Non-LTE spectral models for the gaseous debris-disk component of Ton 345
arXiv:1411.1187 · doi:10.1051/0004-6361/201423690
Abstract
For a fraction of single white dwarfs with debris disks, an additional gaseous disk was discovered. Both dust and gas are thought to be created by the disruption of planetary bodies. The composition of the extrasolar planetary material can directly be analyzed in the gaseous disk component, and the disk dynamics might be accessible by investigating the temporal behavior of the Ca II infrared emission triplet, hallmark of the gas disk. We obtained new optical spectra for the first helium-dominated white dwarf for which a gas disk was discovered (Ton 345) and modeled the non-LTE spectra of viscous gas disks composed of carbon, oxygen, magnesium, silicon, sulfur, and calcium with chemical abundances typical for solar system asteroids. Iron and its possible line-blanketing effects on the model structure and spectral energy distribution was still neglected. A set of models with different radii, effective temperatures, and surface densities as well as chondritic and bulk-Earth abundances was computed and compared with the observed line profiles of the Ca II infrared triplet. Our models suggest that the Ca II emission stems from a rather narrow gas ring with a radial extent of R=0.44-0.94 Rsol, a uniform surface density Sigma=0.3 g/cm2, and an effective temperature of Teff=6000 K. The often assumed chemical mixtures derived from photospheric abundances in polluted white dwarfs - similar to a chondritic or bulk-Earth composition - produce unobserved emission lines in the model and therefore have to be altered. We do not detect any line-profile variability on timescales of hours, but we confirm the long-term trend over the past decade for the red-blue asymmetry of the double-peaked lines.
arXiv comment7 pages, 6 figures, 2 tables
References in corpus (27)
- The Sixth Data Release of the Sloan Digital Sky Survey
- A Tidally-Disrupted Asteroid Around the White Dwarf G29-38
- Are There Unstable Planetary Systems Around White Dwarfs?
- A gaseous metal disk around a white dwarf
- Ancient planetary systems are orbiting a large fraction of white dwarf stars
- Infrared Signatures of Disrupted Minor Planets at White Dwarfs
- The Chemical Composition of an Extrasolar Minor Planet
- Accretion and diffusion in white dwarfs. New diffusion timescales and applications to GD362 and G29-38
- Pollution of single white dwarfs by accretion of many small asteroids
- Chemical Abundances in the Externally Polluted White Dwarf GD 40: Evidence of a Rocky Extrasolar Minor Planet
- A Dusty Disk Around GD 362, a White Dwarf With a Uniquely High Photospheric Metal Abundance
- Debris Disks Around White Dwarfs: The DAZ Connection
- Carbon Deficiency in Externally-Polluted White Dwarfs: Evidence for Accretion of Asteroids
- Runaway accretion of metals from compact debris disks onto white dwarfs
- Echoes of a decaying planetary system: the gaseous and dusty disks surrounding three white dwarfs
- Excess Infrared Radiation from a Massive DAZ White Dwarf: GD362 - a Debris Disk?
- Strengthening the Case for Asteroidal Accrection: Evidence for Subtle and Diverse Disks at White Dwarfs
- SDSSJ084539.17+225728.0: the first DBZ white dwarf with a metal-rich gaseous debris disc
- The Discovery of the Most Metal-Rich White Dwarf: Composition of a Tidally Disrupted Extrasolar Dwarf Planet
- Possible Signs of Water and Differentiation in a Rocky Exoplanetary Body
- A Spitzer Space Telescope Study of the Debris Disks around four SDSS White Dwarfs
- Accretion from debris disks onto white dwarfs : Fingering (thermohaline) instability and derived accretion rates
- Non-LTE models for the gaseous metal component of circumstellar discs around white dwarfs
- AcDc - A new code for the NLTE spectral analysis of accretion discs: application to the helium CV AM CVn
- Radiative Levitation of Silicon in the Atmospheres of Two Hyades DA White Dwarfs
- Spectral modeling of gaseous metal disks around DAZ white dwarfs
- Asymmetric Line Profiles in Spectra of Gaseous Metal Disks Around Single White Dwarfs