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CAS97 - Coincidence of maser emission from OH at 6.035 GHz and methanol at 6.668 GHz

Short title: Caswell (1997)
Authors: Caswell, J. L.
Journal: Monthly Notices of the Royal Astronomical Society, Volume 289, Issue 1, pp. 203-224.
Bibcode:

Target type: Known_Class_II
Transitions: OH_6035,CH3OH_6(II)

Abstract
Massive newly formed stars are obscured by dust, and their clearest signature is often at radio frequencies from strong molecular maser emission. In some cases, both hydroxyl and methanol masers are present. Maser position measurements of both species are then especially useful for exploring the immediate surroundings of the new-born star. The present study used the Australia Telescope Compact Array to observe 6.035-GHz OH maser emission in 35 fields 30 of these were also observed at the 6.668-GHz methanol transition. In many of the fields the masers were found to be grouped into several distinct maser sites, allowing a total of 62 sites to be studied. Relative positions at 6.035 and 6.668GHz could be registered to an accuracy of 0.1arcsec. 29 sites harbour both 6.035-GHz OH and 6.668-GHz methanol, and most of these have sufficient maser features to reveal that the distributions of OH and methanol are largely co-extensive, with total extents between 10 and 30mpc (milliparsec). Elongated morphologies are common in both the OH and methanol distributions. The new-born star associated with each group of masers is not visible, but is expected to generate an enveloping ultracompact H II region. Such H II regions have been detected (as compact radio sources, mostly by searching continuum images made from the present observations) at 23 of the present maser sites. For these, the projected distribution of the masers was mapped relative to the H II region. In most cases, the masers are confined to a zone that covers only a portion of the H II region, and is commonly offset from the centre of the H II region, but rarely lies at its projected boundary. The masing zone can be plausibly identified as centred on the (unseen) principal exciting star of the H II region, with the maser distribution corresponding to a torus or ring, in some cases small enough to suggest that it may be embedded within the H II region. The fact that the typical extent is confined to less than 30mpc can be used in some cases to establish distances once the angular extent has been measured. The sample of maser sites studied here is OH-selected and thus biased towards sites with strong OH emission. The high rate of strong H II region detections among them indicates a marked trend (but not a close correlation) for H II regions to be more prominent towards OH-favoured maser sites than methanol-favoured sites.

Abstract

Massive newly formed stars are obscured by dust, and their clearest signature is often at radio frequencies from strong molecular maser emission. In some cases, both hydroxyl and methanol masers are present. Maser position measurements of both species are then especially useful for exploring the immediate surroundings of the new-born star. The present study used the Australia Telescope Compact Array to observe 6.035-GHz OH maser emission in 35 fields 30 of these were also observed at the 6.668-GHz methanol transition. In many of the fields the masers were found to be grouped into several distinct maser sites, allowing a total of 62 sites to be studied. Relative positions at 6.035 and 6.668GHz could be registered to an accuracy of 0.1arcsec. 29 sites harbour both 6.035-GHz OH and 6.668-GHz methanol, and most of these have sufficient maser features to reveal that the distributions of OH and methanol are largely co-extensive, with total extents between 10 and 30mpc (milliparsec). Elongated morphologies are common in both the OH and methanol distributions. The new-born star associated with each group of masers is not visible, but is expected to generate an enveloping ultracompact H II region. Such H II regions have been detected (as compact radio sources, mostly by searching continuum images made from the present observations) at 23 of the present maser sites. For these, the projected distribution of the masers was mapped relative to the H II region. In most cases, the masers are confined to a zone that covers only a portion of the H II region, and is commonly offset from the centre of the H II region, but rarely lies at its projected boundary. The masing zone can be plausibly identified as centred on the (unseen) principal exciting star of the H II region, with the maser distribution corresponding to a torus or ring, in some cases small enough to suggest that it may be embedded within the H II region. The fact that the typical extent is confined to less than 30mpc can be used in some cases to establish distances once the angular extent has been measured. The sample of maser sites studied here is OH-selected and thus biased towards sites with strong OH emission. The high rate of strong H II region detections among them indicates a marked trend (but not a close correlation) for H II regions to be more prominent towards OH-favoured maser sites than methanol-favoured sites.

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Detection table from Caswell (1997)

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ID	Obs. RA	Obs. Dec	l	b	Group id	Source name	Descr.	Line	V_peak	F_peak	Telescope	Detection	Class	Dist. (parallax)	Date
	(J2000)	(J2000)	(deg.)	(deg.)				CH₃OH (class II)	(km/s)	(Jy)		Yes/No		(kpc)
1	10 24 10.9	-57 52 38.8	284.3516	-0.4191	G284.351-0.418	284.352-0.419		6.6 GHz (II);	3.3	1.7	ATCA	+H₂O -CH₃OH I +CH₃OH II +OH	SFR		95jul
2	11 35 32.2	-63 14 43	294.5114	-1.6212	G294.511-1.621	294.511-1.621		6.6 GHz (II);	-12	12	ATCA	+H₂O +OH			95jul
3	12 34 53.3	-61 39 39.9	300.9688	1.1476	G300.969+1.148	300.969+1.148		6.6 GHz (II);	-37.2	5.5	ATCA	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		93nov
4	13 11 16.9	-62 45 54.7	305.2000	0.0191	G305.200+0.019	305.200+0.019		6.6 GHz (II);	-33.1	44	ATCA	+H₂O -CH₃OH I +CH₃OH II +OH	SFR		93nov
5	13 11 17.2	-62 46 46	305.1995	0.0049	G305.200+0.019	305.199+0.005		6.6 GHz (II);	-42.8	2.28	ATCA	+H₂O -CH₃OH I +CH₃OH II +OH	SFR		93nov
6	13 50 41.8	-61 35 10.1	309.9205	0.4789	G309.921+0.479	309.921+0.479		6.6 GHz (II);	-59.8	635	ATCA	-H₂O +CH₃OH II +OH	SFR		95jul
7	14 06 38.7	-61 58 23.1	311.6427	-0.3800	G311.643-0.380	311.643-0.380		6.6 GHz (II);	32.5	11.6	ATCA	+H₂O +CH₃OH II +OH	SFR_MIXED		95jul
8	15 29 19.3	-56 31 21.3	323.4591	-0.0785	G323.459-0.079	323.459-0.079		6.6 GHz (II);	-66.9	19.2	ATCA	-H₂O +CH₃OH II +OH	SFR		94may
9	15 55 48.4	-52 43 6.7	328.8082	0.6331	G328.809+0.633	328.808+0.633		6.6 GHz (II);	-43.8	240	ATCA	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		94may
10	15 55 48.7	-52 43 5.5	328.8091	0.6328	G328.809+0.633	328.809+0.633		6.6 GHz (II);	-44.2	53	ATCA	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		94may
11	16 12 09	-51 25 47.7	331.5423	-0.0665	G331.543-0.066	331.542-0.066		6.6 GHz (II);	-85.9	7	ATCA	-H₂O +CH₃OH I +CH₃OH II +OH	SFR_MIXED		94may
12	16 12 9.1	-51 25 45.3	331.5430	-0.0662	G331.543-0.066	331.543-0.066		6.6 GHz (II);	-84.1	11.6	ATCA	-H₂O +CH₃OH I +CH₃OH II +OH	SFR_MIXED		94may
13	16 12 27.2	-51 27 38.2	331.5557	-0.1212	G331.556-0.121	331.556-0.121	Descr	6.6 GHz (II);	-103.4	35	ATCA	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		94may
14	16 20 49	-50 38 40.2	333.0680	-0.4469	G333.068-0.447	333.068-0.447		6.6 GHz (II);	-54.5	14.1	ATCA	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		93nov
15	16 20 59.7	-50 35 51.9	333.1210	-0.4337	G333.128-0.432	333.121-0.434		6.6 GHz (II);	-49.3	18.9	ATCA	+H₂O +OH			93nov
16	16 21 2.6	-50 35 54.8	333.1260	-0.4397	G333.128-0.432	333.126-0.440		6.6 GHz (II);	-43.9	3.9	ATCA	+H₂O +OH			93nov
17	16 21 3.3	-50 35 49.4	333.1282	-0.4399	G333.128-0.432	333.128-0.440		6.6 GHz (II);	-44.6	3.6	ATCA	+H₂O +OH			93nov
18	16 21 2.8	-50 35 12	333.1347	-0.4317	G333.128-0.432	333.135-0.431s		6.6 GHz (II);	-53	1	ATCA	+H₂O +OH			93nov
19	16 38 9.5	-47 04 59.9	337.6125	-0.0597	G337.613-0.060	337.613-0.060		6.6 GHz (II);	-43	17	ATCA	+H₂O +CH₃OH II +OH	SFR		94may
20	16 38 19.1	-47 04 53.5	337.6320	-0.0788	G337.632-0.079	337.632-0.079	Descr	6.6 GHz (II);	-57	11.6	ATCA	+CH₃OH II	SFR		94may
21	16 38 29.7	-47 00 35.8	337.7053	-0.0532	G337.705-0.053	337.705-0.053		6.6 GHz (II);	-54.6	120	ATCA	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		95jul
22	16 38 29.1	-47 00 43.2	337.7027	-0.0534	G337.705-0.053	337.703-0.053		6.6 GHz (II);	-44	4.8	ATCA	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		95jul
23	16 38 9.1	-46 11 3.1	338.2803	0.5424	G338.280+0.542	338.280+0.542		6.6 GHz (II);	-56.8	4.8	ATCA	+H₂O +CH₃OH II +OH	SFR		94m ay
24	16 50 14.8	-44 42 26.7	340.7849	-0.0960	G340.785-0.096	340.785-0.096		6.6 GHz (II);	-105.1	144	ATCA	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		94may
25	17 00 10.9	-42 07 19.4	343.9294	0.1249	G343.929+0.125	343.929+0.125		6.6 GHz (II);	14.3	12	ATCA	-H₂O +CH₃OH II +OH	SFR		94may
26	17 05 11.2	-41 29 07	345.0034	-0.2244	G345.003-0.224	345.003-0.224		6.6 GHz (II);	-26.2	73	ATCA	+H₂O +OH	SFR		94may
27	17 05 10.9	-41 29 6.2	345.0030	-0.2235	G345.003-0.224	345.003-0.223		6.6 GHz (II);	-22.5	240	ATCA	+H₂O +OH	SFR		94may
28	16 56 47.6	-40 14 25.7	345.0095	1.7924	G345.010+1.792	345.010+1.792		6.6 GHz (II);	-18	410	ATCA	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		94may
29	16 56 46.8	-40 14 8.9	345.0116	1.7972	G345.010+1.792	345.012+1.797	Descr	6.6 GHz (II);	-12.7	31	ATCA	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		94may
30	17 11 50.9	-39 09 29	347.6279	0.1486	G347.628+0.148	347.628+0.149		6.6 GHz (II);	-96.6	13.5	ATCA	+H₂O +CH₃OH II +OH	SFR		93nov
31	17 11 26.7	-39 09 22.5	347.5833	0.2127	G347.583+0.213	347.583+0.213		6.6 GHz (II);	-102.5	2.4	ATCA	+H₂O +CH₃OH II	SFR		93nov
32	17 11 36	-39 07 07	347.6315	0.2106	G347.631+0.211	347.631+0.211		6.6 GHz (II);	-91.9	11.2	ATCA	+H₂O +CH₃OH II +OH	SFR		93nov
33	17 19 20.4	-39 03 51.6	348.5498	-0.9788	G348.550-0.979	348.550-0.979		6.6 GHz (II);	-10	37	ATCA	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		95jul
34	17 19 20.4	-39 03 49.4	348.5503	-0.9786	G348.550-0.979	348.550-0.979n		6.6 GHz (II);	-20	32	ATCA	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		95jul
35	17 20 53.4	-35 47 1.2	351.4169	0.6453	G351.417+0.645	351.417+0.845		6.6 GHz (II);	-10.4	2600	ATCA	+H₂O +CH₃OH I +CH₃OH II +OH	SFR_MIXED		95jul
36	17 20 53.2	-35 46 59.3	351.4169	0.6461	G351.417+0.645	351.417+0.646	Descr	6.6 GHz (II);	-11.2	1500	ATCA	+H₂O +CH₃OH I +CH₃OH II +OH	SFR_MIXED		95jul
37	17 20 54.6	-35 45 8.6	351.4450	0.6596	G351.446+0.660	351.445+0.660	Descr	6.6 GHz (II);	-9.2	100	ATCA	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		95jul
38	17 25 25.1	-36 01 02	351.7428	-0.2432	G351.743-0.243	351.581-0.353		6.6 GHz (II);	-94.4	44	ATCA	+CH₃OH II +OH			93nov
39	17 25 25.2	-36 12 44.5	351.5814	-0.3529	G351.581-0.353	351.581-0.353n		6.6 GHz (II);	-91.1	2.3	ATCA	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		93nov
40	17 26 42.6	-36 09 16	351.7750	-0.5362	G351.775-0.536	351.775-0.536		6.6 GHz (II);	1.3	230	ATCA	+H₂O +OH	SFR		94may
41	17 30 26.2	-34 41 45.7	353.4098	-0.3602	G353.410-0.360	353.410-0.360		6.6 GHz (II);	-19.9	86.8	ATCA	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		94m ay
42	17 31 15.5	-33 14 5.6	354.7243	0.3001	G354.724+0.300	354.724+0.300		6.6 GHz (II);	93.8	16	ATCA	+H₂O +CH₃OH II +OH	SFR		95jul
43	17 33 29.1	-32 47 58.8	355.3437	0.1472	G355.344+0.147	355.344+0.147		6.6 GHz (II);	20	7.6	ATCA	+H₂O +OH	SFR		95jul
44	17 33 28.8	-32 47 59.7	355.3430	0.1479	G355.344+0.147	355.343+0.148		6.6 GHz (II);	5.7	0.81	ATCA	+H₂O +OH	SFR		95jul
45	17 33 28.9	-32 47 49	355.3457	0.1491	G355.344+0.147	355.346+0.149		6.6 GHz (II);	10	9.2	ATCA	+H₂O +OH	SFR		95jul
46	17 43 25.6	-29 39 18.3	359.1372	0.0315	G359.137+0.031	359.138+0.031		6.6 GHz (II);	-3.9	15.6	ATCA	+H₂O -CH₃OH I +CH₃OH II +OH	SFR_MIXED		95jul
47	17 47 18.6	-28 22 54.6	0.6663	-0.0289	G0.6665-0.0349	0.666-0.029		6.6 GHz (II);	72.2	24.1	ATCA	+H₂O +OH			93nov
48	18 12 11.4	-18 41 29.1	11.9040	-0.1411	G11.904-0.141	11.904-0.141		6.6 GHz (II);	42.8	56	ATCA	+H₂O -CH₃OH I +CH₃OH II +OH	SFR_MIXED		95jul
49	18 12 2.7	-18 40 24.7	11.9031	-0.1023	G11.903-0.102	11.903-0.102	Descr	6.6 GHz (II);	36	1.8	ATCA	-H₂O -CH₃OH I +CH₃OH II +OH	SFR		95jul
50	18 12 17.3	-18 40 2.6	11.9361	-0.1498	G11.936-0.150	11.936-0.150	Descr	6.6 GHz (II);	48.5	1.9	ATCA	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		95jul
51	18 20 24.8	-16 11 34.1	15.0347	-0.6770	G15.034-0.674	15.034-0.677		6.6 GHz (II);	21.2	28.5	ATCA	+H₂O +OH	GALAXY		95jul

DSS colored	2MASS colored	WISE colored
PACS color (70-160 um)	SPIRE color (250-500 um)	GLIMPSE 360
SDSS color	IRAC color I1,I2,I4	NVSS (1.4GHz)
ATLASGAL 870 um	ATLASGAL 870 um + Planck	Bolocam 1.1 mm
UKIDSS K Download UKIDSS K FITS	2MASS K Download 2MASS K FITS

select MAX(met2_data_all.ra_hms) as ra_hms,MAX(met2_data_all.dec_dms) as dec_dms,MAX(met2_data_all.source_name) as source_name,MAX(met2_data_all.ra) as ra,MAX(met2_data_all.dec) as dec,MAX(met2_data_all.l) as l,MAX(met2_data_all.b) as b,MAX(met2_data_all.grp) as grp,MAX(met2_data_all.other_name) as other_name,MAX(met2_data_all.other_desc) as other_desc,BOOL_OR(thermal) as thermal,MAX(met2_data_all.line) as line,MAX(met2_data_all.vrange) as vrange,MAX(met2_data_all.vpeak) as vpeak,MAX(met2_data_all.peak) as peak,MAX(met2_data_all.fwhm) as fwhm,MAX(met2_data_all.int) as int,MAX(met2_data_all.rms) as rms,MAX(met2_data_all.units) as units,MAX(met2_data_all.units_rms) as units_rms,MAX(met2_data_all.date_txt) as date_txt,MAX(met2_data_all.telescope_ref) as telescope_ref,MAX(met2_data_all.telescope_conf) as telescope_conf,MAX(met2_data_all.v_step) as v_step,MAX(met2_data_all.beam) as beam,MAX(met2_data_all.beam_maj) as beam_maj,MAX(met2_data_all.beam_min) as beam_min,MAX(met2_data_all.beam_pa) as beam_pa,MAX(met2_data_all.ref) as ref,MAX(met2_data_all.list_ref) as list_ref,MAX(met2_data_all.ascii) as ascii,MAX(met2_data_all.url) as url,MAX(met2_data_all.image) as image,MAX(met2_data_all.image2) as image2,MAX(met2_data_all.image3) as image3,MAX(met2_data_all.descr) as descr,MAX(met2_data_all.id) as id,BOOL_OR(mjy_flag) as mjy_flag,BOOL_OR(rms_mjy_flag) as rms_mjy_flag,MAX(met2_data_all.dist) as dist,1 as dist_parallax,MAX(met2_data_all.date_txt) as date_txt,MAX(line_det) as line_det,MAX(type) as type,MAX(simbad_types_cat) as simbad_types_cat FROM met2_data_all  LEFT JOIN all_objects_withmet ON met2_data_all.grp=all_objects_withmet.group_name LEFT JOIN object_categories ON all_objects_withmet.group_name = object_categories.group_name_cat AND object_categories.tbl_cat = 'all_objects_withmet' LEFT JOIN transitions ON met2_data_all.line=transitions."Line"  WHERE ref ilike 'CAS97' AND detected=true AND hide=false GROUP BY ref

select met2_data_all.ra_hms,met2_data_all.dec_dms,met2_data_all.source_name,met2_data_all.ra,met2_data_all.dec,met2_data_all.l,met2_data_all.b,met2_data_all.grp,met2_data_all.other_name,met2_data_all.other_desc,met2_data_all.thermal,met2_data_all.line,met2_data_all.vrange,met2_data_all.vpeak,met2_data_all.peak,met2_data_all.fwhm,met2_data_all.int,met2_data_all.rms,met2_data_all.units,met2_data_all.units_rms,met2_data_all.date_txt,met2_data_all.telescope_ref,met2_data_all.telescope_conf,met2_data_all.v_step,met2_data_all.beam,met2_data_all.beam_maj,met2_data_all.beam_min,met2_data_all.beam_pa,met2_data_all.ref,met2_data_all.list_ref,met2_data_all.ascii,met2_data_all.url,met2_data_all.image,met2_data_all.image2,met2_data_all.image3,met2_data_all.descr,met2_data_all.id,met2_data_all.mjy_flag,met2_data_all.rms_mjy_flag,met2_data_all.dist,met2_data_all.dist_parallax,met2_data_all.date_txt,line_det,type,simbad_types_cat FROM met2_data_all   LEFT JOIN all_objects_withmet ON met2_data_all.grp=all_objects_withmet.group_name LEFT JOIN object_categories ON all_objects_withmet.group_name = object_categories.group_name_cat AND object_categories.tbl_cat = 'all_objects_withmet' LEFT JOIN transitions ON met2_data_all.line=transitions."Line"  WHERE ref ilike 'CAS97' AND detected=true AND hide=false ORDER BY detected DESC,id

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CAS97 - Coincidence of maser emission from OH at 6.035 GHz and methanol at 6.668 GHz

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Detection table from Caswell (1997)