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Some real astronomy

For the last few days I've been trying to reduce some rather bad MERLIN data (bad because most of the telescopes are down for maintenance, MERLIN data is normally not this painful), but today I have given up. The trouble is, there were only three working telescopes, and one of those kept going down for engineering work, so it really is quite bad. So we still haven't detected the new supernova in M51, and I haven't got another data point for the SWIFT source either. Never mind...

Today I've gone back to M82, trying to find the masers (like lasers but with microwaves) in a VLA data set. In attempt to be systematic about things I have been writing a script to pick out detections above a certain level. It is quite tricky to find these things because the same gas which is causing the maser emission is also absorbing radio waves at the same frequencies is the conditions are not quite right for a maser to form. So if you look at a spectrum then you might see a peak caused by a maser sat inside a trough caused by the absorption.

What the script does is attempt to remove the absorption, leaving behind any maser emission that might be there.

This image shows a test spectrum which I created to see if the script works. The panel on the left shows an example of the kind of thing you might see in M82. The two dips are the absorption, and the two spikes are the maser emission. The panel on the right shows the correlation of this with a template absorption only spectrum. The peak in this plot shows the point where the best fit between the template and the test spectrum occur.

The left panel shows the template spectrum (dots) and the same spectrum shifted to the position found from the correlation. The final plot shows what happens when you subtract this shifted template from the original test spectrum.

This all works fine for the test spectra, but it needs some modification before it will work reliably on real data.

Posted by Megan on Wednesday 20th Jul 2005 (15:30 UTC) | Add a comment | Permalink


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