Getting flux and magnitude from .corr file but Vega is missing

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Dale Eason

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Oct 10, 2022, 2:42:50 PM10/10/22
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Hello,  I'm use astrometry on Raspberry PI and writing python code to extract flux and the Magnitude of the stars that I find in images that I take with the RPI camera.  The field of view is 15 deg and it solves those images well.

I have Vega in the center of the field of view and the command line command:

solve-field x.jpeg --tag-all -v 

shows it to be one of the stars in the field.  However when using python and the fits library to read the x.corr file Vega is not one of the stars listed.  It's starts listing stars with mag 3 and dimmer.

I can't figure out what is wrong.  I write software in C,C++ and python so I know how to read the code.  But I have not found where the .corr file is written to discover the issue.  Any help would be appreciated to either find the .corr routines or perhaps some command line argument that I'm not applying correctly.

Dale Eason

Dustin Lang

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Oct 10, 2022, 4:42:12 PM10/10/22
to Dale Eason, astrometry
Hi,
The .corr file lists stars that we think are matched up (corresponding).  So perhaps the stars detected in your image are saturated and not detected (or not localized well)?  The .rdls file should contain all catalog stars from the index file.
cheers,
dustin


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Dale Eason

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Oct 10, 2022, 4:45:26 PM10/10/22
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AH,  Yes it is saturated and slightly smeared as well.  Thank you

Dale Eason

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Oct 10, 2022, 5:20:42 PM10/10/22
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Forgive me if this has been addressed before but searching i could not find the answer.
Are there other files or command line parameters I could use instead of the .corr file that will give me the flux of the star in the xylist of stars?

Dustin Lang

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Oct 11, 2022, 10:22:29 AM10/11/22
to Dale Eason, astrometry
Hi,

The xylist file should contain a "flux" column.  This is not a very good measurement of the brightness of the star in your image -- I forget exactly what it's measuring, but it's something like the value of the pixel closest to the center, or something like that.  Not something you'd want to use for photometry.  For Astrometry.net we only use it to sort stars from brightest to faintest.  The RDLS file will contain mags of stars from the reference catalog.  (And if you use --index-xyls <filename> you can convert the RDLS RA,Dec coordinates to X,Y pixel coordinates in your image, if that helps you find your star of interest).

cheers,
dustin


Dale Eason

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Oct 11, 2022, 5:17:09 PM10/11/22
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Thank you.  Yes I know the flux estimation is crude but it might be good enough for my task.  I'm trying to see if the stars in my image follow the magnitude curve more or less.   If so then I estimate the sky transparency is good.  There are other issues of course including the non linearity of the camera image.  I think if I only use the flux values in the middle of the sensor range those values may be linear and then may follow the magnitude curve.  So for it looks like that is the case.  If so I have created a transparency gauge.

Dale

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