Transcript QUINN_2004 - Armagh Observatory

Ciara Quinn
Sacred Heart Grammar School Newry
Nuffield Science Bursary 2004
Methods and materials
Introduction
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.
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.
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.
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.
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.
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The Telescope
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.
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.
Thanks to everyone at Armagh Observatory for all their friendly help and advice especially Dr. Simon Jeffery, project
supervisor.