Alignment (or misalignment) angle between the proper motion vector of the system and the symmetry axis of the bow shock as a function of the peculiar tangential motion. We have classified the bow shock as ‘aligned’, ‘aligned?’, and ‘misaligned’ following the criteria listed in Kobulnicky et al. (2016) (see text); CD-47 4551 and IRAS 08351-3951 are identified as unrelated ISM structures and excluded from the bow shock sample (see text). The misalignment angle shows a wide range for those systems with a low peculiar velocity.