1. 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

2. 1937 Birth of Molecular Astrophysics
Theodore Dunham, Jr
Walter Sydney Adams,
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)
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+

3. CN and the cosmic blackbody radiation
P(1)
R(0)
Te = 2.3 K (= Tr)
Andrew McKellar
A. McKellar, PASP, 51, 233 (1940)
A. McKellar, PDAO, 7, 251 (1941)
W.S. Adams, ApJ, 93, 11 (1941)

4. AV ~ 6
AV ~ 4
Goto, Stecklum, Linz, Feldt, Henning, Pascucci, Usuda, 2006, ApJ, 649, 299

5. The three temperatures
Kinetic temperature Tk Collision
Maxwell 1860 Phil. Mag. 4, 19
α2 = 2kTk/m
Radiative temperature Tr Radiation
Planck Ann. D. Physik 4, 564
θ = Tr
Excitation temperature Te Observed
Boltzmann 1871 Wiener Berichte 63, 712
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 < ∞

6. CH+ in the J = 1 excited rotational level
and radiative temperature of dust emission 2 1
Te = Tr = 14.6 K
R(1)
R(0)
Q(1)
μ = 1.7 Debye
A = s-1 τ = 140 s
ncrit = 3 × 106 cm-3 2 1
CN 4.9 K
CH K HD
Bakker et at. A&A, 323, 469 (1997)

7. CH in the J = 3/2 excited fine structure level
~ 25.6 K
Te = Tr = 6.7 K < 14.6 K
CH+ CH

8. Effect of radiation on DIBs toward Her 36
(B’−B)J(J +1)
Extended Tail toward Red ETR
East Turkestan Republic

9. Simulation of DIB velocity profiles
with high Tr and the 2.7 K cosmic background radiation
Collision only
Radiation and collision ,
Einstein 1916
Goldreich Kwan 1974
ΔJ > 1
Principle of Detailed Balancing Boltzmann, H-theorem
Wiener Berichte 66, 275

10. Rotational distribution n(J)

11. Spectrum Rotation of linear molecules Rotational constant
CH+ 417,568 MHz K
Moment of inertia
HC5N 1,331 MHz 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)
R()
Q(J) J ← J ν = ν0 + B’J(J +1) – BJ(J + 1) = ν (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)

12. Simulated spectra
Tr, Tk, B, μ, C, β, Γ
DIBs
CH+ CH

13. Reservation λ6613 Sarre et al. 1995, MNRAS 277, L41
Kerr et al. 1996, MNRAS 283, L105

14. Other possible mechanisms
Linear molecules
B’ – B μ
General molecules
A’ – A, B’ – B, C’ – C
μa, μb, μc
Special group of molecules: Non-linear ← linear
CH2 (B3Σu- - X3B1), HCO (A2Π – XA’) and NO2 (E2Σu+ - X2A1)
100 %
Vibrational excitation?

15. I am scared Short column length L ≤ 1000 AU
High radiative temperature Tr ~ 80 K