spectral and vlbi-structure monitoring of oh-maser flare in w75n: preliminary results alexey alakoz...

Spectral and VLBI-Spectral and VLBI-structure monitoring of structure monitoring of

OH-maser flare in W75N: OH-maser flare in W75N: preliminary resultspreliminary results

Alexey Alakoz & Vyacheslav Slysh

Astro Space Center

Moscow, Russia

8th EVN Symposium 2006

Exploring the Universe with the real-time VLBI


Exploring the Universe with the real-time VLBI A. Alakoz V. Slysh

OutlineOutline

Background Background Star-forming region W75NStar-forming region W75N Nancey (single dish) observationsNancey (single dish) observations VLBA archive data VLBA archive data Kalyazin 64-m (single dish) Kalyazin 64-m (single dish)

observationsobservations EVN observationsEVN observations Summary Summary


Exploring the Universe with the real-time VLBI A. Alakoz & V. Slysh

Scientific backgroundScientific background To understand To understand

physical physical conditions in conditions in high-mass star-high-mass star-forming regions.forming regions.

To observe To observe strong , long-strong , long-term burst of OH term burst of OH maser emission maser emission at 1665 MHzat 1665 MHz

Regular single-Regular single-dish monitoring dish monitoring (Kalyazin 64m, (Kalyazin 64m, Russia ) Russia )

EVN EVN observations at observations at several epochs several epochs (fine-scale (fine-scale structure, proper structure, proper motions etc.)motions etc.)



W75NW75N

W75N – high mass star forming region at a W75N – high mass star forming region at a distance of 2 kpc (Dickel et al. 1979) in Cyg X distance of 2 kpc (Dickel et al. 1979) in Cyg X containing various UC H II regions and OH, H2O and CH3OH maser emission.

The region of strong OH maser emission coincides with two continuum sources, identified as VLA 1 and VLA 2 by Torrelles et al. (1997)

Since 2003 has become one of the strongest 1665 MHz OH masers ever observed (flux ~ 1 kJy).


Exploring the Universe with the real-time VLBI A. Alakoz V. Slysh



NRAO VLBA data archive search (BF064 V. Fish 11/22/2000 01/06/2001 )



W75N

R.A. offset (mas)

Dec.

off

set

(mas)

Reference position α=20h38m36.414s δ=42o37'’35.44’’



Observations: Kalyazin Observations: Kalyazin 64-m ant., 1665 GHz64-m ant., 1665 GHz

W75N jul 2004 RCP W75N oct 2004 RCP

W75N may 2005 RCP W75N jul 2005 RCP




W75N nov 2005 RCP W75N mar 2006 RCP




W75N may 2005

W75N mar 2006

W75N jul 2005

W75N nov 2005



EVN EVN

EA035A 12h 5 Nov. 2005 Jb Wb Ef Mc Ur On Tr EA035A 12h 5 Nov. 2005 Jb Wb Ef Mc Ur On Tr EA035B 12h 2 Mar. 2006 Jb Wb Ef Mc Ur On Tr EA035B 12h 2 Mar. 2006 Jb Wb Ef Mc Ur On Tr

Nt Nt EA035C 12h 7 Jun. 2006 Jb Wb Ef Mc Ur On Tr EA035C 12h 7 Jun. 2006 Jb Wb Ef Mc Ur On Tr

NtNt

1667+1665 MHz1667+1665 MHz

nchan = 4 samprate = 4 bits= 2 bbfilter nchan = 4 samprate = 4 bits= 2 bbfilter = 0.5 pol= dual, cross= 0.5 pol= dual, cross

+ data from + data from BF079 BF079 V. V. Fish VLBA Fish VLBA 09/16/2004 09/16/2004



W75N

R.A. offset (mas)

Dec.

off

set

(mas)

Reference position α=20h38m36.414s δ=42o37'’35.44’’

VLA1

VLA2



VLA1

VLA2



09/2004-09/2004-06/200606/2006

NN11 NN22

ΔαΔα +1.36 +1.36 masmas

-0.41 -0.41 masmas

+/- 0.3 +/- 0.3 masmas

ΔδΔδ -0.31 -0.31 masmas

+1.29 +1.29 masmas

SummarySummary



•A new flare of the OH maser emission source W75N has appeared in 2003, after the 100-Jy flare of 2000. Three major spectral features N1, N2, and N3 were present at all epochs, with N1 declining and N2 increasing in flux density during the period of observations 2003-2006.• All three features have strong linear polarization approaching 90 per cent. VLBI maps show that along with the strong features N1-3, many weaker features have appeared within 100 mas of the ultra compact HII region VLA 2. •All the maser spots are aligned along two almost orthogonal straight lines centred on VLA 1 and VLA 2, respectively. A possible model involves two edge-on discs surrounding the two ultra compact regions.



•Preliminary analysis of the proper motion for the flare feature N1 gives:Delta alpha=1.36+/-0.3; Delta delta= -0.31+/-0.3 mas in 1.75 years. This corresponds to the tangential velocity of about 8 km/s relative to the rest of the features, and is comparable to the radial velocity range in the VLA 2 disk. •The OH maser flare can be explained as a result of a MHDshock which is travelling from the young star and energizes maser emission in clumps encountered on its way out.

SummarySummary

spectral and vlbi-structure monitoring of oh-maser flare in w75n: preliminary results alexey alakoz...

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