CH+ spectrum and diffuse interstellar bands toward Herschel 36 excited by dust emission

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

Department of Astronomy and Astrophysics, University of Chicago

June 20, 2012, Columbus meeting WH07

1937 Birth of Molecular Astrophysics

Theodore Dunham, Jr. 1897-1984 Walter Sydney Adams, 1876-1956

T. Dunham, Jr. PASP 49, 29 (1937) PAAS 9, 5 (1937)

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

P. Swings & L. Rosenfeld, ApJ 86, 483 (1937)

A. McKellar, PASP 52, 187, 312 (1940) 53, 233 (1941) CH CN

Pub. Dom. Astroph. Obs. 7, 251 (1941) Tr = 2.3 K

A. E. Douglas and G. Herzberg, ApJ 94, 381 (1941) CH+

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 (1941)

Te = 2.3 K (= Tr)

CN

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

AV ~ 4

AV ~ 6

The three temperaturesKinetic temperature Tk Collision Maxwell 1860 Phil. Mag. 4, 19

Excitation temperature Te Observed Boltzmann 1871 Wiener Berichte 63, 712

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

If Tk = Tr, thermal, Boltzmann Te = Tk = Tr

If Tk > Tr, collision dominated thermal Te = Tk

radiation dominated thermal Te = Tr

intermediate non-thermal −∞ < Te < ∞

''

( ')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+ in the J = 1 excited rotational level and radiative temperature of dust emission

CH+ 40.1 K

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

Te = Tr = 14.6 K

0

2

1

2

1

0

R(0)R(1) Q(1)

CN 4.9 K

HD 213985

Bakker et at. A&A, 323, 469 (1997)

CH in the J = 3/2 excited fine structure level

Te = Tr = 6.7 K < 14.6 K

~ 25.6 K

CHCH+

Effect of radiation on DIBs toward Her 36

Extended Tail toward Red ETREast Turkestan Republic

(B’−B)J(J +1)

Simulation of DIB velocity profiles with high Tr and the 2.7 K cosmic background radiation

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 only

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

ΔJ > 1

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

Rotational distribution n(J)

Spectrum Rotation of linear molecules

)1(ˆ2

ˆˆ

2

222

JhBJJHJEI

JH

I

PE

I

hB

28

i

ii zmI 2

Rotational constant

Moment of inertia

R()

CH+ 417,568 MHz 20.04 K

HC5N 1,331 MHz 0.06390 K

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

Q(J) J ← J ν = ν0 + B’J(J +1) – BJ(J + 1) = ν0 + (B’ – B)J(J + 1)

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

1

2 t

Simulated spectra

Tr, Tk, B, μ, C, β, Γ CHCH+DIBs

Reservation λ6613

Sarre et al. 1995, MNRAS 277, L41

Kerr et al. 1996, MNRAS 283, L105

Other possible mechanisms

Linear molecules B’ – B μ

General moleculesA’ – A, B’ – B, C’ – C μa, μb, μc

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

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

100 %

Vibrational excitation?

I am scared

Short column length L ≤ 1000 AU

High radiative temperature Tr ~ 80 K