History of Mt Burnett (Dr John Innis)

The Monash Observatory at Mt Burnett (approx 40 km east of Melbourne) was established in the early 1970’s by Monash University. Originally overseen by the Science Faculty, it soon became a field station of the Physics Department, and has been operated and maintained by Departmental staff (academic and technical) and research students.

Multicolour photoelectric photometry of selected southern variable stars has been carried out since the mid-1970’s, using single channel instruments. The observatory is a small installation, both in terms of instrumentation and staff numbers. However, a variety of work has been undertaken. In the specific area of long term photometric studies of a small number of stars the work of the Observatory has been well received both nationally and internationally. The Observatory has also been used in the astronomy teaching programs of the Physics Department.

The first building on the site was a two storey ‘dome’, housing a 16″ (0.4-m) diameter Newtonian reflector, purchased from the estate of Mr L. Jeffree of Bendigo (in NW Victoria) by the University in the late 1960’s. The telescope was transferred to Mt Burnett in 1972 following initial commissioning and operation on the University campus. In 1975 a pre-fabricated log cabin was installed on the site, providing observers quarters and a display area. In the late 1970’s a second telescope was purchased. This was a 10″ (0.25 m) Newtonian, and was installed soon afterwards, in the early 1980’s, in a ‘roll-off-roof’ shed, affectionately known as the ‘chookhouse’. In 1985 the 16″ telescope was replaced by a 0.45 m Cassegrain/Newtonian of more modern design. This telescope remains the main observatory instrument today. In 1996 a small, modern computer-controlled cassegrain telescope and CCD were purchased with an ARC grant. It is planned that this will replace the 10″ Newtonian at Mt Burnett.

Research Work

Initial work with the 16″ telescope involved the construction of a low-dispersion spectrometer and broad-band photometer for studies of bright stars. The spectra were recorded on glass plates (these were the years well before CCD’s!). Some reasonable spectra of several bright southern stars were obtained – including the legendary ‘Canopus’ spectrum that is still spoken of reverently by older staff! However, the limited light grasp of the telescope, the low quantum efficiency of photographic emulsions, and optical alignment instabilities in the wooden-tubed spectrograph (‘the coffin’), meant that no results of real astrophysical interest were obtained, although much useful experience was gained. The photometer was moderately successful, but problems with the refrigeration unit used to cool the photomultiplier tube meant that reliable operation was not possible.

By the mid 1970’s a new photometer was in operation. This dispensed with the cumbersome refrigeration system of the first photometer by operating with an uncooled 1P21 photomultiplier tube. (The ‘KISS’ principle!) Johnson UBV filters allowed three colour photometry to be obtained with an accuracy of around 0.01 magnitude on stars down to 9th magnitude. This gave many targets for stellar research in the (then) relatively little studied southern skies. As the research group was small in number, and the telescopes(s) were available solely for their use, a research ethos soon established itself where dedicated long-term studies of a relatively small number of objects were undertaken. This compensated somewhat for the relatively cloudy conditions and low altitude of the site. (In an average year, about 50 to 60 nights are suitable for single-channel photoelectric photometry at Mt Burnett, which, while small in percentage terms, is more telescope time than many other astronomers get!) One of the first targets studied was the rapidly pulsating star SX Phe – one of a small number of stars showing a relatively large (approximately 0.7 magnitude in V) amplitude with a short period (about 80 minutes). The star is actually pulsating in both the fundamental (the 80 minute period) and first overtone, producing a strong ‘beat’ in the light curve. Intensive monitoring over many years allowed the periods to be measured accurately, and also period changes to be detected. Such period changes indicate evolutionary changes deep within the star, and are important data for understanding how the structure of stars change with age.

Other pulsating stars studied were of the delta-Scuti class – several new members of this class were identified in the far southern sky. Pulsation periods were refined for others, using both previous measurements by earlier workers and data gathered at Mt Burnett. A compilation of data on such short period pulsating stars from the literature was produced in the early 1980’s by two of the observatory’s research students. This has proved to be a very useful summary for workers in the field – the paper has one of the highest citation indices of papers produced in the Physics Department. Later work on pulsating stars has included the star CY Aquarii, observed as part of an international, multi-telescope campaign, in a search for multiperiodicity. The published frequency-analysis of these multi-site data was carried out largely by an observatory staff member.

Also in the early 1980’s the Observatory work moved more into the field of activechromosphere stars – i.e. those cool stars that show enhanced solar-like activity (starspots, etc.). The Observatory identified a number of stars of this class in the southern sky, and proceeded to follow in detail the changing pattern of light variations of these stars as their starspots grew and decayed over several months or years. Work done at the observatory established that some of these stars were relatively young, comparable in age to the stars in the Pleiades cluster. Also at about this time, as the research programs developed, spectroscopic observations were made with the facilities of Mount and Siding Spring Observatories, and the Anglo-Australian Observatory, and collaborative programs were undertaken with radioastronomers from the then CSIRO Division of Radiophysics in Sydney. Later programs in recent years helped in the optical identification of cool stars detected as X-ray sources by the ROSAT satellite, involving collaboration with astronomers from the UK.

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