Simultaneous time - series spectroscopy and multi - band photometry of the sdBV PG 1605 + 072 ⋆

We present time-series spectroscopy and multi-band photometry of the sdBV PG1605+072 carried out simultaneously at the Calar Alto 2.2m and 3.5m telescopes. The periodogram analysis of the radial velocity curves reveals three frequencies at 2.078, 2.756, and 1.985 mHz for Hβ and at 2.076, 2.753, and 1.978 mHz for Hγ . The corresponding radial velocity amplitudes are 12.7, 8.0, and 7.9 km/s for Hβ and 14.3, 6.5, and 7.2 km/s for Hγ . Furthermore, we found five frequencies that are present in all wavelength bands of the BUSCA photometer. The frequencies detected in the radial velocity curves are recovered by the photometric measurements. Moreover, additional frequencies were present in the periodograms which could not be identified in all four bands simultaneously. The comparison of the amplitudes presented here with previous results from radial velocity and photometric observations of PG1605+072 shows a significant change or even switch in the power of the modes within short time scales, i. e. about one year. No changes in frequency were registered and the phases of the modes show no wavelength dependency within our multi-band photometry.