Identification of PAHs in Spitzer/IRS Spectra of the Icy Environments of YSOs: A Laboratory Study of PAHs embedded in H2O and D2O Ices

Details Identification of PAHs in Spitzer/IRS Spectra of the Icy Environments of YSOs: A Laboratory Study of PAHs embedded in H2O and D2O Ices Identification of PAHs in Spitzer/IRS Spectra of the Icy Environments of YSOs: A Laboratory Study of PAHs embedded in H2O and D2O Ices

Mar 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008sptz.prop50565g&link_type=abstract

Spitzer Proposal ID #50565

Mathematics

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Ices are the main reservoir of volatiles in dense clouds and the envelopes and disks surrounding Young Stellar Objects (YSOs). It is expected that the universally observed Polycyclic Hydrocarbon molecules (PAHs) freeze out on these ice grains. Laboratory experiments have shown that processing of these ices forms species of astrobiological interest. Spitzer/IRS spectra of over 40 YSOs have been analyzed to find several unassigned spectral features that may be due to PAHs embedded in H2O ices [Boogert et al. 2007]. However, lack of quantitative spectral data such as line widths, band shapes and absolute band depths for neutral and ionized PAHs in H2O ices hindered further identification. Recently we have shown that ionized PAHs are stable in astrophysical ices [Gudipati and Allamandola, 2004]. Bernstein et al. [2007] have measured spectra of neutral and ionized PAHs in H2O ices, covering only a narrow spectral region (7-10 microns), omitting the strong 6.2 and 11.3 micron bands essential to analyze the Spitzer/IRS spectra and the 3.3 micron band in complementary ground-based spectra. In order to quantify the PAH content, absolute band depths are needed, which were missing in this publication. We propose to extend the measurements of Bernstein et al. to derive quantitative laboratory mid-infrared (2.5-50 microns, including the Spitzer/IRS spectral range of 5?38 microns) data such as absolute line strengths, positions and widths of neutral and ionized PAHs in H2O and D2O ices. PAH spectra will be deconvolved from the ice-host spectra in the low-extinction regions of the H2O and D2O hosts. A range of PAH sizes will be used, one PAH at a time, embedded in the ice. The influence of CO2 on the PAH bands will also be quantified. These laboratory data will then be used to fit the unidentified features of already processed Spitzer/IRS data of icy mantles of over 40 YSOs and of spectra of background stars tracing quiescent cloud material covered in numerous legacy, GTO, and GO programs.

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