FARADAY ROTATION IN THE TAIL OF THE PLANETARY NEBULA DeHt 5

We present 1420 MHz polarization images of a 5 degrees x 5 degrees region around the planetary nebula (PN) DeHt 5. The images reveal narrow Faraday-rotation structures on the visible disk of DeHt 5, as well as two wider, tail-like, structures behind DeHt 5. Though DeHt 5 is an old PN known to be interacting with the interstellar medium (ISM), a tail has not previously been identified for this object. The innermost tail is similar to 3 pc long and runs away from the northeast edge of DeHt 5 in a direction roughly opposite that of the sky-projected space velocity of the white dwarf central star, WD 2218+706. We believe this tail to be the signature of ionized material ram-pressure stripped and deposited downstream during a >74,000 yr interaction between DeHt 5 and the ISM. We estimate the rotation measure (RM) through the inner tail to be -15 +/- 5 radm(-2), and, using a realistic estimate for the line-of-sight component of the ISM magnetic field around DeHt 5, derive an electron density in the inner tail of n(e) = 3.6 +/- 1.8 cm(-3). Assuming the material is fully ionized, we estimate a total mass in the inner tail of 0.68 +/- 0.33 M(circle dot) and predict that 0.49 +/- 0.33 M(circle dot) was added during the PN-ISM interaction. The outermost tail consists of a series of three roughly circular components, which have a collective length of similar to 11.0 pc. This tail is less conspicuous than the inner tail and may be the signature of the earlier interaction between the WD 2218+706 asymptotic giant branch (AGB) progenitor and the ISM. The results for the inner and outer tails are consistent with hydrodynamic simulations and may have implications for the PN missing-mass problem as well as for models which describe the impact of the deaths of intermediate-mass stars on the ISM.