J/ApJ/438/181ivo://CDS.VizieR/J/ApJ/438/181doi:10.26093/cds/vizier.14380181CDSHill J.K.Cheng K.-P.Bohlin R.C.Cornett R.H.Hintzen P.M.N.,Robert M.S.O'Connell R.W.Roberts M.S.,Smith A.M.Smith E.P.,Stecher T.P.1997-12-09T19:51:33Z1997-12-09T20:51:30ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frh-ii-regionsultraviolet-astronomyImages 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.1995ApJ...438..181Hhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/438/181CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/438/181https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/438/181http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/438/181https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/438/181https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/438/181http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/438/181GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapUVdefaultJ/ApJ/438/181/table2M81 H II region photometryrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintPSK*H II region number from PSKmeta.id;meta.mainintm152Far-UV magnitudemagphot.mag;em.UV.100-200nmfloate_m152Estimated error in m152magstat.errorfloatm249Near-UV magnitudemagphot.mag;em.UV.200-300nmfloate_m249Estimated error in m249magstat.errorfloatfHaH-alpha flux1e-14mW.m**-2phot.fluxfloate_fHaEstimated fractional error in fHa1e-14mW.m**-2stat.errorfloatfHb*[]? H-beta flux1e-14mW.m**-2phot.fluxfloate_fHb*[]? Estimated fractional error in fHb1e-14mW.m**-2stat.errorfloat