Discovery of Photospheric Calcium Line Strength Variations in the DAZd White Dwarf G29-38

Abstract

Metals in the photospheres of white dwarfs with Teff between 12,000 and 25,000 K should gravitationally settle out of these atmospheres in 1-2 weeks. Temporal variations in the line strengths of these metals could provide a direct measurement of episodic metal accretion. Using archival VLT and Keck spectroscopy, we find evidence that the DAZd white dwarf G29-38 shows significant changes in its Ca II K line strength. At the two best-observed epochs, we find that the Ca line equivalent width (EW) = 165 +- 4 mA (in 1996.885) and 280 +- 8 mA (in 1999.653), which is an increase of 70%. We consider the effect that pulsation has on the Ca EWs for this known variable star, and find that it adds an error of < 1 mA to these measurements. Calcium line strengths at other observational epochs support variations with timescales as short as two weeks. These Ca EW variations indicate that the metal accretion process in G29-38, presumably from its debris disk, is episodic on timescales of a few weeks or less, and thus the accretion is not dominated by Poynting-Robertson drag from an optically thin, continuous disk, which has a timescale of ~1 year.

15 pages, 4 figures, ApJ accepted

References in corpus (3)

• Debris Disks Around White Dwarfs: The DAZ Connection
• The accretion-diffusion scenario for metals in cool white dwarfs
• A Dusty Disk Around WD1150-153: Explaining the Metals in White Dwarfs by Accretion from the Interstellar Medium versus Debris Disks

Cited by in corpus (21)

• 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
• Elemental Compositions of Two Extrasolar Rocky Planetesimals
• The New Class of Dusty DAZ White Dwarfs
• Stochastic accretion of planetesimals onto white dwarfs: constraints on the mass distribution of accreted material from atmospheric pollution
• SDSSJ084539.17+225728.0: the first DBZ white dwarf with a metal-rich gaseous debris disc
• A White Dwarf with Transiting Circumstellar Material Far Outside the Roche Limit
• Variable Emission from a Gaseous Disc around a Metal-Polluted White Dwarf
• Spectroscopic Evolution of Disintegrating Planetesimals: Minutes to Months Variability in the Circumstellar Gas Associated with WD 1145+017
• Detection of Weak Circumstellar Gas around the DAZ White Dwarf WD 1124-293: Evidence for the Accretion of Multiple Asteroids
• Dust Production and Depletion in Evolved Planetary Systems
• Horizontal spreading of planetary debris accreted by white dwarfs
• Another one grinds the dust: Variability of the planetary debris disc at the white dwarf SDSS J104341.53+085558.2
• Near-Infrared Constraints on the Presence of Warm Dust at Metal-Rich, Helium Atmosphere White Dwarfs
• A Second Look at the Metal Line Variability of G29-38
• Can Gaia find planets around white dwarfs?
• Pulsational Mapping of Calcium Across the Surface of a White Dwarf
• Deciphering the Pulsations of G 29-38 with Optical Time Series Spectroscopy
• Constraining the Surface Inhomogeneity and Settling Times of Metals on Accreting White Dwarfs
• XMM-Newton Detection of X-ray Emission from the Metal-Polluted White Dwarf G 29-38
• Near-ultraviolet and optical effects of Debris Disks around White Dwarfs