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1. The TESS-Keck Survey. XVIII. A Sub-Neptune and Spurious Long-period Signal in the TOI-1751 System

   https://doi.org/10.3847/1538-3881/ad29ee  

   Desai, Anmol ; Turtelboom, Emma V. ; Harada, Caleb K. ; Dressing, Courtney D. ; Rice, David R. ; Murphy, Joseph M. Akana ; Brinkman, Casey L. ; Chontos, Ashley ; Crossfield, Ian J. M. ; Dai, Fei ; et al ( April 2024 , The Astronomical Journal)

   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,$\log (g)=4.2\pm 0.1$,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${2.77}_{-0.07}^{+0.15}{R}_{\oplus }$. We also use both Keck/HIRES and APF/Levy radial velocities (RV) to derive a planet mass of${14.5}_{-3.14}^{+3.15}{M}_{\oplus }$, 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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2. TOI-5375 B: A Very Low Mass Star at the Hydrogen-burning Limit Orbiting an Early M-type Star* †

   https://doi.org/10.3847/1538-3881/acc651  

   Lambert, Mika ; Bender, Chad F. ; Kanodia, Shubham ; Cañas, Caleb I. ; Monson, Andrew ; Stefánsson, Gudmundur ; Cochran, William D. ; Everett, Mark E. ; Gupta, Arvind F. ; Hearty, Fred ; et al ( April 2023 , The Astronomical Journal)

   The Transiting Exoplanet Survey Satellite (TESS) mission detected a companion orbiting TIC 71268730, categorized it as a planet candidate, and designated the system TOI-5375. Our follow-up analysis using radial-velocity data from the Habitable-zone Planet Finder, photometric data from Red Buttes Observatory, and speckle imaging with NN-EXPLORE Exoplanet Stellar Speckle Imager determined that the companion is a very low mass star near the hydrogen-burning mass limit with a mass of 0.080 ± 0.002M_☉(83.81 ± 2.10M_J), a radius of${0.1114}_{-0.0050}^{+0.0048}{R}_{☉}$(1.0841${}_{0.0487}^{0.0467}{R}_J$), and brightness temperature of 2600 ± 70 K. This object orbits with a period of 1.721553 ± 0.000001 days around an early M dwarf star (0.62 ± 0.016M_☉). TESS photometry shows regular variations in the host star’s TESS light curve, which we interpreted as an activity-induced variation of ∼2%, and used this variability to measure the host star’s stellar rotation period of${1.9716}_{-0.0083}^{+0.0080}$days. The TOI-5375 system provides tight constraints on stellar models of low-mass stars at the hydrogen-burning limit and adds to the population in this important region.

    

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3. The TESS-Keck Survey. XVII. Precise Mass Measurements in a Young, High-multiplicity Transiting Planet System Using Radial Velocities and Transit Timing Variations

   https://doi.org/10.3847/1538-3881/ad1330  

   Beard, Corey ; Robertson, Paul ; Dai, Fei ; Holcomb, Rae ; Lubin, Jack ; Akana Murphy, Joseph M. ; Batalha, Natalie M. ; Blunt, Sarah ; Crossfield, Ian ; Dressing, Courtney ; et al ( January 2024 , The Astronomical Journal)

   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.

    

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4. Confirming the Warm and Dense Sub-Saturn TIC 139270665 b with the Automated Planet Finder and Unistellar Citizen Science Network

   https://doi.org/10.3847/1538-3881/ad2772  

   Peluso, Daniel O’Conner ; Dalba, Paul A. ; Wright, Duncan ; Esposito, Thomas M. ; Sgro, Lauren A. ; Weaver, Ian C. ; Marchis, Franck ; Dragomir, Diana ; Villanueva, Jr., Steven ; Fulton, Benjamin ; et al ( March 2024 , The Astronomical Journal)

   We report the discovery and confirmation of the Transiting Exoplanet Survey Satellite (TESS) single-transit, warm and dense sub-Saturn, TIC 139270665 b. This planet is unusually dense for its size: with a bulk density of 2.13 g cm⁻³(0.645R_J, 0.463M_J), it is the densest warm sub-Saturn of the TESS family. It orbits a metal-rich G2 star. We also found evidence of a second planet, TIC 139270665 c, with a longer period of${1010}_{-220}^{+780}$days and minimum mass$M_P\sin i$of${4.89}_{-0.37}^{+0.66}$M_J. First clues of TIC 139270665 b’s existence were found by citizen scientists inspecting TESS photometric data from sector 47 in 2022 January. Radial velocity measurements from the Automated Planet Finder combined with TESS photometry and spectral energy distributions viaEXOFASTv2system modeling suggested a${23.624}_{-0.031}^{+0.030}$day orbital period for TIC 139270665 b and also showed evidence for the second planet. Based on this estimated period, we mobilized the Unistellar citizen science network for photometric follow-up, capitalizing on their global distribution to capture a second transit of TIC 139270665 b. This citizen science effort also served as a test bed for an education initiative that integrates young students into modern astrophysics data collection. The Unistellar photometry did not definitively detect a second transit, but did enable us to further constrain the planet’s period. As a transiting, warm, and dense sub-Saturn, TIC 139270665 b represents an interesting laboratory for further study to enhance our models of planetary formation and evolution.

    

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5. TOI-5344 b: A Saturn-like Planet Orbiting a Super-solar Metallicity M0 Dwarf

   https://doi.org/10.3847/1538-3881/ad09c2  

   Han, Te ; Robertson, Paul ; Kanodia, Shubham ; Cañas, Caleb ; Lin, Andrea S. J. ; Stefánsson, Gumundur ; Libby-Roberts, Jessica E. ; Larsen, Alexander ; Kobulnicky, Henry A. ; Mahadevan, Suvrath ; et al ( December 2023 , The Astronomical Journal)

   We confirm the planetary nature of TOI-5344 b as a transiting giant exoplanet around an M0-dwarf star. TOI-5344 b was discovered with the Transiting Exoplanet Survey Satellite photometry and confirmed with ground-based photometry (the Red Buttes Observatory 0.6 m telescope), radial velocity (the Habitable-zone Planet Finder), and speckle imaging (the NN-Explore Exoplanet Stellar Speckle Imager). TOI-5344 b is a Saturn-like giant planet (ρ= 0.80${}_{-0.15}^{+0.17}$g cm⁻³) with a planetary radius of 9.7 ± 0.5R_⊕(0.87 ± 0.04R_Jup) and a planetary mass of${135}_{-18}^{+17}{M}_{\oplus }$(0.42${}_{-0.06}^{+0.05}{M}_{\mathrm{Jup}}$). It has an orbital period of${3.792622}_{-0.000010}^{+0.000010}$days and an orbital eccentricity of${0.06}_{-0.04}^{+0.07}$. We measure a high metallicity for TOI-5344 of [Fe/H] = 0.48 ± 0.12, where the high metallicity is consistent with expectations from formation through core accretion. We compare the metallicity of the M-dwarf hosts of giant exoplanets to that of M-dwarf hosts of nongiants (≲8R_⊕). While the two populations appear to show different metallicity distributions, quantitative tests are prohibited by various sample caveats.

    

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