Thu, 01/18/2024 - 15:11
I noticed that in some of my observations, the magnitude as shown in the report is markedly lower than the "consensus" of magnitudes in the light curve. Along wth this, I've noticed that these observations have a much higher airmass (say 1.9) vs the consensus of 1.3 or lower. Is there an airmass value at which point you should forget about submission of an observation (since airmass affects the magnitude of the star). Or am I way off base in my thinking?
I like to stay at airmass less than 1.6 . 1.0 to 1.5 is my comfort zone. But occasionally i go after a setting star that I really need a data point for. On a clear night and when the target is less than ~2 minutes from the comp, I'll go to airmass of 1.7 . That happens about every ~70,000 observations. I throw out more than half of those with airmass 1.6 to 1.7. I operate at 210 meters ASL.
If I operated at 9000 feet and had a big telescope like Sloan Sky Survey, then I might go to airmass 1.8 .
clear skies (helps)
Ray
Perhaps, as Ray suggests, I am privileged to use a 'big' (1-m) telescope at 2200m elevation. But at least for differential photometry, I don't see any real problem with going down to ~3 airmasses or even lower. Yes, the data will be relatively scattered compared to the zenith, and no, not every night or data-point will be a good one. I just reviewed data I have with our 0.7-m telescope on CD-30 6530, an active K-dwarf with rapid rotation (V mag ~11.5, 0.318 days period). This culminates from Flagstaff at sec z ~2.45, and I took frames within an hour of the meridian (70s exposures). Just as an example, a lightcurve from the 2015 season shows rms scatter in the fit of 0.006 mag, full amplitude only 0.05 mag. QED.
\Brian