Evolution and mass loss of evolved stars explored in radio...
Transcript of Evolution and mass loss of evolved stars explored in radio...
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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
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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
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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)
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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)
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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)
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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)
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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
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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)
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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?
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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
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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)
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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?
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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)
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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)
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11 water fountain sources (2008)
V
V V
V V
V
V: VLBA/VERA observations 12 WFs until 2009 January
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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)
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Fast OH maser flow
IRAS 16342-3814 (Claussen et al. 2008)
Vexp~60 km/s
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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?
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Water fountain disappears in planetary nebula
Dispersing water fountain
Photo-dissociation destroying
H2O molecules Time scale
<1000 years
5000 AU
K3-35 (Miranda+ 2001)
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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)
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Inversed velocity gradient!
Inomata, Imai, & Omodaka (2006)
Periodically variable, clear double peaks in H2O maser spectrum (Shintani et al. 2008)
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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.
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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
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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)
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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.
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W43A in detail: Jet precession
• Precession period ~55 years • Precession angle amplitude ~5°
Imai et al. 2005
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Corkscrew jet? Bow shock front?
W43A (Imai & Diamond in prep)
Proper motions with a systemic velocity vector subtracted
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Imai, Sahai & Morris (2007)
IRAS19134+2131
Bow shock front in a corkscrew jet?
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Corkscrew jet! IRAS16342-3814 (Sahai et al. 2005)
Lp image with Keck
Lp (red), Kp (green), HST (blue) image water masers
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Water masers in the jet core
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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
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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
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VLBI astrometry and exploration of AGB envelopes
2. Orbit of water fountain source
Galactic rotation
H2O masers in IRAS 19134+2131 (Imai+ 2007)
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Annual parallax and Galactic rotation
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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
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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◉
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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
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CO J=3−2 emission from IRAS 16342-3814
Combination of 3 spectra with ASTE
H2O maser emission (Likkel et al. 1992)
Imai+ (2009)
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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)
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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
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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.)
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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)
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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
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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)
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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