Effects of low metallicity on the evolution and spectra of massive stars

Jose Groh (Geneva Observatory, Switzerland) Image credits: Image NASA/ESA/J. & Hester A. Loll, State Nebula) U. (Crab Arizona Take Away: effects of low metallicity

Reduced stellar wind mass and angular momentum losses

Stars are more compact, hotter, and more mixed

Spectral lines are weaker and less numerous; more ionizing flux Outline

‣ Background on massive stars and stellar evolution ‣ Effects of low metallicity on stellar evolution ‣ Effects of low metallicity on stellar spectra ‣ Scary things Image credits: Image NASA/ESA/J. & Hester A. Loll, State Nebula) U. (Crab Arizona

Jose Groh - The surprising look of massive stars before death Outline

‣ Background on massive stars and stellar evolution ‣ Effects of low metallicity on stellar evolution ‣ Effects of low metallicity on stellar spectra ‣ Scary things

Jose Groh - The surprising look of massive stars before death Massive stars bridge many fields of (astro)Physics

‣ Star formation ‣ PhotoionizedStar formation regions, chemical evolution ‣ ChemicalSupernova, evolution GRBs, Black Holes, Neutron Stars ‣ DistantSupernova, Universe Black (starbursts, Holes, Neutron first Starsstars, cosmology) ‣ Intergalactic,Cosmology interstellar, circumstellar media ‣ Intergalactic,High-energy physics, interstellar, particle circumstellar physics, ...media

‣ High-energyStellar evolution physics, particle physics, ... credits: Image NASA/ESA/J. & Hester A. Loll, State Nebula) U. (Crab Arizona

Jose Groh - The surprising look of massive stars before death Massive star evolution is challenging

OB-type at ZAMS Luminosity

4.8 Effective4.4 Temperature4.0 3.6 3.2 Massive star evolution is challenging

OB-type at ZAMS

Red Super- Giant Luminosity

4.8 Effective4.4 Temperature4.0 3.6 3.2 Massive star evolution is challenging

Luminous Blue Variable

OB-type at ZAMS Yellow Hyper- Red Giant Super- Giant Luminosity

4.8 Effective4.4 Temperature4.0 3.6 3.2 Massive star evolution is challenging

Luminous Blue Wolf-Rayet Variable OB-type at ZAMS Yellow Hyper- Red Giant Super- Giant Luminosity

4.8 Effective4.4 Temperature4.0 3.6 3.2 Massive star evolution is challenging

Science we want to do Luminous •Evolutionary channels Blue Wolf-Rayet Variable •Initial mass ranges OB-type at ZAMS Yellow •SN type + progenitor Hyper- Red •Single x binary evol. Giant Super- Metallicity effects, ... Giant • Luminosity

4.8 Effective4.4 Temperature4.0 3.6 3.2 Massive star evolution is challenging

Science we want to do Luminous •Evolutionary channels Blue Wolf-Rayet Variable •Initial mass ranges OB-type at ZAMS Yellow •SN type + progenitor Hyper- Red •Single x binary evol. Giant Super- Metallicity effects, ... Giant • Luminosity However •rarity of massive stars •mass loss + rotation 4.8 Effective4.4 Temperature4.0 3.6 3.2 •binarity •models vs. observations Single stellar evolution models binaries: de Mink talk

Five flavors Single stellar evolution models binaries: de Mink talk

Five flavors ‣ non-rotating Eldridge talk Single stellar evolution models binaries: de Mink talk

Five flavors ‣ non-rotating Eldridge talk

‣ differential rotation (NO MAGNETIC FIELDS) Single stellar evolution models binaries: de Mink talk

Five flavors ‣ non-rotating Eldridge talk

‣ differential rotation (NO MAGNETIC FIELDS) Leitherer talk; Levesque talk Single stellar evolution models binaries: de Mink talk

Five flavors ‣ non-rotating Eldridge talk

‣ differential rotation (NO MAGNETIC FIELDS) Leitherer talk; Levesque talk ‣ solid-body rotation (WITH MAGNETIC FIELDS)Yoon talk Single stellar evolution models binaries: de Mink talk

Five flavors ‣ non-rotating Eldridge talk

‣ differential rotation (NO MAGNETIC FIELDS) Leitherer talk; Levesque talk ‣ solid-body rotation (WITH MAGNETIC FIELDS)Yoon talk

‣ differential rotation with surface magnetic braking Single stellar evolution models binaries: de Mink talk

Five flavors ‣ non-rotating Eldridge talk

‣ differential rotation (NO MAGNETIC FIELDS) Leitherer talk; Levesque talk ‣ solid-body rotation (WITH MAGNETIC FIELDS)Yoon talk

‣ differential rotation with surface magnetic braking

‣ solid-body rotation with surface magnetic braking Single stellar evolution models binaries: de Mink talk

Five flavors ‣ non-rotating Eldridge talk

‣ differential rotation (NO MAGNETIC FIELDS) Leitherer talk; Levesque talk ‣ solid-body rotation (WITH MAGNETIC FIELDS)Yoon talk

‣ differential rotation with surface magnetic braking

‣ solid-body rotation with surface magnetic braking

Observational constraints are key ‣ asteroseismology: differential x solid-body rotation ‣ spectroscopy+polarimetry: rotation and magnetic fields ‣ Metallicity dependence? Rotating massive star evolution models at solar metallicity

Z=0.014

85 120

60

40 32 25 20 15 12 9

(Groh+ 13b after Ekstrom+12, Georgy+ 12) Rotating massive star evolution models at solar metallicity

Z=0.014

85 120

60

40 32 25 20 15 12 ~8 to 17 M 9

(Groh+ 13b after Ekstrom+12, Georgy+ 12) Rotating massive star evolution models at solar metallicity

Z=0.014

85 120

60

40 32 25 20 15 OB-type RSG12 SN IIP ~8 to 17 M 9

(Groh+ 13b after Ekstrom+12, Georgy+ 12) Rotating massive star evolution models at solar metallicity

Z=0.014

85 120

60

40 32 ~17 to 30 M 25 20 15 OB-type RSG12 SN IIP ~8 to 17 M 9

(Groh+ 13b after Ekstrom+12, Georgy+ 12) Rotating massive star evolution models at solar metallicity

Z=0.014

85 120

60

40 OB-type RSG32 YHG/LBV SN~17 IIL/b to 30 M 25 20 15 OB-type RSG12 SN IIP ~8 to 17 M 9

(Groh+ 13b after Ekstrom+12, Georgy+ 12) Rotating massive star evolution models at solar metallicity

Z=0.014

85 120 > ~30 M 60

40 OB-type RSG32 YHG/LBV SN~17 IIL/b to 30 M 25 20 15 OB-type RSG12 SN IIP ~8 to 17 M 9

(Groh+ 13b after Ekstrom+12, Georgy+ 12) Rotating massive star evolution models at solar metallicity

Z=0.014

85 120 OB-type LBV WR SN> Ibc ~30 M 60

40 OB-type RSG32 YHG/LBV SN~17 IIL/b to 30 M 25 20 15 OB-type RSG12 SN IIP ~8 to 17 M 9

(Groh+ 13b after Ekstrom+12, Georgy+ 12) Outline

‣ Background on massive stars and stellar evolution ‣ Effects of low metallicity on stellar evolution ‣ Effects of low metallicity on stellar spectra ‣ Scary things Image credits: Image NASA/ESA/J. & Hester A. Loll, State Nebula) U. (Crab Arizona

Jose Groh - The surprising look of massive stars before death A change of metallicity affects:

1. Opacities

2. Equation of state (via mean molecular weight)

3. Nuclear reaction rates

4. Fuel available during MS (X = 1 - Y - Z)

5. Mass and angular momentum losses from stellar winds

6. Rotational effects and angular momentum transport Rotating massive star evolution models at SMC metallicity

Z=0.002 (i.e. 1/7 Zsun)

120 >50 M 85 60 40 32 25 20 8 to 50 M 15 12 9

(Groh+ 15 in prep after tracks from Georgy+ 13) Rotating massive star evolution models at SMC metallicity

Z=0.002 (i.e. 1/7 Zsun)

120 >50 M 85 60 40 32 25 20 OB-type RSG SN IIP 8 to 50 M 15 12 9

(Groh+ 15 in prep after tracks from Georgy+ 13) Rotating massive star evolution models at SMC metallicity

Z=0.002 (i.e. 1/7 Zsun) OB-type YHG/LBV SN IIP or IIn 120 >50 M 85 60 40 32 25 20 OB-type RSG SN IIP 8 to 50 M 15 12 9

(Groh+ 15 in prep after tracks from Georgy+ 13) Rotating massive star evolution models at ~ IZw18 metallicity Z=0.0004 (i.e. 1/50 Zsun)

120 >50 M 85 60 40 32 25 20 8 to 50 M 15 12 9

(Groh+ 2015 in prep) Rotating massive star evolution models at ~ IZw18 metallicity Z=0.0004 (i.e. 1/50 Zsun)

120 >50 M 85 60 40 32 25 20 OB-type RSG/BSG SN8 IIP to 50 M 15 12 9

(Groh+ 2015 in prep) Rotating massive star evolution models at ~ IZw18 metallicity Z=0.0004 (i.e. 1/50 Zsun) OB-type YHG/LBV SN IIP or IIn 120 >50 M 85 60 40 32 25 20 OB-type RSG/BSG SN8 IIP to 50 M 15 12 9

(Groh+ 2015 in prep) Rotating massive star evolution models at ~ IZw18 metallicity Z=0.0004 (i.e. 1/50 Zsun) OB-type YHG/LBV SN IIP or IIn 120 >50 M 85 60 40 32 25 20 OB-type RSG/BSG SN8 IIP to 50 M 15 12 9

(Groh+ 2015 in prep) Stars reach the RSG phase only at late times: less RSGs Metallicity trends in stellar evolution Low metallicity: mass loss diminishes

Groh+ 2015, in prep Low metallicity: stars are more compact and hotter

Groh+ 2015, in prep Low metallicity: faster surface rotation

For high mass stars: Reduced mass and angular momentum losses from stellar winds

Georgy+ 2013 Low metallicity: chemical mixing is favored

At low Z: stars are more compact; transport of angular momentum is less efficient.

Relative Nitrogen enhancement

blue= initial angular velocity Ω/Ωcrit = 0.10 Georgy+ 2013 purple= initial angular velocity Ω/Ωcrit = 0.95 Outline

‣ Background on massive stars and stellar evolution ‣ Effects of low metallicity on stellar evolution ‣ Effects of low metallicity on stellar spectra ‣ Scary things Image credits: Image NASA/ESA/J. & Hester A. Loll, State Nebula) U. (Crab Arizona

Jose Groh - The surprising look of massive stars before death How to compare observations and stellar evolution models?

Issue: massive stars develop winds that become denser as the star evolves, hiding progressively more and more of the stellar surface. How to compare observations and stellar evolution models?

Issue: massive stars develop winds that become denser as the star evolves, hiding progressively more and more of the stellar surface.

low-mass stars (e.g Sun)

phot

r Evol. code

hydr =

r Observations How to compare observations and stellar evolution models?

Issue: massive stars develop winds that become denser as the star evolves, hiding progressively more and more of the stellar surface.

low-mass stars massive stars: (e.g Sun) low Mdot

phot

r

hydr Evol. code Evol. code phot

r

r

hydr =

r Observations Observations How to compare observations and stellar evolution models?

Issue: massive stars develop winds that become denser as the star evolves, hiding progressively more and more of the stellar surface.

low-mass stars massive stars: massive stars: (e.g Sun) low Mdot high Mdot (evolved) Stellar Wind + Atmosphere

phot

r

hydr

phot

phot Evol. code Evol. code hydr Evol. code

r

r r

r

hydr =

r Observations Observations

Observations

Consequence: challenging to compare interior models of massive stars and observations. Solution: merge with an atmospheric code

Stellar Wind + Atmosphere

Geneva

phot Mass hydr

r Magnitudes r evol. code Luminosity Colors Temperature SED CMFGEN Surface code Spectrum abundances Observations Unified stellar evolution and atmospheric modelling

non-rotating 60 M at solar Z

Groh+ 2014, A&A 564, 30 Spectral evolution of a non-rotating 60 Msun star

Groh+ 2014, A&A 564, 30 Spectral evolution of a non-rotating 60 Msun star

Optical

Groh+ 2014, A&A 564, 30 Unified stellar evolution and atmospheric modeling

See also Schaerer+96, Schaerer & de Koter 96

107 (a) O I model stage 3 (c) WC model stage 48 108 Groh+ 2014 106 105 107 merge T and density structures from 106

5 stellar evolution and atmospheric codes 6 10 10 11.0 11.5 12.0 12.5 1.25 1.30 1.35

5 Temperature (K) 10 Temperature (K) 5 Geneva 10 + post-processing on a large grid of models CMFGEN final 104 CMFGEN 1 iter. 104 + flexibility to study the effects of mass loss 1 10 100 1000 0.1 1.0 10.0 100.0 0 10 Radius(b) (ORsun I model) stage 3 Radius(d) ( RsunWC )model stage 48 -5 + effects of line blanketing, wind clumping 10-7 10 0 -6 10-8 10 10 -7 -9 10 10-5 10 -8 10-10 10 10-11 10-9 -5 10-12 10 10-10 -10 10 11.0 11.5 12.0 12.5 1.0 1.2 1.4 1.6 1.8 2.0 Density (g/cm^3) Density (g/cm^3)

-10 10-15 10

1 10 100 1000 0.1 1.0 10.0 100.0 Radius (Rsun) Radius (Rsun)

(Groh+ 14) Unified stellar evolution and atmospheric modeling

See also Schaerer+96, Schaerer & de Koter 96

107 (a) O I model stage 3 107 (a) (c)O IWC model model stage stage 3 48 (c) WC model stage 48 108 108 Groh+ 2014 106 106 105 107 105 107 merge T and density106 structures from 106

5 5 stellar evolution and atmospheric codes 6 10 6 10 10 10 11.0 11.5 12.0 12.5 11.0 11.5 1.25 12.01.30 12.51.35 1.25 1.30 1.35

5 5 Temperature (K) 10 Temperature (K) 10Temperature (K) Temperature (K) 5 5 Geneva 10 Geneva 10 + post-processing onCMFGEN a large final grid of models CMFGEN final 104 CMFGEN 1 iter. 104104 CMFGEN 1 iter. 104 + flexibility to study1 the effects10 of100 mass loss1000 1 0.1 101.0 10010.0 1000100.0 0.1 1.0 10.0 100.0 0 0 10 Radius(b) (ORsun I model) stage 3 10 RadiusRadius(b) (d) (ORsun ( RsunIWC model) )model stage stage 3 48 Radius(d) ( RsunWC )model stage 48 -5 -5 + effects of line blanketing, wind10-7 clumping 10-7 10 10 0 -6 0 -6 10-8 10 10-8 10 10 10 -7 -7 -9 -9 10 10 10-5 10 10-5 10 -8 -8 10-10 10-10 10 10 10-11 10-11 10-9 10-9 -5 -5 10-12 10 10-12 10-10 10 10-10 -10 -10 10 11.0 11.5 12.0 12.5 10 11.0 1.011.51.2 12.01.4 1.612.51.8 2.0 1.0 1.2 1.4 1.6 1.8 2.0 Density (g/cm^3) Density (g/cm^3) Density (g/cm^3) Density (g/cm^3)

-10 -10 10-15 10-1510 10

1 10 100 1000 1 0.1 101.0 10010.0 1000100.0 0.1 1.0 10.0 100.0 Radius (Rsun) RadiusRadius (Rsun (Rsun) ) Radius (Rsun)

(Groh+ 14) Unified stellar evolution and atmospheric modeling

See also Schaerer+96, Schaerer & de Koter 96

107 (a) O I model stage 3 107 (a) (c)O IWC model model stage stage 3 48 (c) WC model stage 48 108 108 Groh+ 2014 106 106 105 107 105 107 merge T and density106 structures from 106

5 5 stellar evolution and atmospheric codes 6 10 6 10 10 10 11.0 11.5 12.0 12.5 11.0 11.5 1.25 12.01.30 12.51.35 1.25 1.30 1.35

5 5 Temperature (K) 10 Temperature (K) 10Temperature (K) Temperature (K) 5 5 Geneva 10 Geneva 10 + post-processing onCMFGEN a large final grid of models CMFGEN final 104 CMFGEN 1 iter. 104104 CMFGEN 1 iter. 104 + flexibility to study1 the effects10 of100 mass loss1000 1 0.1 101.0 10010.0 1000100.0 0.1 1.0 10.0 100.0 0 0 10 Radius(b) (ORsun I model) stage 3 10 RadiusRadius(b) (d) (ORsun ( RsunIWC model) )model stage stage 3 48 Radius(d) ( RsunWC )model stage 48 -5 -5 + effects of line blanketing, wind10-7 clumping 10-7 10 10 0 -6 0 -6 10-8 10 10-8 10 10 10 -7 -7 -9 -9 10 10 10-5 10 10-5 10 -8 -8 10-10 10-10 10 10 10-11 10-11 10-9 10-9 - no feedback effects from the wind onto -5 -5 10-12 10 10-12 10-10 10 10-10 -10 -10 the envelope 10 11.0 11.5 12.0 12.5 10 11.0 1.011.51.2 12.01.4 1.612.51.8 2.0 1.0 1.2 1.4 1.6 1.8 2.0 Density (g/cm^3) Density (g/cm^3) Density (g/cm^3) Density (g/cm^3)

-10 -10 10-15 10-1510 10

1 10 100 1000 1 0.1 101.0 10010.0 1000100.0 0.1 1.0 10.0 100.0 Radius (Rsun) RadiusRadius (Rsun (Rsun) ) Radius (Rsun)

(Groh+ 14) Unified stellar evolution and atmospheric modeling

See also Schaerer+96, Schaerer & de Koter 96

107 (a) O I model stage 3 107 (a) (c)O IWC model model stage stage 3 48 (c) WC model stage 48 108 108 Groh+ 2014 106 106 105 107 105 107 merge T and density106 structures from 106

5 5 stellar evolution and atmospheric codes 6 10 6 10 10 10 11.0 11.5 12.0 12.5 11.0 11.5 1.25 12.01.30 12.51.35 1.25 1.30 1.35

5 5 Temperature (K) 10 Temperature (K) 10Temperature (K) Temperature (K) 5 5 Geneva 10 Geneva 10 + post-processing onCMFGEN a large final grid of models CMFGEN final 104 CMFGEN 1 iter. 104104 CMFGEN 1 iter. 104 + flexibility to study1 the effects10 of100 mass loss1000 1 0.1 101.0 10010.0 1000100.0 0.1 1.0 10.0 100.0 0 0 10 Radius(b) (ORsun I model) stage 3 10 RadiusRadius(b) (d) (ORsun ( RsunIWC model) )model stage stage 3 48 Radius(d) ( RsunWC )model stage 48 -5 -5 + effects of line blanketing, wind10-7 clumping 10-7 10 10 0 -6 0 -6 10-8 10 10-8 10 10 10 -7 -7 -9 -9 10 10 10-5 10 10-5 10 -8 -8 10-10 10-10 10 10 10-11 10-11 10-9 10-9 - no feedback effects from the wind onto -5 -5 10-12 10 10-12 10-10 10 10-10 -10 -10 the envelope 10 11.0 11.5 12.0 12.5 10 11.0 1.011.51.2 12.01.4 1.612.51.8 2.0 1.0 1.2 1.4 1.6 1.8 2.0 Density (g/cm^3) Density (g/cm^3) Density (g/cm^3) Density (g/cm^3)

-10 -10 10-15 10-1510 10 Error of computing spectra assuming Teff(stellar evolution):

1 200-500K10 100(ZAMS)1000 1 0.1 101.0 10010.0 1000100.0 0.1 1.0 10.0 100.0 1500-4000Radius K ( Rsun(O) supergiants) RadiusRadius (Rsun (Rsun) ) Radius (Rsun) 10000s K (WR stars and LBVs) (Groh+ 14) Metallicity effects on stellar spectra: unified models

1.5 N IV He II He II Hdelta He II Hgamma CNO lines 1.0

0.5 C III/ NIII Normalized Flux mid-H burning non-rotating 60 M at Z=0.014 (O4 I; Teff= 43kK)

0.0 4000 4200 4400 4600 4800 Wavelength [Angstrom]

(Groh+ 15 in prep) Metallicity effects on stellar spectra: unified models

1.5 N IV He II He II Hdelta He II Hgamma CNO lines 1.0

0.5 C III/ NIII Normalized Flux mid-H burning non-rotating 60 M at Z=0.014 (O4 I; Teff= 43kK) mid-H burning non-rotating 60 M at Z=0.0004 (O3 V; Teff=47kK) 0.0 4000 4200 4400 4600 4800 Wavelength [Angstrom]

(Groh+ 15 in prep) Metallicity effects on stellar spectra: unified models

He II 4686 line is weaker at low Z = Mdot effect (20x lower) Spectral lines are less numerous (CNO) = abundance effect (50x lower)

1.5 N IV He II He II Hdelta He II Hgamma CNO lines 1.0

0.5 C III/ NIII Normalized Flux mid-H burning non-rotating 60 M at Z=0.014 (O4 I; Teff= 43kK) mid-H burning non-rotating 60 M at Z=0.0004 (O3 V; Teff=47kK) 0.0 4000 4200 4400 4600 4800 Wavelength [Angstrom]

(Groh+ 15 in prep) Metallicity effects on stellar spectra: unified models

2.0 N V 1.5 O IV C IV Fe V forest He II O V

1.0

Normalized Flux 0.5

0.0 mid-H burning non-rotating 60 M at Z=0.014 (O4 I; Teff= 43kK) 1200 1300 1400 1500 1600 1700 Wavelength [Angstrom]

(Groh+ 15 in prep) Metallicity effects on stellar spectra: unified models

2.0 mid-H burning non-rotating 60 M at Z=0.0004 (O3 V; Teff=47kK) N V 1.5 O IV C IV Fe V forest He II O V

1.0

Normalized Flux 0.5

0.0 mid-H burning non-rotating 60 M at Z=0.014 (O4 I; Teff= 43kK) 1200 1300 1400 1500 1600 1700 Wavelength [Angstrom]

(Groh+ 15 in prep) Metallicity effects on stellar spectra: unified models

He II lines are weaker at low Z = Mdot effect (20x lower) Spectral lines are less numerous (Fe, CNO) = abundance effect (50x lower)

2.0 mid-H burning non-rotating 60 M at Z=0.0004 (O3 V; Teff=47kK) N V 1.5 O IV C IV Fe V forest He II O V

1.0

Normalized Flux 0.5

0.0 mid-H burning non-rotating 60 M at Z=0.014 (O4 I; Teff= 43kK) 1200 1300 1400 1500 1600 1700 Wavelength [Angstrom]

(Groh+ 15 in prep) Metallicity effects on stellar spectra: ionizing fluxes

10-5

10-10

10-15

10-20 Flux (erg/s/cm^2/Angstrom] 10-25 mid-H burning non-rotating 60 M at Z=0.014 (O4 I; Teff= 43kK) 100 1000 10000 Wavelength [Angstrom]

(Groh+ 15 in prep) Metallicity effects on stellar spectra: ionizing fluxes

increase in ionizing fluxes (abundance/line blanketing effect)

10-5 mid-H burning non-rotating 60 M at Z=0.0004 (O3 V; Teff=47kK)

10-10

10-15

10-20 Flux (erg/s/cm^2/Angstrom] 10-25 mid-H burning non-rotating 60 M at Z=0.014 (O4 I; Teff= 43kK) 100 1000 10000 Wavelength [Angstrom]

(Groh+ 15 in prep) Scary things: how do they change with metallicity?

‣ Mass loss and eruptions ‣ Wind structure (clumping) ‣ Blackbody vs model atmosp. ‣ Binarity ‣ Magnetic Fields ‣ Rotation ‣ Convection ‣ Eddington limit and inflation Scary things: how do they change with metallicity?

‣ Mass loss and eruptions ‣ Wind structure (clumping) ‣ Blackbody vs model atmosp. ‣ Binarity ‣ Magnetic Fields ‣ Rotation ‣ Convection ‣ Eddington limit and inflation Wind clumping affects line profiles

Teff=52kK Z=0.002 Mdot 2.5e-6 Msun/yr

MPG 355 (O2 III) in NGC 346

(Bouret et al. 2003) Wind clumping affects line profiles

Teff=40kK Z=0.002 Mdot 1e-7 Msun/yr

MPG 368 (O4-5 V) in NGC 346

(Bouret et al. 2003) atmospheric models with clumping not included in Stellar Pop. Synthesis Clumping and Mdot effects?

Starburst99)2014.Models,.with.and.w/o.Rota;on.

Z=0.15.Z! Z=0.15.Z!. Z=0.60.Z!. .

(courtesy C. Steidel) Blackbody vs. Model atmospheres (or why I don’t like blackbodies)

10-6

10-8

10-10

10-12 Black=CMFGEN model, Teff=47kK, Z=0.0004 10-14 Red=Blackbody T=47kK 10-16 Red=Blackbody T=60kK 10-18 Flux (erg/s/cm^2/Angstrom] 10-20 100 1000 10000 Wavelength [Angstrom] Take Away: effects of low metallicity

Reduced stellar wind mass and angular momentum losses

Stars are more compact, hotter, and more mixed

Spectral lines are weaker and less numerous; more ionizing flux