The frequency ratio method and the new multiperiodic γ Doradus star HD 218427

¹ Instituto de Astrofísica de Andalucía, CSIC, PO Box 3004, 18080 Granada, Spain e-mail: eloy@iaa.es
² European Southern Observatory, Alonso de Cordova 3107, Santiago 19, Chile
³ LESIA, Observatoire de Paris-Meudon, UMR 8109, 92190 Meudon, France
⁴ INAF-Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy
⁵ CRAAG, Algiers Observatory, BP 63 Bouzareah, 16340 Algiers, Algeria

Received: 29 July 2005
Accepted: 1 January 2006

Abstract

Oscillations of γ Dor-type were discovered in the star HD 218427 through simultaneous uvby photometric observations carried out in the year 2003. A few H-Crawford measurements were also collected for calibration purposes and they locate this star well inside the γ Dor instability region. We find HD 218427 to be deficient in metals, similar to other well-defined γ Dor stars, and discuss the possibility that it has a λ Boo nature. We carried out frequency analysis for different filters, including the combined “vby” filter, and five frequencies were found as significant with periods ranging between 0.3 and 0.8 days. The recently-developed frequency ratio method is used in order to identify the excited modes. The results are consistent with an identification for all the modes and with high radial quantum numbers () for the three main observed periodicities. The possibility of multiplet structures is also discussed. However, no consistency is found when using the time-dependent convection treatment to discriminate modes. This disagreement can be due to the large rotation velocity taking place in HD 218427 and, consequently, the significant coupling between the modes.