Observations of Post-Asymptotic Giant Branch Objects in the Magellanic Clouds with the Spitzer Infrared Spectrograph

Details Observations of Post-Asymptotic Giant Branch Objects in the Magellanic Clouds with the Spitzer Infrared Spectrograph Observations of Post-Asymptotic Giant Branch Objects in the Magellanic Clouds with the Spitzer Infrared Spectrograph

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...20910102k&link_type=abstract

2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #101.02; Bulletin of the American Astronomical Society,

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We present mid-infrared spectra of two sources in the Magellanic Clouds observed with the Spitzer Infrared Spectrograph (IRS). The spectrum of the object in the Small Magellanic Cloud (SMC), MSX SMC 029, is dominated by a cool dust continuum with an unusual set of spectral features. The IRS data reveal both emission from polycyclic aromatic hydrocarbons (PAHs) and absorption at 13.7 micron from C2H2. This rare combination has been seen in only two other sources, AFGL 2688 and IRAS 13416-6243, both post-asymptotic giant branch (AGB) objects. As in these sources, the PAH spectrum has the unusual traits that the emission peak in the 7-9 micron complex lies beyond 8.0 micron and that the 8.6 micron feature is as strong as the C-C modes that ought to peak 7.7-7.9 micron. The spectrum of the object in the Large Magellanic Cloud, SMP LMC 11, is dominated by absorption features from acetylene, benzene, and polyactylenic chains, many of which are detected in an extragalactic object for the first time. The IRS spectrum from SMP LMC 11 is similar to the infrared spectrum of the post-AGB object AFGL 618. While the optical properties of this object resemble those of a planetary nebula (PN), the infrared spectrum is more consistent with an object in transition from the AGB to PN. Comparisons between MSX SMC 029, SMP LMC 11, AFGL 2688, and AFGL 618 lead us to conclude that MSX SMC 029 is also a very young post-AGB object, probably having evolved off the AGB in only the past few hundred years. As such, MSX SMC 029 is only the 3rd post-AGB object identified in the SMC.
This work is based on observations made with Spitzer, operated by JPL/Caltech under a NASA contract. Support was provided by NASA in part through an award issued by JPL/Caltech.

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