HD 121190: A cool multiperiodic slowly pulsating B star with moderate rotation

Abstract

We have gathered and analysed multicolour Geneva photometry and high-resolution spectroscopy of the stars HD 121190 (B9V) and HD 106419 (B9III) whose short-term periodic variability had become evident from their HIPPARCOS data. We find three significant frequencies for HD 121190 in the Geneva data: 2.6831, 2.6199 and 2.4713 c d^-1 and classify the star as a slowly pulsating B star, the coolest single star of that class known to date. Its amplitude ratios are compatible with low-degree gravity modes. The spectra reveal low-amplitude variability and v sin i=118 km s^-1 which implies that the star rotates at 26% of its critical velocity. For HD 106419 we are unable to confirm the period found from the HIPPARCOS photometry in our ground-based data; rather we find a marginally significant frequency of 0.8986 c d^-1. This star is probably an evolved slowly pulsating B star with complex variations. HD 106409 is also a moderate rotator as the spectra reveal v sin i=78 km s^-1, which is also 26% of its critical velocity.

Based on data gathered with the Swiss 0.7 m telescope equipped with the photometer P7 of the Geneva Observatory and with the FEROS spectrograph attached to the ESO 2.2 m telescope, both situated at La Silla in Chile.