2024A&A...683A..44M

We have computed a 3D hydrodynamic simulation of the merger between a massive (0.4 M_⊙) helium white dwarf (He WD) and a low-mass (0.6 M_⊙) carbon-oxygen white dwarf (CO WD). Despite the low mass of the primary, the merger triggers a thermonuclear explosion as a result of a double detonation, producing a faint transient and leaving no remnant behind. This type of event could also take place during common-envelope mergers whenever the companion is a CO WD and the core of the giant star has a sufficiently large He mass. The spectra show strong Ca lines during the first few weeks after the explosion. The explosion only yields < 0.01 M_⊙ of ⁵⁶Ni, resulting in a low-luminosity Type Ia supernova-like light curve that resembles the Ca-rich transients within this broad class of objects, with a peak magnitude of M_bol ≈ -15.7 mag and a rather slow decline rate of $ \Delta m_{15}^{\mathrm{bol}} \approx 1.5 $ mag. Both its light curve shape and spectral appearance resemble the appearance of Ca-rich transients, suggesting such mergers as a possible progenitor scenario for this class of events.