Going Slitless: Images of Forbidden Line Emission Regions of Classical
T Tauri Stars Observed with the Hubble Space Telescope
Hartigan, P. (Rice), Edwards, S. (Smith) and Pierson, R. (Rice)
We have observed five classical T Tauri stars known to have
strong forbidden line emission with STIS in
slitless mode on the Hubble Space Telescope. This technique
makes it possible to image jets within a few tens of AU of their
exciting sources, a region of great interest for models of accretion disks and jets.
Slitless images generate emission line images at all wavelengths,
including those where no narrowband filters exist. Images of the
forbidden line regions around each object, constructed by
subtracting the stellar continuum and combining observations
taken at different orientations, show [O I] jets
from CW Tau, HN Tau, UZ Tau-E, DF Tau, and the primary of DD Tau.
Jets exist on both sides of the close binary DF Tau, either as
a jet and its counterjet or as separate jets from the primary and
secondary. Several emission lines not previously seen in jets close to
the star exist in the HN Tau jet; the [Fe II] 7155A/8617A ratio
is particularly useful because it measures the electron density in
the densest regions of stellar jets, where log(N_e) >~ 6.
Electron densities in the inner 30 AU of the HN Tau jet range from
log N_e = 6.2 to 6.9. We construct diagnostic diagrams for the density,
temperature, and ionization fraction in jets close to their stars
using various emission lines of O I and O II.
The red auroral [O II] lines are bright close to HN Tau, indicating
that the emitting regions of the inner 35 AU of the jet have a substantial
ionized component -- 20% if the emission comes from a shock, and 50%
for an isothermal flow. We discuss mass loss rates and filling factors for
these two cases. The intensity of the HN Tau jet in [O I] 6300A
declines exponentially with distance beyond ~ 15 AU. The superior
continuum subtraction with slitless data as compared with narrowband images
makes it possible to resolve widths of jets at distances as close as
~ 15 AU of the star. The two best examples, HN Tau and
UZ Tau-E, have jets that expand with distance. When projected back to the
source, the width of the jet in HN Tau is a few AU at the 3-sigma level, while
the jet in UZ Tau-E is spatially unresolved.
The new images of CW Tau reveal proper motions in this jet, which
ejected at least two knots since 1980. There is no indication
that CW Tau brightened when it ejected the largest
of these knots, but the photometric record of this star over the last
two decades is fragmentary.
2004, ApJ 609, 261