Chapter 5 Spectral Lines Kirchhoff’s Laws describe the production of spectral lines. Continuous...
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Transcript of Chapter 5 Spectral Lines Kirchhoff’s Laws describe the production of spectral lines. Continuous...
Chapter 5Spectral Lines
Kirchhoff’s Laws describe the production of spectral lines.
Continuous spectrum – Hot dense gas or solid objects produces a continuum of wavelengths, with no spectral lines.
Emission spectrum – Hot gas produces bright spectral lines.
Absorption spectrum – Cool gas place in front of a continuous source, produces dark, absorption lines, superimposed on the continuous spectrum.
Spectral Lines
Stellar counterparts of Kirchhoff’s Laws
Continuous spectrum – This is produced by the layer of hot, dense gas just below a star’s photosphere.
Emission spectrum – These lines are produced in stars with very hot, expanding photospheres, such as in novae, supernovae, and Wolf-Rayets.
Absorption spectrum – These lines are produced in the photospheres of the vast number of stars.
Spectrographs
In general, spectrographs use a reflection diffraction grating to disperse the incoming light. The grating equation is:
d sin q = nl
where d is the groove spacing,
n is the order (n=0 is the zeroth order). Spectra are taken with n=1, the first order.
l is the wavelength
Spectrographs
Specs of CSM’s SGS spectrograph are:
Resolution 2.2 A
Grating 600 lines/mm
Dispersion1.06 A/pixel
Camera used is SBIG ST-7XME
Wavelength range is 3800 to 7500 A
Low Resolution Grating Spectrographs
In addition to the high resolution spectrographs, there are now low res spectrographs, using just transmission diffraction grating. The two in use are the Star Analyzer (SA), a 100 l/m grating and the Rainbow Optics (RO), a 200 l/mm grating. Pictured below is the SA.
Low Resolution Grating Spectrographs
These gratings are mounted in a filter wheel, attached to the CCD camera. An example of the usage of the SA filter is this spectrum of SN2014J taken by Alex Chassy. The pronounced dip near the center of the spectrum is the absorption line, due to Si II. That is characteristic of a Type Ia supernova.