949 research outputs found
New class I methanol masers
We review properties of all known collisionally pumped (class I) methanol
maser series based on observations with the Australia Telescope Compact Array
(ATCA) and the Mopra radio telescope. Masers at 36, 84, 44 and 95 GHz are most
widespread, while 9.9, 25, 23.4 and 104 GHz masers are much rarer, tracing the
most energetic shocks. A survey of many southern masers at 36 and 44 GHz
suggests that these two transitions are highly complementary. The 23.4 GHz
maser is a new type of rare class I methanol maser, detected only in two
high-mass star-forming regions, G357.97-0.16 and G343.12-0.06, and showing a
behaviour similar to 9.9, 25 and 104 GHz masers. Interferometric positions
suggest that shocks responsible for class I masers could arise from a range of
phenomena, not merely an outflow scenario. For example, some masers might be
caused by interaction of an expanding HII region with its surrounding molecular
cloud. This has implications for evolutionary sequences incorporating class I
methanol masers if they appear more than once during the evolution of the
star-forming region. We also make predictions for candidate maser transitions
at the ALMA frequency range.Comment: 8 pages, 2 figures, to appear in proceedings for IAUS 287: Cosmic
Masers - from OH to H
The Australia Telescope campaign to study southern class I methanol masers
The Australia Telescope Compact Array (ATCA) and the Mopra facility have been
used to search for new southern class I methanol masers at 9.9, 25 (J=5) and
104 GHz, which are thought to trace more energetic conditions in the interface
regions of molecular outflows, than the widespread class I masers at 44 and 95
GHz. One source shows a clear outflow association.Comment: 2 pages, 1 figure (composed from 3 files), to appear in proceedings
of IAU Symposium 242 "Astrophysical masers and their environment" (eds. J.
Chapman and W. Baan
Advances in Calibration and Imaging Techniques in Radio Interferometry
This paper summarizes some of the major calibration and image reconstruction
techniques used in radio interferometry and describes them in a common
mathematical framework. The use of this framework has a number of benefits,
ranging from clarification of the fundamentals, use of standard numerical
optimization techniques, and generalization or specialization to new
algorithms
Adatom incorporation and step crossing at the edges of 2D nanoislands
Adatom incorporation into the ``faceted'' steps bordering the 2D nanoislands
is analyzed. The step permeability and incorporation coefficients are derived
for some typical growth situations. It is shown that the step consisting of
equivalent straight segments can be permeable even in the case of fast egde
migration if there exist factors delaying creation of new kinks. The step
consisting of alternating rough and straight segments may be permeable if there
is no adatom transport between neighboring segments through the corner
diffusion.Comment: 3 pages, one figur
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