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Using the Innes telescope again.

Introduction

On 1 January 1972, after South Africa had re-assessed its policy on astronomical research, it merged the existing establishments at Cape Town and Johannesburg to form the South African Astronomical Observatory and decided to base the observational centre in the Karoo, near the town of Sutherland. By the time that the new outstation at Sutherland was jointly opened by John Vorster and Margaret Thatcher the following year, it was clear that the older telescopes such as the big visual refractor named after R.T.A. Innes at Johannesburg were not regarded as being part of the future of astronomy in the country. This was understandable as the Innes telescope at the Republic Observatory, Johannesburg and the Lamont-Hussey telescope on Naval Hill in Bloemfontein (the latter an outstation of the University of Michigan) were used in a very narrow and focussed line of work--the measurement of visual double stars--and very much depended on the availability of suitably skilled and dedicated observers.

The golden age for double stars was from the mid-1920s to the 1960s when men such as van den Bos and Rossiter were discovering thousands of new systems. In a way that was the easy part, since the real astronomical benefit was only reaped when the discoveries were followed up with further regular measures and the wheat of the binaries separated from the chaff of the line-of-sight pairs. It is equally important however to continue to monitor these systems until the data are sufficient to calculate an apparent orbit, from which the total stellar mass of the binary can be measured.

In the last few years visual astrometry of double stars, particularly those in the southern hemisphere, has been at a low ebb. Although there are several techniques, such as speckle interferometry and 'lucky' imaging which not only record the two components to closer separations than that perceived by eye, but can also measure the relative position of the stars to greater precision.

Early interest in double star measurement

My own interest in double star measurement goes back to 1970 when, during a six-month stay as a student, I used the 28-inch refractor at the Royal Greenwich Observatory whilst it was still located at Herstmonceux in East Sussex, a few miles north-east of Eastbourne. At that time I was a newly-enrolled member in the Webb Society, a UK-based group dedicated to observing deep-sky objects. It had been founded by John Larard and Kenneth Glyn Jones. Larard was an early enthusiast for deep-sky observing and had written a series of articles for The Astronomer called 'From the Night Sky' (see, for instance, Larard 1965). Meanwhile, Glyn Jones had just finished a book for Faber Press called Messier 's Nebulae and Clusters which included his own observations of all 110 objects in the list. The northerly ones were observed using his 8.5-inch reflector in Winkfield, near Windsor, a telescope based on the horseshoe mount design of the 200-inch reflector on Palomar Mountain in California. The most southerly objects were observed at the telescope of Danie Overbeek in Germiston, Transvaal. Photos of the southern objects were largely supplied by Christos Papadopoulos and Hans Vehrenberg.

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The Webb Society

The Webb Society was founded on 12 June 1967 and the first issue of the Quarterly Journal appeared a year later (for current details visit http:// www.webbdeepsky.com). By 1970, John Larard, who was also the first director of the Double Star Section, was finding it difficult to make time to do both this job and that of secretary so I was asked to take on the director's job which I assumed at the first annual meeting in September 1970. This was held in the garden of the Glyn Jones' house 'Wild Rose' in Winkfield. Talks that day included Jim Hysom discussing a new type of catadioptric telescope and David Allen, a professional astronomer from Cambridge relating his recent observing trip to do infra-red astronomy with the 30-inch reflector of the Physics Department of the University of Minneapolis in Minnesota, USA. The next ten years produced little in the way of micrometer work simply because the instruments were not readily available. Instead, we experimented with objective grating micrometers with the help of Maurice Duruy, a veteran French observer.

First visit to South Africa

In 1980 and 19821 travelled out to South Africa several times to do photoelectric photometry on the 20-inch at Sutherland and on the last trip I took the opportunity to travel to Johannesburg to use the Innes telescope which at that time was under the auspices of the Council for Scientific and Industrial Research (CSIR). I spent two weeks in the Park Lane Hotel in Hillbrow and was given the use of an old VW Combi to travel to the dome and back. I remember that the sky was clear every night and being very impressed with how good, on occasion, the imaging of the telescope was, with pairs separated by 0.2 arcseconds being certainly measurable. The results obtained appeared in Astronomy and Astrophysics (Argyle, 1983).

Some years later I spent three years on La Palma in the Canary Islands as a support astronomer at the Isaac Newton Group of telescopes and on return to the UK, with the closure of the RGO at Herstmonceux, transferred to Cambridge. This gave me the opportunity to resume double star observing and as a member of the Cambridge University Astronomical Society I was able to use the venerable 8-inch Cooke telescope, first used by WR. Dawes, for micrometer work. This project started in 1990 and is still ongoing (see, for instance, Argyle (2004)).

Return to the Innes

Towards the end of 2007 I felt it was more than time enough to use the Innes telescope again and I got in contact with members of the Johannesburg Centre of ASSA to ascertain the status of the telescope and micrometer. It was clear that, to use the telescope for a programme of double star measurement was viable and the noises coming from Johannesburg were certainly encouraging, so I went ahead and booked a pair of airline tickets. The main idea behind a visit was two-fold. Firstly to spend a couple of weeks driving around the country and taking in some sights after which my wife would return home whilst I spent three weeks in Johannesburg using the Innes telescope.

We arrived in Cape Town on 26 April 2008 for a short stay but during that time we met Auke Slotegraaf who very kindly drove us around some of the most interesting places such as the Kirstenbosch Botanical Gardens, Boulders Beach and Chapman's Peak.

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Cape Town to Johannesburg

A couple of days later my wife and I set out in a hire car and headed north via Plettenberg Bay, Bloemfontein (where we saw the rather sad sight of the empty Lamont-Hussey shed on Naval Hill) and the Kruger Park where we had a most memorable two night stay. The last leg of the journey took us to Alldays via Pietersburg to stay for a couple of nights at Magda Streicher's farm.

One of the highlights of the weekend, and there were many, was to spend some time with Magda in her observatory with the 12-inch telescope looking at spectacular sights in the southern sky which I had not seen telescopically before, such as Centaurus A, the Jewel Box, the Keyhole Nebula, the Tarantula Nebula, Omega Centauri and, of course, Alpha Centauri. I also took the opportunity of presenting Magda with the 2006 Webb Society Award in recognition of all the contributions she had made to our Society including the compilation of the Bennett catalogue in collaboration with Jenni Kay in Australia.

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After a wonderfully relaxing weekend we reluctantly said goodbye to the Streichers and headed back to Johannesburg. When we arrived at the Innes dome late on the afternoon of 11 May the place was a hive of activity. Half a dozen members of ASSA were busy working on the telescope and it was an opportunity to meet people and put faces to what had been names on e-mail addresses for the last year or so.

Preparing the Innes telescope

It took several days in co-operation with Brian Fraser, Chris Curry and Rodney Hyman to get a few remaining jobs completed to make the telescope usable for double star observation. The biggest problem was that an adaptor plate for the filar micrometer was missing and Brian had to get another one made. Chris Curry purchased a new small camera which allows the observer to read out the Right Ascension of the telescope from the eyepiece, but unfortunately this could not be used to point the telescope and stars had to be acquired by using the finder and a planetarium program which I brought with me on a laptop. The micrometer also needed to have its field illumination restored which Chris did and was soon working well. For an instrument which has been in operation since 1925 or so, the micrometer still works amazingly smoothly.

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Observing started in earnest on 16 May 2008 and finished early on 2 June. During the intervening period 207 mean measures of double stars were made and the results are being incorporated in a paper with a colleague for Astronomische Nachrichten. At least two of the binaries observed are in need of revision to the orbits and this will form the scientific discussion on which the paper will be based.

A neglected southern double star

One of the stars high on my list was Delta Velorum. Although discovered to be double by Solon Bailey at the Harvard outstation at Arequipa in Peru, it was first documented by Robert Innes who found it using a borrowed refractor in Sydney in 1894. It bears the catalogue name I 10 and the companion was estimated at 5th magnitude. Occasional measures over the next half century showed it slowly closing with PA (position angle) reducing. The motion was clearly orbital but also slow. After 1953 it disappeared off the radar screens of double star observers until 1978 when Tango and collaborators (Tango et al, 1979) observed it with the Anglo Australian Telescope and the speckle interferometer of Imperial College, London (Morgan et al 1982). They announced a new component at a distance of 0.62 arcseconds, but there was no mention of the Innes component.

Ten years ago I was making up a list of double stars for Patrick Moore's Yearbook of Astronomy and decided it was time to include some from the southern hemisphere. Delta Vel looked like a good target for a relatively small telescope but the lack of recent observations meant it was going to be difficult to estimate a PA and separation. The most recent measures had been made by the Hipparcos satellite and the values for 1991.25 apparently showed the Tango component had moved almost 55 degrees in angle in 13 years. Close triple stars where the separations between the three stars are comparable, are extremely rare, so I wondered if the Tango component and the Innes star were the same. I wrote to Charles Worley who was in charge of the WDS catalogue at the United States Naval Observatory in Washington. He agreed it was possible, although the position angle from observations of the Tango component seemed hard to explain if it really was the Innes star closed in. Some months later I was in contact with Bill Hartkopf also at Washington. He agreed to try and fit an orbit and made several attempts, none of which was entirely satisfactory.

The problem was lack of recent data as the orbit was highly inclined and the companion was going to reverse direction soon and head back to the discovery position. Fortunately Elliott Horch and colleagues obtained a measure by using the 61 cm Lowell-Tololo telescope at Cerro Tololo in Chile. There was no sign of a third star, confirming that this was indeed a double star in rapid motion. Another colleague, Andreas Alzner, a talented and active double star observer and orbit computer observing from southern Germany agreed to tackle the orbital analysis--full details can be found in the subsequent paper by Argyle, Alzner and Horch (2002). The large angular residual from the observation of Tango et al has not been fully explained but it is possible that it was due to the film on which the observations were made being placed in the processor in the wrong orientation. I contacted Professor Morgan to see if the original film was still available but it had been thrown away only a few weeks before.

The paper includes four other bright southern systems including Beta Phoenicis which has now apparently passed unobserved through periastron. It is lacunae such as this which persuade me that it is vital to actively encourage observers in the southern hemisphere to take up the measurement of double stars on a regular basis. The recent visit to the Innes did not cover the period when Beta Phe was accessible to the telescope so I still have some unfinished business to attend to--but for more news on this star see Anton (2008).

Observations of Delta Velorum

And what about Delta Vel? Unfortunately no sign of the companion could be seen in May 2008 although attempts were made on several nights. The star was quite low in the sky early in the night but the ephemeris from the orbit shows that the expected separation was 0.63 arcsec. Allowing for the large magnitude difference of almost 4 it is not surprising that such a close star should be missed. The orbit predicts that the star will get considerably closer before widening again around 2014. It will thus not be visible in small telescopes for many years.

Delta Vel had one more surprise. Sebastian Otero was looking at data from the Galileo satellite and found that the star is also an eclipsing binary--in fact it is the brightest such object in the sky and can be seen with the naked eye, the V magnitude dropping in total eclipse from 1.95 to 2.46. The period is 45.15 days and further information can be found from Sebastian Otero on the website below. This pair of early A dwarfs, first noted at Narrabri (Hanbury Brown et al 1974) has now been resolved using the VINCI instrument and two of the VLTI siderostats (Kellerer 2008). Here is another example, along with Beta Phe, why we should continue to observe bright binary stars.

So in conclusion, the observing run on the Innes has been successful in that it has generated some scientifically useful data and this in turn hopefully will encourage those responsible for the well-being of the telescope to continue to maintain and improve it. Our stay in South Africa was equally successful and was made more enjoyable through the help of the folk mentioned above. This is a good place to express my gratitude to Lerika Cross who, for the previous year, had organised things behind the scenes such as the liaison with Daphne Legwathi and SAASTA (South African Agency for Science and Technology Advancement). To everyone concerned, thank you for a great experience.

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References

Anton, R., Journal of Double Star Observers, 5, no. 1, p. 65 (http://www jdso.org)

Argyle, R.W., 1983. A&A Supplements, 53, 177.

Argyle, R.W., 2002. A. Alzner & E. Horch, A&A 384, 171.

Argyle, R. W., 2004. in Observing and Measuring Visual Double Stars, Chapter 21, p.265. Springer. Hanbury Brown, R., et al, 1974. MNRAS, 167, 121.

Glyn Jones, K. 1991. Messier's Nebulae and Clusters, Faber 1968, revised CUP.

Kellerer, A. et al, 2008. http://arxiv.org/pdf/astro-ph/0703798.

Larard, J.C.C., 1965. The Astronomer, 2, no. 14, p. 9.

Moore, P.A., (editor), 2008. The Yearbook of Astronomy, Pan Macmillan.

Morgan, B.L., et al, 1982. MNRAS, 198, 817.

Otero, S., 2003. http://ar.geocities.com/varsao/delta_Velorum.htm.

Tango, W, et al, 1979. Proc. Australian Astro. Soc. 3, 323.

R.W. Argyle

Astronomy Survey Unit, Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA, UK
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Title Annotation:the astronomical traveller
Author:Argyle, R.W.
Publication:Monthly Notes of the Astronomical Society of Southern Africa
Geographic Code:6SOUT
Date:Feb 1, 2009
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