Discovery of Reflection Nebulosity around Five Vega‐like Stars

Coronagraphic optical observations of six Vega-like stars reveal reflectionnebulosities, five of which were previously unknown. The nebulositiesilluminated by HD 4881, HD 23362, HD 23680, HD 26676, and HD 49662 resemblethat of the Pleiades, indicating an interstellar origin for dust grains. Thereflection nebulosity around HD 123160 has a double-arm morphology, but nodisk-like feature is seen as close as 2.5 arcsec from the star in K-bandadaptive optics data. We demonstrate that uniform density dust cloudssurrounding HD 23362, HD 23680 and HD 123160 can account for the observed12-100 micron spectral energy distributions. For HD 4881, HD 26676, and HD49662 an additional emission source, such as from a circumstellar disk ornon-equilibrium grain heating, is required to fit the 12-25 micron data. Theseresults indicate that in some cases, particularly for Vega-like stars locatedbeyond the Local Bubble (>100 pc), the dust responsible for excess thermalemission may originate from the interstellar medium rather than from aplanetary debris system.Comment: The Astrophysical Journal, in press for March, 2002 (32 pages, 13 figures