7 research outputs found
A Comparison of the Composition of Planets in Single- and Multi-Planet Systems Orbiting M dwarfs
We investigate and compare the composition of M-dwarf planets in systems with
only one known planet (``singles") to those residing in multi-planet systems
(``multis") and the fundamental properties of their host stars. We restrict our
analysis to planets with directly measured masses and radii, which comprise a
total of 70 planets: 30 singles and 40 multis in 19 systems. We compare the
bulk densities for the full sample, which includes planets ranging in size from
to , and find that single planets have
significantly lower densities on average than multis, which we cannot attribute
to selection biases. We compare the bulk densities normalized by an Earth model
for planets with , and find that multis are also denser
with 99\% confidence. We calculate and compare the core/water mass fractions
(CMF/WMF) of low-mass planets (), and find that the likely
rocky multis (with ) have lower CMFs than singles. We also
compare the [Fe/H] metallicity and rotation period of all single versus
multi-planet host stars with such measurements in the literature and find that
multi-planet hosts are significantly more metal-poor than those hosting a
single planet. Moreover, we find that host star metallicity decreases with
increasing planet multiplicity. In contrast, we find only a modest difference
in the rotation period. The significant differences in planetary composition
and metallicity of the host stars point to different physical processes
governing the formation of single- and multi-planet systems in M dwarfs.Comment: 20 pages, 11 figures, 2 tables. Submitted to ApJ and under review.
Comments welcome
Scaling K2 VII: Evidence for a high occurrence rate of hot sub-Neptunes at intermediate ages
The NASA K2 mission obtained high precision time-series photometry for four
young clusters, including the near-twin 600-800 Myr-old Praesepe and Hyades
clusters. Hot sub-Neptunes are highly prone to mass-loss mechanisms, given
their proximity to the the host star and the weakly bound gaseous envelopes,
and analyzing this population at young ages can provide strong constraints on
planetary evolution models. Using our automated transit detection pipeline, we
recover 15 planet candidates across the two clusters, including 10 previously
confirmed planets. We find a hot sub-Neptune occurrence rate of 79-107% for GKM
stars in the Praesepe cluster. This is 2.5-3.5 sigma higher than the occurrence
rate of 16.54+1.00-0.98% for the same planets orbiting the ~3-9 Gyr-old GKM
field stars observed by K2, even after accounting for the slightly super-solar
metallicity ([Fe/H]~0.2 dex) of the Praesepe cluster. We examine the effect of
adding ~100 targets from the Hyades cluster, and extending the planet parameter
space under examination, and find similarly high occurrence rates in both
cases. The high occurrence rate of young, hot sub-Neptunes could indicate
either that these planets are undergoing atmospheric evolution as they age, or
that planetary systems that formed when the Galaxy was much younger are
substantially different than from today. Under the assumption of the
atmospheric mass-loss scenario, a significantly higher occurrence rate of these
planets at the intermediate ages of Praesepe and Hyades appears more consistent
with the core-powered mass loss scenario sculpting the hot sub-Neptune
population, compared to the photoevaporation scenario.Comment: 14 pages, 6 figures, published in A
Scaling K2. VI. Reduced Small Planet Occurrence in High Galactic Amplitude Stars
In this study, we performed a homogeneous analysis of the planets around FGK
dwarf stars observed by the Kepler and K2 missions, providing spectroscopic
parameters for 310 K2 targets -- including 239 Scaling K2 hosts -- observed
with Keck/HIRES. For orbital periods less than 40 days, we found that the
distribution of planets as a function of orbital period, stellar effective
temperature, and metallicity was consistent between K2 and Kepler, reflecting
consistent planet formation efficiency across numerous ~1 kpc sight-lines in
the local Milky Way. Additionally, we detected a 3X excess of sub-Saturns
relative to warm Jupiters beyond 10 days, suggesting a closer association
between sub-Saturn and sub-Neptune formation than between sub-Saturn and Jovian
formation. Performing a joint analysis of Kepler and K2 demographics, we
observed diminishing super-Earth, sub-Neptune, and sub-Saturn populations at
higher stellar effective temperatures, implying an inverse relationship between
formation and disk mass. In contrast, no apparent host-star spectral-type
dependence was identified for our population of Jupiters, which indicates
gas-giant formation saturates within the FGK mass regimes. We present support
for stellar metallicity trends reported by previous Kepler analyses. Using GAIA
DR3 proper motion and RV measurements, we discovered a galactic location trend:
stars that make large vertical excursions from the plane of the Milky Way host
fewer super-Earths and sub-Neptunes. While oscillation amplitude is associated
with metallicity, metallicity alone cannot explain the observed trend,
demonstrating that galactic influences are imprinted on the planet population.
Overall, our results provide new insights into the distribution of planets
around FGK dwarf stars and the factors that influence their formation and
evolution.Comment: 28 Pages, 12 Figures, 3 Tables; Accepted for Publication A
Spectroscopy of TOI-1259B:an unpolluted white dwarf companion to an inflated warm Saturn
A Reanalysis of the Composition of K2-106b: An Ultra-short-period Super-Mercury Candidate
We present a reanalysis of the K2-106 transiting planetary system, with a focus on the composition of K2-106b, an ultra-short-period, super-Mercury candidate. We globally model existing photometric and radial velocity data and derive a planetary mass and radius for K2-106b of M _p = 8.53 ± 1.02 M _⊕ and , which leads to a density of g cm ^−3 , a significantly lower value than previously reported in the literature. We use planet interior models that assume a two-layer planet comprised of a liquid, pure Fe core and an iron-free, MgSiO _3 mantle, and we determine that the range of the core mass fractions are consistent with the observed mass and radius. We use existing high-resolution spectra of the host star to derive the Fe/Mg/Si abundances ([Fe/H] = −0.03 ± 0.01, [Mg/H] = 0.04 ± 0.02, [Si/H] = 0.03 ± 0.06) to infer the composition of K2-106b. We find that K2-106b has a density and core mass fraction ( ) consistent with that of Earth (CMF _⊕ = 32%). Furthermore, its composition is consistent with what is expected, assuming that it reflects the relative refractory abundances of its host star. K2-106b is therefore unlikely to be a super-Mercury, as has been suggested in previous literature
Scaling K2. VI. Reduced Small-planet Occurrence in High-galactic-amplitude Stars
In this study, we performed a homogeneous analysis of the planets around FGK dwarf stars observed by the Kepler and K2 missions, providing spectroscopic parameters for 310 K2 targets —including 239 Scaling K2 hosts—observed with Keck/HIRES. For orbital periods less than 40 days, we found that the distribution of planets as a function of orbital period, stellar effective temperature, and metallicity was consistent between K2 and Kepler, reflecting consistent planet formation efficiency across numerous ∼1 kpc sight-lines in the local Milky Way. Additionally, we detected a 3× excess of sub-Saturns relative to warm Jupiters beyond 10 days, suggesting a closer association between sub-Saturn and sub-Neptune formation than between sub-Saturn and Jovian formation. Performing a joint analysis of Kepler and K2 demographics, we observed diminishing super-Earth, sub-Neptune, and sub-Saturn populations at higher stellar effective temperatures, implying an inverse relationship between formation and disk mass. In contrast, no apparent host-star spectral-type dependence was identified for our population of Jupiters, which indicates gas-giant formation saturates within the FGK mass regimes. We present support for stellar metallicity trends reported by previous Kepler analyses. Using Gaia DR3 proper motion and radial velocity measurements, we discovered a galactic location trend; stars that make large vertical excursions from the plane of the Milky Way host fewer super-Earths and sub-Neptunes. While oscillation amplitude is associated with metallicity, metallicity alone cannot explain the observed trend, demonstrating that galactic influences are imprinted on the planet population. Overall, our results provide new insights into the distribution of planets around FGK dwarf stars and the factors that influence their formation and evolution