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PDR Workshop Summary I n H 2 Shielding: -- β(τ) vsfull H2, correction for sphere/slab, Go/n alone not whole story -- line overlap important or not? -- determine thin rates with ∫I(λ)σ(λ)dλ (no fit)

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PDR Workshop Summary II n Line Transfer: -- Optically thick, effectively thin line has higher n_i in sphere vs slab (for same T) -- In MC vs ALI beware convergence for τ>>1 -- Check levels n_i not just T R or total I

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PDR Workshop Photon Processes in (Inhomogeneous) PDRs Marco Spaans (Kapteyn) Marco Spaans (Kapteyn)

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PDR Workshop Clumpiness n Parameter k decreases in expression for R n For given N H columns of C+ and C not strongly affected, but spatial extent is n Column density of CO is boosted in dense clumps n Back scattering of UV photons causes complicated clump illumination: (λ) and ω(λ) n Influences C+ -> C -> CO transition

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PDR Workshop n S140, edge-on PDR n n=Fn_c+(1-F)n_i n r=n_c/n_i, clump size l_c=0.02 pc n Iuv=140, F=30%, r=10, n=2(4) cm-3

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PDR Workshop total H density [CI] 609 μm & ¹³CO 2-1

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H 2 emission n Fluorescence: UV – Vis – IR Diagnostic for Iuv/n H No collisional de-excitation if density less than 10^4 cm-3 (same for multiple pumping) n Scaling: I F /Iuv (Rn H /Iuv,N H ) and N H (Rn H /Iuv,Av) n Also pure rotational line emission

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PDR Workshop

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n 26-ray approximation n 3-D n Isotropic illumination n IRAS G236+39: HI 21 cm and 100 μm dust

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Photorates with depth n R=Ro e^(-k Av); Ro strong function of Teff n k is a fit and k~1-3 n CO (absorptions into pre-dissociated states) and H 2 (Lyman-Werner+cascade) self-shield; TH, de Jong et al.: β H2 (τ>10)={τ^-1[ln(τ/π^½)]^½+ (b/τ)^½}erfc(τb/πv^-2)^½ R CO * [1+αβ CO (τ)]/(1+α) or shielding functions van Dishoeck & Black (1988)

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Photorates with depth n Good if line overlap is ignored; edge effects still occur; Iuv/n H ratio crucial n H 2 * (v=6/2.6 eV) versus H 2 (J,v) n Line overlap: H 2, H, CO, C n MC H 2 : N=135, λ=1000 Å, f=3.5(-3), A=5.7(8) s-1, η=0.127 n MC CO: N=33, λ=1002 Å, f=2.0(-2), A=3.0(11), η=1.0

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PDR Workshop Photorates with depth n Should integrate photo-ionization and photo-dissociation cross sections: σ(λ) n Note: CRs and X-rays can be important; CRs no attenuation, X-rays column of N H ~10^22 cm-2

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References n Tielens & Hollenbach 1985 n Kaufman et al. 1999; Spaans 1996; Sternberg & Dalgarno 1995; Stőrzer et al. 1995; Spaans et al. 1994; Wolfire et al. 1993; le Bourlot et al. 1993; Tielens et al. 1993; Boisse’ 1990; van Dishoeck & Black 1988; Sternberg 1988; Black & van Dishoeck 1987; de Jong et al. 1980; Black & Dalgarno 1976 n Maloney et al. 1996

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