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2.3 The Wavelength Range Covered


Table 2.1: Detector definition for the SWS bands
Sect.$ ^1$ Band Order Aper. Filter$ ^2$ Area$ ^3$ Detector Wavelength$ ^4$ Resolution$ ^5$ L$ ^6$
[ $ ''\times''$] type number [$ \mu $m] ( $ R = \lambda/\Delta\lambda$) AOT
SW 1A 4 1 $ Al_2O_3$ 14-20 InSb 1 - 12 2.38 - 2.60 1870 - 2110 756
SW 1B 3 1 $ Al_2O_3$ 14-20 InSb 1 - 12 2.60 - 3.02 1470 - 1750 1043
SW 1D 3 2 $ LiF$ 14-20 InSb 1 - 12 3.02 - 3.52 1750 - 2150 1282
SW 1E 2 2 $ LiF$ 14-20 InSb 1 - 12 3.52 - 4.08 1290 - 1540 867
SW 2A 2 2 $ LiF$ 14-20 Si:Ga 13 - 24 4.08 - 5.30 1540 - 2130 2115
SW 2B 1 2 $ LiF$ 14-20 Si:Ga 13 - 24 5.30 - 7.00 930 - 1250 1377
SW 2C 1 3 $ SrF_2$ 14-20 Si:Ga 13 - 24 7.00 - 12.0$ ^7$ 1250 - 2450 4276
LW 3A 2 1 $ Al_2O_3$ 14-27 Si:As$ ^8$ 25 - 36 12.0 - 16.5 1250 - 1760 2047
LW 3C 2 2 $ LiF$ 14-27 Si:As$ ^8$ 25 - 36 16.5 - 19.5 1760 - 2380 1879
LW 3D 1 2 $ LiF$ 14-27 Si:As$ ^8$ 25 - 36 19.5 - 27.5 980 - 1270 2524
LW 3E 1 3 $ SrF_2$ 20-27 Si:As$ ^8$ 25 - 36 27.5 - 29.0 1300 500
LW 4 1 3 $ SrF_2$ 20-33 Ge:Be 37 - 48 29.0 - 45.2 1020 - 1630 4324
LW 4A$ ^9$ 2 1 $ Al_2O_3$ 20-33 Ge:Be 37 - 48 12.0 - 16.6 1250 - 1760 2047
LW 4C$ ^9$ 2 2 $ LiF$ 20-33 Ge:Be 37 - 48 16.0 - 19.7 1760 - 2380 1879
LW 4D$ ^9$ 1 2 $ LiF$ 20-33 Ge:Be 37 - 48 19.6 - 27.6 980 - 1270 2524
FP1 5A 3 1 $ Al_2O_3$ 10-39 Si:Sb 49 - 50$ ^{10}$ 11.4 - 12.2 20600 - 24000
FP1 5B 2 1 $ Al_2O_3$ 10-39 Si:Sb 49 - 50$ ^{10}$ 12.2 - 16.0 24000 - 32000
FP1 5C 2 2 $ LiF$ 10-39 Si:Sb 49 - 50$ ^{10}$ 16.0 - 19.0 32000 - 34500
FP1 5D 1 2 $ LiF$ 10-39 Si:Sb 49 - 50$ ^{10}$ 19.0 - 26.0 34500 - 35500
FP2 6 1 3$ ^{12}$ $ SrF_2$ 17-40 Ge:Be 51 - 52$ ^{11}$ 26.0 - 44.5 29000 - 31000
Notes:
  1. SW = short-wavelength grating section, LW = long-wavelength grating section, FP = Fabry-Pérot.
  2. The SW section is seen in transmission through the filters while the LW section and the FPs are seen in reflection.
  3. `Aperture area' refers to the dimensions of the SWS detectors projected through the entrance apertures projected onto the sky. The first number refers to the size in the dispersion direction and the second refers to the cross dispersion direction.
  4. These are the validated ranges of the bands. The actual wavelength ranges are slightly greater.
  5. The resolution given is that obtained when observing an extended source
  6. $ L_{AOT}$ = total number of scanner steps in band.
  7. Band 2C ends at 13.16$ \mu $m for SWS07.
  8. Band 3 uses Back-Illuminated Blocked Impurity Band (BIBIB) detectors.
  9. The three extra bands were added as a check to the band 3 data. Data from them are not produced by the standard OLP pipeline, but can only be generated using the Observers SWS Interactive Analysis (OSIA).
  10. Detector 49 is used for FP observations in band 5.
  11. Detector 51 is used for FP observations in band 6.
  12. FP2 observations in band 6 are made through the virtual aperture 4 (see Section 3.6) but are flagged in the data as being through aperture 3.

The design of the SWS instrument subdivides the 2.38-45.2$ \mu $m wavelength range into several different bands. There are 12 grating bands and, for the reduced FP spectral range, 5 FP bands. Sometimes these bands are also referred to as AOT bands. The bands, listed in Table 2.1, are combinations of detector array, aperture and grating orders such that for each band its detector array sees a unique order of light, and hence a unique wavelength. Therefore, a request to observe one wavelength of light defines which array, aperture and grating order to use. At any given time, the astronomical source of interest to the observer was centred on one and only one of the three SWS apertures, feeding light on many, or all, of the 52 detector elements via the two rotatable scanning mirrors. While it was possible to find scanner settings such that all of the detector arrays would contain valid data, the instrument was normally operated such that only one or two of the detector arrays received one order of the grating spectrometer, the other four or five receiving a mixture of orders (and hence producing no valid data). However, the observer or archive user will receive data from all 52 detectors.

Figure 2.4: Block diagram of the SWS. The diagram shows the optical functions of the spectrometer, excluding its internal calibration sources, but including the shutter, the collimation and the imaging optics. It excludes band 3E.
\resizebox {12cm}{!}{\includegraphics{swsblock.eps}}

Figure 2.5: The diagram indicates the six separate entrance slits behind the dichroics after the three apertures. It shows all the spectral order-separation filters and the internal wavelength calibrators. The shutters, collimation and imaging optics and band 3E have been left out.
\resizebox {12cm}{!}{\includegraphics{swsschematic.eps}}

next up previous contents index
Next: 2.4 Signal Detection Up: 2. Instrument overview Previous: 2.2 Instrument Design
ISO Handbook Volume V (SWS), Version 2.0.1, SAI/2000-008/Dc