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SAGES-UCSC / Photometry

Photometry pipeline for SAGES
MIT License
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Best Aperture for UCDs #13

Open AlexaVillaume opened 10 years ago

AlexaVillaume commented 10 years ago

Hey @vincepota -

I've been thinking about the findBestAperture routine, I don't know if it's optimized for UCDs. Do you have any thoughts on how to optimize the aperture for objects as bright as UCDs?

vincepota-zz commented 10 years ago

Hi Alexa. good point. Historically, people have been using iraf/daophot which does aperture photometry. The problem with aperture photometry is that it only works for round point-sources. With the advent of large surveys, astronomers switched to sextractor because it takes care of elongation, axis ratios and it looks for the best aperture radius through mag_auto .

Bright UCDs look more like galaxies and some of them are elongated. If measured with aperture photometry, UCD magnitudes may be underestimated.

So, I think the way to go is to use mag_auto to measure magnitudes of all objects. Once we have the final catalogue for M60, we can test if the magnitudes measured at the best-aperture radius (as from findBestAperture) is indeed equal to mag_auto. If it is, then mag_auto does a job as good as findBestAperture. Moreover, we know a bounce of UCDs in M60 because they have HST photometry. So we can test how aperture photometry affects their magnitudes. Then we can decide how to proceed.