The last two months have been really slow in my attempts to learn C++. I've had the equivalent of doing "mrdfits" in IDL to read some information (namely, plate, mjd, fiber, ra/dec, redshift) from fits files. It has taken so long for me to figure out how to do it. I finally am seeing the light at the end of the tunnel as I only have a few problems to deal with.
The file I'm reading is 450,000 objects (1.6 Gb) and it seems that CCfits isn't able to read the huge file even though I thought I was just trying to define a reference to the file and not actually read the whole file. The steps I'll take to figure out what's going on is to see how big I can make the file such that it still works. Then, I need to setup everything on Franklin so I can try to run this there, just in case my laptop doesn't have enough memory.
The next thing I need to do is to create objects for each quasar which contain the information and soon will also have functions that compute, for example, the mean flux. I understand, on a cursory level, what an object is, but have yet to understand the method of implementation. Well ... I should get cracking!
Thursday 3 March 2011
Monday 12 July 2010
Project Shopping
I'm in the process of project shopping, but at the moment am starting to look at noise properties in the Lyman alpha forest. The goal is to quantify the effects of various components of noise on the power spectrum, P(k), derived from the Ly-alpha forest.
Although the results of the power spectrum are dependent on many physical properties (such as whether to include or how to deal with Damped Lyman Alpha systems, velocity broadening, metal-line systems, and continuum fitting), I plan to study the effects due to the data itself. Namely, four components add sufficient noise to affect our results.
1) Measurement noise -- read, sky & object noise (Poisson)
2) Sky-subtraction
3) Spectro-photometry -- effects due to the amount of light entering the fiber based on position on plate (?), which would largely affect the continuum fits of the Ly-A forest
4) Wavelength calibration
Not sure if this is correct, but it seems as though spectro-photometry and sky subtraction would cause the biggest source of error. The first test I'll conduct will be the effects of sky subtraction. I'll use the mock catalog which has 'perfect' data, unaffected by noise, and add only that noise due to sky subtraction. The mock catalog is made such that to emulate the BOSS survey (while simultaneously made with the correct distribution to give the correct power spectrum), so I'll use sky spectra from fibers closest (in ra/dec) to our mock spectra. After adding sky subtraction noise, I'll compute the correlation function on the sample to see how it deviates from the ideal case.
Although the results of the power spectrum are dependent on many physical properties (such as whether to include or how to deal with Damped Lyman Alpha systems, velocity broadening, metal-line systems, and continuum fitting), I plan to study the effects due to the data itself. Namely, four components add sufficient noise to affect our results.
1) Measurement noise -- read, sky & object noise (Poisson)
2) Sky-subtraction
3) Spectro-photometry -- effects due to the amount of light entering the fiber based on position on plate (?), which would largely affect the continuum fits of the Ly-A forest
4) Wavelength calibration
Not sure if this is correct, but it seems as though spectro-photometry and sky subtraction would cause the biggest source of error. The first test I'll conduct will be the effects of sky subtraction. I'll use the mock catalog which has 'perfect' data, unaffected by noise, and add only that noise due to sky subtraction. The mock catalog is made such that to emulate the BOSS survey (while simultaneously made with the correct distribution to give the correct power spectrum), so I'll use sky spectra from fibers closest (in ra/dec) to our mock spectra. After adding sky subtraction noise, I'll compute the correlation function on the sample to see how it deviates from the ideal case.
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