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Analysis of Anomalous DIBs in the Spectrum of Herschel 36. arXiv:1304.2842. Takeshi Oka, Daniel E. Welty, Sean Johnson , Donald G. York, Julie Dahlstrom, and Lew Hobbs Department of Astronomy and Astrophysics, University of Chicago. - PowerPoint PPT Presentation
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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
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