Abstract
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 (RV) measurements, which makes constraining these properties challenging. The V1298 Tau system of four ∼0.5
R
J
planets transiting a pre-main-sequence star presents an important, if stress-inducing, opportunity to observe and measure directly the properties of infant planets. Suárez Mascareño et al. 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 constrain further 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 Suárez Mascareño et al. 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.
Abstract
TOI-561 is a galactic thick-disk star hosting an ultra-short-period (0.45-day-orbit) planet with a radius of 1.37
R
⊕
, making it one of the most metal-poor (Fe/H = −0.41) and oldest (≈10 ...Gyr) sites where an Earth-sized planet has been found. We present new simultaneous radial velocity (RV) measurements from Gemini-N/MAROON-X and Keck/HIRES, which we combined with literature RVs to derive a mass of
M
b
= 2.24 ± 0.20
M
⊕
. We also used two new sectors of TESS photometry to improve the radius determination, finding
R
b
= 1.37 ± 0.04
R
⊕
and confirming that TOI-561 b is one of the lowest-density super-Earths measured to date (
ρ
b
= 4.8 ± 0.5 g cm
−3
). This density is consistent with an iron-poor rocky composition reflective of the host star’s iron and rock-building element abundances; however, it is also consistent with a low-density planet with a volatile envelope. The equilibrium temperature of the planet (∼2300 K) suggests that this envelope would likely be composed of high mean molecular weight species, such as water vapor, carbon dioxide, or silicate vapor, and is likely not primordial. We also demonstrate that the composition determination is sensitive to the choice of stellar parameters and that further measurements are needed to determine whether TOI-561 b is a bare rocky planet, a rocky planet with an optically thin atmosphere, or a rare example of a nonprimordial envelope on a planet with a radius smaller than 1.5
R
⊕
.
Abstract
Wolf 359 (CN Leo, GJ 406, Gaia DR3 3864972938605115520) is a low-mass star in the fifth-closest neighboring system (2.41 pc). Because of its relative youth and proximity, Wolf 359 offers a ...unique opportunity to study substellar companions around M stars using infrared high-contrast imaging and radial velocity monitoring. We present the results of
Ms
-band (4.67
μ
m) vector vortex coronagraphic imaging using Keck-NIRC2 and add 12 Keck-HIRES and 68 MAROON-X velocities to the radial velocity baseline. Our analysis incorporates these data alongside literature radial velocities from CARMENES, the High Accuracy Radial velocity Planet Searcher, and Keck-HIRES to rule out the existence of a close (
a
< 10 au) stellar or brown dwarf companion and the majority of large gas giant companions. Our survey does not refute or confirm the long-period radial velocity candidate, Wolf 359 b (
P
∼ 2900 days), but rules out the candidate's existence as a large gas giant (>4
M
Jup
) assuming an age of younger than 1 Gyr. We discuss the performance of our high-contrast imaging survey to aid future observers using Keck-NIRC2 in conjunction with the vortex coronagraph in the
Ms
band and conclude by exploring the direct imaging capabilities with JWST to observe Jupiter- and Neptune-mass planets around Wolf 359.
Abstract
Exoplanet systems with multiple transiting planets are natural laboratories for testing planetary astrophysics. One such system is HD 191939 (TOI 1339), a bright (
V
= 9) and Sun-like (G9V) ...star, which TESS found to host three transiting planets (b, c, and d). The planets have periods of 9, 29, and 38 days each with similar sizes from 3 to 3.4
R
⊕
. To further characterize the system, we measured the radial velocity (RV) of HD 191939 over 415 days with Keck/HIRES and APF/Levy. We find that
M
b
= 10.4 ± 0.9
M
⊕
and
M
c
= 7.2 ± 1.4
M
⊕
, which are low compared to most known planets of comparable radii. The RVs yield only an upper limit on
M
d
(<5.8
M
⊕
at 2
σ
). The RVs further reveal a fourth planet (e) with a minimum mass of 0.34 ± 0.01
M
Jup
and an orbital period of 101.4 ± 0.4 days. Despite its nontransiting geometry, secular interactions between planet e and the inner transiting planets indicate that planet e is coplanar with the transiting planets (Δ
i
< 10°). We identify a second high-mass planet (f) with 95% confidence intervals on mass between 2 and 11
M
Jup
and period between 1700 and 7200 days, based on a joint analysis of RVs and astrometry from Gaia and Hipparcos. As a bright star hosting multiple planets with well-measured masses, HD 191939 presents many options for comparative planetary astronomy, including characterization with JWST.
Abstract
We measured the Rossiter–McLaughlin effect of WASP-107b during a single transit with Keck/HIRES. We found the sky-projected inclination of WASP-107b’s orbit, relative to its host star’s ...rotation axis, to be
degrees. This confirms the misaligned/polar orbit that was previously suggested from spot-crossing events and adds WASP-107b to the growing population of hot Neptunes in polar orbits around cool stars. WASP-107b is also the fourth such planet to have a known distant planetary companion. We examined several dynamical pathways by which this companion could have induced such an obliquity in WASP-107b. We find that nodal precession and disk dispersal-driven tilting can both explain the current orbital geometry while Kozai–Lidov cycles are suppressed by general relativity. While each hypothesis requires a mutual inclination between the two planets, nodal precession requires a much larger angle, which for WASP-107 is on the threshold of detectability with future Gaia astrometric data. As nodal precession has no stellar type dependence, but disk dispersal-driven tilting does, distinguishing between these two models is best done on the population level. Finding and characterizing more extrasolar systems like WASP-107 will additionally help distinguish whether the distribution of hot-Neptune obliquities is a dichotomy of aligned and polar orbits or if we are uniformly sampling obliquities during nodal precession cycles.
Abstract
Giant planets on short-period orbits are predicted to be inflated and eventually engulfed by their host stars. However, the detailed timescales and stages of these processes are not well ...known. Here, we present the discovery of three hot Jupiters (
P
< 10 days) orbiting evolved, intermediate-mass stars (
M
⋆
≈ 1.5
M
⊙
, 2
R
⊙
<
R
⋆
< 5
R
⊙
). By combining TESS photometry with ground-based photometry and radial velocity measurements, we report masses and radii for these three planets of between 0.4 and 1.8
M
J
and 0.8 and 1.8
R
J
. TOI-2337b has the shortest period (
P
= 2.99432 ± 0.00008 days) of any planet discovered around a red giant star to date. Both TOI-4329b and TOI-2669b appear to be inflated, but TOI-2337b does not show any sign of inflation. The large radii and relatively low masses of TOI-4329b and TOI-2669b place them among the lowest density hot Jupiters currently known, while TOI-2337b is conversely one of the highest. All three planets have orbital eccentricities of below 0.2. The large spread in radii for these systems implies that planet inflation has a complex dependence on planet mass, radius, incident flux, and orbital properties. We predict that TOI-2337b has the shortest orbital decay timescale of any planet currently known, but do not detect any orbital decay in this system. Transmission spectroscopy of TOI-4329b would provide a favorable opportunity for the detection of water, carbon dioxide, and carbon monoxide features in the atmosphere of a planet orbiting an evolved star, and could yield new information about planet formation and atmospheric evolution.
Abstract The distribution of stellar obliquities provides critical insight into the formation and evolution pathways of exoplanets. In the past decade, it was found that hot stars hosting hot ...Jupiters are more likely to have high obliquities than cool stars, but it is not clear whether this trend exists only for hot Jupiters or holds for other types of planets. In this work, we extend the study of the obliquities of hot (6250–7000 K) stars with transiting super-Earth-sized and sub-Neptune-sized planets. We constrain the obliquity distribution based on measurements of the stars’ projected rotation velocities. Our sample consists of 170 TESS and Kepler planet-hosting stars and 180 control stars chosen to have indistinguishable spectroscopic characteristics. In our analysis, we find evidence suggesting that the planet hosts have a systematically higher 〈 sin i 〉 compared to the control sample. This result implies that the planet hosts tend to have lower obliquities. However, the observed difference in 〈 sin i 〉 is not significant enough to confirm spin–orbit alignment as it is 3.8 σ away from perfect alignment. We also find evidence that within the planet-hosting stars there is a trend of higher obliquity (lower 〈 sin i 〉 ) for the hotter stars ( T eff > 6250 K) than for the cooler stars in the sample. This suggests that hot stars hosting smaller planets exhibit a broader obliquity distribution ( 〈 sin i 〉 = 0.79 ± 0.053 ) than cooler planet-hosting stars, indicating that high obliquities are not exclusive to hot Jupiters and instead are more broadly tied to hot stars.
Abstract
An intriguing pattern among exoplanets is the lack of detected planets between approximately 1.5
R
⊕
and 2.0
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
b
= 2.53 ± 0.07
R
⊕
,
P
b
= 5.41 days,
R
c
= 1.44 ± 0.04
R
⊕
,
P
c
= 7.13 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 and transit-timing variations of the Kepler-105 system, measuring disparate masses of
M
b
= 10.8 ± 2.3
M
⊕
(
ρ
b
= 3.68 ± 0.84 g cm
−3
) and
M
c
= 5.6 ± 1.2
M
⊕
(
ρ
c
= 10.4 ± 2.39 g cm
−3
). 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.
Abstract Hot Neptunes, gaseous planets smaller than Saturn (∼3–8 R ⊕ ) with orbital periods less than 10 days, are rare. Models predict this is due to high-energy stellar irradiation stripping ...planetary atmospheres over time, often leaving behind only rocky planetary cores. Using our TESS full-frame-image pipeline giants in conjunction with Keck/HIRES radial velocity measurements, we present the discovery of TIC365102760 b, a 6.2 R ⊕ (0.55 R J ), 19.2 M ⊕ (0.060 M J ) planet transiting a red giant star every 4.21285 days. The old age and high equilibrium temperature yet remarkably low density of this planet ( ρ p = 0.58 − 0.20 + 0.30 ρ J ) suggest that its gaseous envelope should have been stripped by high-energy stellar irradiation billions of years ago. The present-day planet mass and radius suggest the atmospheric stripping was slower than predicted. Unexpectedly low stellar activity and/or late-stage planet inflation could be responsible for the observed properties of this system. Further studies of this system with more precise photometry in multiple passbands will be capable of revealing more details of this planet’s atmosphere.
Abstract
We combine multiple campaigns of K2 photometry with precision radial velocity measurements from Keck-HIRES to measure the masses of three sub-Neptune-sized planets. We confirm the planetary ...nature of the massive sub-Neptune K2-182 b (
P
b
= 4.7 days,
R
b
= 2.69
R
⊕
) and derive refined parameters for K2-199 b and c (
P
b
= 3.2 days,
R
b
= 1.73
R
⊕
and
P
c
= 7.4 days,
R
c
= 2.85
R
⊕
). These planets provide valuable data points in the mass–radius plane, especially as TESS continues to reveal an increasingly diverse sample of sub-Neptunes. The moderately bright (
V
= 12.0 mag) early K dwarf K2-182 (EPIC 211359660) was observed during K2 campaigns 5 and 18. We find that K2-182 b is potentially one of the densest sub-Neptunes known to date (20 ± 5
M
⊕
and 5.6 ± 1.4 g cm
−3
). The K5V dwarf K2-199 (EPIC 212779596;
V
= 12.3 mag), observed in K2 campaigns 6 and 17, hosts two recently confirmed planets. We refine the orbital and planetary parameters for K2-199 b and c by modeling both campaigns of K2 photometry and adding 12 Keck-HIRES measurements to the existing radial velocity data set (
N
= 33). We find that K2-199 b is likely rocky, at 6.9 ± 1.8
M
⊕
and
7.2
−
2.0
+
2.1
g cm
−3
, and that K2-199 c has an intermediate density at 12.4 ± 2.3
M
⊕
and
2.9
−
0.6
+
0.7
g cm
−3
. We contextualize these planets on the mass–radius plane, discuss a small but intriguing population of “superdense” sub-Neptunes (
R
p
< 3
R
⊕
,
M
p
>20
M
⊕
), and consider our prospects for the planets’ atmospheric characterization.
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