AAO Newsletter July 1996 - Page 9

For further information please contact Raylee Stathakis who will be taking over the responsibility for the sky catalogues or send email to cosmos@aaoepp.aao.gov.au . More background information about both the APM and COSMOS catalogues is available on our "Surveys" page (http://www.aao.gov.au/local/www/surveys/).

Michael Drinkwater

A UKST H-Alpha survey of the Galactic plane

Under the auspices of a major Anglo-Australian collaboration, a UKST H-Alpha survey of the Southern Galactic plane, Magellanic clouds and selected regions has been agreed. The survey will use a new 12 x 12 inch monolithic H-Alpha interference filter of high specification and the excellent Tech Pan emulsion which has exceptional imaging capabilities due to its extremely fine grain with a useful sensitivity peak at H-Aplha. A survey of unprecedented area coverage, depth and resolution should result, superior to any previous optical survey of ionised gas in the galaxy. It is certain to lead to exciting new discoveries and avenues of research.

The survey should commence towards the end of 1996 and will initially include about 160 standard UKST fields. This will then be extended to the outer regions of the Galactic plane and to declinations from +0 to +15 degrees. Exposures will be of the order of 3 hours and the survey will take about 3 years to complete. The narrow-band nature of the H-Alpha filter means that the survey can proceed in grey/bright time when the sky is too bright for normal observations. The photometric integrity of the survey will be assessed via independent narrow band photometry with CCDs on other telescopes and with reference to previously studied objects over a range of UKST fields.

The need for the survey

Considering the importance of star formation and its variation within and between galaxies it is surprising how little survey work has been done, while much work has concentrated on relatively small areas for specific study. The only existing UKST wide area H-Alpha survey work dates to the late 1970s (Davis, Elliot & Meaburn, 1976) using mainly coarse grained (though fast) 098 emulsion and a far from optimum filter. Many parts of the plane are unsurveyed, particularly the outer extensions beyond a few degrees from the Galactic equator, whilst the Northern Milky Way above Dec =-20° has not been covered at all. Progress in other wavebands highlights the paucity of the optical counterpart for the study of Galactic gas. There is a clear need for a high resolution optical survey to complement studies at other wavebands.

Some scientific aims of the Survey

H-Alpha emission lines from HII regions are one of the most direct optical tracers of current star formation activity. These lines also trace out the distribution of ionised gas in the ISM in general, revealing for example: stellar outflows in regions masked by strong reflection nebulae; shocks from high velocity galactic HI clouds; the optical counterparts of supernova remnants; stellar wind-blown bubbles, shells, sheets and filaments and emission nebulosity close to young stellar sources. The spatial extent and detailed morphology of HII regions, OB associations and the wide variety of structures (shells, rings, holes, bubbles, filaments and arcs) over a range of scales from a few arcseconds to tens of degrees can be particularly well studied by H-Alpha imaging.

Survey Availability

The survey will be made available to the astronomical community as quickly as possible. The consortium will help determine field priority selection and have some initial scientific exploitation rights. All original films will be scanned on the SuperCOSMOS machine at 10µm resolution to


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