Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

DustSummary

The molecular chemistry of supernovae
Anders Jerkstrand & Sofie Liljegren
Department of Astronomy, Stockholm University

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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

Dust

Summary

Why are molecules important?
Liljegren+2020

More efficient coolants than atoms• ! can change temperature drastically.

Model without CO
Model with CO

100d200300

4005001 / 25

Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNeMIR predictions

Dust

Summary

Why are molecules important?
Liljegren+2020

More efficient coolants than atoms• ! can change temperature drastically.

Model without CO
Model with CO

100d200300

400500• Governs when and how dust forms by• Locking up dust ingredients.
• Determining when the temperature falls below the dust formationthreshold (1000 2000 K).

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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

Dust

Summary

Why are molecules important?
Liljegren+2020

More efficient coolants than atoms• ! can change temperature drastically.

Model without CO
Model with CO

100d200300

400500• Governs when and how dust forms by• Locking up dust ingredients.
• Determining when the temperature falls below the dust formationthreshold (1000 2000 K).
Abellan+2017

Their molecular IR and radio emis• sion (ALMA, JWST) may be used
to probe mixing and morphology.
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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

DustSummary

SN 1987A : First detection of molecules in SNe
Spyromilio+1988

CO fundamental at 4.6 µm

Wooden+1993

CO overtone at 2.3 µm
SiO fundamental at 8.1 µm

Undulations reveal
expansion velocity(⇠1800 km/s).
Wing extent reveals
temperature(3000-1500 K).

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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

DustSummary

SN 1987A : First detection of molecules in SNe

SiO forms
later than CO (⇠250d)?

56 Co decay

CO overtone declines rapidly
as it requires high T .

Bouchet and Danziger 1993

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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

DustSummaryObservations of molecules in other SNe
SNType IIP/pec:
SN 1987A
SN 1995ad
SN 1998dl
SN 1999em
SN 2002hh
SN 2004dj
SN 2004et
SN 2005af
SN 2017eaw
Type IIn:
SN 1998S
Type Ib/Ic/IIb:
SN 2000ew
SN 2007gr
SN 2011dh
SN 2013ge
SN 2020oi

CO
2.3µm

CO
4.6µm

SiO
8.1µm

Referencexxxxxxxxxx⇤
x⇤
x⇤

xx

x

Spyromilio+1988, many others
Spyromilio & Leibundgut 1996
Spyromilio 2001
Spyromilio 2001
Pozzo+2006
Kotak+2005, Szalai+2011
Kotak+2009
Kotak+2006
Rho+2018

x

Gerardy+2000, Fassia+2001

xxxxx

Gerardy+2002
Hunter+2007
Ergon+2015
Drout+2016
Rho+2020

Adapted (and expanded) from Cherchne↵ & Sarangi 2011. * = right side of band.
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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

Dust

Summary

Observations of molecules in other SNe• SN 2004et (Kotak+2009) is the only other SN than 1987A where wehave complete information about the molecular cooling. Only reemits amoderate fraction of the powering of the O-rich zones.

Jerkstrand+2012
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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictionsDust

Summary

Inferred CO masses in SN 1987A and SN 2017eaw
Other SNe have yielded similar estimates.

CO formation model (Sarangi+2013)
SN 1987A NLTE (Liu+1995)
SN 1987A LTE (Spyromilio+1988)
SN 2017eaw LTE (Rho+2018)
Rho+2018• There is about 0.1 M of C available in the O/C zone, 10 3 M in the
5 / 25H-zone..which zone makes the CO?

Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

Dust

Summary

The physics of CO formation, and implementation into theSUMO code Liljegren+2020,2022
Currently SUMO has a chemical network of 22 molecules, 115 chemical reactions. Fourmolecules (CO, SiO, SiS, SO) are part of the time-dependent NLTE machinery.

Reaction
ExampleCommentFormation
Radiative association C + O ! CO + h⌫
C mostly ionized in the H, He zone
Formation or destr.
Neutral-neutral
C + O2 $ CO + O
Charge exchange
CO+ + O $ CO + O+
Destruction
Compton electrons
CO + efast ! C + O, CO+UV dissociation
To be added.
He+ attack
CO + He+ ! He + C+ + O Prevents formation in He-zone.
See also Petuchowski 1989, Lepp 1990, Liu 1992,1995,1996, Gearhart 1999, Cherchne↵
2008,2009,2010, Sarangi 2013,2015, Höflich (e.g. in Rho 2021,..)• Conditions favorable in dense, mostly neutral, O/C core region of ejecta.
• Conditions less favorable in H and He-layers, whether in ejecta or CSM.
• Expected impact of CSI? Not large : radiation cannot reach SN core for decades.

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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

Dust

Summary

Molecules in NLTE - cross section issues

Currently, neither theoretical nor experimental data is available for all the col• lision rates needed to calculate molecule
NLTE statistical ro-vibrational populationsin (hot) SNe environments.

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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

Dust

Summary

Molecules in NLTE - cross section issues• At least 5 schemes proposed for⌫ 6= 1 collision rates. We use
Chandra & Sharma 2001.
• To split out theexperimental/theory data forvibrational rates to rovibrational,
we assume indepedence of j(Laporta 2012). We allocate therate to j = 0. For now weforce rotational LTE so does notreally matter.
• For other molecules than CO, nothermal collision data at allavailable ! use the CO scheme
for all 4 molecules. Data are
available for fast electrons.

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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

Dust

Summary

Carbon monoxide in Type II SN models Liljegren+2020• A 1-zone study with just C and O, but with self-consistent NLTE
physics for CO formation and cooling.
• Our standard model forms a few times 10 3 M of CO. The mass
grows up to about 250d and is then quite constant in time.

The suppression at earlytimes is mainly due to chargetransfer destruction with O+ .

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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

Dust

Summary

Carbon monoxide in Type II SN models Liljegren+2020• There is a very strong coupling between molecule formation andmolecule cooling ! important to treat both of these self-consistently.

CO cooling allows formation of C dust
already at 200-300d.

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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNeMIR predictions

Dust

Summary

Carbon monoxide in Type II SN models Liljegren+2020• CO time evolution can probe the density and zone powering.

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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

Dust

Summary

Liljegren & AJ 2022 - molecular chemistry of Type Ibc SNe• Improvements• Network extended, updates of reaction rates/cross sections. Issue: SN
environment is hot ! molecules excited. Most other applications gas isquite cold ! molecular data e↵orts geared toward low temperatures.
• High-energy cross sections implemented for CO, SiO, SiS, SO.
• Measured CO thermal collision strengths incorporated.
• Self-consistent Compton destruction, with high-energy cross sections
implemented for CO, SiO, SiS, and SO.
• Full composition (KEPLER models).
• Multi-zone modelling (1-zone in L20).

• Upcoming• Photoionization/dissociation.

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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

DustSummary

CO formation and destruction in Type Ibc SNe• Formation dominated byradiative association C + O !
CO. Latest rate : Gustafsson 2015.

• Destruction first by O+ chargetransfer, (Petuchowski 1989) thenCompton electrons. (Itikawa 2015.)

CO growth when O+ reaction switches o↵.

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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

Dust

Summary

Carbon monoxide in Type Ibc SNe• CO formation is significant only in the O/C zone.
• As in the Type II model, CO mass is quite constant in time. Here afactor ⇠10 lower than in Type II model due to the lower density, ata few times 10 4 M .
• Growth begins at 500-600d as O+ charge transfer switches o↵.
Chemistry now out of steady state so change is slow.

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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

Dust

Summary

Carbon monoxide in Type Ibc SNe• But, again, strong density sensitivity.

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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

Dust

Summary

Impact on temperatures in Ibc SNe : small in standard
model.

Two contributions:• Lower CO mass formed due to lower density.
• Collisional excitation less efficient with cross section data implemented.
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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

Dust

Summary

Carbon monoxide in Type Ibc SNe• CO does not a↵ect emission from the important O/Ne/Mg zone (or theO/Si/S zone). This is important because it suggests low metal masses
inferred from nebular atomic lines (e.g. AJ+2015) is robust.
• It does significant, but still only partial, cooling of the O/C zone :10-40%.

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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

Dust

Summary

Comparison to CO overtone observations in Ibc SNe• Too little data to draw any particular conclusions : hopefully JWST will
improve situation.
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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

Dust

Summary

Impact on optical spectra

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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

Dust

Summary

MIR predictions relevant for JWST
• CO fundamental band ; with SiO overtone at early times.

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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

Dust

Summary

MIR predictions relevant for JWST• SiS fundamental band : detectable early on, swamped by [Ne II] later.

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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

Dust

Summary

Predicted dust formation epochs

Silicates: ⇠400d.

Carbon dust: ⇠300 - 600d.

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Introduction

Observational history

Physics of CO

Type II SNe

Type Ibc SNe

MIR predictions

Dust

Summary

Summary• Observations show that molecules, in particular SiO and CO, appear to form inall types of SN ejecta. Their large cooling abilities means they can dramaticallychange the temperature evolution of the layers where they form.
• This in turn means they governs when dust formation can begin (T . 2000 K).
• A molecular chemical network, and NLTE cooling of CO, SiO, SiS and SO,
have been implemented into the SUMO spectral synthesis code.
• A first 1-zone carbon-oxygen study tailered to Type II SNe shows formation of⇠ 10 3 M of CO, but strong variations with assumed density (clumping).
• A full ejecta model for a Type Ibc SN has also been investigated. The lower
densities in Ibc ejecta leads to less efficient molecular cooling - the standard
model shows only small changes to temperature evolutions. However, thehigher clumping models show larger e↵ects.
• The models give predictions for MIR emission and guidance for what JWST
data may tell us.
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