HD 172189: an eclipsing and spectroscopic binary with a δ Sct-type pulsating component in an open cluster

¹ Instituto de Astrofísica de Andalucía, CSIC, Apdo. 3004, 18080 Granada, Spain e-mail: susana@iaa.es
² European Southern Observatory, Alonso de Cordova 3107, Santiago 19, Chile
³ LESIA, Observatoire de Paris-Meudon, 92195 Meudon Principal Cedex, France
⁴ Instituto de Astronomía, Universidad Nacional Autónoma de Mexico, Apdo. Postal 70-264, 04510 Mexico DF, Mexico
⁵ Institut d'Estudis Espacials de Catalunya/CSIC, Campus UAB, Facultat de Ciències, Torre C5-parell-2a planta, 08193 Bellaterra, Spain
⁶ INAF – Osservatorio Astronomico di Brera, via Bianchi 46, 23807 Merate (LC), Italy

Received: 25 April 2005
Accepted: 1 June 2005

Abstract

We present a study based on more than 2500 uvby-measurements collected on HD 172189, a new eclipsing binary system with a δ Sct-type pulsating component that belongs to the open cluster IC 4756. The great interest of this object lies in that three important characteristics coexist: cluster membership, binarity and pulsation. Its binarity and the δ Sct-type pulsations of one component were detected in the course of several Strömgren photometric campaigns. The frequency analysis of all the uvby out-of-eclipse data reveals a clear frequency of 19.5974 cd^-1as well as the existence of other high values in the range 18–20 cd^-1. We have also carried out a first evaluation of the binary parameters and determined a value of 5.702 d for the orbital period. An additional potential interest of HD 172189 resides in its location in the field of view of the COROT mission and, therefore, this star is an excellent candidate for becoming a target for asteroseismology.