Accretion and Diffusion in the Atmosphere of the V471 Tauri's White Dwarf

Details Accretion and Diffusion in the Atmosphere of the V471 Tauri's White Dwarf Accretion and Diffusion in the Atmosphere of the V471 Tauri's White Dwarf

Dec 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.5001d&link_type=abstract

American Astronomical Society, 181st AAS Meeting, #50.01; Bulletin of the American Astronomical Society, Vol. 24, p.1203

Astronomy and Astrophysics

Astronomy

1

Scientific paper

The discovery of variability in the soft X-ray light curve of V471 Tauri (Jensen et al. 1986, ApJ, 309, L27) indicated the white dwarf is either accreting material from the K star or is undergoing nonradial pulsations. In order to discriminate between the two processes, an optical light curve of V471 Tauri was obtained by Clemens et al. (1992, ApJ, 391, 773), from which they have concluded that the accretion hypothesis is the most viable one. We have explored in detail the accretion model by carrying out time-dependent simulations of diffusion in the envelope of V471 Tauri including the effect of accretion from the companion K star. The study of Mullan et al. (1991, ApJ, 374, 707) demonstrates that the accretion rate on the white dwarf must be reduced by at least four orders of magnitude compared to the rate of 10(-13) M_sun/yr expected from an application of the Hoyle-Bondi theory. We have explicitly verified that for this accretion rate, the amount of metals accreted is incompatible with the optical light curve. Because of this inconsistency we have investigated accretion following a flare on the K star. Our calculations assume that the accretion rate following a flare reaches a value of 5times 10(-15) M_sun/yr during an interval of time about equal to one week. The heavy elements accreted diffuse out the UV photosphere after about two months but remain at an abundance of 10(-3) for helium and 10(-5) for carbon in the soft X-ray/EUV photosphere. Our calculations suggest that, most of the time, the white dwarf in V471 Tauri accretes at a sufficiently low rate that the photospheric abundances of elements heavier than hydrogen are unaffected. However, a short accretion phase following a flare will provide the source of opacity required to darken the magnetic pole of the white dwarf and is consistent with the optical observations. This work has been supported by NASA contracts NAS5-30180 and NAS5-29298.

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