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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. The length of each slit and the occulting bar is 21.6" which spans the 240-pixel vertical height of the array (position angle = 0 degrees). Slits and occulting bar angles can be changed by specifying the angle required as the instrument position angle.

Name Width
Comment a
Open - Imaging Mode
Occulting Bar 2.0 Imaging Mode
S1 0.21 HR 8.2 µm ~ lambdamax/D
S2 0.26 HR 10.0 µm ~ lambdamax/D
S3 0.31 HR 11.7 µm ~ lambdamax/D
S4 0.36 LR & HR 13.5 µm ~ lambdamax/D
S5 0.66 LR 25.0 µm ~ lambdamax/D
S6 0.72 LR 13.5 µm ~ 2lambdamax/D
S7 1.32 LR 25.0 µm ~ 2lambdamax/D

a HR = high resolution; LR = low resolution