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1. Massive White Dwarfs in the 100 pc Sample: Magnetism, Rotation, Pulsations, and the Merger Fraction

   https://doi.org/10.3847/1538-4357/ad6905  

   Jewett, Gracyn; Kilic, Mukremin; Bergeron, Pierre; Moss, Adam; Blouin, Simon; Brown, Warren R; Kosakowski, Alekzander; Toonen, Silvia; Agüeros, Marcel A (October 2024, The Astrophysical Journal)

   Abstract We present a detailed model atmosphere analysis of massive white dwarfs withM> 0.9M_⊙andT_eff≥ 11,000 K in the Montreal White Dwarf Database 100 pc sample and the Pan-STARRS footprint. We obtained follow-up optical spectroscopy of 109 objects with no previous spectral classification in the literature. Our spectroscopic follow-up is now complete for all 204 objects in the sample. We find 118 normal DA white dwarfs, including 45 massive DAs near the ZZ Ceti instability strip. There are no normal massive DBs: the six DBs in the sample are strongly magnetic and/or rapidly rotating. There are 20 massive DQ white dwarfs in our sample, and all are found in the crystallization sequence. In addition, 66 targets are magnetic (32% of the sample). We use magnetic white dwarf atmosphere models to constrain the field strength and geometry using offset dipole models. We also use magnetism, kinematics, and rotation measurements to constrain the fraction of merger remnant candidates among this population. The merger fraction of this sample increases from 25% for 0.9–1M_⊙white dwarfs to 49% for 1.2–1.3M_⊙. However, this fraction is as high as ${78}_{-7}^{+4}$ % for 1.1–1.2M_⊙white dwarfs. Previous works have demonstrated that 5%–9% of high-mass white dwarfs stop cooling for ∼8 Gyr due to the²²Ne distillation process, which leads to an overdensity of Q-branch stars in the solar neighborhood. We demonstrate that the overabundance of the merger remnant candidates in our sample is likely due to the same process. 

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2. The MIRI Excesses Around Degenerates (MEAD) Survey. I. A Candidate Cold Brown Dwarf in Orbit Around the Nearby White Dwarf 2MASS J09424023−4637176

   https://doi.org/10.3847/1538-3881/ae650d  

   Albert, Loïc; Poulsen, Sabrina; Le_Bourdais, Érika; Debes, John H; Boucher, Samuel; Kilic, Mukremin; Reach, William; Mullally, Susan E; Cracraft, Misty; Mullally, Fergal; et al (May 2026, The Astronomical Journal)

   Abstract The MIRI Excesses Around Degenerates Survey is a Cycle 2 James Webb Space Telescope (JWST) survey program designed to image nearby white dwarfs in the mid-IR with the MIRI imaging mode. Only a handful of white dwarfs have previously been observed beyond 8 μm. This survey gathered observations for 56 white dwarfs within 25 pc at 10 and 15 μm, probing each white dwarf for unresolved IR excesses, IR flux deficits indicative of collision-induced absorption, or resolved substellar companions. This paper presents observations of our first target, 2MASS J09424023−4637176 (also UCAC4 217-039132), henceforth called MEAD 62. This is a magnetic DA white dwarf with an estimated age of $6.5_{-2.0}^{+4.0}$ Gyr. A red candidate companion, MEAD 62 B, about 2 mag fainter than its host white dwarf, is detected at an apparent separation of 1 $\stackrel{″}{.}$ 95. If confirmed, MEAD 62 B would be a $0.014_{-0.003}^{+0.002}$ M_⊙brown dwarf withT ${}_{\mathrm{eff}}=343_{-11}^{+7}$ K, according to ATMO2020 evolutionary models. Also, at 20.48  ±  0.01 pc, it would be the third nearest substellar companion to a white dwarf. While the red F1000W − F1500W color of MEAD 62 B is similar to background galaxies, it is also consistent with being an unresolved point source from empirical point-spread function fitting. A false positive analysis yields an expectation number of 0.66 red (F1000W − F1500 ≥ +0.80 mag) unresolved sources within the same separation (r≤ 2″) for the entire MEAD survey. Thus, this candidate companion is as likely to be an actual companion as a false positive unresolved background galaxy. Follow-up JWST observations to measure common proper motion and sample the spectral energy distribution are warranted to confirm the nature of MEAD 62 B. 

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3. A Global View of Post-interaction White Dwarf-main Sequence Binaries

   https://doi.org/10.1088/1538-3873/ae453b  

   Shariat, Cheyanne; El-Badry, Kareem (March 2026, Publications of the Astronomical Society of the Pacific)

   Abstract Common-envelope evolution (CEE) is among the most uncertain phases in binary evolution. To empirically constrain CEE, we construct a uniformly selected sample of eclipsing post–common-envelope binaries (PCEBs). Starting from an unresolved white dwarf–main-sequence (WDMS) candidate sample within 200 pc selected from the Gaia color-magnitude diagram, we identify 39 detached eclipsing WDMS binaries using Zwicky Transient Facility light curves. The binaries contain cool M dwarfs orbiting warm white dwarfs with orbital periods (P_orb) of 0.1–2 days. The sample’s simple selection function allows us to model observational incompleteness and infer intrinsic properties of the PCEB population. We find an orbital-period distribution consistent with being log-uniform over 0.1–2 days, contrary to recent reports of a bimodal distribution. The intrinsic companion-mass distribution peaks around 0.25M_⊙and declines steeply toward larger masses. The estimated local space density is 7.2 × 10⁻⁵pc⁻³, corresponding to a Galaxy-wide birth rate of 0.01 yr⁻¹. Combining our results with recent Gaia-based constraints on wider WDMS binaries, we construct an empirical period distribution of post-interaction WDMS binaries spanning 0.1–1000 days. The emerging period distribution is roughly log-flat ( $dN/d\log P_{\mathrm{orb}}\propto P_{\mathrm{orb}}^0$ ) atP_orb < 2 days and log-increasing ( $dN/d\log P_{\mathrm{orb}}\propto P_{\mathrm{orb}}^1$ ) atP_orb = 100–1000 days. The 10–100 days regime is poorly constrained by existing surveys, but a few nearby systems suggest that it is also well-populated. Short-period PCEBs (P_orb ≲ 2 days) with M dwarf companions are roughly 2–3 times more common than wide (P_orb = 100–1000 days) WDMS binaries with FGK companions, which likely formed through stable mass transfer. These results provide direct observational constraints on CEE and an empirical benchmark for binary-population models. 

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4. The Kinematic and Chemical Properties of the Close-in Planet Host Star 8 UMi

   https://doi.org/10.3847/2041-8213/ad3bb4  

   Chen, Huiling; Huang, Yang; Zhu, Wei; Beers, Timothy C; Xie, Renjing; Zhou, Yutao; Wang, Sharon Xuesong; Wang, Wei; Alexeeva, Sofya; Feng, Qikang; et al (May 2024, The Astrophysical Journal Letters)

   Abstract A recent study by Hon et al. reported that a close-in planet around the red clump star, 8 UMi, should have been engulfed during the expansion phase of its parent star’s evolution. They explained the survival of this exoplanet through a binary-merger channel for 8 UMi. The key to testing this formation scenario is to derive the true age of this star: is it an old “imposter” resulting from a binary merger, or a genuinely young red clump giant? To accomplish this, we derive kinematic and chemical properties for 8 UMi using astrometric data from Gaia DR3 and the element-abundance pattern measured from a high-resolution (R∼ 75,000) spectrum taken by SOPHIE. Our analysis shows that 8 UMi is a normal thin-disk star with orbital rotation speed ofV_ϕ= 244.96 km s⁻¹, and possesses a solar metallicity ([Fe/H] = −0.05 ± 0.07) andα-element-abundance ratio ([α/Fe] = +0.01 ± 0.03). By adopting well-established relationships between age and space velocities/elemental abundances, we estimate a kinematic age of ${3.50}_{-2.00}^{+3.00}$ Gyr, and a chemical age of ${3.25}_{-1.50}^{+2.50}$ Gyr from [C/N] and 3.47 ± 1.96 Gyr from [Y/Mg] for 8 UMi, respectively. These estimates are consistent with the isochrone-fitting age ( ${1.90}_{-0.30}^{+1.15}$ Gyr) of 8 UMi, but are all much younger than the timescale required in a binary-merger scenario. This result challenges the binary-merger model; the existence of such a closely orbiting exoplanet around a giant star remains a mystery yet to be resolved. 

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5. Hubble Space Telescope Imaging of Three Isolated Faint Dwarf Galaxies beyond the Local Group: Pavo, Corvus A, and Kamino

   https://doi.org/10.3847/1538-4357/ae2e9d  

   Mutlu-Pakdil, Burçin; Jones, Michael G; Sand, David J; Crnojević, Denija; Herron, Kai; Strader, Jay; Zaritsky, Dennis; Bennet, Paul; Drlica-Wagner, Alex; Casey, Quinn O; et al (January 2026, The Astrophysical Journal)

   Abstract We present new Hubble Space Telescope (HST) imaging of three recently discovered star-forming dwarf galaxies beyond the Local Group: Pavo, Corvus A, and Kamino. The discovery of Kamino is reported here for the first time. They rank among the most isolated faint dwarf galaxies known; hence they provide unique opportunities to study galaxy evolution at the smallest scales, free from the environmental effects of more massive galaxies. Our HST data reach ∼2–4 magnitudes below the tip of the red giant branch (TRGB) for each dwarf, allowing us to measure their distances, structural properties, and recent star formation histories (SFHs). All three galaxies contain a complex stellar population of young and old stars, and are typical of field galaxies in this mass regime (M_V = −10.62 ± 0.08 and $D=2.16_{-0.07}^{+0.08}$ Mpc for Pavo,M_V = −10.91 ± 0.10 andD = 3.34 ± 0.11 Mpc for Corvus A, andM_V = −12.02 ± 0.12 and $D=6.50_{-0.11}^{+0.15}$ Mpc for Kamino). Our HST-derived SFHs reveal differences among the three dwarfs: Pavo and Kamino show relatively steady, continuous star formation, while Corvus A formed ∼60% of its stellar mass by 10 Gyr ago. These results align with theoretical predictions of diverse evolutionary pathways for isolated low-mass galaxies. 

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