Analysis of Anomalous DIBs in the Spectrum of Herschel 36

Takeshi Oka, Daniel E. Welty, Sean Johnson, Donald G. York, Julie Dahlstrom, and Lew Hobbs

Department of Astronomy and Astrophysics, University of Chicago

May 20, 2013, IAU 297 The Diffuse Interstellar Band, Noordwijkerhout

arXiv:1304.2842

9 Sgr Herschel 36

E(B – V) = 0.33 0.87

Spectra toward two Stars: d ~ 1.5 kpc

> 200 Ordinary Extraordinary

Tr ~ 2.7 K Tr >> 2.7 K

0

2

1

μ = 1.7 DebyeA = 0.0070 s-1 τ = 140 sncrit ~ 3 × 106 cm-3

Tex = 14.6 K = TrTex = 2.3 K A. McKellar, PASP, 53, 233 (1941)

Tex = Tr = 3.22 K Field & Hitchcock, PRL (1966)Tex = Tr = 3.75 K Thaddeus & Clauser, PRL (1966)Tex = Tr = 2.73 K Meyer & Jura, ApJ (1984)

CNμ = 1.48 DebyeA = 1.24 × 10-5 s-1 τ = 0.93 daysncrit ~ 104 cm-3

9 Sgr

Her 36

40.1 K

Direct Evidence Tr=14.6 K, CH+

120.3 K

CH+ CH

Goto, Stecklum, Linz, Feldt, Henning, Pascucci, Usuda, ApJ, 649, 299, 2006

AV ~ 4

AV ~ 6

Spectacular Effect of high Tr on DIBs

CH+

B = 417.7 GHzμ = 1.7 D

High contrast

Spectroscopically makes sense!

HCCCCCNB = 1.3 GHzμ = 4.33 D

0

2

1Huge difference

Huge Effect

20

10

30

Polar non-polar

Many J levels are radiatively pumped

Spectroscopically makes sense

R(J) J + 1 ← J ν = ν0 + 2B’(J + 1) + (B’ – B)J(J + 1)

Q(J) J ← J ν = ν0 + (B’ – B)J(J + 1)

P(J) J ˗ 1 ← J ν = ν0 – 2B’J + (B’ – B)J(J + 1)

East Turkestan Republics

HCCCCCN

HCCCCCNB’ < B

B

BB

'

Extended Tail toward Red (ETR)

The Crucial Parameter β = (B’ – B)/B

HC3N μ = 3.6 DebyeHC5N μ = 4.3 DebyeHC9N μ = 5.6 DebyeC8H- μ = 11.9 Debye

Rotational Distribution at high Tr

1 1( ) ( 1)J Jn J C n J C

11

11

( ) 2 1 2exp( ) exp( )

( 1) 2 1J e J

J Je J kJ

C n J g J hBJE E

n J g J kTC

1

1 1

( 1)( ) (0) (2 1)exp

Jm

m k km

C NhB hBJ Jn J n J

kT kTC

Collision dominated

Radiation and collision

1 1 1 1( )( ) ( 1)( )JJ J J Jn J A B C n J B C Einstein 1916

,

1 1/ /

1 2 1 1( ) 1 ( 1)

1 2 1 1r r

J JJ Jh kT h kT

Jn J A C n J A C

e J e

4/3 2

2 /

41 /3 2

2 /

1 2 1

2 1 1 2 1( ) (0)1 2 1

12 1 1 2 1

k

r

k

r

hBm kTJ hBm kT

m hBm kThBm kT

m mB C e

m e mn J nm m

B C em e m

Goldreich & Kwan 1974

Principle of Detailed Balancing Boltzmann, 1872 H-theorem Wiener Berichte 66, 275

4/3 2

2 /

41 /3 2

2 /

1 2 1

2 1 1 2 1( ) (0)1 2 1

12 1 1 2 1

k

r

k

r

hBm kTJ hBm kT

m hBm kThBm kT

m mB C e

m e mn J nm m

B C em e m

Calculated Rotational Distribution n(J)

Collision dominated

Radiation dominatedSpectral Simulation

T = 2.73 KT = 80 K

T = 2.73 K

T = 80 K

Comparison of Simulated ETR with Observed

Tr, Tk, B, μ, C, β, Γ CHCH+DIBs

Her 36Her 36 SE

Other possible mechanismsLinear molecules J B’ – B μ

General molecules J, Ka, Kc

A’ – A, B’ – B, C’ – C μa, μb, μc

Special group of molecules: Non-linear ← linearCH2 (B3Σu

- - X3B1), HCO (A2Π – XA’) and NO2 (E2Σu+ - X2A1)

A’ – A = A’ 100 %

Vibrational excitation?

ConclusionsFirm conclusions

λ5780.5, λ5797.1, and λ6613.6, which show strong ETR are due to polar molecules. Non-polar molecules such as carbon chains (Cn) or symmetric hydrocarbon chains(HCnH, H2CnH2, NCnN, etc.), symmetric PAHs (benzene, pyrene, coronene, ovalene etc.), or C60, C70 etc. and their cations and anions cannot be the carriers of those DIBs.

Likely conclusions

λ5849.8, λ 6196.0, and λ6379.3 which do not show strong ETR areMost likely due to non-polar molecules.

Carriers of λ5780.5, λ5797.1, and λ6613.6, which show strong ETR are probably not very large, otherwise β is too small.

I am scared

Short column length L ≤ 1000 AU

High radiative temperature Tr ~ 80 K

High column density required > 1014 cm-2

Professor John Maier

Professor Peter Sarre

P. Thaddeus, M. C. McCarthy, Spectrochimica Acta A, 57, 757 (2001)

Sarre et al. 1995, MNRAS 277, L41

Kerr et al. 1996, MNRAS 283, L105

Herschel 36 Trad >> 2.73 KKinetic temperature Tk Collision Maxwell 1860 Phil. Mag. 4, 19

Excitation temperature Tex Observed Boltzmann 1871 Wiener Berichte 63, 712

Radiative temperature Tr Radiation Planck 1901 Ann. d. Physik 4, 564

If Tk = Tr, thermal, Boltzmann Tex = Tk = Tr

Tk > Tr, collision dominated thermal Tex = Tk

radiation dominated thermal Tex = Tr

intermediate non-thermal −∞ < Tex < ∞

''

( ')exp ( ) /

( )J

J J eJ

gn JE E kT

n J g

2

22

3

4v

dn N v e dv

3

5

8 1

1ch

k

hE

e

α2 = 2kTk/m

θ = Tr

CH+, CH, CN DIBs

P. Thaddeus, M. C. McCarthy, Spectrochimica Acta A, 57, 757 (2001)

Reservation λ6613

Sarre et al. 1995, MNRAS 277, L41

Kerr et al. 1996, MNRAS 283, L105

I am scaredShort column length L ≤ 3000 AU

High radiative temperature Tr ~ 80 K

1 in 200

HD 29647 E(B-V) = 1.00 W(5780) = 70 ± 7

Andrew McKellar 1910 -1960

CN and the cosmic blackbody radiation

W.S. Adams, ApJ, 93, 11 (1941)

A. McKellar, PASP, 51, 233 (1940)

R(0)

R(1) P(1)

A. McKellar, PDAO, 7, 251 (1949)

Te = 2.3 K (= Tr)

CN