On the RELCO starter spectrum below, my CCDSPEC spectrum is graphed against the ALPY spectrum from Three HIlls Observatory from Robin above, and I have marked the lines I identified together with those lines that ISIS use for calibration – this gives some more lines for me to use at LRO.
Comment from Robin at Three Hills Observatory (https://stargazerslounge.com/topic/226911-neon-lamp-to-set-spectroscope/), “Your spectrograph has roughly the same resolution as the ALPY (R~500) and these lines are known to be reliable and give a very accurate calibration to better than 1A with the ALPY. I have attached a list of wavelengths of the 13 lines. They correspond to lines identified in the spectrum by Richard Walker using his DADOS with 200l/mm grating (R 900). If you identify as many of the lines in your spectrum as possible and make a 3rd order fit, any wrongly identified lines will immediately stand out as they will have larger errors.”
Lines used by ISIS to calibrate ALPY
Today, I have had a go at calibrating the homemade RELCO Starter bulb calibration lamp I made against 12V compact fluorescent lamp bulb in order to determine the wavelengths of the main lines on the CCDSPEC spectrum of the RELCO bulb.
Download calibration files from analysis by clicking on link below – calibration files RELCO vs CFL CCDSPEC no telescope 30/9/2018:
Spectrum RELCO Starter on CCDSPEC without telescope 300918
Also look at https://stargazerslounge.com/topic/226911-neon-lamp-to-set-spectroscope/?tab=comments#comment-3521335 to find out what happened when I tried to compare the lines I identified below with the atlas of lines from http://www.ursusmajor.ch/downloads/sques-relco-sc480-calibration-lines-5.0.pdf – sadly they don’t seem to match!
RELCO Starter Bulb spectrum taken with CCDSPEC Spectrometer (below):
Spectrum of compact fluorescent light bulb taken with CCDSPEC (below):
Graphing both above spectra together:
Calibrating spectra of both RELCO and CFL using above two lines in RSPEC gives following calibrated spectra:
The following is my final labelled image showing main lines on RELCO starter bulb spectrum (below):
I have had a go at creating a polynomial equation generating Excel spreadsheet for spectrometer calibration which I attach to this post (this is my own creation).
Calculation spreadsheet for higher order polynomials Excel Andrew Thornett generic Sept 2018
The following images are of my analysis of a spectrum of Arcturus I took using my CCDSPEC spectrometer. On this occasion, I used my Sky Watcher Equinox Pro 120mm OTA on EQ6 Pro (although I was hand guiding it rather than using the drives). The camera is a QHY6 and the acquisition software was EZCAP which comes with the camera. I took the spectrum in Lichfield, Staffordshire, UK on 4/8/2018 and analysed it 26/9/2018 using RSPEC software.
- Uncalibrated spectrum line graph (x-projection).
- Calibrated spectrum of Arcturus – I used an amateur spectrum on the internet to provide three data points for the RSPEC Calibration Wizard (linear approximation).
- A plot of my calibrated spectrum against the closest reference spectrum I could find in RSPEC. Arcturus is spectral type K1.5IIIFe-0.5 but closest match I could find on RSPEC was K1iv, so I have plotted against that. In spite of the slight differences, I have been able to identify almost exact matches for range of lines between the two spectra – it amazes me how amateurs can obtain incredibly precise data using spectroscopes on their very modest backyard setups!
- From this I have generated a calibration graph for my own future use which I have also posted here – if you have a better/alternative one you have created please do upload it in response to my post here.
The 12V Compact Fluorescent Light Bulbs I have purchased come in two flavours – 2700K and 6400K (later is daylight). Tonight, I took spectra of both types using my CCDSPEC spectrometer to determine whether the peaks shown on the spectra were the same. It turns out that they are and hence can be readily used for calibration purposes on my spectrometers. The main difference between the two is the intensity of the peaks with the 2700K light bulb having much lower intensities than the 6400K light bulbs.
Information on different colour temperatures of compact fluorescent bulbs can be found at http://www.lamptech.co.uk/Documents/FL%20Colours.htm
Well noticed by Ed in this month’s Astronomy Now magazine – although you can only see the back of our heads! This photo is from Astrofest in London in February of this year.
Ed’s comment :”Astronomy Now this month has finally noticed us😀😀 (Andy, centre in red shirt, and me to his left.)”
This is a re-analysis using RSPEC software of the Vega spectrum I took 4/8/2018 using my Sky Watcher Equinox 80mm Pro telescope & CCDSPEC spectroscope, hand guided on Manfrotto mount.
CCDSPEC spectrum of Vega 4/8/2018
I have now taken out a trial subscription to RSPEC amateur astronomy spectroscopy software https://www.rspec-astro.com/
The following is the original spectrum taken using Nebulosity 6 software:
This is an x-projection of the above from PCSpectra software supplied with the CCDSPEC spectrometer:
The following screenshot shows the above spectrum loaded and displayed in RSPEC software (below):
In the above diagram, I calibrated the x-axis using a Vega spectrum from the internet, using two points. I have created the following Vega spectrum for calibration purposes based on this internet data. Note that I have annotated the lines using Angstroms as RSPEC uses Angstroms on its x-axis and it all gets rather confusing if one graph is in Angstroms and the other in nanometres as it is not obvious that the difference in scale exists on the x-axis and the graphs do not line up.
RSPEC allows reference spectra to be compared to user spectra. Here, I have loaded up a reference spectrum in blue at the same time as my own Vega spectrum in red (below):
Having calibrated my spectrum against two lines on the reference spectrum I created above from other internet resources, there is excellent correlation between the lines on my spectrum and the RSPEC reference spectrum (no – I did not use the RSPEC spectrum to create my calibration Vega spectrum!)
Another interesting feature in RSPEC is to use it to identify elemental lines – using this feature on my spectrum:
I think that the closest elemental match to the lines seen in my graph is found when both Star Type A is ticked (Vega is A0V) and also Hydrogen Balmer series:
I have annotated the following compact fluorescent light spectrum with the wavelengths of the main peaks, in order to make the diagram most useful for spectrometer calibration purposes. I am indebted to Wikipedia for the source information on which this graph is based.
The above is useful for calibrating my CCDSPEC and Science Surplus DIY Spectrometers and other similar spectrometers.
The process involves me taking a spectrum and then identifying the lines on it and calibrating the spectrometer using the process in the relevant software package. This is a spectrum from the Science Surplus DIY Spectrometer of a Compact Fluorescent Light:
The compact fluorescent spectrum can be used to help identify lines on other calibration lights, such as one made from a RELCO neon fluorescent bulb starter:
Further enhancement of calibration can be achieved using alternative calibration standards such as the solar spectrum – here I have annotated that spectrum with the Fraunhofer elemental lines:
Another alternative to calibration standard lights is to use an LED light – this one provides lines in red, green and blue, and is from on a variable colour strip light I purchased from ebay:
Compare the above to a commercially sold white LED calibration light: