Spectral energy distribution signatures of Jovian planets around white dwarf stars

The problem of detecting Jovian-sized planets orbiting white dwarf stars is considered. Significant IR excesses result from warm Jupiters orbiting a w hite dwarf of T-eff = 10,000 K at a distance of similar to 10(3) white eff dwarf radii (corresponding to similar to 10(2) Jupiter radii or a few tenth s of an AU) with an orbital period of similar to 100 days. Such a planet wi ll have a 10 mum flux density at its Wien peak that is comparable to the em ission of the white dwarf at that wavelength. Although the white dwarf is m uch hotter than the planet, the planet will have peak brightness at the IR, well into the Rayleigh-Jeans tail of the white dwarf; plus, Jovians are ab out 10 times larger than white dwarfs, so there is a substantial gain in th e planet-to-star brightness contrast as compared to planets around main-seq uence stars. In the solar neighborhood, there are 51 white dwarf stars with in 13 pc of the Sun. At 10 pc, the IR flux density of "warm" Jupiters (a fe w hundred kelvins) will fall in the range 10-100 mu Jy, which should be obs ervable with SIRTF.