Help with Spectra

theodog (Jeff) · #1 21-09-2009, 07:49 PM

Hi All,
I have attached a compressed .spc from VSpec.
It is of my neon test globe and roughly aligned.
Feel free to give it the works and tell me what you find, eg
A/pix and resolution are my main questions.

Merlin66 (Ken) · #2 22-09-2009, 05:54 PM

Jeff,
A good clean spectrum!
The plate scale of 1.755 A/pixel is pretty close, but I think the focusing is better towards the green than the red. This shows up with the different resolutions ie @5882 it's about 5.3A, and @6503 it's 15.7A Could be the capabilities of the camera lens. Try another image with the same grating setting and re-focus towards the red... see if it's better.
You could also rotate the grating a bit more and bring the 6503A line into the centre of the frame.. see if the resolution changes.

The lines at 6382.99 and 6402.25 are 19.26 A apart so this gives a feel for the possible resolution....

Also I think with the pixel size you have it's under sampled, hence the blocky line profile- a smaller pixel size would be nicer.
BTW your neon shows the line at 5881.89A much stronger than the reference spectrum I have - interesting..

You're almost there! Time to get some practise with guiding on the stars.
(Think about adding a backlight red LED for the slit... it helps!)

sheeny (Al) · #3 22-09-2009, 08:02 PM

G'Day Jeff,

I had a little play in VSpec myself, and overlaid the Ne lines. I recalibrated it and bumped up the reference Ne spectrum to see the less intense lines. At first I thought there may have been other lines like Ar or He, but I don;t think so... just Ne

.

There's some interesting variation in line strengths. The line Ken mentioned it strong in my reference files, but there seems little correlation (in intensity) to quite a few. Interesting (but I have no idea what it means

).

Al.

Merlin66 (Ken) · #4 22-09-2009, 08:21 PM

Al,
I used the reference spectrum from Buil ( not the Vspec element reference) only because it's more representative of the spectrum usually recorded in many spectroscopes. Maybe the relative intensities vary with neon lamps and voltages???
This it the one I use:
www.astrosurf.com/buil/us/spe2/calib2/neon1.gif

sheeny (Al) · #5 22-09-2009, 08:37 PM

That would make some kind of sense to my very mechanical understanding of things electrical, Ken.

I expect a minimum voltage is needed to turn the lamp on, after that the extra energy must go somewhere... sure the intensity will go up, but maybe the peak intensity will shift like the temperature changes in stellar spectra (I'm not saying we achieve stellar temps

). The only other mechanism I could think of for the variance would be resonance in the lamp

... some frequencies reinforce, while others cancel...

...but I'm only guessing...

Al.

theodog (Jeff) · #6 22-09-2009, 10:02 PM

guys for your input.
Ken, where would you recomend the LED?, my thoughts, between the slit & collimation lens.
The cal. globe is from;
http://www.iceinspace.com.au/forum/s...t+globe&page=2
positioned just behind the beam-splitter to reflect off the back of the splitter onto the slit.
Tried tonight to capture a spec. of lightning -no success.

PS Al, do you do much with the USB microscope?

Merlin66 (Ken) · #7 22-09-2009, 11:31 PM

Yes, that's the best location.
I found one of those X wire illuminators, positioned to shine on a small hand polished aluminium bracket, just outside the light cone and reflecting onto the back of the slit.
The image is a "fake" - I superimposed a star to show the set-up!!

sheeny (Al) · #8 23-09-2009, 06:30 AM

Quote:

Originally Posted by theodog

PS Al, do you do much with the USB microscope?

Nice micrograph! What sort of bug?

To be honest I don't do a heap with it. I use it mainly for forensic investigation of failures at work - failed welds, fracture surfaces, etc - at home I just play with it occasionally. When I do get it out, I often end up micrographing all sorts of strange stuff - different materials, match heads

, etc.

Al.