NEWLY IDENTIFIED MAIN-SEQUENCE A STARS WITH CIRCUMSTELLAR DUST

We have searched for stars with circumstellar (CS) dust using data from the Infrared Astronomical Satellite (IRAS) in two stellar samples: (I) all of the 62 A stars in Woolley's Catalogue of Stars within 25 Parsecs of the Sun (1970) and (II) 100 A stars in the Bright Star Catalogue with 4 less-than-or-equal-to m(V) less-than-or-equal-to 5 and nu sin i greater-than-or-equal-to 100 km s-1. Our sample I represents an almost volume-limited sample, of which 29 stars have detections in three (12, 25, and 60-mu-m) or more IRAS bandpasses using the Faint Source Survey (FSS) data base and the new ADDSCAN/SCANPI software. We find 11 nearby A stars having [12] - [25] and [25] - [60] colors consistent with circumstellar dust. If this sample is representative of the Galaxy as a whole, more than 18% (11/62) of all A stars would have circumstellar dust. Among these 11 proto-planetary system candidates, five, namely, HD 29573 (A2 IV), HD 78045 (A2-A3 IV), HD 84121 (A3 IV), HD 159492 (A5 IV-V), and HD 193571 (A0 V) are reported for the first time. The analysis of sample 11 demonstrates that the use of the FSS data base indeed increases the likelihood of identifying A stars with CS dust fainter than m(V) = 4. As a result, we find three more new dusty systems, HD 110411 (A0 V), HD 143894 (A0 IV), and HD 125473 (A3 V) in this sample. All eight of our newly identified dusty systems from both samples have Vega-like colors, which suggests that the IR emission of these systems is from warm dust similar to that seen for Vega (A0 V). So far, beta-Pictoris (A5 IV-V) is the only star within 25 pc of the Sun that displays IR colors indicative of both warm and cool dust. One interpretation is that the absence of cool dust in the vast majority of the systems implies that the dust disks of these stars are much less extended than that seen around beta-Pictoris. This is also consistent with the present negative results from attempts to image dust disks around other nearby stars directly.