# SUSI2

Photometric Solutions and Throughputs

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###### SUSI2 Throughput

For the purpose of observation preparation, the SUSI2 Exposure Time Calculator computes the counts based on the known optics and CCD data for SUSI2. The results are in good agreement with the number of photo-electrons measured at the telescope. The table below gives the average count rates (in adu) of a 15th magnitude star, in one second exposure at an airmass of 1.0. The stability of countrates is excellent, as illustrated by the evolution curves.

 Band U B V R I CCD#45 4780 31200 46050 45100 18200 CCD#46 4690 30840 45770 44920 17950

Count rates (in adu) on SUSI2, for a mag=15 star, 1 second exposure airmass = 1.0

###### SUSI2 Photometric Solution

The photometric parameters of SUSI2 were determined during the commissioning of the instrument, and are measured regularly as part of the Calibration Plan. Typical values obtained using several Landolt standard fields are shown in the following table:

 Typical photometric solutions U = u + 23.52 -airm*0.35 +0.10*(U-B) B = b + 25.46 -airm*0.22 -0.22*(B-V) V = v + 25.74 -airm*0.13 -0.02*(V-R) R = r + 25.61 -airm*0.09 -0.05*(R-I) I = i + 24.61 -airm*0.07 -0.10*(R-I) M: standard magnitude, m: instrumental magnitude (adu/s)

NOTE: These values (and the archive of photometric solutions measured by us during technical nights) should only be used as a reference. Each observer should measure their own photometric solution during their run. Remember that the extinction can change due to global events, and the Zero Points depend on the flat-field you use, or, more specifically, the region used for the normalisation. The latest photometric solution carried out by us can be found at:

/sci/facilities/lasilla/sciops/ntt/susi/docs/susiCounts.html