We present a seismic study of δ Scuti based on a mode identification from multicoulor photometry. The dominant frequency can be associated only with a radial mode and the second frequency is, most probably, a dipole mode. The other six frequencies have more ambiguous identifications. The photometric mode identification provided also some constraints on the atmospheric metallicity [m/H] ≈ +0.5 and microturbulent velocity ξt ≈ 4 km s−1. For models reproducing the dominant frequency, we show that only the fundamental mode is possible and the first overtone is excluded. However, the location of δ Scuti near the terminal age main sequence requires the consideration of three stages of stellar evolution. For the star to be on the main sequence, it is necessary to include overshooting from the convective core with a parameter of at least αov = 0.25 at the metallicity greater than Z = 0.019. It turned out that the value of the relative amplitude of the bolometric flux variations (the non-adiabatic parameter f) is mainly determined by the position of the star in the HR diagram, i.e. by its effective temperature and luminosity, whereas the effect of the evolutionary stage is minor. On the other hand, the convective efficiency in the subphotospheric layers has a dominant effect on the value of the parameter f. Comparing the theoretical and empirical values of f for the radial dominant mode, we obtain constraints on the mixing length parameter αMLT which is less than about 1.0, independently of the adopted opacity data and chemical mixture. This value of αMLT is substantially smaller than for a calibrated solar model indicating rather low to moderately efficient convection in the envelope of δ Scuti.

中文翻译：

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一类脉动恒星原型δ Scuti的模式识别和地震研究

我们提出了基于多色光度法模式识别的 δ Scuti 地震研究。主频率只能与径向模式相关联，而第二频率很可能是偶极模式。其他六个频率的识别更加模糊。光度模式识别还对大气金属丰度 [m/H] ≈ +0.5 和微湍流速度 ξt ≈ 4 km s-1 提供了一些限制。对于再现主频的模型，我们表明只有基模是可能的，第一泛音被排除在外。然而，δ Scuti 的位置靠近末龄主序带需要考虑恒星演化的三个阶段。对于要进入主序星的恒星，必须包括对流核心的超调，其参数至少为 αov = 0。25 金属丰度大于 Z = 0.019。结果表明，辐射通量变化的相对幅度值（非绝热参数 f）主要取决于恒星在 HR 图中的位置，即其有效温度和光度，而进化阶段较小。另一方面，亚光球层中的对流效率对参数 f 的值有主要影响。比较径向主模式的 f 的理论值和经验值，我们获得了对混合长度参数 αMLT 的约束，该参数小于约 1.0，与所采用的不透明度数据和化学混合物无关。