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Sensitivity Tables (AO: NGS and LGS)


  • The sensitivity tables assume photometric conditions (50%-ile cloud cover), grey time (80%-ile sky background) and an airmass of less than 1.2. Note however that the OH sky emission can vary by a factor of ~2 up or down during the night
  • Individual exposure times of 600s were assumed for all cases.
  • Observations are assumed to be at f/32 and dithered (target object in the field at all times); sky subtraction noise is included.

NIRI Sensitivity Tables (no AO)

The values in these tables are based on results from the NIRI Integration Time Calculator. They assume 70-percentile (IQ70, ~average) image quality for all categories, photometric conditions (CC50), and an airmass of less than 1.2 for the sensitivites presented here.

Sensitivity Estimates

The values below are based on measurements at the telescope. These values are similar to what is estimated by the T-ReCS Integration Time Calculator. The overall accuracy of the ITC S/N values is of the order of a factor of 1.2 to 1.4, since conditions at the telescope may vary during an observation, and since for faint targets the assumed square-root of time scaling will not hold exactly. For faint targets we advise people to be conservative in their exposure times to ensure that the desired S/N is obtained. Sensitivity estimates are available for

Observing Overheads

Entrance Window

T-ReCS contains three entrance windows that are interchangeable in real time; the control software selects the window that is best for the specific observation and conditions.

T-ReCS Slits and Occulting Bar

T-ReCS contains 7 slit masks for spectroscopy, plus an "open" mask and an occulting bar for imaging mode. The slit widths are chosen to match the lambda/D and 2*lambda/D conditions at the upper end of the 10 and 20 µm wavelength bands, plus the lambda/D condition at three additional wavelengths in the 10 µm band. The lambda/D slits will generally provide the best spectral resolution in good seeing; the 2*lambda/D slits may be better in poor seeing or for fainter sources.

T-ReCS Diffraction Gratings

T-ReCS contains three diffraction gratings and an optical flat mounted on a rotating turret. Each diffraction grating is used in first order.


T-ReCS contains up to 20 filters mounted in two wheels. This page describes the current set of filters.

Detector Information

T-ReCS contains the same detector as Michelle . Some basic characteristics of the detectors are shown in the table below:
  Initial Setup Observing efficiency
Imaging 6 mins 30%
Spectroscopy (chop-nod mode)