A live comparative star photometry feature?

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timh
Posts: 515
Joined: Mon Aug 26, 2019 5:50 pm

A live comparative star photometry feature?

#1

Post by timh »

Hi Robin,

just thought that a feature like this would be an addition of interest to quite a few folk - especially say for graphically monitoring short period variable stars in real time? It could add livestack type 'immediacy' and accessibility to what is otherwise an area of astronomy that requires patience and post-analysis to 'see'. --- which is probably why I have never explored it :-)

I imagine that it would require at least the ability to select say a 50 pixel circle around each of at least two target stars as well as to designate a control 'dark background' spot within a given frame (or perhaps better within a short substack of frames aligned within livestack). It would then require the ability to measure the integrated signal and standard deviations within the 3 or more areas, do the subtractions and output the signals or signal to noise of the stars to a graph --all within the time that the next frame (or autostack of subframes) was being collected.

Apart from variable stars such a tool might also be useful for monitoring SNR variation at different times for selected objects or parts of objects?

I am guessing that your livestack Frame brightness selection tool monitors the transparency aspect of SNR in a general way across a whole frame by monitoring star count - it too could be a useful number to output?

Possibly too futuristic but I was reflecting that SC already seems to have quite a few of the required capabilities ...although in different parts of the program i.e.

1) successive frames constantly kept accurately aligned live during stacking
2) autostack feature creates substacks that are also aligned with later substacks
3) reticule pointer tool in SC 4.0 that allows you to select a spot within a frame (currently for recentering the image and mount control)


anyway another one for your consideration

best wishes
TimH
procyon12
Posts: 253
Joined: Tue Jan 14, 2020 11:32 am

Re: A live comparative star photometry feature?

#2

Post by procyon12 »

Hello,

A very good idea, Tim. It could also be very useful for (video) occultation timing of asteroids and planetary satellites. Firstly to live check the SNR of stars nearby the target to see if there is need to change the recording parameters (e.g. due high passing clouds). Secondly to get a rough occultation light curve on the fly.
Ideally, the curves should be displayed on the screen and it should also be possible to save them to the hard disk. A requirement would be that there is no slowing down of the recording, and also, the aperture should auto-track the stars in cases where a drift occurs (like sometimes with mobile setups that are not polar aligned perfectly).

Cheers

Christian
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admin
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Re: A live comparative star photometry feature?

#3

Post by admin »

Hi,

thanks for the suggestion - as you've noticed, I've already got a lot of the parts needed to make this happen (in fact more than you might imagine - I now have automatic background calculation and I have total star brightness calculation as part of the star detection routines used for focus, etc).

I will put this in the 'big book of feature ideas' :)

cheers,

Robin
procyon12
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Re: A live comparative star photometry feature?

#4

Post by procyon12 »

Thank you Robin.
Christian
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Joined: Tue Nov 16, 2021 7:41 am

Re: A live comparative star photometry feature?

#5

Post by viator »

Hi,

I was wondering where to put my question - perhaps it fits in here.

I use SharpCap 4 mainly for video recording when observing asteroidal occultations. For these, it is important to determine a meaningful exposure relative to the brightness of the star at a sufficient SNR relative to the background. In the " Tools " tab I discovered the " Pixel Value Readout " function which nicely shows the saturation of the selected pixel. In practice, however, it is slightly problematic to use because the star image is never projected onto the same pixel ( nor is it on a single pixel ) for each frame.
I therefore wanted to ask you if it would be possible to add a new function to the " Pixel Value Readout " tool where I could change the aperture radius for example with the mouse wheel. Ideally it would be if it could track the movement of the star image on the chip and center the aperture on it during exposures. Is this idea realistic ?

Cheers,

Peter
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Re: A live comparative star photometry feature?

#6

Post by admin »

Hi Peter,

having had some time to think about this, I think my preferred approach would be to base any feature off of SharpCap's existing star detection abilities. If you run (for instance) the multi star FWHM focus measuring tool, you will see that SharpCap detects and highlights the stars it finds in the image. Now imagine that as well as drawing a box around the star, the info of the star was drawn on screen for a small selection of stars (maybe the brightest 5 in a selected area?). The info could include the integrated brightness of the star (ADU above background and photon flux), FWHM and possibly more.

Would that sort of functionality cover most of the information needed?

cheers,

Robin
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Re: A live comparative star photometry feature?

#7

Post by viator »

Hi Robin,

it seems ideal to me. In addition to the measured/occulted star, I would also have information about the comparison stars. The information displayed, as per your description, would make it much easier for me to decide what exposure time to set. It would be a complete solution for me. Awesome, thank you !

Cheers,

Peter
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Re: A live comparative star photometry feature?

#8

Post by admin »

Hi Peter,

thanks for the confirmation - as mentioned above, it is in the TODO list, but I can't promise when it will make it to the DONE list :)

cheers,

Robin
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Re: A live comparative star photometry feature?

#9

Post by viator »

Hi Robin,

I understand, I find SharpCap in its current form to be an excellent tool when observing asteroid occultations, but I look forward to the day when this feature is added. :D

Cheers,

Peter
procyon12
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Re: A live comparative star photometry feature?

#10

Post by procyon12 »

Good news, Robin.

Christian
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