DRAGON

Explaining anomalies in the spectra of classical novae

Explaining anomalies in the spectra of classical novae: The optical, ultraviolet and infrared spectra of the debris left over after nova explosions – thermonuclear detonations on the surface of accreting white dwarves in stellar binary systems – contain important fingerprints of the chemical elements synthesized and ejected during these cataclysmic events. However, for some elements, namely argon and calcium, much more than expected seems to be present. This flies in the face of theoretical models of nova explosions which say that nucleosynthesis in novae effectively stops at calcium, with around the same amount of calcium being present after the explosion as before the explosion. The volume of elements from Ar-Ca produced in these scenarios depends sensitively on the strengths of nuclear reactions around that region, in particular proton-induced radiative capture reactions. One of these,  p (³⁸K ,γ)³⁹Ca has now been experimentally measured for the first time using TRIUMF’s DRAGON facility, previously impossible because if the short lifetime of ³⁸K, but accessible to the inverse kinematics technique of DRAGON using an intense ³⁸K beam made at ISAC. This makes p (³⁸K,γ)³⁹Ca the highest mass reaction ever measured using this technique with radioactive beams.      

Relating Hubble observations to the inside of a novae explosion

Relating Hubble observations to the inside of a novae explosion: Several years ago, fluorine was observed in the spectrum of a nova explosion for the first time by a joint exercise between the Hubble Space Telescope and the Nordic Optical Telescope. This provides a powerful tool to compare astronomical observations with theoretical stellar models, because only one stable isotope of fluorine exists, ¹⁹F, and its quantity is extremely sensitive to the nuclear reactions that create and destroy it as well as the temperature & density conditions in the explosion. One such reaction, p (¹⁹Ne,γ)²⁰Na, was measured for the first time at the DRAGON facility, using a beam of short-lived ¹⁹Ne produced at ISAC. This long sought-after reaction cross section was previously inaccessible to direct measurement. The results reduce the uncertainties resulting from nuclear physics inputs to negligible levels when comparing theoretical stellar models to the HST observations.    

Understanding gamma-ray emission from nova explosions

Understanding gamma-ray emission from nova explosions: One of the first signals to emanate from a nova explosion is an intense burst of X- and gamma rays, long before the peak of the optical brightness is reached. At such a time, the 511 keV gamma-ray line is directly linked to the amount of radioactive ¹⁸F synthesized in the explosion. Thus, observing the 511 keV gamma ray intensity in a nova explosion would give astronomers a direct “thermometer” in the heart of the explosion. The problem is that the rates of nuclear reactions that create and destroy ¹⁸F in this environment are highly uncertain, including specifically the ¹⁸F(p,𝛼)¹⁵O and ¹⁸F(p,γ)¹⁹Ne reactions. Complementary to work on the ¹⁸F(p,𝛼)¹⁵O reaction performed at TUDA, DRAGON has measured a key resonance in ¹⁸F(p,γ)¹⁹Ne for the first time, finding it to be much weaker than previously thought, and reducing the uncertainties in the amount of ¹⁸F produced in these scenarios.