A Possible Massive Asteroid Belt around ζ Leporis

Abstract

We have used the Keck I telescope to image at 11.7 and 17.9 mm the dust emission around z Leporis, a main- sequence A-type star at 21.5 pc from the Sun with an infrared excess. The excess is at most marginally resolved at 17.9 mm. The dust distance from the star is probably ≤6 AU, although some dust may extend to 9 AU. The mass of observed dust is ∼1022 g. Since the lifetime of dust particles is about 10 4 yr because of the Poynting- Robertson effect, we robustly estimate at least Vega-like systems, first discovered by IRAS, are main- sequence stars surrounded by dust. The operation of the Poynt- ing-Robertson effect on micron-sized grains, responsible for much of the observed infrared excess, requires that the lifetime of these particles be significantly shorter than the age of the stars (Backman & Paresce 1993). Thus, the dust grains must be re- plenished from a reservoir such as collisions between larger bodies or the sublimation of comets. Studies of Vega-like systems thus afford the opportunity to study the evolution of large solids such as planets, comets, and asteroids. The identification of dust around main-sequence A-type stars is usually made from the IRAS colors (e.g., Mannings & Barlow 1998; Silverstone 2000). Identifying objects with 12 mm excess is difficult because the photosphere usually dominates the total flux at this wavelength. The bulk of the dust associated with main-sequence A-type stars typically has temperatures T ∼ gr K and semimajor axes greater than 50 AU. For example,