AAS 195th Meeting, January 2000
Session 78. Young Stars, Disks and Planets
Display, Friday, January 14, 2000, 9:20am-6:30pm, Grand Hall

[78.03] Search for Dust Around Low Luminosity Main Sequence A-Type Stars

C.H. Chen, M. Jura (UCLA)

We have obtained 11.7 and 18.7 \mum images of 14 nearby A-type main sequence stars at Keck to search for excess emission from dust surrounding stars with luminosities which are low for their temperatures. Our candidate stars lie near \beta Pic, HR 4796 and 49 Cet on the H-R diagram which have low luminosities for their colors. We did not detect excess emission from any of the stars in our sample at either 11.7 or 18.7 \mum. Based on our measurements of the 18.7 \mum fluxes, we have calculated upper limits on the dust mass surrounding the stars with the assumption that the grain temperature is 110 K, the sublimation temperature of ice. We estimate that there is less than 0.01-0.02 M\earth of dust at 110 K surrounding each of these stars. The upper limits for the dust mass are \approx 5 times higher if the grain temperatures are 90 K. Snowball formation of meteor-sized objects may be well advanced during the first 108 years of the evolution of A-type stars.