Are Protostellar Jets Spinning ChinFei Lee, Paul P'T' Ho, Aina Palau, Naomi Hirano, Tyler L' Bourke,

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Are Protostellar Jets Spinning?Chin-Fei Lee,
Paul P.T. Ho, Aina Palau, Naomi Hirano, Tyler L.
Bourke, Hsien Shang, Qizhou Zhang
Protostellar jets are seen associated with
protostars, representing one of the most
intriguing signposts of star formation. They were
not originally anticipated in any theory of star
formation but turn out to be fundamental
phenomena of star formation. They are believed to
be launched from accretion disks around the
protostars, carrying away extra angular momenta
from the disks and thus allowing material to fall
onto the protostars. The amount of angular
momenta carried by the jets is predicted to be
different in different models, allowing us to
determine the launching mechanism. The
Submillimeter Array (SMA) with the capability to
probe warm and dense molecular gas at high
angular resolution, can be used to extract this
crucial information from the jets. Herbig-Haro
(HH) 211 is a well-defined bipolar (two-sided)
jet located at only 1000 light-year away in the
constellation Perseus. Lying close to plane of
the sky, it is one of the best candidates for our
study. The jet has a velocity of 100-200 km/s.
Sitting at the center of the jet is a Class 0
protostar deeply embedded in the cloud. It is
only about 20,000 years old with a mass of only 6
percent of the mass of our Sun. It will
eventually grow into a star like our Sun in tens
of million years.
Top) The two-sided (red for receding and blue for
approaching sides) SiO (J8-7) jet observed with
the SMA (Lee et al. 2007). Gray image shows the
shocked H2 emission produced by the jet (Hirano
et al. 2006). The jet is knotty, consisting of a
chain of knots on each side of the protostar,
with an interknot spacing of 600 - 900 AU. The
innermost pair of knots are only at 500 AU away
from the protostar. These knots likely trace the
internal shocks in the jet produced by a
periodical variation in the jet velocity. The
period of the variation is estimated to be 30
yrs. This periodic variation may be due to a
solar-type magnetic cycle or a periodic
disturbance of an unseen stellar companion
orbiting the protostar at 4 AU away with a
period of 30 yrs. The averaged two-sided
mass-loss rate of the jet is estimated to be
(1-3) x10-6 M? yr-1. Right) Position-velocity
diagrams cut across the first four brightest SiO
knots closest to the protostar. A velocity
gradient is consistently seen across the jet
axis, with the same sense as that seen in the
circumstellar envelope, suggesting that the
velocity comes from jet rotation. If this is the
case, the implied angular momentum of the jet is
lt 50 AU km/s, indicating that the jet must be
launched very close to the protostar, as
predicted in the X-wind model by Shu et al 1995.
Further observations have been proposed to check
it. References1) Hirano, N., Liu, S.-Y.,
Shang, H., et al. 2006, ApJL, 634, L141 2) Lee,
C.-F., Ho, P.T.P., Aina Palau, et al., 2007, ApJ,
670, 1188 3) Shu, F.H., Narita, J., Ostriker,
E.C., Shang, H., 1995, ApJL, 455, L155