Affiliation
Royal Astronomical Society of Canada (RASC)
Thu, 02/12/2015 - 16:59
I ran on Z CAM for an hour last night with my CCD camera an V filter and found that the 94 comp star (000-BBP-625) is out to lunch. If I use the 94 comp star, Z CAM last night was 11.65. If I use the 110 comp star, Z CAM was 11.15. Using the 110 comp star, all the other comp star photometry comes out correct so I am certain the 94 star is the one that is the issue. It is a fairly red star but being 0.5 magnitudes out is a very large error for my system.
Has anyone had issues with this star in their CCD photometry?
Second question: What magnitude threshold are we looking for in order to officially call Z CAM in outburst?
Thanks,
Vance Petriew (PVA)
Regina, Canada
It seem the 'comp
Hi Vance,
It seem the 'comp 94' was saturated on the USNO/Henden photometry that was used to create the sequence for Z Cam. The Tycho2 photometry gives 8.894V (B-V=1.247) for this star, reducing the 0.5 mag offset you experienced. Taking into account the red color of this 'comp star' should be removed from the sequence.
Clear skies,
Robert
Thanks, Robert. That was my conclusion as well based on TYC and NSVS magnitudes of this star. I just wanted to confirm with others. I'll contact Mike Simonsen if he hasn't seen this post already.
It would be interesting to see how much the scatter in this light curve goes down once the comp is removed from tthe sequence, especially on the CCD side.
So that puts my Z CAM measurement from last night at approximately 11.15. I'll upload my data soon.
Thanks!
Vance
A chart error has been reported to the sequence team. You can follow progress here:
http://www.aavso.org/chet
Thanks for all who replied!
Clear Skies,
Vance
Based on Tycho-2 and APASS photometry, the AAVSO sequence of Z Cam has been updated recently. Please download the updated chart and sequence using VPS.
Clear skies,
Robert
First, thank you Vance for pointing out this obvious error. It is a little surprising that it has remained unchanged for so long. People were either not using that star as a comp star or not examining their photometry based on it and some of the other comp stars before submitting data.
It only took a few minutes to be brought to the attention of the charts and sequences team and within an hour or so the issue had been analyzed, a sequence revision submitted and new and revised comp star data uploaded to the comp star DB.
Everyone should plot new charts for this star now. If you had an old one, the new ones are better, and if you weren't observing Z Cam before - you should!
To answer Vance's other initial question, once Z Cam has risen above its normal standstill range (~11.5-12.5V) it is in outburst. At 11.0V it is surely in outburst.
Mike Simonsen (SXN)