Pulsational Mapping of Calcium Across the Surface of a White Dwarf
Susan E. Thompson, M. H. Montgomery, T. von Hippel, A. Nitta, J., Dalessio, J. Provencal, W. Strickland, J. A. Holtzman, A. Mukadam, D., Sullivan, T. Nagel, D. Koziel-Wierzbowska, S. Zola, T. Kundera, M. Winiarski,, M. Drozdz, E. Kuligowska, W. Ogloza, Zs. Bognar, G. Handler
TL;DR
This study maps calcium distribution on a white dwarf's surface by analyzing pulsations, revealing inhomogeneous metal accretion likely concentrated at the poles, using combined spectroscopic and photometric data.
Contribution
It introduces a method to constrain surface metal distribution on white dwarfs through pulsation analysis, specifically identifying polar accretion of calcium.
Findings
Calcium is concentrated at the poles of G29-38.
Inhomogeneous metal distribution is detected via pulsation amplitude ratios.
Polar accretion of calcium is supported by observational data.
Abstract
We constrain the distribution of calcium across the surface of the white dwarf star G29-38 by combining time series spectroscopy from Gemini-North with global time series photometry from the Whole Earth Telescope. G29-38 is actively accreting metals from a known debris disk. Since the metals sink significantly faster than they mix across the surface, any inhomogeneity in the accretion process will appear as an inhomogeneity of the metals on the surface of the star. We measure the flux amplitudes and the calcium equivalent width amplitudes for two large pulsations excited on G29-38 in 2008. The ratio of these amplitudes best fits a model for polar accretion of calcium and rules out equatorial accretion.
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