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Low-Dispersion Survey Spectrograph (LDSS)

LDSS offers the option of either a low-dispersion or a high-dispersion grism which, with a 1.7" slit, give resolutions of 45 and 10Å FWHM respectively. With the low-dispersion grism the peak instrumental throughput is 56% near 5000Å, falling to 34% at 4000 and 7500Å; for the high dispersion grism these figures are reduced by about 15%.

Low resolution. With the Thomson CCD and a wide slit, a star with AB6600=17.7 will give 1 electron/s/Å. In dark time, with 2" seeing and a 1.7" slit, a star with R = 21.9 will give a S/N = 10 per 22.5Å wavelength bin at 6000 Å in 4 hours (broken into 8 x 1800s exposures).

High resolution. With the IPCS and a wide slit, a star with AB4500=16.3 will give 1 count/s/Å. In dark time, with 2" seeing and a 1.7" slit, a star with B = 20.9 will give a S/N of 10 per 5Å wavelength bin at 4500Å in 4 hours.



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