Telescope-scan

Data cubes of emission lines from Sgr A West, M82 and sev al other objects have been obtedned using a telescope-scan observing procedure. An image of Sgr A West in [Ne n] (summed over the resolved line) is shown in Figure 4. 

The telescope-scan procedure can also be used to obtain photometric observations of point sources. With a simple pointed observation, guiding im-certainty with the narrow ( 2") entrance slit makes photometry almost impossible, but by integratiug the intensity in a map, this problem can be overcome. Perhaps surprisingly, the efficiency of this procedure is not mudi worse than that of dropping or nodding, since the decreased S/N on source is compensated by the increased S/N on sky (see the discussion of nodding along a slit). 

Radiotelescopes are used to scan the universe for radiation in the radiofrequency region of the spectrum (see Figure 3.1). As illustrated in Figure 5.11 such a telescope consists of a parabolic reflecting dish which focuses all parallel rays reaching it onto a radiofrequency detector supported at the focus of the paraboloid. The surface of such a dish must be constructed accurately but only sufficiently so that the irregularities are small compared with the wavelength of the radiation, which is of the order of 0.5 m. 

Much larger telescopes owned and operated by groups of universities are also used to scan the sky. Probably the most famous of... 

Lu Z.G. et al. 1994, A balloon borne hard X-ray telescope and its scan imaging to Cyg X-1, submitted to Nucl. Inst, and Meth. 

The imaging capabilities of a crystal diffraction telescope are defined by its beamwidth which is identical to the field of view of the lens for compact sources discrete pointings of the object will be an appropriate observation mode, while extended structures as for example the jets of galactic microquasars will be scanned with the narrow beam. The field of view/angular resolution will typically be 15" FWHM. Below 1 MeV, the narrow line sensitivity is expected to be a few 10 ph cm s (see figure 4). 

The first one is a coded mask telescope of 1.5m length. The mask would have a size of 70 X 70cm and elements of 1X Imm. A detector of 35 X 35cm would be needed, consisting of 36 XMM CCD wafers, to provide a field of view of 24°. In order to use it for continuous scanning, a new reconstruction method has been developed (direct backprojection of each photon) which very effectively smoothes the fixed pattern noise. The scientific requirements are met very well, in particular at the high energy part of the band, for X-... 

Low (1967) has characterized air pollutants at a distance from the site of measurement. He coupled a multiple-scan interferometer to a telescope pointed at a smokestack about 600 feet away and analyzed the infrared radiation emitted by the hot smoke of the stack. He readily detected sulfur dioxide (Fig. 18.19), and it should be noted that the measurements were done at 11 P.M., a time when ordinary methods are not possible. 

The first step is to generate a Sky Map to be fed to the subsequent modules in the Sky Generator Module and the corresponding photon noise, computed in the Sky Photon Noise Module. In parallel, given the parameters defined by the user for the instrument, an interferometric MV-map is created at the v-Map Generator Module from the position of the two telescopes. The FTS Drive module calculates the spectrometer scan parameters. Once a MV-map and the scan parameters are defined, the instrument beam is calculated at the Beam Generator Module. The sky map and the beam are then combined to recreate the observed sky map. 

The output of the instrument simulator FllnS is a set of FITS files where the interferograms corresponding to each baseline and to each FTS scan are stored for a given input sky datacube, Skyi . These FITS files also include fhe mefrology data for the FTS drive and pointing of the telescope, as well as all the information needed to calculate the baseline vector. 

In the MV-map generator module, accounting for the slewing time of the telescopes will be interesting in order to compute the total observation time, as well as fuel calculations. Related to this, the pointing errors of the telescope need to be simulated not only for the different telescope positions, but also the pointing errors during an FTS scan will need to be modelled. To model these some software optimisation is required because this process is computationally heavy. 

The sheets Telescope, WarmOptics, Background and Detector contain the predefined parameters such as emissivity, transmission and temperature of the different elements. The user may modify them according to the preferred observation. In the sheet Interferometer one selects the baseline configuration and range. In FTSme-chanical the number of FTS scans is selected. 

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