University of Exeter Observatory

Our rooftop observatory houses a 0.2m Meade LX-200 Schmidt-Cassegrain telescope. The backend is a SBIG CCD camera. We can fit a filter wheel in front of the camera for broadband colour imaging (currently Bessell BVR), or the SBIG Self-Guided Spectrograph, which uses the CCD camera as its detector.

The observatory is used for teaching second-year undergraduates, using both imaging and spectroscopy. The students spend a few hours at a time using the telescope to observe stars and nebulae, taking data that they then reduce and analyse.

I run the technical side of the observatory, making sure that it's behaving itself, keeping it maintained and sufficiently well-characterised that we know what to expect in student labs.

New Stuff

FAQ: CCDSoft insists on taking subframe

2008 Dec 16: It's easy to tell CCDSoft to take a subframe by mistake: If you click and drag inside an existing CCD frame, it will define that as a subframe, and then only download that subframe from the CCD. You can fix this by going into the 'Take Image' tab, and unticking the 'Subframe' tickbox. The full CCD frame will then be downloaded.

Spectrum of the Ring Nebula

2008 July 20: Finally checked out the focus on the spectrograph. The focus used for the labs was about 3700; at this setting, the image is basically an image of the mirror. This had the advantage that we could easily place the image on the slit, and the disadvantage that there weren't many photons getting through the slit, more-or-less limiting us to 1st magnitude stars. The focus was revised, first on Vega, and then on Sulafat (gamma Lyrae), as Vega started to saturate the detector. The final focus was at 3250+/-10. This meant going inwards, which is the bad direction. If switching from imaging with the CCD + filter wheel to spectroscopy with the SGS, I'd recommend going in by about 600 or 700, all in one go, and then coming out by steps of 20.

As long as I had a reasonable focus on the telescope + spectrograph, I picked up a spectrum of the Ring Nebula, just nearby. With the LX200 sync'd to Sulafat, the Ring Nebula came straight into the guider, with the slit across it. Neat. This image has a 60s on-source integration time.

A section of the CCD image (below), showing the raw spectrum of the Ring Nebula: Integration time 600s (on-source); red is to the left.