I’ve run into a problem with the VPhot tool; the location where the program thinks Barnard’s star should be is pointing to blank sky. The J2000 RA/Dec values of the blank spot are the values on the Target Tool/alert notice, 17h 57m 48s /+4° 41' 36". But I’m pretty sure that Barnard’s star is the one 4 minutes below it, at around 17h 57m 47s /+4° 45’ 36”, based on comparing its location to other confirmed stars around it and the known distance it travels per year (Stellarium also reports this as its current J2000 position). The green target named “Barnard’s Star” is my estimate of its actual location.
Could anyone explain this discrepancy? Is it unique to Barnard's Star? Also, how best can I confirm which star in the image is Barnard's Star?
Screenshots of VPhot:
VPhot is able to identify Barnards star, but is labeling it with an alias: VSX calls it Oph V2500
Notice too that VSX locations are adjusted for proper motion if it is available.
The star is moving nearly due north at 10 arcsec per year, still the fastest proper motion in the sky. An equinox J2000 position at the current epoch (from one of my images from last night) is: 17 57 47.2 +04 45 40 +/- an arcsec or so, not far from what was mentioned earlier in this thread. As far as photometric variability goes, it may be worth noting that whatever variability there is has very small amplitude, no more than ~0.015 in V, with timescale of something like 150 days. Thus to see much of anything one needs long seasonal runs of high (few millimag) internal precision.