Preliminary results from the VERA monitoring ofthe water fountain source IRAS 18113–2503
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Gábor Orosz , Hiroshi Imai , José F. Gómez , J. Ricardo Rizzo , Olga Suárez , Ross Burns!

! ! ! 1Graduate School of Science and Engineering, Kagoshima University, 1-21-35 Korimoto, Kagoshima 890-0065, Japan! !
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! 2Instituto de Astrofísica de Andalucía, CSIC, Apartado 3004, E-18080 Granada, Spain!
! 3Centro de Astrobiología, CSIC-INTA, E-28850 Madrid, Spain!
! 4Laboratorie Lagrange, UMR 7293, Université de Nice Sophia-Antipolis, CNRS Observatorie de la Côte d’Azur, 06300, Nice, France!
! *Contact: gabor.orosz@gmail.com

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xkcd.com

Water fountains

IRAS 18113–2503
This water fountain is located towards the Galactic Centre in the Galactic
thick disk, with jets spanning a very large line-of-sight velocity range of~500km/s. Both of the lobes show a high velocity dispersion as well, ~170km/s. The blue- and redshifted water masers are clustered in two distinct″ ″ regions in the sky, separated by 0.12,″0.1×0.1with PA = –14º (Gómez et al.
2011). In order to measure the secular motion and parallactic distance tothe water fountain, we started monitoring the brighter blueshifted lobe of thesource with the Japanese VLBI Exploration of Radio Astrometry (VERA)
network. Here we present preliminary results derived from the first twoepochs, with a time separation of 69 days.

Water fountain sources are evolved stars with morphologically andkinematically highly collimated fast jets traced by water maser emission(Imai et al. 2002). Interferometric observations showed that the maseremission is shock-excited in bipolar outflows, which are likely driven bymagnetohydrodynamical processes (Vlemmings et al. 2006). Water
fountains are believed to be associated with a very short transitory phase inlate stellar evolution (~1000 years) after the asymptotic giant branch period,
which should play an important role in the sculpting of the intricately shaped
planetary nebulae (Sahai and Trauger 1998). Due to the short lifespans ofwater fountains, only about a dozen have been discovered so far, whichmakes the detailed study of each one important.

-960

0A-beam phase centreRA 18 14 26.743
DEC –25 02 54.75-970-20-980

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

-40vr,far-990

vr,nearΘ-60vl,far
GCvl,near
lac

ga
-80

tic-1010

onti
movLSR [km/s]arneDec. offset [mas]

-1000

Θ

(atΘ0v0,l6.5-1020kpc)-100gaf jet (-120tion odirec)

-1060
-520

-530

-540

Based on the direction and line-of-sight velocity of the water fountain star, it has two
possible kinematic distances. We can calculate the proper motion caused by theGalactic rotation at the two distances, then subtract it from our observed absolutemaser proper motions (we did not model the effect of the parallactic motion). When
we subtract the far distance proper motion, the residual motion matches theexpected outflow from the VLA measurements of Gómez et al. 2011. However,when we subtract the near distance proper motion, the residual vectors are incomplete disagreement with previous results. Thus Dkin = 9.4 kpc is more likely.

r14094b water maser features
r14163a 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)
-550

-560

-570
R.A. offset [mas]

-580

-590

-600

-610-620

Sun!

-140c
kp-1050

9.4

nepla

SNR > 6atn(ctictioalamofG

ticnolactio-1040

VLA)

farecdir-1030v0,r-160

The detected and phase-referenced maser features in the first two epochs wereused to measure the absolute proper motion (internal + secular) of the masers.
Subtracting the independently modeled Galactic rotation from the maser motions, weestimate the internal motions in the outflow. At the far distance, the masers follow thejet axis derived from VLA measurements, with proper motions of ~6.2–8.5 mas/yr.
Based on these results, the 3D outflow velocity at 9.4 kpc is ~300–425 km/s,
probably making this water fountain host the fastest known jets at the moment.

42

Plot file version 2 created 24-JUL-2014 19:57:58
18113-25 r14094b A.CVEL.1
Freq = 22.2360 GHz, Bw = 16.000 MH Calibrated with CL # 7 and BP # 6 (BP mode 1)

Plot file version 1 created 31-JUL-2014 21:37:43
18113-25 r14163a A.CVEL.1
Freq = 22.2350 GHz, Bw = 16.000 MH Calibrated with CL # 7 and BP # 6 (BP mode 1)
68

40

VLA phase centre

66

38

RA 18 14 27.26
DEC −25 03 00.46436+62
Ampl Jy

Ampl Jy

343260583056285426522450
22IF 1(LL)-160

IF 1(LL)-140-120-100

Scalar averaged cross-power spectrum-80-60
KM/S (LSR)
Several baselines averaged

-40

-20

0

-160

-140

-120

Scalar averaged cross-power spectrum

-100

-80
-60
KM/S (LSR)
Several baselines averaged

-40

-20

On the right, we show the previous E-VLA measurements of the water fountain fromGómez et al. 2011. We used these to derive the star’s line-of-sight velocity and thedirection of the jet. On the left, we see that the spectrum components have faded
considerably in the VERA observations. Detected masers are indicated by coloredlines (red: both epochs), showing that we could identify features even where there
were no peaks present in the spectrum. Due to the weakening of the masers, we will
start a single dish monitoring campaign using the Robledo 70m antenna. Axes on allmaps represent spatial offsets relative to the phase center of the observing beam.

This research has made use of the Japanese VLBI network of VLBI Exploration of Radio
Astrometry (VERA). G.O. would like to acknowledge the Ministry of Education, Culture,Sports, Sciences and Technology (MEXT), Japan for financial support under the
Monbukagakusho research scholarship.
Francis, C., & Anderson, E. 2009, NewA, 14, 615!
Gómez, J.F., Rizzo, J.R., Suárez, O., et al. 2011, ApJ, 739, L14!
Imai, H., Obara, K., Diamond, P., Omodaka, T., & Sasao, T. 2002 Nature 417, 829!
Sahai, R., & Trauger, J.T. 1998, AJ, 116, 1357!
Vlemmings, W.H.T., Diamond, P.J., & Imai, H. 2006, Nature, 440, 58
2014.09.24-25.