Multi - Site Observations of Δ Scuti Stars 7 Aql and 8 Aql ( a New Δ Scuti Variable ) : the Twelfth Stephi Campaign in 2003

We present an analysis of the pulsation behaviour of the δ Scuti stars 7 Aql (HD 174532) and 8 Aql (HD 174589) – a new variable star – observed in the framework of STEPHI XII campaign during 2003 June–July. 183 hours 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 multi-channel 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 190μHz–300μHz and 100μHz–145μHz 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 n = 3 while for 7 Aql the range spans from n = 4 to n = 7. Non-radial oscillations have to be present in both stars as well. The expected range of excited modes according to a non adiabatic analysis goes from n = 1 to n = 6 in both stars. Subject headings: techniques:photometric – stars: individual: HD 174532 – stars: individual: HD 174589 – stars: oscillations–δ Scuti.