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Coupled Blind Signal Separation and Spectroscopic Database Fitting of the Mid Infrared PAH Features

Data is increasingly generated by instruments that monitor the environment – telescopes looking at the heavens, DNA sequenc- ers decoding molecules, bar-code readers watching passing freight-cars, patient monitors watching the life-signs of a person in the emergency room, cell-phone and credit-card systems look- ing for fraud, RFID scanners watching products flow through the supply chain, and smart-dust sensing its environment. In each of these cases, one wants to compare. | Astronomy Astrophysics manuscript no. final June 30 2011 ESO 2011 Coupled Blind Signal Separation and Spectroscopic Database Fitting of the Mid Infrared PAH Features M. J. F. Rosenberg1 2 O. Berne1 C. Boersma3 L. J. Allamandola3 and A. G. G. M Tielens1 1 Sterrewacht Leiden Universiteit Leiden Niels Bohrweg 2 NL-2333 CA Leiden The Netherlands e-mail rosenberg@strw.leidenuniv.nl 2 The International Space University Parc d Innovation 1 rue Jean Dominique Cassini 67400 Illkirch Graffenstaden France 3 NASA Ames Research Center Space Science Division Mail Stop 245-6 Moffett Field CA 94035 USA e-mail Louis.J.Allamandola@nasa.gov Christiaan.Boersma@nasa.gov arXiv 1106.5899v1 astro-ph.GA 29 Jun 2011 Received 16-12-2010 Accepted 28-07-2011 ABSTRACT Context. The aromatic infrared bands AIBs observed in the mid infrared spectrum of galactic and extragalactic sources are attributed to Polycyclic Aromatic Hydrocarbons PAHs . Recently two new approaches have been developed to analyze the variations of AIBs in terms of chemical evolution of PAH species Blind Signal Separation BSS and the NASA Ames PAH IR Spectroscopic Database fitting tool. Aims. We aim to study AIBs in a Photo-Dissociation Region PDR since in these regions as the radiation environment changes the evolution of AIBs are observed. Methods. We observe the NGC 7023-North West NW PDR in the mid-infrared 10 - 19.5 pm using the Infrared Spectrometer IRS on board Spitzer in the high-resolution short wavelength mode. Clear variations are observed in the spectra most notably the ratio of the 11.0 to 11.2 pm bands the peak position of the 11.2 and 12.0 pm bands and the degree of asymmetry of the 11.2 pm band. The observed variations appear to change as a function of position within the PDR. We aim to explain these variations by a change in the abundances of the emitting components of the PDR. A Blind Signal Separation BSS method i.e. a Non-Negative Matrix Factorization algorithm is applied to separate the observed spectrum .