The Unusual Spitzer Spectrum of the Carbon Star IRAS 04496-6958: A Different Condensation Sequence in the LMC?
Speck, Angela K.; Cami, Jan; Markwick-Kemper, Ciska; Leisenring, Jarron; Szczerba, Ryszard; Dijkstra, Catharinus; Van Dyk, Schuyler; Meixner, Margaret,
2006, ApJ, 650, 892
Abstract:
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We present a new Spitzer Infrared Spectrograph (IRS) spectrum of the carbon star IRAS 04496-6958 in the Large Magellanic Cloud, which exhibits a fairly broad absorption feature at ~11 μm. This feature is consistent with SiC absorption, as seen in a few Galactic sources. Furthermore, the C2H2 (and other molecular) absorption bands are the deepest ever observed, indicative of a very high column density. While the Galactic sources with SiC absorption have cool colors (continuum temperature ~300 K), IRAS 04496-6958 is much bluer, with a continuum temperature of ~600 K. Based on the Galactic sample, SiC dust at this temperature should still display an emission feature at ~11 μm. If SiC is the cause of the absorption feature, it suggests a subtly different evolutionary path and a change to a different condensation sequence than assumed for Galactic carbon stars. An alternative explanation for this feature is molecular line absorption; however, currently available line lists are not sufficient to properly assess this hypothesis.
PDF version of this paper is available:
Speck_etal_06.pdf
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