Sub-arcsecond 10 micron imaging of newly-formed stars

Abstract

We describe initial results of a program to image massive newly-formed stars with sub-arc second spatial resolution. We discuss high-precision diffraction-limited size measurements at λ = 10 µm made using the 3 m Lick telescope. The point-spread function has FWHM ~ 0.7″; deconvolution yields a spatial resolution of ~ 0.35″. We find that the core component of one such object, LkHα 101, is unresolved at these scales, and we are able to set a 95%-confidence upper limit of 270 AU for the diameter of the circumstellar dust shell. This places the dust at the same radial scale as a strong ionized stellar wind region seen at radio wavelengths. Our observations, when combined with published spectral observations, rule out an optically thick circumstellar disk but allow a radially thin, anisotropic distribution of dust, or alternatively an isotropic distribution of dust with a narrow range of large grain sizes.