Geneva: 9-13 September 2019
Slides (not available yet; 11 Sept)
- "Carbon stars" were first summarized by Bidelman (1956)
- Before ~2000, CEMP stars were thought to come from mass transfer in binaries
- (Aoki+ 2002, Frebel+, Christlieb+) Enhanced light elements (< Mg) in CEMP stars -> signatures of Pop III
- Carbon lines aren't apparent in warm stars (> 5500 K) at [Fe/H] < -3.5 CEMP stars
- Future outlook: (1) Dynamically and chemodynamically tagged groups with GAIA to determine the formation environment; (2) Effective of cooling channels (atomic C vs. dust)
- 14 stars with [Fe/H] < -4.5 currently; 12 have high [C/Fe]
- Do these CEMP stars have special abundance patterns? Pop III signatures?
- There is diversity (spread) in light (A <= 14) light elements but none in heavier elements
- CEMP grouping; different origins? (Caffau+ 2018; ToPoS Paper IV 2018)
- Metallicities from molecular lines are sensitive to NLTE modeling (Gallagher+ 2016)
- HE0107-5240 has a high radial velocity. Long period binary? (Arensten+ 2018)
- n-capture elements: one detected in a sparse region in [Sr/Ba] (?) vs [Fe/H] space. Rapid rotators? (Caffau+ 2019)
- Lithium problem (Bonifacio+ 2019): Li-free stars are "blue stragglers"? However this isn't applicable to ones that have measured low Li abundances
- (Sesito+ 2018) Some EMP stars are in the thick disk (GAIA-DR2) and some even in the thin disk (~100 pc excursions) How?
- 3D effects: comes from granulation (blue/redshifts)
- Cool stars have strong 3D effects since molecular lines from high in the atmosphere (e.g. Collet 2016)
- Radiation scattering from deep in the atmosphere to produce deviations from LTE
- (Amarsi+ 2017, 2018, 2019) Devitation from Fe, C, O, respectively
- 1D -> 3D-NLTE corrections make the [C/O] ratio flatten to a constant value instead of upturning at low oxygen abundances.
- Half of CEMP-no stars drop into the C-normal classification
- This star's abundance pattern is consistent with a single 11.2
$M_\odot$ with a faint SN ($3 \times 10^{50} M_\odot$ ) - However this is done with 1D modeling. But with 3D corrections (CH lines) is not important (-0.05 dex change)
- In oxygen (OH), there are large corrections (
$\pm 0.30$ dex).
- Summary on how to (successfully) search for the most EMP stars
- The combination of hi-res spectra and GAIA will change the field on the understanding of the origin of these stars
- (Starkenburg+ 2017) Locations of EMP stars: outskirts of the halo, dwarfs, and center of the bulge
- (Youakim+ 2017) 1/800 (1/80,000) halo stars have [Fe/H] < -3 (-4)
- Pristine survey: 5000 deg$^2$ (ongoing) outside the Galactic plane
- (Youakim+ submitted) MDF of halo stars between 5-15 kpc from the Galactic center, showing a peak at [Fe/H] = -1.6 with a long EMP tail
- (Arentsen+ submitted) Searching in the bulge for EMPs, using a pre-selection that also peaks at [Fe/H] = -1.6, compared to -0.4 from the raw data.
- In the Galactic center, stars with -1.0 to -0.5 in [Fe/H], there's a rotational component, but it disappears in more metal-poor stars. The velocity dispersion increases from 75 to 150 km/s going from [Fe/H] = -0.5 to -2.0
- (Longeard+ 2018, 2019) What about GCs? For the smallest satellites, the velocity dispersion is low for GCs and dwarfs but the MDF (spread) is much different.
- (Starkenburg+ 2018) Some EMPs have abundance patterns similar to Solar but some agree with "first star chemistry"
- With spec following (WEAVE, 4MOST), they expect 100 (6,000) new stars with [Fe/H] < -4 (-3)
- Using GAIA data, they can determine whether the EMP stars have possible origins in an accreted satellite (eccentric orbit), chaotic eccentric orbits (early infall into the MW), or even circular (!) orbits, including the Caffau star. There's one example that's confirmed in the thin disk.
- ~1/4 of the stars are in planar orbits, but the remaining EMP stars are split between retro- and prograde orbits
- For the stars in the Galactic plane, do they form in the disk? How is this possible if the gas was already enriched? Or are they accreted from satellites from the plane of satellites (retrograde ones could come from the Gaia-Enceladus merger).
- Paper: [http://arxiv.org/abs/1811.03099]
- (Fernandez-Alvar) Outside of 20 kpc, the metallicity of halo stars start to decrease
- (Dietz+ in prep) Peaks of the MDF differ in the thick disk (-0.6), inner halo (-1.6), and outer halo (-2.2). If the sample is restricted to a radius range, the MDF can be modeled with a mix of different populations (inner halo, outer halo, etc) as they orbit through this space
- (Matsuno+ 2019) MDFs of inner halo, Gaia-Enceladus, and outer halo
- There is a difference in the gradients between pro- and retrograde orbits (increasing VMP frequency for prograde)
- If there's a large retrograde merger in the past, this may dominate the signature in the MDFs, metallicity gradients, and dynamics.
- Enrichment from Pop III: Rapid rotators (large amounts of CNO) and Faint SN ("mass cut" in ejecta); internal vs external enrichment (Chiaki+ 2018); mono- vs. multi-enrichment (Hartwig+ 2018)
- Found 15 CEMP new stars and 25 r-process stars in their sample that have been analyzed. Based on these percentages, they expect 67 CEMP stars and 112 r-process stars in their full sample of ~220 CEMP stars
- Abundance patterns, overall metallicities, hydro simulations, and dynamics each hold some amount of information about the early chemical enrichment of the MW
- (Luri+ 2018; Helmi+ 2018) Dynamical data on the origin of halo stars, especially the retrograde stars. Many mergers, one major merger, or something else?
- Anders+ (2019) have published a ~200M stellar catalog for GAIA-DR2, which has about 30M in the Galactic bulge. The bar is apparent in the positional plot
- There are two components in the bulge & bar (old and new) that separate in an alpha-Fe plot
- Many groups since the mid-2000s have focused on Pop III rapid rotators for the initial enrichment of CEMP stars
- (C. Scannapieco+ in prep) Working on explaining abundance scatter due to yields and individual lifetimes from massive stars. Following H, He, C, N, O, Mg, Fe, ... (missed)
- (Norris & Yong 2019) 3D NLTE effects on abundances for [C I] and CH. Changes up to -0.4 dex.
- (Collet+ 2018) Collisional formation and destruction rates for OH dominates over radiative destruction rates in 3D
- (Norris & Yong 2019) Empirical corrections from 1D to 3D-NLTE, using a toy model. They showed that these effects are significant for CEMP stars
- C-rich and hyper-metal-poor stars and C-normal very-metal-poor gas collapses are possible, reproducing Groups II and III (e.g. Yoon+ 2016)
- Skymapper MDF: They find a slope of 1.5 between [Fe/H] = -4 and -3, showing that EMP stars are even more rare than previously thought
- New r-II star with [Fe/H] = -3.6 and [Eu/Fe] = +2.0. It has a scaled solar r-process distribution, and they're looking for more elements in deeper observations (original one was 12 mins!)
- Sculptor metallicities and abundances are different from the MW and other ultra-faint dwarfs (e.g. Chiti+ 2018)
- (Skuladottir+ 2015; Susmitha+ 2017; Spite+ 2018) Unique chemical patterns (especially in [Y/Ba] vs. [Ba/H]), unlike others in dwarf galaxies. Why are CEMP-no stars different in dwarf galaxies than the MW?
- They have [Fe/H] between -2 and -3 but high (Sr,Y,Zr) abundances. 2/3 have high Na. 3/3 have high A(C) = 7.4.
- One is a binary. Are the others? Hypothesis: small masses of gas that experience one event of LEPP/limited r-process, and faint SN (or other C-enhanced channels). Do the small amount of gas and SN Type II enrich the gas up to relatively high [Fe/H] for CEMP-no stars
- Are these stars expected in different environments? Do their formation depend on enviornment? What do they tell us about r-process enrichment?
- Metallicities can be determined more accurately using empirical formulae based on EW of Ni and Cr
- Can use detailed abundance patterns to compare with yield predictions to trace enhancements from FRMS, AGB, jet SNe, and NS mergers
- (Hansen+ 2019) No evidence that their sample of 98 CEMP stars are dynamically separable from other stars. Some have high eccentricity, but all are bound.
- Nearly all are classified as halo stars, and they probably formed in-situ. Equally many CEMP stars are pro- and retrograde.
- (Watson+ in press) First direct detection of Sr in a NS merger (AT2017gfo). Constrained the mass of Sr up to 5e-5
$M_\odot$
- CEMP-s stars are thought to be enriched in binaries with AGB stars, and CEMP-no are thought to have the original composition (Faint SN or rapid rotators)
- ~82% of CEMP-s are binaries, and ~17% of CEMP-no are binaries
- (Arentsen+ 2019) They've detected 4 new CEMP-no binaries that have long periods (~30 years). Above A(C) ~ 6.6 about half are binaries, and below it's around 18%.
- Why are there so few [Fe/H] < -3 CEMP-no stars? and no [Fe/H] < -4 CEMP-no stars?
- (Moe+ 2019) There is an increasing (close; < 10 AU) binary fraction with decreasing [Fe/H]
- But the yields of metal-poor (and metal-free) AGB stars are uncertain. s-process yields depend on metallicity, mass, and rotation.
- The abundance pattern of HE0107-5240 is fit well with a Z = -7 model (proton ingestion event) with dilution (mass transfer).
- (Chiaki+ 2017) Could different cooling (dust vs atomic) mechanisms cause different binarity fractions?
- If some CEMP-no stars are polluted by a companion, this complicates the interpretation of their abundances
- Binarity in CEMP stars: different fractions in CEMP-s, -r/s, and -no
- CEMP-no and EMP-r stars are almost all single stars
(Hartwig) Multiplicity of the first stars from machine learning-based classification of stellar fossils
- (Hartwig+ 2019) Mono- versus multi-enriched stars from previous massive stars and their SN. How to discriminate these from abundances?
- (Salvadori+ 2019) BM+80 245 can be fit with a PISN and a ~30 Myr stellar population
- Using Ishigaki+ (2018) models, they built a basis set for possible enrichment pathways for multi-enriched stars. Caveat: Only consider enrichment from Pop III
- [Ca/Ni] vs [Mg/Fe] is the most informative chemical space to discriminate between mono and multi
- Use machine learning (decision tree and then random forest) to train tree on mock data catalogs, obtaining the most informative elemental ratios
- Using the SAGA database (01/2019), they find that 80% are mono-enriched and 10% multi-enriched, meaning that there is a SN for every 3 star-forming minihalo. Assuming an IMF, this corresponds to ~1.5 Pop III stars per minihalo.
- Does this mean many minihalos blew out all of their gas, not allowing future star formation
- No trends in [C/Fe] vs [Fe/H] for mono- and multi-enriched
- (Yoon+ 2016, 2019) Group II and III CEMP-no star origins. There is a 4 dex spread in Ba and C. How to explain this? Different nucleosynthetic origin from the rest of CEMP-no stars? Multiple faint SNe or spinstar contribution?
- In dwarfs, there might be some differences in the fractions in each group between UFD and dSph galaxies. Similar MDF in A(C) but different in [Fe/H] between the two types, probably because of the more extended SFHs.
- ~28% CEMP frequency in UFDs and ~3% in dSphs (Yoon+ 2019; also see Salvadori+ 2015)
- Kinematics: CEMP-s stars and Group II CEMP-no stars might be associated with the Gaia-Enceladus event. There are also prograde stars in the Group II CEMP-no and G3, suggesting that they were accreted in minor mergers
- When looking at inclination vs. eccentricity, G3 CEMP-no is different than the rest of the stars. Could there be three different preferred orbits? Carbon-normal stars usually have orbits close to polar
- Future work: Need models to explain the origin of Group I and Group 3 CEMP-no stars
- (Yuan+ in prep) CEMP-s and CEMP-no aren't dynamically different populations, using GAIA-DR2. Same for r-I and r-II stars.
- Found five new dynamical groups, using a self-organizing map (SOM). Using 3D inputs to obtain a 2D color map (and 1D distribtions) for group populations.
- Are these new groups associated with previous mergers? One's associated with the Helmi stream, and others with the Gaia Sausage and Sequoia when viewed in action space (Myeong+ 2019; Vasiliev+ 2019)
- (Yuan+ in prep) There are two r-II stars associated with the Rg5 group
- LAMOST-APF (paper) survey goals:
- to increase the statistics below [Fe/H] = -4;
- to determine more accurate light element abundances in new halo stars
- to constrain the origin of these stars to use as tracers of the MW accretion history
- Looking at the kinematics of several CEMP and C-normal stars
- Only one stable Fluorine isotope 19F
- It is extremely sensitive to the formation environment, specifically the initial masses of the AGB star and its metallicity, which can be used to constrain low-mass AGB nucleosynthesis at low metallicities
- F can also form in Type II SNe and WR stars
- Focusing on two CEMP-s stars at [Fe/H] = -2.53 (HE 1429-0551) and -2.28 (HE 1305+0007).
- F is extremely hard to detect through the HF(1-0) R9 line at 2.336 microns. Unfortunately it is on top of a Telluric line and needs to be subtracted
- [F/Fe] differ between the two stars (+2.2 and ~0)
- What's going on?
- Theory: Nuclear physics? AGB nucleo? Binary parameters?
- Observations: model atmospheres, NLTE, Telluric lines
- Looking at (1) GRBs as probes of ISM/IGM enrichment at high-z through absorption spectra, (2)
$f_{\rm esc}$ from GRBs, and (3) kilonovae, deviating from the main focus in this meeting - Usually the host galaxy is too dim even for HST, and the ISM (including dust and molecules) is only probed by such an extreme event (e.g. Hartoog+ 2015)
- GRBs usually probe low metallicities because they are less likely to occur at solar
- Can probe the Lyman-Werner lines (Heintz+ 2019)
- GRBs provide an upper limit on the UV escape fraction, measured from the Ly$\alpha$ absorption line
- GRB 050908 had LyC radiation leakage and a low HI column density. Updated catalog (Tanvir+ 2019). Suggests an escape fraction <1.5% in the GRB hosts
- Absorbing gas is usually between 10s and 100s of parsecs
- (Lamb+ 2019; Troja+ 2019) Kilonovae afterglow spectra. One case suggests a low ejecta mass around 0.01
$M_\odot$ - (Siegel+ 2019) r-process nucleosynthesis in collapsars. Substantial contribution to the total budget (especially at early times)?
- Rotation of Pop III stars (Stacy+ 2011, 2013; Hirano & Bromm 2018) MHD transport of angular momentum in the accretion disk (free-fall -> Keplerian -> magnetic braking)
- Hirano & Bromm found a bifurcation into slow and rapid rotators (but at what ratio?)
- (Ji+ 2015) For different multiplicities, looking at the CEMP fraction w.r.t. peculiar Pop III abundance patterns
- (Jeon+ 2017) CEMP fractions (and their abundances) that were enriched by Pop III SNe
- Fragmentation from fast cooling
- H2 and CIE cooling + viscous dissipative heating
- Fast cooling occurs at densities below
$10^{-11}$ g/cm$^3$. Net heating between$10^{-10}$ and$10^{-8}$ g/cm$^{-3}$, suppressing fragmentation - The disk is Toomre Q-unstable in the outer disk (
$r_{10} > 4$ ). Also see (Lau & Bertin 1978)
- Fragmentation can also occur from chemothermal instabilities
- Can the fragments survive?
- Type I migration occurs quickly
- Type II migration occurs when a gap opens, and the (optically-thick) radiation can escape so that the clump can cool and stop migrating inwards
- The clump can survive if (1) it continues to accrete or (2) the central star is quickly growing
- Accreting clump: needs to radiative its gravitational energy away:
convention cooling, radiative cooling, aerodynamic drag - Fast growing star needs an accretion rate over
$2 \times 10^{-3} M_\odot yr^{-1}$
- No notes for the last two talks (schedule ran over time). I had to attend a telecon :(
- 12C/13C ratio is very constraining on H-burning, mixing, and partial CNO cycle (Maeder+ 2015). Deviations from H-burning can constrain SNe ejecta and wind ejecta. SNe contribution isn't apparent.
- (Choplin+ 2016) Back and forth mixing in the H-burning region where the 12C/13C ratio depends on the mixing factor
- In the Al-Mg cycles, the ratio is about constant and there's no relation with SN nucleosynthesis. It depends on winds at late times. This could be related to the Na-O anti-correlation in globular clusters
- Abundances in CEMP-no stars are consistent with CNO burning with minute contributions from SN
- (Takahashi+ 2014) SN yields from models with and without rotation. Still has difficulties for N.
- (Meynet+ 2010) Spinstars: Wind+SN asymmetric explosion
- If Wind >> SN, CEMP-no. Rich in CNO, 22Ne, Mg, Al
- If Wind << SN, C-normal and metal-poor
- They play an essential role in EMPs, especially with wind mass loss
- Massive stars rotate faster at low-Z -> mixing and mass loss (Maeder+ 1999; Stacy+ 2011)
- More mixing at low-Z (Maeder & Meynet 2002)
- High mass loss in red giant phase (Ekstrom+ 2008)
- Wind ejecta (Arcavi+ 2018; Taddia+ 2018; Bostroem+ 2019)
- Mixing may also play a role in Li-depletion (cf. Aguado)
- Rotation causes mixing between H- and He-burning regions (Takahashi+ 2014; Maeder+ 2015; Choplin+ 2016), and can induce s-process (Choplin+ 2018; Banerjee+ 2019)
- A factor of 30 difference in many elements (CNO, s-process) can be induced by rotation in low-Z stars (0 -> 70% breakup velocity)
- (Choplin+ submitted) Focusing on light elements (C -> Al) on 272 EMP stars from the SAGA database
- Consider a correction from evolutionary effects (rotation, mixing)
- Match with models with rotation and SN yields
- About 40-50% in total can be reproduced. 65% of CEMP stars with a preference for fast rotation. 25% of C-normal stars.
- Extracted rotation speed frequency increase with velocity (up to 600 km/s; 70% critical), whereas solar metallicity stars peak around 200 km/s
- At low-Z, wind loss is low. Can't lose angular momentum through that channel, so the star continues to spin up due to internal AM transport
- How to lose this angular momentum? Mass loss at the equator
- With increasing rotation, the surface temperature decreases and luminosity increases
- Magnetic fields enhances AM transport and surface enrichment
- Be stars are a local analog to fast rotators that lose mass at the equator, creating a disk
- Focusing on Group III stars (Yoon+ 2016) and the large scatter in Na/Mg ratio, suggesting that two different sources are needed
- (Clarkson+ 2018) Using a 45
$M_\odot$ MESA model. Not expected to have a SN in this mass range (40-100$M_\odot$ ) but needed for C/Mg. There should be mass ejecta (Herwig+ 2014). - (Wiescher+ 2010; Clarkson & Herwig in prep) Can Ca be created during H-burning in Pop III stars? With generous assumptions, 80% of Ca is missing. In their new models, there is a lot of mixing between layers
- (Clarkson+ in prep) Mapped the 45
$M_\odot$ model into a 3D simulation with PPMStar- Boundary mixing occurs through convective entrainment. Occurs within 100s of hours over ~10 Mm.
- Convection timescales is ~20 minutes at the He-shell
(Herwig) The origin of CEMP-i stars - Results from a comprehensive multi-method simulations approach
- Observations of [La/Eu] vs. [Ba/La] deviate from the expectations from nuclear physics of r- and s-process, using one-zone models running to equilibrium
- The equilibrium values are dependent on the neutron densities (one-zone)
- As the neutron densities evolve from low (1e6 /cm3; s-process) to high (1e20 /cm3; r-process), it goes through an intermediate (1e15 /cm3) phase, reproducing CEMP-i abundances
- H can be entrained/ingested at the boundary layer during the He-flash that then can propagate inward
- Hypothesizing that i-process elements are created on rapidly accreting white dwarfs (Denissenkov+ 2019). Also dependent on WD mass. Implies a delay time for i-process enrichment.
- (Krticka+ 2011) Episodic mass loss through a decretion disk and through the circumstellar medium
- Using the GENEC (Geneva) stellar evolution code: solar (Ekstrom+ 2012), SMC (Z=2e-3) metallicity (Georgy+ 2013), IZw18 (Z=4e-4) metallicity (Groh+ 2019)
- (Murphy+ in prep) Pop III GENEC models
- Smooth transitions between burning phases -> hotter phases
- Stars spend most of their time at hot surface temperatures -> more ionizing photons
- Rotation are more luminous on the MS with longer MS times
- Between 20% to 40% critical rotation, it transitions from a cooler to a still-hot surface temperature during He-burning
- More massive stars (>60
$M_\odot$ ) reach critical velocities before the end of H-burning, producing mass loss
(Campbell) Low-mass primordial stars: i-process nucleosynthesis during core-flash proton ingestion episodes?
- Intermediate-mass stars (2-3
$M_\odot$ ) will start to chemically enrich the ISM around z=5 - He-flash of a 0.85
$M_\odot$ Pop III star: Compared to a solar metallicity star, it happens much farther out (0.25$M_\odot$ instead of 0.1$M_\odot$ )- Causes the induced convection to break out of the core. Unique to Pop III stars
- This mixes down protons, causing a dual core flash (H and He) and "interesting" nucleosynthesis that mixes to the surface (Campbell & Lattanzio 2008)
- Also unique: a "neutron superburst" in i-process (Campbell+ 2010)
- Currently extending previous work to the KEPLER code to investigate how a more complete reaction network changes the final yields
(Thielemann) r-Process Sites, their Ejecta Composition, and their Imprint in Galactic Chemical Evolution
- Talk cancelled. Slides online.
- Focus on determining the endpoints of Pop III SN: typical core collapse, magnetar-like jet explosions, pair-instability SN?
- (Placco+ 2015) Attempt at trying to fit the EMP abundance patterns to Pop III yields to determine the progenitor mass and SN energy & ejecta mass
- HE 1327-2326 (Frebel star): only [Fe/H] < -5 star that's bright enough in the UV to observe (Ezzeddine+ 2019)
- Detected Zn at [Zn/Fe] = 0.80 +/- 0.25 (1D-NLTE)
- Cannot be fit with a spherical faint SN (3e50 erg), but it is fit well with a jet-like SN (5e51 erg)
- In addition to Zn, Ti has a better fit and explains the N and Sr enhancements from fast rotators and a jet-like SN
- Big picture: fast rotator (producing N and Sr) -> Aspherical jet-like SN (Zn and Ti) -> external enrichment that imprints this unique signature into a minihalo and EMP star
- This scenario could explain the scatter in [Fe/H] < -4 stars. Presence of different enrichment channels -> origin of multiple CEMP-no groups (Yoon+ 2016)
- Origin of different Yoon+ (2016) groups
- Group 1: Extrinsic
- Group 2 & 3: SNe, spinstars, and binary mass transfer
- Two dominant grains: carbon and silicate grains. The former is important in C-rich gas, and the latter is important in less metal-poor stars.
- Group 2 could be enriched by normal type II SN, and Group 3 could be enriched by faint SN.
- (Chiaki & Wise 2019) Investigating Type II SN enrichment (Group 2) with dust formation, using yields from Nozawa+ (2007)
- (Chiaki+ in prep) Considering faint SN enrichment (Group 3) in three progenitor masses: 13, 50, and 80
$M_\odot$ - They have extremely low ([Fe/H] < -8) abundances because of the yields
- All have insufficient enrichment to cool efficiently
- Leads to second-generation Pop III stars and cannot form CEMP-no stars
- Multi-enrichment is required to explain CEMP-no stars, consider with Hartwig+ (2019)
- No notes for my talk (obv)
- (Hirano+ 2018) Semi-analytic model to constrain the Pop III during the early formation of the Milky Way.
- There should be around 1e6 minihalos that merge into the MW.
- Construct a model of halo evolution, collapse, and enrichment that are calibrated by simulations, in particular the Jeans mass
- More massive minihalos have more cold gas but contract slowly (Hirano+ 2014, 2015)
- Dynamical support or streaming velocities can delay star formation (Schauer+ 2019; Wise+ 2019; Hirano+ 2017, 2018)
- (Sugimura+ in prep) Fragmentation of a protostellar disk into a binary. Resimulating some of the Hirano+ (2015) simulations. The total stellar mass is unchanged but contained within a few fragments
- (Susa 2019) 10-100 fragments form in a minihalo (at the beginning of the first MS star) in a study that compiles previous simulation results
- (Machida & Doi 2013) Amplification of B-field during a metal-free collapse. At the smallest scales, there is magnetic braking that transports AM outward, resulting in a smaller protostellar disk, fewer fragments, and slower-rotating and more massive stars.
- (Ishiyama+ 2017, in prep) Running 27 different simulations of MW-mass halos that resolve minihalos down to 1e5
$M_\odot$ - From these merger trees, create a semi-analytic model of Pop III star formation, using critical halo mass, Pop II/III star formation, and LW background intensity
- Using the mass spectrum from Hirano+ (2015), they find a bimodal distribution in the MW-mass halos. They sharply peak at 15 and 100
$M_\odot$ - However if a more broad mass spectrum is used (from Susa 2019), the distribution is nearly flat between 1 and 100
$M_\odot$
- Open questions: can we constrain the Pop III IMF? Did they form below 10
$M_\odot$ ? Can we probe very massive Pop III stars? - All metal poor stars have a total metallicity that is greater than
$10^{-5} Z_\odot$ even though some are severely iron-poor - (Schroek 2009?; Christlieb+ 2009) Observed MDF of the Milky Way
- (de Bennassuti+ 2017) Using semi-analytic model of chemical enrichment of the MW with an assumed Pop III IMF
- CEMP stars are dominant in the EMP population below [Fe/H] = -4, and above there are primarily C-normal stars
- Because there is so much carbon in faint SN, this results in CEMP star formation, and then later star formation drives down [C/Fe] to C-normal star formation
- They predict 20% of [Fe/H] = -5 stars are C-normal. There are few of these stars observed, but 3D-NLTE effects should drive down previous carbon measurements
- Their model favors an IMF that peaks (or plateaus) between 10 and 300
$M_\odot$ . If a flat IMF is used, there are very few CEMP stars. - 50% of CEMP stars are enriched by Pop III AGB stars.
- What about the very high-mass end of the IMF?
- The stars that are enriched by
$M > 60 M_\odot$ Pop III stars usually have [Fe/H] > -3 and are lost in the MW population. Only 0.3% of [Fe/H] = -2 stars are imprinted by these massive stars - (Salvadori+ 2019) Zn, Cu, N, F are always under-abundant (subsolar) if a star is enriched by a pair-instability SN, even when varying the progenitor mass and dilution mass
- Suggests an observational strategy to detect PISN signatures in [Fe/H] = -2 stars that have subsolar abundances in Cu and Zn
- BD 80-145 is one such star
- Best fit model: 50/50 metals from PISN and normal stars (within 30 Myr after PISN) and a dilution factor of 1e-4. Progenitor mass of PISN = 220
$M_\odot$
- The stars that are enriched by
- (Jeon+ 2017, 2019) Inspecting the enrichment of ultra-faint dwarfs and DLAs from Pop III stars
- (Jeon+ 2015) First galaxy simulation: virial mass of 1e8
$M_\odot$ , stellar mass of 1e4$M_\odot$ . Similar to ultra-faint dwarfs. - Some of the first galaxies could experience little star formation after its ancient burst (cf. Weisz+ 2017) because of reionization suppression
- (Jeon+ 2019) Includes C, O, Mg, Ne, Si, Fe in their simulation with diffusion (Greif+ 2009)
- More massive halos (M > 3-4 x 1e9
$M_\odot$ ) experience continuous SF until z=3, whereas the less massive ones are suppressed by reionization - CEMP stars are enriched by Pop III. C-normal stars are enriched by later metal-enriched stars
- The most metal-poor ([Fe/H] < -3) stars are enriched through external process, but it is sensitive to the critical metallicity (Pop III -> II)
- More massive halos (M > 3-4 x 1e9
- (Jeon+ in prep) Improving their 2017 work with radiative feedback and higher resolution
- Halos with M > 1e9
$M_\odot$ are always enriched by multiple populations - Mono-enrichment is possible in the smallest atomic cooling halos
- They recover the different populations of CEMP and C-normal stars
- Halos with M > 1e9
- The most metal-poor DLAs
- (Cooke+ 2017) Detected a z=3.1 [Fe/H] = -2.8 DLA that is consistent with being enriched by a single ~20
$M_\odot$ star - (Jeon+ 2019) Cannot find CEMP dense gas around dwarf galaxies (too metal-rich) or around ultra-faint progenitors (no neutral gas)
- Maybe a larger simulation (bigger sample and large-scale structure) could uncover this type of object
- (Cooke+ 2017) Detected a z=3.1 [Fe/H] = -2.8 DLA that is consistent with being enriched by a single ~20
- What are the sources of reionization?
- AGN: bright but too rare (Shull+ 2012; Giallongo+ 2015; Onoue+ 2017; Parsa+ 2018)
- Massive (binary) stars: contribute the most photons to the ionizing budget. Main unknown: the escape fraction
- X-ray binaries (e.g. BPASS - Stanway & Eldridge; Goetberg+ 2019) should play a role in producing more ionizing photons (e.g. Rosdahl+ 2018; Schaerer & Fragos 2019)
- The hardness of the ionizing radiation will affect the production of different nebular emission lines
- (de Barros+ 2019) Ionizing radiation can be scattered (Case A recombination)
- Recombination and line emission depends on the escape fraction
- Ly$\alpha$ (Verhamme+ 2015), UV absorption lines, and high [OIII]/[OII] emission ratio can be used as probes of escape fraction
- The Ly$\alpha$ will be produced in different ways if UV can escape or not. With small to zero escape fractions, the red/blue peaks will be less than 300 km/s.
- (Jaskot & Oey 2013) [OIII]/[OII] will be ~0.25 if
$f_{esc} = 0$ and ~25 if non-zero - (Heckmann+ 2011; Alexandroff+ 2015) For zero escape fraction, there would be deep UV absorption lines because the covering factor is unity
- (Izotov+ 2016, 2017, 2018, 2019) Green pea galaxies (z ~ 0.3) with [OIII]/[OII] > 4.
- All five that were observed had escape fractions 6-13%, where they confirmed that the three indirect probes were valid.
- They have stellar masses between 1e8 and 1e10
$M_\odot$ . - The lowest mass galaxy has an escape fraction of 70%
- Perhaps these are undergoing their first burst of SF after reionization
- Strong P Cyg OVI lines -> strong outflows
- They all exist in voids
- Future work: Using RT post-processing on the SPHINX simulations (Rosdahl+ 2017) to make further correlations between the indirect probes and escape fraction
- Young galaxies forming during the Epoch of Reionization (EoR) transition from bursty to continuous star formation
- How did the CEMP (and their subclasses) form in the first galaxies?
- Using EAGLE simulation to build a chemical evolution model (including Type II SN, Type Ia, and AGB)
- Initially, stars are enriched by Type II SNe and then AGB. They see a distinction between C-normal and CEMP stars forming.
- CEMP-no stars usually form during EoR
- (Edelmann+ 2016) Dynamical shear occurs at the edges of convective zones. There are very few radiative zones with shear. This induces mixing and AM transport between zones, which is tricky to implement in 1D simulations.
- Convective boundary mixing. Two methods: Penetrative, which is a sharp transition (Zahn 1991) and exponentially decaying diffusion that is smooth (Freytag+ 1996; Herwig 2000)
- (Cristini+ 2017, 2019) 3D LES simulations focusing on silicon burning (convective) in a 15
$M_\odot$ solar metallicity star. - Entrainment speeds are inversely proportional to bulk Richardson numbers (equivalent to a ratio of stabilizing potential to turbulent kinetic energy)
- (Eggenberger+ 2019) Need AM transport to explain the flat rotation speeds in the radiative zones of the Sun.
- Can happen by magnetic fields through MRI (Ruediger+ 2014, 2015) and Tayler-Spruit dynamo (Braithwaite 2006) processes
- (Eggenberger+ 2010) There is less impact (wrt hydro only) by efficient AM transport in low-mass (~Msun) stars because of the opposite effects of MHD (decreasing) and rotation (increasing)
- (Cantiello+ 2014) Small-scale (TS) dynamo isn't strong enough to transport AM
- (Belkacem+ 2015; Pincon+ 2017) Studying the physical nature of the missing AM transport by internal gravity waves and other mixed modes
- (Huber+ 2010) Overview of asteroseismology. Frequency differences and maximum freqencies are related to surface gravity, density (mass and radius), and surface temperature. Therefore one can measure an accurate mass given an effective temperature in red giants.
- Asteroseismology has been done for nearby stars, but can we do this for distant halo stars?
- Do the scaling relations hold at low metallcity?
- Require long-term and very accurate light curves -> Kepler
- Observe 26 stars with high relative velocities (confirmed with GAIA-DR2) and low metallicities (i.e. halo stars)
- (Epstein+ 2014) The mean stellar mass is 1.1
$M_\odot$ , which is too high for halo stars. But this can be corrected through asteroseismology down to 0.97$M_\odot$ (Yu+ 2018) - They find no CEMP stars, but only 10% of [Fe/H] = -2 are C-enhanced. With more observations, there will probably be a CEMP star with asteroseismology.
- (Asplund+ 2009) Update using 3D-NLTE, resulting in a 30% reduction of metallicity
- However, asteroseismology favors the higher metallicity solar models (Z=0.0182)
- What's causing the discrepancies? Not 3D models. Neon is a problem because there are no lines, but is dependent on solar activity and is the 3rd biggest contributor to opacity (at some zone)
- There are uncertainities in opacities from different groups
- (Buldgen+ 2017) Inversion favors a low metallicity (Z ~ 0.01, depending on the opacity table) with the GN93 and GS98 tables, which are ruled out
- Low mass XRBs:
$M_{BH} \sim 8 M_\odot$ average; High mass XRBs:$M_{BH} = 10-16 M_\odot$ - (McClintock+ 2011, 2014) Spin measurements of 9 XRBs. LMXB typically have low (a=0.1-0.7) spins in small orbital periods, and HMXBs have high (a>0.9) spins
- The field can now use GWs to constrain X-ray binaries. The BBH mergers are typically more massive than the observed HMXBs, which is expected because they occur more often in low-Z (Z < 0.003) binaries that produce less stellar wind mass loss
- (Madau & Fragos 2017) Mean stellar metallicity as a function of redshift
- (Fragos & McClintock 2015; Qin+ 2018, 2019; Bavera+ 2019) The observed BH spin doesn't have any memory of the initial rotation but is a result of the merger interaction
- Formation channels: (1) "chemically homogeneous" binary evolution; (2) dynamical BH binary formation; (3) common envelope binary evolution (e.g. Belczynski+ 2016ab)
- 60% of BBHs have low spin (long merger time; formation at z=3), 10% have short merger time and high metallicity, and 30% have short merger time and low metallicity (LIGO selection effect because it's sensitive to high mass BHs)
- (Bavera+ 2019) Distributions of merger and formation redshifts and metallicity with aLIGO
- (Inayoshi+ 2017) Pop III can form BBHs in ~1% of cases; 10-100 times more frequent than metal-enriched stars
- (Hartwig+ 2016) LIGO can't observe Pop III BH mergers because their SFRD is too low. Need to wait until Einstein Telescope & Cosmic Explore (3rd gen)
- (Chandrasekhar 1964) GR instability in supermassive stars (SMS) with
$M > 10^4 M_\odot$ - Why SMSs as a seed of z > 6 quasars? Instead of rapidly accreting at the (super-)Eddington limit, start massive.
- Monolithic model (e.g. Hoyle & Fowler 1963) or rapidly accreting (~1 Msun/yr) massive protostars (Begelman+ 2006; Hosokawa+ 2013; Haemmerle+ 2018, 2019)
- (Woods+ 2017; Haemmerle+ 2018; Umeda+ 2016) SMS masses between 1e5 and 1e6
$M_\odot$ with increasing masses with increasing accretion rates (0.1-10 Msun/yr) - Observational signatures: GWs or ultra-long GRBs
- Monolithic models rotate at critical velocity and are fully convective.
- Rapid accretors slowly rotate (<10% of critical; Maeder & Meynet 2000) and strong differential rotation. This could be a problem because angular momemtum needs to be removed
- (Mayer+ 2015) DCBH formation in a galaxy center after a merger. When a collapse occurs, is it a dark collapse or does a SMS form?
- (Haemmerle+ in prep) How fast can a star accrete? When the accretion timescale equals the sound crossing time, the pressure cannot increase fast enough to maintain equilibrium. Evolution is delayed by a sound crossing time and could result in a dark collapse. This occurs in M < 100 Msun BHs at very high accretion rates (> 100 Msun/yr)