Exoplanet processing software

Ed,

You ask a good question.  I'll try to answer based on my experience with both tools.  I can see the possibility that folks who use each might feel strongly about their favorite, so I am going to try to stay a the high level.  As you know VPHOT is a great tool with a ton of features.  The same can be said about AIJ.  If you want to understand the detailed features in AIJ, these are the primary sources:

User Guide

AIJ Paper

Forum

Collecting exoplanet transit information involves a time series, often hundreds of images.  I have found AIJ superior to VPHOT in this regard.  First, it operates on images on your local PC so an upload is not required.  Second, it can operate of this time series (AIJ calls it an Image Sequence) in a very efficient fashion.  The authors have made it possible to scroll through hundreds of images in a fast, intuitive way to check quality and perform differential photometry.  I have done time series with both VPHOT and AIJ and can say this is an area where AIJ is superior.

For exoplanets, AIJ contains a transit modeling feature that has no parallel in VPHOT.  This is really the focal point of the expected AIJ workflow.  The idea is that you enter information about the star and planet and the program performs a light curve fit.  The fit allows you to specify things like airmass, meridian flip and many other factors that change over the time the series was collect as factors to improve the fit.  Take a look at section 4.4 in the AIJ Paper.

I think the third thing that sets AIJ apart is the graphics capability.  I found a substantial learning curve here, but once I got familiar with it I feel it adds a lot to my understanding of how good my observations are and what they tell me about the transit.

After pointing out these three major areas where I feel AIJ excels for exoplanets, let me also point out where you might be disappointed if you attempt to use it as a replacement for VPHOT.  AIJ is focused on measurement precision, not accuracy in the strict sense of those terms.  AIJ will give you an apparent magnitude, but there is no color transformation or check star.  You can use the output to do this yourself, but it is not there "out of the box".  AIJ does not give you the convenience of importing comp star magnitudes and coordinates as easily as VPHOT.  You can, for example, import a VSP sequence.  However, that requires a program or script to create the proper format.  I have done this and it is pretty straight forward.

Again, the authors of both VPHOT and AIJ have done amazing work.  I use both.  For exoplanet work, I use AIJ.

best regards,

Cliff

Hi Ed:

AIJ utilizes some time based corrections (barycentric JD), and detrending options (e,g., airmass), and modeling tools (R*/Rj radius values) that VPhot was never designed to do.These capabilities are very important for obtaining precise/accurate fits to exoplanet transit curves, especially at millimag transit depths.

More importantly, if you intend to participate in current or future Exoplanet Section campaigns, it will almost certainly be expected that you use AIJ to generate acceptable data.

If that is not your focus, VPhot will provide exoplanet time series photometric results that are similar to those that are typically submitted to the Czech ETD web site.

Ken

PS: I have long ago given up addressing the issue of having to upload images to VPhot. If you need your photometric analysis in less than one or a few hours, then you need a local photometry software package. I upload my images in the AM following a nightly run, go to work (office, house or yard) and do the analysis when I return (often within an hour). Note that I do have a good fios internet connection.  

Thanks Cliff and Ken. OK, I can see the advantages for AIJ. In fact, I downloaded it and played with it a bit. Given Ken's remark about future Exoplanet Section campaigns, looks like I will need to learn its tricks in more depth.

I have one more question, but I will pse that after re-reading the Exoplanet Manual. Might be answered in there.

To Ken: I have never worried about the image upload "lag" in Vphot. I upload hundreds of eclipsing binariy images and understand that sometimes I have to wait a while before the data are available. This is no problem for me. And since I am now imaging obscure eclipsing binaries, it takes Tim and his team a day or two to provide the comps in any case. The Comp Team is super.

Ed

I found AIJ to be a low intensity processing program even on an older Win XP computer.  While actively observing and collecting data on an exoplanet star, I use AIJ on uncalibrated images to see when ingress or egress occurs and then plan out how much more time I need to collect data.  Often exoplanet transits do not occur on time, and so this is useful.  At the same time I use The SkyX to control the mount and camera and PHD to guide.  Actively running AIJ seems to have little effect on the computer's performance.

-Paul

BPAD