Spectroscopic monitoring of the Herbig Ae star HD 104237

Abstract

We present the results of multisite observations spanning two years of the pre-main-sequence Herbig Ae star HD 104237. The star was observed in high resolution spectroscopy (R ≥ 35 000) for a total of 157.3 h of effective expo- sure time, over 42 nights, corresponding to a data base of 1888 individual echelle spectra. We confirm that the HD 104237 system includes a spectroscopic binary, whose primary component HD 104237 A is pulsating. The resulting high quality radial velocity curve allows us to detect for the first time by spectroscopic means multiperiodic oscillations in a pre-main sequence star. Five different modes are detected with very high confidence, with frequencies ranging between 28.5 and 35.6 d −1 , typical of δ Scuti pulsations; an additional 3 frequencies have been extracted from the data, but with a lower level of confidence. The pattern of frequencies indicates that at least some of the detected modes are non-radial. The precise orbit determination and the measurement of the double line spectroscopic binary observed around periastron enabled us to determine a mass ratio of 1.29 ± 0.02 between the primary and the secondary; based on the primary mass of 2.2 ± 0.1 Mwe conclude that the spectroscopic secondary HD 104237 b should have a mass of 1.7 ± 0.1 Mand lie outside the pre-main sequence instability strip towards later spectral types. A search for pulsations in the radial velocity curve of the much weaker secondary component was not con- clusive at this stage. The location of the primary in the HR diagram and its position with respect to recent pre-main sequence evolutionary tracks and isochrones implies a location of the secondary indicative of spectral type K3.