First Hubble Space Telescope Observations of the Brightest Stars in the Virgo Galaxy

As part of both the Early Release Observations from the Hubble Space Telescope and the Key ProjeCt on the Extragalactic Distance Scale, we have obtained multiwavelength BVR WFPC2 images for the face-on Virgo cluster spiral galaxy M100 = NGC 4321. We report here preliminary results from those observations, in the form of a color-magnitude diagram for -11,500 stars down to V 27 mag and a luminosity function for the brightest blue stars which is found to have a slope of 0.7, in excellent agreement with previous results obtained for significantly nearer galaxies. With the increased resolution now available using WFPC2, the number of galaxies in which we can directly measure Population I stars and thereby quantify the recent evolution, as well as test stellar evolution theory, has dramatically increased by at least a factor of 100. Finally, we find that stars are present in M100 at the colors and luminosities expected for the brightest Cepheid variables in galaxies. Subject headings: galaxies: distances and redshiftsgalaxies: individual (M100, NGC 4321)Cepheidsstars: early type