Hi,
The Alert Notice 545 for FO Aqr asks for unfiltered photometry with a V zero point. I did a run last night using a C filter but am having issues with the V zero point. I use Maxim DL v 5.07 for image acquisition and AIP4WIN to reduce the data. I changed the C filter designation in Maxim to read CV so it would appear that way in the final log when processed. Of course there is neither a C or CV filter designation in the field photometry chart. Whereas I got a beautiful fluctuating light curve I have no idea how AIP got that since I did not tell it to use the V comp star mags. In fact, what comp star mags did it use to get that nice light curve?
So, can someone please give me a heads up on how I would take an image with the C filter and then use AIP to reduce this data using the V designations on the star photometry chart?
Thanks,
Keith Graham
For CV You use the V filter comp star magnitude(s) to establish the zero point so your reported CV magnitude becomes
T_clearraw - C_clearraw + C_V, Therefore, the zero point (ZPT) is C_V - C_clearraw. Where C_V is the sequence table reference ("standard") V magnitude from VSP. This is the "Standardized" (MTYPE = STD) CV magnitude you report via WebObs. In V filter photometry the ZPT would be C_V - C_vraw.
CV Just indicates you used a clear filter (usually but not always IR blocking) but the zero point is established using the V filter magnitude of the comp. I don't use AIP4WIN so I can't tell you what it does if you don't set the comp star reference magnitude. If it can make the calculation without the reference magnitude for the comp, it may just give you a differential magnitude. If the magnitude of FO Aqr in the light curve is way out of the range given in VSX (probably a single digit positive or negative number) that may be what is happening.
So just enter the sequence V mag as the comp star reference magnitude and do your photometry as you normally would using a V filter but make sure you identify the reported magnitudes as CV.
Brad Walter