Locally linear embedding: dimension reduction of massive protostellar spectra

We present the results of the application of locally linear embedding (LLE) to reduce the dimensionality of dereddened and continuum subtracted near-infrared spectra using a combination of models and real spectra of massive protostars selected from the Red MSX Source survey database. A brief comparison is also made with two other dimension reduction techniques; Principal Component Analysis (PCA) and Isomap using the same set of spectra as well as a more advanced form of LLE, Hessian locally linear embedding. We find that whilst LLE certainly has its limitations, it significantly outperforms both PCA and Isomap in classification of spectra based on the presence/absence of emission lines and provides a valuable tool for classification and analysis of large spectral data sets.Comment: 8 pages, 7 figures. Accepted for publication in MNRAS 2016 June 2

Determination of the SSME high pressure oxidizer turbopump bearing temperature

The SSME high pressure liquid oxygen turbopump (HPOTP) bearings sometimes wear and experience heating and oxidation of the ball and raceway surfaces. So far it has been impossible to measure the temperature of the bearings directly during operation of the turbopumps. However, a method was developed for determining the surface temperature of the bearings from the composition of the oxides using oxidation samples for calibration and Auger Electron Spectroscopy (AES) for chemical analysis

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

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

How independent? an analysis of GE13 coverage by Malaysia’s online news portal coverage

The May 5, 2013, general election in Malaysia may have marked the move of the nation’s alternative news media—online, unlicensed news portals that challenge the hegemony of the party that has ruled the nation since 1957—into the mainstream. Malaysiakini, The Malaysian Insider, and Free Malaysia Today editors pride themselves on their independence and journalistic role as government watchdogs, a role they claim has been abdicated by newspapers and broadcast outlets. This article critiques the self-professed editorial independence of these three online news portals through analysis of their GE13 campaign coverage. This research will expand knowledge about Malaysia’s evolving news environment and will add to research on media coverage of previous Malaysian elections. The study employs two research methods: content analysis and personal interviews with news portal editors and media scholars. Following an overview of Malaysia’s historically hegemonic mainstream news media, the article traces how the Internet facilitated the introduction of Malaysia’s counter-hegemonic online news portals. Its basic research question is: Did Malaysia’s leading independent news portals provide unbiased news coverage of GE13? The hypothesis was that the sites would be negatively biased against the ruling Barisan Nasional coalition and positively biased toward opposition coalition candidates, However, the study found 8.2 percent more positive BN stories than negative BN stories in overall coverage. A greater disparity appeared in opposition coverage, where positive stories as predicted outnumbered negative stories by 56.1 percent. News portals criticized both parties, leading to the conclusion that they add to the political discourse that is requisite for successful participatory democracy

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

Helium and Hydrogen Line Ratios and The Stellar Content of Compact HII Regions

We present observations and models of the behaviour of the HI and HeI lines between 1.6 and 2.2um in a small sample of compact HII regions. As in our previous papers on planetary nebulae, we find that the `pure' 1.7007um 4^3D-3^3P and 2.16475um 7^(3,1)G-4^(3,1)F HeI recombination lines behave approximately as expected as the effective temperature of the central exciting star(s) increases. However, the 2.058um 2^1P-2^1S HeI line does not behave as the model predicts, or as seen in planetary nebulae. Both models and planetary nebulae showed a decrease in the HeI 2^1P-2^1S/HI Br gamma ratio above an effective temperature of 40000K. The compact HII regions do not show any such decrease. The problem with this line ratio is probably due to the fact that the photoionisation model does not account correctly for the high densities seen in these HII regions, and that we are therefore seeing more collisional excitation of the 2^1P level than the model predicts. It may also reflect some deeper problem in the assumed model stellar atmospheres. In any event, although the normal HeI recombination lines can be used to place constraints on the temperature of the hottest star present, the HeI 2^1P-2^1S/HI Br gamma ratio should not be used for this purpose in either Galactic HII regions or in starburst galaxies, and conclusions from previous work using this ratio should be regarded with extreme caution. We also show that the combination of the near infrared `pure' recombination line ratios with mid-infrared forbidden line data provides a good discriminant of the form of the far ultraviolet spectral energy distribution of the exciting star(s). From this we conclude that CoStar models are a poor match to the available data for our sources, though the more recent WM-basic models are a better fit.Comment: Accepted for publication in MNRA