2026A&A...707A..50D

Aims. The secondaries of massive binary systems can be found as runaway stars after being ejected due to the supernova (SN) of the more massive component. We search for such stars inside supernova remnants (SNRs), where a recent SN is guaranteed to have occurred and the runaway star is expected nearby. In this paper, we present the massive runaway star HD 254577 as the pre-SN binary companion to the progenitor of the SN remnant IC 443 and the neutron star (NS) CXOU J61705.3+222127.
Methods. We performed spectroscopic observations of the runaway star and specified its atmospheric parameters. We also used archival spectroscopic data on neighboring stars. Together with precise Gaia DR3 astrometry and photometry, we identified the possible birth origin of the runaway star. By isochrone fitting, we likewise determined its progenitor mass. From Gaia DR3 proper motions, we specified the possible explosion sites and calculated the NS velocity.
Results. HD 254577 is a hot and evolved star with an effective temperature of 24 000 ± 1000 K (B0.5II) and a surface gravity of log(g [cm/s²]) = 2.75 ± 0.25. It is probably a single star with a peculiar 3D velocity of $ 31.3^{+1.2}_{-0.9} $ km s^–1, lying at a heliocentric distance of $ 1701^{+55}_{-54} $ pc. The cometary tail of the NS implies that it is moving away from the same site as the runaway star. From the flight trajectories, we calculated typical NS pulsar velocities of 254 - 539 km s^–1 at a distance of 1.7 kpc for 10 - 20 kyr ages. Together with the blue-shifted interstellar medium lines in its spectrum, HD 254577 must be the pre-SN binary companion to the progenitor of IC 443. By identifying the pre-SN companion and the possible parent cluster, we show that the progenitor zero-age main-sequence mass is high (31 - 64 M_⊙), favoring the jet scenario previously proposed. The SNR distance is precisely determined as $ 1701^{+55}_{-54} $ pc. We also discuss the expansion dynamics of the SNR due to the highly off-centered explosion site. Our calculated pre-SN binary parameters might not favor a strongly interacting binary.