Current progress in ESTEMA and relevant
EAVN commissioning
Hiroshi Imai(Center for General Education/ Amanogawa Galaxy Astronomy Research Center,Kagoshima University)

On behalf of EAVN Evolved Stars SWG and ESTEMA team

Current members• EAVN Evolved Stars SWG
Hiroshi Imai, Se-Hyung Cho, Bo Zhang (co-chair), Youngjoo Yun, Dong-Hwan Yoon,
Jaeheon Kim, Haneul Yang, D.-J. Kim, Lang Cui, J. Zhou,
G. Wu, Gabor Orosz, Miyako Oyadomari, Akiharu Nakagawa, Ross Burns,
Richard Dodson, Maria Rioja, James Chibueze Okwe, Yuanwei, Wu, Shuangjin Xu,Tomoaki Oyama, Yoshiaki Asaki, Naoko Matsumoto• ESTEMA (EAVN Synthesis of Stellar Maser Animations)
Hiroshi Imai, Youngjoo Yun, Bo Zhang (co-P.I.) , Se-Hyung Cho, Dong-Hwan Yoon,
Jaeheon Kim, Haneul Yang, Dong-Jin Kim, Lang Cui, Jianjun Zhou, Gang Wu,
Gabor Orosz, Miyako Oyadomari, Akiharu Nakagawa, Ross Burns,
Richard Dodson, Maria Rioja, James Chibueze Okwe, Shuangjin Xu, Tomoaki Oyama,
Yoshiaki Asaki, Jun-ichi Nakashima, Andrey M. Sobolev

Our goals
visualization of dynamicstellar mass loss
SiO maser
regionH2O maser
regionwith shock waves
without shock waves

Distance from star (stellar radius)

See also
P24 (poster) by Se-Hyung Cho
Next talk by YoungJoo Yun

Shock waves in C-rich envelope (Höfner et al. 1995)
SiO masers around TX Cam (Gonidakis et al. 2013)

How are materials on the stellar surface lifted up
outward in a circumstellar envelope?
Höfner (2011)

Anthares In CO line center(2.31 μm) (Ohnaka et al. 2017)

Under periodic stellar pulsationand inhomogeneous mass ejectionOur challenges 1: simultaneous mapping of
SiO maser transitions with H2O masers
How to collocate these maser line
regions throughout
stellar pulsation cycles?
 R −2 / 5
Tenvelope = T*   R* T* ≈ 3000 K, R* ≈ 1-10 AU

Are we really watchingtrue physical gas motions€in these maser lines?

SiO maser lines(J→J-1, J=1,2,3, …; ν≈43×J[GHz])

Line overlap
excitation by
Mid-IR H2O radiation

Quasi-optics for multi-band simultaneous observations

Opened (2019)

VERA
In K/Q-bands
Yebes, ATCA (multi-antennas), NARIT(?), Effelsberg(?),...

Incommissioning

Commissioning of K/Q-band quasi-optics in VERAr19052b(W Hya and VX Sgr)W Hya

VX SgrYonseir19052a(S Per)

Ulsan

Gain loss less than
10%(<uncertainty)
by 20” beam offset(in Ishigakijima)
Source-frequency
phase-referencing
technique should betested.

Tamna

H2O masers
Mizusawa

IrikiOgasawara
Ishigakijia

SiO masers

Our challenges 2: operating “hybrid” mode
Three vex files for one-day block

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• KaVA/EAVN: mapping H2O and SiO (43 GHz) masers à should be made in one day in future• KVN: band-to-band phase transfer calibration for SiO masers (43/86/129 GHz)
• VERA: dual-beam astrometry and wide-band recording (for SiO v=3 and v=0 J=1à0 masers)

Our challenges 3: time allocation with high cadence
Target sources of ESTEMA

IRC-10151

Cadence15 d15 d
20 d
20 d
30 d
60 d

Targetingbiweekly (~20 sessions per year) snapshot (<4 hours with > 5 telescopes)

Negotiation in time allocation

IRC-10151

Cadence

15 d
15 d
20 d
20 d
30 d
60 d

Requesting ~550 hours/yr, ~2600 hours in total
lAvoiding condensed LST zone (16—22 hours)
lReducing to ~ 65% with K/Q-band simultaneous observations with VERA
lReducing to ~ 50% by adding more telescopes (Nb, T6, Ur, Tl)

VLBI mapping of 16 circumstellar H2O maser sources- persistent clumps but changed distribution biases AP Lyn

W Hya

50 mas

20 masContour peak: 120.5 Jy beam-1 km s-1

Contour peak: 22.6 Jy beam-1 km s-1

VY CMaContour peak: 5.2 Jy beam-1 km s-1

U Her

Contour peak: 6.9 Jy beam-1 km s-1

RT Vir

20 masContour peak: 27.0 Jy beam-1 km s-1

Decl. offset

10 mas

20 masR.A. offset
Contour peak: 43.9 Jy beam-1 km s-1

R.A. offset
Contour peak: 103.6 Jy beam-1 km s-1

R Cas

NML Cyg

50 masR.A. offset

20 mas

20 masR.A. offset

R.A. offset

Contour peak: 240.4 Jy beam-1 km s-1

Contour peak: 2.1 Jy beam-1 km s-1

IRC-10414

VX Sgr

Decl. offset

S Crt

Contour peak: 3.0 Jy beam-1 km s-1

Decl. offset
50 masContour peak: 871.8 Jy beam-1 km s-1

Contour peak: 420.3 Jy beam-1 km s-1

Contour peak: 5.4 Jy beam-1 km s-1

Decl. offset

Decl. offset

20 masContour peak: 129.6 Jy beam-1 km s-1

20 mas

10 mas

10 mas

S CrB

R Crt

50 masRR AqlDecl. offset

Decl. offset

20 masR Aql

RX BooDecl. offset

S Per

Contour peak: 437.3 Jy beam-1 km s-1

20 masR.A. offset

Contour peak: 86.4 Jy beam-1 km s-1

With full JVN(VERA+NRO+Takahagi+Tsukuba+Kashima(Imai et al. in preparation)

Indicating importance of long-term monitoring of circumstellar H2O masers

What determines the extent and bias in H2O maser distribution?

Time variation of total H2O maser flux toward W Hydrae (Shintani et al. 2008)

What determines the extent and bias in H2O maser distribution?

Phase lag of total H2O flux
(Shintani et al. 2008)

Distribution extent of compact H2O masers around W Hydrae(Imai, Nakagawa & Takaba 2019)

Our decadal effortsØCommissioning works in KaVA/EAVN Evolved Stars SWG
üSince 2011 MayüDemonstration of KaVA full-track / snap-shot imaging
üDevelopment of scheme of hybrid observation modesØKaVA ESTEMA (Expanded Study on Stellar Masers)
ü2015 November—2017 MarchüSnapshot imaging of ~40 stellar maser sources successfully detectedØESTEMA (EAVN Synthesis of Stellar Maser Animations)üFrom 2018 MayüTargeting 6 stars (currently 2 stars) with different stellar pulsation
periods

First KQW-band composite
map of H2O and SiO masers

H2OConfidential(surviving over a decade)SiO v=1 J=1à0SiO v=2 J=1à0
SiO v=1 J=2à1S Per
In direct band-to-band
phase-transfer(Asaki et al. in prep.)First KQW-band composite map of H2O and SiO masers
S Per(Asaki et al. in prep.)Ø Good assumption of maser distribution corresponding to true gasdistribution
Ø Double SiO
maser rings
Ø Radial correlation
among H2O andSiO masers
Ø Episodic
mass ejection
every decade

Confidential

Venn diagram of VLBI fringe detections ofKaVA ESTEMA circumstellar maser sources
80 stars in total(2015̶2017)

11H2O4216

9Image cubesynthesis andstatistical inspection still ongoing

SiO
J=2à127

15

SiO J=1à054(v=2) 51(v=1)

72 3SiO
J=3à25In scalar averaging

Ring (circle)-model fitting
ØKVN-KSP method using maser spot/feature mapsüInformation of maser emission distribution reduced torepresentative brightest peaks in the spots/featuresØEHT method finding azimuthal offset brightness peaküAvailable to a maser ring extremely biased, clumpy, and complicated?

ØESTEMA method finding the sharpest radial profile
1.Determining the ring center at first using data ofa distribution of maser emission areas2.Estimating the ring size and width
Challenging to ring size accuracy better than 0.5 mas
Extension to ellipse fitting àfor masers around red supergiants

r18145a
1 ch à 0.1 mas

ESTEMA method
Cumulative normalized flux

Finding the minimum

D1 (5%̶95%)

Definedring radius

D2 (5%̶50%)

Demonstrated by Miyako Oyadomari

ESTEMA methodr18145a1 ch à 0.1 mas

Number of trials

In 1000 trials in a Monte-Carlo simulation

Demonstrated by Miyako OyadomariDifference in the performances between
SiO v=1 and v=2 J=1à0 maser linesPreliminary
How to track true physical gas
motions on sub-mass scale ?
See also talks byAkiharu Nakagawa(this session) andHaneul Yang and Shuangjing Xu(Astrometry session)
by Miyako Oyadomari

400

Very long time-domain astronomy with image cubes

300

IRAS 18286-0959(water fountain froma dying star)

2006 Sep.ー2007 Feb.
2009 May
2019 March

100

200

+0l Weekly̶monthly
maser flaresl Decadal evolutionl Permanent turn offof a jet to become aplanetary nebulaDecl. offset (mas)New bipolar bullet
ejections-160-80080

LSR velocity [km/s]

160

240

FLASHING early science(Imai et al. 2020 PASJ
Special Issue, submitted)

200 AU
at 3.6 kpc
0

R.A. offset (mas)-100Summary and future perspectivesØCommissioning to deliver the full set of circumstellar H2O and SiO
maser animations
H2O, SiO (v=0, 1, 2, 3, J=1à0 / v=1 J=2à1, J=3à2 / 29SiO v=0, J=1à0)

Toward synchronized operation of VERA (K/Q) and Nobeyama(K/Q/W) with KaVA/EAVN/ and the Global AllianceØKaVA ESTEMA: statistical analyses based on snap-shot image
cubes from ~20 starsüAstrometric registration ongoingüComparisons with latest data: Gaia DR2, VLTI, NESS, ALMA…
ØESTEMA: legacy animations of circumstellar H2O and SIO masersüTracing dynamic mass loss events on week scale