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Merlin66

Spectroscopy -Why no takers??

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Got my Star analyser ordered and now frantically reading more on the subject. Can't wait to get started now.

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Here is my first spectrum, taken with the Star Analyser 100 using 6SE and neximager. 581/600 frames aligned, optimized and stacked in registax with no other adjustments. Resulting image loaded into Paint Shop Pro, where it was rotated to ‘level’, a band 1 pixel high cut out and this band expanded to 30 pixels high and converted to a jpeg.

OK, maybe not the most perfect spectrum you have ever seen, but there are several darkish bands and one very clear dark band towards the far right of the red section. The object on the left of the picture is the star itself. One problem was that the focussing mask did not work very well, so I had to judge the point of focus by the size of the star itself. How do others achieve focus? What I need to do now is start reading up on how to interpret the result.

Any suggestions by the experienced spectroscopy brigade for improvement gratefully received.

All in all, I'm reasonably happy and I hope my first effort will encourage others. Believe me: if I can do it, anyone can do it:o.

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DP,

Congratulations on your first (of many I'm sure!) spectrum.

A good starting point would be a A type star like Vega. It has many Hydrogen Balmer lines which are easily calibrated.

Keep the distance between the grating and CCD short enough to still the get the zero order image of the target star at the edge of the frame and the spectrum across the horizontal width ( setting at an angle gives problems with artifacts and lost of resolution) The TransSpec spreadsheet will help you work out the CCD distance and size of the spectrum.

Initially focus on the star image and then look at the green region....try and get the edges of this area in tight focus. This will give you the best focus point. I usually take a few short exposure images to find the best focus.....

Crop the central area of the star/ spectrum say 5-20 pixel high.

This should be saved as a RAW (if you use a DSLR) or the highest resolution image you can get TIFF/ BMP etc

Import to IRIS and convert to FITS (or PIC)

Then bring it across to Vspec...you can then bin the vertical height into a 1D profile, calibrate and compare with the library spectra.

Drop me a PM if you need more help.

Read through the references detailed above - everything you need to know is there.

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Wow, good stuff Mr the DP. Got my Analyser 100 yesterday morning, so am looking forward to first light.

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Merlin, Thanks for the pointers. I had read somewhere that an M star was the best place to start, but I will certainly have a go at an A star. I will try your focussing suggestions - I'm sure that a well-focussed image will improve my final result! Will track down IRIS and Vspec and have another go when (if?) I get another clear night ...

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DP,

Which scope are you using?

Which camera are you using?

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6SE and neximager.

Don't have a 'proper' ccd camera yet. Was thinking of possibly trying the mintron, but wanted to get 'something' first - then I can build on it.

Also the above combo gives me my smallest fov, so less likely to produce an image with lots of spectra overlapping.

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Nice spectra DP what star was it?

In your processing you shouldn't cut your spectra down to one pixel high as you

are losing a lot of the information in the spectra.

Looking forward to seeing more.

cheers

John

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John

Image was reduced to 1 pixel as per staranalyser manual (http://www.patonhawksley.co.uk/UserManual.htm#processing):

1. Produce a strip spectrum as follows:

Crop the image so it just shows the strip with the spectrum (it will typically only be a few pixels high). Resize the strip to the same width but only one pixel high, then resize again to the same width but 30 pixels high.

I really don't know enough of the theory to be able to defend this position or otherwise ... maybe Ken can comment?

The star was SAO 131907 [aka Betelgeuse], being the brightest M-class star I could find.

Edited by Demonperformer

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DP,

If you only use a one pixel strip you could end up with artifacts from hot or dead pixels. Better to use 5+ this will average the possible error.

In Vspec you can produce a "virtual coloured spectrum" - for show and tell.

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Here is my first spectrum, ...

Looks like we'll be needing a spectroscopy section in the imaging forum... ;-)

Interesting thread. I've been considering spectroscopy for a while now but wanted to get set up with an obs and "normal" imaging and all that first.

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No.

These cheap Gem spectroscopes only have a very small piece of grating inside (at the rear) no collimator or eye lens....

IMHO they are not suitable for astronomy.

Sometimes you see a "prism" direct vision spectroscope come up...

these can be "adapted" to astronomy; can be used visually behind an eyepiece or mounted into a suitable adaptor infront of a camera lens.

Paton Hawksley do a cheaper range of educational gratings. These are mounted in 35mm frames so they're more suited to objective grating (infront of a camera lens - piggyback on the scope) than in the converging beam like the Star Analyser.

Save your money and get a better grating.

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OK, thanks !! I'll leave that well alone then .. ;-)

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I did a quick trial calibration of the star - now I know which star it is.

Roughly 16 to 17 Angstroms per pixel...

The star needs to be better focussed though as Ken said and trying Vega will help you get a more accurate wavelength calibration

Torsten Hansens capture of Betelgeuse using the star analyser can be found at this link here:

http://www.aau.telebus.de/Ver_7/user/Torsten_Hansen/Spektren5/20100323alporiraww.jpg

The profile for your excellent first attempt is here:

jsandse-albums-spectra-picture8422-dp-first-attempt-betelgeuse.html

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As a visual deep-sky observer, I would be interested in spectroscopy of planetary nebulae. Huggins did this in the 1860s. The Webb Society Handbook for nebulae (published in 1980s) describes using a prism held over the eyepiece as a way of spotting stellar PNs. I wonder if something like the Star Analyser might have use for that. Though with a prism you have the option of "blink" comparison, analogous to holding a filter over the eyepeice. A diffraction grating that can be swapped in and out of position with equal ease might be more useful.

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Spectroscopy of nebulae is indeed possible with the star analyser (though I am no expert at this)

Suggest you join the star analyser group here:

staranalyser : staranalyser

and ask the question there to get peoples experiences of taking nebula

An example of a planetary nebula taken with star analyser can be found here:

NGC 7027 Planetary Nebula webcam spectrum with star analyser 100 and SC3 webcam

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Ta - I was really thinking visual rather than imaging so would be interested if anyone has experience of viewing PNs with any kind of grating/prism.

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Actually, I had often thought about Spectroscopy so as to apply some of the Maths & Physics I know, but I'm not sure that Cert High level of Physics & Maths are enough :icon_eek: Also, where would I start....? Don't know...and the costs of equipment?

Edited by Rosanella

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Actually, I had often thought about Spectroscopy so as to apply some of the Maths & Physics I know, but I'm not sure that Cert High level of Physics & Maths are enough :icon_eek: Also, where would I start....? Don't know...and the costs of equipment?
I think, if you understand a bit of Maths & Physics, the following might be sufficient start:

http://en.wikipedia.org/wiki/Bohr_model (Background Theory?)

Hydrogen spectral series - Wikipedia, the free encyclopedia

Diffraction grating - Wikipedia, the free encyclopedia

Prior to "Uni", I spent 6 moths working for (the once great!) ICI pharmaceuticals Ltd. Without much more than the above, I was quickly initiated into the *practical* interpretation of several types of spectra. It's a FUN subject though... with room for intuition, as well as (modest) maths. :D

I reckon the above thread, the "Star Analyser" Guide, plus the "suitable software", manuals should be sufficient for someone of your calibre though? :evil6:

The startup cost would be for the "Star Analyser" (£95) - Plus typical webcam + software,

possibly a few extension tubes? The typical "assorted junk", of basic imaging, really... :)

Edited by Macavity

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At its most basic level you don't need any maths or physics at all to do astronomical spectroscopy...

If you want to understand the basic results of your observations you will need to understand a tiny bit of physics but its not difficult, honest...

Most people start with a star analyser (cost approx £100) which you connect to your telescope - it looks just like a 1 and 1/4 inch filter and then you connect a camera to that - about any astronomical camera will do for starters - from webcams up.

With this equipment you will be able to tell the different types of stars and see the main lines in their spectra.

People have done amazing things with their star analysers like measuring red shifts of distant objects due to expansion of the universe etc....

In order to do observations you need a mount/telescope with the capability of taking reasonable length exposures without

star trails - a couple of minutes would be good - the longer the better.

Next stage on from the star analyser is a full-blown spectroscope which you can build yourself or buy.

Merlin sells the ones he makes - you can check with him for the price of them - well under £1000 I reckon but depends on current price of parts which varies. I have one of his spectroscopes and you can see some of the results in my album.

Stargazers Lounge - jsandse's Album: Spectra

Advantage of this spectroscope over star analyser is it has higher resolution meaning it is able to give more details in the spectra you capture.

Other spectroscopes can be bought from a company called shelyak via ian king imaging they are very good but they tend to be more expensive £3000 up.

Merlins book which I mentioned in a previous post will give lots of info about amateur spectroscopy and would be a worthy investment its link is here:

Amazon.co.uk: Astronomical Spectroscopy for Amateurs: How to Build and Use Spectroscopes (Patrick Moore's Practical Astronomy Series): Explore similar items

Depending where you live it might be worth checking out if someone is doing spectroscopy in your area so you can find out more and maybe see spectroscopy being done at first hand.

Hope this helps

John

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Acey,

I still use a 60 degree prism behind the eyepiece to bring out planetary nebula. A small grating would do the same. Makes identification of faint planetaries very easy. In Hartungs book he mentions it a lot.

Spectroscopy doesn't require a PhD or any formal scientific qualification! If it did I'd be out of business many years ago.

It requires similar skills to astrophotography, but without the light pollution problems! Aquiring spectra is a straight forward process; pre-processing is much easier than imaging and if Vspec is used for calibration and comparison, you'll quickly see the fruits of your labours.

As you gain practise and experience you'll quickly come to terms with the scientific aspect of spectral analysis.

John has described well the learning process...there's some very good websites and Y! groups out there to assist.

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Very interesting. Do you find the prism suitable to use with faint planetaries and small eye lenses? And I suppose there must be some juggling around to get the right viewing angle. I'm guessing that a grating might be better but you seem happy with the prism.

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