Evolution and mass loss of evolved stars explored

in radio emission

Hiroshi Imai Department of Physics and Astronomy,

Graduate School of Science and Engineering Kagoshima University

Outline 1.  Final stage of stellar evolution: HR diagram, nucleosynthesis

2.  Asymptoric giant branch (AGB) stars and radio emission: dust continuum and molecular line emission

3.  VLBI observations of stellar maser emission (microwave amplification by stimulated emission of radiation): Exploration of 3-D spatio-kinematics

4.  Pulsation-driven shock waves in circumstellar envelopes of AGB stars

5.  Cosmic “water fountain” sources traced by maser emission

6.  VLBI astrometry and exploration of AGB envelopes

7.  Current research activity –  International collaboration –  Activities in Kagoshima University

Stellar evolution in HR diagram

Maser excitation t~105years

Stellar mass loss rate: dM/dt > 10-7 Msunyr-1 during AGB, (cf. >10-9 Msunyr-1 during RGB,10-12 Msunyr-1 from Sun)

Stellar evolution in HR diagram (Harwig 2005)

Contribution to cosmic elementary evolution

Fast evolution, rare slow evolution, many quick feedback long-term feedback Fe, Ni, Si Ne, Mg O, N C He r-process s-process (e.g., Au, U) (s.g. S)

Asymptoric giant branch (AGB) stars seen in

infrared and radio continuum emission

•  Heavily obscured in optical emission

•  Poor angular resolution

•  Faint for distant sources

(for CO emission)

Betelgeuse (Mira variable) ⓒ NASA 20000 AU at 2.6 kpc

+ H2O & OH masers

NMA (2.7 mm) (Imai+)

W43A (OH/IR star) (Deguchi + 2007)

Spitzer/GLIMPSE (MIR-FIR)

HST(optical)

AGB stars seen in maser emission  Cluster of

“maser features” resolved by VLBI　

 SiO: indicative of current copious stellar mass loss

 H2O: indicative of envelope development

 OH @1612MHz: indicative of

“super winds” dM/dt >10-4 Msunyr-1

within t<<104 years SiO/H2O/OH masers in VX Sgr

(Chapman & Cohen 1986)

1 arcsec (~1000 AU)

Acceleration of mass loss flow

Reid & Menten 1997

OH masers

H2O masers (for O-rich envelope)

SiO masers (Si in molecule)

Radiative pressure on dust

SiO masers around Mira variable   Stellar radius

measured with VLTI(model fitting)

  Angular resolution of VLBI: 0.1ー10 mas

  Ring pattern caused by tangential maser amplification

  Spherical expansion+large deviation in the spherical flow

  Expansion velocity within 10 km/s (cf. water fountains)

Size of the star

SiO v=1 J=1-0 maser emission around TX Cam (Diamond & Kemball 2003)

Big problems in AGB envelopes •  Stellar pulsation and circumstellar envelope

– Continuous acceleration or shock wave transfer? – Acceleration affected by chemical abundance

•  Asymmetrical stellar mass loss – Large convection cells floating on stellar surface – Driving highly-collimated fast jets (water fountains) – Shaping planetary nebulae

•  Evolution of chemical abundance in envelope – Hot-bottom burning – Binary evolution?

Why periodic variation in H2O masers?

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Single dish observations of H2O masers in a semiregular variable W Hydrae (Shintani+2008)

•  Collisional excitaion of H2O maser emission

E(kinematic) ⇒E(maser) (c.f. Radiative excitation of

SiO and OH maser emission) •  Shock waves should be

taken into account –  Large time lag in flux

variation curve from optical/IR variation curves

Model prediction of the shock waves

Model of dust-induced pulsation-driven shock waves ( Hofner+ 1995 )

Acceleration by shock waves (ΔV~10 km s-1/2-3 month)

Detection of an accelerating blob?

RT Virginis (Imai + 2003)

Acceleration detectable in a proper motion (within a few months) rather than in a line-of-sight velocity.

Why from only one feature?

Transition from spherically symmetric

to asymmetric mass loss flow in AGB phase

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

Egg Nebula ⓒ NASA

Betelgeuse ⓒ NASA

Hen2-90 (Sahai et al. 1998)

water fountain= collimated fast stellar jet

Very fast (>100 km/s) from AGB/post AGB starts Very young/short lived (<100 years)

Very drastic (dM/dt>10-4Msunyr-1)

H2O masers in W43A (Imai & Diamond 2008)

SPITZER/GLIMPSE image around W43A (Deguchi+ 2007)

11 water fountain sources (2008)

V

V V

V V

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V: VLBA/VERA observations 12 WFs until 2009 January

Water fountains identified in Spitzer/GLIMPSE images

IRAS 18286-0950 W43A IRAS 18460-0151

•  Optical and NIR emission detected with HST, 2MASS: post-AGB stars or pre-planetary nebulae (Sahai et al.)

IRAS 16342-3814, IRAS 19134+2131 •  MIR/FIR emission detected with Spitzer:

(possible) AGB or OH/IR stars (Deguchi et al. 2007)

Fast OH maser flow

IRAS 16342-3814 (Claussen et al. 2008)

Vexp~60 km/s

W43A OH masers

Spherical expansion with elongation ~9 km/s in line of sight Opposite velocity gradient against H2O

(Parental) circumstellar OH envelope dynamical age: 150ー300 years

Star position?

Water fountain disappears in planetary nebula

 Dispersing water fountain

 Photo-dissociation destroying

H2O molecules  Time scale

<1000 years

5000 AU

K3-35 (Miranda+ 2001)

WX Piscium Clear double peaks in H2O maser spectrum

Indicative of an OH/IR star with the largest mass loss rate

in the stellar evolution

Launch of a stellar jet (Hofman et al. 2001)

Precursor of water fountain Drilling a circumstellar envelope

Circular distributions of SiO masers (Soria-Ruiz et al. 2005)

Inversed velocity gradient!

Inomata, Imai, & Omodaka (2006)

Periodically variable, clear double peaks in H2O maser spectrum (Shintani et al. 2008)

H2O masers are still in the thicker circumstellar envelope of the OH/IR star.

ρjet∝ ρenv∝

Observer

★ ★ ★

★

A stellar jet may be launched in AGB phase.

W43A

H2O (VLBA) SiO (VLA)

OH (Global VLBI)

Star position?

SiO maser flow: r~10 AU, Vexp~20 km/s

H2O equatorial flow: r~150 AU, Vexp~30 km/s

OH envelope flow: r~500 AU, Vexp~10 km/s

Equatorial H2O flow

IRAS 18460-0151

High velocity jet (~180 km/s)

+ Equatorial/spherical

flow (~15 km/s) Similar scale and

velocity in the H2O and OH regions opposite velocity

gradients

OH

H2O

(Imai et al. 2009 in preparation)

Simultaneous development of a stellar jet and an envelope/torus

•  Common sequence of evolution between

PPNe and water fountains •  Time lag ~ 200-300 years •  Interaction event between

a torus followed by a jet on a short time scale

•  Binary system scenario may produce the interaction event and explain (multiple) discrete mass ejection.

•  The interaction event may occur in AGB phase.

W43A in detail: Jet precession

•  Precession period ~55 years •  Precession angle amplitude ~5°

Imai et al. 2005

Corkscrew jet? Bow shock front?

W43A (Imai & Diamond in prep)

Proper motions with a systemic velocity vector subtracted

Imai, Sahai & Morris (2007)

IRAS19134+2131

Bow shock front in a corkscrew jet?

Corkscrew jet! IRAS16342-3814 (Sahai et al. 2005)

Lp image with Keck

Lp (red), Kp (green), HST (blue) image water masers

Water masers in the jet core

VLBI astrometry and exploration of AGB envelopes

1. Maser source configurations •  Position comparisons: binary or single star?

•  Dynamical center of the H2O maser jet/equatorial flow

•  Dynamical center of the SiO maser flow/disk •  Dynamical center of the OH envelope

•  Using common position reference: quasars •  SiO: VLA/VLBA/VERA/HAS, σ~1 mas •  H2O: VERA/VLBA/EVN, σ~10 mas •  OH: EVN/VLBA, σ~10ー50 mas

W43A

Dynamical centers within 100 AU (OH-SiO) within 10 AU (SiO-H2O in decl.)

H2O (VLBA) SiO (VLA)

OH (Global VLBI)

Star position?

+SiO

VLBI astrometry and exploration of AGB envelopes

2. Orbit of water fountain source

Galactic rotation

H2O masers in IRAS 19134+2131 (Imai+ 2007)

Annual parallax and Galactic rotation

Location and motion

in the Galaxy

•  Annual parallax distance = 8.0+0.9-0.7 kpc

•  Location: (R, θ, z)=(7.4+0.4-0.3 kpc, 62±5 deg, 650+70

-60 pc) •  3D velocity (VR, Vθ, Vz) =(3+53

-46, 125+20-28, 8+48

-39)[km/s]

ⒸKagaya

Location and velocity in the Galaxy

•  Progenitors of bipolar PNe may be higher mass stars located near the Galactic plane (Manchado 2004).

•  Single intermediate-mass evolved star can create both a collimated jet and an equatorial flow

(not accretion disk). (Blackman+ 2001)

Travel time from the Galactic plane   1.1-7.7 x 107 years   M*< 5-5.8 M◉

Towards ALMA and SKA

•  True morphology and kinematics of the envelopes mapped in thermal (e.g. CO, HI) emission

•  Frontier in the southern hemisphere: Galactic center •  Pioneering works with maser emission before

ALMA and SKA era

ALMA @AUI ASTE @NRO

CO J=3−2 emission from IRAS 16342-3814

Combination of 3 spectra with ASTE

H2O maser emission (Likkel et al. 1992)

Imai+ (2009)

Mass loss rate of IRAS 16342-3814

dM/dt≃10-4Msunyr-1 (Present work) •  dM/dt~10-3Msunyr-1

(amorphous silicate absorption feature, Dijkstra et al. 2003) c.f. dM/dt=10-6ー10-5Msunyr-1 for Mira variables

•  Dominant contribution to stellar mass loss by the fast flow

€

˙ M gas =1.4 × Tmbv∞2 D2B2

2×1019 fCO0.85s J( )

(Olofsson et al. 1993)

€

fCO = 5×10−4 for O - rich starss 3( ) = 0.43 (Knapp et al. 1998; Groenewegen et al. 1999)

D ≈ 2 kpc, v∞ ≈120 km s-1 (from H2O double peak)Tmb ≈ 0.033 K , B= 2 ′ ′ 2 (present work)

Conclusions and perspectives •  Leading study of final AGB star evolution from

Kagoshima University with international synergy –  High resolution radio approach to AGB envelopes –  VLBI astrometric approach to AGB envelopes –  Guide sources obtained from MIR/FIR mission

(e.g. SPLITZER, AKARI) •  Roads to exactly tracing stellar mass loss history

–  Direct mass loss rate estimations of C-rich / O-rich AGB stars through true envelope spatio-kinematics

–  Astrometric approach for understanding parental stars •  Future directions: preparatory study now going

–  VERA astrometry of water fountain sources –  H2O maser movies with EAVN –  High resolution mapping of thermal emission with ALMA

and SKA

International collaboration Synergy in astronomical research and education

•  Philip Diamond (Jodrell Bank Center for Astrophysics) •  Mark Morris (University of California Los Angels) •  Raghvendra Sahai (NASA, Jet Propulsion Laboratory) •  Wouter Vlemmings (Bonn University) •  Jun-ichi Nakashima, Sun Kwok, Bosco Yung

(Hong Kong University) toward MoU •  Jinhua He (Yun Nang Observatory) •  Nico Koning (Calgary University) •  Shuji Deguchi, Nobuharu Ukita, Ryuichi Kamohara

(National Astronomical Observatory of Japan) •  Daniel Tafoya, Akiharu Nakagawa (Kagoshima Univ.)

Used telescopes (in the world) Proposal submission is strongly encouraged.

Very Large Array (VLA)

ALMA/ SKA (currently ASTE, SMA, CARMA)

Very Long Baseline Array (VLBA)

VERA (base array) NRO 45m, GBT 100m European VLBI Network (EVN) East Asian VLBI Network (EAVN)

鹿児島大学における研究課題：　学部生向き

•  VERA単一鏡観測ダイナミック・スケジューリング（だいすけ）の 最適化と観測効率の検証

•  Omodaka Lab. Virtual Observatory (OVO)機能追加による メーザー源統計分析ツールの開発

•  VERA: 大質量星形成領域 W51 North/West H2Oメーザー源の 内部運動及びメーザースポット群集団間運動の分析

•  VERA: 大質量星形成領域 G34.26+0.15 (W44) H2Oメーザー 源の内部運動及びメーザースポット群集団間運動の分析

•  VERA: ミラ型変光星年周視差及び銀河系内軌道計測 （既存データ利用）

•  VERA: 銀河系立体地図作製に利用できるH2Oメーザー源の選別　 （フリンジチェック観測データの解析）

※VERA: VEDAによるVERAデータルーチン処理も兼ねる •  赤外線天文衛星「あかり」データを用いた

OH/IR星の探査と統計的性質の分析（９月以降） •  1m鏡: 赤外線天文衛星「あかり」データを用いた

1m光赤外線望遠鏡測光対象天体リストの再構築

鹿児島大学における研究課題：修士課程志望向き

•  VERA: 銀河系内ミラ型変光星の周期ー光度関係の精密化 •  VERA: 大質量星形成領域の距離と銀河系内軌道の精密計測 •  VERA/EAVN： ParselTongueスクリプトを利用したデータ自動

解析パイプラインの開発（主にwide field image cube 作成) •  JVN: SiO v=3 輝線撮像とSiOメーザー励起機構の研究 ※VERA/JVN: VEDAによるVERAデータルーチン処理も兼ねる

•  NRO45m鏡、GBT100m鏡：　赤外線天文衛星「あかり」 サンプルに対するOH/IR星メーザー源(H2O, SiO)の 　　　　 探査と統計的性質の分析

•  VLBA: 深宇宙基準座標系構築のためのQSOペアに対する 高精度位置計測（科研費課題が採択された場合）

•  VLBA: 銀河系立体基準座標系構築のためのメーザー源 年周視差計測（科研費課題が採択された場合）

•  LBA: 南天H2Oメーザー源周辺の参照電波源探査と 試験的高精度位置計測 (VSOP-2 Pre-launch Study)

鹿児島大学における研究課題： 博士課程志望者向き

•  「宇宙の噴水」プロジェクトの推進 VERA/ VLBA/ EVN/ LBA/ EVLA/ SMA/ ALMA/ ASKAP

•  VERA/EAVN/VLBA: 銀河系核円盤(R~100 pc)及び 銀河系中心星団(R~30 pc)の力学的性質に関する研究

•  VERA/EAVN/VLBA: 銀河系内の古い散開星団の距離と軌道 及び力学的性質に関する研究

•  EVLA/ ASKAP: 銀河系ハロー／球状星団における AGB星の探査と統計的分析及び高精度軌道計測

•  LBA, VSOP-2: 大小マゼラン雲の爆発的星形成 （スターバースト）の精密観測

•  EAVN: ミラ型変光星H2Oメーザー源動画の作成 　　 ー脈動衝撃波の直接検出ー

※VERA/EAVN: VEDAによるVERAデータルーチン処理も兼ねる