33 replies to this topic

[Olivier_Garde]

As a reminder, the workshop will take place this Thursday, February 8 at 9pm French time (20H UTC).
There are still a few places available.

 

To register for free : 

 

https://us02web.zoom...W#/registration

Edited by Olivier_Garde, 06 February 2024 - 07:49 AM.

[Olivier_Garde]

The replay of the Alpy 200 workshop of yesterday is available here :
https://youtu.be/0L6LLn9HjUY

 

And an article about the Alpy 200 :

 

https://www.shelyak....-range/?lang=en

Olivier

[akmal89]

Hi,

 

Planned to buy Alpy 200 to start my spectroscopy journey, however, a bit tight on budget. Would like to have someone here to advice on the required gear for a complete and minimal function (minus option).

 

Alpy 200 Spectroscope - https://www.shelyak....oscope/?lang=en

Guiding module - https://www.shelyak....e-alpy/?lang=en

BTW, if no calibration module, is it still be able to complete the object spectrum recording?

 

Here my current gear:

 

Nexstar 5se with f/6.3 reducer

ZWO ASI 120MM

ZWO ASI 533MC

[Organic Astrochemist]

Hi,

 

Planned to buy Alpy 200 to start my spectroscopy journey, however, a bit tight on budget. Would like to have someone here to advice on the required gear for a complete and minimal function (minus option).

 

Alpy 200 Spectroscope - https://www.shelyak....oscope/?lang=en

Guiding module - https://www.shelyak....e-alpy/?lang=en

BTW, if no calibration module, is it still be able to complete the object spectrum recording?

 

Here my current gear:

 

Nexstar 5se with f/6.3 reducer

ZWO ASI 120MM

ZWO ASI 533MC

Hi,

There are lots of things to consider in buying a spectroscope. I have some experience, but Robin and others know much more than I. 

Let me start by saying that STARTING spectroscopy on faint targets is a TERRIBLE IDEA.

 

Start with bright targets. Start with lots of targets. The more spectra you take the better you will become. If you have an SA200, take lots and lots of spectra with that. Increase the distance between the grating and the camera to increase resolution to see more lines - try this for type A stars and see how many Balmer lines you can see. Decrease the distance between the grating and the camera to decrease resolution but to see fainter targets - try this for Wolf Rayet stars, carbon stars, maybe planetary nebulae.

Personally, in general, I think it's more helpful most of the time for most people to see more spectroscopic details (more lines) rather than less. It allows you to discern more differences between targets.

 

As for minimal setup. I have a Borg 55FL (55 mm refractor) and an Alpy 600 = no guiding module and no calibration model, operating in slitless mode. ASI178MM camera. The mount is a skyguider pro. I use a 35 mm Canon camera lens to find my targets (you will need some kind of guidscope probably -- trying to slew to targets with the ALpy guiding camera could be difficult). I wouldn't recommend this setup, certainly not for starting. But I can set it up in a matter of minutes. I can take spectra of lots of bright targets. With small pixel size and star image (f/ 4.5) and great seeing means I get pretty good resolution. I got a bunch of spectra of stars in M45 (the Pleiades) in one night. My point is to show what can be done with minimal setup and why Alpy 600 affords good resolution for beginners. (Eta Tau red, reference blue)

In addition to Balmer lines of hydrogen there are helium and metal lines here. Also note the wide balmer lines of Pleione (28 Tau) due to it's fast rotation and high i sini value (we see it close to equator-on). This is very rewarding spectroscopy. There's a lot to see.

 

If you want to submit to databases then the guiding and calibration modules are probably necessasry

Edited by Organic Astrochemist, 19 January 2025 - 09:13 PM.

[akmal89]

Hi,

 

Currently I have SA200, which a quite exciting when obtained a good and matching star spectra by follows tutorial from Mr Tom Field videos.

Its like fun stopper once tried to have Orion Nebula spectra and the slitless setting really not helping. Tried google for a slit set up and finally end up to Star'ex and Alpy 200 options.

Kindly to have any info if there is available set up for SA200 with slit feature?

 

Thanks

[robin_astro]

Hi,

 

 

Kindly to have any info if there is available set up for SA200 with slit feature?

 

 

If you have not tried slit spectroscopy before then my advice is that the best next step from the SA200 would be a slit spectrograph with more resolution than the SA200 can offer, like the ALPY600 or Star'Ex etc, not the ALPY200. This higher resolution would give you more information about the object than the SA200 or ALPY200 can give.  If you then want to measure very faint objects then adding the ALPY200 module could be a next step

 

If you want to experiment with slit spectroscopy at low cost then you can design  a slit spectrograph using  the Star Analyser (The ALPY 200 which I developed in 2014 from the ALPY 600 is effectively this.)  You need to add some more optics though. Here is a simple design (my SEPSA configuration)

http://www.threehill...troscopy_18.htm

and a more complex fully collimated design my "junk box" spectrograph to which a slit can be added.  http://www.threehill...troscopy_19.htm

These designs do not include the necessary guider module though and designs like the ALPY or 3D printed Star'Ex will work much better.

 

Cheers

Robin

[robin_astro]

 Would like to have someone here to advice on the required gear for a complete and minimal function (minus option).

 

 

The calibration module is useful but not essential but my view is that the mirror slit guider module is almost essential. It is very hard to use a slit spectrograph without  one. This allows you to focus the target, move it onto the slit and keep it there for exposures which can be tens of minutes to an hour or more. Without one you only see anything when the target is actually on the slit and nothing when it is off the slit.

 

A potential limitation of your setup is the ASI533MC colour camera you plan using. There are several reasons why mono cameras are better than colour for spectroscopy. Except for bright targets, cooled cameras are also important because of the long total exposure times.  See this recent thread on the RSpec forum for example.

https://rspec-astron...n/message/15002

 

Cheers

Robin

[robin_astro]

Using just the ALPY600 module in slitless mode without the guider module  (as a kind of higher resolution Star Analyser)  as "Organic Chemist" does could be a first step to a full ALPY system but as it is slitless it has the same limitations as the Star Analyser when measuring extended objects like nebulae etc.

 

Slides 2 and 3   in my presentation "Low Resolution Slit Spectroscopy"  here

https://britastro.or...he-nlo-oct-2015

lists the advantages of the ALPY 600 with the slit over the slitless Star Analyser 

 

Cheers

Robin

[Organic Astrochemist]

Of course Robin is correct that the guiding module is essentiel for slit spectroscopy.

I think it is interesting to talk a little more about slit vs slitless spectroscopy.

Do you have an oberservatory? This is often left unasked but, in my opinion, one should recognize that people who get the best spectra and submit to databases usually have observatories. If you want to get as many good quality spectra as possible on the few nights that you set up your rig, slitless spectroscopy has advantages.

Consider targets — stellar or point sources (could even include small planetary nebulae and bright AGN). As a quick measure 22 chapters in Walker’s “spectral atlas” concern point sources. There are four chapters on extended sources and even there slitless spectroscopy is possible for AGN, planetary nebulae and some planets/moons.

Obviously slit spectroscopy is tremendously important and powerful. But for observers without an observatory especially, how often will you need it for your target? The tradeoffs due to complexity are real — to do it correctly and acquire reference spectra nearby your target you will obtain fewer target spectra for a given night. If you want to submit to databases this is important. If you want to acquire spectra to see the most you can learn about astronomy and astrophysics with your rig, then prioritizing target brightness vs resolution seems more important to me. Even if you get an Alpy or Star ‘ex use your SA200 for fainter targets by decreasing the resolution.

Edited by Organic Astrochemist, 20 January 2025 - 11:41 AM.