The Companion of the White Dwarf G29-38 as a Brown Dwarf

Abstract

The strong infrared excess discovered by Zuckerman and Becklin (1987) in the white dwarf G29-38 (ZZ Psc) has been ascribed to a "brown dwarf". A variety of Palomar spectra of the white dwarf shows it to be an essentially normal DA4V, without spectral peculiarities that might have arisen from accretion or interaction with a close companion. The multichannel spectrophotometry and IUE fluxes fit a model DA of 11500K, log g = 8, except for the infrared excess. The infrared fluxes of the model are subtracted from the Zuckerman and Becklin observation to give the energy distribution of the infrared object G29-38B. The luminosity of the latter is ≈4×10^-5L_sun;, and its temperature between 1100 and 1500K, with a strong preference for the lower half of that range. The radius corresponding to those temperatures, 0.18 - 0.10 R_sun;, is larger than expected, but interpretation as a brown dwarf still appears most plausible. The latter's cooling time requires the lifetime of the white dwarf's progenitor to be ≤2×10⁸yr. The possibility is explored that the infrared object is a dark, large object, heated by close proximity to the white dwarf.