Ranges of typical values of background brightness for INGRID are given in columns 2 and 3 in mag/sq-arc and ADU/s respectively. Variations of the background brightness during specific nights are given here. 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. Background brightness in K and Ks is highly dependent on temperature. During summer nights (T~15 C) background brightnesses in K and Ks are approximately twice the quantities measured in winter time.
The exposure time before saturation and the exposure time which gives background limited signal (rather than readout noise limited signal) are given in the last two columns of the table. These times have been obtained from the values in column 3.
Measurements of the zero points and background brightness in different nights can be found here.
| Filter | Zeropoint (mag per 1 ADU/s) |
Background brightness (mag/sqr-arcsec) |
Background brightness (counts/s/pix) |
Time to saturation * (s) |
Time to be background limited ** (s) |
J | 23.4 | 15.4-16.4 | 35-98 | 800-286 | 89-31 | H | 23.4 | 13.5-14.7 | 184-610 | 153-46 | 17-5 | Ks | 22.9 | 11.9-12.5 | 689-1515 | 41-18 | 4.5-2 | K | 23.0 | 11.7-12.1 | 1589-1769 | 26-16 | 3-1.8 |
