Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21341215w&link_type=abstract
American Astronomical Society, AAS Meeting #213, #412.15; Bulletin of the American Astronomical Society, Vol. 41, p.219
Astronomy and Astrophysics
Astronomy
Scientific paper
We compare high signal-to-noise Spitzer IRS spectra of the brightest regions of the reflection nebulae NGC 1333, NGC 7023, and NGC 2023. The data include Short Hi spectra (R 600) covering 10-20 um and Short Lo Spectra (R 80) covering 6-to-14 um. The spectra are dominated by the broad emission features attributed to Polycyclic Aromatic Hydrocarbons, or PAHs. The illuminating stars of these three nebulae range in type from B1.5 (T 22,000) to B8 (T 11,000), and the total projected starlight energy density at the observed position on the nebulae ranges from 10 to 1000 times the interstellar value. The ultraviolet flux varies by even more than this factor of 100 from one nebula to the next.
Notwithstanding the difference in stellar illumination, the spectra at the brightest positions are remarkably similar from one nebula to the next. A number of smaller features are seen in addition to the well-known PAH bands. When the spectra are normalized to the same total intensity, the shape of both the brighter and the fainter features agree to better than 10% amongst the three nebulae. This similarity applies both to the 6-to-14um low resolution and to the 10-to-20um high resolution spectra, including the newly identified complex of features in the 17um region. The constancy of the spectra amongst these three nebulae must hold clues to the character of the size distribution, ionization state and excitation of PAH molecules in the regions observed. In addition, we will discuss these results with reference to the known variations in the spectra of the aromatic features from nebula to nebula or with a given nebula.
Portions of the work were carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. J. Livingston was a Summer Undergraduate Research Fellow at JPL.
Livingston John
Sellgren Kris
Werner Michael W.
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