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

2. Basic Physical Properties Pop.I, MS stars 7000 K <T eff < 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 Gebran et al., 2007 (poster 05)

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

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

5. Models with Turbulence 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) Can mass loss do the same?

6. Implementation of Mass Loss Physical considerations:  1.  diff >>  conv Homogeneous abundances in CZ  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. Results: 1.5 M  model Observation:  UMa (Hui-Bon-Hoa, 2000) Age~500 Myr, T eff ~7000 K Turbulence and mass loss have slightly different effect on certain elements 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  UMa. 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.