Surface Photometry and Radial Color Gradients of Nearby Luminous
  Early-type Galaxies in SDSS Stripe 82
  We make use of the images from the Sloan Digital Sky Survey Stripe 82 to
present an analysis of r band surface brightness profiles and radial color
gradients (g - r, u - r) in 111 nearby early-type galaxies (ETGs). With Stripe
82 images, we are able to pay special attentions to the low-surface-brightness
areas (LSB areas) of the galaxies. The LSB areas make a difference to the
Sersic fittings and concentration indices, making both the indices less than
the typical values for ETGs. There are about 60% negative color gradients
(red-core) within 1.5Re , much more than the approximately 10% positive ones
(blue-core) within the same radius. However, taking into account of the LSB
areas, we find that the color gradients are not necessarily monotonic: about
one third of the red-core (or blue-core) galaxies have positive (or negative)
color gradients in the outer areas. So LSB areas not only make ETGs' Sersic
profiles deviate from de Vaucouleur ones and shift to the disk end, but also
reveal that quite a number of ETGs have opposite color gradients in inner and
outer areas. These outcomes remind us the necessity of double-Sersic fitting.
These LSB phenomena may be interpreted by mergers and thus different
metallicity in the outer areas. Isophotal parameters are also discussed briefly
in this paper: more disky nearby ETGs are spotted than boxy ones.
