OBSERVATIONS OF CIRCUMSTELLAR DISKS AT CENTIMETER WAVELENGTHS

We present results of a search for centimeter-wavelength dust emission from five embedded young stellar objects and three T Tauri stars. Emission was detected from all of the embedded objects; in three of the five objects, this emission is identified as arising from ionized gas, probably associated with stellar winds. In two cases, NGC 1333 IRAS 4A and 4B, dust emission is suspected to be responsible for between 20 and 100% of the λ = 1.3 cm flux. Emission was detected from only one of the T Tauri stars, RY Tau; it is presently unclear if this emission arises from ionized gas or dust. Using standard circumstellar disk models for the dust emission associated with T Tauri stars, the upper limits to the centimeter-wavelength fluxes for DL Tau and GG Tau can be used to constrain the properties of the circumstellar dust. Assuming a power law form for the dust emissivity (ε ∝ vβ), the upper limits require that β, as measured from millimeter to centimeter wavelengths, is greater than 0.8 for DL Tau and greater than 1.6 for GG Tau. These values of β are considerably larger than values measured at submillimeter wavelengths in the same sources (β∼0.0). If the dust emissivity is described as a two-part power law corresponding to two different values of β, as is suggested for dust in the interstellar medium, the GG Tau data indicate that the value of β changes around λ = 2 mm. This change occurs at an order of magnitude greater wavelength than that proposed for interstellar dust and may reflect the growth of grain size in the circumstellar environment. © 1993 by Academic Press, Inc.