Massive Star Evolution: Plain and Fancy J. Craig Wheeler Department of Astronomy. University of Texas at Austin MESA Summer School, August 11, 2015

Bill Wolf, UCSB Manos Chatzopoulos, Enrico Fermi Fellow, University of Chicago

Pre-supernova evolution of massive stars. Focus on M > 8 M , especially M > 12 M . Basic spherically symmetric, non-rotating, non-magnetic stellar evolution. Stages of nuclear burning, “onion skin” layers, leading to iron core, instability, collapse. Late stages of stellar evolution are probably very different than taught us by Fred Hoyle, Martin Schwarzschild, other pioneers because of rotating, magnetic fields. Start with basics (Paxton+11)

2 – 10 M  non-degenerate degenerate

10 – 100 M  1/3 a T 4 = R/μ ρ T T proportional to ρ 1/3 Dividing line, radiation pressure, gas pressure.

15, 30 M 

M 

“Kipppenhahn” diagram, inner 7 of 25 M  Radial structure versus time, radiative, convective regions

2 – 10 M 

Lifetimes

Recent Example of Use of Stellar Ages Leloudas et al. (2015): hydrogen-poor superluminous supernovae (SLSN) are correlated with extreme emission line galaxies (EELG). Very short bursts of fast star formation. Episode of star formation must be very short, few million years; progenitors of SLSN must be massive to die in the short time. ~7x10 6 yr => M > 25 M  ~4x10 6 yr => M > 60 M  ~3x10 6 yr => M > 120 M 

Manos – MESA struggles to compute lifetimes through core helium burning for M > 35 M . Bill W. – At higher mass, MESA increases “retries.”

Opacities R proportional to T/ρ 1/3

Iron “Bump” OPAL opacities, based on lab work at Los Alamos (Iglesias & Rogers 1993). An issue is the iron opacity bump at T ~ 150,000 K which can cause density inversions, supersonic convection, and locally super-Eddington luminosities, which in turn make the structure numerically unstable. Not known in early work, 1970’s, changes structure, lifetimes..

Iron Bump

Iron opacity bump versus metallicity

Funky, super-Eddington luminosity structure.

Evolution Minilab Compute a range of non-rotating masses,; crowd source the evolution time and other relevant parameters (mass and radius, mass and radius of helium core, mass and radius of C/O core, varcontrol_target, mesh_delta_coeff, final number of zones, number of timesteps). Each group is assigned a ZAMS mass, 7, 8, 10, 12, 15, 18, 20, 22, 25, 30 M  (could easily add an eleventh group). inlists starting at the beginning of core hydrogen burning. Compute the model to the end of core helium burning: Solar Z, basic nuclear network, default mass loss, MLT++. Individuals in a group compute different spatial resolution, constraints on  t. See lab writeup.

Results of Minilab Crowd source: Final total mass of star Mass in helium core Mass in C/O core Radius of star Radius of helium core Radius of C/O core Lifetime from ZAMS to end of core helium burning Note the location of radiative and convective regions varcontrol_target mesh_delta_coeff final number of zones number of timesteps