Dynamical Mass Ejection Events from Red Supergiants
Philipp Podsiadlowski, Matthew Clayton (Oxford),
Natasha Ivanova (Alberta), Stephen Justham (MPA, Munich)Ludwig Biermann (1938, ZA, 16, 29):
• large (super-)giants are dynamicallyunstable⊲ binding energy becomes positive(when including recombinationenergy)⊲ γ̄ < 4/3→ Paczyński & Ziólkowski (1968)

Mira Variable Chi Cygni⊲ causes dynamical ejection of AGB
envelopes (Mira variables)
OutlineI. Some history
II. Dynamical instabilities in extended giants
III. Applications to CE systems, AGB stars,RGB stars, He giants
IV. Implications for Supernovae, RSGs

Hypergiant VY CMa (mass loss
∼ 10−3 M⊙ yr−1)

The Ejection of AGB Envelopes
Paczyński & Ziólkowski (1968) (alsoBiermann 1938, Lucy 1967, Roxburgh1967, Wagenhuber & Weiss 1994):• when the envelope binding energy of theenvelope (including recombinationenergy) becomes positive (i.e. theenvelopes become formally unbound)• not dynamical ejection (radiative losses),
but by a superwind in a Mira phase (withṀ ∼ 5 × 10−5 M⊙ yr−1 ) → rapid mass loss
→ planetary nebulaHan, Ph.P., Eggleton (1994): explains theobserved WD mass distribution and theinitial–ﬁnal mass relation of stars without
adjustable parameters (!)

Implication for CE Ejection• recombination energy important for CEejection (Han+ 1995) → changes post-CE
orbital-period distribution (e.g. sdBOs)• now: 3D hydro simulations require
recombination energy to fully ejectenvelopes (Ivanova, Röpke, De Marco,
Lau . . . )Mass loss from dynamically unstable stellar envelopes
Tuchman, Sack & Barkat (1978, 1979)• ﬁnd dynamical ejections in adiabatic pulsation calculations, but⊲ challenging calculations and uncertainties in input physics• Fox & Wood (1982): no ejections when non-adiabatic eﬀects are taken into
account
but: Mira superwinds seem to turn on (Vassiliadis & Wood 1993) when binding
energies become positive (Han et al. 1994)

Application to Red Supergiants
Heger, Jeannin, Langer & Baraﬀe (1997):“Such properties are similar to those found in
AGB stars and suggest the possibility of a“superwind” to occur before the RSGs explodeas supernovae. We conclude that changes in
global stellar properties during the last few
104 yr before core collapse may lead to drasticchanges in the pulsational and wind propertiesof pre-supernova stars, with marked
consequences for the immediate pre-supernova

Heger et al. (1997)

structure of the star and the circumstellar
medium”

Yoon & Cantiello (2010):• pulsationally driven superwinds→ solutions to the missing RSG problem?
→ CSM for SNe IIn
But: no explicit mass ejections [no shocks!]
Yoon & Cantiello (2010)

“Dynamical Mass Loss from Unstable Giants”
Matthew Clayton(DPhil Thesis, Oxford, 2018)• systematic 1d hydrodynamical study of unstable giants⊲ with applications to CE systems, AGB stars andRSGs• uses Mesa (with fairly standard assumptions)caveats:• uses standard MLT convection model (tests for
instanteous adjustment, frozen convection, time delay;see Heger+ (1997), Langer, G. (1971))• 1d models (convection is 3d; large plumes)• the role of turbulent viscous damping (tested: important
only for probably unrealistic parameters; radiative
cooling most important)Ivanova, Justham, et al. (2013)

Common-Envelope Systems(Clayton, Podsiadlowski, Ivanova & Justham2017)• parameter study of the slow spiral-in phase
for a 1.6 M⊙/100 R⊙ giant• consider various energy inputs (due to theorbital energy release) in diﬀerent regionsof the envelope• ﬁnd recurring, episodic dynamical massejections of up to 0.1 M⊙ (10 %! of envelopemass)• but low eﬃciency (in terms of an αCE )• time-averaged Ṁ ∼ 10−3 M⊙ yr−1
• can possibly eject the remaining envelope(otherwise merger)

Ejection event (I) (Clayton et al. 2017)

Ejection event (II) (Clayton et al. 2017)

Non-ejection event (I) (Clayton et al. 2017)

Non-ejection event (II) (Clayton et al. 2017)

(Clayton et al. 2017)

Dynamical Mass Loss from AGB Stars• ejections (< 1 to 100s of yr) of up to ∼ 0.1 M⊙ (mostly He shell ﬂashes)• average Ṁ ∼ 10−3 M⊙ yr−1
• consistent with WD and initial–ﬁnal mass relation

Mass Loss from Red Supergiant• numerically more challenging (large L/M)
• 131 simulations for 6 masses 15 − 40 M⊙• pulsations in 69 cooler simulations• 26 (11) show (repeated) mass ejections(many become very “violent” and breakdown)• behaviour quite regular: mostly a functionof L/M (i.e. Eddington factor) plus
threshold criterion (log L/M ∼ 4.1 − 4.15)• ejection driven by HeII recombination• mass ejections: for M ≥ 25 M⊙ up to 1 M⊙
for lower-masses• timings: last few 103 yr for 25 − 30 M⊙,∼ 105 yr for M = 40 M⊙

M = 25 M⊙

Possible Implications for Red-Supergiants/Supernovae
The maximum observed RSG luminosity(Davies, Crowther & Beasor 1918)• stars around 40 M⊙ enter the dynamical ejection phase
immediately when becoming RSGs → eject their envelopes inless than 103 yr → “observational” RSG upper luminosity limit
around log L/L⊙ ∼ 5.5
Supernovae IIn• stars with M >∼ 25 M⊙ (> 20 M⊙?) experience very late extreme
3mass loss (<∼ 10 yr) up to the SN stage with ejecta masses up
to ∼ 1 M⊙ → SNe IIn• see SN 1979C? VY CMa?
The Missing RSG Problem(Smartt 2009, 2015, also Davies & Beasor (2018))• not so clear• want extra mass loss just before the SN (o.k.) but for stars aslow as ∼ 17 M⊙
Unstable AGBs/RSGs in Binaries• expect more cases of late mass transfer (case C/D, V Hya?)• as probably needed (trigger CE event?)

The Stability of Helium Giants• He giants have high L/M → expect them to be unstable→ dynamical pre-SN mass loss? SN Ibn?
• the case of SN 2006jc⊲ SN Ibn with a few 0.01 M⊙ ejecta about 2 yr before theexplosion (detected precursor!)⊲ not a massive stellar environment (age ∼ 17 Myr)
⊲ possible companion detection (∼ 12 M⊙) (Sun et al. 2019)→ mass loss from a He giant (also see Wu & Fuller)Modelling the CSM around the symbiotic binary RS Oph