia, distribution, Eurasian elk, Europe, GIS, harvest, moose, population densit
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