T-ReCS Slits and Occulting Bar
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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 (arcsec) |
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