Abstract
LTT 1445 is a hierarchical triple M-dwarf star system located at a distance of 6.86 pc. The primary star LTT 1445A (0.257
M
⊙
) is known to host the transiting planet LTT 1445Ab with an ...orbital period of 5.36 days, making it the second-closest known transiting exoplanet system, and the closest one for which the host is an M dwarf. Using Transiting Exoplanet Survey Satellite data, we present the discovery of a second planet in the LTT 1445 system, with an orbital period of 3.12 days. We combine radial-velocity measurements obtained from the five spectrographs, Echelle Spectrograph for Rocky Exoplanets and Stable Spectroscopic Observations, High Accuracy Radial Velocity Planet Searcher, High-Resolution Echelle Spectrometer, MAROON-X, and Planet Finder Spectrograph to establish that the new world also orbits LTT 1445A. We determine the mass and radius of LTT 1445Ab to be 2.87 ± 0.25
M
⊕
and
1.304
−
0.060
+
0.067
R
⊕
, consistent with an Earth-like composition. For the newly discovered LTT 1445Ac, we measure a mass of
1.54
−
0.19
+
0.20
M
⊕
and a minimum radius of 1.15
R
⊕
, but we cannot determine the radius directly as the signal-to-noise ratio of our light curve permits both grazing and nongrazing configurations. Using MEarth photometry and ground-based spectroscopy, we establish that star C (0.161
M
⊙
) is likely the source of the 1.4 day rotation period, and star B (0.215
M
⊙
) has a likely rotation period of 6.7 days. We estimate a probable rotation period of 85 days for LTT 1445A. Thus, this triple M-dwarf system appears to be in a special evolutionary stage where the most massive M dwarf has spun down, the intermediate mass M dwarf is in the process of spinning down, while the least massive stellar component has not yet begun to spin down.
Abstract
We report the discovery of TOI-2180 b, a 2.8
M
J
giant planet orbiting a slightly evolved G5 host star. This planet transited only once in Cycle 2 of the primary Transiting Exoplanet Survey ...Satellite (TESS) mission. Citizen scientists identified the 24 hr single-transit event shortly after the data were released, allowing a Doppler monitoring campaign with the Automated Planet Finder telescope at Lick Observatory to begin promptly. The radial velocity observations refined the orbital period of TOI-2180 b to be 260.8 ± 0.6 days, revealed an orbital eccentricity of 0.368 ± 0.007, and discovered long-term acceleration from a more distant massive companion. We conducted ground-based photometry from 14 sites spread around the globe in an attempt to detect another transit. Although we did not make a clear transit detection, the nondetections improved the precision of the orbital period. We predict that TESS will likely detect another transit of TOI-2180 b in Sector 48 of its extended mission. We use giant planet structure models to retrieve the bulk heavy-element content of TOI-2180 b. When considered alongside other giant planets with orbital periods over 100 days, we find tentative evidence that the correlation between planet mass and metal enrichment relative to stellar is dependent on orbital properties. Single-transit discoveries like TOI-2180 b highlight the exciting potential of the TESS mission to find planets with long orbital periods and low irradiation fluxes despite the selection biases associated with the transit method.
Some of the most scientifically valuable transiting planets are those that were already known from radial velocity (RV) surveys. This is primarily because their orbits are well characterized and they ...preferentially orbit bright stars that are the targets of RV surveys. The Transiting Exoplanet Survey Satellite (TESS) provides an opportunity to survey most of the known exoplanet systems in a systematic fashion to detect possible transits of their planets. HD 136352 (Nu2 Lupi) is a naked-eye (V = 5.78) G-type main-sequence star that was discovered to host three planets with orbital periods of 11.6, 27.6, and 108.1 days via RV monitoring with the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph. We present the detection and characterization of transits for the two inner planets of the HD 136352 system, revealing radii of R⊕ and R⊕ for planets b and c, respectively. We combine new HARPS observations with RV data from the Keck/High Resolution Echelle Spectrometer and the Anglo-Australian Telescope, along with TESS photometry from Sector 12, to perform a complete analysis of the system parameters. The combined data analysis results in extracted bulk density values of g cm−3 and g cm−3 for planets b and c, respectively, thus placing them on either side of the radius valley. The combination of the multitransiting planet system, the bright host star, and the diversity of planetary interiors and atmospheres means this will likely become a cornerstone system for atmospheric and orbital characterization of small worlds.
Abstract
The Transiting Exoplanet Survey Satellite mission was designed to find transiting planets around bright, nearby stars. Here, we present the detection and mass measurement of a small, ...short-period (≈4 days) transiting planet around the bright (
V
= 7.9), solar-type star HD 86226 (TOI-652, TIC 22221375), previously known to host a long-period (∼1600 days) giant planet. HD 86226c (TOI-652.01) has a radius of 2.16 ± 0.08
R
⊕
and a mass of
M
⊕
, based on archival and new radial velocity data. We also update the parameters of the longer-period, not-known-to-transit planet, and find it to be less eccentric and less massive than previously reported. The density of the transiting planet is 3.97 g cm
−3
, which is low enough to suggest that the planet has at least a small volatile envelope, but the mass fractions of rock, iron, and water are not well-constrained. Given the host star brightness, planet period, and location of the planet near both the “radius gap” and the “hot Neptune desert,” HD 86226c is an interesting candidate for transmission spectroscopy to further refine its composition.
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
Multiplanet systems are valuable arenas for investigating exoplanet architectures and comparing planetary siblings. TOI-1246 is one such system, with a moderately bright K dwarf (
V
= 11.6,
...K
= 9.9) and four transiting sub-Neptunes identified by TESS with orbital periods of 4.31, 5.90, 18.66, and 37.92 days. We collected 130 radial velocity observations with Keck/HIRES and TNG/HARPS-N to measure planet masses. We refit the 14 sectors of TESS photometry to refine planet radii (2.97 ± 0.06
R
⊕
, 2.47 ± 0.08
R
⊕
, 3.46 ± 0.09
R
⊕
, and 3.72 ± 0.16
R
⊕
) and confirm the four planets. We find that TOI-1246 e is substantially more massive than the three inner planets (8.1 ± 1.1
M
⊕
, 8.8 ± 1.2
M
⊕
, 5.3 ± 1.7
M
⊕
, and 14.8 ± 2.3
M
⊕
). The two outer planets, TOI-1246 d and TOI-1246 e, lie near to the 2:1 resonance (
P
e
/
P
d
= 2.03) and exhibit transit-timing variations. TOI-1246 is one of the brightest four-planet systems, making it amenable for continued observations. It is one of only five systems with measured masses and radii for all four transiting planets. The planet densities range from 0.70 ± 0.24 to 3.21 ± 0.44 g cm
−3
, implying a range of bulk and atmospheric compositions. We also report a fifth planet candidate found in the RV data with a minimum mass of 25.6 ± 3.6
M
⊕
. This planet candidate is exterior to TOI-1246 e, with a candidate period of 93.8 days, and we discuss the implications if it is confirmed to be planetary in nature.
Abstract
We present the Distant Giants Survey, a three-year radial velocity campaign to measure P(DG∣CS), the conditional occurrence of distant giant planets (DG;
M
p
∼ 0.3–13
M
J
,
P
> 1 yr) in ...systems hosting a close-in small planet (CS;
R
p
< 10
R
⊕
). For the past two years, we have monitored 47 Sun-like stars hosting small transiting planets detected by TESS. We present the selection criteria used to assemble our sample and report the discovery of two distant giant planets, TOI-1669 b and TOI-1694 c. For TOI-1669 b we find that
M
sin
i
=
0.573
±
0.074
M
J
,
P
= 502 ± 16 days, and
e
< 0.27, while for TOI-1694 c,
M
sin
i
=
1.05
±
0.05
M
J
,
P
= 389.2 ± 3.9 days, and
e
= 0.18 ± 0.05. We also confirmed the 3.8 days transiting planet TOI-1694 b by measuring a true mass of
M
= 26.1 ± 2.2
M
⊕
. At the end of the Distant Giants Survey, we will incorporate TOI-1669 b and TOI-1694 c into our calculation of P(DG∣CS), a crucial statistic for understanding the relationship between outer giants and small inner companions.
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.
Abstract
We present the discovery of two nearly identically sized sub-Neptune transiting planets orbiting HD 63935, a bright (
V
= 8.6 mag), Sun-like (
T
eff
= 5560 K) star at 49 pc. TESS identified ...the first planet, HD 63935 b (TOI-509.01), in Sectors 7 and 34. We identified the second signal (HD 63935 c) in Keck High Resolution Echelle Spectrometer and Lick Automated Planet Finder radial velocity data as part of our follow-up campaign. It was subsequently confirmed with TESS photometry in Sector 34 as TOI-509.02. Our analysis of the photometric and radial velocity data yielded a robust detection of both planets with periods of 9.0600 ± 0.007 and 21.40 ± 0.0019 days, radii of 2.99 ± 0.14 and 2.90 ± 0.13
R
⊕
, and masses of 10.8 ± 1.8 and 11.1 ± 2.4
M
⊕
. We calculated densities for planets b and c consistent with a few percent of the planet mass in hydrogen/helium envelopes. We also describe our survey’s efforts to choose the best targets for James Webb Space Telescope atmospheric follow-up. These efforts suggest that HD 63935 b has the most clearly visible atmosphere of its class. It is the best target for transmission spectroscopy (ranked by the transmission spectroscopy metric, a proxy for atmospheric observability) in the so far uncharacterized parameter space comprising sub-Neptune-sized (2.6
R
⊕
<
R
p
< 4
R
⊕
), moderately irradiated (100
F
⊕
<
F
p
< 1000
F
⊕
) planets around G stars. Planet c is also a viable target for transmission spectroscopy, and given the indistinguishable masses and radii of the two planets, the system serves as a natural laboratory for examining the processes that shape the evolution of sub-Neptune planets.
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