128 research outputs found
Masses and Properties of Extrasolar Planets.
Ph.D. Thesis. University of Hawaiʻi at Mānoa 2018
RadVel: The Radial Velocity Modeling Toolkit
RadVel is an open source Python package for modeling Keplerian orbits in
radial velocity (RV) time series. RadVel provides a convenient framework to fit
RVs using maximum a posteriori optimization and to compute robust confidence
intervals by sampling the posterior probability density via Markov Chain Monte
Carlo (MCMC). RadVel allows users to float or fix parameters, impose priors,
and perform Bayesian model comparison. We have implemented realtime MCMC
convergence tests to ensure adequate sampling of the posterior. RadVel can
output a number of publication-quality plots and tables. Users may interface
with RadVel through a convenient command-line interface or directly from
Python. The code is object-oriented and thus naturally extensible. We encourage
contributions from the community. Documentation is available at
http://radvel.readthedocs.io.Comment: prepared for resubmission to PAS
Exoplanet Transit Spectroscopy Using WFC3: WASP-12 b, WASP-17 b, and WASP-19 b
We report analysis of transit spectroscopy of the extrasolar planets WASP-12
b, WASP-17 b, and WASP-19 b using the Wide Field Camera 3 on the HST. We
analyze the data for a single transit for each planet using a strategy similar
in certain aspects to the techniques used by Berta et al. (2012), but we extend
their methodology to allow us to correct for channel- or wavelength-dependent
instrumental effects by utilizing the band-integrated time series and
measurements of the drift of the spectrum on the detector over time. We achieve
almost photon-limited results for individual spectral bins, but the
uncertainties in the transit depth for the the band-integrated data are
exacerbated by the uneven sampling of the light curve imposed by the orbital
phasing of HST's observations. Our final transit spectra for all three objects
are consistent with the presence of a broad absorption feature at 1.4 microns
potentially due to water. However, the amplitude of the absorption is less than
that expected based on previous observations with Spitzer, possibly due to
hazes absorbing in the NIR or non-solar compositions. The degeneracy of models
with different compositions and temperature structures combined with the low
amplitude of any features in the data preclude our ability to place unambiguous
constraints on the atmospheric composition without additional observations with
WFC3 to improve the S/N and/or a comprehensive multi-wavelength analysis.Comment: 20 pages, 21 figures. Accepted for publication in ApJ. Figure and
table positioning is preliminary and subject to change prior to final
publicatio
Wide-Field Imaging Interferometry Spatial-Spectral Image Synthesis Algorithms
Developed is an algorithmic approach for wide field of view interferometric spatial-spectral image synthesis. The data collected from the interferometer consists of a set of double-Fourier image data cubes, one cube per baseline. These cubes are each three-dimensional consisting of arrays of two-dimensional detector counts versus delay line position. For each baseline a moving delay line allows collection of a large set of interferograms over the 2D wide field detector grid; one sampled interferogram per detector pixel per baseline. This aggregate set of interferograms, is algorithmically processed to construct a single spatial-spectral cube with angular resolution approaching the ratio of the wavelength to longest baseline. The wide field imaging is accomplished by insuring that the range of motion of the delay line encompasses the zero optical path difference fringe for each detector pixel in the desired field-of-view. Each baseline cube is incoherent relative to all other baseline cubes and thus has only phase information relative to itself. This lost phase information is recovered by having point, or otherwise known, sources within the field-of-view. The reference source phase is known and utilized as a constraint to recover the coherent phase relation between the baseline cubes and is key to the image synthesis. Described will be the mathematical formalism, with phase referencing and results will be shown using data collected from NASA/GSFC Wide-Field Imaging Interferometry Testbed (WIIT)
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
Three Super-Earths Orbiting HD 7924
We report the discovery of two super-Earth mass planets orbiting the nearby
K0.5 dwarf HD 7924 which was previously known to host one small planet. The new
companions have masses of 7.9 and 6.4 M, and orbital periods of 15.3
and 24.5 days. We perform a joint analysis of high-precision radial velocity
data from Keck/HIRES and the new Automated Planet Finder Telescope (APF) to
robustly detect three total planets in the system. We refine the ephemeris of
the previously known planet using five years of new Keck data and high-cadence
observations over the last 1.3 years with the APF. With this new ephemeris, we
show that a previous transit search for the inner-most planet would have
covered 70% of the predicted ingress or egress times. Photometric data
collected over the last eight years using the Automated Photometric Telescope
shows no evidence for transits of any of the planets, which would be detectable
if the planets transit and their compositions are hydrogen-dominated. We detect
a long-period signal that we interpret as the stellar magnetic activity cycle
since it is strongly correlated with the Ca II H and K activity index. We also
detect two additional short-period signals that we attribute to
rotationally-modulated starspots and a one month alias. The high-cadence APF
data help to distinguish between the true orbital periods and aliases caused by
the window function of the Keck data. The planets orbiting HD 7924 are a local
example of the compact, multi-planet systems that the Kepler Mission found in
great abundance.Comment: Accepted to ApJ on 4/7/201
The California-Kepler Survey. IV. Metal-rich Stars Host a Greater Diversity of Planets
Probing the connection between a star's metallicity and the presence and
properties of any associated planets offers an observational link between
conditions during the epoch of planet formation and mature planetary systems.
We explore this connection by analyzing the metallicities of Kepler target
stars and the subset of stars found to host transiting planets. After
correcting for survey incompleteness, we measure planet occurrence: the number
of planets per 100 stars with a given metallicity . Planet occurrence
correlates with metallicity for some, but not all, planet sizes and orbital
periods. For warm super-Earths having days and , planet occurrence is nearly constant over metallicities spanning
0.4 dex to +0.4 dex. We find 20 warm super-Earths per 100 stars, regardless
of metallicity. In contrast, the occurrence of warm sub-Neptunes () doubles over that same metallicity interval, from 20 to 40
planets per 100 stars. We model the distribution of planets as , where characterizes the strength of any metallicity
correlation. This correlation steepens with decreasing orbital period and
increasing planet size. For warm super-Earths ,
while for hot Jupiters . High metallicities in
protoplanetary disks may increase the mass of the largest rocky cores or the
speed at which they are assembled, enhancing the production of planets larger
than 1.7 . The association between high metallicity and short-period
planets may reflect disk density profiles that facilitate the inward migration
of solids or higher rates of planet-planet scattering.Comment: 32 pages, 15 figures, 9 tables, accepted for publication in The
Astronomical Journa
Characterizing K2 Candidate Planetary Systems Orbiting Low-mass Stars. I. Classifying Low-mass Host Stars Observed during Campaigns 1–7
We present near-infrared spectra for 144 candidate planetary systems identified during Campaigns 1–7 of the NASA K2 Mission. The goal of the survey was to characterize planets orbiting low-mass stars, but our Infrared Telescope Facility/SpeX and Palomar/TripleSpec spectroscopic observations revealed that 49% of our targets were actually giant stars or hotter dwarfs reddened by interstellar extinction. For the 72 stars with spectra consistent with classification as cool dwarfs (spectral types K3–M4), we refined their stellar properties by applying empirical relations based on stars with interferometric radius measurements. Although our revised temperatures are generally consistent with those reported in the Ecliptic Plane Input Catalog (EPIC), our revised stellar radii are typically 0.13 [subscript ⊙](39%) larger than the EPIC values, which were based on model isochrones that have been shown to underestimate the radii of cool dwarfs. Our improved stellar characterizations will enable more efficient prioritization of K2 targets for follow-up studies
A low stellar obliquity for WASP-47, a compact multiplanet system with a hot Jupiter and an ultra-short period planet
We have detected the Rossiter-Mclaughlin effect during a transit of WASP-47b,
the only known hot Jupiter with close planetary companions. By combining our
spectroscopic observations with Kepler photometry, we show that the projected
stellar obliquity is . We can firmly exclude a
retrograde orbit for WASP-47b, and rule out strongly misaligned prograde
orbits. Low obliquities have also been found for most of the other compact
multiplanet systems that have been investigated. The Kepler-56 system, with two
close-in gas giants transiting their subgiant host star with an obliquity of at
least 45, remains the only clear counterexample.Comment: 5 pages, 2 figures, Accepted for publication on ApJL, comments
welcom
Discovery of a White Dwarf Companion to HD 159062
We report on the discovery of a white dwarf companion to the nearby late G
dwarf star, HD 159062. The companion is detected in 14 years of precise radial
velocity (RV) data, and in high-resolution imaging observations. RVs of HD
159062 from 2003-2018 reveal an acceleration of ,
indicating that it hosts a companion with a long-period orbit. Subsequent
imaging observations with the ShaneAO system on the Lick Observatory 3-meter
Shane telescope, the PHARO AO system on the Palomar Observatory 5-meter
telescope, and the NIRC2 AO system at the Keck II 10-meter telescope reveal a
faint companion 2.7'' from the primary star. We performed relative photometry,
finding magnitudes,
magnitudes, and magnitudes for the companion from
these observations. Analysis of the radial velocities, astrometry, and
photometry reveals that the combined data set can only be reconciled for the
scenario where HD 159062 B is a white dwarf. A full Bayesian analysis of the RV
and imaging data to obtain the cooling age, mass, and orbital parameters of the
white dwarf indicates that the companion is an old white dwarf with an orbital period of years, and a cooling age of Gyr.Comment: 10 pages, 9 figure
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