1.1.1 Wavelength Range

The designed and laboratory measured wavelength ranges are given in the table below:

Chan    Designed Wavelength     Bin Range      Lab. Measured Wavelength
 1       1.7636 -- 1.8044       212 -- 28        1.7597 -- 1.8121
 2       1.8298 -- 1.8942       224 -- 36        1.8284 -- 1.8957
 3       3.1631 -- 3.1912       27 -- 229        3.1633 -- 3.1933
 4       5.0160 -- 5.1143       40 -- 234        5.0163 -- 5.1143

It should be stressed that these wavelengths are only valid at the designed, nominal BCS boresight. Because of the nature of the way a bent crystal spectrometer works, if a source is observed at other than the boresight then the wavelength range observed by the detector is shifted. In order to allow the SXT to observe more of the northern polar corona, the Yohkoh spacecraft is normally pointed several arcmins north of its designed pointing; because the dispersion axes of the crystals are oriented in the north-south direction, with this offset pointing channels 1 and 2 are normally seeing wavelengths that are slightly shorter than designed, and channels 3 and 4 slightly longer than designed. Consequently, during times of the year when the north pole of the Sun is tilted towards the Earth (i.e. Oct-Jan), if the active region is in the southern solar hemisphere, then this offset pointing severely compromises the ability of the BCS to observe the blue-wing in Ca XIX (channel 3).

The bin shifts caused by an offset in the pointing were measured in the laboratory to be (6.6340.039) 10 bins/arcsec, (4.7300.025) 10 bins/arcsec, (8.2180.062) 10 bins/arcsec and (4.3050.028) 10 bins/arcsec for channels 1 to 4 respectively (note: these are per single bin - channels 3 and 4 are often double binned). These values are being confirmed by in-orbit measurements which compare the bin of the resonance line with the source position observed by SXT. The above values correspond to 15.074, 21.142, 12.168 and 23.229 arcsec/bin.