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Etoka, S.; Squeren, A. M. Le

doi:10.1023/a:1000792807929

Cited by 25 publications

(50 citation statements)

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“…As mentioned in Section 3.2.3, the velocity peak and spread of the OH flaring emission and the 22-GHz H2O are the same. This additional clue strongly supports the suggestion that the OH maser flaring emission observed here indeed originates from a region closer to the star than the standard OH maser CSE distances, in agreement with the findings of Etoka & Le Squeren (1997). Furthermore, as also mentioned Section 3.2.3, the long term monitoring of the 22-GHz H2O maser emission shows that OH flaring events seem to appear when the 22-GHz H2O is relatively fainter.…”

Section: Implication Of the Flare Location With Respect To The Standasupporting

confidence: 92%

“…The general flaring characteristics observed for o Ceti are similar to those observed for flares in isolated Miras in terms of IRAS colour-colour properties, velocity range in relation to the stellar velocity, spectral characteristics and polarisation behaviour as described by Etoka & Le Squeren (1997), which are quite distinct from what is observed towards standard Miras (Etoka & Le Squeren 2000). These common characteristics suggest that the flaring locations in terms of radius in the CSE is similar for all these events and all indicate that these regions of transient OH maser activity are distinct from the standard OH maser zone.…”

Section: Role Of Binarity In the Flaring Events Towardssupporting

confidence: 72%

“…These flares occur at velocities close to the stellar velocity, suggesting that they emanate from closer to the star compared to the distance at which standard OH emission arises in the CSE (Jewell et al 1981, Etoka & Le Squeren 1996, 1997, but this has never been confirmed by imaging.…”

Section: The Authorsmentioning

confidence: 96%

“…The first record of such an event was made towards U Ori at 1612 MHz (Jewell, Webber & Snyder, 1981). Five other events were then recorded, at 1612 MHz towards U Her and R LMi, and in the main lines towards X Oph, R Leo, and R Cnc (Etoka & Le Squeren, 1996, 1997. A study based on all 6 objects was presented in Figure 15.…”

Section: Comparison With Previously Recorded Flaring Eventsmentioning

confidence: 99%

“…Etoka & Le Squeren's (1996Squeren's ( , 1997 spectral records of the LHC and RHC spectra of the previous flaring events occuring in the 1665-MHz transition clearly show hints of Zeeman splitting signatures but a confirmation and accurate measurement of the associated magnetic field strength was not possible since no maps of these events were available.…”

Section: Polarisation and Underlying Magnetic Field Structurementioning

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: Implication Of the Flare Location With Respect To The Standasupporting

confidence: 92%

Section: Role Of Binarity In the Flaring Events Towardssupporting

confidence: 72%

Section: The Authorsmentioning

confidence: 96%

Section: Comparison With Previously Recorded Flaring Eventsmentioning

confidence: 99%

Section: Polarisation and Underlying Magnetic Field Structurementioning

confidence: 99%

See 3 more Smart Citations

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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OH masers in oxygen-rich late-type stars

Etoka

Squeren

2002

Symp. - Int. Astron. Union

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We present here some noteworthy results of two related studies on oxygen-rich late type stars. The aim of this work was to study the OH circumstellar shell properties in terms of evolution. These studies are based on an OH monitoring programme carried out with the Nançay Radio Telescope. The first study concerns seven Miras distributed along the colour-colour diagram. They were observed at two or three different epochs covering one to seven cycles over a period from 1980 to 1995 at 1612, 1667 and 1665 MHz in both circular polarizations. The second study concerns thirty objects covering a wide range of mass loss rate from Miras to OH/IR stars. They were observed in 1994 at 1665 & 1667 MHz in both circular polarizations.

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Signposts of transitional phases on the Asymptotic Giant Branch

Etoka

2022

Proc. IAU

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When low- and intermediate-mass stars pass through the Asymptotic Giant Branch (AGB) they experience dramatic changes in their circumstellar shell (CSE) influenced by their mass loss, the possible presence of a (closeby) companion and the magnetic field. Masers, well spread in this environment, provide a powerful tool to reveal the CSE changes occurring when the stars undergo a transitional phase on the AGB. These can be indirect, via for instance the modification of the pumping conditions or a direct consequence of e.g. a companion and/or of the magnetic field. Evidences of such changes have been observed towards Miras, materialized by strong - both in intensity and degree of polarisation - (OH) flaring events and towards stars believed to be transitioning from the Mira to the OH/IR phase, showing an unusual high degree of polarisation. How OH maser emission can be used as a signpost of transitional phases along the AGB is explored.

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Cited by 25 publications

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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

OH masers in oxygen-rich late-type stars

Signposts of transitional phases on the Asymptotic Giant Branch

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