[ROE home page] [WFAU] [IfA] [ATC] [UKST home page] [AAO home page] [AAO H-alpha page] [Search]

The new AAO/UKST H-alpha survey

N.B. All images above are clickable for a larger version and more information/additional images

SUMMARY

The UK Schmidt Telescope (UKST) at the Anglo-Australian Observatory (AAO). is undertaking an H-alpha survey of the Southern Galactic Plane and Magellanic Clouds using a single-element interference filter of exceptional quality. With a clear aperture of 305mm it is the largest of its kind for astronomy. Used in combination with fine grained Tech Pan film, a survey with an unprecedented combination of coverage, resolution and sensitivity is being produced, superior to any other survey of optical line emission in our Galaxy. The Wide-Field Astronomy Unit (WFAU) of the Institute for Astronomy (IfA) will also be the principal archive centre for the resultant survey data products. The survey began in July 1997 and is expected to take 4 years to complete.

The need for the survey

Despite the importance of star formation in our own galaxy, its variation between galaxies and the need to understand the resultant gaseous emission line structures visible on a wide range of angular scales, little survey work has been undertaken in a form that combines both large area coverage, high sensitivity and good resolution. The nearest star forming complexes may lie as close as 100pc with sizes of tens of parsecs. Such structures often subtend angular sizes of a degree or more yet exhibit fine detail at arc-second level. To study the interaction of these ionized structures with their large scale environment we need surveys of considerable extent at good angular resolution. Most work to date has concentrated on relatively small regions for specific study at high spatial or velocity resolution or very large areas at low resolution. It is only now that surveys are beginning to simultaneously tackle issues of coverage, sensitivity and resolution in either a spatial sense (this survey) or in velocity space (e.g. the Reynolds et al WHAM survey) There is a clear need for a high angular resolution optical survey to complement studies at other wavebands.

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 ionized 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 couterparts 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.

The only previous UKST H-alpha survey work dated from the late 1970's (Davis, Elliot & Meaburn, 1976) which used mainly coarse grained (though fast) 098 emulsion and a far from optimum filter. Many parts of the Galactic plane were unsurveyed at decent resolutions, particularly the outer extensions beyond a few degrees from the Galactic equator, whilst the Northern Milky-Way above Dec -20degrees has not been covered at all. Progress in other wavebands highlighted the paucity of the optical counterpart for the detailed study of Galactic gas.

CCDs cannot yet provide the combination of wide-area coverage, uniformity and high resolution required. The new AAO/UKST H-alpha survey fills this gap by combining an exceptional quality H-alpha narrow-band filter in combination with fine grained Tech-Pan films as detector.

Table 1 gives a list of most of H-alpha surveys currently underway and known to the authors together with the KYOTO survey (Kogure et al. 1982) as an example from the older photographic work.

The CTIO based robotic `El Nano' telescope is also currently mapping the Southern Sky in H-alpha light with a resolution of 45arcsec/pixel.

Our new survey will clearly contribute much to the detailed investigation of star formation and the general ISM in terms of its coverage and resolution.

Survey Details

The H-alpha survey is a new, non-proprietorial, fully supported AAO/UKST survey

It is the first narrow-band survey to combine large area coverage, sensitivity and good (arcsec) resolution

Survey includes 233 Galactic Plane and 40 Magellanic Cloud fields on 4-deg centres

Survey commenced in July 1997 and will take ~4 years to complete

The H-alpha survey exposures are 3 hours duration and the contemporaneous short red (SR) exposures 15 minutes

Community access will be via an on-line atlas of SuperCOSMOS data from original film scans

Both H-alpha and matching contemporaneous short-red `SR' films will be scanned

The WFAU of the IfA will act as the data repository (like STScI for the DSS) with access via a www interface

This is the first time a UKST survey will be released to the astronomical community in digital form

Survey Phases

There are 4 distinct but overlapping H-alpha survey phases:

The H-alpha survey observational phase (July 1997- early 2001)

SuperCOSMOS scanning phase (l999-2001 desirable)

The digital data calibration process (2000-2001)

Release of on-line digital survey products to the community (2000-2001)

The H-alpha filter and Detector

The survey is being undertaken with a specially commissioned narrow-band interference filter together with fine grained Tech-Pan film-based emulsion as the detector. CCDs cannot yet match the wide-area coverage, uniformity and resolution of the UKST/Tech Pan combination for undertaking a Galactic Plane H-alpha survey.

The Filter

BARR Associates provided an interference filter of exceptional specification and quality that covers a substantial fraction of the UKST's large field. The choice of central wavelength (6590 Angstroms) and bandpass (70 Angstroms) work effectively in the UKST's fast f/2.48 converging beam. The 305mm diameter filter is coated on a 356 x 56 mm RG610 (red) substrate giving a 5.5 deg diameter field. Peak filter transmission is >85%.

The CSIRO National Measurement Laboratory in Sydney, Australia have independently confirmed that the filter meets the stringent optical specifications set. The superb optical quality of the filter was demonstrated on the telescope during survey commissioning during April 1997. H-alpha exposures taken in good seeing exhibit excellent imaging and uniformity across the entire field and confirmed the clear (circular) aperture of excellent H-alpha sensitivity of close to 305 mm, or a little over five degrees on the sky.

Figure.1a-b gives 5x6 arcminute areas taken from one of the first 2 hour H-alpha test exposures.

Full H-alpha filter specifications can be found HERE

The Detector: Tech-Pan Film

The successful implementation of high resolution, panchromatic Tech-Pan film on the UKST, coupled with its peak sensitivity at H-alpha was a prime motivation behind the new Galactic Plane survey. Generally speaking in good seeing Tech-Pan UKST `R' band exposures go about 1 magnitude deeper than the equivalent standard IIIaF `R' band images with improved imaging, resolution and lower noise characteristics. It is an ideal wide-field photographic detector for use with an H-alpha filter. Further details of the properties of Tech-Pan can be found in Parker & Malin (1999)

Figure.2 gives the IIIaF and Tech-Pan emulsion sensitivities as a function of wavelength which demonstrates that there was no speed, sensitivity or reciprocity penalty in adopting Tech-Pan for use with a narrow-band H-alpha filter c.f. IIIaF.

Tech-Pan's superiority can also be seen in Figure.3a-d which shows various comparisons between results from the new filter/emulsion combination and past UKST exposures taken with other filters and emulsions of the same area of sky.

The high resolution of Tech Pan H-alpha imaging should represent a significant advance in the ability to:

Resolve out point sources from more extended emission
Enable detection of more distant planetary nebulae in the Magellanic clouds.
Determine accurately surface brightness and its variations in extended regions.
Provide better definition of the sharp shock fronts seen around ionized gas clouds.
Investigate in more detail the morphology and environment of Herbig-Haro objects and find more distant or less extended examples.

Survey planning and logistics & tie-ins with other surveys

The new survey, timely in respect of telescope loading, commenced in April 1997.

A map of the proposed Galactic-Plane area that will comprise the new survey is given HERE.

This map should be updated every month. The coloured fields denote the survey area. The code is: blue (nominal `a' grade obtained), pink with diagnonal line (nominal b-grade film available), light blue (c-grade film available). Yellow fields are currenlty outside the survey area. Note that the exposure grading represented in the maps does not yet reflect proper survey quality control (QC). The maps will be updated once proper QC grading is available. Also note that the 40 fields in and around the Magellanic Clouds are not shown on this map as they have their own distinct 4-degree field centres. A seperate listing of their field centres is given HERE.

A better quality postscript version of the Galactic Plane survey field map can be obtained HERE.

Given the filter's 5.5 degree circular field, normal UKST 5 degree field centres could not provide full contiguous H-alpha sky coverage due to the 1.5degree overlap between the 6.5x6.5 sized fields. A small 1degree area in the overlap regions was missed. We have thus adopted a conservative 4 degree field centre separation which ensures no gaps in H-alpha coverage. Consequently 233 such fields are needed to cover the Southern Galactic Plane. This may later be extended to the outer regions of the Galactic Plane and to declinations from +0 to +15 degrees. Exposures are of the order of 3 hours and the initial survey region will take about 3 years to complete. Although not sky-limited, the 3 hour exposure times are a good compromise between survey progress and exposure quality due to the increased likelihood of seeing variations, cloud interruptions and effects of field rotation.

The narrow-band nature of the H-alpha filter means that the survey could continue in good seeing grey/bright time when the sky is too bright for normal observations.

The photometric integrity of the survey is currently being assessed via independent narrow band CCD photometry from the Curtis Schmidt at CTIO and with reference to previously studied objects over a range of UKST fields.

Tie-ins with other surveys

Of particular interest on the large scale will be comparisons between H-alpha emission and other indicators of interstellar gas and/or star formation activity. These include giant molecular cloud complexes and the general molecular ISM traced by CO observations, radio continuum emission, gamma-rays, HI, dust clouds or IRAS far infra-red flux. This survey should complement the radio maps from the ATNF and MOST, those of the new Parkes HI multibeam survey, the NIR maps from DENIS, 2MASS and the MSX satelite as well as those from mm wave telescopes here and overseas.

The prospects for collaboration and comparison from studies in other wavebands are excellent. Any interested groups or individuals are encouraged to contact the H-alpha survey consortium or the Wide Field Astronomy Unit at ukstu@roe.ac.uk for further information.

The roles of the AAO and WFAU

Given the location of SuperCOSMOS within the new WFAU and the presence of key personnel the WFAU/IfA will play a crucial role in ensuring proper exploitation and dissemination of the survey data products. The WFAU will be closely involved in survey scanning strategy, on-line digital atlas construction, data quality control, archival of both film and pixel data and crucially community access to the H-alpha survey data products via a suitable www interface. Full survey Quality Control is also being carried out on the survey material when it arrives back at the WFAU.

Apart from providing the filter the AAO has prime responsibility for undertaking the survey on the UKST and to provide basic support for the survey as well as the day to day operational tasks such as processing, initial quality control and shipment of the film material to the WFAU for archival and SuperCOSMOS scanning.

Survey Availability and requests for new material

The survey has been designated as a fully supported AAO survey to maximise the survey's availability and usefulness to the community and as such there will be no proprietary period on the survey data.

Rigorous quality control of the survey is being undertaken to ensure that as far as possible a survey of uniform quality and depth is obtained.

It is intended that the WFAU will produce a digitised survey map of 10micron resolution pixel data which will be released to the astronomical community via a suitable www interface. Unlike previous UKST surveys film copies of the survey material are unlikely to be available.

The current status of survey films scanned by SuperCOSMOS is given here.

This list only includes survey `A' grades after the application of proper survey quality control but is for both the H-alpha and SR exposure pairs of each field.

Requesting H-alpha exposures on non-survey fields

The community is invited to submit proposals for particular fields that are not part of the survey area if they would like H-alpha imaging in special non-galactic plane/Magellanic cloud regions. Potential users of the survey material are encouraged to contact the AAO or WFAU for further details (see below).

UKST photographic application forms can be obtained HERE

General contact details for queries etc are:

 UK applicants 

Mike Read                             Tel: 0131 668 8328 
Wide Field Astronmy Unit,             fax: 0131 662 1668
Institute for Astronomy,            email:ukstu@roe.ac.uk
Royal Observatory
Blackford Hill, 
Edinburgh
EH9 3HJ

 Australian applicants 

Paul Cass                             Tel: 061 68 42 6316/6291
AAO                                   fax: 061 68 84 2298
Coonabarabran                       email: cpc@aaocbn.aao.gov.au
NSW 2357
Australia

Other nationalities can apply to either panel.

Preliminary H-alpha image comparisons

New images from the new H-alpha filter

An impression of the significant information gains from the new Tech-Pan H-alpha filter combination compared to previous UKST H-alpha imaging is presented in the figure below (parts a-d) of an identical 6 x 5arcmin area in an interesting LMC emission bubble from 5 different UKST H-alpha exposures taken with a range of filters/emulsions and exposure times. Figure `a' (top left) is data from a 2 hour Tech-Pan exposure with the new filter whilst figure `b' (top right) is an 80minute equivalent (same emulsion and filter). There is a dramatic increase in information in the longer exposure with no degradation in image quality. Figure `c' (bottom left) gives a 90 minute exposure through the old 120 Angstrom FWHM AAO656 10inch H-alpha filter with the fast, coarse-grained 098-04 emulsion. This is the worst performing combination for tracing/discovering the fine detailed structure visible in the new exposures. Finally Figure `d' (bottom right) is a 3 hour exposure taken with the same AAO656 filter with the standard IIIaF red-sensitive emulsion. Despite the wider passband and longer exposure the depth and detail of the Tech-Pan new filter equivalent in Figure `a' is far superior.

Figure a-d. H-alpha imaging comparisons between new and old H-alpha data

The H-alpha Survey Consortium

The H-alpha Survey consortium was set-up by the PI's of the original approved H-alpha survey proposal (T/1049) to ensure a coherent exploitation plan by the scientists closely involved in pushing for the survey. They have played a key role in the planning and overall shape of the H-alpha survey but have no proprietary rights to the survey data. They retain an interest in ensuring that the survey is well defined, efficiently undertaken and carefully produced so that the maximum scientific use can be obtained by the community from the released data products.

Although they have no formal responsibilities wrt the H-alpha survey the consortium has nevertheless endeavoured to do the following:

To promote the H-alpha survey to the community via the www, articles, an international workshop and scientific papers

To, where necessary, provide feedback and advice to the AAT Board, AAO and WFAU management and the Wide Field Astronomy Panel (WFAP) on the scientific strategy, dividends and opportunities offered by the survey

To undertake scientific evaluation and exploitation of the survey material including obtaining CCD calibration data for every survey field

To provide via the co-PI's the overall scientific leadership of the survey

Consortium Membership

Principal Investigators: Q.A.Parker (WFAU) qap@roe.ac.uk and S.Phillipps (Bristol) s.phillipps@bristol.ac.uk

Prof.W.J.Zealey, + Stacy Mader & Andrew Walker, (University of Wollongong)

Dr.A.Green & Dr Vince McIntyre (Univ.Sydney),

Mr.M.Hartley, Dr.J.Bland-Hawthorn, Dr.D.Malin, Dr.R.D.Cannon (AAO)

Dr.M.Fillipovic, Dr.G.White + students (Univ.Western Sydney)

Dr.M.Mashedar, Robin Walker & John Precious (Univ.Bristol), Dr.M.G.Edmunds (Univ.Cardiff)

Dr.D.Morgan (Royal.Obs.Edinburgh).

Survey Discoveries and Projects

Selection of current projects underway within the H-alpha survey consortium

Simple visual scrutiny of the H-alpha survey films reveals stunning detail and imaging which has already resulted in the discovery of many new features and objects. A variety of different projects are underway to exploit the survey resolution, coverage and depth which have already resulted in a range of discoveries and publications. Most results so far are from visual scans of the survey material which bodes well for the provision of digital data which is now becoming available. A selection of some of the most important on-going projects are:

Searches for new Planetary Nebulae in the disc and Bulge (Parker et al)

New Galactic Plane Supernova remnants (SNR) project (Walker, Zealey)

Large scale Galactic Plane study (Phillipps, Parker, Precious + consortium)

LMC SuperCOSMOS multiple-exposure field stacking project (Morgan, Parker, Cannon)

Search for Magellanic Cloud emission line objects (Morgan, Parker, Fillipovic)

Herbig-Haro objects in Orion (Mader, Zealey, Parker, Masheder)

Wolf-Rayet stars from the survey (Morgan, Parker)

Comparison with MSX imaging (Cohen, Cannon, Parker)

HII region mapping and comparison bewtween the Marseille Faby-Perot H-alpha survey and the AAO/UKST H-alpha survey (Georgelin, Russeil, Parker et al)

Further details on the various research projects underway (including some discovery images) can be found HERE.

This list above is by no means exhaustive and simply reflects some of the current interests of the consortium and affiliates. The general community is invited to consider their own research projects and are free to contact consortium members for advice, information, collaboration opportunities etc.

A selection of publications in print, in press or submitted can be found HERE in either pdf or ps format.

H-alpha International Workshop
(took place April 16-18th 1997)

A very successful 3 day International Workshop was held in Sydney, Australia from April 16-18, 1997 to highlight the science that can be expected from the new UKST H-alpha survey.The aims of the workshop were primarily to showcase the new survey, to discuss the science likely to be produced and hopefully to generate new ideas and collaborations, particularly in the radio and millimetre regimes (and hence to tie in with these associated surveys). It became clear that our new survey would set the benchmark for wide-field high resolution imaging of our Galaxy in ionized gas. The workshop proceedings appeared in a special issue of `Publications of the Astronomical Society of Australia' PASA . which is a refereed journal (Volume 15, No.1).

Details concerning the workshop and proceedings can be found HERE

Pages maintained by: Dr. Quentin A Parker (H-alpha Survey manager, WFAU, IfA)

e-mail: qap@roe.ac.uk

Last revision: 23rd October 2000