A New Distance to the Virgo Cluster Galaxy M100 Using the Hubble Space Telescope
Session 24 -- The Distance Scale
Display presentation, Monday, 9, 1995, 9:20am - 6:30pm

## [24.03] A New Distance to the Virgo Cluster Galaxy M100 Using the Hubble Space Telescope

L.Ferrarese (JHU,STSCI), R.Hill (OCIW), W.L.Freedman (OCIW), B.F.Madore (IPAC), J.R.Mould (MSSSO), R.C.Kennicutt (U.Arizona), A.Saha (STSCI), P.B.Stetson (DAO/HIA/NRC), J.A.Graham (CIW), H.C.Ford (STSCI,JHU), J.G.Hoessel (U.Wisc.), J.Huchra (Harvard,CfA), S.M.Hughes (GRO), G.D.Illingworth (UCSC)

We have obtained Hubble Space Telescope (HST) images of the Virgo galaxy M100 to identify and measure Cepheid variables, and employ the Cepheid Period-Luminosity relation to determine a primary distance to this galaxy. The observations are part of the HST Key Project on the Extragalactic Distance Scale, which aims to provide an absolute calibration for a number of secondary distance indicators (including, for example, the Tully-Fisher relation and the Expanding Photosphere Method) by measuring Cepheid distances to approximately 20 galaxies within a redshift of $\sim$ 1500 km s$^{-1}$.

A total of 25 $V$ band and 9 $I$ band exposures of M100 were obtained at 12 $V$ and 4 $I$ epochs, using the Wide Field and Planetary Camera 2 in the first half of 1994, spanning a time interval of approximately 2 months. ALLFRAME (Stetson 1993) and a variant of DoPHOT (Schechter et al 1993) were used independently to perform the photometric reduction of the frames. Approximately 60 Cepheids have been found so far, from which a preliminary distance to M100 of 17.1 $\pm$ 1.8 Mpc is derived (Freedman et al, 1994, Ferrarese et al. 1995). This distance is in good agreement with the distance calculated using the Tully-Fisher relation (Pierce and Tully 1988), and with the distance inferred from SN1979C by applying the Expanding Photosphere Method (Schmidt, Kirshner, Eastman 1992).