Test exposures on spectrophotometric standard stars, taken by several observers and analysed by Darragh O'Donoghue, show that the Grade 1 chip has essentially the same sensitivity as the Grade 2 device. Several improvements have been made to the spectrograph operations. Atmospheric dispersion may rotate the spectra very significantly at large zenith distance, however, and the turntable on the 1.9m is too stiff to allow the parallactic angle of the slit to be selected for individual spectra. This limitation of the telescope turntable also means that the instrument is unsuitable for long slit observations of galaxies and other nebulae where the position angle of the slit needs to be aligned with significant directions in the object. Three new gratings have been added in 1998 to take advantage of the great red sensitivity of the CCD and the first two are available now.
Special attention needs to be given to correcting for atmospheric features.
The problem with the first order red spectrum overlapping, and in the case of red stars swamping, the blue second order spectrum has been overcome by adding a second BG39 filter in place of one of the now largely redundant neutral density filters in the star beam filter wheels. The use of the two filters in series, giving a total of 4 mm of blue glass, enables the blue spectra of even the reddest carbon stars, with B-V of 5 magnitudes or more, to be recorded in second order. Such contamination may not be obvious until the spectra have been reduced and calibrated, so it is suggested that these filters are used in any first order work on red stars in the violet. Tests are continuing but it is likely to be beneficial to bin the spectra along the slit at all times. Tom Lloyd Evans Press Releases Archive of SAAO News Items SAAO Newsletter .