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VLE11 - Zeeman splitting of 6.7 GHz methanol masers. On the uncertainty of magnetic field strength determinations

Short title: Vlemmings et al. (2011)
Authors: Vlemmings, W. H. T.Torres, R. M.Dodson, R.
Journal: Astronomy & Astrophysics, Volume 529, id.A95, 12 pp.
Bibcode:

Non-detection table: Show non-detection table
Detection table: Show detection table (59 detection) Non-detection table: Show non-detection table (5 non-detection)
Target type: Known_Class_II
Transitions: CH3OH_6(II)

Abstract
Context. To properly determine the role of magnetic ﬁelds during massive star formation, a statistically signiﬁcant sample of ﬁeld measurements probing diﬀerent densities and regions around massive protostars needs to be established. However, relating Zeeman splitting measurements to magnetic ﬁeld strengths needs a carefully determined splitting coeﬃcient. Aims. Polarization observations of, in particular, the very abundant 6.7 GHz methanol maser, indicate that these masers appear to be good probes of the large scale magnetic ﬁeld around massive protostars at number densities up to nH2 ≈ 109 cm𕒷. We thus investigate the Zeeman splitting of the 6.7 GHz methanol maser transition. Methods. We have observed of a sample of 46 bright northern hemisphere maser sources with the Eﬀelsberg 100-m telescope and an additional 34 bright southern masers with the Parkes 64-m telescope in an attempt to measure their Zeeman splitting. We also revisit the previous calculation of the methanol Zeeman splitting coeﬃcients and show that these were severely overestimated making the determination of magnetic ﬁeld strengths highly uncertain. Results. In total 44 of the northern masers were detected and signiﬁcant splitting between the right- and left-circular polarization spectra is determined in >75% of the sources with a ﬂux density >20 Jy beam𕒵. Assuming the splitting is due to a magnetic ﬁeld according to the regular Zeeman eﬀect, the average detected Zeeman splitting corrected for ﬁeld geometry is 𕙘.6 m s𕒵. Using an estimate of the 6.7 GHz A-type methanol maser Zeeman splitting coeﬃcient based on old laboratory measurements of 25 GHz E-type methanol transitions this corresponds to a magnetic ﬁeld of � mG in the methanol maser region. This is signiﬁcantly higher than expected using the typically assumed relation between magnetic ﬁeld and density (B ∝ nH0.247) and potentially indicates the extrapolation of the available laboratory measurements is invalid. The stability of the right- and left-circular calibration of the Parkes observations was insuﬃcient to determine the Zeeman splitting of the Southern sample. Spectra are presented for all sources in both samples. Conclusions. There is no strong indication that the measured splitting between right- and left-circular polarization is due to non- Zeeman eﬀects, although this cannot be ruled out until the Zeeman coeﬃcient is properly determined. However, although the 6.7 GHz methanol masers are still excellent magnetic ﬁeld morphology probes through linear polarization observations, previous derivations of magnetic ﬁelds strength turn out to be highly uncertain. A solution to this problem will require new laboratory measurements of the methanol Landé-factors.

Abstract

Context. To properly determine the role of magnetic ﬁelds during massive star formation, a statistically signiﬁcant sample of ﬁeld measurements probing diﬀerent densities and regions around massive protostars needs to be established. However, relating Zeeman splitting measurements to magnetic ﬁeld strengths needs a carefully determined splitting coeﬃcient. Aims. Polarization observations of, in particular, the very abundant 6.7 GHz methanol maser, indicate that these masers appear to be good probes of the large scale magnetic ﬁeld around massive protostars at number densities up to nH2 ≈ 109 cm𕒷. We thus investigate the Zeeman splitting of the 6.7 GHz methanol maser transition. Methods. We have observed of a sample of 46 bright northern hemisphere maser sources with the Eﬀelsberg 100-m telescope and an additional 34 bright southern masers with the Parkes 64-m telescope in an attempt to measure their Zeeman splitting. We also revisit the previous calculation of the methanol Zeeman splitting coeﬃcients and show that these were severely overestimated making the determination of magnetic ﬁeld strengths highly uncertain. Results. In total 44 of the northern masers were detected and signiﬁcant splitting between the right- and left-circular polarization spectra is determined in >75% of the sources with a ﬂux density >20 Jy beam𕒵. Assuming the splitting is due to a magnetic ﬁeld according to the regular Zeeman eﬀect, the average detected Zeeman splitting corrected for ﬁeld geometry is 𕙘.6 m s𕒵. Using an estimate of the 6.7 GHz A-type methanol maser Zeeman splitting coeﬃcient based on old laboratory measurements of 25 GHz E-type methanol transitions this corresponds to a magnetic ﬁeld of � mG in the methanol maser region. This is signiﬁcantly higher than expected using the typically assumed relation between magnetic ﬁeld and density (B ∝ nH0.247) and potentially indicates the extrapolation of the available laboratory measurements is invalid. The stability of the right- and left-circular calibration of the Parkes observations was insuﬃcient to determine the Zeeman splitting of the Southern sample. Spectra are presented for all sources in both samples. Conclusions. There is no strong indication that the measured splitting between right- and left-circular polarization is due to non- Zeeman eﬀects, although this cannot be ruled out until the Zeeman coeﬃcient is properly determined. However, although the 6.7 GHz methanol masers are still excellent magnetic ﬁeld morphology probes through linear polarization observations, previous derivations of magnetic ﬁelds strength turn out to be highly uncertain. A solution to this problem will require new laboratory measurements of the methanol Landé-factors.

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ID	Obs. RA	Obs. Dec	l	b	Group id	Source name	Other name	Image	Line	V_peak	F_peak	∫F dv	Telescope	Beam	Detection	Class	Dist. (parallax)	Date
	(J2000)	(J2000)	(deg.)	(deg.)			Other name		CH₃OH (class II)	(km/s)	(Jy/beam)	(Jy/beam*km/s)		(arcsec)	Yes/No		(kpc)
1	18 09 1.5	-20 05 08	10.3226	-0.1598	G10.322-0.148	G10.32-0.15	IRAS 18060-2005	Image	6.6 GHz (II);	10	100	152	EFF	120	+H₂O +CH₃OH I +CH₃OH II	SFR_MIXED		2008 June 17-27
2	18 08 38.2	-19 51 49.5	10.4724	0.0274	G10.472+0.027	G10.47+0.026	IRAS 18056-1952	Image	6.6 GHz (II);	75	38	96	EFF	120	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 June 17-27
3	18 16 22.1	-19 41 27.5	11.4973	-1.4854	G11.499-1.485	G11.49-1.486	IRAS 18134-1942	Image	6.6 GHz (II);	6.2	77	176	EFF	120	+H₂O -CH₃OH I +CH₃OH II	SFR		2008 June 17-27
4	18 12 1.8	-18 31 55.5	12.0255	-0.0314	G12.025-0.032	G12.02-0.03	IRAS 18090-1832	Image	6.6 GHz (II);	108	102	118	EFF	120	-H₂O -CH₃OH I +CH₃OH II +OH	SFR		2008 June 17-27
5	18 13 54.2	-18 01 44	12.6802	-0.1801	G12.681-0.182	G12.68-0.186	W33B	Image	6.6 GHz (II);	52	378	996	EFF	120	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 June 17-27
6	18 11 51.5	-17 31 28.8	12.8890	0.4891	G12.889+0.490	G12.89+0.49	IRAS 18089-1732	Image	6.6 GHz (II);	39	57	75	EFF	120	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 June 17-27
7	18 15 41.7	-16 38 57	14.0966	0.1031	G14.101+0.087	G14.09+0.10	IRAS 18128-1640	Image	6.6 GHz (II);	15.1	51	84	EFF	120	+H₂O -CH₃OH I +CH₃OH II	SFR		2008 June 17-27
8	18 17 54.1	-12 06 48	18.3426	1.7874	G18.340+1.772	G18.34+1.78	IRAS 18151-1208	Image	6.6 GHz (II);	27.7	44	23	EFF	120	+H₂O +CH₃OH I +CH₃OH II	SFR		2008 June 17-27
9	18 27 44.6	-11 14 54.6	20.2369	0.0654	G20.237+0.065	G20.24+0.07	IRAS 18249-1116	Image	6.6 GHz (II);	71.4	23	21	EFF	120	+H₂O -CH₃OH I +CH₃OH II +OH	SFR		2008 June 17-27
10	18 34 39.3	-08 31 39	23.4367	-0.1844	G23.437-0.184	G23.44-0.186	IRAS 18319-0834	Image	6.6 GHz (II);	103	90	178	EFF	120	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 June 17-27
11	18 36 12.6	-07 12 11.5	24.7896	0.0832	G24.790+0.083	G24.78+0.08	W42	Image	6.6 GHz (II);	113	129	188	EFF	120	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 June 17-27
12	18 34 20.9	-05 59 40.5	25.6501	1.0497	G25.649+1.050	G25.65+1.04	IRAS 18316-0602	Image	6.6 GHz (II);	41.9	99	43	EFF	120	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 June 17-27
13	18 38 3.2	-06 24 15	25.7095	0.0438	G25.709+0.044	G25.71+0.04	IRAS 18353-0628	Image	6.6 GHz (II);	95.6	625	620	EFF	120	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 June 17-27
14	18 42 12.4	-03 25 39.5	28.8294	0.4876	G28.842+0.494	G28.82+0.48		Image	6.6 GHz (II);	83.3	1.6	3.1	EFF	120	+H₂O -CH₃OH I +CH₃OH II	SFR		2008 June 17-27
15	18 45 59.5	-02 44 47	29.8671	-0.0417	G29.862-0.045	G29.86-0.04		Image	6.6 GHz (II);	101.4	67	87	EFF	120	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 June 17-27
16	18 46 3.7	-02 39 21.4	29.9556	-0.0160	G29.956-0.016	G29.95-0.02	W43S	Image	6.6 GHz (II);	96	169	227	EFF	120	+H₂O +CH₃OH I +CH₃OH II	SFR_MIXED		2008 June 17-27
17	18 47 15	-01 44 07	30.9102	0.1402	G30.907+0.140	G30.91+0.14		Image	6.6 GHz (II);	104	12	28	EFF	120	-H₂O -CH₃OH I +CH₃OH II	SFR		2008 June 17-27
18	18 49 37.3	-00 45 47	32.0458	0.0561	G32.045+0.059	G32.03+0.06	IRAS 18470-0050	Image	6.6 GHz (II);	98.7	117	165	EFF	120	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 June 17-27
19	18 54 0.6	+02 00 50	35.0174	0.3462	G35.025+0.350	G35.02+0.35	IRAS 18515+0157	Image	6.6 GHz (II);	44	26	29	EFF	120	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 June 17-27
20	19 07 21.9	+07 25 17.3	41.3477	-0.1365	G41.348-0.136	G41.34-0.14	IRAS 19049+0720	Image	6.6 GHz (II);	12	18	27	EFF	120	+H₂O -CH₃OH I +CH₃OH II +OH	SFR		2008 June 17-27
21	19 11 55.1	+09 36 00	43.7999	-0.1300	G43.795-0.127	G43.80-0.136	W49N	Image	6.6 GHz (II);	40	40	38	EFF	120	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 June 17-27
22	19 23 53.6	+14 34 54	49.5718	-0.3878	G49.582-0.385	G49.57-0.38	IRAS 19216+1429	Image	6.6 GHz (II);	59.3	2.6	2.4	EFF	120	+H₂O +CH₃OH II	SFR		2008 June 17-27
23	22 28 52	+64 13 22	108.1825	5.5136	G108.186+5.518	G108.18+5.51	IRAS 22272+6358	Image	6.6 GHz (II);	-10.9	51	34	EFF	120	-H₂O -CH₃OH I +CH₃OH II	SFR		2008 June 17-27
24	23 13 45.4	+61 28 10.6	111.5421	0.7769	G111.542+0.769	G111.53+0.76	NGC 7538	Image	6.6 GHz (II);	-56.2	240	552	EFF	120	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 June 17-27
25	06 14 37.1	+13 49 37	196.4538	-1.6772	G196.454-1.677	G196.45-1.69	S269	Image	6.6 GHz (II);	15	18	14	EFF	120	+H₂O -CH₃OH I +CH₃OH II +OH	SFR		2008 June 17-27
26	18 01 57.2	-23 12 37	6.7936	-0.2558	G6.794-0.256	G06.78-0.27	IRAS 17589-2312	Image	6.6 GHz (II);	26.9	63	191	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
27	18 06 23.5	-21 37 23	8.6800	-0.3699	G8.669-0.357	G08.68-0.36	IRAS 18032-2137	Image	6.6 GHz (II);	43	193	194	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
28	18 06 14.7	-20 31 31.6	9.6212	0.1958	G9.621+0.195	G09.62+0.20	IRAS 18032-2032	Image	6.6 GHz (II);	1	6002	2769	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
29	18 13 54.2	-18 01 44	12.6802	-0.1801	G12.681-0.182	G12.68-0.18	W33B	Image	6.6 GHz (II);	52	527	1382	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
30	18 14 39.5	-17 52 00	12.9086	-0.2603	G12.908-0.260	G12.90-0.26	IRAS 18117-1753; W33A	Image	6.6 GHz (II);	39	328	378	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
31	19 01 45.6	+01 13 28	35.1992	-1.7373	G35.200-1.737	G35.20-1.74	IRAS 18592+0108; W48	Image	6.6 GHz (II);	43.5	623	780	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR_MIXED		2008 Aug 15-18
32	19 23 44.5	+14 30 31	49.4900	-0.3900	G49.488-0.387	G49.49-0.39	IRAS 19213+1424	Image	6.6 GHz (II);	59	1045	879	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH -SiO	SFR		2008 Aug 15-18
33	06 07 47.9	-06 22 57	213.7050	-12.5969	G213.705-12.597	G213.70-12.6	IRAS 06053-0622; MonR2	Image	6.6 GHz (II);	12	499	264	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR_MIXED		2008 Aug 15-18
34	07 32 9.8	-16 58 12.5	232.6204	0.9957	G232.621+0.996	G232.62+0.99	IRAS 07299-1651	Image	6.6 GHz (II);	23	211	105	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
35	08 48 47.9	-42 54 28	263.2501	0.5138	G263.250+0.514	G263.25+0.52	IRAS 08470-4243	Image	6.6 GHz (II);	13	82	72	PRS	192	+H₂O -CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
36	11 11 53.4	-61 18 23.5	291.2741	-0.7085	G291.274-0.709	G291.27-0.70	IRAS 11097-6102	Image	6.6 GHz (II);	-30	78	109	PRS	192	+H₂O -CH₃OH I +CH₃OH II	SFR		2008 Aug 15-18
37	13 11 14.4	-62 34 26	305.2099	0.2102	G305.208+0.206	G305.21+0.21	IRAS 13079-6218	Image	6.6 GHz (II);	-38	517	464	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
38	13 50 41.9	-61 35 11	309.9206	0.4787	G309.921+0.479	G309.92+0.47	IRAS 13471-6120	Image	6.6 GHz (II);	-60	1185	1371	PRS	192	-H₂O +CH₃OH II +OH	SFR		2008 Aug 15-18
39	13 51 54.2	-61 16 18	310.1333	0.7518	G310.144+0.760	G310.13+0.75	IRAS 13484-6100	Image	6.6 GHz (II);	-56	80	103	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
40	14 44 18.4	-59 55 12	316.6403	-0.0868	G316.640-0.087	G316.64-0.08	IRAS 14404-5942	Image	6.6 GHz (II);	-20	132	242	PRS	192	+H₂O +CH₃OH II +OH	SFR		2008 Aug 15-18
41	15 00 55.4	-58 58 53.5	318.9478	-0.1964	G318.948-0.196	G318.94-0.19		Image	6.6 GHz (II);	-35	801	746	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
42	15 18 34.3	-56 38 10	322.1600	0.6400	G322.161+0.635	G322.16+0.64		Image	6.6 GHz (II);	-63	376	768	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
43	15 31 45.4	-56 30 50	323.7401	-0.2626	G323.740-0.263	G323.74-0.26	IRAS 15278-5620	Image	6.6 GHz (II);	-51	3544	5674	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR_MIXED		2008 Aug 15-18
44	15 43 18	-54 07 57	326.4703	0.6913	G326.475+0.703	G326.47+0.70	IRAS 15394-5358	Image	6.6 GHz (II);	-38.1	150	155	PRS	192	+H₂O +CH₃OH I +CH₃OH II	SFR		2008 Aug 15-18
45	15 57 58.3	-53 59 22.5	328.2366	-0.5472	G328.237-0.547	G328.23-0.54	IRAS 15541-5349	Image	6.6 GHz (II);	-44.9	1661	1295	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
46	16 00 33.3	-53 13 02	329.0301	-0.2099	G329.031-0.200	G329.02-0.20	IRAS 15566-5304	Image	6.6 GHz (II);	-37.5	156	305	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
47	16 11 26.6	-51 41 56.5	331.2782	-0.1881	G331.278-0.188	G331.27-0.18	IRAS 16076-5134	Image	6.6 GHz (II);	-78.1	111	277	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
48	16 35 9.3	-48 46 47	336.0181	-0.8272	G336.018-0.826	G336.01-0.82	IRAS 16313-4840	Image	6.6 GHz (II);	-45	105	218	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
49	16 38 29.6	-47 00 35	337.7054	-0.0530	G337.705-0.053	G337.70-0.05	IRAS 16348-4654	Image	6.6 GHz (II);	-54.6	218	297	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
50	16 44 49.1	-46 10 14	339.0530	-0.3150	G339.053-0.315	G339.05-0.31	IRAS 16411-4604	Image	6.6 GHz (II);	-111.6	168	153	PRS	192	-H₂O +CH₃OH II +OH	SFR		2008 Aug 15-18
51	16 52 4.7	-46 08 34	339.8840	-1.2588	G339.884-1.259	G339.88-1.25	IRAS 16484-4603	Image	6.6 GHz (II);	-39	1980	3408	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
52	16 50 17	-44 42 22	340.7900	-0.1001	G340.785-0.096	G340.79-0.10	IRAS 16465-4437	Image	6.6 GHz (II);	-107	175	328	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
53	16 52 17.9	-44 26 41	341.2202	-0.2100	G341.218-0.212	G341.22-0.21	IRAS 16487-4423	Image	6.6 GHz (II);	-38	196	356	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
54	17 05 10.9	-41 29 6.5	345.0029	-0.2236	G345.003-0.223	G345.00-0.22	IRAS 17016-4124	Image	6.6 GHz (II);	-22	119	283	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
55	16 56 47.6	-40 14 25.5	345.0095	1.7925	G345.010+1.792	G345.01+1.79	IRAS 16533-4009	Image	6.6 GHz (II);	-18	334	705	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
56	17 04 22.9	-40 44 23	345.5044	0.3482	G345.505+0.348	G345.50+0.34	IRAS 17008-4040	Image	6.6 GHz (II);	-18	369	945	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
57	17 20 53.4	-35 47 02	351.4167	0.6451	G351.417+0.645	G351.41+0.64	IRAS 17175-3544; NGC 6334F	Image	6.6 GHz (II);	-10	3784	3096	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR_MIXED		2008 Aug 15-18
58	17 26 42.6	-36 09 17.5	351.7746	-0.5364	G351.775-0.537	G351.77-0.53	IRAS 17233-3606	Image	6.6 GHz (II);	2	332	290	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18
59	17 30 16.8	-33 14 13	354.6101	0.4700	G354.615+0.472	G354.61+0.47	IRAS 17269-3312	Image	6.6 GHz (II);	-23	221	355	PRS	192	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2008 Aug 15-18

Non-detection table from Vlemmings et al. (2011)

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ID	Obs. RA	Obs. Dec	l	b	Group id	Source name	Other name	Line	Telescope	Beam	Detection	Class	Date
	(J2000)	(J2000)	(deg.)	(deg.)			Other name	CH₃OH (class II)		(arcsec)	Yes/No
1	18 13 43.4	-17 58 06	12.7129	-0.1135	G12.713-0.113	G12.71-0.11		6.6 GHz (II);	EFF	120	-H₂O +CH₃OH II	SFR	2008 June 17-27
2	18 45 59.5	-02 44 47	29.8671	-0.0417	G29.862-0.045	G29.86-0.04		6.6 GHz (II);	EFF	120	+H₂O +CH₃OH I +CH₃OH II +OH	SFR	2008 June 17-27
3	18 49 37.3	-00 45 47	32.0458	0.0561	G32.045+0.059	G32.03+0.06		6.6 GHz (II);	EFF	120	+H₂O +CH₃OH I +CH₃OH II +OH	SFR	2008 June 17-27
4	18 53 45.2	+00 32 47	33.6822	-0.2660	G33.682-0.266	G33.68-0.26	IRAS 18512+0029	6.6 GHz (II);	EFF	120	+CH₃OH II	UNK	2008 June 17-27
5	19 11 55.1	+09 36 00	43.7999	-0.1300	G43.795-0.127	G43.80-0.136		6.6 GHz (II);	EFF	120	+H₂O +CH₃OH I +CH₃OH II +OH	SFR	2008 June 17-27

Distribution of sources in all sky (l,b)

Distribution of sources in all sky using Aladin

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Distribution of sources in IRAS color-color diagram

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Original color diagram is taken form van der Veen & Habing (1987)

Type	Description
I	Oxygen-rich non-variable stars without circumstellar shells
II	Variable stars with "young" O-rich circumstellar shells
IIIa	Variable stars with more evolved O-rich circumstellar shells
IIIb	Variable stars with thick O-rich circumstellar shells
IV	Variable stars with very thick O-rich circumstellar shells
V	Planetary nebulae and non- variable stars with very cool circumstellar shells
VIa	Variable stars with relatively cold dust at large distances; a significant part of the stars is carbon-rich
VIb	Variable stars with relatively hot dust close to the star and relatively cold dust at large distances; Some of the objects have proven to be O-rich
VII	Variable stars with more evolved C-rich circumstellar shells
VIII	Different sort of objects

Distribution of the detection velocities versus galactic longitude from VLE11

Tip: Use "Box select" or "Lasso select" to display velocity-selected sources in Aladin all-sky view