Protostars in the Elephant Trunk Nebula

Abstract

The optically dark globule IC 1396A is revealed using Spitzer Space Telescope images at 3.6, 4.5, 5.8, 8, and 24 μm to be infrared-bright and to contain a set of previously unknown protostars. The mid-infrared colors of the 24 μm detected sources indicate several very young (Class I or 0) protostars and a dozen Class II stars. Three of the new sources (IC 1396A:γ, 1396A:δ, and 1396A:ε) emit over 90% of their bolometric luminosities at wavelengths greater than 3 μm, and they are located within ~0.02 pc of the ionization front at the edge of the globule. Many of the sources have spectra that are still rising at 24 μm. The two previously known young stars LkHα 349a and 349c are both detected, with component c harboring a massive disk and component a being bare. On the order of 5% of the mass of material in the globule is presently in the form of protostars in the 10^5-10^6 yr age range. This high star formation rate was likely triggered by radiation from a nearby O star.

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