Astronomical News

­trying to find a single formation channel SN Ia”. Soker stressed that the main Acknowledgements or explosion mechanism may be a uto­ open questions in stellar evolution are It is a pleasure to thank all the speakers, and more pian endeavour. However Type Ia SNe related to angular momentum (AM) evolu­ particularly the invited ones, for highly inspiring are still very good distance indicators and tion, as AM is crucial both at the birth talks that allowed us to fulfil the aim of this cross-­ as such have led to the best determina­ and at the death of stars. In this regard, disciplinary workshop to bring together specialists tion of the Hubble constant, and have the most important source of AM is either in quite different areas and have them share their expertise. Many thanks also to all the participants helped to confirm the existence of dark the contraction of a cloud/envelope — and we apologise that the lack of space did not energy. Further progress in this area will important during birth and core collapse allow us to discuss the numerous and very interest­ require good data at z > 1, but mostly SNe — or a binary companion (includ- ing posters that were presented. We would also like more infrared data at z > 0.5. It is never­ ing brown dwarfs and planets). Binarity to warmly thank Maria Eugenia Gomez, Paulina Jirón, Amy Tyndall and Catherine McEvoy for their theless rather annoying that the origin of seemed to be a major ingredient to the enthusiastic and efficient logistical help in making such important objects is still unknown. many topics discussed during the work­ this workshop a success. shop, and is perhaps the underlying fil The state of our current knowledge was rouge. Links summarised in the final talk of the con­ ference by Noam Soker: “If WDs knew Most of the workshop talks are available 1 Workshop web page: http://www.eso.org/sci/­ theory, they would not have exploded as on the meeting webpage1. meetings/2013/dslg2013/program.html

ESO’s Early Seeing Expedition to South Africa

Kristen Rohlfs1 of ESO have been described by Blaauw Observatory at Cape Town; the Radcliffe (1991) and in the more recent history Observatory with a 74-inch telescope in Madsen (2012). This article recalls an at Pretoria; and the Boyden Observatory 1 Institut für Astrophysik, Universität aspect only touched on in Blaauw’s with a 60-inch telescope at Bloemfontein. Bochum, Germany ­monograph (p. 23). The seeing expedition had the task of finding a fully satisfactory place for a I joined the South African seeing expedi­ modern observatory, but it was not clear Site-testing for a joint European obser- tion in November 1956 when I had just what the meteorological conditions were vatory in the south began in the 1950s finished my Staatsexamen fur das Höhere that had to be fulfilled to meet the in South Africa, following the decla­ Lehramt with a thesis on cosmology with request. ration of the intent to build a large opti- Prof. Otto Heckmann at Hamburg as cal telescope in the southern hemi- advisor. At that time the plans for the The climate of South Africa is divided into sphere. First hand reflections of one European Southern Observatory were two different regimes: in the southern of the early site-testing teams working still very informal, and nothing had been part there is a Mediterranean-type climate in South Africa, based at the Boyden definitely decided yet. Not even the name with winter rain, and the more northern Station, are described. Practical prob- of the enterprise was definite, and we subtropical region has rain in the summer lems related to seeing measurement were known at the time by the garage season. Therefore it was decided to split and site assessment are discussed. that serviced the expedition cars as “Joint the expedition into two groups; one was European”. to investigate the winter rain region, the other the summer rain region further The long-term result of the meeting of north. Both regions have a large number leading European astronomers with Observing conditions in South Africa of clear nights when compared to Euro­ ­Walter Baade in Leiden in 1953 was the pean conditions. foundation of ESO in 1962. One of its At that time very little was known about immediate consequences, however, was seeing and seeing conditions in South The group that worked in the south (under the decision to send an expedition to Africa, only that the number of clear J. Dommanget) chose Oudtshoorn as South Africa with the aim of finding a suit­ nights in that country was much larger their headquarters, while the other group able place for a large astronomical obser­ than in Europe and several observatories (under H. Elsässer) selected Boyden vatory. The foundation and early history had been established there: the Cape ­Station near Bloemfontein. Starting from

42 The Messenger 152 – June 2013 Figure 1. Photograph of the Harvard Observatory's Boyden Station in South Africa in the 1950s during the time when ESO site-testing was taking place. Dawid van Jaarsveldt

these locations sites were selected that available electronic valve technique with Zeekoegat, just north of the Swartberg looked promising for a closer inspection. photographic registration of the measure­ Mountains in the southern part of the For this the seeing quality and the zenith ments, its use was exceedingly bother­ Great Karroo — and therefore we extinction were estimated several times some under field conditions. Experience dropped the Oudtshoorn headquarters per night for periods of about 14 days. in South Africa quickly showed that the and served Zeekoegat from Boyden sta­ After about one year, with more than 200 difference in the extinction at different tion. In the northern region there were nights on duty and about 100 000 kilo­ places is quite small if the sky is clear, still several places to be investigated. We metres covered with the cars, a new crew and so extinction was no longer a strong even decided to include another site in was needed, and this was the situation criterion for site selection and extinction our investigation: a place on a mountain when I joined the seeing expedition. measurements could be dropped safely. range close to Calvinia in the northwest part of the Cape Province. Atmospheric conditions similar to those at the Califor­ Site-testing instrumentation The seeing expeditions nian astronomical observatories could hopefully be expected in this area, caused In order to be able to investigate the During my stay in South Africa the seeing by the cold Benguela current. Since the astronomical quality of a site two different expedition consisted of Dr Walther Tripp mountains were not accessible by car, types of instruments were provided to from Göttingen, Father Bertiau SJ from we arranged an exploratory stay with the the expedition. One was a very rugged, Belgium and myself, and for a short time help of local people and the South Afri­ high quality 25-centimetre reflector on an we were reinforced by a retired gentle­ can Air Force, who provided us with heli­ ­azimuthal mount, quite similar to a man, whose name I unfortunately don’t copter transport. W. Tripp and I stayed ­Dobson mounting, that could be tracked remember, who had been occupied on the mountain for 14 days and made manually and exceedingly smoothly so ­during his active time by taking plates for seeing estimates. While the seeing was that a magnification of 700 times could the Franklin–Adams charts. We had reasonable, the weather was impaired be used on a routine basis. The seeing our headquarters at the Boyden Obser­ by high ranging cirrostratus. Since the could then be judged by a method vatory, which at that time had been sky was clear at Boyden at the same time, invented by Danjon, based on the visibil­ closed down by Harvard Observatory we dropped Calvinia from the agenda. ity and quality of the diffraction rings and was rented by a consortium from the of the telescopic stellar images. The other Hamburg Observatory, Sweden and It turned out to be fortunate that Boyden type of instrument was a small refractor Northern Ireland (see Figure 1). was a working observatory. At that time on an equatorial mounting with a simple Jürgen Stock from the Hamburg Ob­­ photoelectric photometer using an 1P21 At that time the southern group had boiled servatory was the local supervisor, and photomultiplier. Because of the then down their search to a single place — he was doing photoelectric photometry

The Messenger 152 – June 2013 43 Astronomical News Rohlfs K., ESO’s Early Seeing Expedition to South Africa

with the 60-inch telescope, while we The problem in measuring the image we sat down to convert our experience were doing our routine seeing estimates. motion is that it is exceedingly difficult to into a report. At that time Xerox copy Quite naturally we discussed our seeing distinguish the part that is caused by machines were not yet available, and it problems with him and compared our the atmospheric disturbance from that was not a trivial matter to produce sev­ seeing estimates with his estimates at caused by mechanical vibrations of the eral copies. We tried to do this with the the 60-inch at midnight tea. The results telescope. Either one needs a telescope help of a printing shop, but then their were confusing — sometimes they with a very stable mounting and an copy machine broke down, and therefore agreed and sometimes we obtained dif­ exceedingly smooth drive, or one has to only very few copies were eventually ferent results and so we decided to utilise a differential procedure, where two made. I do not know who got them and I investigate this more closely. The 60-inch separate telescopes on a single mount- did not have one myself. telescope had a rather thin mirror blank, ing have common vibrations, so that the and the mirror cell had three supporting separation of their images is only affected The seeing expedition to South Africa pads whose pressure could be adjusted by the atmospheric image motions. Quite continued using a different setup. At two from the eyepiece so that the mirror naturally we discussed ways to make sites — Zeekoegat and at Klavervlei near shape could be adjusted manually. This these measurements, but under expedi­ Beaufort West at the northern border of was an art and a kind of active optics tion conditions it turned out not to be pos­ the Great Karroo — semi-permanent avant le temps. J. Stock was quite good sible to provide an appropriate instrument. small observatories with medium-sized at this and at the same time he obtained telescopes were set up and used for a good impression of the seeing. When Another problem connected with the ­regular astronomical programmes. By he did this, he gave us notice so that ­seeing in South Africa could however be these means, longer-term experience we could do our seeing estimates at the solved. According to astronomical folk­ with the seeing quality could be obtained. same time. lore at Boyden Observatory, the seeing quite often deteriorates markedly after The members of the first seeing expe­ midnight, so that the observers could go dition all returned to Europe. Father The seeing measurements to bed safely at convenient times. We ­Bertiau returned to his congregation, had to do our regular seeing runs at mid­ Tripp became a personal assistant to Plotting the seeing estimates for our night and at four o’clock irrespective of Heckmann for some time, and after that 10-inch telescopes against those of the the prevailing seeing and so we noticed, he left astronomy for a consulting firm. 60-inch we obtained a generally positive as had other observers before, that the I returned to Hamburg and helped Stock correlation, but one with a peculiar scat­ failing seeing is connected with falling for some time as a student assistant ter. When we found a medium value for temperatures. This occurred mainly in the and worked on my PhD thesis. After its the 10-inch seeing, the 60-inch showed winter months with quiet clear skies, completion I switched to radio astronomy mostly medium-quality seeing too. It when an inversion layer was forming in and eventually became involved in the could, however, just as well give bad see­ the air close to the ground. As soon as construction of the Effelsberg 100-metre ing. The same was true if the 10-inch the telescope is covered by this cold telescope; I have never been concerned seeing was excellent. But we never found air, the seeing deteriorates dramatically. with ESO matters since. Unfortunately the situation that a bad or medium We tested this by observing along the my photographs from the time of the 10-inch seeing was accompanied by an roads leading up to Boyden Kopje, rising ­seeing expedition have been lost in the excellent 60-inch seeing. In long discus­ by about 50 metres and then going to course of several removals, as well as sions with J. Stock and the members Naval Hill in Bloemfontein, rising about my notes and letters. So I have to rely on of the seeing expedition, we arrived at a 100 metres. A hill with an elevation my memories. But because I am one of simple explanation of this result. of more than 100 metres above its sur­ the very few of those active in the seeing roundings and the facility to drain the expedition who is still alive, I thought it The air in front of the telescope is not cold air downhill should therefore be a might be worthwhile to put my memories ­uniform, but shows minute temperature suitable place for an observatory. Just a to print. fluctuations that result in similar variations few kilometres north of Bloemfontein of the index of refraction. If the linear we found a suitable kopje and we did scale of these variations is smaller than some seeing observations from the top Acknowledgements the telescope diameter, they will produce and found it quite suitable. Later on we I thank Claus Madsen for locating the photograph of a loss in the sharpness of the stellar heard that Walter Baade had already the Boyden Station. images, scales larger than the telescope pointed out this very place as a possible diameter, on the other hand, will produce site for an observatory some years earlier. a lateral shift of the image, and when References the fluctuating density field is moving, the Blaauw, A. 1991, ESO’s Early History – The European stellar images will move too. Therefore, Aftermath Southern Observatory from Concept to Reality, if we want to obtain good estimates for (Garching: ESO) large-telescope seeing, we have to be As 1957 drew to a close it was decided Koorts, W. 2012, MNASSA, 71, 248 Madsen, C. 2012, The Jewel on the Mountaintop – able to measure both the small-telescope to end the seeing expedition to South The European Southern Observatory through Fifty seeing and the image motion. Africa in its then-present form and so Years, (Weinheim: Wiley-VCH)

44 The Messenger 152 – June 2013