KaVA ESTEMA and the Large Program on circumstellar masers
Hiroshi Imai*1, Se-Hyung Cho*2, Yoshiharu Asaki3, Yoon-Kyong Choi2, Youngjoo Yun2,Naoko Matsumoto5, Cheul-Hong Min4, Tomoaki Oyama4, S.-C. Yoon5, D.-H. Kim5,
Richard Dodson6, Maria J. Rioja6, Gabor Orosz1, Miyako Oyadomari1, Ross, A. Burns7,
Bo Zhang8, Jaeheon Kim8, Akiharu Nakagawa1, James Chibueze O.9; Jun-ichi Nakashima10,Andrey M. Sobolev10; Lang Qui11; and Jiangbo Su12 (KaVA ESTEMA team)*co-PI; 1Kagoshima Univ.; 2KASI KVN; 3NAOJ Chile; 4NAOJ Mizusawa; 5Seoul National Univ.;
6ICRAR/UWA; 7JIVE; 8SHAO; 9Univ. Nigeria; 10Ural Fed. Univ.; 11XAO; 12Yuncheng Univ.

Figure 1

Schematic view of thestructure of a circumstellar
envelope around an O-richlong-period pulsating starand hosting SiO and H2O
masers. Gas ejected fromthe stellar surface forms
molecules, then O-/Si-richdust. The dust particles
are transparent andaccelerated by stellar
radiative pressure received
through scattering of stellar
infrared radiation. The dust
condensation, turbulence,and shock waves should
be linked and explored in
KaVA maser animation
synthesis.

Figure 2

Composite map of
H2O and SiO(J=2→1 and 1→0)
masers associatedwith the redsupergiant
S Persei, obtainedin the KaVA
(K/Q-bands)/
KVN (K/Q/W-band)commissioning
observation(Asaki et al.
in prep.).

H2O (22GHz) SiO J=1 0 v=1 (43GHz) SiO J=1 0 v=2 (43GHz)
SiO J=2 1 (86GHz, one KVN baseline)

Figure 4

Venn diagram showing theoverlap in occurrence ofdetections of maser emission
in long-integration scalaraveraged spectra in KaVAESTEMA.

Table 1

Target maser and phase-reference/delay calibration sources in new ESTEMA

Figure 3

First images of H2O and SiO masers around Y Cas
observed in KaVA ESTEMA. Righ-shaped morphologiesof the SiO masers are visible even in limited integration
time (~2 hours). The H2O masers exhibit a highly biased

distribution, but such distribution is typically seen incircumstellar H2O masers even in high sensitivity
imaging (Imai et al. in preparation).

KaVA/EAVN Large Programs on circumstellar masersPhase 1: KaVA ESTEMA (Extended Study on Stellar Masers)
2015 October ̶2017 March

Snapshot imaging of H2O and SiO masers in circumstellar
envelopes (Figure 1), around 80 stars. Using multi-frequency
phase-referencing, composite maps will be produced (Figure 2).
Image synthesis is ongoing (Figure 3), but we can find at least
15 stars suitable for the phase 2 project (Figure 4).

Figure 5 Scan patterns that will be adopted in the new
ESTEMA sessions. Each session in one day suppose ablock of 3―9 hours for 1―3 maser sources.

Phase 2: new ESTEMA (EAVN Synthesis of Stellar Maser Animations)2018̶2027, ~450 hours/year

10 pulsating stars (P=306—1433 days) monitoring SiO andH2O masers in every 1/20 pulsation cycle over a few pulsation
cycles for “stellar maser animation” synthesis. The newESTEMA sessions will adopt the scan patterns (Figure 5),
similar to those in KaVA ESTEMA. The time allocation modelfor the monitoring observations are considerd (Figure 6) for
realistic monitoring program for a decade. K-/Q-band
simultaneous observations shall be conducted in the wholeKaVA. Tianma, Nanshan, Sejong, and Nobeyama will be added
dependent on available setup, season, and time allocation rule.

Figure 6 Model of session allocations for new ESTEMA.