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This presentation discusses the abundance analysis of sharp-lined B-type stars in three young clusters (NGC6611, N11, NGC346) and presents the selection criteria, analysis methods, results table, and plots of the findings. Conclusions and remaining issues are also discussed.
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Abundance analysis of sharp-lined B-type stars in three young clusters. Belfast June ’05 Ian Hunter Queen’s University of Belfast
Outline of Presentation • Selection Criteria • Analysis • Table of Results • Plots of Results • Conclusions and Remaining Issues
Selection Criteria • Young Clusters in the three galaxies • NGC6611 – Galaxy (5 stars?) • N11 – LMC (18+ stars) • NGC346 – SMC (15 stars)
137 136 105-205 157 153 137 183 NGC346 178 173 160-240 120-270 148 168 167 ~160
Selection Criteria • Spectral Type in range O9-B3 • Temperature limit of 35000 K • Sharp-lined spectra • vsini < 50 km/s in SMC • vsini < 100 km/s in LMC and Galactic
Selection Criteria • No apparent contamination from a binary object • Temperature Diagnostic • Si III/Si IV • Si II/Si III
Analysis • Velocity corrections • Velocities accurate to 5km/s • Equivalent width measurements • Overlap of Si III lines, EW’s accurate to 10 % • TLUSTY models used to derive atmospheric parameters and chemical compositions
Analysis - TLUSTY • Temperature • From 12000K to 35000K • Log g • From Eddington Limit to 4.50 dex
Analysis - TLUSTY • Microturbulence • 0, 5, 10, 20, 30 km/s • Metallicity • Gal, LMC, SMC, MCB • Abundances • Normal, +0.8, +0.4, -0.4, -0.8
Analysis – Effective Temperature • Si III/Si IV in majority of stars • Compares well (~1000K) with temperature from He II lines in the hottest stars although appears to be systematically higher • Si II/Si III in a few cool objects
Analysis – Surface Gravity • Estimated from Hd and Hg lines • Agreement usually better than 0.1 dex • Error of ~0.2 dex when error in Teff is included
Analysis- Microturbulence • Estimated from Si III triplet of lines • 4552, 4567, 4574 Å • Very sensitive to EW measurements • Uncertainty of 3 km/s • Affects strong lines more than weak lines • NGC6611 Si abundance changes by 0.4 dex when error in x is taken into account • Generally increases as surface gravity decreases
Analysis - Microturbulence • Microturbulence from O II lines • Using all O II lines • Greater than microturbulence from Si III lines • By up to 10 km/s in SMC cluster stars • By up to 20 km/s in Galactic cluster stars • Using a single O II multiplet • Not available for all stars, especially at low metallicity • Better agreement with Si microturbulence (~5 km/s)
Analysis – v sin i • Projected rotational velocity- v sin i • Estimated from the Si III triplet of lines • Agreement between the v sin i derived from each of the three lines was usually better than 5 km/s
Analysis - Abundances • Abundances • Estimated for the following species • C II, C III, N II, O II, Mg II, Si II, Si III & Si IV • Poor agreement between the abundance derived from the C II and C III lines • Problem with temperature or C III model ion? • C II abundance is fairly constant although there is some evidence for decreasing carbon abundance with increasing nitrogen abundance in the SMC
