NIRC Filter Macros

The leftmost column contains the command name. The following two columns show the filter combination's central wavelength and FWHM. Next are the two filter wheel positions (inner and outer). The sixth column gives an estimate of the background rate in electrons/sec (using 6 electrons/DN). This of course can vary from night to night, and position in the sky. The seventh column gives an estimate of the sensitivity, in the form of a "zero-point" magnitude. This is 2.5 times the log (base 10) of the number of electrons/sec expected from a zeroth magnitude star. Note that standard star measurements exist only for standard passbands; all other estimates (shown in italics) are approximate. Also note that atmospheric conditions will cause the apparent sensitivity to vary from night to night. The icons in the last column link to plots of the individual filter passbands.

Macro Wavelength FWI FWO Background Sensitivity  Plot?
CMD Central FWHM Pos Pos electrons/sec  
Broad-Band Filters  
z   1.03225   0.1565 2 19
j   1.251   0.292 3 10 2000 28.13
jh   1.30   0.60 1 10
h   1.6575   0.333 4 10 6400 27.80
hk   1.967   1.13 9 19
kp   2.1235   0.337 6 19 3800 26.92
ks   2.155   0.33 7 19 3600 26.78
k   2.2135   0.427 8 19 7200 27.16
kw   2.249   0.594 10 19 30,000 27.50
ch4   2.269   0.155 5 10
ls   2.9785   1.023 12 19 3,200,000* 26.62
kl   3.1475   2.003 14 19
lw   3.492   1.490 15 19 45,000,000 26.94
lp   3.831   0.620 13 19 9,700,000* 26.24
lm   3.945   2.002 17 19
m   4.718   0.628 16 19 95,000,000 24.87
mw   5.022   1.356 18 19
Thermal Blocking Filters  
uv22i   1.45   2.5 11 19      
uv22o   1.45   2.5 19 10      
Narrow-Band Filters  
hei   1.0829   0.0136 19 0 49 24.70
pgamma   1.0930   0.0104 11 1 47 24.62
oii   1.23605   0.0105 19 2 86 24.31
pbeta   1.2823   0.0146 11 3 350 24.72
feii   1.6471   0.0176 11 4 330 24.12
h210   2.12495   0.0235 11 11 150 22.98
brgamma   2.1647   0.0224 11 12 200 23.21
h221   2.24855   0.0239 11 13 138 22.95
kcont   2.25965   0.0531 19 15 570 24.43
co20   2.2973   0.0274 19 14 240 23.41
pahcs   3.0825   0.1007 19 16 285,000 24.25
pah   3.3100   0.063 19 17 540,000 23.53
pahl   3.4128   0.0734 19 18 490,000 23.92
bralphacont   3.9923   0.0483 19 5 930,000 23.51
bralpha   4.0455   0.0524 19 6 1,320,000 23.40

* Empirical fits of the background rate as a function of airmass, AM:

Background rate in Ls = (1.8 * AM + 1.4) x 10^6 electrons/sec
Background rate in L' = (2.8 * AM + 6.9) x 10^6 electrons/sec

Remember in these formulae that AM is always greater than or equal to 1!

These formulae can be interpreted as a sky background rate, which depends on AM, and a telescope+instrument background rate, which is independent of AM.

Last Update: 1/29/98

Name: Bob Goodrich

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