Bright star tests

Today I spent some time trying to understand how Addstar is working and where things are going wrong. In a word, that was a fail. Addstar seems to be skipping over some artificial stars that I've indicated in my input file and I couldn't find a reason for it to do so. As I mentioned yesterday, Addstar was inserting only those stars in every other row. I found that when I decreased the spacing of the artificial stars it was then inputting alternating columns and rows to give a diamond grid effect.

While I couldn't solve the mystery of Addstar, I decided to go ahead and do more testing using only bright artificial stars in order to find a way to troubleshoot the problem. I found that Addstar added the same pattern of artificial stars for a given spacing of stars. So as long as I am careful to keep my spacing the same or double check the resulting artificial star pattern in a bright star test for a new spacing, I figure I can reliably make a new file with only those stars addstar is actually inputting for comparison later when I calculate the completeness levels.

In addition to the spacing tests, I also went back to the original artificial star input to make sure that I was only inputting stars that appear on all exposures of the same chip. When I do my Allframe analysis, I require stars to have both g and r information (all of my input artificial stars do) and to be found in at least 2 exposures. (Because the exposures are dithered from one another, there could be stars near the edges that appear on only one exposure. My method for choosing my artificial stars before today would've meant this would only be the case near the edges of my reference frame, so it should not have had a huge effect, but I did this correction to eliminate the edge factor altogether.) It ended up just being easier to ensure that all of my artificial stars appear on the overlap of all exposures. This means I'm inputting fewer stars per Allframe run than I had previously. This is fine because I can always run more than 10 artificial star tests or further decrease the artificial star spacing per run to get more artificial stars for the end statistics.

My next project will be completing the effective Addstar files (including the positions and mags of only artificial stars that actually appear in the fake images). I've been thinking about whether it will be using to run Allframe on the bright artificial star tests. I'm not sure it will provide much more insight than running the actual tests will. Instead, I'll practice making the effective Addstar files and double checking the art star positions. Then I'll apply that technique to the real files and Allframe the real files again. I'll then go back to Beth's method of looking at the number of stars per magnitude on the true and artificial frames as compared to the input. If there are still major problems, it might worthwhile to do the full Allframe analysis on the bright artificial star images.


Notes:

For now, I've settled on a 50 pix spacing in both the x and y directions. I've determined that the area that overlaps all exposures has coords
xmin = 439.4917
xmax = 3989.424
ymin = 251.866
ymax = 1840.46

I rounded the min values up and the max values down for good measure. In all, I'm inserting 70 stars in the x direction and 31 stars in the y direction. r181 still have signficant astrometry problems, so I've ignored it when calculating these values (it's one of the 2 exposures that's not used in the analysis, so I haven't even bothered to run it through DAOphot and Allstar. r183 is the other, but it will at least generate an allstar output in the usual amount of time, so I run it with the others for simplicity, though it is not used at all in the Allframe analysis.)

Ideas about Addstar:

Just talked to Beth about a few other things to consider when figuring out the best way to work with Addstar. First, I'll generate a fraction of the stars I currently have to see if we're somehow exceeding a limit Addstar has for the number of stars that can be input at one time. The second idea is to just cut the spacing in half to see if I can get the spacing I had wanted in the first place. I mentioned this idea yesterday and it's the desired way to do things because we want to fit a reasonable max number of stars into each AST so that we can cut down on Allframe computing time. Additionally, it'll be easiest to generate the effective Addstar file using this approach. Right now, the easiest spacing for that seems to be 56 pix in either direction, but tomorrow morning I'll try larger pixel spacing, perhaps 28 pix (half the original) to see what the pattern looks like.

Completeness problem found!

I was still having completeness problems up until group meeting this afternoon. So Beth gave me some suggestions to sanity check things in more detail. I went back to the image files of the original data, artificial star data, and art star-subtracted data. Turns out half of the stars I was inputting weren't showing up. I looked for stars brighter than 21.5 mag and wasn't finding most of them. So, again at Beth's suggestion, I created a new .add file of artificial stars that all had a magnitude of 20 (clearly bright enough to see by eye). When I ran this file through DAOphot, Addstar, and Allstar, every other row of artificial stars were missing. That would explain at least in part why I wasn't finding many artificial stars.

This is more or less taking me back to square one but that's a good thing in this case. I need to take a look at how I'm running addstar and see if there's an obvious solution. Otherwise I think I could just troubleshoot the problem by putting in twice as many stars with half the spacing in the vertical direction (to get the originally intended effect). Then before calculating completeness I'll just need to create a .add file with the artificial stars that actually appear in the output of addstar.

Making the addstar fix is next on the agenda and will hopefully alleviate all of my problems, but we'll see. I'm also still going to check the aperture photometry on a few of the stars in the artificial images to be sure that the photometry is looking sane. I'll check both the bright grid and the one generated from the fake CMD.

Tomorrow is AstroPhilly! So I won't be doing much of this tomorrow, but I'll be back to it on Thursday.

June 7 Update

Today I worked on finishing up the data section of the paper and proofreading what I have. I sent the draft of the first 2 sections to Beth for comments.

I also went back to looking at the completeness stuff and going through it very carefully. Beth gave me an alternate calculation to try. Instead of matching positions, she recommended I match based on CMDs to see what the completeness levels are looking like. That way I'll know if it's still a problem with the position transformations or if Allframe simply isn't finding the stars. There are a few things that are complicating this process. The first was the error in positions. The second is that I can't be sure that the magnitudes coming out of the pipeline are matching those I put in. I'm getting the sense that this isn't a huge concern, but I'll need to test this hypothesis thoroughly tomorrow.

Tomorrow is finishing the coding on this new completeness calculation. There's also group meeting and Bruce's talk in the afternoon.

Paper Outline

I met with Beth earlier today to discuss the outline of my paper. Here it is:

1. Intro
2. Observations and Data Reduction
-Astrometry
-Photometry
--Allframe
--Calibration
--star selection
-Completeness
3. Results
-Age, metallicity, distance
-Absolute Magnitude
-Structural Properties (incl surface brightness)
-Morphology
--KPNO
--simulated
((mass seg))
4. Implications of tidal features
-Assuming circular orbit --> instantaneous tidal radius
-assuming GC M/L (= a few) --> instantaneous tidal radius
-assuming Wolf et al. mass --> tidal radius
-assuming tidal radius = visible size --> M/L
-assuming 10:1 orbit and currently at apocenter --> tidal radius
5. Conclusions
6. Discussion

I've decided to take a break on the completeness stuff to get moving on the paper. Today and tomorrow I'll work on the first two sections. Then I'll get back to the completeness thing so that I can calculate the magnitude uncertainties. From there I'll work on determining the distance using fiducials and isochrones. When I've decided on a distance I'll use it to inform me about Wil1's age and metallicity. Then I'll go back to the structural properties to finalize them given the results of the completeness testing and also to calculate the Wil1 surface brightness. After that we've got to get back to working on the simulated galaxy to fix problems with the morphology of the simulation.

After all that gets done I'll just have the final calculations for section 4 and interpreting all the data for the conclusions and discussion section. No big deal. (If time permits, we'll then check out the possibility of mass segregation, at least in a preliminary sense.)

Completeness woes

I've been working on the artificial star testing this week and having trouble calculating the completeness. Last Thursday I ran Allframe for the first time on the fake frames. Then on Friday I completed the post-Allframe analysis and dug into calculating the completeness but I was getting crazy values that were nowhere near what they should have been.

After digging through on Monday and Tuesday I had fixed a few bugs. But it wasn't until yesterday that I realized a conversion error between pixel values and ra and dec. The coordinates in the reference frame were correct, but all other frames appeared to have some distortion in the placement of artificial stars. In fact, many of the stars were offset by 2", and so that explains why I wasn't finding them within 0.5" of where I thought I had input them.

Unfortunately, even when I increased the match length to 2.5", I still wasn't matching all of the stars as I had expected if that was the only problem. I chose to re-run Allframe using the fix, but I don't think that will completely solve the problem. One of the things I do in the process of matching Allframe is match between all of the frames to make sure i have at least 2 detections of each star. It is possible that I was losing stars in this step because the inserted stars weren't necessarily coincident between frames (though they were meant to be), however it looked to me as though all frames other than the reference were using the same ra and dec values for the artificial stars. So there should have been only a very few stars lost, namely those appearing on only the reference frame. Still, this problem needed to be fixed and it's very possible that additional errors were introduced when the transformation between frames was calculated using DAOmaster.

I've corrected several bugs in my calculation of the completeness including how I was selecting stars. Today, I'll finish analyzing the latest Allframe run and incorporate that to my completeness calculation to see if I'm matching things any better. I also plan to meet with Beth to discuss an outline for the paper. Then I'll jump into writing the intro.

First day back on the job

It's been a fairly productive day. I met with Beth this morning to discuss directions for the summer and we seemed to be on the same page. I spent this morning going through my files on squid and getting rid of a lot of the old stuff. There were a lot of files that were unnecessarily taking up space simply because I had found better ways to do things and never had the time to go through and delete the old stuff. Along the way I would occasionally use the old files for reference so I had to go through and see exactly what needed to be kept and what could go. It was interesting seeing how far I've come over the past year and a half or so.

After cleaning out my corner of squid, the next priority is getting moving on the artificial star tests. Those are necessary to double check the completeness and the magnitude limits we set on the data for the ML code, etc. Last I had messed with that stuff, I had allstar and daophot automatically running on all the files, but hadn't checked the result because I was focusing on my thesis. It's now time to go back and revisit that work and come up with a real completeness cut-off. That will be this week's project.

Tomorrow Beth and I leave for a workshop at the University of Maryland: Advances in Theoretical and Observational Cosmology. It looks like it will be interesting and I'll be staying both Wednesday and Thursday. I'm looking forward to the observational stuff which I'm familiar with, but also the theoretical side. I know I just got back on campus, but I suppose it will also be nice to break up the not-quite-yet-established monotony.

It will also be good to return to maintaining the blog. It seems to keep me on a productive path and makes it especially easy for me to reference notes to myself. I've virtually given up my written notebook in favor of this online version.

Here's to a good summer!

Summer 2010: Goals

Back at Haverford for another exciting summer. (And it's already raining.)

This summer will be my last and Haverford and will really focus on getting the paper together for publication. I'll also wrap up some loose ends from all the works I've done.

Long-term goals:
-Write a draft of the paper

Shorter-term goals:
-Complete artificial star testing
-Fix Wil1 simulations
-Re-examine the luminosity function as a function of distance from the center of Wil1
-Quantify asymmetry in Wil1

Artificial star testing is the first priority. Then I'll probably write up something to quantify the asymmetry. Next week Beth and I will talk about the luminosity function results from the 2006 paper, my thesis, and the structure of the new paper. In a few weeks we'll look more in depth into the Wil1 simulation problem.