6 replies to this topic

[v8vantage]

I am just starting out with spectroscopy and need advice for improving my setup.

 

I am really an amateur PN Hunter and have a setup in Spain dedicated to that, but I would love to be able to help classify potential PN's by also doing spectroscopy.

 

So I set up a second observatory here in Sweden, using stuff that I had laying around, got an Alpy600 + guiding and calibration unit, tried out BASS, RSpec, ISIS, settling for Demetra, and started my journey into the field of spectroscopy. And it works great for bright targets like M57 or M27 and even magnitude 15 "Jones 1"!

 

Now, since I use "leftovers", the setup is not ideal for faint targets like magnitude >18 PN:s. I use an Edge14" with reducer and a 3.8uM asi6200mm camera. Olivier Garde and Lionel Mulato warned me that I really should have a lower f-ratio scope and a large pixel CCD that can benefit from binning.

 

I will keep the f/7.7 Edge14" for now, but I will get a better suited camera, so;

What is the best camera for faint PN spectroscopy?

 

 

And yes, I am considering the Alpy200 core module or, more likely, a 50uM slit to match the large aperture. Seeing here in Falun, Sweden is around 2".

 

 

Thanks!
/Sven

Edited by v8vantage, 06 October 2024 - 09:28 AM.

[robin_astro]

Hi Sven,

 

I am the person who originally developed the ALPY200 (10 years ago now though Shelyak have only just offered a commercial version)

http://www.threehill...troscopy_20.htm

It is optimised for spectroscopy of supernovae which are stellar objects with very broad lines so is a significantly different application to PNe which have narrow lines and may not appear stellar.  Because of this the ALPY600 (or probably a spectrograph with even higher resolution), used with a slit width matched the target size would likely work better than an ALPY200 for this application 

 

You don't say what your typical seeing is (arcsec) this is a key factor with stellar spectroscopy as in good seeing  a larger apertures telescope can still match well to a spectrograph designed for use with smaller telescopes in poorer seeing.  This will be less of a factor with PNe though if they do not appear stellar. In any case, the ALPY works down to f4 so I would recommend reducing your telescope to this to minimise the image size at the slit.

 

Finally, to answer your question on what camera. It must be a cooled mono camera with low thermal noise as exposures will be an hour or more in total on faint targets. With CMOS cameras binning makes no difference though a good pixel size will help keep read noise to a minimum.  (I am still CCD and use an ATIK428 camera with the ALPY with a 23um slit and 2x binning to reduce read noise)

 

Cheers

Robin

[robin_astro]

Sorry, I missed that your seeing is 2 arcsec. This is a bit better than mine at ~3 arcsec. With a 14 inch at f7 the ALPY with the standard 23um slit is a good match for stellar targets, but if the PNe are non stellar opening up the slit to increase the light grab will also reduce the resolution. (The spectrograph is optimised for detecting faint emission lines when the resolution matches the width of the lines, which are narrow in PNe)

Edited by robin_astro, 06 October 2024 - 08:42 AM.

[robin_astro]

The ASI 6200mm pro is already an excellent camera. I doubt that you would see any significant improvement by changing to another camera

[v8vantage]

Hi Robin!

Yes, I recently saw you on the Alpy200 workshop you participated in during the spring!

In that workshop François also emphasize that a larger slit with the Alpy600 would be better than an Alpy200, give a larger aperture:

 

 

 

But that makes it even more important to have a camera that support "on-sensor" binning, keeping read-out noise low.

 

 

So, what is the best possible spectroscopy camera, given my other equipment and my kind of targets.

 

 

Seeing here in Falun, Sweden is about 2".

 

 

 

Cheers,
/Sven

[v8vantage]

The ASI 6200mm pro is already an excellent camera. I doubt that you would see any significant improvement by changing to another camera

Yes, I am approaching that conclusion as well. Comparing with for instance a Moravian G3-16200 with QE of 60% and read out noise of 10, I can do a software bin2 with the same total read out noise and QE of 80%. And save 4000 Euros...

[robin_astro]

The best CCD camera for the ALPY was considered to be the  ATIK414 with 6.5um pixels and very low thermal noise (and low read noise for a CCD,with the advantage of on sensor binning). It is still available 

https://www.atik-cam...ccd/atik-414ex/

 

but I suspect CMOS probably now matches this. Oversampling can be used to advantage to reduce the non thermal telegraph noise that CMOS show (described in Christian Buil's CMED technique)

 

Christian Buil talks about using your camera for spectroscopy and CMED processing in sections 5 and 6 here.

http://www.astrosurf...buil/asi6200mm/

(With a high resolution echelle so a different application. Except in very dark skies, I suspect the sky background may be the limiting factor)

 

Cheers

Robin