As mentioned in the last post I’ve begun an evaluation of the trial version of Tom Field’s RSpec spectroscopy software. Since the target hardware, the Lowres compact stellar spectrograph is far from completion I’ll use the solar spectrograph as the source for the evaluation process. The 1st thing I ran across was that the camera (ZWO) I’m using requires a DirectX capable driver installed for video capture. No worries there. I download and installed the driver and it promptly crashed RSpec when selecting the camera. I noticed that after installing the driver the installation included a simple app (USB CAMERA)to test the camera using the above DirectX video mode. This worked correctly and I saved a test AVI. Going back to RSpec and reopening the camera dialog and everything worked well. Good, it needs to do this reliably. Next I imported an image file previously recorded with Sharpcap. This is a Neon calibration bulb spectrogram capture recorded with the CSS in the 1st order (~1.5 Ang/pixel) shown below:
RSpec, as part of it’s core functionality, includes both spectral references as well as prominent spectral lines of various elements. Neon is included in the element list (other elements may be added easily if needed). I ended up using, to accomplish a simple 2-point calibration, an annotated neon spectral profile found online below:
One could also use the built-in element lines to calibrated the target spectrum but as I’m a newbie to the RSpec software package I deemed this a reasonable place to start. Actually the application includes a 3-point non-linear calibration procedure which I believe would be the better choice. As it is I used the above profile for the 2-point calibration and results of which are shown below:
Included in the above profile is the superposition of the Neon elements data file. The correlation is quite good with the exception of the extremes. This is probably due to lens aberration / non-linearity’s present in the spectrograph. The 3-point calibration would have helped here. Since the early 2000’s I’ve used a Spectrum simulator called Spectrum written and offered by Richard Gray. Link to the program and documentation is here. The program will synthesize (in my case the solar spectrum) any portion from UV to IR at a high resolution and is capable of smoothing out it’s output data file to match the resolution of your own spectrograph. The nice thing is RSpec is capable of reading directly the synthetic data output and display it as a profile graph along with a color/BW spectral image. The data files can be saved within RSpec as a reference and used for comparison(s). Below is the Spectrum program running under Windows:
Here’s a spectrogram I recently captured using Sharpcap of a portion of the solar spectrum covering the Sodium doublet to the Magnesium triplet (~ 515.4 to 591.25 nmeters).
Next we have the imported spectrum and both the calibrated acquired spectrum (red) and it’s Spectrum application reference data file (blue) overlayed in the profile window:
Next we need to correct the acquired spectra profile for spectral response of the instrument.This response is calculated by dividing the acquired spectrum by the library spectrum. (in this case the G5V library file)
Here we’ve added (blue) the data file from our Spectrum prgm. simulation run and smoothed to our instrument resolution:
And lastly a 2nd detail of our calibrated spectrum vs. simulated spectra:
Next time I’ll give RSpec’s built in video input capabilities a go and see if we can capture live spectra of our nearest star.