From schuehle@linmpi.mpg.de Tue Nov 18 16:45:58 2003 Date: Mon, 6 Sep 1999 17:44:15 +0200 From: "[iso-8859-1] \"Schühle Dr., Udo\"" Reply-To: sumer-soft@esa.nascom.nasa.gov To: 'SUMER_SOFT' Subject: SUMER-SOFT: obscuration of SUMER slit with B detector [ The following text is in the "iso-8859-1" character set. ] [ Your display is set for the "US-ASCII" character set. ] [ Some characters may be displayed incorrectly. ] An analysis of B detector data provided by Davina Innes (thanks!) has shown that the slit length in recent images is shorter than expected. A short investigation has been carried out that confirmed this finding. The obscuration is most likely due to a change in the thermal environment of SUMER after the SOHO accident. No data before the accident have been found which would show this obscuration. Data after the SOHO accident show that not the full length of the unobstructed slit is visible on the B detector. Since the slit reference position is not the same for the A detector, this problem does not exist with the A detector. The slit obstruction is however dependent upon the thermal environment of the instrument in a way that it may deform the instrument structure which we must compensate by adjusting the slit reference position such that the short, central slit is always in full coverage with the detector readout window. As it is now, the obscuration of the (long) slit image is about eight to ten pixels (<3% of the slit length) when observed with the B detector. The upper part of the images of the long slits (slit 1, slit 2) and the short slits (slit 3 and slit 6) are effected by this obscuration when the B detector is used. The data analist is advised to make his own assessment of the length of the slit image when it is needed for data interpretation. The nominal length of the unobstructed slit image, if needed, can be computed with help of the MAGNIFICATION program supplied with the radiometry software of Klaus Wilhelm which is in the software tree. Udo Schuehle, MPAE, 9. September 1999