SIMBAD references

We show that the burning of a small mass fraction X₁₂ of ¹²C in a neutron star ocean is thermally unstable at low accumulated masses when the ocean contains heavy ashes from the hydrogen-burning rapid proton process. The key to early unstable ignition is the decreased thermal conductivity of a heavy-element ocean. The instability requires accretion rates, M{dot}, in excess of 1/10 the Eddington limit when X₁₂<0.1. Lower M{dot}'s will stably burn a small mass fraction of ¹²C. The unstable flashes release ∼10⁴²-10⁴³ ergs over hours to days and are likely the cause of the recently discovered large type I bursts (the so-called superbursts) from six Galactic low-mass X-ray binaries. In addition to explaining the energetics, recurrence times, and durations of the superbursts, these mixed ¹²C flashes also have an M{dot} dependence of unstable burning similar to that observed. Although the instability is present at accretion rates ~M{dot}_Edd, the flashes provide less of a contrast with the accretion luminosity there, thus explaining why detection is easier when M{dot}~(0.1-0.3)M{dot}_Edd.