Stellar water fountainsHiroshi Imai (Kagoshima University)

Contents• Discovery and identification

of the water fountains• Properties of the water fountains and

circumstellar envelopes– Stellar evolution and the water fountains– Corkscrew jets? Equatorial flows?– Precursors of water fountains?

• Stellar kinematics in the Galaxy• Earlier than the water fountain phase

• Summary

From spherically symmetric

to asymmetric mass loss flow

When/how is a bipolar jet launched in the final stellarevolution?

Betelgeuse NASAⓒ

Egg Nebula NASAⓒ

First high velocity flow seen in

water maser emission

W43A (Genzel & Downes 1977)“This is an extremely interesting source,

probably a late-type star.”

but might be a young stellar object?

“Water fountains” in AGB/post-AGB phases

• Associated with evolved stars

• Faster than expansion velocity of

OH maser shell(Vexp >> 30 km/s)

W43A

IRAS16342-3814

IRAS19134+2131

High velocity H2O maser sources(Likkel et al. 1992)

10 water fountains identified to date – W43A (Diamond et al. 1985; Imai et al. 2002, 2005; Vlemmings et al. 2006)– IRAS19134+2131 (Imai et al. 2004; 2007) – IRAS16342-3814 (Sahai et al. 1999; Morris et al. 2003; Claussen et al. 2004)– OH 12.8-0.9 (Boboltz & Marvel 2005)

– IRAS18286-0959 (Imai et al. 2007) – IRAS18460-0151 (Imai et al. 2007)– IRAS18596+0315 (Deacon et al. 2007)– IRAS15445-5449 (Deacon et al. 2007)– IRAS15544-5332 (Deacon et al. 2007)– IRAS18043-2116 (Deacon et al. 2007)

W43A: First identification ofa water fountain in maser images

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Imai et al. 2002Nature 417, 829

Periodic OH maser variation (P~360 days) (Hertman & Habing 1985)

Jet velocity =145 km/s, dynamical age ~50 yr

Quenching water fountainwithin < 1000 years

Continuum radio emission (=planetary nebula) and H2O/OH masers in K3-35

(Miranda et al. 2001)

Photodissociation destroying

H2O moleculesCollimated jet before full

photoionizationDispersing water fountain in Pre-PN phase5000 AU

IRAS 19134+2131

• Optically visible → in pre-planetary nebula (PPN) phase

• Flow dynamical age ~50 years

Imai et al. (2007)

HST image

-23 - -10 km/s -121- -117 km/s

Dynamical ages < 100 years

IRAS 16342-3814(Morris, Sahai & Claussen 2003)

OH 12.8-0.9(Boboltz & Marvel 2005)

W43A: AGB phase

• No nebulosity, detected by SPITZER GLIMPSE (Deguchi et al. 2007)• OH maser shell (R~500 AU, Vexp=9km/s)• SiO maser detection (Nakashima & Deguchi 2002)• Dust envelope radius < 3000 AU • Dynamical age T~ 260 yr (OH), 1600 yr (dust)

W43A details: Jet precession

• Precession period ~55 years• Precession angle amplitude ~5°• (10-year scale) length growth speed

≈ (1-year scale) maser feature proper motions

Imai et al. 2005

Magnetohydrodynamical (MHD) jet

• Zeeman effect and linear polarization(Vlemmings, Diamond & Imai 2006, Nature 440, 58)

Bow shock?Spiral flow?

(VLA)

500 AU at 8 kpc

(VLBA)

(VLBA)

Imai et al. (2004) Imai et al. (2007) IRAS19134+2131

Corkscrew jets?Bow shocks?

W43A (Imai & Diamond in prep)

IRAS16342-3814 (Sahai et al. 2005)

Biconical SiO maser flow

(~15 km/s)|

within 10 AU|

H2O maser jet

(Imai et al. 2005)(Imai et al. in prep.)

SiO/H2O and continuum locations

Where is a disk?

Equatorial flow?

Proper motion in the equatorial flow

W43A (Imai & Diamond in prep)

• Flow velocity ~30 km/s

New water fountains

IRAS 18286-0959(Deguchi et al. in prep.)

New water fountains

IRAS 18460-0151(Deguchi et al. in prep.)

Equatorial flow ?(see Miyaji’s talk)

Maser source astrometry with position-reference QSO

Galacticrotation

H2O masers in IRAS 19134+2131 (Imai et al. 2007)

Annual parallax and Galactic rotation

Location and velocity

in the Galaxy

IRAS 19134+2131(Imai et al. 2007)

– Annual parallax distance = 8.0+0.9-0.7 kpc

– Location: (R, θ, z)=(7.4 kpc, 62deg, 650 pc)– 3D velocity (VR, Vθ, Vz) =(3, 125, 8)[km/s]

• Travel time from the Galactic plane > 7.7 x 107 years >> M*< 5 Msun

c.f. Progenitors of bipolar nebulae may be higher mass stars located near the Galactic plane.

SummaryMagneto-hydrodynamicalCorkscrew/precessing jetV> 100 km/s, T~100 years

Equatorial flow V~ 20-30 km/sEvolution from AGB flow?

M*< 5 Msun single AGB/post-AGB star(or binary <10 AU?)

Only 10 water fountainsin the whole Galaxy?