Affiliation
American Association of Variable Star Observers (AAVSO)
Tue, 07/08/2014 - 10:39
I've found some differences in the measurements for the comps being used on the campaign site compared with the AAVSO photometry table for EE Cep.
For example, the comps b (112) and c (113) have the same measurement in B @11.47
In the AAVSO table label 112 is 11.427 and label 113 is 11.491 in B.
There are differences in other comps too.
I think I'll just report to the AAVSO using the latest photometry table, rather than report to two places using two different sets of comps.
Douglas.
I think the Sequence Team will discuss this issue soon. I'm quite sure that at leat the brighter stars with TASS photometry will be replaced.
Clear skies,
Robert
Hi,
We're planning on sending the Alert Notice today. Arne and I will probably do one more iteration of the text before we send it, but at the moment we are suggesting people use the 104 and 119 stars for CCD comparisons, primarily because the 112 and 113 are NSV stars. (You can submit observations of these two stars, by the way.)
The data in our photometry table are from Henden/Sonoita, so I would suggest using our photometry. However, please use the "charts" field in WebObs to make clear whether you're using AAVSO sequence data (with an AAVSO ChartID) or using data from the Copernicus group. As long as data users have that information, they can adjust observers to be on the same zero-point.
Matthew
Adding further to what Matt said, there are several areas where comparison stars can be improved for this field. As Robert mentioned, the brighter stars (V brighter than 104) are from TASS, so these measures have larger error than from other sources. We do have 3 nights of BSM calibration of the field that I haven't finished processing, and those might be helpful, as well as using Tycho2 for the brighter B,V magnitudes. Note, however, that the brighter stars are quite distant, and the variable never gets that bright, so certainly for visual observations, they would never be used. Two of the Polish comparison stars are suspected variables; these are probably ok (most suspected variables are constant), but need to be checked before relying on them. Finally, the Polish comparison stars have Johnson R,I magnitudes, not Cousins. If only for this reason, I suggest using the Sonoita photometry so that results are consistent.
We've been observing this field for several months using Coker30, and I'll be comparing the calibration results from all sources to further refine the photometry in the next week or so.
For observations submitted to the AAVSO, we'd prefer that you use the calibration photometry shown on the VSP charts/tables. This is much easier to do with VPHOT for example, than entering your own comparison star table. In addition, it is easier to submit with the chartID in that way. If you want to use the Polish magnitudes, then be sure to add a note to your observations indicating where you got the photometry, or even the actual magnitudes used for the comparison star, so that researchers can properly correct for any differences.
Arne
Hello Arne and John
Thanks for pointing this out to everyone. I had submitted a nice run on EE Cep, and the B and V values aligned with the community nicely while the R and I were 0.15 fainter, and in the minority. Now we know why.
Gary
WGR
I'm glad Arne made the note about R and I:
Looking at the latest for EE Cep in lightcurve generator the R observations are bimodal with one group of observers reporting brighter R values and the other reporting fainter R values. From my own images, the AAVSO comp values off the current AAVSO chart generated by VSP gave me values consistent with the fainter R values and using the values on the Polish campaign page gave me brighter R values. Based on Arne's advice and my experiment I think it is safe to say that, the fainter R values are closer to the actual Cousins R values.
I think it might be prudent for everyone that has submitted R and I observations to the IAD to go back to their data and audit what they submitted so far.
Whew! I stayed clear of the NSV stars and used 104 and 119 from the get go.