http://arxiv.org/abs/1711.02174
Underlying nearly every quantitative discussion of the Cygnus Loop supernova remnant is uncertainty about its distance. Here we present optical images and spectra of nebulosities around two stars whose mass-loss material appears to have interacted with the remnant’s expanding shock front and thus can be used to estimate the Cygnus Loop’s distance. Narrow passband images reveal a small emission-line nebula surrounding an M4 red giant near the remnant’s eastern nebula NGC 6992. Optical spectra of the nebula show it to be shock-heated with significantly higher electron densities than seen in the remnant’s filaments. This along with its strong bow-shaped morphology suggests it is likely red giant mass-loss material shocked by passage of the Cygnus Loop’s blast wave. We also identify a B7 star located along the remnant’s northwestern limb which also appears to have interacted with the remnant’s shock wave. It lies within a small arc of nebulosity in an unusually complex region of strongly curved and distorted filaments along the remnant’s northeastern shock front suggestive of a localized disturbance in the shock front due to the B star’s stellar winds. With the assumption that these two stars lie inside the remnant, we propose a distance to the Cygnus Loop of 1 +/- 0.2 kpc. Although larger than several recent estimates of 500 – 800 pc, a distance around 1 kpc helps resolve difficulties with the remnant’s observed P(cosmic ray)/P(gas) ratio and estimated supernova explosion energy.
R. Fesen, J. Neustadt, C. Black, et. al.
Wed, 8 Nov 17
7/84
Comments: 16 pages, 14 figures; submitted to the Astrophysical Journal
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