SS433 is a close binary system displaying bidirectional jets, which
has often been called the star that is "both coming and going", depending
on the attitude of its precessing jets that display changing redshifts.
It is a bizarre 14th magnitude object about 11,000 light
years away , lying in the constellation of Aquila. Ever since its
peculiar nature was discovered in 1979 by Paul Murdin
and David Clark, it has been scrutinized at many wavelengths.
It was labelled by the popular press as " the star that's both
coming and going ", since it displays both redshifted and blueshifted
spectral features.
It is now believed to be a binary system, with gas from the primary
being torn off by the gravitational attraction of a dense neutron star
or black hole companion. X-rays are emitted where this gas falls onto an
accretion disk, and the doppler
shifted spectra could be explained by gas being emitted at
80,000 km per sec along two opposed jets. The blue-shifted jet is
directed towards us on the Earth, while the red-shifted one points away.
These jets are believed to precess like a
rotating lawn sprinkler in a period of 164 days, which accounts
for the nightly variation in the spectral emission lines.
The binary period of the stars themselves is believed to be 13.08 days
with a range of magnitude 0.6-0.7. In addition there are variations on
time scales from 0.5 - 6 hours with amplitudes of 10%. This is an exceptionally
intriguing star to
monitor, and worth regularly observing.
In reply to a request by Dr. Kawai of Osaka-Kyoiku University for optical observations os SS433 simultaneous to X-ray observations from the ASCA satellite, I was invited to join in this international observing project . This proved to be a useful exercise in comparing amateur CCD photometry with those of professional observatories since participants were linked with an e-mail exploder.
CCD Photometry at Worth Hill Observatory
A 50 cm f/4 Newtonian is used in conjunction with a Starlite Xpress CCD camera. Recent CCD photometry tests on the star cluster M67 showed that it was possible to achieve consistent results providing due care was taken in the acquisition of dark frames and flat fields.
Procedure: It was hoped to obtain eight or
more CCD images of SS433 on each nights observing run. A master flat
field was obtained by averaging 12 images of the late dusk
sky. Each of these flat fields was exposed to get an image nearing 80%
saturation and prior to averaging each was dark framed. Care
was taken to ensure that the telescope was pre-focussed and that the "V"
filter was in place.
SS 433 is a 14th mag star, and in the 10x7 CCD field of
view the brightest comparison star was 11.5 mag. It was hoped that
exposures of 160 - 320 sec would give a sufficient photon count.
320 sec exposures were felt to result in the best degree
of saturation although not all these images were successfully guided.
Four consecutive images were stored on each disk together with a dark framed
image. Photometry was carried out using Pixwin and having selected a 7
pixel window, measurements were obtained by searching for the maximum reading
with the mouse driven cursor when selecting
SS433 and the comparison star - no. 2 in above image.
Results
Although there is limited comparison data to date, the results look promising. The primary minimum was predicted for 0h UT on May 3rd. The faintest magnitude I recorded occurred on 950503.129. My "V" band photometry was in general agreement with the Kagoshima Space Centre and of particular note was the result obtained on May 4th 2358h UT which agreed exactly with that obtained at the Wise Observatory, Israel ten minutes earlier at V= 13.91.
Acknowledgements
I should like to thank Norman Walker for loan of Johnson's "V" filter and for assistance in the initial CCD photometry tests, Richard Perry for his encouragement and finally Dr. Kawai for allowing me to partake in this exciting project.
For the results of this campaign take a trip to Japan.......
SS433
Home Page
Or go back to .....
Main Index