AAVSO Alert Notice 572 announces an observing campaign on the symbiotic variable AG Dra. Please see the Alert Notice for details and observing instructions.
Many thanks, and good observing,
Elizabeth Waagen, AAVSO HQ
I like the new format.
The correct thread for the April 2017 observing campaign on AG Dra is this one. The URL for it is https://www.aavso.org/ag-dra-observing-campaign
However, in Alert Notice 572, I accidentally gave the URL for a 2013 campaign on AG Dra: https://www.aavso.org/content/ag-dra-observing-campaign . Do not use this URL.
I have corrected the online text of Alert Notice 572 so it links to the right forum thread.
Please be sure to post all of your comments/questions about the current (April 2017) campaign to the correct thread (https://www.aavso.org/ag-dra-observing-campaign)! My apologies for the error and any confusion it may have caused.
I notice that the two closest comp stars are 99 and 105, but their true Vmag are 9.85 and 10.46, respectively. Now, this is resulting in my estimates being 0.05 mag fainter than they actually are, due to this coincidental "roundoff" error, more like a type of systematic error. Should I adjust my observations brighter by 0.05 mag, or leave them based on the roundoff?
I ahve submitted 4 visual observations of this star recently, and I notice a definite brightening trend of about half a magnitude. However, looking at the light curve https://www.aavso.org/lcg/plot?star=AG+DRA&height=450&visual=on&grid=on&...
The CCD measurements in B and V are pretty constant in the same interval. Also, the visual observers seem to be split, with half seeing the same brightening trend as I do, and the other half constant, similar to the CCD.
This is really baffling to me. If there was a marked color change occuring, that might explain it, but the B-V looks unchanged. There is no explanation of this divergence of estimates that comes to my mind !
Mike, I suspect that noticed discrepancy could be caused by Purkinje effect in action... After all, AG Dra is pretty red star.
Ok Toni, well Purkinje would explain offsets between visual and CCD estimates, but if CCD were constant, the star was in fact constant, the visual estimates by same observer would not be expected to change due to Purkinje alone.
However, another idea came to mind. I suspect my observed variations are real. I see other visual observers showing similar 0.5 mag differences over the same period, even though on average the CCD are "constant". My guess is that just by random chance, my 3 observations which were significantly fainter than my most recent one (v=9.75) were just made at the times when the star had short dips in brightness. Its possible none of the CCD measurements have caught any of these short dips.
But what are the time duration of these dips? Is this star a possible eclipser too? I think more dense coverage, esp. CCD time series may uncover these "dips".
There is some suggestive data at 2454305.6 to 2454305.9.
It mimics your 0.5 mag observation.
245598.6 to 245598.9 suggests datataking during haze then clearing for the bottom of another possible eclipse.