KaVA Large Programs of Circumstellar MasersKaVA Evolved Stars sub-Working GroupHiroshi Imai*1, Se-Hyung Cho*2, Miyako Oyadomari1, Gabor Orosz1, Akiharu Nakagawa1, Youngjoo Yun2, Jaeheon Kim2, Yoon-Kyong Choi2, Taehyun Jung2, Soon-Wook Kim2, Naoko Matsumoto3, Cheul-Hong Min3, Jeong-Sook Kim3, Yoshiharu Asaki4, Fujika Watari5, Maria J. Rioja6, Richard Dodson6, and Tao An7

*co-chair of sub-WG; 1Kagoshima Univ.; 2KVN/KASI; 3NAOJ Mizusawa; 4ISAS/JAXA; 5Yokohama City Univ.; 6ICRAR/UWA; 7SHAO

Specification of the Large ProgramsPhase 1: ESTEMA (Expanded Study on Stellar Masers)during 2015̶2016, ~200 hoursSnapshot imaging of H2O and SiO masersin circumstellar envelopes (Figure 1) around ~80 stars● statistics of stellar masers i. maser spot sizes and phapes ii. distributions of H2O masers with respect to locations of SiO masers iii. correlation with kinematic parameters of circumstellar envelopes and stars● yielding a larger sample of stars as targets of the Phase 2 project

Phase 2: Intensive monitoring campaignduring 2016̶2024, 400̶500 hours/year16—20 pulsating stars (P=300—1600 days)monitoring SiO and H2O masers in every 1/20 pulsation cycle over a few pulsation cycles for “stellar maser movie” synthesis● detecting (both or either) i) propagation of pulsation-driven shock waves (Figure 2) ii) periodic change in physical conditions affected by stellar radiation● Comprehensive synergy with ALMA, VLTI, Nano-JASMINE

Figure 3 (top left) H2O maser map in S Per taken with KaVA (by K. Kusuno, Y. Asaki)Figure 4 (bottom left) SiO maser map in BX Cam taken with KaVA/KJCC (by H. Imai)

v=1 peak flux = 53.7 Jy channel /beam Levs = 0.54*(1, 2.6, 6.6, 16.8, 43, 69)

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v=2 peak flux = 87.4 Jy channel /beam Levs = 0.88*(1, 2.600, 6.600, 16.80, 43, 69)

SiO v=1 J=1→0SiO v=2 J=1→0

BX Cam

Figure 1 Schematic view of the spatial and density structure of a circumstellar envelope of an oxygen-rich (intermediate-mass) long-period pulsating star that hosts SiO and H2O masers. Gas ejected from the stellar surface forms molecules, then oxygen/silicon-rich dust (e.g. silicate and olivine). The dust particles are accelerated by stellar radiative pressure received through scattering of stellar infrared radiation. The microscopic (dust condensation) and macroscopic (turbulence, shock waves) process should be linked and explored in the KaVA projects.

H2O maserSiO v=1 maserSiO v=2 maser

VLBI position uncertainty

SiO maser ring

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Figure 2 Schematic view of the radial velocity field of a circumstellar envelope of a pulsating star and the locations of the hosting SiO and H2O masers. Pulsation driven shock waveswill be detectable by directly finding the velocity field and its time variation in the intensive KaVA monitoring program over a few stellar pulsation cycles.

Current progress towards the Large ProgramsImaging feasibilityimage quality comparable to that with the VLBA (figure 3, 4)Snapshot imaging feasibilityFocused image in <2 hour integration time with a good (u,v) coverageFeasibility of maser map registration onto a common coordinate systemFeasible in the source-frequency phase-referencing technique (Figure 5)Now testing it in KaVA operationFeasibility of maser source astrometryfeasible with VERA dual beam, testing in antenna fast-nodding modeScheduling of single observation sessiontesting hybrid operation (KaVA imaging + VERA astrometry + KVN SFPR) Modeling of long-term campaignConfirming the reality of biweekly-monthly monitoring operation, including scheduling, array operation, correlation, data processing, and archive

S Per on 2012 March 30

Peak flux = 0.24 Jy channel /beam Levs = 0.024* (-10, -9, -8, -7, -6, -5, -4, -3, -2, -1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

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Figure 5 Demonstration of the source-frequency phase-referencing technique (SFPR) with KVN (Dodson et al. 2014). This technique will be adopted in the KaVA Large Programs. Note that this request high precision maser source astrometry as made with VERA as well.