The POINT-AGAPE survey - I. The variable stars in M31

For the purposes of identifying microlensing events, the POINT-AGAPE collaboration has been monitoring the Andromeda galaxy (M31) for three seasons (1999-2001) with the Wide Field Camera on the Isaac Newton Telescope. In each season, data are taken for one hour per night for roughly 60 nights during the six months that M31 is visible. The two 33 x 33 arcmin(2) fields of view straddle the central bulge, northwards and southwards. We have calculated the locations, periods and brightness of 35 414 variable stars in M31 as a by-product of the microlensing search. The variables are classified according to their period and brightness. Rough correspondences with classical types of variable star (such as Population I and II Cepheids, Miras and semiregular long-period variables) are established. The spatial distribution of Population I Cepheids is clearly associated with the spiral arms, while the central concentration of the Miras and long-period variables varies noticeably, the brighter and the shorter period Miras being much more centrally concentrated.

Gemini observations of Wolf-Rayet stars in the Local Group starburst galaxy IC 10

We present Gemini-N GMOS and CFHT MOS spectroscopy of Wolf-Rayet candidates in the Local Group dwarf galaxy IC 10 that were previously identified by Massey et al. and Royer et al. From the present spectroscopic survey, the WC/WN ratio for IC 10 remains unusually high, given its low metallicity, although none of the WC9 stars suspected from narrow-band imaging are confirmed. Our spectroscopy confirms 9 newly discovered Wolf-Rayet candidates from Royer et al., whilst spectral types of 14 Wolf-Rayet stars previously observed by Massey & Armandroff are refined here. In total, there are 26 spectroscopically confirmed Wolf-Rayet stars in IC 10. All but one of the fourteen WC stars are WC4-6 stars, the exception being # 10 from Massey et al., a broad-lined, apparently single WC7 star. There are a total of eleven WN stars, which are predominantly early WN3-4 stars, but include a rare WN10 star, # 8 from Royer et al. # 5 from Massey et al. is newly identified as a transition WN/C star. Consequently, the WC/WN ratio for IC10 is 14/11similar to1.3, unusually high for a metal-poor galaxy. Re-evaluating recent photometric data of Massey & Holmes, we suggest that the true WC/WN ratio may not be as low as similar to0.3. Finally, we present ground-based finding charts for all confirmed WR stars, plus HST/WFPC2 charts for twelve cases.

The WR content of IC10 - first detection of WC9 stars in a low metallicity environment?

We present deep, narrow-hand photometry of the Local Group starburst galaxy IC10. Our dedicated photometric system provides detection of 13 new Wolf-Rayet (WR) stars and allows spectral subtypes to be assigned. Three of these new stars appear to be WC9 subtypes. If confirmed, these would be the very first WC9 stars ever detected in a low metallicity environment, hence putting strong new constraints on the formation and evolution models of massive stars. Eight of the new WR stars are of the WC subtype, which does not significantly modify the anomalously high WC/WN ratio in IC10. However it is likely that a number of Wolf-Rayet stars of the WNE and WC spectral subtypes are still to be discovered in the heart of the galaxy.

A UKST survey of blue objects towards the galactic centre - a search for early-type stars

We have begun a search for early-type stars towards the galactic centre which are potentially young objects situated within the inner few kiloparsecs of the disk. U and V (or I) band photographic photometry from the UK Schmidt Telescope has been obtained to identify the bluest candidates in nineteen Schmidt fields (centred close to the galactic centre). We have spectroscopically observed these targets for three fields with the FLAIR multi-fibre system to determine their spectral types. In particular; ten early B-type stars have been identified and equivalent width measurements of their Balmer and HeI lines have been used to estimate atmospheric parameters. These early-type objects have magnitudes in the range 11.5 less than or equal to V less than or equal to 16.0, and our best estimates of their distance (given probable highly variable reddening in this direction together with errors in the plate photometry) suggest that some of them originated close to (i.e R-g

New identifications for blue objects towards the Galactic center: post-AGE stars, Be/disk stars and others

As part of a programme to investigate spatial variations in the Galactic chemical composition, we have been searching for normal B-type stars and A-type supergiants near the Galactic center. During this search we have found eleven peculiar stars, and in some cases performed detailed abundance analyses of them which suggest that they may be at a post-AGB evolutionary stage.

The carbon abundance in main-sequence B-type stars towards the Galactic anti-centre

Differential carbon abundances (based on the C II doublet at 6580 Angstrom) are presented for eight early type stars, towards the Galactic anti-centre. All the stars have similar atmospheric parameters with effective temperatures in the range 25000-29000 K and surface gravities between log g = 3.9-4.3 dex. The derived photospheric abundances vary by up to 0.6 dex, and with the exception of one star, RLWT-41, the differential abundances are found to be closely correlated with those of nitrogen. This implies that both elements may have been formed by similar mechanisms and that the lack of correlation between the nitrogen and oxygen abundances previously found in this sample is not directly due to CNO-processed core material being mixed to the stellar surface.

Efficient extreme UV harmonics generated from picosecond laser pulse interactions with solid targets

The generation of high harmonics created during the interaction of a 2.5 ps, 1053 nm laser pulse with a solid target has been recorded for intensities up to 10(19) W cm(-2). Harmonic orders up to the 68th at 15.5 nm in first order have been observed with indications up to the 75th at 14.0 nm in second-order diffraction. No differences in harmonic emission between s and p polarization of the laser beam were observed. The power of the 38th high harmonic at 27.7 nm is estimated to be 24 MW.

The VLT-FLAMES survey of massive stars: NGC 346-013 as a test case for massive close binary evolution

Context. NGC 346-013 is a peculiar double-lined eclipsing binary in the Small Magellanic Cloud (SMC) discovered by the VLT-FLAMES survey of massive stars.

Critical energies for ssb and dsb induction in plasmid DNA by vacuum-UV photons: an arrangement for irradiating dry or hydrated DNA with monochromatic photons

Purpose: Theoretical modelling techniques are often used to simulate the action of ionizing radiations on cells at the nanometre level, Using monoenergetic vacuum-UV (VUV) radiation to irradiate DNA either dry or humidified, the action spectra for the induction of DNA damage by low energy photons and the role of water and can be studied. These data provide inputs for the theoretical models.

Predicting organic acid concentration from UV/vis spectrometry measurements - A comparison of machine learning techniques

The concentration of organic acids in anaerobic digesters is one of the most critical parameters for monitoring and advanced control of anaerobic digestion processes. Thus, a reliable online-measurement system is absolutely necessary. A novel approach to obtaining these measurements indirectly and online using UV/vis spectroscopic probes, in conjunction with powerful pattern recognition methods, is presented in this paper. An UV/vis spectroscopic probe from S::CAN is used in combination with a custom-built dilution system to monitor the absorption of fully fermented sludge at a spectrum from 200 to 750 nm. Advanced pattern recognition methods are then used to map the non-linear relationship between measured absorption spectra to laboratory measurements of organic acid concentrations. Linear discriminant analysis, generalized discriminant analysis (GerDA), support vector machines (SVM), relevance vector machines, random forest and neural networks are investigated for this purpose and their performance compared. To validate the approach, online measurements have been taken at a full-scale 1.3-MW industrial biogas plant. Results show that whereas some of the methods considered do not yield satisfactory results, accurate prediction of organic acid concentration ranges can be obtained with both GerDA and SVM-based classifiers, with classification rates in excess of 87% achieved on test data.

Plume characteristics and dynamics of UV and IR laser-desorbed oligonucleotides

Laser desorption of dye-tagged oligonucleotides was studied using laser-induced fluorescence imaging. Desorption with ultra violet (UV) and infra-red (IR) lasers resulted in forward directed plumes of molecules. In the case of UV desorption, the initial shot desorbed approximately seven-fold more material than subsequent shots. In contrast, the initial shot in IR desorption resulted in the ejection of less material compared to subsequent shots and these plumes had a component directed along the path of the laser. Thermal equilibrium of the molecules in the plume was achieved after approximately 25 µs with a spread in molecular temperature which was described by a modified Maxwell-Boltzmann equation.