VERA observations of SiO maser emission from R Aquarii

Kamohara, Ryuichi; Bujarrabal, V.; Honma, Mareki; Nakagawa, Akiharu; Matsumoto, Naoko; Oyama, Tomoaki; Hirota, Tomoya; Imai, Hiroshi; Shibata, Katsunori M.; Kobayashi, Hideyuki; Sato, Katsuhisa; Ueno, Yuji

doi:10.1051/0004-6361/200912439

Cited by 28 publications

(38 citation statements)

References 31 publications

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“…Observations of SiO maser emission in R Aqr (e.g. Cotton et al 2004;Kamohara et al 2010;Pardo et al 2004) show properties completely similar to those found in standard AGB stars. VLBI maps show, in particular, that the SiO maser in general occupy a ring-like region (with radius ∼5 × 10 13 cm) that is comparable to those typical of AGB stars.…”

Section: Numerical Model Of Line Formationsupporting

confidence: 69%

“…SiO maser emission (v > 0 lines at mm wavelengths) in R Aqr is relatively "normal" compared to what is observed in standard AGB stars (e.g. Pardo et al 2004;Cotton et al 2004;Kamohara et al 2010). We recall that SiO maser emission comes from the innermost circumstellar regions, in our case at about 5 × 10 13 cm.…”

Section: Introductionsupporting

confidence: 55%

“…The 12 CO emission is detected in R Aqr and CH Cyg, two bright and nearby symbiotic stars that have been extensively studied over the whole spectral range. The distance to R Aqr has been accurately determined from recent VLBI measurements of its parallax by Kamohara et al (2010), so we adopted their distance value, D = 214 +45 −32 . A distance of 244 +49 −35 pc was measured for CH Cyg from Hipparcos data (van Leeuwen 2007).…”

Section: Introductionmentioning

confidence: 99%

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CO observations of symbiotic stellar systems

Bujarrabal

Mikołajewska

Quintana-Lacaci

2010

A&A

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Aims. We have studied the molecular content of the circumstellar environs of symbiotic stellar systems, in particular of the well know objects R Aqr and CH Cyg. The study of molecules in these stars will help for understanding the properties of the very inner shells around the cool stellar component from which molecular emission is expected to come. Methods. We performed mm-wave observations with the IRAM 30 m telescope of the 12 CO J = 1−0 and J = 2−1, 13 CO J = 1−0 and J = 2−1, and SiO J = 5−4 transitions in the symbiotic stars R Aqr, CH Cyg, and HM Sge. The data were analyzed by means of a simple analytical description of the general properties of molecular emission from the inner shells around the cool star. Numerical calculations of the expected line profiles were also performed that took the level population and radiative transfer under such conditions into account. Results. Weak emission of 12 CO J = 1−0 and J = 2−1 was detected in R Aqr and CH Cyg and a good line profile of 12 CO J = 2−1 in R Aqr was obtained. The intensities and profile shapes of the detected lines are compatible with emission coming from a very small shell around the Mira-type star, with a radius comparable to or slightly smaller than the distance to the hot dwarf companion, 10 14 −2 × 10 14 cm. We argue that other possible explanations are improbable. This region probably shows properties similar to those characteristic of the inner shells around standard AGB stars: outwards expansion at about 5-25 km s −1 , with a significant acceleration of the gas, temperatures decreasing with radius between about 1000 and 500 K, and densities ∼10 9 −3 × 10 8 cm −3 . Our model calculations are able to explain the asymmetric line shape observed in 12 CO J = 2−1 from R Aqr, in which the relatively weaker blue part of the profile would result from selfabsorption by the outer layers (in the presence of a velocity increase and a temperature decrease with radius). The mass-loss rates are somewhat higher than in standard AGB stars, as often happens for symbiotic systems. In R Aqr, we find that the total mass of the CO emitting region is ∼2−3 × 10 −5 M , corresponding toṀ ∼ 5 × 10 −6 −10 −5 M yr −1 and compatible with results obtained from dust emission. Considering other existing data on molecular emission, we suggest that the limited extent of the molecule-rich gas in symbiotic systems is mainly due to molecule photodissociation by the radiation of the hot dwarf star.

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Section: Numerical Model Of Line Formationsupporting

confidence: 69%

Section: Introductionsupporting

confidence: 55%

Section: Introductionmentioning

confidence: 99%

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CO observations of symbiotic stellar systems

Bujarrabal

Mikołajewska

Quintana-Lacaci

2010

A&A

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“…We have not considered the presence of a companion star in our calculations. This approach is justified because our calculations show that the v = 1, J = 3 − 2 CO line is formed very close to the star (r 3 R ) and maser emission lines formed at similar distances observed towards close binaries AGB stars, such as R Aqr, do not show distinct features from those observed towards single AGB stars (see, e.g., Kamohara et al 2010). We note, however, that the five AGB stars discussed here are peculiar in some way because of interactions with their companions.…”

Section: Modellingmentioning

confidence: 77%

ALMA observations of the vibrationally excited rotational CO transition v = 1, J = 3 − 2 towards five AGB stars

Khouri

Vlemmings

Ramstedt

et al. 2016

Monthly Notices of the Royal Astronomical Society: Letters

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ALMA observations of the vibrationally-excited rotational CO transition v = 1, J = 3 − 2 towards five AGB stars ABSTRACTWe report the serendipitous detection with ALMA of the vibrationally-excited purerotational CO transition v = 1, J = 3 − 2 towards five asymptotic giant branch (AGB) stars, o Cet, R Aqr, R Scl, W Aql, and π 1 Gru. The observed lines are formed in the poorly-understood region located between the stellar surface and the region where the wind starts, the so-called warm molecular layer. We successfully reproduce the observed lines profiles using a simple model. We constrain the extents, densities, and kinematics of the region where the lines are produced. R Aqr and R Scl show inverse P-Cygni line profiles which indicate infall of material onto the stars. The line profiles of o Cet and R Scl show variability. The serendipitous detection towards these five sources shows that vibrationally-excited rotational lines can be observed towards a large number of nearby AGB stars using ALMA. This opens a new possibility for the study of the innermost regions of AGB circumstellar envelopes.

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“…The Hipparcos catalog (Perryman & ESA 1997b) gives a value of 211 +71 −42 pc, while Kamohara et al (2010) estimated the distance to 214 +45 −32 pc via maser observations. The mass and luminosity, obtained from modeling and observations, are 1 M and 3470 L , respectively (Hofmann et al 2000).…”

Section: R Aquilaementioning

confidence: 99%

Dust and molecular shells in asymptotic giant branch stars

Zhao-Geisler

Quirrenbach

Köhler

et al. 2012

A&A

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Context. Asymptotic giant branch (AGB) stars are one of the largest distributors of dust into the interstellar medium. However, the wind formation mechanism and dust condensation sequence leading to the observed high mass-loss rates have not yet been constrained well observationally, in particular for oxygen-rich AGB stars. Aims. The immediate objective in this work is to identify molecules and dust species which are present in the layers above the photosphere, and which have emission and absorption features in the mid-infrared (IR), causing the diameter to vary across the N-band, and are potentially relevant for the wind formation. Methods. Mid-IR (8-13 μm) interferometric data of four oxygen-rich AGB stars (R Aql, R Aqr, R Hya, and W Hya) and one carbonrich AGB star (V Hya) were obtained with MIDI/VLTI between April 2007 and September 2009. The spectrally dispersed visibility data are analyzed by fitting a circular fully limb-darkened disk (FDD). Results. The FDD diameter as function of wavelength is similar for all oxygen-rich stars. The apparent size is almost constant between 8 and 10 μm and gradually increases at wavelengths longer than 10 μm. The apparent FDD diameter in the carbon-rich star V Hya essentially decreases from 8 to 12 μm. The FDD diameters are about 2.2 times larger than the photospheric diameters estimated from K-band observations found in the literature. The silicate dust shells of R Aql, R Hya and W Hya are located fairly far away from the star, while the silicate dust shell of R Aqr and the amorphous carbon (AMC) and SiC dust shell of V Hya are found to be closer to the star at around 8 photospheric radii. Phase-to-phase variations of the diameters of the oxygen-rich stars could be measured and are on the order of 15% but with large uncertainties. Conclusions. From a comparison of the diameter trend with the trends in RR Sco and S Ori it can be concluded that in oxygen-rich stars the overall larger diameter originates from a warm molecular layer of H 2 O, and the gradual increase longward of 10 μm can be most likely attributed to the contribution of a close Al 2 O 3 dust shell. The chromatic trend of the Gaussian FWHM in V Hya can be explained with the presence of AMC and SiC dust. The observations suggest that the formation of amorphous Al 2 O 3 in oxygenrich stars occurs mainly around or after visual minimum. However, no firm conclusions can be drawn concerning the mass-loss mechanism. Future modeling with hydrostatic and self-consistent dynamical stellar atmospheric models will be required for a more certain understanding.

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VERA observations of SiO maser emission from R Aquarii

Cited by 28 publications

References 31 publications

CO observations of symbiotic stellar systems

CO observations of symbiotic stellar systems

ALMA observations of the vibrationally excited rotational CO transition v = 1, J = 3 − 2 towards five AGB stars

Dust and molecular shells in asymptotic giant branch stars

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