VLBI observations of circumstellar masers with JVN/KaVA/EAVN
Hiroshi Imai (Center for General Education / Amanogawa Galaxy Astronomy Research Center, Kagoshima University)
On behalf of: KaVA ESTEMA (Expanded Study on Stellar Masers) Team
new ESTEMA (EAVN Synthesis of Stellar Maser Animations) Teamthe Team of the JVN Large Project on Circumstellar H2O Masers※※Hiroshi Imai, Miyako Oyadomari, Yoshiharu Asaki, Yoshinori Yonekura, Kenta Fujisawa,

Naoko Matsumoto, HIroshi Takaba, Makoto Nagai, Mamoru Sekido (VLBI Univerity Alliance)

KaVA ESTEMA (Expanded Study on Stellar Masers)

During 2015 October ̶2017 March, for ~280 hours, towards 80 stars
Snapshot imaging of detected H2O and SiO masers in circumstellar envelopes around ~40 stars. Using multifrequency phase-referencing, composite maps will be produced. Automated image scube ynthesis is ongoing.

New ESTEMA (EAVN Synthesis of Stellar Maser Animations)

During 2018 May̶2027, for 200̶300 hours/year, towards 6 stars with pulsation periods P=300—1000 days (Table 1)
Intensive monitoring of SiO and H2O masers in every 1/20 pulsation cycle over a few pulsation cycles
Producing and archiving stellar maser animation in the database(eDAMS, Nakashima et al. 2018)
JVN Large Projecrt on Circumstellar
Still snapshot imaging (~3 hours), but image quality will beMasers (VERA 15B-111)
secured by at least five KaVA/EAVN telescopes (Figure 2)2016 May, for ~50 hours, towards 20 stars
Snapshot imaging of H2O masers
Table 1 Target maser and phase-reference/delay calibation sources in
For statistics of maser spot/feature shapes
new ESTEMA. In 2018, BX Cam and NML Cyg have been focused.
expected to have possible correlation withstellar type and the evolution of circumstellar
envelope, which is under investigation(Figure 3)
SiO v=1 J=1→0
SiO v=2 J=1→0

Figure 1 Allocation model of the ESTEMA observation session. In 2018 ー2019, each session is composed of a pair of K-/Q-band blocks (~3 hours)
for VERA. Later, each session shall adopt K-/Q-band simultaneous
observations with full KaVA and EAVN telescope. Each star shall bemonitored in 2 ー 3 stellar pulsation cycles (700 ー 1500 days).
AP LynS Per

W HyaFigure 2 KaVA imaging of SiO J=1→0 masers

around BX Cam, which was conducted in 2018 May.
The registration of the two maser map should bemade more relilably on the basis of astrometry.
R Aql

RX BooRR Aql3.0
Jy beam-1 km s-1

Decl. offset

5.2
Jy beam-1 km s-1
5.4
Jy beam-1 km s-1

Contour peak:
120.5 Jy beam-1 km s-1

22.6
Jy beam-1 km s-1
20 masVY CMa129.6
Jy beam-1 km s-1

50 mas

20 mas

10 mas

S CrB

R Crt

U Her

420.3
Jy beam-1 km s-1

20 mas10 mas

NML Cyg

R Cas

Decl. offset

6.9
Jy beam-1 km s-1

50 mas871.8
Jy beam-1 km s-1

27.0
Jy beam-1 km s-1
20 mas

20 masVX SgrRT VirS Crt
43.9
Jy beam-1 km s-1

50 mas

IRC-10414

Decl. offset

103.6
Jy beam-1 km s-1

10 mas

20 mas437.3
Jy beam-1 km s-1

50 mas86.4
Jy beam-1 km s-1

20 mas240.4
Jy beam-1 km s-1
R.A. offset

2.1
Jy beam-1 km s-1
20 mas

20 masR.A. offset

Figure 3 Distrutions of H2O masers associatedwith 16 stars. They were obtained with the JVN
in 2016 May. Used telescopes were: four VERA
telescopes, Nobeyama, Kashima, Tsukuba, andTakahagi. Each star was scanned for 2--3 hours.
The synthesized beams are displayed at thebotton-left corners of the subpanels. The maser
distributions are heavily biased in the envelopes.