GRAVITATIONAL LENS MODELS OF ARCS IN ABELL-2218

Abell 2218, with redshift z = 0.17, is one of the first clusters in wh ich gravitationally lensed arcs have been found. Abell 2218 contains s everal arcs, and although none are as large as some of the more studie d arcs (Abell 370, Cl 2244-02), they are interesting nonetheless. We p resent photometric and spectroscopic data of the cluster taken at the NOAO 4 m telescope. We show broadband spectra of some of the more inte resting objects in the field. One are in the cluster is redder than a typical galaxy, which is unusual since most lensed arcs have a bluer c olor. The spectrum of this are reveals a redshift of 0.703. There is a n almost perfectly circular blue ring surrounding one galaxy. There ar e several other blue arclets including two, called the twin arcs, that are on either side of two close galaxies. We model the system with a simple mass distribution consisting of the visible galaxies and a diff use dark matter component. We are able to model the red are and the tw in arcs, but we find that the ring is most likely not a gravitationall y lensed image. Combining this with the observed velocity dispersion o f galaxies, we set limits on the masses of some of the galaxies and on the parameters describing the distribution of dark matter. We compare the distributions with the X-ray surface brightness variation of the, cluster and find that the dark matter component for the lensing models is more compact than the X-ray distribution. We shall discuss this in a future publication.