pahfitMCMC

I've developed a Python version of J.D. Smith's PAHFIT code, pahfitMCMC.py. The goal of either code is to decompose IRS SL/LL spectra and calculate properties of emission lines and PAH features. mcmcPAHFIT also calculates silicate indices based on the line-subtracted spectrum; see Spoon et al. (2007) for an explanation of silicate index.

From the name you can guess that it uses Markov Chain Monte Carlo as the optimizer. The advantage is that uncertainties are properly generated from samples of the posterior probability distribution. Perhaps a more significant advantage is that no IDL license is required, and Python is free as in beer.

You may download a tar-ball here: pahfitMCMC.tgz. Documentation is contained within.

Here's an example decomposition of PG0050+124 (Link goes to the CASSIS website). Notice that pahfitMCMC fits the 14 micron "jump" that results from the change in slit-width between SL and LL.

As far as I'm concerned, you are free to use it in exchange for a thoughtful and kind acknowledgement to yours truly. The (simple) silicate emission model that is used in pahfitMCMC is discussed in Gallimore et al. (2010).

Comet Lovejoy Photobombed by Meteor

We have a new large format camera for the Bucknell Observatory, and I recently tested it on Comet Lovejoy. The reward was a chance appearance of a meteor, visible as a diagonal streak just above the comet.  For reference, the field-of-view is roughly 1/2 degree across, or roughly the width of a full moon.

Two new papers! One by Dinalva Sales et al. (I'm an et al.) on detailed observations of the OH megamaser galaxy IRASF 16399-0937, actually a merger between two galaxies. The other paper is by Billy Vasquez et al. (I'm an et al. again) on infrared/optical reverberation measurements of the active galaxy NGC 6418.

Dinalva and Billy did all the hard work. My main contribution to Dinalva's paper was the introduction of clumpyDREAM, a galaxy SED fitting tool that uses the DREAM(ZS) algorithm (ter Braak and Vrugt 2008). For Billy's paper, I performed the Spitzer Space Telescope infrared measurements.