1. arXiv:1304.2842 OBSERVATIONS AND ANALYSIS
OF EXTENDED TAIL TOWARD RED (ETR)
IN THE DIFFUSE INTERSTELLAR BANDS (DIBs)
OF HERSCHEL 36
arXiv:
Takeshi Oka, Daniel E. Welty, Sean Johnson,
Donald G. York, Julie Dahlstrom, and Lew Hobbs
Department of Astronomy and Astrophysics,
University of Chicago
June 20, 2013, Columbus Meeting

2. Spectra toward two Stars in M8: d ~ 1.5 kpc
Tr ~ 2.7 K
Tr >> 2.7 K
9 Sgr Herschel 36
> 200 Ordinary
Extraordinary
E(B – V) =

3. Direct Evidence Tr=14.6 K, CH+
High radiative Temperature, Tr=14.6 K CH+
Direct Evidence Tr=14.6 K, CH+
9 Sgr
Her 36
CH+ CH
120.3 K 2
μ = 1.7 Debye
A = s-1
τ = 150 s
ncrit ~ 3 × 106 cm-3
Tex = 14.6 K = Tr
40.1 K 1

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

5. Spectacular Effect of high Tr on DIBs30 2 20 1
Huge difference 10
Huge Effect
Many J levels are radiatively pumped
Sharp contrast
Polar non-polar
CH+
B = GHz
μ = 1.7 D
HCCCCCN
B = 1.3 GHz
μ = 4.33 D
Spectroscopically makes sense!

6. Spectroscopically makes sense
Extended Tail toward Red (ETR)
R(J) J + 1 ← J ν = ν0 + 2B’(J + 1) + (B’ – B)J(J + 1)
Q(J) J ← J ν = ν (B’ – B)J(J + 1)
P(J) J ˗ 1 ← J ν = ν0 – 2B’J (B’ – B)J(J + 1)
B’ < B
HCCCCCN
HCCCCCN

7. The Crucial Parameter β = (B’ – B)/B
HC3N μ = 3.6 Debye
HC5N μ = 4.3 Debye
HC9N μ = 5.6 Debye
C8H- μ = 11.9 Debye

8. Rotational Distribution at high Tr
Collision dominated
Radiation and collision ,
Einstein 1916
Goldreich & Kwan 1974
Principle of Detailed Balancing Boltzmann, H-theorem
Wiener Berichte 66, 275

9. Calculated Rotational Distribution n(J)

10. Spectral Simulation Radiation dominated Collision dominated T = 2.73 K

11. Comparison of Simulated ETR with Observed
Tr, Tk, B, μ, C, β, Γ
DIBs
CH+ CH
Her 36
Her 36 SE

12. Other possible mechanisms
Linear 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 ← linear
CH2 (B3Σu- - X3B1), HCO (A2Π – XA’) and NO2 (E2Σu+ - X2A1)
A’ – A = A’ 100 %
Vibrational excitation?

13. Conclusions Firm conclusions Likely 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 , and λ which do not show strong ETR are
Most 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.

14. I am scared High column density 1014 cm-2 CH2CC
P. Thaddeus, M. C. McCarthy, Spectrochimica Acta A, 57, 757 (2001)

15. Herschel 36 Trad >> 2.73 K
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 Tex Observed
Boltzmann 1871 Wiener Berichte 63, 712
If Tk = Tr, thermal, Boltzmann Tex = Tk = Tr
Tk > Tr, collision dominated thermal Tex = Tk
radiation dominated thermal Tex = Tr
intermediate non-thermal −∞ < Tex < ∞
CH+, CH, CN
DIBs