The Circumstellar Environments of the Cool Hypergiants: Implications for the Mass Loss Mechanism Roberta M Humphreys University of Minnesota VY CMa NML Cyg IRC

The Cool Hypergiants -- lie just below the upper luminosity envelope with spectral types A to M, high mass loss rates, photometric and spectroscopic variability, large infrared excess, circumstellar ejecta Evolutionary state? M supergiants Intermediate – type or “yellow” hypergiants

Intermediate –Type IRC (A – F Ia) rho Cas (F8 p Ia) HR 8752 (G0 – 5 Ia) HR 5171a (G8 Ia) M Supergiants VY CMa (M5e Ia) NML Cyg (M6 I) S Per (M3 – 4 e Ia) VX Sgr ( M4e Ia – M9.5 I) mu Cep (M2e Ia) HST WFPC2 multi-wavelength imaging No detections – rho Cas, HR 8752, HR 5171a, mu Cep VX Sgr and S Per (both OH/IR sources) – both marginally resolved NML Cyg (OH/IR source) -- ejecta shaped by its environment VY CMa and IRC (OH/IR sources) – extensive CS nebula

IRC Strong IR excess High mass loss rate 3-6 x Warmest maser source Spectroscopic variation late F  mid A Complex CS Environment One or more distant reflection shells Within 2 “ – jet-like structures, rays, small nearly spherical shells or arcs Evidence for high mass loss ejections in the past few hundred years

IRC – excellent candidate for post– red supergiant evolution In post RSG evolution, these stars will enter a region ( K) of increased dynamical instability, high mass loss, increasing opacity – deJager’s “yellow void” HST/STIS spatially resolved spectroscopy – Halpha – uniform outflow, nearly spherical distribution Wind is optically thick  variations in apparent temperature not due to evolution Mass loss history Origin of ejecta – stellar activity, convection and magnetic fields?

rho Cas and the yellow hypergiants rho Cas – famous shell ejection episodes, , , 2002 develops TiO bands, very high but temporary mass loss (~ ), quickly returns to its normal F-type supergiant spectrum  formation of an optically thick wind Most recent 2002 – variability indicative of pulsational instability. Lobel et al (2003) demonstrated the outburst was due to the recombination of H as atmosphere cooled due to expansion.

Variable A in M33 – a cool hypergiant ~ 45 years in eruption! One of the original Hubble – Sandage variables. “Eruption” or shell ejection began in faded 3 mags or more becoming very red. Spectrum M supergiant, CS IR excess Spectrum and energy distribution F-type, bluer, but stayed faint.

NML Cyg – Circumstellar Ejecta Interacting with Its Environment Optically obscured star embedded in a small asymmetric bean-shaped nebula, strong OH/IR source, 6 x Similar in shape to HII contours (30” away) due to interaction of RSG wind with ionizing photons hot stars in Cyg OB2 Schuster, Humphreys & Marengo (2006) showed this is the molecular photodissociation boundary

VY CMa -- the extreme red supergiant, powerful OH/IR source Famous asymmetric red nebula, > 10” across, visible in small ground based telescopes. HST/WFPC2 images revealed complex environment – numerous knots, filamentary arcs, prominent nebulous arc Due to multiple, asymmetric ejection episodes -- analogous to solar/stellar activity mass loss rate 4 x 10 -4

High Resolution, Long-Slit Spectroscopy --Keck HIRES Spectrograph Reflected absorption lines -- A strong velocity gradient across the NW arc Moving mirror effect -> expanding at 50 km/s

K I emission lines Across the NW arc

K I emission -- across Arcs 1 and 2

2 nd epoch images > 6 yrs later  transverse motions Combined with radial or Doppler velocities  total space motion and direction of motion Results: Expansion velocities relative to star and ejection times NW Arc + 46 km/s at ~ +22 o towards WNW, ~ 500 yrs ago Arc km/s at -33 o towards SW, ~ 800 yrs ago Arc km/s at -17 o towards SSE, ~ 460 yrs ago SW knots -36 km/s at -25 o towards W, ~ 250 yrs ago S knots -17 km/s at -27 o towards SE, ~ 160 yrs ago

VY CMa -- Work in Progress, polarimetry with HST/ACS VY CMa is highly polarized -- up to 70% 3D Morphology of VY CMa Polarization combined with color  relative distance along line of sight Together with space motion and vector

What drives the mass loss of red supergiants and cool hypergiants ?? Pulsational instability? -- rho Cas, irregular and LPVs Non-radial pulsations and/or convective activity (starspots)? VY CMa – no general spherical outflow, looplike structures, clumps of knots, ejected at different times and from different positions on star. Magnetic field ~ 1 – 2 G SiO masers IRC – outermost arcs ~ 3000 yrs ago  RSG, but looplike structures, arcs and knots close to star, high mass loss episode < 600 yrs ago ended ~ 90 yrs ago. Magnetic field 1 mG OH masers  few G at star

Supernova Impostors -- = SN1954j Recent examples V1 in N 2363 SN 1997bs in N 3627 SN 1999bw in N 3198 SN 2000ch in N 3432 SN 2001ac in N 3504 SN 2002kg = V74 in N 2403 SN 2003gm in N 5334 SN 2003hy in IC 5145