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We present deep H-alpha images of portions of the X-ray bright but opticallyfaint Galactic supernova remnant G156.2+5.7, revealing numerous and delicatelythin nonradiative filaments which mark the location of the remnant's forwardshock. These new images show that these filaments have a complex structure notvisible on previous lower resolution optical images. By comparing H-alphaimages taken in 2004 at the McDonald Observatory and in 2015-2016 at the KisoObservatory, we set a stringent 1-sigma upper limit of expansion to be 0.06arcsec/yr. This proper motion, combined with a shock speed of 500 km/s inferredfrom X-ray spectral analyses, gives a distance of > 1.7 kpc. In addition, asimple comparison of expansion indices of several SNRs allows us to infer theage of the remnant to be a few 10,000 yr old. These estimates are morestraightforward and reliable than any other previous studies, and clearly ruleout a possibility that G156.2+5.7 is physically associated with part of theTaurus-Auriga cloud and dust complex at a distance of 200-300 pc.

Constraining the Age and Distance of the Galactic Supernova Remnant G156.2+5.7 by H-alpha Expansion Measurements