The most massive stars The most massive stars Stars For All, Lund - - PowerPoint PPT Presentation

Paul Crowther (Sheffield), Olivier Schnurr (AIP), Raphael Hirschi (Keele), Liza Yusof (Univ Malaya), Richard Parker (ETH), Simon Goodwin (Sheffield), Hasan Kassim (Univ Malaya)

The most massive stars The most massive stars

Atm Models Binaries Interior Models Clusters Dynamics

Stars For All, Lund Observatory

Lower stellar mass limit Lower stellar mass limit

Firm lower limit to stellar mass sequence (~0.085 M), below which H- burning never commences (brown dwarfs). Is there a comparable upper limit to stellar masses? 10-3 Gyr 101 Gyr

Burrows et al. 1993

Upper stellar mass limit? Upper stellar mass limit?

1 M = 2 x 1030 kg = 300,000 MEarth = 1,000 MJupiter 0.1 M 1 M 8 M ?? M

Historical perspective Historical perspective

R136a: Supermassive star?

30 Dor

74inch at 74inch at Radcliffe Radcliffe Observatory (South Africa) Observatory (South Africa)

Feast et al.1960 SMC: R1-50 LMC: R51-158

Radcliffe Radcliffe #136 (=R136) #136 (=R136)

MR136a = 250-1,000 M? (Feilzinger et al. 1980) Feast et al.: Central ‘star’ in 30 Dor but is probably composite.

R136a: R136a: Supermassive Supermassive Star? Star?

R136

R136a: Dense star cluster R136a: Dense star cluster

ESO HST

Upper mass limit? Upper mass limit?

``The very concept of an `upper mass cut-off‘ has to be considered carefully; at what mass does the IMF predict one

• ne star?’’

Massey & Hunter (1998)

30 Dor Arches

Arches cluster Arches cluster

VLT/NACO (Espinoza et al. 2009)

http://www.eso.org/public/news/eso0921/

~150 M ~150 Mo

• upper mass limit?

upper mass limit?

Figer (2005), Nature

R136 m3=150 Mo High mass 0.5% Intermediate mass 3% Low mass 70% BD 30%

Issues? Issues?

• Eddington limit?

Mass-Luminosity Relation Mass-Luminosity Relation

L∝Mα α~2.5 α~1.5

Eddington Eddington parameter parameter

Γe = ge g = 3.10−5q L /Lo M /Mo

Limit

Issues? Issues?

• Eddington limit?
• Interpretation challenging for masses
• Gold standard: Close spectroscopic binary

with known inclination

• Silver standard: Direct radius measurement +

spectroscopic gravity

• Bronze standard: Indirect radius from

atmospheric models + spectroscopic gravity

• `Sub-standard’: Mass from comparison

between (Teff, logL) from atmospheric models with evolutionary model predictions

Issues? Issues?

• Eddington limit?
• Interpretation challenging for masses
• Gold standard: Close spectroscopic binary

with known inclination

• Silver standard: Direct radius measurement +

spectroscopic gravity

• Bronze standard: Indirect radius from

atmospheric models + spectroscopic gravity

• Sub-standard: Mass from comparison

between (Teff, logL) from atmospheric models with evolutionary model predictions

Conti (1986) IAU Symp 116

Recent 100M Recent 100M

+ contenders..

+ contenders..

Pistol star η Carinae R136a1

Pistol star? Pistol star?

200-250 M (Figer et al. 1998) 100 M

(Najarro et al.2009)



η η Carinae Carinae

Historically identified as the most massive star in the Milky Way..

ESO 2.2m/WFI (BVR)

Homunculus Homunculus

η Car erupted in 19th Century, becoming 2nd brightest star in sky, forming the Homunculus. AAT η Car now identified as a ~120 + 90 M binary (~5.5 yr period, Damineli 1996).

R136a1 R136a1

M~136-155 M for R136a1 (Teff calibrations for OB stars!) + WFPC2 photometry (Massey & Hunter 1998)

Campbell et al. (2010)

4” (1pc)

Multi-Conjugate Adaptive Optics Multi-Conjugate Adaptive Optics Demonstrator (MAD) imaging Demonstrator (MAD) imaging

VLT/MAD + SINFONI VLT/MAD + SINFONI

0.8 0.8” ” (0.2pc) (0.2pc) Schnurr Schnurr et et

• al. (2009)
• al. (2009)

c c b b a3 a3 a1 a1 a2 a2 a5 a5

R136a1: mK=11.1 AK=0.2 MK=-7.6

Reassessment of brightest Reassessment of brightest stars in R136 stars in R136

No evidence for short period binaries from VLT/SINFONI (Schnurr et al. 2009). Stellar properties re-assessed (Crowther et al. 2010): (a) VLT/SINFONI spectroscopy + (b) VLT/MAD photometry + (c) Contemporary stellar atmosphere models (suited to emission line stars) + (d) Evolutionary models for very massive stars

Stellar temperatures.. Stellar temperatures..

Atmospheric model fits to UV (HST/FOS), optical (HST/FOS) & infrared (VLT/SINFONI) spectroscopy.

Stellar luminosities.. Stellar luminosities..

(a) Optical/IR photometry (HST/WFC3+VLT/MAD)+ (b) Large Magellanic Cloud distance (50kpc) + (c) Correction for interstellar dust (AV=1.7, AK=0.2).

Stellar masses? Stellar masses?

Comparison of (Teff, logL) with evolutionary models ⇒Mcurrent

Initial masses? Initial masses?

Evolutionary models adopt theoretical rates

• f mass loss

(several x 10-5 Msun/yr*) Minit=165-320Mo Mcurrent = 135-265 Mo, ages ~ 1.5-2 Myr *Spectroscopic dM/dt ~ 5 x 10-5 Msun/yr

8,700,000 1 0.001 Luminosity L 0.002 0.01 35 300 10 1.4 1 1 1,000 140 0.1 0.1 Lifetime Gyr Density H2O=1 Radius R Mass M

Vital statistics Vital statistics

Density (VY CMa) = 0.000000003 Density (H2O) = 1.0 Density(NS) = 1,000,000,000,000,000

Sky & Telescope (Oct 2010)

30 Dor Arches NGC 3603

Gold standard or sub-standard? Gold standard or sub-standard?

NGC 3603 hosts an eclipsing binary A1a+b for which dynamical masses have been derived Mdyn:116±31Mo + 89±16Mo (Schnurr et al. 2008) Spectral analysis + evolutionary models Mcurrent:120 Mo + 92 Mo

R136 m3=150 Mo R136 m3=300 Mo

Very Massive Stars Very Massive Stars vs vs OB stars OB stars

27 70 53,000 265: R136a1 0.4 0.002 26,000 14 B1V B0V O9V O7V O5V O3V Star/Sp Type 1.0 1.6 2.8 3.8 5.6 Rs pc* 0.025 30,000 19 0.13 33,000 25 0.7 37,000 36 1.6 41,000 51 5 45,000 74 N(LyC) 1049 s-1 Teff K Mass Mo

*Rs for ne~102 cm-3

High High m mup

up

from SDSS galaxies? from SDSS galaxies?

Problems with population synthesis models for high surface brightness SDSS galaxies using Mup=120 Mo. g-r colours and EW(Hα) do not match predictions.. “At the highest luminosities & surface brightnesses the [population synthesis] fit is improved by allowing even more massive stars to form.” (Hoversten & Glazebrook 2008, 2010)

Formation & death of Formation & death of very massive stars very massive stars

Star formation: low mass Star formation: low mass

• Fragmentation of

Molecular Clouds to low mass (~0.01 Mo) seeds.

• Accretion, at

Macc~2x10-7 Mo/yr

• ver ~5 Myr(!)

required to build up Solar-type stars (Protostar ⇒T Tauri ⇒ ZAMS)

Star formation: High mass Star formation: High mass

• High mass stars ?
• Rapid formation (0.1 Myr)

requires high accretion rate (Macc~10-4 M/yr), to build up 10 solar mass star. Accretion hindered by radiation pressure in star..

• Very high mass stars 
• V.high accretion rate (Macc~10-3

M/yr) to form a 100 solar mass star if radiation pressure

• vercome OR mergers of lower

mass stars in dense protocluster cores..

W33A Joshua Barnes

Cycle 19 HST/STIS Cycle 19 HST/STIS programme programme

Crowther (PI) Start date: Apr 2012

Formation of R136a? Formation of R136a?

Simulation courtesy of Ian Bonnell

New Scientist (Feb 2010)

Thermonuclear Type Ia SN (low mass stars in close binary) Core-collapse Type II or Ib/c (high mass stars) Pair-instability (Very high mass)

Supernovae Supernovae

End state of very massive stars? End state of very massive stars?

Heger et al. 2003 Mass Metallicity

End state of very massive stars? End state of very massive stars?

Heger et al. 2003 Mass Metallicity

Core- collapse SN (NS/BH) Pair instability SN

Super-supernovae Super-supernovae

Several super-bright Type Ic SN have now been seen (SN 2007bi; MR=-21.3 mag)

Gal-Yam et al. 2009 Young et al. 2010

LMaxSN 2007bi = 130 x LMaxSN 1987A = 30 billion x LSun

Local PISN? Local PISN?

Radioactive 56Ni (several M) & total ejected mass (100M+) from the light-curve evolution of SN 2007bi are consistent with pair instability SN models.

Pair instability Pair instability SNe SNe & & upper mass limit upper mass limit

SN2007bi (*if* a PISN) should not exist if mup~150Mo. Upper mass limit required to be much higher for the possibility of PISN in local universe..

Langer (2009)

Death of Very Massive Stars Death of Very Massive Stars

PISN restricted to SMC metallicities (or lower). Depends critically on post- MS mass-loss recipes Yusof & Hirschi (Priv. Comm.)

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