Atomic Diffusion in Stars by Georges Michaud Georges Alecian & Jacques Richer

Author:Georges Michaud, Georges Alecian & Jacques Richer
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

Figure 9.9 illustrates the effect of varying the strength of turbulence on surface abundances. The different models vary in strength, in their depth dependence (value of n) and in anchorage [Eq. (7.​24) or Eq. (7.​26)]. For instance, in the 5.3D100-4 model the mixed zone extends down to the bottom of the iron peak convection zone while it is ten times deeper in mass in the 5.3D1M-4 model and another 2.5 times deeper in mass in the 5.4D1M-4 model. It is striking how little the patterns of anomalies change as turbulence changes: the curves practically never cross. It is only the overall size of anomalies that changes. This implies that, given an age and stellar mass, there is only one pattern of anomalies that can be predicted by these simple turbulence or mass loss models. The pattern is characterized by overabundances of iron peak elements and underabundances of species lighter than Na. Within each group, the relative anomalies also follow a simple dependence. An odd-even effect is apparent between Ne and Ca. It is caused by saturation of the radiation field which reduces g rad most for the more abundant even-Z elements. The insert illustrates that the elements which are most sensitive to details of models are around Ca and that one must be able to determine abundance anomalies to better than 0.1 dex if one is to distinguish between models.

Fig. 9.9Surface abundances in 2. 5 M models at 100 My. Each curve corresponds to the use of a different turbulence profile. They are labeled as follows (see § 7.3.3 for parameter definitions): (1) T5.30D100-4; (2) T5.30D200-4; (3) T5.30D1K-4; (4) T5.30D10K-4; (5) T5.30D10K-3; (6) R1K-2 (dot-dash); (7) T5.25D1M-4 (dotted); (8) T5.30D1M-4; (9) T5.40D1M-4 (dashed). Some isotopes are included, slightly shifted horizontally. Horizontal bars on the right show the spread of corresponding surface metallicities [Z∕H]. Effective temperatures range from 10,300 to 10,400 K. Inset: differences between anomalies of two more models (10 & 11) and those of model (4); (10, dotted) R92-3 has the same as (4), while (11, solid) R163-3 was adjusted to give a near perfect fit for helium at 100 My and has a slightly larger . From Richer et al. (2000), Fig. 12

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