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J/ApJ/438/181                Observations of H II Regions in M81 (Hill+ 1995)
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Ultraviolet Imaging Telescope and Optical Emission-Line Observations of H II
Regions in M81
     Hill J.K., Cheng K.-P., Bohlin R.C., Cornett R.H., Hintzen P.M.N.,
     O'Connell R.W., Roberts M.S., Smith A.M., Smith E.P.,
     Stecher T.P.
    <Astrophys. J. 438, 181 (1995)>
    =1995ApJ...438..181H
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ADC_Keywords: H II regions ; Ultraviolet
Keywords: dust, extinction - galaxies: individual (M81) -
          galaxies: stellar content - H II regions - ultraviolet: galaxies

Abstract:
    Images of the type Sab spiral galaxy M81 were obtained in far-UV and
    near-UV bands by the Ultraviolet Imaging Telescope (UIT) during the
    Astro-1 Spacelab mission of 1990 December. Magnitudes in the two UV
    bands are determined for 52 H II regions from the catalog of Petit,
    Sivan, & Karachentsev (1988A&AS...74..475P). Fluxes of the H-alpha and
    H-beta emission lines are determined from CCD images. Extinctions for
    the brightest H II regions are determined from observed Balmer
    decrements. Fainter H II regions are assigned the average of published
    radio-H-alpha extinctions for several bright H II regions. The
    radiative transfer models of Witt, Thronson, & Capuano (1992, ApJ,
    393, 611) are shown to predict a relationship between Balmer Decrement
    and H-alpha extinction consistent with observed line and radio fluxes
    for the brightest 7 H II regions and are used to estimate the UV
    extinction. Ratios of Lyman continuum flux (computed from the
    extinction corrected H-alpha flux) to the extinction corrected far-UV
    flux are compared with ratios predicted by model spectra computed for
    IMF slope equal to -1.0 and stellar masses ranging from 5 to 120 Msun.
    Ages and masses are estimated by comparing the H-alpha and far-UV
    fluxes and their ratio with the models. The total of the estimated
    stellar masses for the 52 H II regions is 1.4x10^5^ Msun. The
    star-formation rate inferred for M81 from the observed UV and H-alpha
    fluxes is low for a spiral galaxy at ~0.13 Msun/yr, but consistent
    with the low star-formation rates obtained by Kennicutt
    (1983ApJ...272...54K) and Caldwell et al. (1991ApJ...370..526C) for
    early-type spirals.

File Summary:
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 FileName    Lrecl    Records    Explanations
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ReadMe          80          .    This file
table2.dat      47         52    M81 H II region photometry
table2.tex      71        109    LaTeX version of Table 2
aastab.sty      72        115    Modified AAS table style file
environ.tex     77        125    Custom LaTeX environments and related macros
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Byte-by-byte Description of file: table2.dat
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   Bytes Format  Units       Label    Explanations
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   1- 3   I3     ---         PSK     *H II region number from PSK
   4- 9   F6.2   mag         m152     Far-UV magnitude
  10-14   F5.2   mag         e_m152   Estimated error in m152
  15-20   F6.2   mag         m249     Near-UV magnitude
  21-25   F5.2   mag         e_m249   Estimated error in m249
  26-31   F6.2   10-14mW/m2  fHa      H-alpha flux
  32-36   F5.2   10-14mW/m2  e_fHa    Estimated fractional error in fHa
  37-42   F6.2   10-14mW/m2  fHb     *[]?=0.0 H-beta flux
  43-47   F5.2   10-14mW/m2  e_fHb   *[]?=0.0 Estimated fractional error in fHb
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Note on PSK:
  H II region number from Petit, Sivan, & Karachentsev (1988A&AS...74..475P)
Note on fHb, e_fHb:
  For 11 H II regions not measurable in the H-beta line, the H-beta
  fluxes and the corresponding errors are both set to 0.0.
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Origin: AAS CD-ROM series, Volume 4, 1995         Lee Brotzman [ADS] 06-May-1995
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(End)                                                         [CDS]  11-Jul-1995