Download mass loss and stellar evolution

The Role of Giant LBV Eruptions in the
Evolution of Very Massive Stars
Nathan Smith
CASA, U. Colorado
In collaboration with
Stan Owocki (U. Delaware)
In the near future:
Smith & Owocki (2006)
ApJ Letters, submitted
120
LBV
M/M
WR
20
t=0
2.5-3 Myr
CLUMPING IN LINE-DRIVEN WINDS OF HOT STARS
Observational mass-loss rates come from H emission and IR/radio free-free.
Both are sensitive to 2.
 2 
Fc 
  2
If winds are highly clumped (FC>>1)
.
Then M from H and free-free is much lower.
Examples:

• Fullerton et al. (2006); factors of 10-20 reduction in Mdot.
• Bouret et al. (2005); factors of >3.
see poster by
Martins &
Schaerer
• Puls et al. (2006); median of 20, but as much as 100x lower
• see also Crowther et al. 2003; Hillier et al. 2003; Massa et al. 2003; Evans et al. 2004.
MASS LOSS AND STELLAR EVOLUTION
120
MS
LBV
WR
SN
M/M
120

20
?
Mdot
3e-6
2e-4
3e-5
T(yr)
3e6
5e4
5e5
M lost
10
10
15
M/M sun
60

12
LBV
?
?
M/M
M dot
1e-6
2e-4
2e-5
T(yr)
5e6
5e4
5e5
M lost
5
10
10
20
t=0
Smith & Owocki (2006)
ApJ Letters, submitted)
WR
2.5-3 Myr
So, the burden of mass loss must fall on post-MS phases.
LBVs on the upper HR Diagram
L*
L*

~
LEdd M *
• Eta Car
=0.9
=0.5
+
RSGs
Smith, Vink, & de Koter (2004)
During eruption
LBol=20x106 L
Tstar=8,500K
(
After eruption
LBol=5x106 L
Tstar=30,000K
)
present-day
properties
The historical light curve of Eta Car
Total mass
ejected was
>12 M.
MASS LOSS AND STELLAR EVOLUTION
SUPERNOVA IMPOSTORS
(extragalactic Eta Car analogs)
• Historical Type V supernovae:
(Eta Carinae / P Cygni)
SN1954j in NGC2403
SN1961v in NCG1058
• Recent faint SNe in SN searches:
All have been faint with spectral
class Type IIn (but not all
Type IIn’s are SN impostors)
KE
1
Lt
(Humphreys, Davidson, & Smith 1999)
(SN 1954j)
(Van Dyk et al. 2000)
OBSERVED MASSES OF LBV NEBULAE
In circumstellar shells
around other LBVs and
LBV candidates, a mass
of ~10 M is typical for
stars with L>106 L.
In Eta Carinae, at least,
we know this is ejecta
from a single outburst
and not swept-up
material.
Smith & Owocki (2006)
ApJ Letters, submitted
SN and GRB Environments
Recent observations reveal very massive shells around SN and GRBs:
This means that the progenitor stars may have had eruptive mass-loss events
shortly before exploding……….
• SN1988z, nebula = 15 M (Aretxaga et al. 1999; Williams et al. 2002; Van
Dyk et al. 1993; Chugai & Danziger 1994).
• SN2002hh, nebula =10-15 M
(Barlow et al. 2005).
• massive shells around SN2001em and SN1994w
Chugai et al. 2004).
(Chugai & Chevalier 2006;
• massive shells around GRB021004 and GRB050505 (Mirabel et al. 2003;
Berger et al. 2005).
• circumstellar gas around other GRBs
(H.-W. Chen, D. Fox, this meeting)
MULTIPLE ERUPTIONS…
This has happened before:
Smith et al. 2005
• Outside the bipolar Homunculus of
Eta Car, there are ionized “outer
ejecta” from probably 2 previous
eruptions separated by several
hundred to 1000 yr….(proper motions:
Walborn et al. 1978; Walborn & Blanco
1988).
• P Cygni also shows multiple
separate nebular shells separated by
several hundred years (Meaburn
2001; Meaburn et al. 1996, 1999,
2000, 2004; O’Connor et al. 1998).
HST/WFPC2
F502N [O III]
F658N [N II]
Each burst will remove a substantial fraction of the star’s mass
and will affect its evolution…how many times will this happen?
MASS LOSS AND STELLAR EVOLUTION
MS
LBV
WR
SN
M/M
120

20
?
Mdot
3e-6
2e-4
3e-5
T(yr)
3e6
5e4
5e5
M lost
10
10
15
M/M sun
60

12
M dot
1e-6
2e-4
2e-5
T(yr)
5e6
5e4
5e5
5
10
10
120
M/M
M lost 20
t=0
?
LBV
Smith & Owocki (2006)
ApJ Letters, submitted
WR
2.5-3 Myr
Giant LBV outbursts a la Eta Carinae apparently dominate the post-MS mass
loss of very massive stars…..but we still don’t know what triggers them.
WHAT IF THIS PICTURE IS WRONG?
Consider some Alternatives:
• LBV phase is longer or core He-burning massive
stars masquerade as some other type of BSGs?
• Mass loss by mass transfer/RLOF?
• Massive stars explode early - end of the LBV phase?
120
LBV
?
M/M
WR
20
t=0
2.5-3 Myr
MASS LOSS AND STELLAR EVOLUTION
The 10 M ejected in this type of eruption may be enough to fix the
mass discrepancy in the post-MS evolution of massive stars.
• Evolutionary tracks for massive stars depend on adopted mass loss
rates (e.g., Maeder & Meynet 1994, 2000, 2003).
• To reproduce correct ratio of OB/WR stars, WR star M and L, etc.,
these calculations need to adopt mass-loss rates on MS that are
2 X HIGHER than “standard” mass loss rates.
(de Jager et al. 1988; Nieuwenhuijzen & de Jager 1988)
• Problem: more recent modeling of spectra of O stars winds find much
LOWER mass-loss rates due to clumping by about 10x or more.
120
LBV
M/M
WR
20
t=0
2.5-3 Myr
Angular
Momentum?
WHAT DRIVES THE EXREME MASS LOSS?
So, 12 M is a safe Lower Limit to the total mass ejected during the
19th century Great Eruption of Eta Carinae (could be 20-30 M).
• Mass Loss rate during the 20-yr eruption > 0.5 M yr -1.
(Probably much higher, since proper motions indicate a small
range of ejection dates.) Lines are saturated!
• HUGE amount of Kinetic Energy
( ½mv2=1050 ergs. But this is a lower limit...)
KE
1
Lt
Luminous energy
~1049.5 ergs
Typical M  typical t for other
LBV eruptions implies mass-loss
rates of order 10-2 to ~1 M/yr.
There’s NO WAY these can be line driven winds…either superEddington continuum-driven winds or hydrodynamic explosions.
(see Owocki et al. 2005; Arnett et al. 2005)
MASS LOSS AND LOW METALLICITY
THE FIRST STARS (Pop III)
• The “first stars” may have been mostly
massive (peak ~100 M) and luminous,
and may have re-ionized the Universe
(Bromm & Larson 2004, Bromm this meeting).
• Hot stars have line-driven winds (opacity
dominated by Fe), but the “first stars” have
no metals…so they don’t have any mass
loss…….?
…but…
• Giant eruptions like Eta Carinae and the
“supernova impostors” are insensitive to
metallicity (electron-scattering opacity, or
hydrodynamic explosions).
Important for mass loss in the first stars?
(Abel et al. 2000)
MASS LOSS AND LOW METALLICITY
Heger et al. 2003
Using standard mass-loss rates (Nieuwenhuijzen & de Jager 1988).
MASS LOSS AND LOW METALLICITY
Pop III
120
LBV
M/M
WR
20
t=0
2.5-3 Myr
At solar metallicity, MS mass loss is not very different from First stars!
SUMMARY/CONCLUSIONS
MASS LOSS - Main Implications
• Because of clumping, mass-loss rates for line-driven winds have been revised
downward by an order of magnitude.
• Thus, line-driven winds on the main-sequence are vastly insufficient to remove
the H envelope and produce WR stars (MWR20 M)…best alternative is that
LBV eruptions dominate the mass loss of the most massive stars.
• The mass loss of giant LBV eruptions is insensitive to metallicity --- their
extreme mass-loss rates cannot arise from line-driven winds.
//////////// ROAD BLOCK: we don’t know what triggers LBV eruptions \\\\\\\\\\\\\\\\\
• The possibility that the mass loss of massive stars even at solar metallicity
may be dominated by a metallicity-independent mechanism should at least raise
caution signs for the notion that Pop III stars did not suffer mass loss.
Pop III stars were massive -- could they shed mass through LBV eruptions?
Proving this wrong will tell us a great deal about stellar evolution.
DUST MASS (from the ISO spectrum)
100 x M(dust)
400K 200K 140K
0.02 M 1.5 M 11 M
Total = 12.5 M
Total mass (gas+dust) of
Homunculus > 10 M ----- HUGE!
Smith et al. 2003
Total IR luminosity
4.3x106 L
Previous estimates from =2-12 m
typically gave 2-3 M.
Higher mass comes from cool dust
emitting at  > 12 m.
DUST MASS (from the ISO spectrum)
Total mass (gas+dust) of Homunculus > 10 M ----- HUGE!
Conservative assumptions…
• Optically thin emission
• Large grains (a~1 m silicate):
(small grains have poor QABS at long IR wavelengths)
• Gas : Dust mass ratio =100
(Eta’s ejecta are C and O poor, Fe in gas phase in inner shell)
Thin walls of the H2 shell…
Gemini South/Phoenix
R=60,000
The ejecta expand as a
Hubble flow, so if
R/R ~ t/t
then t ≤ 5 yr. (proper
motions agree…) This would
require a HUGE mass-loss
rate during the eruption of
several M/yr. Implies that
the 19th century event was an
explosion.
Typical M  typical t for other
LBV eruptions implies massloss rates of order 10-2 to ~1
M/yr.
1.644 m [Fe II]
2.122 m H2 1-0 S(1)
Smith (2006), ApJ, 644 (June 20)
Thin walls of the H2 shell…
CLOUDY models: The
survival of H2 in a thin layer
around Eta Car requires a
density of nH  107 cm-3 in the
outer shell.
For the volume of the outer H2
shell, this implies a total gas
mass of 20-30 M.
Smith & Ferland (2006, almost done)
P Cygni:
the other nebula from a Galactic giant
LBV eruption that was actually
observed.
+
Image: Clampin
et al. (1997)
The historical light curve of P Cygni
LBVs on the upper HR Diagram
P Cygni:
• Eta Car
=0.9
=0.5
+
Smith, Vink, & de Koter (2004)
P Cygni: bright [Fe II] 1.644 m emission
but no H2, and almost no dust.
(less mass/lower optical depth after ejection)
MASS:
Can’t use dust,
but from [Fe II]
lines,
M=0.1 M
Mass and KE +
much less than
Eta Car in
1843, but
similar to 1980
outburst of Eta
Car (Little
Homunculus)
Smith & Hartigan (2006)
Smith (2006), ApJ, 644 (June 20)
Outer shell
Cool dust 140 K
Molecular hydrogen
Thin shell
Inner Shell
Warm dust 200 K
[Fe II] emission, etc.
Thick shell
ne=104 cm-3
Hot dust near star
Equatorial clumps
( >400 K )
Bipolar Geometry
Shape of the Homunculus
Smith (2006)
Bipolar Geometry
Smith (2006)
Almost 75% of total mass and more than 90% of total KE above θ = 45°…
Bipolar Geometry
Smith (2006)
Important constraints on shaping mechanism:
1. Rules out spherical shell/wind shaped by
circumstellar torus (mass at equator)…
2. Rules out deflection by companion star.
(KE in polar ejecta > binding energy of orbit)
Merger??? (Morris & Podsiadlowski 2006)
3. Must have been an inherently bipolar
explosion of the star (ROTATION?).
Almost 75% of total mass and more than 90% of total KE above θ = 45°…
Instabilities (or lack thereof) in
the smooth H2 shell…
Gemini South/Phoenix
R=60,000
Structure does not resemble typical
Rayleigh-Taylor instabilities.
Instead, it looks like a clumpy,
fragmented thin shell.
Suggests structure is not dominated by gasdynamic
effects, but by thermal instabilities/fragmentation of
a dense thin shell shortly after ejection.
1.644 m [Fe II]
2.122 m H2 1-0 S(1)