Michelle Introduction

Michelle is a mid-infrared (7-26 micron) imager and spectrometer, formerly in use at UKIRT but now on long-term loan at Gemini. Michelle is available for imaging and spectroscopy with all of its gratings and its echelle.

Michelle's detector is a Si:As IBC array with a format of 320x240 pixels. When configured in its imaging mode, Michelle has a 0.1005 arcsec/pixel plate scale and critically samples the diffraction limited mid-infrared Gemini PSF. When configured as a long slit spectrometer, Michelle has a plate scale of 0.201 arcsec/pixel and employs five gratings covering a range of wavelengths and resolutions. With the lowest resolution gratings, spectra of the entire 8-13 micron or 16-25 micron windows can be recorded in a single exposure. At medium and high resolutions the detailed profiles of dust and hydrocarbon emission and absorption features can be observed as well as the velocity profiles of broad lines. Michelle's echelle provides velocity resolved observations of narrow emission lines. Michelle provides background limited performance in all of these modes except, in some cases, at the highest spectral resolution.

An overview of Michelle's capabilities is given below. For detailed information on Michelle follow the link to Performance and Use on the left-hand menu or click here.

Further details on e.g. filters, grating, slits and other Michelle components can be found by following the link to Michelle Components on the left-hand menu bar or by clicking here.

Overview of Michelle's Capabilities

Science Modes:	Imaging though medium and narrow-band 10um and 20um filters (chop and nod) Imaging polarimetry through medium and narrow-band filters (chop and nod) Low resolution long-slit spectroscopy (chop and nod): R ~ 200 (with 2 pixel wide slit) at 7-14 microns R ~ 110 (with 3 pixel wide slit) at 16-26 microns Medium and High resolution long-slit spectroscopy (stare and nod) R ~ 1000 with 2 pixel wide slit) at 7-26 microns R ~ 3000 (with 2 pixel wide slit) at 7-26 microns R ~ 10000-30000 (echelle, with 2-3 pixel wide slit) at 7-22 microns - with some limitations
Wavelength Coverage:	7-26 microns
Detector:	Raytheon 320x240 pixel Si:As IBC array Switchable-capacitance: deep-well mode for broad-band imaging, medium-well mode for spectroscopy
Imaging:	Image quality approaching the diffraction limit (FWHM ~ 1.22 lambda/D ~ 0.31" at 10 microns, ~0.63" at 20 microns) Pixel dimension = 0.1005" (imaging only) Field of view = 32"x24" in imaging mode (but note that current maximum chop throw is 15") Imaging usually not available using the broad band N and Q filters, due to saturation problems
Imaging Polarimetry:	Imaging polarimetry was commissioned in December 2005, and has been offered for regular science usage since semester 2006B. Michelle contains two half-wave plates and two wire grids that permit measurement of linear polarization in the N-band and Q-band atmospheric windows.
Spectropolarimetry:	Spectral polarimetry has not yet been commissioned and so is not currently offered.
Spectroscopy:	Pixel dimension 0.201" (spectroscopy only) Slit length = 43.2" (note that current maximum chopper throw is 15") Slit widths = 0.201" to 1.608"; normally the 2 pixel wide - 0.402" slit is used for point sources in the 10um region and the 3 pixel wide - 0.603" slit is used in the 20um region
Wavefront Sensing:	No on-instrument sensors; uses facility Peripheral Wavefront Sensors. For chopped observations, PWFS2 should be used. Guiding is on one side of chop only for imaging and low resolution spectroscopy. Medium resolution and echelle spectroscopy are performed in stare mode, guiding at all times.

Last update August 23, 2006; R. Mason & A. Verma