onomical Instrumentation astronomers use additional optics between the telescope optics and detectors. This is called the instrumentation. It can range from a very colour filter to a highly-sophisticated multi-beam spectrograph. atories try to provide instruments with a range of spectral resolution ng a wide range in wavelength. al resolution, defined as can be as low as 4 for imaging in the filter, where =800 nm and =200 nm, and as high as 1000000 for a high-resolution spectrograph, with velocity resolution of 300 m/s.
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Astronomical Instrumentation Often, astronomers use additional optics between the telescope optics and their detectors. This is called the instrumentation.
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Astronomical Instrumentation
Often, astronomers use additional optics between the telescope optics and their detectors. This is called the instrumentation. It can range from a verysimple colour filter to a highly-sophisticated multi-beam spectrograph.Observatories try to provide instruments with a range of spectral resolutioncovering a wide range in wavelength.
Spectral resolution, defined as can be as low as 4 for imaging in the
I-band filter, where =800 nm and =200 nm, and as high as 1000000 fora ultra high-resolution spectrograph, with velocity resolution of 300 m/s.
Instruments available for the Subaru Telescope (Japan)
Imagers
These are the simplest instrument. Even though imaging instruments can workwithout any optics, they usually do contain several optical components:
• Filters – select a certain wavelength range
• Focal Reducers – change the scale at the detector. For a large telescope the field is usually small (size inversely proportional to telescope diameter), and in this way the scale at the detector can be enlarged.
As well as components like baffles, coronographs, etc., to avoid contaminationfrom ambient light.
Grating Equation: mλ = d(sinß + sin α) m = order number λ=wavelength d = groove distance α=incident angle ß=diffracted angle dß /dλ = m /d cosßAngular dispersion can be increased either by increasing the number of grooves/mm (smaller d) or by working at high orders m (Echelle spectrographs).
The higher the orders, the smaller will be the FREE SPECTRAL RANGE: two wavelengths in fact will overlap as soon as mλ = (m+1) λ’
Dλ = λ’ - λ = λ/m
The higher the order, the shorter is the FREE SPECTRAL RANGE. Given angular dispersion and wavelength, the larger is the number of lines/mm, the larger is the FREE SPECTRAL RANGE.
Types of grating spectrographsTypes of grating spectrographs
• Grating & prism spectrographs with collimator/camera optics - long spectrum (linear format)
• Echelle spectrometers - cross-dispersion, square format
• Objective prism or grating - slitless spectroscopy
• grism (grating/prism) - insert into optical path of a camera
• Integral-field spectrographs
• Multi-object spectrographs
Cross Dispersion
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Echelle grating(used in high order #)
Cross-disperser (used in low order)slit
Detector focal plane
Keck HIRES:HH 444
[SII]
Telluric O2
H [NII]
[SII]
The Solar Spectrum (from Kitt Peak’s McMath-Pierce Solar Telescope): 2960 – 13000 angstroms
Integral Field Spectroscopy – Obtaining Spectra in 2D
Pupil array
Spectra
Integral Field SpectroscopyIntegral Field Spectroscopy
• Properties - Cosmic Rays: 5 to > 103 e- produced by each charged particle usually effects 1 or few pixels. non-gaussian charge distribution (different from stellar image or PSF) - Well depth: 5 x 104 to 106 e- - Pixel size: 6 m to 30 m - Array size: 512 x 512 to 4096 x 4096