  We investigate the stellar kinematics and line strength indices in the outer
halos of brightest cluster galaxies (BCGs) in the Coma cluster to obtain the
outer halo V_rot and sigma profiles and to derive constraints on the formation
history of these objects. Methods: We analyzed absorption lines in deep,
medium-resolution, long-slit spectra in the wavelength range ~ 4500 - 5900
Angstrom, out to ~50 kpc for NGC 4874 and ~65 kpc for NGC 4889, probing regions
with a surface brightness down to mu_R ~24 mag/arcsec^2. Results: These data
provide stellar velocity and velocity dispersion profiles along the major axes
of both BCGs, and also along the minor axis of NGC 4889. The kinematic
properties of NGC 4874 and NGC 4889 halos extend the previous relations of
early-type galaxy halos to bright luminosities and indicate that the stars in
the outer regions are still bound to these galaxies. For NGC 4889 we also
determine Hbeta, Mg and Fe line strength indices, finding strong radial
gradients for Mg and Fe. The current dataset for NGC 4889 is one of the most
extended in radius, including both stellar kinematics AND line strength index
measurements.
