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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
Background brightness
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).

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Last modified: 17 June 2012