Deep and fast Solar System flybys: The controversial case of WD 0810-353

Abstract

Context. Most flybys in the Galactic disk are distant, beyond 10,000 AU, and have characteristic velocities of about 70 km/s. However, deep and fast encounters also take place, albeit with lower probability, particularly if one of the objects involved is a stellar remnant ejected during a supernova. WD 0810-353 might be a high velocity white dwarf, and it was recently identified as heading straight for the Solar System; however, the Gaia DR3 data that support its future deep and fast flyby are regarded as suspicious. Aims. Here, we reanalyze the Gaia DR3 data set associated with WD 0810-353 to confirm or reject the reality of its Solar System flyby and also to investigate its possible runaway status. Methods. We studied the evolution of WD 0810-353 forward in time using N-body simulations. We computed the distribution of distances of closest approach and their associated times of perihelion passage. We used a statistical analysis of the kinematics of this object to assess its possible hypervelocity. We compared its mean BP/RP spectrum to those of other well-studied white dwarfs. Results. We confirm that WD 0810-353 is headed for the Solar System, but the actual parameters of the encounter depend strongly on its radial velocity. The Gaia DR3 value of -373.74+/-8.18 km/s is strongly disfavored by our analyses. Its mean BP/RP spectrum suggests a value over ten times higher based on the position of its putative Halpha line. However, spectral matching using other white dwarfs with non-Gaia data indicate a radial velocity in the interval (-60, -70) km/s. Conclusions. These results confirm the future flyby of WD 0810-353 near the Solar System, although the relative velocity could be high enough or the minimum approach distance large enough to preclude any significant perturbation on the Oort cloud.

10 pages, 9 figures. Accepted for publication in Astronomy and Astrophysics

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