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Two thousand and thirteen was a year in which the Occultation Section continued its consolidation, attracted a number of new members, and reported a record number of observed minor planet occultations in Australasia. It was especially pleasing to see the number of new observers, underscoring that the field of occultations continues to grow both observationally, and in the development of new equipment and techniques.
During the year a record 56 positive observations of minor planet occultations were recorded (including one event reported from Sumatra and Singapore), up from 51 in 2012. Some highlights were:
Observing enough well-spaced chords across an asteroid remains the most important aspect of these observations, and the resolution of the data will increase as the increasing number of observers provides both more geographical coverage, and greater observational density. As can be seen from the events above where well-spaced chords are noted, the resolution allowed by the occultation technique is truly remarkable, providing semi-major and semi-minor axes with formal errors of often only a few kilometres.
In addition the observation of single-chord events provides astrometric data for the asteroid up to ten times better than that routinely obtained by other means. Through the efforts of Dave Herald in collating this information our observers are now frequently acknowledged in the Minor Planet Circulars.
The year 2013 also saw two positive occultations involving Trans-Neptunian Objects (TNOs), with increasing interest in these events partly fuelled by a deepening collaboration with Felipe Braga-Ribas and Bruno Sicardy at the Paris Observatory. TNOs remain one of the high-profile areas of professional astronomy and the involvement of amateurs in Australia and New Zealand is significant.
During 2013, 637 disappearance and 138 reappearance lunar occultations (a total of 775) were observed by 13 observers in Australia and New Zealand. While the majority of events were timed using video with time insertion, 18.5% of them were contributed by 3 observers using visual techniques. A total of 5 grazing occultation events were also successfully observed, all in Australia. In one instance, by careful selection of the observing position, the grazes of two stars were observed from the same site on the same night.
In addition reports were received of 184 timings of double star occultations. These covered observations made in Japan, and a number of countries in Europe and in the U.S.A. in addition to Australia and New Zealand. More 2013 observation reports are likely to be received from the northern hemisphere in the next few months. Observations led to the discovery of 12 new double stars. There were also 57 timings of previously known doubles. In a number of cases these led to a determination of the position angle and separation of the component stars of the double. In addition 71 of the observations reported demonstrated that stars previously reported as possibly double as a result of earlier visual observations are in fact single stars.
The observations of double star occultations resulted in the submission of papers, written by observers, to the on-line Journal of Double Star Occultations, reporting some of the newly discovered doubles. A more general paper reporting many more of the observations has also been submitted to the Journal and is due for publication in April 2014.
The 7th Trans-Tasman Symposium on Occultations (TTSO7) was held in Invercargill over May 27-28, immediately following the RASNZ Conference. The meeting attracted one of the largest turnouts (26) for a TTSO with eighteen Kiwis and eight Australians participating. The general consensus was that the meeting was one of the most successful yet held. TTSO8 will be held in Melbourne, Australia, in conjunction with the NACAA convention over 2014 April 20 & 21.
Through the diligent efforts of our editor, Murray Forbes, the Section is continuing to catch up on its backlog of observations to be published. During the year three Circulars appeared, a 64-page monster presenting all the observational reports from 2009, followed by two additional Circulars covering the first six months of 2010.
During the year the Section’s website, which for many years has been hosted by the Wellington Community Net, was moved to a new hosting provider with a consequent change in URL to http://www.occultations.org.nz.
That the Section is running so efficiently is entirely due to the volunteers who have taken on responsibility for their respective areas. As Director I am very grateful to our assistants who ‘make things happen’ at the appropriate time with minimal input from me. So as always it is a real pleasure to thank: Peter Litwiniuk, John Sunderland and Greg Bolt who prepare, annotate, publish and update minor planet occultation predictions on the Section’s website; John Talbot who collects and analyses minor planet occultation reports and publishes summaries of positive events online; Brian Loader and Dave Gault who collect and collate total and grazing occultation observations for New Zealand and Australia respectively; Brian who prepares the annual overview of upcoming grazing occultations for the website as well as collating the results of lunar occultations of suspected double stars; Dennis Lowe who prepares and publishes lists of bright lunar occultations for the forthcoming year to the website; Steve Kerr who continues to advertise our work through his column on occultations in Australian Sky & Telescope; and Murray Forbes who organised the most successful TTSO7 meeting, as well as doing such an excellent job of preparing our publications. My final thanks are to our observers who make our efforts so worthwhile.
Graham Blow, Director, RASNZ Occultation Section, February 2014