Thursday, May 28, 2009

Initial Progress

Well, the search for info has given some results. It just took a while to track down the requisite papers.
In response to comments: The GOODS covers an area of 10'x16' in each of it's two fields. I think that comes out to about 0.0000007 % of the total sky area...

The magnitude limits on the bands were given to be:
B,V= 28.1+/- 0.3
i = 27.4 +/- 0.3
z = 26.95 +/- 0.35

Wednesday I made my first official plot! RA vs Dec of all of the objects in the survey. It wasn't so great at first; I was having a little trouble with the coding. After our group meeting, Beth took a look and helped me out. Turns out I didn't tell it not to connect all of the points, so the funny look was a ton of lines crisscrossing the plot. This was corrected, and then it looked like it should! It then took me longer than it should have to successfully save the image. The next observation was just the sheer multitude of data. All of the survey objects were included.

Since I'm going to be looking at stars, the next step is to sift through and set aside all of the galaxy objects. I had hopes that this wouldn't be all too complicated, as there was a conveniently labeled column in the catalog that read star-galaxy classification parameter. No such luck. The column appears to be a measure on a continuous scale from 0 to 1, and I have been unsuccessful in finding any documentation explaining it. I have decided to e-mail the "help" address given on the GOODS website, as I did for information about the mysterious 10 unlabeled columns (to which the response was that they had been used by the survey team to check for photometric consistency and overlapping in their tiles, and could be ignored for my purposes).

Another idea proposed at our group meeting that I am looking into is to use a random number generator to pick a sample population to plot. Lastly, it was proposed that I combine the catalogs of four bands together. Since I had not previously considered this, I didn't know how difficult it would be, if the objects listed were consistent, or in order. Sphere matching could be used to help this, and pick out matching objects between the catalogs.

Upon examination, I found that no such worries were needed, that the objects in each catalog matched one another. In fact, the first 16 columns of data are all positional information (RA, dec, assigned section numbers, x and y coordinates assigned to describe positions on the tiles, etc), and these were unvarying between all four bands- as it should be! So, I don't think as much work will be required to match up rows to combine them, and maybe there is a relatively easy was to grab non-repeated columns from three of the catalogs and add them to the first. --> probably a good project for today.

The whole of Thursday was spent researching and reading through more papers on the GOODS and its data.

Goal for Friday: Make a plan on how to combine catalogs and make some headway doing so. Also waiting to hear back from "Help" about classification parameter interpretation in order to move on that.

Tuesday, May 26, 2009

Early Stages

The first few days working at the computer have felt rather unproductive, but there has been progress. I have mainly been reading articles and familiarizing myself with my computer system, and beginning to learn IDL.

Early research:

I am working with data from the Great Observatories Origins Deep Survey (GOODS), from the Hubble Telescope's Advanced Camera for Surveys. Four fields were imaged, with broad, non-overlapping filters: F435W (B), F606W (V), F775W (i), and F850W (z). Exposure times were 3, 2.5, 2.5, and 5 orbits, respectively. It is not a very deep survey, but is much larger than previous programs carried out (data was taken in 2002-2003). It's primary goal at the time was to gather information about small faint galaxies, at high redshift, and hopefully lead to information about the formation of our own galaxy. I will be using this data to examine for small faint blue sources, to see if they fit the profile of Blue Horizontal Branch stars.

The data set:

Data releases were posted online by the survey, where I accessed the latest set, version 2.0 (which had some updates and improvements on the previous version). The data was downloaded from the catalog, in the set of 8 text files (4 from the northern portion of the sky, and the 4 taken in the southern portion). These data tables illustrated 104 columns of position coordinates, fluxes, magnitudes, etc. so the next step was determining just which data would be useful. I will primarily be using the RA and dec information, along with apparent magnitudes, angular size, and the full width at half maximum (FWHM).

Next: The long and somewhat tedious foray into the realm of IDL.

I spent a couple of days going through tutorials and aclimating myself with the some of the language. Ideas I know have some grasp of (and could follow instructions to make examples of): Procedures, Functions, Objects.

To summarize a bit: Procedures are like to do lists. Functions are like procedures, but give an end result (like a mathematical function, duh). Both of these things are kinds of Methods.
Objects are like Methods with data embeded in them. There are a number of kinds of objects, which are grouped by Class. The main pieces of a typical object could include an initial function, a cleanup procedure, display procedure, and a defining procedure. Following use of the example tutorial object, it warned to take note that by deleting the name that refers to the object the object itself has not been deleted, that that has to be destroyed as well (the reference is an entity separate from its referent, and one will leave the other behind if destroyed).

Near-future goal:
Read-in file to make position plots from RA, dec data.

Thursday, May 21, 2009

Intro: Week 1 on the job

I have begun doing research in astrophysics this summer at Haverford with Professor Beth Willman. In just a few days, I've already been swept up in articles, the Sloan Digital Sky Survey website, data from Hubble Telescope, and have jumped into a new computer world with unknown operating systems and foreign programming languages. This is certainly going to be an adventure.

Exploring to infinity, and beyond! ...from a computer lab. ;)