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The Physical Properties of Red Supergiants

The Physical Properties of Red Supergiants. Emily Levesque IfA, University of Hawaii/SAO, Harvard. Hot Massive Stars: A Lifetime of Influence Lowell Observatory 10.13.08. Collaborators: Philip Massey (Lowell Observatory) Knut Olsen (NOAO) Bertrand Plez (Université de Montpellier)

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The Physical Properties of Red Supergiants

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  1. The Physical Properties of Red Supergiants Emily Levesque IfA, University of Hawaii/SAO, Harvard Hot Massive Stars: A Lifetime of InfluenceLowell Observatory 10.13.08

  2. Collaborators: Philip Massey (Lowell Observatory) Knut Olsen (NOAO) Bertrand Plez (Université de Montpellier) Eric Josselin (Université de Montpellier) Andre Maeder (Geneva Observatory) Georges Meynet (Geneva Observatory) Geoff Clayton (Louisiana State University) Dave Silva (NOAO/TMT) Brian Skiff (Lowell Observatory)

  3. 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 is a red supergiant? • Red supergiants are a He-burning evolutionary stage of moderately high-mass (10 - 40 M) stars. • physically largest stars in the universe • high visual luminosities (MV = -6 to -9) allow study beyond our galaxy • populate upper right region of HRD

  4. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? Red Supergiants and the H-R DiagramWhy are we interested in them? Massive star evolutionary tracks didn’t agree with the position of red supergiants on the H-R diagram.

  5. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? Hayashi limit  Levesque et al. 2005

  6. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? forbidden region Levesque et al. 2005

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

  8. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? Levesque et al. 2005

  9. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? Fitting Red Supergiant Spectra How do I get the parameters from spectral fitting?

  10. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? Fitting Red Supergiant Spectra How do I get the parameters from spectral fitting? TiO band strengths

  11. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? Fitting Red Supergiant Spectra How do I get the parameters from spectral fitting?

  12. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? We can fit spectrophotometry of RSGs with the MARCS stellar atmosphere models: Levesque et al. 2005 K2 I  4000 K K5 I  3750 K M1 I  3625 K M3 I  3500 K

  13. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? Levesque et al. 2005

  14. 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 we observe: , , Determining Physical Properties MW What we want:

  15. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? Levesque et al. 2005

  16. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? Levesque et al. 2005

  17. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? adapted from Levesque et al. 2005 Dust and Red Supergiants Excess NUV flux, correlated with high “excess” reddening  excess circumstellar dust

  18. 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 Dust and Red Supergiants • 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?

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

  20. 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 CMa ! adapted from Massey et al. 2006

  21. 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 Majoris: a particularly unusual RSG-extraordinarily luminous -large dust reflection nebula, high mass loss rate -previous work assigned a very cold temperature (2800 K) 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) VY CMa 3650 K 3450 K Massey et al. 2006

  22. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? adapted from Massey et al. 2006 but…

  23. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? …our luminosity estimate is contradicted by VY CMa’s measured thermal dust emission • luminosity of dust emission is ~5 times higher than our reported VY CMa luminosity! • suggests our measure of the luminosity is too low One explanation: If the circumstellar dust envelope is large-grain and “grey”, this would lead to our underestimate of VY CMa’s luminosity. Smith et al. 2001

  24. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? 0.47Z LMC Levesque et al. 2006 Red Supergiants in the Magellanic Clouds

  25. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? 0.47Z 0.47Z LMC LMC Levesque et al. 2006 Levesque et al. 2006 0.27Z Red Supergiants in the Magellanic Clouds SMC Levesque et al. 2006

  26. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? Milky Way  SMC  LMC  Red Supergiants in the Magellanic Clouds Levesque et al. 2006

  27. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? 0.47Z LMC Levesque et al. 2006 0.47Z 0.47Z New effective temperature scales give much better agreement with the LMC: LMC LMC Levesque et al. 2006

  28. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? 0.47Z 0.47Z New effective temperature scales give much better agreement with the LMC: LMC LMC Levesque et al. 2006

  29. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? 0.47Z LMC Levesque et al. 2006 0.27Z But when it comes to the SMC… SMC Levesque et al. 2006

  30. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? 0.27Z There’s still a few problems… SMC Levesque et al. 2006

  31. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? 0.27Z There’s still a few problems… weaker MS stellar winds at low metallicity increased rotational mixing as a result enhanced He abundance from mixing SMC Levesque et al. 2006

  32. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? 0.47Z 0.47Z The cool new LMC RSG: WOH G64 van Loon et al. (2005) placed it similarly to VY CMa… LMC LMC Levesque et al. 2006

  33. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? 0.47Z 0.47Z The cool new LMC RSG: WOH G64 Ohnaka et al. (2008) recently updated its luminosity… LMC LMC Levesque et al. 2006

  34. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? 0.47Z 0.47Z The cool new LMC RSG: WOH G64 ? We suspect that Teff still needs to be re-examined… LMC LMC Levesque et al. 2006

  35. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? The average RSG subtype in the Clouds shifts to earlier types with decreasing metallicity: Z Milky Way K0-1 K2-5 K5-7 M0 M1 M2 M3 M4 M5 adapted from Massey & Olsen 2003

  36. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? The average RSG subtype in the Clouds shifts to earlier types with decreasing metallicity: 0.47Z LMC K0-1 K2-5 K5-7 M0 M1 M2 M3 M4 M5 adapted from Massey & Olsen 2003

  37. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? The average RSG subtype in the Clouds shifts to earlier types with decreasing metallicity: 0.27Z SMC K0-1 K2-5 K5-7 M0 M1 M2 M3 M4 M5 adapted from Massey & Olsen 2003

  38. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? K2 I K5 I M1 I M3 I Levesque et al. 2005 Levesque et al. 2005 Shift in Spectral Subtype 1) Line depth effects from changing metallicity

  39. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? Milky Way  SMC  LMC  Shift in Spectral Subtype 1) Line depth effects from changing metallicity Levesque et al. 2006 3650 K  M2 I (MW), M1-1.5 I (LMC), K5-M0 I (SMC)

  40. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? Shift in Spectral Subtype 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 Levesque et al. 2006

  41. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? Shift in Spectral Subtype 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… LMC Levesque et al. 2006

  42. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? Shift in Spectral Subtype 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… SMC Levesque et al. 2006

  43. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? The Late-Type Red Supergiant Sample Despite 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 SMC 055188 M 3-4 SMC average is K5-M0 LMC 143035 M 4.5 LMC average is M 1 Levesque et al. 2007

  44. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? 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  HV 11423- an unusual find in the SMC

  45. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? 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 HV 11423- an unusual find in the SMC

  46. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? 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 HV 11423- an unusual find in the SMC

  47. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? 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 HV 11423- an unusual find in the SMC

  48. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? Massey et al. 2007 Massey et al. 2007 Massey et al. 2007 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 HV 11423- an unusual find in the SMC 2004

  49. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? Massey et al. 2007 Massey et al. 2007 Massey et al. 2007 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 HV 11423- an unusual find in the SMC 2005 Be sure to say what it’s doing explicity HERE; don’t wait until the next slide: warmer = brighter, dustier, more luminous

  50. Galactic RSGs • - Teff scale • - H-R Diagram • - Dust & VY CMa • Cloud RSGs • - H-R Diagram • - WOH-G64 • - Spectral types • HV 11423 • Where to next? Massey et al. 2007 Massey et al. 2007 Massey et al. 2007 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 HV 11423- an unusual find in the SMC When HV 11423 getswarmer it is also brighter, dustier, and moreluminous. Be sure to say what it’s doing explicity HERE; don’t wait until the next slide: warmer = brighter, dustier, more luminous

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