A high resolution HI study towards the supernova remnant Puppis A and
  its environments
  We observed the supernova remnant (SNR) Puppis A in the 21 cm line with the
Australia Telescope Compact Array with the aim of determining the systemic
velocity and, hence, the corresponding kinematic distance. For the compact,
background sources in the field, we obtain absorption spectra by applying two
methods: (a) subtracting profiles on- and off-source towards continuum
emission, and (b) filtering short spacial frequencies in the Fourier plane to
remove large scale emission. One of the brightest features to the East of the
shell of Puppis A was found to be a background source, probably extragalactic.
Removing the contribution from this and the previously known unrelated sources,
the systemic velocity of Puppis A turns out to be limited between 8 and 12 km
s$^{-1}$, which places this source at a distance of 1.3 $\pm$ 0.3 kpc. From the
combined images that include both single dish and interferometric data, we
analyze the distribution of the interstellar hydrogen. We suggest that an
ellipsoidal ring at $v \sim $+8 km s$^{-1}$ could be the relic of a bubble
blown by the progenitor of Puppis A, provided the distance is $\lesssim$ 1.2
kpc. The main consequences of the new systemic velocity and distance as
compared with previous publications ($v =$ +16 km s$^{-1}$ and $d = $2.2 kpc)
are the absence of a dense interacting cloud to the East to explain the
morphology, and the decrease of the shell size and the neutron star velocity,
which are now in better agreement with statistical values.
