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超広帯域／高感度 VLBI が切り開く 変光星脈動による物質放出機構 の研究

大学 VLBI 連携・東アジア VLBI 観測網ワークショップ 2010 年 11 月 12 日. 超広帯域／高感度 VLBI が切り開く 変光星脈動による物質放出機構 の研究. Hiroshi Imai Graduate School of Science and Engineering Kagoshima University. Contents: Proposal as an EAVN key science project. What can we learn from stellar masers? Current trial observations

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超広帯域／高感度 VLBI が切り開く 変光星脈動による物質放出機構 の研究

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  1. 大学VLBI連携・東アジアVLBI観測網ワークショップ 2010年11月12日 超広帯域／高感度VLBIが切り開く変光星脈動による物質放出機構の研究 Hiroshi Imai Graduate School of Science and Engineering Kagoshima University

  2. Contents:Proposal as an EAVN key science project • What can we learn from stellar masers? • Current trial observations • Acceleration in an H2O maser clump motion in RT Virginis (Imai et al. 2003) • Mapping SiO v=1, 2, 3 (J=1-0) lines in W Hydrae (Imai et al. 2010) • Possible observation plan with EAVN • H2O masers @13 mm with VERA+KVN+EAVN • SiO masers @7 mm (v=1, 2, 3 J=1-0) with VERA+KVN+NRO45m/NICT 34m 1GHz band width recording and spectroscopy

  3. Stellar maser: the movie― What can we learn from stellar masers? ― • Maser movie visualizes… • expansion • contraction /convection • rotation/ radial acceleration • ballistic and non-ballistic motions • Maser motions visualize • giant gas clumps floating from giant convective cells • jets or spurs • shock wave transfer (H2O) • Maser motions fascinate public people as well as astronomers! SiO masers around TX Cam (Gonidakis, Diamond & Kemball 2010, 75 epochs, every 2 weeks)

  4. From surface to envelope 20 AU • Inhomogeneity in stellar mass loss flow • Transfer of pulsation-driven shock waves Radio photosphere SiO masers H2O masers H2O velocity-integrated flux Optical magnitude • Observed phase lags • 0.7 ≦ Δφ(H2O—opt)≦1.5 (Shintani et al. 2008) • 0.5 ≦ Δφ(H2O—SiO)≦1.4 (Ueda et al. 2011 in prep.) Reid & Menten (2007) with VLA

  5. Open issues in stellar maser astrophysics • True kinematics and physical conditions in maser clumps/regions • SiO maser pumping mechanism (collisional, radiative) • Velocity gradient, acceleration, “Christmass tree effect” • Their relation of stellar pulsation and mass loss flow • Distance measurement • Extended atmosphere preventing from accurate astrometry

  6. Current trial observations Mapping SiO v=1, 2, 3 (J=1-0) lines in W Hydrae Imai et al., PASJ, 62, 431-439 (2010) Acceleration in an H2O maser clump motion in RT Virginis Imai et al., ApJ, 590, 460-472 (2003)

  7. SiO v=1, 2, 3 maser maps in W Hydrae Switching pumping schemes? 2009 February 27-28(with 4 VERA telescopes) ALMA band 10 beam Size of the star 2009 April 11-12 (with 6 JVN telescopes)

  8. True maser excitation model tells us true physical condition in the envelope. ーLine overlapping between SiO and H2O molecules ー IR H2O radiation Pump from SiO v=1 J=0 to v=2 J=1 resulting in … • excitation of v=2 J=1-0 maser • quench of v=2 J=2-1 maser

  9. Small difference in v=1,2 maser distributions between two major pumping schemes • Collisional pumping: resulting in larger difference between the v=3 and v=1/v=2 maser distribution • Line overlapping: resulting in coexistence among the three masers. (classical) radiative pumping model collisional pumping model Modeling v=1, 2, 3 SiO lines (Locket & Elitzur 1992)

  10. Detection of a pulsation-driven shock wave? RT Virginis (Imai et al. 2003) Constant radial acceleration

  11. Shock wave transfer in the envelope Acceleration by shock waves (ΔV~10 km s-1/2-3 months) Shock ignition Model of dust-induced pulsation-driven shock waves (Hofner et al. 1995 )

  12. EAVN array configuration Unique specifications 7 telescopes daily specialized in VLBI astronomy (VERA, KVN) compact configuration within 1000 km (>30 km) Capability of multiband mapping and astrometry

  13. Possible observation setups and scheduling • Biweekly monitoring VLBI mapping (≧ 5 telescopes) • SiO: KVN(3) +VERA(4) (7 tels.)+NRO 45m/NICT 34m • H2O: KVN (3) or VERA (4)+ EAVN (≧3) • Spanning 1—2 years, >20 epochs • 1GHz band width (4 Gbps) recording • ADS3000+ (A/D) / OCTAVIA (formatter)/ OCTADISK, • Multi-IF filtering and high resolution spectroscopy • e.g. 2048 ch in 32 MHz/IF × 4IFs = 8192 channels • Astrometry in multi-bands/IFs for map registration • Dual beam in VERA • Dual K/Q band receiving system in KVN • Annual parallax measurement

  14. Stellar pulsation explored in ALMA era • Direct imaging of stellar continuum and line emission • Asymmetric structures of evolved stars and their envelopes • Planet search around evolved stars • Movie of nearby Mira variables and their envelopes • Stellar pulsation and periodic mass ejection • Within reasonable hours of observation time (< 1 hr/epoch) • Exploration of binary systems belonging to AGB stars • Symbiotic stars • Stellar molecular jets (water fountains) • What VLBI can find before ALMA? • 3D velocity field of the envelope and its time variation • Trigonometric parallax distance measurement • Finding ALMA target candidates

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