The following presentations were made at the National Australian Convention of Amateur Astronomers (NACAA) in 2016.
Of all the night sky, no fields are so rich or challenging to observe than the Large and Small Magellanic Clouds. What follows are some highlights of historical observations of these fields, along with recent visual variable star estimates of selected stars. The first research article mentioning the Clouds available here was published in 1774, after Neville Maskelyne’s trip to the island of St. Helena in the South Atlantic. 60 years later the really pivotal work was undertaken by John Herschel from the Cape of Good Hope in South Africa. In fact, in my opinion Herschel’s chart of the Large Magellanic Cloud published in 1847 is of more practical use than some high profile modern charts of the area. Several stars in the current observing program can be found on this chart. Recent observations focus on what has been done from Linden Observatory west of Sydney, but other people’s work is introduced as much as possible. An unexpected result of writing this talk is that a much more useful observing program of these two galaxies is in place today than existed before.
A basic digital single lens reflex (DSLR) camera can provide research-quality photometry if appropriate care is taken when recording and analysing images. This talk will give a general background to the equipment and techniques employed by the author. This will be followed by descriptions of several research projects in which DSLR photometry has complemented professional spectroscopic studies.
V1338 Centauri, V1430 Scorpii and V1307 Scorpii are high amplitude delta Scuti stars for which the last period determinations were made in 2006, 2004 and 2001 respectively. In view of the elapse of time since, DSLR photometry was taken from April to August 2015. Fourier analysis with the software PERIOD04 identified the dominant frequencies of pulsation to be 7.6372 +/- 0.0001 c/d (cycles/day), 11.93629 (+/- 0.00004) c/d and 8.54475 (+/- 0.0007) c/d respectively, corresponding to periods similar to those found by other authors. For all three stars, additional harmonic frequencies were found, integer multiples of each of the dominant oscillations, representing the extent to which the light curves are skewed from pure sinusoids. Furthermore, an additional low amplitude frequency of 18.4335 (+/- 0.0008) c/d was identified for the star V1430 Sco, which is a new discovery. Subtle shoulders were identified on the descending limbs of the light curves of V1338 Cen and V1430 Sco. Precise times of the peaks of the light curves were calculated with the software PERANSO. Using these times of maximum and those reported previously in the literature, new linear ephemerides were calculated, yielding the following periods, similar to those reported by other authors, but now with greater precision: 0.13093808 (+/- 0.00000003) d for V1338 Cen, 0.08377709 (+/- 0.00000001) d for V1430 Sco, and 0.11703066 (+/- 0.00000001) d for V1307 Sco. High-amplitude delta Scuti stars are suitable objects for study by amateur astronomers, who can make significant contributions to the literature using modest equipment.
Colour photometry as a simple alternative to spectra was introduced with the development of filtered photoelectric photometry in the 1950s. It is cruder in some ways and relies heavily upon empirical relationships. However, it is quicker and simpler than spectra and can reach much fainter magnitudes. This presentation initially explains what it is and how it has been used, with a variety of practical examples. It then discusses observational possibilities in a range of astrophysical aspects of stars which show evolutionary or other changes in their light and colour curves.
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.