I have been surprised by absence of comp stars for SN 2025rbs. Maybe there are limitations caused by its position?
Everyone uploading data for SN 2025rbs appear to be rolling their own sequences. One is using the rare published Arp supernova search charts.
Do you know how to request a new sequence be made?
Jim (DEY)
Peter Stetson has BVRI data for the field at:
The V sequence goes from 13.4 down to 19.5 with mean errors mostly < 0.015.
One could also use the existing ATLAS refcat2 data for g,r,i, perhaps transforming if necessary.
\Brian
It is just that if noone requests a sequence and there wasn’t a supernova before in the same galaxy that has had a sequence made, then there is no reason for comp stars to be shown in that field, since the AAVSO charts (for now) show sequences made on demand.
You have to request a sequence sending an email to compstars@aavso.org
including the information required here.
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In case it is of interest, here are coords and UBV data for the stars observed by Arp in this galaxy. Source paper + chart is in 1961ApJ…133..883A. Note that for the first two entries the data were determined photgraphically; the rest are from photoelectric photometry using the Palomar 200-inch telescope. I would assign mean errors of 0.05 for the two photographic stars, and 0.03 to the photoelectric data (Arp gave no uncertainties).
\Brian
Name RA (J2000) Dec V B-V U-B
NGC 7331 Arp A1 22 36 57.1 +34 28 01 13.63 0.58 1" cpm pair
NGC 7331 Arp A2 22 36 57.71 +34 28 33.8 13.40 1.04
NGC 7331 Arp A 22 37 01.78 +34 23 54.0 15.05 0.68 0.11
NGC 7331 Arp B 22 37 00.59 +34 24 19.1 15.62 0.71 0.18
NGC 7331 Arp C 22 37 06.87 +34 23 57.5 15.02 0.72 0.22
NGC 7331 Arp D 22 37 08.47 +34 26 12.1 14.08 0.61 0.07
NGC 7331 Arp F 22 37 01.91 +34 26 27.8 16.07 0.79 0.44
Thank you folks for the replies, I’ve sent the request finally.
(Un)expected trouble with bright galaxy core: in spite of not very bad image of SN,VPhot shows absolutely oversaturated spot, and manipulations with limits in Image Display do not help 
BTW, there was SN 2014С in the NGC 7331, but comp stars have not been selected - probably, due to problems with photometry weak SN had just 5 observations.
Wow, Roger Venne prepared excellent sequence for SN!
Even awful black galaxy on the VPhot image does not prevent to correct star detection and evaluations. Gotten CR, TG and TB magnitudes are fully realistic, in spite of the first impression.
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That’s great!
I did some Seestar photography of the galaxy and noticed the Supernova was easily visible in the image. I did not attempt the photometry yet.. Looks like you’re getting great results in VPhot so I’ll try.
Well, background is very bright: SNR of SN is about 30, when comp stars have SNR 300-800. Obviously, SN spot will dissolve in the galaxy shine soon.
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I took my Mak-Cas 180 out for a long drive to an observing site I rarely use on the night of 2025 September 1 - 2. Using a Pentax Kp DSLR was able to get transformed B,V,Rc magnitudes of the SN.
The Mak-Cas 180 is f/15 so the field-of-view is relatively small but the image scale is perfect to sample the Bayer matrix well and the SN 2025rbs is well separated from the nucleus of the galaxy.
Jim (DEY)
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I use the similar device (M-C 150/1800), but regretfully my last RGB points are far from Jim’s evaluations. SN is clear visible on the images, SNR is about 20, but VPhot returns background brightness, I suppose. I tried to shift centroid, but result stays almost the same. I marked last two datasets with Z, and I do not plan further observations, regretfully.
The last night I observed it with my ES127 + 0.7x + Atik490EX, not reported (yet). The image scale is not nearly as good as with the Mak-Cas 180.
The problem is as SN 2025rbs has faded and the fact we are using aperture photometry the background of the galaxy contributes relatively more to the sky background introducing significant biases compared to the comps far from the galaxy which have no galaxy background sky contamination. I have the ability to mask pixels in the sky ring, the brighter parts of the galaxy glow, so they are not used in the sky background estimation but the SNR as the SN fades makes even that not useful.
Nothing to worry about, IMHO. We have covered much of the interesting part of the light curve. I’ve probably gotten it for the last time with my equipment.
Those with big scopes and good seeing can probably still get it. Say a 16-inch or larger!
Jim (DEY)
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