Affiliation
Vereniging Voor Sterrenkunde, Werkgroep Veranderlijke Sterren (Belgium) (VVS)
Sun, 02/10/2013 - 18:32
Have a look at this 800 days lightcurve of WY GEM:
http://www.aavso.org/lcg/plot?auid=000-BBK-812&starname=WY%20GEM&lastda…
There seem to be two distinct "populations" of observations. Is there a misidentification, are two sets of comparison stars, ... ?
What hit me here was the huge scatter. What you mention looks just like seasonal gaps when WY Gem is unobservable. It is on the ecliptic after all!
It may be on the ecliptic, but it is not circumpolar. These are seasonal gaps in the data, occurring around June/July when Sun is at 7hrs RA.
The bigger problem is the sequence. This is one of those stars whose sequence has not been revised, and I see that the two bright sequence stars are both variable. My guess is that the binary population of observations is due to this. I'll ask the sequence team to make a revision. Thanks for pointing this out, Bruno!
Arne
Looking at all the estimates of WY Gem on the light curve below magnitude 7.9 reveals the vast majority of them where made using non AAVSO charts. The BAA VSS chart used seems to be an old one which isn’t in the current catalogue of charts on their website, so I couldn’t see what the comparison stars are. But I do know that on a lot of the BAA charts, particular the older ones, they use magnitudes modified by the “Howarth and Bailey formula” of v = V + 0.16(B-V) which of course gives a lower (fainter) value than the V magnitudes used on the current AAVSO VSP charts.
I think this does highlight a problem, that due to different values for the same comparison stars being used, it straight away increases the scatter of visual data.
A good example is the comp stars for U Mon, the current VSP charts give the value for HD 59730 (the comp star just to the south of U Mon) as 6.6, whereas the BAAVSS and AFOEV charts used by some observers submitting their visual data to the AAVSO, give its value as 7.0 !
Going back a little further with trivial filtering makes the distinct groups even more obvious.
I can provide details of the filter term upon request.
David
Thank you all for alerting us to this discrepancy. I have done some research on the observations, communicated with the appropriate parties, compared charts and sequences used, and think we have found the sequence discrepancy (which was partly caused by the use of old charts).
Please rest assured that the solution is in work.
Sara