Centroid Error

[Maxim Usatov]

Hi All,

For some reason AIJ started to tell me this when I am doing differential photometry and trying to place apertures:
***ERROR: No signal for centroid in aperture T1 of image Calibrated-T18-blackhaz-WTF Star-20160828-020624-Ha-BIN1-W-300-001.fit.
********: Measurements are referenced to the non-centroided aperture location

There's star in the aperture. Exactly on the same image, yesterday, I was able to do this without problems. Nothing changed in the image. Tested on different images, I get the same error everywhere.

Any ideas?

Max

[karenacollins]

Hi Max,

Are the images properly calibrated? In other words, does the background happen to have negative values? If so, the centroid will not work. In that case, re-calibrate the images with appropriate bias, and/or darks, and/or flats. If this is not the problem, please post an example of a screen shot showing the aperture T1 placement on the star. Also post the Sky/Pixel_T1 value from the measurements table for that image and aperture number.

Karen

On 9/10/2016 2:50 AM, Maxim Usatov [via AstroImageJ] wrote:

Hi All,

For some reason AIJ started to tell me this when I am doing differential photometry and trying to place apertures:
***ERROR: No signal for centroid in aperture T1 of image Calibrated-T18-blackhaz-WTF Star-20160828-020624-Ha-BIN1-W-300-001.fit.
********: Measurements are referenced to the non-centroided aperture location

There's star in the aperture. Exactly on the same image, yesterday, I was able to do this without problems. Nothing changed in the image. Tested on different images, I get the same error everywhere.

Any ideas?

Max

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[karenacollins]

Hi Max,

Are the images properly calibrated? In other words, does the background
happen to have negative values? If so, the centroid will not work. In
that case, re-calibrate the images with appropriate bias, and/or darks,
and/or flats. If this is not the problem, please post an example of a
screen shot showing the aperture T1 placement on the star. Also post the
Sky/Pixel_T1 value from the measurements table for that image and
aperture number.

Karen

[Maxim Usatov]

Hi Karen,

Yes, they are properly calibrated. AIJ worked fine on this data yesterday. I was able to resolve the problem by removing by ~/Library/Preferences/AIJ_Prefs.txt and it began working beautifully again. I am not sure what happened. If you still need me to post my data, let me know.

Max

[karenacollins]

Okay, great. If it happens again, let me know and we will work out a way
for you to send the AIJ_Prefs.txt file to me so I can find what setting
is causing the problem.

Karen