Observing Proposals

This page contains the information necessary to prepare an observing proposal for IRIS2. This incluldes exposure time calculators for the imaging and spectroscopic modes of IRIS2 and a link to the IRIS2 Observing Manual


IRIS2 imaging exposure time calculator

The table below gives an indication of zero-points and limiting magnitudes for the IRIS2 broad band filters, as well as "typical" long-term average sky brightnesses. The sky brightness shortward of 2 microns has no clear seasonal variation, but can vary by up to 30% between (and especially within) nights. The K/Ks sky brightness is roughly a factor of 2 greater in summer (S) than winter (W), so the sky brightness and 5-sigma sensitivities are given separately for each.

The median optical seeing of 1.5" at the AAT corresponds to 1.2" at H-band (FWHM ~ lambda-1/5), which is what should be assumed when preparing proposals. It is worth keeping in mind however that since the commissioning of the dome air-conditioning system, up to half of all IRIS2 nights have experienced sub-arcsecond seeing.

Broadband Imaging Figures of Merit
Filter Zeropoint
(1 ADU/s at 1 airmass)
Flux for mag=0
Sky Brightness
5-sigma limiting magnitude
in 1 hr (on sky)
1.2" seeing, 2" aperture.
Z 21.16 2.9e8 17.0 21.9
J 22.58 5.9e9 15.7 22.0
H 22.79 7.2e9 14.1 21.3
Ks 22.37 4.9e9 13.5 (W)
12.6 (S)
20.7 (W)
20.3 (S)
K 22.35 4.8e9 13.3 (W)
12.3 (S)
20.6 (W)
20.1 (S)


IRIS2 Spectroscopic exposure time calculator

  • Exposure time estimates should assume 1.2" seeing for IRIS2 proposal purposes.
  • Nodding along the slit is assumed. If the target object is nodded to blank sky, then your S/N will be a factor of sqrt(2) worse in a given exposure time than that provided.