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LBVs, Hypergiants, and Impostors – the Evidence for High Mass Loss Events

LBVs, Hypergiants, and Impostors – the Evidence for High Mass Loss Events. Roberta M Humphreys University of Minnesota. Pacific Rim Conference on Stellar Astrophysics. Dec. 2015. The Upper HR Diagram. The evidence for episodic high mass loss events.

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LBVs, Hypergiants, and Impostors – the Evidence for High Mass Loss Events

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  1. LBVs, Hypergiants, and Impostors – the Evidence for High Mass Loss Events Roberta M Humphreys University of Minnesota Pacific Rim Conference on Stellar Astrophysics. Dec. 2015

  2. The Upper HR Diagram The evidence for episodic high mass loss events

  3. VY CMa -- the extreme red supergiant, powerful OH/IR source 10” Distance ~ 1.3 kpc Luminosity ~ 3 x 105 L sun Initial Mass ~ 30 M sun Mass Loss rate 2 -- 4 x 10-4 M sun / year Size ~ 8 -- 10 A.U., or ~ 1500 -- 2000 Rsun It is visible as a small red nebula ~ 10 arcsec across 1” = 1500 AU Due to multiple, asymmetric ejection episodes possibly from large-scale convective regions on the star. Smith, Humphreys, Davidson, Gehrz, & Schuster, 2001

  4. High Resolution, Long-Slit Spectroscopy --Keck HIRES Spectrograph 2D spectra of strong K I emission lines across the arcs NW Arc Arcs 1 and 2

  5. Second epoch HST images Measure transverse velocities combined with radial velocities long slit spectra (Keck) of K I em line (resonant scattering) Total velocity, orientation, direction and age  3D morphology Feature Vel. Orientation Direction Age (yrs) km/s relative to sky of motion NW arc 46 22 degrees ~ west 500 Arc 1 68 -33 SW 800 Arc 2 64 -17 ~ south 460 SW knots 36 -25 ~ west 250 S knots 42 -27 SSE 157 SE loop 65 -21 SE 320 Humphreys, Helton & Jones, 2007, Jones, Humphreys, & Helton 2007

  6. Results from LMIRCam (2 – 5mm) on the LBT with AO The SW clump – in the visible resolved into individual knots but very red and dusty. In the near-IR an unresolved knot . Clump is optically thick. Mass > 5 x 10-3Msun Shenoy, et al. 2013 ALMA obs. At 321 & 658 GHz: O’Gorman et al. (2015) Mass 2 – 4 x 10-3 Msun

  7. Origin of the Discrete Ejecta Arcs and Knots are spatially and kinematically distinct; ejected in different directions at different times; not aligned with any axis of symmetry. They represent localized, relatively massive (few x 10-3 Msun) ejections Large-scale surface activity -- starspots Surface asymmetries supergiants, AGBs (Tuthill et al. 1999, Monnier et al. 2004) Convective activity  Magnetic Fields200 – 400G (Vlemmings et al. 2005) magnetic fields measured in ejecta (OH, H2O, SiO masers) VY CMa, VX Sgr, S Per, NML Cyg etc.

  8. SOFIA imaging 20 – 37 mm Note asymmetric shape. Outer ejecta at most about 1200 yrs old avg mass loss rate 6 x 10 -4 37mm contours on HST visual image Shenoy et al. 2015

  9. Interesting Chemistry 20 different molecules in the ejecta (Ziurys et al. 2007, 2009) including carbon molecules CO, HCN, CS, HNC, CN, HCO+ . HNC and sulfur compounds in the outflows. Suggest C molecules produced in shocks in the outflows (also NML Cyg) Kwok (2008) Another chemical peculiarity – 12C/13C ratio 25– 46 , compared to 3 -14 in O rich supergiants (Milam et al. 2009) Ti02 @ 312 - 314 GHz: de Beck et al. (2015)

  10. Post-RSGs ( and post-AGBs) and a dynamical instability

  11. The Warm Hypergiants and post RSG evolution HD179821 – 11.7 um (Jura & Werner 1999) Post RSG or AGB? IRC+10420 IRAS 17163-3907 – 12mm (the fried egg) Lagedec et al 2011 Jones et al 1993 Oudmaijer et al 1994, 1996 Humphreys et al.1997, 2002 Other examples of post RSGs (Var A in M33, r Cas, HR5171a, HR8752 etc.)

  12. The Yellow or Intermediate-type Post Red Supergiant IRC +10420 Strong IR excess L ~ 5 x 105 Lsun High mass loss rate 3-6 x 10-4 Warmest maser source Spectroscopic variation late F  mid A Complex CS Environment One or more distant reflection shells ejected ~3000 yrs ago Within 2 “ – jet-like structures, rays, small nearly spherical shells or arcs Evidence for high mass loss ejections in the past few hundred years 1” = 5300 AU Jones et al 1993 Oudmaijer et al 1994, 1996 Humphreys, Smith, Davidson, Jones, et al.1997 Humphreys, Davidson & Smith, 2002

  13. 3D Morpholgy of IRC +10420 – 2nd epoch images from HST spectra from HST/STIS Numerous, arcs, knots ejected at different times (100- 400 yrs), directions, and all within a few degrees of plane – viewing nearly pole-on Tiffany, Humphreys, Jones & Davidson 2010 Oudmaijer and de Wit 2013 VLT interferometry Shenoy et al 2014 polarimetry Semi-circular arcs – expanding bubbles? or loops?

  14. Maser distribution IRC +10420 -- circular polarization of OH (Nedoluha & Bowers 1992) -> 300 – 400 G at the star (based on Vlemmings 2008) Arcs and loops associated with surface activity SOFIA, MIRAC, LMIRCam, 2 – 37mm 2 mass loss episodes (Shenoy et al. 2015), 2 x 10-3 Msun up until 2000 yrs ago, ~ 10-4 Msun . Mass lost in earlier ~ 7 Msun

  15. The Evolutionary State and Mass loss mechanism for RSGs , post-RSGs ? Pulsation Convection + ? A correlation among: Surface asymmetries (spots) -> convective cells? -> mass loss -> circumstellar dust/ejecta Enhanced surface activity -> magnetic activity? -> high mass loss events -> complex CS ejecta

  16. Some thoughts on the evolutionary state of the RSGs Why not more VY CMa’s ? Evidence for increased mass loss, CS ejecta, with higher luminosity and cooler temperatures Do RSGs evolve through the red supergiant stage getting apparently cooler, more extended envelopes and high mass loss episodes? Like lower mass stars, could there be more than one RSG stage?  warm hypergiant  RSG again – extreme RSG (VY CMa) ?

  17. Luminous Blue Variables (LBVs) Conti (1984) suggested -- “luminous blue variable” eta Car vars, P Cyg stars, S Dor vars, H-S vars

  18. What is an LBV/S Dor variable? Distinguished by their photometric and spectroscopic variability In quiescence – hot, luminous star, sp. types late O to mid B, Of/WN7 Some emission lines H, He I, Fe II, P Cyg profiles mass loss rates – typical In “eruption” – rapid rise in apparent visual brightness -- weeks – months apparent shift in sp. type ( late A to early F) or apparent temp -- shift in bolometric correction ~ constant luminosity star develops, slow, dense, optically thick wind mass loss rate increases ~ 10-4 – few x 10-5 Msun/yr) this optically thick wind stage may last years – decades R127 (Walborn et al. 2008)

  19. S Doradus or LBV Instability Strip Wolf (1989) Note – in “eruption” – all about same temp ~ 7500 – 8000K Davidson (1987) – opaque wind model (as opacity and mass loss rate increase, temperature approaches a minimum)

  20. Examples of reflection nebulae associated with LBVs (K. Weis) ejecta and atmospheres are N and He rich  Evolved post MS Same linear scale Weis 2008

  21. The Cause of the Instability? Most explanations -- the star is near the Eddington Limit LEdd = 4pcGMsun/k , GEdd = const k (L/Lsun) (M/Msun) -1 Opacity modified limit is temperature dependent 1. opacity – modified Eddington Limit (Davidson, Lamers, Appenzeller) as temp decreases, opacity increases (“bi-stability jump”, Pauldrach & Puls 1990 Lamers et al 1995) 2. Omega limit -- add rotation to the Eddington Limit (Langer) W = vrot/vcrit > 1, v2crit = (1 –G) GM/R 3. Vibration/Pulsation -- e mechanism (in the core) no longer considered applicable to evolved stars -- k mechanism in the envelope periods of weeks to months 4. Sub-photospheric – violent mode or strange mode instabilities Glatzel et al, Guzik, Stothers & Chin Caused by increase in opacity due to Fe at base of photosphere leading to ionization induced instability

  22. For stars > 30 --40Msun -- do not become RSGs, this is a critical high mass loss stage For lower mass stars – have been RSGs, lowered surface gravity Problem: – the S Dor instability strip has not been explained ! -- it depends on initial mass of star -- note there are normal hot stars in the strip and a few to the right

  23. Giant Eruptions and Supernova Impostors Giant Eruption LBVs (Humphreys & Davidson (1994) -- increase their luminosity during the eruption SN 1954J Zwicky’s Type V SN

  24. Collaborators VY CMa Kris Davidson Andrew Helton George Herbig Terry J. Jones Gerald Ruch Dinesh Shenoy Nathan Smith George Wallerstein LBVs Dominik Bomans Kris Davidson Kerstin Weis IRC+10420 Kris Davidson Terry J. Jones Dinesh Shenoy Nathan Smith Chelsea Tiffany h Car Kris Davidson Bish Ishibashi John Martin Andrea Mehner

  25. Variable A in M33 – a warm hypergiant ~ 45 years in eruption!

  26. Var A – Spectrum and Circumstellar IR excess 45 years in “eruption” Cool dense wind Looked like an M supergiant Humphreys et al. 1987, 2006

  27. NML Cyg Optically obscured RSG embedded in a small asymmetric bean-shaped nebula, strong OH/IR source mass loss rate 6 x 10-5 L ~ 5 x 105Lsun HII contours (30” away) due to interaction of RSG wind with ionizing photons hot stars in Cyg OB2 (Morris & Jura 1983) 0”.25 = 500 AU Schuster, Humphreys & Marengo (2006) , Schuster et al. (2009) showed this is the molecular photodissociation boundary 21 cm HI recombination

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