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Session 5 - Accretion and Outflows in YSOs.
Display session, Wednesday, January 07
We present new HST images of the young stars CoKu Tau/1 and Th 28. These nearby (d\sim 140 pc) objects were selected for study because their low radial velocity emission line jets and relatively faint K magnitudes suggest that they are edge-on disk systems similar to HH 30. Broad-band VRI images were obtained with WFPC2 as a part of the GTO science program, while complementary JHK images were taken with NICMOS under GO program 7418.
CoKu Tau/1 possesses complex circumstellar nebulosities at optical and near-IR wavelengths. The optical jet is resolved into several irregular emission knots within 700 AU of the star, including a broad feature similar to a bow shock. Four widely-separated ``arms'' of reflection nebulosity extend outward from the source; their alignment relative to the jet axis suggests they are the illuminated walls of an outflow cavity. A dark clump of material, approximately 200 AU across, appears backlit by the nebulosity NE of the star. The central star is indistinctly seen at optical wavelengths, but clearly emerges in the near-IR. We find that CoKu Tau/1 has an infrared companion at a separation of 0.3 arcsec; it may be the jet source.
Th 28 (Krautter's Star) is embedded within a compact nebula extending along the jet axis. Direct starlight dominates the system at K band, but contributes less than 20% of the flux at I band. Several diffuse jet knots (FWHM\sim 70 AU) are seen in R band within 300 AU of the star. The images show no direct evidence for a disk extending perpendicular to the jet axis.
These results illustrate that a variety of morphologies can be seen for Herbig-Haro jet sources at 10 AU resolution, and underscore the uniqueness of HH 30 as a prototypical disk/jet system.
Program listing for Wednesday