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1. The K2 Galactic Archaeology Program Data Release 3: Age-abundance Patterns in C1–C8 and C10–C18

   https://doi.org/10.3847/1538-4357/ac2c83  

   Zinn, Joel C. ; Stello, Dennis ; Elsworth, Yvonne ; García, Rafael A. ; Kallinger, Thomas ; Mathur, Savita ; Mosser, Benoît ; Hon, Marc ; Bugnet, Lisa ; Jones, Caitlin ; et al ( February 2022 , The Astrophysical Journal)

   We present the third and final data release of the K2 Galactic Archaeology Program (K2 GAP) for Campaigns C1–C8 and C10–C18. We provide asteroseismic radius and mass coefficients,κ_Randκ_M, for ∼19,000 red giant stars, which translate directly to radius and mass given a temperature. As such, K2 GAP DR3 represents the largest asteroseismic sample in the literature to date. K2 GAP DR3 stellar parameters are calibrated to be on an absolute parallactic scale based on Gaia DR2, with red giant branch and red clump evolutionary state classifications provided via a machine-learning approach. Combining these stellar parameters with GALAH DR3 spectroscopy, we determine asteroseismic ages with precisions of ∼20%–30% and compare age-abundance relations to Galactic chemical evolution models among both low- and high-αpopulations forα, light, iron-peak, and neutron-capture elements. We confirm recent indications in the literature of both increased Ba production at late Galactic times as well as significant contributions tor-process enrichment from prompt sources associated with, e.g., core-collapse supernovae. With an eye toward other Galactic archeology applications, we characterize K2 GAP DR3 uncertainties and completeness using injection tests, suggesting that K2 GAP DR3 is largely unbiased in mass/age, with uncertainties of 2.9% (stat.) ± 0.1% (syst.) and 6.7% (stat.) ± 0.3% (syst.) inκ_Randκ_Mfor red giant branch stars and 4.7% (stat.) ± 0.3% (syst.) and 11% (stat.) ± 0.9% (syst.) for red clump stars. We also identify percent-level asteroseismic systematics, which are likely related to the time baseline of the underlying data, and which therefore should be considered in TESS asteroseismic analysis.

    

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2. TESS Asteroseismic Analysis of HD 76920: The Giant Star Hosting an Extremely Eccentric Exoplanet

   https://doi.org/10.3847/1538-4357/acb8ac  

   Jiang 姜, Chen 晨. ; Wu 吴涛, Tao ; Feinstein, Adina D. ; Stassun, Keivan G. ; Bedding, Timothy R. ; Veras, Dimitri ; Corsaro, Enrico ; Buzasi, Derek L. ; Stello, Dennis ; Li 李亚光, Yaguang ; et al ( March 2023 , The Astrophysical Journal)

   The Transiting Exoplanet Survey Satellite (TESS) mission searches for new exoplanets. The observing strategy of TESS results in high-precision photometry of millions of stars across the sky, allowing for detailed asteroseismic studies of individual systems. In this work, we present a detailed asteroseismic analysis of the giant star HD 76920 hosting a highly eccentric giant planet (e= 0.878) with an orbital period of 415 days, using five sectors of TESS light curve that cover around 140 days of data. Solar-like oscillations in HD 76920 are detected around 52μHz by TESS for the first time. By utilizing asteroseismic modeling that takes classical observational parameters and stellar oscillation frequencies as constraints, we determine improved measurements of the stellar mass (1.22 ± 0.11M_⊙), radius (8.68 ± 0.34R_☉), and age (5.2 ± 1.4 Gyr). With the updated parameters of the host star, we update the semimajor axis and mass of the planet asa= 1.165 ± 0.035 au and$M_{\mathrm{p}}\sin i=3.57\pm 0.22M_{\mathrm{Jup}}$. With an orbital pericenter of 0.142 ± 0.005 au, we confirm that the planet is currently far away enough from the star to experience negligible tidal decay until being engulfed in the stellar envelope. We also confirm that this event will occur within about 100 Myr, depending on the stellar model used.

    

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3. Kepler and TESS Observations of PG 1159-035

   https://doi.org/10.3847/1538-4357/ac8871  

   Oliveira da Rosa, Gabriela ; Kepler, S. O. ; Córsico, Alejandro H. ; Costa, J. E. S. ; Hermes, J. J. ; Kawaler, S. D. ; Bell, Keaton J. ; Montgomery, M. H. ; Provencal, J. L. ; Winget, D. E. ; et al ( September 2022 , The Astrophysical Journal)

   PG 1159-035 is the prototype of the PG 1159 hot (pre-)white dwarf pulsators. This important object was observed during the Kepler satellite K2 mission for 69 days in 59 s cadence mode and by the TESS satellite for 25 days in 20 s cadence mode. We present a detailed asteroseismic analysis of those data. We identify a total of 107 frequencies representing 32ℓ= 1 modes, 27 frequencies representing 12ℓ= 2 modes, and eight combination frequencies. The combination frequencies and the modes with very highkvalues represent new detections. The multiplet structure reveals an average splitting of 4.0 ± 0.4μHz forℓ= 1 and 6.8 ± 0.2μHz forℓ= 2, indicating a rotation period of 1.4 ± 0.1 days in the region of period formation. In the Fourier transform of the light curve, we find a significant peak at 8.904 ± 0.003μHz suggesting a surface rotation period of 1.299 ± 0.002 days. We also present evidence that the observed periods change on timescales shorter than those predicted by current evolutionary models. Our asteroseismic analysis finds an average period spacing forℓ= 1 of 21.28 ± 0.02 s. Theℓ= 2 modes have a mean spacing of 12.97 ± 0.4 s. We performed a detailed asteroseismic fit by comparing the observed periods with those of evolutionary models. The best-fit model hasT_eff= 129, 600 ± 11 100 K,M_*= 0.565 ± 0.024M_⊙, and$\log g={7.41}_{-0.54}^{+0.38}$, within the uncertainties of the spectroscopic determinations. We argue for future improvements in the current models, e.g., on the overshooting in the He-burning stage, as the best-fit model does not predict excitation for all of the pulsations detected in PG 1159-035.

    

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4. A 20 Second Cadence View of Solar-type Stars and Their Planets with TESS: Asteroseismology of Solar Analogs and a Recharacterization of π Men c

   https://doi.org/10.3847/1538-3881/ac3000  

   Huber, Daniel ; White, Timothy R. ; Metcalfe, Travis S. ; Chontos, Ashley ; Fausnaugh, Michael M. ; Ho, Cynthia S. K. ; Van Eylen, Vincent ; Ball, Warrick H. ; Basu, Sarbani ; Bedding, Timothy R. ; et al ( January 2022 , The Astronomical Journal)

   We present an analysis of the first 20 second cadence light curves obtained by the TESS space telescope during its extended mission. We find improved precision of 20 second data compared to 2 minute data for bright stars when binned to the same cadence (≈10%–25% better forT≲ 8 mag, reaching equal precision atT≈ 13 mag), consistent with pre-flight expectations based on differences in cosmic-ray mitigation algorithms. We present two results enabled by this improvement. First, we use 20 second data to detect oscillations in three solar analogs (γPav,ζTuc, andπMen) and use asteroseismology to measure their radii, masses, densities, and ages to ≈1%, ≈3%, ≈1%, and ≈20% respectively, including systematic errors. Combining our asteroseismic ages with chromospheric activity measurements, we find evidence that the spread in the activity–age relation is linked to stellar mass and thus the depth of the convection zone. Second, we combine 20 second data and published radial velocities to recharacterizeπMen c, which is now the closest transiting exoplanet for which detailed asteroseismology of the host star is possible. We show thatπMen c is located at the upper edge of the planet radius valley for its orbital period, confirming that it has likely retained a volatile atmosphere and that the “asteroseismic radius valley” remains devoid of planets. Our analysis favors a low eccentricity forπMen c (<0.1 at 68% confidence), suggesting efficient tidal dissipation (Q/k_2,1≲ 2400) if it formed via high-eccentricity migration. Combined, these early results demonstrate the strong potential of TESS 20 second cadence data for stellar astrophysics and exoplanet science.

    

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5. Asteroseismology and Spectropolarimetry of the Exoplanet Host Star λ Serpentis

   https://doi.org/10.3847/1538-3881/acf1f7  

   Metcalfe, Travis S. ; Buzasi, Derek ; Huber, Daniel ; Pinsonneault, Marc H. ; van Saders, Jennifer L. ; Ayres, Thomas R. ; Basu, Sarbani ; Drake, Jeremy J. ; Egeland, Ricky ; Kochukhov, Oleg ; et al ( September 2023 , The Astronomical Journal)

   The bright starλSer hosts a hot Neptune with a minimum mass of 13.6M_⊕and a 15.5 day orbit. It also appears to be a solar analog, with a mean rotation period of 25.8 days and surface differential rotation very similar to the Sun. We aim to characterize the fundamental properties of this system and constrain the evolutionary pathway that led to its present configuration. We detect solar-like oscillations in time series photometry from the Transiting Exoplanet Survey Satellite, and we derive precise asteroseismic properties from detailed modeling. We obtain new spectropolarimetric data, and we use them to reconstruct the large-scale magnetic field morphology. We reanalyze the complete time series of chromospheric activity measurements from the Mount Wilson Observatory, and we present new X-ray and ultraviolet observations from the Chandra and Hubble space telescopes. Finally, we use the updated observational constraints to assess the rotational history of the star and estimate the wind braking torque. We conclude that the remaining uncertainty on the stellar age currently prevents an unambiguous interpretation of the properties ofλSer, and that the rate of angular momentum loss appears to be higher than for other stars with a similar Rossby number. Future asteroseismic observations may help to improve the precision of the stellar age.

    

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