The Abundances of Carbon and Nitrogen in the Be Star NGC330-B12 in the Small Magellanic Cloud
FUSE Cycle 7 GI Program G076
PI: Geraldine Peters (University of Southern California)
CoIs: Saul Adelman (The Citadel), David McDavid (University of Virginia)
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Abstract We propose a FUSE observation of the Be star B12 in NGC 330 in the Small Magellanic Cloud to determine the abundances of carbon and nitrogen in its photosphere. During the past two decades there has been a consensus that the rotation rates in Be stars are rapid but far short of their critical values (0.50 < V/Vcr < 0.85). But recently there has been a renewed interest in the possibility that Be stars are critical rotators (Townsend, Owocki, & Howarth 2004). Abundance studies can provide a test for the latter hypothesis, as stellar evolution modeling by Meynet & Maeder (2000) has predicted a significant enhancement in the photospheric N abundances in very rapidly rotating OB stars due to mixing of CNO processed material from their interiors. The FUV is the best spectral region for determining CN abundances in Be stars as the strongest lines of C II, III and N II, III fall in this region and the flux contribution from the disk is not important. The Be star B12 in NGC 330 is ideal for an abundance analysis as it has relatively sharp lines. A recent abundance study from optical data (Lennon et al. 2005) suggested a low N abundance, but the result was inconclusive as it was based upon only one very weak line. The low N abundance in the SMC renders it an ideal environment in which to look for altered abundances due to rotational mixing. We also propose an observation of a well-known, sharp-lined non-emission B star in NGC 330 (B30) in order to be able to compare the CN abundances in NGC330-B12 with a benchmark value for the cluster.
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![[IMAGE: NGC330 Finding Chart B12, B30]](ngc330_ft1.png)