chemical composition of cosmic dust in the solar …lana/dust2016/...of dust coming from outside our...
TRANSCRIPT
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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
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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
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Solar neighbourhood
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- 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
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- 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:
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)
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- 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:
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)
new work (Heuschneider, Nieva et al. in prep.)
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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
Multiple phases IS Dust (ISM-SPP) Garching– 15.09.2016
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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
Multiple phases IS Dust (ISM-SPP) Garching– 15.09.2016
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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
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We have to model their atmospheres
Multiple phases IS Dust (ISM-SPP) Garching– 15.09.2016
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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
Multiple phases IS Dust (ISM-SPP) Garching– 15.09.2016
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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
Multiple phases IS Dust (ISM-SPP) Garching– 15.09.2016
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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 !
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minimising systematics !
Nieva & Przybilla (2012)
Multiple phases IS Dust (ISM-SPP) Garching– 15.09.2016
Non-LTE Diagnostics: Stellar Parameters & Abundances
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C
N
O
Ne
Mg
Si
Fe
Non-LTE Diagnostics: Tests & Additional Constraints
Nieva & Przybilla (2012)
Distances: right log g SEDs: right Teff
No abundance trends
nuclear path of CN cycle: right abundances
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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
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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
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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
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Dust Depletion
Nieva & Przybilla (2012) - similar abundance distributions in gas & stars
Multiple phases IS Dust (ISM-SPP) Garching– 15.09.2016
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CAS & Consequences for Dust Composition
Nieva & Przybilla (2012)
- 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
Multiple phases IS Dust (ISM-SPP) Garching– 15.09.2016
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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
Multiple phases IS Dust (ISM-SPP) Garching– 15.09.2016
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- 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:
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)
new work (Heuschneider, Nieva et al. in prep.)
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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
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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
Multiple phases IS Dust (ISM-SPP) Garching– 15.09.2016
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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, ...
Multiple phases IS Dust (ISM-SPP) Garching– 15.09.2016
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ISM gas: observational data UV: solar Neighbourhood
IUE International Ultraviolet Explorer Hubble Space Telescope
ISM
Jenkins (2012)
Thomas Heuschneider, Veronika Schaffenroth (Innsbruck)
OB star
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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
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Normal single OB dwarfs and giants vs. detached eclipsing binaries
Nieva & Przybilla (2014)
RESULTS: this is what you expect from us (spectroscopists)
Multiple phases IS Dust (ISM-SPP) Garching– 15.09.2016
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The massive star zoo
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Multiple phases IS Dust (ISM-SPP) Garching– 15.09.2016
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The massive star zoo
Credit: O. Kochukhov http://www.astro.uu.se/~oleg/
Chemical abundance spots Non-radial pulsations Strong magnetic field
Multiple phases IS Dust (ISM-SPP) Garching– 15.09.2016
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Fast rotators/Classical Be stars
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See review by Rivinius et al. (2013)
The massive star zoo
Multiple phases IS Dust (ISM-SPP) Garching– 15.09.2016
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When your favorite star is actually a team...
Nieva & Przybilla (2012)
Multiple phases IS Dust (ISM-SPP) Garching– 15.09.2016
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Identifying the individual component contributions to the spectra in different phases
Go
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a triple system
Multiple phases IS Dust (ISM-SPP) Garching– 15.09.2016
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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)
Multiple phases IS Dust (ISM-SPP) Garching– 15.09.2016