Hello! I ran a sequence with YZ CMi last night, but I am hesitant of uploading my results. Each magnitude is about 2 less than what others have obtained. Since I just posed about a possible V0844 HER outburst (vs. error), I’m wondering if something happened to my sequences last night.
Additionally, the coordinates of YZ CMi are a bit different on plate solving my images compared to what is listed - 07:44:39.54 and +03:32:57.0 vs catalog of 07:44:40.17 and +03:33:08.8.
I tried running the reduction using only stars brighter than 12.5, but that did not change the results.
Could someone have a look at an image and see what you think?
For example, when I calculated the magnitude in B of the image taken at 11:38 central time with Canopus, I obtained 15.407 with an error of 0.074 mags. I realize that this is much higher error than the 0.01 mag desired, but I am concerned about the difference between B in LCG and my values. (As well as I and V filters)
Thank you.
Mike
YZ CMi_LIGHT_B_180.00_-9.79_2026-03-28_0018_P.fits (767.8 KB)
Hi Mike,
regarding YZ CMi coordinates, please see my post here.
These red dwarfs are very high proper motion objects, so they will move a lot and you need to double check where they are in the sky now.
YZ CMi typically has V= 11.2 and B= 12.8.
I downloaded your image and, using the 125 comp in the AAVSO chart (B= 13.517) I got B= 12.68, not 15.41.
You are probably not including the star in the photometric aperture due to the coordinate mismatch.
Cheers,
Sebastian
Thanks! I’ll rearrange things. Thank you for the coordinate guidance. Best regards.
Mike
Hello! I ran through everything for the last two nights. The numbers are the same.
I used coordinates from plate solving - 07:44:40.17 and +03:33:08.8 - along with the 13 comps listed in a 20x20 arc-min field, and using star 125 for a comp. The results were the same - B about 15, V about 13.5, and I about 10.5.
Next, I eliminated all comps except those with B-V close to 1, as with comp 125. (BBN-642, 666,628; BJT-417; BJK-159) My errors improved dramatically - close to 0.00 for all. However, the respective mags in B,V,I are nearly the same.
I've deleted my previous observations and I have not uploaded the revised observations since they do not agree with other observers.
I'd like to clarify what other folks are using - what target coordinates are being used and what comps? Thank you and best regards.
Mike
Hi Mike,
Your coordinates are fine as Sebastian stated. If I can make a suggestion, rotate your camera about 45 degrees which would make north up and make it much simpler so find stars in the finder charts.
Your magnitude of 15.07 seems to be way off as AIJ came up with a peak of about 3950 for YZ CMi and a peak of 2002 for 133 which is a bit over 14m. I’m not sure where Canopus came into the picture but I would use 125 as the comparison star and 119 and 133 as check stars.
Sounds like you are learning and having fun anyway. Your scope much have a long focal length for that small off a field of view. I cranked the star chart down to 30 minutes and it was still much bigger.
Clear skies,
Steve
Thanks! I’ll try with one check and one comp star.
The setup has a direct connection to the SCT and camera threads, so I cannot rotate it without it coming lose. Oh well!
Mike
Hello! I suspect that the coordinates that I’ve been using for YZ CMi are wrong. There are three stars in my images that seem to match where YZ CMi might be each separated b 20 arc-sec or so (since the star motion suggests that the finder chart coordinates are not current); however, since I do not have an updated image that specifies which star to use as the target, I’m at a loss which coordinates to plate solve for the YZ CMi target.
The most likely candidate is at 07:44:39.54/+03:32:57.0. Is this what folks have been using?
If anyone can provide the current coordinates for YZ CMi, that would be helpful. Absent that, a link to a recent image that has YZ CMI identified would be helpful so that I can coordinate the reference image with my plate solved images and obtain the target coordinates based on that. Thank you.
Mike
Got it! It took me a minute to get Canopus to accept the coordinates in the previous reply. Once that happened, the mags are consistent.
I cannot double check the coordinates themselves, so I’m relying on those more experienced than I so that when my data matches, I assume to coordinates match!
Thank you for everyone’s help. Best regards.
Mike
This brings back the topic discussed a few years ago concerning the VSP chart coordinate center. J2000.0 currently for the variable position.
The VSX gives the proper motion of YZ CMi as -345.25 mas/y in RA and -450.70 mas/y in Dec. So by JNow of 2026.0 the star has moved by -8.9765 arc seconds in RA and -11.7182 arc seconds in Dec in the J2000.0 system.
I still recommend the proper motion be printed on the VSP charts below the J2000.0 positions for those of us who still use charts, at least for those whose proper motion are “large”. If you are more automated then you need to check VSX and be sure of your IDs when setting up your observing program or adding new objects.
Carte du Ciel gives no proper motion for YZ CMi from info sourced from the GCVS. However, HIP 37766 = YZ CMi Carte du Ciel applies the proper motion and shows it at the current epoch position which btw is significantly different from the J2000.0 position.
Attached is a snip of a CdC chart of the YZ CMi area. YZ CMi is position without application of 26 years of proper motion and HIP 37766 is the position with the 26 years of proper motion applied.
Jim (DEY)
Thank you for your feedback!
Mike