Observations of hydrodynamical instabilities
in interstellar space

Orion nebula (near infrared with ESO-VISTA)

Olivier Berné Post-doc, at IRAP (CNRS/Univ. Toulouse,)

andJ. Cernicharo / N. Marcelino (Centro de astrobiologia, CSIC/INTA, Madrid, Spain)
C. Joblin (CNRS/Univ. Toulouse, France)
A. G. G. M. Tielens (Leiden observatory)

Outline- The infrared interstellar medium- Evolution of carbonaceous nano-grains in the interstellar medium- Using mid-IR emission of carbonaceous nanograins to probe astrophysicalenvironments- Discovery of Kelvin-Helmholtz instability in the interstellar medium- If there is time: the story of the Football/Soccerball molecule in space- AcknowledgementsMy «career»x (2010-2011)

x (Born)x (2000-2003)

x (2004-2008)& now
x (2008-2009)Research interests- I am an observer- Mostly infrared observations, especially spectroscopy in the infrared- Galactic nebulae, starforming regions, protoplanetary disks- Astrochemistry- Signal processing (especially blind signal separation)

Outline- The infrared interstellar medium- Evolution of carbonaceous nano-grains in the interstellar medium- Using mid-IR emission of carbonaceous nanograins to probe astrophysicalenvironments- Discovery of Kelvin-Helmholtz instability in the interstellar medium- If there is time: the story of the Football/Soccerball molecule in space- Acknowledgements

Infrared spectroscopy

[CII]
[OI]

[SIII]
H2

H2

COInfrared spectroscopy

[CII]
[OI]

[SIII]
H2

H2

BG
VSG

PAH

PAH

CO

Infrared spectroscopy

SOFIA
2011-20..
Spitzer
2003-2009

VLT

Herschel

Spitzer

[CII]

JWST

ョン

Herschel
2009-2013

SPICA[SIII]

ELT

H2

H2

JWST
2017-2022

図

[OI]

BG

ALMA
IRAM

VLT
In function

COと「あかり」の解像度の比較

VSGになり、望遠鏡の口径を一定とすれば、衛星は小型化される。さらに、打ち却されていなければ無駄な真空容器は不要になり、衛星は画期的に軽量化さにより、逆に、衛星全体の重量を同じとすれば、従来よりもはるかに大口径
能になる。

ミッション

SPICA
2018-2023
図IRAM 30m
In function

PAH

の概念図

ALMA
Starting operations

Infrared spectroscopy

Spitzer
2003-2009

Spitzer

[CII]
[OI]

[SIII]
H2

H2

IRAM

BG
VSG

PAH

CO

IRAM 30m
In function

Lifecycle of low mass stars
M<8MsunLifecycle of low mass stars
M<8Msun

10

2500

2000

5
ï1

Intensity (Mj.sr )Intensity (Mj.srï1)

15

0
5

10

h (µ m)

15

1500

1000

500

0
5

10

15

h (µ m)What is a the origin of these spectral variations ?
How are they connected to local physicalconditions in these regions ?
30

Intensity (Mj.srï1)

25

20

15

10

5
5

6

7

8

9

10

h (µ m)

11

12

13

14

Outline- The infrared interstellar medium- Evolution of carbonaceous nano-grains in the interstellar medium- Using mid-IR emission of carbonaceous nanograins to probe astrophysicalenvironments- Discovery of Kelvin-Helmholtz instability in the interstellar medium- If there is time: the story of the Football/Soccerball molecule in space- Acknowledgements

Evidence for PAH evolution in the ISM

12

NGC 7023, Infrared Array Camera (Spitzer 8 μm).

11
10
9

Intensity

8
7
6
5
4
3

NGC 7023, Infrared Spectrograph, 8 μm

20.1 pc

1
5

6

7

8

9

10

11

Wavelength (μm)

12

13

14

- Each observed spectrum is a linear combination of elementary spectra- We observe different mixtures of the same elementary spectraMathematical modelrfor evolution of PAHs!

xi (λ) =

aij Sj , i = 1, . . . , mxi (λ) = ai1 × S1 (λ) + ai2 × S2 (λ) + ai3 × S3 (λ) . . .

j=1
Linear instantaneousmodelrxi (λ) = a!
i1 × S1 (λ) + ai2 × S2 (λ) + ai3 × S3 (λ) . . .
xi (λ) =aij Sj , i = 1, . . . , m







xi (

xm





xi (λ)a.
.
.
aX= A × S
1,1
1,r
!



 

x (λ) =x (λ)
aa S .,. .i = a1, . . . , m S (λ)
 .. ..  =  ..  ....  ×  ..  r .." m =×..   .  . x (λ)



 . 
.
.
(λ)
. . . aa(λ)
aa
SS (λ)
 ..  ..
  .. .
.
 .  =  .
 ×  . .. .
.
xm (λ)aa
X = A×S
m,1
m,r
x (λ)
a
... a
S (λ)
j=1
r

i i

ij j
1,1

1,r

1

with

j=1

i
m

X

X

1,1
m,1

Observationmmatrix= A × S

= A × S× S

Mixingm,1 matrix

1,r
m,r

r1

m,r

Matrix ofm spectra«source»

X = A×S

X = A×S

X =A×S

Matrice
Goal identifying
A and deS, from X
X ≈ W ×H
poids
Matrice! de spectres
Xij(Xij log− Xij + (W H)ij )D(X|W H) =Source(W H)ijHaµ ← Haµ..  ×  .. =S  ..
X ..= A ×
Solvingmatrixfactorizationxmthe(λ) problem using
am,1X Non-negative
.
.
.
a
S
(λ)
m
≈
W H m,r(II.1.7)(NMF)= A × S
S
where W is a m × r non-negative
a rA
××
n non-negative
matrix
X = Aweight× S matrix and HXis =of approximate ”source”
in eq. (II.1.7) can be
Thesignals.
problem The approximate quantity
Approach:
optimized
the non-negative matrices W and H so as to minimize the
X = A by×adaptingS
X ≈ D(X|W
WX×=HAH)×(LeeX = #XA ×−SW H#2 or the divergencesquared Euclidian distance
S and Seung
2001), defined as
The criteria, Euclidian distance / Kullback’s divergence :
!
X!
ij
2
2 H)
X
≈ ij
W)X×=
HA × S (II.1.8)
D(X|W H)X
= ≈#X
(X
log
W
ijWH
ij +
−×
H# =
(Xij−−X(W
H)(W
ij )
(W H)
ij

ij

ij

!
(
Xij
(
and
XW
D(X|W
H) =
(Xij log µ Haµ Xiµ− /(WXij +H)(W
H)) ×H
ij ia Xiµ /(W
X
≈
ijW
H)
iµ
iµ
i
log
−
X
+
(W
H)
)
(W H)
ij
ij
ij
(
(
H
,
W
←
W
aµ (W H)ia
ia
ij!
ij WkaXij ( ν Haν
k (D(X|W H) =(Xij log−X(II.1.9)!
ij + (W H)ij ).
X
Hijaµ Xiµ
/(W
H)(W
(W
H)
Xiµ
/(W H)iµ H) )
ij
(
iµ
µ
D(X|W
H)
=
(X
log
−
X
+
i Wia
ij
ij
ij
ij
(/(W H)iµ , W(
Haµ ← HaµHaµ Xiµ
←
W
ia
ia
The algorithm (W H)ij H
µ
W
ij
aν
ka
k
ν
(
←
W
a Lee &iaSeung’s NMF algorithm
Matrice de
(
(aν
H
ν
ia Xiµ /(W H)iµµ Haµ Xiµ /(W H)iµi Wpoids((
Haµ ← Haµ
, Wia ← Wia
Matricede using classical gradient
The adjustment of W
and H canbealthoughaνkaachieved
ν Hdescent
Matricedek W
spectrespoids 2001). Therefore, these authors have prothis
canbeproblematic
(see
Lee
&
Seung
ce de
- We set the numbers Sourceor rows of H
Matricede spectres
posed two newalgorithms,
which
are basedon the fact that the Euclidian distance is- W and H must be positive
Matrice dedesdsnon increasing- Weunder
start iteration
withrandom W
and H ruletheMatrice
iterative
updateSource[Lee and Seung, Nature, 2001]
Resultsdonotdependon
initialization
poids
observations
spectres
MatricedesTMatrice de spectres
T
(W
X)
(XH
)ia
aµ
Cube
rce
observations
H ←H,W ← W(II.1.10)

Photochemical evolution of PAHs

Extracted spectra

Spatial distribution

PAH clusters ([PAH]n)
0.2

0.1

! (µm)

PAH Neutrals! (µm)

PAH Cations

0.15
0.1

"

I (A.U.)

0
0.2

0.05
0
0.3
0.25
0.2
0.15
0.1
0.05
0

6

7

8

9

10

11

12

13

14

15

16

! (µm)

Figure 5.12: Map of the correlation cp of each extracted signal with observations, Signal 1 in red,

UV

Signal 2 in green and Signal 3 in blue. The contours are the Infrared Array Camera (IRAC) emission
at 8 µm showing the filamentary structure+of this PDR. The illuminating star is situated in the lower
left hand corner. In this region a slight artifact correlation of Signal 1 with observations is seen due
to the presence of a continuum emanating from big grains at thermal equilibrium.

UVe-[Rapacioli et al. Astron. Astrophys. 2005, Berné et al. Astron. Astrophys. 2007]

Outline- The infrared interstellar medium- Evolution of carbonaceous nano-grains in the interstellar medium- Using mid-IR emission of carbonaceous nanograins to probe astrophysicalenvironments- Discovery of Kelvin-Helmholtz instability in the interstellar medium- If there is time: the story of the Football/Soccerball molecule in space- Acknowledgements

Constructing a model

PAH 00

1.5

PAH

1
0.5
0
1.5

6

7

8

9

10+
PAH

11

12

13

6

7

8

9

10
VSG

11

12

13

10 x
PAH

11

12

13

10

11

12

13

Intensity (Arbitrary Units)

1

PAH+

Spectra adaptedfromdecomposition

0.5
0
1.5

PAH clusters

Spectra of large (>100 carbon
atoms) ionized PAHs inspired from
Quantum Chemistry results

1
0.5
0
1.5

6

7

8

9

6

7

8dBF 9

PAHx[Joblin et al 2008, Bauschlischer 2008, P. by C. Boersema, J.
Cami]

1
0.5
0
1.5

12µm BF
1

8µm BF
0.5
0

6

8

10

! (µm)

12

14

[Pilleri et al. A&A 2012 accepted]
Observations
Model
Go: intensity of UV radiation field emitted by stars into the ISM
80

Horsehead60

Clust : 68 %VSG
PAH0: 31 %PAH+: %
PAHX: %
AV : 6.6 mag
fC : 0.85

Go=1004020
040

Ced201VSG
Clust : 62 %PAH0: 34 %PAH+: %
PAHX: 2 %AV : 7.8 mag
fC : 0.81

30
20
10
0
100

Clust : 46 %VSG
PAH0: 53 %PAH+: %
PAHX: %
AV : 0.8 mag
fC : 0.68

IC 63

80
60
40
20
0
400

P18 (S)

Clust : 25 %VSG
PAH0: 46 %PAH+: 17 %PAHX: 9 %AV : 9.6 mag
fC : 0.47

300
200
100
0
6

8

10
12
Wavelength (µm)

14

16

400

P18 (N)

Clust : 23 %VSG
PAH0: 53 %PAH+: 14 %PAHX: 8 %AV : 18.9 mag
fC : 0.44

OrionBar (P4)

Clust: 21 %VSG
PAH0: 68 %PAH+: 6 %PAHX: 2 %AV : 12.6 mag
fC : 0.41

Monoceros R2 (3)Clust: 17 %VSG
PAH0: 15 %PAH+: 46 %PAHX: 21 %AV : 21.9 mag
fC : 0.34

300
200
100
0
8000
6000
Intensity (MJy sr21)

Intensity (MJy sr.1 )Model benchmarking in galactic nebulae

4000
2000
0
10000
8000
6000
4000
2000
0
3000
2500
2000
1500
1000
500
0

Monoceros R2 (1)68Go=1e5

10
12Wavelength (µm)

Clust: 13 %VSG
PAH0: 61 %PAH+: 10 %PAHX: 14 %AV : 34.0 mag
fC : 0.281416Model benchmarking in galactic nebulae
Observations
Model
Go: intensity of UV radiation field emitted by stars into the ISM
P. Pilleri et al.: The PAH/VSG transition: a new tool to characterise the UV radiation field Fraction offCPAH clusters

1.0

0.8

NGC 7023 NW
NGC 7023 S

Horsehead

NGC 7023 E
NGC 2023 N

7

Oph−W
NGC 2023 S

Ced 201
IC 63

0.6
M82 Out
M82 Nuc
P18 (S)P18 (N)

0.4

OrionBar
MonR2 (1)
MonR2 (3)

0.2
101

102

103
104
G0 (Habings)

105

106

Fig. 5. Correlation between the fraction of carbons in VSGs compared to the local radiation field. Colored points refer to the objects in table 1, forwhich we determined the profiles of fC and of the radiation field. Red points represent values of fC determined from the fitting procedure and forwhich an estimate of the radiation field has been obtained from equation 11

Application to nearby galaxy M82
IV.2.1 Nearby galaxies

145

Engelbracht et al. (2006) showed using IRAC images and LL-IRS spectroscopy thatthe outflow contains a large proportion of PAHs. The central and star-forming region
was mapped with the IRS-SL and Beirão et al. (2008) published an analysis of spectral
variations of the mid-IR spectrum. We have reanalyzed this data using our fitting
technique on each spectrum of the cube (e.g. Fig.IV.2.2). From this analysis we could
build maps of the different populations of very small dust emitters in the central regionof M82. These maps are presented in Fig.IV.2.3.

Observation [NeII]
Model
Continuum

5

5.0

Figure IV.2.2: Fit (in blue) of a spectrum from the M82 IRS-SL cube using the fitting procedure
introduced in the previous Chapter.

4.5

4

g(
o
L

)
o
G

3.5

3

5

3. 0

The resulting maps show very strong contrasts. PAH0/+/x and VSG emissions arelocated in distinct regions. Both PAH+ and PAHx emissions correlate spatially with
the IRAC 3.6 µm emission tracing the regions of intense star formation where theUV field is the strongest. The PAHx emission is somewhat more extended but also
more intense in the very central region of M82, probably where the conditions are
the harshest. VSG emission is seen at several kpc from the central regions in morequiescent material. The high abundance of VSGs in the region situated north east of
the galactic center is well correlated with a dust lane observed in the optical. Most
surprising however is the strong correlation of neutral PAHs with the bipolar winds seenin Hα . This presence of PAH0 implies that the conditions prevailing in the outflow areof moderate radiation field which is consistent with the lower abundance of massive
young stars. However, the presence of Hα emission argues in favor of the presence

UV field is also a tracer of star-formation
4.5

4

3.5

Application to remote galaxies(data from K. Dasyra)

Luminous IR Galaxy

Galaxies at z <1

Ultra-Luminous IR Galaxy

Galaxies at z >1

[Bouwens et al. Nature 2010]

ription of the proposed programme (cont.)

Application to the «Gomez hamburger» protoplanetary disk
S c a tte re d lig h t (v is ib le )1 3 C O (m illim e te r)

60
Observation
40
ModelofContinuum
GoHam200 Left:

Clusters
PAH0
PAH+
PAHx

P A H (m id - IR )1 2 C O m illim e te r

Abundance of PAH clusters
13: Observations
Overlay of the red- and blue-shifted
CO components (cone Hubble Space Telescope visible image. Right: Overlay of the red- and blue-shifted 12 CO compours) on the VLT-VISIR image in the PAH1 band.
Radiation field

Star luminosity

For the following:

Mid-IR PAH emission is a high angularresolution, optically thin tracer ofof UV illuminated couds in star forming regions

Outline- The infrared interstellar medium- Evolution of carbonaceous nano-grains in the interstellar medium- Using mid-IR emission of carbonaceous nanograins to probe astrophysicalenvironments- Discovery of Kelvin-Helmholtz instability in the interstellar medium- If there is time: the story of the Football/Soccerball molecule in space- Acknowledgements

Background- Since the seminal work of Lyman Spitzer 1954 (ApJ 120) it was proposed thathydrodynamic instabilities can happen in star-forming regions- This is important because it will determine the structure of the ISM, induce turbulence,and chemical mixing of heavy elements injected by massive stars

Schematic morphology of star-forming region
Neutral gas, Molecular cloud(n=104 cm-3, T=20K)

Rayleigh Taylor instability

Low mass protostars

HII region

Ionized gas, HII region(n=20 cm-3, T=104K)

Molecular cloud?
Massive star

?

?

?

The Rayleigh Taylor instability ?

Pillars of creation
Neutral gas(n=104 cm-3, T=20K)

Ionized gas(n=20 cm-3, T=104K)

Horsehead nebula
Neutral gas(n=104 cm-3, T=20K)

Ionized gas(n=20 cm-3, T=104K)

Studies with radio-telescopes show that velocity fields do not match models of RT instability[M. Pound ApJ 1998, ApJ 2003]

Study of Orion visible vs infrared[Berné, Marcelino & Cernicharo, Nature 2012]

Visible lightMid-infrared PAH emission

HII region

Study of Orion infrared vs millimeter[Berné, Marcelino & Cernicharo, Nature 2012]

Mid-infrared PAH emission

Observations by N. Marcelino

IRAM 30m radio-telescope, 12CO (2-1) spatial resolution of 11’’,
spectral resolution of 2km.s-1

Study of Orion visible vs infrared[Berné, Marcelino & Cernicharo, Nature 2012]

Visible light!"Mid-infrared PAH emission

#$

#"

%$

%"

$

LETTERS
1) Ripple

2)

3)

The Orion «Ripples», geometry

Molecular cloudbehinda

1 Ripple[Berné, Marcelino & Cernicharo, Nature 2012]

CO (2-1) 2
12
CO (2-1)

TA* (K)20

To Trapezium

3

12

a

To Trapezium
To Trapezium

Molecular
cloud
behind10 PAH emission + integrated CO map
Morpholgy:

Geometrical model
Geometrical model

Plasma

0

)

U

0

b

5

VLSR

10

(km s–1)

15

0

5

VLSR

10

15

0

(km s–1)

5

UV Photons
UV Photons

Plasma 15
10

VLSR (kmPlasmas–1)

HII region
HII region

IRS Cut3)IRS2) cut2
1

1)

3

Molecular cloudToobserver
observerTo

IRAC 3.6 µm IRAC 3.6 µm
12CO
12CO

0.0
0.0
PAH
emission
PAH emission
CO emission
emissionCOcIntensity (MJy.sr! -1)

160
140
120
100
80
60
40
20

Intensity variations (Normalised)

180

d)

(0-0) S(1) [S III]
2
S(1)H[SIII]
PAH
180 H20-0PAH

Intensity (MJy sr–1)

200dRipple summit

140

Ripple summit
Ripple valley

100

Ripple valley

H II region

60

HII region
HH2 shock

20
15

16

17

18

19

20

WavelengthHH2
(µm)
Shock

21

Intensity variations (normalized)

0.1 pc0.1 pc!
!

Molecular cloud
Molecular cloud

EastEast

1.1 1.1
1

PAH
PAH

H2

H2

0.2
0.2

0.1
0.1

Expectedintensity
intensityvariations
variations
Expected

West West
12CO

12CO

b

0.9

0.7

0.0

0.1

PAH emission
CO emission

0.9
0.0
0.1
0.0
0.1
IRAC 3.6
3.6 (PAH(PAH emission)
emission)
IRAC
IRAM 30m
30m (CO(CO emission)
emission)IRAM

0.8 0.7
Noshocks !

0.3
0.3

0.2
0.2

0.3
0.3

0.2
0.2
Distance
Distance(pc)
(pc)

0.3
0.3

Observedintensity
intensityvariations
variations
Observed

0.5

0.6

0.5 0.3
0.4

0

0.02

0.04

0.06

0.08

Distance (pc) 0.0
0.0

0.1
0.1
0.1

c

0.0

0.1

proposonsquelasaturat
The Orion «Ripples», kinematics

inhomogène et filamentaire[Berné, Marcelino & Cernicharo, Nature 2012]

LETTERSmanière étroite avec lesKinematics with the CO line Doppler shifta2
3
reprenantdesconditionsp
CO (2-1)

1 Ripple

12CO (2-1)
12

1

2

3

TA* (K)

20

Molecular
cloud
behindOrion), et fournissant des10«Orion Ripples» mid infrared PAH emission

0
0

b

5

VLSR

(échellesde temps,
taille ca
VV10(km s–1)➙ Wavelike periodic structure (no high velocity shock)➙ Evidence for a strong velocity gradient

15

0

5

10

LSR

15

0

(km s–1)

5

LSR

10

(km s–1)

15

IRS cut2
1

3

Kelvin-Helmholtz instability [Chandrasekhar 1961]

0.1 pcy (MJy sr–1)c
180

Low density
140 gas(HII region)
100

d
PAH

H2 (0-0) S(1) [S III]
Ripple summit
Ripple valley

1.1
0.9
0.7

East

[Matsumoto & Seki 2010]

IRAC 3.6 µm
High density gas
12
CO(Molecular cloud)tions (normalized)

0.1 pc

PAH

West
H2

12

CO



ngth
zltz
wavelength
wavelength

The Orion «Ripples», first level analysis

r an interface between fluids ofdensitiesand ρf Nature 2012][Berné,Marcelinoρ&cCernicharo,locityvf andinainterface
gravitational
fieldfluidsof acceleration
wavelength
forforananofand ρρff) wavelengthinterfacebetween
betweenfluidsof densities
densities ρ
ρcc andwithflow
velocity
vfvfand
y),
with
flow
velocity
andinina agravitational
gravitational field
field ofof acceleration
accelerationr, 1961):khar,1961):
2
π × vf (ρ)/gc .
(8)
Kelvinwavelength
f /ρcHelmholtz
2
< λkh
= 2π
(8)
λkh
= 2π
××
vf2v(ρ
(8)
c )/g
f /ρ
c )/g
c .c .
f (ρ
f /ρ

wth
rate
h rateλ = 0.1pc) instability growth rates (resp. ωrt and ωkh ) for anorhereafter)
instability
rates(resp.
(resp.
and ωωkh )) foranρf(RT, hereafter)witha flow
velocity growth
vfgrowth
are definedby (seee.g.
RTinstability
ratesωωrtrt and
for
an
kh
densities
and, with
flowvelocity
velocityvvf areare defined
defined byby (seee.g.
growthrate
c Helmholtz
sities Kelvinρc ρandρf ρ, fwith
a aflow(seee.g.
f2 ρ ρ v2kf c f
2
2 ρ ρ v2
k
,2
ωρkh
=
(9)
−
ρ
f c 2f2c
f22
ωrt = ρka
, f + ρ2cω)kh =k ρf ρc vf 2
(9)c − ρf (ρ= ka ρc + ρ, f
ωkh = (ρf + ρc2)
(9)
ρc + ρ1f to which the(ρc )subject to. Withf + ρise acceleration
cloud

umber and a the<acceleration
to which the cloud is subject to. With
3Myrs
ber become:and a ωtheacceleration to which the cloud is subject to. Withonskhbecome:k2 ρf vf2

22 =ω
ωrtkh= ka,k2 ρf vf2

.ω 2 =k2 ρ v 2 .
(10)
(10)
2
kh
f
2
ρ
f
2
ρc .
c ω2 =
ωrt
= ka,
(10)
kh
2
ρc
The observed structure is compatible
with a KH instability for velocities and densities of the HII region

assumingthat assuming
the flowing
windmolecular
amatedbe estimatedthatthe andflowing
wind and molecular
max cancanestimatedassumingthatflowingwind
and molecular
is,
thebe
wind
all
it’sthekinetic
tolibrium.
Thathasis, transferedthewind hastransferedallenergy
it’skinetic
energy toxNew images

Near IR images of Orion Ripples from European Southern Observatory in ChileOutline- The infrared interstellar medium- Evolution of carbonaceous nano-grains in the interstellar medium- Using mid-IR emission of carbonaceous nanograins to probe astrophysicalenvironments- Discovery of Kelvin-Helmholtz instability in the interstellar medium- If there is time: the story of the Football/Soccerball molecule in space- Acknowledgements

Soccerball molecule in space
Fullerenes (buckyballs) in space !

REPORTS
B

A

C60

Tc1 planetary nebula (evolved star)

C60
C70

No. 1, 2010

C60 IN REFLE.sciencemag.org on May 13, 2011ν

(MJy/sr)(MJy/sr)
I (MJy/sr)ν

I (MJy/sr)ν250
NGC 7023
200
150[Cami et al. Science 2010]
100
C70 bands. The red and blue curves below the data are thermal
ig. 1. The Spitzer IRS spectrum of Tc 1. (A) The entire range, 5 toNo.
37 mm.
1,(B)2010
C60emission
IN REFLE
ontinuum-subtracted spectrum between 5 and 23 mm, where known for- models
for all infrared active bands of C60 and C70 at temperatures of 330 K
50
NGC
7023
reflection
nebulathe(interstellar
medium)idden
emissionlines
aremasked(19).
We
fitteda
cubic
splinetospectraland180
K,
respectively(19).
We
convolved
bands
with
a
Gaussian
profile- Discovered in the lab in 1985
0
−1
−1
anges
devoidetof features
to determine(s = 2.55 cm for all C70 bands, s = 4.5 cm for the C60 bands in the SH/LH
700[Krotoal. Nature
1985]the dust continuum (red dashed line). 250
NGC7023
he broad plateau between 11 and 13 mm is attributed to emission from SiC 200
module, and s = 10 cm−1 for those in the SL
module).
Apparent weak emis600
NGC
2023
ust (34, 35), and the well-known broad feature longward of 23 mm is be- 500
sion bumps near 14.4, 16.2, 20.5, and 20.9 mm are artifacts. The nature of
in Redspace
IR
eved-toDiscovered
be due to MgS (36).
arrowsthroughmark the wavelengthsof all infrared 150
the weak feature near 22.3 mm is unclear because it appears differently in
400
ctivespectroscopy
modes for C60; blue arrows
both nods.
thoseinof thefour strongest, isolated 300
with denote
Spitzer
2010
100
200
50
100
Present
inevolved
stars
and
in
the
ISM
nes that are characteristic for the low-density pected for thermal emission at0330 K when using lower temperatures derived for the fullerenes thus
imply
that12these species
are 16in direct contact
with
as environment of PNe. The infrared continuum experimentally obtained absorption
700 coefficients.
6
8
10
14
18
20
- toFormation? dust. For
600laboratory experi- a much cooler material.
In
thisenvironment,theIt is well established fromdue
emission fromprocess
circumstellar
NGC
2023
Wavelength(µm)[Sellgren
et
al.
ApJ.
2010]
500 and bandwidths most likely solid material is the surface of thearbon-rich environments, this dust is typically ments that the peak wavelengths
400
abundant
carbonaceous
grainspresent
out-4!! north(24). The peakwave- (solidmorphous carbon, which results in a featureless are temperature-dependent
Figure 1. Spitzer-IRS
spectracurves)of NGC
7023(25in!! theeast,
solids !!are in radiative equilibrium
ontinuum. Other common dust components re- lengths in Tc 1 agree, within
300 uncertainty, with flow. These!! west,ofHD200775;
top)
and
NGC
2023
(29
8 southfield,of HD
and 37903;
thus theirbottom),those found in laboratory experiments
obtained at with the stellar radiation
eal their presence through emission bands.
200

Standard formation process (bottom-up)- Aggregation of C atoms, through rings,
chains...
- In the dense and hot and H poor envelopesof evolved stars: nH >1011 cm-3,T=1500K[Cherchneff et al. A&A 2000]

A. Fasolino (Radboud Univ. Nijmegen) 400 C atoms at 2000 K

C60

-3

NGC 7023 nebula

-4

10

I

C60

/ I

FIR

10

-4

10

(1)

-5

10

PAH

ï1
ï1
IntensityIntensity(MJy.srï1(MJy.sr)) IntensityIntensity(MJy.srï1(MJy.sr))

Herschel 70 µm
HD 200775
Spitzer 8.0 µm
Spitzer 3.6 µm Data: [Abergel et al. A&A 2010]
800

I PAH / IFIR

(2)

-1

10

-1

10

-2

10

[Werner et al. ApJS 2004]

600
PAH
800
400
600
200
PAH
PAH
400
PAH
0
10
11
12
13
14
200
2000
10
11
150 PAH
200
100
150
50
100
0
10
11
50

12

13

14

PAH

(1)
PAH

13

35

30

25

20

Distance to star (")

15

15

16

17

18

19

C60 is formed in the interstellar medium,at low density (nH=100 cm-3) !

15

16

17

18

19
(2)

Aggregation process not possible !

PAH

PAH

C60

C60

UV photons control C60 formation and
PAH destruction and evolution ?

PAH

12

Fraction of elemental C locked in specie

An unexpected discovery using Spitzer and Herschel

14
15
16
Wavelength (µm)

17

18

19

[Berné & Tielens PNAS 2012]

a

c

b

d

The roll up route[National Center for electron microscopy]ef[Chuvilin et al. Nature Chem. 2010]+0.201 eV/atom+0.197 eV/atom+0.178 eV/atomE(eV/atom)–0.261 eV/atom+0.059 eV/atom

+0.3

(b)
+0.2

Etchedgraphene

+0.1

(c)

(d)

Flat graphenewith pentagons

Curvedgraphenewith pentagons

(a)

(e)
Bowl-shaped
structure

Graphene
–0.1
–0.2

(f)
Fullerene

–0.3

b’

d’

e’

f’

- GrapheneFigure
is a2 |sheetof C atoms in hexagonal network, Graphene is an infinite PAH with no H
Quantum chemical modelling of the four critical stages of fullerene formation from a small graphene flake. a–d, Loss of carbon atoms at theedge (a ! b); formation of pentagons (b ! c); curving of the flake (c ! d); formation of new bonds, leading to zipping of the flake edges (d ! e). e, Topand side views of a bowl-shaped
intermediate structure.
(in eV perundercarbon atom)of the intermediate
structures and resultant fullerene- Direct transformationof a graphene
flake Stabilization
into C60energies
observed
electron
irradiation′ ′ ′C60 (f), relative to the flat defect-free flake of graphene shown in a, are presented pictorially and graphically. b ,d –f , Top views of the graphene flake (b′ ),curved graphene intermediates (d′ ,e′ ) and the fullerene C60 molecule (f ′ ) adsorbed on the underlying graphene substrate and simulated TEM images
corresponding to each structure, showing how they would appear in TEM experiments.
NATURE CHEMISTRY | VOL 2 | JUNE 2010 | www.nature.com/naturechemistry!

!

© 2010 Macmillan Publishers Limited. All rights reserved.!

451

photon emission,

irmeasured
carbonskeleton,toandbecarbon
thetheed
The rate of this reaction
hasinside
beentheka ¼ at by
Ref.PAHs
31 finds
theoreticalvalue
numberbound.
of small(28, a34).
We
1.5 × 10−10 cm3 s−1 for astrongly
thenebkðEÞ where
the C parameter,
atoms
Moreover,theoretic
the[11]IRemissionrate at aanzig-zag
energyE. Fora E
k ðEÞ is thenH ∕k. Withdissociationψinternal¼ kaedge.
adopt
frag
; can irdefine −10
pd ðEÞ ¼−1
ergiesnotflux
a goodmeasurefor
Arrhenius¼ 7 × 10PAH,
N c Gkoir, ðEÞ
whereis theof UVin theunits
nebulaekðEÞ þ kir highlyðEÞ kuvexcitedis Gapproximately
1 photons
sPNAS
. The
total
fragoare[Berné
& Tielens2012]
mentation rate is then olecular dissociation experiments (33). Given theof gas phase carbon,H-loss
the reverse reaction is unimp
where kir ðEÞ is the IR emission rate at an internal energy E. For a
140
140
−1
−1
chemicallifetime
[τ
¼
k
ðEÞ]
has
to
be
comp
frag
excited PAH, kir ðEÞ is approximately 1 s . The total frag- kfrag ¼ pd ðEÞkuv ðEÞ;chem- UV inducedhighly
dehydrogenation[12]
namicallifetimeoftheregion.
We
haveevaluatedmentation rate is then120a120
lifetime for a typical internal energy of 10 eV as- UV induced removal of single atoms at the whereedge oftheflake
absorption
rateof UV photons
withenergy,E.are skuv ðEÞ is the[12]
size
of
the
graphenesheet,
N,andtheresults
¼
p
ðEÞk
ðEÞ;
k
c
frag
uv
d
make pentagons in the hexagonal network whichThe
curls
the
100 H loss is balanced by reactions of100
photochemicallydrivenmolecule till zipping of open edges
Application to NGC
7023.namely,
atomichydrogenwith
PAHs;
photonswith energy,
E. dehydrogenated
where kuv ðEÞ is the absorption rate of UV
To evaluate
graphene formation in NGC 7023,80w
80
The photochemically driven H loss is balanced by reactions of- DFT calculations
thatwithonly
C loss requires
energy,stability.
Thephysicalconditions in the nebula,
þH→
PAH
þ hν:
[13] chPAH−H
atomic showhydrogendehydrogenatedPAHs;
namely,pentagon migration & roll up is barrier-lessparameters
G0 and nH , can be obtained (SI Text
60
60
Fig. 4,has
H lossis very
efficient inþ hν:rate of this[13]PAH−H þ H → PAHThereactionbeenmeasured
toNGC
be 7023
ka ¼for P
C atoms.
We then evaluate the timescale for the
−10
3 −1
40 l
40
cm
s
for
a
number
of
small
PAHs
(28,
34).
We
1.5
×
10
The rate of this reaction has been measured to be ka ¼
by the graphene flakes and compare this to the dy−10
3 −1. Withcandefinethedissociation
parameter,
ka nPAH
H ∕kfrag
cm s for a number UVof small PAHs (28, 34). We
1.5 × 10the nebula
for a ≃70ψC¼atom(Fig.
4). It 20
app20A) Dehydrogenation−10
kuv ψ¼¼7k×
Go , where
G10oE-3isthein9 units to-1 flux
5 rapid
1 ofCUV. cWithcan define the dissociation parameter,adopt
iscompareda n10
H ∕kfragNo ¼
10 7 10103.6510 3loss
10photons
10
10eV,
−10
kuv ¼ 7 × 10 N c Go , where Go is the flux of UV photons in units
nebula.
G /nH

Proposed formation route in the ISM

diffuse ISM

NCNCD) Zipping

80

404 ∣

100
100

www.pnas.org/cgi/doi/10.1073/pnas.1114207108

80
80

60

60

40

40

NGC70237023
age of NGC

100C) Curling

diffuse ISM

120

diffuse ISM

UVH-lossB

Fig.
4. Photochemistry of PAHs in NGC 7023 (A) The red
curve shows the evolution of the
H-lossC-lossof the physical conditions (G0 ∕nH where G0 is the radiation field in Habing units and nH is
the number of carbon atoms in the PAH molecule NC . Above this line, PAHs are stable aga
1207023 is shown; dark blue represents the “narrow” raatoms. The value of G0 ∕nH for NGC
120
parameter (SI Text). (B) Timescale for the loss of a carbon atom by UV photon absorpti

NC

A 140

0

A
140
B 140

NGC 7023

B) C loss and Pentagon
formation

NGC 7023

B

A

60
40

20 based on Le Page et al.
- Evaluation with photochemical model
10 -3 10 -1 10 1 10 3 10 5 10 7 10 92003 and lab data, for UV photons of 10 eV

G0/nH

20
1
3
7
-3
5
9
11
-1
2010 10 10 10 10 10 10 10
1 [yr] 3
τchem
10 10 5 10 7 10 9
10 -3 10 -1 10

G /nProposed formation route in the ISM

C atoms in a hexagon only
C atoms in a pentagon

Acknowledgments- University of Toulouse for financial support- Prof. Matsumoto for financial support- Yosuke Matsumoto for organizing this trip
- All the staff/students/postdocs here in Chiba for their kindness