Detached shells as tracers of asymptotic giant branch–interstellar medium bow shocks

Wareing, C. J.; Zijlstra, A. A.; Speck, A. K.; O’Brien, T. J.; Ueta, Toshiya; Elitzur, Moshe; Gehrz, R. D.; Herwig, Falk; Izumiura, Hideyuki; Matsuura, M.; Meixner, M.; Stencel, R. E.; Szczerba, R.

doi:10.1111/j.1745-3933.2006.00227.x

Cited by 36 publications

(46 citation statements)

References 30 publications

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“…An apparent large detached shell may also arise from the interaction of the AGB wind with the ISM. Ueta et al (2006) and Wareing et al (2006) detected a far-IR nebula at a distance of about 100 arcsec to the west. This is explained by a slowing-down of the stellar wind by surrounding matter.…”

Section: R Hydraementioning

confidence: 95%

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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Section: R Hydraementioning

confidence: 95%

Dust and molecular shells in asymptotic giant branch stars

Zhao-Geisler

Quirrenbach

Köhler

et al. 2012

A&A

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“…The controlling parameter is the ratio of wind speed to star velocity. Much like with spirals, fast growth of the KHI may strongly disturb the cometary structure at large distances, as seen in some hydrodynamical simulations (Wareing et al 2006(Wareing et al , 2007.…”

Section: To Spiral or Not To Spiralmentioning

confidence: 97%

Impact of orbital motion on the structure and stability of adiabatic shocks in colliding wind binaries

Lamberts

Dubus

Lesur

et al. 2012

A&A

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Context. The collision of winds from massive stars in binaries results in the formation of a double-shock structure with observed signatures from radio to X-rays. Aims. We study the structure and stability of the colliding wind region as it turns into a spiral owing to the orbital motion. We focus on adiabatic winds, where mixing between the two winds is expected to be restricted to the Kelvin-Helmholtz instability. Mixing of the Wolf-Rayet wind with hydrogen-rich material is important for dust formation in pinwheel nebulae such as WR 104, where the spiral structure has been resolved in infrared. Methods. We use the hydrodynamical code RAMSES to solve the equations of hydrodynamics on an adaptive grid. A wide range of binary systems with different wind velocities and mass-loss rates are studied with two-dimensional simulations. A specific threedimensional simulation is performed to model WR 104. Results. Orbital motion leads to the formation of two distinct spiral arms where the Kelvin-Helmholtz instability develops differently. We find that the spiral structure is destroyed when there is a large velocity gradient between the winds, unless the collimated wind is much faster. We argue that the Kelvin-Helmholtz instability plays a major role in determining whether the structure is maintained. We discuss the consequences for various colliding-wind binaries. When their spiral structure is stable, there is no straightforward relationship between the spatial step of the spiral, the wind velocities, and the orbital period. Our 3D simulation of WR 104 indicates that the colder, well-mixed trailing arm has more favourable conditions for dust formation than the leading arm. The single-arm infrared spiral follows more closely the mixing map than the density map, suggesting that the dust-to-gas ratio may vary between the leading and trailing density spirals. However, the density is much lower than what dust formation models require. Including radiative cooling would lead to higher densities, and also to thin shell instabilities whose impact on the large-scale structure remains unknown.

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“…Wareing et al successfully modelled bow shocks for AGB stars using 3-D hydrodynamical models (R Hya and Mira in Wareing et al 2006Wareing et al , 2007a. Their models were able to reproduce in great detail all the components of a bow shock (astropause, astrotail, vortices) and constrain the space velocity of the star, the ISM density, and the mass-loss rate.…”

Section: Space Motion Of the Star And The Ism Flow Velocitymentioning

confidence: 99%

HerschelPACS and SPIRE imaging of CW Leonis

Ladjal¹,

Barlow

Groenewegen

et al. 2010

A&A

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Herschel PACS and SPIRE images have been obtained over a 30 × 30 area around the well-known carbon star CW Leo (IRC +10 216). An extended structure is found in an incomplete arc of ∼22 diameter, which is cospatial with the termination shock due to interaction with the interstellar medium (ISM) as defined by Sahai & Chronopoulos from ultraviolet GALEX images. Fluxes are derived in the 70, 160, 250, 350, and 550 μm bands in the region where the interaction with the ISM takes place, and this can be fitted with a modified black body with a temperature of 25 ± 3 K. Using the published proper motion and radial velocity for the star, we derive a heliocentric space motion of 25.1 km s −1 . Using the PACS and SPIRE data and the analytical formula of the bow shock structure, we infer a de-projected standoff distance of the bow shock of R 0 = (8.0 ± 0.3) × 10 17 cm. We also derive a relative velocity of the star with respect to the ISM of (106.6 ± 8.7)/ √ n ISM km s −1 , where n ISM is the number density of the local ISM.

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Detached shells as tracers of asymptotic giant branch–interstellar medium bow shocks

Cited by 36 publications

References 30 publications

Dust and molecular shells in asymptotic giant branch stars

Dust and molecular shells in asymptotic giant branch stars

Impact of orbital motion on the structure and stability of adiabatic shocks in colliding wind binaries

HerschelPACS and SPIRE imaging of CW Leonis

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