Affiliation
American Association of Variable Star Observers (AAVSO)
Tue, 01/19/2016 - 20:24
AAVSO Alert Notice 535 announces a new observing campaign on the symbiotic/Mira variable R Aqr.
THIS CAMPAIGN BEGINS TONIGHT - 2016 JANUARY 19.
Please see the notice for details.
Many thanks and good observing,
Elizabeth Waagen, AAVSO HQ
For my FOV, which is most of a Chart Scale F (18.5 arcminutes), there is only one star with an established magnitude. I see that the field is rather sparce, but if at least one more star could be added to the sequence, I would appreciate it. I have all the requested filters (BVRI) and I'd like to add this star to my observing plans.
I also note that R Aqr is not currently well placed for high quality observations (it is below 40 degrees altitude at sunset, for me). Do you think observations under these circumstances would sill be worthwhile?
Whit Ludington
LWHA
I looked at an E chart (30 min). Separation from the 106 star to taget is about 16’ and from the 110 to the 122 is also about 16’ So since the longest distances are on the diagonals, I think you can get R Aqr, 106, 122 and 110 on the chip if you have a 15’ by 15’ FOV or larger. In the past I often had to rotate my camera to Fit stars in. My old ST7 only gave me about 7’ by 5’ FOV.
Brad Walter
Thanks Brad for the suggestion. I hadn't thought about that, so I used TheSkyX and its FOVI for my scope/Camera setup to see if it would work. Yes, it would, but I'm worried the stars would be too close to the edges of the chip. I looked at a couple of different FOV orientations and the best one is attached (Option B). Do you think this will be OK? I do have vignetting of up to 15% at the corners.
Whit Ludington, LWHA
I agree that is too tight. Looks like you are only going to get the target and one comp in your FOV. however there is a 12.1 magnitude GSC star just SW of the 110 star that has been observed by APASS and is in SeqPlot that I think will fit in your FOV as an unofficial check star. At least that will give you a check on you photometry.
121,23,43,13.83,-15,28,42.5,12.122,0.021,0.635,0.037,NA,NA,0.38,0.06,0.356,0.06,0.736,0.085,29,#
Or you could do what the PEP guys do. Alternate images of comp and target with each placed at the center of your image. These are both pretty bight stars so exposures would be short. Average the comp fluxes from comp images on either side of a target measurement to calculate a comp raw magnitude to compare to the intervening target magnitude and use it to measure the magnitude of the 122 star which should be far enough away from the edge of our image of the target. It's a bit of a pain, but not very difficult. using the PEP like method allows you to place your target and comp star images on the same pixels which helps accuracy. Flat fielding is often the weakest point in the calibration chain and common pixels helps. It doesn't really matter if there is a small constant offset for the 122 star due to its distance from center if your flat fielding doesn't "exactly" remove all vignetting (and it might not if you use dome flats, light box flats or EL screen flats). You are primarily interested in the constancy the check star magnitude.
In your situation, I would probably employ the method PEPers use.
Brad Walter, WBY