Results of KVN observations
toward evolved stars

SiO v=1 J=1-0
IK TauYoungjoo Yun, Se-Hyung Cho, Dong-Hwan Yoon,
Haneul Yang, Dong-Jin Kim
12th East Asian VLBI WorkshopIbaraki, 23 – 27 September 2019

Outline•

Introduction to KVN Key Science Project•

Results of KVN observations•Summary and future works

Scientific goals of KSP

To Study• Characteristics of stellar masers• Spatial structure, relative location, intensity• Temporal variability• Masing conditions• Kinematic and chemical properties ofcircumstellar envelopes• Pulsation and shock propagation• Molecular abundance• Dust condensation• Mass-loss mechanism and history• Dust-driven stellar wind
• Shell morphology: spherical, bipolar, irregular, …
• Mass-loss rate and stellar evolution

Total 341 VLBI observations in KSP
Aug. 2014 – Jun. 2019

Key technique of KSP observations
Source Frequency Phase Referencing method

May the SFPR
be with you!

Richard Dodson and Maria J. Rioja (2014)

Development of KVN pipeline• SFPR method for KVN observations is completely
implemented.
• Fully-automated procedures of pipeline save a hugeamount of time by replacing human eye inspection.
• Consistency and repeatability of data reduction canbe achieved by using the pipeline along the multiepoch observations.

Examples of KVN pipeline
Procedures for continuum reference source for phase referencing

Group delay solutions of continuum source

Phase solutions of continuum source andconnected phases

Examples of KVN pipeline
Procedures for continuum reference source for phase referencing

Find
wrapping
point

Find
outliers

Examples of KVN pipeline
Procedures for maser line source for fringe fitting

Spectrum of 22 GHz H2O maser of VY CMa

Candidates of reference channel
229, 241, 247, 261, 293

Examples of KVN pipeline
Procedures for maser line source for fringe fitting
Closure phases of maser line channels

229241261293247

Reference channel of maser line
can be automatically determinedfrom the qualities of fringe phasesolutions and closure phases.

Results of VX Sgr by Dong-Hwan Yoon

Single dish monitoring observations of KVN
Result of VX Sgr reduced by Dong-Hwan Yoon
Light curve and maser intensity

Spectra of 22 GHz H2O maser

VLBI monitoring observations of KVN
Result of VX Sgr reduced by Dong-Hwan Yoon

SiO v=1 J=1-0 (43 GHz) maser images

VLBI monitoring observations of KVN
Result of VX Sgr reduced by Dong-Hwan Yoon

SiO v=1 J=1-0 (43 GHz) maser images

Results of R Crt by Dong-Jin Kim

VLBI monitoring observations of KVN
Result of R Crt reduced by Dong-Jin Kim

Relative spatial distribution of7mm and 3 mm SiO masers
Average ring size
3 mm < 7 mm

Opposite case tothe common ones

Results of V627 Cas by Haneul Yang

In preparationVLBI monitoring observations of KVN
Result of V627 Cas reduced by Haneul Yang

Need to know how the spatial distribution of H2O and SiO masers
are associated with the orbital motion of hot companion.

Spatial distributions and structures of masers
W Hya
22 GHz42 GHz86 GHz129 GHz43 GHzSpatial distributions and structures of masers
W Hya

86 GHzClear arc structure with bumps innorthern part of 3 mm SiO maser

129 GHz

Largely bumped features innorthern part of 2 mm SiO maser

Spatial distributions and structures of masers
W Hya• Locally-violent massejection like a flare• Inhomogeneous propertyof surrounding material• Asymmetric spatial
distribution of water maser• SiO masers are located in
the middle of water maser

The 2 mm SiO
maser is located at
the most outer part.

Closely distributed
andlargely overlapped
Largely separated

Spatial distributions and structures of masers
W Hya
𝜙=0.2

𝜙=0.27𝜙=0.4570 days

30 days

40 daysObservations of 2 mm
SiO maser failed.

7 mm SiO maser follows and catches
up the 3 mm SiO maser.
Weakened and disappearing bumpedfeatures of 3 mm SiO masers
Episodic mass-loss phenomena
in local region of CSEs

𝜙=0.56

Clumpy structure of dust
W Hya

2015-7-8
𝜙=0.9

Visible polarimetric imaging of W Hya observed with VLT/SPHERE-ZIMPOL
Ohnaka et al. (2016)

Clumpy structure of dust
W Hya

2015-7-8
𝜙=0.9
Cone-shaped density enhancement

Visible polarimetric imaging of W Hya observed with VLT/SPHERE-ZIMPOL
Ohnaka et al. (2016)

Spatial distributions and structures of masers
W Hya
86 GHz

Perpendicular to LOS

Slanted to LOS(approaching)
129 GHz42 km/s

Summary and future works• Successful operation of the 1st KSP providing
important results for the study of late stage ofstellar evolution• Spatial distributions, clumpy structures, intensities of stellar
masers observed at four frequency bands• Mass-loss phenomena indicated from the temporalvariabilities of the maser properties• Planning the 2nd phase of KSP• New target sources (GX Mon, R Aqr)
• Intensive monitoring for the strong maser sources• Including polarization observation for a few sources• Further physical interpretation• Combining other facilities (EAVN, ALMA, VLA, …)• Theoretical research by using numerical simulations