439 research outputs found
IAU (Maser) Symposium 287 Summary
I'm trying to summarize the science communicated via oral presentations and
by posters at the IAU Symposium 287 "Cosmic Masers - from OH to H_0", which
took place from January 29 to February 3, 2012 in Stellenbosch, South Africa.Comment: 12 pages, to be published in Proc. IAU Symp. 287: Cosmic Masers -
from OH to H_0, eds. R. Booth, E. Humphreys, & W. Vlemming
The Clump Mass Function of the Dense Clouds in the Carina Nebula Complex
We want to characterize the properties of the cold dust clumps in the Carina
Nebula Complex (CNC), which shows a very high level of massive star feedback.
We derive the Clump Mass Function (ClMF), explore the reliability of different
clump extraction algorithms, and investigate the influence of the temperatures
within the clouds on the resulting shape of the ClMF.
We analyze a 1.25x1.25 deg^2 wide-field sub-mm map obtained with LABOCA
(APEX), which provides the first spatially complete survey of the clouds in the
CNC. We use the three clump-finding algorithms CLUMPFIND (CF), GAUSSCLUMPS (GC)
and SExtractor (SE) to identify individual clumps and determine their total
fluxes. In addition to assuming a common `typical' temperature for all clouds,
we also employ an empirical relation between cloud column densities and
temperature to determine an estimate of the individual clump temperatures, and
use this to determine individual clump masses.
While the ClMF based on the CF extraction is very well described by a
power-law, the ClMFs based on GC and SE are better represented by a log-normal
distribution. We also find that the use of individual clump temperatures leads
to a shallower ClMF slope than the assumption of a common temperature (e.g. 20
K) of all clumps.
The power-law of dN/dM \propto M^-1.95 we find for the CF sample is in good
agreement with ClMF slopes found in previous studies of other regions. The
dependence of the ClMF shape (power-law vs. log-normal distribution) on the
employed extraction method suggests that observational determinations of the
ClMF shape yields only very limited information about the true structure of the
cloud. Interpretations of log-normal ClMF shape as a signature of turbulent
pre-stellar clouds vs. power-law ClMFs as a signature of star-forming clouds
may be taken with caution for a single extraction algorithm without additional
information.Comment: 8 pages, 7 figures, accepted by A&
Turbulent entrainment origin of protostellar outflows
Protostellar outflow is a prominent process that accompanies the formation of
stars. It is generally agreed that wide-angled protostellar outflows come from
the interaction between the wind from a forming star and the ambient gas.
However, it is still unclear how the interaction takes place. In this work, we
theoretically investigate the possibility that the outflow results from
interaction between the wind and the ambient gas in the form of turbulent
entrainment. In contrast to the previous models, turbulent motion of the
ambient gas around the protostar is taken into account. In our model, the
ram-pressure of the wind balances the turbulent ram-pressure of the ambient
gas, and the outflow consists of the ambient gas entrained by the wind. The
calculated outflow from our modelling exhibits a conical shape. The total mass
of the outflow is determined by the turbulent velocity of the envelope as well
as the outflow age, and the velocity of the outflow is several times higher
than the velocity dispersion of the ambient gas. The outflow opening angle
increases with the strength of the wind and decreases with the increasing
ambient gas turbulence. The outflow exhibits a broad line width at every
position. We propose that the turbulent entrainment process, which happens
ubiquitously in nature, plays a universal role in shaping protostellar
outflows.Comment: 15 pages, accepted for publication in A&
A 500 pc filamentary gas wisp in the disk of the Milky Way
Star formation occurs in molecular gas. In previous studies, the structure of
the molecular gas has been studied in terms of molecular clouds, but has been
overlooked beyond the cloud scale. We present an observational study of the
molecular gas at 49.5 degree <l<52.5 degree and -5.0 km/s <v_lsr <17.4 km/s.
The molecular gas is found in the form of a huge (>= 500 pc) filamentary gas
wisp. This has a large physical extent and a velocity dispersion of ~5 km/s.
The eastern part of the filamentary gas wisp is located ~130 pc above the
Galactic disk (which corresponds to 1.5-4 e-folding scale-heights), and the
total mass of the gas wisp is >= 1 X 10^5 M_sun. It is composed of two
molecular clouds and an expanding bubble. The velocity structure of the gas
wisp can be explained as a smooth quiescent component disturbed by the
expansion of a bubble. That the length of the gas wisp exceeds by much the
thickness of the molecular disk of the Milky Way is consistent with the
cloud-formation scenario in which the gas is cold prior to the formation of
molecular clouds. Star formation in the filamentary gas wisp occurs at the edge
of a bubble (G52L nebula), which is consistent with some models of triggered
star formation.Comment: Accepted for publication in A&
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