Super-AGB Stars


Astronomy research
  Software Infrastructure:
     My instruments
  White dwarf pulsations:
     12C(α,γ) & overshooting
     Probe of 12C(α,γ)16O
     Impact of 22Ne
     Impact of ν cooling
     Variable white dwarfs
     MC reaction rates
  White dwarf supernova:
     Stable nickel production
     Remnant metallicities
     Colliding white dwarfs
     Merging white dwarfs
     Ignition conditions
     Metallicity effects
     Central density effects
     Detonation density
     Tracer particle burning
     Subsonic burning fronts
     Supersonic fronts
     W7 profiles
  Massive stars:
     Pop III with HST/JWST
     Rotating progenitors
     3D evolution to collapse
     MC reaction rates
     Pre-SN variations
  Massive star supernova:
     Yields of radionuclides
     26Al & 60Fe
     44Ti, 60Co & 56Ni
     SN 1987A light curve
     Constraints on Ni/Fe
     An r-process
     Effects of 12C +12C
  Neutron Stars and Black Holes:
     Black Hole spectrum
     Mass Gap with LVK
     Compact object IMF
     He burn neutron stars
  Neutrino Emission:
     Neutrino emission from stars
     Identifying the Pre-SN
     Neutrino HR diagram
     Pre-SN Beta Processes
     Pre-SN neutrinos
     Hypatia catalog
     SAGB stars
     Nugrid Yields I
     He shell convection
     BBFH at 40 years
     γ-rays within 100 Mpc
     Iron Pseudocarbynes
  Pre-Solar Grains:
     C-rich presolar grains
     SiC Type U/C grains
     Grains from massive stars
     Placing the Sun
     SiC Presolar grains
  Chemical Evolution:
     Radionuclides in 2020s
     Zone models H to Zn
     Mixing ejecta
  Thermodynamics, Opacities & Networks
     Radiative Opacity
     Skye EOS
     Helm EOS
     Five EOSs
     Equations of State
     12C(α,γ)16O Rate
     Proton-rich NSE
     Reaction networks
     Bayesian reaction rates
  Verification Problems:
     Validating an astro code
Software Instruments
AAS Journals
   2024 AAS YouTube
   2024 AAS Peer Review Workshops

2024 ASU Energy in Everyday Life
2024 MESA Classroom
Outreach and Education Materials

Other Stuff:
   Bicycle Adventures

Contact: F.X.Timmes
my one page vitae,
full vitae,
research statement, and
teaching statement.
Turbulent Chemical Diffusion In Convectively Bounded Carbon Flames (2016)

Here we describe an idealized model of convectively bounded carbon flames with 3D hydrodynamic simulations of the Boussinesq equations using the pseudospectral software instrument Dedalus.

On Carbon Burning in Super Asymptotic Giant Branch Stars (2015)

In this article we explore the detailed and broad properties of carbon burning in SAGB stars with 2755 MESA stellar evolution models. The location of first carbon ignition, quenching location of the carbon burning flames and flashes, angular frequency of the carbon core, and carbon core mass are studied as a function of the ZAMS mass, initial rotation rate, and mixing parameters such as convective overshoot, semiconvection, thermohaline and angular momentum transport.

In general terms, we find these properties of carbon burning in SAGB models are not a strong function of the initial rotation profile, but are a sensitive function of the overshoot parameter. We quasi-analytically derive an approximate ignition density, ρign ≈ 1.3 × 106 g cm-3, to predict the location of first carbon ignition in models that ignite carbon off-center. We also find that overshoot moves the ZAMS mass boundaries where off-center carbon ignition occurs at a nearly uniform rate of Δ MZAMS/Δfov ≈ 1.6 M. For zero overshoot, fov=0.0, our models in the ZAMS mass range ≈ 8.9 to 11 M show off-center carbon ignition. For canonical amounts of overshooting, fov=0.016, the off-center carbon ignition range shifts to ≈7.2 to 8.8 M. Only systems with fov ≥ 0.01 and ZAMS mass ≈7.2 - 8.0 M show carbon burning is quenched a significant distance from the center. These results suggest a careful assessment of overshoot modeling approximations on claims that carbon burning quenches at an appreciable distance from the center of the carbon core.


SAGB illustration

3 slices, 2418 MESA models
kippenhahn 7.5 M
ignition point moves inwards
angular momentum evolution
ignition location in mass-over plane

Advanced burning stages and fate 8-10 M stars
The stellar mass range 8 ≲ M/M ≲ 12 corresponds to the most massive AGB stars and the most numerous massive stars. It is host to a variety of supernova progenitors and is therefore very important for galactic chemical evolution and stellar population studies. In this article, we study the transition from super-AGB star to massive star and find that a propagating neon-oxygen burning shell is common to both the most massive electron capture supernova (EC-SN) progenitors and the lowest mass iron-core collapse supernova (FeCCSN) progenitors.

Of the models that ignite neon burning off-center, the 9.5 M would evolve to an FeCCSN after the neon-burning shell propagates to the center, as in previous studies. The neon-burning shell in the 8.8 M, however, fails to reach the center as the URCA process and an extended (0.6 M) region of low Ye (0.48) in the outer part of the core begin to dominate the late evolution; the model evolves to an EC-SN. This is the first study to follow the most massive EC-SN progenitors to collapse, representing an evolutionary path to EC-SN in addition to that from SAGB stars undergoing thermal flashes. We also present models of an 8.75 M super-AGB star through its entire thermal pulse phase until electron captures on 20Ne begin at its center and of a 12 M star up to the iron core collapse. We discuss key uncertainties and how the different pathways to collapse affect the pre-supernova structure. Finally, we compare our results to the observed neutron star mass distribution.

HR diagram
Divergence after C burn
kippenhahn 8.8 M
kippenhahn 9.5 M
kippenhahn 12 M
flame temperature profiles 8.8 M