Stellar Windsand

Hydrodynamic Atmospheresof

Stars

Rolf KudritzkiSpring Semester 2010

I. IntroductionFirst suspicion of existence of continuous stellar winds:

1929 C. BealsMNRAS 90, 202

91, 966 (1931)1934 S. Chandrasekhar

MNRAS 94, 522 Optical spectrum of P CygniB2 hypergiant

and LBV :

broad H, HeI, metal lines withblue-shifted absorptionred-shifted emission

Optical spectrum of Wolf-Rayet

stars

:

broad He, C, N emission linesno hydrogen lines

widths of lines Doppler-shifts of out-flowing atmospheresVexpansion

≈

200 km/s to 3000 km/s

H and HeI

lines of P Cygni

Note different y-scale of plots

Emission in Hα

is hugeHδ

is much weaker

Najarro, Kudritzki

et al. 1997

Same Fig. as before,but now

replaced by

estimate ofoutflow

velocities

P Cygni - B2 hypergiant and LBV: Model atmosphere fit - optical lines

Najarro, Kudritzki et al. 1997

I. IntroductionFirst suspicion of existence of continuous stellar winds:

1929 C. BealsMNRAS 90, 202

91, 966 (1931)1934 S. Chandrasekhar

MNRAS 94, 522 Optical spectrum of P CygniB2 hypergiant

and LBV :

broad H, HeI, metal lines withblue-shifted absorptionred-shifted emission

Optical spectrum of Wolf-Rayet

stars

:

broad He, C, N emission linesno hydrogen lines

widths of lines Doppler-shifts of out-flowing atmospheresVexpansion

≈

200 km/s to 3000 km/s

Conc

epci

on 2

007 Wolf-Rayet

star in NGC 300 at 2 Mpc

distance

WN11 star

Bresolin, Kudritzki, Najarro

et al. 2002, ApJ

Letters 577, L107

emission line diagnostics:first detailed abundance pattern outside Local Group

1934 Adams and McCormack

ApJ

81, 119 optical spectra of M supergiantsα

Ori

M2 Ib

α1

Sco

M1 Ibα1

Her M5 IIblue-shifted absorption cores of groundstatelines of MnI, CaI, CrI

etc. (“0.00 eV

lines”)

modern spectra (high res. & S/N) narrow P Cygni

profile superimposed

to photospheric

line core(Bernat

& Lambert, 1976, ApJ

204, 830)

vexp

≈

10 to 20 km/s but vesc

= [2GM/R]1/2

escape velocity isof same order!

Is the flow able to escape the gravitational potential ????

α

Ori

tiny P Cygni

profile superimposed to photosperic

line core

Bernat

& Lambert, 1976 ApJ

204, 830

MnIλ

4030.8 Å

λ

4033.1 Å

1956 Armin J. Deutsch

ApJ

123, 210Mt. Palomar 5m Coude

spectra with very high resolution

of M supergiants

with earlier spectral-type companions

α1

Sco

M1 Ibα2

Sco

B2 V CaII, TII etc. lines very unsual

for B2

α1

Her M5 IIα1

Her G0 III MNI, CrI

etc. very unusual for G0

circumstellar

linesproduced wind of M supergiant

Model by Kudritzki

& Reimers, 1978, A&A 70, 227

wind envelope extension ≈

1000 Rstarvexp

≈

20 km/s >> Vexp

>> Vesc

(r) M supergiants

have winds !!!

vesc

= [2GM/r]1/2

≈

1/30 vesc-photosphere

1951 Ludwig Biermann

Zeitschrift

fuer

Astrophysik

29, 274all comet plasma tails point away from sun

solar wind with v ≈

400 km/s

1962 Neugebauer

& Snyder Science,138, 1169Mariner 2 probe to Venus findsfast solar wind present all times

v ≈

500 ±

300 km/s at Earth orbitnwind

= 5 cm-3 highly variable= some 10-13

Msun

/yr

1958 Eugene Parker ApJ

128, 664first hydrodynamic theory of solar wind

Solar wind

II. Spectroscopic evidence for stellar winds

1. Spectral lines in hydrostatic atmospheres

Hydrostatic

barometric formula

thin, plane-parallel atmosphere with temperature gradient

symmetric absorptionline aroundcentralwavelengthλ0

Width of line determined by

a) thermal motion of gas

b) stellar rotation

c) Pressure broadening, stellar gravity

1. Line scattering in expanding atmospheres

in front of stellar disk: blue-shiftedscattering by gas moving towards observer

remaining envelope: red-

& blue-shiftedscattering by gas moving towards and away from observer

P Cygni

profile

width determined by vmax

Note: “line scattering”

is special re-emission process

photon is absorbed and re-emitted by spontaneous emission in same line transition

de factoscattering

number of photons is conserved

Nabs

= Nem

typical process for resonance lines

2. Thermal or recombination emissionin expanding atmospheres

If τspont

> τcoll

absorbed photon not re-emittedand destroyed by collisionallevel excitation or de-excitationre-emission coupled to local T(r)since wind envelope can a huge volume,an emission line might occur

width determined by vmax

pure emission profile

If ionization of the atoms with subsequent recombination dominates, then the population of the upper level is controlled from electron transitions cascading from above

ionization from groundor excited level

cascade of subsequent spontaneous emissions

pure emission line

3. Other signatures of stellar winds

Stellar winds are ubiquitous in all stellar domains !!!

Radio:

hot stars: free-free emission of winds“

radio-

excess”

cool stars: maser emission of windsOH, H2

O, SiO, NH3

IR: ground-based & satellite telescope (IRAS, ISO, Spitzer, Herschel)

hot stars: free-free emission of windsweaker than “

radio-

excess”

rich emission line spectra H, He, metalscool stars: dust emission in winds, PAHs

Najarro & Kudritzki, 1997

P Cygni - B2 hypergiant and LBV: Model atmosphere fit – IR (ISO)

P Cygni

mid IR (ISO)

Najarro, 2005

Optical:

line diagnostics of mass-loss rateswind velocitieschemical composition

A-supergiant in M31 –

stellar wind

McCarthy, Kudritzki,Venn, Lennon,Puls1997, ApJ

482, 757

Keck, Hires

Hα

emission B superrgiant

–

stellar wind

Kudritzki et al. 1999,A&A 350, 970

Model calculation

Hα

emission O-star Model calculation

Variation ofby ± 20% M

Kudritzki & Puls, 2000, AARA 38, 613

Conc

epci

on 2

007 Wolf-Rayet

star in NGC 300 at 2 Mpc

distance

WN11 star

Bresolin, Kudritzki, Najarro

et al. 2002, ApJ

Letters 577, L107

emission line diagnostics:first detailed abundance pattern outside Local Group

Conc

epci

on 2

007 NGC 300 WN11 star

non-LTE line-blanketed

hydrodynamic model atmospheres

with stellar winds

stellar parameters

wind parameters

H, He, CNO, Al, Si, Fe abundances

Bresolin, Kudritzki, Najarro

et al. 2002, ApJ

Letters 577, L107

Conc

epci

on 2

007 NGC 300 WN11 star

Conc

epci

on 2

007

Najarro, Urbaneja, Kudritzki, Bresolin

2005

LBVLBV

Teff

= 10000K, L = 3.1 105

Lsun

mass fraction X/Xsun

H 0.688 0.97He 0.301 1.06Mg 1.5 10-4

0.22Fe 1.5 10-3

1.08

NGC 36217 Mpc

UV:

satellite telescopes: Copernicus, IUE, HST, ORFEUS,EUVE, FUSE

very rich stellar wind spectra of hot and cool stars

OVI, OV, OIV, OIII, NV, NIV, NIII, CIV, CIII, CII, SiIV, SiIII, SVI, SV, MgII, FeII

…..

Conc

epci

on 2

007 UV spectrum of O4

supergiant z Puppis Pauldrach, Puls, Kudritzki et al. 1994, SSRev, 66, 105

Conc

epci

on 2

007

HD 93129A O3IaTaresch, Kudritzki et al. 1997, A&A, 321, 531

X-ray: hot stars: emit X-rays through shocks in their winds strong X-ray emitters

cool stars: have coronae, except M supergiants/giants

Conc

epci

on 2

007 time dependent stellar wind radiation-hydro

shocks

(Owocki

et al., 1988; Feldmeier, 1997)

Conc

epci

on 2

007

ζ

Pup, O4 If ι

Ori

O9 III 15 Mon O7 V

Calculated spectra and ROSAT observationsFeldmeier, Kudritzki et al., 1997

theory

convolved withROSAT FWHM

●

ROSAT

III. Stellar winds and Astronomy

1. Stellar winds and galaxies

Massive stars dominate light of star forming galaxies

Strong and broad stellar wind lineseasily detectable in spectraof integrated stellar populationsExample: starburst galaxies at high z

UV shifted to optical/IR

population synthesis, metallicities,Energy and momentum input galactic winds, star formation Nuclear burned material input

chemical evolution of galaxies

P Cygni profiles and metallicity

Galaxy LMC SMC

Kudritzki, 1998

cB58

@ z=2.7

non-LTE atmospheres with windsplus stellar evolution models

Synthetic spectra of galxies

at high z as a function of Z, IMF, SFR

Population synthesis of highPopulation synthesis of high--z galaxiesz galaxies

Galaxy spectra

Stellar spectra

Stellar Population

Initial Mass Function

Star Formation History MetallicityStellar Evolution

NGC 5253

Leitherer

et al. 2001, ApJ, 550, 724

Starburst99 population synthesis models

+

UV stellar libraries at ~solar and ~0.25 solar (LMC,

SMC) abundance

Rom

e 200

5Spectral diagnostics of high-z starbursts

Rix, Pettini, Leitherer, Bresolin, Kudritzki, Steidel, 2004, ApJ 615, 98

Starburst models - fully synthetic spectra based on model atmospheres

Rom

e 200

5Spectral diagnostics of high-z starbursts

Rix, Pettini, Leitherer,Bresolin, Kudritzki, Steidel2004, ApJ 615, 98

cB58 @ z=2.7

fully synthetic spectravs. observation

2. Winds and stellar evolution Winds affect stellar evolution significantly

winds mass-loss

mass M is decisive parameterfor stellar structure/evolution

crucial in certain phases, because it changes stellar mass

stars with significant during red giant

stage

good approximationReimers

–

formulaReimers, 1975; Kudritzki

& Reimers, 1978, A&A 70, 227

Note:

tremendous mass-loss in RGS and AGB –

phasestar with 8 Msun

on main sequence ends up with 1 Msun

7 Msun

re-cycled to ISMejection of Planetary Nebula at tip of AGB

Late stages of low-mass stellar evolution: CSPN

depends on L

small, but ≈

mass of hydrogenburning shell

tevol

strongly modifiedby winds

for review of CSPN winds seeKudritzki, Mendez et al., 1997, Proc. IAU Symp. 180, 64Kudritzki

et al., 2006, Proc. IAU Symp. 234, 119

White Dwarfs: extremely narrow mass distribution

without mass-loss stars with such masses cannot have evolved from the main sequence within Hubble time

from the HRDs

of open clusters we know the all stars with

have formed WDs

The mass spectrum observed can be explained by IMF and stellar evolution with mass-loss applying Reimers

-

formula

stars with Stellar winds observable during whole evolution

Kudritzki

& Puls, 2000, AARA 38, 683Kudritzki

& Urbaneja, 2009

strong forno evolution towardsred supergiants

stars can lose up to 90% of their mass until He-ZAMS

Wolf-Rayet

stars: massive stars on He-ZAMS with no Hvery strongwinds !!!

3. Winds and galaxy evolution stellar winds Energy and momentum input into ISM

affects star formationcauses “galactic winds”recycles nuclear burned matterinto ISMaffects chemical evolution