Possible? Any of you doing it?

Check out Spectrashift.com
The first website dedicated to amateur radial velocity studies

http://www.spectrashift.com/

There was a poster around here several years ago that was doing some, IIRC as a science project with his daughter. A search around might find something.

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At night the stars put on a show for free (Carole King)

One Earth, One Sky - IYA 2009

Maurice Gavin, among others, are doing good spectral work in the UK.

doug

I've had some experience with SBIG's self-guiding spectrograph, which seems to be financially within the range of very serious amateurs (something like $5000 plus a matching CCD for imaging and simultaneous guiding). It's a very elegant little box, with two back-to-back gratings. Trying it on a 0.4-meter telescope, it can do a good job at classifying stellar spectra, showed a nice emission/absorption profile on the recent 9th-magnitude nova in Vulpecula, convinced students that Titan really does have a methane-ric atmosphere, and can show the diagnostic spectral lines in bright Seyfert galaxies. I haven't managed SS 433 yet with this setup, as exciting as watching the changing Doppler shifts would be.

This box can deliver enough spectral resolution to detect the Earth's orbital motion from annual changes in the Doppler shifts of stars in various directions.

Huh... Do you have a sample spectra from it that I could look at? I'd be curious to see what it can do (Seyfert, maybe?). A fits file, or PNG quicklook would be great!

Thanks in advance!

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"What do you care what other people think?" -- Richard Feynman
"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." -- Feynman, at the conclusion of his Challenger report

Here are some plots of 1-D extracted spectra for NGC 4151 and the planetary nebula NGC 2392 (from the comparison one can get a good redshift for NGC 4151). Also a 2D image after dark subtraction and nothing else, of a 5-minute exposure at the core of M82. The main sensitivity limitation seems to be the detector's dark-count rate with this setup, a much bigger issue than with broadband imaging. Also, our site usually has poor seeing, so in a sense we ought to be getting rather more light down the slit. The NGC objects were observed for 15 minutes each through the "narrow" SGS slit (about 2 arcseconds on our 0.4m f/8 setup) with the low-dispersion grating (about 4 A/pixel), spanning from H-beta and [O III] to H-alpha and [N II]. For M82, we used the high-dispersion grating (something like 1.25 A/pixels) to get velocity structure. I had hoped to be able to have students measure a flat rotation curve on some bright alaxy, but so far velocity differences within the innermost part of M82 is as far as we've been able to get internal motions within galaxies.

Attached Images

	specNGC4151.png (24.3 KB, 9 views)
	specNGC2392.png (28.3 KB, 6 views)
	m82_5m.jpg (20.6 KB, 6 views)

That's pretty good! You'll probably need more than 15 minutes, eventually: what's your tracking like? And what is typical seeing, around 3"? What's the effective spectral range of the grating, and have you tried calibrating it on a standard lamp?

We may well have the same telescope as you (16" Meade LX200GPS), and I've been slowly working the bugs out of the system (got focus lock working, reduced focus slop, improving tracking, etc.). Might be something for us to consider investing in, in the future.

Sorry about all the questions, I've had an interest in something like this for a while, and your post caught my eye. Thanks for the reply.

__________________
"What do you care what other people think?" -- Richard Feynman
"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." -- Feynman, at the conclusion of his Challenger report

Our exposures have so far been limited mostly by patience in taking dark frames. The telescope is a DFM instrument. It tracks very well - I can usually manage 5-minute unguided direct images. The SGS has a standard guide connection, like the SBIG direct cameras, so it can take over guiding chores when there is a suitable star (I haven't had as much success autoguiding with light off the slit jaws as I had expected). The box has a port with diffuser that will let, say, a He, Hg, or other calibration source illuminate the spectrograph; I've also tried shining a gas-discharge tube onto the inside of the dome. Wavelength calibration works as well as one would expect (subpixel over short periods). In direct images, we usually get 2-3" FWHM for star images. Oddly enough, on or part of the country we can get the best seeing when it is ridiculously hot (so I've got some nice images from a couple of weeks ago). Probably something to do with the ridiculously high specific heat of water.

The grating tilt can be changed with a micrometer on the fly (this could be a weak point in the stability of the wavelength scale). We get around 3500 A of coverage with the low-dispersion grating and 1000 or so at high dispersion. The two gratings are back-to-back, flippable with a lever from outside. If you don't mind misalignment among the pixel grid, dispersion, and slit projection, you can switch between the two gratings while observing. Normally one would open the spectrograph and rotate the camera to line things up better when changing gratings.