Samuel K. Grunblatt

Transiting warm Jupiters orbiting bright stars are scarcely known, but a substantial number of these planets have been uncovered by the TESS mission. In this work, we report the discovery and confirmation of a transiting warm Jupiter orbiting the bright ( V = 8.70) subgiant star HD 715 (TOI-6893). HD 715 b was originally identified from a single transit event in TESS Sector 70. We acquired two seasons of radial velocity follow-up using the PFS, TRES, and MINERVA-Australis spectrographs, which clearly detect the planetary orbit. At M _* = 1.60 ± 0.04 M _⊙ , HD 715 thus becomes one of the most massive stars known to host a transiting warm Jupiter. From a joint fit to the TESS transit and our RVs, we find that HD 715 b has a 56.4 0 − 0.23 + 0.19 day orbital period and measure a precise mass and radius of 0.635 ± 0.056 M _J and 1.07 ± 0.04 R _J , rendering it a relatively typical member of the warm Jupiter population. The moderate orbital eccentricity of 0.2 1 − 0.08 + 0.07 contrasts with the higher eccentricities of other similar warm Jupiters orbiting evolved stars, indicating a greater diversity in orbital eccentricities than previously known. The absence of additional transits in preceding TESS observations in Sectors 42 and 43 allows us to further refine the range of possible orbital periods to [56.01, 56.35] days. Though the ephemeris uncertainty remains substantial, future photometric observations may nonetheless allow for recovery of the transit of HD 715 b.

Robust stellar age measurements are essential to understanding the life cycles of planetary systems. However, precise measurements of stellar age are only available for a small subset of exoplanetary systems. Here, we present an asteroseismic analysis of the TOI-2669 and TOI-4551 systems. We determined the maximum frequency (ν _max ) and the large frequency separation (Δ ν ) using the pySYD package. These values were then combined with existing photometric and spectroscopic constraints to achieve more accurate and precise measurements of the stellar parameters using the isoclassify package. We find a stellar mass, radius, and age of 1.12 ± 0.03 M _⊙ , 4.221 ± 0.048 R _⊙ and 7.3 ± 0.9 Gyr for TOI-2669 and 1.10 ± 0.04 M _⊙ , 3.454 ± 0.060 R _⊙ and 8.5 ± 1.5 Gyr for TOI-4551. Further asteroseismic analysis of TESS systems will improve our understanding of planetary demographics.

Constraining stellar models using asteroseismic and spectroscopic observations is a powerful method for precisely determining the fundamental properties of stars in different kinematic components of our Galaxy. We use spectroscopy and individual oscillation mode frequencies to perform a homogeneous modeling study of eight evolved metal-poor stars enhanced in α -elements. We compare a full treatment of α -enhancement against an ad hoc correction to the total metallicity and show that the stellar properties inferred from asteroseismic modeling using both sets of models agree with each other. Additionally, we find that the uncertainties on stellar parameters derived from both α -enhanced modeling methods are comparable. This is in qualitative disagreement with existing works showing red giant ages constrained by only the global asteroseismic parameters to depend strongly on the opacities and abundances assumed in 1D modeling. We also show that the observed frequency of maximum oscillation power ( ν _max ) is larger than the value predicted from applying the ν _max scaling relation to the masses, radii, and temperatures inferred from the detailed modeling. This discrepancy is pronounced at low metallicities, consistent with recent findings indicating a breakdown of the ν _max scaling relation for metal-poor stars. Understanding the extent to which the ν _max scaling relation fails for low-metallicity solar-like oscillators through detailed modeling will enable more accurate mass and age determinations for hundreds of giant stars in the Galactic halo for which only global asteroseismic parameters are available.

Detecting small planets via the radial velocity (RV) method remains challenged by signals induced by stellar variability, versus the effects of the planet(s). Here, we explore using Gaussian process (GP) regression with Transiting Exoplanet Survey Satellite (TESS) photometry in modeling RVs to help to mitigate stellar jitter from oscillations and granulation for exoplanet detection. We applied GP regression to simultaneous TESS photometric and RV data of HD 5562, a G-type subgiant ( M _⋆ = 1.09 M _⊙ , R _⋆ = 1.88 R _⊙ ) with a V magnitude of 7.17, using photometry to inform the priors for RV fitting. The RV data is obtained by the Magellan Planet Finder Spectrograph. The photometry-informed GP regression reduced the RV scatter of HD 5562 from 2.03 to 0.51 m s ⁻¹ . We performed injection and recovery tests to evaluate the potential of GPs for discovering small exoplanets around evolved stars, which demonstrate that the GP provides comparable noise reduction to the binning method. We also found that the necessity of photometric data depends on the quality of the RV dataset. For long baseline and high-cadence RV observations, GP regression can effectively mitigate stellar jitter without photometric data. However, for intermittent RV observations, incorporating photometric data improves GP fitting and enhances detection capabilities.

Detecting small planets via the radial velocity method remains challenged by signals induced by stellar variability, versus the effects of the planet(s). Here, we explore using Gaussian Process (GP) regression with Transiting Exoplanet Survey Satellite (TESS) photometry in modeling radial velocities (RVs) to help to mitigate stellar jitter from oscillations and granulation for exoplanet detection. We applied GP regression to simultaneous TESS photometric and RV data of HD 5562, a G-type subgiant ($M_\star=1.09M_{\odot}$, $R_\star=1.88R_{\odot}$) with a V magnitude of 7.17, using photometry to inform the priors for RV fitting. The RV data is obtained by the Magellan Planet Finder Spectrograph (PFS). The photometry-informed GP regression reduced the RV scatter of HD~5562 from 2.03 to 0.51 m/s. We performed injection and recovery tests to evaluate the potential of GPs for discovering small exoplanets around evolved stars, which demonstrate that the GP provides comparable noise reduction to the binning method. We also found that the necessity of photometric data depends on the quality of the RV dataset. For long baseline and high-cadence RV observations, GP regression can effectively mitigate stellar jitter without photometric data. However, for intermittent RV observations, incorporating photometric data improves GP fitting and enhances detection capabilities.

Tidal interactions are one of the primary drivers of orbital evolution for massive planets with short orbital periods. Tidal dissipation within host stars can cause the orbits of such planets to decay. However, the mechanisms of tidal dissipation are difficult to probe. Generally, tidal dissipation is parameterized by the modified stellar tidal quality factor, or Q * ′ , but the lack of observational evidence of orbital decay to confirm dissipation theories has resulted in orders of magnitude of uncertainty in Q * ′ . We present a new transit timing analysis of 54 systems with varying stellar evolutionary states in an attempt to search for orbital decay across multiple stages of stellar evolution. For each system, we obtained mid-transit times from new TESS data and evaluated potential departures from a linear ephemeris using the Bayesian information criterion. We then determined tidal quality factors using widely tested theoretical relations. Of the systems studied, 25 showed evidence of a decrease in orbital period over time and eight showed evidence of a decrease that was inconsistent with zero by three standard deviations: CoRoT-2, TrES-5, WASP-4, WASP-12, WASP-19, WASP-45, WASP-99, and XO-3. However, the significance of some of these detections may be influenced by unreliable transit time measurements. Similarly, we see that the lower limit on Q * ′ for evolved systems is marginally lower than it is for the sample of all systems, though both limits are orders of magnitude below the expected theoretical values for both samples. These new constraints on transit times and Q * ′ values will help to narrow the search for orbital decay in the future and place important constraints on current theories of star–planet interactions.

We report the masses, sizes, and orbital properties of 86 planets orbiting 55 stars observed by NASA’s K2 Mission with follow-up Doppler measurements by the HIRES spectrometer at the W. M. Keck Observatory and the Automated Planet Finder at Lick Observatory. Eighty-one of the planets were discovered from their transits in the K2 photometry, while five were found based on subsequent Doppler measurements of transiting planet-host stars. The sizes of the transiting planets range from Earth-size to larger than Jupiter (1–3 R _⊕ is typical), while the orbital periods range from less than a day to a few months. For 32 of the planets, the Doppler signal was detected with significance greater than 5σ (51 were detected with >3σ significance). An important characteristic of this catalog is the use of uniform analysis procedures to determine stellar and planetary properties. This includes the transit search and fitting procedures applied to the K2 photometry, the Doppler fitting techniques applied to the radial velocities (RVs), and the spectral modeling to determine bulk stellar parameters. Such a uniform treatment will make the catalog useful for statistical studies of the masses, densities, and system architectures of exoplanetary systems. This work also serves as a data release for all previously unpublished RVs and associated stellar activity indicators obtained by our team for these systems, along with derived stellar and planet parameters.

We present the discovery of TOI-7041 b (TIC 201175570b), a hot Saturn transiting a red giant star with measurable stellar oscillations. We observe solar-like oscillations in TOI-7041 with a frequency of maximum power of ν max = 218.50±2.23 μHz and a large frequency separation of Δν = 16.5282±0.0186 μHz. Our asteroseismic analysis indicates that TOI-7041 has a mass of 1.07±0.05(stat)±0.02(sys) M _⊙ and a radius of 4.10 ± 0.06(stat)±0.05(sys) R _⊙, making it one of the largest stars around which a transiting planet has been discovered with the Transiting Exoplanet Survey Satellite (TESS), and the mission's first oscillating red giant with a transiting planet. TOI-7041 b has an orbital period of 9.691±0.006 days and a low eccentricity of e = 0.04 ± 0.04. We measure a planet radius of 1.02 ± 0.03 R _Jup with TESS photometry, and a planet mass of 0.36±0.16 M _Jup (114±51 M _⊕) with ground-based radial velocity measurements. TOI-7041 b appears less inflated than similar systems receiving equivalent incident flux, and its circular orbit indicates that it is not undergoing tidal heating due to circularization. The asteroseismic analysis of the host star provides some of the tightest constraints on the stellar properties of a TESS planet host and enables precise characterization of the hot Saturn. This system joins a small number of TESS-discovered exoplanets orbiting stars that exhibit clear stellar oscillations and indicates that extended TESS observations of evolved stars will similarly provide a path to improved exoplanet characterization.

Very-metal-poor stars ([Fe/H] < −2) are important laboratories for testing stellar models and reconstructing the formation history of our galaxy. Asteroseismology is a powerful tool to probe stellar interiors and measure ages, but few asteroseismic detections are known in very-metal-poor stars and none have allowed detailed modeling of oscillation frequencies. We report the discovery of a low-luminosity Kepler red giant (KIC 8144907) with high signal-to-noise ratio oscillations, [Fe/H] = −2.66 ± 0.08 and [α/Fe] = 0.38 ± 0.06, making it by far the most metal-poor star to date for which detailed asteroseismic modeling is possible. By combining the oscillation spectrum from Kepler with high-resolution spectroscopy, we measure an asteroseismic mass and age of 0.79 ± 0.02(ran) ± 0.01(sys) M _⊙ and 12.0 ± 0.6(ran) ± 0.4(sys) Gyr, with remarkable agreement across different codes and input physics, demonstrating that stellar models and asteroseismology are reliable for very-metal-poor stars when individual frequencies are used. The results also provide a direct age anchor for the early formation of the Milky Way, implying that substantial star formation did not commence until redshift z ≈ 3 (if the star formed in situ) or that the Milky Way has undergone merger events for at least ≈12 Gyr (if the star was accreted by a dwarf satellite merger such as Gaia-Enceladus).