Spectroscopy Part 3 - Vega Spectrum Calibration
Wednesday, November 5, 2014 at 12:13AM Continued from Part 2
I am working on my previous 135mm lens Vega spectrum today using RSpec and first show the Vega image adjacent to the generated raw profile.
To calibrate the spectrum I need two reference points. The first one is easy. The star image has passed directly through the grating without deflection and so zero Angstroms corresponds to the pixel position of the star as shown below.
The second reference relates to the Balmer Series Hydrogen Beta line which is clearly visible in the raw spectrum and corresponds to a wavelength of 486.1 nm or 4861 Angstroms. I entered this value which corresponds to the pixel position of 2722 pixels on the Canon chip.
This is how I calculated the Hydrogen Beta line wavelength for the above calibration value - as shown in the extract from my spreadsheet below.
The Balmer series of lines are all caused by an electron transition between orbit 2 and higher orbits. For the Beta line it is between orbits 2 and 4.
Once the x-axis changes to Angstroms, the number of Angstroms per pixel is shown - in this case it is 4.3 A/pixel. Now that is known, in future I will only need to set the zero point to produce a calibrated profile on any star using the 135mm and grating with the same camera.
I will continue with this in Part 4.