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Stacking and Data Capture: Spectroscopy

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#1 Xshovelfighter

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Posted 14 April 2019 - 02:39 PM

Hi all, 

 

I dabbled with the Star Analyzer 100 and RSpec a few years back but then got sidetracked taking "pretty" pictures and the astrophotography end of things.  I am now ready to get back into things, which actually works out now that I have a better setup and equipment to do spectroscopy as well.  My question is regarding data collection.  My concern is with stacking the subframes that I collect. Deep Sky Stacker (DSS) is great but when I am collecting spectra of brighter stars and have very short exposures, no other stars are really going to show up and DSS obviously needs more than 1 - 2 stars.  This wouldn't be a cocnern when imaging dimmer stars, as there would be several stars brighter than the target star.  Any suggestions for this?

 

My next question is along the same line.  It looks like it is possible to do my data collection in RSpec itself...?  I fiddled with my camera and the software during the daytime today and really like the live play and image averaging/stacking option.  My question is how to take this live feed and save it to a single image for use in the RSpec analysis?  Further, assuming this is a pretty easy thing to do, is this a good method that would yield quality results as compared with a third party software?  I really like Sequence Generator Pro for data collection but if RSpec could handle data collection and also cover the stacking end of things as well.

 

Thanks for any insight or help with this!  



#2 robin_astro

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Posted 14 April 2019 - 04:38 PM

You could check with Tom Field but I don't think RSpec can align and stack on the fly currently so my advice would be to use RSpec to set everything up and get best focus. Then take a series of frames and align and stack them (either on the fly or off line using your favourite software) Using the zero order as the reference and choosing the sharpest as for planetary imaging  to produce a aligned and stacked composite image which you can then pass back to RSpec or other spectrum processing software. (You only need one star to align on as field rotation is not a problem because the spectrum is always in the same direction relative to the camera.)

 

You can see the outline of the similar procedure I use here but using the capture software provided with my camera and ISIS software for the processing

http://www.threehill.../spectra_42.htm

 

Cheers

Robin  


Edited by robin_astro, 14 April 2019 - 04:50 PM.


#3 Xshovelfighter

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Posted 15 April 2019 - 05:47 PM

Robin,

 

Thank you very much for the help!  Which softwares allow for stacking with only 1 or very few stars?  This is my main sticking point as I don't know how to produce a stacked image when there are only 1 or 2 stars.  DSS can't do this as far as I know.  Guess I may have to learn a new software?

 

Thanks again!



#4 robin_astro

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Posted 15 April 2019 - 08:17 PM

I use either K3CCDTools (which I have used since I first started with webcam imaging over 15 years ago but it is rather old now and there might be better programs around) or ISIS which is a very powerful program for spectroscopy and also has an alignment tool but ISIS can be a bit a bit tricky to get used to.  Any planetary imaging software should be able to do it though, provided you can manually select a single point or small region containing the zero order to align on.

 

Cheers

Robin


Edited by robin_astro, 15 April 2019 - 08:18 PM.


#5 Organic Astrochemist

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Posted 19 April 2019 - 09:55 AM

Nebulosity has a very intuitive stacking procedure (Batch, Combine & Align Images, select translation and confirm the position of the star in each image).

Here I stacked forty 15 second images that I acquired with Sharpcap (with darks). Remember, I used a $100 70 mm achromat, $300 iOptron Skytracker Pro camera mount, Star Analyzer 100 and ASI290MM-Cool camera:

NP UMa cropped.jpg

Obviously I have the mother-of-all chromatic aberration, but this simple system has exceeded my expectations. Those stars are mag 8.0 - 8.6, acquired in 10 minutes with a full moon in the heart of the city of Miami light dome. I used an instrument response from a week ago. Last night I would not have taken out my 8" telescope. It took me about ten minutes to take out this gear, set up and start observing.

HD 110105 with F2III.png

This is the brightest star (at the bottom in the image), mag 8.0 HD 110105 (F2) compared to a F2III reference.

 

Y Uma is a very red semi-regular variable (M7II-III). This showed the chromatic aberration very badly (the huge circle in the middle), but I could still reasonably classify the star.

Y UMa with M7III.png

Basically, I get about a 200 nm range in which stars put out enough light for me to achieve good S/N. Between 600 nm - 800 nm the spectrum most closely matches the M7III reference.

 

The star that I was really going after was NP UMa (HD 110463) which is a K3V member of the nucleus of the Ursa Major Moving Group at a distance of ~80 light years.

NP Uma with K3V.png

Not a great spectrum, but it matched K3V more than any other reference.

 

I have the 3.8 degree prism. Maybe I should try that too.



#6 JohnW*

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Posted 19 April 2019 - 04:22 PM

Jim

 

Nebulosity has a very intuitive stacking procedure (Batch, Combine & Align Images, select translation and confirm the position of the star in each image).

Here I stacked forty 15 second images that I acquired with Sharpcap (with darks). Remember, I used a $100 70 mm achromat, $300 iOptron Skytracker Pro camera mount, Star Analyzer 100 and ASI290MM-Cool camera:

attachicon.gif NP UMa cropped.jpg

Obviously I have the mother-of-all chromatic aberration, but this simple system has exceeded my expectations. Those stars are mag 8.0 - 8.6, acquired in 10 minutes with a full moon in the heart of the city of Miami light dome. I used an instrument response from a week ago. Last night I would not have taken out my 8" telescope. It took me about ten minutes to take out this gear, set up and start observing.

attachicon.gif HD 110105 with F2III.png

This is the brightest star (at the bottom in the image), mag 8.0 HD 110105 (F2) compared to a F2III reference.

 

Y Uma is a very red semi-regular variable (M7II-III). This showed the chromatic aberration very badly (the huge circle in the middle), but I could still reasonably classify the star.

attachicon.gif Y UMa with M7III.png

Basically, I get about a 200 nm range in which stars put out enough light for me to achieve good S/N. Between 600 nm - 800 nm the spectrum most closely matches the M7III reference.

 

The star that I was really going after was NP UMa (HD 110463) which is a K3V member of the nucleus of the Ursa Major Moving Group at a distance of ~80 light years.

attachicon.gif NP Uma with K3V.png

Not a great spectrum, but it matched K3V more than any other reference.

 

I have the 3.8 degree prism. Maybe I should try that too.

Jim,

 

Interesting set up for quick spectra acquisition.  My first M42 spectra was on a c6 on a Losmandy Time lapse mount (basically  a G-8 without dec.)  A lot easier to setup than my G-11 which currently has a board in for repair.  Plan to use my DSS-7 on a C8 with that setup.

 

Concerning stacking, Images Plus allows you to manually combine aligned images on 1-3 stars.  It works quite well.

 

John

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Edited by JohnW*, 19 April 2019 - 04:47 PM.

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#7 robin_astro

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Posted 19 April 2019 - 06:00 PM

Note if you are using the star analyser you definitely should not try to eliminate any field rotation by aligning on more than one star  as this will blur the spectrum. The grating and camera alignment are fixed relative to each other so the spectrum is always at a fixed angle in the camera field, independent of any field rotation. 

 

Cheers

Robin



#8 robin_astro

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Posted 19 April 2019 - 06:11 PM

 

Obviously I have the mother-of-all chromatic aberration, 

Wow !  That has to be the worst chromatism I have ever seen, even for an achromat. Care to name and shame ?  You might do better optimising the focus more towards the red end( An achromat should at least be in focus at 2 points in the spectrum) but I don't think a wedge prism is going to be of much help here.

 

Cheers

Robin



#9 Xshovelfighter

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Posted 21 April 2019 - 11:25 AM

Thanks everyone, I'll check out some of those programs for stacking.  I use Pixinsight for all of my astrophotography processing - anyone have experience manually stacking with Pixinsight?

 

Thanks 



#10 Organic Astrochemist

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Posted 21 April 2019 - 02:36 PM

Wow ! That has to be the worst chromatism I have ever seen, even for an achromat. Care to name and shame ? You might do better optimising the focus more towards the red end( An achromat should at least be in focus at 2 points in the spectrum) but I don't think a wedge prism is going to be of much help here.

Cheers
Robin

I'm using an Orion multi-use 70 mm finder scope. Others have severely criticized the optics. But I've been pleased. Even in this case, I think there was some "operator error". I tried the wedge prism and you were right that made as many problems as it solved. So I paid very close attention to the focus. If I focused too much on the red, things looked really bad in the blue. I think I found the compromise. But I see now that when I processed the spectra I was sampling too narrow a region and thereby losing red light.
Here is a screenshot of my spectral region selected in RSpec (fifteen images of 10 seconds stacked with Nebulosity). I subtracted the regions in blue and green and used the region in orange for the spectrum. I used the stretch display function to exaggerate the faint red parts of the spectrum.

Mu Cen.jpg

I used a nonlinear calibration and made an instrument response on the fly with Iota Centari. Below is the resulting spectrum of Mu Centari (B2IVe) compared to a reference in blue (B2IV). I was happy with the shape of the continuum across the spectrum. I was able to see the hydrogen and helium absorptions. I was also very happy to see H-alpha in emission. It wasn't a sharp peak, but given issues with focus, chromatic aberration and chromatic coma, this is probably the best I can do. The strength of this system is its portability and ease of use. Performance in the red end is its greatest weakness. Stacking allows observation of many many more targets. Although not up to BeSS standards, at least this afforded me an observation of a Be star that hasn't be reported there in over two years.

Mu Cen with B2IV.png

Edited by Organic Astrochemist, 21 April 2019 - 02:41 PM.



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