and then there was COLOR!
by johnb on Jul.28, 2010, under Astronomy, Tech Talk
Fiddling around with the spectrograph again today… the goal: to install the software, drivers and hardware for the guiding camera. The unit is a little, tiny, compact (did I say small?) video camera made by Watek and a USB video grabber. The AudeLA software has a built in module which can see the video from the camera as a webcam device. It then can connect to and control the telescope as any autoguider can. I like the idea: live video with autoguiding built in! This reminds me a lot of the webcam used in the Coude Feed Spectrograph at Kitt Peak, though I think their guide camera is an older TV-style imager. The systems pretty much works the same way: the video camera is focused on a mirror in the guide/imaging head attached to the telescope using a small lens system. The mirror has a 50 micron hole it it. The idea is to place your target (to be spectra’ed –> I know, it’s not a real verb) on that hole. The mirror then feeds an image of that star/planet/whatever, the hole and the surrounding star field for the guide camera to see. It’s pretty slick. This allows real time focusing, real time pointing, and a secure knowledge that you are grabbing spectra of the target of interest. No more trying to get that star on the invisible slit!
While I was playing with all that, I wanted also to try attaching a camera to the spectrograph to see the spectra in color. Why not? The lens used to bring the spectra to a focus on the CCD is made by Canon, and is an EOS standard lens. Sure enough, the Canon camera was able to bring the images to a focus. Here is a colorful sample.
Above is an image of the flat field lamp used to generate flats for later calibration. Nice looking rainbow there. You now get the idea of an echelle spectrograph: the orders at the top are the long wavelengths while the shorter ones are at the bottom.
Still playing a bit, the above is a spectra of the basement lights where I have this all setup. You can see the tell tale emission lines from the fluorescent lights used down there.
The above is my favorite: this is the calibration lamp spectra of thorium-argon. All those little lines have very well known wavelengths and allow each order to be precisely calibrated. Such fun!
