2025ApJ...982..122Z

In this study, we calculate for the first time the impacts of neutron star (NS) structure on the type I X-ray burst ashes using the MESA code. We find an increased mass fraction of the heavier elements with increasing surface gravity (increased mass or decreased radius), resulting in a higher average mass number (A_ash) of burst ashes (except for higher-mass NSs due to the competition between the envelope temperature and the recurrence time). The burst strength (α) increases as the surface gravity increases, which indicates the positive correlation between A_ash and α with changes in surface gravity. If the α value is higher, heavier p-nuclei should be produced by the type I X-ray burst nucleosynthesis. Besides, the effects of various burst input parameters, e.g., base heating (Q_b), metallicity (Z), and some new reaction rates, are calculated for comparison. We find that the heavier nucleus synthesis is inversely correlated with the base heating/metallicity; the smaller the base heating/metallicity, the greater the mass fraction of the heavier elements. The α value decreases as Q_b or Z decreases, which also indicates the positive correlation between A_ash and α with variation in Q_b or Z. The new reaction rates from the (p, γ) reactions on ¹⁷F, ¹⁹F, ²⁶P, ⁵⁶Cu, and ⁶⁵As and the (α, p) reaction on ²²Mg have only minimal effects on burst ashes. In hydrogen-rich X-ray binary systems, nuclei heavier than ⁶⁴Ge are fertile, produced with larger NS mass, smaller NS radius, smaller base heating, and smaller metallicity.