16 research outputs found
The Sizes of 1720 MHz OH Masers: VLBA and MERLIN Observations of the Supernova Remnants W44 and W28
We have used the NRAO Very Long Baseline Array (VLBA) to image OH(1720 MHz)
masers in the supernova remnants W28 and W44 at a resolution of 40 mas. We also
used MERLIN to observe the same OH(1720 MHz) masers in W44 at a resolution of
290 x 165 mas. All the masers are resolved by these VLBA and MERLIN
observations. The measured sizes range from 50 to 180 mas and yield brightness
temperature estimates from 0.3--20 x 10**8 K. We investigate whether these
measured angular sizes are intrinsic and hence originate as a result of the
physical conditions in the supernova remnant shock, or whether they are scatter
broadened sizes produced by the turbulent ionized gas along the line of sight.
While the current data on the temporal and angular broadening of pulsars,
masers and extragalactic soures toward W44 and W28 can be understood in terms
of scattering, we cannot rule out that these large sizes are intrinsic. Recent
theoretical modeling by Lockett et al. suggests that the physical parameters in
the shocked region are indicative of densities and OH abundances which lead to
estimates of sizes as large as what we measure. If the sizes and structure are
intrinsic, then the OH(1720 MHz) masrs may be more like the OH(1612 MHz) masers
in circumstellar shells than OH masers associated with HII regions. At two
locations in W28 we observe the classical S-shapes in the Stokes V profiles
caused by Zeeman splitting and use it to infer magnetic fields of order 2
milliGauss.Comment: 24 pages, 6 figures, accepted by Ap
A Uniform CO Survey of the Molecular Clouds in Orion and Monoceros
We report the results of a new large scale survey of the Orion-Monoceros
complex of molecular clouds made in the J = 1->0 line of CO with the
Harvard-Smithsonian 1.2m millimetre-wave telescope. The survey consists of
52,288 uniformly spaced spectra that cover an area of 432 square degrees on the
sky and is the most sensitive large-scale survey of the region to date.
Distances to the constituent molecular clouds of the complex, estimated from an
analysis of foreground and background stars, have provided information on the
three dimensional structure of the entire complex.Comment: Accepted for publication in Astronomy and Astrophysics. 19 pages with
17 colour figures - 39 if you count the sub-figures separately. The figures
here have been bit-mapped with some loss of quality and beauty. The paper
version in A&A will be in greyscale with the on-line version in colour. In
the meantime the colour version can be obtained by following links at
http://www.star.bris.ac.uk/mrwm . The 9MB PostScript is recommended if you
have appropriate bandwidth or otherwise the 2.3MB PDF is usabl
New Herbig-Haro Objects and Giant Outflows in Orion
We present the results of a photographic and CCD imaging survey for
Herbig-Haro (HH) objects in the L1630 and L1641 giant molecular clouds in
Orion. The new HH flows were initially identified from a deep H-alpha film from
the recently commissioned AAO/UKST H-alpha Survey of the southern sky. Our
scanned H-alpha and broad band R images highlight both the improved resolution
of the H-alpha survey and the excellent contrast of the H-alpha flux with
respect to the broad band R. Comparative IVN survey images allow us to
distinguish between emission and reflection nebulosity. Our CCD H-alpha, [SII],
continuum and I band images confirm the presence of a parsec-scale HH flow
associated with the Ori I-2 cometary globule and several parsec-scale strings
of HH emission centred on the L1641-N infrared cluster. Several smaller
outflows display one-sided jets. Our results indicate that for declinations
south of -6 degrees in L1641, parsec-scale flows appear to be the major force
in the large-scale movement of optical dust and molecular gas.Comment: 14 pages, Latex using MN style, 21 figures in JPEG format. Higher
resolution figures available from S.L. Mader. Accepted by MNRAS. Email
contact for higher resolution images: [email protected]
Multiwavelength observations of the supernova remnant G349.7+02 interacting with a molecular cloud
We present molecular-line observations at millimetre, centimetre and infrared
wavelengths of the region containing OH(1720 MHz) masers in the supernova
remnant (SNR) G349.7+0.2, using the Australia Telescope (AT) Mopra antenna, the
Swedish-ESO Submillimeter Telescope, the AT Compact Array and the UNSW Infrared
Fabry-Perot narrow-band filter installed on the Anglo-Australian Telescope.
Several molecular transitions were observed between 1.6 and 3 mm to constrain
the physical parameters of the molecular cloud interacting with the SNR and to
investigate the effects of the SNR shock on the gas chemistry. We detected
shock-excited near-infrared H2 emission towards the centre of the SNR,
revealing highly clumped molecular gas and a good correlation with published
mid-infrared images from the Spitzer Space Telescope. An excellent correlation
between the H2 clumps and OH(1720 MHz) maser positions supports the shock
excitation of the OH(1720 MHz) maser emission. Furthermore, we detected OH
absorption at 1665 and 1667 MHz which shows a good correlation with the shocked
H2 emission and the masers. We found maser emission at 1665 MHz near the
OH(1720 MHz) masers in this SNR, which is found to be associated with a GLIMPSE
source SSTGLMC G349.7294+00.1747. We also detected 1665 and 1667 MHz OH masers,
and weak 4.8 GHz H2CO absorption towards the ultracompact HII region IRAS
17147-3725 located to the southeast of the SNR. We found no 4.7- or 6-GHz
excited-state OH masers or 6-GHz CH3OH maser towards either the SNR or the HII
region.Comment: 25 pages, 13 figures, published in MNRA
Replication data for: Orion (DHT27)
The sampling of this survey was unique among those in the archive -- two interleaved 0.125
° grids. For the cubes presented here, the data were spatially smoothed and placed on a single 0.125° grid. The interpolated cube is recommended as it fills in a small number of missing spectra at random locations as well as the 1/4° sampling on the survey's high-longitude edge
Replication data for: Orion (DHT27)
The sampling of this survey was unique among those in the archive -- two interleaved 0.125 ° grids. For the cubes presented here, the data were spatially smoothed and placed on a single 0.125° grid. The interpolated cube is recommended as it fills in a small number of missing spectra at random locations as well as the 1/4° sampling on the survey's high-longitude edge
Multibeam Maser Survey of methanol and excited OH in the Magellanic clouds: new detections and maser abundance estimates
âThe definitive version is available at www.blackwell-synergy.com.â Copyright Blackwell Publishing DOI: 10.1111/j.1365-2966.2008.12888.xPeer reviewe