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The Effects of Mass Loss on the Evolution of Chemical Abundances in Fm Stars

This study investigates the impact of mass loss on the evolution of chemical abundances in Fm stars, focusing on the anomalies observed in elements such as Li, CNO, Ca, Sc, iron peak elements, and rare earths. The results show that mass loss rates of the order of the solar mass loss rate can reduce these anomalies to desired levels. Turbulence and mass loss affect the anomalies differently, indicating the need for further observations and more massive models to determine their relative importance.

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The Effects of Mass Loss on the Evolution of Chemical Abundances in Fm Stars

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  1. The Effects of Mass Loss on the Evolution of Chemical Abundances in Fm Stars Mathieu Vick1,2 Georges Michaud1 Département de physique, Université de Montréal, Canada GRAAL / UMR5024, Université Montpellier II, France

  2. Pop.I, MS stars 7000 K <Teff< 10 000 K Non magnetic Abundance anomalies => Slow rotators Binaries Typical abundance patterns underabundances : Li, CNO, Ca, Sc overabundances : Iron peak elements (2-5) Rare earths (10 or more) Fm’s are expected to have the same patterns Basic Physical Properties Gebran et al., 2007 (poster 05)

  3. Michaud (1970): separation in radiative zone leads to observed abundance anomalies Anomalies predicted by purely diffusive models are larger than those observed Other processes? The Basic Model 1.4M: Diffusion only (black), mass loss (red, blue, green), turbulence (orange).

  4. Competition between g and grad approx. determines movement of elements Position of BSCZ and g = grad (vdrift= 0) Large scale effects can hinder diffusion Diffusion time scales grow with increasing density Transport Processes Mass Loss

  5. Richer et al (2000): Sirius A: 1 free parameter (mixed mass) 12 of 16 elements observed are well reproduced Other papers: Richard et al. (2001) Michaud et al. (2005) Models with Turbulence Can mass loss do the same?

  6. Implementation of Mass Loss Physical considerations: 1.tdiff >> tconvHomogeneous abundances in CZ 2. Convective overshoot mixes the atmosphere and links H-He CZ (Latour et al. ,1981) The mass loss rates considered are: • chemically homogenous (with the same composition as the SCZ) • spherically symmetrical • weak enough not to influence nuclear burning in the core or the stellar structure

  7. Implementation of Mass Loss • Can’t simply add to total velocity field (many numerical problems encountered) • But with simple hypotheses these problems can be avoided: (1) homogeneous CZ (2) Mass lost has same composition as SCZ • Mechanism is not important

  8. Implementation of Mass Loss • where: In SCZ Under SCZ

  9. Models with Mass Loss • The evolutionary calculations take into detailed account time-dependant abundance variations of 28 chemical species and include all effects of atomic diffusion and radiative accelerations. • These are the first fully self-consistent evolutionary models which include mass loss. • Models were calculated for 1.35, 1.40, 1.45 and 1.50 M. • All the models have evolved from the homogenous pre-main sequence phase with a solar metallicity (Z=0.02). • The mass loss rates considered varied from 1 x 10-14 to 3 x 10-13 Myr-1.

  10. Observation: tUMa (Hui-Bon-Hoa, 2000) Age~500 Myr, Teff~7000 K Turbulence and mass loss have slightly different effect on certain elements Results: 1.5 M model Fe convection zone appears naturally!

  11. Results (cont.) • Anomalies appear with decreasing importance down to stars of 1.35M. • Reasonable mass loss rates can reduce anomalies to the desired levels

  12. Conclusions • With a mass loss rate of the order of the solar mass loss rate we can successfully reproduce the observed anomalies of tUMa. • It is shown that turbulence and mass loss affect anomalies differently. It is thus possible that additional observations (and more massive models) could help constrain the relative importance of each process. • Observations of elements between Al and Ar could allow us to determine if there is separation between the Fe and H-He convection zones. • In any case, it is seen that mass loss can effectively reduce the predicted anomalies to observed levels.

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