The H$_0$ Key Project: The Stellar Content of M81

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Session 5 -- Cosmology and Gravitational Lenses
Display presentation, Monday, 9:20-6:30, Heller Lounge Room

[5.02] The H$_0$ Key Project: The Stellar Content of M81

A. Turner, R.C. Kennicutt (U. Arizona), S.M.G. Hughes, J.R. Mould, B.F. Madore (Caltech), S.M. Faber, G.D. Illingworth (U.C.S.C.), W.L. Freedman, M.G. Lee, R. Hill (O.C.I.W.), L. Ferrarese, H.C. Ford (J.H.U.), J.A. Graham (D.T.M.), J.E. Gunn (Princeton), J.G. Hoessel (U. Wisconsin), J.P. Huchra (CfA), P.B. Stetson (DAO)

As part of the Hubble Space Telescope H$_0$ Key Project, two Cepheid variable search fields in M81 were imaged with the Wide Field Camera (WFC), for a total of 400 minutes each in V and 180 minutes each in I during Cycles 1 and 2. These observations provide some of the deepest exposures obtained with HST on the resolved stellar populations in a nearby galaxy, as a byproduct of the Cepheid program. Co-added WFC V and I images will be presented for a field located along the NE major axis of M81. Despite the spherical aberration stars are detected to V$>$26. We have used the ALLFRAME PSF-fitting photometry (reported in a companion poster by Hughes et al.) to analyze the V and I luminosity functions and the I vs V-I color-magnitude (CMD) diagram of this field. For I$<$24, where the photometry is most reliable, the CMD is dominated by blue and red supergiants. The overall CMD morphology closely resembles that of the disk of M33, which is consistent with the location of this field in an active star forming spiral arm of M81. The field contains several of the largest giant HII regions and OB associations in M81, and these associations and clusters are well resolved in the WFC data.

Monday program listing