Day 185 Tuesday 30th September 2014 Photometry of LP Cam in NGC 1502

I used telescope T21 in New Mexico to take B and V images of the open cluster NGC 1502. The images were 90 second exposures. [I intend to transform the measured magnitude of a variable star in the field so I needed V and B images to be able to apply the transformation coefficients that are supplied by itelescope.com.]

This is the cluster using a B filter

 This is the cluster using a V filter

 

This is the V image of NGC 1502 loaded into VPhot. 

 I aim to obtain the current magnitude of the variable star LP Cam and have designated a comparison star and check star as shown. BD+61 675 is the comparison star which has a V magnitude of 9.62 and Tycho 4068:1471 is the check star with a V magnitude of 11.15 from the Tycho catalogue. 

The comparison star had some close neighbours - this is how I positioned the annuli. The central circle takes in just the star and the nearby stars are all positioned in the gap. The outer annulus only includes sky background which is subtracted from the signal in the inner circle (based on the same sky signal per pixel) to give just the flux from the star. The central circle is the same radius of 10 pixels (essential that they are the same) as the other two stars concerned but the outer annulus varies as shown - the scale is different for each image with a common 10 pixel central circle radius.

   

This is the photometry report

So the untransformed V magnitude of the target is 11.168