Astronomy and Astrophysics, volume 542A, 24-24 (2012/6-1)
Pulsation spectrum of δ Scuti stars: the binary HD 50870 as seen with CoRoT and HARPS.
MANTEGAZZA L., PORETTI E., MICHEL E., RAINER M., BAUDIN F., GARCIA HERNANDEZ A., SEMAAN T., ALVAREZ M., AMADO P.J., GARRIDO R., MATHIAS P., MOYA A., SUAREZ J.C., AUVERGNE M., BAGLIN A., CATALA C. and SAMADI R.
Abstract (from CDS):
We present the results obtained with the CoRoT satellite for HD 50870, a δ Sct star which was observed for 114.4d. The aim of these observations was to evaluate the results obtained for HD 50844, the first δ Sct star monitored with CoRoT, on a longer time baseline. The 307,570 CoRoT datapoints were analysed with different techniques. The photometric observations were complemented over 15 nights of high-resolution spectroscopy with HARPS on a baseline of 25d. These spectra were analysed to study the line profile variations and to derive the stellar physical parameters. Some uvby photometric observations were also obtained to better characterize the pulsation modes. HD 50870 proved to be a low-amplitude, long-period spectroscopic binary system seen almost pole-on (i≃21°). The brighter component, which also has the higher rotational velocity (v sin i=37.5km/s), is a δ Sct-type variable with a full light amplitude variation of about 0.04mag. There is a dominant axisymmetric mode (17.16d–1). Moreover, there are two groups of frequencies (about 19) in the intervals 6-9 and 13-18d–1, with amplitudes ranging from a few mmag to 0.3mmag. After the detection of about 250 terms (corresponding to an amplitude of about 0.045mmag) a flat plateau appears in the power spectrum in the low-frequency region up to about 35d–1. We were able to detect this plateau only thanks to the short cadence sampling of the CoRoT measurements (32s). The density distribution vs. frequency of the detected frequencies seems to rule out the possibility that this plateau is the result of a process with a continuum power spectrum. The spacings of the strongest modes suggest a quasi-periodic pattern. We failed to find a satisfactory seismic model that simultaneously matches the frequency range, the position in the HR diagram, and the quasi-periodic pattern interpreted as a large separation. Nineteen modes were detected spectroscopically from the line profile variations and associated to the photometric ones. Tentative l,m values have been attributed to the modes detected spectroscopically. Prograde as well as retrograde modes are present with l values up to 9. There are no traces of variability induced by solar-like oscillations.