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OT Details

This page explains how to configure T-ReCS in the Observing Tool:

Observation Preparation

This section contains instructions for configuring T-ReCS at phase II. It is organised as follows:

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.

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.

  Initial Setup Observing efficiency
Imaging 6 mins 30%
Spectroscopy (chop-nod mode)