atomic data and spectral models for lowly ionized iron-peak species

Atomic Data and Spectral Models

for Lowly Ionized Iron-peak

Species

Manuel Bautista, Vanessa Fivet

(Western Michigan University)

Pascal Quinet

(Mons University, Belgium)

Connor Ballance

(Auburn University)

• Reliable modeling of neutral through doubly ionized Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu is of great importance in various areas, e.g. H II regions, SNe remnants, AGN, supernovae light curves as cosmological candles, atmospheres of the Sun and late type stars, afterglows of GRBs, etc.

Emission spectra of η Carinae

Absorption spectrum of QSO 0059-2735. The spectrum is dominated by

absorption features from the ground and excited levels of Cr II, Fe II, Fe III,

Co II, Ni II, Mn II, and possibly Ti II

• For most of these ions there are yet no

spectral models available because even

the fundamental atomic parameters are

unknown.

• For those ions that have been studied in

the past, such as Fe II and Fe III, there

was mounting evidence on that the models

were inaccurate.

• For instance, predicted line intensities for

Fe II in the Orion nebula, the simplest and

best known nebular environment to

astronomy, disagree with observations by

up to several factors.

Ratio of CLOUDY predicted [Fe II] line intensities to

observed values in the Orion nebula (Verner et al 2000).

[Fe III] and [Fe IV]

• A discrepancy of about a factor ~3 remains in

the Fe abundances derived from [Fe III] and

[Fe IV]

• Rodriguez & Rubin (2004) argue that the errors

could be either in the collision strengths or the

total Fe3++e -> Fe++ recombination

• Current collision strengths (Zhang 1996), but

McLaughlin et al. (2002) report LS collision

strengths lower by a factor of 2

Fe II

• Excitation mechanisms for Fe II include electron

impact, photoexcitation by continuum radiation,

and fluorescence by Lyα.

• Current models include over 800 levels

(>300.000 transitions), e.g. Bautista et al.

(2004).

• But data still incomplete and unchecked.

Collisional coupling of pseudo-

metastable levels

Bautista et al. (2004)

Comparison between bound-free cross sections of

Bautista (1997) and hydrogenic approximations

Comparison of theoretical and observed emergent fluxes of

the solar atmosphere

Goals of the project

• Computation of reliable and complete data sets (A-values for allowed and forbidden transitions, collision strengths, photoionization cross sections and recombination rate coefficients) for neutral, singly and doubly ionized iron-peak species

• Construction of spectral and opacity models whose quality will be benchmarked by modeling spectra of AGN and Eta Carinae

• Distribution of the data and models among the scientific community

• Implementing the atomic models into the photoionization modeling codes XSTAR (Kallman & Bautista 2001) and CLOUDY (Ferland et al. 1998)

Atomic Physics

iii EH

H p2i

2mei1

N

Ze2

rii1

N

e2

ri rji j

ZN

NN

electronone

electrontwo )1(

2

1

2

1

4

1 For neutral atoms

Atomic Physics, cont.

• The two electron terms yield electron-

electron correlations (radial and angular)

• Current methods deal with electron

correlations by:

1) optimization of radial functions

2) configuration interaction (CI)

(CI: correlated solutions are written as

linear combinations of non-correlated

configurations)

Why are low Fe-peak ions

difficult? • Very large number of metastable levels

that participate in the spectra.

• Strong radial correlations

• Strong angular correlations

• CI: always large but difficult to reach

convergence

• Relativistic effects

Atomic structure calculations

• We use a combination of methods and codes:

- HFR (Cowan codes)

- MCDF (GRASP/GRASP92)

- TFD central potential (SUPERSTRUCTURE)

- We derive non-spherical multipole corrections

to the TFD potential (Bautista 2008) that account

for polarization and electron-electron

correlations of filled and half-filled shells.

Angular electron correlation

Experiment (Ry) Theory (Ry)

3P 0 0

1D 0.144 0.160

1S 0.308 0.374

Calculated vs. measured energies in O I (2p4)

The O I problem

• Ground configuration 1s22s22p4

• Two important lines are the trans-auroral

line at 2972Å (1S0-3P1) and the green line

at 5577Å (1S0-1D2)

3PJ 0 Ry

1D 0.144 Ry

1S 0.307 Ry

• The A-values recommended by NIST are

A(2972 Å) = 7.54e-2

A(5577 Å) = 1.26

and

A(5577Å)/A(2972Å) = 16.7

From Froese Fischer (1983) and Baluja &

Zeippen (1988)

Accuracy rating: B+

Theoretical Determination of the

OI 557.7/297.2 nm Intensity Ratio

• Condon, 1934 11.1

• Pasternack, 1940 24.4

• Garstang, 1951 16.4

• Yamanouchie and Horie, 1952 30.4

• Garstang, 1956 17.6

• Froese Fischer and Saha, 1983 13.6

• Baluja and Zeippen, 1988 13.0

• Galavis, et al., 1997 14.2

• Froese Fischer and Tachiev, 2004 16.1

• NIST 16.7

Observational Determination of

the OI 557.7/297.2 nm Ratio

• Sharp and Siskind, 1989 ~9

• Slanger et al., 2006 9.8±1.0

• Gattinger et al., 2009 9.3±0.5

• Gattinger et al., 2010 9.5±0.5

A(1S0-1D2 ) A(1S0-

3P1 ) Ratio

n=3 single prom. 1.50 0.28 5.3

n=3 double prom. 1.44 0.29 4.9

n=4 single prom. 6.36 0.38 18.8

n=4 double prom. 1.45 0.29 4.9

n=4 trip prom. 1.45 0.24 6.2

n=5 double prom. 1.50 0.069 21.8

n=5 triple prom. 2.26 0.073 30.9

The Fe III problem

Ratio of observed [Fe III] lines in the Orion nebula lines to

predictions by previous models.

Approaches for scattering

calculations • LS R-matrix + ICFT: allows for very large

CI/CC expansions and ICFT includes

relativistic effects in the outer-box region

• Breit Pauli R-matrix: includes relativistic

effects, but limited CI=CC expansion

• DARC: fully relativistic calculation but for

small CC expansion.

Maxwellian-averaged Collision

Strengths at 10,000 K for Fe III Upper lRM+ICFT DARC Zhang 5D3 4.57E+0 2.54E+0 2.92E+0 5D2 1.94E+0 1.11E+0 1.24E+0 5D1 8.79E-0 5.33E-1 5.95E-1 5D0 2.51E-1 1.60E-1 1.80E-1 3P22 7.14E-1 7.14E-1 5.80E-1 3P21 1.84E-1 1.96E-1 1.65E-1 3P20 3.83E-2 3.25E-2 2.13E-2 3H6 2.66E+0 1.21E+0 1.34E+0 3H5 1.10E+0 9.84E-1 4.89E-1 3H4 2.41E-1 5.33E-1 9.26E-2 3F24 1.47E+0 4.54E-1 1.07E+0 3F23 6.42E-1 1.91E-1 4.35E-1 3F22 2.11E-1 1.73E-1 1.57E-1 3G5 1.11E+0 1.36E+0 1.10E+0 3G4 1.24E+0 1.11E+0 4.28E-1 3G3 4.52E-1 4.21E-1 1.09E-1

New Fe III model (I

the

o-I

obs)/

I ob

s

• Collision strengths for forbidden transitions

are dominated by resonances.

• All previous calculations use LS-coupling

R-matrix, which does not include

relativistic effects in resonance positions

• Fully relativistic R-matrix methods are

needed

Photoionization of Fe+

3p63d64s h

3p63d6

3p63d54s

3p63d5nl

e

3p53d8

3p53d 74s

3p63d6

3p63d54s

3p63d5nl

e

Top: LS cross section of Nahar & Pradhan (2002). Middle:

present DARC calculations. Lower: experiment

(Kjeldsen et al. (2002)

The Fe II problem

• We are carrying out fully relativistic

R-matrix calculations for Fe II

• We compare here with 75 lines measured

in the optical spectrum of Orion by

Mesa-Delgado et al. (2009).

• Density and temperature are known from

other species (ne=1.4x104 cm-3, T=9000K)

Spectral models for iron-peak ions

Sc Ti V Cr Mn Fe Co Ni

I

II B07 B06 M06 B10a B05 B04

III B10b B01

IV Z97 M05

Photoionization cross sections for

Iron-peak ions

Conclusions

• Atomic data underpins most astronomical

studies, from modeling microphysics processes,

to diagnostics of plasma conditions, to full

analysis of spectra.

• Atomic data for neutral and singly ionized

species are important in Op/UV astronomy.

• Though, these computations test the limits of

atomic methods.

Conclusions, cont.

• For effective collision strengths @ 104 K one

must a good representation of low energy

resonances, mostly formed in the inner-box

region

=> relativistic calculations must be performed

(DARC)

• When doing LS-calculations the larger the

expansion the worse the results

Conclusions, cont.

• New theoretical methods and computational

tools are needed to treat electron-electron

correlations.

• We have created a new open forum (blog) to

discuss atomic data issues in astronomy

http://astroatom.wordpress.com/