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CAS00 - Methanol masers at 107.0 and 156.6GHz

Short title: Caswell et al. (2000)
Authors: Caswell, J. L.Yi, JiyuneBooth, R. S.Cragg, D. M.
Journal: Monthly Notices of the Royal Astronomical Society, Volume 313, Issue 3, pp. 599-616.
Bibcode:

Target type: Known_Class_II
Transitions: CH3OH_107(II),CH3OH_156(II)

Abstract
From a search of more than 80 southern class II methanol maser sites, we report measurements of 22 masers at 107.0GHz and four at 156.6GHz, mostly new discoveries. Class II sites, recognized by their strong emission at the 6.6-GHz methanol transition, are indirect indicators of new-born massive stars, and several hundred have been documented only a handful of these had previously been found to exhibit maser emission at the 107.0- or 156.6-GHz transition. The present survey increases the number of known 107.0-GHz masers to 25, providing a sufficiently large sample to assess their general properties. For the stronger ones, our position measurements confirm that, to an accuracy of 5arcsec, they coincide with the dominant maser emission at 6.6GHz. Intensity variations exceeding 50 per cent have occurred in some 107.0-GHz maser features that we observed in both 1996 October and 1998 June. We find that masers are rare at the 156.6-GHz transition. Two new detections increase the total now known to four. Each 156.6-GHz maser is substantially weaker than its corresponding 107.0-GHz maser. Despite the scarcity of masers, our 156.6-GHz spectra at most observed sites show emission, but apparently of a quasi-thermal variety it is usually accompanied by somewhat weaker thermal emission at 107.0GHz, and the intensity ratio of the transitions allows us to begin exploration of the physical characteristics of the small molecular clouds (diameter less than 60mpc) at these sites. The thermal emission thus provides estimates of the environmental conditions that are needed to support strong masing from spots that are apparently embedded within these clouds.

Abstract

From a search of more than 80 southern class II methanol maser sites, we report measurements of 22 masers at 107.0GHz and four at 156.6GHz, mostly new discoveries. Class II sites, recognized by their strong emission at the 6.6-GHz methanol transition, are indirect indicators of new-born massive stars, and several hundred have been documented only a handful of these had previously been found to exhibit maser emission at the 107.0- or 156.6-GHz transition. The present survey increases the number of known 107.0-GHz masers to 25, providing a sufficiently large sample to assess their general properties. For the stronger ones, our position measurements confirm that, to an accuracy of 5arcsec, they coincide with the dominant maser emission at 6.6GHz. Intensity variations exceeding 50 per cent have occurred in some 107.0-GHz maser features that we observed in both 1996 October and 1998 June. We find that masers are rare at the 156.6-GHz transition. Two new detections increase the total now known to four. Each 156.6-GHz maser is substantially weaker than its corresponding 107.0-GHz maser. Despite the scarcity of masers, our 156.6-GHz spectra at most observed sites show emission, but apparently of a quasi-thermal variety it is usually accompanied by somewhat weaker thermal emission at 107.0GHz, and the intensity ratio of the transitions allows us to begin exploration of the physical characteristics of the small molecular clouds (diameter less than 60mpc) at these sites. The thermal emission thus provides estimates of the environmental conditions that are needed to support strong masing from spots that are apparently embedded within these clouds.

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Detection table from Caswell et al. (2000)

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ID	Obs. RA	Obs. Dec	l	b	Group id	Source name	Image	Line	V_peak	FWHM	F_peak	Telescope	RMS	Beam	Detection	Class	Dist. (parallax)	Date
	(J2000)	(J2000)	(deg.)	(deg.)				CH₃OH (class II)	(km/s)	(km/s)	(Jy)		(Jy)	(arcsec)	Yes/No		(kpc)
1	06 08 53.3	+21 38 29.2	188.9461	0.8859	G188.946+0.887	188.946+0.886	Image	107 GHz (II);	10.9	1	15.5	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	MIXED		1996 October 10-17
2	06 12 54	+17 59 24	192.6001	-0.0480	G192.599-0.048	192.600-0.048	Image	107 GHz (II);	4.2	4m	5.8	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II	MIXED		1996 October 10-17
3	13 51 58.5	-61 15 42.4	310.1439	0.7594	G310.144+0.760	310.144+0.760	Image	107 GHz (II);	-56	3m	23	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
4	15 00 55.4	-58 58 52.8	318.9478	-0.1962	G318.948-0.196	318.948-0.196	Image	107 GHz (II);	-34.2	1	5.7	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
5	15 00 55.4	-58 58 52.8	318.9478	-0.1962	G318.948-0.196	318.948-0.196		156.6 GHz (II);	-34.2		2.4	SEST	1.000	34	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
6	15 18 34.6	-56 38 24.9	322.1583	0.6361	G322.161+0.635	322.158+0.636	Image	107 GHz (II);	-57.2	5.8	9.9	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
7	15 18 34.6	-56 38 24.9	322.1583	0.6361	G322.161+0.635	322.158+0.636		156.6 GHz (II);	-57.2		26	SEST	1.000	34	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
8	15 31 45.5	-56 30 50.1	323.7401	-0.2626	G323.740-0.263	323.740-0.263	Image	107 GHz (II);	-50	3m	12.5	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	MIXED		1996 October 10-17
9	15 47 32.7	-53 52 38.4	327.1196	0.5108	G327.120+0.511	327.120+0.511	Image	107 GHz (II);	-89.8	1	9.2	SEST	1.000	48	+H₂O -CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
10	15 55 48.4	-52 43 6.6	328.8083	0.6330	G328.809+0.633	328.808+0.633	Image	107 GHz (II);	-43.5	1	5.5	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
11	16 35 9.3	-48 46 47.4	336.0180	-0.8272	G336.018-0.826	336.018-0.827	Image	107 GHz (II);	-40	2m	6	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
12	16 38 29.6	-47 00 35.5	337.7053	-0.0531	G337.705-0.053	337.705-0.053	Image	107 GHz (II);	-48.8	8.3	2.6	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
13	16 38 29.6	-47 00 35.5	337.7053	-0.0531	G337.705-0.053	337.705-0.053		156.6 GHz (II);	-48.8		6.4	SEST	1.000	34	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
14	16 52 4.7	-46 08 34.2	339.8840	-1.2588	G339.884-1.259	339.884-1.259	Image	107 GHz (II);	-33.6	8m	56	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
15	16 52 4.7	-46 08 34.2	339.8840	-1.2588	G339.884-1.259	339.884-1.259		156.6 GHz (II);	-33.6		4.9	SEST	1.000	34	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
16	16 48 13.9	-45 21 43.5	340.0544	-0.2436	G340.054-0.244	340.054-0.244	Image	107 GHz (II);	-62.8	1	2.9	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
17	16 50 14.8	-44 42 26.3	340.7850	-0.0960	G340.785-0.096	340.785-0.096	Image	107 GHz (II);	-105.9	18m	6.1	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
18	17 04 7.8	-42 18 39.5	344.2275	-0.5687	G344.228-0.569	344.227-0.569	Image	107 GHz (II);	-21.5	6.2	3.7	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
19	17 04 7.8	-42 18 39.5	344.2275	-0.5687	G344.228-0.569	344.227-0.569		156.6 GHz (II);	-21.5		9.8	SEST	1.000	34	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
20	17 05 10.9	-41 29 6.2	345.0030	-0.2235	G345.003-0.223	345.003-0.223	Image	107 GHz (II);	-26.9	2m	3.5	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
21	16 56 47.6	-40 14 25.8	345.0095	1.7924	G345.010+1.792	345.010+1.792	Image	107 GHz (II);	-21.7	4m	82	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
22	16 56 47.6	-40 14 25.8	345.0095	1.7924	G345.010+1.792	345.010+1.792		156.6 GHz (II);	-21.7		18	SEST	1.000	34	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
23	17 04 22.9	-40 44 22.4	345.5046	0.3483	G345.505+0.348	345.504+0.348	Image	107 GHz (II);	-17.7	<1	2.3	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
24	17 20 4.1	-38 58 30.9	348.7037	-1.0436	G348.720-1.039	348.703-1.043	Image	107 GHz (II);	-3.3	5m	7.6	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
25	17 20 53.4	-35 47 1.2	351.4169	0.6452	G351.417+0.645	351.417+0.645	Image	107 GHz (II);	-10.2	4	14.8	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	MIXED		1996 October 10-17
26	17 30 26.2	-34 41 45.6	353.4098	-0.3602	G353.410-0.360	353.410-0.360	Image	107 GHz (II);	-20	2m	5.5	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
27	18 06 14.7	-20 31 32.4	9.6210	0.1957	G9.621+0.195	9.621+0.196	Image	107 GHz (II);	-0.5	3m	22	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
28	18 14 39.5	-17 52 00	12.9086	-0.2603	G12.908-0.260	12.909-0.260	Image	107 GHz (II);	39.5	5m	5.5	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
29	18 34 40.3	-09 00 38.3	23.0097	-0.4106	G23.010-0.411	23.010-0.411	Image	107 GHz (II);	75.9	4m	5.2	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
30	18 34 39.2	-08 31 24.3	23.4401	-0.1822	G23.437-0.184	23.440-0.182	Image	107 GHz (II);	97.2	2m	4.4	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		1996 October 10-17
31	19 01 45.5	+01 13 35	35.2008	-1.7362	G35.200-1.737	35.201-1.736	Image	107 GHz (II);	42	7.5m	24	SEST	1.000	48	+H₂O +CH₃OH I +CH₃OH II +OH	MIXED		1996 October 10-17
32	19 01 45.5	+01 13 35	35.2008	-1.7362	G35.200-1.737	35.201-1.736		156.6 GHz (II);	42		4.6	SEST	1.000	34	+H₂O +CH₃OH I +CH₃OH II +OH	MIXED		1996 October 10-17

Non-detection table from Caswell et al. (2000)