58 research outputs found
Investigating the Atmospheric Mass Loss of the Kepler-105 Planets Straddling the Radius Gap
An intriguing pattern among exoplanets is the lack of detected planets
between approximately R and R. One proposed
explanation for this "radius gap" is the photoevaporation of planetary
atmospheres, a theory that can be tested by studying individual planetary
systems. Kepler-105 is an ideal system for such testing due to the ordering and
sizes of its planets. Kepler-105 is a sun-like star that hosts two planets
straddling the radius gap in a rare architecture with the larger planet closer
to the host star ( R, days, R, days). If photoevaporation sculpted the
atmospheres of these planets, then Kepler-105b would need to be much more
massive than Kepler-105c to retain its atmosphere, given its closer proximity
to the host star. To test this hypothesis, we simultaneously analyzed radial
velocities (RVs) and transit timing variations (TTVs) of the Kepler-105 system,
measuring disparate masses of M ( g cm) and M ( g cm). Based on these masses, the difference in gas
envelope content of the Kepler-105 planets could be entirely due to
photoevaporation (in 76\% of scenarios), although other mechanisms like
core-powered mass loss could have played a role for some planet albedos.Comment: 14 pages, 3 figures, 2 table
The TESS-Keck Survey: Science Goals and Target Selection
Space-based transit missions such as Kepler and TESS have demonstrated that
planets are ubiquitous. However, the success of these missions heavily depends
on ground-based radial velocity (RV) surveys, which combined with transit
photometry can yield bulk densities and orbital properties. While most Kepler
host stars are too faint for detailed follow-up observations, TESS is detecting
planets orbiting nearby bright stars that are more amenable to RV
characterization. Here we introduce the TESS-Keck Survey (TKS), an RV program
using ~100 nights on Keck/HIRES to study exoplanets identified by TESS. The
primary survey aims are investigating the link between stellar properties and
the compositions of small planets; studying how the diversity of system
architectures depends on dynamical configurations or planet multiplicity;
identifying prime candidates for atmospheric studies with JWST; and
understanding the role of stellar evolution in shaping planetary systems. We
present a fully-automated target selection algorithm, which yielded 103 planets
in 86 systems for the final TKS sample. Most TKS hosts are inactive,
solar-like, main-sequence stars (4500 K < Teff < 6000 K) at a wide range of
metallicities. The selected TKS sample contains 71 small planets (Rp < 4 Re),
11 systems with multiple transiting candidates, 6 sub-day period planets and 3
planets that are in or near the habitable zone of their host star. The target
selection described here will facilitate the comparison of measured planet
masses, densities, and eccentricities to predictions from planet population
models. Our target selection software is publicly available (at
https://github.com/ashleychontos/sort-a-survey) and can be adapted for any
survey which requires a balance of multiple science interests within a given
telescope allocation.Comment: 23 pages, 10 figures, 5 table
The young HD 73583 (TOI-560) planetary system: two 10-M-circle plus mini-Neptunes transiting a 500-Myr-old, bright, and active K dwarf
We present the discovery and characterization of two transiting planets observed by TESS in the light curves of the young and bright (V = 9.67) star HD73583 (TOI-560). We perform an intensive spectroscopic and photometric space-and ground-based follow-up in order to confirm and characterize the system. We found that HD73583 is a young (∼500 Myr) active star with a rotational period of 12.08 ± 0.11 d, and a mass and radius of 0.73 ± 0.02 M and 0.65 ± 0.02 R, respectively. HD 73583 b (Pb = 6.3980420-0.0000062+ 0.0000067 d) has a mass and radius of 10.2-3.1+ 3.4 M and 2.79 ± 0.10 R, respectively, which gives a density of 2.58-0.81+ 0.95 g, cm-3. HD 73583 c (Pc = 18.87974-0.00074+ 0.00086 d) has a mass and radius of 9.7-1.7+ 1.8 M and 2.39-0.09+ 0.10 R, respectively, which translates to a density of 3.88-0.80+ 0.91g, cm-3. Both planets are consistent with worlds made of a solid core surrounded by a volatile envelope. Because of their youth and host star brightness, they both are excellent candidates to perform transmission spectroscopy studies. We expect ongoing atmospheric mass-loss for both planets caused by stellar irradiation. We estimate that the detection of evaporating signatures on H and He would be challenging, but doable with present and future instruments
Overfitting Affects the Reliability of Radial Velocity Mass Estimates of the V1298 Tau Planets
Mass, radius, and age measurements of young (<100 Myr) planets have the power
to shape our understanding of planet formation. However, young stars tend to be
extremely variable in both photometry and radial velocity, which makes
constraining these properties challenging. The V1298 Tau system of four ~0.5
Rjup planets transiting a pre-main sequence star presents an important, if
stress-inducing, opportunity to directly observe and measure the properties of
infant planets. Su\'arez-Mascare\~no et al. (2021) published
radial-velocity-derived masses for two of the V1298 Tau planets using a
state-of-the-art Gaussian Process regression framework. The planetary densities
computed from these masses were surprisingly high, implying extremely rapid
contraction after formation in tension with most existing planet formation
theories. In an effort to further constrain the masses of the V1298 Tau
planets, we obtained 36 RVs using Keck/HIRES, and analyzed them in concert with
published RVs and photometry. Through performing a suite of cross validation
tests, we found evidence that the preferred model of SM21 suffers from
overfitting, defined as the inability to predict unseen data, rendering the
masses unreliable. We detail several potential causes of this overfitting, many
of which may be important for other RV analyses of other active stars, and
recommend that additional time and resources be allocated to understanding and
mitigating activity in active young stars such as V1298 Tau.Comment: 26 pages, 12 figures; published in A
TOI-1416: A system with a super-Earth planet with a 1.07d period
TOI 1416 (BD+42 2504, HIP 70705) is a V=10 late G or early K-type dwarf star
with transits detected by TESS. Radial velocities verify the presence of the
transiting planet TOI-1416 b, with a period of 1.07d, a mass of and a radius of , implying a slightly sub-Earth
density of g cm. The RV data also further indicate a tentative
planet c with a period of 27.4 or 29.5 days, whose nature cannot be verified
due to strong suspicions about contamination by a signal related to the Moon's
synodic period of 29.53 days. The near-USP (Ultra Short Period) planet TOI-1416
b is a typical representative of a short-period and hot ( 1570
K) super-Earth like planet. A planet model of an interior of molten magma
containing a significant fraction of dissolved water provides a plausible
explanation for its composition, and its atmosphere could be suitable for
transmission spectroscopy with JWST. The position of TOI-1416 b within the
radius-period distribution corroborates that USPs with periods of less than one
day do not form any special group of planets. Rather, this implies that USPs
belong to a continuous distribution of super-Earth like planets with periods
ranging from the shortest known ones up to ~ 30 days, whose period-radius
distribution is delimitated against larger radii by the Neptune desert and by
the period-radius valley that separates super-Earths from sub-Neptune planets.
In the abundance of small-short periodic planets against period, a plateau
between periods of 0.6 to 1.4 days has however become notable that is
compatible with the low-eccentricity formation channel. For the Neptune desert,
its lower limits required a revision due to the increasing population of short
period planets and new limits are provided. These limits are also given in
terms of the planets' insolation and effective temperatures.Comment: 31 pages, 31 figures, 8 tables, accepted for publication in A&
The TESS-Keck Survey. XV. Precise Properties of 108 TESS Planets and Their Host Stars
We present the stellar and planetary properties for 85 TESS Objects of
Interest (TOIs) hosting 108 planet candidates which comprise the TESS-Keck
Survey (TKS) sample. We combine photometry, high-resolution spectroscopy, and
Gaia parallaxes to measure precise and accurate stellar properties. We then use
these parameters as inputs to a lightcurve processing pipeline to recover
planetary signals and homogeneously fit their transit properties. Among these
transit fits, we detect significant transit-timing variations among at least
three multi-planet systems (TOI-1136, TOI-1246, TOI-1339) and at least one
single-planet system (TOI-1279). We also reduce the uncertainties on
planet-to-star radius ratios across our sample, from a median
fractional uncertainty of 8.8 among the original TOI Catalog values to
3.0 among our updated results. With this improvement, we are able to
recover the Radius Gap among small TKS planets and find that the topology of
the Radius Gap among our sample is broadly consistent with that measured among
Kepler planets. The stellar and planetary properties presented here will
facilitate follow-up investigations of both individual TOIs and broader trends
in planet properties, system dynamics, and the evolution of planetary systems.Comment: Accepted at The Astronomical Journal; 21 pages, 9 figure
Radial velocity confirmation of a hot super-Neptune discovered by TESS with a warm Saturn-mass companion
We report the discovery and confirmation of the planetary system TOI-1288.
This late G dwarf harbours two planets: TOI-1288 b and TOI-1288 c. We combine
TESS space-borne and ground-based transit photometry with HARPS-N and HIRES
high-precision Doppler measurements, which we use to constrain the masses of
both planets in the system and the radius of planet b. TOI-1288~b has a period
of d, a radius of
R, and a mass of M, making this planet a hot
transiting super-Neptune situated right in the Neptunian desert. This desert
refers to a paucity of Neptune-sized planets on short period orbits. Our
2.4-year-long Doppler monitoring of TOI-1288 revealed the presence of a
Saturn-mass planet on a moderately eccentric orbit ()
with a minimum mass of M and a period of
d. The 5 sectors worth of TESS data do not cover our expected mid-transit time
for TOI-1288 c, and we do not detect a transit for this planet in these
sectors.Comment: 16 pages, 17 figures, under review MNRA
Physical Parameters of the Multiplanet Systems HD 106315 and GJ 9827
HD 106315 and GJ 9827 are two bright, nearby stars that host multiple super-Earths and sub-Neptunes discovered by K2 that are well suited for atmospheric characterization. We refined the planets' ephemerides through Spitzer transits, enabling accurate transit prediction required for future atmospheric characterization through transmission spectroscopy. Through a multiyear high-cadence observing campaign with Keck/High Resolution Echelle Spectrometer and Magellan/Planet Finder Spectrograph, we improved the planets' mass measurements in anticipation of Hubble Space Telescope transmission spectroscopy. For GJ 9827, we modeled activity-induced radial velocity signals with a Gaussian process informed by the Calcium II H&K lines in order to more accurately model the effect of stellar noise on our data. We measured planet masses of M_b = 4.87 ± 0.37 M_⊕, M_c = 1.92 ± 0.49 M_⊕, and M_d = 3.42 ± 0.62 M_⊕. For HD 106315, we found that such activity radial velocity decorrelation was not effective due to the reduced presence of spots and speculate that this may extend to other hot stars as well (T_(eff) > 6200 K). We measured planet masses of M_b = 10.5 ± 3.1 M_⊕ and M_c = 12.0 ± 3.8 M_⊕. We investigated all of the planets' compositions through comparison of their masses and radii to a range of interior models. GJ 9827 b and GJ 9827 c are both consistent with a 50/50 rock-iron composition, GJ 9827 d and HD 106315 b both require additional volatiles and are consistent with moderate amounts of water or hydrogen/helium, and HD 106315 c is consistent with a ~10% hydrogen/helium envelope surrounding an Earth-like rock and iron core
Giant Outer Transiting Exoplanet Mass (GOT 'EM) Survey. IV. Long-term Doppler Spectroscopy for 11 Stars Thought to Host Cool Giant Exoplanets
Discovering and characterizing exoplanets at the outer edge of the transit
method's sensitivity has proven challenging owing to geometric biases and the
practical difficulties associated with acquiring long observational baselines.
Nonetheless, a sample of giant exoplanets on orbits longer than 100 days has
been identified by transit hunting missions. We present long-term Doppler
spectroscopy for 11 such systems with observation baselines spanning a few
years to a decade. We model these radial velocity observations jointly with
transit photometry to provide initial characterizations of these objects and
the systems in which they exist. Specifically, we make new precise mass
measurements for four long-period giant exoplanets (Kepler-111 c, Kepler-553 c,
Kepler-849 b, and PH-2 b), we place new upper limits on mass for four others
(Kepler-421 b, KOI-1431.01, Kepler-1513 b, and Kepler-952 b), and we show that
several "confirmed" planets are in fact not planetary at all. We present these
findings to complement similar efforts focused on closer-in short-period giant
planets, and with the hope of inspiring future dedicated studies of cool giant
exoplanets.Comment: 35 pages, 24 figures, 11 tables. Accepted for publication in ApJ
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