No Comp Stars for R Crb at its current brightness

Wed, 09/24/2014 - 21:37

R Crb is getting brighter. It's now brighter than 10th magnitude. I got a CCD image (with a V filter) and while R Crb is well exposed (24500 max ADU), at this exposure only one star shows up as a comp star (122). I can select it as a Check Star and a Comp Star, but the result I get from this doesn't look right (it says that R Crb is dimmer than 10th magnitude).

So, we need some brighter comp stars in the field for R Crb. R Crb gets to 6th magnitude at its brightest.

Can new, brighter stars be added?


American Association of Variable Star Observers (AAVSO)
comp stars

There are brighter comp stars, for example a 7.4 to the north.  Unfortunately, you can't "make" stars - there just isn't anything bright near R CrB, especially for CCD observers.  There are two possible approaches:

- offset the variable in the field, such that a brighter comparison fits into the frame.

- stack several images together.  If R CrB is not saturated in any individual frame, then the stack will have higher signal/noise and larger dynamic range, so that the fainter stars will still act as reasonable comparison stars.


Arne... Thanks..

Arne.. ok, I can set the RA and DEC for the star to include stars to the north. As things happen now, the subject star is dead-center in the field, and while it'd be nice to be able to change the fov, that's not possible.

I'll try multiple images with stacking and see if some of the dimmer comp stars pop out as usable.

I've been following this star since 2007 so I would like to be able to monitor it if and when it returns to mag 6.

Thanks  ..Bill

Did it... moved the center of the imaging field north...


Thanks for the suggestion. I've moved the imaging field north and I get R Crb and the 7.4 mag comp star in the field simultaneously. R Crb is hanging around at 8.4 magnitude, and I'm watching it closely. smiley

It won't get to mag 6 without us noticing.