The Variable Star Section was formed in June 1998 to educate and assist members to observe stars that change in brightness. Members are encouraged to submit their observations to international databases (AAVSO, RASNZ etc) where the data is used by professional astronomers to determine how stars behave and evolve over time. Variable star observing is one of the few fields where amateur astronomers can make a real contribution to the science of astronomy.
The Variable Star Section of the Astronomical Association of Queensland comprises a group of people who have a research interest in stars that vary in brightness over time. We are also members of other organizations that promote the study of variable stars, including the American Association of Variable Star Observers (AAVSO) (www.aavso.org) and Variable Stars South (www.variablestarssouth.org). Members of the Variable Stars Section have published papers base on their results in refereed journals, an example of the fact that amateur astronomers can make significant contributions to this field of astronomy.
There are several types of variable stars, and their detailed classification is quite complex. Stars vary in brightness due to the effects of one or more physical processes. Some of these processes are:
- Pulsation over regular or irregular cycles, with expansion and contraction of the outer layers of the stars, resulting in changes in surface temperature and therefore changes in brightness and colour. Examples are long period variables such as those of Mira type, and short period pulsating stars of the delta Scuti type.
- Rotation of stars with non-uniform surface brightness and/or ellipsoidal shapes. The non-uniform brightness in the surface of the star may be due, for example, to starspots (equivalent to sunspots on the Sun, but much larger).
- Cataclysmic events in which stars show sudden, dramatic increases in their brightness caused by thermonuclear processes in their surface layers (novae) or deep in the interior (supernovae). These are examples of cataclysmic variables. Every year, several novae in our galaxy and supernovae in other galaxies are discovered by amateur astronomers.
- Eclipse of one star by a nearby companion. These are close (in the sense of distance between the stars) binary eclipsing stars, with the planes of the orbits parallel (or nearly parallel) to the line of sight from Earth. When one star passes between earth and the other star, the apparent brightness of the system decreases. Detailed studies of such events allow astrophysical properties of the eclipsing systems (such as masses of the stars) to be determined from amateur observations.
If you have a CCD or CMOS camera designed for astroimaging, or a DSLR camera attached to your telescope, you can perform photometry of variable stars.
Using the naked eye, binoculars or telescopes, the variable star and nearby non-variable stars of known brightness are observed, and the brightness of the variable star, at a particular time, is estimated by comparing it with the appearance of these adjacent comparison stars.
In 2018, Professor David Moriarty was awarded the Page Medal for work on eclipsing binary stars and its application to models of stellar evolution.
In 2016, Dr Roy Axelsen was awarded the Page Medal for high-precision photometric observations and the Fourier analysis of Delta Scuti variables.
Most recent papers by members
Digital single lens photometry in white light: a new concept tested on data from the high amplitude δ Scuti star V703 Scorpii
A novel method of digital single lens reflex (DSLR) photometry is described. It derives non-transformed instrumental magnitudes from white light (green, blue, and red channels of the DSLR sensor combined), and is assessed by comparing the results with non-transformed instrumental magnitudes from the green channel alone, and with green channel magnitudes transformed to the Johnson V standard.
The high amplitude δ Scuti star AD Canis Minoris was studied by photoelectric photometry (PEP) during one night in February 2011 and by digital single lens reflex (DSLR) photometry during seven nights in January and February 2016.
Recently refined periods for the high amplitude δ Scuti stars V1338 Centauri, V1430 Scorpii, and V1307 Scorpii
Digital Single Lens Reflex (DSLR) photometry of the high amplitude δ Scuti stars V1338 Centauri, V1430 Scorpii, and V1307 Scorpii was taken during the southern autumn and winter of 2015.
The δ Scuti star ZZ Microscopii (HD 199757) was studied by photoelectric photometry (PEP) on three nights in 2008 and by DSLR photometry on three nights in 2014.
DSLR photometry of the δ Scuti star EQ Eridani (HD 28665) was undertaken on six nights between 2 November and 8 December 2013.
Methods for O-C (observed minus computed) diagrams and for the determination of light elements of variable stars with linear and second order polynomial ephemerides.
Methods are described for the construction and analysis of O–C (observed minus computed) diagrams and for the determination of light elements (ephemerides) of variable stars and the standard errors of the elements.
V393 Carinae is a 7th magnitude δ Scuti star which has a principal period of 0.1413 d and an amplitude of 0.2 magnitude in V.
Photoelectric and DSLR photometry of the monoperiodic high amplitude δ Scuti star RS Gruis yielded 16 times of maximum determined by the author from 2007 to 2013.
DSLR photometry of the monoperiodic, high amplitude δ Scuti star BS Aquarii yielded five times of maximum in September and October.