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:

9 Sgr Herschel 36 E(B – V) = Spectra toward two Stars: d ~ 1.5 kpc > 200 OrdinaryExtraordinary T r ~ 2.7 KT r >> 2.7 K

0 2 1 μ = 1.7 Debye A = s -1 τ = 140 s n crit ~ 3 × 10 6 cm -3 T ex = 14.6 K = T r T ex = 2.3 K A. McKellar, PASP, 53, 233 (1941) T ex = T r = 3.22 K Field & Hitchcock, PRL (1966) T ex = T r = 3.75 K Thaddeus & Clauser, PRL (1966) T ex = T r = 2.73 K Meyer & Jura, ApJ (1984) CN μ = 1.48 Debye A = 1.24 × s -1 τ = 0.93 days n crit ~ 10 4 cm -3 High radiative Temperature, T r =14.6 K CH + 9 Sgr Her K Direct Evidence T r =14.6 K, CH K CH + CH

Goto, Stecklum, Linz, Feldt, Henning, Pascucci, Usuda, ApJ, 649, 299, 2006 A V ~ 4 A V ~ 6

Spectacular Effect of high T r on DIBs CH + B = GHz μ = 1.7 D High contrast Spectroscopically makes sense! HCCCCCN B = 1.3 GHz μ = 4.33 D Huge difference Huge Effect Polar non-polar Many J levels are radiatively pumped

Spectroscopically makes sense R(J) J + 1 ← J ν = ν 0 + 2B’(J + 1) + (B’ – B)J(J + 1) Q(J) J ← J ν = ν 0 + (B’ – B)J(J + 1) P(J) J ˗ 1 ← J ν = ν 0 – 2B’J + (B’ – B)J(J + 1) East Turkestan Republics HCCCCCN B’ < B Extended Tail toward Red (ETR)

The Crucial Parameter β = (B’ – B)/B HC 3 N μ = 3.6 Debye HC 5 N μ = 4.3 Debye HC 9 N μ = 5.6 Debye C 8 H - μ = 11.9 Debye

Rotational Distribution at high T r Collision dominated Radiation and collision Einstein 1916, Goldreich & Kwan 1974 Principle of Detailed Balancing Boltzmann, 1872 H-theorem Wiener Berichte 66, 275

Calculated Rotational Distribution n(J)

Collision dominated Radiation dominated Spectral Simulation T = 2.73 K T = 80 K T = 2.73 K T = 80 K

Comparison of Simulated ETR with Observed T r, T k, B, μ, C, β, Γ CHCH + DIBs Her 36 Her 36 SE

Other possible mechanisms Linear molecules J B’ – B μ General molecules J, K a, K c A’ – A, B’ – B, C’ – C μ a, μ b, μ c Special group of molecules: Non-linear ← linear CH 2 (B 3 Σ u - - X 3 B 1 ), HCO (A 2 Π – XA’) and NO 2 (E 2 Σ u + - X 2 A 1 ) A’ – A = A’ 100 % Vibrational excitation?

Conclusions Firm conclusions λ5780.5, λ5797.1, and λ6613.6, which show strong ETR are due to polar molecules. Non-polar molecules such as carbon chains (C n ) or symmetric hydrocarbon chains (HC n H, H 2 C n H 2, NC n N, 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.

I am scared Short column length L ≤ 1000 AU High radiative temperature T r ~ 80 K High column density required > 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 T rad >> 2.73 K Kinetic temperature T k Collision Maxwell 1860 Phil. Mag. 4, 19 Excitation temperature T ex Observed Boltzmann 1871 Wiener Berichte 63, 712 Radiative temperature T r Radiation Planck 1901 Ann. d. Physik 4, 564 If T k = T r, thermal, Boltzmann T ex = T k = T r T k > T r, collision dominated thermal T ex = T k radiation dominated thermal T ex = T r intermediate non-thermal −∞ < T ex < ∞ α 2 = 2kT k /m θ = T r 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 scared Short column length L ≤ 3000 AU High radiative temperature T r ~ 80 K 1 in 200

HD E(B-V) = 1.00 W(5780) = 70 ± 7

Andrew McKellar 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) T e = 2.3 K (= T r ) CN