Searching for solar-like oscillations in the δ Scuti star ρ Puppis★

Despite the shallow convective envelopes of δ Scuti pulsators, solar-like oscillations are theoretically predicted to be excited in those stars as well. To search for such stochastic oscillations, we organized a spectroscopic multisite campaign for the bright, metal-rich δ Sct star ρ Puppis. We obtained a total of 2763 high-resolution spectra using four telescopes. We discuss the reduction and analysis with the iodine cell technique, developed for searching low-amplitude radial velocity variations, in the presence of high-amplitude variability. Furthermore, we have determined the angular diameter of ρ Puppis to be 1.68 ± 0.03 mas, translating into a radius of 3.52 ± 0.07 R⊙. Using this value, the frequency of maximum power of possible solar-like oscillations is expected at ∼43 ± 2 c d−1 (498 ± 23 μHz). The dominant δ Scuti-type pulsation mode of ρ Puppis is known to be the radial fundamental mode which allows us to determine the mean density of the star, and therefore an expected large frequency separation of 2.73 c d−1 (31.6 μHz). We conclude that (1) the radial velocity amplitudes of the δ Scuti pulsations are different for different spectral lines; (2) we can exclude solar-like oscillations to be present in ρ Puppis with an amplitude per radial mode larger than 0.5 m s−1.