The SN 1006 remnant: Optical proper motions, deep imaging, distance, and brightness at maximum

We report the first measurement of proper motions in the SN 1006 remnant (G327.6+14. 6) based entirely on digital images. CCD images from three epochs spanning a period of 11 yr are used: 1987 from Las Campanas and 1991 and 1998 from Cerro Tololo Inter-American Observatory. The laments in SN 1006 are nonradiative, appearing only in the Balmer lines of hydrogen. Delicate laments probably thin sheets seen in projection delineate the shock front along the northwestern rim of the remnant. We use the center of curvature of the laments to de ne a convenient geometry and integrate along short segments to obtain one-dimensional profiles. These remain unchanged, within seeing and statistical errors, from one epoch to another. Measuring the shift in a direction perpendicular to the laments, we obtain proper motions of 280+/-8 mas yr(-1) along the entire length where the laments are well defined, with little systematic variation along the laments. In addition to the measurements of the well-defined laments in the northwest of SN 1006, we also report very deep Halpha imaging observations of the entire remnant that clearly show very faint emission surrounding almost the entire shell, as well as some diffuse emission regions in the ( projected) interior. Combining the proper-motion measurement with a recent measurement of the shock velocity based on spectra of the same laments by Ghavamian et al. leads to a distance of 2.18+/-0.08 kpc to SN 1006. Several lines of argument suggest that SN 1006 was a Type Ia event, so the improved distance measurement can be combined with the peak luminosity for SNe Ia, as recently determined for events in galaxies with Cepheid-based distances, to calculate the apparent brightness of the spectacular event that drew wide attention in the 11th century. The result, V-max = -7.5+/-0.4, lies squarely in the middle of the wide range of estimates based on the historical observations.