Simple aperture correction question
Gabriel wrote on Jan 29, 2010
Hi,
I perform PSF photometry over a frame and when I get to the aperture correction part I have a problem. To perform the aperture correction I use the same PSF stars I used doing the photometry. The thing is that when I run the 'phot' task (with the two apertures: the one I used with the standards and the smaller one I used during the photometry) I get all INDEF's values for the MAG value with the big aperture (the one I used wiht the standards) and a '305' error in the PIER parameter (which means 'Bad data pixels') So to fix this I diminish the 'datamin' parameter until enough stars are found with MAG!=INDEF using the big aperture and so I can compute a mean aperture correction. My question is: will this diminishing of the 'datamin' parameter affect the outcome of the aperture correction in any way? I mean: does it make any difference, the value I use for 'datamin', if what I want are the MAG values? Will changing 'datamin' affect the 'MAG' values I get and so affecting the aperture correction?
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Edit: I realize that choosing more or less stars when performing the aperture correction will change the value of the aperture correction.What I mean is: does changing the 'datamin' value have any influence other than having more or less stars with MAG!=INDEF or with 'Bad data pixels'?
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Hope I made myself clear.
Cheers!
Gabriel
I perform PSF photometry over a frame and when I get to the aperture correction part I have a problem. To perform the aperture correction I use the same PSF stars I used doing the photometry. The thing is that when I run the 'phot' task (with the two apertures: the one I used with the standards and the smaller one I used during the photometry) I get all INDEF's values for the MAG value with the big aperture (the one I used wiht the standards) and a '305' error in the PIER parameter (which means 'Bad data pixels') So to fix this I diminish the 'datamin' parameter until enough stars are found with MAG!=INDEF using the big aperture and so I can compute a mean aperture correction. My question is: will this diminishing of the 'datamin' parameter affect the outcome of the aperture correction in any way? I mean: does it make any difference, the value I use for 'datamin', if what I want are the MAG values? Will changing 'datamin' affect the 'MAG' values I get and so affecting the aperture correction?
---------------------------
Edit: I realize that choosing more or less stars when performing the aperture correction will change the value of the aperture correction.What I mean is: does changing the 'datamin' value have any influence other than having more or less stars with MAG!=INDEF or with 'Bad data pixels'?
---------------------------
Hope I made myself clear.
Cheers!
Gabriel
Francisco Valdes wrote on Jan 29, 2010
I am not very expert in this area so take my answer as an educated guess.
I would expect that as long as the value of datamin is the same for the multiple apertures used to derive the correction that this would be fine. However, using one datamin for the smaller aperture and a different one for the larger aperture would probably be wrong.
Yours,
Frank Valdes
I would expect that as long as the value of datamin is the same for the multiple apertures used to derive the correction that this would be fine. However, using one datamin for the smaller aperture and a different one for the larger aperture would probably be wrong.
Yours,
Frank Valdes
Last post on Jan 29, 2010