Chemical composition of cosmic dust in the solar …lana/DUST2016/...of dust coming from outside our...

Chemical composition of cosmic dust in the solar vicinity

Derived indirectly from massive stars

María Fernanda Nieva*

Norbert Przybilla

Institute for Astro- and Particle Physics

AUSTRIA * Lise-Meitner Fellow

New work in the UV: Veronika Schaffenroth (stars), Thomas Heuschneider (gas)

More observations in the optical (besides ours): Sergio Simon-Diaz

Sepctroscopic binaries: Andreas Irrgang

Institute for Astro- and Particle Physics

AUSTRIA

Other collaborators in current work

Edward Jenkins, Miguel Urbaneja, Marilyn Latour, David Wessmeyer

Solar neighbourhood

- presence of dust in cold/warm (<104 K) ISM: reddening & extinction

- chemical composition difficult to be determind directly: lack of spectroscopic indicators ► indirect methods (X/H)dust = (X/H)ref – (X/H)gas [ppm]

astrophysical notation for elemental abundances:

e(X) = log + 12 N(X) N(H)

Chemical composition of ISM dust

Multiple phases IS Dust (ISM-SPP) Garching– 15.09.2016






our previous work (Nieva & Przybilla 2012)

e(X) = log + 12 N(X) N(H)







e(X) = log + 12 N(X) N(H)

new work (Heuschneider, Nieva et al. in prep.)

Quest for a Suitable Abundance Reference

abundance reference: Sun, local F & G stars, B stars

Sun: + star that can be studied best + independent abundances from different indicators - 4.56 Gyr old, representative for present-day ISM? - formed 2 kpc away from current position

F&G stars: + differential abundances relative to Sun + increased number statistics - difficult age determination - non-LTE & 3D-corrections (convection) not considered

early B stars: + short-lived: formed out of presen-day ISM + simple atmospheric physics - non-LTE dominated

Sofia & Meyer (2001): recommendation of Sun and F&G stars

since then: revision of solar abundances, new work on early B stars


Early B-type stars

objects considered: - spectral type: B0 – B2 - LC V – III (ZAMS to TAMS) - masses: 8 ... 18 M

8

► lifetime of up to few tens of Myr - Teff: 18000 ... 32000 K - luminosity: 104 ... 105 L

8

► constraints on elemental abundances @ present day


Spatial Distribution of Sample Stars

Nieva & Przybilla (2012)

solar neighbourhood d ≤ 400 pc associations: - Sco-Cen - Ori OB1 - Per OB2 - Lac OB1 - Cas-Tau

+ field stars

+ Ori OB1 Ia-Id sample of Nieva & Simon-Diaz (2011)

Multiple phases IS Dust (ISM-SPP) Garching– 15.09.2016 New sample: > 250 stars @ d< 1 kpc

We have to model their atmospheres


Przybilla et al. (2001)

(Restricted) Non-LTE

•transfer equation

•statistical equilibrium: • radiative rates: • collisional rates: • excitation, ionization, charge exchange, dielectronic recombination, etc.

non-local

local

model atoms

Non-Local Thermodynamic Equilibrium

MgII


Atomic data

W=1 Van Regemorter Formula

CII

Example: collisional excitation by e--impact replacing approximations by experimental or ab-initio data Schrödinger equation LS-coupling: low-Z Breit-Pauli Hamiltonian

Methods: • R-matrix/CC approximation • MCHF • CCC

huge amounts of atomic data:

OP/IRON Project & own

what we have

what we need


Non-LTE Diagnostics: Stellar Parameters & Abundances

using hybrid non-LTE approach, robust analysis

methodology & comprehensive model atoms

- ionization equilibria ► Teff/log g

elements: e.g. He I/II, C II/III/IV, O I/II, Ne I/II, Si II/III/IV, S II/III, Fe II/III

DTeff / Teff ~ 1…2% usually: 5…10%

- Stark broadened hydrogen lines ► log g/Teff

D log g ~ 0.05…0.10 (cgs) usually: 0.2

- microturbulence, helium abundance, metallicity

+ other constraints, where available: SED’s, near-IR, …

- abundances: Dloge ~ 0.05...0.10 dex (1s-stat.) usually: factor ~2

Dloge ~ 0.07...0.12 dex (1s-sys.) usually: ???

minimising systematics !

minimising systematics !



Non-LTE Diagnostics: Stellar Parameters & Abundances

C

N

O

Ne

Mg

Si

Fe

Non-LTE Diagnostics: Tests & Additional Constraints


Distances: right log g SEDs: right Teff

No abundance trends

nuclear path of CN cycle: right abundances

Nieva & Przybilla (2012) Quantitative Spectroscopy

• observations: FEROS@ESO 2.2m, FOCES@CA 2.2m, ELODIE@OHP 1.93m • high S/N, high resolution R ~ 40 - 48000

telluric lines

Quantitative Spectroscopy Nieva & Przybilla (2012)

• several 104 lines: ~30 elements, 60+ ionization stages • complete spectrum synthesis in visual (& near-IR) ~95% in NLTE

Chemical composition of solar neighbourhood @ present day

red: Nieva & Przybilla (2012)

1s ~ 0.05 dex

black: OB stars literature

chemical homogeneity ► Cosmic Abundance Standard

X=0.715 Y=0.271 Z=0.014 Multiple phases IS Dust (ISM-SPP) Garching– 15.09.2016

Dust Depletion

Nieva & Przybilla (2012) - similar abundance distributions in gas & stars


CAS & Consequences for Dust Composition


- Dust in diffuse ISM: relatively carbon poor & silicate-rich - checksum Mg+Si+Fe vs. O match (some extra O may be in unidentified constituent) - comparison with Orion dust: graphite minor species ► C in PAHs - homogeneity over hundreds of parsecs: highly efficient mixing


The Cosmic Dust Analyser on the Cassini spacecraft has detected the faint but distinct signature of dust coming from outside our Solar System, from the local interstellar cloud.

Altobelli et al. (2016): “It can be verified that Mg/Si, Fe/Si, Mg/Fe, and Ca/Fe ratios are on average CI chondritic (carbonaceous chondrite of type Ivuna whose composition is considered as a proxy of solar or cosmic element abundances) and similar to a composition inferred for LIC-ISM dust (Przybilla et al. 2008, Nieva & Przybilla 2012).

Interstellar dust at Saturn

Credit: ESA / NASA / JPL / Space Science Institute








e(X) = log + 12 N(X) N(H)

new work (Heuschneider, Nieva et al. in prep.)

Current study

Self-consistent study of

spatial distribution and chemical composition of

massive (OB) stars, gas and dust

for ~250 lines-of-sight within ~1 kpc distance from the Sun

Chemical composition of ISM gas #1

- determination of hydrogen column density: via IS Lya damping wings ► e.g. continuum reconstruction technique (Bohlin 1975)

multiplication of flux by et(l) = e s(l) N(HI) to correct for damping

s(l) = l0 = 1215.67Å hydrogen column density: N(H) = N(HI) + N(H2)

Diplas & Savage (1994)

4.26· 10-20 cm2

6.04· 10-10 + ( l - l0 )2


Chemical composition of ISM gas #2

- metal abundances from unsaturated lines from ground states e.g. semi-forbidden CII] l2325Å

Sofia (2004) HST GHRS: S/N~850 Wl ~ 0.2 mÅ

- metal column density via Wl ~ N(X)· fij· s(l)

- chemical homogeneity of gas-phase in solar neighbourhood from many sightlines: C, O, Mg, Si, S, Fe, Zr, Kr, ...


ISM gas: observational data UV: solar Neighbourhood

IUE International Ultraviolet Explorer Hubble Space Telescope

ISM

Jenkins (2012)

Thomas Heuschneider, Veronika Schaffenroth (Innsbruck)

OB star

Own observational database in the optical:~ 300 high resolution spectra of background sources

FEROS in La Silla (Chile) ESO

PIs: Nieva, Przybilla (collected along ~10 years + additional data)

FOCES @ Calar Alto (Spain)

UVES @ VLT (Chile) ESO

FIES @ NOT (La Palma) Spain This work

Normal single OB dwarfs and giants vs. detached eclipsing binaries


RESULTS: this is what you expect from us (spectroscopists)


The massive star zoo

Cre

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NA

SA

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ESO

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Cre

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M. Sh

ultz/

Bin

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Credit: O. Kochukhov http://www.astro.uu.se/~oleg/

Chemical abundance spots Non-radial pulsations Strong magnetic field


Fast rotators/Classical Be stars

htt

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See review by Rivinius et al. (2013)



When your favorite star is actually a team...



Identifying the individual component contributions to the spectra in different phases

Go

nza

les

et

al. (

in p

rep

)

a triple system


After solving the orbital parameters and individual stellar parameters of the system: check for

reproduction of observed time-series spectra

Gonzales et al. (in prep)


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Chemical composition of cosmic dust in the solar …lana/DUST2016/...of dust coming from outside our...

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