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: http://www.stsci.edu/instrument-news/handbooks/ghrs/GHRS_11.html
Дата изменения: Wed Feb 14 17:44:46 1996 Дата индексирования: Sat Dec 22 16:57:52 2007 Кодировка: |
Very High Signal-to-Noise Spectroscopy
The best achievable signal-to-noise with STIS is likely to be about 100 because of inherent limitations in the stability of the flat fields of the MAMA detectors. On the other hand, the GHRS has been shown to be able to obtain signal-to-noise ratios in excess of 1,000 when special techniques are employed. We suggest that you consult Gilliland et al. (1992) and Lambert et al. (1994) to see how the GHRS may be used in this way. Counting Photons at High Rates
For bright objects, STIS will be limited to a maximum local count rate of approximately 50 counts per second per pixel and a global count rate of 300,000 counts per second. However, the GHRS, even at a rate of 20,000 counts per second per diode, can be corrected for paired pulses to an accuracy of about 1%. Thus there are very bright objects for which excellent spectra can be obtained with the GHRS in a short time, whereas STIS may need substantially longer because a neutral density filter would be required. We suggest that you consult the STIS Mini-Handbook to determine how well STIS is likely to perform, and to emphasize the better efficiency of the GHRS in your proposal if there is a substantial difference in exposure time.