165 research outputs found
The Extended Methanol Maser Emission in W51
The European VLBI Network (EVN) has been used to make phase referenced,
wide-field (several arcminute) spectral line observations of the 6.7-GHz
methanol maser emission towards W51. In the W51main region, the bulk of the
methanol is offset from an UCHII region. This probably indicates the methanol
emission arises at the interface of the expanding UCHII region and not from an
edge-on circumstellar disc, as previously suggested. Near the W51 IRS2 region,
the methanol emission is associated with a very compact, extremely embedded
source supporting the hypothesis that methanol masers trace the earliest stages
of massive star formation. As well as these two previously well studied sites
of star formation, many previously unknown regions star formation are detected,
demonstrating that methanol masers are powerful means of detection young
massive stars.Comment: 5 pages, 3 figure
A Search for Hydroxylamine (NH2OH) toward Select Astronomical Sources
Observations of 14 rotational transitions of hydroxylamine (NH2OH) using the
NRAO 12 m Telescope on Kitt Peak are reported towards IRC+10216, Orion KL,
Orion S, Sgr B2(N), Sgr B2(OH), W3IRS5, and W51M. Although recent models
suggest the presence of NH2OH in high abundance, these observations resulted in
non-detection. Upper limits are calculated to be as much as six orders of
magnitude lower than predicted by models. Possible explanations for the lower
than expected abundance are explored.Comment: 18 pages, 3 figures, 3 table
37 GHz methanol masers : Horsemen of the Apocalypse for the class II methanol maser phase?
We report the results of a search for class II methanol masers at 37.7, 38.3
and 38.5 GHz towards a sample of 70 high-mass star formation regions. We
primarily searched towards regions known to show emission either from the 107
GHz class II methanol maser transition, or from the 6.035 GHz excited OH
transition. We detected maser emission from 13 sources in the 37.7 GHz
transition, eight of these being new detections. We detected maser emission
from three sources in the 38 GHz transitions, one of which is a new detection.
We find that 37.7 GHz methanol masers are only associated with the most
luminous 6.7 and 12.2 GHz methanol maser sources, which in turn are
hypothesised to be the oldest class II methanol sources. We suggest that the
37.7 GHz methanol masers are associated with a brief evolutionary phase (of
1000-4000 years) prior to the cessation of class II methanol maser activity in
the associated high-mass star formation region.Comment: 14 pages, 4 figures, accepted for publication in Ap
Glycolaldehyde formation via the dimerization of the formyl radical
Glycolaldehyde, the simplest monosaccharide sugar, has recently been detected in low- and high-mass star-forming cores. Following our previous investigation into glycolaldehyde formation, we now consider a further mechanism for the formation of glycolaldehyde that involves the dimerization of the formyl radical, HCO. Quantum mechanical investigation of the HCO dimerization process upon an ice surface is predicted to be barrierless and therefore fast. In an astrophysical context, we show that this mechanism can be very efficient in star-forming cores. It is limited by the availability of the formyl radical, but models suggest that only very small amounts of CO are required to be converted to HCO to meet the observational constraints
Spectral imaging of the Sagittarius B2 region in multiple 3-mm molecular lines with the Mopra telescope
Using the Mopra telescope, we have undertaken a 3-mm spectral-line imaging
survey of a 5 x 5 arcmin^2 area around Sgr B2. We covered almost the complete
spectral the range from 81.7 to 113.5 GHz, with 2.2 MHz wide spectral channels
or ~ 6 km/s, and have observed 24 lines, with 0.033 MHz wide, or ~ 0.1 km/s
channels. We discuss the distribution of around 50 lines, and present
velocity-integrated emission images for 38 of the lines. In addition, we have
detected around 120 more lines, mostly concentrated at the particularly
spectral line-rich Sgr B2(N) source. There are significant differences in
molecular emission, pointing to both abundance and excitation differences
throughout the region. Seven distinct spatial locations are identified for the
emitting species, including peaks near the prominent star forming cores of Sgr
B2(N), (M) and (S) that are seen in IR-to-radio continuum images. The other
features are a 'North Ridge' and a 'North Cloud' to the north of the Sgr B2
N-M-S cores, a 'South-East Peak' and a 'West Ridge'. The column density, as
evident through C^{18}O, peaks at the Sgr B2(N) and (M) cores, where strong
absorption is also evident in otherwise generally bright lines such as HCO^{+},
HCN and HNC. Most molecules trace a ridge line to the west of the Sgr B2 N-M-S
cores, wrapping around the cores and extending NE to the North Cloud. This is
most clearly evident in the species HC_{3}N, CH_{3}CN, CH_{3}OH and OCS. They
are found to be closer in distribution to the cooler dust traced by the sub-mm
continuum than either the warmer dust seen in the mid-IR or to the radio
continuum. The molecule CN, in contrast, is reasonably uniform over the entire
region mapped, aside from strong absorption at the positions of the Sgr B2(N)
and (M) cores.Comment: 22 pages, 12 figures, 5 tables. MNRAS in press. Version 2 with small
changes after referee's comment
New 9.9-GHz methanol masers
The Australia Telescope Compact Array (ATCA) has been used to make the first
extensive search for the class I methanol masers at 9.9 GHz. In total, 48
regions of high-mass star formation were observed. In addition to masers in
W33-Met (G12.80-0.19) and G343.12-0.06 (IRAS 16547-4247) which have already
been reported in the literature, two new 9.9-GHz masers have been found towards
G331.13-0.24 and G19.61-0.23. We have determined absolute positions (accurate
to roughly a second of arc) for all the detected masers and suggest that some
class I masers may be associated with shocks driven into molecular clouds by
expanding HII regions. Our observations also imply that the evolutionary stage
of a high-mass star forming region when the class I masers are present can
outlast the stage when the class II masers at 6.7 GHz are detectable, and
overlaps significantly with the stage when OH masers are active.Comment: accepted for publication in MNRAS, 14 pages, 3 figures, 4 table
A Submillimeter HCN Laser in IRC+10216
We report the detection of a strong submillimeter wavelength HCN laser line
at a frequency near 805 GHz toward the carbon star IRC+10216. This line, the
J=9-8 rotational transition within the (04(0)0) vibrationally excited state, is
one of a series of HCN laser lines that were first detected in the laboratory
in the early days of laser spectroscopy. Since its lower energy level is 4200 K
above the ground state, the laser emission must arise from the inner part of
IRC+10216's circumstellar envelope. To better characterize this environment, we
observed other, thermally emitting, vibrationally excited HCN lines and find
that they, like the laser line, arise in a region of temperature approximately
1000 K that is located within the dust formation radius; this conclusion is
supported by the linewidth of the laser. The (04(0)0), J=9-8 laser might be
chemically pumped and may be the only known laser (or maser) that is excited
both in the laboratory and in space by a similar mechanism.Comment: 11 pages, 3 figure
Detection of new sources of methanol emission at 107 and 108 GHz with the Mopra telescope
A southern hemisphere survey of methanol emission sources in two millimeter
wave transitions has been carried out using the ATNF Mopra millimetre
telescope. Sixteen emission sources have been detected in the 3(1)-4(0)A+
transition of methanol at 107 GHz, including six new sources exhibiting class
II methanol maser emission features. Combining these results with the similar
northern hemisphere survey, a total of eleven 107-GHz methanol masers have been
detected. A survey of the methanol emission in the 0(0)-1(-1)E transition at
108 GHz resulted in the detection of 16 sources; one of them showing maser
characteristics. This is the first methanol maser detected at 108 GHz,
presumably of class II. The results of LVG statistical equilibrium calculations
confirm the classification of these new sources as a class II methanol masers.Comment: 11 pages, 6 figures, accepted for publication in MNRAS, mn.sty
include
W51 IRS 2: A Massive Jet Emerging from a Molecular Cloud into an H II Region
We have mapped [Ne II] (12.8um) and [S IV] (10.5um) emission from W51 IRS 2
with TEXES on Gemini North, and we compare these data to VLA free-free
observations and VLT near-infrared images. With 0.5" spatial and 4 km/s
spectral resolution we are able to separate the ionized gas into several
components: an extended H II region on the front surface of the molecular
cloud, several embedded compact H II regions, and a streamer of high velocity
gas. We interpret the high velocity streamer as a precessing or fan-like jet,
which has emerged from the molecular cloud into an OB star cluster where it is
being ionized.Comment: 3 pages, 4 figures, 2 movie
Masers and Outflows in the W3(OH)/W3(H2O) region
Methanol masers and molecular shock tracers were observed in the
W3(OH)/W3(HO) region with the BIMA array and the Onsala 20m radiotelescope.
Characteristics of the outflows in the region are discussed. A model of the
W3(OH) methanol maser formation region is constructed.Comment: 4 pages, 2 figures, numerous journal misprints are correcte
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