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1. Exploration of a Dissolving Association Made Up of IC 2602, Tucana–Horologium, and Other Young Comoving Groups

   https://doi.org/10.3847/1538-4357/ad5b56  

   Popinchalk, Mark; Faherty, Jacqueline_K; Gagné, Jonathan; Curtis, Jason_L; Moranta, Leslie; Kiman, Rocio; Couture, Dominic; Jusino, Alyana; Paliwal, Gaurav; Mouzakitis, Ioannis; et al (September 2024, The Astrophysical Journal)

   Abstract Recently Gagné et al. suggested that young moving groups with similar kinematic properties could be part of larger dissolving structures. One example was IC 2602 as the core of a group of associations, including its corona (CIC 2602), Tucana-Horologium (THA), and parts of Theia 92. We explore this hypothesis by measuring the rotation periods of 953 objects selected using Gaia DR3 kinematics from IC 2602, CIC 2602, Theia 92, and a newly identified group of stars that bridge IC 2602 and THA. We use Transiting Exoplanet Survey Satellite (TESS) full frame images to measure new rotation periods and combine these with the rotation periods for THA from Popinchalk et al. to compare their rotation period distributions and other youth indicators where available to examine if the groups could be coeval. We find strong agreement between the rotation distributions of IC 2602, CIC 2602, and THA, suggesting a shared age of ∼40 Myr, and which in combination could serve as an example of a typical distribution at this age. Theia 92 does not agree at the same level, and we explore the potential kinematic reasons it does not match the rotation period distribution of the larger groups. Additionally, in our light curve analysis we identify ∼50 potential binaries, as well as four new M dwarf complex rotators that show major morphological changes between TESS cycles. Finally, using the amplitudes of the rotation periods we measured, we find strong agreement with the amplitude–age relation presented in Morris for our 40 Myr groups. 

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2. A hidden population of massive white dwarfs: two spotted K + WD binaries

   https://doi.org/10.1093/mnras/stae517  

   Rowan, Dominick M; Jayasinghe, Tharindu; Tucker, Michael A; Lam, Casey Y; Thompson, Todd A; Kochanek, Christopher S; Abrams, Natasha S; Fulton, Benjamin J; Ilyin, Ilya; Isaacson, Howard; et al (February 2024, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT The identification and characterization of massive (≳ 0.8 M⊙) white dwarfs is challenging in part due to their low luminosity. Here, we present two candidate single-lined spectroscopic binaries, Gaia DR3 4014708864481651840 and 5811237403155163520, with K-dwarf primaries and optically dark companions. Both have orbital periods of P ∼ 0.45 d and show rotational variability, ellipsoidal modulations, and high-amplitude radial velocity variations. Using light curves from the Transiting Exoplanet Survey Satellite (TESS), radial velocities from ground-based spectrographs, and spectral energy distributions, we characterize these binaries to describe the nature of the unseen companion. We find that both systems are consistent with a massive white dwarf companion. Unlike simple ellipsoidal variables, star-spots cause the light-curve morphology to change between TESS sectors. We attempt to constrain the orbital inclination using phoebe binary light-curve models, but degeneracies in the light curves of spotted stars prevent a precise determination. Finally, we search for similar objects using Gaia DR3 and TESS, and comment on these systems in the context of recently claimed compact object binaries. 

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3. Measuring Long Stellar Rotation Periods (>10 days) from TESS FFI Light Curves is Possible: An Investigation Using TESS and ZTF

   https://doi.org/10.3847/1538-3881/add0ab  

   Hattori, Soichiro; Angus, Ruth; Foreman-Mackey, Daniel; Lu, Yuxi Lucy; Colman, Isabel (June 2025, The Astronomical Journal)

   Abstract The rotation period of a star is an important quantity that provides insight into its structure and state. For stars with surface features like starspots, their periods can be inferred from brightness variations as these features move across the stellar surface. TESS, with its all-sky coverage, is providing the largest sample of stars for obtaining rotation periods. However, most of the periods have been limited to shorter than the 13.7 days TESS orbital period due to strong background signals (e.g., scattered light) on those timescales. In this study, we investigated the viability of measuring longer periods (>10 days) from TESS light curves for stars in the Northern Continuous Viewing Zone (NCVZ). We first created a reference set of 272 period measurements longer than 10 days for K and M dwarfs in the NCVZ using data from the Zwicky Transient Facility (ZTF) that we consider as the “ground truth” given ZTF’s long temporal baseline of 6+ years. We then used theunpopularpipeline to detrend TESS light curves and implemented a modified Lomb–Scargle (LS) periodogram that accounts for flux offsets between observing sectors. For 179 out of the 272 sources (66%), the TESS-derived periods match the ZTF-derived periods to within 10%. The match rate increases to 81% (137 out of 170) when restricting to sources with a TESS LS power that exceeds a threshold. Our results confirm the capability of measuring periods longer than 10 days from TESS data, highlighting the data set’s potential for studying slow rotators. 

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4. Rotation Periods of TESS Objects of Interest from the Magellan-TESS Survey with Multiband Photometry from Evryscope and TESS

   https://doi.org/10.3847/1538-3881/ac0fe3  

   Howard, Ward S; Teske, Johanna; Corbett, Hank; Law, Nicholas M; Wang, Sharon Xuesong; Ratzloff, Jeffrey K; Galliher, Nathan W; Gonzalez, Ramses; Soto, Alan Vasquez; Glazier, Amy L; et al (September 2021, The Astronomical Journal)

   Abstract Stellar radial-velocity (RV) jitter due to surface activity may bias the RV semiamplitude and mass of rocky planets. The amplitude of the jitter may be estimated from the uncertainty in the rotation period, allowing the mass to be more accurately obtained. We find candidate rotation periods for 17 out of 35 TESS Objects of Interest (TOI) hosting <3R_⊕planets as part of the Magellan-TESS survey, which is the first-ever statistically robust study of exoplanet masses and radii across the photoevaporation gap. Seven periods are ≥3σdetections, two are ≥1.5σ, and eight show plausible variability, but the periods remain unconfirmed. The other 18 TOIs are nondetections. Candidate rotators include the host stars of the confirmed planets L 168-9 b, the HD 21749 system, LTT 1445 A b, TOI 1062 b, and the L 98-59 system. Thirteen candidates have no counterpart in the 1000 TOI rotation catalog of Canto Martins et al. We find periods for G3–M3 dwarfs using combined light curves from TESS and the Evryscope all-sky array of small telescopes, sometimes with longer periods than would be possible with TESS alone. Secure periods range from 1.4 to 26 days with Evryscope-measured photometric amplitudes as small as 2.1 mmag in $g\prime$. We also apply Monte Carlo sampling and a Gaussian process stellar activity model fromexoplanetto the TESS light curves of six TOIs to confirm the Evryscope periods. 

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5. Pulsating hydrogen-deficient white dwarfs and pre-white dwarfs observed with TESS: III. Asteroseismology of the DBV star GD 358

   https://doi.org/10.1051/0004-6361/202142153  

   Córsico, A. H.; Uzundag, M.; Kepler, S. O.; Silvotti, R.; Althaus, L. G.; Koester, D.; Baran, A. S.; Bell, K. J.; Bischoff-Kim, A.; Hermes, J. J.; et al (March 2022, Astronomy & Astrophysics)

   Context. The collection of high-quality photometric data by space telescopes, such as the completed Kepler mission and the ongoing TESS program, is revolutionizing the area of white-dwarf asteroseismology. Among the different kinds of pulsating white dwarfs, there are those that have He-rich atmospheres, and they are called DBVs or V777 Her variable stars. The archetype of these pulsating white dwarfs, GD 358, is the focus of the present paper. Aims. We report a thorough asteroseismological analysis of the DBV star GD 358 (TIC 219074038) based on new high-precision photometric data gathered by the TESS space mission combined with data taken from the Earth. Methods. We reduced TESS observations of the DBV star GD 358 and performed a detailed asteroseismological analysis using fully evolutionary DB white-dwarf models computed accounting for the complete prior evolution of their progenitors. We assessed the mass of this star by comparing the measured mean period separation with the theoretical averaged period spacings of the models, and we used the observed individual periods to look for a seismological stellar model. We detected potential frequency multiplets for GD 358, which we used to identify the harmonic degree ( ℓ ) of the pulsation modes and rotation period. Results. In total, we detected 26 periodicities from the TESS light curve of this DBV star using standard pre-whitening. The oscillation frequencies are associated with nonradial g (gravity)-mode pulsations with periods from ∼422 s to ∼1087 s. Moreover, we detected eight combination frequencies between ∼543 s and ∼295 s. We combined these data with a huge amount of observations from the ground. We found a constant period spacing of 39.25 ± 0.17 s, which helped us to infer its mass ( M ⋆  = 0.588 ± 0.024  M ⊙ ) and constrain the harmonic degree ℓ of the modes. We carried out a period-fit analysis on GD 358, and we were successful in finding an asteroseismological model with a stellar mass ( M ⋆ = 0.584 −0.019 +0.025   M ⊙ ), compatible with the stellar mass derived from the period spacing, and in line with the spectroscopic mass ( M ⋆  = 0.560 ± 0.028  M ⊙ ). In agreement with previous works, we found that the frequency splittings vary according to the radial order of the modes, suggesting differential rotation. Obtaining a seismological model made it possible to estimate the seismological distance ( d seis  = 42.85 ± 0.73 pc) of GD 358, which is in very good accordance with the precise astrometric distance measured by Gaia EDR3 ( π  = 23.244 ± 0.024,  d Gaia  = 43.02 ± 0.04 pc). Conclusions. The high-quality data measured with the TESS space telescope, used in combination with data taken from ground-based observatories, provides invaluable information for conducting asteroseismological studies of DBV stars, analogously to what happens with other types of pulsating white-dwarf stars. The currently operating TESS mission, together with the advent of other similar space missions and new stellar surveys, will give an unprecedented boost to white dwarf asteroseismology. 

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