Spectral analysis of cool white dwarfs accreting from planetary systems: from the UV to the optical

Abstract

The accretion of planetary debris into the atmospheres of white dwarfs leads to the presence of metal lines in their spectra. Cool metal-rich white dwarfs, which left the main-sequence many Gyr ago, allow the study of the remnants of the oldest planetary systems. Despite their low effective temperatures ($T_{\mathrm{eff}}$), a non-neglible amount of their flux is emitted in the near ultraviolet (NUV), where many overlapping metal lines can potentially be detected. We have observed three metal-rich cool white dwarfs with the Space Telescope Imaging Spectrograph (STIS) onboard the Hubble Space Telescope (HST), and compare the results determined from the NUV data with those previously derived from the analysis of optical spectroscopy. For two of the white dwarfs, SDSSJ1038-0036 and SDSSJ1535+1247, we find reasonable agreement with our previous analysis and the new combined fit of optical and NUV data. For the third object, SDSSJ0956+5912, including the STIS data leads to a ten percent lower $T_{\mathrm{eff}}$, though we do not identify a convincing explanation for this discrepancy. The unusual abundances found for SDSSJ0956+5912 suggest that the accreted parent-body was composed largely of water ice and magnesium silicates, and with a mass of up to $\simeq 2\times 10^{25}$g. Furthermore SDSSJ0956+5912 shows likely traces of atomic carbon in the NUV. While molecular carbon is not observed in the optical, we demonstrate that the large quantity of metals accreted by SDSSJ0956+5912 can suppress the C${}_2$ molecular bands, indicating that planetary accretion can convert DQ stars into DZs (and not DQZs/DZQs).

arXiv comment13 pages, 6 figures, 4 tables, accepted for publication in MNRAS

References in corpus (52)

• A 3D Dust Map Based on Gaia, Pan-STARRS 1 and 2MASS
• A Tidally-Disrupted Asteroid Around the White Dwarf G29-38
• Galactic Reddening in 3D from Stellar Photometry - An Improved Map
• A disintegrating minor planet transiting a white dwarf
• Are There Unstable Planetary Systems Around White Dwarfs?
• The frequency of planetary debris around young white dwarfs
• A gaseous metal disk around a white dwarf
• Ancient planetary systems are orbiting a large fraction of white dwarf stars
• The Chemical Composition of an Extrasolar Minor Planet
• On the Spectral Evolution of Hot White Dwarf Stars. I. A Detailed Model-Atmosphere Analysis of Hot White Dwarfs from SDSS DR12
• Distant future of the Sun and Earth revisited
• Can Planets survive Stellar Evolution?
• Evidence for Water in the Rocky Debris of a Disrupted Extrasolar Minor Planet
• A Giant Planet Candidate Transiting a White Dwarf
• A planetesimal orbiting within the debris disc around a white dwarf star
• Accretion of a giant planet onto a white dwarf
• Constraints on the Lifetimes of Disks Resulting from Tidally Destroyed Rocky Planetary Bodies
• Cool DZ white dwarfs II: Compositions and evolution of old remnant planetary systems
• An aluminum/calcium-rich, iron-poor, white dwarf star: evidence for an extrasolar planetary lithosphere?
• The Chemical Composition of an Extrasolar Kuiper-Belt-Object
• Long-term evolution of three-planet systems to the post-Main Sequence and beyond
• Analysis of Helium-Rich White Dwarfs Polluted by Heavy Elements in the Gaia Era
• $Gaia$ white dwarfs within 40 pc II: the volume-limited northern hemisphere sample
• Likely detection of water-rich asteroid debris in a metal-polluted white dwarf
• Detectable close-in planets around white dwarfs through late unpacking
• A Trio of Metal-Rich Dust and Gas Disks Found Orbiting Candidate White Dwarfs with K-Band Excess
• I Spy Transits and Pulsations: Empirical Variability in White Dwarfs Using Gaia and the Zwicky Transient Facility
• A White Dwarf with Transiting Circumstellar Material Far Outside the Roche Limit
• A New Generation of Cool White Dwarf Atmosphere Models. I. Theoretical Framework and Applications to DZ Stars
• Cool DZ white dwarfs I: Identification and spectral analysis
• Full-lifetime simulations of multiple unequal-mass planets across all phases of stellar evolution
• Interpretation and diversity of exoplanetary material orbiting white dwarfs
• New white dwarf envelope models and diffusion. Application to DQ white dwarfs
• Gaseous Material Orbiting the Polluted, Dusty White Dwarf HE1349-2305
• Element abundances in cool white dwarfs. II. Ultraviolet observations of DZ white dwarfs
• Trace hydrogen in helium atmosphere white dwarfs as a possible signature of water accretion
• Carbon to oxygen ratios in extrasolar planetesimals
• Recurring Planetary Debris Transits and Circumstellar Gas around White Dwarf ZTF J0328$-$1219
• Alkali metals in white dwarf atmospheres as tracers of ancient planetary crusts
• White dwarf pollution by hydrated planetary remnants: Hydrogen and Metals in WD J204713.76-125908.9
• Discovery of Beryllium in White Dwarfs Polluted by Planetesimal Accretion
• White dwarfs with planetary remnants in the era of Gaia I: six emission line systems
• Carbon-rich (DQ) white dwarfs in the Sloan Digital Sky Survey
• Horizontal spreading of planetary debris accreted by white dwarfs
• Bayesian constraints on the origin and geology of exo-planetary material using a population of externally polluted white dwarfs
• Lithium pollution of a white dwarf records the accretion of an extrasolar planetesimal
• Magnesium abundances in cool metal-polluted white dwarfs
• The evolution of carbon-polluted white dwarfs at low effective temperatures
• GD424 -- a helium-atmosphere white dwarf with a large amount of trace hydrogen in the process of digesting a rocky planetesimal
• A New Generation of Cool White Dwarf Atmosphere Models. III. WD J2356$-$209: Accretion of a Planetesimal with an Unusual Composition
• Modelling the distributions of white dwarf atmospheric pollution: a low Mg abundance for accreted planetesimals?
• Line Profiles of the Calcium I Resonance Line in Cool Metal-polluted White Dwarfs

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• The spectral evolution of white dwarfs: where do we stand?
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• A DZ white dwarf with a 30 MG magnetic field
• Asynchronous accretion can mimic diverse white dwarf pollutants II: water content
• The ubiquity of carbon dredge-up in hydrogen-deficient white dwarfs as revealed by GALEX
• Missing metals in DQ stars: A simple explanation
• Measurement of stellar and substellar winds using white dwarf hosts
• Do White Dwarfs Sample Water-Rich Planetary Material?
• Search of nearby resolved neutron stars among optical sources