No 75 October 1995
2dF Official Opening Ceremony
The assembled guests at the 2dF opening ceremony watch as the instrument rises up to be placed on the telescope. The ceremony marks the last stages in the completion of 2dF, with full commissioning due to start early next year. David Malin gives a personal account of the ceremony inside, and Keith Taylor and Russell Cannon also sum up the current status of 2dF.
The last quarter has seen some momentous developments at the AAO, developments which are themselves partly responsible for the delay in the appearance of this issue. The most important public event was the opening ceremony for the 2dF facility, held in the AAT dome at Siding Spring on Monday, 20 November. Reports on the day's activities appear elsewhere in this Newsletter; it was surely an occasion which most of those who got there will remember for the rest of their lives, but in the end the assembled guests, visitors and staff were treated to a virtuoso display of the whole 2dF top-end being mounted on the telescope. The week prior to the opening was used for 2dF commissioning, as described below, when a great deal was achieved despite some atrocious weather. To make life even more interesting, interviews for the AAO Directorship were held during the same week as the 2dF opening ceremony, but the outcome of that process will not be known until after this issue has gone to press. Russell Cannon
From Underneath to Over the Top.
Rising like some wayward lunar module, the dark shape of 2dF emerged slowly into view through the huge hatch in the main floor of the AAT dome. It rose to the strains of the theme from Kubrik's 2001, over-the top-music made even more majestic by the weird acoustics of the dome itself. Its stately arrival was watched by a crowd of almost 200 people, an assembly that included guests from the local community, staff and their spouses, friends of the AAO, distinguished visitors from Australia and overseas, board members and prospective directors of the AAO. They looked on as Russell Cannon introduced Keith Taylor, the 2dF's Project Scientist. Keith told us why, how and by whom the mysterious edifice before us was conceived, designed and built.
Ian Corbett, Lawrence Cram, Michael Pitman, Russell Cannon and Keith Taylor watch as 2dF is positioned on the telescope.
Keith Taylor was followed by Lawrence Cram, Chairman of the AAT Board, who explained what a remarkable acheivement we were witnessing, and by Ian Corbett from PPARC, who emphasised the importance of the project to the continued success of the AAT. The `opening' itself was performed by Professor Michael Pitman, Australia's Government Chief Scientist, who remarked on the wonderful combination of engineering, technology and pure science that was embodied its construction. He described the dome as a cathedral of science, with the 2dF as its focus. The ribbon cut, the enigmatic structure rose high above the assembled guests and was attached to the top of a floodlit AAT, which then slewed slowly to the south so the 2dF hovered over the assembly below in a graceful, imperious bow. Those of us of practical mind were worried about an assembly of a different kind, that holding the 2dF in place, but nothing amiss occured. Champagne appeared, and the telescope slewed to the north as 2dF made itself more accessible to those who had gathered at prime focus access.
Many stories remain be told about the conception, design and construction of this remarkable instrument. Even the opening ceremony produced its traveller's tales, but the 2dF is likely to remain the most complex instrument ever attached to a major telescope for a long time to come. Its construction has demanded the full engineering and technical resources of the Observatory for almost five years and there is no-one at the AAO that has not contributed something to it. We are proud of what we have achieved and now fervently hope the thing works as flawlessly as the lunar module, and not only in Apollo 13's `lifeboat' mode. David Malin
The 2dF team was able - just - to get a complete hardware system on the AAT for the first time in mid-November. While the full complement of 2 x 400 fibres are ready, we chose to mount only a third of them for this run and concentrated on bringing just one of the spectrographs into commission. The week prior to the opening ceremony had been allocated for engineering tests of 2dF, the principal objectives being to verify the astrometric accuracy of fibre placement, to test the autoguider system software and if possible to get some real spectra. In the event the weather was entirely consistent with previous experience during 2dF commissioning runs, yielding only an hour or two on one night when the dome could even be opened. The time was not wasted since the engineers made excellent use of the opportunity to test many aspects of 2dF while it was in action on the telescope. (It was suggested, however, that we could generate a significant secondary industry by hawking the 2dF to various drought-stricken areas of the state!)
There remains much to be done; although the first spectrograph has been assembled and the first laboratory spectra have been obtained, optical alignment has still to be refined and its electronic control system installed; the second spectrograph is close on the heels of the first. Great strides have been made recently in controlling the positioner; it now operates smoothly, reliably and very fast. However, before we can begin to tackle the massive surveys for which the instrument was built, considerably more tests and some tuning are required not only to achieve the demanding configuration time specification but also to accumulate sufficient confidence in its performance and reliability. Thus although very little clear time occurred during the November commissioning run, Keith Taylor as Project Manager took the decision to bring the positioner assembly back to the Epping Laboratory rather than wait for more cloudy time in December. The time originally allocated for 2dF commissioning in January had already been re-allocated to approved PATT and ATAC back-up observing programmes. The whole 2dF should make its final journey back up to Coonabarabran in about three months, ready for astronomical commissioning early in Semester 1996A. Russell Cannon and Keith Taylor
10m Polarisation Map of NGC1068
NGC1068 is perhaps the best studied of all active galaxies because of its proximity and luminosity. It was the first Seyfert 2 in which broad permitted lines were observed through the use of spectropolarimetry, revealing the underlying Seyfert 1 core, and giving the unified model of AGN a significant boost. The image shown above is the first ever 10m polarisation image of an extragalactic source. It was obtained using the ADFA mid-infrared camera/polarimeter NIMPOL on the AAT. The image is essentially diffraction limited (). Total on-source integration time to derive the polarisation vectors (shown in white) was four hours. The signal-to-noise on the image itself at the peak of the emission is over 1000. The low level continuum emission shows considerable extension along the axis of the radio jet (which runs NE and SW from the nucleus).
The polarisation present is due to emission from aligned dust grains. The
magnetic field runs perpendicular to the polarisation vectors. The perceptible
increase in polarisation away from the centre may give evidence for dilution
from an unpolarised underlying point source on the nucleus. It is unclear as
yet whether or not such a source could be the active core itself, or merely
even hotter dust that obscures the central accretion disk. High spatial
resolution K band data (not
shown) shows the same dust screen but this time as an obscuring source, with
polarisation arising from dichroic absorption of the background light. The
polarisation at K is almost exactly perpendicular to that at 10m as
expected in such a model.
Stuart Lumsden, Joss Bland-Hawthorn (AAO)
Toby Moore, Craig Smith and Tak Fujiyoshi (ADFA)
David Malin has, with his usual eloquence, described the 2dF Official Opening Ceremony and all its excitement above. I'd like to express my admiration for the efforts of Keith Taylor, in his dual parental capacity as Project Scientist for 2dF, and Daddy of a beautiful daughter, Olivia, and the AAO staff in this challenging project. It was a truly exciting experience for all of us. To Llew Denning and the AAT team congratulations on the organisation of a magnificant 2dF opening ceremony. Many thanks to John Dawe and staff for their assistance on the day. And our sincere gratitude to Margaret Noy and staff for the wonderful lunch they provided for 170 people. A grand opening for a magnificent instrument.
Turning to staff matters, Fred Watson returned to the Schmidt Telescope in mid-August in his new role as Astronomer-in-Charge. We are all delighted to have you with us again Fred, and FLAIR is too. Many thanks to Malc Hartley for his acting A-i-C expertise.
Jessica Chapman has also slotted into a slightly different role. A new joint AAO/ATNF part-time position has been established and Jessica will hold this position for the next two years.
Sadly, several AAO staff have either recently left, or their departure is imminent. Mark Noonan was given a farewell BBQ prior to his return to Melbourne with his family. Mark was one of the technicians who spent many months working on the electronics for 2dF. We wish him and his family well and the best of luck with his continuing studies. Shanta Goundar decided she would prefer part-time work and left the AAO in October. Our new Receptionist is Victoria Thompson. Victoria has settled in very quickly, dealing with the many and varied duties of this position cheerfully and efficiently.
Imminent departees are Robyn Shobbrook, Librarian, and Carol Carmichael. Robyn has decided to retire in December so she can join Bob, just recently retired. Together they have a multitude of plans for the future. Many thanks Robyn for your untiring efforts over many years which have always ensured the smooth running of the Library. Its reputation, both nationally and internationally, speaks for itself. We wish you and Bob the best of luck for the future. Carol Carmichael, our computer assistant, has secured a position with the University of Newcastle and will be leaving the AAO soon. For the past four years Carol has had to commute from Newcastle to Epping, an all- round trip of four hours daily. As you can imagine the prospect of a 10 minute jaunt to Newcastle University is something Carol is looking forward to. Sadly, the Scottish accent and effervescent personality will also depart with Carol.
Visitors to the AAO include Peter Brand, from ROE, on twelve months sabbatical. Peter is based at Epping but is also undertaking research with Michael Burton at UNSW. Ram Sagar, from the Indian Institute of Astrophysics, Bangalore, spent six weeks at the AAO, working with Russell Cannon on globular clusters.
Finally, an unforgettable BBQ was organised to celebrate the forthcoming marriages of Lew Waller and Akhila, and James Wilcox and Kate. James was presented with a pair of his underpants (complete with seaweed) which were unceremonously taken from him during the ``boys night out'' on Sydney Harbour. James was left marooned in the altogether on Shark Island for an hour. Lew was presented with a brand new pair of red underpants, covered in gold sequins, which Carol Carmichael assured him would be most appropriate to wear under his white suit on his wedding day. Lew said he wasn't sure whether he should show them to Akhila. Annette Callow
Letter From Coonabarabran
Very quiet it's been, with some very peculiar weather, but for all that there has been some solid work done on the observing front.
Of course, the 2dF people have been flat out, and the pace frenetic. With the Big Day fast approaching ( Editor's note: Rhonda wrote this before the opening ceremony so graphically described by David above) for its inauguration all stops are out to have it prepared -- suitably grand and impressive music has been chosen, guests invited and lunch bespoken for all concerned -- it should all be very dramatic.
Also very busy at the telescope, and mostly responsible for bringing foul weather, have been the adaptive optics people from Sydney University. John O'Byrne, Julia Bryant and Robert Minard are here so often now they have become part of the furniture, adaptive optically of course.
A very popular visitor from Hughes Aerospace was Tony Danks, a very tall person with a great fund of stories and who paraded the corridors in either red shorts and singlet or black tights. It might be true to say that the AAO has not seen anybody quite like him before -- when he left Coonabarabran he was going to an opera at the Sydney Opera House and we cannot help wondering whether he wore the red shorts or tights -- that would have stirred up the stuffy Sydney-siders no end. Tony spent quite a bit of time in Coonabarabran trying to find a boomerang that was not manufactured in China!
Very welcome also was the very knowledgeable astronomer-to-the-masses, John Dobson. John had a very successful visit generally to Australia, visiting schools and showing children how to grind their own mirrors and it was good to see him at Siding Spring. Rhonda Martin
Instrumentation at the Schmidt Telescope
The proposed filter described by Quentin Parker below is just one of a number of instrumentation initiatives currently getting under way at the Schmidt Telescope. All are driven by potential gains in the science that will be delivered.
The remarkable improvements in FLAIR sensitivity produced by the new thinned CCD (see AAO Newsletter No. 74, page 4) mean that the system's turn-around time for new fields is now limited by fibre set-up time rather than integration time, for the types of project normally carried out. It was a similar bottleneck in the late 1980s (following the introduction of a dye-coated CCD) that led to the introduction of AutoFred and the FLAIR II plateholder design in 1991/92. Both flexibility and observing efficiency now stand to gain significantly from further developments.
Two options for improvements in fibre set-up are currently being costed. Both would replace the existing cemented fibre-ferrules with 2dF-type magnetic buttons. In `FLAIR 2.5', the current computer-assisted manual set-up would be retained, but `FLAIR 3' would introduce a fully-automated off-telescope fibre positioner. Responsibility for these investigations will be taken by Quentin as FLAIR Instrument Scientist.
Besides immediate staff-effort savings, there is a longer-term stimulus behind the deliberations. This is the exciting possibility of using FLAIR to carry out an all-sky galaxy redshift-survey to . The Schmidt Telescope Panel has already invited interested groups to put forward their ideas for long-term FLAIR projects; the invitation is re-iterated here.
At its meeting in June, ACIAAT discussed the possibility of a wide-field focal-surface CCD camera for the Schmidt Telescope. The committee endorsed a proposal that a design study should be carried out, and this is now beginning. As well as investigating the technical and scientific aspects of the new camera, broader strategic issues need to be addressed.
A number of other programmes (including the implementation of the CCD autoguider, procurement of new filters for use with Tech-Pan film, and upgrades to the FLAIR spectrograph) are also in hand. Comments on these or any other aspect of existing and proposed instrumentation for the Schmidt are welcomed from the user communities.
Finally, the Schmidt Telescope group is delighted to welcome the AAT to the `37.5 metredegree club'! With the commencement of 2dF operations, the AAO's two telescopes now have almost identical (and huge) values of the product, representing a truly formidable combination for wide-field astronomy. Fred Watson
UKST News: A major new UKST Tech-Pan survey of the Galactic plane
planned in light
Although no new whole hemisphere sky surveys are planned for the UKST in the medium term a proposal for a major new UKST survey of the Galactic Plane using an interference filter mosaic has been approved by the Schmidt Telescope Panel or `STP' (subject to the availability of suitable filters). The survey will use Tech-Pan film. Originally instigated by Parker and Hartley at the UKST and Phillipps at Bristol the project has now grown into a major bi-national collaboration involving the AAO, University of Wollongong (headed by Bill Zealey) and University of Sydney in Australia and the Universities of Bristol and Cardiff and the ROE in the UK. The survey will be made available to the entire community in a timely manner. It is intended that superCOSMOS will scan the original films before a CD-rom Southern Galactic Plane atlas of pixel data is produced (exact resolution still to be decided).
The initial plan for a full aperture objective filter mosaic is now looking increasingly unlikely due to the extreme optical specifications required and the resulting costs. A study is currently underway to determine the best optical performance that can be obtained with high quality interference filters placed at the focal surface. However initial tests with existing focal surface filters and Tech-Pan have already indicated that significant information gains over previous imaging are achieved. A suitable vendor has been identified to produce the new filter components to the rather stringent optical tolerances that will still be required.
Such a survey, taking advantage of the improved resolution and sensitivity of Tech-Pan film (which has a handy peak at ), should provide unprecedented and detailed mapping of the southern Milky Way in light and will undoubtedly lead to many new and exciting discoveries. Indeed large areas of the Milky Way have yet to mapped at all at these wavelengths. At current progress with filter specifications etc, it is hoped that the survey can commence in 1996 to take advantage of the gaps in the UKST survey program that are now opening up. Watch this space for further news or contact firstname.lastname@example.org. Quentin Parker
Charge shuffling with CCDs
In an earlier AAO newsletter (no. 74), we introduced the new Anglo-Australian Tuneable Filter (AATF) facility. One of the proposed modes is charge shuffling and frequency switching (CSFS) which will permit us to obtain FORS-quality, low-resolution spectra at every position within a 10 3.3\ field. With this approach, there are no seeing losses and the spectral bandpass is of order 2000Å. This requires that we shuffle charge to-and-fro (``va et vient'') on the chip as we switch between a broad (100Å) and narrow (10Å) bandpass with the tuneable filter (Fig. 1). Averaged over 10-20 shuffles, in each frame, we spend 90% of the exposure observing through the narrow (``on'') bandpass and 10% in a broad (``off'') bandpass which is used to correct the narrowband sub-images for atmospheric variations. Charge shuffling loses two-thirds of the potential field but requires only a small overhead in exposure time. Many astrophysical applications do not require the full 10 field as we will demonstrate in future issues of AAO Newsletter.
Figure 1: The planned strategy is to shuffle charge on the chip backwards and forwards at the same rate that the AATF plates are scanned between a broad bandpass and a narrow bandpass. The chip is read out only once. In this way, we can build up a series of images sequential in wavelength but where the upper third of each frame is a short exposure (broad bandpass) of the same field at the same off frequency. The point sources in the broad bandpass allow the narrow bandpass subimages to be scaled to the same exoatmospheric scale.
Modern CCDs are buried channel devices where charge packets are confined to a channel that lies beneath the surface of the silicon. An extra n-dopant is applied to the surface to reshape the potential well so that electrons are forced to collect below the Si-SiO interface. Thus interface traps which drastically lower the efficiency of surface channel devices are largely avoided. This gives the buried channel device a much higher charge transfer efficiency (typically 99.999%). However, electron traps do exist in buried channel devices and are the main obstacle to our new charge shuffling mode (see Fig. 2). For ground-based observations, the most important trapping site is the `bulk trap'. These are due to deep-level metallic impurities or lattice defects associated with the silicon material on which the CCD is built. Bulk traps that happen to lie within the charge transfer channel will trap only single electrons.
Figure 2: A 20 min dark frame shuffled (a) 10 times, (b) 100 times, (c) 1000 times, (d) 10000 times. The effect of bulk trapping sites becomes apparent after shuffling more than 100 times.
Electron trapping sites. The charge transfer efficiency (CTE) is a measure of the ability of the device to transfer charge from one pixel to the next. For well-made buried channel devices, the CTE will be in the range of 0.99999 to 0.999999 for strong signals ( e). If we assume a CTE of 0.999999, for a CCD of 1000 pixels on the side, 99.4% of the charge that was originally in the pixel furthest from the output will actually be read out for that pixel (this assumes 2000 pixel transfers where each pixel requires three transfers in a three-phase clocking scheme). We find that the CTE for our Tek chips may be significantly better than 0.99999 since shuffling allows us to examine the loss of charge over many shuffles. The sharp response of a bright cosmic ray suffers substantial leakage into neighbouring pixels after 100 shuffles or more.
Charge shuffling. More generally, the charge shuffling mode enables the astronomer to build up a CCD exposure comprising several on-chip charge movements made, generally, into and out of an aperture of a masked CCD. The state of an external device (etalon, filter wheel, polariser, telescope position, chopping secondary, etc) may be synchronised to these movements (shuffles) as can the opening and closing of a shutter. Alternatively, no mask may be used, resulting in superimposed images from each of the phases, these images being separated spatially by the vertical shuffling. Also, the shutter, opened at the start of the exposure, may be left open throughout the charge shuffling process and closed at the end of the exposure prior to reading out the CCD.
Charge-shuffled exposures may range in complexity from the simplest two-image shuffle comprising only 2 phases per cycle, through to a large number of image phases each comprising a chopping between two conditions. A very fast flash facility which fills the CCD in a single burst over a short interval is also available to, for example, sample transient phenomena, e.g. occultations at rates almost down to 1ms, if required.
The external device (etalon, filter wheel, polariser, telescope position, chopping secondary, etc.) responds to sync pulses from the micro and must be programmed and set up in such a way that the series of sync pulses will cause the external device to cycle through a known and predetermined sequence of conditions corresponding to each shift of the charge on the CCD.
Shutter operation. A choice between shuttered or unshuttered exposures is available. A shuttered exposure enables unsmeared exposures to be made with a maximum phase time of 650 seconds. However the shortest opening times and maximum repetition rates (max may be 10Hz for physically small shutters) of the particular shutter being used and even perhaps how rapidly the shutter might wear out may limit phase times to relatively long values.
Unshuttered exposures open the shutter at the start of the exposure and close it at the end just before the CCD is read out. These exposures offer phase times that may be very short (down to about a millisecond) but may suffer from objectionable image smearing, depending how rapidly the CCD charge shifting occurs (CCD dependent) and how much of the phase or cycle time is used in moving the charge.
Phase definition table. A charge shuffling sequence is specified by a phase definition table which has been generated by the observer in an editing session. The table is downloaded to the CCD controller when setting up a shuffle readout. The table comprises a number of phase definitions. Each line of the phase definition table enables or disables the following operations to be performed for that particular phase:
On issuing the run command several other parameters are sent to the controller. These are (i) the number of repeat cycles to be done (the repeated part of the phase table is the running sequence portion; the start and end sequences are not part of the cycle); (ii) the resolution of the phase time and exposure time clock can be set from 1s to 10ms; (iii) a minimum phase time to be used in bias frames; (iv) a delay time associated with the settling of the external device; (v) a selection of either the internal clocks or hardware sync inputs (two off) or a combination of both used to start and stop the exposure and to time the phases; (vi) a control byte defining the shutter action and whether a normal exposure, dark frame or a bias frame is requested (the shutter action determines whether the shutter opens continuously - unshuttered phase - or whether it is opened and closed each phase - shuttered phase).
Figure 3: A demonstration of charge shuffling with four LED sources illuminating a Tek chip.
A laboratory demonstration of charge shuffling is shown in Fig. 3. The right panel shows the result of shuffling the left panel 10 times by 340 rows up and down. There are no useful data on the lower third of the chip due to the shuffling process. The integrity of the data is preserved by the shuffle process. We believe that this technique, when shuffling 10-20 times during the course of each 5-10 min exposure, will allow us to reconstruct low-resolution spectra with photometric integrity comparable to or exceeding that of the FORS spectrograph. This AATF mode will also allow high performance for standard on-band/off-band imaging.
We acknowledge micro firmwave developed by Llew Waller, in particular, and
software by John Straede and Don Mayfield.
Joss Bland-Hawthorn and John Barton
For those who haven't heard via the grapevine, this will be my last update on what is happening in and around the AAO library. Yes I have finally decided to join those who spend their days playing golf, water-colour painting, gardening and lunching out. After twenty years at the AAO it is time for a change. Exciting new technology has emerged in recent years and I feel lucky to have experienced a little of what is really a revolution in information access and retrieval. I will follow the future activities of the Observatory with keen interest; the staff and the many visitors have made it a very special place to work. I would like to thank Russell Cannon in particular for his support in my professional endeavours; without it some of my projects like the ``Astronomy Thesaurus'' would not have reached completion.
There is now a World Wide Web interface for the multi-lingual supplement
to the main thesaurus. Dave Fullagar of Mount Stromlo has been responsible
for the conversion and I think everyone should find it very user-friendly.
The software used has made it possible for there to be a fully expanded
thesaurus now for the French, German, Italian and Spanish terms. Thank you
Dave for undertaking the work, it is brilliant. If anyone has any
comments to make on the interactive Web version, Dave would be pleased to
hear from you. To access the WWW version
the address is: URL: http://msowww.anu.edu.au/library/thesaurus/
Marlene Cummins (a collaborator in the compilation of the original thesaurus) of the University of Toronto astronomy library has agreed to post revisions to the thesaurus. If you would like to contribute new terms or suggest changes to existing terms you should contact Marlene via e-mail. Her address is: email@example.com
The next issue of the AAO Newsletter should contain news of my replacement.
Thank you to everyone at the AAO and to all belonging to the astronomy librarians network at home and overseas for your friendship and help over the years. If in my travels I am in the vicinity of an observatory I will surely drop in and say hello.
Robyn Shobbrook (E-mail: LIB)