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

Abstract

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.

Discovery of water vapour in the carbon star V Cygni from observations withHerschel/HIFI

“…As part of the HIFISTARS guaranteed time key program, we will carry out a survey for water vapour in eight carbon-rich stars at distances greater than that (∼170 pc) of IRC+10216. Here, we report the detection of water vapour in the very first carbon star targeted in this survey: V Cygni, a Mira variable of spectral type C6 (Wallerstein & Knapp 1998), with an apparent V magnitude varying from 13.9 to 7.7 mag, a period of 421 days, and a distance of ∼400 pc (Bieging & Wilson 2001).…”

Probing the mass loss history of carbon stars using CO line and dust continuum emission

“…This suggests an isotropic mass loss mechanism with a variability on a broad range of, relatively short, time scales ∼40−800 yr. Moreover, spatially resolved interferometric CO millimetre observations currently have the potential to trace mass loss rate modulations on the order of a factor 2−3 down to a time scale of several hundred years (Bieging & Wilson 2001). For changes of the mass loss rate over longer periods of time, 10 5 yr, statistical studies are generally required.…”