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.


  1. What are the limiting apparent magnitudes in B, V, i, and z of this dataset?

  2. Also - what is the size of the GOODS survey footprint and what fraction of the sky does that represent?

  3. The portion of the sky in each of the two fields is 10' x 16', centered on the Hubble Deep Field North and the Chandra Deep Field South.

    Still looking to limiting apparent magnitudes... Not entirely sure what I'm looking for, but the search has been futile all afternoon...

    Info search shall continue in the morning.