The long baseline simultaneous multiband (BVRI) observations of blazar 3C 273 are presented. We have made 758 optical multiband observations with the Yunnan Astronomical Observatory (YAO) 103 cm and Shanghai Astronomical Observatory (SHAO) 156 cm from 2003 January to 2005 April. In our observational campaign, the average colour indices are B−V= 0.21, V−R= 0.26 and R−I= 0.31. The mean magnitudes in B, V, R and I are 12.895, 12.698, 12.441 and 12.139, respectively. The source is in a steady state over observational campaign. The correlations between colour index and brightness are discussed. We find that the correlations of B−V versus B, V−R versus V and R−I versus R have significant negative correlation, while B−V versus V, V−R versus R and R−I versus I have positive correlation. These strong correlations imply that the spectrum becomes bluer (flatter) when the source becomes brighter, and redden (softer) when the source fades both in intraday and long‐term variability. The spectral evolution trends of 3C 273 are consistent with those of BL Lac objects.

Grids of DAV star models are evolved by WDEC, taking the element diffusion effect into account. The grid parameters are hydrogen mass log(M H /M * ), helium mass log(M He /M * ), stellar mass M * , and effective temperature T eff for DAV stars. The core compositions are from white dwarf models evolved by MESA. Therefore, those DAV star models evolved by WDEC have historically viable core compositions. Based on those DAV star models, we studied the rate of period change (Ṗ (k)) for different values of H, He, M * , and T eff . The results are consistent with previous work. Two DAV stars G117-B15A and R548 have been observed around forty years. The rates of period change of two largeamplitude modes were obtained through O-C method. We did asteroseismological study on the two DAV stars and then obtained a best-fitting model for each star. Based on the two best-fitting models, the mode identifications (l, k) of the observed modes for G117-B15A and R548 are consistent with previous work. Both the observed modes and the observeḋ P s can be fitted by calculated ones. The results indicate that our method of evolving DAV star models is feasible.