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Two Issues With T-ReCS Optical Performance

5 March 2005

Two recent issues regarding T-ReCS optical performance have recently come to our attention.

Filter and Window Changes; Implementation of an Occulting Bar

24 January 2008

Filter Red Leaks Fixed

The problems discussed in the 5 March 2005 Hot News concerning the red leaks in the Si-3 9.7 um and Si-4 10.4 um filters have been fixed. The old BaF2 blocking elements were replaced in November 2005 with CaF2 elements and have since been shown to be reliable in removing any light leaks.

Calculated Standard Star Flux Densities for Michelle Filters

A text file containing flux densities of standard stars calculated for the Michelle filters can be found at this link.The values in the file are in-band flux densities in Jy unless there is a "*" after the name, in which case the values in mJy. Those stars with values in mJy are calibration stars for SPITZER and so are unlikely to be used by Michelle. All values are calculated for zero airmass (i.e. outside the atmosphere).

Example mireduce output

mi> mireduce N20050903S0360 rawpath=datapath$
MIREDUCE ------------------------------------------------------------------
MIREDUCE Log opened at [Sat 18:03:54 18-Feb-2006]
MIREDUCE --------------------
MIREDUCE Input Parameters:
MIREDUCE      inimages       = N20050903S0360
MIREDUCE      outimages      = 
MIREDUCE      rawpath        = datapath$
MIREDUCE      outpref        = r
MIREDUCE      fl_background  = no
MIREDUCE      fl_view        = no
MIREDUCE      fl_mask        = no
MIREDUCE      bpm            = 
MIREDUCE      fl_flat        = no

Atmospheric Transmission Data

A set of atmospheric transmission files at resolutions comparable to those available with Michelle and T-ReCS is available below. The files were generated using ATRAN. All of them are for the summit of Mauna Kea, a telescope zenith angle of 30 degrees, and 1.6 mm of precipitable H2O.

The file format is: index, wavelength (um), transmission. Spectral sampling is 2 data points per resolution element.

Bright Stars with Spectral Types B-G

A list of bright telluric standard stars of spectral types B-G for calibration of Michelle spectra is provided below, along with estimated (in most cases) magnitudes at N and Q. Note the following advice on use of the stars in the list below.

T-ReCS Pupil Lens Wheel

The Pupil Lens Wheel is mounted between Fold Mirrors 1 and 2, close to the plane where the beam passes through the optical bench. By inserting a lens into the beam at this point, an image of the pupil (the telescope secondary mirror M2) is formed on the detector. The wheel has a diameter of ~XXX mm and has four positions.

T-ReCS Aperture Stop Wheel

The Aperture Stop wheel is positioned at the f/16 focal plane just inside the dewar. The 5-position wheel can hold up to 4 stops; the fifth position is reserved for the window imaging lens.

Optomechanical Layout

The diagram below shows the T-ReCS optical path from the entrance window to the focal-plane array.

Click on any element for more details of its design and function.

T-ReCS Mirrors

T-ReCS contains 3 off-axis paraboloid mirrors, 3 fixed folding flat mirrors, and 1 additional optical flat on the grating turret. Each mirror is diamond-turned from aluminum alloy with a protected gold coating. The all-reflective optical design ensures that images are confocal across the full wavelength range of the instrument.