SEARCHING FOR DUST AROUND HYPER METAL POOR STARS

We examine the mid-infrared fluxes and spectral energy distributions for stars with iron abundances [Fe/H] < -5, and other metal-poor stars, to eliminate the possibility that their low metallicities are related to the depletion of elements onto dust grains in the formation of a debris disk. Six out of seven stars examined here show no mid-IR excesses. These non-detections rule out many types of circumstellar disks, e. g., a warm debris disk (T <= 290 K), or debris disks with inner radii <= 1 AU, such as those associated with the chemically peculiar post-asymptotic giant branch spectroscopic binaries and RV Tau variables. However, we cannot rule out cooler debris disks, nor those with lower flux ratios to their host stars due to, e. g., a smaller disk mass, a larger inner disk radius, an absence of small grains, or even a multicomponent structure, as often found with the chemically peculiar Lambda Bootis stars. The only exception is HE0107-5240, for which a small mid-IR excess near 10 m is detected at the 2s level; if the excess is real and associated with this star, it may indicate the presence of (recent) dust-gas winnowing or a binary system.