Prototype 1.25 inch filter cell grating - Delta Virginis 13th May 2005

This is a test of a prototype 100 l/mm diffraction grating mounted in a standard 1.25 filter cell and screwed into the nosepiece of a Toucam webcam fitted with an eyepiece adapter. An ATIK focal reducer was also screwed into the adapter to reduce the size of the star image.

The VC200L aperture was reduced to 80mm with a mask to allow an estimate to be made of the faintest object for which a spectrum could be produced using an unmodified webcam.

Delta Virginis was easily recorded at mag +3.4 It is a cool star of spectral class M3iii and shows a high IR content and broad molecular absorption bands. The spectrum was orientated diagonally across the chip to maximise the available length and allow the zero order to be recorded while still allowing the IR to be measured to beyond 900nm.

The spectrum was compared with the library spectrum for type M3iii in VisualSpec. There is good correspondence in the detail. The broad difference in shape is due to the combined effects of the spectral response of the CCD and grating and atmospheric absorption.