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
K2-136 is a late-K dwarf (0.742 ± 0.039
M
⊙
) in the Hyades open cluster with three known, transiting planets and an age of 650 ± 70 Myr. Analyzing K2 photometry, we found that planets ...K2-136b, c, and d have periods of 8.0, 17.3, and 25.6 days and radii of 1.014 ± 0.050
R
⊕
, 3.00 ± 0.13
R
⊕
, and 1.565 ± 0.077
R
⊕
, respectively. We collected 93 radial velocity (RV) measurements with the High-Accuracy Radial-velocity Planet Searcher for the Northern hemisphere (HARPS-N) spectrograph (Telescopio Nazionale Galileo) and 22 RVs with the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) spectrograph (Very Large Telescope). Analyzing HARPS-N and ESPRESSO data jointly, we found that K2-136c induced a semi-amplitude of 5.49 ± 0.53 m s
−1
, corresponding to a mass of 18.1 ± 1.9
M
⊕
. We also placed 95% upper mass limits on K2-136b and d of 4.3 and 3.0
M
⊕
, respectively. Further, we analyzed Hubble Space Telescope and XMM-Newton observations to establish the planetary high-energy environment and investigate possible atmospheric loss. K2-136c is now the smallest planet to have a measured mass in an open cluster and one of the youngest planets ever with a mass measurement. K2-136c has ∼75% the radius of Neptune but is similar in mass, yielding a density of
3.69
−
0.56
+
0.67
g cm
−3
(∼2–3 times denser than Neptune). Mass estimates for K2-136b (and possibly d) may be feasible with more RV observations, and insights into all three planets’ atmospheres through transmission spectroscopy would be challenging but potentially fruitful. This research and future mass measurements of young planets are critical for investigating the compositions and characteristics of small exoplanets at very early stages of their lives and providing insights into how exoplanets evolve with time.
Abstract 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.
Abstract
With JWST’s successful deployment and unexpectedly high fuel reserves, measuring the masses of sub-Neptunes transiting bright, nearby stars will soon become the bottleneck for characterizing ...the atmospheres of small exoplanets via transmission spectroscopy. Using a carefully curated target list and observations from more than 2 yr of APF-Levy and Keck-HIRES Doppler monitoring, the TESS-Keck Survey is working toward alleviating this pressure. Here we present mass measurements for 11 transiting planets in eight systems that are particularly suited to atmospheric follow-up with JWST. We also report the discovery and confirmation of a temperate super-Jovian-mass planet on a moderately eccentric orbit. The sample of eight host stars, which includes one subgiant, spans early-K to late-F spectral types (
T
eff
= 5200–6200 K). We homogeneously derive planet parameters using a joint photometry and radial velocity modeling framework, discuss the planets’ possible bulk compositions, and comment on their prospects for atmospheric characterization.
Abstract
We report the discovery of TOI-1444b, a 1.4
R
⊕
super-Earth on a 0.47 day orbit around a Sun-like star discovered by TESS. Precise radial velocities from Keck/HIRES confirmed the planet and ...constrained the mass to be 3.87 ± 0.71
M
⊕
. The RV data set also indicates a possible nontransiting, 16 day planet (11.8 ± 2.9
M
⊕
). We report a tentative detection of phase-curve variation and a secondary eclipse of TOI-1444b in the TESS bandpass. TOI-1444b joins the growing sample of 17 ultra-short-period planets (USPs) with well-measured masses and sizes, most of which are compatible with an Earth-like composition. We take this opportunity to examine the expanding sample of ultra-short-period planets (<2
R
⊕
) and contrast them with the newly discovered sub-day ultrahot Neptunes (>3
R
⊕
, >2000
F
⊕
TOI-849 b, LTT9779 b, and K2-100). We find that (1) USPs have predominately Earth-like compositions with inferred iron core mass fractions of 0.32 ± 0.04 and have masses below the threshold of runaway accretion (∼10
M
⊕
), while ultrahot Neptunes are above the threshold and have H/He or other volatile envelopes. (2) USPs are almost always found in multi-planet systems consistent with a secular interaction formation scenario; ultrahot Neptunes (
P
orb
≲1 day) tend to be “lonely,” similar to longer-period hot Neptunes (
P
orb
1–10 days) and hot Jupiters. (3) USPs occur around solar-metallicity stars while hot Neptunes prefer higher metallicity hosts. (4) In all these respects, ultrahot Neptunes show more resemblance to hot Jupiters than the smaller USP planets, although ultrahot Neptunes are rarer than both USPs and hot Jupiters by 1–2 orders of magnitude.
Management plans for North Atlantic right whales Eubalaena glacialis focus on preventing mortality from ship strikes and fishing gear entanglement. However, recovery may also be limited because ...individuals are under nutritional stress. We quantified the food requirements of North Atlantic right whales by age, sex and reproductive state and compared their predicted needs with field estimates of prey consumption to assess whether any demographic group of right whales might be nutritionally stressed. Energy requirements were estimated using a bioenergetics model that accounted for uncertainty in energy inputs and outputs. Consumption was estimated with prey samples taken near feeding whales in Cape Cod Bay (n = 28 net collections) and the Bay of Fundy (n = 19 optical plankton recordings). We found that calves required the least energy (~1767 MJ d−1) and that lactating females required the most (~4120 MJ d−1). Juveniles required considerably more energy than adult males and non-reproductive females. Our estimates of energy requirements for juveniles (~1906 MJ d−1), adult males (~1793 MJ d−1), and non-reproductive females (~2104 MJ d−1) compared favorably with estimates of actual consumption in Cape Cod Bay and the Bay of Fundy (i.e. they differed by ≤15%), suggesting that our model was reliable. However, lactating females appear to have obtained considerably less than their predicted energy requirements in both habitats. These findings suggest that lactating females may be experiencing an energy deficit, which may affect reproductive rates and slow population recovery. Nutritional stress may thus be limiting the recovery of North Atlantic right whales.
We report the detection of a Saturn-size exoplanet orbiting HD 332231 (TOI 1456) in light curves from the Transiting Exoplanet Survey Satellite (TESS). HD 332231—an F8 dwarf star with a V-band ...magnitude of 8.56—was observed by TESS in Sectors 14 and 15. We detect a single-transit event in the Sector 15 presearch data conditioning (PDC) light curve. We obtain spectroscopic follow-up observations of HD 332231 with the Automated Planet Finder, Keck I, and SONG telescopes. The orbital period we infer from radial velocity (RV) observations leads to the discovery of another transit in Sector 14 that was masked by PDC due to scattered light contamination. A joint analysis of the transit and RV data confirms the planetary nature of HD 332231 b, a Saturn-size (0.867 (+0.027,-0.025 R(J)), sub-Saturn-mass (0.244 ± 0.021M(J)) exoplanet on a 18.71 day circular orbit. The low surface gravity of HD 332231 b and the relatively low stellar flux it receives make it a compelling target for transmission spectroscopy. Also, the stellar obliquity is likely measurable via the Rossiter–McLaughlin effect, an exciting prospect given the 0.14 au orbital separation of HD 332231 b. The spectroscopic observations do not provide substantial evidence for any additional planets in the HD 332231 system, but continued RV monitoring is needed to further characterize this system. We also predict that the frequency and duration of masked data in the PDC light curves for TESS Sectors 14–16 could hide transits of some exoplanets with orbital periods between 10.5 and 17.5 days.
Abstract
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.
Abstract
We present the stellar and planetary properties for 85 TESS Objects of Interest (TOIs) hosting 108 planet candidates that compose 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 light-curve 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 multiplanet 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
R
p
/
R
⋆
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.
We report the measurement of a spectroscopic transit of TOI-1726c, one of two planets transiting a G-type star with V = 6.9 in the Ursa Major Moving Group (∼400 Myr). With a precise age constraint ...from cluster membership, TOI-1726 provides a great opportunity to test various obliquity excitation scenarios that operate on different timescales. By modeling the Rossiter-McLaughlin (RM) effect, we derived a sky-projected obliquity of . This result rules out a polar/retrograde orbit and is consistent with an aligned orbit for planet c. Considering the previously reported, similarly prograde RM measurement of planet b and the transiting nature of both planets, TOI-1726 tentatively conforms to the overall picture that compact multitransiting planetary systems tend to have coplanar, likely aligned orbits. TOI-1726 is also a great atmospheric target for understanding differential atmospheric loss of sub-Neptune planets (planet b 2.2 R⊕ and c 2.7 R⊕ both likely underwent photoevaporation). The coplanar geometry points to a dynamically cold history of the system that simplifies any future modeling of atmospheric escape.
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