Subject: correction of previous message

From: Xiaohui Fan

Submitted: Mon, 4 Mar 1996 16:57:32 -0500 (EST)

Message number: 25 (previous: 24, next: 26 up: Index)

sorry, the g' efficiency in item 2 should be
0.100 instead of 0.100, typo. correct message attached below

 Dear DSC users,

 I repeated the efficiency calculation similar to what posted
ealier by Kris Stanek on 3.5m + DSC + SDSS filter + CCD system,
the result is similar to what Kris got. Details are :

 1. Based on observations of Oke-Gunn standards under SDSS filters
during Feb08/09, 09/10 nights. Both nights are  ~0.01mag level
photometric nights.

 2. Total efficiency of the system ( no correction for filter
transmission, reflection, secondary, in the sense identical to
the previous measurement of Stanek):
     u' : 0.027
**   g' : 0.100
     r' : 0.173
     i' : 0.144
     z' : 0.085
  Stanek's value which states 0.14 for v filter is quite consistent
  with current measurement. The above numbers assume the central
  wavelength and FWHM of SDSS filters as given in Fikugita et al.

  Richmond  took the new filter transmission curve posted recently by Jim
  Gunn and convlove it with Oke-Gunn standards. The results are L
     u' : 0.036
     g' : 0.110
     r' : 0.167
     i' : 0.136
     z' : 0.038 

 3. When assuming 0.85 reflection (three times) and secondary :
     u' : 0.045
     g' : 0.166
     r' : 0.290
     i' : 0.242
     z' : 0.143

 4. In Fikugita et al. paper on SDSS filter system, they 
     assume the filter transmission and  CCD Q.E. curve, and
     give the predicted number of photons per cm^2 in SDSS filters,
    below are the ratio of what I measured to what they predicted
    under a 3.5m telescope and three times 0.85 reflectivity :
      u' : 0.332
      g' : 0.444
      r' : 0.695
      i' : 0.718
      z' : 0.641
    which means this system is sth like 1/3 to 2/3 efficient as it
    should be.

Xiaohui Fan
Princeton University Observatory
Peyton Hall
Princeton, NJ 08544

email :
tel   : (609) 258-5153 (O)
        (609) 683-1315 (H)
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