A study of type I X-ray bursts from an NS accreting pure helium

Using the Modules for Experiments in Stellar Astrophysics (MESA) code, we investigate Type I X-ray bursts (XRBs) produced by neutron stars (NSs) accreting pure helium, which are called intermediate XRBs in observations. We simulate 21 models for intermediate XRBs with various mass-accretion rates (Ṁ) from 2.5 × 10⁻⁸ to 5 × 10⁻¹⁰ M _⊙ yr⁻¹. Compared with normal XRBs, in which the NS accretes matter with solar metallicity, intermediate XRBs have higher luminosity and longer recurrence time, which are essentially consistent with observations. We find that the recurrence time of intermediate XRBs is proportional to Ṁ ^−2.0. (paper)