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Session 10 - Interstellar Medium and Star Formation.
Display session, Monday, June 08
Atlas Ballroom,
We present HST/NICMOS observations of six young stellar objects in the Taurus star-formation region. The objects included in our survey are three Class I IRAS sources (IRAS 04016+2610, IRAS 04248+2612, and IRAS 04302+2247) and three low-luminosity Herbig Haro object exciting stars (DG Tau B, Haro 6-5b, and CoKu Tau/1). The broad-band images show that the near-infrared radiation from these sources is dominated by light scattered from dusty circumstellar material distributed in a region 10 - 40 times the size of our solar system. Although the detailed morphology of the individual objects are unique, the observed young stellar objects share common features. All of the circumstellar nebulae are crossed by dark lanes from 300 - 750 AU in diameter and from less than 30 to 100 AU in apparent thickness. The absorption lanes extend perpendicular to known optical and millimeter outflows in these sources. We interpret the dark lanes as optically thick circumstellar disks seen in silhouette against bright reflection nebulosity. The bipolar reflection nebulae extending perpendicular to the dust lanes appear to be produced by scattering from the upper and lower surfaces of the disks and from dusty material within or on the walls of the outflow cavities. Out of five objects in which the central source is directly detected, two are found to be subarcsecond binaries surrounded by circumbinary disks. Detailed analysis of these images and comparison to models will yield the mass, infall rate, orientation and other important parameters of these pre-main sequence disk/envelope systems.
