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G. Gupta, P.F. Winkler (Middlebury Coll.), K.S. Long (STScI)
We report the first measurement of proper motions in the SN~1006 remnant based entirely on digital images. CCD images from three epochs spanning a period of 11 years are used: 1987 from Las Campanas, and 1991 and 1998 from CTIO. The filaments in SN~1006 are non-radiative, appearing only in the Balmer lines of hydrogen. Delicate filaments---probably thin sheets seen in projection---delineate the shock front along the northwest rim of the remnant. We use the center of curvature of the filaments to define 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 filaments, we obtain a proper motions of 0.28 arcsec year-1\ along the entire length where the filaments are well defined.
Since Balmer filaments occur only at the leading edge of the primary shock moving through tenuous material, these proper motions indicate the outward motion of the shock itself. The H\alpha\ line has a broad component whose width indicates the shock velocity, which can be combined with the proper motions to give a geometry-based distance. We will present new measurements of the line profile and discuss the implications for the distance to SN~1006.
This research has been supported by the NSF through grant AST-9618465.
The author(s) of this abstract have provided an email address for comments about the abstract: gupta@middlebury.edu