1,131 research outputs found
Pumping of the 4.8 GHz HCO masers and its implications for the periodic masers in G37.55+0.20
Periodic or regular flaring of class II methanol masers in nine high mass
star forming regions is now a well established phenomenon. Amongst the nine
star forming regions, G37.55+0.20 is the only case at present where apart from
the presence of a periodic class II methanol maser, correlated flaring of
another masing species, formaldehyde in this case, has been detected. We
perform numerical calculations to investigate under which conditions the 4.8
GHz transition of ortho-formaldehyde is inverted in order to address the
question of the correlated flaring of the 6.7 GHz methanol and 4.8 GHz
formaldehyde masers in G37.55+0.20. We developed a numerical code to study the
population inversion of o-formaldehyde. Equilibrium solutions for the level
populations are found by integrating the rate equations using Heun's method. It
is found that collisional excitation with H as well as radiative excitation
by the free-free radio continuum radiation from a nearby ultra- or
hyper-compact HII region can invert the 4.8 GHz transition. It is also found
that radiative excitation by the dust infrared radiation field does not lead to
an inversion of the 4.8 GHz transition. The 14.5 GHz and 28.9 GHz transitions
are inverted only in the presence of the free-free continuum radiation field of
a very compact HII region. Due to the different pumping mechanisms of the
formaldehyde and methanol masers it is unlikely that the near simultaneous
flaring of the methanol and formaldehyde masers in G37.55+0.20 is due to
changes in the pumping of the masers.Comment: Accepted for publication in Astronomy and Astrophysic
A near-infrared study of the star forming region RCW 34
We report the results of a near-infrared imaging study of a
arcmin region centered on the 6.7 GHz methanol maser associated with the
RCW 34 star forming region using the 1.4m IRSF telescope at Sutherland. A total
of 1283 objects were detected simultaneously in J, H, and K for an exposure
time of 10800 seconds. The J-H, H-K two-colour diagram revealed a strong
concentration of more than 700 objects with colours similar to what is expected
of reddened classical T Tauri stars. The distribution of the objects on the K
{\it vs} J-K colour-magnitude diagram is also suggestive that a significant
fraction of the 1283 objects is lower mass pre-main sequence stars. We also
present the luminosity function for the subset of about 700 pre-main sequence
stars and show that it suggests ongoing star formation activity for about
years. An examination of the spatial distribution of the pre-main
sequence stars shows that the fainter (older) part of the population is more
dispersed over the observed region and the brighter (younger) subset is more
concentrated around the position of the O8.5V star. This suggests that the
physical effects of the O8.5V star and the two early B-type stars on the
remainder of the cloud out of which they formed, could have played a role in
the onset of the more recent episode of star formation in RCW 34.Comment: Accepted for publication in The Astronomical Journa
On the pumping of the CS() masers in W51 e2e
We present the results of numerically solving the rate equations for the
first 31 rotational states of CS in the ground vibrational state to determine
the conditions under which the J=1-0, J=2-1 and J=3-2 transitions are inverted
to produce maser emission. The essence of our results is that the CS()
masers are collisionally pumped and that, depending on the spectral energy
distribution, dust emission can suppress the masers. Apart from the J=1-0 and
J=2-1 masers the calculations also show that the J=3-2 transition can be
inverted to produce maser emission. It is found that beaming is necessary to
explain the observed brightness temperatures of the recently discovered CS
masers in W51 e2e. The model calculations suggest that a CS abundance of a few
times and CS() column densities of the order
are required for these masers. The rarity of the CS
masers in high mass star forming regions might be the result of a required high
CS abundance as well as due to attenuation of the maser emission inside as well
as outside of the hot core.Comment: 13 pages, 15 figure
On the Identification of High Mass Star Forming Regions using IRAS: Contamination by Low-Mass Protostars
We present the results of a survey of a small sample (14) of low-mass
protostars (L_IR < 10^3 Lsun) for 6.7 GHz methanol maser emission performed
using the ATNF Parkes radio telescope. No new masers were discovered. We find
that the lower luminosity limit for maser emission is near 10^3 Lsun, by
comparison of the sources in our sample with previously detected methanol maser
sources. We examine the IRAS properties of our sample and compare them with
sources previously observed for methanol maser emission, almost all of which
satisfy the Wood & Churchwell criterion for selecting candidate UCHII regions.
We find that about half of our sample satisfy this criterion, and in addition
almost all of this subgroup have integrated fluxes between 25 and 60 microns
that are similar to sources with detectable methanol maser emission. By
identifying a number of low-mass protostars in this work and from the
literature that satisfy the Wood & Churchwell criterion for candidate UCHII
regions, we show conclusively for the first time that the fainter flux end of
their sample is contaminated by lower-mass non-ionizing sources, confirming the
suggestion by van der Walt and Ramesh & Sridharan.Comment: 8 pages with 2 figures. Accepted by Ap
New Periodic 6.7 GHz Class II Methanol Maser Associated with G358.460-0.391
Eight new class II methanol masers selected from the 6.7 GHz Methanol
Multibeam survey catalogues I and II were monitored at 6.7 GHz with the 26m
Hartebeesthoek Radio Astronomy Observatory (HartRAO) radio telescope for three
years and seven months, from February 2011 to September 2014. The sources were
also observed at 12.2 GHz and two were sufficiently bright to permit
monitoring. One of the eight sources, namely G358.460-0.391, was found to show
periodic variations at 6.7 GHz. The period was determined and tested for
significance using the Lomb-Scargle, epoch-folding and Jurkevich methods, and
by fitting a simple analytic function. The best estimate for the period of the
6.7 GHz class II methanol maser line associated with G358.460-0.391 is 220.0
0.2 day.Comment: 8 pages, 11 figures, accepted for publication in MNRAS. The appendix
of 4 pages (with 16 figures) will be published as online versio
Last mile cold chain distribution challenges for privately-owned and retail pharmacies in Auckland Park and surrounding areas, Johannesburg
Abstract: Research objective: The primary research objective was to determine the challenges prevailing in the last mile distribution of cold chain medication to privately-owned and retail pharmacies in Auckland Park and surrounding areas. Methodology: A positivist research philosophy guided a descriptive quantitative survey design. Structured questionnaires were hand-delivered to all 43 privately-owned and retail pharmacies in the Auckland Park and surrounding areas. Findings: Some discrepancies were found in the cold chain distribution process that could compromise the quality of the cold chain medication. Although these pharmacies mostly used the correct storage systems for cold chain medication within the specified temperature range, the appropriate mode of transportation for delivery to the pharmacy is questionable..
Molecular Line Observations of Infrared Dark Clouds: Seeking the Precursors to Intermediate and Massive Star Formation
We have identified 41 infrared dark clouds from the 8 micron maps of the
Midcourse Space Experiment (MSX), selected to be found within one square degree
areas centered on known ultracompact HII regions. We have mapped these infrared
dark clouds in N2H+(1-0), CS(2-1) and C18O(1-0) emission using the Five College
Radio Astronomy Observatory. The maps of the different species often show
striking differences in morphologies, indicating differences in evolutionary
state and/or the presence of undetected, deeply embedded protostars. We derive
an average mass for these clouds using N2H+ column densities of ~2500 solar
masses, a value comparable to that found in previous studies of high mass star
forming cores using other mass tracers. The linewidths of these clouds are
typically ~2.0 - 2.9 km/s. Based on the fact that they are dark at 8 micron,
compact, massive, and have large velocity dispersions, we suggest that these
clouds may be the precursor sites of intermediate and high mass star formation.Comment: Accepted to ApJS, 22 pages, 10 pages of figures. For full-resolution
images, see http://www.astro.lsa.umich.edu/~seragan/pubs/fcrao/figures.tar.g
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