Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.mso.anu.edu.au/~brian/A3002/lect11.pdf Дата изменения: Mon Oct 23 08:54:07 2006 Дата индексирования: Tue Oct 2 01:34:46 2012 Кодировка: Поисковые слова: stars

Chemical Evolution of the Universe

As we look back in time, photons have wavelengths shortened by (1+z)

at z=6400, Universe becomes photon dominated... T~17000K At increasingly higher z, we can achieve any temperature we want

In the few minutes after the Big Bang, the initial Composition of the Big Bang is set by a series of nuclear reactions...

So at T>10 at T=10

10.5

(t < 0.2s)

10.5

(t = 0.2s) (t < 0.9s)

So at T~10

10.14

End up with mainly protons, neutrons and electrons (some neutrinos) when Universe is 1 second old With ratio of N/P set as

Neutrons decay with half-life of 887 seconds Formation/Destruction of Deuterium Neutrons converted to D at roughly 200s From Saha equation (but Neutron Decay!, etc)
Each reaction dependent on T, and density of the species involved
0 1 2 3 4 5 6 7 8 9

10 9 8 7 6 5 4 3 2 1 0 Series1

In Subsequent reactions (200s worth), almost all neutron end up in He-4. Except those neutrons that decay ... So if 1/7th of all nucleons are a neutron, and Helium-4 has equal numbers of neutrons and protons...then 2/7th of all nucleons will end up in He-4 ­ or 28% of the mass of the Universe...A bit less 28%*exp(-100s/900s) =24% when one takes into account neutron decay...


Prediction of BBN

Burles et al/Ned Wright

Measuring He abundance

H II regions are gas clouds ionized by young, massive stars

(Fields & Olive 1998, ApJ 506, 177)

There are several ways to deal with the uncertainty associated to the ionization structure

Historical Problems amd their solutions

problem

solution Hope Physics has this right stellar libraries tailored models

physics
1. applying selection criteria 2. building tailored photoionization models 3. using narrow-slit data

atomic parameters

stellar absorption stellar parameters

ionization structure

nebular temperature structure self-consistent solution parameters Better Modeling, especially at H I collisions
low Z


Two Recent Results Source Izotov et al. 1999 Peimbert et al. 2002 YPrimordial 0.2452 0.0015 0.0070 0.2391 0.0020 0.0010

Measure D/H Ratio

QSO at z=2.6 from Kirkman et al

D

H


Continuum level

Line confusion Stellar Processing

Measuring 3He
· 3He is processed by stars being created from Deuteurium but also burned into heavier elements. But 3He seems to be constant as a function of metallicity for most stars
Relatively Stays with Therefore uniformly complex (and undeveloped model) suggests He3 stars most of the time, only 10% of time ejected ­ solar abundance is correct???? This is not accepted ­ generally agreed should not use He3
Li-Fe

Measuring Lithium, Beryllium and Boron
Observe in primitive (Pop II) stars
evolution
Spite & Spite 82

·

Plateau at low Fe

·

No plateau for Be and B:
! Not primordial, ! Made by Galactic process(es)

BBN Prediction:
6

Thomas, Schramm, Olive, BDF 93

Li, Be, B unobservably small Consistent with observations "time"

Abundance

! const. abundance at early epochs ! Li is primordial


Lithium does evolve slowly due to SN? Or other sources..

Choose stars without convective envelopes... Measure...

Ryan et al, 2000 A=log(Li/H)+12

Fits all the Data We Can Compare to CMB measures Of ! when we Talk about the CMB