Nicola Pietro Gentile Fusillo

Many planetary systems survive the metamorphosis of their host stars into white dwarfs, as demonstrated by the detection of dusty circumstellar discs around these stellar remnants and chemical signatures of planetary debris in atmospheres of these stars. A small fraction of these circumstellar discs also contain gas, detected in the form of emission lines from various ionic transitions (most commonly the near-infrared Ca II triplet). All of the 21 known gas discs exhibit double-peaked line profiles characteristic of a rotating flat disc. The mechanism behind the generation of gas is still debated, but for at least one system it has been linked with the presence of a surviving planetesimal embedded within the dust disc. Here we report the discovery of WD J132800.85–145019.95, a new gas-disc system that exhibits quadruple-peaked instead of double-peaked line profiles. These emission lines originate from two separate gaseous rings extending from 0.14 R _⊙ to 0.34 R _⊙ and from 0.54 R _⊙ to 1.93 R _⊙ . We propose that this structure results from the presence of two distinct planetary bodies within these discs, ranging in size from a few kilometres to the size of Pluto. The detection this stable double-disc presents a new challenge for the current models of debris disc formation and evolution.

White dwarfs (WDs) with F-, G-, or K-type binary companions are the last common ancestor to a zoo of exotic phenomena. Finding a clean sample of such systems is difficult, as WDs in such binaries are usually outshone at optical wavelengths by their non-degenerate companion. It is useful to have a sample of such binaries; they can be studied to investigate binary evolution, as they may have undergone a previous phase of mass transfer. Using Gaia data release 3 and GALEX, we compile a sample of 2597 candidate WD + FGK systems within 350 pc. These were identified via their ultraviolet excesses relative to MESA Isochrones and Stellar Tracks model predictions consistent with the Gaia parameters of their non-degenerate companions. We estimate the mass, surface gravity, and effective temperature of the WDs by fitting the excess ultraviolet flux to models, or through interpolation where only one ultraviolet band was available. We also estimate the age of the system where possible, by comparing against any wide WD companions in higher-order stellar systems, or by checking if the system is a member of a cluster. On comparing against Simbad, we estimate the level of contamination within our sample to be between 10 per cent and 35 per cent. This is a valuable sample for investigating WD + FGK binaries, particularly those containing hotter WDs ($T_\mathrm{eff, WD} \gtrsim 25$ kK), and systems with post-main-sequence companions.

Metal-enriched white dwarfs provide a unique insight into the composition of exoplanet interiors. These stars accrete the debris of disrupted planetary bodies, and hence, measuring the stellar parameters and photospheric abundances yields the bulk compositions of the parent bodies. At present, over 1750 debris-accreting white dwarfs are known, but just a few dozen are sufficiently enriched to allow a detailed abundance study. Here, we report the analysis of 12 highly metal-enriched white dwarfs observed within the Data Release 1 of the Dark Energy Spectroscopic Instrument (DESI). We characterized their stellar parameters and photospheric metal abundances, and we identified between three and ten different elements in their optical spectra, including most of the rock-forming species: O, Mg, Si, Ca, and Fe. We conclude that the accreted bodies broadly resemble compositions found within the inner Solar system such as primitive meteorites, processed material, or planetary cores. Six of the systems allowed a more thorough analysis: four of the parent bodies are composed of dry rock-forming elements; and two of them of something akin to a water-rich planetesimal. Thus, this study establishes DESI as a potent survey for identifying metal-rich targets, yielding reliable compositions of accreted exoplanetary material.

Mapping the local and distant Universe is key to our understanding of it. For decades, the Sloan Digital Sky Survey (SDSS) has made a concerted effort to map millions of celestial objects to constrain the physical processes that govern our Universe. The most recent and fifth generation of SDSS (SDSS-V) is organized into three scientific “mappers”: the Milky Way Mapper, which aims to chart the various components of the Milky Way and constrain its formation and assembly; the Black Hole Mapper, which focuses on understanding supermassive black holes in distant galaxies across the Universe; and the Local Volume Mapper, which uses integral field spectroscopy to map the ionized interstellar medium in the Local Group. This paper describes the scope and content for the nineteenth data release (DR19) of SDSS, which is the most substantial to date in SDSS-V. DR19 is the first to contain data from all three mappers. Additionally, we also describe nine value-added catalogs that enhance the science that can be conducted with the SDSS-V data. Finally, we discuss how to access SDSS DR19 and provide illustrative examples and tutorials.

The fifth-generation Sloan Digital Sky Survey (SDSS-V) includes the first large-scale spectroscopic survey of white dwarfs (WDs) in the era of Gaia parallaxes. SDSS-V collects multiple exposures per target, making it ideal for binary detection. We present a search for hydrogen atmosphere (DA) double WD (DWD) binaries in this rich dataset. We quantify radial velocity variations between subexposures to identify binary candidates, and we measure the orbital period for a subset of DWD binary candidates. We find 60 DWD binary candidates, of which 43 are new discoveries, and report tentative periods for 9 of these binaries. From these binary candidates, we derive a Galactic WD binary fraction f _bin,0.4 = 9% for binary separations α = −0.62. Using the simulated binary population, we find that approximately two to five super-Chandrasekhar-mass binaries that merge within a Hubble time are expected in our sample at a 95% confidence interval. We predict that approximately two systems in our sample should be detectable via gravitational waves by the Laser Interferometer Space Antenna (LISA), one of which has already been identified as a LISA verification source. We also estimate a total of about 10,000–20,000 LISA-detectable DWD binaries in the Galaxy. Our catalog of WD+WD binary candidates in SDSS-V is now public and promises to uncover a large number of exciting DWD systems.

We present new spectroscopic data for Gaia DR3 2309499817384726016 (WD 0008-350A) and its two wide, comoving, low-mass companions. We confirm the white dwarf is a hydrogen rich DA, with T _eff = 6200 ± 90 K and a mass of 0.63 ± 0.03 M _⊙ , close to that of the average white dwarf. Near-infrared spectra of the two stellar companions to WD 0008-350A reveal that the inner companion is an M dwarf, exhibiting a spectral type of M8. Furthermore, the outer companion is identified as a possible M6 + M9 binary. This paper examines the evidence which suggests the system may be quadruple.

The Sloan Digital Sky Survey V (SDSS-V) is pioneering panoptic spectroscopy: it is the first all-sky, multiepoch, optical-to-infrared spectroscopic survey. SDSS-V is mapping the sky with multiobject spectroscopy (MOS) at telescopes in both hemispheres (the 2.5 m Sloan Foundation Telescope at Apache Point Observatory and the 100-inch du Pont Telescope at Las Campanas Observatory), where 500 zonal robotic fiber positioners feed light from a wide-field focal plane to an optical ( R ∼ 2000, 500 fibers) and a near-infrared ( R ∼ 22,000, 300 fibers) spectrograph. In addition to these MOS capabilities, the survey is pioneering ultra–wide-field (∼4000 deg ² ) integral field spectroscopy enabled by a new dedicated facility (LVM-I) at Las Campanas Observatory, where an integral field spectrograph (IFS) with 1801 lenslet-coupled fibers arranged in a 0 . ° 5-diameter hexagon feeds multiple R ∼ 4000 optical spectrographs that cover 3600–9800 Å. SDSS-V’s hardware and multiyear survey strategy are designed to decode the chemodynamical history of the Milky Way and tackle fundamental open issues in stellar physics in its Milky Way Mapper program, trace the growth physics of supermassive black holes in its Black Hole Mapper program, and understand the self-regulation mechanisms and the chemical enrichment of galactic ecosystems at the energy injection scale in its Local Volume Mapper program. The survey is well timed to multiply the scientific output from major all-sky space missions. The SDSS-V MOS programs began robotic operations in 2021; IFS observations began in 2023 with the completion of the LVM-I facility. SDSS-V builds on decades of heritage of SDSS’s pioneering advances in data analysis, collaboration spirit, infrastructure, and product deliverables in astronomy.

Polluted white dwarfs offer a unique way to directly probe the compositions of exoplanetary bodies. We examine the water content of accreted material using the oxygen abundances of 51 highly polluted white dwarfs. Within this sample, we present new abundances for three H-dominated atmosphere white dwarfs that showed promise for accreting water-rich material. Throughout, we explore the impact of the observed phase and lifetime of accretion disks on the inferred elemental abundances of the parent bodies that pollute each white dwarf. Our results indicate that white dwarfs sample a range of dry to water-rich material, with median uncertainties in water mass fractions of ≈15%. Among the He-dominated white dwarfs, 35/39 water abundances are consistent with corresponding H abundances. While for any individual white dwarf it may be ambiguous as to whether or not water is present in the accreted parent body, when considered as a population, the prevalence of water-rich bodies is statistically robust. The population as a whole has a median water mass fraction of ≈25%, and enforcing chondritic parent body compositions, we find that 31/51 WDs are likely to have nonzero water concentrations. This conclusion is different from a similar previous analysis of white dwarf pollution and we discuss reasons why this might be the case. Pollution in H-dominated white dwarfs continues to be more water-poor than in their He-dominated cousins, although the sample size of H-dominated white dwarfs remains small and the two samples still suffer a disjunction in the range of host star temperatures being probed.

Leveraging the large sample size of low-resolution spectroscopic surveys to constrain white dwarf stellar structure requires an accurate understanding of the shapes of hydrogen absorption lines, which are pressure broadened by the Stark effect. Using data from both the Sloan Digital Sky Survey (SDSS) and the Type Ia Supernova Progenitor Survey, we show that substantial biases (5–15 km s⁻¹) exist in radial velocity measurements made from observations at low spectral resolution relative to similar measurements from high-resolution spectra. Our results indicate that the physics of line formation in high-density plasmas, especially in the wings of the lines, are not fully accounted for in state-of-the-art white dwarf model atmospheres. We provide corrections to account for these resolution-induced redshifts in a way that is independent of an assumed mass–radius relation, and we demonstrate that statistical measurements of gravitational redshift with these corrections yield improved agreement with theoretical mass–radius relations. Our results provide a set of best practices for white dwarf radial velocity measurements from low-resolution spectroscopy, including those from SDSS, the Dark Energy Spectroscopic Instrument, the 4 m Multi-Object Spectroscopic Telescope, and the Wide-Field Multiplexed Spectroscopic Facility.