Metal-poor stars and the chemical enrichment of the universe Anna Frebel
Observations, stellar abundances, and chemical evolution
Prof. Anna Frebel Massachusetts Institute of Technology (MIT) & chemical enrichment Observations, abundances
1 Bio sketch
• 1999-2002: BSc equivalent in physics (Freiburg, Germany)
Anna Frebel • 2002-2003: Work experience at Mt. Stromlo Observatory (Canberra, Australia) • 2003-2006: PhD at Australian National University (Canberra, Australia) • 2006-2008: McDonald Postdoctoral Fellow (Univ. of Texas, Austin) • 2009-2011: Clay Postdoctoral Fellow (Harvard-Smithsonian CfA) • 2012-now: Assistant Professor of Physics (MIT, USA)
• Feel free to ask questions! • Available at NIC school: only Monday and Tuesday! & chemical enrichment at the 6.5m Magellan Telescope in Chile Observations, abundances
2 Research interests
Stellar archaeology: Near-field cosmology: Anna Frebel • The most metal-poor stars, • The first stars, • chemical evolution of the Milky • early star and galaxy Way and dwarf galaxies, formation, • stellar kinematics and galactic • galaxy assembly on structure, small scales, • supernova nucleosynthesis and • dwarf galaxies, neutron-capture processes, • the formation of the • nuclear astrophysics, Galactic halo • stellar evolution, (theoretically + observationally), • stellar abundances, • the age of the Universe. • spectroscopic observations and
& chemical enrichment analyses. Observations, abundances
3 Freely available at http://arxiv.org/abs/1102.1748
4 OutlineOutline Anna Frebel
Demo! & chemical enrichment Observations, abundances
5 Anna Frebel & chemical enrichment Observations, abundances
6 A long time ago...
nd First stars 2 and later generations of stars (<1 M ) Anna Frebel (100 M)
Big Bang today
first galaxies today’s galaxies
Larson & Bromm 2001
Cosmic time (not to scale) & chemical enrichment Observations, abundances
7 chemical evolution
All the atoms (except H, He & Li)
Anna Frebel were created in stars!
Pop III: zero-metallicity stars Pop II: old halo stars Pop I: young disk stars
We are made of stardust! ⇒ Old stars contain fewer elements (e.g. iron) than younger stars & chemical enrichment Zentrum Zentrum fuer und Astronomie Astrophysik, TU Berlin Observations, abundances
8 Stellar archaeology
Through chemical abundance studies Anna Frebel
Big Bang
~13 billion years in between
early gas cloud: Metal-poor star formation stars today in the metal-poor stars Milky Way
9 About a star... Anna Frebel
H He metals & chemical enrichment Observations, abundances
10 Astronomer’s periodic table Anna Frebel
Metals Z
[ Fe often used to trace metallicity Z ] & chemical enrichment Observations, abundances
11 What can we learn from old halo stars?
Low-mass stars (M < 1 M) Hertzsprung-Russell-diagram
Anna Frebel ⇒ lifetimes > 10 billion years ⇒ unevolved stars are still around! ______
Using “fossil” metal-poor stars to reconstruct... Origin and evolution of chemical elements Luminosity Relevant nucleosynthesis processes and sites Chemical and dynamical history of the Galaxy Lower limit to the age of the Universe APOD Temperature ... and to provide constraints Nature of the first stars & initial mass function Nucleosynthesis & chemical yields of first/early SNe Early star & early galaxy formation processes Hierarchical merging of galaxies (observed abundances are ‘end product’ that have to be reproduced by any comprehensive galaxy formation model) Formation of the galactic halo by detailed understanding of its stellar content & chemical enrichment Observations, abundances
12 The Milky Way
✷ ✷ ✷ ✷ ✷
✷ ✷ dwarf ✷ ✷ galaxies ✷ Halo
Disk Bulge
Metal-poor halo stars
13 The Role of Metal-poor stars
The abundances of the elements in stars more metal-poor than the Sun have the potential to inform our understanding of conditions from the beginning of time through the formation of the first stars and
Anna Frebel galaxies, and up to the relatively recent time when the Sun formed:
• The most metal-poor stars ([Fe/H] ~ −4.0), with primitive abundances of the heavy elements (atomic number Z > 3), are most likely the oldest stars so far observed.
• The lithium abundances of extremely metal-poor near main-sequence-turnoff stars have the potential to directly constrain conditions of the Big Bang.
• The most metal-poor objects formed at epochs of redshifts z > 6, and probe conditions when the first heavy element producing objects formed. The study of objects with [Fe/H] < –3.5 permits insight into conditions at the earliest times that is not readily afforded by the study of objects at high redshift.
• They constrain our understanding of the nature of the first stars, the initial mass function, the explosion of super- and hypernovae, and the manner in which their ejecta were incorporated into subsequent early generations of stars.
• Comparison of detailed observed abundance patterns with the results of stellar evolution calculations and models of galactic chemical enrichment strongly constrains the physics of the formation and evolution of stars and their host galaxies.
• In some stars w/ [Fe/H] ~ −3.0, overabundances of heavy-neutron-capture elements are so large that Th and U can be measured which leads to independent estimates of their ages and of the Galaxy.
• Stars with [Fe/H] ~ –0.5 inform our understanding of the evolution of the Milky Way system. Relationships between abundance, kinematic, and age distributions – the defining characteristics of stellar & chemical enrichment populations – permit choices between the various paradigms of how the system formed and has evolved. Observations, abundances
14 Solar abundance distribution
Needs to be known in order to calculate other stellar abundances!!
Anna Frebel (hence, if solar abundances change, everything else will change) & chemical enrichment Observations, abundances
15 Solar abundances
Photospheric (= “stellar” abundance) • Anders, Grevesse & Sauval ‘89 Anna Frebel • Grevesse & Sauval ‘98 • Asplund, Grevesse &Sauval ‘05 • Grevesse, Asplund & Sauval ‘07 • Asplund, Grevesse, Sauval & Scott ‘09 • Series of new papers ’14 • reference element: H • technique: calculation
Meteoritic (= “star dust” grain analysis) • Lodders 03 • Lodders, Palme & Gail 09 • reference element: Si • technique: measurement
• Volatile elements depleted, incl. the most abundant elements: H, He, C, N, O, Ne cannot rely on meteorites to determine the primordial Solar System abundances for such elements
& chemical enrichment • For each application, the most similarly obtained solar abundances should be use to minimize systematic Observations, abundances uncertainties! 16 Definitions: log ε(x) abundances
Stellar ‘abundances’ are number density calculations with
Anna Frebel respect to H and the solar value
On a scale where H is 12.0:
logε(X) = log10 (NX /N H ) +12 for element X
This quantity is the output of all model atmospheres!
i.e. MOOG code (of Chris Sneden, publicly available) + € Kurucz models (publicly available)
For lithium, the abundance is mostly expressed as A(Li) = logε(Li); and for hydrogen, by definition, log10ε(H) = 12.
& chemical enrichment For stellar abundances in the literature, results are generally presented relative to their values in the Sun, using the so-called “bracket notation”. Observations, abundances
17 definitions: [fe/h] Anna Frebel
where NFe and NH is the no. of iron and hydrogen atoms per unit of volume respectively.
⎡ ⎤ ⎡ ⎤ NO NO NFe NFe = ⎢log 10( )star − log10( )sun ⎥ −⎢log 10( )star − log10( )sun ⎥ ⎣ N H N H ⎦ ⎣ N H N H ⎦
€ & chemical enrichment [A /H] − [B /H] = [A /B] for elements A and B Observations, abundances
18
€ spectroscopic comparison Anna Frebel “Look-back time” “Look-back Galactic chemical evolution chemical Galactic
Abundances are derived from integrated absorption line strengths equals 1/250,000th of the solar Fe [Fe/H] = log(NFe/NH) − log(NFe/NH) & chemical enrichment * abundance Observations, abundances
19 Success over decades! Anna Frebel & chemical enrichment Observations, abundances
20 Metal-poor star related definitions Anna Frebel & chemical enrichment Observations, abundances
21 classification scheme
Range Term Acronym # Anna Frebel [Fe/H] ≥ +0.5 Super metal-rich SMR some [Fe/H] = 0.0 Solar — a lot! [Fe/H] ≤ –1.0 Metal-poor MP very many [Fe/H] ≤ –2.0 Very metal-poor VMP many [Fe/H] ≤ –3.0 Extremely metal-poor EMP ~100 [Fe/H] ≤ –4.0 Ultra metal-poor UMP 1 [Fe/H] ≤ –5.0 Hyper metal-poor HMP 2 [Fe/H] ≤ –6.0 Mega metal-poor MMP --
& chemical enrichment Extreme Pop II stars! as suggested by Beers & Christlieb 2005 Observations, abundances
22 What sort of stars are we looking for?
Low-mass stars
Anna Frebel with < 1 Msun ensures
⇒ Long lifetimes
Unevolved nature ensures
⇒Unmixed surface layers
This avoids surface abundances contamination with nuclear burning products from the stellar core and billion yr long preservation of & chemical enrichment abundances
Observations, abundances © B.J. Mochejska (APOD) 23 Three Observational Steps to Find Metal-Poor Stars Anna Frebel 1. Sample selection and visual inspection: Find appropriate candidates (Ca scales with Fe!)
2. Follow-up spectroscopy (medium resolution): Derive estimate for [Fe/H] from the Ca II K line
3. High-resolution spectroscopy: Detailed abundances analysis & chemical enrichment
Observations, abundances Frebel et al. 2005b 24 Halo Metallicity distribution function (MDF) Anna Frebel Previous ‘as observed’, raw MDF is not a realistic presentation!
(but shows that we have been doing a good job in finding these stars..) Non-zero tail!!!
Schoerck et al. 2008 The most metal-poor stars are & chemical enrichment extremely rare but extremely important! Observations, abundances
25 Stellar spectra
• Assessment and
Anna Frebel identification of different absorption lines and features
• Existence of lines indicates presence of given element in star
• Relative line strengths indicate element abundances
• Then: stellar parameters and abundances can be calculated & chemical enrichment Observations, abundances
26 How do we interpret stellar spectra?
Anna Frebel Overall, one needs to know:
1. Model atmosphere analysis techniques 2. Knowledge about a. Stellar evolution b. Nucleosynthesis c. Chemical evolution 3. Cosmological understanding of the MW stellar populations and galaxy formation & chemical enrichment Observations, abundances
27 Abundance determinations Shopping list: What you need to have and do to determine chemical abundances
1. Normalized high-resolution spectrum (e.g. from VLT) 2. Model atmosphere (e.g. Kurucz model) 3. Abundance code (e.g. MOOG) 4. Line list with spectral and atomic data
4. Measure equivalent widths of absorption lines 5. Determine stellar parameters 6. Spectrum synthesis of blended features => Calculate abundances w/ solar abundances as reference
28 Existance of line ⇒ Element present in star
Text
Line strength ⇒ Abundance of element
A. Frebel 29 Mg TheCa cosmicCH Mg chemicalNa H barcode
Mg
A. Frebel The cosmic chemical barcode 30 important spectral absorption lines in stars • H lines 6562Å, 4860Å, 4340Å, 4101Å Anna Frebel • CH g-band @ 4313Å and others • Li @ 6707Å
• Mg b lines @ ~5170Å • Ca K line @ 3933Å • Na D lines @ ~5880Å Fe lines are everywhere in the spectrum -- always • Eu @ 4129Å easily accessible • Sr @ 4077Å, 4215Å
& chemical enrichment • Ba @ 4554Å Observations, abundances
31 Atomic data
• every absorption line is an atomic transition
Anna Frebel • determined by atomic physics parameters • Vienna Atomic Line Database (VALD) http://vald.astro.univie.ac.at/ ~vald/php/vald.php • National Institute for Standards and Technology (NIST) http:// www.nist.gov/pml/data/asd.cfm
From [email protected] Mon Nov 1 10:03:10 2010 Date: Tue, 31 Aug 2010 23:56:00 +0200 From: [email protected] Subject: Re: ======job.012302 ======# begin request # extract all Stronger line <=> lower excit <=> higher log gf # default configuration # short format # # 4057.0, 4058.5 # end request Damping parameters Lande & chemical enrichment Elm Ion WL(A) Excit(eV) log(gf) Rad. Stark Waals factor References
Observations, abundances 'Ti 1', 4057.0060, 2.3340, -4.645, 7.735,-5.924,-7.491, 0.230,' 1 1 1 1 1 1 1'
32 Model atmosphere analysis techniques Anna Frebel Stellar parameters fully characterize a star:
effective temperature Teff surface gravity log g metallicity [Fe/H]
(microturbulent velocity vmic) & chemical enrichment Observations, abundances
33 Hertzsprung- Russell-Diagram
Lower metallicity leads to decreased opacity ⇒ Metal-poor stars are hotter than solar equivalents ⇒ Look bluer (bluer colors)
Needs to be taken into account: for temperature measurements for abundance analyses for stellar populations studies
34 Chemical analysis of stars determine The position and stellar strength of the parameters absorption lines tell us about the chemical composition of the star
prism, spectrograph...
measure equivalent widths of absorption lines
35 Abundance determination demonstration Anna Frebel
make screenshot & chemical enrichment Observations, abundances
36 definitions: [fe/h] Anna Frebel
where NFe and NH is the no. of iron and hydrogen atoms per unit of volume respectively.
⎡ ⎤ ⎡ ⎤ NO NO NFe NFe = ⎢log 10( )star − log10( )sun ⎥ −⎢log 10( )star − log10( )sun ⎥ ⎣ N H N H ⎦ ⎣ N H N H ⎦
€ & chemical enrichment [A /H] − [B /H] = [A /B] for elements A and B Observations, abundances
37
€ how to calculate chemical abundances
• Need a spectrum => measure equivalent width of
Anna Frebel absorption lines (=integrated line strength) • Need atomic data (excit. potential+log gf values) => feed both into “model atmosphere” • Get: calculated abundance (number density) log ε (X) • Calculate [Fe/H] with solar abundances
• Example:
• log ε (Mg)star = 5.96; log ε (Fe)star = 5.50
• log ε (Mg)sun = 7.60; log ε (Fe)sun = 7.50
• [Mg/H] = log ε (Mg)star - log ε (Mg)sun = -1.64 • [Mg/Fe] = [Mg/H] - [Fe/H] = -1.64 - (-2.0) = 0.36 & chemical enrichment Observations, abundances
38 1d vs 3d model atmospheres • 1D readily available • 3D custom made for each star, hard work
• Large abundance differences, especially CNO because comes from CH, NH, OH (molecular)
• => Needs to be kept in mind!
39 How metal-poor?
classical example:
Anna Frebel early universe: primordial gas how metal-poor is the next-generation star?
canonical SN Fe yield: 0.1 M 6 sun Mtot 10 Msun 6 N H = = available gas mass: 10 Msun mH mH
Mtot 0.1Msun NFe = = mFe 56mH €
logε(Fe)sun = log(NFe /N H )sun +12 = 7.50 € ⇒ log(NFe /N H )sun = 7.50 −12 = −4.50 −7 NFe 0.1Msun mH 10 = × 6 = N H 56mH 10 Msun 56
−7 & chemical enrichment €10 ⇒ [Fe /H] = log( ) − (−4.50) = −4.2 Observations, abundances 56 € 40
€ Anna Frebel
Part II & chemical enrichment Observations, abundances
41 Movies
• You can get these movies on youtube and my website annafrebel.com
• Enjoy!
42 chemical evolution
All the atoms (except H, He & Li)
Anna Frebel were created in stars!
Pop III: zero-metallicity stars Pop II: old halo stars Pop I: young disk stars
We are made of stardust! ⇒ Old stars contain fewer elements (e.g. iron) than younger stars & chemical enrichment Zentrum Zentrum fuer und Astronomie Astrophysik, TU Berlin Observations, abundances
43 The universe 4.5 Gyr ago
Big question in nuclear astrophysics: Anna Frebel How did the solar abundances come about? & chemical enrichment Observations, abundances
44 Reconstructing chemical evolution with metal-poor stars Anna Frebel => By establishing abundances trends with ‘time’ => By going back to the onset of chemical evolution & chemical enrichment Observations, abundances
45 Reconstructing chemical evolution with metal-poor stars Anna Frebel => By establishing abundances trends with ‘time’ => By going back to the onset of chemical evolution
• We can reconstruct individual supernova (enrichment) events with the abundance signatures of the most metal-poor stars
Big Bang
2nd generation stars Primordial First star First chemical forming from
& chemical enrichment gas cloud exploding enrichment enriched material Observations, abundances
46 Halo Metallicity distribution function (MDF)
How are the most metal-poor stars defined?
Schoerck et al. 2008
47 Halo Metallicity distribution function (MDF)
The most metal-poor stars
-7 -6.5 -6 -6.5 -5
Schoerck et al. 2008
48 What is so special About the most Fe-poor stars? Anna Frebel Aoki, Frebel et al. 2006, ApJ
hyper ultra extremely very hyper ultra extremely very Fe-poor Fe-poor Fe-poor Fe-poor Fe-poor Fe-poor Fe-poor Fe-poor
The very different chemical signature of the hyper iron-poor stars is crucial for understanding the formation of the elements! & chemical enrichment Observations, abundances
49 Pre-enrichment by a “faint SN”
• “Faint” SN with mixing and
Anna Frebel fallback: Post-explosion abundance distribution
–Explains high C, N, O, Mg (Smaller mass cut for HE1327-2326 to account for high [Mg/Fe]) Science 309 451 309 Science –Explain other metal-poor stars with [Fe/H]<−3.5
–Neutron-capture elements not included Iwamoto et al. 2005 et Iwamoto al. 2005
M=25M, Z=0, low E & chemical enrichment Observations, abundances
50 How and when did these early stars form?
e.g. HE 1327-2326 Big Bang Anna Frebel
2nd generation stars Primordial First star First chemical forming from
gas cloud exploding enrichment enriched material [X/Fe] Tominaga et al. 2007 Heger & WoosleyHeger 2008
Why important? Metal-poor stars provide the only available diagnosis for zero- & chemical enrichment metallicity Pop III nucleosynthesis and early chemical enrichment Observations, abundances
51 … with some more upper limits Anna Frebel Iwamoto et al. 2005 Science 309 451 309 Science et Iwamoto al. 2005 & chemical enrichment Observations, abundances
52 most important reactions in stellar nucleosynthesis:
* Hydrogen burning:
Anna Frebel - The proton-proton chain - The CNO cycle All textbooks, wikipedia * Helium burning: .... - The triple-alpha process - The alpha-capture process * Burning of heavier elements: - Carbon burning process Timmes+ ~95 - Neon burning process Woosely&Weaver 1995 - Oxygen burning process Heger & Woosley 2008 - Silicon burning process * Production of elements heavier than iron: - Neutron capture: - The r-process - The s-process Many details not - Proton capture: known, but good models - The rp-process out there - Photo-disintegration:
& chemical enrichment - The p-process Observations, abundances
53 “Regular” chemical evolution • The exception first: Lithium Anna Frebel
• Li is destroyed by the star itself as its convection zone deepens (when it becomes a red giant) • Majority of depletion seems to be taking place in the range 5500-5600 K & chemical enrichment
Observations, abundances • Li depletion does not significantly depend on metallicity
54 Carbon & nitrogen
⇒ Huge carbon Anna Frebel abundance ([C/Fe]= +3.7): (=> not so carbon-poor...)
5,000 Synthetic spectrum: red lines and 12,000 times Carbon (CH) band more carbon and nitrogen exist than iron!
⇒ Huge nitrogen abundance ([N/Fe]= +4.1): (=> not so nitrogen-poor...)
Synthetic spectrum: red lines
Reminder: Nitrogen (NH) band
& chemical enrichment Solar ratio [C,N/Fe] = 0
Observations, abundances Frebel et al. 2008, ApJ subm. 55 Carbon
•Another small Anna Frebel exception... •Surface carbon abundance DOES change with evolutionary status! •BUT, can be accounted for!
•s-process stars (come with high carbon) •r-process stars & chemical enrichment
Observations, abundances •regular metal-poor stars 56 Carbon
•Excluding the s-process Anna Frebel stars (have known origin of carbon):
•There are two populations of metal- poor stars: CEMP stars and regular metal-poor stars
•Why?? & chemical enrichment Observations, abundances
57 Mg b lines Ca II K line HE 1327-2326 Calcium often used as Mg, Ca are alpha-elements; proxy for the Fe abundance! Anna Frebel can tell about chemical evolution (..and Fe for metallicity)
–5.4 & chemical enrichment Observations, abundances Frebel et al. (2005), Nature 58 Chemical evolution of light elements - tada! Anna Frebel & chemical enrichment Observations, abundances
59 Abundance trends
[Mg/Fe] Alpha- Anna Frebel elements
[Si/Fe] Alpha elements multiple of He: (C,O), Ne, Mg, Si, S, Ar, Ca, Ti (not pure) [Ca/Fe]
Synthesis during stellar evolution and α-capture in supernova explosion of Pagel & Tautvaišiene (1995) massive stars (>8 M)
Fe and α-elements produced Fe-rich ejecta in the explosions of massive from the SN of stars (SN type II) low-mass stars & chemical enrichment (SN type Ia) Observations, abundances
60 With abundance trends Anna Frebel Most trends are flat or increasing but not all of them!
• 3D/NLTE effects listed & chemical enrichment when known Observations, abundances
61 Chemical evolution of neutron-capture elements Anna Frebel & chemical enrichment Observations, abundances
62 • halo stars Anna Frebel
• classical dwarf galaxies
• ultra-faint dwarf galaxies
• Segue 1 (faintest dwarf galaxy) & chemical enrichment Observations, abundances
63 Eu!
Anna Frebel • The Eu 4129A line indicates some level of r- process pre- enrichment of the birth gas cloud & chemical enrichment Observations, abundances
64 Stellar nucleosynthesis and chemical enrichment Anna Frebel & chemical enrichment Observations, abundances
65 B2FH Anna Frebel
... there are old stars with r-process signature being discovered! & chemical enrichment Observations, abundances
66 neutron-capture processes
_ Anna Frebel - β-decay: n => p + e v e
• s-process: neutron-capture longer than beta-decay timescale
& chemical enrichment • r-process: neutron-capture shorter than beta-decay timescale Observations, abundances
67 r and s process patterns Anna Frebel & chemical enrichment Observations, abundances
68 r-Process Enhanced Stars (rapid neutron-capture process)
r-process is responsible for the production of heavy elements in the early universe Anna Frebel Weak component: responsible for lighter (
Most likely production site: SN type II => pre-enrichment ~5% of metal-poor stars with [Fe/H] < − 2.5 (Barklem et al. 05)
=> Only ~16 stars known so far with [r/Fe] > 1.0 show a Chemical “fingerprint” of previous nucleosynthesis event
Nucleo-chronometry: obtain stellar ages from radioactive Th, U and stable r-process elements (e.g. Eu, Os, Ir)
oldest stars [Th and U can also be measured in the Sun, but chemical evolution has progressed too r-process in the far; required are metal-poor stars when only very few SNe had exploded in the universe]
69 Weak r-process stars Anna Frebel oldest stars r-process in the
70 HE1002-0755 HE1523-0901 Anna Frebel
© Anthony Ayiomamitis (Greek amateur astronomer) Evidence for rapid nucleosynthesis in stars Magnitude: V: 14.1 mag 11.1 mag Metallicity: [Fe/H]: −3.0 −3.0 “Extremely metal-poor stars”
Frebel et al. 2007, ApJ 660, L117 (HE1523-0901) Frebel et al. 2013, in prep. (HE1523-0901+HE1002-0755) oldest stars r-process in the
71 How and when did r-process stars form?
Star explodes as supernova and ejects the metals into the interstellar medium Anna Frebel
Big Bang
next generation Primordial 8-10 M star Chemical star forms from gas cloud exploding enrichment enriched material
SN
BB SN star -- decay -- today oldest stars r-process in the
72 Our Cosmic Lab Anna Frebel & chemical enrichment Observations, abundances
73 rapid nucleosynthesis evidence: HE 1523-0901 Anna Frebel
observed spectrum synthetic spectrum “best fit”
Frebel et al. (2013), in prep. oldest stars
r-process in the Lanthanides or rare earth elements: i.e. Eu, Gd, Dy
74 Observing neutron- capture elements Anna Frebel
HD 122563: r-process deficient star
CS 22892-052: r-process strong star
oldest stars Sneden, Cowan & Gallino 08, ARAA r-process in the
75 The r-Process Pattern Anna Frebel Very good scaled solar agreement r-process pattern with scaled solar r- process decayed Th,U pattern for Z>56 HE 1523-0901 According to metal-poor star abundances, the r-process is universal! & chemical enrichment Frebel et al. (2007) Observations, abundances
76 Precision at work!
Anna Frebel CS 22892-052
Scaled solar HD 115444 r-process element BD +17 3248 pattern!! CS 31082-001
HD 221170 HE 1523-0901
Cowan 2007, priv. comm They all have the same abundance pattern, particularly among heavy neutron-capture elements!
& chemical enrichment r-process must be a universal process! Observations, abundances
77 Stellar ages
• Easy! Anna Frebel
• & chemical enrichment Observations, abundances
78 Stellar ages
• Easy! Anna Frebel
• Well, not so much... • Observational uncertainties are large because of difficult measurements • Theoretical initial production ratios extremely uncertain
& chemical enrichment • 0.02dex change => 0.5Gyr !!! :( Observations, abundances
79 Thorium II Line 4019Å
Abundance:
Anna Frebel Synthetic spectrum (based on atomic data and model atmosphere) to match observed spectrum
Synthetic spectrum that includes NO thorium
‘Best fit’ synthetic spectrum
Th
HE 1523-0901 & chemical enrichment Frebel et al. (2015), in prep. in et al. (2015), Frebel Observations, abundances
80 Uranium in HE 1523-0901
Synthetic spectrum that includes NO uranium
Anna Frebel Synthetic spectrum with U abundance if it had NOT decayed
Frebel et al. (2007)
‘Best fit’ synthetic spectrum & chemical enrichment Observations, abundances
81 Cosmo-Chronometry Needs good observations...
232Th 238U Δt = 46.8 * (log (Th/r)0 − log (Th/r)obs ) Anna Frebel Δt = 14.8 * (log (U/r) log (U/r) ) TH = TH = 0 − obs 14Gyr 4.5Gy
Δt = 21.8 * (log (U/Th)0 − log (U/Th)obs) 208Pb 206Pb Age can be obtained from comparison of observed Th/Eu: “most commonly” used chronometer abundance ratio of a radioactive “famous” example: CS22892-052 element (e.g. Th, U) to a stable r- ~14-15Gyr; (Sneden et al. 96,03) process element (e.g. Eu, Os, Ir) and a theoretically derived initial U/Th: Uranium only confidently measured production ratio (e.g. Schatz et al. in one star before: CS31082-001 2002, Cowan et al. 2005, Duphas ~14Gyr (Cayrel et al. 01, Hill et al. 02); et al. 2005). oldest stars r-process in the => Ultimate goal: Use as many chronometers as possible!
82 Cosmo-Chronometry ...relies on nuclear physics! The Age of HE 1523-0901 Anna Frebel Frebel et al. (2007) Frebel
WMAP age of the Universe: 13.7 Gyr oldest stars r-process in the
83 Cosmo-Chronometry ...relies on nuclear physics! The Age of HE 1523-0901 Anna Frebel
For the first time more than one chronometer was be employed for a stellar age measurement! Frebel et al. (2007) Frebel ⇒ (WMAP model-) independent lower limit for age of the Universe
⇒ Universality of r-pattern (by observations; over >~5 Gyr) constraints r-process modelling of the heaviestWMAP nuclei age of the Universe: 13.7 Gyr ⇒ Other similarly metal-poor stars are probably similarly old oldest stars r-process in the
84 Chronometric Ages
Initial production ratios for nucleosynthesis taken from Schatz et al. 2002 Anna Frebel oldest stars r-process in the Roederer et al. (2009) 85 “Reverse engineering” or: let the observers make
• Assume age for star, e.g. 13 Gyr • Take observed ratios (at face value) & calculate initial prod. ratios Anna Frebel • Need star(s) with many measured chronometer ratios. Only available so far: HE 1523-0902 => NEED MORE STARS!!!
Ratio Observed Derived initial Derived Stars ratios prod. ratio ages (Gyr) derived from HE1523-0901 Th/Eu -0.62, -0.51, -0.222 18.6, 13.5, CS 22892-052, BD 17 3248, -0.60, -0.60 17.7, 17.7 HD221170, HD 115444 Th/Os -1.59, -1.63 -1.022 26.6, 28.5 CS 22892-052, BD 17 3248
Th/Ir -1.47, -1.48 -1.082 18.2, 18.6 CS 22892-052, BD 17 3248
U/Eu -1.33 -0.562 11.4 BD 17 3248
U/Os -2.45 -1.362 16.1 BD 17 3248
U/Ir -2.30 -1.422 13.0 BD 17 3248
oldest stars U/Th -0.82 -0.344 10.4 CS 31082-001 r-process in the
86 At the end of everything: Lead (Pb) Different Pb production channels: – Direct Pb production from decay of Th and U
Anna Frebel – Additional prod. channels e.g.from transuranic elements (those don’t go via the actinide path)
A known Pb abundance in HE1523-0901 helps disentangling what the different production channels are! oldest stars r-process in the
87 Lead in HE 1523-0901
Telescope/spectrograph: VLT/UVES Star brightness: V=11.1mag Th, U *and* Pb
Anna Frebel Spectral quality: S/N~450-500 detected Spectral resolution: R=85K (!)
Exposure time: texp~13h
Synthetic spectrum that includes NO lead oldest stars r-process in the Prelim. results! Frebel et al. (2013), in prep. 88 lead abundance prediction first “U” star total Pb from decay: log ε(Pb) = –0.72 t=0 t=13 Gyr HE CS31082-00 Anna Frebel 1523-0901 1 log(Th/U) 0.26 0.84 0.86 0.89
log(Th/Pb) -1.327 -1.316 -0.85 -0.43
log(U/Pb) -2.208 -2.161 -1.71 -1.32
log(Pb) -0.426 -0.346 ~-0.35 -0.55
Classical “waiting-point r- reasonable agreement...! process model” calculations (Frebel & Kratz 2009, ...poor agreement! Frebel et al. 2012, in prep) oldest stars r-process in the
89 lead abundance prediction first “U” star total Pb from decay: log ε(Pb) = –0.72 t=0 t=13 Gyr HE CS31082-00 Anna Frebel 1523-0901 1 log(Th/U) 0.26 0.84 0.86 0.89
log(Th/Pb) -1.327 -1.316 -0.85 -0.43
log(U/Pb) -2.208 -2.161 -1.71 -1.32
log(Pb) -0.426 -0.346 ~-0.35 -0.55
Big Picture: Classical “waiting-point r- reasonable agreement...! process“Textbook” model” stars like HE1523 are crucial for self- calculationsconsistency tests of rapid nucleosynthesis (Frebel & Kratz 2009, via Th-U-Pb predictions...poor agreement! Frebel et al. 2012, in prep) BUT: need more r-process model predictions! oldest stars r-process in the
90 Facing the challenges: Looking ahead
Observations: • SkyMapper Survey (now) + existing 6-10m telescopes Anna Frebel => lots more metal-poor stars (+ new r-process stars) Possible: predict initial production ratios => constrain r-process models • 25m Giant Magellan Telescope (after 2018) => enables follow-up of fainter r-process stars
Nuclear physics: • FRIB (after 2020) => better understanding of neutron-rich nuclei => improved r-process modeling => nucleo-chronometry’s “only hope”
Other: oldest stars More lab astro atomic data required for precise absorption line measurem. r-process in the
91 Skymapper telescope
1.3m telescope Siding Spring Observatory Australia PI: Brian Schmidt
SkyMapper is taking shallow data now! Provides new metal-poor halo stars now and will ultimately also find more dwarf galaxies!
92 What does SkyMapper observe? The filter set Keller et al.PASP2007, et Keller
93 Skymapper & Magellan: Match made in heaven
• New r-process stars will be found with SkyMapper • Also, other stars with interesting neutron-capture element patterns • Videos about observing with Magellan: youtube and annafrebel.com
Candidate metal-poor stars and observed w/ Clay 6.5m Magellan telescope selected with high efficiency... (on left) at Las Campanas Observatory, Chile
94 25m optical Giant Magellan Telescope From the GMT siteMagellan telescope Anna Frebel
G-CLEF spectrograph has been selected as first-light instrument!!! (AF is instrument scientist)
GMT will be located at Las Campanas, Chile oldest stars r-process in the
95 Gaia: surveying a billion stars http://sci.esa.int/gaia/
• “Gaia is an ambitious mission to chart a three-dimensional map of our Galaxy, the Milky Way, in the process revealing the composition, formation and evolution of the Galaxy. • Gaia will provide unprecedented positional and radial velocity measurements with the accuracies needed to produce a stereoscopic and kinematic census of about one billion stars in our Galaxy and throughout the Local Group. • This amounts to about 1 per cent of the Galactic stellar population.”
96 JINA III: CENTER FOR THE EVOLUTION OF THE ELEMENTS
97 Thank you!
Enjoy the rest of the school and the NIC conference!
98