La Superba and Spectrum

Photographer: Greg Parker Spectroscopist: George RobertsSummary Author: Greg Parker

I recently started collaborating with George Roberts, a spectroscopist capturing the spectra of stars. I use my Mini WASP array of telescopes at the New Forest Observatory (UK) to image stars and other deep-sky objects. George asked me for my choice of a star for our first collaborative subject. There was one that immediately sprang to mind, La Superba, but I was sure that the spectrum of this star was all over the Internet and perhaps not a suitable subject. I was therefore completely taken aback to find that far from lots of spectra being freely available, I could only track down one. Hence, the spectrum of this carbon star was our first effort.

Above you can see the image of La Superba, together with its spectrum. The full imaging details for La Superba are given in the Earth Science Picture of the Day of October 4, 2016. To obtain the spectrum, George used a 127 mm Meade apochromatic refractor at f#7.5 to collect the photons, and a 500 lines per mm grating with a QHY5-11m CMOS camera to create and detect the spectrum. George 3D-printed the housing for the grating and camera. Note that the whole assembly can be seen in the above image.

The data was subsequently stacked and processed using BASS (Basic Astronomical Spectroscopy Software, with Castor A as the calibration star. On the spectra the position of various absorption lines and emission bands are shown. In particular the Swan bands are a characteristic of the spectra of carbon stars, comets and burning hydrocarbon fuels. The dashed line shows the Planck curve (Black-Body) radiating at a temperature of 2750K superimposed on the La Superba spectrum. La Superba’s temperature is believed to be about 2760K making it one of the coolest true stars known.

New Forest Observatory, U. K. Coordinates: 50.819444, -1.59

Related Links:Carbon Stars of Kemble's CascadeLa Superba