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DOD02 - A search for 4750- and 4765-MHz OH masers in southern star-forming regions

Interferometry data

Short title: Dodson & Ellingsen (2002)
Authors: Dodson, R. G.Ellingsen, S. P.
Journal: Monthly Notices of the Royal Astronomical Society, Volume 333, Issue 2, pp. 307-317.
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Target type: High_mass_SFR,OH
Observations category: SF.general
Facility type: interferometer
Transitions: OH_1612,OH_1665,OH_1667,OH_1720,OH_4750,OH_4765,OH_6030,OH_6035

Abstract
We have used the Australia Telescope Compact Array (ATCA) to make a sensitive (5Ïƒ~=100mJy) search for maser emission from the 4765-MHz <SUP>2</SUP>Î <SUB>1/2</SUB> F=1->0 transition of OH. 55 star formation regions were searched and maser emission with a peak flux density in excess of 100mJy was detected toward 14 sites, with 10 of these being new discoveries. In addition we observed the 4750-MHz <SUP>2</SUP>Î <SUB>1/2</SUB> F=1->1 transition towards a sample of star formation regions known to contain 1720-MHz OH masers, detecting marginal maser emission from G348.550-0.979. If confirmed this would be only the second maser discovered from this transition. The occurrence of 4765-MHz OH maser emission accompanying 1720-MHz OH masers in a small number of well-studied star formation regions has led to a general perception in the literature that the two transitions favour similar physical conditions. Our search has found that the presence of the excited-state 6035-MHz OH transition is a much better predictor of 4765-MHz OH maser emission from the same region than 1720-MHz OH maser emission is. Combining our results with those of previous high-resolution observations of other OH transitions we have examined the published theoretical models of OH masers and find that none of them predicts any conditions in which the 1665-, 6035- and 4765-MHz transitions are inverted simultaneously.

Abstract

We have used the Australia Telescope Compact Array (ATCA) to make a sensitive (5Ïƒ~=100mJy) search for maser emission from the 4765-MHz 2Î 1/2 F=1->0 transition of OH. 55 star formation regions were searched and maser emission with a peak flux density in excess of 100mJy was detected toward 14 sites, with 10 of these being new discoveries. In addition we observed the 4750-MHz 2Î 1/2 F=1->1 transition towards a sample of star formation regions known to contain 1720-MHz OH masers, detecting marginal maser emission from G348.550-0.979. If confirmed this would be only the second maser discovered from this transition. The occurrence of 4765-MHz OH maser emission accompanying 1720-MHz OH masers in a small number of well-studied star formation regions has led to a general perception in the literature that the two transitions favour similar physical conditions. Our search has found that the presence of the excited-state 6035-MHz OH transition is a much better predictor of 4765-MHz OH maser emission from the same region than 1720-MHz OH maser emission is. Combining our results with those of previous high-resolution observations of other OH transitions we have examined the published theoretical models of OH masers and find that none of them predicts any conditions in which the 1665-, 6035- and 4765-MHz transitions are inverted simultaneously.

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Detection table from Dodson & Ellingsen (2002)

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ID	Obs. RA	Obs. Dec	RA offset	Dec offset	l	b	Group id	#	Maser spot	Source name	Image	Descr.	Line	Frequency	V_peak	F_peak	Telescope	V_step	RMS	Beam	Detection	Class	Dist. (parallax)	Date
	(J2000)	(J2000)	(mas)	(mas)	(deg.)	(deg.)							OH	(MHz)	(km/s)	(Jy)		(km/s)	(Jy)	(arcsec)	Yes/No		(kpc)
1	+11 35 32.208	-63 14 43			294.511437	-1.621165	G294.511-1.621			G294.511-1.621	Image		4750 MHz;	4750	..	..	ATCA	0.3	0.020	1.5	+H₂O -CH₃OH I +CH₃OH II +OH	SFR		1999 August 25-26
2	+17 30 26.189	-34 41 45.74			353.409783	-0.360197	G353.410-0.360			G353.410-0.360	Image	Descr	4750 MHz;	4750	..	..	ATCA	0.3	0.040	1.5	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1999 August 25-26
3	+17 47 20.143	-28 23 6.18			0.666444	-0.035301	G0.6665-0.0344			G0.666-0.035	Image		4750 MHz;	4750	..	..	ATCA	0.3	0.100	1.5	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1999 August 25-26
4	+07 44 51.971	-24 07 42.32			240.315796	0.071173	G240.316+0.071			G240.316+0.071	Image		4765 MHz;	4765	62.9 .. 66.7	0.11 .. 0.31	ATCA	0.3	0.016	1.5	+H₂O -CH₃OH II +OH	SFR_MIXED		2000 September 15-16
	+07 44 51.982	-24 07 42	164.4 mas	319.2 mas	240.315740	0.071254		1	G240.316+0.071	G240.316+0.071					65	0.31
	+07 44 51.982	-24 07 42	164.4 mas	319.2 mas	240.315740	0.071254		2	G240.316+0.071	G240.316+0.071					62.9	0.17
	+07 44 52	-24 07 22	434.4 mas	20319.2 mas	240.310964	0.074092		3	G240.311+0.074	G240.311+0.074					66.7	0.11
5	+11 35 32.208	-63 14 43			294.511437	-1.621165	G294.511-1.621			G294.511-1.621	Image		4765 MHz;	4765	-12	2.02	ATCA	0.3	0.018	1.5	+H₂O -CH₃OH I +CH₃OH II +OH	SFR		2000 September 15-16
	+11 35 32.232	-63 14 43.12	360 mas	-119.2 mas	294.511490	-1.621184		1	G294.511-1.621	G294.511-1.621					-12	2.02
6	+13 50 41.773	-61 35 10.08			309.920516	0.478934	G309.921+0.479			G309.921+0.479	Image		4765 MHz;	4765	-60.9	0.17	ATCA	0.3	0.016	1.5	-H₂O +CH₃OH II +OH	SFR		2000 September 15-16
	+13 50 41.77	-61 35 9.9	-44.4 mas	178.8 mas	309.920522	0.478984		1	G309.921+0.479	G309.921+0.479					-60.9	0.17
7	+15 54 6.437	-53 11 41.11			328.307038	0.43026	G328.307+0.430			G328.307+00.43			4765 MHz;	4765	-91.8 .. -90.5	0.12 .. 0.16	ATCA	0.3	0.022	1.5	+H₂O -CH₃OH II +OH	SFR		2000 September 15-16
	+15 54 3.94	-53 11 32.2	-37455.6 mas	8910.8 mas	328.303806	0.436137		1	G328.304+0.436	G328.304+0.436					-91.8	0.12
	+15 54 6.38	-53 11 41	-855.6 mas	110.8 mas	328.306947	0.430374		2	G328.307+0.430	G328.307+0.430					-90.5	0.16
8	+15 55 48.387	-52 43 6.69			328.808191	0.633099	G328.809+0.633			G328.808+0.633	Image		4765 MHz;	4765	-44.6 .. -43.4	0.14 .. 0.17	ATCA	0.3	0.020	1.5	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2000 September 15-16
	+15 55 48.33	-52 43 6.5	-856.8 mas	190 mas	328.808114	0.633232		1	G328.808+0.633	G328.808+0.633					-44.6	0.17
	+15 55 48.42	-52 43 6.2	493.2 mas	490 mas	328.808342	0.633150		2	G328.809+0.633	G328.809+0.633					-43.4	0.14
9	+16 21 2.821	-50 35 12.01			333.134738	-0.431682	G333.128-0.432			G333.135-0.431	Image		4765 MHz;	4765	-54.3 .. -51.2	0.1 .. 0.14	ATCA	0.3	0.024	1.5	+H₂O +CH₃OH I +CH₃OH II +OH	SFR_MIXED		2000 September 15-16
	+16 21 2.8	-50 35 10.1	-314.4 mas	1908.4 mas	333.135073	-0.431267		1	G333.135-0.431	G333.135-0.431					-51.2	0.14
	+16 21 2.78	-50 35 12.7	-614.4 mas	-691.6 mas	333.134526	-0.431741		2	G333.135-0.431s	G333.135-0.431s					-54.3	0.1
10	+17 30 26.189	-34 41 45.74			353.409783	-0.360197	G353.410-0.360			G353.410-0.360	Image		4765 MHz;	4765	-20.8	1.78	ATCA	0.3	0.016	1.5	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2000 September 15-16
	+17 30 26.182	-34 41 46.15	-105.6 mas	-409.6 mas	353.409675	-0.360240		1	G353.410-0.360	G353.410-0.360					-20.8	1.78
11	+17 47 20.143	-28 23 6.18			0.666444	-0.035301	G0.6665-0.0344			G0.666-0.035	Image		4765 MHz;	4765	49.6	0.07	ATCA	0.3	0.036	1.5	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2000 September 15-16
	+17 47 20.143	-28 23 6.18	0.6 mas	0 mas	0.666444	-0.035301		1	G0.666-0.035	G0.666-0.035					49.6	0.07
12	+18 12 11.437	-18 41 29.05			11.903955	-0.141128	G11.904-0.141			G11.904-0.141	Image		4765 MHz;	4765	41.8	1	ATCA	0.3	0.018	1.5	+H₂O -CH₃OH I +CH₃OH II +OH	SFR		2000 September 15-16
	+18 12 11.437	-18 41 29	0.6 mas	50.8 mas	11.903967	-0.141122		1	G11.904-0.141	G11.904-0.141					41.8	1
13	+19 10 12.006	+09 06 11.25			43.163356	0.016088	G43.166+0.011			W49N	Image		4765 MHz;	4765	2.3 .. 11.9	0.12 .. 0.63	ATCA	0.3	0.022	1.5	+H₂O +CH₃OH I +CH₃OH II +OH	SFR_MIXED		2000 September 15-16
	+19 10 10.9	+09 05 23	-16590 mas	-48250 mas	43.149366	0.013936		1	W49SW	W49SW					8.6	0.24
	+19 10 10.9	+09 05 23	-16590 mas	-48250 mas	43.149366	0.013936		2	W49SW	W49SW					11.9	0.12
	+19 10 13.51	+09 06 15	22560 mas	3750 mas	43.167137	0.011081		3	W49N	W49N					2.3	0.63
	+19 10 14.3	+09 06 24	34410 mas	12750 mas	43.170855	0.009352		4	W49NW	W49NW					2.7	0.34

Non-detection table from Dodson & Ellingsen (2002)