1,557 research outputs found
Clumpy Ultracompact HII Regions I: Fully Supersonic Wind-blown Models
We propose that a significant fraction of the ultracompact HII regions found
in massive star-forming clouds are the result of the interaction of the wind
and ionizing radiation from a young massive star with the clumpy molecular
cloud gas in its neighbourhood. Distributed mass loading in the flow allows the
compact nebulae to be long-lived. In this paper, we discuss a particularly
simple case, in which the flow in the HII region is everywhere supersonic. The
line profiles predicted for this model are highly characteristic, for the case
of uniform mass loading. We discuss briefly other observational diagnostics of
these models.Comment: To appear in Monthly Notices of the Royal Astronomical Society. 5
pages LaTeX (uses mn.sty and epsf.sty macros) + 4 PS figures. Also available
via http://axp2.ast.man.ac.uk:8000/Preprints.htm
Deep Halpha imagery of the Eridanus shells
A deep \ha image of interlocking filamentary arcs of nebulosity has been
obtained with a wide-field ( 30\degree diameter) narrow-band filter
camera combined with a CCD as a detector. The resultant mosaic of images,
extending to a galactic latitude of 65, has been corrected for field
distortions and had galactic coordinates superimposed on it to permit accurate
correlations with the most recent H{\sc i} (21 cm), X-ray (0.75 kev) and FIR
(IRAS 100 m) maps.
Furthermore, an upper limit of 0.13 arcsec/yr to the expansion proper motion
of the primary 25\degree long nebulous arc has been obtained by comparing a
recent \ha image obtained with the San Pedro Martir telescope of its
filamentary edge with that on a POSS E plate obtained in 1951.
It is concluded that these filamentary arcs are the superimposed images of
separate shells (driven by supernova explosions and/or stellar winds) rather
than the edges of a single `superbubble' stretching from Barnard's Arc (and the
Orion Nebula) to these high galactic latitudes. The proper motion measurement
argues against the primary \ha emitting arc being associated with the giant
radio loop (Loop 2) except in extraordinary circumstances.Comment: 9 pages, 5 figures, accepted for MNRAS publicatio
Towards an explanation for the 30 Dor (LMC) Honeycomb nebula - the impact of recent observations and spectral analysis
The unique Honeycomb nebula, most likely a peculiar supernova remnant, lies
in 30 Doradus in the Large Magellanic Cloud. Due to its proximity to SN1987A,
it has been serendipitously and intentionally observed at many wavelengths.
Here, an optical spectral analysis of forbidden line ratios is performed in
order to compare the Honeycomb high-speed gas with supernova remnants in the
Galaxy and the LMC, with galactic Wolf-Rayet nebulae and with the optical line
emission from the interaction zone of the SS433 microquasar and W50 supernova
remnant system. An empirical spatiokinematic model of the images and spectra
for the Honeycomb reveals that its striking appearance is most likely due to a
fortuitous viewing angle. The Honeycomb nebula is more extended in soft X-ray
emission and could in fact be a small part of the edge of a giant LMC shell
revealed for the first time in this short wavelength domain. It is also
suggested that a previously unnoticed region of optical emission may in fact be
an extension of the Honeycomb around the edge of this giant shell. A secondary
supernova explosion in the edge of a giant shell is considered for the creation
of the Honeycomb nebula. A microquasar origin of the Honeycomb nebula as
opposed to a simple supernova origin is also evaluated.Comment: 12 pages, 9 figures, accepted for publication in MNRA
The development of advanced practice roles: implications in the international nursing community
This article examined the critical elements that have been identified in the development of advanced practice roles of nurses in four countries: Brazil, Thailand, the United Kingdom and the United States of America. Several socio-political and professional forces were examined for possible insights and ways in which they may have shaped the development and evolution of the roles of advanced practice nurses (APNs). These forces were: the socio-political environment; the health needs of society; the health workforce supply and demand; governmental policy and support; intra- and interprofessional collaboration; the development of nursing education; and documentation of effectiveness of the advanced role. The development of APN roles in the four social systems was reviewed to illustrate how socio-political and professional forces may have shaped nursing roles in each health care delivery system. Commonalities and distinguishing features across the four health and social systems were analysed to assess the predictive forces that may be identified as advanced roles in nursing have evolved in the global community.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74797/1/j.1466-7657.2001.00065.x.pd
CO abundances in a protostellar cloud: freeze-out and desorption in the envelope and outflow of L483
CO isotopes are able to probe the different components in protostellar
clouds. These components, core, envelope and outflow have distinct physical
conditions and sometimes more than one component contributes to the observed
line profile. In this study we determine how CO isotope abundances are altered
by the physical conditions in the different components. We use a 3D molecular
line transport code to simulate the emission of four CO isotopomers, 12CO
J=2-1, 13CO J=2-1, C18O J=2-1 and C17O J=2-1 from the Class 0/1 object L483,
which contains a cold quiescent core, an infalling envelope and a clear
outflow. Our models replicate JCMT (James Clerk Maxwell Telescope) line
observations with the inclusion of freeze-out, a density profile and infall.
Our model profiles of 12CO and 13CO have a large linewidth due to a high
velocity jet. These profiles replicate the process of more abundant material
being susceptible to a jet. C18O and C17O do not display such a large linewidth
as they trace denser quiescent material deep in the cloud.Comment: 9 figures, 13 pages, 2 table
The HCO+ emission excess in bipolar outflows
A plausible model is proposed for the enhancement of the abundance of
molecular species in bipolar outflow sources. In this model, levels of HCO+
enhancement are considered based on previous chemical calculations, that are
assumed to result from shock-induced desorption and photoprocessing of dust
grain ice mantles in the boundary layer between the outflow jet and the
surrounding envelope. A radiative transfer simulation that incorporates
chemical variations within the flow shows that the proposed abundance
enhancements in the boundary layer are capable of reproducing the observed
characteristics of the outflow seen in HCO+ emission in the star forming core
L1527. The radiative transfer simulation also shows that the emission lines
from the enhanced molecular species that trace the boundary layer of the
outflow exhibit complex line profiles indicating that detailed spatial maps of
the line profiles are essential in any attempt to identify the kinematics of
potential infall/outflow sources. This study is one of the first applications
of a full three dimensional radiative transfer code which incorporates chemical
variations within the source.Comment: MNRAS, accepted. 10 pages, 6 figure
Rotation of the pre-stellar core L1689B
The search for the onset of star formation in pre-stellar cores has focussed
on the identification of an infall signature in the molecular line profiles of
tracer species. The classic infall signature is a double peaked line profile
with an asymmetry in the strength of the peaks such that the blue peak is
stronger. L1689B is a pre-stellar core and infall candidate but new JCMT HCO+
line profile data, presented here, confirms that both blue and red asymmetric
line profiles are present in this source. Moreover, a dividing line can be
drawn between the locations where each type of profile is found. It is argued
that it is unlikely that the line profiles can be interpreted with simple
models of infall or outflow and that rotation of the inner regions is the most
likely explanation. A rotational model is developed in detail with a new 3D
molecular line transport code and it is found that the best type of model is
one in which the rotational velocity profile is in between solid body and
Keplerian. It is firstly shown that red and blue asymmetric line profiles can
be generated with a rotation model entirely in the absence of any infall
motion. The model is then quantitively compared with the JCMT data and an
iteration over a range of parameters is performed to minmize the difference
between the data and model. The results indicate that rotation can dominate the
line profile shape even before the onset of infall.Comment: Accepted by MNRAS, 7 pages, 4 figure
Low Velocity Ionized Winds from Regions Around Young O Stars
We have observed seven ultracompact HII regions in hydrogen recombination
lines in the millimeter band. Toward four of these regions, there is a high
velocity (full width to half maximum 60-80 km/s) component in the line
profiles. The high velocity gas accounts for 35-70% of the emission measure
within the beam. We compare these objects to an additional seven similar
sources we have found in the literature. The broad recombination line objects
(BRLOs) make up about 30% of all sources in complexes containing ultracompact
HII regions. Comparison of spectral line and continuum data implies that the
BRLOs coincide with sources with rising spectral indices, >=0.4 up to 100 GHz.
Both the number of BRLOs and their frequency of occurrence within HII region
complexes, when coupled with their small size and large internal motions, mean
that the apparent contradiction between the dynamical and population lifetimes
for BRLOs is even more severe than for ultracompact HII regions. We evaluate a
number of models for the origin of the broad recombination line emission. The
lifetime, morphology, and rising spectral index of the sources argue for photo-
evaporated disks as the cause for BRLOs. Existing models for such regions,
however, do not account for the large amounts of gas observed at supersonic
velocities.Comment: 36 pages, 8 figure
The representation of scientific research in the national curriculum and secondary school pupils’ perceptions of research, its function, usefulness and value to their lives
Young people’s views on what research is, how it is conducted and whether it is important, influences the decisions they make about their further studies and career choices. In this paper we report the analysis of questionnaire data with a particular focus on pupil perceptions of research in the sciences and of the scientific method. The questionnaire was a 25-item Likert Scale (1-5) distributed to seven collaborating schools. We received 2634 returns from pupils across key stages 3, 4 and 5. We also asked teachers to complete the questionnaire in order to explore how they thought their pupils would respond. We received 54 teacher responses. Statistically significant differences in the responses were identified through a chi-square test on SPSS. As what is being taught influences secondary pupil views on research we also consider how the term ‘research’ appears in the national curriculum for England and Wales and the three main English exam boards. The main theoretical construct that informs our analysis of the questionnaire data and the national curriculum is Angela Brew’s 4-tier descriptor of perceptions of research (domino, trading, layer, journey). We use this framework in order to map what, when and how research is presented to school pupils in England and Wales. We also use this framework in order to highlight and discuss certain pupil views that emerged from the questionnaire data and which indicate areas where curriculum and pedagogy intervention may be necessary: pupils seem less confident in their understanding of research as involving the identification of a research question; and, they often see research as a means to confirm one’s own opinion. They do however understand research as involving the generation of new knowledge and the collection of new data, such as interviews and questionnaires as well as laboratory work, field trips and library searches and they appear relatively confident in their statements about their ability to do research, their school experiences of research and the importance of research in their future career choice
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