Oxygen Isotopes Anomalies of the Sun and the Original

Environment of the Solar System

Jeong-Eun Lee

UCLA

collaboratorsEdwin A. Bergin (Univ. of Michigan)James R. Lyons (UCLA)

Matter from stars (stellar winds of red giant stars and supernova explosions) is expelled to ISM.

The molecular clouds are sites for star formation. Extensive chemical and physical processing of

materials in the Solar nebula and planetary bodies destroys the ISM heritage.

But: Asteroids and comets have escaped significant Asteroids and comets have escaped significant

alteration by the reprocessing.alteration by the reprocessing. Primitive bodies such as comets, meteorites, and IDPs Primitive bodies such as comets, meteorites, and IDPs

possibly preserve the oldest solar system solids possibly preserve the oldest solar system solids material to provide opportunities to probe the material to provide opportunities to probe the astrophysical environment when the Sun formed.astrophysical environment when the Sun formed.

The solar system and ISM

Complete isotopic homogenization is expected from the chemical and physical processing of solar system materials.

Thus:

any surviving presolar material will have an exotic isotopic composition, which could not have resulted from processes occurring in the solar system.

Exotic Isotopic Ratios measured from IDPs, Meteorites, and Comets (connected to ISM):

D/H, D/H, 1515N/N/1414N, N, 1818O/O/1616O (O (1717O/O/1616O)O)

Isotopic Anomalies

Oxygen Isotopes Oxygen isotope production

16O produced in stellar nucleosynthesis by He burning

provided to ISM by supernovae

rare isotopes 17O and 18O produced in CNO cycles

novae and supernovae Expected that ISM would have regions that are

inhomogeneous Is an observed galactic gradient (Wilson and Rood 1992) Solar values 16O/18O 500 and 17O/18O 2600

Oxygen Isotopes chemical fractionation can also occur in ISM

except for H, kinetic chemical isotopic effects are in general of order a few percent

distinguishes fractionation from nuclear sources of isotopic enrichment

almost linearly proportional to the differences in mass between the isotopesEx: a chemical process that produces a factor of x

change in the 17O/16O ratio produces a factor of 2x change in the 18O/16O ratio

so if you plot so if you plot ((1717O/O/1616OO )/ )/ ((1818O/O/1616OO) then the ) then the slope would be 1/2slope would be 1/2

Oxygen Isotopes in Meteorites

In 1973 Clayton and co-workers discovered that calcium-aluminum-rich inclusions (CAI) in primitive meteorites had anomalous oxygen isotopic ratios.

Oxygen Isotopes in MeteoritesEarth, Mars, Vesta

follow slope 1/2 line indicative of mass-dependent fractionation

primitive CAI meteorites (and other types) follow line with slope ~ 1 indicative of mass independent fractionation

Terrestr

ial

line

Met

eorit

ic

line

SMOW = standard mean ocean water

€

δ(X O) =

xO16O

⎛ ⎝ ⎜ ⎞

⎠ ⎟source

x O16O

⎛ ⎝ ⎜ ⎞

⎠ ⎟s tan dard

⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟− 1

⎧

⎨ ⎪

⎩ ⎪

⎫

⎬ ⎪

⎭ ⎪

1000

Oxygen Isotopes in Meteorites

meteoritic results can be from mixing of 2 reservoirs

Terrestr

ial line

Met

eorit

ic lin

e- 16O poor

- 16O richSolar value?-The initial value of molecular cloud

2 Disparate Measurements: δ18O = δ17O = -50 per mil

lowest value seen in meteorites

seen in ancient lunar regolith (exposed to solar wind 1-2 Byr years ago; Hachizume & Chaussidon 2005)

δ18O = δ17O = 50 per mil contemporary lunar soil

(Ireland et al. 2006)

differences are very difficult to understand.

Huss 2006

Considerable controversy regarding the Solar oxygen isotopic ratios.

Oxygen Isotopes in the Sun

Theory stellar nucleosynthesis

lack of similar trend seen in other elements chemical reactions that are non-mass dependent

(Thiemens and Heidenreich 1983) known to happen in the Earth’s atmosphere (for ozone)no theoretical understanding of other reactions that can

link to CO and H2Ophoto-chemical CO self-shielding

suggested by Clayton 2002 at in the inner nebula at the edge of the disk (X point)

active on disk surface (Lyons and Young 2005)active on cloud surface and provided to disk (Yurimoto and Kuramoto 2004)

CO Photodissociation and Oxygen Isotopes

0.5 < Av < 2

C18O + h -> C + 18O

C16O

18O + gr -> H218Oice

C16O + h -> C + 16O

C18O + h -> C + 18O

Av < 0.5 Av > 2

C16O

C18O

CO Self-Shielding Models

active in the inner nebula at the edge of the disk (Clayton 2002)only gas disk at inner edge, cannot make

solids as it is too hot active on disk surface and mixing to midplane

(Lyons and Young 2005)mixing may only be active on surface where

sufficient ionization is presentcannot affect Solar oxygen isotopic ratio

CO Self-Shielding Models

active on cloud surface and provided to disk (Yurimoto and Kuramoto 2004)did not present a detailed modelcan affect both Sun and disk

Model chemical-dynamical model of Lee, Bergin, and

Evans 2004use Shu 1977 “inside-out” collapse modelcloud mass of 3.6 M◉

approximate pre-collapse evolution as a series of Bonner-Ebert solutions with increasing condensation

examine evolution of chemistry in the context of physical evolution

model updated to include CO fractionation and isotopic selective photodissociation

two questionstwo questions what level of rare isotope enhancement is provided to disk?what level of rare isotope enhancement is provided to disk?what is provided to Sun?what is provided to Sun?

Temperature and Density Evolution in the Model

δ18O Evolution with a Range of UV Enhancements

Issues large enhancements in δ18O and δ17O are provided to the

disk at all radii in the form of water ice. This material is advected inwards and provided to the

meteorite formation zone (r < 4 AU). BUT: - the gas has an opposite signature - enriched in 16O in the

form of CO - gas and grain advection in the disk must be decoupled in

some way to enrich inner disk in heavy oxygen isotopes relative to 16O

Icy grains drift inward due to gas dragIcy grains drift inward due to gas drag (Cuzzi et al . 2004)(Cuzzi et al . 2004) Gas orbits more slowly than solids at a given radiusGas orbits more slowly than solids at a given radius

–results in a headwind on particles that causes them to drift inwardsresults in a headwind on particles that causes them to drift inwards

ModelAssume material provided at inner radius of our

model (100 AU) is advected unaltered to the inner disk

Assume significant grain evolution has occurred and material fractionation has occurred (gas/ice segregation) in the disk. time this fractionation begins is a variableafter fractionation begins assume that water is

enhanced over CO by a factor of 5 - 10

constraintsconstraintsthe solar oxygen isotope ratiosthe solar oxygen isotope ratiosthe solar C/O ratio - need to assume (C/O)the solar C/O ratio - need to assume (C/O)initialinitial > (C/O) > (C/O)◉◉

The Solar Oxygen Isotope Ratio

Mf = amount of solar mass affected by fractionationMf = 0.1 if fractionation begins 4 x 105 yrs after collapse

δ (18O)◉ = 50 per mil implies a slightly enhanced UV field (G0 = 10) with Mf ~ 0.1 M◉

δ(18O)◉ = -50 per mil implies a weak (G0 = 1) or a strong UV field (G0 = 105) with Mf ~ 0.1 M◉

1.8x105 2.7x105 3.6x105 time fractionation starts

G0 = 0.4

G0 = 10

G0 = 103

G0 = 105

The solar C/O ratio

G0 = 0.4

G0 = 10

G0 = 103

G0 = 105

All relevant solutions G0 = 0.4, 10, and 105 can matchsolar C/O ratio if Mf ~ 0.05 - 0.1 M◉

1.8x1052.7x105

3.6x105 time fractionation starts

More constraints on G0

Have 3 potential solutions with variable radiation field that depend on the solar value

More constraints?More constraints? meteoritic and planetary meteoritic and planetary

isotope ratiosisotope ratios water ices in comets…water ices in comets…

Go=10Go=1055 !!! !!!

Our model of oxygen isotopes suggests Our model of oxygen isotopes suggests the presence of a massive O star in the the presence of a massive O star in the vicinity of the forming Sun 1 million years vicinity of the forming Sun 1 million years before collapse and that the Solar value is before collapse and that the Solar value is δδ((1818O)O)◉◉ = -50 per mil. = -50 per mil.

Looking Back in Time: Before the Sun was Born

Looking Back in Time: Before the Sun was Born Recently the presence of the extinct radionuclide 60Fe (1/2 =

1.5 Myr) is inferred in meteorites with varied composition (Tachibana & Huss 2003; Mosteraoui et al. 2005; Tachibana et al. 2006) cannot be produced by particle irradiation abundance consistent with production in nucleosynthesis

in a Type II supernova or an intermediate-mass AGB star and provided to the solar system before formation

probability of an encounter between Sun and intermediate mass AGB star is low (< 3 x 10-6; Tachibana et al. 2006)

taken as strong evidence that Sun formed in a stellar taken as strong evidence that Sun formed in a stellar cluster near an O starcluster near an O star