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• Target type: High_mass_SFR
  Observations category: SF.general
  Facility type: interferometer
  Transitions: OH_1720,OH_4765
  

• Abstract

  We report Very Long Baseline Array (VLBA) observations of maser emission from the rotationally excited 2Π1/2,J=1/2 state of OH at 4765 MHz. We made phase-referenced observations of W3(OH) at both 4765 and 1720 MHz and found emission in three fields within a ~2000 AU diameter region and verified that in two of the three fields, 4765 and 1720 MHz emission arise from the same position to within ~4 mas (~8 AU). We imaged DR 21EX without phase referencing and detected six ~5 AU diameter emission regions along an approximately north-south arc with linear extent ~500 AU. In addition, we carried out phase-referenced observations of 4765 MHz emission from K3-50. We searched for the 4765 MHz line in W49 (without phase referencing) and W75N (phase-referenced to the strongest 4765 MHz maser feature in DR 21EX); we were unable to detect these sources with the VLBA. For 21/2 years (including the dates of the VLBA observations), we carried out monitoring observations of 4765 MHz emission with the Very Lary Array. Constraints on models for maser emission at 1720 and 4765 MHz are derived from the observations. These observations are then briefly compared with existing models.

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ID	Obs. RA	Obs. Dec	RA offset	Dec offset	l	b	Group id	grpv	#	Maser spot	Source name	Line	Frequency	Vpeak	Fpeak	Major	Minor	Telescope	Vstep	RMS	Beam	PA	Detection	Class	Dist. (parallax)	Date
	(J2000)	(J2000)	(mas)	(mas)	(deg.)	(deg.)						OH	(MHz)	(km/s)	(Jy/beam)	(arcsec)	(arcsec)		(km/s)	(mJy/beam)	(arcsec)	(deg.)	Yes/No		(kpc)
1	+02 27 3.81	+61 52 24.3			133.947348	1.064113	G133.947+1.064	G133.9475+1.0643			W3(OH)	4765 MHz;	4765	-45 .. -43.28	0.026 .. 0.41			NRAOVLA	0.29	5.000	0.003 x 0.002		+H2O +CH3OH I +CH3OH II +OH	SFR		2000 Jan 30 - 2002 Jul 24
	+02 27 3.8311	+61 52 25.097	316.5 mas	795.8 mas	133.947307	1.064335			1	1	W3(OH)		4765	-43.28	0.41	0.003	0.001
	+02 27 3.812	+61 52 24.14	30 mas	-161.2 mas	133.947368	1.064073			2	2	W3(OH)		4765	-43.39	0.042	0.013	0.004
	+02 27 3.7126	+61 52 24.661	-1461 mas	359.8 mas	133.947133	1.064138			3	3N	W3(OH)		4765	-45	0.033	0.020	0.004
	+02 27 3.7118	+61 52 24.642	-1473 mas	340.8 mas	133.947134	1.064132			4	3C	W3(OH)		4765	-45	0.032	0.011	0.004
	+02 27 3.7125	+61 52 24.633	-1462.5 mas	331.8 mas	133.947136	1.064130			5	3S	W3(OH)		4765	-45	0.026	0.015	0.006
2	+02 27 3.7687	+61 52 24.581			133.947244	1.064157	G133.947+1.064	G133.9475+1.0643			W3(OH)	1720 MHz;	1720	-45.6 .. -42.7	0.12 .. 20.8			NRAOVLA	0.29	5.000	0.006	49	+H2O +CH3OH I +CH3OH II +OH	SFR		2000 Jan 30 - 2002 Jul 24
	+02 27 3.8364	+61 52 25.317	1015.2 mas	735 mas	133.947295	1.064395			1	1	W3(OH)		1720	-43.47	9.1	0.003	0.003
	+02 27 3.8336	+61 52 25.305	973.2 mas	723 mas	133.947291	1.064390			2	1	W3(OH)		1720	-44.91	0.15	0.004	0.002
	+02 27 3.8324	+61 52 25.295	955.2 mas	713 mas	133.947289	1.064387			3	1	W3(OH)		1720	-45.6	20.8	0.004	0.002
	+02 27 3.8116	+61 52 24.144	643.2 mas	-438 mas	133.947367	1.064074			4	2	W3(OH)		1720	-43.77	2.9	0.007	0.004
	+02 27 3.8101	+61 52 24.153	620.7 mas	-429 mas	133.947363	1.064075			5	2	W3(OH)		1720	-44.53	0.21	0.007	0.005
	+02 27 3.7121	+61 52 24.664	-849.3 mas	82 mas	133.947132	1.064138			6	3	W3(OH)		1720	-45.26	0.15	0.035	0.007
	+02 27 3.8364	+61 52 25.317	1015.2 mas	735 mas	133.947295	1.064395			7	1	W3(OH)		1720	-42.7	14.6	0.003	0.003
	+02 27 3.8338	+61 52 25.306	976.2 mas	724 mas	133.947291	1.064391			8	1	W3(OH)		1720	-43.98	0.12	0.005	0.003
	+02 27 3.8323	+61 52 25.293	953.7 mas	711 mas	133.947289	1.064386			9	1	W3(OH)		1720	-44.87	15.5	0.004	0.003
	+02 27 3.8116	+61 52 24.143	643.2 mas	-439 mas	133.947367	1.064074			10	2	W3(OH)		1720	-43.13	2.7	0.007	0.004
	+02 27 3.8102	+61 52 24.152	622.2 mas	-430 mas	133.947363	1.064075			11	2	W3(OH)		1720	-43.43	0.88	0.006	0.004
	+02 27 3.712	+61 52 24.663	-850.8 mas	81 mas	133.947132	1.064138			12	3	W3(OH)		1720	-44.66	0.13	0.031	0.008
3	+20 01 45.7824	+33 32 45.446			70.29345	1.600257	G70.293+1.600	G70.2928+1.6004			K3-50	4765 MHz;	4765	-20.35	0.62			NRAOVLA	0.29	5.000	0.004		+OH	SFR_MIXED		2000 Jan 30 - 2002 Jul 24
	+20 01 45.7249	+33 32 44.938	-862.5 mas	-507.2 mas	70.293225	1.600352			1		K3-50		4765	-20.35	0.62	0.006	0.003
4	+20 39 0.4235	+42 24 38.901			81.744878	0.591135	G81.762+0.596	G81.7444+0.5910			DR21EX	4765 MHz;	4765	2.37 .. 5.69	0.25 .. 0.89			NRAOVLA	0.29	5.000	0.006 x 0.004	23	+H2O +CH3OH I +CH3OH II +OH	SFR		2000 Jan 30 - 2002 Jul 24
	+20 39 0.3801	+42 24 37.332	-652.5 mas	-1569.6 mas	81.744451	0.590976			1	1	DR21EX		4765	2.37	0.54	0.005	0.003
	+20 39 0.377	+42 24 37.28	-699 mas	-1621.6 mas	81.744433	0.590974			2	2	DR21EX		4765	3.48	0.89	0.005	0.003
	+20 39 0.3759	+42 24 37.259	-715.5 mas	-1642.6 mas	81.744427	0.590974			3	3	DR21EX		4765	3.72	0.25	0.005	0.004
	+20 39 0.3772	+42 24 37.204	-696 mas	-1697.6 mas	81.744417	0.590961			4	4	DR21EX		4765	4.46	0.38	0.006	0.002
	+20 39 0.378	+42 24 37.19	-684 mas	-1711.6 mas	81.744415	0.590957			5	5	DR21EX		4765	4.95	0.44	0.007	0.004
	+20 39 0.3791	+42 24 37.111	-667.5 mas	-1790.6 mas	81.744400	0.590941			6	6	DR21EX		4765	5.69	0.32	0.004	0.003
5	+20 38 36.5584	+42 37 34.83			81.871514	0.780325	G81.871+0.781	G81.8715+0.7806			W75N	4765 MHz;	4765	..	..			NRAOVLA	0.29	5.000			+H2O +CH3OH I +CH3OH II +OH	SFR_MIXED		2000 Jan 30 - 2002 Jul 24
6	+19 10 10.9478	+09 05 17.592			43.148124	0.013068	G43.166+0.011	G43.1490+0.0131			W49	4765 MHz;	4765	..	..			NRAOVLA	0.29	5.000			+H2O +CH3OH I +CH3OH II +OH	SFR_MIXED		2000 Jan 30 - 2002 Jul 24