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 .