Thermonuclear flashes in the accreting envelopes of hot neutron stars.II. M=10 dexp(16), 10 dexp(18) g/sec.

The effects of changes in mass-accretion rate (MAR) and initial chemical composition on the dynamics of thermonuclear flashes in hot neutron stars are calculated for model stars with MARs ranging from 10 Pg/s to Eg/s. The results are presented in tables and graphs and discussed in detail. A critical MAR of about 40 Pg/s is identified, below which He layers are formed and above which H-He flashes occur. The fast-fast, fast-slow, and double-type flashes observed in the burster XB 1608-522 by Murakami et al. (1980) using the Hakucho satellite are found to be consistent with a model having a MAR near the critical value. In general, even small changes in the H/He ratio before a flash can lead to pronounced changes in the nature of the flash.