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In 1999, Santa Barbara Instrument Group (SBIG) released a novel product, a spectrometer, into the amateur market place.

If you are interested in spectroscopy join the SBIG spectrometer user group.

  wpe33.jpg (63832 bytes)    Click on picture for a larger version.

The spectrometer is designed to operate with the ST-7/8. The object that is to be analyzed is viewed on the tracking CCD, simultaneously with the slit. The slit is backlit by an LED during setup to render it clearly visible on the tracking CCD. The object is manually maneuvered onto the slit using the telescope controls, and is held there using SELF GUIDING during a long exposure. The spectra is recorded by the imaging CCD, oriented long-ways so the spectra falls across 765 pixels, with a height of about 16 pixels for stellar sources. Two gratings and two slits are available for maximum versatility. The standard grating, 150 rulings per mm, gives a dispersion of 4.28 angstroms per pixel (476 Angstroms per mm), and allows the user to capture the entire interesting range from the calcium H and K lines to H-Alpha (3000 Angstroms) with a single exposure. Depending on the slit size, the resolution will be 10 or 38 angstroms per pixel. An interchangeable high resolution grating can also be used that gives 1.06 angstrom per pixel (118 Angstroms per mm) dispersion, with a resolution of about 2.4 angstroms when used with the narrow slit. The spectral range is smaller, being only about 750 angstroms. This resolution is adequate to detect the Doppler shift due to the earths motion around the sun when carefully calibrated, and detect spectroscopic binaries.

Features of the SBIG Self-Guiding Spectrometer:


Several modifications to the spectrometer have been made which makes operation more convenient:


                                              Spectrometer attached to rear of C-14 via flip mirror

A motor has been added to the micrometer which is controlled from a console at my computer table. This idea came from Maurice Gavin, an amateur leader in the area of spectroscopy who lives in the UK.
The illumination slit likewise is controlled from the console.
A fiber optic lead feeds from two gas discharge tubes (Hg and H2) into the spectrometer which allows for the imprinting of wavelength standards onto the spectrum for calibration. These emission tubes are also controlled from the console.


                                      Gas discharge tubes with fiber optic leads to spectrometer





Processing Spectra




I have found the following steps to work well for processing spectra. Following expansion of the spectra in SBIG's software package SPECTRA to give 1) above, I save the image and use Software Bisque's CCDSOFT to perform a gentle sharpen to give 2) followed by an unsharp mask giving 3). Whether I do both these steps and in which order depends strongly upon the signal to noise ratio in the image and requires experimentation with each image in order to best bring out the spectral lines present in the spectra. Caution is important because one can introduce artifacts into the image with to much processing.

The software SPECTRA will also save a text file of wavelength versus pixel # once you have calibrated. This text file can be imported into Microsoft Excel or other graphing programs where you can create custom graphs such as those I have done with the emission spectra of planetary nebula.

Identifying elements requires much work using tables where elements and ions have had there wavelengths of emission or absorption tabulated. The handbook of Physics and Chemistry has extensive tabulated data for all elements as does the Astrophysics literature.


See  Calibration  page for more details on wavelength and flux calibration.

Please visit my other pages to see some of the things that can now be accomplished by an amateur in the back yard.