Astron. Astrophys. 344, 632-638 (1999)
7. Summary and conclusions
We have presented in this work a set of observations intended to
search for the exciting source of the jet GGD 34 and study the
detailed structure of the outflow. Our main results are:
We have found a radio source close to the apex of the cavity from
which the jet emerges. This radio source has a spectral index of
0.70.5, consistent with the value of
0.6 expected for a thermal jet. The 12CO(3-2) observations
show molecular gas redshifted by
km s-1 with respect
to the cloud at this location.
The improved resolution of the CFHT images show that GGD 34 is
a narrow (unresolved) jet which roughly bisects an extended faint
envelope. The jet is visible at three points along its length: at the
base where it emerges from the cloud core (GGD 34/A), at the head
where the working surface is (GGD 34/C) and at approximately the
middle point (GGD 34/B).
We have identified 5 main knots in the jet. Some of them are
resolved; they are typically between 0.9 and 1.5 arcsec (900-1500 AU)
in size. These sizes are significantly larger than the inferred from
recent HST images of YSOs jets suggesting that they may be composed of
finer structures unresolved in the CFHT images. The
H/[S II] ratio has been
determined for the knots indicating that the gas is significantly more
excited at the head of the jet and, particularly, in Knot 5.
The high resolution images show that the [S II] emission from
the working surface has an arrow shaped morphology; the body of the
jet is clearly distinguished as well as two backtails disposed in an
approximately symmetric manner with respect to the jet axis. The
H emission is concentrated at the head
of the jet. We suggest that Knot 5 traces the location of the Mach
disk since the spectra of GGD 34 suggest that its density is low
with respect to its external environment.
We have compared images obtained several years apart and we have
not obtained any measurable proper motions. We have however detected
changes in the excitation degree of the head of the jet.
The high resolution images show that the envelope around
GGD 34 connects smoothly with the back tails at the head of the
jet. We have examined whether this envelope could be tracing backflow
from the jet and show that although the expected velocity of this
backflow (32 km s-1) is consistent with the degree of
excitation of the envelope, the time required to form the observed
envelope is twice the dynamical time scale of the jet.
In summary, the new images have shown that the GGD 34 jet is a
narrow (unresolved) beam of gas with small wiggles which are alike
those observed in other YSO jets. However the origin of the asymmetric
low-surface luminosity envelope which surrounds the jet remains
uncertain as well as the cause of the peculiar radial velocity field
along the jet. High spatial resolution long slit spectroscopy is
required to separate the contribution of the envelope to the GGD 34
spectrum and get further insight into this object characteristics.
Good measurements of GGD 34's proper motions are also necessary.
© European Southern Observatory (ESO) 1999
Online publication: March 18, 1999