  Red (S > 10%/0.1 micron) spectral slopes are common among Centaurs and
trans-Neptunian objects (TNOs) in the outer solar system. Interior to and
co-orbital with Jupiter, the red (S approx. = 10%/0.1 micron) slopes of D-type
main-belt and Jupiter Trojan asteroids are thought to reflect their
hypothesized shared origin with TNOs beyond the orbit of Jupiter. In order to
quantify the abundance of red-sloped asteroids within the main belt, we
conducted a survey using the NASA Infrared Telescope Facility and the Lowell
Discovery Telescope. We followed up on 32 candidate red objects identified via
spectrophotometry from the Sloan Digital Sky Survey's Moving Object Catalog to
confirm their steep spectral slopes and determine their taxonomic
classifications. We find that our criteria for identifying candidate red
objects from the Moving Object Catalog result in an approx. 50% confirmation
rate for steeply red-sloped asteroids. We also compare our observations of
main-belt asteroids to existing literature spectra of the Jupiter Trojans and
steeply red-sloped main-belt asteroids. We show that some red-sloped asteroids
have linearly increasing reflectance with increasing wavelength, while other
red-sloped asteroids show a flattening in slope at longer near-infrared
wavelengths, indicating a diversity among the population of spectrally red
main-belt asteroids suggestive of a variety of origins among the population of
steep-sloped asteroids.
