Download JVN22GHzWS2010_Imai

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
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
 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
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)
From surface to envelope
 Inhomogeneity in stellar mass loss flow
 Transfer of pulsation-driven shock waves
20 AU
Radio photosphere
SiO masers
H2O masers
H2O velocity-integrated flux
Optical magnitude
 Observed phase lags
Reid & Menten
(2007) with VLA
 0.7 ≦ Δφ(H2O—opt) ≦1.5 (Shintani et al. 2008)
 0.5 ≦ Δφ(H2O—SiO) ≦1.4 (Ueda et al. 2011 in prep.)
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
• 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)
SiO v=1, 2, 3 maser maps
in W Hydrae
Switching pumping schemes?
ALMA
band 10 beam
Size of the star
2009 February 27-28
2009 April 11-12
(with 4 VERA telescopes)
(with 6 JVN telescopes)
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
 R 2 / 5
Tenvelope  T* 
R* 
T*  3000 K, R*  1-10 AU
 (v = 1, 2, 3)
 600 MHz!

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)
Detection of a pulsation-driven shock wave?
RT Virginis
(Imai et al. 2003)
Constant radial acceleration
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 )
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
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
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