Frequencies and mode identifications of the δ Scuti star EE Camelopardalis

摘要

Aims. EE Cam belongs to a group of slightly evolved main-sequence A stars with intermediate rotational velocities. The pulsation frequencies and their mode identification of this star are of interest in order to compare these with those known for the high-amplitude δ Scuti stars (HADS) and the common fast-rotating low-amplitude δ Scuti pulsators. Methods. The variability of the δ Scuti star EE Cam was observed photometrically for more than 300 nights from 2006 to 2010. Results. Forty pulsation frequencies are identified, ranging from 3.4 to 13.3 cd-1 (40 to 154 μHz). The frequency distribution of the residuals suggests the presence of a large number of additional small-amplitude modes in the same frequency range. We compare the observed phase differences and amplitude ratios with those predicted by pulsation models. The dominant mode at 4.93 cd-1 is found to be a radial mode, while the mode at 5.21 cd-1 is identified as a nonradial ? = 1 mode. Furthermore, when we compare the frequency range of the detected modes with detailed stellar models of pulsational instability, the radial mode is found to be the fundamental mode. Conclusions. We have studied and presented the pulsation behavior of EE Cam. It demonstrates that a moderately rotating star can exhibit the behavior of the two groups of δ Scuti stars: the identification of the dominant mode as the radial fundamental is similar to that found in the slowly rotating HADS, and the presence of a very large number of low-amplitude nonradial modes resembles the property of the fast rotating low-amplitude δ Scuti stars.