Affiliation
American Association of Variable Star Observers (AAVSO)
Mon, 04/27/2020 - 14:35
Greeting,
I received 8 B images of BH Cru from BSM South from the 24th. The first 3 where trailed in dec. The exposure time was 300". The other 5 images where taken at 45" look normal.
I wondered why only B images. No V,R, and I. Looking at the pipeline report it appears only B images were taken of all the targets that night.
So my question is why 300" exposures and why only images in B?
Dennis
Dennis:
I set up the BH Cru plan and I have my own personal opinion about how to cover a star that has a large magnitude range. That is, I chose to set up two simultaneous plans. One with short exposures to cover the bright end of the cycle and one with long exposures to cover the faint end. Thus, there are 45 sec exposures in one and 300 sec exposures in the other. Both plans did run back to back. Good!
The fact that the BSM_S mount cannot track well enough to run 300 sec images is quite clear, so that idea will not work. I'll go back to Arne's procedure of just increasing the number of short images so that stacking can try to resolve the large magnitude difference. I'm not a believer in this for such a large magnitude difference but long exposures are not going to work until the mount is changed to a Paramount some time in the future!?
I'm not sure why ACP did not run the VRI images that DO exist in the plan?? Did Scheduler just not run them in ANY plans for some reason? Something going on with filter wheel? Will check? Time will tell?
BTW, how well did the shorter B exposures work for getting a magnitude measurement? IOW, what is the SNR right now? Is BH Cru near its max right now?
Ken
Ken,
Okay that explains the 300" images. The SNR was 73. About the same as I got from BSM Berry acouple days ago. I got a magnitude of 11.547. Slightly brighter the the estimate from Berry. BH Cru may be getting close to max. VSX has max in V at 6.55. My V mag from Berry was 7.68. Looking back over 5000 days the min and max change. I did have to change the telescope name from BSM_S2 to BSM_S.
Do you think we could change the B exposures to 60 or even 75 seconds? Would be nice to get the SNR over 100.
Dennis
Hi Dennis:
Your message was a little too sparse. Please separate the V and B mag info above. A table would help.
What B SNRs / Mags did you get, with and without stacking? Same for V SNR/Mags, with and without stacking. Stacking should increase SNR by sqrt N. RI data also?
I can/will certainly adjust exposures within reason to avoid trailing. I would hope to increase exposures at max part of curve to give more like SNR=700 (50000 ADU?). We may still have about 1 mag more to go, 2.5x flux? It would help to know more about values you have gotten from both BSM_S and BSM_Berry. Want to get it right without revising exposures many times?
Ken
Ken
I have sent you an email with the data you ask about.
Dennis