PHYSICS REPORTS (Review Section of Physics Letters) 227, Nos. 1—5 (1993) 223—234 PHYSICS REPORTS North-Holland 22Na and 26A1 production in nova outbursts S. Starrfielda, J.W. Truranb, M. Politanoa, W.M. Sparksc, I. Nofar~’ and G. Shavivd ‘Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287-1504, USA bDepartment of Astronomy and Enrico Fermi Institute, University of Chicago, Chicago, IL 60637, USA CApplied Theoretical Physics Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA dDepartment of Physics and Asher Space Institute, The Technion, Haifa, 32000, Israel Abstract: The consequences of accretion of hydrogen rich material onto ONeMg white dwarfs with masses of 1.0, 1.25, and 1.35 M 0 are examined. Our results demonstrate that novae produce both 22Na and 26A1 in astrophysically interesting amounts. Hot hydrogen burning on ONeMg white dwarfs can produce as much as 2% of the ejected material as 26A1 and 3% as 22Na. The largest amount of 22Na is produced by the highest mass ONeMg white dwarf nova systems which are predicted to be the fastest and most luminous of all types of nova. The largest amount of 26A1 is produced in the lowest mass whitedwarfs, which according to our evolutionary calculations, should eject the largest amount of material. In support of this prediction, the observations of QU Vul, a slow ONeMg nova, indicate that it has ejected about lO~M®. However, such a large amount of ejected mass is inconsistent with a typical ONeMg white dwarf mass> 1.25 M 0. 1. Introduction Urey [1955] was the first to suggest that radioactive decay of 26A1 was important for the heating of the small bodies in the solar system. However, it was not until Lee, Papanastassiou and Wasserburg [1977] found that large excesses of 26Mg were correlated with the ratio of 27A1/24Mg in the Allende meteorite, that it was demonstrated that 26Al, the radioactive parent of 26Mg, was present in the early solar system. Because its half life, 7.2 x iO~ yr, is short compared to a Hubble time, this result implied that 26A1 must have been produced by some astrophysical process shortly before the formation of the solar system and then mixed with the pre-solar nebula just prior to its collapse. Its presence in the interstellar medium (ISM) was confirmed by the discovery, by HEAO-3, of the 1.809 MeV ‘y-ray line, which results from the decay of 26A1 to the first excited state of 26Mg [Mahoney et al. 1982]. Mahoney et a!. also reported that the ‘y-ray photons appeared to originate from the general direction of the galactic plane. Mahoney et a!. [1984] later used their detection to estimate that there was about 3 M® of 26A1 in the ISM and examined the possibility that novae could produce this isotope. The Mahoney et al. results were confirmed by measure- ments with the SMM 7-ray spectrometer [Share et al. 1985]. The discovery of the existence of 26A1, both in meteorites and the ISM, has stimulated a variety of studies to determine both the astrophysical site and the mechanisms which could produce this isotope. An excellent review of the 26Al problem can be found in Clayton and Leising [1987], and we refer the reader to that reference for more details. We also note that the launch of GRO has provided a much more sensitive instrument to study the distribution of this radioactive element in the ISM. Possible mechanisms for the production of 26A1 must include the arguments presented in Ward and Fowler [1980]. They pointed out that 26A1 cannot be synthesized at too high a temperature, since both ~ and 26mAl (the “g” and “m” in the superscripts refer to the two isomeric states of 0370-1573/93/$6.00 © 1993 Elsevier Science Publishers B.V. All rights reserved