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NEU21 - Terahertz Water Masers. II. Further SOFIA/GREAT Detections Toward Circumstellar Outflows, and a Multitransition Analysis

Short title: Neufeld et al. (2021)
Authors: Neufeld, David A.Menten, Karl M.Duran, CarlosGusten, RolfKaufman, Michael J.Kraus, AlexMazumdar, ParichayMelnick, Gary J.Ortiz-Leon, Gisela N.Wiesemeyer, HelmutWyrowski, Friedrich
Journal: The Astrophysical Journal, Volume 907, Issue 1, id.42, 16 pp.
Bibcode:

Target type: star
Transitions: H2O_22,H2O_183,H2O_321,H2O_325,H2O_437,H2O_439,H2O_470,H2O_474,H2O_1296

Abstract
Following up on our discovery of terahertz water masers, reported in 2017, we report two further detections of water maser emission at frequencies above 1 THz. Using the GREAT instrument on SOFIA, we have detected emission in the 1.296411 THz 8₂₇ - 7₃₄ transition of water toward two additional oxygen-rich evolved stars, omicron Ceti (Mira) and R Crateris, and obtained an upper limit on the 1.296 THz line emission from U Orionis. Toward these three sources, and toward the red supergiant star VY Canis Majorae from which 1.296 THz line emission was reported previously, we have also observed several lower-frequency (sub)millimeter water maser transitions using the APEX 12 m telescope along with the 22 GHz transition using the Effelsberg 100 m telescope. We have used a simple model to analyze the multi transition data thereby obtained. Adopting, as a prior, independent literature estimates of the mass-loss rates in these four sources and in W Hydrae, we infer water abundances in a remarkably narrow range: n(H₂O)/n(H₂) = 1.4-2.5 - 10^-4. For o Cet, VY CMa, and W Hya, the model is successful in predicting the maser line fluxes to within a typical factor ~1.6-3. For R Crt and U Ori, the model is less successful, with typical line flux predictions lying an order of magnitude above or below the observations such discrepancies are perhaps unsurprising given the exponential nature of maser amplification.

Abstract

Following up on our discovery of terahertz water masers, reported in 2017, we report two further detections of water maser emission at frequencies above 1 THz. Using the GREAT instrument on SOFIA, we have detected emission in the 1.296411 THz 8₂₇ - 7₃₄ transition of water toward two additional oxygen-rich evolved stars, omicron Ceti (Mira) and R Crateris, and obtained an upper limit on the 1.296 THz line emission from U Orionis. Toward these three sources, and toward the red supergiant star VY Canis Majorae from which 1.296 THz line emission was reported previously, we have also observed several lower-frequency (sub)millimeter water maser transitions using the APEX 12 m telescope along with the 22 GHz transition using the Effelsberg 100 m telescope. We have used a simple model to analyze the multi transition data thereby obtained. Adopting, as a prior, independent literature estimates of the mass-loss rates in these four sources and in W Hydrae, we infer water abundances in a remarkably narrow range: n(H₂O)/n(H₂) = 1.4-2.5 - 10^-4. For o Cet, VY CMa, and W Hya, the model is successful in predicting the maser line fluxes to within a typical factor ~1.6-3. For R Crt and U Ori, the model is less successful, with typical line flux predictions lying an order of magnitude above or below the observations such discrepancies are perhaps unsurprising given the exponential nature of maser amplification.

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Detection table from Neufeld et al. (2021)

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ID	Obs. RA	Obs. Dec	l	b	Group id	Source name	Image	Line	V_range	V_peak	F_peak	∫F dv	Telescope	V_step	Beam	Detection	Class	Distance	Dist. (parallax)	Date
	(J2000)	(J2000)	(deg.)	(deg.)				H₂O	(km/s)	(km/s)	(Jy)	(Jy*km/s)		(km/s)	(arcsec)	Yes/No		(kpc)	(kpc)
1	02 19 20	-02 58 39.5	167.7502	-57.9847	G167.754-57.983	o Cet	Image	22 GHz;	42;50	46.89	3.8	5.1 (0.02)	EFF	0.02	40	+H₂O -OH +SiO	EVOLVED	0.093		2018 11/30-12/6
2	02 19 20	-02 58 39.5	167.7502	-57.9847	G167.754-57.983	o Cet	Image	183 GHz;	45;48	46.9	143	271 (5)	APEX	0.5	34	+H₂O -OH +SiO	EVOLVED	0.093		2018 11/30-12/6
3	02 19 20	-02 58 39.5	167.7502	-57.9847	G167.754-57.983	o Cet	Image	325 GHz;	45;48	47	116	127 (12)	APEX	0.5	13	+H₂O -OH +SiO	EVOLVED	0.093		2018 11/30-12/6
4	02 19 20	-02 58 39.5	167.7502	-57.9847	G167.754-57.983	o Cet	Image	1.29 THz;	43;49	46	400	1730 (160)	SOFIA	1.12	20	+H₂O -OH +SiO	EVOLVED	0.093		2018 11/30-12/6
5	11 00 33	-18 19 29.6	269.2659	37.1940	G269.270+37.196	R Crt	Image	22 GHz;	3;17	9.1	521	1675 (1)	EFF	0.02	40	+H₂O +OH +SiO	EVOLVED	0.238		2018 11/30-12/6
6	11 00 33	-18 19 29.6	269.2659	37.1940	G269.270+37.196	R Crt	Image	321 GHz;	3;25	10.6	5	39 (2)	APEX	0.5	13	+H₂O +OH +SiO	EVOLVED	0.238		2018 11/30-12/6
7	11 00 33	-18 19 29.6	269.2659	37.1940	G269.270+37.196	R Crt	Image	325 GHz;	4;17	9	161	794 (7)	APEX	0.5	13	+H₂O +OH +SiO	EVOLVED	0.238		2018 11/30-12/6
8	11 00 33	-18 19 29.6	269.2659	37.1940	G269.270+37.196	R Crt	Image	1.29 THz;	0;23	8	230	1200 (499)	SOFIA	1.12	20	+H₂O +OH +SiO	EVOLVED	0.238		2018 11/30-12/6
9	05 55 49	+20 10 30.7	188.7148	-2.4927	G188.715-2.492	U Ori	Image	22 GHz;	-42;-36	-38.4	6.5	10.8 (0.1)	EFF	0.02	40	+H₂O +OH +SiO	EVOLVED	0.228		2018 11/30-12/6
10	07 22 58	-25 46 3.2	239.3520	-5.0665	G239.352-5.065	VY CMa	Image	22 GHz;	-6;48	12.8	1244	7675 (1)	EFF	0.02	40	+H₂O -CH₃OH I -CH₃OH II +OH +SiO	EVOLVED	1.200		2018 11/30-12/6
11	07 22 58	-25 46 3.2	239.3520	-5.0665	G239.352-5.065	VY CMa	Image	183 GHz;	-10;63	0.1	692	19622 (16)	APEX	0.5	34	+H₂O -CH₃OH I -CH₃OH II +OH +SiO	EVOLVED	1.200		2018 11/30-12/6
12	07 22 58	-25 46 3.2	239.3520	-5.0665	G239.352-5.065	VY CMa	Image	321 GHz;	6;36	18	312	1080 (6)	APEX	0.5	13	+H₂O -CH₃OH I -CH₃OH II +OH +SiO	EVOLVED	1.200		2018 11/30-12/6
13	07 22 58	-25 46 3.2	239.3520	-5.0665	G239.352-5.065	VY CMa	Image	325 GHz;	-9;51	13	284	5362 (61)	APEX	0.5	13	+H₂O -CH₃OH I -CH₃OH II +OH +SiO	EVOLVED	1.200		2018 11/30-12/6
14	07 22 58	-25 46 3.2	239.3520	-5.0665	G239.352-5.065	VY CMa	Image	437 GHz;	-1;44	29	509	6493 (22)	APEX	0.5	13	+H₂O -CH₃OH I -CH₃OH II +OH +SiO	EVOLVED	1.200		2018 11/30-12/6
15	07 22 58	-25 46 3.2	239.3520	-5.0665	G239.352-5.065	VY CMa	Image	439 GHz;	-1;36	14	161	2444 (47)	APEX	0.5	13	+H₂O -CH₃OH I -CH₃OH II +OH +SiO	EVOLVED	1.200		2018 11/30-12/6
16	07 22 58	-25 46 3.2	239.3520	-5.0665	G239.352-5.065	VY CMa	Image	470 GHz;	-7;41	22	190	3835 (28)	APEX	0.5	13	+H₂O -CH₃OH I -CH₃OH II +OH +SiO	EVOLVED	1.200		2018 11/30-12/6

Non-detection table from Neufeld et al. (2021)