Thursday, March 18, 2010

V842 Cen observations to support Hubble Cosmic Origins Spectrograph run

V842 Cen first came to attention in 1986 as a Nova and follow up studies by Warner/Woudt published in the journal of physics identified it as exhibiting similar behaviour to GW Lib. Thus both these stars are now the subject of Dr Paula Szkody's study using the cosmic origins spectrograph on the HST.

This observation task was somewhat more difficult than last week's effort as the variable star map coverage is somewhat problematic as there are few comparison stars of similar magnitude. However just 7 arcsecs and 20 arcsecs away are two known catalog stars that were selected for comparitive magnitudes. Which effectively places them close to the annulus/skybackground settings of Photometric measurement tools. At 1.22arcsec per pixel on my trusty FLI that's a tight shot!!!! Normal practice is to try and get the annulus to 2-2.5 times the FWHM of the star. So its tight!

Here at least I was able to adjust the annulus and the inner sky radius such that 0323-0709135 was kept away from the target calculation area. (ie between the two)

The image below I have zoomed in a little to illustrate the difficulty of the task.

One surprise was that the catalog star 0323-0709135 seemed to be a little brighter visually than expected. Instructions from AAVSO alert 418 indicated 0323-0709135 was expected to be slightly fainter than its near neighbor 0323-079110 at 14.88.

Either way V842 Cen appears to be 15.43 at my measurement which I submitted to the AAVSO this morning. I suspect the tightness of the shot and 0323-0709135 sneeking into 0323-0709110's sky background may have V842 Cen a little closer to 0323-0709135's magnitude than it actually is - you can see this in the photo.


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