Astron. Astrophys. 344, 632-638 (1999)

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.

Online publication: March 18, 1999
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