Author Topic: Astronomical Spectroscopy  (Read 5450 times)

oldfrankland

  • Observer
  • Posts: 19
    • View Profile
    • Astrophotography by Jim Ferreira
Astronomical Spectroscopy
« on: June 13, 2015, 11:22:13 AM »
Anyone in the group dabbling in stellar spectroscopy?  A few years ago I acquired a Star Analyzer 100 and found its use surprisingly addictive.  A little over a year ago I picked up a Alpy 600 and have been exploring active O & B type stars, planetary nebulae, even the sodium cloud around Io.

http://www.lafterhall.com/spectroscopy_shelyak_alpy_600_spectrograph.html

Jim Ferreira
Livermore
bakerst@comcast.net
Jim Ferreira, Livermore
Dabble in Astrophotography, Spectroscopy, Solar Astronomy
http://www.lafterhall.com/astro.html

buynoski

  • Observer
  • Posts: 26
    • View Profile
Re: Astronomical Spectroscopy
« Reply #1 on: June 14, 2015, 05:45:44 AM »
I also dabble in spectroscopy, at least visually; the computer fol-de-rol associated with taking detailed spectra is too tedious for me.  My spectroscopes are a Baader DADOS and a Shelyak LHIRES Lite.   For looking at relatively non-detailed stellar spectra I have a Rainbow Optics slitless transmission grating.

Given the amount of light required for seeing color in a spread-out spectrum, really detailed spectra of stars are somewhat problematical visually unless you have a really big telescope (mine is a C14…not so big).  They are, except for a few very bright stars, kind of "washed out".  However, as you note, even the relatively non-detailed spectra provided by the transmission gratings are captivating.

The real winner is solar spectroscopy.  You don't even need a telescope or a mount more complex than a decent photo tripod, and you will see tremendous detail (my LHIRES Lite shows hundreds to thousands of spectral lines).  Your Alpy will show somewhat less detail (600 lpm grating vs. the LHIRES' 2,400 lpm) but that's OK…you'll still get a fantastic, brightly colored view with dozens to hundreds of lines…be sure to set the Alpy to its narrowest slit width when you do this.

If you'd like to see the DADOS and LHIRES, send me an email  (leave out the $  and % from the following):
buy$no%ski@b$atn%et, c$om 

I also have a little introductory article about spectroscopy here on TAC.  If you'd like to read it, it's in the "New Subscribers and Beginners: Start Here" section.

oldfrankland

  • Observer
  • Posts: 19
    • View Profile
    • Astrophotography by Jim Ferreira
Re: Astronomical Spectroscopy
« Reply #2 on: June 14, 2015, 12:49:24 PM »
Indeed, a splendid little spectroscopy intro article.  Wow, you could do some pretty serious spectroscopy with your instruments and the C14 capturing spectra with a CCD.  Particularly Be type stars, zeroing in on the H-alpha line.  Can you see much spectra of brighter planetary nebula?  I've had a look visually at the solar spectra, but quickly becomes ho-hum at only 600 l/mm.  Is your Dados 900 l/mm?
Jim Ferreira, Livermore
Dabble in Astrophotography, Spectroscopy, Solar Astronomy
http://www.lafterhall.com/astro.html

buynoski

  • Observer
  • Posts: 26
    • View Profile
Re: Astronomical Spectroscopy
« Reply #3 on: June 14, 2015, 04:17:42 PM »
      A C14 is capable of providing enough light to a CCD but the exposures required are still pretty long. Almost any decent size and quality amateur telescope will work. The real limit is the mount, because keeping the star's light in the narrow slit openings takes autoguiding every bit as good or better than required for astrophotograpy. For that reason, plus all the work at the computer required with dark frames, instrument calibration, getting the scaling right with reference lines, etc, etc, I stick with visual only.
     I've looked at planetaries with a grating only a little bit, as they are very dim visually and look more like points than spectra.  They turn out to be remarkably easy to find: sweep the Milky Way with a transmission grating installed and all the stars spread out into spectra, but the planetaries don't.
     The DADOS comes with both 200 and 900 gratings, but I generally have the 900 installed.  It will be somewhat more detailed than what the Alpy presents, but not a whole lot.  The LHIRES Lite is a definite cut above in that regard (2,400 lpm).  However, massive detail is not the whole story; DADOS (and likely your Alpy) has the advantage, for solar spectra, of seeing almost the entire spectrum in one view; with the LHIRES, only a chunk at a time can be seen. 
     Were you certain that you had the Alpy's narrowest slit  (25 micron?) in place?  Wider slits will degrade the resolution and obscure detail. The LHIRES Lite also has an advantage in slit width (15 micron) but of course, it was designed specifically for solar viewing and doesn't have any means of attachment to a telescope; its more sophisticated (and more expensive :-) cousin, the LHIRES 3, is for stellar spectra using a telescope.


oldfrankland

  • Observer
  • Posts: 19
    • View Profile
    • Astrophotography by Jim Ferreira
Re: Astronomical Spectroscopy
« Reply #4 on: June 15, 2015, 06:32:56 PM »
Yeah, I've used both an 80mm and 4 inch refractor, and 9 inch SCT with both the Star Analyzer 100 and Alpy 600.  I use autoguiding with each system, with spectra exposure times as much as 600 seconds for stars down to 8th magnitude or slightly fainter.  My Alpy has an off-axis mirror slit - 23u wide - for autoguiding.  Works well with a simple video camera and PHD guiding software with either my GM8 or G11 mounts. 

As for shooting darks, flats, reference stars, etc., it all really depends on what you are looking to do, or see.  With brighter stars darks and flats generally are not needed for comparitive spectrosopy.  Spectra of fainter stars with better S/N ratios can be had by using darks.  On the post processing end, calibrating the spectra with software is not particularly difficult, but can be time consuming going through the literature looking for spectra that pertain to the star of interest.  With O, B, A stars, adequate calibration for R-700 to R-1500 resolution can be done quite adequately using the Balmer lines of the star itself and/or comparison star.  Higher resolution systems like the LHIRES III require the more involved calibration procedures.

We have a LHIRES Lite up a Chabot Observatory for solar demonstrations.  Very good for students with some understanding of spectroscopy, but less useful for the general public.  As to my 'ho-hum' reference to solar spectroscopy.....unless the spectrometer is on a telescope that can isolate individual features like sunspots, flares and prominences or look for doppler line shifts, the general solar spectra remains largely unchanged - textbook, as it were.
Jim Ferreira, Livermore
Dabble in Astrophotography, Spectroscopy, Solar Astronomy
http://www.lafterhall.com/astro.html

buynoski

  • Observer
  • Posts: 26
    • View Profile
Re: Astronomical Spectroscopy
« Reply #5 on: June 16, 2015, 06:23:46 AM »
    Gee, I sure hope the solar spectrum doesn't change :-) :-)

    Most of what I do with the solar equipment is giving demos at the local high school for the astronomy class. But the non-class population around (teachers, other students) also are invited to take a peek and generally find the solar spectrum very interesting, if only because it has so much detail. 
    When these demos are done, the solar spectroscope is one of 3 stations, the other two being a hydrogen-alpha telescope and a white-light-solar-filtered regular telescope.  This gives the viewer three different views of the Sun: spectral, chromospheric, and photospheric.  Together, these reinforce each other and leave them with a good appreciation of how interesting and complicated the Sun is.  We also have some big posters to look at (Sun at various wavelengths, major solar observatory spectra) and books to peruse (e.g. Lang's  "The Sun from Space").

oldfrankland

  • Observer
  • Posts: 19
    • View Profile
    • Astrophotography by Jim Ferreira
Re: Astronomical Spectroscopy
« Reply #6 on: June 16, 2015, 02:22:34 PM »
Oh, excellent; school astro demos - bravo.  I don't do them much any more because of hearing loss, but the last school-public science demo I did here in Livermore, I never got my scope setup.  I setup my laptop and answered a few questions by showing students a handful of solar and planetary animations, the interest was overwhelming.  The teens instantly related to the use of camera and computer -- something I have advocated for some time in EAS/Chabot.

http://www.lafterhall.com/activated_prominence_movie_01jul2013_001.gif

http://www.lafterhall.com/surge_prominences_ar11754_30may2013_001.gif

http://www.lafterhall.com/ganymede_eclipse_25nov2012_001.gif

http://www.lafterhall.com/jupiter-europa_18oct2012_ferreira_001.gif

Astronomy rocks!
Jim Ferreira, Livermore
Dabble in Astrophotography, Spectroscopy, Solar Astronomy
http://www.lafterhall.com/astro.html