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An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| The Peak Brightness of Supernovae in the U Band and the Hubble Constant
The peak magnitudes of Type I supernovae in the U band can be used toanswer various questions relating to supernovae and the Hubble constant:(1) Well-observed normal Type Ia supernovae are placed in a color-colordiagram along the extinction line of (B - V) = 1.25(U - B) + 0.15 with ascatter of 0.1 mag in each color. (2) The peak B - V colors measured atthe Asiago Observatory are far from this relation, hence supporting theearlier conclusions that these data are unreliable. (3) The intrinsic B- V at B peak of normal Type Ia events is 0.00 +/- 0.04 or perhapsslightly redder, hence implying that these are good standard candles.(4) The dereddened absolute magnitude in the U band at the time of Bpeak is -18.88 +/- 0.15 for H0 = 75. (5) The U- and H-band light curvesof SN 1972E yield low values for the Hubble constant.
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