134 research outputs found
Observations of ground-state OH in the Large Magellanic Cloud
We have carried out a series of observations of the 1665- and 1667-MHz
transitions of the 2Pi_3/2, J=3/2 OH ground state towards six selected HII
regions in the Large Magellanic Cloud (IRAS 05011-6815 and MRC 0510-689,
0513-694B, 0539-691, 0540-696B, 0540-697A) using the Australia Telescope
Compact Array. The study has provided the first accurate positions for known
1665- and 1667-MHz OH masers as well as detecting several new masers. The
regions all contain H_2O or CH_3OH masers but OH masers were detected in only
four. The 1.6-GHz continuum emission was also imaged to investigate its spatial
relationship to the associated OH maser. Although some masers are close to
compact continuum components, in other cases they are near the continuum
distribution boundaries and perhaps have been created as a result of the HII
region interacting with the surrounding interstellar medium.Comment: Accepted for publication in MNRAS 6 pages, 9 figure
Ground-state OH observations towards NGC 6334
We have made observations of the four hyperfine transitions of the 2Pi(3/2),
J=3/2 ground state of OH at 1612, 1665, 1667 and 1720 MHz and the related
1.6-GHz continuum emission, towards NGC 6334 using the Australia Telescope
Compact Array. The observations covered all the major radio continuum
concentrations aligned along the axis of NGC 6334 (V, A to F). We have detected
seven OH masers plus a possible faint eighth maser; two of these masers are
located towards NGC 6334-A. Absorption at 1665 and 1667 MHz was detected
towards almost all the continuum distribution. All transitions showed non-LTE
behaviour. The 1667-/1665-MHz intensity ratios ranged from 1.0 to 1.2,
significantly less than their LTE value of 1.8. The results of the OH `Sum
Rule' suggest that this discrepancy cannot be explained solely by high optical
depths. The 1612- and 1720-MHz line-profiles showed conjugate behaviour whereby
one line was in absorption and the other in emission. In addition, the profiles
commonly showed a flip from absorption to emission and vice versa, which has
been interpreted as a density gradient. The OH line-to-continuum distribution,
optical depth and velocity trends are consistent with a bar-like shape for the
molecular gas which wraps around the continuum emission.Comment: 12 pages, 12 figures, accepted for publication in MNRA
Assessing Group Efficacy: Comparing Three Methods of Measurement
Two hundred eighty-two undergraduate students (94 groups) participated in a laboratory study designed to compare three methods of assessing group efficacy: an aggregate of self-efficacy perceptions, an aggregate of individual perceptions of group efficacy, and a consensual approach. Findings indicate that the three methods of measuring group efficacy do not differ in their capacity to discriminate high and moderate task-difficulty conditions nor do they differ in terms of their consistency, the magnitude of their relationship with goals, or the degree to which they are affected by performance. Findings suggest that any of the three methods can be applied when studying the effects of group efficacy, at least for tasks with low interdependence
CH 3 GHz Observations of the Galactic Center
A 3 3 map of the Galactic Center was made at 9\arcmin resolution
and 10\arcmin spacing in the CH , J=1/2, F=1-1 transition at
3335 MHz. The CH emission shows a velocity extent that is nearly that of the
CO(1-0) line, but the CH line profiles differ markedly from the CO. The 3335
MHz CH transition primarily traces low-density molecular gas and our
observations indicate that the mass of this component within 30 pc of
the Galactic Center is 9 10 M. The CO-H
conversion factor obtained for the low-density gas in the mapped region is
greater than that thought to apply to the dense molecular gas at the Galactic
Center. In addition to tracing the low-density molecular gas at the Galactic
Center, the CH spectra show evidence of emission from molecular clouds along
the line of sight both in the foreground and background. The scale height of
these clouds ranges from 27 - 109 pc, consistent with previous work based on
observations of molecular clouds in the inner Galaxy.Comment: 29 pages, 12 figure
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&
The Giant Pillars of the Carina Nebula
Results are presented from a multi-wavelength study of the giant pillars
within the Carina Nebula. Using near-IR data from 2MASS, mid-IR data from MSX,
843MHz radio continuum maps from the MOST, and molecular line and continuum
observations from the SEST, we investigate the nature of the pillars and search
for evidence of ongoing star formation within them. Photodissociation regions
(PDRs) exist across the whole nebula and trace the giant pillars, as well as
many ridges, filaments, and condensations (Av > 7 mag). Morphological
similarities between emission features at 21um and 843MHz adjacent to the PDRs,
suggests that the molecular material has been carved by the intense stellar
winds and UV radiation from the nearby massive stars. In addition, star forming
cores are found at the tips of several of the pillars. Using a stellar density
distribution, several candidate embedded clusters are also found. One is
clearly seen in the 2MASS images and is located within a dense core
(G287.84-0.82). A search for massive young stellar objects and compact HII
regions using mid-IR colour criteria, reveal twelve candidates across the
complex. Grey-body fits to SEDs for four of these objects are suggestive of
OB-stars. We find that massive star formation in the Carina Nebula is occurring
across the whole complex and confirm it has been continuous over the past 3
Myrs.Comment: 14 pages, 10 figures (low resolution), accepted by A&
On the Neutral Gas Content and Environment of NGC 3109 and the Antlia Dwarf Galaxy
As part of a continuing survey of nearby galaxies, we have mapped the neutral
gas content of the low surface brightness, Magellanic-type galaxy NGC 3109 ---
and its environment, including the Antlia dwarf galaxy --- at unprecedented
velocity resolution and brightness sensitivity. The HI mass of NGC 3109 is
measured to be (3.8 +/- 0.5) x 10^8 Msun. A substantial warp in the disk of NGC
3109 is detected in the HI emission image in the form of an extended low
surface brightness feature. We report a positive detection in HI of the nearby
Antlia dwarf galaxy, and measure its total neutral gas mass to be (6.8 +/- 1.4)
x 10^5 Msun. We show the warp in NGC 3109 to lie at exactly the same radial
velocity as the gas in the Antlia dwarf galaxy and speculate that Antlia
disturbed the disk of NGC 3109 during a mild encounter ~1 Gyr in the past. HI
data for a further eight galaxies detected in the background are presented.Comment: Accepted for publication in A
Identification campaign of supernova remnant candidates in the Milky Way - I: Chandra observation of G308.3-1.4
ROSAT all-sky survey (RASS) data have provided another window to search for
supernova remnants (SNRs). In reexamining this data archive, a list of
unidentified extended X-ray objects have been suggested as promising SNR
candidate. However, most of these targets have not yet been fully explored by
the state-of-art X-ray observatories. For selecting a pilot target for a
long-term identification campaign, we have observed the brightest candidate,
G308.3-1.4, with Chandra X-ray observatory. An incomplete shell-like X-ray
structure which well-correlated with the radio shell emission at 843 MHz has
been revealed. The X-ray spectrum suggests the presence of a shock-heated
plasma. All these evidences confirm G308.3-1.4 as a SNR. The brightest X-ray
point source detected in this field-of-view is also the one locates closest to
the geometrical center of G308.3-1.4, which has a soft spectrum. The intriguing
temporal variability and the identification of optical/infrared counterpart
rule out the possibility of an isolated neutron star. On the other hand, the
spectral energy distribution from Ks band to R band suggests a late-type star.
Together with a putative periodicity of \sim1.4 hrs, the interesting excesses
in V, B bands and H-alpha suggest this source as a promising candidate of a
compact binary survived in a supernova explosion (SN).Comment: 19 pages, 10 figures, 2 tables, accepted for publication in Ap
Chandra Observations of the Crab-like Supernova Remnant G21.5-0.9
Chandra observations of the Crab-like supernova remnant G21.5-0.9 reveal a
compact central core and spectral variations indicative of synchrotron burn-off
of higher energy electrons in the inner nebula. The central core is slightly
extended, perhaps indicating the presence of an inner wind-shock nebula
surrounding the pulsar. No pulsations are observed from the central region,
yielding an upper limit of ~40% for the pulsed fraction. A faint outer shell
may be the first evidence of the expanding ejecta and blast wave formed in the
initial explosion, indicating a composite nature for G21.5-0.9.Comment: 4 pages, 2 figures, formatted with emulateapj, submitted to ApJ
How to win friends and influence people: the value of the cohort in a doctoral research training programme
open access articleThis article is not about retention and attrition rates, or about
successful outcomes, or about supervision, even though these are at
the nub of most research on the doctoral experience. This article
concerns the experiences of doctoral students undertaking educational
research methods training, as opposed to the experiences of the PhD
itself. The specific phenomenon identified in this small group study is
the value of peer interaction within the cohort. Three strands of this
relationship, namely peer support, cultural mix and bonding/ad-hoc
social gatherings have been investigated. Our findings illustrate the
importance and unexpected value of the âcohortâ on the participants in
this study as they journey towards academia
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