Variable Stars 2017

This year my main interest has moved on from deep sky imaging. This started when a club member publicised an upcoming minimum in the most well known variable star Algol in the constellation of Perseus. At the time I had little interest in variable stars or in direct observing. It occurred to me that I could image the event by taking an image of the star when at it’s dimmest and again when at it’s brightest and create an animation. This can be seen below.

Although this is very pretty it is not very scientific and does not represent what is really happening. So I started looking into how the brightness of stars could be measured by an amateur. Having been on an Open University Practical Observing course in Majorca some years ago I tried using the software MaximDL which I already had and used on that course. For the first month or so of the year I tried measuring the brightness as a function of time for a couple of variable stars recommended for beginners from the website of the BAA (British Astronomical Association).

Following advice from members of the BAA Variable star section I changed to using the free software MUNIWIN. Below are the results of some of the stars I studied during the year.

EG Cep in the constellation Cepheus varies in brightness in a regular fashion with period about 13 hours as it is an Eclipsing Binary Star. I.e. it is two stars in orbit around each other so that they eclipse each other. The large dip in brightness is due to the fainter star passing in front of the brighter and the smaller dip is when the fainter star passes behind. This plot, known as a phase diagram, was made from observations using a CCD camera to be combined to show the full cycle.

This chart showing the light curve for HL Au was taken on one night only and so only shows one part of the cycle, namely the primary eclipse. The times are in UT (=GMT)

I received a circular from the BAA to say that the star OV Boo had gone into super outburst. It was normally of magnitude in the range 18 - 20.6 and was discovered to now be magnitude between 11 and 12. I was lucky enough to find it and confirm that observation and then carried out time-series photometry on as many times as the sky was clear.

OV Boo is also an eclipsing binary star with an incredible period of around 70 minutes but was decaying in brightness over a much longer time period. The first chart below shows the full period of my observations and below the detail of a sample of those one night observations.

The following charts show results from other variable stars the I observed in 2017. A minimum that is flat indicates that the eclipse is total. I.e. the cooler less bright star is smaller than the brighter one and once it covers the disc of the brighter star does not change until it starts to come off.


All the data has been submitted to the BAA database and to the AAVSO database. It is very rewarding when I am notified that some of the data has been used by professionals or students in their research.