Two New White Dwarfs With Variable Magnetic Balmer Emission Lines

Abstract

We report the discovery of two apparently isolated stellar remnants that exhibit rotationally modulated magnetic Balmer emission, adding to the emerging DAHe class of white dwarf stars. While the previously discovered members of this class show Zeeman-split triplet emission features corresponding to single magnetic field strengths, these two new objects exhibit significant fluctuations in their apparent magnetic field strengths with variability phase. The Zeeman-split hydrogen emission lines in LP $705-64$ broaden from $9.4$ MG to $22.2$ MG over an apparent spin period of $72.629$ minutes. Similarly, WD J$143019.29-562358.33$ varies from $5.8$ MG to $8.9$ MG over its apparent $86.394$-minute rotation period. This brings the DAHe class of white dwarfs to at least five objects, all with effective temperatures within $500$ K of $8000$ K and masses ranging from $0.65-0.83M_{\odot }$.

7 pages, 3 figures. Accepted for publication in MNRAS

References in corpus (18)

• Array Programming with NumPy
• The Transiting Exoplanet Survey Satellite
• The K2 Mission: Characterization and Early results
• A catalogue of white dwarfs in Gaia EDR3
• On the Spectral Evolution of Hot White Dwarf Stars. I. A Detailed Model-Atmosphere Analysis of Hot White Dwarfs from SDSS DR12
• The CatWISE2020 Catalog
• Found: The missing blue opacity in atmosphere models of cool hydrogen white dwarfs
• Binary Star Origin of High Field Magnetic White Dwarfs
• 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
• $\text{Gaia}$ white dwarfs within 40 pc I: spectroscopic observations of new candidates
• Kepler and the seven dwarfs: detection of low-level day-timescale periodic photometric variations in white dwarfs
• Spectrophotometric analysis of magnetic white dwarf I: Hydrogen-rich compositions
• Lithium pollution of a white dwarf records the accretion of an extrasolar planetesimal
• Single magnetic white dwarfs with Balmer emission lines: A small class with consistent physical characteristics as possible signposts for close-in planetary companions
• DAHe white dwarfs from the DESI survey
• Magnetic dynamos in white dwarfs -- II. Relating magnetism and pollution
• A test of the planet-star unipolar inductor for magnetic white dwarfs
• Periodic optical variability and debris accretion in white dwarfs: a test for a causal connection