1,340 research outputs found
Milliarcsecond structure of water maser emission in two young high-mass stellar objects associated with methanol masers
The 22.2 GHz water masers are often associated with the 6.7 GHz methanol
masers but owing to the different excitation conditions they likely probe
independent spatial and kinematic regions around the powering young massive
star. We compared the emission of these two maser species on milliarcsecond
scales to determine in which structures the masers arise and to test a
disc-outflow scenario where the methanol emission arises in a circumstellar
disc while the water emission comes from an outflow. We obtained high-angular
and spectral resolution 22.2 GHz water maser observations of the two sources
G31.581+00.077 and G33.641-00.228 using the EVN. In both objects the water
maser spots form complex and filamentary structures of sizes 18-160 AU. The
emission towards the source G31.581+00.077 comes from two distinct regions of
which one is related to the methanol maser source of ring-like shape. In both
targets the main axis of methanol distribution is orthogonal to the water maser
distribution. Most of water masers appear to trace shocks on a working surface
between an outflow/jet and a dense envelope. Some spots are possibly related to
the disc-wind interface which is as close as 100-150 AU to the regions of
methanol emission.Comment: 10 pages, accepted to Astronomy and Astrophysic
Magnetic field in Cepheus A as deduced from OH maser polarimetric observations
We present the results of MERLIN polarization mapping of OH masers at 1665
and 1667 MHz towards the Cepheus A star-forming region. The maser emission is
spread over a region of 6 arcsec by 10 arcsec, twice the extent previously
detected. In contrast to the 22 GHz water masers, the OH masers associated with
H II regions show neither clear velocity gradients nor regular structures. We
identified ten Zeeman pairs which imply a magnetic field strength along the
line-of-sight from -17.3 to +12.7 mG. The magnetic field is organised on the
arcsecond scale, pointing towards us in the west and away from us in the east
side. The linearly polarized components, detected for the first time, show
regularities in the polarization position angles depending on their position.
The electric vectors of OH masers observed towards the outer parts of H II
regions are consistent with the interstellar magnetic field orientation, while
those seen towards the centres of H II regions are parallel to the radio-jets.
A Zeeman quartet inside a southern H II region has now been monitored for 25
years; we confirm that the magnetic field decays monotonically over that
period.Comment: 10 pages, 6 figures,accepted for publication in MNRA
Binary systems: implications for outflows & periodicities relevant to masers
Bipolar molecular outflows have been observed and studied extensively in the
past, but some recent observations of periodic variations in maser intensity
pose new challenges. Even quasi-periodic maser flares have been observed and
reported in the literature. Motivated by these data, we have tried to study
situations in binary systems with specific attention to the two observed
features, i.e., the bipolar flows and the variabilities in the maser intensity.
We have studied the evolution of spherically symmetric wind from one of the
bodies in the binary system, in the plane of the binary. Our approach includes
the analytical study of rotating flows with numerical computation of
streamlines of fluid particles using PLUTO code. We present the results of our
findings assuming simple configurations, and discuss the implications.Comment: 5 pages, 3 figures, Proceedings IAU Symposium No. 287, 2012, Cosmic
masers - from OH to H
Instabilities in the dissolution of a porous matrix
A reactive fluid dissolving the surrounding rock matrix can trigger an
instability in the dissolution front, leading to spontaneous formation of
pronounced channels or wormholes. Theoretical investigations of this
instability have typically focused on a steadily propagating dissolution front
that separates regions of high and low porosity. In this paper we show that
this is not the only possible dissolutional instability in porous rocks; there
is another instability that operates instantaneously on any initial porosity
field, including an entirely uniform one. The relative importance of the two
mechanisms depends on the ratio of the porosity increase to the initial
porosity. We show that the "inlet" instability is likely to be important in
limestone formations where the initial porosity is small and there is the
possibility of a large increase in permeability. In quartz-rich sandstones,
where the proportion of easily soluble material (e.g. carbonate cements) is
small, the instability in the steady-state equations is dominant.Comment: to be published in Geophysical Research Letter
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