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).
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Last Updated: 30 January 2008
Ian Skillen, wji@ing.iac.es |