Near Infrared Spectroscopy of the Ultracompact HII region G45.12+0.13

We present complete, low resolution IJHK spectroscopy of the ultracompact HII region, G45.12+0.13. From the observed HI line strengths, we derive a near infrared extinction law that is slightly steeper than the average. After correction with this extinction law, we find good agreement between the observed line ratios of HeI, Fe+, Fe++, S+ and S++ and the available atomic data. Our data show that the density within the core of G45.12+0.13 must be at least 10^4/cm^3. This is consistent with the known radio structure of the HII region and in considerable disagreement with previous work using mid and far infrared lines. There must also be considerable opacity in the HeI 2 3P-2 3S transition, and we show how the observed strengths of the other HeI lines are consistent with this. From modelling the photoionisation structure, we find good agreement with most of the observed data if the hottest star present has Teff < 42000K. Consideration of the helium ionisation state places a lower limit on this value so that we can also constrain Teff > 38000K. Discrepancies still exist between some of the observed and model line ratios, but the most obvious tend to be the mid-IR observations.Comment: 17 pages Latex source, 5 postscript figures and macros. gzipped tar file. TO appear in Monthly Notices of the Royal Astronimcal Society. Also available by anonymous ftp from ftp://aaoepp.aao.gov.au/local/sll/g45.uu (uuencoded gzipped tar file

Web-based writing support: making it useable for distance teachers

This paper considers the issues that distance teachers in higher education who are not writing specialists face in supporting their students’ academic writing development. We discuss the usefulness of open web-based writing support resources, and propose the need for a system that serves as an interface with these resources. Such a system should help teachers to make quick selections of materials that can be offered to students to address specific problems in the students’ assignments. We consider principles for the design of such a system, based on the experience of building and testing a small prototype for tutors on an Open University Masters in Education course

What sort of standard candle is Orion for studying molecular hydrogen line emission in galaxies

The total shocked and fluorescent molecular hydrogen 1-0 S(1) line luminosities from Orion have been measured to be about 2.5 solar luminosity and about 2.0 solar luminosity, respectively. The implications for using Orion to study the interstellar medium in galaxies is discussed

Infrared Helium-Hydrogen Line Ratios as a Measure of Stellar Effective Temperature

We have observed a large sample of compact planetary nebulae in the near-infrared to determine how the 2^1P-2^1S HeI line at 2.058um varies as a function of stellar effective temperature, Teff. The ratio of this line with HI Br g at 2.166um has often been used as a measure of the highest Teff present in a stellar cluster, and hence on whether there is a cut-off in the stellar initial mass function at high masses. However, recent photoionisation modelling has revealed that the behaviour of this line is more complex than previously anticipated. Our work shows that in most aspects the photoionisation models are correct. In particular, we confirm the weakening of the 2^1P-2^1S as Teff increases beyond 40000K. However, in many cases the model underpredicts the observed ratio when we consider the detailed physical conditions in the individual planetary nebulae. Furthermore, there is evidence that there is still significant 2^1P-2^1S HeI line emission even in the planetary nebulae with very hot (Teff>100000K) central stars. It is clear from our work that this ratio cannot be considered as a reliable measure of effective temperature on its own.Comment: 24 pages 11 figures (in 62 separate postscript files) Accepted for publication in Monthly Notices of the Royal Astronomical Societ

Infrared spectroscopy of the dwarf starburst galaxy Henize 2-10

Researchers present 1.2 to 2.2 micron spectra of the nucleus of Henize 2 to 10, taken at United Kingdom Infrared Telescope (UKIRT) with the cool grating spectrometer 2 (CGS 2). This galaxy displays strong line emission from interstellar H (+) (1.282 and 2.166 microns) and (Fe (+)) (1.256 and 1.644 microns), in common with other star-forming galaxy nuclei. However, the 1 to 0 S(1) line of molecular hydrogen at 2.122 micron is not detected - the upper limit of 0.15 (3 sigma) for the value of the flux ratio I sub 1-os(1)/I sub Br gamma is much lower than the typical values of 0.4 to 0.9 measured in a sample of 28 non-interacting starburst galaxies. From the Pa beta/Br gamma line ratio researchers derive a total extinction of A sub v approx. 4 mag. The de-reddened H (+) and (Fe (+) line fluxes are used to estimate the total ionizing luminosity and the average supernova rate in the central 150 pc of He 2 to 10. By comparison of these estimates with existing Infrared Astronomy Satellite (IRAS) and radio continuum data, researchers are able to set limits on the range of stellar masses present in this unevolved (less than 10(exp 7) year old) starburst nucleus. Possible reasons for the low H2/H+ line ratios observed in young starburst systems (He 2 to 10, NGC 7714, IIZw40; e.g., Moorwood and Oliva 1988) are briefly discussed

Near Infrared Spectra of Compact Planetary Nebulae

This paper continues our study of the behaviour of near infrared helium recombination lines in planetary nebula. We find that the 1.7007um 4^3D-3^3P HeI line is a good measure of the HeI recombination rate, since it varies smoothly with the effective temperature of the central star. We were unable to reproduce the observed data using detailed photoionisation models at both low and high effective temperatures, but plausible explanations for the difference exist for both. We therefore conclude that this line could be used as an indicator of the effective temperature in obscured nebula. We also characterised the nature of the molecular hydrogen emission present in a smaller subset of our sample. The results are consistent with previous data indicating that ultraviolet excitation rather than shocks is the main cause of the molecular hydrogen emission in planetary nebulae.Comment: Accepted for publication in MNRA

Vigorous star formation in galactic nuclei

This thesis presents a study of vigorous star formation in the nuclei of nearby galaxies. A variety of techniques have been employed to investigate several aspects of this phenomenon.Analysis of m i d - an d far-infrared data, taken by the Infrared Astronomical Satellite, suggests that am o n g s t nearby spiral galaxies the presence of a stellar bar is a necessary condition for the existence of vigorous star-formation activity. Such regions contribute, on average, one third of the luminosity of the host galaxy.Medium-resolution radio continuum observations s h o w that active star formation occurs in the central regions of galaxies, supporting the hypothesis that it is caused by a bar-driven inflow of disk material.Near-infrared spectrophotometry has been used to study several of these highly dust-obscured regions in greater detail. Detection of the hydrogen recombination line Brq, which arises in photoionized gas, is further evidence for the presence of a p o p u ­ lation of massive stars. M e asurements of molecular hydrogen lines demonstrate that this gas is also photo-excited, in contrast with previous studies. Models of the gas excitation in star-forming regions are constructed an d comparison of the predicted line intensities with observations yields information regarding the gas density an d structure of the complexes.The ionized gas in the archetypal starburst galaxy M 82 is examined in greater detail through measurements made in mm-wavelength recombination lines ( H 4 0 and H53a). These observations avoid the problems which occur when shorter-wavelength lines are employed since they are unaffected by dust attenuation. The ionization state of the gas an d the total luminosity are used to infer the range of stellar masses present in this galaxy. This range may be very narrow

The Near-Infrared Extinction Law in Regions of High Av

We present a spectroscopic study of the shape of the dust-extinction law between 1.0 and 2.2um towards a set of nine ultracompact HII regions with Av > 15 mag. We find some evidence that the reddening curve may tend to flatten at higher extinctions, but just over half of the sample has extinction consistent with or close to the average for the interstellar medium. There is no evidence of extinction curves significantly steeper than the standard law, even where water ice is present. Comparing the results to the predictions of a simple extinction model, we suggest that a standard extinction law implies a robust upper limit to the grain-size distribution at around 0.1 - 0.3um. Flatter curves are most likely due to changes in this upper limit, although the effects of flattening due to unresolved clumpy extinction cannot be ruled out.Comment: 9 pages, 7 figure

Enhanced star formation: The importance of bars in spiral galaxies

It was found that among an IR luminous subset of nearby spiral galaxies, nearly all of the systems with IRAS colors and luminosities indicative of enhanced star formation are barred. Radio continuum and IR spectroscopic results support the hypothesis that this emission originates within the central 2 kpc; possibly in a circumnuclear ring. It was also found that outer rings are over represented among these barred systems and suggest possible reasons for this phenomena

A contextualised online writing support system: Creating the links between generic skills and the discipline

This paper describes an ongoing research and development project aimed at providing contextualised, individualised online writing support for postgraduate students. It is the result of a collaboration between UK and NZ academics who share similar challenges and concerns. The massification of higher education globally means that many tertiary students drawn from non traditional or second language backgrounds struggle to master the academic literacy requirements of particular discipline areas. These writing difficulties can, and often do, impact negatively on their academic success. Universities attempt to address this problem by providing online generic resources for students. Unfortunately research indicates that students are not successful in transferring generic concepts to their own discipline. We are attempting to devise an online programme where lecturers will be able to draw on these generic resources and, following models provided, construct a link between the specific and the generic in their own discipline area