Espectroheliografia

Spectro-heliography

Spectro-heliography consist in building in an indirect way an image of the Sun from a specific wavelength.

My spectro-heliograph is composed by a 85mm f600mm Apo refractor, diaphragmed to f/10, a Littrow spectrograph with a diffraction grating of 2400 lines per mm, 2 webcams and an equatorial mount.

The method is simple: Let the Sun pass perpendicularly through the slit of the spectrograph, by stopping the RA movement of the mount, while recording an AVI. Using the program Iris the AVI is decomposed in frames. Next, one must choose the column of pixels corresponding to the wavelength of interest and a SCAN2PIC command is executed. The resulting image suffer from deformation due to the fact that the speed of capture is different from the sidereal speed (not a real drift scan); geometric corrections must be preformed. Although this method hardly result in perfect images, it gives us the possibility to study the Sun in all wavelengths in the visible, near IR and near UV. The figure in the left show how the solar image is assembled from the frames. The line represented correspond to the CaH; the black horizontal trace in the spectrum side correspond to the solar spot.

The image at right show the Ha line due to the chromosphere. This line seem of absorption at the solar disk but of emission at the solar limb, where a prominence is seen. However, the absorption line is due essentially to the colder external layer of the photosphere. As the chromosphere is hotter than the photosphere, an emission of Ha take place, weaker, overlaid to the absorption line. This frame piece belong to the first image in the gallery, and correspond to the prominence seen at 8 o'clock.