Envelope structures and optical/radio positions of cool stars

Bowers, P. F.; Johnston, K. J.; Vegt, C. de

doi:10.1086/167411

Cited by 45 publications

(43 citation statements)

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“…This shell extends out about 0"28, which corresponds to a radius of about 500 AU given our derived distance of 1.78 kpc. The size of this halo matches well with the size of OH shells surrounding nearby Mira variables observed by Bowers et al (1990) supporting the idea that the halo is the circumstellar shell created by the Mira variable prior to the outburst. The extended high-velocity features observed by Solf could then correspond to the ends of the bipolar flow, seen in Fig.…”

Section: Discussionsupporting

confidence: 79%

Imaging the bipolar nebula around HM Sagittae

Hack¹,

Paresce²

1993

PASP

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ABSTRACT. Hubble Space Telescope Faint Object Camera UV images are presented for HM Sagittae showing a bipolar optical nebula similar to that in R Aquarii and RX Puppis. The nebula extends to a distance of 0"174 with a P.A. of 135° inside a faint halo extending to a radius of 0"28. A kinematical distance to HM Sge based on positions of features in the nebula is found to be 1.78 ±0.1 kpc. Comparisons between our UV images, radio maps taken in 1982, and IUE spectra all demonstrate that this system is still undergoing dramatic changes.

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Section: Discussionsupporting

confidence: 79%

Imaging the bipolar nebula around HM Sagittae

Hack¹,

Paresce²

1993

PASP

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“…At a larger diameter of around 330 mas, Lane et al (1987) and Brand et al (1994) detected H 2 O maser emission. Studies of OH masers were performed by Bowers et al (1989), Etoka & Le Squeren (2000) and He et al (2005), showing that this maser emission originates in a region with a diameter between 2000 and 3000 mas. Matsuura et al (2002) modeled the extended molecular spheres of R Aql with two layers of water vapor of different temperatures.…”

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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“…Most of the observed lines have line widths in excess of 17 km s −1 . However, a few lines are considerably narrower, (Bowers et al 1989). The CO expansion velocity derived from ground-based CO J = 1-0 data is also indicated .…”

Section: Velocity Structurementioning

confidence: 99%

Water content and wind acceleration in the envelope around the oxygen-rich AGB star IK Tauri as seen byHerschel/HIFI

Decin

Justtanont

Beck

et al. 2010

A&A

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During their asymptotic giant branch evolution, low-mass stars lose a significant fraction of their mass through an intense wind, enriching the interstellar medium with products of nucleosynthesis. We observed the nearby oxygen-rich asymptotic giant branch star IK Tau using the highresolution HIFI spectrometer onboard Herschel. We report on the first detection of H 16 2 O and the rarer isotopologues H 17 2 O and H 18 2 O in both the ortho and para states. We deduce a total water content (relative to molecular hydrogen) of 6.6 × 10 −5 , and an ortho-to-para ratio of 3:1. These results are consistent with the formation of H 2 O in thermodynamical chemical equilibrium at photospheric temperatures, and does not require pulsationally induced non-equilibrium chemistry, vaporization of icy bodies or grain surface reactions. High-excitation lines of 12 CO, 13 CO, 28 SiO, 29 SiO, 30 SiO, HCN, and SO have also been detected. From the observed line widths, the acceleration region in the inner wind zone can be characterized, and we show that the wind acceleration is slower than hitherto anticipated.

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Envelope structures and optical/radio positions of cool stars

Cited by 45 publications

References 0 publications

Imaging the bipolar nebula around HM Sagittae

Imaging the bipolar nebula around HM Sagittae

Dust and molecular shells in asymptotic giant branch stars

Water content and wind acceleration in the envelope around the oxygen-rich AGB star IK Tauri as seen byHerschel/HIFI

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