231 research outputs found
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
The Effects of Stellar Companions on the Observed Transiting Exoplanet Radius Distribution
Understanding the distribution and occurrence rate of small planets was a fundamental goal of the Kepler transiting exoplanet mission, and could be improved with K2 and Transiting Exoplanet Survey Satellite (TESS). Deriving accurate exoplanetary radii requires accurate measurements of the host star radii and the planetary transit depths, including accounting for any "third light" in the system due to nearby bound companions or background stars. High-resolution imaging of Kepler and K2 planet candidate hosts to detect very close (within ~0.”5) background or bound stellar companions has been crucial for both confirming the planetary nature of candidates, and the determination of accurate planetary radii and mean densities. Here we present an investigation of the effect of close companions, both detected and undetected, on the observed (raw count) exoplanet radius distribution. We demonstrate that the recently detected "gap" in the observed radius distribution (also seen in the completeness-corrected distribution) is fairly robust to undetected stellar companions, given that all of the systems in the sample have undergone some kind of vetting with high-resolution imaging. However, while the gap in the observed sample is not erased or shifted, it is partially filled in after accounting for possible undetected stellar companions. These findings have implications for the most likely core composition, and thus formation location, of super-Earth and sub-Neptune planets. Furthermore, we show that without high-resolution imaging of planet candidate host stars, the shape of the observed exoplanet radius distribution will be incorrectly inferred, for both Kepler- and TESS-detected systems
Long-Period Giant Companions to Three Compact, Multiplanet Systems
Understanding the relationship between long-period giant planets and multiple smaller short-period planets is critical for formulating a complete picture of planet formation. This work characterizes three such systems. We present Kepler-65, a system with an eccentric (e = 0.28 ± 0.07) giant planet companion discovered via radial velocities (RVs) exterior to a compact, multiply transiting system of sub-Neptune planets. We also use precision RVs to improve mass and radius constraints on two other systems with similar architectures, Kepler-25 and Kepler-68. In Kepler-68 we propose a second exterior giant planet candidate. Finally, we consider the implications of these systems for planet formation models, particularly that the moderate eccentricity in Kepler-65\u27s exterior giant planet did not disrupt its inner system
SImMER: A Pipeline for Reducing and Analyzing Images of Stars
We present the first public version of SImMER, an open-source Python
reduction pipeline for astronomical images of point sources. Current
capabilities include dark-subtraction, flat-fielding, sky-subtraction, image
registration, FWHM measurement, contrast curve calculation, and table and plot
generation. SImMER supports observations taken with the ShARCS camera on the
Shane 3-m telescope and the PHARO camera on the Hale 5.1-m telescope. The
modular nature of SImMER allows users to extend the pipeline to accommodate
additional instruments with relative ease. One of the core functions of the
pipeline is its image registration module, which is flexible enough to reduce
saturated images and images of similar-brightness, resolved stellar binaries.
Furthermore, SImMER can compute contrast curves for reduced images and produce
publication-ready plots. The code is developed online at
\url{https://github.com/arjunsavel/SImMER} and is both pip- and
conda-installable. We develop tutorials and documentation alongside the code
and host them online. With SImMER, we aim to provide a community resource for
accurate and reliable data reduction and analysis.Comment: 12 pages, 5 figures. Accepted to PAS
Assessing the Effect of Stellar Companions from High-Resolution Imaging of Kepler Objects of Interest
We report on 176 close (<2") stellar companions detected with high-resolution
imaging near 170 hosts of Kepler Objects of Interest. These Kepler targets were
prioritized for imaging follow-up based on the presence of small planets, so
most of the KOIs in these systems (176 out of 204) have nominal radii <6 R_E .
Each KOI in our sample was observed in at least 2 filters with adaptive optics,
speckle imaging, lucky imaging, or HST. Multi-filter photometry provides color
information on the companions, allowing us to constrain their stellar
properties and assess the probability that the companions are physically bound.
We find that 60 -- 80% of companions within 1" are bound, and the bound
fraction is >90% for companions within 0.5"; the bound fraction decreases with
increasing angular separation. This picture is consistent with simulations of
the binary and background stellar populations in the Kepler field. We also
reassess the planet radii in these systems, converting the observed
differential magnitudes to a contamination in the Kepler bandpass and
calculating the planet radius correction factor, . Under the assumption that planets in bound binaries are equally
likely to orbit the primary or secondary, we find a mean radius correction
factor for planets in stellar multiples of . If stellar
multiplicity in the Kepler field is similar to the solar neighborhood, then
nearly half of all Kepler planets may have radii underestimated by an average
of 65%, unless vetted using high resolution imaging or spectroscopy.Comment: 23 pages, 12 figures. Accepted for publication in The Astronomical
Journa
The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets
The size of a planet is an observable property directly connected to the
physics of its formation and evolution. We used precise radius measurements
from the California-Kepler Survey (CKS) to study the size distribution of 2025
planets in fine detail. We detect a factor of 2 deficit
in the occurrence rate distribution at 1.5-2.0 R. This gap splits
the population of close-in ( < 100 d) small planets into two size regimes:
R < 1.5 R and R = 2.0-3.0 R, with few planets in
between. Planets in these two regimes have nearly the same intrinsic frequency
based on occurrence measurements that account for planet detection
efficiencies. The paucity of planets between 1.5 and 2.0 R supports
the emerging picture that close-in planets smaller than Neptune are composed of
rocky cores measuring 1.5 R or smaller with varying amounts of
low-density gas that determine their total sizes.Comment: Paper III in the California-Kepler Survey series, accepted to the
Astronomical Journa
The California-Kepler Survey. II. Precise Physical Properties of 2025 Kepler Planets and Their Host Stars
We present stellar and planetary properties for 1305 Kepler Objects of
Interest (KOIs) hosting 2025 planet candidates observed as part of the
California-Kepler Survey. We combine spectroscopic constraints, presented in
Paper I, with stellar interior modeling to estimate stellar masses, radii, and
ages. Stellar radii are typically constrained to 11%, compared to 40% when only
photometric constraints are used. Stellar masses are constrained to 4%, and
ages are constrained to 30%. We verify the integrity of the stellar parameters
through comparisons with asteroseismic studies and Gaia parallaxes. We also
recompute planetary radii for 2025 planet candidates. Because knowledge of
planetary radii is often limited by uncertainties in stellar size, we improve
the uncertainties in planet radii from typically 42% to 12%. We also leverage
improved knowledge of stellar effective temperature to recompute incident
stellar fluxes for the planets, now precise to 21%, compared to a factor of two
when derived from photometry.Comment: 13 pages, 4 figures, 4 tables, accepted for publication in AJ; full
versions of tables 3 and 4 are include
HAT-P-11: Discovery of a Second Planet and a Clue to Understanding Exoplanet Obliquities
HAT-P-11 is a mid-K dwarf that hosts one of the first Neptune-sized planets
found outside the solar system. The orbit of HAT-P-11b is misaligned with the
star's spin --- one of the few known cases of a misaligned planet orbiting a
star less massive than the Sun. We find an additional planet in the system
based on a decade of precision radial velocity (RV) measurements from
Keck/HIRES. HAT-P-11c is similar to Jupiter in its mass ( ) and orbital period ( year), but has a
much more eccentric orbit (). In our joint modeling of RV and
stellar activity, we found an activity-induced RV signal of 7 m s,
consistent with other active K dwarfs, but significantly smaller than the 31 m
s reflex motion due to HAT-P-11c. We investigated the dynamical coupling
between HAT-P-11b and c as a possible explanation for HAT-P-11b's misaligned
orbit, finding that planet-planet Kozai interactions cannot tilt planet b's
orbit due to general relativistic precession; however, nodal precession
operating on million year timescales is a viable mechanism to explain
HAT-P-11b's high obliquity. This leaves open the question of why HAT-P-11c may
have such a tilted orbit. At a distance of 38 pc, the HAT-P-11 system offers
rich opportunities for further exoplanet characterization through astrometry
and direct imaging.Comment: 16 pages, 11 figures, 4 tables. Accepted to A
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