The impact of the revised ¹⁷O(p, α)¹⁴N reaction rate on ¹⁷O stellar abundances and yields

¹ INAF, Osservatorio Astronomico di Teramo, 64100 Teramo, Italy
e-mail: straniero@oa-teramo.inaf.it
² INFN, Laboratori Nazionali del Gran Sasso (LNGS), 67100 Assergi, Italy
³ Gran Sasso Science Institute, INFN, Viale F. Crispi 7, 67100 L’ Aquila, Italy
⁴ Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr 400, 01328 Dresden, Germany
⁵ SUPA, School of Physics and Astronomy, University of Edinburgh, EH9 3 FD Edinburgh, UK
⁶ Università di Napoli “Federico II” and INFN, Sezione di Napoli, 80126 Napoli, Italy
⁷ INFN, Sezione di Padova, via Marzolo 8, 35131 Padova, Italy
⁸ Department of Physics and Astronomy, University of Padova, via Marzolo 8, 35131 Padova, Italy
⁹ Università degli Studi di Genova and INFN, Sezione di Genova, via Dodecaneso 33, 16146 Genova, Italy
¹⁰ Institute for Nuclear Research (MTA ATOMKI), PO Box 51, 4001 Debrecen, Hungary
¹¹ Università degli Studi di Torino and INFN, Sezione di Torino, via P. Giuria 1, 10125 Torino, Italy
¹² Università degli Studi di Milano and INFN, Sezione di Milano, via G. Celoria 16, 20133 Milano, Italy
¹³ INFN, Sezione di Roma La Sapienza, Piazzale A. Moro 2, 00185 Roma, Italy
¹⁴ Università degli Studi di Bari and INFN, Sezione di Bari, 70125 Bari, Italy
¹⁵ South Dakota School of Mines, 501 E. Saint Joseph St., SD 57701, USA
¹⁶ INFN, Sezione di Perugia, 06123 Perugia, Italy

Received: 31 August 2016
Accepted: 20 October 2016

Abstract

Context. Material processed by the CNO cycle in stellar interiors is enriched in ¹⁷O. When mixing processes from the stellar surface reach these layers, as occurs when stars become red giants and undergo the first dredge up, the abundance of ¹⁷O increases. Such an occurrence explains the drop of the ¹⁶O/¹⁷O observed in RGB stars with mass larger than ~ 1.5M_⊙. As a consequence, the interstellar medium is continuously polluted by the wind of evolved stars enriched in ¹⁷O.

Aims. Recently, the Laboratory for Underground Nuclear Astrophysics (LUNA) collaboration released an improved rate of the ¹⁷O(p, α)¹⁴N reaction. In this paper we discuss the impact that the revised rate has on the ¹⁶O/¹⁷O ratio at the stellar surface and on ¹⁷O stellar yields.

Methods. We computed stellar models of initial mass between 1 and 20 M_⊙ and compared the results obtained by adopting the revised rate of the ¹⁷O(p, α)¹⁴N to those obtained using previous rates.

Results. The post-first dredge up ¹⁶O/¹⁷O ratios are about 20% larger than previously obtained. Negligible variations are found in the case of the second and the third dredge up. In spite of the larger ¹⁷O(p, α)¹⁴N rate, we confirm previous claims that an extra-mixing process on the red giant branch, commonly invoked to explain the low carbon isotopic ratio observed in bright low-mass giant stars, marginally affects the ¹⁶O/¹⁷O ratio. Possible effects on AGB extra-mixing episodes are also discussed. As a whole, a substantial reduction of ¹⁷O stellar yields is found. In particular, the net yield of stars with mass ranging between 2 and 20 M_⊙ is 15 to 40% smaller than previously estimated.

Conclusions. The revision of the ¹⁷O(p, α)¹⁴N rate has a major impact on the interpretation of the ¹⁶O/¹⁷O observed in evolved giants, in stardust grains and on the ¹⁷O stellar yields.