EF Chamaeleontis: Warm Dust Orbiting a Nearby 10 Myr Old Star

Abstract

Most Vega-like stars have far-infrared excess (60 μm or longward in IRAS, ISO, or Spitzer MIPS bands) and contain cold dust (<~150 K) analogous to the Sun's Kuiper Belt region. However, dust in a region more akin to our asteroid belt and thus relevant to the terrestrial planet building process is warm and produces excess emission in mid-infrared wavelengths. By cross-correlating Hipparcos dwarfs with the MSX catalog, we found that EF Cha, a member of the recently identified, ~10 Myr old, ``Cha-Near'' moving group, possesses prominent mid-infrared excess. N-band spectroscopy reveals a strong emission feature characterized by a mixture of small, warm, amorphous, and possibly crystalline silicate grains. Survival time of warm dust grains around this A9 star is <~10<sup>5</sup> yr, much less than the age of the star. Thus, grains in this extrasolar terrestrial planetary zone must be of a ``second generation'' and not a remnant of primordial dust and are suggestive of substantial planet formation activity. Such second generation warm excess occurs around ~13% of the early-type stars in nearby young stellar associations.