Faraday Rotation in the Tail of the Planetary Nebula DeHt 5
  We present 1420 MHz polarization images of a 5x5 degree 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 approximately 3 pc long and runs away
from the north-east 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 rad/m^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 solar masses, and
predict that 0.49 +/- 0.33 solar masses 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 approximately 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.
