Download Chemical composition of cosmic dust in the solar vicinity

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
* Lise-Meitner Fellow
AUSTRIA
Other collaborators in current work
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
Edward Jenkins, Miguel Urbaneja, Marilyn Latour, David Wessmeyer
Institute for Astro- and Particle Physics
AUSTRIA
Solar neighbourhood
Chemical composition of ISM dust
- 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
N(X)
+ 12
N(H)
Multiple phases IS Dust (ISM-SPP)
Garching– 15.09.2016
Chemical composition of ISM dust
- presence of dust in cold/warm (<104 K) ISM: reddening & extinction
- chemical composition difficult to be determind directly: lack of spectroscopic indicators
our previous work (Nieva & Przybilla 2012)
► indirect methods
(X/H)dust = (X/H)ref – (X/H)gas
[ppm]
astrophysical notation for elemental abundances:
e(X) = log
N(X)
+ 12
N(H)
Multiple phases IS Dust (ISM-SPP)
Garching– 15.09.2016
Chemical composition of ISM dust
- presence of dust in cold/warm (<104 K) ISM: reddening & extinction
- chemical composition difficult to be determind directly: lack of spectroscopic indicators
our previous work (Nieva & Przybilla 2012)
► indirect methods
(X/H)dust = (X/H)ref – (X/H)gas
[ppm]
new work (Heuschneider, Nieva et al. in prep.)
astrophysical notation for elemental abundances:
e(X) = log
N(X)
+ 12
N(H)
Multiple phases IS Dust (ISM-SPP)
Garching– 15.09.2016
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
Early B-type stars
objects considered:
- spectral type: B0 – B2
- LC V – III
(ZAMS to TAMS)
- masses: 8 ... 18 M8
► lifetime of up to few
tens of Myr
- Teff: 18000 ... 32000 K
- luminosity: 104 ... 105 L8
► constraints on
elemental abundances
@ present day
Multiple phases IS Dust (ISM-SPP)
Garching– 15.09.2016
Spatial Distribution of Sample Stars
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)
Nieva & Przybilla (2012)
New sample: > 250 stars @ d< 1 kpc
Multiple phases IS Dust (ISM-SPP)
Garching– 15.09.2016
We have to model their atmospheres
Multiple phases IS Dust (ISM-SPP)
Garching– 15.09.2016
(Restricted) Non-LTE
Non-Local Thermodynamic Equilibrium
•transfer equation
•statistical equilibrium:
• radiative rates:
non-local
• collisional rates:
local
MgII
Przybilla et al. (2001)
• excitation, ionization, charge exchange,
dielectronic recombination, etc.
model atoms
Multiple phases IS Dust (ISM-SPP)
Garching– 15.09.2016
Atomic data
Example: collisional excitation by e--impact
replacing approximations
by experimental or
ab-initio data
what we
CII
have
Schrödinger equation
LS-coupling:
W=1
what
we
Van
Regemorter
need
Formula
low-Z Breit-Pauli Hamiltonian
huge amounts of
atomic data:
OP/IRON Project & own
Methods:
• R-matrix/CC approximation
• MCHF
• CCC
Multiple phases IS Dust (ISM-SPP)
Garching– 15.09.2016
Non-LTE Diagnostics: Stellar Parameters & Abundances
using hybrid non-LTE approach, robust analysis
methodology & comprehensive model atoms
minimising
systematics !
- 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.)
Dloge ~ 0.07...0.12 dex (1s-sys.)
usually: factor ~2
usually: ???
Non-LTE Diagnostics: Stellar Parameters & Abundances
minimising
systematics !
Nieva & Przybilla (2012)
Multiple phases IS Dust (ISM-SPP)
Garching– 15.09.2016
Non-LTE Diagnostics: Tests & Additional Constraints
SEDs: right Teff
Distances: right log g
C
No abundance trends
N
O
Ne
Mg
nuclear path of CN cycle:
right abundances
Si
Fe
Nieva & Przybilla (2012)
Quantitative Spectroscopy
Nieva & Przybilla (2012)
• observations: FEROS@ESO 2.2m, FOCES@CA 2.2m, ELODIE@OHP 1.93m
• high S/N, high resolution R ~ 40 - 48000
Quantitative Spectroscopy
Nieva & Przybilla (2012)
telluric lines
• 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
1s ~ 0.05 dex
black: OB stars literature
red: Nieva & Przybilla (2012)
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
- similar abundance distributions in gas & stars
Nieva & Przybilla (2012)
Multiple phases IS Dust (ISM-SPP)
Garching– 15.09.2016
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
Interstellar dust at Saturn
Credit: ESA / NASA / JPL / Space Science Institute
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).
Multiple phases IS Dust (ISM-SPP)
Garching– 15.09.2016
Chemical composition of ISM dust
- presence of dust in cold/warm (<104 K) ISM: reddening & extinction
- chemical composition difficult to be determind directly: lack of spectroscopic indicators
our previous work (Nieva & Przybilla 2012)
► indirect methods
(X/H)dust = (X/H)ref – (X/H)gas
[ppm]
new work (Heuschneider, Nieva et al. in prep.)
astrophysical notation for elemental abundances:
e(X) = log
N(X)
+ 12
N(H)
Multiple phases IS Dust (ISM-SPP)
Garching– 15.09.2016
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)
Diplas & Savage (1994)
multiplication of flux by et(l) = e s(l) N(HI) to correct for damping
s(l) =
hydrogen column density:
4.26· 10-20 cm2
6.04· 10-10 + ( l - l0 )2
N(H) = N(HI) + N(H2)
l0 = 1215.67Å
Multiple phases IS Dust (ISM-SPP)
Garching– 15.09.2016
Chemical composition of ISM gas #2
- metal abundances from unsaturated lines from ground states
e.g. semi-forbidden CII] l2325Å
HST GHRS: S/N~850 Wl ~ 0.2 mÅ
Sofia (2004)
- 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
ISM gas: observational data UV: solar Neighbourhood
OB star
ISM
Thomas Heuschneider,
Veronika Schaffenroth
(Innsbruck)
Jenkins (2012)
IUE International Ultraviolet Explorer
Hubble Space Telescope
Own observational database in the optical:~ 300
high resolution spectra of background sources
PIs: Nieva, Przybilla (collected along ~10 years + additional data)
FEROS in La Silla (Chile) ESO
FOCES @ Calar Alto (Spain)
UVES @ VLT (Chile) ESO
This work
FIES @ NOT (La Palma) Spain
RESULTS: this is what you expect from us (spectroscopists)
Normal single OB dwarfs and giants vs. detached eclipsing binaries
Nieva & Przybilla (2014)
Multiple phases IS Dust (ISM-SPP)
Garching– 15.09.2016
Credit: M. Shultz/BinaMIcS
Credit: NASA
Credit: ESO/L. Calçada
The massive star zoo
Multiple phases IS Dust (ISM-SPP)
Garching– 15.09.2016
The massive star zoo
Non-radial pulsations
Chemical abundance spots
Strong magnetic field
Credit: O. Kochukhov
http://www.astro.uu.se/~oleg/
Multiple phases IS Dust (ISM-SPP)
Garching– 15.09.2016
The massive star zoo
http://lasp.colorado.edu/~cranmer/cranmer_st_hot.html
Fast rotators/Classical Be stars
See review by Rivinius et al. (2013)
Multiple phases IS Dust (ISM-SPP)
Garching– 15.09.2016
When your favorite star is actually
a team...
Nieva & Przybilla (2012)
Multiple phases IS Dust (ISM-SPP)
Garching– 15.09.2016
Gonzales et al. (in prep)
a triple system
Identifying the individual component
contributions to the spectra in different phases
Multiple phases IS Dust (ISM-SPP)
Garching– 15.09.2016
Gonzales et al. (in prep)
After solving the orbital parameters and individual
stellar parameters of the system: check for
reproduction of observed time-series spectra
Multiple phases IS Dust (ISM-SPP)
Garching– 15.09.2016