steve desch nicolas ouellette jeff hester laurie leshin arizona state university
DESCRIPTION
The Meaning of 60 Fe: A Nearby Supernova Injected Short-Lived Radionuclides into our Protoplanetary Disk. Steve Desch Nicolas Ouellette Jeff Hester Laurie Leshin Arizona State University. Outline. Our early Solar System contained 60 Fe It wasn’t created by in-situ spallation... - PowerPoint PPT PresentationTRANSCRIPT
The Meaning of 60Fe: A Nearby Supernova Injected
Short-Lived Radionuclides into our Protoplanetary Disk
Steve Desch
Nicolas Ouellette
Jeff Hester
Laurie Leshin
Arizona State University
Outline• Our early Solar System contained 60Fe
• It wasn’t created by in-situ spallation...
• It wasn’t inherited from our molecular
cloud...
• It wasn’t injected by an AGB star...
• It had to come from a supernova...
• It was probably injected directly into
our protoplanetary disk
Early Solar System Contained 60Fe
60Fe/56Fe ~ 2 - 5 x 10-7
Semarkona + Bishunpur pyroxene chondrules
(Tachibana et al 2005)
60Fe/56Fe ~ 9 x 10-7
Semarkona troilites + magnetites (Mostefaoui
et al 2005)
60Fe/56Fe ~ 7 x 10-7
Semarkona troilites + pyroxenes (Mostefaoui et
al 2004)
60Fe/56Fe ~ 3 - 4 x 10-7
Bishunpur + Krymka troilites (Tachibana &
Huss 2003)
Tachibana & Huss (2003)
60Fe/56Fe ~ 5 x 10-7
60Fe wasn’t created by spallationIrradiation of rocky material at 0.1 AU in principle can produce radionuclides like 60Fe
Only 64Ni(p,p)60Fe reaction can happen, but 64Ni is rare and cross section is < 0.1 mbarn
Predicted yields:
60Fe/56Fe ~ 10-11
(Lee et al 1998; Leya et al 2003)
Shu et al (1996)
60Fe wasn’t inherited from our molecular cloud
Harper (1996)
Supernovae, Wolf-Rayet winds, novae, AGB stars maintain steady-state levels of 60Fe, etc., in the Galaxy
60Fe
26Al
129I
Steady-state “average” abundance of 60Fe is 60Fe/56Fe ~ 3 x 10-7 (Harper 1996) or 60Fe/56Fe ~ 3 x 10-8 (Wasserburg et al 1996)
But then 129I/127I ~ 10-2, 182Hf/180Hf ~ 10-3, etc.
60Fe wasn’t inherited from our molecular cloud
Our molecular cloud was isolated from sources of radionuclides for >> 107 yr (Wasserburg et al 1996; Harper 1996)
Much of the radionuclides produced by supernovae go into hot phase, and don’t enter molecular clouds for ~108 yr
M 109
supernova
new star-forming molecular clouds
In the meantime, 60Fe completely decays
60Fe wasn’t injected by an AGB starAGB outflows do eject 60Fe, but only for ~ 1 Myr, after star has evolved for > 2 Gyr
AGB stars randomly distributed in Galaxy: no reason to associate them with star-forming regions
Odds per 1 Myr that a parcel of gas in a molecular cloud will be contaminated with AGB material:
< 3 x 10-6
(Kastner & Myers 1994)
AGB stars also do not eject appreciable 53Mn, 182Hf (Gallino et al 1998)
60Fe is ejected by supernovae associated with star-forming regions!Live 60Fe discovered in ocean crust 3 Myr old (Knie et al 2004)
Only plausible source is supernovae in Scorpius-Centaurus star-forming region (Maiz-Appelaniz 2001; Fields et al 2004)
P. Frisch, U. Chicago
60Fe
Fe
60Fe will be injected into disks associated with those supernovae
~ 0.2 pc
1 Ori C: 40 M star will supernova in < 1 Myr
protoplanetary disks
HST image, Orion Nebula
Sufficient 60Fe can be injected without destroying disk
Iron likely in form of dust grains: gas-phase Fe disappeared from SN 1987A ejecta at same time (1-2 years post-explosion) that 10-3 M of dust formed (Colgan et al 1994)
Mass of 60Fe ejected by 25 M supernova ~ 8 x 10-6 M (Woosley & Weaver 1995)
Fraction intercepted by 30 AU radius disk at 0.3 pc away ~ (30 AU)2 / 4 (0.3 pc)2 ~ 6 x 10-8
Mixed with 0.01 M of solar composition
material, 60Fe / 56Fe ~ 1 x 10-6
Sufficient 60Fe can be injected without destroying disk
Worst-case scenario: fast cooling
Ouellette et al (2005), in prep
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Sufficient 60Fe can be injected without destroying disk
Ouellette et al (2005), in prep
With realistic cooling
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Conclusions60Fe in early solar system could not be inherited, could not be produced by spallation, almost certainly was not from AGB star
Only plausible source of the 60Fe is a nearby supernova
Protoplanetary disks are observed near (~ 0.3 pc) massive stars that will soon go supernova
Supernova ~0.3 pc away can inject 60Fe-bearing dust grains into a protoplanetary disk, yielding 60Fe/56Fe ~ 10-6 in the disk material, without destroying disk