177 research outputs found
Sequentially Triggered Star Formation in OB Associations
We discuss observational evidence for sequential and triggered star formation
in OB associations. We first review the star formation process in the
Scorpius-Centaurus OB association, the nearest OB association to the Sun, where
several recent extensive studies have allowed us to reconstruct the star
formation history in a rather detailed way. We then compare the observational
results with those obtained for other OB associations and with recent models of
rapid cloud and star formation in the turbulent interstellar medium. We
conclude that the formation of whole OB subgroups (each consisting of several
thousand stars) requires large-scale triggering mechanisms such as shocks from
expanding wind and supernova driven superbubbles surrounding older subgroups.
Other triggering mechanisms, like radiatively driven implosion of globules,
also operate, but seem to be secondary processes, forming only small stellar
groups rather than whole OB subgroups with thousands of stars.Comment: Invited talk at the IAU Symposium 237: "Triggered Star Formation in a
Turbulent ISM", Prague, Czech Republic, August 200
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&
The multiplicity of massive stars in the Orion Nebula cluster as seen with long-baseline interferometry
The characterization of multiple stellar systems is an important ingredient
for testing current star formation models. Stars are more often found in
multiple systems, the more massive they are. A complete knowledge of the
multiplicity of high-mass stars over the full range of orbit separations is
thus essential to understand their still debated formation process.
Observations of the Orion Nebula Cluster can help to answer the question about
the origin and evolution of multiple stars. Earlier studies provide a good
knowledge about the multiplicity of the stars at very small (spectroscopic) and
large separations (AO, speckle) and thus make the ONC a good target for such a
project. We used the NIR interferometric instrument AMBER at VLTI to observe a
sample of bright stars in the ONC. We complement our data set by archival NACO
observations of \theta 1 Ori A to obtain more information about the orbit of
the close visual companion. Our observations resolve the known multiple systems
\theta 1 Ori C and \theta 1 Ori A and provide new orbit points, which confirm
the predicted orbit and the determined stellar parameters for \theta 1 Ori C.
Combining AMBER and NACO data for \theta 1 Ori A we were able to follow the
motion of the companion from 2003 to 2011. We furthermore find hints for a
companion around \theta 1 Ori D and a previously unknown companion to NU Ori.
With a probability of ~90% we can exclude further companions with masses of > 3
Msun around our sample stars for separations between ~2 mas and ~110 mas. We
conclude that the companion around \theta 1 Ori A is most likely physically
related to the primary star. The newly discovered possible companions further
increase the multiplicity in the ONC. For our sample of two O and three B-type
stars we find on average 2.5 known companions per primary, which is around five
times more than for low-mass stars.Comment: accepted by A&
Herschel far-infrared observations of the Carina Nebula Complex. - III: Detailed cloud structure and feedback effects
The Carina Nebula complex (CNC) represents one of the most massive
star-forming regions in our Galaxy and shows strong feedback from the high
massive stars. We use our Herschel FIR observations to study the properties of
the clouds over the entire area of the CNC. The good angular resolution of the
Herschel maps corresponds to physical scales of 0.1 - 0.4 pc, and allows us to
analyze the small-scale structures of the clouds. The full extent of the CNC
was mapped with PACS and SPIRE from 70 to 500 micron. We determine temperatures
and column densities at each point in this maps by modeling the observed FIR
SEDs. We also derive a map showing the strength of the UV field. We investigate
the relation between the cloud properties and the spatial distribution of the
high-mass stars, and compute total cloud masses for different density
thresholds. Our Herschel maps resolve, for the first time, the small-scale
structure of the dense clouds. Several particularly interesting regions,
including the prominent pillars south of eta Car, are analyzed in detail. We
compare the cloud masses derived from the Herschel data to previous mass
estimates based on sub-mm and molecular line data. Our maps also reveal a
peculiar "wave"-like pattern in the northern part of the Carina Nebula.
Finally, we characterize two prominent cloud complexes at the periphery of our
Herschel maps, which are probably molecular clouds in the Galactic background.
We find that the density and temperature structure of the clouds in most parts
of the CNC is dominated by the strong feedback from the numerous massive stars,
rather than random turbulence. Comparing the cloud mass and the star formation
rate derived for the CNC to other Galactic star forming regions suggests that
the CNC is forming stars in an particularly efficient way. We suggest this to
be a consequence of triggered star formation by radiative cloud compression.Comment: Accepted for publication in Astronomy & Astrophysics. A high quality
preprint is available at
http://www.usm.uni-muenchen.de/people/preibisch/publications.htm
- …