219 research outputs found
The Molecular Accretion Flow in G10.6-0.4
We have observed the ultracompact HII region G10.6-0.4 with the VLA in 23 GHz
continuum and the NH3(3,3) inversion line. By analyzing the optical depth of
the line as well as the kinematics, we have detected a flattened, rotating,
molecular accretion flow. We detect the fact that the highest column density
gas is more flattened, that is, distributed more narrowly, than the lower
column density gas, and that there is some inclination of the rotation axis.
The rotation is sub-Keplerian, and the molecular gas is not in a rotationally
supported disk. We do not find a single massive (proto)star forming in a scaled
up version of low mass star formation. Instead, our observations suggest a
different mode of clustered massive star formation, in which the accretion flow
flattens but does not form an accretion disk. Also in this mode of star
formation the central object can be a group of massive stars rather than a
single massive star.Comment: 20 pages, 6 figures Accepted for publication in the Astrophysical
Journa
Experimental Observation Of Correlated Magnetic Reconnection And Alfvénic Ion Jets
Correlations between magnetic reconnection and energetic ion flow events have been measured with merging force free spheromaks at the Swarthmore Spheromak Experiment. The reconnection layer is measured with a linear probe array and ion flow is directly measured with a retarding grid energy analyzer. Flow has been measured both in the plane of the reconnection layer and out of the plane. The most energetic events occur in the reconnection plane immediately after formation as the spheromaks dynamically merge. The outflow velocity is nearly Alfvenic. As the spheromaks form equilibria and decay, the flow is substantially reduced
SMA outflow/disk studies in the massive star-forming region IRAS18089-1732
SMA observations of the massive star-forming region IRAS 18089-1732 in the
1mm and 850mu band reveal outflow and disk signatures in different molecular
lines. The SiO(5--4) data show a collimated outflow in the northern direction.
In contrast, the HCOOCH3(20--19) line, which traces high-density gas, is
confined to the very center of the region and shows a velocity gradient across
the core. The HCOOCH3 velocity gradient is not exactly perpendicular to the
outflow axis but between an assumed disk plane and the outflow axis. We
interpret these HCOOCH3 features as originating from a rotating disk that is
influenced by the outflow and infall. Based on the (sub-)mm continuum emission,
the mass of the central core is estimated to be around 38M_sun. The dynamical
mass derived from the HCOOCH3 data is 22Msun, of about the same order as the
core mass. Thus, the mass of the protostar/disk/envelope system is dominated by
its disk and envelope. The two frequency continuum data of the core indicate a
low dust opacity index beta ~ 1.2 in the outer part, decreasing to beta ~ 0.5
on shorter spatial scales.Comment: 7 pages of text, 1 table, 3 figures, accepted for ApJ Letter
Submillimeter Array multiline observations of the massive star-forming region IRAS 18089-1732
Submillimeter Array (SMA) observations of the high-mass star-forming region
IRAS 18089-1732 in the 1 mm and 850 m band with 1 GHz bandwidth reveal a
wealth of information. We present the observations of 34 lines from 16
different molecular species. Most molecular line maps show significant
contributions from the outflow, and only few molecules are confined to the
inner core. We present and discuss the molecular line observations and outline
the unique capabilities of the SMA for future imaging line surveys at high
spatial resolution.Comment: Accepted for ApJ Letters, SMA special volum
Spherical Infall in G10.6-0.4: Accretion Through an Ultracompact HII Region
We present high resolution (0.''12 x 0.''079) observations of the
ultracompact HII region G10.6-0.4 in 23 GHz radio continuum and the NH3(3,3)
line. Our data show that the infall in the molecular material is largely
spherical, and does not flatten into a molecular disk at radii as small as 0.03
pc. The spherical infall in the molecular gas matches in location and velocity
the infall seen in the ionized gas. We use a non-detection to place a stringent
upper limit on the mass of an expanding molecular shell associated with
pressure driven expansion of the HII region. These data support a scenario in
which the molecular accretion flow passes through an ionization front and
becomes an ionized accretion flow onto one or more main sequence stars, not the
classical pressure-driven expansion scenario. In the continuum emission we see
evidence for externally ionized clumps of molecular gas, and cavities evacuated
by an outflow from the central source.Comment: Accepted for publication in Astrophysical Journal Letter
Mapping the Outflow from G5.89-0.39 in SiO(5-4)
We have mapped the ultracompact HII region, G5.89-0.39, and its molecular
surroundings with the Submillimeter Array at 2".8 x 1".8 angular resolution in
1.3 mm continuum, SiO(5-4), and eight other molecular lines. We have resolved
for the first time the highly energetic molecular outflow in this region. At
this resolution, the outflow is definitely bipolar and appears to originate in
a 1.3 mm continuum source. The continuum source peaks in the center of the HII
region. The axis of the outflow lines up with a recently discovered O5V star.Comment: 3 Figures, Accepted for publication in ApJ Letter
Search for Calibrators for the Submillimeter Array: I. High-Mass Star Forming Regions
We present initial results of an ongoing search for interferometric
calibrators at submillimeter (sub-mm) wavelengths with the Submillimeter Array
(SMA). Powerful radio galaxies are commonly used as calibrators at centimeter
and millimeter wavelengths, but many are not strong enough to serve as
calibrators at sub-mm wavelengths because of their rapidly declining flux
densities toward shorter wavelengths. The inability to find a calibrator close
to the target source may limit or even prevent us from imaging many interesting
sources at sub-mm wavelengths. Here, we investigate whether high-mass
protostellar objects and ultracompact HII regions can serve as useful
calibrators for the SMA. The dust emission associated with these objects makes
them among the brightest sub-mm sources in the sky. Our observations at 0.85 mm
(345 GHz) with an angular resolution of ~3" reveal that although a large
fraction of the dust emission originates from an extended ``halo'' component, a
compact unresolved component often remains that when sufficiently strong may
serve as a useful calibrator. These observations also provide a first glimpse
at the small-scale distribution of dust around ultracompact HII regions and
high-mass protostellar objects at sub-mm wavelengths. We discuss the origin of
the core-halo structure seen in many sources, and conclude with suggestions for
future searches for calibrators with the SMA.Comment: 3 figures, accepted for publication in ApJ Letter
ATCA 3mm observations of NGC6334I and I(N): dense cores, outflows and an UCHII region
Aims: Investigation of the dense gas, the outflows and the continuum emission
from the massive twin cores NGC6334I and I(N) at high spatial resolution.
Methods: We imaged the region with the Australia Telescope Compact Array (ATCA)
at 3.4mm wavelength in continuum as well as CH3CN(5_K-4_K) and HCN(1-0)
spectral line emission. Results: While the continuum emission in NGC6334I
mainly traces the UCHII region, toward NGC6334I(N) we detect line emission from
four of the previously identified dust continuum condensations that are of
protostellar or pre-stellar nature. The CH3CN(5_K-4_K) lines are detected in
all K-components up to energies of 128K above ground toward two protostellar
condensations in both regions. We find line-width increasing with increasing K
for all sources, which indicates a higher degree of internal motions closer to
the central protostars. Toward the main mm and CH3CN source in NGC6334I we
identify a velocity gradient approximately perpendicular to the large-scale
molecular outflow. This may be interpreted as a signature of an accretion disk,
although other scenarios, e.g., an unresolved double source, could produce a
similar signature as well. No comparable signature is found toward any of the
other sources. HCN does not trace the dense gas well but it is dominated by the
molecular outflows. While the outflow in NGC6334I exhibits a normal Hubble-law
like velocity structure, the data indicate a precessing outflow close to the
plane of the sky for NGC6334I(N). Furthermore, we observe a wide (~15.4km/s)
HCN absorption line, much broader than the previously observed CH3OH and NH3
absorption lines. Several explanations for the difference are discussed.Comment: 14 pages, 14 figures, accepted for A&
Detection of vibrationally excited methyl formate in W51 e2
Methyl formate in its first torsionally excited state (vt=1 at 131 cm-1) is
detected for the first time toward W51 e2. All transitions from excited methyl
formate within the observed spectral range are actually detected (82
transitions) and no strong lines are missing. The column density of the excited
state is comparable to that of the ground state. For a source size of 7'' we
find that Trot = 104 +/- 14 K and N = 9.4 +4.0/-2.8 x 10^16 cm-2 for the
excited state and Trot = 176 +/- 24 K and N = 1.7 +.2/-.2 x 10^17 cm-2 for the
ground state. Lines from ethyl cyanide in its two first excited states (vt=1,
torsion mode at 212 cm-1) and (vb=1, CCN in-plane bending mode at 206 cm-1) are
also present in the observed spectrum. However blending problems prevent a
precise estimate of its abundance. With regard to the number of lines of
excited methyl formate and ethyl cyanide detected in W51 e2, it appears that
excited states of large molecules certainly account for a large number of
unidentified lines in spectral survey of molecular clouds
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