The Physical Properties of Red Supergiants Emily Levesque IfA, University of Hawaii/SAO, Harvard Hot Massive Stars: A Lifetime of Influence Lowell Observatory

The Physical The Physical Properties of Red Properties of Red

SupergiantsSupergiants

Emily Levesque Emily Levesque

IfA, University of Hawaii/SAO, HarvardIfA, University of Hawaii/SAO, Harvard

Hot Massive Stars: A Lifetime of InfluenceHot Massive Stars: A Lifetime of InfluenceLowell Observatory Lowell Observatory

10.13.0810.13.08

Collaborators:Collaborators:Philip Massey (Lowell Observatory)Philip Massey (Lowell Observatory)

Knut Olsen (NOAO) Knut Olsen (NOAO)

Bertrand Plez (Université de Bertrand Plez (Université de Montpellier)Montpellier)

Eric Josselin (Université de Eric Josselin (Université de Montpellier)Montpellier)

Andre Maeder (Geneva Observatory)Andre Maeder (Geneva Observatory)

Georges Meynet (Geneva Observatory)Georges Meynet (Geneva Observatory)

Geoff Clayton (Louisiana State Geoff Clayton (Louisiana State University)University)

Dave Silva (NOAO/TMT)Dave Silva (NOAO/TMT)

Brian Skiff (Lowell Observatory)Brian Skiff (Lowell Observatory)

• Galactic RSGs - Teff scale - H-R Diagram - Dust & VY CMa• Cloud RSGs - H-R Diagram - WOH-G64 - Spectral types• HV 11423• Where to next?

What What isis a red a red supergiant?supergiant?

Red supergiants are a Red supergiants are a He-He-burningburning evolutionary stage evolutionary stage of of moderately high-mass moderately high-mass (10 - 40 M(10 - 40 M)) stars. stars.

• physically largest stars in the physically largest stars in the universeuniverse

• high visual luminosities (Mhigh visual luminosities (MVV = -6 = -6 to -9) allow study beyond our to -9) allow study beyond our galaxygalaxy

• populate upper right region of populate upper right region of HRD HRD

Red Supergiants and the H-R Red Supergiants and the H-R DiagramDiagram

Why are we interested in Why are we interested in them?them?

Massive star evolutionary tracks didn’t agree with the position of red supergiants on the H-R diagram.


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are needed to see this picture.

Levesque et al. 2005

Hayashi Hayashi limit limit





forbiddenforbidden region region


Red Supergiants and the H-R Red Supergiants and the H-R DiagramDiagram

Why are we interested in them?Why are we interested in them?

Massive star evolutionary tracks don’t agree with the position of red supergiants on the H-R diagram.

Why?- Difficulties with the evolutionary tracks:

uncertain opacities highly extended atmosphere high-velocity convective layers

- …or problems with the observationally-determined location of these stars






Fitting Red Supergiant SpectraFitting Red Supergiant Spectra

How do I get the parameters from How do I get the parameters from spectral fitting?spectral fitting?












TiO band strengthsTiO band strengths














We can fit spectrophotometry of RSGswith the MARCS stellar atmosphere models:

K2 I 4000 K K5 I 3750 K

M3 I 3500 KM1 I 3625 K






Determining Physical Determining Physical PropertiesProperties What we observe: , ,

What we want:


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MW











Excess NUV flux, correlated with high “excess”

reddening excess circumstellar dust

adapted from Levesque et al. 2005

Dust and Red SupergiantsDust and Red Supergiants• Galactic RSGs - Teff scale - H-R Diagram - Dust & VY CMa• Cloud RSGs - H-R Diagram - WOH-G64 - Spectral types• HV 11423• Where to next?

For Milky Way RSGs, dust production rate is about8.5 x 10-9 M yr-1 kpc2

In starburst galaxies at large lookback times, we would expect RSGs to be major contributors to the ISM



• What are the mechanisms that drive this dust production?

• How does this mass-loss relation change with metallicity?

• What reddening law does the dust follow? How does this affect our determinations of RSG luminosities?

Dust and Red SupergiantsDust and Red Supergiants• Galactic RSGs - Teff scale - H-R Diagram - Dust & VY CMa• Cloud RSGs - H-R Diagram - WOH-G64 - Spectral types• HV 11423• Where to next?

VY Canis MajorisVY Canis Majoris: a particularly unusual RSG -extraordinarily luminous -large dust reflection nebula, high mass loss rate -previous work assigned a very cold temperature (2800 K)


adapted from Massey et al. 2006





!

VY CMa


VY Canis MajorisVY Canis Majoris: a particularly unusual RSG -extraordinarily luminous -large dust reflection nebula, high mass loss rate -previous work assigned a very cold temperature (2800 K)



3650 K

3450 K

Massey et al. 2006

VY CMa

We measured a much warmer temperature of ~3650 K, which in turn suggests a much smaller radius and a lower luminosity.

(note additional fit in the blue, showing a disparity between red and blue lines)






adapted from Massey et al. 2006

but…but…




- luminosity of dust emission is ~5 times higher than our reported VY CMa luminosity!

- suggests our measure of the luminosity is too low

Smith et al. 2001

…our luminosity estimate is contradicted by VY CMa’s measured thermal dust emission

One explanation: If the circumstellar dust envelope is large-grain and “grey”, this would lead to our underestimate of VY CMa’s luminosity.


Red Supergiants in the Magellanic Red Supergiants in the Magellanic CloudsClouds



LMCLMC


0.47Z





LMCLMC


0.47Z





LMCLMC


0.47Z





SMCSMC

0.27Z



LMC SMC

Milky Way






LMCLMC

0.47Z

New effective temperature scales give much better agreement with the LMC:





LMCLMC


0.47Z



LMCLMC


0.47Z




LMCLMC

0.47Z

New effective temperature scales give much better agreement with the LMC:





LMCLMC


0.47Z




LMCLMC


0.47Z

But when it comes to the SMC…





SMCSMC

0.27Z





There’s still a few problems…







SMCSMC

0.27Z





There’s still a few problems…







SMCSMC

0.27Z


weaker MS stellar winds at low metallicityincreased rotational mixing as a resultenhanced He abundance from mixing




LMCLMC

0.47Z

The cool new LMC RSG: WOH The cool new LMC RSG: WOH G64G64





LMCLMC


0.47Z

van Loon et al. (2005) placed it similarly to VY CMa…




LMCLMC

0.47Z






LMCLMC


0.47Z

Ohnaka et al. (2008) recently updated its luminosity…




LMCLMC

0.47Z






LMCLMC


0.47Z

We suspect that Teff still needs to be re-examined…

?


The average RSG subtype in the Clouds shifts to earlier types with decreasing metallicity:

QuickTime™ and aTIFF (Uncompressed) decompressor


adapted from Massey & Olsen 2003

K0-1 K2-5 K5-7 M0 M1 M2 M3 M4 M5

Milky Way Z










LMC 0.47Z


K0-1 K2-5 K5-7 M0 M1 M2 M3 M4 M5









SMC 0.27Z


K0-1 K2-5 K5-7 M0 M1 M2 M3 M4 M5

Shift in Spectral SubtypeShift in Spectral Subtype

1) Line depth effects from changing metallicity







K2 I K5 I

M1 I M3 I


3650 K M2 I (MW), M1-1.5 I (LMC), K5-M0 I (SMC)

LMC SMC

Milky Way


1) Line depth effects from changing metallicity




2) Metallicity-dependent shift of Hayashi limit

Limits of hydrostatic equilibrium get warmer at lower metallicities, imposing limits on how cool (and hence, how late-type), massive stars can get…




Milky Way








LMC








SMC


The Late-Type Red Supergiant The Late-Type Red Supergiant SampleSampleDespite evolutionary limitations, some Cloud RSGs are later than would be expected

Investigated the properties of 7 late-type LMC stars and 5 late-type SMC stars, reobserved in 2005





M 4.5

M 3-4

SMC 055188

LMC 143035


SMC average is K5-M0

LMC average is M 1


HV 11423HV 11423 - an unusual find in the SMC



Massey et al. 2007

Date of Observation2004

Spectral Type:K0 I

Temperature:4300

Reddening (AV):

1.35

V magnitude:11.84

Bolometric magnitude:-9.1





Massey et al. 2007

Date of Observation2004 2005

Spectral Type:K0 I M4 I

Temperature:4300 3500

Reddening (AV):

1.35 0.10

V magnitude:11.84 12.46

Bolometric magnitude:-9.1 -8.5





Massey et al. 2007




Reddening (AV):

1.35 0.10







Massey et al. 2007






Reddening (AV):

1.35 0.10







Massey et al. 2007



Massey et al. 2007




Reddening (AV):

1.35 0.10





Massey et al. 2007



Massey et al. 2007

20042004





Massey et al. 2007



Massey et al. 2007




Reddening (AV):

1.35 0.10





Massey et al. 2007



Massey et al. 2007

20052005





Massey et al. 2007



Massey et al. 2007




Reddening (AV):

1.35 0.10





Massey et al. 2007



Massey et al. 2007


When HV 11423 gets warmer it is also brighter, dustier, and more luminous.

Three more Three more “unusual “unusual finds”…finds”…



M4.5 I

M1.5 I

M4.5 I



M2 I

M4.5 I

M3-4 I



Mo I

M2 I

K2-3 I


Two more SMC stars and one LMC star exhibit the same unusual behaviors: when these stars are warmer they are also brighter, dustier, and more luminous.

While V variability in RSGs is common, such spectral variability is unheard of!

• Galactic RSGs - Teff scale - H-R Diagram - Dust & VY CMa• Cloud RSGs - H-R Diagram - WOH-G64 - Spectral types• HV 11423 & Co.!• Where to next?




20042004







20052005







We suspect that these stars are in a unique unstable We suspect that these stars are in a unique unstable evolutionary state not previously observed in red supergiants.evolutionary state not previously observed in red supergiants.




Where To Next?Where To Next? Continuing to expand our

metallicity rangeIn published work: factor of 4In Local Group: factor of 15!




M31: 2Z 2Z




M31: 2Z…Z? Z




M31: 2Z…Z?

WLM: 0.12Z



Local Group Galaxy Local Group Galaxy SurveySurvey




M31: 2Z…Z?

WLM: 0.12Z

Improved studies of RSGs and dust

Study these variables in more detail!

- What effect does this behavior have on stellar yields and mass-loss-dependent properties?- What new properties and environmental effects should evolutionary models strive to accommodate?- What will these variable stars evolve into?


Questions?Questions?

Mountains from the Cerro Tololo 4-Mountains from the Cerro Tololo 4-metermeter


Documents

The Physical Properties of Red Supergiants Emily Levesque IfA, University of Hawaii/SAO, Harvard Hot Massive Stars: A Lifetime of Influence Lowell Observatory