AAVSO Centennial Conference Poster Paper: RASNZ Photometry Section

The RASNZ Photometry Section was formally set up in 1985 to develop the ‘electronic’ aspects of variable star observing. Brian Marino and Stan Walker were appointed as joint directors. With Marino’s ill health in the 1990s Bill Allen then replaced him. Later, Marc Bos was also appointed a director. This section worked closely with Edwin Budding of the Carter Observatory and with astronomers from various New Zealand universities and researchers around the world.

It incorporated an existing framework of observers in New Zealand and Australia and their collaborations which had seen many observational type papers published, either as time series photometry, or as analyses of colour photometry. The Section continued to promote the very succesful PEP series of conferences where a wide variety of professional and amateur astronomers met in congenial surroundings.

This display presents some of the work of the Section and its progenitor, the Auckland Photoelectric Observers’ Group, and other amateur photometrists.

Introduction

Whilst this review centres upon the RASNZ Photometry Section it’s necessary to see how this came about. It all began in 1966 with the revival of visual variable star observing in Auckland. But it gained momentum in 1967 with the opening of the Auckland Observatory in the One Tree Hill Domain in which was housed the 500mm Edith Winstone Blackwell Telescope, at that time the largest in New Zealand. The question was asked “what do you do with this telescope”?

It was a 500mm Zeiss Cassegrain reflector, f 13.3 on an offset German equatorial mount weighing about 1.5 tonnes all up. Tracking was very precise and it had a beautiful f 7, 110mm refractor as a finding telescope. So good was this finder that often the target star was within the 31” focal plane aperture of the photometer using this alone. The telescope was very user friendly.

We began by forming an Observing Committee comprising Stan Walker, Brian Marino, Deryk Fisher and Graham Loftus. This explored several aspects of visual VSO - flare star monitoring in conjunction with Bruce Slee of the Australian CSIRO, the possibility of determining sequences of comparison stars for observers and the study of CVs to determine orbital periods by timing eclipses. But it soon became clear that most flares were small amplitude and hard to be certain of visually, that visual sequence estimation was far more difficult than expected and that most of the CVs we looked at did not have eclipses. Nevertheless we determined an approximate orbital period for VW Hydri and recorded behaviour in EX Hydrae which was later recognised as the spin pattern of the white dwarf component of that system.

The Birth of PEP in Auckland

Auckland has a good public library and some prescient librarian had purchased a copy of Brad Wood's book 'Photoelectric Photometry for Amateurs'. The cover was rather SF appearing but the contents were fascinating. After our local society council's initial shock that we wished to build and use a photometer the idea grew fast.

  • The RASNZ granted funds for two EMI high performance photomultiplier tubes.
  • A group from the Canterbury Astronomical Society visited Auckland and allowed us to use their prototype photometer.
  • The University of Auckland through Bob White and Alex Chisholm established a liaison with us to develop and participate in astronomy. They supplied much of the electronic equipment.

We were also fortunate that we selected a road which avoided the use of temperamental DC amplifiers and that technology—instead we opted for the sensitive but expensive EMI 9502 pm tubes. These could be used directly with an analogue to digital A/D converter designed by Clive Rowe around the Schmidt trigger concept and feeding the output to a digital frequency meter. These low noise/high gain pm tubes did not need cooling to avoid noise—a great advantage in Auckland's humid climate.

The original design was so effective we never built the Mark II version. But Bruce Griffiths and Rodger Freeth of the University of Auckland developed a high speed, pulse (photon) counting system which could, with a teletype tape punch, operate at up to eight measures per second. Even today the original Mark I unit is still usable.

As soon as we had the equipment going well we were persuaded by Stefan Mochnacki, then a graduate student of the University of Canterbury, that we needed to calibrate the photometer to work in the standard UBV system. It turned out to be a interesting challenge. Our first method was to use an open cluster - IC 4665 probably - to make V and B measures. But then Norman Rumsey of the DSIR came to our rescue by providing a copy of Royal Observatory Bulletins 45 and 64 and details of the Cape photometric standards observed by Cousins and Stoy. So we measured various E Regions, worked out extinction factors and with guidance from Hardie's article in Stars and Stellar Systems we were on our way.

But only in B-V as we believed Johnson’s comment that we could not get acceptable measures of U at sea level. It was left to a pair of university students, unaware of this limitation, to produce a beautiful, fully calibrated V, B-V, U-B colour curve of AI Velorum. Don’t believe everything you’re told!

Early Photometry

One of the first projects involved flare stars and the change from visual to pe measures worked well. Using only the B filter we would be part of 3-5 programmes each year. Some stars were active, particularly UV Ceti on which we once detected two 4 magnitude flares on one night. Without computers we used teams of people to plot each 10 second measure on millimetre graph paper. Dedication! We were especially gratified when Bruce Slee mentioned an accuracy of 0.003 for the data.

RS Columbae was another early venture and we submitted a paper to PASP in 1970 but were somewhat overawed by the referee's comments and this did not proceed. In retrospect the comments were very helpful and we should have finished the project.

About this time Graham Hill of the DAO came home to Auckland for a vacation and assured us that what we were doing was quite acceptable, in fact, surprisingly high in quality. So we measured anything which caught our eye. Barry Menzies and Peter Gordon also began a cooperative project with Frank Bateson to provide V, B-V sequences for as many variable stars as possible.

Almost from the start we had been measuring CVs in the attempt to detect eclipses. We followed Brian Warner's ideas and used unfiltered white light but made UBV measures a few times each night.

VW Hydri was one of our targets but we couldn't make sense of the data. There were easily detectable orbital humps but sometimes these appeared to fit an orbital period—at other times not. This star is about V = 13.5 when quiescent but reaches V = 8.8 during bright outbursts. There were similar looking humps at both stages but the data wouldn't fit together. We resolved the puzzled by ignoring the outbursts, then by matching the quiescent humps we determined an orbital period. This was published in IBVS 864 where we noted the newly discovered period and indicated that the humps during the bright outbursts were something else. This kindled the interest of others and the study of superhumps began. It's still going on!

Colour Photometry

Whilst the group at Auckland made many time series measures the use of UBV photometry to understand the physical nature of some of our targets was not overlooked. One of our main targets was still VW Hydri, probably in 2011 the most studied CV in the sky, but not so in the 1970s.

In these days of CCDs it’s more normal to speak of BVRI photometry but earlier detectors were strong in the blue regions, hence most of the work was in those passbands. I’ve done some BVRI photometry using the ST6B. But most of our early photometry was UBV which has its own advantages. For non-photometrists think of all of this as akin to spectroscopy in that the colours allow spectral classification (but do not provide velocity measures) with the advantage that colour photometry can be applied to much fainter stars. As well, it shows the effects of interstellar absorption.

BH Crucis has recently undergone a dramatic change in period from 421 days to 525 days. Unfortunately there is little colour photometry available from this twentyfirst century. But back in the 1970s the star was measured in UBV from Auckland – largely because its variability was detected by Ron Welch, one of our colleagues, but also because it appeared to be one of the small group of double maxima Mira stars. The light and colour curve then and now is interesting.

The graph shows four cycles of BH Crucis phased to the elements shown. There are two well-defined maxima and the B-V colour, indicative of temperature, follows these reasonably closely. But the U-B curve is dramatically different. In this star the secondary maximum was brighter, in R Normae they are much the same, in R Centauri the first maximum is the brighter. But is the strange U-B curve telling us something that has been missed? BH Crucis has now turned into a single maximum Mira with a noticeable hump where the first maximum used to be, but it’s also rather brighter overall and the B-V colour shows it’s much cooler. The period change may well be a mode change rather than evolutionary. For an interesting discussion of this star see JAAVSO 2009 37,87.

One interesting result was with SN 1987A. Auckland measures in UBV were the first, a few hours after discovery, mainly as a result of Albert Jones’ good work and a phone call – even if longitude robbed him of being the first to see it. We also measured it the following night and many nights thereafter.

In the first few days the expanding wavefront from a supernova is fairly dense and can be treated as a black body for temperature purposes. Hence B-V is a good temperature indicator. So using the B-V colours it’s easy enough to deduce a temperature. There was little reddening in this instance to confuse the issue. So if the apparent brightness on each night is known, and temperatures are able to be deduced from the colours, application of the relationship L = T4*R2 will provide the radius values of the expanding shell on each of two nights. Then it’s simple to convert everything into distance, divide by time elapsed and establish an expansion value. Crude, but it gave a supernova level velocity – about 8-10,000km/sec from memory!

Other Groups

In those days the main problem was building the photometer. It’s not as simple as it seems and few groups had access to the necessary engineering and electronic workshops. Almost everyone successfully involved in photometry had connections to a university at some level.

Bill Allen set up the Vintage Lane Observatory in 1982 using equipment from Otago University’s Beverly Begg Observatory. The Auckland group had two photometers and frequently used the high speed unit with telescopes at either Black Birch or Mt John, operated by Carter Observatory and Canterbury University respectively.

Our success encouraged others—Harry Williams, Marc Bos and Trevor Rounthwaite all set up observatories with PEP facilities. The Auckland Astronomical Society commissioned another photometer which I still use occasionally at Waiharara. But other local societies were less successful.

The RASNZ Photometry Section

In the 1980s we set up the RASNZ Photometry Section in order to develop the ‘electronic’ aspects of variable star observing. Brian Marino and Stan Walker were appointed as joint directors. With Marino’s ill health in the 1990s Bill Allen replaced him. Later, Marc Bos was also appointed a director. This section worked closely with Edwin Budding of the Carter Observatory, also Auckland and Mt John observatories.

These events led to the spread of PEP in New Zealand and, to some extent, Australia. Back in 1973 the Carter Observatory had appointed a new director, Murray Lewis, who set out to do photometry from Wellington. Regretfully he used classical designs and was slow in getting it all going.

Even before this George Eiby was the first in New Zealand to build and use a photometer - about 1950 – a rather crude machine by later standards. In the mid-1960s overseas astronomers were doing PEP at Mt John but using rather dated equipment. Clive Rowe constructed a photometer about 1966 using a better detector – the EMI 6256 – with an A/D converter and digital frequency meter. The effectiveness of this saw many people involved. The West Melton Observatory in Christchurch continued to use the original Rowe photometer although the observatory’s distance from the city was an obstacle. In 1968 Auckland came into the picture – with the advantages of a good telescope and observatory. For many years it was the best in the country and we did the faintest photometry – from a city site!

In Queensland, Arthur Page and Harold Kennedy both developed effective sites but several other New Zealand attempts failed. A stimulus to all came in 1978 with the fiftieth anniversary of the RASNZ VSS and IAU Colloquium 46. Most of the active southern professional and amateur variable star people were there, along with many northerners. The AAVSO was represented, amongst others, by Clint Ford.

Chris Stercken and Nicholas Vogt with assistance from Brian Warner organised one of the earliest world wide photometry collaborations by involving the Auckland group, also Harold Kennedy, Bill Allen and Arthur Page, in four countries – NZ, Australia, Chile and Zimbabwe– in an assault on the puzzling star EX Hydrae, now one of the best known intermediate polars. Very successful in its results, it pointed the way ahead.

There were many other stars observed—for some examples see RASNZ Observations.

The PEP Photoelectric Conferences

About 1976 Lewis decided the Carter Observatory should host the “First NZ PEP Conference”. Successful in getting together people with an interest in photometry, it introduced to us the concept of occasional specialised conferences with both amateur and professional participants. By today’s standards it was fairly low key, with about 20 participants. The ‘banquet’ was fish and chips from the Kelburn Takeaways. Most of the papers were presented by Auckland participants.

PEP2 was held in Auckland in 1982 at the Auckland Observatory with the Teacher’s Training College providing accommodation and meals. There was a strong contingent of University of Canterbury graduate students and several overseas professionals. Unlike at Carter, there were many papers from outside the Auckland area and some amateurs from Australia participated. The success of this meeting with over 40 participants whetted everone’s enthusiasm. The “Small Telescope Conference”, IAU Symposium 118, in Christchurch in 1985 continued the theme.

PEP3 was organised by Bill Allen in Blenheim in 1989 and saw much greater professional participation. One of the ‘highlights’ of the meeting was that it was targeted by demonstrators on the basis that the astronomers at the US Naval Observatory southern station on Black Birch were in some way connected with the Waihopai satellite station near Motueka which has some obscure security aspects. We made the front page!

Mike Bessell was one of the participants and I was chairing an after dinner section on photometric systems and calibration. Quite quickly I recognised a master and handed over the chair! Other professionals included Brian Warner, Dave Crawford, Mike Zeilik and others as well as a young student from Canterbury, Karen Pollard, now vice-president of Commission 27.

Hanmer saw PEP4 in 1992 with a very strong professional contingent including John Percy. PEP 5 at Toowoomba in 1996 was organised by Arthur Page and Joe Patterson attended Conference 2002 in Nelson.

These were enjoyable and quite valuable in stimulating Proam cooperation and observations. But with the Carter Observatory and Auckland Observatory both shifting away from research to education in the 1990s they have disappeared from the calendar.

Transitions to the Present

The Auckland group was seriously affected in 1990 when the Auckland Observatory administration appointed the local astronomical society to operate research. This caused problems so that all effective PEP shifted to private observatories – Harry Williams at Milton Road, Marc Bos at Mount Molehill and the author at Wharemaru, a long way north of Auckland at Waiharara.

In 1996 I contacted Joe Patterson of the CBA and was startled when he offered a CCD camera. So in 1997 I returned to time series CV measures. We were immediately successful with a project on V803 Centauri, with outburst intervals of ~23 hours, monitored from Chile, South Africa and Waiharara. [Time Series Photometry & CBA]

participants of the RASNZ Photometry Section then became interested in CCD time series photometry which for beginners is much simpler than colour photometry. So with a grant from the NZ Lottery Board we purchased some more CCDs and Marc Bos, Fred Velthuis, Jennie McCormick and others ended up joining the CBA.

The Photometry Section continued into the 2000s but, with the advent of Variable Stars South in early 2009, it finally was wound up and the funds - and most participants - transferred to that group.

More recently some of these people, as well as Grant Christie, have become involved with the planetary lensing groups. Very successfully, but the story is not part of APOG in the variable star field. Nor is the development of the Bootes 3 project in Marlborough which studies gamma ray bursters. But one of the PEP stalwarts, Bill Allen, oversees the telescope and observatory involved in this.

Conclusion

The Photometry Section observers and other groups in this part of the world made and published many thousands of UBV measures and collected thousands of hours of unfiltered time series measures, the latter mainly of CVs. Many of the UBV measures have been passed over to AAVSO and appear in the International Database. Regretfully the early APOG time series measures are not in machine readable form and are still in intensity values only – and many of the UBV measures need to be computerised. Neither the RASNZ Photometry Section or its precurser, APOG, was strictly a variable star observers’ group, but more than 90% of their measures were in this field.

New Zealand photolectric photometry was fortunate in that it began at a time, in the late 1960s, when PEP was becoming standardised – but in its newness had hardly touched vast areas of astronomy. Thus there were many opportunities. As well, the groups received generous assistance from a large number of professional astronomers, many of them very eminent in their fields. Whilst we made some random measures of objects which might later prove interesting most of the observing was of particular stars as parts of various projects.

Most of the experience and expertise developed in these projects has transferred across to Variable Stars South and the background to that is discussed in a separate paper at this Centennial.


Enter your existing account details to login,
or click "Register" to open a new account.
VSS members can log in using their
username or registered email address.

          Forgot login?   Register