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1. HIP 65426 is a High-frequency Delta Scuti Pulsator in Plausible Spin–Orbit Alignment with its Directly Imaged Exoplanet

   https://doi.org/10.3847/1538-3881/ad4964  

   Sepulveda, Aldo_G ; Huber, Daniel ; Bedding, Timothy_R ; Hey, Daniel_R ; Murphy, Simon_J ; Zhang, Zhoujian ; Liu, Michael_C ( June 2024 , The Astronomical Journal)

   HIP 65426 hosts a young giant planet that has become the first exoplanet directly imaged with JWST. Using time-series photometry from the Transiting Exoplanet Survey Satellite (TESS), we classify HIP 65426 as a high-frequencyδScuti pulsator with a possible large-frequency separation of Δν= 7.23 ± 0.02 cycles day⁻¹. We check the TESS data for pulsation-timing variations and use the nondetection to estimate a 95% dynamical mass upper limit of 12.8M_Jupfor HIP 65426 b. We also identify a low-frequency region of signal that we interpret as stellar latitudinal differential rotation with two rapid periods of 7.85 ± 0.08 hr and 6.67 ± 0.04 hr. We use our TESS rotation periods together with published values of radius and$v\sin i$to jointly measure the inclination of HIP 65426 to$i_{\star }={107}_{-11}^{+12}$°. Our stellar inclination is consistent with the orbital inclination of HIP 65426 b (${108}_{-3}^{+6}$°) at the 68% percent level based on our orbit fit using published relative astrometry. The lack of significant evidence for spin–orbit misalignment in the HIP 65426 system supports an emerging trend consistent with preferential alignment between imaged long-period giant planets and their host stars.

    

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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. 20 s Cadence TESS Photometry of HR 8799

   https://doi.org/10.3847/2515-5172/acafea  

   Sepulveda, Aldo G. ; Huber, Daniel ; Li, Gang ; Bedding, Timothy R. ; Zhang, Zhoujian ; Liu, Michael C. ( January 2023 , Research Notes of the AAS)

   We analyzed 20 s cadence Transiting Exoplanet Survey Satellite time-series photometry of the exoplanet host star HR 8799 collected in Sector 56. The amplitude spectrum shows Gamma Doradus (γ Dor) pulsations consistent with previous space-based photometry from MOST. Assuming that HR 8799 is a representative ofγ Dor stars in the Kepler sample, the dominant dipole mode at 1.98 cycles day⁻¹implies a core rotation period of ∼0.7 day, which combined with$v\sin i$and stellar radius measurements would result in a preliminary stellar inclination of ∼28° assuming rigid rotation. We find no significant residual photometric variation after removing the pulsation signal aside from a ∼9 days trend that is likely a systematic effect or an artifact from performing aggressive frequency subtraction in the presence of red noise.

    

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5. Stellar Companions to TESS Objects of Interest: A Test of Planet–Companion Alignment

   https://doi.org/10.3847/1538-3881/ac53a7  

   Behmard, Aida ; Dai, Fei ; Howard, Andrew W. ( March 2022 , The Astronomical Journal)

   We present a catalog of stellar companions to host stars of Transiting Exoplanet Survey Satellite Objects of Interest (TOIs) identified from a marginalized likelihood ratio test that incorporates astrometric data from the Gaia Early Data Release 3 catalog (EDR3). The likelihood ratio is computed using a probabilistic model that incorporates parallax and proper-motion covariances and marginalizes the distances and 3D velocities of stars in order to identify comoving stellar pairs. We find 172 comoving companions to 170 non-false-positive TOI hosts, consisting of 168 systems with two stars and 2 systems with three stars. Among the 170 TOI hosts, 54 harbor confirmed planets that span a wide range of system architectures. We conduct an investigation of the mutual inclinations between the stellar companion and planetary orbits using Gaia EDR3, which is possible because transiting exoplanets must orbit within the line of sight; thus, stellar companion kinematics can constrain mutual inclinations. While the statistical significance of the current sample is weak, we find that${73}_{-20}^{+14}\%$of systems with Kepler-like architectures (R_P≤ 4R_⊕anda< 1 au) appear to favor a nonisotropic orientation between the planetary and companion orbits with a typical mutual inclinationαof 35° ± 24°. In contrast,${65}_{-35}^{+20}$% of systems with close-in giants (P< 10 days andR_P> 4R_⊕) favor a perpendicular geometry (α= 89° ± 21°) between the planet and companion. Moreover, the close-in giants with large stellar obliquities (planet–host misalignment) are also those that favor significant planet–companion misalignment.

    

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