Cool DZ white dwarfs in the SDSS

Abstract

We report the identification of 26 cool DZ white dwarfs that lie across and below the main sequence in the Sloan Digital Sky Survey (SDSS) u-g vs. g-r two-color diagram; 21 of these stars are new discoveries. The sample was identified by visual inspection of all spectra of objects that fall below the main sequence in the two-color diagram, as well as by an automated search for characteristic spectral features over a large area in color space that included the main sequence. The spectra and photometry provided by the SDSS project are interpreted with model atmospheres, including all relevant metals. Effective temperatures and element abundances are determined, while the surface gravity has to be assumed and was fixed at the canonical value of log g = 8. These stars represent the extension of the well-known DZ sequence towards cooler temperatures and fill the gap around Teff = 6500 K present in a previous study. The metal abundances are similar to those in the hotter DZ, but the lowest abundances are missing, probably because of our selection procedures. The interpretation is complicated in terms of the accretion/diffusion scenario, because we do not know if accretion is still occurring or has ended long ago. Independent of that uncertainty, the masses of the metals currently present in the convection zones - and thus an absolute lower limit of the total accreted masses - of these stars are similar to the largest asteroids in our solar system.

Accepted by Astronomy and Astrophysics

References in corpus (9)

• A gaseous metal disk around a white dwarf
• Pollution of single white dwarfs by accretion of many small asteroids
• On the Spectral Evolution of Cool, Helium-Atmosphere White Dwarfs: Detailed Spectroscopic and Photometric Analysis of DZ Stars
• Carbon Deficiency in Externally-Polluted White Dwarfs: Evidence for Accretion of Asteroids
• The accretion-diffusion scenario for metals in cool white dwarfs
• SDSSJ104341.53+085558.2: A second white dwarf with a gaseous debris disc
• The Discovery of the Most Metal-Rich White Dwarf: Composition of a Tidally Disrupted Extrasolar Dwarf Planet
• The Magnetic and Metallic Degenerate G77-50
• Near-Infrared Constraints on the Presence of Warm Dust at Metal-Rich, Helium Atmosphere White Dwarfs

Cited by in corpus (46)

• SDSS DR7 White Dwarf Catalog
• New white dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 12
• New white dwarf stars in the Sloan Digital Sky Survey Data Release 10
• Circumstellar Debris and Pollution at White Dwarf Stars
• Simulations of two-planet systems through all phases of stellar evolution: implications for the instability boundary and white dwarf pollution
• Elemental Compositions of Two Extrasolar Rocky Planetesimals
• 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
• Analysis of Helium-Rich White Dwarfs Polluted by Heavy Elements in the Gaia Era
• White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 14
• Stochastic accretion of planetesimals onto white dwarfs: constraints on the mass distribution of accreted material from atmospheric pollution
• Detectable close-in planets around white dwarfs through late unpacking
• Rocky Extrasolar Planetary Compositions Derived from Externally-Polluted White Dwarfs
• Signs of a faint disc population at polluted white dwarfs
• A common origin of magnetism from planets to white dwarfs
• Spitzer Observations of White Dwarfs: the Missing Planetary Debris Around DZ Stars
• Scars of Intense Accretion Episodes at Metal-Rich White Dwarfs
• Water Fractions in Extrasolar Planetesimals
• Hydrogen delivery onto white dwarfs from remnant exo-Oort cloud comets
• Compositions of Planetary Debris around Dusty White Dwarfs
• Two Extrasolar Asteroids with Low Volatile-Element Mass Fractions
• Interpretation and diversity of exoplanetary material orbiting white dwarfs
• A wide binary trigger for white dwarf pollution
• Numerical Simulations of Collisional Cascades at the Roche Limits of White Dwarf Stars
• The frequency of gaseous debris discs around white dwarfs
• The Solar Neighborhood. XXXIX. Parallax Results from the CTIOPI and NOFS Programs: 50 New Members of the 25 Parsec White Dwarf Sample
• SDSSJ2222+2745 A Gravitationally Lensed Sextuple Quasar with Maximum Image Separation of 15.1" Discovered in the Sloan Giant Arcs Survey
• The incidence of magnetic fields in cool DZ white dwarfs
• The White Dwarfs within 25 Parsecs of the Sun: Kinematics and Spectroscopic Subtypes
• Transient outburst events from tidally disrupted asteroids near white dwarfs
• Polluted White Dwarfs: Mixing Regions and Diffusion Timescales
• Herschel Observations of Debris Discs Orbiting Planet-hosting Subgiants
• Extrasolar Refractory-Dominated Planetesimals: an Assessment
• Linking long-term planetary $N$-body simulations with periodic orbits: application to white dwarf pollution
• Mass and eccentricity constraints on the planetary debris orbiting the white dwarf WD 1145+017
• No evidence for a strong decrease of planetesimal accretion in old white dwarfs
• The spectral evolution of white dwarfs: where do we stand?
• Magnesium abundances in cool metal-polluted white dwarfs
• A Pilot Search for Evidence of Extrasolar Earth-analog Plate Tectonics
• Search for carbon stars and DZ white dwarfs in SDSS spectra survey through machine learning
• A Study of Cool White Dwarfs in the Sloan Digital Sky Survey Data Release 12
• A New Generation of Cool White Dwarf Atmosphere Models. III. WD J2356$-$209: Accretion of a Planetesimal with an Unusual Composition
• Extreme abundance ratios in the polluted atmosphere of the cool white dwarf NLTT19868
• The polluted atmosphere of the white dwarf NLTT 25792 and the diversity of circumstellar environments
• Characterizing planetary material accreted by cool helium atmosphere white dwarfs using an exponentially decaying disc model
• J-PLUS: The fraction of calcium white dwarfs along the cooling sequence