Young stellar flares and meteoritic isotopic anomalies

Service d'Astrophysique, Centre d'Études de Saclay, France and Department of Astronomy & Astrophysics, Pennsylvania State University, USA

Abstract

A long-standing enigma in planetary science has been the presence of daughter products of radioactive isotopes with short (τ ~ 10⁶ yr) lifetimes. Some models are based on the injection of freshly synthesized nuclides from stellar sources (e.g. a supernova remnant) into the molecular cloud from which the solar system formed. Other models produce these radionuclides within the disk via spallation by high fluences of MeV baryons. We report here the first quantitative measure of magnetic reconnection flaring in Myr-old analogs of the early Sun from Chandra X-ray Observatory observations of the Orion Nebula Cluster. We show that virtually all analogs of the ≤1 Myr Sun exhibit X-ray flares that are ~30 times more powerful and ~300 times more frequent than the most powerful flares seen on the contemporary Sun. We infer that the proton fluence of the early Sun was 10⁵ times that seen today, and argue that these protons may plausibly have bombarded solids in the protoplanetary disk. Others have demonstrated that such particle fluences are sufficient to produce several of the most troublesome excesses of short-lived CAI isotopes via spallation of normal nebular material. Our results thus strengthen the astronomical foundation for local irradiation models of meteoritic short-lived isotopic anomalies. This work is described in detail by Feigelson et al.  (2002b).