Isotopic 32 S/ 33 S ratio as a diagnostic of presolar grains from novae

Abstract

Measurements of sulphur isotopes in presolar grains can help to identify the astrophysical sites in which these grains were formed. A more precise thermonuclear rate of the 33 S(p, γ ) 34 Cl reaction is required, however, to assess the diagnostic ability of sulphur isotopic ratios. We have studied the 33 S( 3 He,d) 34 Cl proton-transfer reaction at 25 MeV using a high-resolution quadrupole-dipole-dipole-dipole magnetic spectrograph. Deuteron spectra were measured at ten scattering angles between 10 • and 55 • . Twentyfour levels in 34 Cl over E x = 4.6-5.9 MeV were observed, including three levels for the first time. Proton spectroscopic factors were extracted for the first time for levels above the 33 S + p threshold, spanning the energy range required for calculations of the thermonuclear 33 S(p, γ ) 34 Cl rate in classical nova explosions. We have determined a new 33 S(p, γ ) 34 Cl rate using a Monte Carlo method and have performed new hydrodynamic nova simulations to determine the impact on nova nucleosynthesis of remaining nuclear physics uncertainties in the reaction rate. We find that these uncertainties lead to a factor of ≤ 5 variation in the 33 S(p, γ ) 34 Cl rate over typical nova peak temperatures, and variation in the ejected nova yields of S-Ca isotopes by ≤ 20%. In particular, the predicted 32 S/ 33 S ratio is 110-130 for the nova model considered, compared to 110-440 with previous rate uncertainties. As recent type II supernova models predict ratios of 130-200, the 32 S/ 33 S ratio may be used to distinguish between grains of nova and supernova origin.

STELLAR ORIGINS OF EXTREMELY 13C- AND 15N-ENRICHED PRESOLAR SIC GRAINS: NOVAE OR SUPERNOVAE?

“…As a result, protoncapture isotopic signatures of classical nova nucleosynthesis could be produced by explosive H burning in CCSNe, with contribution from nova-like isotopic signatures of the O zone in the 25T-H model of P15. Although Parikh et al (2014) have recently pointed out enhancement in the 33 S/ 32 S ratio as a diagnostic isotopic signature of nova grains, in fact, the 25T-H model predictions for the 33 S/ 32 S ratio are also positive in both the O (nova-like) zone and the He/C zone of CCSNe. Thus, the 33 S/ 32 S ratio is not specifically diagnostic of grains from novae, but more in general of H-burning at high temperatures in stars.…”

Discovery of 34g,mCl(p, γ)35Ar Resonances Relevant for Classical Nova Nucleosynthesis

“…However, this value is consistent with the solar isotopic ratio, and therefore it would need to be measured alongside the 32 S/ 34 S isotopic ratio and/or ratios for other elements to identify nova grains. Reference [10] predicts the 32 S/ 34 S ratio to be ≈ 100, which is distinct from the solar value of 22. However, this value depends strongly on the 34 Cl(p, γ) 35 Ar reaction rate.…”

Discovery of34g,mCl(p,γ)35Arresonances activated at classical nova temperatures

“…Ref. [10] 34m Cl is destroyed (with an effective half life of 1-10 seconds) due to thermally induced transitions to the ground state [16]. However, recent work by Grineviciute et al [17] studying the role of excited states in thermonuclear proton capture reaction rates shows that capture onto thermally populated 34m Cl plays a larger role in the reaction rate than previously expected.…”

“…Current nova grain candidates have low 12 C/ 13 C and 14 N/ 15 N ratios, 30 Si excesses, and close to solar 28 Si/ 29 Si ratios [6,8]. However, these signatures do not eliminate the possibility that some of these grains were produced in supernovae, and further isotopic signatures would help to distinguish between nova and supernova origins [9,10].…”

“…Recent experimental [10,[12][13][14] and modeling [10] work has been done to constrain the expected 32 S/ 33 S ratio for nova grains to a range of 110-130, which distinguishes it from the supernova predictions. However, this value is consistent with the solar isotopic ratio, and therefore it would need to be measured alongside the 32 S/ 34 S isotopic ratio and/or ratios for other elements to identify nova grains.…”