Confirmation of the planetary nebula nature of HaTr 5

Context. The identification of the nebula HaTr 5 with the shell remnant of the historic Nova Sco 1437 around the low-accretion rate cataclysmic variable 2MASS J17022815-4306123 has been used in the framework of the hibernation scenario to set an upper limit of ≤580 yr on the transition time from a nova-like binary to a dwarf nova. Aims. This work is aimed at clarifying the nature of HaTr 5, which has also been deemed a possible planetary nebula in previous works. Methods. We obtained intermediate- and high-dispersion long-slit spectra of HaTr 5 and analyzed them in conjunction with archival optical and infrared images to investigate its spectral properties using photoionization models. In addition, we sought to derive its Hα flux and ionized mass and determine its spatio-kinematic by means of 3D models to clarify its true nature. Results. The Hα flux of HaTr 5 implies an ionized mass of 0.059 M⊙ at the 0.99 kpc distance of 2MASS J17022815-4306123, namely, ∼1000 times the typical ejecta of a nova. If HaTr 5 were actually an unrelated planetary nebula, its Hα flux would imply a distance of 2.25 kpc and an ionized mass of 0.47 M⊙. The expansion velocity of HaTr 5 is found to be ≃27 km s−1, with a heliocentric radial velocity of −1 km s−1. Conclusions. The ionized mass of HaTr 5 and its expansion velocity (and associated kinematic age) are clearly inconsistent with those expected for a nova remnant, all strongly support a planetary nebula nature. The association of 2MASS J17022815-4306123 with HaTr 5 is further called into question based on their differing radial velocities and almost orthogonal motions on the plane of the sky. We have concluded that HaTr 5 is an old, evolved planetary nebula unrelated to the remnant of Nova Sco 1437 or to the cataclysmic variable 2MASS J17022815-4306123, with the latter being by chance projected onto HaTr 5.