Issue |
A&A
Volume 432, Number 1, March II 2005
|
|
---|---|---|
Page(s) | 149 - 160 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20034439 | |
Published online | 22 February 2005 |
Jet rotation: Launching region, angular momentum balance and magnetic properties in the bipolar outflow from RW Aur*
1
Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany e-mail: woitas@tls-tautenburg.de
2
INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
3
School of Cosmic Physics, Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2, Ireland
Received:
3
October
2003
Accepted:
28
October
2004
Using STIS on board the HST we have obtained a spectroscopic
map of the bipolar jet from RW Aur with the slit parallel to the
jet axis and moved across the jet in steps of . After applying
a velocity correction due to uneven slit illumination
we find signatures of rotation within the first
300 AU of the jet (1
5 at the distance of RW Aur). Both lobes rotate in
the same direction (i.e. with different helicities), with toroidal velocities
in the range 5–30 km s-1 at 20 and 30 AU from the symmetry
axis in the blueshifted and redshifted lobes, respectively.
The sense of rotation is anti-clockwise looking from the tip of the blue lobe
(PA 130° north to east) down to the star.
Rotation is more evident in the [OI] and [NII] lines and at the
largest sampled distance from the axis.
These results are consistent with other STIS observations carried out with
the slit perpendicular to the jet axis, and with
theoretical simulations.
Using current magneto-hydrodynamic models for the launch of the jets,
we find that the mass ejected in the observed part of the outflow
is accelerated from
a region in the disk within about 0.5 AU
from the star for the blue lobe, and within 1.6 AU from the star
for the red lobe.
Using also previous results we estimate upper and lower limits
for the angular momentum transport rate of the jet.
We find that this can be a large fraction
(two thirds or more) of the estimated rate transported through the relevant
portion of the disk.
The magnetic lever arm (defined as the ratio
between the Alfvèn
and footpoint radii) is in the range 3.5–4.6
(with an accuracy of 20–25%),
or, alternatively, the ejection index
is in the range
0.025–0.046 (with similar uncertainties). The derived values are in
the range predicted by the models, but they also suggest that some
heating must be provided at the base of the flow.
Finally, using the general disk wind theory we derive the ratio
of the toroidal and poloidal components of
the magnetic field at the observed location (i.e. about 80–100 AU
above the disk).
We find this quantity to be
at 30 AU from the axis in the
red lobe and
at 20 AU from the axis
in the blue lobe (assuming cylindrical coordinates centred on the star and
with positive z along the blue lobe).
The toroidal component appears to be dominant, which would be consistent
with magnetic collimation of the jet. The field appears
to be more tightly wrapped on the blue side.
Key words: ISM: Herbig-Haro objects / ISM: jets and outflows / stars: formation / stars: pre-main sequence / stars: individual: RW Aur
© ESO, 2005
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