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VLE14 - From the ashes: JVLA observations of water fountain nebula candidates show the rebirth of IRAS 18455+0448

Short title: Vlemmings et al. (2014)
Authors: Vlemmings, W. H. T. Amiri, N. van Langevelde, H. J. Tafoya, D.
Journal: Astronomy & Astrophysics, Volume 569, id.A92, 8 pp.
Bibcode:

Non-detection table: Show non-detection table
Detection table: Show detection table (1 detection) Non-detection table: Show non-detection table (2 non-detection)
Target type: pAGB_PN

Abstract
Context. The class of water fountain nebulae is thought to represent the stage of the earliest onset of collimated bipolar outflows during the post-asymptotic giant branch phase. They thus play a crucial role in the study of the formation of bipolar planetary nebulae (PNe). To date, 14 water fountain nebulae have been identified. The identification of more sources in this unique stage of stellar evolution will enable us to study the origin of bipolar PNe morphologies in more detail. Aims: Water fountain candidates can be identified based on the often double peaked 22 GHz H₂O maser spectrum with a large separation between the maser peaks (often >100 km s^-1). However, even a fast bipolar outflow will only have a moderate velocity extent in its maser spectrum when located close to the plane of the sky. In this project we aim to enhance the water fountain sample by identifying objects whose jets are aligned close to the plane of the sky. Methods: We present the results of seven sources observed with the Jansky Very Large Array (JVLA) that were identified as water fountain candidates in an Effelsberg 100 m telescope survey of 74 AGB and early post-AGB stars. Results: We find that our sample of water fountain candidates displays strong variability in their 22 GHz H₂O maser spectra. The JVLA observations show an extended bipolar H₂O maser outflow for one source, the OH/IR star IRAS 18455+0448. This source was previously classified as a dying OH/IR star based on the exponential decrease of its 1612 MHz OH maser and the lack of H₂O masers. We therefore also re-observed the 1612, 1665, and 1667 MHz OH masers. We confirm that the 1612 MHz masers have not reappeared and find that the1665/1667 MHz masers have decreased in strength by several orders of magnitude during the last decade. The JVLA observations also reveal a striking asymmetry in the red-shifted maser emission of IRAS 19422+3506. Conclusions: The OH/IR star IRAS 18455+0448 is confirmed to be a new addition to the class of water fountain nebulae. Its kinematic age is ~70 yr, but could be lower, depending on the distance and inclination. Previous observations indicate, with significant uncertainty, that IRAS 18455+0448 has a surprisingly low mass compared to available estimates for other water fountain nebulae. The available historical OH maser observations make IRAS 18455+0448 unique for the study of water fountain nebulae and the launch of post-AGB bipolar outflows. The other candidate sources appear high mass-loss OH/IR stars with partly radially beamed H₂O masers. eprintid: arXiv:1407.6709

Abstract

Context. The class of water fountain nebulae is thought to represent the stage of the earliest onset of collimated bipolar outflows during the post-asymptotic giant branch phase. They thus play a crucial role in the study of the formation of bipolar planetary nebulae (PNe). To date, 14 water fountain nebulae have been identified. The identification of more sources in this unique stage of stellar evolution will enable us to study the origin of bipolar PNe morphologies in more detail.
Aims: Water fountain candidates can be identified based on the often double peaked 22 GHz H₂O maser spectrum with a large separation between the maser peaks (often >100 km s^-1). However, even a fast bipolar outflow will only have a moderate velocity extent in its maser spectrum when located close to the plane of the sky. In this project we aim to enhance the water fountain sample by identifying objects whose jets are aligned close to the plane of the sky.
Methods: We present the results of seven sources observed with the Jansky Very Large Array (JVLA) that were identified as water fountain candidates in an Effelsberg 100 m telescope survey of 74 AGB and early post-AGB stars.
Results: We find that our sample of water fountain candidates displays strong variability in their 22 GHz H₂O maser spectra. The JVLA observations show an extended bipolar H₂O maser outflow for one source, the OH/IR star IRAS 18455+0448. This source was previously classified as a dying OH/IR star based on the exponential decrease of its 1612 MHz OH maser and the lack of H₂O masers. We therefore also re-observed the 1612, 1665, and 1667 MHz OH masers. We confirm that the 1612 MHz masers have not reappeared and find that the1665/1667 MHz masers have decreased in strength by several orders of magnitude during the last decade. The JVLA observations also reveal a striking asymmetry in the red-shifted maser emission of IRAS 19422+3506.
Conclusions: The OH/IR star IRAS 18455+0448 is confirmed to be a new addition to the class of water fountain nebulae. Its kinematic age is ~70 yr, but could be lower, depending on the distance and inclination. Previous observations indicate, with significant uncertainty, that IRAS 18455+0448 has a surprisingly low mass compared to available estimates for other water fountain nebulae. The available historical OH maser observations make IRAS 18455+0448 unique for the study of water fountain nebulae and the launch of post-AGB bipolar outflows. The other candidate sources appear high mass-loss OH/IR stars with partly radially beamed H₂O masers. eprintid:

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Detection table from Vlemmings et al. (2014)

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ID	Obs. RA	Obs. Dec	l	b	Group id	Source name	Frequency	V_range	V_peak	F_peak	List	Detection	Class	Dist. (parallax)	Ref.
	(J2000)	(J2000)	(deg.)	(deg.)			(MHz)	(km/s)	(km/s)	(Jy)		Yes/No		(kpc)
1	18 48 2.3	+04 51 30.4	36.8730	2.9677	G36.873+2.968	IRAS 18455+0448	1667	6.0	30.0	0.022	ENG15	+H₂O +OH	EVOLVED		VLE14

Non-detection table from Vlemmings et al. (2014)

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ID	Obs. RA	Obs. Dec	l	b	Group id	Source name	Line	F_peak	List	Detection	Class	Ref.
	(J2000)	(J2000)	(deg.)	(deg.)			OH	(Jy)		Yes/No
1	18 48 2.3	+04 51 30.4	36.8730	2.9677	G36.873+2.968	IRAS 18455+0448	1.612 GHz;	0.020	ENG15	+H₂O +OH	EVOLVED	VLE14
2	18 48 2.3	+04 51 30.4	36.8730	2.9677	G36.873+2.968	IRAS 18455+0448	1.665 GHz;		ENG15	+H₂O +OH	EVOLVED	VLE14

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 VLE14

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