V Hydrae - A carbon star in transformation to a bipolar nebula

Tsuji, Takashi; Unno, Wasaburo; Kaifu, N.; Izumiura, Hideyuki; Ukita, Nobuharu; Cho, S.; Koyama, Kouichi

doi:10.1086/185132

Cited by 22 publications

(28 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This means that a strong asymmetry already sets in in the very close stellar environment at less then 2 photospheric radii with an elongation along a north-south direction, therefore, a similar orientation as found by e.g. Tsuji et al (1988); Kahane et al (1988Kahane et al ( , 1996; Sahai et al (2003) and particular also by Lagadec et al (2005) in the mid-infrared (cf. Sect.…”

Section: Asymmetriessupporting

confidence: 74%

“…V Hya is a classical (N type) carbon star (Zuckerman et al 1977) and is believed to be in a short-lived but critical stage in the evolution of a mass-losing AGB star into a bipolar PN (Tsuji et al 1988;Kahane et al 1996). This dust-enshrouded star has a C/O ratio of 1.05 and an effective temperature of about 2650 K (Lambert et al 1986).…”

Section: Hydraementioning

confidence: 99%

“…(Zuckerman & Dyck 1986;Sahai & Wannier 1988;Lloyd Evans 1991;Knapp et al 1997;Olivier et al 2001;Hirano et al 2004;Sahai et al 2009). The low-velocity circumstellar environment component is flattened or has a disk-like shape, and is elongated along the north-south direction (Tsuji et al 1988;Kahane et al 1988Kahane et al , 1996Sahai et al 2003). This may enable or enhance the formation of an accretion disk and supports a model in which the jet is driven by an accretion disk around an unseen, compact companion.…”

Section: Semestermentioning

confidence: 99%

See 2 more Smart Citations

Dust and molecular shells in asymptotic giant branch stars

Zhao-Geisler

Quirrenbach

Köhler

et al. 2012

A&A

View full text Add to dashboard Cite

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.

show abstract

Section: Asymmetriessupporting

confidence: 74%

Section: Hydraementioning

confidence: 99%

Section: Semestermentioning

confidence: 99%

See 1 more Smart Citation

Dust and molecular shells in asymptotic giant branch stars

Zhao-Geisler

Quirrenbach

Köhler

et al. 2012

A&A

View full text Add to dashboard Cite

show abstract

“…It is a Mira variable with a 421 day period and an apparent V magnitude that varies from 7.7 to 13.9 mag. The IRAS Ñux densities are 665, 234, and 49 Jy at 12, 25, and 60 km, which yield colors that place the star in region VII of the IRAS two-color diagram deÐned by van der Veen & Habing (1988), i.e., typical for an optically bright carbon star.…”

Section: Observations and Data Reductionmentioning

confidence: 93%

“…The bipolar structure is probably a result of interaction between the red giant wind and the (close) binary companion. The carbon star V Hya, has a bipolar envelope in CO emission (Kahane et al 1988 ;Tsuji et al 1988) that may be a result of a close binary companion that went through a common envelope phase resulting in a spin-up of the giant that has a large measured rotational velocity (Barnbaum, Morris, & Kahane 1995). The binary S star n1 Gru has an asymmetric CO distribution that can be modeled by an inclined disk geometry for the CSE (Knapp et al 1999).…”

Section: Asymmetric Mass L Ossmentioning

confidence: 99%

High-Resolution Images of CO [ITAL]J[/ITAL] = 2–1 Emission from the Carbon Star V Cygni

Bieging

Wilson

2001

The Astronomical Journal

View full text Add to dashboard Cite

This paper presents observations of the CO J \ 2È1 emission from the circumstellar envelope of the mass-losing carbon star V Cyg. The observations were made with the Caltech Millimeter Array. A previously published single-dish map was used to construct short-spacing visibilities not sampled by the interferometer data, thereby recovering missing Ñux in extended low brightness emission. The images have an angular resolution of with a velocity resolution of 1 MHz (1.3 km s~1). The channel maps D1A .2 are consistent with an expanding envelope that is roughly spherical, but they also show evidence for asymmetric structure, as well as small-scale clumping. We compare these observations, as well as other published spectra, with statistical equilibrium models for CO in a circumstellar envelope. Models that Ðt the spherically averaged data must invoke a mass-loss rate, that has decreased with time by a factor M 0 , of D2È3 over the past several hundred years. The model kinetic temperature structure in radius, T K (r), decreases as r~0.8 out to r B 6 ] 1015 cm and levels o † to a constant value at K beyond. The T K \ 23 secular change in may be related to changes in the stellar luminosity or temperature, as predicted by M 0 recent numerical hydrodynamic models for mass loss. The inferred kinetic temperature structure suggests that heating by the photoelectric e †ect on dust grains is important in the outer envelope.

show abstract

High-luminosity single carbon stars in stellar and galactic evolution

Jura¹

1991

The Astron Astrophys Rev

View full text Add to dashboard Cite

V Hydrae - A carbon star in transformation to a bipolar nebula

Cited by 22 publications

References 0 publications

Dust and molecular shells in asymptotic giant branch stars

Dust and molecular shells in asymptotic giant branch stars

High-Resolution Images of CO [ITAL]J[/ITAL] = 2–1 Emission from the Carbon Star V Cygni

High-luminosity single carbon stars in stellar and galactic evolution

Contact Info

Product

Resources

About