KaVA ESTEMA (Expanded Study on Stellar Masers)
Hiroshi Imai*1, Se-Hyung Cho*2, Yoshiharu Asaki3, Yoon-Kyong Choi2, Jaeheon Kim2,Youngjoo Yun2, Naoko Matsumoto5, Cheul-Hong Min4, Tomoaki Oyama4, S.-C. Yoon5, D.-H. Kim5,
Richard Dodson6, Maria J. Rioja6, Ross, A. Burns1, Gabor Orosz1, Miyako Oyadomari1,
Akiharu Nakagawa1, James Chibueze O.7, Juni-ichi Nakashima8, and Andrey M. Sobolev8*co-PI; 1Kagoshima Univ.; 2KASI KVN; 3NAOJ Chile; 4NAOJ Mizusawa; 5Seoul National Univ.; 6ICRAR/UWA; 7Univ. Nigeria;
8Ural Fed. Univ.

Figure 1

Time line and specification of theKaVA Large Programs on
circumstellar masers

Schematic view of the spatial anddensity 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, thenoxygen/silicon-rich dust (e.g.
silicate and olivine). The dust
particles are accelerated by stellar
radiative pressure received throughscattering of stellar infrared
radiation. The microscopic (dustcondensation) and macroscopic(turbulence, shock waves) process
should be linked and explored in
the KaVA projects.

Phase 1: ESTEMA (approved)
during 2015 autumn̶2016, 2 years ×120 hours

Snapshot imaging of H2O and SiO masers
in circumstellar envelopes (Figure 1)
around ~80 stars (source list in public)● statistics of stellar masers
i. maser spot sizes and shapes
ii. distributions of H2O masers withrespect to locations of SiO masersiii. correlation with kinematic parametersof circumstellar envelopes and stars● yielding a larger sample of stars
as targets of the Phase 2 project

15

With shock waves

10shock wave propagation per year
KaVA angular resolution at 1 kpc

5● 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

Expansion velocity [km/s]

20Figure 2

SiO masers

0Phase 2: Intensive monitoring campaign
during 2016̶2024, 400̶500 hours/year
16—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

05

Without shock waves

H2O masers
10

Distance from the star (stellar radus)-235
SiO v=1 J=1→0
SiO v=2 J=1→0

BX CamDecl. offset (milliarcsecond)

-240

-245

-250

-255

-260

430

425

420

415

405

R.A. offset (milliarcsecond)

410

400

v=1 peak flux = 53.7 Jy channel /beam Levs = 0.54*(1, 2.6, 6.6, 16.8, 43, 69)
v=2 peak flux = 87.4 Jy channel /beam Levs = 0.88*(1, 2.600, 6.600, 16.80, 43, 69)

15

Schematic view of the radial velocity
field of a circumstellar envelope ofa pulsating star and the locations ofthe hosting SiO and H2O masers.
Pulsation driven shock waves will be
detectable by directly finding thevelocity field and its time variationin the intensive KaVA monitoring
program over a few stellar pulsation
cycles.

ESTEMA operation design
Scan patterns in each session (Figure 3, 4)
Two-day pairs of blocks for K&Q-bands with VERA for K/Q/W/D bands with KVNThis yields a good (u,v) coverage(~60 min + ~120 min integration with VERA and KVN, respectively)
Baseband channel allocation (Figure 5)
Covering 1 H2O and 5 SiO (3, 1, 1 lines at Q-, W-, D-bands, respectively) lines
Data analysis mission for multiple scientific outcomes
1. KaVA snapshot images of 1 H2O and 2 SiO (v=1 & J=1→0) maser lines
2. Astrometry (VERA dual beam & slow antenna nodding)
3. mm VLBI with KVN (SiO v=1 & J=2→1 and J=3→2 maser lines, with SFPR)
Data analysis processing (using AIPS/ParselTongue/Python)a. ESTEMA ingest pipeline: amplitude calibration and data splitting for each mission
b. Standard data calibration pipelines for KaVA imaging and astrometryc. Advanced data processing: SFPR
d. Data archiving: calibrated visibilities, image cubes, important plots, pipeline inputs

Figure 3 ESTEMA imaging demonstration
resulted from the KaVA data of the SiO
masers around BX Cam (including astrometric map registration).

Figure 4 Scan patterns adopted in the KaVA ESTEMA sessions.
The ESTEMA sessions suppose a block of 6 hours for 4 maser sources.

Figure 5 Baseband channel allocations for ESTEMA.