Publications of the MPIfR
Optical & Infrared
Interferometry Group
Kraus, S., Balega, Y., Elitzur, M.,
Hofmann, K.-H., Preibisch, Th., Rosen, A., Schertl, D., Weigelt, G.,
Young, E.T.
Outflows from the high-mass protostars NGC 7538
IRS1/2 observed with bispectrum speckle interferometry -- Signatures of
flow precession
Astronomy & Astrophysics, Vol.455, pg.521-537
(2006)
Abstract
NGC 7538 IRS1 is a high-mass (approx. 30 M_sun) protostar with a CO
outflow,
an associated UCHII region, and a linear methanol maser structure,
which might
trace a Keplerian-rotating circumstellar disk. The directions of the
various
associated axes are misaligned with each other. We investigate the
near-infrared morphology of the source to clarify the relations among
the
various axes. K'-band bispectrum speckle interferometry was performed
at two
6-meter-class telescopes -- the BTA 6m telescope and the 6.5m MMT.
Complementary IRAC images from the Spitzer Space Telescope Archive were
used to
relate the structures detected with the outflow at larger scales.
High-dynamic
range images show fan-shaped outflow structure in which we detect 18
stars and
several blobs of diffuse emission. We interpret the misalignment of
various
outflow axes in the context of a disk precession model, including
numerical
hydrodynamic simulations of the molecular emission. The precession
period is
approx. 280 years and its half-opening angle is 40 degrees. A possible
triggering mechanism is non-coplanar tidal interaction of an
(undiscovered)
close companion with the circumbinary protostellar disk. Our
observations
resolve the nearby massive protostar NGC 7538 IRS2 as a close binary
with
separation of 195 mas. We find indications for shock interaction
between the
outflow activities in IRS1 and IRS2. Indications of outflow precession
have
been discovered to date in a number of massive protostars, all with
large
precession angles 20--45 degrees. This might explain the difference
between the
outflow widths in low- and high-mass stars and add support to a common
collimation mechanism.
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