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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. 

Abstract The MIRI Excesses Around Degenerates (MEAD) Survey is a Cycle 2 JWST program designed to image nearby white dwarfs with MIRI at 10 and 15μm. This survey targeted 56 white dwarfs within 25 pc to search for mid-infrared excesses, flux deficits from collision-induced absorption, and resolved substellar companions. In this paper we present our analysis of WD 0644+025, an unusually massive white dwarf (0.95M_⊙) and the MEAD target exhibiting the most significant mid-infrared excess. The observed JWST MIRI photometry shows a 7.3σexcess at 15μm and a 3.6σexcess at 10μm, which may be associated with either a planetary companion or a circumstellar dust disk. This excess corresponds to a companion mass of 6.8M_Jup(T_eff= 261 ±9 K) with orbital distance <11.8 au, although substantially lower masses are possible if we consider a closely orbiting isolated companion. No spatially resolved sources are detected within 200 au, with contrast curve analysis excluding planets more massive than 2M_Jupbeyond ∼12 au. Metal pollution is confirmed in both archival Keck HIRES spectra from 1999 and new observations from 2025, with no evidence suggesting that the accretion rate has substantially changed over the decades. We explore possible dust disk morphologies to describe the observed IR excess and find that traditional debris disks struggle to fit our data. WD 0644+025 thus represents a compelling case study in the growing population of white dwarfs with cold infrared excesses and highlights JWST’s ability to probe planetary system remnants inaccessible to prior infrared observatories. 

Abstract White dwarf stars with high abundances of heavy elements in their atmospheres and infrared excesses are believed to be accreting planetary material. GD 362 is one of the most heavily polluted white dwarfs and has an exceptionally strong mid-infrared excess, reprocessing 2.4% of the star’s light into the mid-infrared. We present a high signal-to-noise, medium-resolution spectrum of GD 362 obtained with JWST, covering 0.6–17μm, along with photometry out to 25.5μm. The mid-infrared spectrum is dominated by an exceptionally strong 9–11μm silicate feature, which can be explained by a combination of olivine and pyroxene silicate minerals. Grains such as carbon, hotter than silicates, are required to explain the near-infrared emission. The silicates and carbon reside in a disk from 140 to 1400 stellar radii, and the disk scale height is greater than half the stellar radius. The elemental abundances of the solid material, relative to Si, are within a factor of 2 of meteoritic (CI chondrites) for C, O, Mg, Al, and Fe, with Al elevated and O slightly depleted. A similar pattern is observed for the abundances of accreted material in the stellar photosphere. Hydrogen is an exception, because no significant H-bearing minerals or water were detected in the disk, despite a large H abundance in the photosphere. 

Abstract Despite being only 85 pc away, the open cluster Coma Berenices (Coma Ber) has not been extensively studied. This is due in part to its sparseness and low proper motion, which together made Coma Ber’s membership challenging to establish. Gaia data for ≈400 previously cataloged candidate cluster stars allowed us to identify ≈300 as members. With [Fe/H] measurements for nine members, we found that Coma Ber has a solar metallicity, and then fit isochrones to its color–magnitude diagram to determine that it is 675 ± 100 Myr old. With photometry obtained by the Transiting Exoplanet Survey Satellite and Zwicky Transient Facility, we measured rotation periods (P_rot) for 137 of Coma Ber’s low-mass stars, increasing the sample of members with measuredP_rotby a factor of six, and extending the rotational census for the cluster from its late F stars through to its fully convective M dwarfs. By measuring the equivalent width of the Hαline for ≈250 stars and collecting X-ray detections for ≈100 (≈85% and ≈33% of the cluster’s members, respectively), we characterized magnetic activity in Coma Ber and examined the dependence of chromospheric and of coronal activity on rotation in these stars. Despite having a metallicity that is 0.2 dex below that of their coeval cousins in Praesepe and the Hyades, low-mass stars in Coma Ber seem to follow a similar rotation–activity relation. In detail, however, there are differences that may provide further insight into the impact of metallicity on this still poorly understood relation. 

Abstract We present precise parameters for two compact double white dwarf (DWD) binaries, SDSS J232230.20+050942.0 (J2322+0509) and SDSS J063449.92+380352.2 (J0634+3803), with orbital periods of 20 and 26.5 minutes, respectively. These systems will serve as verification sources for the Laser Interferometer Space Antenna (LISA). To significantly improve the electromagnetic (EM) constraints on these two systems and the LISA detectability predictions, we conducted spectroscopic follow-up observations using Hubble Space Telescope/Space Telescope Imaging Spectrograph, Keck I/LRIS, and Keck II/Echellette Spectrograph and Imager. Our analysis significantly improves the temperature, surface gravity, and mass constraints for both primary and secondary components in J2322+0509, as well as dynamical properties such as radial velocities and orbital periods in both systems. For J2322+0509, we derive an updated inclination ofi= 25 ${}_{-3.0}^{+4.5}$ deg, while for J0634+3803, we obtaini= 43 ${}_{-5.6}^{+7.0}$ deg. We assess the detectability of these sources using LDASOFT. Incorporating EM priors on inclination significantly enhances the gravitational-wave signal recovery, reducing uncertainties in amplitude by a factor of 2–4 and shortening the detection time by up to a few months. Our results underscore the importance of multimessenger observations in characterizing DWD binaries and maximizing LISA’s early scientific capabilities. 

Abstract We conduct a model atmosphere analysis on all magnetic white dwarfs (MWDs) in the Sloan Digital Sky Survey (SDSS) 100 pc sample. We have 163 magnetic targets in this sample, 87 of which are new discoveries, making this the largest volume-limited survey of MWDs to date. We discuss the distribution of multiple parameters, including mass, cooling age, and field strength. We find strong evidence of two populations of MWDs that form through separate mechanisms based on a cluster analysis of these parameters. The young, high-mass objects typically have high field strengths which indicate a merger origin, while old, average-mass objects have weaker fields that likely originated through a crystallization-induced dynamo or previous evolution stages. When comparing young and old objects, two-sample Kolmogorov–Smirnov tests yield statistically significant differences between the field strengths and masses of the magnetic targets. We use a Gaussian mixture model to identify where these populations lie in parameter space, and we find two groups centered at distinct cooling ages, masses, and field strengths of 2.9 Gyr, 0.71M_⊙, 3.7 MG and 1.8 Gyr, 0.96M_⊙, 84 MG, respectively. Our results further support the dual formation channel previously reported in the literature. The occurrence of magnetism strongly correlates with the onset of crystallization. However, given the breakout times required for a crystallization dynamo, we find that many of our older, average-mass objects can be better explained with a core-convective dynamo that forms on the main sequence. 

Abstract After carbon and oxygen,²²Ne is the most abundant element in white dwarf (WD) interiors. As C/O WDs crystallize, they are predicted to go through a distillation process in the central layers if they have a sufficiently high²²Ne mass fraction of ≳2.5%. Observational evidence for distillation comes from an overdensity of WDs on the Q-branch in Gaia color–magnitude diagrams, which indicates that ∼6% of massive WDs are delayed in their cooling by as much as ∼10 Gyr. However, it is unclear how these stars end up with such a high concentration of²²Ne and if a significant fraction of the more common average-mass WDs go through distillation. We argue that a significant metal-rich stellar population in the solar neighborhood should lead to distilled WDs, without requiring a binary merger. We use MESA along with the carbon, nitrogen, and oxygen abundances derived from high-resolution spectroscopy of stars included in the Hypatia catalog to predict the²²Ne mass fraction in their descendant WDs. We find that 0.6%–2.5% of the WDs in the solar neighborhood have sufficient²²Ne in their interiors to go through multi-Gyr cooling delays, which could significantly inflate their numbers in the observed samples. Hence,²²Ne distillation and long-lived habitable zones around WDs should be relatively common in the solar neighborhood. We also use a Galactic model to predict the fraction of WDs that go through distillation as a function of Galactocentric distance. The fraction of distilled WDs is ∼2%–8% near the Galactic center and declines steadily toward the outer disk. 

ABSTRACT Double white dwarf (DWD) binaries are an important remnant of binary evolution as they are possible Type Ia supernova progenitors and strong sources of gravitational waves in the low-frequency regime. The double-lined double white dwarf (DBL) survey searches for compact DWDs where both stars can be spectrally disentangled. Candidates are identified by being overluminous compared to the cooling sequence of a typical-mass, single white dwarf. In this second instalment of the DBL survey, we present full orbital solutions of 15 DWD binaries from our ongoing campaign to accurately measure a magnitude-limited mass–period distribution. For the first time, 12 of these systems are fully solved. A long-standing bias in the full population has been evident, favouring systems with orbital periods up to a few hours, with little exploration of the majority of the compact DWD population, whose orbital period distribution centres at approximately 20 h. The 15 systems in this study span the orbital period range $$5< P_\textrm {orb}< 75$$ h, significantly augmenting the number of well-characterized systems over these periods, and in general have two similar mass stars combining to $$\approx$$1.0 M$$_\odot$$. We witness that the orbitally derived mass ratios generally show excellent agreement with those deduced from atmospheric fits to double-lined spectra in previous work, emphasizing the power of wide-scale spectroscopic surveys to efficiently locate the highest-mass, double-lined DWDs in the local Galaxy. 

Abstract The majority of merging white dwarfs leave behind a white dwarf remnant. Hot/warm DQ white dwarfs with carbon-rich atmospheres have high masses and unusual kinematics. All evidence points to a merger origin. Here, we demonstrate that far-UV (FUV) and optical photometry provides an efficient way to identify these merger remnants. We take advantage of this photometric selection to identify 167 candidates in the Galaxy Evolution Explorer All-Sky Imaging Survey footprint, and provide follow-up spectroscopy. Out of the 140 with spectral classifications, we identify 75 warm DQ white dwarfs withT_eff > 10,000 K, nearly tripling the number of such objects known. Our sample includes 13 DAQ white dwarfs with spectra dominated by hydrogen and (weaker) carbon lines. Ten of these are new discoveries, including the hottest DAQ known to date, withT_eff ≈ 23,000 K andM = 1.31M_⊙. We provide a model atmosphere analysis of all warm DQ white dwarfs found, and present their temperature and mass distributions. The sample mean and standard deviation areT_eff = 14,560 ± 1970 K andM = 1.11 ± 0.09M_⊙. Warm DQs are roughly twice as massive as the classical DQs found at cooler temperatures. All warm DQs are found on or near the crystallization sequence. Even though their estimated cooling ages are of order 1 Gyr, their kinematics indicate an origin in the thick disk or halo. Hence, they are likely stuck on the crystallization sequence for ∼10 Gyr due to significant cooling delays from distillation of neutron-rich impurities. Future all-sky FUV surveys like Ultraviolet Explorer have the potential to significantly expand this sample. 

ABSTRACT We present the characteristics of interstellar comet 3I/Asteroid Terrestrial-impact Last Alert System (ATLAS), discovered on 2025 July 1 by the ATLAS. The comet has eccentricity $$\simeq$$6.1 and velocity at infinity $$\simeq$$57 km s−1, indicating an interstellar origin. We obtained B, V, R, I, g, r, i, and z photometry at Kottamia Astronomical Observatory, Palomar Observatory, and Apache Point Observatory on 2025 July 2, 3, and 6. We measured colour indices B–V = 0.98 $$\pm$$ 0.23, V–R = 0.71 $$\pm$$ 0.09, R–I = 0.14 $$\pm$$ 0.10, g–r = 0.84 $$\pm$$ 0.05, r–i = 0.16$$\pm$$0.03, i–z = –0.02$$\pm$$0.07, g–i = 1.00$$\pm$$0.05, and a spectral slope of 16.0 $$\pm$$ 1.9 $${{\ \rm per\ cent}}$$/100 nm. We estimate the comet’s dust cross-section within 10 000 km to be 184.6 $$\pm$$ 4.6 km$^2$, assuming a 0.1 albedo. 3I/ATLAS’s coma has full width at half-maximum $$\simeq$$ 2.2 arcsec and A(0$$^\circ$$)f$$\rho$$ = 280.8 $$\pm$$ 3.2 cm. We estimate 3I/ATLAS is ejecting $$\mu$$m to mm dust at $$\sim$$0.01–1 m s−1, with a mass-loss of $$\sim$$0.1–1.0 kg s−1.