The Spitzer-IRS spectrum of SMP LMC 11

J. Bernard-Salas (Cornell), E. Peeters (NASA Ames) G.C. Sloan (Cornell), J. Cami (NASA Ames), S. Guiles (Cornell), J.R. Houck (Cornell)

2006, ApJ Letters, 652, L29

Full manuscript available from astro-ph (0603607) or locally: PDF or PS.

We present the first mid-infrared spectra of SMP LMC 11 in the Large Magellanic Cloud. While this object resembles a planetary nebula in the optical, its infrared properties are more similar to an object in transition from the asymptotic giant branch to the planetary nebula phase. A warm dust continuum dominates the infrared spectrum. The peak emission corresponds to a mean dust temperature of 330 K. The spectrum shows overlapping molecular absorption bands from 12 to 17 µm corresponding to acetylene and polyacetylenic chains and benzene. This is the first detection of C₄H₂, C₆H₂, C₆H₆, and other molecules in an extragalactic object. The infrared spectrum of SMP LMC 11 is similar in many ways to that of the pre-planetary nebula AFGL 618. The IRS spectrum shows little evidence of nitrogen-based molecules which are commonly seen in Galactic AGB stars. Polycyclic aromatic hydrocarbons are also absent from the spectrum. The detection of [Ne II] in the infrared and other forbidden emission lines in the optical indicates that an ionized region is present.

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Last modified 21 November, 2006. © Gregory C. Sloan and others.