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Observation Preparation

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

Guiding Options

Guiding with Michelle (and T-ReCS) can currently only be performed on one side of the chop. The reasons for and implications of this are discussed in more detail in the Mid-IR Resources section.

Observing Overheads

Mid-IR observing overheads can be significant and must be taken into account when proposing for time on Michelle. The following table summarises the overheads and efficiency, but please be sure to read the detailed notes below.

Sensitivity and Overheads

This section contains information on the sensitivity and performance of Michelle in its various observing modes. Go directly to:

Entrance Window

Michelle uses an entrance window made of Potassium Bromide (KBr). KBr has a transmission of ~90% across the mid-infrared. Since KBr is hygroscopic, all contact between water with the window must be minimized. This includes dew that may form on the window while observing under high humidity conditions. The humidity limit for observing with Michelle at Gemini is a relative humidity of 80%. During its use at UKIRT, a protective "sacrificial window" system was implemented to help prevent damage to the cryostat window that serves as the vacuum seal between the dewar and the atmosphere.


A list of the Michelle broad and narrow-band filters is presented here. Since the filter wheel is common to both the imaging and the spectroscopic light paths the filters are available in both modes. The longpass filters are used for lowN and MedN1 spectroscopy, while the narrow-band filters are used with the higher-resolution modes (all spectroscopy filter selection is done internally by Michelle and need not be specified by the PI). Transmission data are available for some filters, as indicated.

Waveplates and Wire Grids

Michelle contains two half-wave plates, one for the N-band window and one for the Q-band window, along with two wire grids. Together these allow polarimetric observations.

Detector Information

Michelle contains the same detector as T-ReCS. Some basic characteristics of the detectors are shown in the table below:


Imaging polarimetry for Michelle was commissioned in December 2005/January 2006. This observation mode has been offered for science usage starting in semester 2006B. This page gives some guidelines on carrying out Michelle polarimetry observations. These guidelines may change as we get more experience with such observations. Spectral polarimetry is not yet commissioned and so is not offered at this time.


Michelle's slit mask currently contains five slits for spectroscopy as well as an "open" mask for imaging. Resolving power is inversely proportional to slit width. The width of the two-pixel wide slit (~0.4") somewhat exceeds the diffraction limit in the 10um window (1.2 lambda/D at Gemini corresponds to 0.3" at 10.0um), and is narrower than the diffraction limit in the 20um window. The three-pixel wide slit is a better match at 20um. Our best estimate of the imaging pixel scale is 0.1005 arc-seconds per pixel, based upon binary star separation measurements.