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An obsession

I don't have anything new to add so i am going to write about an obsession of mine. Almost an year back, I was at IIST Trivandrum working with Prof. Anand Narayanan on Quasars. It was my first serious summer project on astronomy and i was having a fun time learning about quasars and working with python and sql query. I was asked to reproduce the results of the richards et al. 2001 paper but as I eventually learnt, it was getting harder and harder to find the original data set. So, instead of reproducing the results from the original data set, I intended to extend the results to a new data set - the data for quasars from the SDSS DR9. The original data set in question was put together using quasars from the SDSS DR3 and other surveys. As i reproduced the results for the new (much larger) data set, weird artifacts started popping up in the results. As i dug deeper, I found that these artifacts were grouped in red-shift space and in coordinate space. Further, when i looked at the spectra for these objects, they looked nothing like those of quasars. Either their SNR was too low or the spectra looked more like that of late-M type stars. I kept dugging up digital sky survey and SDSS images for the portion of sky where these objects were grouped and went through my data analysis one more time to be sure i didn't make any mistakes. Eventually, I mailed Prof. Richards with my data set and doubts I had. He replied saying that the pipeline which identifies quasars from the SDSS data is (ofcourse) not perfect (DUH!) and if I wanted a data set which was only quasars, I should use either Schender et al. 2010 or Paris et al. 2014 which were checked and cleared of such artifacts which could've crept through the SDSS pipeline. I spent close to two months on this only to come at the conclusion that I should've used a more refined data set and not the crude one. I wouldn't say that the time spent was a complete waste because i got better at python. The data set is available as a github repository here and you can look at my previous blog posts on this topic from June and July 2013 for more on quasars and my work.

21:00:30 - 21:19:00

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