July 12: Nuclear Reactions in Type-I X-ray Bursts

Nuclear Reactions in Type I X-ray Bursts
Mini-workshop at the INT Program The Neutron Star Crust and Surface
July 12
Room C421, Physics and Astronomy Building, University of Washington.

Thermonuclear burning in the atmospheres of neutron stars
accreting H- and He- rich matter from companions in X-ray binaries
determines the chemical makeup of the neutron star atmospheres and crusts. A quantitative understanding of these thermonuclear processes -- in particular, the breakout from the CNO cycles and the subsequent rapid proton capture process -- is needed to ascertain the properties of the atmosphere and crust. This mini-workshop will focus on completed and future nuclear physics experiments, and how their results impact processes in the neutron star crust and atmosphere.

The workshop will be centered around short talks scheduled on a timetable, but with the intention of expanding into the rest of the day, in both formal and informal discussions.

Speakers:
10:30-11:00 Barry Davids (TRIUMF)
11:15-11:45 Chris Ruiz (TRIUMF)
2:00-2:30 Ed Brown (MSU, JINA)
2:30-3:00 Andrew Cumming (McGill)
3:00-3:30 Randall Cooper (Harvard/CfA)
3:30-5:00 Coffee & Discussion


==ABSTRACTS===
Barry Davids (TRIUMF)
Experimental Efforts to Determine the 15O(a,g)19Ne Reaction Rate

I will review worldwide efforts to ascertain the rate of this nuclear
reaction, which apparently plays a critical role in the ignition of Type-I
X-Ray Bursts. As direct measurements are not yet possible,
indirect measurements have been the only option. I will present these
experiments in a manner I hope will be comprehensible to observational
astronomers and theoretical astrophysicists.

Chris Ruiz (TRIUMF)
Nuclear Astrophysics of neutron-deficient nuclei - experimental
approaches at ISAC

To give observational astronomers and theoreticians a taste of what experiments in Nuclear Astrophysics consist of, I will present an overview of the DRAGON and TUDA facilities at TRIUMF-ISAC. I will discuss how these measurements pertain to reactions and observables in novae and x-ray bursts, highlighting the considerable challenges in making these crucial measurements, and developing the accelerated beams. I will also describe future endeavors to measure Q-values of (p,$\gamma$) reactions taking
place in the &\nu$-rp process using the TITAN facility.

Ed Brown (MSU, JINA)
The X-ray Burst—Crust Connection

The crust of an accreting neutron star is composed of the ashes of X-ray bursts. The heating from electron captures in the crust depends sensitively on the composition of these ashes. In turn, the heating in the crust influences the ignition of bursts for which H is not consumed steadily by the HCNO cycle, for example, superbursts and X-ray bursts from low mass accretion rate systems. I will describe the relation between the burst composition and the crustal heating, and speculate on what may happen in the inner crust.

Andrew Cumming (McGill)
Constraints on the rp-process from X-ray Bursts

I discuss the ways in which X-ray burst observations potentially constrain the rp-process. In particular I will show comparison of model X-ray burst lightcurves with observations of GS 1826-24, and then discuss current constraints on the amount of carbon needed to power superbursts, which is critically dependent on the duration of the rp-process path.


Randall Cooper (Harvard/CfA)
Nuclear Reactions During the Onset of Type I X-ray Bursts

I will review our current understanding of the physics of the
onset of type I X-ray bursts, with an emphasis on the pertinent nuclear
reactions. In particular, I will discuss the roles that both the hot CNO
cycles and their breakout reactions 15O(a,g)19Ne and 18Ne(a,p)21Na play in
the stability of thermonuclear burning and the
rising phase of X-ray bursts.