Comet Lovejoy Photometry - 15 Jan 2014

[SamD]

First go at comet imaging ! 23 x 1mins at f/4.5 and focal length 360mm with an Atik314L+ (VMag 19 skies suburban Brisbane), stacked with DSS. Scope was an ED80 with a 0.6x reducer.

Not entirely sure what to do with processing comets, but fumbled along in Photoshop. Tail was much better than 5 days ago from Brisbane, I can now see about 10 streamers. FOV is about 1.6 degrees on diagonal.

Also ran through some photometry on the comet showing tail from 21.5 to 23 VMag/arcsec^2. I start to lose the tail from my skies at about 23.1, which equates to a SNR of about 2.5. Total integrated magnitude comes out at VMag 4.3+-0.2.

[geolindon]

:eyepop: IMPRESSIVE . . . . i look foward to your posts when you get the hang of it!!!!
thanks, Lindon

[SteveInNZ]

What Lindon said + 1.

What did you use to get the photometry ?

[SamD]

Thanks Lindon and Steve !

Photometry is code I've written with .NET.

I first plate solve using Astrometry. Then I count the total camera ADU for each of the brighter stars (net of local background). Then I fit these observed ADU counts to reference star VMags from APASS.

Once you get the formula for VMag as a function of net ADU, you can transform the net ADU at each pixel to an equivalent VMag per pixel. Since you know the image arcsec/px scale, you can then adjust to VMag/arcsec^2.

Final step is a colour mapping, I use Dave Green's cubehelix colour scheme.

[algwat]

Hey Sam,
that's an interesting way to get info(data) from your images.
It is the first time I have seen this concept.

kind regards, Alan