Monday, June 14, 2010

Yes yes, yes. Without the oops...

Today was semiproductive. I started off with a simple test to see if the proper motions I'd calculated for the star particles was right: I added the components together (vector-wise), that would give the magnitude of the total proper motion. Another easy way to get this is to take the total velocity and subtract off the radial velocity (again, vector-wise). These should give the same numbers, but unfortunately do not. I spent most of the morning finding little problems with my definitions of each component, but this didn't seem to help. In the afternoon I emailed Adi and Beth for help, but so far there's still a (fairly large) discrepancy.

I also read through the manual for StarFISH (available here: and am going to start playing with it and seeing what's what.

On the astronomy side of things, I looked through ADS for some papers on absolute magnitudes of BHB, RR Lyrae and RGB stars. I found a couple that could be valuable and am reading through them now. I'm glad I have something to balance the computational side of things right now, because otherwise I'd go mad from all of the debugging. But now that I'm getting absolute magnutudes for tracer stars, I can start plugging them in with the estimated errors for the LSST and make some proper motion plots (once I get that straightened out).

1 comment:

  1. Nice approach to sanity checking your results! Too bad they don't agree yet :) I haven't read your email to Adi/me carefully... let me know if you're still stuck a day from now.

    I think that the next step in evaluating how bad of an idea it will be to push the StarFISH thing any more will be to create a simple 2D spatial array with the smoothed local density of star particles. The idea is that you create a 2D array, where each bin is some spatial pixel... just like in your digital camera. You use the (l,b), or (Ra,Dec) or whatever coordinates to determine which pixel each star lies in. You then smooth it with a spatial filter to enhance features with some "typical" scale that you expect the features you are interested in to have. (Did Belokuorov use smoothing when creating Field of Streams?)

    Gail has code that makes smoother spatial figures given an input list of ra, dec, an ra and dec range that you want the figure to have, the angular size of the smoothing filter, the angular sizes of pixels... I think maybe given one other thing as well. Ask Gail about this code. Its actually a set of functions/procedures that I've written and I gave her a code that uses them together and makes a product. She can show you the product as well. Read carefully the documentation I've written in each of the functions/procedures (jeez, I hope I documented things!) because they aren't very straightforward to use. Then give them a go! (Feel free to send me questions, buggy code, etc.)