Topics in Astronomical Spectroscopy : Evolution of Chemical Abundances based on the High Resolution Stellar Spectroscopy 2010, 1 학기 대학원 이상각 19 동

Aims : Evolution of Chemical Abundances based on the High Resolution Stellar spectroscopy is the subtitle of this course and aims to cover the recent developments of the understanding of chemical evolution of the cosmos as a whole, as well as that of the Galaxy. This leads into the outline of the recent studies of the high resolution stellar spectroscopy for investigation of the history of matter from the Big Bang to the present, based on the Big Bang Nucleosysthesis, Supernovae and Stellar Nucleosynthesis.

References The recent papers on the subject of evolution of chemical abundances for each class discussion will be announced in the class bulletin board. There is no text book for this course. However the following reference books may be useful. Nucleosynthesis and Chemical Evolition of Galaxies, 2nd Edition, B. J. Pagel, 2009 Cambridge, Supernovae and Nucleosynthesis, D. Arnett, 1996, Princeton An Introduction to Cosmochemistry, C. Cowley, 1995, Cambridge

Credits The classes will be mainly the round table discussing seminar. All enrolled students have to present the review of an assigned paper and conduct the class by leading discussion with other students and report his or her review in written form. It will be graded for 45% of the course credit. Mid & final exam : 50% class attendance : 5%

Basic topics I. Big Bang Nucleosythesis II. Early Universe III. Pop III Stars, First Stars IV. Metal-Poor Stars V. Milky Way VI. Galaxies VII. n-processes VIII. Stellar Nucleosythesis IX. Sne : SNe II, PISNe, SN Ia

a) the large abundances of H and He; b) the deep “hole” coresponding to Li/Be/B; c) a series of peaks, particularly prominent for the α nuclei, corresponding to the products of stellar burning between mass 12 and mass ∼ 40; d) a mass peak near Fe, A ∼ 56-60; e) rare heavier elements, but with mass peaks near A ∼ 130 and A ∼ 195.

Cosmic Abundance

Five groups of elements 1. The dominant elements : H & He by mass : 1 H ∼ 0.75, 4 He ∼ 0.25  primarily to nuclear and weak interaction processes occuring in the first few minutes after the big bang 2. the lighter “1p-shell” nuclei (He < < C) : relatively rare, lower by 8-10 orders of magnitudes 6 Li ∼ 7.75E-10 7 Li ∼ 1.13e-8 9 Be ∼ 3.13E B ∼ 5.22E B ∼ 2.30E-9 7 Li can be produced in the Big Bang. Li, Be, and B can also be produced in the interstellar medium, when energetic cosmic-ray protons collide with elements like C, N, and O. Li, Be, and B can also be synthesized by core-collapse supernovae, directly by the interactions of neutrinos in the carbon shells of such stars.

The evolution of galactic Li as a function of metallicity Li abundance plateau – called the Spite plateau – at low metallicity, indicating that some baseline of Li existed when the first stars were formed. This is assumed to be the primordial value. Note the great spread of values for stars of solar metallicity. The two circles correspond to the expected standard solar model Li (the high value) and the measured Li. The sun managed to destroy mosts of its Li – most likely by dredging Li to depth (to high temperatures, where it can be burned) – during some past epoch. Also shown are various theoretical mechanisms proposed for synthesizing Li. From Ryan et al., astro-ph/ /.

Li

α -stable elements 3. α -stable elements C, N, O, Ne, Mg, Si, a multiple of 4 He, (N,Z)=(2,2).  An important property of the nuclear force is pairing: nucleons are fermions with spin ½. The α-stable nuclei are more tightly bound than their neighbors with broken pairs.  thermodynamically-favored products of nuclear burning 12 C ∼ 3.87E-3 14 N ∼ 0.94E-3 16 O ∼ 8.55E-3 20 Ne ∼ 1.34E-3 24 Mg ∼ 0.58E-3 28 Si ∼ 0.75E-3

Iron group and n-processes elements 4. peak near iron-group nuclei: Elements near Fe and Ni have the largest binding energy/nucleon.  the last possible products of a sequence of fusion reactions 5. heavy elements, A ∼ > 100 Many of these elements are very rare, but a function of A or N shows interesting patterns – several abundance peaks. each peak is actually a double peak, with the two components split by ∼ 10 mass units.  (n,γ) reactions : weak neutron sources, extremly high neutron densites.

Binding Energy

Nuclear transformation

Neutron and proton capture

detailed view of solar system heavy element abundances : From Truran et al., astro-ph/

how are the differences in abundances among these groups explained? wide variety of nucleosynthetic signatures : analysis and interpretation of the chemical signatures and enrichment histories revealed by stellar spectra

Imprints in spectra Top : a) carbon star X Cancri with 12 C/ 13 C ~4 from H-burning by the CNO cycle and enhanced Zr b) peculair C star HD without 13 C and H-deficient c) C star HD52432 with 12 C/ 13 C ~4 Middle; a) normal C star HD showing CH and H  b) peculiar(H-poor) C star HD showing C2 but weak H  bottom: a) normal F b) HD metal-poor star

Imprints in spectra Top : a) normal G b) BaII starHD c) M giant 56 Leo showing TiO d) S type AGB, R And showing Zr Bottom : c) Tc in R And which indicate s-process and dredge-up within a few half-lives of Tc 99 (2* 10 5 yr)

Cosmic Chemical Evolution