New advances in photoionization codes:

New advances in photoionization codes, how and what for?

New advances in photoionization codes:

Barbara Ercolano, UCL

How and What for?


Ionising radiation transferThermal equilibriumIonisation balance

Electron temperature

Ionisation structure

Emission linespectrum

Ionising source

Atomic data

Chemical composition Gas density

distribution

Processes stationaryStatic medium

Spherical symmetry

Photoionization models – How?


Lexington 2000 codes

(Pequignot et al. 2001, PASP 247, 533)

• Cloudy (G. Ferland) • Harrington (P. Harrington)

• Ion (H. Netzer)

• Mappings (R. Sutherland)

• (Infant) Mocassin (B. Ercolano)

• Nebu (D. Pequignot)

• Nebula (R. Rubin)

• XStar (T. Kallman)

Ercolano et al., 2003, MNRAS 340, 1136


Lexington 2000 codes

(Pequignot et al. 2001, PASP 247, 533)

• Cloudy (G. Ferland) • Harrington (P. Harrington)

• Ion (H. Netzer)

• Mappings (R. Sutherland)

• (Infant) Mocassin (B. Ercolano)

• Nebu (D. Pequignot)

• Nebula (R. Rubin)

• XStar (T. Kallman)





New advances – How ?

•Atomic data updates •Time-dependence effects•Inclusion of dust RT•Expansion to PDR •Development of 3-D Codes



•Atomic data updates –Collision strengths & transition probs–Radiative+Dielectronic recombination–Recombination data for ORLs (R. Bastin)–Data for cold (0.5-2kK) ionized plasma (as suggested by ORL analyses)





(Henney et al., 2005 ApJ, 621,328)

• Shock ionization (Mappings III)

• Source variation (PNe in recombination)

• Short gas-flow time scales– Cloudy (Henney et al.,

2005 ApJ, 621,328)

Time-dependent effects





Gas and Dust Interactions: the dust thermal balance

Absorption of resonance

emission lines

Dust-gascollisions

Absorption of UV photons

Photoelectricemission

from grains

Cloudy (Van Hoof et al., 2004, MNRAS 350, 1330)

Mocassin (Ercolano et al., 2005, MNRAS submitted)

Radiation from grains

Dust Heating

Dust Cooling


Effects of dust grains on emission lines ratios

Cloudy (Van Hoof et al., 2004, MNRAS 350, 1330)





Self-consistent Photoionization+PDR

Radiation field on PDR comes from ionised region

Dust dominates the opacity in the PDR

Must include a chemical network

PNe emission line spectra modified by PDRs

Cloudy (Shaw et al., 2005, ApJ 624, 794;Abel et al., 2005, ApJ 609, 247)

Mocassin+UCL_PDR (Ercolano et al., in prep.)

Barbara

Important to understand the formation processes of PNe. Some lines are predominantly formed in the PDR (e.g. [OI] lines) -> read P Van Hoof 2004





3D codes: What for? NGC6543 – The Cat’s eye Nebula NGC2392 – The Eskimo Nebula

MyCn18 – The etched hourglass nebula

Images from www.hubblesite.org

NGC7009 – The Saturn Nebula Central region of Abell 30


Projected model images of NGC 3918 in three Projected model images of NGC 3918 in three infrared fine-structure lines observed by the infrared fine-structure lines observed by the ISO ISO

SWSSWS



3D photoionization codes chronology

• 1990 Baessgen et al., A&A, 201, 237– Fixed grid resolution, 6 most abundant elements

included, OTS diffuse field• 1997 São Paolo, Gruenwald et al., ApJ, 480, 283

– More flexible grid, 12 elements included, iterative techniques for the diffuse field

• 2003 MOCASSIN, Ercolano et al., MNRAS, 340, 1136– Flexible grids, 30 elements included, Monte Carlo

RT, diffuse field treated self-consistently • 2004 Wood, Mathis & Ercolano, MNRAS 348, 1337

– Monte Carlo RT - tailored for the study of Galactic HII regions

• (2004 Nebu-3D, Morisset et al., MNRAS, 360, 499)– A quick pseudo-3D photoionization code


2D Projections [NII]

[OIII] [OI]

Sahai et al., 1999, AJ 118,468

H

Neal et al. (in prep)


2D Projections [NII]

[OIII] [OI]

H

Neal et al. (in prep)

Sahai et al., 1999, AJ, 118, 468


The future for 3D photoionization

• Study of diffuse field dominated regions – the Helix knots and tails?

• Chemical inhomogeneities – ORL/CEL discrepancy? (Y. Tsamis)

• Realistic models of spatially resolved objects

• Interface with hydro-codes


CAVEAT: Horses for courses!!!

• 1D codes allow faster computations– Parameter space explored more efficiently – Large grids of models can be produced quickly

“Never use a sledge-hammer to squash a fly!!!“(Anonymous referee)

• 1D codes can be used in the case of – Spatially unresolved objects– Diffuse field unimportant (Nebu 3D)

… Moores law on the other hand….


Overview

•Photoionization Codes: What for?•Photoionization Codes: How?•New Advances: How?•3D codes: How & What for?•Near & near-ish future


Photoionization models – What for?

• Interpretation of spectroscopic observations to determine – Properties of ionizing star(s)– Gas density and elemental abundances– Electron temperature and ionization

structure

• Testing physical assumptions, atomic physics and astrophysical knowledge– e.g. charge exchange process, low

temperature dielectronic recombination


3D (analytical) photoionization: How?

• São Paolo code: – Descendent of 1D Aangaba (Gruenwald

& Viegas, 1992), descendant of ‘early NEBU’ (Pèquignot et al, 1988)

– Stellar and diffuse fields accounted for• Local radiation field is calculated taking into

account attenuation from intervening cells

– Several PNe modelled (Monteiro et al., 2000,2004,2005) • Distance determinations


• Discrete description of radiation field (energy packets)

• Simulating the individual absorption/emission/scattering events

• Packets trajectories determined stochastically according to the local opacities and emissivities.

• Gas properties determined by imposing ionisation balance and thermal equilibrium

3D (MonteCarlo) photoionisation: How?

Barbara

v similar to how a dust rt code works - many of them around. why only one photoionisation code? more difficult due to temperature dependance of gas opacities. need to iterate. mocassin is also a dust rt code and dust and gas are coupled thorugh the competition to UV photons, the attenuations of resonance lines, gas+dust collisions, phtoelectric heating.. all this in Ercolano et al. 2005. can elaborate more at the end.


Gas and Dust Interactions: the dust thermal balance

Dust Heating

Gas Heating Dust Cooling

Gas Cooling

Absorption of resonance

emission lines

Dust-gascollisions

Absorption of UV photons

Photoelectricemission

from grains

Cloudy (Van Hoof et al., 2004); Mocassin (Ercolano et al., submitted)

Radiation from grains


MOnteCArloSimulationSofIonisedNebulae

(Version 2.01.16)… can treat …

• Bipolar, irregular geometries etc..• Density &/or chemical inhomogeneities• Multiple ionising sources• 3D gas &/or dust radiative transfer

… can provide …• Emission line intensity tables• Spectral energy distributions (SEDs)• 3D (gas &/or dust) temperature distributions• 3D ionization structures• Emission line(s), continuum band projections through any line of sight


Heating and cooling contributions in knot J3 of Heating and cooling contributions in knot J3 of Abell 30Abell 30

Positive x

Negative xPositive zphoto: heating by photoionization dust: heating by photoelectric emission from dust grainscoll: cooling by collisionally excited linesrec: cooling by recombinationff: cooling by free-free radiation

d/g(core)= 0.077

d/g(env)= 0.107

Ercolano et al., 2003 MNRAS 344, 1145

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New advances in photoionization codes: