; exposure-time calculation for CHIRON, fiber mode ; Mar 10, 2011 ; Input parameters ron = 5.5 ; electrons npix = 2.5 ; pixels across order nbin = 4. ; binning in dispersion direction eff = 0.05 ; total efficiency f0 = 3.4e5 ; photons/s/pixel unbinned, V=0-mag pixel 0.0202 A n = 50 ; number of points time = 10^(1. + findgen(n)/(n-1)*alog10(120)) ; 10s to 1000s vmag = [5.,7.5, 10, 12.5] ; stellar magnitude nmag = 4 snr = fltarr(n,nmag) flux = nbin*f0*eff*10^(-0.4*vmag) ; flux, el/s/pixel for i=0,nmag-1 do snr[*,i] = time*flux[i]/sqrt(time*flux[i] + npix*ron^2) !p.charsize = 1.5 jj = 35 plot, time, snr[*,0], xtitle='Exposure time, s', ytitle='SNR', /xlog, /ylog, yr=[1,1000], xs=1 for i=1,nmag-1 do oplot, time, snr[*,i], li=i for i=0,nmag-1 do xyouts, time[jj], 1.7*snr[jj,i], 'V='+string(vmag[i],'(F4.1)') ;----