SMA 200-400 GHz Survey for 10 faint Class II Disks in the Taurus Molecular Cloud

Abstract

We have performed Submillimeter Array (SMA) observations of 198.0-407.5 GHz broadband spectra of 10 Class II protoplanetary disks in the Taurus-Auriga region. The 337 GHz flux densities ($F_{\rm 337 GHz}$) of these objects are in the range of 8.2-34 mJy. The median and standard deviation of the 198-358 GHz spectral indices ($α_{198-358}$) of these 10 Class II disks are 1.9 and 0.3, respectively. Compared to the recent, similar SMA survey on another 47 Class II disks that are brighter at (sub)millimeter bands ($F_{\rm 337 GHz}\sim$20-730 mJy), there is no evidence that these newly observed 10 fainter Class II disks have systematically different $α_{198-358}$ values. At $>$230 GHz frequencies, the optical depths of these 10 fainter Class II disks may be as high as those of the brighter sources, which may be $\gtrsim$5. In addition, the low ($<$2.0) values of $α_{198-358}$ in some faint objects may be explained by the effect of dust self-scattering, with maximum dust grain size ($a_{\rm max}$) $\sim$ 100 $μ$m, or by contamination by free-free emission.