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Telescope: Meade LXD75 SN6
Camera: Meade DSI Pro III
Grating: Star Analyser 100
Luminance: 150x30sec, saved as FITS
RGB: None
Guide scope: Meade DSX-90, PHD
Software: Envisage, Autostar Image Processing, Photoshop, Excel, KaleidaGraph
This is an 800x600 pixel crop of one of the early images taken with my new Star Analyser 100 low dispersion grating mounted in the filter slide of my DSI Pro III. The purpose of this image was to capture the emission spectrum of a bright, nearly stellar planetary nebula to calibrate the dispersion of this particular configuration. IC2149 is an 11th magnitude planetary nebula in Auriga that emits radiation primarily in O(III) (501nm) and H-alpha (656nm). Using these values the spectrum shown in the inset was extracted from the source image. The spectrum also shows an unexpected emission at 990nm that may be due to S(III) (953nm) though this feature is too faint in this image to be reliable as a calibration point. The emission lines for the nebula are riding on top of the continuum from the hot blue central star. Note how this spectrum peaks in the blue at about 440nm. For reference the measured emission spectrum of a yellow G-type star (phi Ori, G8) is also shown. The relative intensity has been corrected for the response of the CCD from 350 to 1000nm.
As a footnote, some of the emission characteristics of the Star Analyser 100 are shown using the 9.4 magnitude star GSC 3361:328 at the bottom (north) of the image. The image of the star itself is light that passes straight through the grating; the 0th order image. The grating spreads the light out in a series of orders (1st, 2nd, 3rd etc.) to the right and left. The Star Analyser 100 is blazed to maximize the brightness of the first order of the right-hand spectrum (with the grating mounted in the orientation used here). It’s interesting how fast you get accustomed to looking at the raw spectral images and in this case the shape and structure of this particular star’s spectrum shows that it is deeply red, probably a type M. Note that this is just a crop of the original image and it’s fascinating how much information is contained in this one frame.
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