Multisite Observations of δ Scuti Stars 7 Aql and 8 Aql (a New δ Scuti Variable): The Twelfth STEPHI Campaign in 2003

Abstract

We present an analysis of the pulsation behavior of the δ Scuti stars 7 Aql (HD 174532) and 8 Aql (HD 174589), a new variable star, observed in the framework of the STEPHI XII campaign during 2003 June and July; 183 hr of high-precision photometry were acquired by using four-channel photometers at three sites on three continents during 21 days. The light curves and amplitude spectra were obtained following a classical scheme of multichannel photometry. Observations in different filters were also obtained and analyzed. Six and three frequencies have been unambiguously detected above a 99% confidence level in the range 190-300 μHz and 100-145 μHz in 7 Aql and 8 Aql, respectively. A comparison of observed and theoretical frequencies shows that 7 Aql and 8 Aql may oscillate with p-modes of low radial orders, typical among δ Scuti stars. In terms of radial oscillations the range of 8 Aql goes from n = 1 to 3, while for 7 Aql the range spans from n = 4 to 7. Nonradial oscillations have to be present in both stars as well. The expected range of excited modes according to a nonadiabatic analysis goes from n = 1 to 6 in both stars.