Universität zu Köln

Gaches, Brandt A. L., Walch, Stefanie ORCID: 0000-0001-6941-7638, Offner, Stella S. R. and Muenker, Carsten (2020). Aluminum-26 Enrichment in the Surface of Protostellar Disks Due to Protostellar Cosmic Rays. Astrophys. J., 898 (1). BRISTOL: IOP PUBLISHING LTD. ISSN 1538-4357

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Abstract

The radioactive decay of aluminum-26 (Al-26) is an important heating source in early planet formation. Since its discovery, there have been several mechanisms proposed to introduce Al-26 into protoplanetary disks, primarily through contamination by external sources. We propose a local mechanism to enrich protostellar disks with 26Al through irradiation of the protostellar disk surface by cosmic rays accelerated in the protostellar accretion shock. We calculate the Al-26 enrichment, [Al-26/Al-27], at the surface of the protostellar disk in the inner au throughout the evolution of low-mass stars, from M-dwarfs to proto-Suns. Assuming constant mass accretion rates, m., we find that irradiation by MeV cosmic rays can provide significant enrichment on the disk surface if the cosmic rays are not completely coupled to the gas in the accretion flow. Importantly, we find that low accretion rates, (m) over dot < 10(-7) M-circle dot yr(-1), are able to produce canonical amounts of Al-26, [Al-26/Al-27] approximate to 5 x 10(-5). These accretion rates are experienced at the transition from Class I- to Class II-type protostars, when it is assumed that calcium-aluminum-rich inclusions condense in the inner disk. We conclude that irradiation of the inner disk surface by cosmic-ray protons accelerated in accretion shocks at the protostellar surface may be an important mechanism to produce Al-26. Our models show protostellar cosmic rays may be a viable model to explain the enrichment of Al-26 found in the solar system.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Gaches, Brandt A. L. UNSPECIFIED UNSPECIFIED UNSPECIFIED Walch, Stefanie UNSPECIFIED orcid.org/0000-0001-6941-7638 UNSPECIFIED Offner, Stella S. R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Muenker, Carsten UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-327447
DOI:	10.3847/1538-4357/ab9a38
Journal or Publication Title:	Astrophys. J.
Volume:	898
Number:	1
Date:	2020
Publisher:	IOP PUBLISHING LTD
Place of Publication:	BRISTOL
ISSN:	1538-4357
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language EARLY SOLAR-SYSTEM; SHORT-LIVED RADIOISOTOPES; EXTINCT RADIOACTIVITIES; SUPERNOVA; RADIONUCLIDES; CHONDRITES; ACCRETION; ALLENDE; OBJECT; BIRTH Multiple languages Astronomy & Astrophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/32744