Methods and materials 

To calculate the frequencies present in the light curve of KPD 1930+2752, a Fourier transform is needed. However, in order to complete this transform, I need data concerning the change in magnitude of KPD 1930+2752. I obtained this data though a process called high-speed photometry. In this process, a large number of short duration exposures are taken of KPD 1930+2752, using a CCD camera attached to Faulkes Telescope north in Hawaii.

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The Telescope

Faulkes telescope is a 2m reflector telescope located on the mountain Haleakala on the Hawaiian island Maui. It was set up to make a research grade telescope available to school children to enable them to carry out their own research astronomy projects.

The telescope is controlled from a computer and the user can choose the object to be viewed, the exposure time of the image and the filter on the telescope.

It provides young astronomers with the invaluable resource and the experience of controlling a high quality, research telescope to carry out their own research in an area of science that interests them an experience that was previous unavailable.

In total I was given three and a half hours on Faulkes telescope to observe KPD 1930+2752. This time was divided into two sessions, one 2 hours long and the other 1½ hours. During this time I was in control of the telescope.

As each exposure was read off the chip, the image recorded was shown on the screen. This, along with the use of a star map, allowed me to identify KPD 1930+2752. The image below is an example of the images provided by Faulkes Telescope, immediately after the exposure has been taken. The circled star is KPD 1930+2752.

When all the imaged had been captured, I used the photometry tool in AIP4WIN to obtain numerical values for the change in magnitude of KPD 1930+2752. Using this data, I was able to produce 2 graphs showing the change in magnitude of the star over time.

I also used this data to produce a Fourier transform of the data in the computer program Period98.

Thanks to everyone at Armagh Observatory for all their friendly help and advice especially Dr. Simon Jeffery, project supervisor.

Results

The graphs below represent the change in magnitude of KPD 1930+2752 over time. The first graph shows the data collected during the first observing period of 1 ½ hours and the second graph the data collected during the second observing session on Faulkes telescope which was 2 hours long.

The following graph is the Fourier transform produced by Period98 from the data I collected over 2 observing sessions on Faulkes Telescope.The peaks on the graph represent the individual frequencies present in the light emitted from KPD 1930+2752.

Introduction

During my 6 week placement at Armagh observatory, I was set the project of studying the change in magnitude of a variable star, KPD 1930+2752. KPD 1930+2752 is actually 2 stars, known as a binary system, it consists of 2 stars, one hot, bright sub-dwarf B star orbiting round a smaller, denser white dwarf in a period of 137 minutes.

KPD 1930+2752 is known to be pulsing. When the surface of the star contracts, it becomes opaque. All the photons under the surface become trapped. This causes the pressure of the gas to increase and the volume expand. The surface expands and becomes transparent, allowing the photons to escape. The pressure drops and the surface contracts again, becoming opaque. This process is occurring all over the surface of KPD 1930+2752. There is another type of variation present in the star. The hot sdB star is physically distorted by the white dwarf star, making it become egg shaped. This means that the star is brightest when the viewed side on, I.e. when more of the star is is view.

Ciara Quinn Sacred Heart Grammar School Newry Nuffield Science Bursary 2004