Not So Fast, Not So Furious: Just Magnetic

Abstract

WD 0810-353 is a white dwarf within the 20 pc volume around the Sun. Using Gaia astrometric distance and proper motions, and a radial velocity derived from Gaia spectroscopy, it has been predicted that this star will pass within 1 pc of the solar system in about 30 kyr. However, WD 0810-353 has been also shown to host a magnetic field with a strength of the order of 30 MG. Its spectrum is therefore not like those of normal DA stars of similar effective temperature. We have obtained and analyzed new polarized spectra of the star around Hα. Our analysis suggests that the visible surface of the star shows two regions of different field strength (~30 and ~45 MG, respectively), and opposite polarity. The spectra do not change over a 4 yr time span, meaning that either the stellar rotation period is no shorter than several decades, or that the field is symmetric about the rotation axis. Taking into account magnetic shift and splitting, we obtain an estimate of the radial velocity of the star (+83 ± 140 km s<SUP>-1</SUP>); we reject both the value and the claimed precision deduced from the Gaia DR3 spectroscopy (-373.7 ± 8.2 km s<SUP>-1</SUP>), and we conclude that there will probably be no close encounter between the solar system and WD 0810-353. We also reject the suggestion that the star is a hypervelocity runaway star, a survivor of a Type Ia supernova explosion. It is just a stellar remnant in the solar neighborhood with a very strong and complex magnetic field.