[Previous] | [Session 66] | [Next]
P. Kalas, J.R. Graham (U.C. Berkeley), S.V.W. Beckwith (STScI), D.C. Jewitt (IFA, U. Hawaii), Initials Lloyd (U.C. Berkeley)
The Vega Phenomenon, excess far-infrared emission from main-sequence stars, is thought to flag the formation of extrasolar planetesimals that collisionally replenish circumstellar debris disks. We present the discovery of reflection nebulosity around six Vega Phenomenon stars using optical and near-infrared coronagraphy. The nebulosities illuminated by HD 4881, HD 23362, HD 23680, HD 26676, and HD 49662 resemble that of the Pleiades, indicating an interstellar origin for dust grains. The reflection nebulosity around HD 123160 has a double-arm morphology, but no disk-like feature is seen as close as 2.5 arcsec from the star in K-band adaptive optics data. We demonstrate that a uniform density dust cloud surrounding HD 23362, HD 23680 and HD 123160 can account for the observed 12-100 micron spectral energy distributions. For HD 4881, HD 26676, and HD 49662 an additional emission source, such as from a circumstellar disk or non-equilibrium grain heating, is required to fit the 12-25 micron data. These results indicate that in some cases, particularly for Vega Phenomenon stars located beyond the Local Bubble (>100 pc), the dust responsible for excess thermal emission may originate from the interstellar medium rather than from a planetesimal debris system.