734 research outputs found
Identifying the outflow driving sources in Orion-KL
The enigmatic outflows of the Orion-KL region have raised discussions about
their potential driving sources for several decades. Here, we present C18O(2-1)
observations combined from the Submillimeter Array and the IRAM30m telescope.
The molecular gas is associated on large scales with the famous
northwest-southeast high-velocity outflow whereas the high-velocity gas on
small spatial scales traces back to the recently identified submm source SMA1.
Therefore, we infer that SMA1 may host the driving source of this outflow.
Based on the previously published thermal and maser SiO data, source I is the
prime candidate to drive the northeast-southwest low-velocity outflow. The
source SMA1 is peculiar because it is only detected in several submm wavelength
bands but neither in the infrared nor cm regime. We discuss that it may be a
very young intermediate- to high-mass protostar. The estimated outflow masses
are high whereas the dynamical time-scale of the outflow is short of the order
10^3yrs.Comment: 4 pages, 3 figures, Astrophysical Journal Letters in press, a
high-resolution version is available at
http://www.mpia.de/homes/beuther/papers.htm
Precursors of UCHII regions & the evolution of massive outflows
Since this contributions was meant to cover two subjects which are both in
the field of massive star formation but which in its details can be discussed
separately, this paper is divided in two sections. First, we present
characteristics of precursors of UCH{\sc ii} regions and their likely
evolutionary properties. The second section discusses massive molecular
outflows, their implications for high-mass star formation, and a possible
evolutionary sequence for massive outflows.Comment: 15 pages, 4 figures, in the Proceedings to the "Cores to Clusters"
meeting held in Porto/Portigal in October 2004. Also available at
http://cfa-www.harvard.edu/~hbeuther
Rotational Structure and Outflow in the Infrared Dark Cloud 18223-3
We examine an Infrared Dark Cloud (IRDC) at high spatial resolution as a
means to study rotation, outflow, and infall at the onset of massive star
formation. Submillimeter Array observations combined with IRAM 30 meter data in
12CO(2--1) reveal the outflow orientation in the IRDC 18223-3 region, and PdBI
3 mm observations confirm this orientation in other molecular species. The
implication of the outflow's presence is that an accretion disk is feeding it,
so using high density tracers such as C18O, N2H+, and CH3OH, we looked for
indications of a velocity gradient perpendicular to the outflow direction.
Surprisingly, this gradient turns out to be most apparent in CH3OH. The large
size (28,000 AU) of the flattened rotating object detected indicates that this
velocity gradient cannot be due solely to a disk, but rather from inward
spiraling gas within which a Keplerian disk likely exists. From the outflow
parameters, we derive properties of the source such as an outflow dynamical age
of ~37,000 years, outflow mass of ~13 M_sun, and outflow energy of ~1.7 x 10^46
erg. While the outflow mass and energy are clearly consistent with a high-mass
star forming region, the outflow dynamical age indicates a slightly more
evolved evolutionary stage than previous spectral energy distribution (SED)
modeling indicates. The calculated outflow properties reveal that this is truly
a massive star in the making. We also present a model of the observed methanol
velocity gradient. The rotational signatures can be modeled via rotationally
infalling gas. These data present evidence for one of the youngest known
outflow/infall/disk systems in massive star formation. A tentative evolutionary
picture for massive disks is discussed.Comment: 11 pages, 9 figures. Accepted for publication in A&A. Figures 2,3,6,
and 9 are available at higher resolution by email or in the journal
publicatio
Fragmentation, infall, and outflow around the showcase massive protostar NGC7538 IRS1 at 500 AU resolution
Aims: Revealing the fragmentation, infall, and outflow processes in the
immediate environment around massive young stellar objects is crucial for
understanding the formation of the most massive stars. Methods: With this goal
in mind we present the so far highest spatial-resolution thermal submm line and
continuum observations toward the young high-mass protostar NGC7538 IRS1. Using
the Plateau de Bure Interferometer in its most extended configuration at 843mum
wavelength, we achieved a spatial resolution of 0.2"x0.17", corresponding to
~500AU at a distance of 2.7\,kpc. Results: For the first time, we have observed
the fragmentation of the dense inner core of this region with at least three
subsources within the inner 3000 AU. The outflow exhibits blue- and red-shifted
emission on both sides of the central source indicating that the current
orientation has to be close to the line-of-sight, which differs from other
recent models. We observe rotational signatures in northeast-southwest
direction; however, even on scales of 500 AU, we do not identify any Keplerian
rotation signatures. This implies that during the early evolutionary stages any
stable Keplerian inner disk has to be very small (<=500 AU). The high-energy
line HCN(4-3)v2=1 (E_u/k=1050K) is detected over an extent of approximately
3000 AU. In addition to this, the detection of red-shifted absorption from this
line toward the central dust continuum peak position allows us to estimate
infall rates of ~1.8x10^(-3)Msun/yr on the smallest spatial scales. Although
all that gas will not necessarily be accreted onto the central protostar,
nevertheless, such inner core infall rates are among the best proxies of the
actual accretion rates one can derive during the early embedded star formation
phase. These data are consistent with collapse simulations and the observed
high multiplicity of massive stars.Comment: Accepted for Astronomy & Astrophysics, 8 pages, also available at
http://www.mpia.de/homes/beuther/papers.htm
Multiple outflows in IRAS 19410+2336
PdBI high-spatial resolution CO observations combined with near-infrared H2
data disentangle at least 7 (maybe even 9) molecular outflows in the massive
star-forming region IRAS19410+2336. Position-velocity diagrams of the outflows
reveal Hubble-like relationships similar to outflows driven by low-mass
objects. Estimated accretion rates are of the order 10^-4 Msun/yr, sufficiently
high to overcome the radiation pressure and form massive stars via
disk-mediated accretion processes. The single-dish large-scale mm continuum
cores fragment into several compact condensations at the higher spatial
resolution of the PdBI which is expected due to the clustering in massive star
formation. While single-dish data give a simplified picture of the source,
sufficiently high spatial resolution resolves the structures into outflows
resembling those of low-mass star-forming cores. We interpret this as further
support for the hypothesis that massive stars do form via disk-accretion
processes similar to low-mass stars.Comment: 10 pages, 4 figures, higher resolution version of images at
http://cfa-www.harvard.edu/~hbeuther/. A&A, accepte
From high-mass starless cores to high-mass protostellar objects
Aims: Our aim is to understand the evolutionary sequence of high-mass star
formation from the earliest evolutionary stage of high-mass starless cores, via
high-mass cores with embedded low- to intermediate-mass objects, to finally
high-mass protostellar objects. Methods: Herschel far-infrared PACS and SPIRE
observations are combined with existing data at longer and shorter wavelengths
to characterize the spectral and physical evolution of massive star-forming
regions. Results: The new Herschel images spectacularly show the evolution of
the youngest and cold high-mass star-forming regions from mid-infrared shadows
on the Wien-side of the spectral energy distribution (SED), via structures
almost lost in the background emission around 100mum, to strong emission
sources at the Rayleigh-Jeans tail. Fits of the SEDs for four exemplary regions
covering evolutionary stages from high-mass starless cores to high-mass
protostellar objects reveal that the youngest regions can be fitted by
single-component black-bodies with temperatures on the order of 17K. More
evolved regions show mid-infrared excess emission from an additional warmer
component, which however barely contributes to the total luminosities for the
youngest regions. Exceptionally low values of the ratio between bolometric and
submm luminosity additionally support the youth of the infrared-dark sources.
Conclusions: The Herschel observations reveal the spectral and physical
properties of young high-mass star-forming regions in detail. The data clearly
outline the evolutionary sequence in the images and SEDs. Future work on larger
samples as well as incorporating full radiative transfer calculations will
characterize the physical nature at the onset of massive star formation in even
more depth.Comment: 4 pages, A&A Herschel special issu
Physics and chemistry of hot molecular cores
Young massive star-forming regions are known to produce hot molecular gas cores (HMCs) with a rich chemistry. While this chemistry is interesting in itself, it also allows to investigate important physical parameters. I will present recent results obtained with high-angular-resolution interferometers disentangling the small-scale structure and complexity of various molecular gas components. Early attempts to develop a chemical evolutionary sequence are discussed. Furthermore, I will outline the difficulty to isolate the right molecular lines capable to unambiguously trace potential massive accretion disks
Disk and outflow signatures in Orion-KL: The power of high-resolution thermal infrared spectroscopy
We used the CRIRES spectrograph on the VLT to study the ro-vibrational
12CO/13CO, the Pfund beta and H2 emission between 4.59 and 4.72mu wavelengths
toward the BN object, the disk candidate source n, and a proposed dust density
enhancement IRC3. We detected CO absorption and emission features toward all
three targets. Toward the BN object, the data partly confirm the results
obtained more than 25 years ago by Scoville et al., however, we also identify
several new features. While the blue-shifted absorption is likely due to
outflowing gas, toward the BN object we detect CO in emission extending in
diameter to ~3300AU. Although at the observational spectral resolution limit,
the 13CO line width of that feature increases with energy levels, consistent
with a disk origin. If one attributes the extended CO emission also to a disk
origin, its extent is consistent with other massive disk candidates in the
literature. For source n, we also find the blue-shifted CO absorption likely
from an outflow. However, it also exhibits a narrower range of redshifted CO
absorption and adjacent weak CO emission, consistent with infalling motions. We
do not spatially resolve the emission for source n. For both sources we conduct
a Boltzmann analysis of the 13CO absorption features and find temperatures
between 100 and 160K, and H2 column densities of the order a few times
10^23cm^-2. The observational signatures from IRC3 are very different with only
weak absorption against a much weaker continuum source. However, the CO
emission is extended and shows wedge-like position velocity signatures
consistent with jet-entrainment of molecular gas, potentially associated with
the Orion-KL outflow system. We also present and discuss the Pfund beta and H2
emission in the region.Comment: 12 pages, 15 pages, accepted for A&A, you find a high-resolution copy
at http://www.mpia-hd.mpg.de/homes/beuther/papers.htm
Looking for outflow and infall signatures in high mass star forming regions
(Context) Many physical parameters change with time in star forming regions.
Here we attempt to correlate changes in infall and outflow motions in high mass
star forming regions with evolutionary stage using JCMT observations. (Aims)
From a sample of 45 high mass star forming regions in three phases of
evolution, we investigate the presence of established infall and outflow
tracers to determine whether there are any trends attributable to the age of
the source. (Methods) We obtained JCMT observations of HCO+/H13CO+ J=4-3 to
trace large scale infall, and SiO J=8-7 to trace recent outflow activity. We
compare the infall and outflow detections to the evolutionary stage of the host
source (high mass protostellar objects, hypercompact HII regions and
ultracompact HII regions). We also note that the integrated intensity of SiO
varies with the full width at half maximum of the H13CO+. (Results) We find a
surprising lack of SiO detections in the middle stage (Hypercompact HII
regions), which may be due to an observational bias. When SiO is detected, we
find that the integrated intensity of the line increases with evolutionary
stage. We also note that all of the sources with infall signatures onto
Ultracompact HII regions have corresponding outflow signatures as well.Comment: 9 pages, 5 figures, 5 tables. Accepted by A&
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