30-DORADUS - ULTRAVIOLET AND OPTICAL STELLAR PHOTOMETRY

Stellar photometry is presented for 314 stars in a 97 x 9.7 field in the 30 Dor nebula centered on R136. Magnitudes are computed from Ultraviolet Imaging Telescope images in up to 4 bands with effective wave-lengths from 1615 to 2558 A, and from a ground-based CCD image in the B band. Spectral types and extinctions are estimated using a least-squares technique, based on a spectrophotometric library compiled from IUE spectra. The fit spectral types agree to one library spectral type bin and two luminosity classes with types determined from optical slit spectra, for 34 of 39 non-WR stars. Approximately 35% of the 314 stars are fitted to main-sequence spectral types earlier than B1. Extinction of the more reddened stars in 30 Dor is shown to follow the Fitzpatrick 30 Dor extinction curve combined with a nebular curve of Fitzpatrick and Savage, where E(B-V) for each component is determined by the least-squares fit. Assuming a foreground extinction of E(B-V) = 0.10, average values of the color excess internal to 30 Dor are E(B-V)F = 0.11 +/- 0.03, from the Fitzpatrick 30 Dor extinction curve component, and E(B-V)FS = 0.17 +/- 0.17 from the Fitzpatrick and Savage nebular extinction curve component. Most stars within the high surface brightness area centered near R136 have low nebular extinction [E(B-V)FS < 0.03], while stars outside this area typically have E(B-V)FS < 0.30. Dust grains following the nebular extinction curve may have been expelled from the central regions of 30 Dor by stellar winds, or stars in the outer regions may be behind or within dust clouds. We also suggest that the difference between the Galactic extinction curve and the Fitzpatrick 30 Dor extinction curve may result from the lower cumulative nucleosynthesis in the LMC and the long time necessary for the component producing the local maximum at 2200 A (presumably carbon) to reach the interstellar medium in the form of grains.