Previous
abstract 
Next
abstract
We present intermediate-resolution ($\lambda/\Delta \lambda \approx 50$) infrared (2--14 $\mu$m) spectroscopy of four early-type main-sequence stars, conducted with the Aerospace Corp.\ Infrared Spectrograph. We observed $\beta$ UMa (A1 V), $\alpha$ Aql (A7 V), and $\beta$ Leo (A3 V) at the 1.3-m KPNO telescope in May 1993, and $\zeta$ Lep (A2 V) at the 3.0-m IRTF telescope in Nov.\ 1993. The Vega-type stars $\beta$ UMa and $\zeta$ Lep showed weak but definite excess flux at $\sim$ 10 $\mu$m in previous groundbased photometric surveys (Fajardo-Acosta, Telesco \& Knacke 1994, in preparation; Aumann \& Probst 1991, ApJ, 368 , 264). We observed $\alpha$ Aql and $\beta$ Leo to confirm that their $\sim$ 10 $\mu$m spectra do not show any excess. The weak $\sim$ 10 $\mu$m excess features in our spectra of $\beta$ UMa and $\zeta$ Lep are probably indicative of large grains and/or a small quantity of dust around these stars. Their weak features contrast with the prominent silicate emission feature previously seen in $\beta$ Pic and 51 Oph. The grains are hotter in $\zeta$ Lep than in $\beta$ UMa, as indicated by an excess already present at short wavelengths ($\sim$ 8.5 $\mu$m) in the spectrum of the former, as opposed to the 10--11 $\mu$m excess of the latter. Dust around these two stars could be an assemblage of amorphous minerals, probably of a variety of sizes, as suggested by their broad features. We compared the excess spectra of $\zeta$ Lep and $\beta$ UMa with those of comets (reviewed by Hanner, Lynch, \& Russell 1994, ApJ, 425 , 274) and found they resemble those of dust-poor comets such as Austin 1990 V and Okazaki-Levy-Rudenko 1989 XIX.
