Hi,
How do you calculate its magnitude please ?
Hi Kwong,
A variety of software packages can do photometry, including some image processing packages such as MaxIm DL. If the software you are already using doesn’t have the ability to calculate magnitudes, then I would opt for a free package that is easy to use, unless you are sure you will get into photometry of variable stars, exoplanets or asteroids.
There is a list of some software packages at the top of this page on submitting to the BAA Photometry database.
https://britastro.org/vssdb/notes_submissions.php
I’ve not tried them all, but MuniPack might be the easiest to get started with.
The trick is you have to measure the magnitude of the target star (the supernova) as well as several comparison stars. The comparison stars need to be carefully chosen, to avoid variable stars and to ensure they themselves have a robust magnitude. The AAVSO chart plotter is the perfect place for this.
The other key point. The supernova and none of the comparison stars must be over exposed as that would cause the calculation to go wrong. A good rule of thumb is for the peak counts in any pixel of those stars should be at most 2/3rds the full well capacity of your camera.
Good luck with your observations.
Andy (BAA Variable Star Section Database Secretary)