Radioactive Probes of the Supernova‐contaminated Solar Nebula: Evidence that the Sun Was Born in a Cluster

We construct a simple model for radioisotopic enrichment of the protosolarnebula by injection from a nearby supernova, based on the inverse square lawfor ejecta dispersion. We find that the presolar radioisotopes abundances(i.e., in solar masses) demand a nearby supernova: its distance can be nolarger than 66 times the size of the protosolar nebula, at a 90% confidencelevel, assuming 1 solar mass of protosolar material. The relevant size of thenebula depends on its state of evolution at the time of radioactivityinjection. In one scenario, a collection of low-mass stars, including our sun,formed in a group or cluster with an intermediate- to high-mass star that endedits life as a supernova while our sun was still a protostar, a starless core,or perhaps a diffuse cloud. Using recent observations of protostars to estimatethe size of the protosolar nebula constrains the distance of the supernova at0.02 to 1.6 pc. The supernova distance limit is consistent with the scales oflow-mass stars formation around one or more massive stars, but it is closerthan expected were the sun formed in an isolated, solitary state. Consequently,if any presolar radioactivities originated via supernova injection, we mustconclude that our sun was a member of such a group or cluster that has sincedispersed, and thus that solar system formation should be understood in thiscontext. In addition, we show that the timescale from explosion to the creationof small bodies was on the order of 1.8 Myr (formal 90% confidence range of 0to 2.2 Myr), and thus the temporal choreography from supernova ejecta tometeorites is important. Finally, we can not distinguish between progenitormasses from 15 to 25 solar masses in the nucleosynthesis models; however, the20 solar mass model is somewhat preferred.Comment: ApJ accepted, 19 pages, 3 figure