Drift-scan CCD method

applied to the HIP11333 occultation by Palma


An occultation of the HIP 11333 star by Palma was predicted for the August 7th 2000 near 3h25m TU. My observatory is located outside the pathway predicted for that occultation. Nevertheless, I recorded the magnitude of these objects with an Audine CCD camera (Kaf401E) and a LX200 (8") telescope.


Image of HIP11333 field at 3h21 TU.
Exposure time is 10 second and binning 2x2 (384x256 pixels)
HIP 11333 was placed in the white frame to be acquired by a scan.

HIP11333 has a magnitude of V = 7.28 (B-V=1.69) and the drop of brightness, due to the occultation, should be 5. Maximum duration predicted of the occultation was 8.2 seconds. The technique I used to record the magnitude variations is based on the drift-scan technique. The telescope is motorized and compensate the diurnal Earth rotation during the recording. The scan consists to read the CCD lines slowly in order to obtain a star image expanded versus time (remember that the drive motor of the telescope is on). The time resolution can be tuned with the duration of exposure between two line shifts.

We used the AudeLA software and its scan acquisition function. AudeLA used is a beta version. A final version should be achieved in the next weeks. The acquistion script was :

set largeur 100
set hauteur 3000
set binning 2
set intervalle_de_temps 200

cam1 scan $largeur $hauteur $binning $intervalle_de_temps
vwait status_cam1

I used 0.2 second per vertical shift, 2x2 binning. Scan begun at 3h21m45s TU and was ended 10 minutes after. As the image below shows, no occultation was observed near the predicted time. Two manual "occultations" of the aperture of the telescope allowed to calibrate the scan.

Compared to the motor-off-scan technique, the motor-on-scan technique allows to record a many minute event a allows the tune the time resolution.