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Comp Stars; Aavso chart does not have them...

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#1 scubaanddreams

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Posted 30 September 2012 - 04:27 PM

Situation:

AAVSO Field does not have comp stars; it has been requested but been informed this may take a while (AAVSO is awesome by the way this is no diss in any way). Other than performing allsky photometry is there another way to find out the Vmag of a star in the field (other than AAVSO)? Attempting qatar-1b and my FOV is pretty small given my setup 20x20 arcmins or so.

#2 NJScope

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Posted 30 September 2012 - 10:01 PM

The coordinates for the host star of qatar 1b are RA 20:13:31.61, DEC +65:09:43.4. Plug this value into Aladin on the SIMBAD site and it will resolve all the stars in the FOV (adjustable). By selecting (file/load catalog/Surveys in VizieR) an appropriate catalog survey (eg TYCHO-2, 2MASS etc), you should be able to get the Vmags for many of the surrounding stars. A survey specific correction factor will need to be applied in order to transform survey magnitudes to the standardized BVRI Johnson-Cousins system (http://www.aerith.ne...conversion.html).

#3 scubaanddreams

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Posted 01 October 2012 - 04:42 AM

Thanks Kevin!

#4 scubaanddreams

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Posted 01 October 2012 - 01:42 PM

And here are my results. This is my first attempt at an observation of an exoplanet. Too bad I can't tell time and was off by an hour, hence only have data for the first half. Utilized Kevin's technique (thanks again!) outlined above, but obviously made a mistake somewhere as I am off by .2 in Vmag. Taken last night, 30 Sep 2012 from the Netherlands.

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#5 gavinm

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Posted 02 October 2012 - 03:33 PM

Nice results. This is pretty much the only use for my g'r'i filters - finding checkstars. I take a set of colour calibration frames before my imaging run. I then use this to measure the colour of my target and all the neighbouring stars. I then find checkstars in the FOV with about the same magnitude and colour. There are usually 3 or 4. I then choose the one that is the least variable. For transits (ie short) variability seems to be less of an issue.






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