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Interstellar extinction and the problem of cosmic abundances
Nikolai Voshchinnikov Sobolev Astronomical Institute St. Petersburg University


Interstellar medium (ISM)
Main components: gas and dust Location: IS clouds (diffuse, dense, translucent) Main problem: determination of the chemical composition of the ISM + study of the chemical evolution of Galaxy (galaxies)


IS gas
Observational manifestations: absorption lines and bands ( clouds); emission lines (HII regions, hot gas)

IS dust
Observational manifestations: IS extinction and polarization ( clouds); e scattered radiation (nebulae, circumstellar shells); IR radiation (continuum + bands; clouds, nebulae, CS shells,...)


IS gas + dust = cosmic abundance

[X/H]g + [X/H]d = [X/H]cosmic 5 elements: C, O, Mg, Si, Fe
Gas: absorption lines
Dust: IS extinction curves


Abundances:
Reference, cosmic, interstellar, solar

COSMIC

Sun

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Interstellar dust grains consist of five the most «important» elements:

C, O ­ primary Units:

Mg, Si, Fe ­ major ppm ­ parts per million -----------------------------------------------------------

N(X)/N(H)*10^6 Na, Al, Ca, Ni ­ minor (less
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than 3 ppm)

K, Ti, Cr, Mn, Co ­ traces (less than 0.3 ppm)

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Abundances
old solar new solar stellar (1989) (2004) (1996) zeta Oph (dust)

C 363 O 851 Mg 38.0 Si 35.5 Fe 32.4

245 457 33.9 34.2 28.2

214 457 25 18.6 27

110 126 31.9 32.6 28.2


1996, Snow & Witt: C /H(Sun) ­ 363 ppm C /H(stars) ­ 214 ppm ~150 ppm! has been taken from the solid phase Result: CARBON CRISIS
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«Time variations» of carbon and oxygen abundances in the solar atmosphere

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261ppm


IS dust composition
C ­ amorphous carbon, graphite O ­ oxides (FeO, Fe2O3, Fe3O4, MgO, SiO, H2O) Si ­ silicates (olivines, pyroxenes) Mg ­ silicates, oxide Fe ­ pure iron, silicates, oxides
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10 :

Si - O

Olivines
(- )

Pyroxenes
( . «» + «»)

Mg2xFe2-2xSiO4, 0<=x<=1
X=1:
(A.J. Forster ­ )

MgxFe1-1xSiO3, 0<=x<=1
X=1:

Mg2SiO4 - forsterite

MgSiO3 - enstatite

( .

«», )

X=0:

( . , -)

Fe2SiO4- fayalite

X=0:

FeSiO3- ferrosilite

(

)

­ (interstitial solid solutions)


IS gas
IS absorption lines: equivalent line width W gives Nx ­ column density of atom (ion)

Method: curve of growth


Ions and lines
Eion, eV Ions
C 11.3 O 13.6 Mg 7.65 Si 8.1 Fe 7.87 CI, CII OI MgII SiII FeII

Lines, A
2325, ... 1356, ... 1026, 1240, ... 2235,... 1055, 1143, 2249, 2267


Results
Dependencies N(X)/N(H)
on D ­ distance to the star = N(H)/D - mean concentration of H f(H2) ­ fraction of H2 on the line of sight E(B-V) ­ colour excess ......


Miller et al. ApJ 659, 441, 2007 (STIS+FUSE)


Cartledge et al. ApJ 641, 327, 2006 (STIS)


Jensen & Snow ApJ 669, 378, 2007 (STIS+FUSE)


Jensen & Snow ApJ 669, 401, 2007 (STIS+FUSE)


Recent results
Data: (gas-phase abundances) O: Cartledge...2001 ApJ 562, 394 (11
stars) Jensen,....2005 ApJ 619, 891 (26 stars; 10 HST) Cartledge...2004 ApJ 613, 1037 (36/ stars) Meyer...1998 ApJ 493, 222 (7 stars) Andre...2003 ApJ 591, 1000 (19 stars) Jensen, Snow, 2007 (44 stars) Cartledge,... ApJ 641, 327, 2006 (47 stars) Miller,2007 ApJ 659, 441 (6 stars) Jensen, Snow, 2007 (51 stars) Snow et al., ApJ 573, 662, 2002 (18 stars)

Mg: Fe:

+ D, E(B-V), A(V), R(V)=A(V)/E(B-V),...
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77 stars

70 stars

88 stars
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[Fe/H]

Sun=28.2ppm

[Mg/H]Sun=33.9ppm [O/H]Sun=457ppm
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Some conclusions
Dust-phase abundance of Mg and Fe (?) decreases with growth of distance to the star

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Stars in Orion and rho Oph cloud

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Some conclusions
It seems there is no correlation of dustphase abundances of Mg, Fe and O with R(V) and A(V)

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Some conclusions
It seems there is correlation of dustphase abundances of Mg-Fe and O-Mg (for not very distant stars)

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IS dust
It is possible to determine: A() ­ interstellar extinction (reddening) curve, usually normalized

It is possible to estimate: chemical composition + size of dust grains Method: modelling on the basis of the light scattering theory
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( ) = 4.19x 10-22 A ( ) A (V )
Lc (912 A)

gas dust



UV extinction



LMC/SMC dust?

NO! Scattered radiation! Kruegel, 2008


Interpretation


UV extinction: small particles in the ISM


Bump 2200 ­ small graphite particles


Interplanetary dust grains
(NASA collection)

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Cometary's (?) grains

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Interstellar (?) grains

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Absolute extinction and abundances


Problem ??? How to model extinction,... taking into account dust-phase abundances, inhomogeneous particle structure,...???


Three approaches to the modelling
1. Two or more populations of compact particles Calculations: Mie theory 2. Mixing of materials (refractive indices) inside a particle: effective medium theory, EMT Calculations: EMT-Mie 3. Inhomogeneous (composite) consisting of different materials in the form of inclusions (or layers) Calculations: DDA (nMie)

IMPORTANT:
Vacuum can be included in (2) and (3) !

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DDA vs layered spheres

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Interstellar extinction: normalized cross sections


Modelling: extinction (zeta Oph) + dust-phase abundances (single size dust particles)

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Interstellar extinction and abundances
Voshchinnikov et al., Astron. Astrophys., 445, 167, 2006;

zeta Oph (HD 149757) (I) & (III) - ver y porous particles Av = 0.94 mag. obs model C 110 219 ppm O 126 124 Mg 32 22.7 Si 33 28.2 Fe 28 36.1


Interstellar extinction and abundances
Voshchinnikov et al., Astron. Astrophys., 445, 167, 2006;

sigma Sco (HD 147165) (I) & (III) - very porous particles Av = 1.13 mag. obs model C 176 137 ppm O 85 71 Mg 30.9 17.7 Si 32.4 8.8 Fe 27.9 26.6


Some conclusions
· It is possible to model IS extinction taking into account dust-phase abundances

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Some conclusions
· Cosmic abundances: · solar ? ---- YES (local ISM) · > solar (old solar) ? --- may be (large · distances)

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X-ray abundances
( K- L- ­ !)

new solar Cyg X-1 Cyg X-2 4U1820-30 (2004) 71/+3/2kpc 87/-11/13kpc 3/-8/8kpc

C 245 O 457 Mg 33.9 Si 34.2 Fe 28.2

492 59? 37? 16.5

478

485

24.3 18.9


·! ·THANKS!
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Cartledge et al. ApJ 641, 327, 2006 (STIS)

+


Fitting ()

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c2

c3

c4

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