Throughput and Background Brightness
The table below contains the
most recent determinations of the INGRID/NAOMI
zero points (
zp). These are
the magnitudes, in each band, that give
1 ADU/s. Note that the zeropoints can change
from time to time, mainly due to cleanness of the telescope and NAOMI's
mirrors.
zp =
m + 2.5 log (
F) +
kx, where
m is the star's magnitude,
F is the flux in ADU/s,
k is the extinction constant and
x is the airmass.
Ranges of typical values of background brightness are
given in columns 2 and 3, in mag/sqr-arcsec and ADU/s respectively. The
background brightness in J and H is dominated by
airglow emission and
can vary considerably from night to night, and also during the same
night. Changes up to ~150% of the values shown here are not unlikely.
The K/Ks backgrounds are dominated by
emissivity.
The exposure time before saturation (obtained from the values in
column 3) is given in the last column of the table.
Filter |
Zeropoint
(mag per 1 ADU/s) |
Background brightness
(mag/sqr-arcsec) |
Background brightness
(counts/s/pix) |
Time to saturation *
|
J |
22.6 |
15.4-16.4 |
1.2-0.5 |
~ 6.5-16.5 hours
|
H |
22.7 |
13.5-14.7 |
7.3-2.4 |
~ 1-3 hours
|
Ks |
22.0 |
9.7 |
125.5 |
~ 3.7 mins
|
* Time to reach the full well limit (28000 ADU).