Occultation by asteroid 329 Svea
Observed: 7 Nov 2007
9 Nov 2007
Updated 30 Nov 2007
Revised 28 Dec 2007 (GPS time uncertainty)
The minor planet 329 Svea was observed occulting a 11.54 mag star:
the size of the shadow flying over my location was 68.8km.
The occultation of mag 11.54 star 2UCAC31985164 (GSC115-01328) by the
asteroid 329 Svea on 8 Nov 2007 UT in the vicinity of my location was
predicted by S. Preston:
The observation was carried out with a 203mm f/6.3 SC telescope, a Clear
filter and a SBIG ST7E camera (KAF401E CCD). The exposure was 60s long,
starting at 00:33:28 TU: I let the telescope tracks for about 10s, then
I switched off the RA drive.
I estimate the uncertainty on the time with my NMEA GPS as 2s (I compared
with the French Horloge Parlante 3699). Futhermore, MaximDL3 records the time
to the nearest second. The total uncertainty on the timing of the beginning of the
occultation is then +/-2.5s.
A part of the resulting image is:
1: the occulted star at the beginning of the exposure;
2: the beginning of the occultation;
3: its end;
4: the occulted star at the end of exposure.
I solved the astrometry of the image: The image is 0.2937° and 765 pixels
width. The angular distance between 2 and 4 is 4.26'+/-2pixels or 17.0+/-0.2s,
then the beginning of the occultation 2 is at 0:34:11 TU +/- 2.7s. The
angular distance between 2 and 3 is 1.93'+/-2pixels and the duration of
the occultation is 7.7+/-0.2s.
Another analysis is to rotate the image so that the trails are parallel
to the X axis; this was done with MaximDL 4.60, the rotation being 1.36°.
The intensity profile of the trail with the occultation can then be extracted:
The average intensity during the occultation is 211.5+/-3.1 where the
uncertainty is the standard deviation, for the trail it is 228.8+/-3.4,
and after the trail (the image background) the intensity is 211.7+/-2.9.
The lengths are measured at mid-heights (I checked that
a 60s exposure with MaximDL does give a trail of 653pixels). The
distance between 2 and 4 is then 188.0+/-1.6pixels or 17.32+/-0.15s, yielding
the time at the beginning of the occultation of 00:34:10.68+/-2.65UT.
And the occulation duration is 83.75+/-0.55pixel or 7.72+/-0.05s.
At the time of the occultation, the angular velocity of the asteroid
was 25.76"/h and the geocentric distance 1.7255au. The size of the shadow
that flew over my location was then 68.8km (+/-1.8km with the first calculation,
+/-0.5 with the second one) and its velocity 8.9km/s.
Telescope and camera configuration.
Computer and software configuration.