  In this paper, we report on our analysis using Hubble Space Telescope
astrometry and Keck-I HIRES spectroscopy of the central six stars of Tycho's
supernova remnant (SN 1572). With these data, we measured the proper motions,
radial velocities, rotational velocities, and chemical abundances of these
objects. Regarding the chemical abundances, we do not confirm the unusu- ally
high [Ni/Fe] ratio previously reported for Tycho-G. Rather, we find that for
all metrics in all stars, none exhibit the characteristics expected from
traditional SN Ia single-degenerate-scenario calculations. The only possible
exception is Tycho-B, a rare, metal-poor A-type star; however, we are unable to
find a suitable scenario for it. Thus, we suggest that SN 1572 cannot be
explained by the standard single-degenerate model.
