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VOR05 - The 6.7- and 25-GHz methanol masers in OMC-1

Interferometry data

Short title: Voronkov et al. (2005)
Authors: Voronkov, M. A. Sobolev, A. M. Ellingsen, S. P. Ostrovskii, A. B.
Journal: Monthly Notices of the Royal Astronomical Society, Volume 362, Issue 3, pp. 995-1005.
Bibcode:

Non-detection table: Show non-detection table
Detection table: Show detection table (1 detection)
Target type: High_mass_SFR
Transitions: CH3OH_9(I),CH3OH_25-30_GHz(I),CH3OH_36(I),CH3OH_44(I),CH3OH_84(I),CH3OH_95(I),CH3OH_104(I),CH3OH_6(II)

Abstract
The Australia Telescope Compact Array (ATCA) has been used to search for methanol maser emission at 6.7 GHz towards the Orion Molecular Cloud 1 (OMC-1). Two features peaking at 7.2 and -1.1kms^-1 have been detected. The former has at least two components close in both velocity and position. It is located south-east of the Orion Kleinmann-Low (Orion-KL) nebula in the region of outflow traced by the 25-GHz methanol masers and the 95-GHz methanol emission. It is shown by modelling that, in contrast to the widespread opinion that simultaneous masing of methanol transitions of different classes is impossible, there are conditions for which simultaneous masing of the class II transition at 6.7 GHz and some class I transitions (e.g. the series at 25 GHz) is possible. A relevant example is provided, in which the pumping occurs via the first torsionally excited state and is driven by radiation of the dust intermixed with the gas in the cloud. In this regime, the dust temperature is significantly lower (T~ 60 K) than in the case of bright 6.7-GHz masers (T > 150 K). The narrow spectral feature at -1.1kms^-1 has a brightness temperature greater than about 1400 K, which suggests that it is probably a maser. It emanates from the Orion South region and is probably associated with the approaching part of outflow seen in CO. The 25-GHz maser associated with OMC-1 was observed quasi-simultaneously with the 6.7-GHz observations. No 25-GHz emission associated with the -1.1kms^-1 6.7-GHz feature towards Orion South was detected. eprintid: arXiv:astro-ph/0507048

Abstract

The Australia Telescope Compact Array (ATCA) has been used to search for methanol maser emission at 6.7 GHz towards the Orion Molecular Cloud 1 (OMC-1). Two features peaking at 7.2 and -1.1kms^-1 have been detected. The former has at least two components close in both velocity and position. It is located south-east of the Orion Kleinmann-Low (Orion-KL) nebula in the region of outflow traced by the 25-GHz methanol masers and the 95-GHz methanol emission. It is shown by modelling that, in contrast to the widespread opinion that simultaneous masing of methanol transitions of different classes is impossible, there are conditions for which simultaneous masing of the class II transition at 6.7 GHz and some class I transitions (e.g. the series at 25 GHz) is possible. A relevant example is provided, in which the pumping occurs via the first torsionally excited state and is driven by radiation of the dust intermixed with the gas in the cloud. In this regime, the dust temperature is significantly lower (T~ 60 K) than in the case of bright 6.7-GHz masers (T > 150 K). The narrow spectral feature at -1.1kms^-1 has a brightness temperature greater than about 1400 K, which suggests that it is probably a maser. It emanates from the Orion South region and is probably associated with the approaching part of outflow seen in CO. The 25-GHz maser associated with OMC-1 was observed quasi-simultaneously with the 6.7-GHz observations. No 25-GHz emission associated with the -1.1kms^-1 6.7-GHz feature towards Orion South was detected. eprintid: arXiv:astro-ph/0507048

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Detection table from Voronkov et al. (2005)

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ID	Obs. RA	Obs. Dec	RA offset	Dec offset	l	b	Group id	#	Source name	Image	Line	V_peak	F_peak	∫F dv	Major	Minor	PA	Telescope	V_step	Beam	Detection	Class	Dist. (parallax)	Date
	(J2000)	(J2000)	(mas)	(mas)	(deg.)	(deg.)					CH₃OH (class I)	(km/s)	(Jy)	(Jy*km/s)	(arcsec)	(arcsec)	(deg.)		(km/s)	(arcsec)	Yes/No		(kpc)
1	+05 35 15	-05 23 42.53			209.012979	-19.391939	G208.993-19.385		OMC-1	Image	24.959 GHz (I);	7.34 .. 9.92	14 .. 89	..				ATCA	0.05	120	+H₂O +CH₃OH I +CH₃OH II +OH +SiO	SFR_MIXED		2003 June 9-10
	+05 35 14.87	-05 22 44	-1950 mas	58529.2 mas	208.997349	-19.385065		1	OMC-1			7.34	35 (2)		29.600	18.600	-63.000
	+05 35 14.83	-05 22 42.8	-2550 mas	59729.2 mas	208.996954	-19.385063		2	OMC-1			7.58	48 (2)		30.400	18.400	-64.000
	+05 35 14.33	-05 22 36.5	-10050 mas	66029.2 mas	208.994305	-19.386121		3	OMC-1			7.95	68 (5)		38.100	18.900	-57.000
	+05 35 14.02	-05 22 30.9	-14700 mas	71629.2 mas	208.992217	-19.386564		4	OMC-1			8.28	89 (4)		40.000	19.300	-53.000
	+05 35 14.02	-05 22 31.8	-14700 mas	70729.2 mas	208.992454	-19.386677		5	OMC-1			8.75	45 (1)		35.600	20.500	-50.000
	+05 35 14.19	-05 22 14	-12150 mas	88529.2 mas	208.988117	-19.383811		6	OMC-1			9.92	14 (1)		29.900	20.700	-60.000

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 VOR05

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