3,017 research outputs found
Water masers accompanying OH and methanol masers in star formation regions
The ATCA has been used to measure positions with arcsecond accuracy for 379
masers at the 22-GHz transition of water. The principal observation targets
were 202 OH masers of the variety associated with star formation regions (SFR)s
in the Southern Galactic plane. At a second epoch, most of these targets were
observed again, and new targets of methanol masers were added. Many of the
water masers reported here are new discoveries. Variability in the masers is
often acute, with very few features directly corresponding to those discovered
two decades ago. Within our current observations, less than a year apart,
spectra are often dissimilar, but positions at the later epoch, even when
measured for slightly different features, mostly correspond to the detected
maser site measured earlier, to within the typical extent of the whole site, of
a few arcseconds. The precise water positions show that approximately 79% (160
of 202) of the OH maser sites show coincident water maser emission, the best
estimate yet obtained for this statistic; however, there are many instances
where additional water sites are present offset from the OH target, and
consequently less than half of the water masers coincide with a 1665-MHz
ground-state OH maser counterpart. We explore the differences between the
velocities of peak emission from the three species (OH, methanol and water),
and quantify the typically larger deviations shown by water maser peaks from
systemic velocities. Clusters of two or three distinct but nearby sites, each
showing one or several of the principal molecular masing transitions, are found
to be common. In combination with an investigation of correlations with IR
sources from the GLIMPSE catalogue, these comparative studies allow further
progress in the use of the maser properties to assign relative evolutionary
stages in star formation to individual sites.Comment: 51 pages, 7 figure
Constraining the properties of 1.2-mm dust clumps that contain luminous water masers
We have conducted a sensitive water maser search with the ATCA towards 267
1.2-mm dust clumps presented in the literature. We combine our new observations
with previous water maser observations to extend our sample to 294 1.2-mm dust
clumps, towards which we detect 165 distinct water maser sites towards 128
1.2-mm dust clumps. Within the fields of our observations, we additionally find
four water masers with no apparent associated 1.2-mm dust continuum emission.
Our overall detection rate of 44 per cent appears to vary as a function of
Galactic longitude. We find that there is an excellent correspondence between
the locations of the detected water masers with the peak of the target 1.2-mm
dust clump sources. As expected from previous similar studies, the water masers
are chiefly detected towards the bigger, brighter and more massive 1.2-mm dust
clumps. We find further evidence that the water masers tend to increase in flux
density (and therefore luminosity), as well as velocity range, as the sources
evolve. We also show that the current sample of water maser sources suffer less
from evolutionary biases than previous targeted searches. A higher fraction of
dust clump sources in our sample are only associated with water masers (41)
than only associated with methanol masers (13). This suggests that water masers
can be present at an even earlier evolutionary stage than 6.7-GHz methanol
masers. Comparison of the water maser detection rates associated with different
combinations of methanol maser and radio continuum, as well as those with
neither tracer, shows that the highest detection rate is towards those sources
which also exhibit methanol maser emission. We have tested a previously
hypothesised model for water maser presence towards 1.2-mm dust clumps. We
suggest refinements and future work which will further constrain the nature of
the driving sources associated with water masers.Comment: accepted to MNRA
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
A search for 4750- and 4765-MHz OH masers in Southern Star Forming Regions
We have used the Australia Telescope Compact Array (ATCA) to make a sensitive
(5- 100 mJy) search for maser emission from the 4765-MHz
F=10 transition of OH. Fifty five star formation regions
were searched and maser emission with a peak flux density in excess of 100 mJy
was detected toward fourteen sites, with ten of these being new discoveries. In
addition we observed the 4750-MHz F=11 transition towards a
sample of star formation regions known to contain 1720-MHz OH masers, detecting
marginal maser emission from G348.550-0.979. If confirmed this would be only
the second maser discovered from this transition. The occurrence of 4765-MHz OH
maser emission accompanying 1720-MHz OH masers in a small number of well
studied star formation regions has lead to a general perception in the
literature that the two transitions favour similar physical conditions. Our
search has found that the presence of the excited-state 6035-MHz OH transition
is a much better predictor of 4765-MHz OH maser emission from the same region
than is 1720-MHz OH maser emission. Combining our results with those of
previous high resolution observations of other OH transitions we have examined
the published theoretical models of OH masers and find that none of them
predict any conditions in which the 1665-, 6035- and 4765-MHz transitions are
simultaneously inverted.
Erratum abstract:
Dodson & Ellingsen (2002) included several observations with significant
pointing errors, invalidating the upper limits found in these directions. These
have now been reobserved or recalculated. A new table of upper limits has been
generated, and two more masers that would have been seen have been found.Comment: Included an Erratum with Max as another author. This erratum was
rejected by MNRAS (Feb 04) as it contained too much data. Resubmitted as a
paper (Jun 04). Rejected (Sep 04) it had too little data. Resubmitted as
reduced erratum (Apr 05). Still waitin
12.2-GHz methanol maser MMB follow-up catalogue - II. Longitude range 186 to 330 degrees
We present the second portion of a catalogue of 12.2-GHz methanol masers
detected towards 6.7-GHz methanol masers observed in the unbiased Methanol
Multibeam (MMB) Survey. Using the Parkes radio telescope we have targeted all
207 6.7-GHz methanol masers in the longitude range 186 to 330 degrees for
12.2-GHz counterparts. We report the detection of 83 12.2-GHz methanol masers,
and one additional source which we suspect is thermal emission, equating to a
detection rate of 40 per cent. Of the 83 maser detections, 39 are reported here
for the first time. We discuss source properties, including variability and
highlight a number of unusual sources. We present a list of 45 candidates that
are likely to harbor methanol masers in the 107.0-GHz transition.Comment: Accepted MNRAS 19 July 201
“Two Wars and the Long Twentieth Century:” A Response
Drew Gilpin Faust, president of Harvard University and renowned historian of the American Civil War, authored an article in the New Yorker recently entitled “Two Wars and the Long Twentieth Century.” Taken primarily from her remarks in the Rede Lecture delivered at the University of Cambridge earlier in 2015, Faust’s article takes advantage of the proximity of the anniversaries of the First World War and the American Civil War to advocate for a dialogue of greater continuity between the two conflicts. [excerpt
12.2-GHz methanol maser MMB follow-up catalogue - I. Longitude range 330 to 10 degrees
We present a catalogue of 12.2-GHz methanol masers detected towards 6.7-GHz
methanol masers observed in the unbiased Methanol Multibeam (MMB) survey in the
longitude range 330\circ (through 360\circ) to 10\circ. This is the first
portion of the catalogue which, when complete, will encompass all of the MMB
detections. We report the detection of 184 12.2-GHz sources towards 400 6.7-GHz
methanol maser targets, equating to a detection rate of 46 per cent. Of the 184
12.2-GHz detections, 117 are reported here for the first time. We draw
attention to a number of 'special' sources, particularly those with emission at
12.2-GHz stronger than their 6.7-GHz counterpart and conclude that these
unusual sources are not associated with a specific evolutionary stage.Comment: accepted to MNRAS 21 Dec 201
The Relationship between Class I and Class II Methanol Masers
The Australia Telescope National Facility Mopra millimetre telescope has been
used to search for 95.1-GHz class I methanol masers towards sixty-two 6.6-GHz
class II methanol masers. A total of twenty-six 95.1-GHz masers were detected,
eighteen of these being new discoveries. Combining the results of this search
with observations reported in the literature, a near complete sample of
sixty-six 6.6-GHz class II methanol masers has been searched in the 95.1-GHz
transition, with detections towards 38 per cent (twenty-five detections ; not
all of the sources studied in this paper qualify for the complete sample, and
some of the sources in the sample were not observed in the present
observations). There is no evidence of an anti-correlation between either the
velocity range, or peak flux density of the class I and II transitions,
contrary to suggestions from previous studies. The majority of class I methanol
maser sources have a velocity range that partially overlaps with the class II
maser transitions. The presence of a class I methanol maser associated with a
class II maser source is not correlated with the presence (or absence) of
main-line OH or water masers. Investigations of the properties of the infrared
emission associated with the maser sources shows no significant difference
between those class II methanol masers with an associated class I maser and
those without. This may be consistent with the hypothesis that the objects
responsible for driving class I methanol masers are generally not those that
produce main-line OH, water or class II methanol masers.Comment: 21 pages, 6 figures, accepted for publication in MNRA
Statistical properties of 12.2 GHz methanol masers associated with a complete sample of 6.7 GHz methanol masers
We present definitive detection statistics for 12.2 GHz methanol masers
towards a complete sample of 6.7 GHz methanol masers detected in the Methanol
Multibeam survey south of declination -20 degrees. In total, we detect 250 12.2
GHz methanol masers towards 580 6.7 GHz methanol masers. This equates to a
detection rate of 43.1%, which is lower than that of previous significant
searches of comparable sensitivity. Both the velocity ranges and the flux
densities of the target 6.7 GHz sources surpass that of their 12.2 GHz
companion in almost all cases. 80 % of the detected 12.2 GHz methanol maser
peaks are coincident in velocity with the 6.7 GHz maser peak. Our data support
an evolutionary scenario whereby the 12.2 GHz sources are associated with a
somewhat later evolutionary stage than the 6.7 GHz sources devoid of this
transition. Furthermore, we find that the 6.7 GHz and 12.2 GHz methanol sources
increase in luminosity as they evolve. In addition to this, evidence for an
increase in velocity range with evolution is presented. This implies that it is
not only the luminosity, but also the volume of gas conducive to the different
maser transitions, that increases as the sources evolve. Comparison with
GLIMPSE mid-infrared sources has revealed a coincidence rate between the
locations of the 6.7 GHz methanol masers and GLIMPSE point sources similar to
that achieved in previous studies. Overall, the properties of the GLIMPSE
sources with and without 12.2 GHz counterparts are similar. There is a higher
12.2 GHz detection rate towards those 6.7 GHz methanol masers that are
coincident with extended green objects.Comment: Accepted to ApJ March 2011. 28 pages, 9 figure
Superior Mirage: Aesthetic Recollections of the Great Lakes
Superior Mirage is a body of work that speaks of my deep connection to place of origin and how it has shaped the way I see, think, and create art in object or written (spoken word) forms. The Great lakes area has inspired my muse for its rugged beauty and hardy souls who live, work, and, play amongst the dichotomy of nature and industry. This rugged aesthetic carries over to both the industrial giant that built this nation and the natural world of a fragile ecosystem that is in constant flux with invasive species and climate change. The balance between the economic and the environmental is very delicate because we as humans need to find viable solutions for our future generations to prosper.
This dichotomy is the catalyst for the methods of how and why I create with materials/objects of both the natural and the manufactured as I believe that they need to live in harmony with each other. This body of work is a representation of what I have experienced as a rural lake dweller that appreciates the breathtaking beauty of the natural and the power of industry
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