Tag Archives: astro

Searching for Nearest-Neighbors between Two Coordinate Catalogs

Say I have two catalogs of points, each in two-dimensional space. For each object in a catalog, I want to find the nearest object(s) in the other catalog. I can do this by computing the distances between every single unique … Continue reading

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Installing kcorrect (v4_2) for IDL Locally on Linux

I usually stay away from IDL but wanted to test the new version of kcorrect which usually runs on IDL.  Fortunately a Linux box in the department has IDL installed, so I decided to test it there, installing kcorrect locally.  … Continue reading

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g3data

This is all I needed to use this: Love Debian.

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Half-Light Radii for Various Profiles

For a radial profile of , the enclosed flux within the radius is given by     I’m only concerned about azimuthal symmetric cases, so .  The idea is to solve     for . Gaussian Profile Say the Gaussian … Continue reading

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Comparing the Efficiencies of Gaussian Convolution Routines

These days I quite often need to convolve (i.e., smooth) 2D images by some Gaussian. There are quite a few routines that can do this with varying efficiencies. So I compared a couple of them. On my laptop, this script … Continue reading

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Suppressing Warnings in PyFITS

PyFITS is obviously a great Python package if you ever need to deal with data in astronomy. One thing that consistently annoyed me however was their use of warning messages.  For example, whenever you overwrite an existing FITS file, the … Continue reading

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SExtractor on Debian Squeeze (AMD64)

Installing from Debian Repository $ sudo aptitude install sextractor This version is rather old (v2.4.4) though. Installing from Source I need FFTW and ATLAS installed already, and assume that FFTW was installed at /usr/local/fftw, and ATLAS at /usr/local/atlas following the … Continue reading

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Installing IRAF version 2.15 on Debian Squeeze

My way of installing IRAF v2.15, now 64-bit by default. First create a regular user named “iraf”: $ sudo adduser iraf $ sudo aptitude install csh $ sudo ln -s /usr/lib/libncurses.so /usr/lib/libtermcap.so.2 The second line installing csh is necessary because … Continue reading

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Some Physics Units Cheat Sheet

Before I forget: In CGS:     where        

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Estimating Standard Deviation from N Data Points

In astronomy people often estimate a standard deviation in, say, background counts from the observed data themselves, since it is very difficult to know what true standard deviations are. Then the question is this: How many measurements (e.g., the number … Continue reading

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