Best method to define aperture radii

[SCO]

Hi, AstroImageJ has several options on the Multi-Aperture Measurements screen for defining the aperture(s) to be used throughout the set of images (slices).  They are:

1) Fixed Apertures as selected above
2) Auto Fixed Apertures from first image T1 radial profile
3) Auto Variable Apertures from multi-image T1 radial profiles
4) Auto Variable Apertures from each image T1 FWHM

My question is, which one of the four options is best for getting the most accurate and precise measurements for all slices and thus the lowest RMS of the residuals in the light curve?  I have searched around for some documentation on that question but I was not able to find anything..

My assumption would be that option 3 or 4 would be best because the apertures would then be customized for each particular slice.  But if that is a valid assumption then, which option (3 or 4) is best?

Here is the problem: If one of the four options is best, why are the other three even there?  As far as I can tell, there are only three possible reasons:

1) The best option to choose depends on the user's environment, goals, equipment, limitations, etc.
2) There is a disagreement or uncertainty among users and/or developers as to which option is best.
3) I completely misunderstand the meaning of these options.

That is what I have been trying to get documentation on.  Such documentation does not exist, or at least I can't find it.  That is why I opened this post.

Thanks!

Ed

I am not getting much response.. so I will rephrase my question.  Has anyone had better luck using one method vs. another?

[karenacollins]

The answer to your main question is numbers 1 and 2. There is no universal best aperture selection option. It depends on your goals, the stars in the observed field, the personal preference of the user, etc. However, I can write-down general guidelines. I will do that and post a link back here.

In the mean-time, I think you are not on the latest build. I recommend the latest "daily build" in the update option. It has a new multi-aperture option between your number 1 and number 2. It is called "Auto Fixed Apertures from multi-image T1 radial profiles". If there is no star near your target star, I recommend getting started with it. If there is a star contaminating that automatically selected aperture, then I recommend using the first option (Fixed aperture) and selecting an aperture radius that maximizes the flux in the aperture from the target star, while minimizing the flux from the contaminating star. If the stars are similar brightness, then you'd want to set the aperture radius to be half the distance between the two stars.

Karen

[SCO]

Thanks Karen, that is very helpful.  Yes, an explanation for the various reasons for choosing among the various aperture options would be very helpful!  When you post that here I am sure it will be a benefit to others as well.

Regarding the version of AIJ, the first thing I did was to download the latest Daily Build (as of December 31).  Dennis emphasized how important that was!  I did that before I did anything else.  I did not get any errors during the process, AIJ ended and I restarted it, and the version it gave me was 1.53K.  I am not sure why I would not have been using the latest version once I restarted AIJ.  Strange..  I will try the update process again today and see if I get something different. Thanks!

Ed

[karenacollins]

With the latest version, if you click in the bottom of the toolbar, you should see AIJ 5.2.0.06, ImageJ 1.53k (the latter is just the underlying ImageJ version number).

You should see these 5 Multi-Aperture options in the current version. The first and third options from the top are the options that I recommended:



Karen

[SCO]

Yes, that is the version I have, 5.2.0.06.  Perhaps I missed that fifth option.