Abstract
Radial velocity (RV) measurements of transiting multiplanet systems allow us to understand the densities and compositions of planets unlike those in the solar system. Kepler-102, which ...consists of five tightly packed transiting planets, is a particularly interesting system since it includes a super-Earth (Kepler-102d) and a sub-Neptune-sized planet (Kepler-102e) for which masses can be measured using RVs. Previous work found a high density for Kepler-102d, suggesting a composition similar to that of Mercury, while Kepler-102e was found to have a density typical of sub-Neptune size planets; however, Kepler-102 is an active star, which can interfere with RV mass measurements. To better measure the mass of these two planets, we obtained 111 new RVs using Keck/HIRES and Telescopio Nazionale Galileo/HARPS-N and modeled Kepler-102's activity using quasiperiodic Gaussian process regression. For Kepler-102d, we report a mass upper limit
M
d
< 5.3
M
⊕
(95% confidence), a best-fit mass
M
d
= 2.5 ± 1.4
M
⊕
, and a density
ρ
d
= 5.6 ± 3.2 g cm
−3
, which is consistent with a rocky composition similar in density to the Earth. For Kepler-102e we report a mass
M
e
= 4.7 ± 1.7
M
⊕
and a density
ρ
e
= 1.8 ± 0.7 g cm
−3
. These measurements suggest that Kepler-102e has a rocky core with a thick gaseous envelope comprising 2%–4% of the planet mass and 16%–50% of its radius. Our study is yet another demonstration that accounting for stellar activity in stars with clear rotation signals can yield more accurate planet masses, enabling a more realistic interpretation of planet interiors.
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 In order to understand the relationship between planet multiplicity, mass, and composition, we present newly measured masses of five planets in two planetary systems: Kepler-323 and ...Kepler-104. We used the HIRES instrument at the W.M. Keck Observatory to collect 79 new radial velocity (RV) measurements for Kepler-323, which we combined with 48 literature RVs from TNG/HARPS-N. We also conducted a reanalysis of the Kepler-104 system, using 44 previously published RV measurements. Kepler-323 b and c have masses of 2.0 − 1.1 + 1.2 M ⊕ and 6.5±1.6 M ⊕ , respectively, whereas the three Kepler-104 planets are more massive (10.0±2.8 M ⊕ , 7.1 − 3.5 + 3.8 M ⊕ , and 5.5 − 3.5 + 4.6 M ⊕ for planets b, c, and d, respectively). The Kepler-104 planets have densities consistent with rocky cores overlaid with gaseous envelopes ( 4.1 − 1.1 + 1.2 g cc −1 , 2.9 − 1.5 + 1.7 g cc −1 , and 1.6 − 1.1 + 1.5 g cc −1 respectively), whereas the Kepler-323 planets are consistent with having rocky compositions ( 4.5 − 2.4 + 2.8 g cc −1 and 9.9 − 2.5 + 2.7 g cc −1 ). The Kepler-104 system has among the lowest values for gap complexity ( C = 0.004) and mass partitioning ( Q = 0.03); whereas, the Kepler-323 planets have a mass partitioning similar to that of the Inner Solar System ( Q = 0.28 and Q = 0.24, respectively). For both exoplanet systems, the uncertainty in the mass partitioning is affected equally by (1) individual mass errors of the planets and (2) the possible existence of undetected low-mass planets, meaning that both improved mass characterization and improved sensitivity to low-mass planets in these systems would better elucidate the mass distribution among the planets.
Abstract
Despite the importance of Jupiter and Saturn to Earth’s formation and habitability, there has not yet been a comprehensive observational study of how giant exoplanets correlate with the ...architectural properties of close-in, sub-Neptune-sized exoplanets. This is largely because transit surveys are particularly insensitive to planets at orbital separations ≳1 au, and so their census of Jupiter-like planets is incomplete, inhibiting our study of the relationship between Jupiter-like planets and the small planets that do transit. To investigate the relationship between close-in, small and distant, giant planets, we conducted the Kepler Giant Planet Survey (KGPS). Using the W. M. Keck Observatory High Resolution Echelle Spectrometer, we spent over a decade collecting 2844 radial velocities (RVs; 2167 of which are presented here for the first time) of 63 Sunlike stars that host 157 transiting planets. We had no prior knowledge of which systems would contain giant planets beyond 1 au, making this survey unbiased with respect to previously detected Jovians. We announce RV-detected companions to 20 stars from our sample. These include 13 Jovians (
0.3
M
J
<
M
sin
i
<
13
M
J
, 1 au <
a
< 10 au), eight nontransiting sub-Saturns, and three stellar-mass companions. We also present updated masses and densities of 84 transiting planets. The KGPS project leverages one of the longest-running and most data-rich collections of RVs of the NASA Kepler systems yet, and it will provide a basis for addressing whether giant planets help or hinder the growth of sub-Neptune-sized and terrestrial planets. Future KGPS papers will examine the relationship between small, transiting planets and their long-period companions.
Abstract We confirm a massive sub-Neptune-sized planet on a P = 22.8 days orbit around the star TOI-1824 ( T eff = 5200 K, V = 9.7 mag). TESS first identified TOI-1824 b (formerly TOI-1824.01) as an ...object of interest in 2020 April after two transits in Sector 22 were matched with a single transit in Sector 21. TOI-1824 was subsequently targeted for ground-based Doppler monitoring with Keck-HIRES and APF-Levy. Using a joint model of the TESS photometry, radial velocities, and Ca ii H and K emission measurements as an activity indicator, we find that TOI-1824 b is an unusually dense sub-Neptune. The planet has a radius R p = 2.63 ± 0.15 R ⊕ and mass M p = 18.5 ± 3.2 M ⊕ , implying a bulk density of 5.6 ± 1.4 g cm −3 . TOI-1824 b's mass and radius situate it near a small group of “superdense sub-Neptunes” ( R p ≲ 3 R ⊕ and M p ≳ 20 M ⊕ ). While the formation mechanism of superdense sub-Neptunes is a mystery, one possible explanation is the constructive collision of primordial icy cores; such giant impacts would drive atmospheric escape and could help explain these planets' apparent lack of massive envelopes. We discuss TOI-1824 b in the context of these overdense planets, whose unique location in the exoplanet mass–radius plane make them a potentially valuable tracer of planet formation.
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
In this work, we present the discovery and confirmation of two hot Jupiters orbiting red giant stars, TOI-4377 b and TOI-4551 b, observed by Transiting Exoplanet Survey Satellite in the ...Southern ecliptic hemisphere and later followed-up with radial-velocity (RV) observations. For TOI-4377 b, we report a mass of $0.957^{+0.089}_{-0.087} \ M_\mathrm{J}$ and a inflated radius of 1.348 ± 0.081 RJ orbiting an evolved intermediate-mass star (1.36 M⊙ and 3.52 R⊙; TIC 394918211) on a period of of 4.378 d. For TOI-4551 b, we report a mass of 1.49 ± 0.13 MJ and a radius that is not obviously inflated of $1.058^{+0.110}_{-0.062} \ R_\mathrm{J}$, also orbiting an evolved intermediate-mass star (1.31 M⊙ and 3.55 R⊙; TIC 204650483) on a period of 9.956 d. We place both planets in context of known systems with hot Jupiters orbiting evolved hosts, and note that both planets follow the observed trend of the known stellar incident flux-planetary radius relation observed for these short-period giants. Additionally, we produce planetary interior models to estimate the heating efficiency with which stellar incident flux is deposited in the planet’s interior, estimating values of $1.91 \pm 0.48~{{\ \rm per\ cent}}$ and $2.19 \pm 0.45~{{\ \rm per\ cent}}$ for TOI-4377 b and TOI-4551 b, respectively. These values are in line with the known population of hot Jupiters, including hot Jupiters orbiting main-sequence hosts, which suggests that the radii of our planets have re-inflated in step with their parent star’s brightening as they evolved into the post-main sequence. Finally, we evaluate the potential to observe orbital decay in both systems.
Abstract
We present a radial velocity (RV) analysis of TOI-1136, a bright Transiting Exoplanet Survey Satellite (TESS) system with six confirmed transiting planets, and a seventh single-transiting ...planet candidate. All planets in the system are amenable to transmission spectroscopy, making TOI-1136 one of the best targets for intra-system comparison of exoplanet atmospheres. TOI-1136 is young (∼700 Myr), and the system exhibits transit timing variations (TTVs). The youth of the system contributes to high stellar variability on the order of 50 m s
−1
, much larger than the likely RV amplitude of any of the transiting exoplanets. Utilizing 359 High Resolution Echelle Spectrometer and Automated Planet Finder RVs collected as part of the TESS-Keck Survey, and 51 High-Accuracy Radial velocity Planetary Searcher North RVs, we experiment with a joint TTV-RV fit. With seven possible transiting planets, TTVs, more than 400 RVs, and a stellar activity model, we posit that we may be presenting the most complex mass recovery of an exoplanet system in the literature to date. By combining TTVs and RVs, we minimized Gaussian process overfitting and retrieved new masses for this system: (
m
b−g
=
3.50
−
0.7
+
0.8
,
6.32
−
1.3
+
1.1
,
8.35
−
1.6
+
1.8
,
6.07
−
1.01
+
1.09
,
9.7
−
3.7
+
3.9
,
5.6
−
3.2
+
4.1
M
⊕
). We are unable to significantly detect the mass of the seventh planet candidate in the RVs, but we are able to loosely constrain a possible orbital period near 80 days. Future TESS observations might confirm the existence of a seventh planet in the system, better constrain the masses and orbital properties of the known exoplanets, and generally shine light on this scientifically interesting system.
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.
Abstract We present and confirm TOI-1751 b, a transiting sub-Neptune orbiting a slightly evolved, solar-type, metal-poor star ( T eff = 5996 ± 110 K, log ( g ) = 4.2 ± 0.1 , V = 9.3 mag, Fe/H = −0.40 ...± 0.06 dex) every 37.47 days. We use TESS photometry to measure a planet radius of 2.77 − 0.07 + 0.15 R ⊕ . We also use both Keck/HIRES and APF/Levy radial velocities (RV) to derive a planet mass of 14.5 − 3.14 + 3.15 M ⊕ , and thus a planet density of 3.6 ± 0.9 g cm −3 . There is also a long-period (∼400 days) signal that is observed in only the Keck/HIRES data. We conclude that this long-period signal is not planetary in nature and is likely due to the window function of the Keck/HIRES observations. This highlights the role of complementary observations from multiple observatories to identify and exclude aliases in RV data. Finally, we investigate the potential compositions of this planet, including rocky and water-rich solutions, as well as theoretical irradiated ocean models. TOI-1751 b is a warm sub-Neptune with an equilibrium temperature of ∼820 K. As TOI-1751 is a metal-poor star, TOI-1751 b may have formed in a water-enriched formation environment. We thus favor a volatile-rich interior composition for this planet.
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