Periodic optical variability and debris accretion in white dwarfs: a test for a causal connection

Abstract

Recent Kepler photometry has revealed that about half of white dwarfs (WDs) have periodic, low-level (~ 1e-4 - 1e-3), optical variations. Hubble Space Telescope (HST) ultraviolet spectroscopy has shown that up to about one half of WDs are actively accreting rocky planetary debris, as evidenced by the presence of photospheric metal absorption lines. We have obtained HST ultraviolet spectra of seven WDs that have been monitored for periodic variations, to test the hypothesis that these two phenomena are causally connected, i.e. that the optical periodic modulation is caused by WD rotation coupled with an inhomogeneous surface distribution of accreted metals. We detect photospheric metals in four out of the seven WDs. However, we find no significant correspondence between the existence of optical periodic variability and the detection of photospheric ultraviolet absorption lines. Thus the null hypothesis stands, that the two phenomena are not directly related. Some other source of WD surface inhomogeneity, perhaps related to magnetic field strength, combined with the WD rotation, or alternatively effects due to close binary companions, may be behind the observed optical modulation. We report the marginal detection of molecular hydrogen in WD J1949+4734, only the fourth known WD with detected H_2 lines. We also re-classify J1926+4219 as a carbon-rich He-sdO subdwarf.

arXiv commentMNRAS, in press

References in corpus (52)

• The chemical composition of the Sun
• The VizieR database of Astronomical Catalogues
• The Occurrence and Architecture of Exoplanetary Systems
• A Tidally-Disrupted Asteroid Around the White Dwarf G29-38
• Absolute Calibration of the Infrared Array Camera on the Spitzer Space Telescope
• The Cosmic Origins Spectrograph
• The frequency of planetary debris around young white dwarfs
• Evolutionary and pulsational properties of white dwarf stars
• Hot subluminous stars
• Spectroscopic Analysis of DA White Dwarfs: Stark Broadening of Hydrogen Lines Including Non-Ideal Effects
• Ancient planetary systems are orbiting a large fraction of white dwarf stars
• Accretion and diffusion in white dwarfs. New diffusion timescales and applications to GD362 and G29-38
• Point Source Extraction with MOPEX
• Know Your Neighborhood: A Detailed Model Atmosphere Analysis of Nearby White Dwarfs
• Evidence for Water in the Rocky Debris of a Disrupted Extrasolar Minor Planet
• White Dwarf Rotation as a Function of Mass and a Dichotomy of Mode Linewidths: Kepler Observations of 27 Pulsating DA White Dwarfs Through K2 Campaign 8
• Spectropolarimetric Survey of Hydrogen-rich White Dwarf Stars
• High-resolution UVES/VLT spectra of white dwarfs observed for the ESO SN Ia Progenitor Survey. III. DA white dwarfs
• Debris Disks Around White Dwarfs: The DAZ Connection
• Beaming Binaries - a New Observational Category of Photometric Binary Stars
• First Kepler results on compact pulsators I. Survey target selection and the first pulsators
• DA white dwarfs in SDSS DR7 and a search for infrared excess emission
• The Chemical Composition of an Extrasolar Kuiper-Belt-Object
• The accretion-diffusion scenario for metals in cool white dwarfs
• The chemical diversity of exo-terrestrial planetary debris around white dwarfs
• The frequency of snowline-region planets from four-years of OGLE-MOA-Wise second-generation microlensing
• The ELM Survey. VII. Orbital Properties of Low Mass White Dwarf Binaries
• Doppler-imaging of the planetary debris disc at the white dwarf SDSS J122859.93+104032.9
• Discovery of kilogauss magnetic fields in three DA white dwarfs
• The separation distribution and merger rate of double white dwarfs: improved constraints
• The fraction of double degenerates among DA white dwarfs
• A Spitzer White Dwarf Infrared Survey
• White dwarfs in the UKIDSS Large Area Survey: The Substellar Companion Fraction
• On The Evolution of Magnetic White Dwarfs
• First Kepler results on compact pulsators VI. Targets in the final half of the survey phase
• A brief introductory guide to TLUSTY and SYNSPEC
• Kepler and the seven dwarfs: detection of low-level day-timescale periodic photometric variations in white dwarfs
• Anomalous cooling of the massive white dwarf in U Geminorum following a narrow dwarf nova outburst
• A search for planetary eclipses of white dwarfs in the Pan-STARRS1 medium-deep fields
• Detection of Weak Circumstellar Gas around the DAZ White Dwarf WD 1124-293: Evidence for the Accretion of Multiple Asteroids
• Rotational period of WD1953-011 - a magnetic white dwarf with a star spot
• The binary fraction, separation distribution, and merger rate of white dwarfs from SPY
• O vi in the local interstellar medium
• The Hyades Cluster: Identification of a Planetary System and Escaping White Dwarfs
• Can magnetic fields suppress convection in the atmosphere of cool white dwarfs? A case study on WD2105-820
• High ions towards white dwarfs: circumstellar line shifts and stellar temperature
• Discovery of Molecular Hydrogen in White Dwarf Atmospheres
• Searching for giga-Jansky fast radio bursts from the Milky Way with a global array of low-cost radio receivers
• Monitoring and modelling of white dwarfs with extremely weak magnetic fields
• Multi-wavelength observations of the EUV variable metal-rich white dwarf GD 394
• DA White Dwarfs in the Kepler Field
• TLUSTY User's Guide III: Operational Manual

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• Two New White Dwarfs With Variable Magnetic Balmer Emission Lines
• Optical detection of the 1.1-day variability at the white dwarf GD 394 with TESS
• A wavelet analysis of photometric variability in Kepler white dwarf stars