Paper · 2025
Ancient, eclipsing, tidally locked: A blue lurker progenitor in the population of extreme-velocity star candidates
J1903−0023 looked like a hypervelocity star. X-shooter spectroscopy makes it a very metal-poor halo binary instead, tidally synchronised and eclipsing, and a plausible progenitor of a blue lurker.
Abstract
J1903−0023 was flagged as a promising hypervelocity star candidate in Gaia DR3. We analysed it with spectroscopy from X-shooter at the ESO VLT, together with the available photometry.
The star turns out to be of spectral type F, very similar to the extreme-velocity star J0725−2351, and both share the characteristics of very metal-poor and old halo main-sequence (sdF) stars. J1903−0023 rotates rapidly, at 42.3 ± 2.0 km s−1, and shows eclipses on the same period as its rotation.
We conclude that J1903−0023 is a high-velocity tidally synchronised binary, most likely with a metal-poor M dwarf companion, rather than a genuine hypervelocity star travelling freely through the Galaxy. As a close, ancient, tidally locked pair it is a candidate progenitor of a blue lurker.