Spectroscopy

[Terry B]

For my Chrissy present I "arranged":D that my wife gave me a star analyser as a present.
It is not the easiest thing to master but I'm giving it a go. I have taken spectra of various stars and tried to calibrate them using my ST9E.
The programme recommended id Visual Spec and it is far from user friendly and a bit prone to crashing.
anyway here is my first reasonably successful attempt.
The star is V385 Car. This is a may 7.7 WR star with strong emission lines.
The exposure is only 15 secs.
I'm pleased that I have been able to calibrate the image reasonably well compared with a spectrum I downloaded from CDS.
Now to try to identify other things.

[renormalised]

Terry, if you want to learn more about spectra and how to analyse them, I can give you an exercise I used as part of my course, dealing with spectra and how to interpret them. It's quite interesting to do the exercise:D

However I can tell you that the broad peak you've got near the beginning is most likely a NII/III line, down around the 450nm (4350-4550A) area. If you look at the CDS graph, you'll see the peak right at the beginning, that would be your HeI or even II peak. The Ha line would be emission from hydrogen present on or near the star. WR stars are typically hydrogen poor in their spectra (usually none) and where a strong Ha line appears, it's most likely from one of the least evolved of the type, a WNL (late type). The strong NII/III (ionised Nitrogen) peak indicates it's a WNL star and probably a WN7-8 by the strength of the peak. The strong CIII peak is unusual in that nitrogen normally predominates over carbon in these types, however there is some carbon present in their spectra.

All in all, that's a nice spectrum you took there and a fine job taking it:D

[jjjnettie]

Hi Terry,
Here's a link to quite a good book on the subject.
http://freebookspot.org/TopTen.aspx?Category_ID=96
Just scroll down and you'll find.....
"Spectroscopy: The Key to the Stars: Reading the Lines in Stellar Spectra"
You can download the book as a .pdf, and if you like it go buy the hardcopy.
Hope you find it useful.

[Terry B]

Thanks for the info. Thanks for the link to the book. I've downloaded it and will read it later. I do have some astrophysics texts from my masters and will have to read them again also.

The star is WR40 and it is a WN8 star according to the catalogue.
I attached a pic with the wavelengths on it and I'm sure you are correct with the id of the lines. I just didn't bother labelling anymore:D

[renormalised]

The star analyser...is that the screw in filter like glass you can get from the U.K.??

[Terry B]

Yes
See http://www.patonhawksley.co.uk/staranalyser.html

[renormalised]

Might go and check them out.

[Merlin66]

The Star Analyser is a 100line/mm transmission grating, similar to Rainbow Optics one from the US. Baader had a 201lpm version, but not sure it's still available.
Paton-Hawksley also sell an "educational" range of gratings, 100/200/300 lpm at very reasonable prices. Great way to start spectroscopy.
VSpec and IRIS are very good freeware programs to capture and analyse spectra.

[Enchilada]

Thanks very much for the link. There is a lot of material available with this resource other than spectroscopy - some of which is very useful for many registered IISers users.
For me, I've just downloaded the brilliant "Encyclopaedia of astronomy and astrophysics" in three parts, which to read (and carry) for me had to be done at the local library. 'nough reading for months!
Again this basically highlights a small discussion area for Books and Literature, as indirectly discussed in another thread.
Good stuff!

[Merlin66]

Robinson's book is very good, well worth having. The other is Kaler's "Stars and spectra"

[Terry B]

I've had another go at this using my genesis CCD rather than the ST9.
The difference is that the ST9 calibrates to ~44 A/pixel and the Genesis/Audine (with 9um pixels) gives me 13.5 A/pixel. This gives better resolution.
The attached file is a graph of Beta Car processed with Vspec.
It is calibrated for instrument response but not for absolute flux.
The spectrum is synthesized from the the spectral data as my original was taken with a mono camera.. The H lines are clearly visible even into the deep purple end.
The absorption from atmospheric O2 and H2O are also clearly visible.

[renormalised]

Good work, Terry:)

[Merlin66]

Looking good!!
I'd be interested in your set up.
Which telescope?
What distance between the SA and the CCD chip?
You seem to be able to get down below 400nm which is very good.
I'm just struggling a bit so far down in the UV. My "trials" with a 80mm cemented doublet definately showed you didn't need a UV-IR filter! The lens does it for you! I made the mistake of trying to use the Canon ( convenience!) and wondered what was going wrong.

The Canon is no good, drops to about 10%, the MX7c & DSI II are just below 40-50% efficient, the QHY5 drops to 30%, the webcam's are below 20% and the best so far are the Atik16ic at around 60% and the DMK21 at 50%
Keep it up; you're getting some good results!!!

[Terry B]

Thanks
I haven't measured the distance from the SA to the CCD- not that easy to do. The SA is in a filter wheel and the CCD cameras don't have the position of the CCD on the outside.
The scope is a VC200L. This has no corrector plate but does have a correcting lens in the draw tube.
My Genesis/Audine camera does have a very old UV filter as it's front glass but it obviously doesn't block the deep violet very well.
The kodak chips in my 2 cameras are both "E" chips that are suppose to have an improved blue response but they are still much more responsive in the red. I have found doing photometry with a blue filter that I need about 2x the exposure in blue for a similar flux compared to a V filter. The red needs 2/3 the exposure of the V and IR is about the same as the V filter.
I haven't tried a colour camera yet but might give it a go with my 40D.

[theodog]

Great work Terry.:P

I had a dabble with the star analyser a while ago. I still have it and your work has me thinking about doing some more.

I too used the grid in my filter-wheel, difficult to align the lines with the camera (ST-7).

Great work, look forward to seeing more.:)

Now off to check out the book site.
:D

[Terry B]

You don't need to align the lines with the ST7 (although this does make it easier)
You just open the image in Iris, select a region of the spectrum and issue the command "L_ori"
It then tells you the angle that the image needs to be rotated. You then use the "ROT" command with this angle in it and the spectrum is nicely horizontal.

[theodog]

Cheers Terry

[Merlin66]

The distance from the grating to the CCD, when its used in a converging beam affects the resolution. The further from the chip the better the resolution.
If you can, you should align the spectra to be parallel to the CCD pixels. This significantly reduces the amount of artifacts which can be produced during processing. IRIS does a good job, but initial alignment is even better!!
Would be interested to see the results from various camera's. Betelgeuse with its broad bands makes a good object.
Next thing you'll be looking at fitting a slit to observe nebulae!!

[sheeny]

Excellent work, Terry!:thumbsup:

I've been playing with my SA too but I'm struggling for blue/violet response:shrug:

Al.

[renormalised]

Al, what scope are you using for your spec' work??

Your main scope or a guidescope??

[Merlin66]

If your camera responce can handle it, the best solution seems to be an all mirror reflector ie Newtonian/ classical Cass. Then there's NO UV attenuation.

[renormalised]

True...you don't have the UV/blue light being bounced around or absorbed off/by corrector plates, lenses etc.

[sheeny]

ATM I'm using my C8... so the corrector is the likely culprit? hmmm

Al.

[Merlin66]

Al,
Won't help, but it will depend on the responce of the CCD as well, see my previous notes.....

[sheeny]

Yeah, I used the DMK 21 this last time, and you may recall I started with the ToUcam. Both appear to be blue deficient. I'll ask around on the SA list as well.

Al.

[Merlin66]

Hmmmm.
Actually, according to the data, the chip in the DMK is one of the better CCD's down in the UV. The graph shows around 55% efficiency at 400nm; better than the webcam.

[theodog]

Is it possible to use "standard spectra" to calibrate the efficiencies at various W.L. for any camera/scope system?

I suppose it would be something like a flat-field spectra? Using a tungstan light globe?:shrug:
:D

[Heian]

Hi Ken, Al,
Can I ask a question here?
I recently got the DSI3 Pro, which uses the Sony ICX285AL chip. Haven't had a chance to try it out with the staranalyser yet, but some info I've seen comments that it's also good down below 400nm. Does that make sense from your data Ken?

cheers Mark

[Heian]

Jeff,
when I first started using the SA, one of the comments from experienced users was to take a ref star spectra ("A" class if possible), from the same area of sky, at much the same time, as you catch the target spectra.
The aim being to compensate for the changing atmospherics, and recalibrate the instrument response.

I guess it all depends on how precise you want to be, and what you want to do with the data.

Mark

[Terry B]

Yes. You take an image of a reference star with a simple curve like a A2 star. (I have used beta Car). You then calibrate the frequency and divide this by a catalogue reference spectra. (these come with Vspec)
The resulting graph is then smoothed out to remove the absorption lines.
The final result is a reasonable approximation of the instrument response of your camera.
You can then divide your unknown spectra by reference graph- similar process to dividing by a flat field.

[theodog]

Thanks Mark & Terry.

Now, the version of Vspec I have is in French. Not a bad language, but I can't understand it, is there an English version available?

:D

[Terry B]

Yes.
http://www.astrosurf.com/vdesnoux/download.html

[theodog]

Got it, that's better, thanks.

[renormalised]

Here's a little DIY project to sink your teeth into. If I can find a decent prism I may try this myself....

Spectroscopy on a Budget (http://www.lpl.arizona.edu/%7Erhill/spect/spect.html)

[Merlin66]

Re. Objective prisms...
An easier and simpler method is to buy a Paton-Hawksley transmission grating and blu-tac it into the lens hood; this will show the spectra of the brighter stars pretty well with a 135mm telelens.
Calibration; Terry has outlined the method very well. The issue is; if there's no or very little signal in the UV, a far longer exposure will be required to pick up the detail or limit your spectra to that above 400nm.
The Vspec tutorials are very good and well worth the effort of working through.
Glad to see all this interest in Spectroscopy, its a very engaging subject.
Heian, re ICX285AL I'll check the data curves and get back to you....

[renormalised]

Might work alright....could give that a try too. See which works the best, or even have two setups. Might look into some other ways of obtaining spectra, vise a vie, construction of spectroscopes.

[Merlin66]

I can assure you it works very well! I started this way, with a 100 lpm P-H grating, a Zuiko 135mm and OM1
Heian,
Looking at the Sony data sheet for the ICX285AL; it looks as good as the DMK (ICX098BL) in the lower frequences, should give you reasonabe response in the 350nm> +/- 50%, Well worth trying!
Working with prisms is fun, but they are very difficult to calibrate ( non-linear responce). I recently built a 3 prism "train" spectroscope with 3 60 deg 50mm face prisms. Interesting, but not exactly user friendly; how the early guys like Huggins managed to get the results they did is truely amazing. Gratings are MUCH easier!!
(Plug: don't forget to check out the construction details of a Classic and Littrow spectroscope in the "Projects and Articles section")

[renormalised]

Will go checkout the spectroscope page, for sure.

[Merlin66]

Just had another look at that ICX285AL CCD chip data( DSI III).
It's a VERY GOOD chip!!!
The responce between 500nm and 600nm is well above 95%, and peaks at almost 100% between 510nm and 540nm Fantastic!
It's well above 80% across the 450nm to 680nm range.
One of the best I've seen so far.... should be a great astronomical camera for all types of imaging....

[Merlin66]

BTW the ICX285AL chip is the same as the one in the Starlight SXV-H9 camera
Maurice Gavine, a long time spectroscopist has just put a very good video on Quasars up on YouTube, well work watching!
http://uk.youtube.com/watch?v=FZn8g1A04a8

[sheeny]

OK Ken, and all you other Spectrogurus, here is a spectrum from Eta Carina I captured tonight. It is a stack of 4 still frames, with a single point calibration in VSpec at 11.7 A/pixel. The magenta image on the left is of course the zero order image (synthesized from the spectrum).

I have labelled the peaks. As I don't have a spectrum from Eta to compare it to, can any one confirm the correct wavelengths for the peaks? I just want to check that I haven't done something silly when working out my dispersion from my Betelgeuse image the other night.

Thanks,

Al.

[renormalised]

Well, you've definitely got a strong Ha line there, but it appears to be slightly redshifted, as they all do (if they're all hydrogen lines, in fact). Since I don't have a calibrated reference spectra on me, it's hard to tell what the other lines are. However, you do have a couple of close lines...the one at 488.3nm is close to the Hb (hydrogen beta) line and the one at 436.6nm is close to the Hg (hydrogen gamma) line.

Just to help you out here....read this (luckily it jogged my memory when I read the equations...simple stuff, really)... Hydrogen Balmer Series (http://en.wikipedia.org/wiki/Balmer_series)

If they're indeed redshifted Hydrogen lines, then it's because of the motions within the Homonculus itself. Most likely from the lobe moving away from us. Or at least from gases (including the lobe) that are in motion away from us.

[Merlin66]

That's a great spectra! What was the set-up and total exposure??

OK, here's what I see....
Re-calibrate on the bright Ha in the red; this should be 6563A.
If I re-set your wavelengths by 28A ( 6591-6563) then I see:
From the blue to red>
Hgama @4340A
Hbeta @ 4861A
OIII @ 4959/5007A
the double bump @ 5154A; not sure? could be Mg?
This spectra is very typical of a hydrogen emission area. You can see now why the Ha/Hb/OIII filters work so well on this type of object.

For completeness the following are usually also in nebulae spectra:
NeIII @ 3869A
HeII @ 4686A
NII @ 6584A

All this coming from a guy who hasn't seen a star since Xmas!!

[renormalised]

5154A....might be one of the Fe lines, although B class stars (which eta probably is...most likely B0 on the assumed temp) don't normally show such strong Fe lines. Fe and Ca II (H and K) lines are usually associated, and normally appear strongly in the cooler classes....namely F, G and K. Usually from about F4 to K5-6, where after they diminish in favour of the strong metal oxide and hydroxyl lines (all molecular lines instead of the monatomic lines). Before then, they lose intensity and the hydrogen lines begin to dominate.

Although, if these spectra are coming from the nebula as well, you'll be getting the other lines mixed in with the pure spectrum from the star.

[Merlin66]

Hmmmm.
I have the FeI lines at 4956/5270/5328/5455 etc can't see anything close to the 5154A. The first of the Mg triplet is at 5167A.......

Found a spectra in Kaler's book, p243; taken in 1922 it shows many FeII lines around the Hgama region, 4244/4287/4359/4414A
Kaler thinks the original F supergiant has collapsed and become a luminous O supergiant " with an extraordinary absolute bolometric magnitude near -12.5" - maybe on its way to a WR star and/or ready to go "Nova"!!!!!!!

[renormalised]

You're most likely right....as I said it might be a Fe line. It was only a guess as I don't have any calibrated references to look at.

Very good spectra, though:)

[sheeny]

Thanks for the link. I'll be honest... at this stage of my spectroscopic experience sometimes it all looks a bit daunting:lol:... so I'm not confident at identifying when to expect Balmer lines, and Fraunhofer lines, etc but I can see it simple when it's pointed out!:lol::P

Each image was about (from memory) 0.6s, 0 brightness, moderate gain with the DMK, SA, C8 combo unguided. Images were stacked in Registax, so they are averaged, not added.



That could be true. The homunculus was starting to appear in the zero order image.

The fact that EtaCar isn't stable is what has me interested.;)



Thanks for your encouragement, guys! So much to learn... I love it!:thumbsup: I'll fire up the lappy and have another play with it... maybe calibrate off the Ha and Hb lines and see how things look then. But in answer to my original question 11.7A/pixel doesn't seem to be way off the mark, so I guess the lack of blue response is real.

Al.

[Heian]

Al,
that's where I find the response + dispersion calibration against a A or B class star is effective. You can work off the zero order and the H alpha line. Provided you keep the optical system the same, it can then be used over multiple sessions, with only minor adjustments to get the dispersion fine tuned.

cheers
Mark

[renormalised]

That's what I would expect.....FeII being the doubly ionised form, occurs at much higher temps than FeI and in the bluer/UV region of the spectrum. How strong are the lines??

LBV's, especially one as massive as Eta, wouldn't normally stay an F class Hypergiant for very long...too unstable hydrostatically. I'd say most of it's existence in the post MS was as an O or B class Hypergiant. I'd even push that bolometric mag up a notch or two (although, -12.5 is close enough). Also stars that massive don't normally become WR stars...too much mass to lose. They never expose their cores like that before they go pop. Most of the stars that become WR sit around the 30-50 solar mass area. At the most massive up to around 70, but many stars in the 60-70 solar mass area also go pop before reaching the WR stage.

[sheeny]

Understood. Not that I've had any success at that yet:P... I've attached an example: a spectrum of Rigel I captured the other night. B8Ia star but not much evidence of a Ha line in my spectrum:rolleyes::whistle:. As you can see, the blue response is also down on the DMK (it was also down on the ToUcam which makes me wonder it it isn't something else:shrug: other than the camera?).

I've just done this exercise to try and get my head around the camera response. At the moment I'm not getting a consistent camera response curve from different spectra (so I have more learning to do:P) though I expect to get a handle on that as I learn.:whistle:

But I think I'm missing something... I think I should be able to save the camera response curve and use it on other spectra, shouldn't I? How do I do that? Each Time I try I get another copy of the raw spectrum, not the camera response curve...:screwy::doh:

Al.

[Terry B]

I had the same problem with saving the response curve. The .spc files will only save 4 graphs.
I display the camera response curve that you want to save and then rename it as the 2nd reference graph. There is a way to do this in the "edit" menu. (I will look up the correct button when I get home as I don't have the program here at work.)
The other option is to save the response curve as a .dat file.
You can then open up the file you want to calibrate as well as the response curve and using the "divide" function correct the unknown graph.

[Heian]

Terry / Al,
the attached pdf, (hope you can read it OK) were instructions given to me by Robin Leadbetter on how to process spectra, and get a camera response curve. It may be going over old ground, but I thought it may help. Certainly helped me!:)
Another comment from Robin was on the use of a focal reducer to improve the image. The aim was to get the smallest size zero order image, (basically increase FOV) and prevent significant focus shift and also smearing across the spectra. I've been using a 120mm f8 refractor and I get far better spectra when I use a 0.6x reducer and drop it to f5.
The exposure times are virtually unaffected.

cheers
Mark

[Terry B]

Thanks Mark
This is what I have been doing also. My hassle was the saving of the instrument response graph to use on other spectra that I hadn't identified.
At present I'm using my VC200L at f8 and find that the focus seems to be best on the spectrum when the zero order image of the star is also at it's sharpest. I use my home made bahinov(?sp) mask. (It gives an interesting effect on the spectrum also).
With the scope at f8 my ST9E gives ~40A/pixel. I don't want to make it any smaller with a focal reducer. I have ordered a spacer that will extend the camera further from the grating and this should give me about 25A/pixel. I will experiment with the focal reducer when this arrives.

[sheeny]

Thanks, Mark! Sounds exactly like what I've been missing.:thumbsup: I'll have a play.


Thanks for the document, I've had a read - just the right mix of stuff I knew and stuff I didn't.:thumbsup:Thanks!

Some interesting stuff in there about losing detail in the blue... maybe I'll have to play about with my FR again, etc (I haven't been using it, but the seeing might be destroying all detail in the short wavelengths.

Al.

[Merlin66]

Al,
On the Rigel graph/ curve, all the "data" below 400nm is suspect... I would dump it and ignore, I lay a bet it's not real. The atmosphere cuts out most of everything below 350nm and there's effectively zero response from the DMK at 300nm.......
Robin's note is great. VSpec, Tutorial 5, (http://astrosurf.com/Vdesnoux/tutorial5.html)
gives the VSpec method in detail ( just remember, see page 7, to "Edit-Replace")
re Camera response: I occasionally use the Canon 350D with Canon and Zuiko lenses with the Baader grating mounted infront of the lens.
I find the response curve can change dramatically depending on the lenses being used!!
Terry, A little surprised to get best spectra focus when the zero order is focussed... I usually have to tweek the focus to get best results ( 12" LX200, 200mm Littrow, 1200lpm grating). The reducer also reduces the scale of the spectra ( ie shorter focal length). The distance from the grating to the CCD chip I find is more imprortant for dispersion and resolution.
Great stuff... we seem to be generating some interest looking at the number of hits on the thread!!!

[renormalised]

Al, here's another site of interest...you may already have it!!...

Maurice Gavin's Spec Page (http://www.astroman.fsnet.co.uk/spectro.htm)

[sheeny]

I hadn't come across that one yet, so thanks for the link!:thumbsup:

Al.

[sheeny]

OK Ken. So you're saying the drop off of the spectra below 400nm is to be expected, so I shouldn't be expecting to capture a spectrum similar to the library spectrum in this range... so I probably shouldn't be so concerned about my apparent lack of blue response.:whistle:

I must say I'm loving this thread! I'm learning heaps! Thanks guys!

Al.

[Terry B]

Another Attempt.
The attached images is a spectrum of OY Car. This is an eclipsing dwarf nova that is currently in outburst. I have done some short time series over a few nights of this star and the series from the same night as the spectrum is attached.
I can't really identify any of the lines. Any suggestions. A summed spectrum form MNRAS is here (http://articles.adsabs.harvard.edu//full/1981MNRAS.194P..17B/L000019.000.html) but this seems different.

[renormalised]

You may have a H(gamma), H(beta), HeI and maybe a H(epsilon). You may even have a H(delta) line...but they're all pretty broad. I don't think the resolution of the spectra is high enough to say for certain, though. I can't see any Ha line there...unless you have a redshifted Ha line at 6720A??!!.

[renormalised]

If that is a redshifted Ha line, then the nova's outburst is traveling at 7176.6kms!!!!:eyepop::scared:

[Merlin66]

An interesting one, for sure!!
I'm assuming the large peak in Hb....
What happens to the Ha?????? None in this type of star?
I'll have a go at the spectrum later today. Keep you posted.

[renormalised]

Hope we can get a better result....

[Merlin66]

http://cbastro.org/results/highlights/iyuma-b/iyuma.pdf

The above reference was the only one I've come across which shows the spectra of a CV from 450nm through to 740nm. This one is IY UMa, but I would have expected some similarities.
Figure 14 Shows the Hb emission with a central trough ( also the Ha),
HeI absorptions at 4921, 5015, 5876, 6678, 7065
and another (?) emission at 5861.
Trying to match any of these to the OY Car spectra is very difficult.
If we assume the large hump shown at around 4750 is Hbeta(4861) , then the next two emission "bumps" seem to match the IY UMa data (??) and the hump at 6710 is Halpha (6563). Based on the Balmer series the strength of the Ha should be twice the Hb so it doesn't look right???
I think we need a higher resolution spectra to be able to go much further.
An excellent example to "practise" with!!!! Well done.

[Terry B]

I had another go at imaging OY Car last night. This image is better as I took 3 exposures of 5 mins and this has increased the SN ratio. Unfortunately I cant increase the resolution until a spacer that I have ordered arrives (hopefully next week).
The lines are very similar. I angled the camera slightly differently so any background stars different. I'm still not sure what the lines are. I have attached a ".dat" file if you wan't to open it in Vspec.(it is zipped as the forum won't accept ".dat" files)
cheers

[renormalised]

That spectrum is very similar to the others, only the peaks are a bit pointier. You may have also found the "real" Ha peak, but it's quite weak.

[Terry B]

I have also found more info on these variables at http://www.astrosurf.com/buil/us/peculiar2/cvs.htm

[Merlin66]

terry,
Did you normalise the spectra using a calibrated camera resonse curve?
For some reason I'm still surprised with the lack of Ha.
I'll punch it into Vspec and see if I can find anything for you.

[Terry B]

Yes. I have normalised it to beta car (A2 star)

[Merlin66]

Terry,
No luck so far.
I've tried Ha,Hb, Hgama etc in emission and also in absorption; He and Fe, can't find much to latch onto. Unfortunately looks like higher resolution is required?
Sorry mate.

[Heian]

I had the chance to try out the DSI3 on sat night, and got a number of spectra OK. These are the only 2 processed so for. I'm getting just a fraction over 11 Ang/px with the current setup. Trying to better it as there's enough room on the ccd for a longer spectra.
The images show quite a bit of fishtailing at the blue end (problem with using an achromatic refractor :shrug:). The ccd seems to be providing some reasonable response below 400nm, probably good to 350nm.

cheers
Mark

[renormalised]

Good specs there, Mark:)

Decent Ha peak in the Eta Carina profile!!:)

[sheeny]

Good stuff, Mark. The DSI3 must have a bigger sensor than the DMK21 to get down into IR at that dispersion. The images don't look that dissimilar to what I get off the DMK in the blue/violet range but your camera response correction seems to bring out the detail better than I've achieved so far.:thumbsup:

Al.

[theodog]

OK Guys, you have got me further than I have been before down this road.

The image shows where I'm up to.

I have what I think is a good spectra (?) of Beta Grus and have V-spec to give the intensity graph. Included is the zero dispersion image (star).

Can anybody identify some lines to help me callibrate?:doh:

Any, I say, any help is greatly appreciated.:P:P
:D
Please forgive my ignorance.

[Heian]

Jeff,
beta grus is an M5 class so it's a relatively cool star and the absorption lines you've recorded are mainly molecular groups. TiO among others. That does make it a bit harder to work out calibration lines, as they also tend to be broader.
I used the Sirius curve to recheck my new system. As an A class, the lines are fairly well seen, reasonably thin, and they are basically just Hydrogen.
You didn't happen to get a spectra of alpha grus (B class) did you as that one would be great!
Can you post the actual spectra image? What system did you use to capture the image? CCD, scope etc....
I'll have a look tonight (unless someone answers your questions before hand:))

[Heian]

Al,
it's a 1.4mega pixel chip, 6.45 x 6.45 micron, Sony ICX285AL. I deliberately got the b+w version so the bayer filter was not a problem. It can also do 2x2 binning, which is probably of limited use in spectra images.
cheers
Mark

[renormalised]

You may have a Hb (hydrogen beta) line (the one just before the red line), however you'll have to check it against an A star (like Mark said), to calibrate it. Cool classes like M tend to be a nest of spectral lines, especially in the red region where you're getting "44 million" molecular lines showing up!!.

[renormalised]

Here's a little help....has a M5 class giant:)

[theodog]

Thanks Heian & Renormalised,



I use a 12" f5 reflector GSO, and a ST7e camera. Grating on the filter-wheel. Not sure of the grating/imager distance.
I will try for A-Grus tonight, if not then another A1-2.

:D

[theodog]

Found one of A-Grus.

Same details as below.

Still I'll try for a freshy tonight.

[Terry B]

My suggestion with the alp Gru image is to perform a 2 line calibration making the first line the star image at 0. Then pick that deep line and call it Ha, Hb or Hg at 6563,4861, 4340.
Then overlay a b5 spectra and see which one lines up with the iter lines the best. You should have absorptions at 6869 for O2 and 7605 for H2O as well.
If the first one doesn't work then call it Hb etc until it seems right. I think it is likely to be Hg at 4340.

[Merlin66]

I think the results we're seeing are great!
Who would have thought that a bunch of amateurs with a small transmission grating costing less that an eyepiece could do so much.
I think we owe Robin Leadbeater a round of congratulations!! - you've been vindicated.
For those who don't know about him, Robin is a dedicated amateur from NW England who championed the idea of commercialising the Star Analyser grating with Paton-Hawksley. I'm sure if it wasn't for his strenuous efforts the SA would not have become a reality.
Keep up the good work!

[renormalised]

I'd say he would be feeling chuffed, and we're all eternally grateful:)

[Heian]

There are any number of ways you can use the SA. Check out the performance of any filters you may have! Put a filter in front of the SA, check out the before and after shots, how good is that sky glow filter?...
Measure the spectra of street lights, a backyard bug zapper (not much to see, mainly in the UV)!
Make a holder, put it in front of a std lens on a 350D DSLR and you can measure star spectra with 6 secs non tracked exposures...
I've used a 135mm lens + a 2x teleconverter and achieved approx 2.5 ang/px. Measure the sun spectra by using a reflection of a needle or polished ball bearing...

cheers
Mark

[renormalised]

CD or DVD are just as good....basically diffraction gratings with music or movies:P:D

[Merlin66]

Jeff,
According to VSpec, Alpha Grus is a B7iv.
If I work on your spectra, the deepest absorption feature appears to be Hbeta, this then gives the series of Hgama, delta, epsilon towards the UV.
The "dip" around the 4500A, between Hbeta/Hgama I think may be a CIII feature(?) This calibration then shows the slight dip of Ha.
What do the others think???
If we agree, it would be good to post a data file with the graph(s); this allows others to run the actual spectra through VSpec.....what do you think??

[theodog]

Great idea. I'll have a go.:)
I have hopefully attached a zipped file containing two data files from VSpec.
One has the uncalibrated spec. the other calibrated with H-Beta as the deep dip in spectra. Both are of Aph Grus.

Others are welcome to view and decipher.:thumbsup:
Please let me know what you find.;)
:D

[Merlin66]

Theodog,
I tried for a couple of hours to get your spectra to register with a reference B6v spectra; then played with H emission data.....
I wasn't able to get a good match. Even with, what I still think are H beta, H gama etc absorption features I can't seem to get a good scale to give them an acceptable registration.....
Hmmmm. Let me sleep on it.
Anyone else have any success??

[Terry B]

I had a quick play and had the same problem.
May I suggest taking an image of beta Car (Miaplacidus) that is an A2 star that has easier absorption lines to identify. It is the only bright star between the false cross and the SCP so is easy to find. This will then give the A/pixel for your set up and from that the other spectra can be calibrated.

[theodog]

Will try beta Car tonight, failing storms again.

[Heian]

I had a quick try at them as well. Didn't go too well either.

I found a spectra of alpha grus I took some time ago, and it seems the deep absorption line is H beta (4830A if I remember). I do recall sort of giving up trying to process the spectra as it seemed "a bit odd".

I am happy to be proven wrong, but I always thought ccd's couldn't capture UV wavelengths.:shrug:

cheers
Mark

[theodog]

Hi All,
Beta Carinae Spec.
Due to poor weather it is only one exposure of 3 seconds, possibly with cloud.
This set-up is different to other s taken, but hopefully is the final set-up.
Looks strange to me.:screwy:
Dark subtracted but no flat or bias.
12" f5 scope.

[Terry B]

OK
I'll have a look at it tonight.

[theodog]

Hi All,
Firstly must apologise:(. My last B Car WAS rubbish.

Tonight I obtained much better data.:thumbsup:

15x 3sec darks & Bias.
:)

[Terry B]

I think I have worked it out. The camera is pretty insensitive in the blue.
See the attached image.
I have attached an image I took of Beta Car with the shutter open. This produced long streaks that highlight the hydrogen absorption lines.

[theodog]

Now that is supprising. I will spec some other stars to check this out. It was the ST7e.

Thanks Terry. I now have some idea how to process the spectra.:thumbsup:

Is the 3rd image straight from your camera or have you processed the .spc info in some way?
:D

[Merlin66]

Good analysis Terry!
An extraordinary outcome; 24.1 A/pixel is pretty low resolution even for a SA grating... the distance to the chip could be increased i.e. almost doubled. The severe drop off in the blue-UV is not unusual, but the deep absorption threw me- it just looked to much like a H beta point! Moral of the story? - the info's in the spectra - somewhere!
Looks like Terry's curve has at least been corrected for CCD response and fitted to the Planck curve. ( Tutorial #5)
I've got to ask... Jeff - what was the issue with your first betcar spectra?
Are you doing some pre-processing??

[theodog]

I just thought I'd have another go at it. When I did the lines seemed much better defined.:)


No, no preprocessing except for dark and bias. I'm flat-out getting my head around just displaying the graph with scale.:sadeyes:

I agree with the distance to CCD/scale problem 'though. I have my grating practically at the front of the ST in a filter wheel. I will have to move the mirror forward to allow for further seperation due to focus issues.

I do appreciate the help everyone has supplied so far, its been great. At the moment I sit here in 30+ temps trying to better my data.
:)

[theodog]

???????

[Merlin66]

The shape of the spectral curve indicates that the camera/ CCD responce curve has been calculated and the spectra corrected. Knowing the spectral "shape" of a reference star, you can also correct the curve to match the Planck temperature curve. This is pretty well covered in VSpec's #5 tutorial which you should download. There are 10 tutorials in all.
Hope this helps.

[Merlin66]

Another comment. If you have an UV-IR filter it may well be worth trying on this camera. My Baader has a UV cut-off just below 400nm and an IR cut-off at 700nm. This covers most (all) the visible spectrum and "focuses" the graph in this region. Just a thought.

[Merlin66]

http://www.cloudynights.com/photopost/data/500/11401sa-illum.jpg

Maurice Gavin prepared this graphic based on discussions re the resolution of the SA grating in a converging beam.
The resolution of any grating is measured by the number of lines illuminated by the star.
If the grating is placed say 20mm infront of the CCD in an f10 beam, the size of the star image at the grating will be 2mm.
If the grating is say 100lpm, then the out of focus star image passes through only 200 lines of the grating. If the distance is doubled to 40mm, the resolution is also doubled!!!!
You can see then why it's always better to work in a large collimated beam of light through the grating; it illuminates more lines!!!

[theodog]

Hi All,

My last night efforts I think may have lead to some success.
I thought I would gather data on a F star, having done an A classification.
Having found one near B Car, I am now trying to relocate it in Guide to post details. When I located it the first time Guide stated that its Class (F5) was uncertain.

The images;
Plot based on 1x40sec -drk and bias
My data -blue
Library spec x my data -green
I measure the resolution at 22.9 A/Pix
Order
F5i, F5v, K01ii, K0iv and M0v.

If I am going about this correctly I should be looking at the closest match. This I believe is the K0iv spec.

I have also included the .dat file of the F5? plot.

Feedback please.:thumbsup:
:D

[Terry B]

Hi Jeff
Sorry I haven't replied but I've been away from the puter.
My graph has been corrected for the instrument response. This is done by dividing it by the catalogue spectra, smoothing out any emission or absorption lines and then dividing the original graph by the smoothed graph.
This works if the star has a reasonably smooth spectra to start ie an A F or G star.
I have saved some standard smooth graphs and use them on other stars.

[Terry B]

My resolution depends on which camera I use. With my ST9E at f8 I get ~32A/pixel as the pixels are 20um square. If I use my Audine type camera with a KAF0401E CCD at 9um pixels I get ~12.4A/pixel.
I can't easily increase the distance with the ST9 as I run out of back focus and it is a hassle to change the cameras. I use the ST9 for photometry so leave it in place usually on the scope.
It is a trade off I suppose.

[Merlin66]

Jeff,
Those are looking good!! I'll "play" with them later
Exactly which star did you image?
With the data you've collected you should be able construct a camera calibration......
Next step, when you get a good match, is to look for the metal absorption lines......
Gray's "Spectrum" is a great way of building a comparison specta....

[theodog]

I am sure now that the star I imaged was Hipparcos #44599 or TYC 9203 2759.
Guide 8 gave its Spec Type as F6II-III or F5 ?
"Spectral type is from miscellaneous sources". -Guide 8

Although my graphs don't demonstrate this. So leads to confusion.:shrug:
:)

[renormalised]

The problem with F class giants is that they're in the Instability Strip....they tend to be Cepheids, which means their spectra may vary as they pulsate. That can throw your readings out if you don't know what you're looking at. Here's a site that might help out..... McMaster Cepheid Photometry and Radial Velocity Archive (http://crocus.physics.mcmaster.ca/Cepheid/HomePage.html)

[theodog]

Cheers Renormalised.
Unfortunately my cataloge states that "No variability detected (stable)".
But it's only early days and I have much to learn. I need to image more classes of stars to nail this technique.

[Terry B]

I had another go with my ST9 and took 7 images of Gam Vel. This is the brightest WR star and has great lines. The dispersion is only 32A/pixel with this setup but it still is a nice image.

[renormalised]

I'd find that a little incredulous....nearly all A, F and G class giants show some sort of variability. Unless it's in a quite period, of course. Polaris, for example, just went through one of these phases. It's a classic Cepheid, but the periodicity and the luminosity changes almost disappeared at one stage. They became so small it was almost impossible to measure them, but now it's slowly coming back to normal. Probably was going through some state in its evolution into a red supergiant, at a later stage.

[renormalised]

Very nice spec' Terry:)

[theodog]

Apparently not this one;

"Comments from the Hipparcos Catalog:
Hipparcos #44599
Click here for SIMBAD data
RA (J2000.0): 09 05 08.83
declination -72 36 09.7
(Above is the computed position for J1991.25)
magnitude in Johnson V: 4.47
Magnitude derived from ground-based observations
Trigonometric parallax 7.18 ± 0.45 milliarcseconds
Proper motion in RA: -8.44 ± 0.48 milliarcseconds/year
Proper motion in dec: -4.72 ± 0.39 milliarcseconds/year
Mean BT magnitude: 5.217 ± 0.002
Mean VT magnitude: 4.540 ± 0.002
Johnson B-V colour: 0.607 ± 0.010
Johnson B-V source is ground-based observations
Color index (V-I) in Cousins' system: 0.67 ± 0.02
Median magnitude in Hipparcos system (Hpmag): 4.5979 ± 0.0005
Scatter on Hpmag is 0.004 magnitudes
Hpmag is based on 118 observations
Hpmag at maximum (5th percentile): 4.59
Hpmag at minimum (95th percentile): 4.61
No variability detected ("constant")
CP -72 779
Spectral type F6II-III
Spectral type is from miscellaneous sources"

From Guide 8.
:)

[renormalised]

I'd be wary of the Hipparcos catalogue...it named quite a few stars as NSV (Newly Suspected Variables) when in fact they weren't.

I've got a paper for you here and 2 MS Word documents on the stars they looked at. Hip44599 is listed as HR3643...it's F9II and definitely variable, but very small amplitude = 0.02mag, probably why it appears as "constant".

You'll also have plenty of other stars to look at from the lists:)

[theodog]

Cheers Renormalised, will do so soon.

Terry,
I have managed to spec Gamvel myself and have the raw results below Resol= 13A/pix through the 4" f9.
Do these seem right to you?
If so, I'm on the right track & what do I do from here?
:)

[renormalised]

Here's a copy of the document that is referred to by the other paper....

[Terry B]

This is verygood. It is quite similar to mine. I have corrected mine for the instrument response. This star probably isn't a good one to use as the basis for working out the instrument response. Choose a A or F star taken with the same configuration as Gamvela.
Open it and calibrate it. Then open a catalogue spectra of the same class of star.
Divide your spectra by the catalogue spectra. This will give you something like the first pic. The raw image is blue and the divided in green.
Then under the radiometry tab there is a function called "compute continuum"
Hit this and another toolbar appears. Push the first button to make it select points. Then select points along the continuum missing the absorption or emission lines.
When you are happy push the 4th button and a sloder appears. Change the number to 2000 and push the x10 button. I found it needs to be about 1200 to give a nice smooth graph. The result is your instrument response graph.
Go into the edit menu and push the replace button. Replace the ref 2 withthis graph then save the profile. It will then save it for future use.
After this you need to divide your raw gamma vela spectra by the instrument response graph. It should end up looking more like mine.
:D

[theodog]

Thanks Terry.
I have been working through this proceedure but have many divide by zero and unforseen error messages.:( I did almost get an instrument curve once.:D
It seems Vspec errors are a problem.
:)

[sheeny]

I got a heap of those for a while too, Jeff. I found I got on top of them when I started cropping the spectrum before doing the division. Are you doing that?

Al.

[Heian]

Hi Jeff,
I don't know if you saw it, but back at post #52 of this thread, I added a pdf file of some emails I got from Robin Leadbetter on how to process a spectra to get an instrument response from an image.
I've added it to this post as well.
If you follow the steps from Robin, it should work fine. I have avoided Vspec errors by doing it his way :)
The curves / spectra you're collecting look pretty good to me...

cheers
Mark

[theodog]

Yes I saw it, did I pay attention to it -no:doh:. I am printing as I type. Thanks Mark.



As above -No, but I'm about to try it:thumbsup:. Cheers Al.
:)

[theodog]

Yep, many thanks all.
Without your help I would never have worked this out.:bowdown:

Any way here is my final result for Gamma Vela.

Issues?

OK next target?
:D

[Merlin66]

Onward and upward!!!
I can smell success in the air!
What about Betelgeuse? Some nice bands in the spectra.
Beta Gem (KO) should show also the K-H bands.
I'm still struggling with the wet and snow/ weather over here!!!!
I'd be interested to see you camera correction curve.
I found when I did a couple for the Canon 350 the curve varied from lens to lens ie the Canon std lens were VERY much different from the Ol' Zuiko lenses....

[Heian]

Jeff,
what about the stars of Crux? Gamma Crux is a M class, Epsilon Crux is K class, the other's B class. Al (Sheeny) did a fantastic shot showing the colours by a de-focussing technique.
Grabbing their spectra would show what the colour differences represent in terms of star temp + chemical makeup...

It's a project I've been meaning to do, but have had to wait till the stars cleared a tree in my yard

just a thought
Mark

[theodog]

I feel I'm about to have a week of foul weather here to:(.

Both sound great. I have also been thinking of the other thread about the reddest star.
http://www.iceinspace.com.au/forum/showthread.php?t=41125
Spec. may contribute to that debate as well.

Clear skies
:D

[Terry B]

The Crux stars does sound like an interesting project. The wind, cloud and spitting rain has put paid to any imaging for the last few days and will continue for a while yet.:sadeyes:

[Merlin66]

Yeah.....
Go for the Red Carbon Star XTrA!!!!!!!!!!!!!!!

[sheeny]

Don't forget about etacar.;) I've got one spectrum from it so far, but it should change quite a bit.

Al.

[sheeny]

What traps could be expected moving the SA further away from the camera to increase dispersion?

I know the spectrum will get dimmer. Is focusing likely to get more difficult or critical? Seeing would also become more critical wouldn't it?

With my current setup, I'm achieving about 11.64A/pixel with the DMK 21. I was think about replacing the lens in my 2x barlow with the SA. That should roughly double the distance between the SA and the CCD... which would work well if I had a DMK 41;):P I think! Shame about the exchange rate at the moment...

Al.

[theodog]

Al,
Would it move the zero image and the spec to far apart? Wouldn't matter if you dont need the zero image in callibration.

I think there must be a point where resolution of the spectrum would not be improved due to the resolution of the grating (lines/").
I moved my grating out to about 35mm and focus is a real issue, but I just get the full spec and zero image in the frame of the ST7.

I'm no expert, as can be seen, just my thoughts.
:D

[Terry B]

The other hassle with a more spread out spectrum is interference from background stars. It is tricky to make the spectrum miss the background stars if it is longer.
I wouldn't know at present as I've had cloud since 9th Feb.:sadeyes:

[theodog]

Here's my eta from last night.
Callibrated using a spec of B Car taken just before.
8x1min Median combined -darks
Divided by camera response.
:)

[Heian]

Look good Jeff :thumbsup:

Now, if someone knows how to resample different spectra in Vspec, they could grab my image from post #71, adjust it to the same ang/px as your spectra, and we could see if Eta has changed over the last 4 weeks or so!!


cheers
Mark

[Merlin66]

Mark/ Jeff
If you can post your .spc files for the Eta Car spectra I'd love to have a go at combining etc.
At the moment I'm scanning some old (like 1880!) spectra to see if they can be converted and used for current comparisons. A little difficult as they were taken with prisms and are "artistic engravings"....

[sheeny]

Here's a few Spectra (reprocessed... nothing new;)). Since it is cloudy I'm still playing with VSpec to improve my grip of it.:)

I'll post my etacar.spc too Ken.

Al.

[sheeny]

OK guys, here's my etacar spectrum to play with.

C8, SA, DMK21AU.AS

Corrected for camera response and normalised.

Al.

[theodog]

Done. I have been reluctant as I still have little confidence in my processing. Getting there 'though.:) The more processed spectra I get from you "experts" the better I can check my processing. I have included my raw data for all to fiddle.:thumbsup:



Al,
Nice set of spectra. Looking Good.
I have used your calibrated eta to calibrate mine from 20/2/09. The results are below. (Croped to simalar spec range). Hope you don't mind.
I'm happy that our two spec look similar as it seems I'm on the right track.:D

[Heian]

Ken,
Will do this evening...
Might get a chance to do another spectra this evening, if the clouds don't hear me! :lol:

cheers
Mark

[sheeny]

Yes, I realised that would be an issue with a 1/4" sensor. For some stars with distinct lines that wouldn't be a problem, but it's a real limitation for others. When I get a chance I'll do a trial with the DMK on either etacar or Betelgeuse and see how I go.


Yeah, especially on dim stars... the long exposures make any background stars brighter...

Al.

[Terry B]

You guys are doing very well. I've been busy with work so haven't been able to use my SA.:sadeyes:

[Heian]

Ken,
this zip file has my eta carina spc file. The image was taken on the 30th Jan.
I've also included some spc files of Be stars in Puppis, HD57150 + HD68980. There is also a file labelled TYC7115-03011, also in Puppis. TYC7115 is at RA 7h 18m 32s DEC -36deg 46' 11"

The reason I've included the Tycho star is the unusual emission line around about 4500 ang. I did a search and there doesn't appear to be a background star interfering with the spectra, but I'm probably wrong. :)
The stars were selected from the ArasBeam website listing.
I'd be interested in your comments.

cheers
Mark

[sheeny]

Here are a couple of links I thought you guys might be interested in if you haven't already discovered them.;)

http://www.physics.uq.edu.au/people/ross/phys2080/spec/analyz.htm

http://physics.nist.gov/PhysRefData/Handbook/index.html

Al.

[theodog]

Yep, thanks Al, I now have them bookmarked.:thumbsup:

Lately my mind has turned to Quasars and I've been looking for suitably bright ones in the far south. Any ideas?:shrug:
:)

[Merlin66]

In Kaler's book "Stars" he gives some interesting, annotated spectra.
P Cyn is thought to be similar to Eta Car.
There's also a diagram of the various strengths of the element lines across the H-R diagram; useful to "first-guess" which elements may be in a star spectra.

[Merlin66]

I just checked the catalogue of Quasars in AstroPlanner.....
There's over 146,000 listed!!!
I can do a list of southern ones, but will probably have to limit the magnitude (!!??) to come up with a reasonable list.
Watch this space..
OK this is a list of the top 20 south of +10 deg. Magnitudes are around +13mag!!!!

[theodog]

Thanks Merlin,
This is my first feeble attempt at a quasar.
I hope you can see the faint spectra indicated by the red line.
I had trouble with bright spec from outside each side of the field, the target spectra was just above it. Also interfered by lots of faint background stars. However, in the original I can see absorption lines in the left portion of the spec.
The origional image is from 3x10min through the 4"-darks.
The graph is at 12.45A/Pix from other image scales and the zero image is on the extreem left, no camera balance -raw image.
IRAS 09149-6206 Mag ~13.
:)

[Merlin66]

Before I start I should make you aware of the following references:
www.etacarinae.iag.usp.br/ (http://www.etacarinae.iag.usp.br/)
www.espacioprofundo.com.ar/foros/about8064.html (http://www.espacioprofundo.com.ar/foros/about8064.html)
The first shows the movements of the HeII (4686) and N+(5755), the second a SA spectra of the 12 Feb.
Just started on Mark's "eta carinae spectra crop.spc"- #1 [BLUE] and Jeff's "ecara.spc" -#2 [RED] and straight away you can see similarities and some ( significant?) differences!!
#1 has a double Ha peak, were #2 is single
A second peak at 6876 on #1 is missing on #2
Neither of these match the foros spectra which has a large "ramp" up to the Ha and seems to have a line "reversal" at around 4860.
let the fun begin....................

[Heian]

All,
thanks for the links to the other websites Ken, there has certainly been some major changes in parts of the spectra.
Regarding the differences between Jeff's spectra and mine, perhaps it's the skyglow I image through in suburban Wollongong compared to Coonabarabran! Overall, they are very similar in shape and the size of the responses.
Comparing the spectra from the website and my resolution (11A/px), the changes he shows from 4660 to 4720 A, cover 5 pixels on my ccd. :eyepop:
If the sky clears tonight, I might try with the unmodded 350D, as I can get down to 2.5A/px with 135mm lens + 2x teleconverter.

cheers
Mark

[Merlin66]

Guys,
Through the Staranalyser forum, Robin has re-worked the "foros" spectra and found differences to the original posted. It looks like the spectra may have been incorrectly processed. The latest one looks more like Mark/Jeff/Al's versions. I'll post it when I can extract the graphic.

[Heian]

Ken,
I saw the messages as well as the reworked spectra that Robin did. It looked like it was the raw spectrum, and not instrument corrected. To do a comparison, would you need the raw, unprocessed spectra as well??

cheers
Mark

[Merlin66]

I'll start with what's available. Let's see what other info I get over the next few days.

[theodog]

Hi All,
Found this, this morning on amature quasar spec.


http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/2897676/Main/2894974

Interesting:D
:)

[Merlin66]

Here's Maurice's YouTube on Quasar's
http://www.youtube.com/watch?gl=GB&hl=en-GB&v=FZn8g1A04a8

I didn't realise he also posted on Cloudy nights!
Maurice lives about 15 miles from me!

[Terry B]

I took a spectra of eta car on 27th Feb and have processed it with Marks spectra. The 2 spectra are attached. Mine was taken with a ST9E at 31.6A/pixel.
They are quite similar.

[sheeny]

Cool!:thumbsup: Clouds and visitors have been conspiring against me:whistle::lol:

Al.

[theodog]

Looks good Terry.:thumbsup:
It would be interesting to see a direct plot of your plot and mine. There seems to be some large difference around 5000A.

Like Al, I've similar prob's with the weather. I wish it would at least rain out of this bloody cloud.:mad2:
:D

[Heian]

They do look good Terry. I'm guessing you resampled my spectra at the 31A/px resolution?? I must learn how to do that. :shrug:
I was all set up to get a spectra from Lulin, on fri night, managed to get one just as the cloud rolled back in again :( What I obtained was unusable, but there was a spectra, so it can be done:)

C.Buil got one using a 150l/mm spectroscope, so a star analyser should give similar results..see:http://astrosurf.com/buil/lulin/result.htm

cheers
Mark

[Terry B]

To put you spectra on mine is easy. I just open both plots at once. I highlighted your plot and copied it. There is a button on the task bar. I then simply paste it into my plot. It is automagically resampled.

[Terry B]

I took a spectrum of lulin on the same night but it was crap.
Christian Buil's was taken with a slit. With a slitless spectrum light we are using it was just smeared out and had no discernable features.

[Heian]

I thought it may have been some hi-level cloud interfering. I'll try again but it won't be a major project...

cheers
Mark

[Rob_K]

Great thread people! :thumbsup: Just beginning, Star Analyser arrived a week or two back & all I've done is to see if I can get a spectrum in the first place, and to download, print & bind the Visual Spec manual (146 pages!!!). I'm up to, well... the index! :rolleyes:
I've calibrated my images straight out of the camera at 17Å/pixel (1.7nm/px), using the Mg lines (5167.3 & 5172.7Å, averaged at 5170Å) in the Betelgeuse spectrum.

Here's my first try at a graph, uncorrected for instrument, atmosphere or anything else for that matter - just a simple binning.

Thanks for all the information and links posted - lots of things to chase up in those idle moments! :)

Cheers -

[Terry B]

:thumbsup:

Why is the image of the star bifid?

[Rob_K]

Absolutely no idea Terry - just the straight FIT file binned. I need to get further into the manual...

Cheers -

[Merlin66]

Rob,
If you post your .spc file we can do a full comparison with the standard M2 lab spectra. The inversion maybe due to the extreme brightness??
Based on your calibration you should show the full wavelength range in the graph.
A very good start never the less. What instrument set-up? Scope and camera??

Jeff/Al/Mark- still interested in the secondary peak at Ha and the bump around 6800?? I'll get back to it when I finish some processing on the latest ( and only!) solar images!!

[theodog]

Nice start Rob.
Plenty of lines in that one.
How far is your SA from the CCD?
It seems to me, but I may be wrong, that you have some of the 2nd order spectrum mixed with the first. It is possibly the cause of the purple colour to the right.
If so, you may need to increase the distance between the SA and sensor.
Please correct me if I'm on the wrong track.:shrug:

[theodog]

Hi All,
Skies cleared early tonight so I took the advantage to do some A Ori Spect.

Two files:
One is the raw from the camera .spc file for you to check.

Other is processed and divided by M2 type star. Is this right:shrug:
:)

[Merlin66]

Jeff,
I haven't had the time to do much with the spectra....
When you divide a Raw but calibrated spectra by a library reference spectra, for the same star type, you end up with a Camera responce curve.
This can then be used to "correct" future spectra taken by the same instrument and set-up. i.e. when you take your next raw spectra divide it by the camera responce to get a calibrated "corrected" spectra.
Not sure what you get when you already have a corrected spectra then divide by a reference library spectra..... the differences only I guess????

[theodog]

sorry,
I did divide by M2 to produce camera responce and then divided the raw to get the result below. So it is corrected for camera responce. My mistake in previous post.

[sheeny]

OK... I've done a little trial...:D

I captured two spectra of Betelgeuse tonight - 1 at 11.63 A/pixel and one at 6.69 A/pixel.

The first was captured at 11.63 with my normal setup, but I took an extra spectrum without the zero order star image and merged the two prior to processing in V spec to get more in the red end.

The second was captured with the SA replacing the lens in my 2x barlow to increase the distance from the ccd. I had no problems with focus, or exposure - though the seeing was pretty ordinary.

Both spectra are in the zip file.

Now... if I had a DMK41 I could get zero order in the one frame....:whistle:

Al.

[Merlin66]

Guys,
I thought I'd just show you my "final" set-up with the Littrow on the Meade 10"LX200.
The various adaptors are to get from the SCT thread to 2". the beamsplitter ( with a 1.25" to 2" epoxied in place!); the QHY5 guide camera at the end of a 50mm extension; the spectro with the 1.25" to T adaptor.
Fitted with the Baader modified 300D... a little bit more complex than the SA!! I need 1.0Kg of balance weight up front.

I also enclose a couple of images of an adaptor I made using 3mm customwood and a couple of old filter rings to allow the SA to be mounted in a standard 2" filter thread.. this gives more opportunity to mount it further from the CCD ie in the end of a 2" adaptor...
To round it off, I've also glued up (!!) a 1.25" adaptor to hold the 50micron or 9micron fibre optic; I want to do some trials and feed this into the specto on the bench....amazing what you get up to when its raining!!!!!

[Merlin66]

Robin posted a note in the forum to remind us of the H20 lines at 6900, 7200, and 7600.
These are shown well in Buil's Vega spectra:
http://www.astrosurf.com/buil/us/vatlas/vatlas.htm

Looks like you've picked them up in the Betelgeuse spectra!

[sheeny]

Yeah, the 7600 band is very obvious... I wondered what that was:P:lol:.

I haven't corrected for H2O - with my standard setup I usually capture say 3000 to 7000 Å. I'll have a further play with the data to see if I can get a better spectrum. These were quickies stacked in registax, and I found some alignment issues, so I may be able to do better either by selecting the best single frame or spending some time manually ensuring the alignment points are right before stacking.

Al.

[Heian]

Hi all,
just have some questions that have occurred to me:
Is there a definite advantage in chasing an increase in resolution, (ang/px), say from 11 to 6 ang/px?
You have roughly doubled the resolution, have you doubled the quality / usefulness of the spectra?

I can get up to approx 2.5 ang/px using my 350D with a 270mm lens, and just placing the SA in front of the lens. You end up with a 31mm aperture, but it's good for the bright objects :). The questions came up because I have unused pixels either side of the zero image and spectra, at 11ang/px, on the dsi3. An extension tubes that I currently have is too long, so I'll be buying some filters and removing the glass to make spacers, using up as much of the horizontal length of the chip as possible. It won't be that costly, but it made me think, "Is it necessary?"
The answer would depend on what I wanted to do with the spectra I suppose..

cheers + sorry for confused ramble..:screwy:
Mark

[sheeny]

I think the limit of the useful dispersion depends on the size of the focussed image. The smaller the focussed image (i.e. the sharper the focus, better the seeing and larger the aperture) the greater dispersion you should be able to make real use of.

In my little experiment last night, I increased the dispersion, but I don't think I really achieved a corresponding increase in resolution of the spectra largely because of the seeing (I think:P). But I hope that in conditions of excellent seeing, at least some of that increase in dispersion might be usable.

Maybe a slit is necessary to really make use of low dispersion spectra?:shrug:

Do you have a short barlow, Mark? Even an old cheapie would be ideal... unscrew the barlow lens and screw in the SA (That's what I did;)) and it's easy to align (or even change) the spectrum image:thumbsup:.

As for why go to lower dispersion... I did a few calcs based on my system.

Applying Raleighs Criteria with my C8, SA and DMK21 the best resolution I could get is a star image of radius 9.4µm at the red end of the spectrum. That's a star image 3.36pixels in diameter. So at the red end of a spectrum, while my dispersion is 11.63Å/pixel, but the best resolution I can theoretically achieve is 11.63 x 3.36 = 39Å.

Now if I decrease dispersion to 6.63Å/pixel then the resolution of my spectra becomes 6.63 x 3.36 = 22Å.

So going to lower dispersion means you can resolve closer lines in the spectra subject to the performance of seeing, focusing, optics, etc.

Al.

[theodog]

Hi All,
In light of the recent discussion I have found this link,

http://hyperphysics.phy-astr.gsu.edu/HBASE/phyopt/gratcal.html
I hope the link works.

I have put in an example from my numbers and the results seemed to make sense.
eg -lines/ inch
-distance to sensor and
-Ha wavelength
It may be usefull for designing spectroscopy systems.

I have a grating of 600 l/mm and am looking at putting it into an old filter cell to see how it goes. The grating is from an educational kit made by the same makers of the SA.
:D

[Barrykgerdes]

Hi

About 12 years ago I came across a DOS program on spectroscopy for beginners who have a suitable telescope. Most Amateur telescopes qualify.
It includes a difraction grating that can be printed on a clear media with a laser printer and samples of spectra generated with it. The program "Spectra" is shareware but I don't remember where I got it. It is also small enough to be attached as a zip file so check it out if you like.

Barry

[Merlin66]

Here's a few designs I've come across:
http://www.lightfrominfinity.org/spettroscopia.htm
Mete's design for a reflection grating and cylinderical lens is very interesting
http://www.burwitz-astro.de/spectrographs/tragos/index.html
This transmission design is pretty neat!!!!
http://www.unitronitalia.it/baader-dados/dados.htm
This is Baader's answer to the LiHiresIII and the SBig SGS

I also have a compact design for a transmission grating; a couple of bino lenses, 2 front surface mirrors and a transmission grating. I found it in a BAA Journal way back in the 80's and built a quick prototype from heavy card. I'll find my sketch and post it.
(Jeff, the BAA design would be good for the 600lpm grating!)

[Terry B]

There is also Christian Buils version at http://www.astrosurf.com/buil/us/loris/loris.htm

[theodog]

Ok -I think I have taken this as far as I can go.

I obtained a surplus demo grating from work, it contained 100, 300 and 600l/mm gratings.
Because they had been used with students and were so old (they had l/inch) marked on them, they were in poor condition, with fingerprints etc..
I cut the 300 from the set, as I thought the 600 would be to diverse for the ST7 and I already have a 100 in the SA, and cleaned it up. This still left it covered with scratches.
I turned up an attachment to hold it to a nosepiece, as per Picture 1.

The results are shown in the following images. The spect was far removed from the zero image (about 2 frames) and background stars were a problem, but it did show some lines.

Merlin - those sites look good, I wish our dollar would gain some ground on the Pound or Euro. Isn't your economy dying like ours:shrug:.

Terry - welcome back, remember you started this.:lol:

[Merlin66]

Well here it is.
Based on the secondary image, it shows the Ha emission....

[Merlin66]

Jeff,
What was the star being measured?
4.2A/pixel - That's interesting
I was getting 6.58A/pixel with the Baader 207lpm grating about 25mm infront of the T ring; about 60mm from the Canon 300 CDD.

[theodog]

The star is etacar. The grating, 300l/mm, is possibly 50-60mm from the CCD.
I used both Ha and Hb for a calibration with 2 lines. The images included are full width frames from the ST7.
As these were taken through the 4" the star images were large at focus.
I could not move to capture more of the spectra as the star would move off the gtating.
I also imaged betcru and used similar lines from an alpori for line calibration and obtained similar figures (+/- 0.1l/p). I think the SA is a better system.
:)

[Zaps]

Hi everybody, I've been following this thread and others very intently because I'm becoming very interested in practical amateur spectroscopy.

However there's an aspect which is confusing me, and that's the ionic notation which is often used by some people.

A very long time ago, I studied chemistry - A VERY long time ago, so my memory is not to be relied upon!

But as I recall, 'I' (as in HI, OI, etc) signified the Unionised or Ground state, II signifies the (singly) ionized state, III signifies the doubly ionized state, IV the triply ionized state, and so on.

The '[]' (as in [OIII]) indicated a forbidden transition, commonly seen in low density gaseous nebulae, etc.

Yet I've seen, say, the 'II' notation (whether forbidden or not) referred to here and elsewhere as double ionization, rather than single, and 'III' as triple ionization.

Am I missing something, or is the latter use of the notation erroneous?

Thanks guys.

Zaps.

[renormalised]

Using II as doubly ionised (of anything) is erroneous. Doubly ionised gases are denoted as such.."III". Same applies for all other ionisation states...IV (triply ionised), II (singly ionised) etc.

[Zaps]

Okay, that's reassuring. Ironically, one of your posts caused some of my confusion and uncertainty:

"That's what I would expect.....FeII being the doubly ionised form, occurs at much higher temps than FeI and in the bluer/UV region of the spectrum."

http://www.iceinspace.com.au/forum/showpost.php?p=406390&postcount=49

:)

[theodog]

Where have you read this in IIS Spectroscopy?:shrug: I see it now -no further comment from me on checking posts.:whistle:
As for elsewhere -that's their mistake.

single = II
double = III
triple = IV

Yes forbidden lines are possible in highly rarified gas.
;)

[theodog]

Could I subtract the stars to stop them interfering with the spectra?

Images/process

1. Raw spec and background stars
3. Background starfield
2. Raw minus starfield:sadeyes:
4. Rotated ready for VSpec
5. VSpec results aligned on Ha and Hb.

Didn't work as well as expected, but seems to show some helium lines.

Comments?:shrug:
:)

[Merlin66]

I like the concept!
Another idea that came to mind while looking at your images...
What if we had a diaphragm say about 5mm diameter over the grating, centred on the star under observation. The OOF star size obviously will depend on the focal ratio and the distance between the grating and the CCD.
This would stop any of the nearby stars showing up in the spectra????
Yes-No???

[sheeny]

Good thinking Jeff. That's a process worth developing for faint star spectra!:thumbsup:

Al.

[Heian]

Ken,
I had thought of something like that myself. An adjustable slit in the system will basically reduce the light source, and I'd always thought a mask would do a similar job, but it would be easier to locate and not worry about the focus issue.
It would be worth some experiments if nothing else...:)

Mark

[Terry B]

I thought about a slit also but maybe just a straight mask on the SA. You only need to block the stars on the side that the spectrum is projected.
Maybe a piece of aluminium foil on the SA and then position the target star just of the edge of the foil.

[sheeny]

Guys,

I stumbled on this page last week and promptly lost it...:rolleyes:

Now that I've found it again, I thought I'd post it:

http://etacar.umn.edu/archive/

There is an archive of old spectra of eta carinae. I haven't done it yet but if we can open these in VSpec then there's a ready made source of spectra to practice with and learn our way around VSpec.;)

Al.

PS. Guys... might not be as simple as I thought. The spectra fits files are .tar files. It sounds like you need a program called tar to uncompress... I'll see what I can find...

[Terry B]

tar files are just linux compressed files. There should be a windows program to untar them otherwise it is very easy to do in linux.

[Merlin66]

The knife edge idea would work.... I rather like the diaphragm idea though..It effectively hides everything other than the star image going through the SA. You can quickly estimate the size of the hole required from the distance between the grating and the CCD and the focal ratio.
Think about it; no "extra" star images to contaminate the spectra and no additional spectra of other stars.........

[sheeny]

:shrug: Winzip is supposed to do it, I believe, but so far all I've tried have given errors.:(

Al.

[theodog]

I'm looking into 2 possibilities.
When I get hold of some 2" aluminium bar I will make a 2" "mask into which the 1 1/4 SA will slide into, similar to a 2" adapter, with a small hole to allow a small field through.:)
Also I have come across an old microscope slide mover that is used to move microscope slides around the stage. I am looking into how this may be used to move an adjustable slit around under the SA, major engineering.:shrug:
:)

[sheeny]

You don't want to hole in the centre though do you? You want the star image near the edge of the FOV of your camera, so don't forget to offset the hole by a smidgin less than half the width of your camera sensor corrected for the focal ratio of your scope.:)

Al.

[theodog]

Yep, working through these issues, if only things were simple. Terry's idea of aluminium foil would help to develop measurements.:D

Working through the micro-slide idea, maybe easier to make a full spectroscope.:rolleyes:

Can't open the .tar files either using winzip.:(
:)

[Zaps]

You can open .tar and .gz files in Windows with WinZip, so long as you have it configured correctly. Otherwise you can use 7-zip, gzip, WinAce, WinRAR, or TAR for Windows, plus a few others.

[sheeny]

:lol:

Glad it's not just me that's having trouble opening the .tar files.:P



I didn't think there was any configuration to do in Winzip:shrug:... I've just had another look and can't see anything obviously useful. If you can be more specific, that would be appreciated!

I keep getting an "invalid archive directory" error., which may be the result of:

The archive file does not exist or is in use by another program.
The specified folder does not exist.
The file is not an archive.
The archive has been damaged or corrupted.
There were disk errors or insufficient memory while reading the archive.
The archive contains invalid or illegal filenames.If anyone has success opening the .tar files of the spectra I'd appreciate some tips on what you did...:whistle:.

Al.

[Zaps]

Go to WinZip/Options/Configuration/System/Associations and make sure .TAR files are associated with WinZip.

[sheeny]

Thanks Zaps... that was all good... so that's not the problem.

Al.

[theodog]

Yep, tried 7zip and no cigar.

Yes, get them too.

The image below is a mask I made this morning for the SA. It places a solid screen close, has a small ridge, but not touching the glass grating. It is stoped by the retaining ring.
My question, to save me some time, is "Where (from center) should I drill the hole?:shrug: My main spec. set-up is a meade 4" f9 with a ST7e.
:)

[Heian]

It all looks very promising to me!
I did some experiments last night on a convenient street light and was able to get some further distance between the SA and the DSI3 chip. It is now in the order of 105 - 110mm.
The set up is: DSI3 - SA spacer - 0.6focal reducer - ext tube - SA. :)

Not sure of the ang/px yet, but it should be about 6-7, as the zero order and then spectra covered 75 - 80% of the long axis.
That'll do for the moment, if only the stupid clouds would go away...:mad2: :lol:

cheers
Mark

[sheeny]

Here's my calcs, Jeff. I don't have enough info to give you a dimension but I think I can give you enough to work it out;).

Your ST7e is 756 x 510 pixels at 9µm, corrrect? That makes the CCD 6.804mm wide, so the edge is 3.4mm from centreline. You want to drill the hole in from this just enough to compensate for the f/9 focal ratio of your scope and allow a bit either in position or hole size to get the zero order image just off the edge.

So:

x = 3.4mm - 3.4y/F

where
x = the distance from the centreline to the projection of the edge of your ccd on the mask;
y = distance from the ccd to the mask;
F = focal length of your scope = 900mm.

I would suggest maybe x is OK for the position of the hole if you allow a little extra in the size of the hole.

The minimum diameter of the hole is d = y/9 + 9µm (allowance for raleighs criteria) + a gnat's whisker to get the zero order image off the edge and for userfriendliness while trying to align your star;):lol:.

Al.

[sheeny]

Sounds good Romeo... er... Mark!:thumbsup:

Al.

[theodog]

Thanks Al. The drill press is on.

So, who do we have? Shakespeare OR Knoffler:rolleyes:
:)

[sheeny]

I guess technically it's Shakepeare via Knopfler...;)

I just realised my previous calcs were wrong... :doh:Don't do it Jeff! Not yet!

f in the previous calc should be F (the scope's focal length!) It's now corrected, but I hope you weren't too quick on the drill!:rolleyes::whistle:

Al.

[Heian]

:doh:

a slight slip of the keyboard, but I knew what I meant....

:lol:

cheers
Mark

[theodog]

OK here is version 1.
I suppose Investigation #3

Thanks Al for your help.:D

If there are problems I'll have another go until it's right.:doh:
Then we'll know.:thumbsup:
:D

[Merlin66]

Jeff,
Looking very good!!
Just remember to position the diaphragm in line with the dispersion!!
I'm looking forward to the results.....

BTW still having problems with the .TAR ( I get the same error message with WinZip 12)
Any other ideas?????

[sheeny]

It does look good, doesn't it?

The only other thing I can think of with the .TAR files, Ken is that maybe they are legal filenames/directory names for Unix inside the .TAR file, but they aren't legal for windows:shrug:. I don't know if that's possible, I'm out of touch with unix/linux these days...

Maybe if someone has a Linux system they can try and let us know?

Al.

[theodog]

Hi all,
Some success.:P

Below;
1) Spec, full width frame, during slew. -no stars in spectra

2) Full raw frame minus dark, no stars in spectra

3) VSpec results.

The mask is on the wrong side so I had to mirror the frame:doh:. Easily fixed by rotating the mask by 180deg.
Focus is much much more difficult.:(
:)
Only 1x7sec exp for each

As for .tar, maybe somebody with linux could open them and resave as .zip. Big job I imagine.

[Merlin66]

Now that looks good!!!!!!
I think the potential is there to give a cleaner spectra, with no loss of resolution, what do you think??
Believe me getting a star image in a 3mm hole is NOTHING compared with the fun and games of finding and hold one on a 20 micron slit!!!!!!
Re the TAR; I downloaded a trial version of Alphazip which reads TAR files etc and found ALL the files I downloaded from the HST site were corrupt in one way or another...I'll give it a miss...

[Heian]

Jeff,
looking good :thumbsup:, I'm getting more interested by the minute...

How does the 7 sec exposure compare to what you would normally use to get a spectra from a star this bright?

cheers
Mark

[Terry B]

Very good. Raining here so no testing for me.:shrug:

[Terry B]

I tried downloading some of the tar files in linux but they are empty files.
I could get successful files from here http://archive.stsci.edu/
Just enter eta carina and optical/ IR and download the data sets. They open in linux easily. Haven't tried windows yet.

[Merlin66]

BTW
I think we are now breaking records for the most read, and longest Thread on IIS.... say's something about the general interest in the Subject!!!!!!

[Heian]

Gents,
confirmed that my setup with now work at 7 ang/px without too much drama..:) I tried it in the 120mm + the 80mm refractor and was iniitially surprised that I got the same result for each scope. The brain fade cleared and it was another :doh:moment!
Ang/px is irrelevant to the scope, it's 100% to do with the SA - CCD distance.

cheers
Mark

[Merlin66]

You got it!!!!
You could also change your camera: a webcam has 5.6 micron pixels whereas my 300D has 7.1 micron and my MX7c 8.6micron.....

[Heian]

Ken,
the DSI3 pixels are 6.5 x 6.5 micron, and it's a b+w chip so that avoids another issue.
I noticed that you and Robin had some interesting chats on the yahoo site about the use of the aperture mask on the SA.
A filter slide or wheel that could move the SA in and out of the optical train would allow you to take an image of the star field, then the spectra without removing the camera from the scope. It would make it easier to flat field away the background stars... what do you think!!

Mark

[Terry B]

I have tried this as I have my SA on a filter wheel. It will make it easy to position a star on a knife edge etc as I can frame it with a clear filter first. I tried subtracting a clear image but it didn't work probably becuse of different focus with the SA and the clear filter.

[theodog]

Yes, I had to refocus and then readjust the frame size to get the stars to match. Also you can see I didn't place the camera back in exactly the same position after removing the SA.:sadeyes:
It was a fiddly job.:(

How does the knife edge/SA distance affect the image?
Ah next investigation.;)

[Terry B]

Not sure yet as it has been cloudy. In theory it should be as close to the CCD as possible. The image is not focussed when it passes through the SA so the knife edge should have a blurry side. I read somewhere that the resolution of the spectrum is determined by (among other things) the number of grating lines the star image crosses on the grating. This means the more blurry at the SA the better. This will blurr the edge also.
I will have to experiment.

[Merlin66]

The resolution of the SA is dependent on the distance from focus.
The more out of focus the star image is at the plane of the grating, the more lines are illuminated, the better the resolution.
The SA is 100lpm grating , so a 4mm OOF star would illuminate 400 lines, a 6mm image, 600 lines ( a 50% increase in resolution!) etc etc
You still loose efficency with large star images...
When the beam is collimated ( and a slit added) you have the potential of the full SA aperture 28mm, 2800 lines.... x7 the resolution.

[theodog]

Hi all,
I have used the spacer to extend the SA from the CCD and rotated the aperture diaphram to the correct position. Included is a .zip of the image of alptau as a .fit. This image has the dark removed.
It is 5sec through the 4".
Feel free to play and post what you find. I would be very interested in any calibrations for wavelength sensitivity for my ST7.:thumbsup:
:)

[Merlin66]

Terry,
The stsci site works well under winXp... downloaded a couple of the spectra.

[Merlin66]

Jeff,
Still working on your spectra...
Would a dispersion of 14.7133A/pixel make sense to you? Compared to the Vspec library K5 III.....
I'm seeing out to about 9000A at the moment - I think, with atmos absorption at around 7000 and 7200???
Did you/ do you have any IR filter on the CCD?
I'll post later the curves I've got.

[theodog]

Yes, I measured around 15.



Not that I know of. Just the class window of the ST7.

[Terry B]

I had a go at Jeffs image of alp Tau.
I measure 15.136 A/pixel.
This is similar to my genesis CCD using the same KAF0401 chip. I get ~12.5 A/pixel.
see attached.

[Merlin66]

Found this quoted on the Spectro-L forum:
Based on Alain Lopez - for the Star Analyser - 100lpm
Dispersion ( A/pixel)= 10000 x Pixel size (micron)/100 x Distance ( in mm, distance from the grating to the CCD)

[Merlin66]

Jeff,

I think Terry has done a creditable job....
I'm having problems getting all the obvious "lumps and bumps" to align just using a single A/pix calibration...
The spectra seems to vary from 14.88 to 15.13 as you go towards the IR.
I'll dump a graphic to show the differences...
Hmmmm, don't understand yet?? different focus???

You can see the registration of the lines at 4973/5124 and 8484/8621 but this starts to "drift" across the middle graph, ie 7077 misses and slight drift in 5851???

[Merlin66]

BTW Jack Martin gives a good (albeit small scale!) comparison spectra on p89 of the PAS book. Covers 3100 to 6600A
Some interesting comparisons with Jeff's one.

[Merlin66]

Jeff,
The attached image is my comparison between your alptau0012 and the K5 III library, after correction for your camera responce.
I also include a copy of the responce curve I generated and used; maybe Terry can compare this with his one??

[theodog]

Thanks Terry and Merlin, I really appreciate your time and efforts.
You seem to have identified the issue.
When I calibrated using the O2 line, I got one l/pix reading, but as I refined it after croping the l/pix changed.
I don't understand how the focus could change, unless the spectral image is not flat?:screwy:

Would the multi-line calibration produce a better result?:shrug:

I will post an image of etacar taken with the same setup, on the same night.

[theodog]

These files contain the images of eta and beta carina. I will repeat these images when this crappy, sorry ordinary, weather has passed.:)

[Merlin66]

jeff,
If you use the camera responce curve to "correct" the raw spectra; remember each new configuration ie scope/ grating distance/ camera will require a new responce curve, a three line calibration will improve the result. For the alp tau you could try the 4973 or 5124, 5851 and the 8484..
still don't know where the distortion is coming from??

[theodog]

Thanks Merlin.
Here is one from the same night of etacar.
12x5sec -dks stacked.
Camera response from my alptau spec.
:D

[Merlin66]

Besides the H2o absorptions given in the Vspec library, there are also significant absorptions at 6900, 7200, and 7600 ( as see in your results!!)

[Terry B]

Interesting results. I don't think we can take too much notice of the more distant IR part of the graph. The blue end of the 2nd order spectrum starts to interfere.
Take a look at the images towards the bottom of this page. http://www.astrosurf.com/buil/us/loris/loris.htm

[theodog]

I agree with Terry, the far IR could be interferred by the UV.
I must try to measure where the UV starts.

[Terry B]

I had a little time last night before the clouds rolled in to take an image with a bit of foil across the SA. I blocked about 2/3 of the filter. It meant that about 2/3 of the image is blocked and didn't seem to cause any darkening of the star image on the edge of the field.
I'm not sure if it made much difference with eta car but should reduce stars interfering with the spectrum.
See attached.

[sheeny]

Looks promising :thumbsup:

Al.

[theodog]

Yep, looks nice Terry.:thumbsup:

I'll be out of action for a short time, the laptop has gone belly-up.:(
I have nothing to drive the scope and camera.:sadeyes:
Thank God I have copies of my software, but lost 6 months of images.
Still get to IIS on the desktop 'though.:D

Back soon.
:)

[sheeny]

Hope you get the lappy back up soon, Jeff.

Ken started a bit of a discussion on the SA forum about Jeff's mask, which I bought into as well as there seemed to be a little bit of misunderstanding about what Jeff's mask was trying to do, but one suggestion Robin made was why not use a sliding mask... actually a filter wheel or filter slide could do basically the same thing (once it's oriented right;)) with the advantage that it can be moved out of the way for a full frame view when needed.

But of course that doesn't help much if you have your SA in the filter wheel...:rolleyes::lol: ... but than maybe it can by having the SA offset i.e. simply rotate or slide it out of position:shrug:... hmmm...

Al.

[Terry B]

A sliding mask would be good. I currently have my SA on a filter wheel. This makes positioning the star on the side of the frame easy by selecting a clear filter, positioning the star then moving the SA in.
An interesting effect of the foil mask is that my Bahtinov mask no longer works to focus the spectrum. Only 2 lines show up rather than the 3. I will have to try a different way of focussing.

[sheeny]

I usually have to tweak the focus for the spectrum anyway. So why not use the Bahtinov mask through your clear filter to get it close, and then tweak the spectrum with the SA is flipped in?:thumbsup:

Al.

[theodog]

I have been thinking of a filter-wheel with two positions. One clear, the other with a slit to suit the focal length.
It would screw into the SA* on one side and have a 2" nosepiece on the other.
*This side could maybe have an 1 1/4" "socket to recieve the SA and nosepiece of the camera.
Because there would be no thick filters on the carriage, just one large hole and one small for the mask, the whole unit could be made thinish and smallish.

Something to do tonight under these beautiful clear skies.:(

[Terry B]

Maybe something like this http://www.surplusshed.com/pages/item/m1570d.html
would be adaptable.

[sheeny]

I got my filter wheel today, so I'm looking forward to having a play to see what sort of dispersions I get:). Should be slightly more dispersion than each option without.

Al.