THE ASTROPHYSICAL JOURNAL, 413:604-610, 1993, August 20

            30 DORADUS: ULTRAVIOLET AND OPTICAL STELLAR PHOTOMETRY

        JESSE K. HILL [1], RALPH C. BOHLIN [2], KWANG-PING CHENG [3,4],
    MICHAEL N. FANELLI [3], PAUL HINTZEN [5,4,6], ROBERT W. O'CONNELL [7],
     MORTON S. ROBERTS [8], ANDREW M. SMITH [5], ERIC P. SMITH [5,4], AND
                            THEODORE P. STECHER [5]


                                   ABSTRACT

      Stellar photometry is presented for 314 stars in a 9.7 x 9.7 arcmin
    field in the 30 Dor nebula centered on R136.  Magnitudes are computed
    from Ultraviolet Imaging Telescope images in up to 4 bands with
    effective wavelengths 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 +/- 0.02, 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.


    Subject headings:  dust, extinction -- ISM: individual (30 Doradus) --
                       Magellanic Clouds -- techniques: photometric --
                       ultraviolet: stars


1 Hughes STX, 4400 Forbes Blvd., Lanham, MD, 20706.
2 Space Telescope Science Institute, Homewood Campus, Baltimore MD, 21218.
3 NRC Postdoctoral Fellow, NASA/GSFC, Greenbelt, MD 20771.
4 Visiting Astronomer at the Kitt Peak National Observatory of the NOAO operated
  by AURA, Inc., under contract to the NSF.
5 Laboratory for Astronomy and Solar Physics, NASA/GSFC, Greenbelt, MD 20771
6 Department of Physics and Astronomy, California State University, Long Beach,
  CA 90840.
7 University of Virginia, P.O. Box 3818, Charlottesville, VA 22903.
8 National Radio Astronomy Observatory, Operated by Associated Universities Inc.
  under cooperative agreement with the NSF, Edgemont Rd., Charlottesville, VA
  22903