AAO Newsletter


No 76                                                                                           January 1996


Taurus Tunable Filter


The end of conventional narrowband imaging?

A demonstration of the new TAURUS Tunable Filter (TTF) and charge shuffling/frequency switching recently developed at the AAO. The top panel shows the planetary nebula NGC 2438 in a 10Å bandpass centred on [SII]6731, the lower panel at [SII]6717. In an exposure time of 12 mins, the TTF was switched between two discrete frequencies 18 times, synchronized with charge being shuffled up and down on the Tek 1024 chip. The charge is read out only once. See p. 10 for more details.


Director's Message

I had not intended to write a special message for this issue of the Newsletter but several very significant events have occurred. The AAO has lost two long-serving staff members: Annette Callow, my Personal Assistant since 1986, very sadly died suddenly on the 26th of January; and Robyn Shobbrook, AAO Librarian since 1975, retired at the end of the same month. Both women played major roles in defining the character of the Observatory, particularly for external users and visitors. Also in January, the Board announced the appointment of the new Director, Brian Boyle, who is due to take over in September. These important changes at the AAO are taking place against a backdrop of continuing negotiations for Australia to join the European Southern Observatory and participate in the VLT project, and as this issue goes to press the Australian Minister of Science, Senator Cook, has just announced his Government's intention to provide funding for this. There will however now be a hiatus in the discussions, pending the outcome of the Federal elections at the beginning of March. Meanwhile the scientific work of the AAO continues, with the latest highlight being the introduction of a revolutionary new technique for high precision narrow-band imaging of faint sources, as reported in the cover story by Joss Hawthorn. More on all these developments can be found elsewhere in this issue. This is therefore a time of challenge and change at the AAO, but we are confident that the Observatory has an exciting future and will continue to provide its users with world-leading facilities for the advancement of astronomy.


Annette Callow

As many of our readers will know already, Annette Callow died suddenly and completely unexpectedly, at home, on Friday the 26th of January. Although she had been slightly ill there was no indication that anything was seriously wrong and indeed it is still not clear whether there was any connection between that and her death, whose cause is unknown. However the simple fact is that she is gone. Her funeral on the 31st of January was attended by many AAO staff from both Epping and Coonabarabran, and by other astronomical colleagues and friends. As news of her death has spread through the international astronomical community we have been inundated with messages and expressions of sympathy; let me take this opportunity to thank everyone on behalf of the AAO.

Annette joined the AAO early in 1987, coming from the Law School at Macquarie University, and so had been my Personal Assistant for nine years. But she was much more than just the Director's PA. She worked with all the senior staff of the Observatory and with the whole team of Research Astronomers, acting sometimes as a secretary, sometimes as an advisor or even confidant, especially for new arrivals and younger staff, but always as a friend. She was also for many people the public face of the AAO, in that she was the first point of contact for many of our colleagues, visitors and outside organisations. Annette was unfailingly helpful and cheerful in her dealings with other people, always trying to solve problems and willing to make an extra effort on their behalf. And although she was always friendly and good natured, she was a very determined person who would fight hard for what she believed in

One of Annette's biggest recent jobs was handling the bulk of the invitations and travel arrangements for the official opening ceremony for the 2dF in Coonabarabran last November, a great success despite appalling weather on the day. And although my signature appeared on most of the notes, it was Annette who initiated and organised the annual distribution of AAO calendars. This was her idea, given my lack of enthusiasm for corporate Christmas cards and her conviction that an organisation has to have a way of saying `thank you' to its clients and friends. She also of course contributed the regular Epping `Gossip column' to this Newsletter.

Although Annette did so much for the Observatory, she gave even higher priority to her duties as a wife and mother. Our loss is great, but small compared with that of her family and especially her husband Neil, to whom she was devoted; our thoughts go to them.

Annette's death has reminded us all once again how tenuous is our hold on life; the typical modern life expectancy of over 70 years is just that, a statistical expectation, not a personal guarantee. But the memory of her personality, and the example she set, will live on; Annette was truly one of the people who made the AAO the kind of place it is today and we will endeavour to maintain the traditions she helped to establish. Russell Cannon


AAT Board News

AAO Director

The Anglo-Australian Telescope Board is pleased to announce that Dr Brian Boyle has accepted the position of Director of the AAO, and is expected to commence in September 1996, when Russell Cannon will complete his second five year term in the post.

Brian Boyle is currently a senior scientific officer at the Royal Greenwich Observatory, Cambridge, UK, a position he has held since October 1994. He graduated with a BSc (Hons) from the University of Edinburgh in 1982 and obtained his PhD from the University of Durham in 1986. Since then, he has held fellowships at the University of Edinburgh (86-87), the Anglo-Australian Observatory (88-90) and the University of Cambridge (90-94), including the award of a Royal Society University Research Fellowship from 1990-1994.

His main areas of interest are in cosmology and the properties of active galactic nuclei. Brian Boyle has had a long association with the AAO. His PhD thesis was based on the statistical properties of a large sample of quasars selected from UK Schmidt photographic material and observed with the FOCAP fibre-optic system. He has also used the AAO extensively throughout the last 12 years to conduct numerous scientific studies: the clustering of faint galaxies; the nature of galaxies associated with distant quasars; the origin of the X-ray background; the identification of distant supernovae; the space density of low surface brightness galaxies; and is currently the Principal Applicant on a proposal to use the new 2dF system to obtain redshifts for over 30000 quasars, with which to map the structure of the Universe on the largest scales.

AAT Board

From January 1996, Professor Roger Davies of University of Durham is the new UK member of the AAT Board. He replaces Professor Richard Ellis who retired from the Board in December last year. Professor Davies will also take over the role of Deputy Chair. The full Board is therefore:

Australia:

Professor Lawrence Cram, University of Sydney (Chair)
Professor Jeremy Mould, Mount Stromlo Observatory
Professor Max Brennan, Australian Research Council

United Kingdom:

Professor Roger Davies, University of Durham (Deputy Chair)
Professor John Peacock, Royal Observatory Edinburgh
Dr Ian Corbett, PPARC

Honour for Dr R H Frater

Congratulations to Bob Frater, Director of CSIRO's Institute of Information Science & Engineering, who was appointed an Officer of the Order of Australia (AO) for services to radio astronomy, particularly for the construction of the Australia Telescope National Facility, in the Australia Day Honours list on 26 January. Bob was Chair of the AAT Board from 1990 to 1993, and a Board member for eleven years, and has remained a strong supporter of the AAO. This is a well deserved award indeed, recognising his longstanding contribution to Australian astronomy.

ATAC Deadline

The closing date for ATAC proposals for Semester 1996B is Wednesday 8 May. Full details will be circulated in early April.

Sandra Harrison


AAT Observations of the Impacts of SL-9 with Jupiter: A Progress Report

Introduction

Between 16 and 22 July 1994, over 20 fragments of Comet Shoemaker-Levy 9 collided with Jupiter. Although the impacts occurred on the far side of Jupiter, just beyond the morning limb, observations of the event were made by almost every major ground-based telescope, and by HST and the Galileo spacecraft. After 18 months of intense debate in the scientific literature and at a series of workshops and conferences, many of the details concerning the impact processes are far from being resolved. However, a consensus on a working model of the impact events has been reached and is described below.

When a comet fragment enters the Jovian atmosphere, a brief meteoric flash (the `first precursor') is observed by ground-based observers. This flash lasts only a few seconds. Approximately 10s later, the fragment explodes deep in the Jovian atmosphere, out of Earth view, releasing a fireball that is observed directly by instruments on board the Galileo spacecraft. One minute after the first precursor the expanding fireball rises over the limb of Jupiter and is seen by ground-based observers as the `second precursor'. This afterglow from the initial explosion takes minutes to fade. Six minutes after the fragment entered the atmosphere, the ballistic ejecta in the collapsing fireball plume impacts denser levels of Jupiter's atmosphere, heating the atmosphere surrounding the impact site to temperatures exceeding 2000K, and producing atomic and molecular emission. This phenomenon is extremely energetic, at least 1000 times brighter than the first precursor, and was dubbed `the main event', or `the splash'. The main event increases in brightness until it reaches a peak in the near-infrared at about 12 minutes after the first precursor, and then fades steadily, as the collapsing plume flattens into a thin impact cloud. This impact cloud gradually rotates into view over the dark morning limb. Approximately 20 minutes after the first precursor, the impact cloud rotates into sunlight and can be seen as a bright scattering source in the near-infrared.

The AAT/IRIS Observing Campaign

As part of the ground-based monitoring effort, we used IRIS on the AAT to observe 8 collisions of the Comet Shoemaker-Levy 9 fragments with Jupiter during the impact week. Spatially-resolved near-infrared spectral image cubes were collected during six of the impact events (C, D, G, K, R, and W), while fast-rate near-infrared photometry was used to monitor the smaller impacts of fragments N and V. Images of the impacts for each of the fragments observed are shown in Figure 1.

Figure 1: The AAT SL-9 `Family Portrait'. Images at 2.3m taken near the peak of the `main event' for all impacts observed at the AAT. North on Jupiter is at the top.

Figure 2: Composition of the K ``splash". The solid line shows a spectrum taken during the splash phase of the K impact. The other lines show modelling results for individual gases in the splash. CO - dotted line, HO - dashed line, NH - dot-dash line. The slight shift between data and model near 2.3m is due to early wavelength calibration problems in the data.

The IRIS data set is unique, providing the only time-resolved spectral description of the entire fragment impact sequence -- from the time the fragments entered the Jovian atmosphere, until their collapsed explosion plumes crossed the limb of Jupiter and traversed the planet's day side. The comet fragments had a wide range of pre-impact brightnesses (and presumably a wide range of masses). The IRIS data can therefore be used to explore the relationship between the pre-impact brightness and the impact energetics, chemistry, and depth of penetration in the Jovian atmosphere. This article summarizes the significant results to date, and describes future work planned for this data set.

Spectral Sequences

For the larger impacts of fragments C, D, G, K, R, and W, IRIS was driftscanned across the disk of Jupiter to obtain spatially resolved K--band (1.98--2.38m) spectra. These spatially (0.6pixel) and temporally (<2 minutes) resolved, moderate-resolution (300 ) spectra display phenomena that are highly time-variable. In the earlier stages of the impacts, the spectra are typically dominated by a red continuum, and CH absorption features at 2.20, 2.32 and 2.37m. During the splash phase of the impacts, the spectra are dominated by emission from several molecular species, including CH (2.20m), NH (2.03m), CO (m), HO (2.0 and 2.3m), and H (2.122m). Figure 2 compares an observed spectrum of the splash with synthetic spectra of the characteristic emission spectra for hot CO, HO and NH in this wavelength region.

Selected K-band spectra from the IRIS observations of the K fragment impact are shown in Figure 3, and are used here as an example of the phenomena that were observed in the majority of these impacts. The panels run sequentially from top to bottom and left to right.

Panel 1 shows a spectrum of the limb of Jupiter at the impact latitude of 45 S. The emission seen between 2.0 and 2.10m is due to reflected sunlight from the Jovian atmosphere. Between 2.1 and 2.4m this emission is reduced by strong absorption from CH in the Jovian stratosphere. Panel 2 shows the first precursor, which manifests itself as a weak blue continuum, most visible in the 2.1--2.4m methane absorption region. Panels 3 and 4 show the second (fireball) precursor, a stronger, redder continuum showing strong methane absorption at 2.2m, and a pronounced `knee' at 2.03m due to NH emission. NH and CH are common components of the Jovian atmosphere, with CH more abundant in the stratosphere than NH. The enhanced absorption by cold CH indicates that we see the fireball through a long path-length in the Jovian atmosphere. Panels 5 and 6 show the beginning of the main (splash) event, which was usually detected 6--7 minutes after the first precursor. CH can still be seen weakly in absorption, as the continuum becomes brighter and redder. Panels 7 and 8 show spectra taken during the rapid increase in brightness just after the start of the main event. CH is now seen in emission at 2.20m, as ejecta from the plume are now in direct Earth view. Panels 9--11 show the emergence of strong emission from hot (2000K) CO and HO, twelve minutes after impact, and some six minutes after the first appearance of CH and NH. The last panel shows the collapsed impact site as it rotates into sunlight. The continuum emission now observed is due to scattering from the impact cloud, which is high in the stratosphere, and relatively unaffected by methane absorption.

The strong molecular emission is most probably produced when the impact plume collapses on the upper atmosphere. The early appearance of NH and CH emission suggests that these relatively abundant Jovian atmospheric constituents are ejected from the impact site at low energies and land first. The delayed appearance of the CO and HO emission implies that these

Figure 3: Selected K-band spectra showing the time evolution of the K impact. Panels run from top to bottom and from left to right. Panel 1 - the limb of Jupiter before impact; panel 2 - the first precursor; panels 3,4 - the second precursor; panels 5--11 - the main event, or splash; panel 12 - the fresh impact site in sunlight. The dashed line is an attempt to fit a blackbody to the spectrum, and the temperature given is an indication of the colour of the spectrum, but does not necessarily reflect the true temperature of the plume.

oxygen-rich constituents are ejected at higher velocities, and travel to higher altitudes before splashing back. One model of the impacts suggests that cometary material will be ejected with the highest velocities. This would imply that the CO and HO observed in the IRIS spectra are of cometary origin, although entrainment of Jovian water from the putative water cloud in the deep Jovian atmosphere is another possible source. However, in light of just-released results from the Galileo probe mission, a cometary origin for the oxygen observed in the IRIS spectra is favoured, as the probe results show the Jovian atmosphere to be far drier than anticipated, with no data to suggest the presence of significant water clouds.

AAT Imaging of the Impacts of N and V

Based on their low pre-impact brightnesses, the impacts for fragments N and V were expected to be significantly less energetic than those for the brighter fragments. Consequently, rather than obtaining spectra of the N and V impacts, we used IRIS to obtain fast rate 2.34m photometric images. For the N impact, the IRIS detector was windowed down to obtain consecutive 0.45s exposures, which were stacked in 100 exposure sets in the large external memory and then dumped, with all the readout time occurring at the end of the exposure set. The resulting N lightcurve is shown in Figure 4. The first 400s of the lightcurve is affected by noise, due to a combination of poor seeing and the proximity of the old D/G multiple impact site, which was rising on the morning limb at the same time as the expected impact for fragment N. Nonetheless, a faint point source at Jovian latitude 45 S can be seen on the morning limb in the image.

Figure 4: The N impact light curve at 2.34m. Each cross is the sum of four 0.45s exposures. The time of the precursor is labelled, and the inset image shows a disk subtracted image of Jupiter with the precursor on the morning (left) limb. The dark and bright patterns on the disk of Jupiter in this image are due to residuals after subtraction of the South polar cap and several previous impact sites. The main event can be seen in the light curve between 400 and 600 seconds after UT 10:28:00. The gap in the lightcurve after this time was due to an instrument failure. The triangular symbols near the bottom of the plot show the timing of the flash observed by the Solid State Imager, on board the Galileo spacecraft. The intensity is not to scale.

The flash is first observed at 10:29:14 UT and fades until it is no longer detected at 10:29:34 UT. At approximately the same time the Galileo SSI camera detected a flash. The near-coincidence of these phenomena may suggest that the N fireball was produced higher up in the Jovian atmosphere than that of the larger fragments, whose fireballs presumably had to rise from deep in the Jovian atmosphere and were seen by ground-based observers minute after they were detected by instruments on board Galileo.

Figure 5: AAT observations of the time evolution of the V impact event at 2.3m.

The V impact was also observed using 2.35m imaging with 0.45s exposures, but IRIS was put into repeat mode, and each exposure was read out separately, with approximately 9 seconds between each 0.45s exposure. This mode precluded the possibility that we would miss the impact, by allowing us to take evenly spaced samples indefinitely, without significant cube readout periods. Continuous repeat mode exposures were taken over 40 minutes bracketing the expected impact time. No flash was detected in real time. However, subsequent data reduction revealed the sequence shown in Figure 5 which shows a weak flash at latitude 45 S, seen in two of the exposures. The timing for this impact flash was confirmed by simultaneous measurements taken by Phil Nicholson at Palomar observatory.

Preliminary Modelling Results

Preliminary attempts have been made to model the IRIS splash spectra using the Atmospheric Radiative Transfer model (ART), developed by Dave Crisp. The splash model currently includes emission from CO, HO, NH and CH gases only (no particulates). The nominal Jovian atmospheric temperature profile for pressures greater than 10 mbar is assumed. At lower pressures (higher altitudes) the model was run consecutively for enhanced stratospheric temperatures ranging from 500 to 3000K. The effects of varying the mixing ratios of CH and HO in the stratosphere were also explored. Two synthetic splash spectra with differing HO and CH abundances are shown in Figure 6.

Figure 6: Synthetic spectra produced by our preliminary model of the impact splash phase. Note that all the emission seen here is produced by gases only. At IRIS resolution, molecular band emission from CH blends together to produce a pseudo-continuum in the spectra. These results should be compared with panels 9--11 in Figure 3.

Principal results of this modelling show that 1) a splash containing ambient Jovian CH abundances produces a spectrum that is far more strongly dominated by CH emission than is seen in our data. CH therefore appears to either be suppressed by the splash process, or a large fraction of the CH emission is reabsorbed by the Jovian atmosphere. 2) although the model contains only gases and no particulates, the large number of absorption lines in the molecular bands, particularly from CH, produce a smooth continuum (at IRIS resolution), similar to that observed in the data after the peak of the main event. However, emission from particulates may still be needed to fully explain the slopes observed in the AAT data, especially in the initial stages of the main event. 3) CO estimates are very sensitive to the CH abundance. When the CH abundances are suppressed (suppressing the `continuum' also), much less CO is needed to account for the observed spectral shape. 4) Calculation of the cooling rates for 2000K shock-heated Jovian stratosphere indicate that it will cool extremely rapidly, (200K/s). As our spectra of the impacts are separated by >40s, the CO molecules seen emitting in one spectrum are not the same CO molecules that are emitting in the subsequent spectrum. This complicates the task of determining the total amount of emitting CO, by requiring that each spectrum throughout the sequence be modelled separately to determine the total emitting CO at that time, and then integrating these values over the entire length of the splash process.

Future Work

Attempts are currently being made to improve the initial photometric calibration of the spectral data, and to prepare the final data cubes for archiving. Modelling efforts are also continuing to improve the splash model and provide a better match to the observations. This will include adding particulates to the model. The improved model will then be used to quantify the emission, and determine the abundance, temperature and spatial distribution of the emitting molecules. These efforts will provide observational input to constrain current physical and chemical models of the impact processes. Vikki Meadows and David Crisp (JPL)


Instrument News

First Light for the AAT Tunable Filter

We report on the outcome of a Director's Night (14/15 Jan 1996) which was used to test the new TAURUS Tunable Filter (TTF) and related concepts, in particular, charge shuffling and frequency switching. In summary, the system works to specification and has the potential to revolutionize how narrowband filter imaging is normally carried out at observatories. The astronomer can now conduct imaging at discrete bandpasses in the range 6Å to 60Å at any wavelength in the range 6500Å to 9500Å (see Fig. 1). The bandpass profile is equivalent to, say, a Barr Associates 2-cavity filter, but the TTF throughput is expected to be significantly better. The author feels that there is little point in purchasing expensive, monolithic interference filters if their properties are within range of the TTF.

The spectral properties of the TTF were summarised in AAO Newsletter 74. At low resolution, conventional R or I band filters can be used to block neighbouring orders. At high resolution, it is necessary to block with a narrower filter (see Fig. 2). Presently, we have four 5-cavity filters (90% transmission) spread out over the spectral range (central wavelength/bandpass in Å): 7100/285, 7600/325, 8150/370, 9100/465. We suspect that these filters, since they are placed between the OH bandheads, will be of interest in their own right. At the AAT, the unvignetted field is limited by the collimator to about 9 at f/8 and 4.5 at f/15. The Tek scales are 0.594/pix (f/8) and 0.315/pix (f/15); the Thomson scales are 0.470/pix (f/8) and 0.250/pix (f/15). The different chip responses are illustrated in AAO Newsletter 62. The Thomson chip has a much weaker fringe pattern at narrow bandpasses compared with the Tek chip. The TTF throughput (including telescope and optics, but not detector) is expected to be 25%. The TTF will also work with Taurus on the WHT: the characteristics of the WHT TAURUS system are available from the ING WWW page.

Figure 1: The expected distribution of allowable bandpasses with the TTF in the R and I bands. At high resolution, a narrow order-sorting filter is required (see Fig. 2). The curves correspond to different spectral orders (m=4 at top).

Figure 2: Currently available order-sorting filters for use with TTF. Conventional R and I filters are also shown.

Tunable filters allow for a range of interesting experiments, not least charge shuffling and frequency switching. This concept was introduced in AAO Newsletter 75. We tried this with both the Tek and Thomson chips with great success. The front cover shows the result of shuffling on two [SII] lines; Fig. 3 shows the result of shuffling on H and [NII]. We will soon be able to shuffle on an arbitrary number of discrete frequencies and bandpasses. Negligible time is lost to the shuffle/switch process, being limited only by the 100mm diameter shutter (0.1s/cycle). A disadvantage of this method is that a large part of the chip area is used for storage. However, this will be overcome with the MIT and EEV 2K4K chips currently on order. The advantages of the TTF are numerous. If shuffled at 2 cycles/min, say, atmospheric and detector sensitivity variations between independent images are averaged out. Furthermore, all bands are observed through the same optical train and the spectral response profile has the same form at all frequencies. Like all filters in all beams, there is a slight phase effect across the field of view, being more severe at narrower bandpasses. Unlike conventional imaging systems, this effect can be calibrated exactly with minimal effort.

Figure 3: A demonstration of the TTF and charge shuffling/frequency switching recently developed at the AAO. The top panel shows the planetary nebula NGC 2438 in a 10Å bandpass centred on H, the lower panel at [NII]6583. In an exposure time of 6 mins, the TTF was switched between two discrete frequencies 9 times, synchronized with charge being shuffled up and down on the Tek 1024 chip.

Generous amounts of time have already been allocated for the TTF at both the WHT and the AAT. If there is sufficient demand for the TTF, we will investigate a system for covering the B and V bands. For further details, please contact jbh@aaoepp.aao.gov.au. Finally, we are indebted to John Barton, Llew Waller and Tony Farrell for their brilliant efforts - while distracted with 2dF issues - in getting the charge shuffle mode operational.

Joss Bland-Hawthorn


IPCS retirement

The AAO is planning to decommission the IPCS detector later on this year. This instrument has been in use for over twenty years and has been used to produce many excellent scientific results. However, the IPCS is now largely superseded by the available CCDs which have far higher quantum efficiencies, and now have low readout noise, and hence provide higher signal/noise data.

At present the IPCS is only scheduled for use with the UCL echelle spectrograph (UCLES). No time has been allocated for the IPCS during the present semester (96A) while during the previous semester (95B), the IPCS was used for one observing programme of 2 nights.

Users who have strong reasons for keeping the IPCS in operation, or who would like further details on its performance, should contact Jessica Chapman at the AAO (jmc@aaoepp.aao.gov.au).

Jessica Chapman


Letter From Coonabarabran

Judging from the smug looks on farmers' faces, we think the drought just might be broken and if the very unsmug faces of frustrated astronomers are anything to go by, it probably is! It is being said that even the plague locusts have footrot!

The 2dF inauguration was the biggest event we have had for some time -- it rained for that, too. We sat at Coona airport with the buses waiting for the guests to arrive and looking dubiously at the lowering ceiling of cloud and wondered..... Came the sound of aircraft engines which circled and kept circling and then they faded and we just looked at each other in the drizzle and waited some more. Then we were informed that they had all landed at Dubbo, not without incident, and those people who were not dead from air sickness were being bussed up -- good start for the day, we thought.

As it turned out, however, although events were postponed an hour or so, the day was a roaring success. The ANU Lodge people served a superb meal and our thanks go to them working under extremely difficult conditions. People ate in the not very salubrious ambience of the AAT Ground Floor but such was the feeling of camaraderie and anticipation that nobody minded, not even the poor people coming off the bus from Dubbo, some with faces of various shades of green in memory of that morning's interesting flight from Sydney.

Then came THE moment! People crammed into the chairs on the Main Floor, with a light highlighting the massive form of the 2dF top end suspended in the hatchway. The speeches of the Director, the Chief Scientist and members of the Board concluded, the ribbon cut -- then to the strains of the theme from 2001, 2dF sailed serenely over the heads of the audience -- we were all very surprised when everyone clapped at the choice of music -- I mean, what else could you use? Then, to the Blue Danube waltz, Brendan placed the top end delicately on the telescope, finishing exactly on the last note. All in all, a great success with many interested people going to Prime Focus to have a close look.

The people for Sydney girded their loins and boarded the bus for Dubbo and hopefully a quieter flight back to Sydney.

Visitors over this period, and very welcome too, were two Sydney schools who came first and second in the University of NSW Telescope Building Contest. These children, from Northern Beaches Christian School and Abbotsleigh Girls' High, were treated to a tour of the mountain, the winners being shown the night sky from the ANU 24 telescope and the second place getters viewed through Tom Cragg's 12 telescope -- both lots were very keen and learnt a great deal. Judges of the competition included Russell Cannon and John Dobson.

Before I finish I would just like to say how saddened and shocked we all are at the untimely death of Annette Callow, the Director's Personal Assistant. Annette was well liked and respected by everyone who knew her and I, personally, will miss her a great deal.

Rhonda Martin


Staff news

Sadly, as recorded elsewhere in this Newsletter, we have lost the author of our usual Epping 'Gossip column'. However, we still have quite a few staff changes to report including two departures foreseen in the previous issue.

Carol Carmichael left on the 5th of December after a series of memorable farewell parties. Her successor as Computer Systems Support, Siobhan McClaughlin, arrived on the 29th of January 1996. She comes to us from the University of Canberra where she just completed a Degree in computer studies. Another very recent arrival is Daniel Doyle, who joined us on the 5th of February as Electronics Technician, replacing Mark Noonan.

Robyn Shobbrook, AAO librarian since September 1975, departed on the 31st of January 1996 after a short overlap with her successor, Sandra Ricketts, who introduces herself below. But we aren't going to lose touch with Robyn completely; to our surprise and perhaps hers too, the Shobbrooks are going to move up to Coonabarabran for the next couple of years so that Bob can pursue his renewed enthusiasm for observing variable stars at Siding Spring. Not to be outdone, Robyn is going to spend several months at the Institute of Astronomy in Cambridge, advising on library matters. It is hard to know which was more important, Robyn's work in making the AAO Library one of the most popular with visiting astronomers, or her many contributions to international astronomical librarianship, but there is no doubt that she set new standards and has had a major impact in her field.

Another departure in January was Charlene Heisler, who after two and a half years as the AAO ARC/PPARC Research Fellow has moved to a similar position at Mount Stromlo. She takes with her valuable expertise in infrared astronomy, as one of the few people thoroughly familiar with IRIS. Her successor as AAO Fellow, Helen Johnston, is about to arrive as this issue goes to press.

Meanwhile, another arrival should have been recorded in the previous issue but was missed, perhaps because he has managed to spend a fair fraction of his time overseas observing on other telescopes, especially in Hawaii which has some special attraction. Karl Glazebrook joined the AAO as a Research Astronomer on the 4th of September 1995. He will be particularly involved in commissioning and exploiting the 2dF, and also has a lot of experience in infrared astronomy. Karl came to us from Cambridge, where he held a Research Assistantship under Richard Ellis at the Institute of Astronomy.

We also welcome Anna Vassilimis, who has just joined us temporarily as Director's Personal Assistant.

As this issue was going to press we learned that Jennifer Sutton was about to move to Canberra to take up a new job which she will be able to combine with undertaking a Bachelor of Commerce in Accounting at the University of Canberra. Her place too is being quickly filled on a temporary basis, by Wendy Carmichael who is no stranger in the admin section and seems to share her mother's passion for daily rail travel.

We welcome all the new arrivals and wish all the departing staff the very best for the future.

Finally, our congratulations to Peter Brand, who is spending most of a sabbatical year at the AAO, on his appointment to a Personal Chair in Astrophysics at the University of Edinburgh.

Russell Cannon


Library News

January has seen the arrival of a new librarian to replace Robyn. She is Sandra Ricketts, ex-Maths teacher and most recently from the NRMA Automotive Library. (Sorry I'm not much use for fixing dead cars though!) Robyn is staying on for two weeks to demonstrate the ropes. Both Robyn and Sandra went to Coonabarabran in January, the main activity being the moving of back issues of several journals to the studies across the hall from the library. On the 2nd of February they will be travelling to Canberra to attend a mini-conference of astronomy librarians. Thanks to everyone for making me welcome at the AAO and I'm looking forward to working with all of you.

Sandra Ricketts (E-mail: LIB)


Schmidt News

Astrometry for 2dF Projects

At the recent meeting of the Schmidt Telescope Panel the issue of using UK Schmidt data to provide target coordinates for 2dF projects was discussed. It was noted that some prospective 2dF users were probably not aware of the need for very accurate target coordinates and where to obtain them. The requirement is that relative positions of the targets and guide stars should have rms errors less than 0.25 arcseconds over a field of 2 degrees diameter. We ask prospective 2dF users to note the following points.

1. Accurate astrometry from digitised UKST Plates
For users without specific expertise and their own plate material, the best source of UKST data is one of the online catalogues. There are catalogues online at Cambridge (APM) and AAO Epping (COSMOS) which provide quick access to the digitised plate material. We stress here (for Australian users in particular) that the COSMOS catalogue was not intended for astrometric precision and is not accurate enough for 2dF projects (there are systematic errors of order 0.3 arcseconds on scales of 2 degrees; see Drinkwater, Barnes & Ellison, 1995, PASA, 12, 248).

At the time of writing we recommend that all users obtain 2dF target coordinates from the APM catalogue at Cambridge. The APM coordinates are adequate for 2dF use (Irwin, 1994, in H. MacGillivray, ed., IAU Working Group on Wide Field Imaging Newsletter No.5, 25). Details of this service are given by Irwin, Maddox & McMahon (1994, Spectrum: Newsletter of the Royal Observatories, No.2, 14). Briefly, it can be accessed on the internet by logging in to apm3.ast.cam.ac.uk (131.111.68.56) as ``catalogues'' (no password). There is also a pointer to this in the sky surveys and catalogues section of the AAO WWW homepage.

Australian network access to Cambridge can be very slow: we are investigating the best way to provide an improved service at the AAO. Please consult the AAO WWW pages (under ``2dF'' or ``Sky Surveys'') for the latest information.

2. Using new photographic UKST data for 2dF projects.
Some more specialized 2dF projects require new UKST data. These needs should be discussed in detail with the UKST staff in Australia or the UKST Unit staff at ROE in the UK. We would like to note, however, that if 2dF projects highly ranked by ATAC or PATT are dependent on new UKST photographic material we will do our best to accommodate them by scheduling the requests at high priority. The usual time constraints imposed by the weather and the need to transport the material to the UK for scanning still apply.

Although the UKST now routinely uses photographic film as well as plate material, tests by Mike Irwin with the APM have shown that the coordinates measured directly from films show systematic distortions at the 0.25 arcsecond level and are not suitable for 2dF use without correction. The distortions on the film can be mapped out by calibrating them with respect to a reference plate: please contact the UKST (schmidt@aaocbn.aao.gov.au) staff if you are proposing to observe with film for 2dF projects.

Michael Drinkwater, Australian Secretary to the STP
Peter Wood, Chair, ATAC


Visitors to the Schmidt Telescope

The Schmidt staff were pleased to play host to vacation student Rachel Mendham during December and January. Rachel is a student at Melbourne University, and is about to enter her final year. At the Schmidt she worked with Quentin Parker on his galaxy redshift survey.

Among other recent visitors to the telescope were Yanda pilot Roland Parker, who thought the telescope's control console looked a lot like the inside of his cockpit. Fortunately, Yanda's aircraft are not quite so liberally spread with large spiders.

Fred Watson

FLAIR News

With the commissioning of the new FLAIR CCD (see AAO newsletter no.74) many FLAIR projects can now be accommodated with a significantly lower impact on overall UKST time. Furthermore, entirely new types of project become feasible such as the possible determination of galaxy velocity dispersion measures with the use of higher dispersion gratings. Likewise, previously difficult projects that required the very best conditions (such as QSO candidate observations) can now be confidently attempted. A few S/N results are given below for some faint point source observations, of QSO candidates kindly provided by Katrina Sealey (UNSW), as an indication of the current performance. Both B and R magnitudes are given.

R B S/N
1 16.6 17.4

20

2 17.7 19.6

10

3 17.9 19.7

6

These few individual fibre results are averages from several 3000sec exposures with observations through 100m (6.7) fibres. The S/N results depend quite strongly on seeing, individual fibre transmission efficiency etc but are nevertheless indicative. A more detailed report on the performance of FLAIR for faint point source observations will appear in due course.

FLAIR operation over bright of moon
As part of the new CCD commissioning tests some FLAIR observations were obtained on an unscheduled UKST night during the bright-of-moon (BOM) period on July 8th 1995. A set of 40 galaxies with B17.1 were observed in survey field 406 using grating 300B. There were about 2 hours of unused dark time at the end of the night. However 2x1800sec exposures were also attempted with the moon still up (phase 0.8). At this phase the night sky brightness in B is 20.0. This is 3 magnitudes brighter than during dark time. An independent reduction of the moon affected frames gave excellent agreement with the few dark frames obtained. The mean radial velocity difference was 12km/s from absorption line results and -15km/s from emission line results. The redshift identification success rate was also identical (95%). This success raises some interesting possibilities for extending FLAIR use during BOM and outside of normal UKST scheduled time should demand warrant it. Certainly there is the possibility for undertaking all sorts of stellar projects with FLAIR during BOM.

Figure: Examples of 2 consecutive FLAIR galaxy spectra taken from the reduced dark frames and moon frames respectively. The spectra are sky-subtracted and wavelength calibrated after accounting for fibre-fibre transmission variations. The counts are the average counts per 1800sec exposure. The bright sky seems to have subtracted out quite well from the moon affected frames though the odd cosmic-ray event remains.

Future developments
With the new CCD operational the biggest hurdle to a much more flexible and efficient mode of FLAIR operation lies in the semi-manual fibre-positioning system. This is such a large overhead that it precludes maximum productivity with FLAIR. A much more automatic system based on magnetic buttons and derivative autofib/2dF technology would yield very considerable benefits. In particular it would be of enormous help with several very large surveys that have been proposed for FLAIR. Implementing this major proposed upgrade is currently at the planning stage. Other FLAIR developments are also being actively considered with possibilities for new plateholder(s) and a suite of dedicated FLAIR gratings. Orders for 2 such gratings (600V and 1200B) will be placed shortly. They are a necessity with the adoption of more flexible FLAIR scheduling and the advent of 2dF with which we currently share gratings.

Applying for FLAIR time
The next FLAIR application deadline for the August 1996-January 1997 semester is May 8th. Full details on application procedures were given in the 5th issue of Spectrum (March 1995). Applicants are encouraged to seek advice and raise queries before submitting proposals. Latex application forms are available from Mike Read at ROE (M.Read@roe.ac.uk) or from the AAO home pages on the WWW.

Quentin Parker


New AAO Preprints


AAO PP293 -- Ryan, S.G., Beers, T.C., Delyannis, C.P., Thorburn, J.A. ``Lithium Processing in Halo Dwarfs, and T, [Fe/H] Correlations on the Spite Plateau.'' in press
AAO PP294 -- Tinney, C.G., Reid, I.N., Gizis, J., Mould, J.R.. ``Trigonometric Parallaxes and the HR Diagram at the Bottom of the Main Sequence.'' in press
AAO PP295 -- Bland-Hawthorn, J., Cecil, G.N.. ``Classical Spectroscopy''. Methods of Experimental Physics, Vol. 29B, eds. Dunning, F.B., Hulet, R.G.
AAO PP296 -- Lumsden, S.L., Hoare, M.G. ``An IR study of the velocity structure of the cometary compact HII region G29.96--0.02.'' in press
AAO PP297 -- Lumsden, S.L., Puxley, P.J. ``Near infrared spectroscopy of the ultracompact HII region G45.12+0.13.'' in press
AAO PP298 -- Drinkwater, M.J., Schmidt, R.W., ``The large scale distribution of radio sources.'' PASA in press
AAO PP299 -- Douglas, N.G., ``Optical methane-band observations of Jovian Shoemaker-Levy 9 impact debris.'' in press
AAO PP300 -- Drinkwater, M.J., Currie, M.J., Young, C.K., Hardy, E., Yearsley, J.M. ``Blue compact dwarf galaxies and new velocities in Virgo.'' in press

LUNAR CHIAROSCURO

Bright Grey(3) Dark Grey(1) Bright
1996 Aug

1-4

5-7

8-18 19-22 23-31
Sep

1-2

3-6

7-16 17-20 21-30
Oct

1

2-5

6-16 17-19 20-31
Nov

1-4

5-14 15-17 18-30
Dec

1

2-5

6-14 15-17 18-31
1997 Jan

1

2-4

5-13 14-16 17-31


Editor: Stuart Lumsden
Editorial assistant: Sandra Ricketts
ISSN: 0728--5833
Published by Anglo--Australian Observatory, PO Box 296 Epping, NSW 2121 Australia


Helen Davies - hdd@aaoepp.aao.gov.au

Monday 26 Feb 1996