Jump to content

Narrowband

Spectroscopy -Why no takers??


Recommended Posts

Time to start building a spectrometer perhaps, as I have a number of reflection gratings from scrapped spectrometers......

Would another solution (lighter and easier to add to a 'scope) be to use a narrow-band H alpha filter to isolate the H alpha region, coupled with a small tunable fabry-perot etalon (I have one of these too that can be tuned by changing the pressure)..?

Chris

Link to comment
Share on other sites

  • Replies 128
  • Created
  • Last Reply

Chris,

If you have the technical ability to set-up and tune a F-P filter it certainly would be an interesting exercise. Do you know the bandwidth and finesse of the etalon? If you want to work with an H alpha blocking fliter the bandwidth needs to match the parameters of the etalon - similar to using a solar observing Ha scope.

I have no experience of using spectroscopic etalons so can't comment on the possible outcome.

If you do decide to build something more conventional....I can help:D

Link to comment
Share on other sites

Rosanella,

Interesting thought... a Star Analyser grating on the front of a camcorder lens...

A couple of things come to mind:

The pixel size and resolution of the CCD in the camcorder ( any info available?)

The focal length of the lens - I'd assume this may be short so the final spectrum length would also be pretty short.

Can the video file be saved as an AVI for processing through Registax?

Tom Field's Rspec can handle live view....maybe also a camcorder...

...don't know :) I'll take note of above, search & ponder... Cheers! :)

Link to comment
Share on other sites

Merlin66 - many thanks. On looking closely at the etalon and doing a few quick sums, I don't think it will have the reolution I need and I suspect I might do better with a small grating spectrometer.

I do happen to have a 15mm square 3400 lpm grating which I suspect might be the answer - I'll start looking at some possible "do-able" designs....

Chris

Link to comment
Share on other sites

A 15mm grating is rather small ( The 3500 lpm sounds odd...these are usually in the 300 to 1800 l/mm range)

I have some basic designs in the files area of the Y! group astronomical_spectroscopy. Buil also has some very good stuff on his website.

You can drop me a PM for more info.

Link to comment
Share on other sites

  • 1 month later...

I'm a beginner in spectroscopy, recently acquired the Star Analyzer and realise my first photo of a spectrum using a camera SPC900NC without IR filter. The target was Arcturus, the result it´s below ( Arcturus don´t appear but it´s in the right side):

espectro%20%282%29.gif

I performed the preprocessing of the image on Iris and then tried to identify the spectral lines in the Vspec, but my inability certainly caused me to make some mistake.

This chart is the spectrum, but I'm finding it very strange that he has registered as regions including 21,680 Angstroms (even though the SPC900NC is working with near-infrared regions)!

spectrum_final2.jpg

I think that the spectral lines marked as Ha and Hb should also be wrong.

Some of the more experienced colleagues of the forum could point me what I actually missed in the analysis of the spectrum?

Attached to this message are the zip file with original image in "bmp" and "pic" formats, and the VSPEC profile.

Thanks in advanced !

Arcturus.zip

Link to comment
Share on other sites

Welcome to the lounge!

Always nice to see someone starting spectroscopy.

Looking at your image:

I thing the star zero image would be off to the LHS ( blue side of the spectrum)

It would be nice to know the distance to the CCD chip, this makes the analysis a little easier.

The dark feature you show at 18320 and 21000 are more probably Telluric (Atmospheric) lines around 6869 and 7606A

You should have a look at Richard Walkers stellar spectra Atlas:

Richard Walkers Page

(The link to the pdf is near the bottom of the page)

Link to comment
Share on other sites

Welcome to the lounge!

Always nice to see someone starting spectroscopy.

Looking at your image:

I thing the star zero image would be off to the LHS ( blue side of the spectrum)

It would be nice to know the distance to the CCD chip, this makes the analysis a little easier.

The dark feature you show at 18320 and 21000 are more probably Telluric (Atmospheric) lines around 6869 and 7606A

You should have a look at Richard Walkers stellar spectra Atlas:

Richard Walkers Page

(The link to the pdf is near the bottom of the page)

Hi Merlin66 ! Thanks for the tips !

Yes, the star zero image are outside left to blue side of the spectrum.

The transmission grating stay at 3,5 cm of my webcam ccd chip.

I try do the calibration again, using the excelent Richard Walkers Spectral Atlas and your tips, I supose think that I could reach better results:

Clipboard03.jpg

Attached are the zip file with the new profile. If you could take a little look if it´s all fine I will be really grateful ( and happy cause that register and correctly analyse a star spectrum it´s a old dream ! ).

Thank you again !

Arcturus_2.zip

Link to comment
Share on other sites

I'll have a look and get back to you, but the new spectrum looks much better!

Now you have the dispersion, in A/pix for your camera and spacing; if nothing changes, you can use that in the future to assist in Calibration.

Onwards and Upwards!!

Link to comment
Share on other sites

I'm a beginner in spectroscopy, recently acquired the Star Analyzer and realise my first photo of a spectrum using a camera SPC900NC without IR filter. The target was Arcturus, the result it´s below ( Arcturus don´t appear but it´s in the right side)

.....

I'll be following this thread with interest :hello2: and learn.

How long did it take to generate this spectrum? Roughly....

Just downloaded Spectroscopic Atlas from Richard Walkers's page. Shame the tutorial is not in English :hello2:

Link to comment
Share on other sites

Rosanella,

The usual exposure times for bright stars are only a few seconds.

Richard's atlas is pretty well self contained - I don't think you need the tutorial.

(Look away now - this is a plug for the "Book")

The "Astronomical Spectroscopy for Amateurs" -available through Springer covers everything you'll be likely to need to know, and probably more!!

Link to comment
Share on other sites

Hello Rosanella !

Actually can not says "exposure time" since the espectrum was recorded in a movie made ​​by my SPC900NC ( unmodded ).

I just turned off the motor drive and pointed the telescope (a simple refractor Celestron 80mm ) to the star and let the spectrum running along the screen.

After what I did was open the movie file in Registax and select the best frame, one in which I could distinguish more clearly the spectral lines. So I save it and did the preprocessing in IRIS and then analyze it in VSPEC.

I know this procedure are not correct, not really fulfill basic care necessary for a good record of the spectrum, but I was anxious to record a spectrum, my first stellar spectrum, something that I dreamed for years!

Fortunately I got a good record in the sense of having achieved a significant number of spectral lines (it was lucky!) but after some readings I found that Arcturus is a star who's getting tricky to deal with the identification of these lines (and for worse, Arcturus is a star type K2III but it have atypical features. So your spectra does't fit easily into comparisons with the patterns of the class ! )

Now I think that stars like Regulus ( or better yet Theta Leonis ) with strong hydrogen Balmer lines would be ideal to start getting the hang with the calibration of the spectrum.

And these stars will be my next targets !

Link to comment
Share on other sites

Here is a sample spectrum taken with a 600 lpm grating and a canon EOS Rebel DSLR ... not bad for an 8 second exposure of Arcturus, drift widened with a 8" aperture. Lines are real, not artifacts of widening the spectrum in photoshop. :-)

arcturus.jpg

Link to comment
Share on other sites

Wow. I am currently reading science with the OU and have met this subject a couple of times and found it fascinating. I am quite excited by this thread to discover how accessible this analysis can be, especially with the limited kit required for low res. Once I can find, focus, frame and follow an object of my choice at a decent magnification, I think I might slide a grating in there :D

Link to comment
Share on other sites

Hi I have a question or two regarding uncertainty if I may.

I have seen experiments where the full spectrum is shone through a single element in its gas state and analysis shows the band corresponding to the elements wavelength is missing and therefore absorbed. So how much impact does our atmosphere have on these results, are there some elements that we cannot measure, is there some way of compensating for it or is it indeed negligible?

And regarding planetary analysis; as the light that is measured originated from our sun, are the results squewed by the omission of some wavelengths before they even reach the planet? Or are the differences between the suns spectra and that of the planet compared in some way to identify additional absorption/emission?

Link to comment
Share on other sites

Good questions!

The first is easier....

The atmospheric lines due to water and O2 (Telluric lines) are very well mapped and infact are used for spectral calibration. They can easily be removed from a spectrum.

The moon and planets all reflect sunlight (albedo). The visible spectrum of the planets can be analysed by subtracting the "standard" Sun's spectrum - nominally a G2V spectrum and this leaves behind the "fingerprints" of the planet's atmosphere.

This method has been used by amateurs to show the methane bands in the gas giants.

Hope this helps.

Link to comment
Share on other sites

The moon and planets all reflect sunlight (albedo). The visible spectrum of the planets can be analysed by subtracting the "standard" Sun's spectrum - nominally a G2V spectrum and this leaves behind the "fingerprints" of the planet's atmosphere.

But surely there are limits? Say, the sun has a particular absorption line in its spectrum. You wouldn't be able to tell whether the planet would have the same absorption line since it does not receive light of that wavelength and therefore can't absorb or reflect it. Or am I missing something? ;-)

Link to comment
Share on other sites

Thanks for the info as it will help me with a better understanding of the subject as our first lecture on the Advance Course I am doing at my Observatory is on this very subject.

Link to comment
Share on other sites

yesyes,

That is true.

Planets are cool bodies and they emit radiation of their own outside the optical region at very long wavelengths.

Rest of the radiation that gets emitted from planet is reflection of energy from the sun.

This energy from the sun can come in two forms - charged particles (solar wind) and light.

Light emitted by the planet due to the solar wind is of course the aurora - but that would be difficult to detect for amateurs with their telescopes (its difficult enough to see on the earth!)

Then there is the reflection of sunlight depending on the albedo of the planet and in the main an absorption line in the solar spectrum will thus remain an absorption line in the spectra from the planet

cheers

John

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.