AAS 207th Meeting, 8-12 January 2006
Session 175 Recent Discoveries in the Far UV
Poster, Thursday, 9:20am-4:00pm, January 12, 2006, Exhibit Hall

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[175.09] The Abundances of the Fe Group Elements in Three Early B Stars in the Large Magellanic Cloud

G. J. Peters (University of Southern California), S. J. Adelman (The Citadel)

The photospheric abundances of V, Cr, and Fe have been determined for three sharp-lined early B stars in the Large Magellanic Cloud using FUV spectra obtained from the Far Ultraviolet Spectroscopic Explorer (FUSE) and the Kurucz LTE model atmosphere/spectrum synthesis codes ATLAS9/SYNTHE. The program stars include NGC1818/D1, NGC2004/B15, and NGC2004/B30 (star designations are from Robertson 1974, A&AS, 15, 261). The calculations were carried through with model parameters close to those adopted by Korn et al. (2000, A&A, 353, 655). Values of \rm Teff, log~g, \rm \xiT, and v~sin~I are 25000/4.0/0/30, 20000/3.1/6/25, and 23500/3.3/14/30 for NGC1818/D1, NGC2004/B15, and NGC2004/B30, respectively. The abundances quoted below are in sequence for the latter stars. The vanadium abundances, [V/H], determined from V~III \lambda\lambda1150,1152 (UV~2), are -0.6, -0.9, and -0.9 dex. Cr was determined from Cr~III \lambda\lambda1118,1136. Values of -0.5, -0.8, and -0.7 dex were found. Uncertainties in the V and Cr abundances are ~0.3 dex. The Fe abundance is primarily from 7 lines of Fe~III (UV~1) in the region \lambda\lambda1122-32. Values are -0.8±0.3, ~-1.1, and -0.4±0.3. Since there is no evidence for N enhancement in the program stars ([N/H] ~ -0.9, -1.0, and -0.6 from the N~III doublet at 1183,1184~Å) the photospheric abundances have probably not been altered by mixing of processed material from the star's interior and the derived abundances represent pristine values for the two young clusters in the LMC. It should be noted that the N and Fe abundances derived for NGC1818/D1 are about 0.5 dex lower than those determined by Korn et al. from much weaker optical lines. We will discuss possible reasons for the discrepancy. The generally low abundances for the Fe group elements in these young cluster B stars imply that supernova activity has been minimal in the regions of the LMC in which the stars were formed. GJP appreciates support from NASA grant NAG5-13212.

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