1,646 research outputs found
Discovery of Two New Class II Methanol Maser Transitions in G345.01+1.79
We have used the Swedish ESO Submillimetre Telescope (SEST) to search for new
class II methanol maser transitions towards the southern source G345.01+1.79.
Over a period of 5 days we observed 11 known or predicted class II methanol
maser transitions. Emission with the narrow line width and characteristic
velocity of class II methanol masers (in this source) was detected in 8 of
these transitions, two of which have not previously been reported as masers.
The new class II methanol maser transitions are the 13(-3)-12(-4)E transition
at 104.1 GHz and the 5(1)-4(2)E transition at 216.9 GHz. Both of these are from
transition series for which there are no previous known class II methanol maser
transitions. This takes the total number of known class II methanol maser
series to 10, and the total number of transitions (or transition groups) to 18.
The observed 104.1 GHz maser suggests the presence of two or more regions of
masing gas with similar line of sight velocities, but quite different physical
conditions. Although these newly discovered transitions are likely to be
relatively rare, where they are observed combined studies using the Australia
Telescope Compact Array and the Atacama Large Millimeter Array offer the
prospect to be able to undertake multi-transition methanol maser studies with
unprecedented detail.Comment: 8 pages, 3 figures, accepted for publication in ApJ Letter
A Search for Biomolecules in Sagittarius B2 (LMH) with the ATCA
We have used the Australia Telescope Compact Array to conduct a search for
the simplest amino acid, glycine (conformers I and II), and the simple chiral
molecule propylene oxide at 3-mm in the Sgr B2 LMH. We searched 15 portions of
spectrum between 85 and 91 GHz, each of 64 MHz bandwidth, and detected 58
emission features and 21 absorption features, giving a line density of 75
emission lines and 25 absorption lines per GHz stronger than the 5 sigma level
of 110 mJy. Of these, 19 are transitions previously detected in the
interstellar medium, and we have made tentative assignments of a further 23
features to molecular transitions. However, as many of these involve molecules
not previously detected in the ISM, these assignments cannot be regarded with
confidence. Given the median line width of 6.5 km/s in Sgr B2 LMH, we find that
the spectra have reached a level where there is line confusion, with about 1/5
of the band being covered with lines. Although we did not confidently detect
either glycine or propylene oxide, we can set 3 sigma upper limits for most
transitions searched. We also show that if glycine is present in the Sgr B2 LMH
at the level of N = 4 x 10^{14} cm^{-2} found by Kuan et al. (2003) in their
reported detection of glycine, it should have been easily detected with the
ATCA synthesized beam size of 17.0 x 3.4 arcsec^{2}, if it were confined to the
scale of the LMH continuum source (< 5 arcsec). This thus puts a strong upper
limit on any small-scale glycine emission in Sgr B2, for both of conformers I
and II.Comment: 12 pages, 2 figures, 5 tables, accepted by MNRA
Models of class II methanol masers based on improved molecular data
The class II masers of methanol are associated with the early stages of
formation of high-mass stars. Modelling of these dense, dusty environments has
demonstrated that pumping by infrared radiation can account for the observed
masers. Collisions with other molecules in the ambient gas also play a
significant role, but have not been well modelled in the past. Here we examine
the effects on the maser models of newly available collision rate coefficients
for methanol. The new collision data does not alter which transitions become
masers in the models, but does influence their brightness and the conditions
under which they switch on and off. At gas temperatures above 100 K the effects
are broadly consistent with a reduction in the overall collision cross-section.
This means, for example, that a slightly higher gas density than identified
previously can account for most of the observed masers in W3(OH). We have also
examined the effects of including more excited state energy levels in the
models, and find that these play a significant role only at dust temperatures
above 300 K. An updated list of class II methanol maser candidates is
presented.Comment: 14 pages, 4 figures, Accepted for publication in MNRA
Class II methanol maser candidates
Model spectra are presented for Class II methanol masers under a variety of conditions. The model is that of Sobolev & Deguchi, which includes pumping through levels of the second and first torsionally excited states. All the currently identified Class II methanol masers appear as strong masers in one or more of the model regimes, and a number of new maser candidates are identified. © 1997 RAS
Multi-transition study and new detections of class II methanol masers
We have used the ATNF Mopra antenna and the SEST antenna to search in the
directions of several class II methanol maser sources for emission from six
methanol transitions in the frequency range 85-115 GHz. The transitions were
selected from excitation studies as potential maser candidates. Methanol
emission at one or more frequencies was detected from five of the maser
sources, as well as from Orion KL. Although the lines are weak, we find
evidence of maser origin for three new lines in G345.01+1.79, and possibly one
new line in G9.62+0.20.
The observations, together with published maser observations at other
frequencies, are compared with methanol maser modelling for G345.01+1.79 and
NGC6334F. We find that the majority of observations in both sources are
consistent with a warm dust (175 K) pumping model at hydrogen density ~10^6
cm^-3 and methanol column density ~5 x 10^17 cm^-2. The substantial differences
between the maser spectra in the two sources can be attributed to the geometry
of the maser region.Comment: 13 pages, 6 figures, Accepted for publication in MNRA
A sensitive search for predicted methanol maser transitions with the Australia telescope compact array
We have used theAustralia Telescope Compact Array to search for a number of centimetrewavelengthmethanol transitions which are predicted to show weak maser emission towards star formation regions. Sensitive, high spatial, and spectral resolution observations towards four high-mass star formation regions which show emission in a large number of class II methanol maser transitions did not result in any detections. From these observations, we are able to place an upper limit of 1 300 K on the brightness temperature of any emission from the 31A+-31A-, 17-2-18-3 E (vt = 1), 124-133 A-, 124-133 A+, and 41A+-41A- transitions of methanol in these sources on angular scales of 2 arcsec. This upper limit is consistent with current models for class II methanol masers in high-mass star formation regions and better constraints than those provided here will likely require observations with next-generation radio telescopes. © Astronomical Society of Australia 2016
A Search for 6.7 GHz Methanol Masers in M33
We report the negative results from a search for 6.7 GHz methanol masers in
the nearby spiral galaxy M33. We observed 14 GMCs in the central 4 kpc of the
Galaxy, and found 3 sigma upper limits to the flux density of ~9 mJy in
spectral channels having a velocity width of 0.069 km/s. By velocity shifting
and combining the spectra from the positions observed, we obtain an effective
3sigma upper limit on the average emission of ~1mJy in a 0.25 km/s channel.
These limits lie significantly below what we would expect based on our
estimates of the methanol maser luminosity function in the Milky Way. The most
likely explanation for the absence of detectable methanol masers appears to be
the metallicity of M33, which is modestly less than that of the Milky Way
Detection of 6.7 GHz methanol absorption towards hot corinos
Methanol masers at 6.7 GHz have been found exclusively towards high-mass star
forming regions. Recently, some Class 0 protostars have been found to display
conditions similar to what are found in hot cores that are associated with
massive star formation. These hot corino sources have densities, gas
temperatures, and methanol abundances that are adequate for exciting strong 6.7
GHz maser emission. This raises the question of whether 6.7 GHz methanol masers
can be found in both hot corinos and massive star forming regions, and if not,
whether thermal methanol emission can be detected. We searched for the 6.7 GHz
methanol line towards five hot corino sources in the Perseus region using the
Arecibo radio telescope. To constrain the excitation conditions of methanol, we
observed thermal submillimeter lines of methanol in the NGC1333-IRAS 4 region
with the APEX telescope. We did not detect 6.7 GHz emission in any of the
sources, but found absorption against the cosmic microwave background in
NGC1333-IRAS 4A and NGC1333-IRAS 4B. Using a large velocity gradient analysis,
we modeled the excitation of methanol over a wide range of physical parameters,
and verify that the 6.7 GHz line is indeed strongly anti-inverted for densities
lower than 10^6 cm^-3. We used the submillimeter observations of methanol to
verify the predictions of our model for IRAS 4A by comparison with other CH3OH
transitions. Our results indicate that the methanol observations from the APEX
and Arecibo telescopes are consistent with dense (n ~ 10^6 cm^-3), cold (T ~
15-30 K) gas. The lack of maser emission in hot corinos and low-mass
protostellar objects in general may be due to densities that are much higher
than the quenching density in the region where the radiation field is conducive
to maser pumping.Comment: Accepted by A&
Isoferritins in acute leukaemia.
Leucocytes containing a high proportion of blast cells were obtained from 11 patients with acute myeloid leukaemia, and leucocytes were also obtained from 2 normal subjects. Ferritin was partially purified from leucocyte extracts and subjected to anion-exchange chromatography and isoelectric focusing. The Fe content of leucocyte ferritin was low, and in all but one case the preparations contained isoferritins corresponding to those found in normal tissues or serum. Only some of the preparations contained the relatively acidic isoferritins which have been described as "carcinofoetal", but which are also present in normal heart and kidney. Ferritin from one patient contained isoferritins of lower isoelectric point than heart ferritin. These results show that there does not appear to be any specific isoelectric focusing pattern for leukaemic cells, and that assays for acidic isoferritins are unlikely to be of use in the diagnosis of leukaemia and in monitoring treatment. However, the very acidic protein found in one preparation suggests that the search for abnormal subunits of ferritin may be fruitful in acute leukaemia
Investigating high-mass star formation through maser surveys
Interstellar masers are unique probes of the environments in which they arise. In studies of high-mass star formation their primary function has been as signposts of these regions and they have been used as probes of the kinematics and physical conditions in only a few sources. With a few notable exceptions, we know relatively little about the evolutionary phase the different maser species trace, nor their location with respect to other star formation tracers. While detailed studies of a small number of maser regions can reveal much about them, other information can only be obtained through large, systematic searches. In particular, such surveys are vital in efforts to determine an evolutionary sequence for the common maser species, and there is growing evidence that methanol masers may trace an earlier phase than the other common maser species of OH and water. © 2008 International Astronomical Union
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