Astronomy and Astrophysics – Astronomy
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...210.1506w&link_type=abstract
American Astronomical Society Meeting 210, #15.06; Bulletin of the American Astronomical Society, Vol. 39, p.113
Astronomy and Astrophysics
Astronomy
Scientific paper
We report the first measurement of [Zn IV] 3.625 microns in an extragalactic planetary nebula, SMP 62 in the Large Magellanic Cloud, obtained with GNIRS on Gemini South. This fine-structure line was first identified in two bright Galactic planetary nebulae by Dinerstein & Geballe (2001, ApJ, 562, 515), but until recently its emissivity was not known. Using a collision strength calculated by K. Butler (2007, in preparation), the flux of [Zn IV] relative to nearby H I lines can be used to derive the ionic abundance ratio n(Zn+3)/n(H+) for SMP 62. After correcting for ionization structure, we find an elemental abundance n(Zn)/n(H) = 5.7 x 10-9, about 14% of the solar value, or [Zn/H] = -0.85. Since Zn is relatively unaffected by depletion into dust and is known empirically to track Fe closely in stars of metallicities down to [Fe/H] < -2, we assume that the zinc abundance of SMP 62 is a reliable indicator of the Fe-group element abundances in its progenitor star. Comparing to the abundances of O, Ne, S, and Ar in SMP 62, which are approximately 1/3 solar (Leisy & Dennefeld 2006, A&A, 456, 415), we find [alpha/Fe] +0.3. The [alpha/Fe] ratio is of interest because it potentially provides a diagnostic of the star formation history and relative contributions of massive-star supernovae (which produce most of the alpha elements) vs. Type Ia supernovae (which are more dominant for the Fe-group elements) to the chemical composition of a stellar population. Our study illustrates a novel approach for investigating chemical evolutionary histories, via observations of planetary nebulae associated with a given stellar population.
This research was supported by NSF grant AST 04-06809.
Dinerstein Harriet L.
Geballe Thomas Ronald
Wood Jessica L.
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