Wed, 04/19/2023 - 09:09
Hello! I've sen discussion several times about trying to match target and comp star colors in order to obtain accurate photometry.
Usually, I try to choose comp stars that have good S/N in order to get good results. However, I did not pay attention to color since I thought that the comp stars for a target variable had already been pre-selected for the target variable. Given my 15 arc-min FOV, typically comps range from 2 to 6 or 7.
Should I pay more attention to matching the colors of the comps that appear in the target field to the target? Best regards.
Mike
You wrote: "Given my 15 arc-min FOV, typically comps range from 2 to 6 or 7." There's some mismatch here: the typical 15 arcmin field would typically have _zero_ comp stars of V mag 2 to 6 or 7. So either your field is much larger, or you are perhaps talking magnitude differences?
But, yes, matching comp star colors as best you can is helpful since it reduces transformation errors. Stars as late as red giants of spectral type K5III or even M0III (roughly B-V ~1.5) are stable for red stars (for instance), and hardly any common dwarf stars in the F-G-K range are variable (roughly 0.4 < B-V < 0.9). It is useful of course to check in SIMBAD and/or VIzieR on the status of variability of any particular candidate comp star. Using your own data to confirm them against other stars is worthwhile, too.
\Brian