C-WAYS source matching work

Introduction

Several people have done prior studies in BRC 27, BRC 34, and BRC 38 before. You worked hard to find all of these articles in the context of the proposal. Now we actually have to do the work of figuring out which sources are which in all the papers - are the sources called out in paper 1 the same or different sources as paper 2, etc., until all the papers are exhausted, and we have a complete catalog of all the previously studied sources in the region.

The thing that makes this complicated is that, even though everyone is reporting in RA and Dec, not everyone is using exactly the same system (some are 1950 coordinates and some are 2000 coordinate), and not everyone has the same coordinate accuracies (some are working off of photographic plates, and some are working off large-format CCDs). This is where it gets tricky, and where you have to apply your brain! Spitzer, WISE, and 2MASS are all using exactly the same, high-accuracy coordinate system. We need to update the old coordinates by comparing what the old papers say to the 2mass data, as well as fold in the objects with newer coordinates into our collection of sources.

An analogy

Review the differences between the 1950 and 2000 coordinate systems. REMINDER: THE STARS ARE NOT MOVING. The coordinate system is moving, not the stars. (Well, the stars may really be moving, but we don't have that information, and the size of any such motion will be on the order of a tenth of an arcsec or less; the change due to coordinates is much greater.) An analogy can provide an example. Through Google Maps, I can see that there is a Baskin Robbins near Ms. Linahan's school (from the NITARP 2011 class). I can give you the position of that Baskin Robbins in any of a number of ways:

• 346 North Lake St, Mundelein, IL
• 8 long blocks roughly west of the school
• 4 minutes west of the school (if you drive)
• 20 minutes west of the school (if you walk)
• latitude 42.269711, longitude -88.004308

Or, I could be really pathological and/or vague and say:

• the 3rd oldest Baskin Robbins in Mundelein (NB: i'm just making this up)
• the 5th oldest ice cream store in Munelein (NB: i'm just making this up)
• An ice cream store on Lake, south of Loch Lomond

Are the coordinates different in these systems? Yes, but they are pointing to the same physical location. Is the Baskin Robbins really moving? No.

That is what is going on in these BRCs. The most obvious difference is between B1950 coordinates and the J2000 coordinates -- these are different coordinate systems, and we are trying to translate one into the other, but we are also trying to understand the intrinsic errors of the earlier studies, and figure out which object they were 'really' talking about. In our example above, we want to translate each of the bullets in the above into "latitude 42.269711, longitude -88.004308". The added complication here is that the previous authors were not working in particularly precise coordinate systems. That's true of the list above too. Given the list above, your steps in finding the 'true location' of this store would be slightly different for each bullet, and in the end, might include identifing all the ice cream stores on Lake, south of Loch Lomond, figuring out how old the ice cream stores are in Mundelein, figure out how far you could get in radius in a 4min drive from the school, figure out how far you could get in radius in a 20 min walk from school, etc. In this case, you know that all of these pointers are trying to indicate the same physical location, so you could then look at the commonalities in all of those results, and then, eventually, assert with confidence that all of them point to lat/long (42.269711, -88.004308). In the case of the BRCs, we don't know for sure that each object in each paper actually does have a match. Sometimes they don't. Sometimes there really are two objects close to each other, not just one.

So all of this is what we have to do with the BRCs. We have lots of lists of objects, all in slightly different systems and coming from different ways of searching for young stars. We have to apply our brain and figure out which objects each paper is talking about -- which ones are new objects and which ones are the same as objects previously identified.