RSGs and AGBs in the Optical and Infrared -- Mass Loss, Circumstellar Ejecta and Episodic Events Roberta M Humphreys University of Minnesota VY CMa IRC +10420 ESO Workshop – Stellar End Products June 2015 Cep NML Cyg
Jan 16, 2016
RSGs and AGBs in the Optical and Infrared -- Mass Loss, Circumstellar Ejecta and Episodic Events
Roberta M Humphreys University of Minnesota
VY CMa
IRC +10420
ESO Workshop – Stellar End Products June 2015
Cep
NML Cyg
A Little Bit of History – infrared, CS dust, RSGs, AGBs, masers and the OH/IR stars
10 silicate feature in RSGs
(Woolf and Ney 1969)
LPVs – oxygen and carbon-rich
OH maser emission (Wilson & Barrett 1968) from LPVs, and very red supergiants, followed by H2O, SiO maser emission. Identified with strong infrared sources (Wilson, Barrett &Moran 1970, Hyland 1972) -- the OH/IR stars – RSGs, LPVs (AGBs)
Mass loss mechanism ? -- radiation pressure on grains? pulsation (LPVs) convection (RSGs) But ---
The Upper HR Diagram
The evidence for episodic high mass loss events
VY CMa -- the extreme red supergiant, powerful OH/IR source
Due to multiple, asymmetric ejection episodes possibly from large-scale convective regions on the star.
1” = 1500 AU
10”
Smith, Humphreys, Davidson, Gehrz, & Schuster, 2001
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
NW Arc
Arc 2
Arc 1
S Knots SW Knots/clump
Complex structure in ejecta
Prominent arcs, numerous filaments and clumps of knots, overall mass loss rate 5 x 10-4
Humphreys, Davidson, Ruch & Wallerstein 2005
High Resolution, Long-Slit Spectroscopy --Keck HIRES Spectrograph
From surface brightness of NW arc mass ~ 3 x 10-3 Msun . With a
dynamical timescale of ~ 3yrs, suggest a mass loss rate of 10-3
2D spectra of strong K I emission lines across the arcs
NW Arc
Arcs 1 and 2
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
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
Results from LMIRCam (2 – 5m) 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 .
Shenoy, et al. 2013
Clump is optically thick. Mass loss > 5 x 10-3 Msun
SOFIA imaging 20 – 37 m
37m contours on HST visual image
Note asymmetric shape. Outer ejecta at most about 1500 yrs old
Shenoy et al. 2015 submitted
Ziurys et al 2007 noted molecules in red/blue outflows. 8.5 arcsec
Asymmetric Mass Loss Events and the 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 – Ori, Sco, Her, VX Sgr, NML Cyg, VX Sgr, IK Tau etc. (Tuthill et al. 1999, Monnier et al. 2004)
Convective activity Magnetic Fields 200 – 400G (Vlemmings et al. 2005)
VY CMa light curve (Robinson 1971)
XMM observations (Montez, Kastner, Humphreys et al. 2015) set an upper limit on the X-ray flux and the surface magnetic field, f B <= 2 x 10-3G.
9 -12 m imaging MMT/MIRAC/AO
Recent results on the iconic RSG – Cep
Shenoy et al. 2015 submmited
Mass loss for inner region – 3– 8 10-7 Msun/yr
SOFIA 11- 37 m
Herschel 70m (Cox et al 2012)
Shenoy et al. 2015 submitted
Mass loss outer ejecta 6 x 10-7 Msun/yr
Post-RSGs ( and post-AGBs) and a dynamical instability
The Warm Hypergiants and post RSG evolution
IRAS 17163-3907 – 12m (the fried egg) Lagedec et al 2011
HD179821 – 11.7 um (Jura & Werner 1999)Post RSG or AGB?
Jones et al 1993 Oudmaijer et al 1994, 1996Humphreys et al.1997, 2002
Other examples of post RSGs ( Cas, HR5171a, HR8752 etc.)
IRC+10420
Variable A in M33 – a warm hypergiant ~ 45 years in eruption!
Var A – Spectrum and Circumstellar IR excess
Humphreys et al. 1987, 2006
45 years in “eruption”Cool dense windLooked like an M supergiant
Other supergiants
NML Cyg (M6 I, OH/IR) -- extended CS ejecta (HST)S Per (M4 Ia, OH/IR) -- extended CS ejecta (HST/MIRAC/SOFIA) VX Sgr (M4 Ia –M8 , OH/IR) -- extended CS ejecta (HST) W Per (M3 Iab) -- null RW Cep (K0: Ia +) -- extended CS ejecta (MIRAC) RW Cyg (M3-4 Ia) -- extended CS ejecta (MIRAC) BD +24 3902 (M1 Ia+ ) -- extended CS ejecta (MIRAC) T Per (M2 Iab) -- extended CS ejecta (MIRAC)
A correlation among:
Surface asymmetries (spots) -> convective cells? -> mass loss -> circumstellar dust/ejecta
Enhanced surface activity -> high mass loss events -> complex CS ejecta
Mass loss mechanism for RSGs? Pulsation Convection + ?
Some thoughts on the evolutionary state of the RSGs
Why not more VY CMa’s ?
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) ?
Evidence for increased mass loss, CS ejecta with higher luminosity and cooler temperatures (?)
Clusters – RSG clusters (Figer, Davies, Clark) Stepenson2, N7419 (Negueruela)and even Per OB1
Collaborators Kris Davidson
Andrew HeltonGeorge HerbigTerry J. JonesGerald Ruch Dinesh ShenoyNathan Smith George Wallerstein
Kris Davidson Terry J. JonesDinesh ShenoyNathan SmithChelsea Tiffany
Terry J. Jones
Massimo Marengo
Dinesh Shenoy
Michael Schuster
Michael SchusterMassimo Marengo