Circumstellar HI and CO around the carbon stars V1942 Sgr and V CrB

Abstract

Context. The majority of stars that leave the main sequence are undergoing extensive mass loss, in particular during the asymptotic giant branch (AGB) phase of evolution. Observations show that the rate at which this phenomenon develops differs highly from source to source, so that the time-integrated mass loss as a function of the initial conditions (mass, metallicity, etc.) and of the stage of evolution is presently not well understood. Aims. We are investigating the mass loss history of AGB stars by observing the molecular and atomic emissions of their circumstellar envelopes. Methods. In this work we have selected two stars that are on the thermally pulsing phase of the AGB (TP-AGB) and for which high quality data in the CO rotation lines and in the atomic hydrogen line at 21 cm could be obained. Results. V1942 Sgr, a carbon star of the Irregular variability type, shows a complex CO line profile that may originate from a long-lived wind at a rate of ~ 10^-7 Msol/yr, and from a young (< 10^4 years) fast outflow at a rate of ~ 5 10^-7 Msol/yr. Intense HI emission indicates a detached shell with 0.044 Msol of hydrogen. This shell probably results from the slowing-down, by surrounding matter, of the same long-lived wind observed in CO that has been active during ~ 6 10^5 years. On the other hand, the carbon Mira V CrB is presently undergoing mass loss at a rate of 2 10^-7 Msol/yr, but was not detected in HI. The wind is mostly molecular, and was active for at most 3 10^4 years, with an integrated mass loss of at most 6.5 10^-3 Msol. Conclusions. Although both sources are carbon stars on the TP-AGB, they appear to develop mass loss under very different conditions, and a high rate of mass loss may not imply a high integrated mass loss.

arXiv commentAccepted for publication in Astron. Astrophys

References in corpus (13)

• IRIS: A new generation of IRAS maps
• Cool bottom processes on the thermally-pulsing AGB and the isotopic composition of circumstellar dust grains
• Models of circumstellar molecular radio line emission: Mass loss rates for a sample of bright carbon stars
• Preplanetary Nebulae: An HST Imaging Survey and a New Morphological Classification System
• Near-Infrared Photometry of Carbon Stars
• The Kr85 s-process Branching and the Mass of Carbon Stars
• Multiple Molecular Winds in Evolved Stars I. A Survey of CO(2-1) and CO(3-2) Emission from 45 Nearby AGB Stars
• HI in circumstellar environments
• Discovery of an HI Counterpart to the Extended Tail of Mira
• The formation of a detached shell around the carbon star Y CVn
• VLA Observations of HI in the Circumstellar Envelopes of Asymptotic Giant Branch Stars
• HI and CO in the circumstellar environment of the oxygen-rich AGB star RX Lep
• How semiregular are irregular variables?

Cited by in corpus (10)

• Fuel Efficient Galaxies: Sustaining Star Formation with Stellar Mass Loss
• Discovery of a detached HI gas shell surrounding alpha Orionis
• Pulsation-triggered dust production by asymptotic giant branch stars
• HI Observations of the Asymptotic Giant Branch Star X Herculis: Discovery of an Extended Circumstellar Wake Superposed on a Compact High-Velocity Cloud
• An HI Imaging Survey of Asymptotic Giant Branch Stars
• Discovery of Bright Galactic R Coronae Borealis and DY Persei Variables: Rare Gems Mined from ACVS
• Modeling Hot Gas Flow in the Low-Luminosity Active Galactic Nucleus of NGC3115
• HI line observations of 290 evolved stars made with the Nancay Radio Telescope -- I. Data
• Hot Gas Flows on Parsec Scale in the Low-Luminosity Active Galactic Nucleus NGC 3115
• Pressure broadening and shift of D1 line of Ag by He, Ar and N2