Distributions of Short-Lived Radioactive Nuclei Produced by Young Embedded Stellar Clusters

Abstract

Most star formation in the Galaxy takes place in clusters, where the most massive members can affect the properties of other constituent solar systems. This paper considers how clusters influence star formation and forming planetary systems through nuclear enrichment from supernova explosions, where massive stars deliver short-lived radioactive nuclei (SLRs) to their local environment. The decay of these nuclei leads to both heating and ionization, and thereby affects disk evolution, disk chemistry, and the accompanying process of planet formation. Nuclear enrichment can take place on two spatial scales: [1] Within the cluster itself ($\ell \sim 1$pc), the SLRs are delivered to the circumstellar disks associated with other cluster members. [2] On the next larger scale ($\ell \sim 2-10$pc), SLRs are injected into the background molecular cloud; these nuclei provide heating and ionization to nearby star-forming regions, and to the next generation of disks. For the first scenario, we construct the expected distributions of radioactive enrichment levels provided by embedded clusters. Clusters can account for the SLR mass fractions inferred for the early Solar Nebula, but typical SLR abundances are lower by a factor of $\sim 10$. For the second scenario, we find that distributed enrichment of SLRs in molecular clouds leads to comparable abundances. For both the direct and distributed enrichment processes, the masses of ${}^{26}$Al and ${}^{60}$Fe delivered to individual circumstellar disks typically fall in the range $10-100p{M}_{\odot }$ (where $1p{M}_{\odot }=10^{-12}{M}_{\odot }$). The corresponding ionization rate due to SLRs typically falls in the range ${\zeta }_{SLR}\sim 1-5\times 10^{-19}$ sec${}^{-1}$. This ionization rate is smaller than that due to cosmic rays, ${\zeta }_{CR}\sim 10^{-17}$ sec${}^{-1}$, but will be important in regions where cosmic rays are attenuated (e.g., disk mid-planes).

52 pages, 13 figures, accepted to The Astrophysical Journal

References in corpus (16)

• Theory of Star Formation
• A Spitzer Survey of Young Stellar Clusters within One Kiloparsec of the Sun: Cluster Core Extraction and Basic Structural Analysis
• The nucleosynthesis of Al26 and Fe60 in solar metallicity stars extending in mass from 11 to 120 Msun: the hydrostatic and explosive contributions
• Dust Formation and Survival in Supernova Ejecta
• Magnetorotational Core-Collapse Supernovae in Three Dimensions
• Asymmetries in core-collapse supernovae from maps of radioactive ${}^{44}$Ti in CassiopeiaA
• Abundance, distribution, and origin of 60Fe in the solar protoplanetary disk
• Star Cluster Demographics. I. A General Framework and Application to the Antennae Galaxies
• Close encounters in young stellar clusters: implications for planetary systems in the solar neighbourhood
• Interaction of Supernova Ejecta with Nearby Protoplanetary Disks
• UV Radiation Fields Produced by Young Embedded Star Clusters
• Radioactive Probes of the Supernova-Contaminated Solar Nebula: Evidence that the Sun was Born in a Cluster
• `Tail-end' Bondi-Hoyle accretion in young star clusters: Implications for disks, planets, and stars
• Supernova Propagation And Cloud Enrichment: A new model for the origin of ${}^{60}$Fe in the early solar system
• On the likelihood of supernova enrichment of protoplanetary disks
• Enhanced Cosmic Ray Flux and Ionization for Star Formation in Molecular Clouds Interacting with Supernova Remnants

Cited by in corpus (4)

• Constraining the X-ray and Cosmic Ray Ionization Chemistry of the TW Hya Protoplanetary Disk: Evidence for a Sub-interstellar Cosmic Ray Rate
• Volatile Delivery to Planets from Water-rich Planetesimals around Low Mass Stars
• Exclusion of Cosmic Rays in Protoplanetary Disks. II. Chemical Gradients and Observational Signatures
• Tracing Embedded Stellar Populations in Clusters and Galaxies using Molecular Emission: Methanol as a Signature of the Low-Mass End of the IMF