K-Band Spectroscopy of the Extragalactic Planetary Nebula Hen 2-436
Abstract
We present a 2.115 to 2.300 micron spectrum of the extragalactic planetary nebula Hen 2-436, obtained with GNIRS on Gemini South at a resolution of R = 5900. This object has been identified as a member of the Sagittarius dwarf elliptical galaxy, which is being tidally disrupted by the Milky Way, on the basis of its radial velocity and overall metallicity of roughly 0.3 solar (Walsh et al. 1997, ApJ, 487, 651). In addition to H I Brackett gamma, two He I lines, H2 1-0 S(1) 2.121 and 1-0 S(0) 2.223 microns, we detect two lines of trans-iron elements: [Kr III] 2.199 and [Se IV] 2.287 microns (Dinerstein 2001, ApJ, 550, L223). These elements can be self-enriched in the envelopes of thermally-pulsing AGB stars, the progenitors of planetary nebulae, by s-process nucleosynthesis in the H-He intershell region, followed by convective dredge-up. Using ionization correction procedures developed by Sterling, Dinerstein, & Kallman (2006, ApJ, submitted), we find a Se/H abundance of about twice solar, and a Kr/H value of several times solar. Due to the subsolar initial abundances of the progenitor star, the actual Se and Kr enrichment factors are greater than 5 and 10, respectively. These large enrichments are consistent with other evidence that the progenitor star of Hen 2-436 underwent extensive third dredge-up (Dudziak et al. 2000, A&A, 363, 717; Pequignot et al. 2000, A&A, 361, L1). These measurements represent the first detection of s-process enrichments in a planetary nebula from a low-metallicity progenitor. Further observations of planetary nebulae in diverse stellar populations will enable us to study the relationship between s-process enrichment and metallicity. This research was supported by NSF grant AST 04-06809.
- Publication:
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American Astronomical Society Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AAS...20915607W