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VAN95 - New detections of 5_1_-6_0_A^+^-methanol masers towards IRAS sources.

Short title: van der Walt et al. (1995)
Authors: van der Walt, D. J. Gaylard, M. J. MacLeod, G. C.
Journal: Astronomy and Astrophysics Supplement, v.110, p.81
Bibcode:

Target type: UCHII
Transitions: CH3OH_6(II)

Abstract
We present the results of our second search for 6.7-GHz methanol masers towards colour-selected IRAS sources. Five hundred and twenty IRAS sources that meet the far-infrared colour criteria set by Wood & Churchwell for ultra-compact HII regions were searched for 6.7-GHz methanol maser emission, to a sensitivity limit of 5Jy. Thirty one new maser sources were detected. We also compare the FIR colours of the newly detected maser sources with those detected by Schutte et al. (1993) and the IRAS counterparts of sources that have both methanol and hydroxyl maser emission. It was found that the average flux distribution of the newly detected sources differs significantly from that of all other known 6.7-GHz methanol maser sources. It is argued that the differences may be due either to intrinsic differences between the three groups of sources or to interstellar extinction. An analysis of the relation between the 6.7-GHz maser and IRAS flux densities shows that the maser flux density is always less than the 100 mum flux density while only three sources have a maser flux density greater than the 60 mum flux density. Far-infrared pumping of the 6.7-GHz methanol masers is therefore in principle viable although it was found that the apparent maser efficiency will exceed 10 per cent for a significant number of sources in the case of FIR pumping by photons between 50 and 100mum. The overall detection rates on the IRAS [25-12] vs [60-12] two-colour diagram are also presented. Possible new search strategies for masers in colour-selected IRAS sources are discussed.

Abstract

We present the results of our second search for 6.7-GHz methanol masers towards colour-selected IRAS sources. Five hundred and twenty IRAS sources that meet the far-infrared colour criteria set by Wood & Churchwell for ultra-compact HII regions were searched for 6.7-GHz methanol maser emission, to a sensitivity limit of 5Jy. Thirty one new maser sources were detected. We also compare the FIR colours of the newly detected maser sources with those detected by Schutte et al. (1993) and the IRAS counterparts of sources that have both methanol and hydroxyl maser emission. It was found that the average flux distribution of the newly detected sources differs significantly from that of all other known 6.7-GHz methanol maser sources. It is argued that the differences may be due either to intrinsic differences between the three groups of sources or to interstellar extinction. An analysis of the relation between the 6.7-GHz maser and IRAS flux densities shows that the maser flux density is always less than the 100 mum flux density while only three sources have a maser flux density greater than the 60 mum flux density. Far-infrared pumping of the 6.7-GHz methanol masers is therefore in principle viable although it was found that the apparent maser efficiency will exceed 10 per cent for a significant number of sources in the case of FIR pumping by photons between 50 and 100mum. The overall detection rates on the IRAS [25-12] vs [60-12] two-colour diagram are also presented. Possible new search strategies for masers in colour-selected IRAS sources are discussed.

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Detection table from van der Walt et al. (1995)

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ID	Obs. RA	Obs. Dec	l	b	Group id	Source name	Line	V_range	F_peak	∫F dv	Telescope	Beam	Detection	Class	Dist. (parallax)	Date
	(J2000)	(J2000)	(deg.)	(deg.)			CH₃OH (class II)	(km/s)	(Jy)	(Jy*km/s)		(arcsec)	Yes/No		(kpc)
1	10 32 12.8	-58 02 26.3	285.3460	-0.0037	G285.337-0.002	10303-5746	6.6 GHz (II);		10.0	7.4	HartRAO	420	-CH₃OH I +CH₃OH II +OH	SFR		July 1992 - January 1993
2	10 48 3.3	-58 26 50.2	287.3676	0.6457	G287.371+0.644	10460-5811	6.6 GHz (II);	-3;-1	63.8	45.5	HartRAO	420	+H₂O -CH₃OH I +CH₃OH II +OH	SFR		July 1992 - January 1993
3	13 17 18.4	-62 43 14.4	305.8911	0.0024	G305.887+0.017	13140-6226	6.6 GHz (II);	-35;-31	10.8	7.7	HartRAO	420	+H₂O +CH₃OH I +CH₃OH II	SFR_MIXED		July 1992 - January 1993
4	13 40 51.2	-61 45 29.2	308.7428	0.5548	G308.754+0.549	13374-6130	6.6 GHz (II);	-52;-40	11.2	21.3	HartRAO	420	+H₂O +CH₃OH II +OH	SFR		July 1992 - January 1993
5	13 51 54.2	-61 16 19	310.1333	0.7515	G310.144+0.760	13484-6100	6.6 GHz (II);	-58;-54	137.9	277.7	HartRAO	420	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		July 1992 - January 1993
6	14 20 5.4	-60 42 40.6	313.5671	0.3168	G313.577+0.325	14164-6028	6.6 GHz (II);	-49;-46	149.1	68.6	HartRAO	420	+H₂O +CH₃OH II +OH	SFR		July 1992 - January 1993
7	14 51 8.1	-59 17 32.5	317.6904	0.1056	G317.701+0.110	14473-5904	6.6 GHz (II);	-44;-41	32.0	37.5	HartRAO	420	+CH₃OH II	SFR_MIXED		July 1992 - January 1993
8	15 43 18	-54 07 58.1	326.4701	0.6911	G326.475+0.703	15394-5358	6.6 GHz (II);	-51;-37	108.5	120.3	HartRAO	420	+H₂O +CH₃OH I +CH₃OH II	SFR		July 1992 - January 1993
9	16 00 18.1	-51 35 8.3	330.0672	1.0503	G330.070+1.064	15565-5126	6.6 GHz (II);	-44;-38	13.2	13.4	HartRAO	420	+H₂O +CH₃OH II	SFR		July 1992 - January 1993
10	16 02 6.7	-52 36 32.5	329.6062	0.0952	G329.606+0.095	15584-5230	6.6 GHz (II);	-62;-58	29.7	27.5	HartRAO	420	+CH₃OH II	SFR		July 1992 - January 1993
11	16 05 44.5	-49 12 20.4	332.2912	2.2642	G332.295+2.280	16019-4903	6.6 GHz (II);	-27;-20	108.8	103.4	HartRAO	420	+H₂O +CH₃OH II +OH	SFR		July 1992 - January 1993
12	16 12 13.2	-51 34 56.7	331.4459	-0.1852	G331.442-0.187	16084-5127	6.6 GHz (II);	-94;-84	54.4	141.2	HartRAO	420	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		July 1992 - January 1993
13	16 35 6.3	-48 47 1.6	336.0097	-0.8239	G336.018-0.827	16313-4840	6.6 GHz (II);	-55;-39	410.0	441.7	HartRAO	420	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		July 1992 - January 1993
14	16 36 26.5	-47 52 28.1	336.8310	-0.3749	G336.830-0.375	16327-4746	6.6 GHz (II);	-27;-22	41.5	46.1	HartRAO	420	+H₂O +CH₃OH II	SFR		July 1992 - January 1993
15	16 40 51.5	-46 23 35.9	338.4353	0.0541	G338.432+0.058	16371-4617	6.6 GHz (II);	-31;-29	35.4	14.4	HartRAO	420	+H₂O +CH₃OH II	SFR		July 1992 - January 1993
16	17 23 31.6	-37 01 40.2	350.6936	-0.4978	G350.686-0.491	17200-3658	6.6 GHz (II);	-16;-13	31.3	14.6	HartRAO	420	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		July 1992 - January 1993
17	17 29 17.7	-36 04 41.2	352.1283	-0.9280	G352.132-0.944	17258-3602	6.6 GHz (II);	-18;-7	20.1	24.3	HartRAO	420	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		July 1992 - January 1993
18	17 41 20.2	-30 45 47.6	357.9574	-0.1686	G357.967-0.163	17381-3043A	6.6 GHz (II);	-6;1	39.6	103.4	HartRAO	420	+H₂O +CH₃OH I +CH₃OH II +OH	SFR_MIXED		July 1992 - January 1993
19	17 46 51.7	-28 07 28.3	0.8351	0.1890	G0.8351+0.1890	17436-2806	6.6 GHz (II);	3;4	8.9	3.7	HartRAO	420	+CH₃OH II	SFR		July 1992 - January 1993
20	17 47 8.1	-28 46 58.2	0.3034	-0.2037	G0.315-0.201	17439-2845	6.6 GHz (II);	14;21	29.5	60.4	HartRAO	420	+H₂O -CH₃OH I +CH₃OH II +OH	SFR		July 1992 - January 1993
21	17 49 41.7	-31 29 30.2	358.2674	-2.0748	G358.263-2.061	17463-3128	6.6 GHz (II);	1;7	16.7	16.2	HartRAO	420	-H₂O +CH₃OH II +OH	SFR		July 1992 - January 1993
22	18 01 58.7	-23 13 51	6.7785	-0.2708	G6.795-0.257	17589-2312	6.6 GHz (II);	14;30	78.9	146.4	HartRAO	420	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		July 1992 - January 1993
23	18 17 58.4	-12 07 47.6	18.3364	1.7641	G18.340+1.772	18151-1208	6.6 GHz (II);	27;29	46.1	22.5	HartRAO	420	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		July 1992 - January 1993
24	18 34 20.8	-05 59 59.1	25.6452	1.0478	G25.649+1.050	18316-0602	6.6 GHz (II);	40;43	113.3	33.4	HartRAO	420	+H₂O +CH₃OH I +CH₃OH II	SFR_MIXED		July 1992 - January 1993
25	18 36 5.8	-07 31 18.6	24.4939	-0.0386	G24.494-0.039	18334-0733	6.6 GHz (II);	113;116	33.1	18.1	HartRAO	420	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		July 1992 - January 1993
26	18 37 18.4	-06 38 38.4	25.4114	0.0983	G25.411+0.105	18345-0641	6.6 GHz (II);	94;100	34.8	24.9	HartRAO	420	+H₂O +CH₃OH I +CH₃OH II -OH	SFR		July 1992 - January 1993
27	18 40 38.6	-05 43 36.9	26.6067	-0.2182	G26.602-0.220	18379-0546	6.6 GHz (II);	102;105	10.0	12.8	HartRAO	420	-H₂O +CH₃OH I +CH₃OH II +OH	SFR		July 1992 - January 1993
28	18 49 38.5	-00 45 29.1	32.0524	0.0540	G32.045+0.059	18470-0049	6.6 GHz (II);	91;102	103.6	135.5	HartRAO	420	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		July 1992 - January 1993
29	18 51 27.8	+00 04 13.7	32.9976	0.0263	G32.993+0.038	18488+0000	6.6 GHz (II);	89;93	16.3	13.3	HartRAO	420	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		July 1992 - January 1993
30	18 59 47.6	+01 01 51.2	34.8023	-1.3883	G34.800-1.387	18572+0057	6.6 GHz (II);	43;48	20.8	36.1	HartRAO	420	-H₂O +CH₃OH II -OH	SFR		July 1992 - January 1993
31	19 25 25.4	+13 47 41.3	49.0544	-1.0872	G49.043-1.079	19230+1341	6.6 GHz (II);	33;38	24.3	26.3	HartRAO	420	+H₂O +CH₃OH I +CH₃OH II -OH	SFR		July 1992 - January 1993

Non-detection table from van der Walt et al. (1995)