Thermonuclear burst sources accreting helium-rich material
Thermonuclear (type-I) bursts occur in low-mass X-ray binaries (LMXBs) by unstable nuclear burning of the material accreted onto the neutron star (NS) surface. A catalogue listing the observed properties of more than 1200 bursts observed by RXTE from 48 LMXBs has been recently published, and an even larger database ( 3400 bursts from 65 sources observed by RXTE and other instruments) is being compiled. We use these large burst samples to do a detailed and systematic comparison of their properties with predictions of state-of-the-art numerical models. According to these models, the observed burst properties (e.g. the burst recurrence time and fluence) depend not only on the composition of the accreted material, but also on the NS crust temperature. For certain ignition regimes (e.g. helium-rich accreted material, relatively high accretion rates) the burst properties are much more sensitive to the internal heat. We show that observations of such bursts, with precisely identified ignition conditions, can in principle be used to constrain the properties of the underlying NS crust, and present preliminary results of the first attempts to do so.