Searching for Organics in Star-forming Regions

Tin Tran


Vibrations of solid-state molecules can be seen through infrared frequencies. Therefore, the presence and abundance of molecules in astronomical environments can be studied through the method of infrared spectroscopy. In cold regions of space, the presence of molecular solids shows up as absorption features. Some of these features are not easily identified with specific molecules and are likely mixed with other constituent molecules. For example, the 5 to 8 μm region contains two absorption features that are not yet completely identified. This wavelength region shows prominent absorption features at 6.0 μm and 6.8 μm. These absorption features are seen in infrared spectra of both high-mass star – about 3 times the mass of the sun, and low-mass star – about the mass of the sun, forming regions and quiescent dense clouds regions. Several experiments and observations indicate that the Polycyclic Aromatic Hydrocarbons (PAHs) might contribute to the absorption features seen at those wavelengths. PAHS are hydrocarbons that consist of fused aromatic rings and are abundant in the Interstellar Medium (ISM) nearby to sources of ultraviolet radiation which excites the PAHs, causing them to emit energy; thus PAHs have always been observed in emission. This research hopes to solve the question of whether the PAHs may cause these absorption features. A computer program was developed to process the infrared data obtained by NASA’s Spitzer Space Telescope and the Infrared Space Observatory (ISO) and to interact with the NASA Ames PAH Infrared Spectral database, which contain mainly computationally-generated spectra of many PAH species that vary in size and charge state. The goals of our project are: to be able to fit different groups of PAHs to the astronomical data, record and categorize each individual PAHs, rank each PAH to identify the bad ones, and recommend candidate PAH species to be experimentally measured in the NASA Ames’s Astrochemistry Laboratory.


Polycyclic Aromatic Hydrocarbon; Astrobiology; Infrared Spectroscopy

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