Lecture 2

Abundances

Any study of nucleosynthesis must have one ofits key objectives an accurate, physically motivated explanation for the pattern of abundances that we find in nature -- in the solar system (i.e., the sun) and in other locations in the cosmos(other stars, the ISM, cosmic rays, IGM, and other galaxies)

Key to that is accurate information on that pattern in the sun.

For solar abundances there are three main sources:

• The Earth - good for isotopic composition only

• The solar spectrum

• Meteorites, especially primitive ones

The solar abundance distribution - should reflect the composition of the ISM when and where the sun was born

+ +

Elemental(and isotopic)compositionof Galaxy at location of solarsystem at the timeof it’s formation

solar abundances:

Bulge

Halo

Disk

Sun

History:

1889, Frank W. Clarke read a paper before the PhilosophicalSociety of Washington “The Relative Abundance of the Chemical Elements”

Current “abundance” distribution of elements in the earths crust:

(current, not 1889)

Fe

CNO

normalized to 106 Si atoms

SOLAR ABUNDANCES

The solar abundance pattern

256 “stable” isotopes 80 stable elements

1956 Suess and Urey “Abundances of the Elements”, Rev. Mod. Phys. 28 (1956) 53

1895 Rowland: relative intensities of 39 elemental signatures in solar spectrum

1929 Russell: calibrated solar spectral data to obtain table of abundances

1937 Goldschmidt: First analysis of “primordial” abundances: meteorites, sun

H. Schatz

1957 Burbidge, Burbidge, Fowler, Hoyle

H. Schatz

Since that time many surveys by e.g.,

Cameron (1970,1973)

Anders and Ebihara (1982); Grevesse (1984)

Anders and Grevesse (1989) - largely still in use

Grevesse and Sauval (1998)

Lodders (2003)

Asplund, Grevesse and Sauval (2007) - assigned reading

see class website

Absorption Spectra:

provide majority of data for elemental abundances because:• by far the largest number of elements can be observed• least fractionation as right at end of convection zone - still well mixed• well understood - good models available

solar spectrum (Nigel Sharp, NOAO)

H. Schatz

Complications:

• Oscillator strength:

Needs to be measured in the laboratory - still not done with sufficient accuracyfor a number of elements.

• Line width

Depends on atomic properties but also thermal and turbulent broadening. Need an atmospheric model.

• Ionization State

Emission Spectra:

Disadvantages: • less understood, more complicated solar regions (it is still not clear how exactly these layers are heated)• some fractionation/migration effects for example FIP: species with low first ionization potential are enhanced in respect to photosphere possibly because of fractionation between ions and neutral atoms

Therefore abundances less accurate

But there are elements that cannot be observed in the photosphere(for example helium is only seen in emission lines)

Solar Chromospherered from H emissionlines

this is how Heliumwas discovered bySir Joseph Lockyer ofEngland in 20 October 1868.

H. Schatz

MeteoritesMeteorites can provide accurate information on elemental abundancesin the presolar nebula. More precise than solar spectra if data in some cases. Principal source for isotopic information.

But some gases escape and cannot be determined this way (for example hydrogen, or noble gases)

Not all meteorites are suitable - most of them are fractionatedand do not provide representative solar abundance information.

Classification of meteorites:

Group Subgroup Frequency

Stones Chondrites 86%

Achondrites 7%

Stony Irons 1.5%

Irons 5.5%

One needs primitive meteorites that underwent little modification after forming.

H. Schatz

Use carbonaceous chondrites (~6% of falls)

Chondrites: Have Chondrules - small ~1mm size shperical inclusions in matrix believed to have formed very early in the presolar nebula accreted together and remained largely unchanged since then

Carbonaceous Chondrites have lots of organic compounds that indicate very little heating (some were never heated above 50 degrees)

Chondrule

H Schatz

“Some carbonaceous chondrites smell. They contain volatile compounds that slowly give off chemicals with a distinctive organic aroma. Most types of carbonaceous chondrites (and there are lots of types) contain only about 2% organic compounds, but these are very important for understanding how organic compounds might have formed in the solar system. They even contain complex compounds such as amino acids, the building blocks of proteins.”

http://www.psrd.hawaii.edu/May06/meteoriteOrganics.html

AGS04 Lod03 Lod03 AG89 ZAMS* ZAMS*

H 0.7392 0.7491 0.7110 0.7066 He 0.2486 0.2377 0.2741 0.2742 Z 0.0122 0.0133 0.0149 0.0191

* gravitational settling effects included

He from Solar models Helioseismology Emission lines H II regions

Grevesse andSauval (1998)

quite similar toAnders and Grevesse (1989)

Differences between solar photospheric and meteoritic abundances in 1998. Most discrepancies were by then less than a factor of 30% but there were notable exceptions –Tb, In, W, Li..

Grevesse and Sauval, Spac. Sci. Rev., 85, 161, (1998)

W

Tb

Bord and Cowley (Solar Physics, 211, 3 (2002))

Remaining discrepancies resolved for Ho, Lu, Tb as a consequence of better atomic physics for the spectral model. In and W remain problems. In especially a mystery.Is it volatility or atomic physics or both?

In

W

Summary: (Lodders 2003)

• 41 out of 56 rock forming elements, photospheric and meteoritic agree to within 15%

• Relatively large disagreements still exist for elements with uncertain oscillator strengths - Au, Hf, In, Mn, Sn, Tm, W, and Yb - and for elements uncertain in meteorites - Cl, Ga, Rb

• Most discrepant are W and In

• X(4He) - protosolar - 0.2741 +- 0.012

• Li depleted in sun by factor of 150. Be and B not depleted in the sun

• Ne and Ar are mainly from solar wind and flares and thus uncertain (< 0.2 dex). Ar has been seen in the solar spectrum. Kr and Xe abundances based in part on theory (n-capture cross sections)

Major recent revisions:

Lodders (2003) ApJ, 591, 1020 Asplund, Grevesse, and Sauval (2007)

*Lower CNO abundances based upon the non-LTE 3D hydrodynamical modeling of the of the solar photosphere by Allende-Prieto et al (2001), ApJL, 556, L63 and (2002) ApJL, L137.

All these papers are available on the class website!

Lodders (2003)

Asplund, Grevesse, and Sauval (2004)

Grevesse, Asplund, and Sauval (Spac Sci Rev, 130, 105 (2007))

Solar oxygen abundance based on log H = 12.0

Anders and Grevesse (1989) 8.93 0.0189Grevesse and Sauval (1995) 8.83 0.017

Grevesse, Asplund and Sauval (2007) 8.66 0.0122 (3D atmosphere; non-LTE Ni 6.23)Scott, Asplund, Grevesse and Sauval (2009) 8.71 (revised Ni abn 6.17)

ZO

Many papers have noted that the large downwards revision of the solar metallicity gives a sound speed that is in discord with valuesinferred from solar oscillations. See Grevesse et al (2007) for a list.

Grevesse, Asplund and Sauval (2007) choices for ZAMS solar Z and He

Z = 0.0132 (now 0.0122)

He = 0.2735

r

s

p

FeCNO

Different processes ofnucleosynthesis have theirdistinctive signature inthe abundance distribution.

Abundances outside the solar neighborhood ?

Abundances outside the solar system can be determined through:

• Stellar absorption spectra of other stars than the sun• Interstellar absorption spectra• Emission lines, H II regions• Emission lines from Nebulae (Supernova remnants, Planetary nebulae, …)• -ray detection from the decay of radioactive nuclei• Cosmic Rays• Presolar grains in meteorites

H. Schatz

E.g, metallicity gradient in Galactic disk:

Hou et al. Chin. J. Astron. Astrophys. 2 (2002) 17data from 89 open clustersradial iron gradient = -0.099 +_ 0.008 dex/kpc

Many other works on this subjectSee e.g. Luck et al, 132, 902, AJ (2006)radial Fe gradient = - 0.068 +_ 0.003 dex/kpcfrom 54 Cepheids

Si

S

Ca

Ti

/H /Fe

From Luck et al.

Y

La

Nd

Eu

/H /Fe

Y shows gradientEu maybeNd noisyLa ?

Kobayashi et al, ApJ, 653, 1145, (2006)Variation with metallicity

Kobayashi et al, ApJ, 653, 1145, (2006)

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CS 22892-052Sneden et al, ApJ, 591, 936 (2003) [Fe/H] ~ -3.1

Abundances in a damped Ly-alpha system at redshift2.626. 20 elements.

Metallicity ~ 1/3 solar

Fenner, Prochaska, and Gibson, ApJ, 606, 116, (2004)

Fenner et al (2004) vs WW95

Best fit, 0.9 B, = 1.35, mix = 0.0158, 10 - 100 solar massesHeger and Woosley 2007, in preparation)

A&A, 416, 1117

Data are for 35 giants with -4.1 < [Fe/H] < -2.7

28 metal poor stars in the Milky Way Galaxy -4 < [Fe/H] < -2; 13 are < -.26

Integrated yield of 126 masses 11 - 100 Me (1200 SN models), with Z= 0,

compared with low Z observations by Lai et al (ApJ, 681, 1524, (2008))

Best fit

E = 1.2 B M

20⎛⎝⎜

⎞⎠⎟

−1/2

=1.35

20-100Me Mix=0.0063

Frebel et al, ApJ, 638, 17, (2006)Aoki et al, ApJ, 639, 896, (2006)

Best fit

E = 0.9 B M

20⎛⎝⎜

⎞⎠⎟

−1/2

=1.35

13.5-100Me Mix=0.0158

Christlieb et al 2007, in prepartion

[Fe/H] = -5.1

Abundances of cosmic rays arriving at Earthhttp://www.srl.caltech.edu/ACE/

Advanced Composition Explorer (1997 - 1998)

time since accelerationabout 107 yr. Note enhanced

abundances of rare nuclei madeby spallation