Collimation, Proper Motions, and Physical Conditions in the HH 30 Jet fromHubble Space TelescopeSlitless Spectroscopy

We present Space Telescope Imaging Spectrograph (STIS) spectral images of theHH~30 stellar jet taken through a wide slit over two epochs. The jet isunresolved spectrally, so the observations produce emission-line images foreach line in the spectrum. This rich dataset shows how physical conditions inthe jet vary with distance and time, produces precise proper motions of knotswithin the jet, resolves the jet width close to the star, and gives a spectrumof the reflected light from the disk over a large wavelength range at severalpositions. We introduce a new method for analyzing a set of line ratios basedon minimizing a quadratic form between models and data. The method generatesimages of the density, temperature and ionization fraction computed using allthe possible line ratios appropriately weighted. In HH 30, the density declineswith distance from the source in a manner consistent with an expanding flow,and is larger by a factor of two along the axis of the jet than it is at theperiphery. Ionization in the jet ranges from ~ 5% to 40%, and highionization/excitation knots form at about 100 AU from the star and propagateoutward with the flow. These high-excitation knots are not accompanied bycorresponding increases in the density, so if formed by velocity variations theknots must have a strong internal magnetic pressure to smooth out densityincreases while lengthening recombination times