arXiv subjects

Nicola Gentile Fusillo

Publications and source records attributed to Nicola Gentile Fusillo.

12 recordsLinked to original sources

arXiv2026

Spectroscopic Characterization of WD J000801.25-350450 and its Two Co-Moving Companions

We present new spectroscopic data for Gaia DR3 2309499817384726016 (WD0008-350A) and its two wide, co-moving, low-mass companions. We confirm the white dwarf is a hydrogen-rich DA, with T$_{\rm eff}$=6200$\pm$90~K and a mass of 0.63$\pm$0.03~M${\odot}$, close to that of the average white dwarf. Near-infrared spectra of the two stellar companions to WD0008-350A 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.

astro-ph.SR↗

arXiv2025

The Galactic White Dwarf Population

The ESA Gaia mission has revolutionized our understanding of the white dwarf population, delivering an unprecedented census of these nearby remnants and revealing previously unseen structures in the Hertzsprung-Russell (HR) diagram. However, while Gaia has expanded the scope of white dwarf astrophysics, it has also exposed new questions related to atmospheric composition, spectral evolution, crystallization, magnetism, and merger-driven pathways. Many of these open problems are encoded in the detailed morphology of the Gaia HR diagram, where precise spectroscopic characterization is essential for interpreting the underlying physical processes. Spectroscopic characterization, obtainable with current and future ESO facilities, can provide the effective temperatures and surface gravities that are required to derive accurate white dwarf masses, cooling ages, and luminosities. These fundamental parameters not only enable studies of spectral evolution, interior physics, and the origin of magnetic and high-mass white dwarfs, but also guarantee the construction of robust mass distributions and luminosity functions, essential for constraining the initial-to-final mass relation, probing the initial mass function, and reconstructing the star formation history of the local Galaxy, among other applications. Looking toward the 2040s, future multi-fiber spectrographs operating in survey mode on 10--15 meter class telescopes will be able to collect a complete spectroscopic sample of white dwarf, enabling the detailed characterization of their population. Achieving spectroscopic completeness for the nearby Galactic population and securing high signal-to-noise, moderate-to-high resolution spectra across the HR diagram with ESO instrumentation will be critical steps toward resolving these longstanding questions in white dwarf astrophysics.

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arXiv2025

Resolution-Corrected White Dwarf Gravitational Redshifts Validate SDSS-V Wavelength Calibration and Enable Accurate Mass-Radius Tests

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 and the Type Ia Supernova Progenitor Survey, we show that substantial biases (5-15 km/s) 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 the Sloan Digital Sky Survey, the Dark Energy Spectroscopic Instrument, the 4-meter Multi-Object Spectroscopic Telescope, and the Wide-Field Multiplexed Spectroscopic Facility.

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arXiv2025

A Large Catalog of DA White Dwarf Characteristics Using SDSS and Gaia Observations

We present a catalog of 8545 and 19,257 unique DA white dwarfs observed in SDSS Data Release 19 and previous SDSS data releases, respectively. This is the largest catalog of both spectroscopic and photometric measurements of DA white dwarfs available to date, and we make this catalog and all code used to create it publicly available. We measure the apparent radial velocity, spectroscopic effective temperature and surface gravity, and photometric effective temperature and radius for all objects in our catalog. We validate our measurements against other published white dwarf catalogs. For apparent radial velocities, surface gravities, and effective temperatures measured from spectra with signal-to-noise ratios $>50$, our measurements agree with published SDSS white dwarf catalogs to within 7.5 km/s, 0.060 dex, and $2.4\%$, respectively. For radii and effective temperatures measured with Gaia photometry, our measurements agree with other published Gaia datasets to within $0.0005$ $R_\odot$ and $3\%$, respectively. We use this catalog to investigate systematic discrepancies between white dwarfs observed in SDSS-V and previous generations of SDSS. For objects observed in both SDSS-V and previous generations, we uncover systematic differences between measured spectroscopic parameters depending on which set of survey data is used. On average, the measured apparent radial velocity of a DA white dwarf is $11.5$ km/s larger and the surface gravity is $0.015$ dex smaller when a white dwarf's spectroscopic parameters are measured using SDSS-V data compared to using data from previous generations of SDSS. These differences may be due to changes in the wavelength solution across survey generations.

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arXiv2024

Detection of the Temperature Dependence of the White Dwarf Mass-Radius Relation with Gravitational Redshifts

Models predict that the well-studied mass-radius relation of white dwarf stars depends on the temperature of the star, with hotter white dwarfs having larger masses at a given radius than cooler stars. In this paper, we use a catalog of 26,041 DA white dwarfs observed in Sloan Digital Sky Survey Data Releases 1-19. We measure the radial velocity, effective temperature, surface gravity, and radius for each object. By binning this catalog in radius or surface gravity, we average out the random motion component of the radial velocities for nearby white dwarfs to isolate the gravitational redshifts for these objects and use them to directly measure the mass-radius relation. For gravitational redshifts measured from binning in either radius or surface gravity, we find strong evidence for a temperature-dependent mass-radius relation, with warmer white dwarfs consistently having greater gravitational redshifts than cool objects at a fixed radius or surface gravity. For warm white dwarfs, we find that their mean radius is larger and mean surface gravity is smaller than those of cool white dwarfs at 5.2σ and 6.0σ significance, respectively. Selecting white dwarfs with similar radii or surface gravities, the significance of the difference in mean gravitational redshifts between the warm and cool samples is >6.1σ and >3.6σ for measurements binned in radius and surface gravity, respectively, in the direction predicted by theory. This is an improvement over previous implicit detections, and our technique can be expanded to precisely test the white dwarf mass-radius relation with future surveys.

astro-ph.SR↗

arXiv2024

Simultaneous emission from dust and gas in the planetary debris orbiting a white dwarf

There is increasing evidence for the presence and variability of circumstellar dust and gas around white dwarfs that are polluted with exoplanetary material, although the origin of this dust and gas remains debated. This paper presents the first near-simultaneous observations of both circumstellar dust (via broadband emission) and gas (via emission lines) around a polluted white dwarf. From the optical spectra the gaseous emission lines, notably the calcium infrared triplet and magnesium lines, show significant increases and decreases in their strength over timescales of weeks, while the oxygen and iron lines remain relatively stable. Near-infrared JHKs photometry reveals dust emission changes of up to 0.2 magnitudes in the Ks band over similar timescales, marking the shortest variability timescales observed to date. The two epochs with the strongest emission were correlated between the dust (Ks band brightening) and gas (strengthened calcium and magnesium lines), showing for the first time that the dust and gas must be produced near-simultaneously with a common origin, likely in collisions.

astro-ph.EP↗

arXiv2023

WD0141-675: A case study on how to follow-up astrometric planet candidates around white dwarfs

This work combines spectroscopic and photometric data of the polluted white dwarf WD0141-675 which has a now retracted astrometric super-Jupiter candidate and investigates the most promising ways to confirm Gaia astrometric planetary candidates and obtain follow-up data. Obtaining precise radial velocity measurement for white dwarfs is challenging due to their intrinsic faint magnitudes, lack of spectral absorption lines, and broad spectral features. However, dedicated radial velocity campaigns are capable of confirming close in giant exoplanets (a few M$_{\textrm{Jup}}$) around polluted white dwarfs, where additional metal lines aid radial velocity measurements. Infrared emission from these giant exoplanets is shown to be detectable with JWST MIRI and will provide constraints on the formation of the planet. Using the initial Gaia astrometric solution for WD0141-675 as a case study, if there were a planet with a 33.65 d period or less with a nearly edge on orbit, 1) ground-based radial velocity monitoring limits the mass to $<$ 15.4 M$_{\textrm{Jup}}$, and 2) space-based infrared photometry shows a lack of infrared excess and in a cloud-free planetary cooling scenario, a sub-stellar companion would have to be $<$ 16 M$_{\textrm{Jup}}$ and be older than 3.7 Gyr. These results demonstrate how radial velocities and infrared photometry can probe the mass of the objects producing some of the astrometric signals, and rule out parts of the brown dwarf and planet mass parameter space. Therefore, combining astrometric data with spectroscopic and photometric data is crucial to both confirm, and characterise astrometric planet candidates around white dwarfs.

astro-ph.EP↗

arXiv2023

The ESO's Extremely Large Telescope Working Groups

Since 2005 ESO has been working with its community and industry to develop an extremely large optical/infrared telescope. ESO's Extremely Large Telescope, or ELT for short, is a revolutionary ground-based telescope that will have a 39-metre main mirror and will be the largest visible and infrared light telescope in the world. To address specific topics that are needed for the science operations and calibrations of the telescope, thirteen specific working groups were created to coordinate the effort between ESO, the instrument consortia, and the wider community. We describe here the goals of these working groups as well as their achievements so far.

astro-ph.IM↗

arXiv2022

The population of hot subdwarf stars studied with Gaia -- IV. Catalogues of hot subluminous stars based on Gaia EDR3

In light of substantial new discoveries of hot subdwarfs by ongoing spectroscopic surveys and the availability of the Gaia mission Early Data Release 3 (EDR3), we compiled new releases of two catalogues of hot subluminous stars: The data release 3 (DR3) catalogue of the known hot subdwarf stars contains 6,616 unique sources and provides multi-band photometry, and astrometry from Gaia EDR3 as well as classifications based on spectroscopy and colours. This is an increase of 742 objects over the DR2 catalogue. This new catalogue provides atmospheric parameters for 3,087 stars and radial velocities for 2,791 stars from the literature. In addition, we have updated the Gaia Data Release 2 (DR2) catalogue of hot subluminous stars using the improved accuracy of the Gaia EDR3 data set together with updated quality and selection criteria to produce the Gaia EDR3 catalogue of 61,585 hot subluminous stars, representing an increase of 21,785 objects. The improvements in Gaia EDR3 astrometry and photometry compared to Gaia DR2 have enabled us to define more sophisticated selection functions. In particular, we improved hot subluminous star detection in the crowded regions of the Galactic plane as well as in the direction of the Magellanic Clouds by including sources with close apparent neighbours but with flux levels that dominate the neighbourhood.

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arXiv2020

White dwarf pollution by hydrated planetary remnants: Hydrogen and Metals in WD J204713.76-125908.9

WD J204713.76-125908.9 is a new addition to the small class of white dwarfs with helium-dominated photospheres that exhibit strong Balmer absorption lines and atmospheric metal pollution. The exceptional abundances of hydrogen observed in these stars may be the result of accretion of water-rich rocky bodies. We obtained far-ultraviolet and optical spectroscopy of WD J204713.76-125908.9 using the Cosmic Origin Spectrograph on-board the Hubble Space Telescope and X-shooter on the Very Large Telescope, and identify photospheric absorption lines of nine metals: C, O, Mg, Si, P, S, Ca, Fe and Ni. The abundance ratios are consistent with the steady state accretion of exo-planetesimal debris rich in the volatile elements carbon and oxygen, and the transitional element sulphur, by factors of seventeen, two, and four respectively compared to bulk Earth. The parent body has a composition akin to Solar System carbonaceous chondrites, and the inferred minimum mass, $1.6 \times 10^{20}$ g, is comparable to an asteroid 23 km in radius. We model the composition of the disrupted parent body, finding from our simulations a median water mass fraction of eight per cent.

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arXiv2019

Astro 2020 Science White Paper: Evolved Planetary Systems around White Dwarfs

Practically all known planet hosts will evolve into white dwarfs, and large parts of their planetary systems will survive this transition - the same is true for the solar system beyond the orbit of Mars. Spectroscopy of white dwarfs accreting planetary debris provides the most accurate insight into the bulk composition of exo-planets. Ground-based spectroscopic surveys of ~260, 000 white dwarfs detected with Gaia will identify >1000 evolved planetary systems, and high-throughput high-resolution space-based ultraviolet spectroscopy is essential to measure in detail their abundances. So far, evidence for two planetesimals orbiting closely around white dwarfs has been obtained, and their study provides important constraints on the composition and internal structure of these bodies. Major photometric and spectroscopic efforts will be necessary to assemble a sample of such close-in planetesimals that is sufficiently large to establish their properties as a population, and to deduce the architectures of the outer planetary systems from where they originated. Mid-infrared spectroscopy of the dusty disks will provide detailed mineralogical information of the debris, which, in combination with the elemental abundances measured from the white dwarf spectroscopy, will enable detailed physical modelling of the chemical, thermodynamic, and physical history of the accreted material. Flexible multi-epoch infrared observations are essential to determine the physical nature, and origin of the variability observed in many of the dusty disks. Finally, the direct detection of the outer reservoirs feeding material to the white dwarfs will require sensitive mid- and far-infrared capabilities.

astro-ph.EP↗

arXiv2019

A planetesimal orbiting within the debris disc around a white dwarf star

Many white dwarf stars show signs of having accreted smaller bodies, implying that they may host planetary systems. A small number of these systems contain gaseous debris discs, visible through emission lines. We report a stable 123.4min periodic variation in the strength and shape of the CaII emission line profiles originating from the debris disc around the white dwarf SDSSJ122859.93+104032.9. We interpret this short-period signal as the signature of a solid body held together by its internal strength.

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