near-ir spectroscopy of ob stars with crires · • objects: ob main sequence & giant stars...

NearNear--IRIR SpectroscopySpectroscopy of OB of OB starsstars withwith CRIRES:CRIRES:pilotpilot studystudy forfor an ELT an ELT sciencescience casecase

M. Fernanda Nieva

Norbert Przybilla (Obs. Bamberg/ Univ. Erlangen)Andreas Seifahrt (Univ. Göttingen)

Keith Butler (LMU München)Hans-Ulrich Käufl (ESO)

Andreas Kaufer (ESO)

Max-Planck-Institute for Astrophysics (MPA)

OB-type dwarfs & giants

Young age ~ 107 yrsMassive M ~ 9-20 MsunHot Teff ~ 20-35 x104 KLuminous L ~ 104 Lsun

in contrast to late-type stars:no convective envelope

no chromosphere

in contrast to OB supergiants:no strong mass loss & winds

OB OB starsstars: : latelate O & O & earlyearly BB--typetype

Precise & absolute (physical) chemical composition @ present day

Well-understood atmospheric structureradiative envelope thin atmosphere

Max-Planck-Institute for Astrophysics JENAM 2008 – Science with the ELTVienna, 09.11.2008

M.F. Nieva

Jascheck & Jascheck

Muliple science motivationsMuliple science motivations

OB dwarfs and giants:

- metallicity indicators in starstar--formation regionsformation regions

- present-day chemical abundance indicators @ short and large distances in the Milky Way and neighbour galaxies:galactochemical evolutiongalactochemical evolution

-- progenitors of BA-supergiants: stellar evolutionstellar evolution

- OB stars in the Galactic CenterGalactic Center previous talk by N. Przybilla


M.F. Nieva


M.F. Nieva

e.g. OB stars in stare.g. OB stars in star--formation regionsformation regions

1- deposit energy & momentum to the ISM

2- can ionize gas clouds through UV radiation

3- less evolved dwarfs & giants: similar composition than parent

clouds

4- luminous: can be studied at large distance

NGC 3603: original image courtesy ESO

N

e.g. OB stars in the Galactic Centere.g. OB stars in the Galactic Center

http://www.mpe.mpg.de/ir/GC/

“ON THE NATURE OF THE FAST MOVING STAR S2 IN THE GALACTIC CENTER”F. Martins et al. 2008 (Genzel Group, MPE)“A high quality SINFONI H and K band spectrum obtained from co-adding 23.5 hours of observation between 2004 and 2007 reveals that S2 is an early B dwarf (B0–2.5V)…”


M.F. Nieva

Southern Hemisphere

Some Galactic regions observable both in optical & near-IRBUT: some regions observable in near-IR onlyPresent and future generation of telescopes

Why nearWhy near--IR spectroscopy of OB stars?IR spectroscopy of OB stars?

Galactic stellar astronomy

diffraction-limited observation with ELTusing AO near-IR spectroscopy

Future generation of ELTsExtragalactic stellar astronomy


M.F. Nieva

Pilot study withPilot study with CRIRES CRIRES for future ELT applications:for future ELT applications:why 1st high resolution?

Telluric lines resolved (R~100 000)

Spectral line identification (detailed line profiles)

Comparison observation / synthetic spectrum

Model atoms calibrations (non-LTE physics)

Benchmark study


M.F. Nieva

Aim of present workAim of present work

Atmospheric parameter & chemical abundancefrom the near-IR spectrum

in agreement with precise results in the optical

+ metal line identification


M.F. Nieva

SpectraSpectra

• objects: OB main sequence & giant starssolar neighbourhoodapparently slow rotators

well studied in the visual

• data: high-S/N CRIRES spectra broad wavelengh range: ~ .99 – 4.3 μm

• data reduction: 1st approach: pipelinenow: customized reduction

Käufl et al. (2004)

VLT / ESO


M.F. Nieva

Previous work in the opticalPrevious work in the optical

precise atmospheric parameters & metal abundancesunprecedented reduction of systematic uncertainties

stellar analyses from quantitative spectroscopy:

derivation of stellar parameters & abundances from spectrum


M.F. Nieva

Nieva & Przybilla / Przybilla et al. seriestalk by N. Przybilla

Simultaneous fits to most measurable H/He linesSimultaneous fits to most measurable H/He lines

Data: FEROS, ESO

H Balmer

He I

He II

HR 3055

Visual

H Paschen

Data: FOCES, Calar Alto, Spain

He I K-Band

Data: Subaru, Hawaii

Nieva & Przybilla 2007Nieva & Przybilla 2007Near-IR

Data: FEROS, ESO

S/N up to 800

Fits to C linesFits to C lines

All lines have very similar abundances

low 1σ−uncertainties

Similar analysis for other metals

C II

C IV

C III

τ Sco

Visual

Precise quantitative analysis

Nieva & Przybilla 2008Nieva & Przybilla 2008

ModelsModels

• Hybrid non-LTE approach: hydrostatic metal blanketed model atmospheres in plan-parallel geomety + non-LTE line formation (DETAIL+SURFACE)

good for OB dwarfs & giants Nieva & Przybilla (2007)

• State-of-the-art model atoms in visual:H: Przybilla & Butler (2004)He: Przybilla (2005)C: Nieva & Przybilla (2006, 2008)α–elements: from Munich group (Butler, Becker, Przybilla, ...), updated

extended to the near-IR

• Non-LTE effects much larger in near-IR than in visual


M.F. Nieva

Difficulties from observations: Difficulties from observations: regions with strong telluric lines

Telluric lines modeling: 1st approach

(Now: improved !)

(Example for old data reduction)

Hydrogen

Modeling CRIRES stellar spectraModeling CRIRES stellar spectra

H lines Teff & log gHe lines Teff & ε(He)HeI/II ioniz. equil. Teff & log g

preliminary analysis:

• consistency with visual• strong NLTE effects

B1.5 III

Nieva et al. 2008

Helium

H lines Teff & log gHe lines Teff & ε(He)He I/II ioniz. equil. Teff & log gCC II/IIIII/III ioniz. equil.ioniz. equil. TTeffeff & log g& log g

Quantitative agreement with visual

Also: α-elements


M.F. Nieva

standard modelNieva et al. 2008

our models

Modeling CRIRES stellar spectraModeling CRIRES stellar spectra

Model: so far NLTE populations from visual !

Still no best fits from grid interpolations

Customized data reductionCustomized data reduction


M.F. Nieva

telluric linesSeveral new observable spectral lines arose from

new data reduction !

New data reduction + our modelsNew data reduction + our models


M.F. Nieva

ByBy--product: OB stars as telluric standardsproduct: OB stars as telluric standards

• sucsessful modeling and analysis of most identified lines

• OB stars have fewer lines than cooler stars

OB stars: ideal telluric standardstelluric line removal of other science spectra


M.F. Nieva

Achievements (so far)

unprecedented metal line identification in massive stars @ high resolutionreliable modeling of most identified lines (H, He & metals)hotter stars: simultaneous He I/II& C II/III ionization balance

In agreement with analysis in the optical

OB stars as science spectraOB stars as science spectra

Important for chemical abundance studies in Important for chemical abundance studies in regions observable in nearregions observable in near--IR onlyIR only


M.F. Nieva

Some lines are still unidentified !

NearNear--IR @ ELTsIR @ ELTsdirect application of present models & analysis


M.F. Nieva

near-IR spectroscopic studies of massive starschemical composition @ high precision (star formation regions/stellar & galactochemical evolution/GC)

in the Milky Way & other galaxies (Local Group – Sculptor)telluric standards for other science spectralower resolution R~ 10 000-20 000 (limited also by stellar vsini)

Cerro Macon (Northern Argentina)

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M.F. Nieva

near-ir spectroscopy of ob stars with crires · • objects: ob main sequence & giant stars...

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