Wed, 10/31/2018 - 01:50
Hello! I've started to follow RR CET again after an absence of several years. It is an RRab star.
Looking at the data for the last few weeks, I can almost imagine low amplitude ripples in the light curve with a freqquency of 60 to 90 minutes.
I doubt my equipment and technique are good enough to evaluate this since the amplitude is so small, so I thought I would ask folks for their thoughts. Thank you and best regards.
Mike
Hi,
had a quick look to your recent data on RR Cet. It is mag 9.x in I band and maybe you have issues with saturation of either your variable or your comp stars. Please give info about your equipment and exposure times. Please also check what ADU values you get when you take your images in different bands as well as for your comp stars.
You could also compare your results to the other observers for this star as you are not the only one observing it. Just download those data via the AAVSO website and plot them.
Josch
Hello! Thank you for your note.
I am using an 8" LX200 classic with SBIG ST-402 and Robofocus. I use MPO Connections to obtain the images and Canopus to reduce the data. I obtained two 60-second exposures in each filter - B,V, and I - and then averaged these two after flat and dark frame application. Finally, I used transforms from Landolt images (last obtained in September 2018) during reductions.
Using AIP4Win star tool, it appears that the variable has a count of 14424; and the comps, 2317, 1854, and 1325 in I band for the first image (brightest) in my last run. All within the linearity of the camera when I last checked, though perhaps if I had a higher exposure that might help? The FWHM was 4 for these images, so a bit high.
Would I upload the actual images as an attachment to a forum post, or upload other data elsewhere in AAVSO?
Thank you and best regards.
Mike
Hi Mike,
Whenever I see a low-amplitude signal on top of a much higher amplitude variable, I first try to see if the comp star ensemble is causing the problem. Pick another star in the field (there are a couple over towards the west, such as the 89 comp, especially if you offset a bit) and treat it as a variable, and see if the ripples show up in its "light curve". The other thing that often happens with long time series is that the target will move across the field. It can often follow a pattern of drifting east for a while, then drifting back west, for example, and it could be that you are "drifting" across a bad pixel. Or, your focus could be drifting, perhaps even being corrected back every hour or so. Lots of ways in which you can get small signals, even looking like periodic signals, that are not physical. When I'm working on a star that is known to be pretty consistent in its light curve (other than, say, a Blazhko effect), then I'm careful to eliminate any possible error source before getting excited!
Arne
Thank you for your guidance!
Mike