ㅇMotion of Water Masers Associated witha Star-Forming Region W75N†
Soon-Wook Kim *1, Jeong-Sook Kim 1,21Korea Astronomy and Space Science Institute2Kyunghee University, Department of Astronomy and Space ScienceABSTRACT
Water masers in a star-forming region W75N is observed with VERA in 2007 January and May. The observations were carried out with phase referencing byadopting another target of dual beam, Cyg X-3. Maser spots were detected in VLA-1 and VLA-2 regions. In VLA-1, we cannot confirm the signature ofelongated outflow observed with VLBA in 1999, due to lacks of spots in 2007 January. On the contrary, our observation of 2007 May is almost consistent with1999 VLBA observations: a central object is driving an outflow, expanding in multiple direction.

† Collaboration with Honma, Mareki (VERA觀測所) Kurayama, Tomoharu (韓國天文硏究院) Sasao, Tetsuo (亞州大學校, KVN)

Summary: Maser Features Observed with VERAW75N: Introduction
1850• W75N region is an area of continuing• W75N is situated close to a compact
HⅡ regions and most of W75N region isin a proto-stellar phase based on thepresent of water, OH and methanol
maser .

2007 May1450

VLA-1
1250
1050
850
650
450250-200

0200400600

8001000mas• It lies at an approximate distance 2kpc.
• In W75N (B), there are three radio
continuum sources (VLA-1, VLA-2 andVLA-3) within a region of 1.”5.

2007 January

2007_January
2007_May

1650

mas

active star formation of the northeastern edge of the Cygnus-X complex
about 1°.5 to the north-east of theCygnus –OB2 association.

VLA-1:
Water masers were detected within ~800 and ~1,300 mas, similar to 1999 VLBA
observations. However, unlike Torrelles et al., we cannot define the pattern of the distributionof spots in VLA-1 due to a small number of spots.
This can be, for example, due to disappearance of number of spots observed in 1999.

Figure 1: A color image of the full D21/W75 mosaic observed with the Spitzer
Space Telescope, composed from image in 3.6㎛ (blue), 4.5㎛(greem) and 8㎛(red). Counters represent the 850㎛ emission mapped using SCUBA and JCMT
(Kumar et al,2007,MNRAS).

502007 January
2007_May
2007_January

2007 May0-100-50

0VLBA Observations of W75N in 1999

VLA1

VLA2(VLA3)

Figure 2. Self-calibrated image of W75N
region observed with VLBA (Torrelles et al.
ApJ 598, L115, 2003 December 1)• Active water maser-emitting regions in
W75N were observed with VLBA threetimes in 1999 April, May & June (Torrelleset al. 2003).
• The self-calibration was performed withAIPS.
• Clusters of water masers were setectedin VLA-1 and VLA-2 regions. On thecontrary, no maser spot was found inVLA-3.
• In total, ∼700 spots were detected inVLA1 & VLA2, with 54 spots at all threeepochs and 44 in only two epochs.
• The distribution of water masers inVLA-1 are extended to ~1600 AU, andseem to be a collimated outflow parallelto the elongated radio continuum
structure, with proper motions of~2 mas/yr (~19 km/s) for 2 kpc.
• On the contrary, in VLA-2, watermasers are distributed on a shell with aradius of ~160 AU, expanding outward
from the central source with a mean
proper motion of ~3 mas/yr (~28 km/s).

VERA Observation of W75N
• We here present our two VERA observations carried out on 2007 January 20
and May 18, time span of 4 months, for H2O maser (616 → 523: ν = 22235.080
MHz).
• This time span is set by flare activity in Cyg X-3, another target of the dualbeam with 2.2 degree.
• W75N data was analyzed with phase referencing technique by adopting fringe
results of Cyg X-3.

50100150200

2007
January-50-100-150

VLA-2-200

VLA-2:
Quite similar to 1999 VLBA observations, a cluster of 2007
water masers with radius of ≥150 masMay
was detected in our observations in 2007.
The feature of expanding shell of spots also look alike, except missing motions of spots in thedirections of north-east and south-west from 1999 VLBA observations.
This is probably due to much longer time span of 4 months, enough for spots to change theirstructure, compared with shorter,1- 1.5 month interval in 1999 VLBA observations.

Discussion & Future works• Features of water maser spots in W75N we presented here are based on phase referencing
with respect to Cyg X-3, another target of the dual-beam. In addition to these observationsof 2007 January and May, we also observed W75N in 2007 February, which cannot be donewith the phase referencing due to the low flux state of Cyg X-3 under VERA’s detection limit.
• Only with a relatively long, five-month, interval of January-May, we could not compare ourobservation directly to 1999 VLBA observations of Torrelles et al., in particular for VLA-1
region.
• In our observation of 2007 Janaury and May, VLSR ranges from +5 to +15 km/s, while, inTorrelles et al., broader range of VLSR, -10~+15 km/s, were presented in 1999.
• We, therefore, will perform the self-calibration of W75N all for 2007 January, February andMay.
• With the January-February interval, it is expected to see the motion of maser spots moreclearly than the case of January-May interval we presented here. In addition, the correlationof spots among January, February and May will be clarified.
• Since we have newly adopted two known quasars in the 2008-2009 VERA Open User
Observations, we will investigate the proper motion of W75N.