There is some chance that I have detected variability in Polaris with CONCAM data. Now Polaris is known to be a Cepheid-like variable, rumored in the recent past to show variability at the 10 percent level.
I used data from the Kitt Peak (KP) CONCAM2 photometry tables. In there, Polaris, also known as Alpha Ursa Minoris (Alp UMi for short), has a high enough altitude to be recorded routinely. Being the pole star, it is always visible in a cloudless sky.
I copied nightly KP CONCAM2 data into an Excel spreadsheet as discussed at the bottom of this thread. I did this for seven nights in a row. I averaged all of the data for each night, a technique that only works in this raw form for Polaris, as its altitude does not change appreciably. I was lucky it was (relatively) clear!
In the Excel spreadsheet, linked here, I found on the first sheet that Polaris' average nightly brightness did appear to vary from night to night. I did not know if this variation was really Polaris itself or a variable atmosphere, or some sort of systematic error.
I therefore did the same thing for Alpha Cas for KP for the same night. This time I aligned all sidereal measurements. I found that Alpha Cas was constant over the entire night, in contrast to Polaris! Wow!
I found that between 2004 September 13 and 14, Polaris appeared to change by about 2 percent, above four sigma for a standard error of about 0.5 percent. In contrast, as seen on Excel spreadsheet two, Alpha Cas changed by 0.3 percent, roughly the same as the one-sigma standard error. Therefore, Alpha Cas was likely completely constant, and KP photometry appears to be quite accurate!
This is only a start, however. I have asked Lior to tune WOLF to automatically take photometric measurments of Polaris for both MK and HL stations. (I don't yet trust CI.) If Polaris varies in unison on all three, while a star like Alpha Cas remains constant on all three, THEN I would really believe that CONCAM data is taking useful variability measurements for Polaris. Which would give NSL data an unparallel uniform baseline for photometry of one of the sky's most famous stars.
- RJN