Models of circumstellar molecular radio line emission - Mass loss rates for a sample of bright carbon stars
By F. Schoeier, H. Olofsson. 2001
164 citations recorded by the source corpus.
Using a detailed radiative transfer analysis, combined with an energy balance equation for the gas, we have performed extensive modelling of circumstellar CO radio line emission from a large sample of optically bright carbon stars, originally observed by Olofsson et al. (ApJS, 87, 267). Some new observational results are presented here. We determine some of the basic parameters that characterize circumstellar envelopes (CSEs), e.g., the stellar mass loss rate, the gas expansion velocity, and the kinetic temperature structure of the gas. Assuming a spherically symmetric CSE with a smooth gas density distribution, created by a continuous mass loss, which expands with a constant velocity we are able to model reasonably well 61 of our 69 sample stars. The derived mass loss rates depend crucially on the assumptions in the circumstellar model, of which some can be constrained if enough observational data exist. Therefore, a reliable mass loss rate determination for an individual star requires, in addition to a detailed radiative transfer analysis, good observational constraints in the form of multi-line observations and radial brightness distributions. In our analysis we use the results of a model for the photodissociation of circumstellar CO by Mamon et al. (1988). This leads to model ts to observed radial brightness proles that are, in general, very good, but there are also a few cases with clear deviations, which suggest departures from a simple r 2 density law. The derived mass loss rates span almost four orders of magnitude, from 51 0 9 M yr 1 up to 21 0 5 M yr 1 , with the median mass loss rate being 31 0 7 M yr 1 . We estimate that the mass loss rates are typically accurate to50% within the adopted circumstellar model. The physical conditions prevailing in the CSEs vary considerably over such a large range of mass loss rates. Among other things, it appears that the dust-to-gas mass ratio and/or the dust properties change with the mass loss rate. We nd that the mass loss rate and the gas expansion velocity are well correlated, and that both of them clearly depend on the pulsational period and (with larger scatter) the stellar luminosity. Moreover, the mass loss rate correlates weakly with the stellar eective temperature, in the sense that the cooler stars tend to have higher mass loss rates, but there seems to be no correlation with the stellar C/O-ratio. We conclude that the mass loss rate increases with increased regular pulsation and/or luminosity, and that the expansion velocity increases as an eect of increasing mass loss rate (for low mass loss rates) and luminosity. Five, of the remaining eight, sample stars have detached CSEs in the form of geometrically thin CO shells. The present mass loss rates and shell masses of these sources are estimated. Finally, in three cases we encounter problems using our model. For two of these sources there are indications of signicant departures from overall spherical symmetry of the CSEs. Carbon stars on the AGB are probably important in returning processed gas to the ISM. We estimate that carbon stars of the type considered here annually return0.05M of gas to the Galaxy, but more extreme carbon stars may contribute an order of magnitude more. However, as for the total carbon budget of the Galaxy, carbon stars appear to be of only minor importance.
Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics
View Paper: https://www.semanticscholar.org/paper/b41a49709eeccaff30fde9303d031ff23ea90054
How researchers see this paper
The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.
In Astronomy and Astrophysics
In Atomic and Molecular Physics, and Optics
Citations in the corpus
- An atomic and molecular database for analysis of submillimetre line observations (2004, background): “A number of more sophisticated, non-local radiative transfer codes have been developed for the interpretation of molecular line emission (e.g., Bernes 1979; Juvela 1997; Hogerheijde & van der Tak 2000; Ossenkopf et al. 2001; Schöier & Olofsson 2001, see van Zadelhoff et al. 2002 for a review).”
- Does IRAS 16293–2422 have a hot core? Chemical inventory and abundance changes in its protostellar environment (2002, result): “This was also the conclusion reached by Schöier & Olofsson (2001) for a large survey of carbon stars.”
- Production of dust by massive stars at high redshift (2011, background): “During the AGB evolution the stars develop quite strong winds with increasing mass-loss rates towards their late stages whereby th y lose some of their matter (e.g., Schöier and Olofsson, 2001).”
- Mass loss of stars on the asymptotic giant branch (2018, methodology): “Major studies of CSEs based on CO line emission and a radiative transfer analysis have been done by, e.g., Schöier and Olofsson (2001) (C-stars), Olofsson et al. (2002) (M-stars), Ramstedt et al. (2009) (S-stars), and Teyssier et al. (2006), De Beck et al. (2010), Ramstedt and Olofsson (2014), and…”
- Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles. II. CO line survey of evolved stars: derivation of mass-loss rate formulae (2010, unknown): “A correction for the envelope size (see Neri et al. 1998, and references therein) would decrease the discrepancy found by Schöier & Olofsson (2001).”