$I$-Band CCD Surface Photometry and a Total Magnitude for M31
Session 48 -- Spiral, Dwarf and Irregular Galaxies
Display presentation, Wednesday, 1, 1994, 9:20-6:30

## [48.07] $I$-Band CCD Surface Photometry and a Total Magnitude for M31

P. Guhathakurta (STScI), S. Raychaudhury (SAO), A. Berlind (Princeton U)

We present accurate $I$-band surface photometry of the nearby spiral galaxy M31. A $4^\circ\times3^\circ$ image of this galaxy, at $2''$ resolution, has been constructed by mosaicking together 41 $2048\times2048$ CCD frames obtained using the KPNO/CWRU Burrell Schmidt telescope. The individual CCD frames have an unvignetted, circular field of view of $\sim1^\circ$ diameter; generous overlap between the 41 CCD frames allows them to be matched to one another with a high degree of accuracy. The distinctive features of our dataset are: (1) the wide angular extent of the image makes accurate determination of the sky'' background possible; and (2) the relatively high angular resolution ($2''$) enables identification and removal of bright foreground stars. By measuring the total magnitude of M31, we are able to calibrate the $I$-band Tully-Fisher relation for spiral galaxies in the Coma supercluster, and thereby estimate the value of the Hubble constant ($H_0$).