Dear friends, after almost a whole month off due to bad weather, I finally had a chance to observe some variables. For the first time, I took on the star KZ Gem. I admit that the night was not very good, fog appeared and I had to close the observatory at midnight. Nevertheless, I tested the star with a few frames of 2 min exposure. The target's signal was not very good, around SNR ~50. I got an average of about 14.7 mag in V. However, compared with other observers' results, I got nearly 2 mags. difference and I doubt the reliability of my data. The average error is about 0.02, which is pretty good for such faint objects. The check star (136) comes out accurately, averaging around the catalog value of 13.552. I don't see how AZ Gem could have "jumped" 2 magnitudes in such a short time!
I used AstroImageJ for photometry and calibration. I admit I had a problem with the flat frames and at some point threw them out, relying on the comparison stars being visibly close to the target in the frame. I checked in ASTAP also and got the same result, average magnitude of the target star ~ 14.7.
Looking for better observing conditions!
Regards,
Nikola,
V=14.7 doesn't seem odd. KZ Gem is a dwarf nova that several observers have recently measured about 14.5-15 at peak. A dwarf nova can rise in outburst very quickly. Since you weren't able to calibrate the images and the skies were muddy, I'm not sure I would submit that photometry. When you get good weather and are able to calibrate your images before doing the photometry, sounds like your numbers are good and ready to go.
-Walt
KZ Gem is currently running at about mag 17. There is a 14.7 comp star right beside it (just north of it)-- you might be measuring the comp star instead of the variable (there are a couple of other observers who seem to be doing this too). Make sure that your charts go deep enough and that they have a small enough field of view to show the variable separate from the comp star. Here is the chart that I am using, X34550BHK. If you'd like to take a look at it, you'll see just how close KZ Gem is to the 147 comp star.
Tom (RTH)
Nikola,
There is a neighbor star only 9 arc seconds away from KZ Gem. You might check your photometry to make sure AIJ isn't jumping the centroid to the neighbor star and so measuring the wrong star. If you look up KZ Gem on VSX, there is a link under supporting documents called "Identification images of KZ Gem." That links to a very nice image that shows KZ Gem at quiescence and at outburst to make clear which star is actually KZ Gem.
-Walt
Thank you so much for…
Guys!
Thank you so much for pointing me to where the problem is. That explains everything!
Probably other observers who have reported similar magnitudes like me have gone the same way.