OH maser emission in the circumstellar envelopes of U Herculis, R Cassiopeiae and W Hydrae

Chapman, Jessica M.; Sivagnanam, P.; Cohen, R. J.; Squeren, A. M. Le

doi:10.1093/mnras/268.2.475

Cited by 43 publications

(53 citation statements)

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“…So, one expects the OH (mainline) standard shell size to be roughly related to the period of the central Mira, which is indeed in agreement with the typical sizes found by mapping (Chapman, Cohen & Saikia 1991;Chapman et al 1994). In particular, Chapman, Cohen & Saikia (1991) measured the radius of the loci of the strongest OH emission around U Ori, a thin-shell Mira with a similar period duration (368 days, Kukarkin et al 1970) located at ∼306 ±61 pc (Mondal & Chandrasekhar (2005) using Whitelock & Feast's (2000) Period-Luminosity relation), to be 0.…”

Section: Location Of the Flaring Regionssupporting

confidence: 83%

“…Note also that Winters et al (2003) do not provide any uncertainties, but a step of 0.25 km s −1 has been used for the fits (Le Bertre, private communication). Knowing that the terminal expansion velocity of the CSE of o Ceti, measured in the CO transitions, is only VCO exp ∼ 6 ± 0.2 km s −1 (Knapp & Morris 1985) and that a small acceleration is still present at the location of the OH shell of Miras (e.g., Chapman et al 1994), it is likely that for o Ceti VOH exp ≃[4 -5] km s −1 . This means that the flaring emission of o Ceti is also characterised by |Vstar−V flare | < VOH exp since |Vstar−V flare | < 3 km s −1 , regardless of the actual stellar velocity (cf .…”

Section: Comparison With Previously Recorded Flaring Eventsmentioning

confidence: 99%

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Recurring OH Flares towards o Ceti: I. location and structure of the 1990s’ and 2010s’ events

Etoka

Gérard

Richards

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We present the analysis of the onset of the new 2010s' OH flaring event detected in the OH ground-state main line at 1665 MHz towards o Ceti and compare its characteristics with those of the 1990s' flaring event. This is based on a series of complementary single-dish and interferometric observations both in OH and H 2 O obtained with the Nançay Radio telescope (NRT), the Medicina and Effelsberg Telescopes, the European VLBI Network (EVN), and (e)Multi-Element Radio Linked Interferometer Network ((e)MERLIN). We compare the overall characteristics of o Ceti's flaring events with those which have been observed towards other thin-shell Miras, and explore the implication of these events with respect to the standard OH circumstellar-envelope model. The role of binarity in the specific characteristics of o Ceti's flaring events is also investigated. The flaring regions are found to be less than ∼400±40 mas (i.e., ≤ 40 ± 4 AU) either side of o Ceti, with seemingly no preferential location with respect to the direction to the companion Mira B. Contrary to the usual expectation that the OH maser zone is located outside the H 2 O maser zone, the coincidence of the H 2 O and OH maser velocities suggests that both emissions arise at similar distances from the star. The OH flaring characteristics of Mira are similar to those observed in various Mira variables before, supporting the earlier results that the regions where the transient OH maser emission occurs are different from the standard OH maser zone.

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Section: Location Of the Flaring Regionssupporting

confidence: 83%

Section: Comparison With Previously Recorded Flaring Eventsmentioning

confidence: 99%

Recurring OH Flares towards o Ceti: I. location and structure of the 1990s’ and 2010s’ events

Etoka

Gérard

Richards

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…It has been detected in a number of circumstellar molecular line emissions, e.g., CO (Wannier & Sahai 1986;Loup et al 1993;Cernicharo et al 1997;Kerschbuam & Olofsson 1999), SiO maser (Pardo et al 2004) and OH maser lines (Szymczak et al 1998;Chapman et al 1994;Etoka et al 2003). It was also detected in water lines using the Infrared Space Observatory's (ISO) Short-and Long Wavelength Spectrometers (SWS and LWS) by Neufeld et al (1996) and Barlow et al (1996), respectively.…”

Section: Introductionmentioning

confidence: 98%

W Hya through the eye of Odin

Justtanont¹,

Bergman²,

Larsson³

et al. 2005

A&A

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Abstract. We present Odin observations of the AGB star W Hya in the ground-state transition of ortho-H 2 O, 1 10 − 1 01 , at 557 GHz. The line is clearly of circumstellar origin. Radiative transfer modelling of the water lines observed by Odin and ISO results in a mass-loss rate of (2.5 ± 0.5) × 10 −7 M yr −1 , and a circumstellar H 2 O abundance of (2.0 ± 1.0) × 10 −3 . The inferred mass-loss rate is consistent with that obtained from modelling the circumstellar CO radio line emission, and also with that obtained from the dust emission modelling combined with a dynamical model for the outflow. The very high water abundance, higher than the cosmic oxygen abundance, can be explained by invoking an injection of excess water from evaporating icy bodies in the system. The required extra mass of water is quite small, on the order of ∼0.1 M ⊕ .

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“…References. A97: Alvarez & Mennessier (1997); C91: Chapman et al (1991); C94: Chapman et al (1994); C07: Cenarro et al (2007); D87 : Diamond et al (1987); H74: Humphreys (1974); K87: Kirrane (1987); L05: Levesque et al (2005) kpc from Earth, without losing significant emission due to missing interferometer spacings. We measured the sizes of individual maser spots by fitting Gaussian components, allowing us to investigate the variations of maser size with intensity, position in the line profiles and other factors.…”

Section: Introductionmentioning

confidence: 99%

Observational evidence for the shrinking of bright maser spots

Richards

Elitzur

Yates

2010

A&A

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Context. The nature of maser emission means that the apparent angular size of an individual maser spot is determined by the local amplification process as well as by the instrinsic size of the emitting cloud. Highly sensitive radio interferometry images made using MERLIN spatially and spectrally resolve water maser clouds around evolved stars. Aims. We used measurements of the cloud properties, around the red supergiant S Per and the AGB stars IK Tau, RT Vir, U Her and U Ori, to test maser beaming theory. In particular, spherical clouds are expected to produce an inverse relationship between maser intensity and apparent size, which would not be seen from very elongated (cylindrical or slab-like) regions. Methods. We analysed the measured properties of the maser emission in order to estimate the saturation state. We analysed the variation of observed maser spot size with intensity and across the spectral line profiles. Results. Circumstellar masers emanate from discrete clouds from about one to 20 AU in diameter depending on the star. Most of the maser features have negative excitation temperatures close to zero and modest optical depths, showing that they are mainly unsaturated. Around S Per and (at most epochs) RT Vir and IK Tau, the maser component size shrinks with increasing intensity, although in some cases the slope is shallower than predicted, probably due to shape irregularities and the presence of velocity gradients within clouds. In contrast, the masers around U Ori and U Her tend to increase in size, with a larger scatter. Conclusions. The water masers from S Per, RT Vir and IK Tau are mainly beamed into spots with an observed angular size much smaller than the emitting clouds. The brighter spots at the line peaks are smaller than those in the wings. This suggests that the masers are amplification-bounded, emanating from clouds which can be approximated as spheres. Many of the masers around U Her and U Ori have apparent sizes which are more similar to the emitting clouds and have less or no dependence on intensity, which suggests that these masers are matter-bounded. This is consistent with an origin in flattened clouds and these two stars have shown other behaviour indicating the presence of shocks which could produce this effect.

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OH maser emission in the circumstellar envelopes of U Herculis, R Cassiopeiae and W Hydrae

Cited by 43 publications

References 0 publications

Recurring OH Flares towards o Ceti: I. location and structure of the 1990s’ and 2010s’ events

Recurring OH Flares towards o Ceti: I. location and structure of the 1990s’ and 2010s’ events

W Hya through the eye of Odin

Observational evidence for the shrinking of bright maser spots

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