Variable Asymmetry of the Circumstellar Envelope in IK Tauri Traced by SiO Maser Emission

Matsumoto, Naoko; Omodaká, Toshihiro; Imai, Hiroshi; Shimizu, Rie; Bushimata, Takeshi; Choi, Yoon Kyung; Hirota, Tomoya; Honma, Mareki; Inomata, Noritomo; Iwadate, Kenzaburo; Jike, Takaaki; Kameno, Seiji; Kameya, Osamu; Kamohara, Ryuichi; Kan-ya, Yukitoshi; Kawaguchi, Noriyuki; Kobayashi, Hideyuki; Kuji, Seisuke; Kurayama, Tomoharu; Maeda, Tamaki; Manabe, S.; Miyaji, Takeshi; Nakagawa, Akiharu; Nagayama, Tomonori; Nakashima, K.; Oh, Chung Sik; Oyama, Tomoaki; Sakai, Satoshi; Sakakibara, Sei-ichiro; Sasao, Tetsuo; Sato, Katsuhisa; Shibata, Katsunori M.; Shintani, Motonobu; Sofue, Yoshiaki; Sora, Kasumi; Suda, Hiroshi; Tamura, Yoshiaki; Tsushima, Miyuki; Yamashita, K.

doi:10.1093/pasj/60.5.1039

Cited by 17 publications

(19 citation statements)

References 31 publications

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“…Previous similar results have been proposed by several authors from standard VLBI experiments not including absolute coordinate measurements (e.g. Desmurs et al 2000;Matsumoto et al 2008). But, because of the lack of absolute astrometry, the comparison of the positions of both lines in those observations was difficult and the results were uncertain and controversial.…”

Section: Discussionsupporting

confidence: 59%

VERA observations of SiO maser emission from R Aquarii

Kamohara¹,

Bujarrabal²,

Honma³

et al. 2010

A&A

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Aims. We aim to study the spatial distribution of the v = 1 and v = 2 J = 1−0 SiO maser emission from R Aqr, a well known stellar symbiotic system. In particular, we intend to determine the annual parallax and proper motion of the source by means of measurements of the absolute coordinates of the maser spots. Methods. We performed VLBI observations of the v = 1 and v = 2 J = 1−0 maser emission, at 7 mm wavelength, using VERA. We present observations made in 11 epochs, between December 2004 and October 2006, and observations by other authors are also discussed. VERA provides very high spatial resolution and accurate astrometric measurements, thanks to its double-beam observing system. From fitting ring-like structures to the maser spot distributions, we determine absolute J2000 coordinates of the central star.(SiO maser emission is known to be distributed around the star forming spot rings at a few stellar radii.) Results. Maps with accurate absolute coordinates were obtained in 8 epochs. From the coordinates determined for the central star, we measured parallax and linear proper motion. We obtain π = 4.7 ± 0.8 mas, compatible with, but much more accurate than, the Hipparcos value (5.07 ± 3.15 mas), and deduce a distance of R Aqr D = 214 +45 −32 pc. Our accurate astrometry also yields a reliable comparison between the spot distributions of both v = 1 and v = 2 J = 1−0 lines. We find that both masers come from similar regions, i.e. at similar distances from the star and defining common spot clusters, confirming previous results. But the coincidences between spots of both lines are very rare, within the spatial and spectral resolution of our experiments. This result is found for eight epochs, spanning more than one pulsation cycle (of the cool Mira-type component). We argue that explaining the finer details of the v = 1, 2 J = 1−0 distributions found here would require new theoretical efforts. Finally, our observations also allow the study of the structure and dynamics of the close circumstellar shells in R Aqr. We do not confirm the previous suggestion that these shells are rotating; instead, we conclude that the observed kinematics is very probably caused by pulsations and random movements. The spatial distribution of the maser spots is found to be variable, but to show a stable axial symmetry.

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Section: Discussionsupporting

confidence: 59%

VERA observations of SiO maser emission from R Aquarii

Kamohara¹,

Bujarrabal²,

Honma³

et al. 2010

A&A

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“…However, at this point, the gas densities have been rescaled from the previous radial position and just have been shocked again at the new radial position (see description in Gobrecht et al 2016). For a period of 470 days and with T 0 at JD ∼ 2 453 025 (Matsumoto et al 2008), the ALMA data of IK Tau are obtained around φ = 0.98. The method applied by Gobrecht et al (2016) implies that a relative comparison between the retrieved and predicted molecular abundance stratifications is best carried out using Fig.…”

Section: Gas-phase Aluminium Budgetmentioning

confidence: 99%

Study of the aluminium content in AGB winds using ALMA

Decin

Richards

Waters

et al. 2017

A&A

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Context. The condensation of inorganic dust grains in the winds of evolved stars is poorly understood. As of today, it is not yet known which molecular clusters form the first dust grains in oxygen-rich (C/O < 1) asymptotic giant branch (AGB) winds. Aluminium oxides and iron-free silicates are often put forward as promising candidates for the first dust seeds. Aims. We aim to constrain the dust formation histories in the winds of oxygen-rich AGB stars. Methods. We obtained Atacama Large Millimeter/sub-millimeter array (ALMA) observations with a spatial resolution of 120 × 150 mas tracing the dust formation region of the low mass-loss rate AGB star, R Dor, and the high mass-loss rate AGB star, IK Tau. We detected emission line profiles of AlO, AlOH, and AlCl in the ALMA data and used these line profiles to derive a lower limit of atomic aluminium incorporated in molecules. This constrains the aluminium budget that can condense into grains. Results. Radiative transfer models constrain the fractional abundances of AlO, AlOH, and AlCl in IK Tau and R Dor. We show that the gas-phase aluminium chemistry is completely different in both stars with a remarkable difference in the AlO and AlOH abundance stratification. The amount of aluminium locked up in these three molecules is small, ≤1.1 × 10 −7 w.r.t. H 2 , for both stars, i.e. only ≤2% of the total aluminium budget. An important result is that AlO and AlOH, which are the direct precursors of alumina (Al 2 O 3 ) grains, are detected well beyond the onset of the dust condensation, which proves that the aluminium oxide condensation cycle is not fully efficient. The ALMA observations allow us to quantitatively assess the current generation of theoretical dynamical-chemical models for AGB winds. We discuss how the current proposed scenario of aluminium dust condensation for low mass-loss rate AGB stars within a few stellar radii from the star, in particular for R Dor and W Hya, poses a challenge if one wishes to explain both the dust spectral features in the spectral energy distribution (SED) in interferometric data and in the polarized light signal. In particular, the estimated grain temperature of Al 2 O 3 is too high for the grains to retain their amorphous structure. We advocate that large gas-phase (Al 2 O 3 ) n clusters (n > 34) can be the potential agents of the broad 11 µm feature in the SED and in the interferometric data and we propose potential formation mechanisms for these large clusters.

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“…We took the stellar periods from GCVS (Samus et al 2011) and also the origin and amplitude for RT Vir and W Hya, adjusted by eye in the latter case to fit the current data. The origin and amplitude for IK Tau were taken from Matsumoto et al (2008). during imaging was chosen to provide the best resolution without increasing the noise by more than 20%. In all cases, the dynamic range was limited to a few hundred, or about one hundred for low-declination sources with poor visibility-plane coverage.…”

Section: Data Acquisition and Analysismentioning

confidence: 99%

Evolved star water maser cloud size determined by star size

Richards

Etoka

Gray

et al. 2012

A&A

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Context. Cool, evolved stars undergo copious mass loss but the detailed mechanisms and the form in which the matter is returned to the ISM are still under debate. Aims. We investigated the structure and evolution of the wind at 5 to 50 stellar radii from asymptotic giant branch and red supergiant stars. Methods. 22-GHz water masers around seven evolved stars were imaged using MERLIN, at sub-AU resolution. Each source was observed at between 2 and 7 epochs, covering several stellar periods. We compared our results with long-term single dish monitoring provided by the Pushchino radio telescope. Results. The 22-GHz emission is located in approximately spherical, thick, unevenly filled shells. The outflow velocity increases twofold or more between the inner and outer shell limits. Water maser clumps could be matched at successive epochs separated by less than two years for AGB stars, or at least 5 years for RSG. This is much shorter than the decades taken for the wind to cross the maser shell, and comparison with spectral monitoring shows that some features fade and reappear. In five sources, most of the matched maser features brighten or dim in concert from one epoch to the next. A number of individual maser features show idiosyncratic behaviour, including one cloud in W Hya caught in the act of passing in front of a background cloud leading to 50-fold, transient amplification. The masing clouds are one or two orders of magnitude denser than the wind average and contain a substantial fraction of the mass loss in this region, with a filling factor <1%. The RSG clouds are about ten times bigger than those round the AGB stars. Conclusions. Proper motions are dominated by expansion, with no systematic rotation. The maser clouds presumably survive for decades (the shell crossing time) but the masers are not always beamed in our direction. Only radiative effects can explain changes in flux density throughout the maser shells on short timescales. The size of the clouds is proportional to that of the parent star, being of a similar radius to the star once the clumps reach the 22-GHz maser shell. Stellar properties such as convection cells must determine the clumping scale.

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Variable Asymmetry of the Circumstellar Envelope in IK Tauri Traced by SiO Maser Emission

Cited by 17 publications

References 31 publications

VERA observations of SiO maser emission from R Aquarii

VERA observations of SiO maser emission from R Aquarii

Study of the aluminium content in AGB winds using ALMA

Evolved star water maser cloud size determined by star size

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