Trigonometric distance and maser kinematics ofthe fastest (and farthest) water fountain source
Gabor Orosz (PI), Hiroshi Imai, Jose F. Gomez, J. Ricardo Rizzo , Olga Suarez, Ross Burns, Akiharu Nakagawa
Department of Physics and Astronomy, Kagoshima University, Kagoshima, Japan
Contact: gabor.orosz@gmail.com
xkcd.com

Water fountains

IRAS 18113–2503

Water fountain sources are evolved stars with morphologically andkinematically highly collimated fast jets traced by water maser emission.
Interferometric observations show that the maser emission is shock-excitedin bipolar outflows. Water fountains are believed to be associated with avery short transitory phase in late stellar evolution (~1000 years) after theAGB period, which should play an important role in the sculpting of the
intricately shaped planetary nebulae (Sahai and Trauger 1998). Due to theshort lifespans of water fountains, only about a dozen are known so far.

This water fountain is located towards and beyond the Galactic Centre in the
thick disk, with jets spanning a very large line-of-sight velocity range of ~500
km/s. Both lobes show a high velocity dispersion as well, ~170 km/s. Thiscan be interpreted as the jets having a large opening angle, or as internal
shocks along the jet, generated by episodic mass-loss events with increasing
velocities. To measure the motion and distance of the water fountain, we
conducted monitoring observations of the brighter blueshifted lobe with VERA
over a year in 9 epochs. We derived a parallax of 0.082 mas with a relative
accuracy of 19%, making this source the farthest known water fountain todate and only the third with a measured trigonometric distance.

Gomez et al 2011-960

0Proper motion components(internal + secular)

10 mas/yr-970-20-980-40+VLA phase centre-990

RA 18 14 27.26
DEC −25 03 00.4

-60

lacga
-80

tic-1010

timovLSR [km/s]

arneonDec. offset [mas]-1000(at6.5-1020kpc)

-100

VLA)
f jet (tion odirec

9.4

nepla

(atcticonalaoti

fGm
tic

nolac

tio-140c)kp

SNR > 7-1060
-520

-530

-120

μ = 6.2 – 8.5 mas/yr
3D vel. ≈ 300 – 425 km/sr14094b water maser featuresr14163a water maser features
absolute proper motion [mas/yr]
source’s near galactic motion subtracted [mas/yr]
source’s far galactic motion subtracted [mas/yr]

VERA synthesized beam
(2x1 mas)⇡ = 0.082 ± 0.016 mas

6.07 ± 0.16 mas/yr

ga

ec-1040-1050µ̄RA =dir-1030

far

The VLA observation shows the fastest bipolar outflow in a water fountain. Dueto the large spread in velocity, we could only observe one lobe with VERA.
Maser features show extended internal structures along the axis of the outflow(likely caused by their high velocity), making identification between epochs
challenging. The parallax is consistent with the far kinematic distance to 1.5-σ.

-540-550-560

-570

-580

-590

-600

-610-620-160
R.A. offset [mas]Subtracting the independently modeled Galactic rotation from the measured
maser proper motions, we can estimate the internal motions in the outflow. At thefar kinematic distance, the residual maser motions follow the jet axis derived fromVLA observations. The large spread in the calculated 3D velocities favors theepisodic mass-loss scenario. We are currently analyzing new VLBA data tomeasure the internal motions directly and characterize the kinematic structure.
+3.0
d = 12.2 2.0 kpc

1.40 ± 0.44 mas/yrµ̄Dec =R0 = 8.0 kpc

l = 6.5662ºΘ0 = 240 km/s

b = –3.6421ºΘ = Θ0 (flat rot. curve)

vr = 100 km/s

U = 7.5 km/s

Dnear = 6.5 kpc

V = 13.5 km/s

Dfar = 9.4 kpc

W = 6.8 km/s

vr,farvr,near
ΘSpectrum components show rapid variability on monthly scales (left), making it
difficult to trace the masers over a year. The integrated maser intensity also varies
on a longer scale (right), however it is not clear whether this is the fading of thesource or a recurring event from e.g. discontinuous mass loss. (Perhaps both?)800

Flux density (Jy)Integrated intensity (Jy km/s)

2014.09.05.
2014.10.03.

40

2014.11.03.
30

20

Episodic event?
400

200

General fading?
0
-120

-100

-80
-60
LSR velocity (km/s)-40-20vl,near

Θ0v0,lv0,rSun0

Francis & Anderson 2009 (gal. param)600

10-140vl,farGC

GBT (O. Suarez), VLA (J. Gomez),
KVN (Yoon et al 2014), VERAVERA epoch50Θ02010

2011

2012
2013
Date (calendar yr)

2014

2015

This research has made use of the Japanese VLBI network of VLBI Exploration of Radio
Astrometry (VERA). I would like to thank NAOJ and Monbukagakusho:MEXT
for financial support, and the help of my colleagues and friends.
Francis, C., & Anderson, E. 2009, NewA, 14, 615
Gómez, J.F., Rizzo, J.R., Suárez, O., et al. 2011, ApJ, 739, L14
Sahai, R., & Trauger, J.T. 1998, AJ, 116, 1357
Yoon, D.H. et al. 2014, ApJS, 211, 15

2015.09.24-25.