Centroid Error

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Centroid Error

David Emory
I open a set of apertures and then try to do a stack align or multi-aperature photometry.

I get a "Centroid ERROR: no signal in aperture for moment widths!' message.

There is clearly a star in the aperture.

I have tried this numerous times.
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Re: Centroid Error

karenacollins
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Hi David,
    I looked at your images this evening. The sky background is negative in the region around the apertures you sent. The negative background is what is causing the centroid operation to fail. It sounds like you have everything working now by aligning using stars in a region with positive sky background, and then turning centroid off to run photometry on the larger set of stars, some of which have negative background counts.
    If you are still having trouble, an alternate approach would be to process each of the three images independently with a custom set of apertures generated from WCS headers by John's python script, one for each image. Since the apertures from the python script are supposed to be aligned to the stars to within a pixel, you can leave centroid turned off when running photometry on each image. You will just need to open the appropriate aperture file for each image (or drag and drop it on the image, whichever is easiest to you), before you run multi-aperture. As long as you leave the measurementstable open, new measurements will be appended to the current table.

Karen

On 7/19/2013 5:15 PM, David Emory [via AstroImageJ] wrote:
I open a set of apertures and then try to do a stack align or multi-aperature photometry.

I get a "Centroid ERROR: no signal in aperture for moment widths!' message.

There is clearly a star in the aperture.

I have tried this numerous times.


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