CDROM/APJ/V438/P181 Observations of H II Regions in M81 (Hill+ 1995) ================================================================================ Ultraviolet Imaging Telescope and Optical Emission-Line Observations of H II Regions in M81 Jesse K. Hill, K.-P. Cheng, Ralph C. Bohlin, Robert H. Cornett, P. M. N. Hintzen, Robert W. O'Connell, Morton S. Roberts, Andrew M. Smith, Eric P. Smith, And Theodore P. Stecher <1995, ApJ, 438, 181> =1995ApJ...438..181H ================================================================================ 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 (1988, A&AS, 74, 475). 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 1.4 x 10^5 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 (1983, ApJ, 272, 54) and Caldwell et al. (1991, ApJ, 370, 526) for early-type spirals. Keywords: dust, extinction -- galaxies: individual (M81) -- galaxies: stellar content -- H II regions -- ultraviolet: galaxies File Summary: -------------------------------------------------------------------------------- File Name Lrecl Records Explanations -------------------------------------------------------------------------------- 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 -------------------------------------------------------------------------------- Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 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 -------------------------------------------------------------------------------- Notes for file: table2.dat -------------------------------------------------------------------------------- PSK: H II region number from Petit, Sivan, & Karachentsev 1988, A&AS, 74, 475 (PSK). 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. -------------------------------------------------------------------------------- ================================================================================ (End) Lee Brotzman [ADS] 06-May-1995