Minimum magnitud star in you picture
Stacking program, astrometric (plate) solver, fits file viewer
Brought to you by:
han59
Menu
▾
▴
Hello Han
What about having an ASTAP tool that once your image is plate solved, can
inform you about the minimum start magnitude, and show you circled in
color, those dimmest stars in your picture compared with the H18 database.
In this way, for example, you could easily understand which optics/lens and
exposure time combination you have to use to reach a certain asteroid,
comet, extragalactic supernovae, etc… you might be interested in capturing.
This would be a handy tool in my light polluted sky.
In essence with this tool, I would study my old images, and anticipate and
plan my magnitude limits in advance for any future observing run.
Thank you.
Hello Jordi,
The latest ASTAP version have something similar. It is a little hidden but it is in "Magnitude (measured) annotation menu. It is a little slow but annotates all detected stars and reports the limiting magnitude. See screen shot.
I will add reporting the limiting magnitude reporting to menu "Calibrate photometry" . That will be easy. Adding limiting magnitude reporting to the solving could slow it down and is less desirable.
Is this what you like to have?
p.s. I have corrected a few weeks ago the documentation to "maximum magnitude" equals limiting magnitude.
Han
Okay, I added something else in the photometry calibration routine (viewer tools menu):
It is an estimate by extrapolation of the bright stars. It is a little tricky since the measuring aperture reduces for fainter stars. So for fainter stars the SNR improves because the program use a smaller aperture. The 10σ limiting magnitude value is more accurate because it actual tested.
Yo get both values in the log as above if you use "TOOLS", "Magnitude measured annotation" The values will differ a little but see how it works for you.
Download this development version 0.9.563 (Windows):
http://www.hnsky.org/astap_setup.exe
If you need a Linux version or else tell me.
The accuracy of the estimate will be better if I select a fixed aperture. I will do that later.
Han
Hello Han,
I tested it and it is wonderful. Good job.
I cannot believe I could reach 18 mag with my 10" F/4 scope in 30s exp. in
my heavily light polluted sky
[image: image.png]
[image: image.png]
Then I tested my deepest image ever, 2h18min exposure of the same region
and I got 20.7 !!!! mag.
[image: image.png]
I just cannot believe
[image: image.png]
what do you think?
maybe it is counting up the noise.
Thank you very much !
Jordi
Last edit: han.k 2021-07-29
I'm doing some more testing and add some more improvements. This is not finished. :)
Han
Try this version 0.9.564 (Windows):
http://www.hnsky.org/astap_setup.exe
Measuring limiting magnitude is more difficult then expected. Tried several methods. Many where unreliable. Is now only available under menu "calibrate photometry. Report in log. Set the aperture in tab photometry on 3.
Han
Last edit: han.k 2021-07-30
Check the faint star magnitudes with tool option to retrieve online the magnitude from Gaia.
Hello Han,
I just tried 0.9.564 but it doesn't work for me.
[image: image.png]
all stars read 32763 after setting aperture to 3.0
and looking at the log there no mention to any magnitude as in version
0.9.563
[image: image.png]
maybe I'm doing something wrong...
Last edit: han.k 2021-07-30
Can you share the image(s)? e.g. via: ufile.io
It looks like your image are pretty oversampled (HFD=8.4) That makes it more diffiuclt to measure the limiting magnitude because these relative big circles tend to disappear partly in the noise
Note it only reports the magnitude in menu "Calibrate photometry". Shortcut ctrl+C. The magnitude is reported in the log only.
Han
Yes your correct, It is missing. I have removed too many experimental code lines. Let me fix it.
Fixed the 32763 problem . Will do some more fine tuning in the menu now.
Try this version 0.9.564a (Windows):
http://www.hnsky.org/astap_setup.exe
The limiting magnitude is now reported in "Magnitude (measured annotation" and "Star database annotation"
Han
I tested with some pictures and the results seem quite reasonable now.
Thank you very much.
Jordi
Missatge de han.k
Last edit: han.k 2021-07-31
For comparison, use the "Gaia online query" and the Gaia BP (blue) magnitude to compare. Biggest error could occur for the faintest stars but error should be equals or less then 0.5 magnitudes.
Your image go deeper if you bin till the HFD values reach 2 to 3. So bin x 4. This could be by achieved bin twice x2.
Small note, replying to the post makes email addresses visible. It is better to remove the emails from the reply.
Clear skies, Han
Last edit: han.k 2021-08-02
Thanks, Han, for adding this feature!
Regards Achim