Talk

Long-term oscillations in the orbital period of RR Cen: third body or Applegate effect?

Jonathan Powles

Variable Stars South, SASER, Canberra Astronomical Society, University of Canberra

RR Cen is an EW-type contact binary that has been continuously observed since 1894. The first calculation of orbital elements and basic modelling were performed by South-African-based Scottish astronomer Alexander Roberts in 1903, and subsequent models had been computed by Knipe (1965), Bookmeyer (1968), King and Hilditch (1984) and Yang, Quian, Zhu et al. (2005) (YQZ). The density of this coverage has provided a good data set for observing changes to the orbital period, and YQZ computed a linear increase in orbital period, which they attributed to mass transfer, coupled with a small 60-year sinusoidal variation in orbital period, which they attributed to a third body in the system. Subsequent observations, including those by VSS members Mark Blackford and Jonathan Powles in 2014-2015, reveal the orbital period increase to itself be part of a sinusoidal oscillation with a longer, 90-year period and much larger amplitude. This paper suggests that a better explanation for such periodic variations would be the Applegate effect - regular oscillations caused by the consequences of the magnetic field cycle of one of the stars - however this theory too has problems in its applicability to a star of such early classification (F0). 

The Stellar Detective - reading the clues in light curves

Tom Richards

RASNZ, VSS, ASA, RAS

Capturing a light curve of stellar eclipses, transits, or occultations - by stars or planets - can often be done in a single night with electronic imaging. Although sophisticated software is available to help you derive astrophysical information from the light curve (by trial and error), a thoughtful contemplation of it can yield a very great deal of information about the system. This presentation will show how.

Observing Betelgeuse in the near IR

Jonathan Powles (for Carl Knight)

Variable Stars South

Betelgeuse is a highly-evolved red supergiant with multiple modes of pulsation and variability in V. With a surface temperature around 3000 K, its peak emission lies in the near infra-red (IR). Some features, such as its large convective cells, are only visible in near IR. It is a candidate for the next type II supernova in our neighbourhood. It has attracted considerable professional interest but, with a V magnitude less than 0.5, J magnitude less than -2.99 and H less than -3.99, it is much too bright for professional observatories. In this presentation, the case is made for amateur photometric observations, particularly in the J and H near IR bands.

Dating Active Young Stars

Donna Burton

Of all the parameters relating to stars, age is one of the most important but also one of the most difficult to get right. This presentation provides a review of current methods of determining age, tells why it matters and asks how can we do it better.

Discovering Southern double stars - the 20th century

Ross Gould

Canberra Astronomical Society

The Southern Hemisphere was systematically surveyed for double stars later than the Northern Hemisphere. I will look at the work of Innes, Hussey, van den Bos, Rossiter, Voute and others, the emphasis being on the work done in South Africa. The era covered will be from the 1890s to the 1960s. The purpose of searching for doubles is to find the gravitationally bound pairs, the genuine binaries, for establishing over time the orbits and thereby the stellar masses of these objects, and to provide statistical information regarding double and hierarchical systems. As Dr Paul Couteau of Nice Observatory (Fr) has pointed out, by the time the surveys had concluded, more close pairs - the ones most likely to be gravitationally bound - were known in the South than in the North.

Spectroscopy with RSpec

Stephen Broderick

St Ursula's College, Toowoomba QLD

Getting started in spectroscopy is now easy and inexpensive, thanks to the Star Analyser grating costing under $200. The Star Analyser attaches to a CCD camera and allows you to easily see the spectra of distant stars in real time. You can even use an unguided DSLR camera — no telescope needed. RSpec ("Hot product", Sky & Telescope 2011) is the simple but powerful software program used to analyse spectra. Video tutorials explain step-by-step how to analyse and interpret the data contained in these spectra.

Some possible activities being presented in this session include:

• analysing the spectrum of the Sun, Venus, Jupiter and Saturn;
• making a soar spectrometer;
• detecting Neptune’s methane atmosphere;
• determining any star’s OBAFGKM star-type and temperature from its spectrum curve;
• identifying the composition of a star or nebula from its emission and absorption lines;
• detecting the cosmological red-shift of a distant quasar!
• measuring the blue-shift of a supernova’s expanding shell as it races towards us at millions of kilometres/hour.

The Star of Bethlehem ... Fact, Fiction, Myth or Miracle

Ray Johnston

Star Dreaming Australia, Astronomical Association of Queensland

Did the Star of Bethlehem exist? If so, what was it? Was it a close conjunction of Venus and Jupiter in 2BC? The conjunctions of 2015 and 2016 have raised this speculation again and the presentation will search the biblical and historical records, confusing as they may be, in an endeavour to make some determination. Myriad possibilities have been put forward and comparisons will be made between some of the competing theories.

The Parramatta Star Catalogue: A New Perspective

Andrew James

Non-Affiliated Independent Amateur Astronomers (NAIAA)

The Parramatta Star Catalogue (PSC), made during the 1820s, was the first serious attempt to produce a useable and accurate catalogue of southern stars down to eighth magnitude. It was originally instigated by Sir Thomas Brisbane as a private concern, involving the creation of Parramatta Observatory in Australia, furnishing its astronomical equipment, and hiring the observers, Charles Rümker and James Dunlop. Completed on 2nd March 1822, they began setting up the 5 1/2-foot Troughton Transit Telescope and 2-foot Mural Circle.

Nearly continuous astrometric observations were made from 2nd May 1822 to 1824, becoming more sporadic until they ended on 2nd March 1826. Although the final catalogue is in Brisbane’s name, most of these measures were made by James Dunlop. They were later officially reduced at Royal Observatory, Greenwich, by William Richardson, from the recorded manuscript, then finally published in 1835. At first, the 7385 catalogued stars were heralded as a most significant achievement, but careful examination of the results showed many flaws or significant and inexplicable errors. These were mostly attributed to equipment damage, though others consider that the instrumentation was adjusted too much and that these changes were not properly recorded, or that the observers were not diligent enough and lacked support.

Perhaps the greatest problem of this whole work was the inexcusable large number of missing stars that exist well above the stated catalogue magnitude limit. The presenter has recently created and released a new digital version of this catalogue, that is usefully cross referenced to modern sources. This will be the author's first presentation regarding some new insights in its astrometric weaknesses, development and overall completeness. (During the NACAA, the author hopes to discuss the upcoming bicentennial of the creation of Parramatta Observatory, and the possibility of an organised special astronomical conference to celebrate the event in 2021 or 2022.)

The Australian Variable Star Hunt

Mike Thompson, Jacinta Lee Den Besten

Backyard AstroScience, Melbourne University, ASV, iTelescope

Backyard AstroScience is working with Melbourne University and the ASV to coordinate teams of novice astronomers hunting for variable stars in the southern skies. The teams initially come from Melbourne University's Telescopes-in-Schools programme and the ASV's Junior Section. Each team is provided with easy-to-follow instructions and support to get started with using their own 'scopes to capture, analyse and share photometric data. Teams can also use iTelescope and VPHOT (AAVSO) to refine their observations and zero-in on candidate stars. This presentation provides an update on our progress and challenges new teams to get involved.

Infrared Studies of Jupiter's Atmosphere

Barry Adcock

ASV, BAS, BAA

Storms and prominent features in the atmosphere of Jupiter are seen as dark or white spots, often rather irregular in shape. The smaller features may be seen to develop, evolve and fade in a short period of time. The lifetime of some features has been studied over a range of infrared wavelengths from 600 nm to 1000 nm. The data lead to the development of a temperature profile of the features. A technique for the study of subtle differences in the brightness of features as a function of wavelength has been developed.