During the course of an ongoing CCD monitoring program to investigate low-level light variations in subdwarf B (sdB) stars, we have serendipitously discovered a new class of low amplitude, multimode sdB pulsators with periods of the order of an hour. These periods are more than a factor of ten longer than those of previously known multimode sdB pulsators (EC 14026 stars), implying that they are due to gravity modes rather than pressure modes. The longer period pulsators are found only among cooler sdB stars, where they are surprisingly common. The iron opacity instability that drives the short period EC 14026 stars is effective only in hot sdB's, leaving the driving mechanism for the deeper gravity modes in cool sdB's currently unknown. We present the first observational results for our newly identified sdB variables, and discuss possible implications.

Abstract. We present time-series spectroscopy and multi-band photometry of the sdBV PG 1605+072 carried out simultaneously at the Calar Alto 2.2-m and 3.5-m telescopes. The periodogram analysis of the radial velocity curves reveals three frequencies at 2.078, 2.756, and 1.985 mHz for H β and at 2.076, 2.753, and 1.978 mHz for H γ . The corresponding radial velocity amplitudes are 12.7, 8.0, and 7.9 km s −1 for H β and 14.3, 6.5, and 7.2 km s −1 for H γ . 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 PG 1605+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.

We present the first high-redshift gal axy cluster candidate sample from the HIROCS survey found in the COSMOS field. It results from a combination of public COSMOS with proprietary H-band data on a 0.66• part of the COSMOS field and comprises 12 candidates in the redshift range 1.23 ≤ z ≤ 1.55. We find an increasing fraction of blue cluster members with increasing redshift. Many of the blue and even some of the reddest member galaxies exhibit disturbed morphologies as well as signs of interaction.

A new class of pulsating subdwarf B stars has recently been announced by Green and coworkers. Here we present a follow-up paper describing our observations and the pulsation structure of the class prototype PG 1716+426. The oscillations are multiperiodic with periods between 0.8 and 1.4 hr (180-340 Hz) and semiamplitudes less than 0.2%. We also observe that the periods and amplitudes appear variable, making the pulsation structure of PG 1716 complicated. The periods are an order of magnitude longer than those seen in EC 14026 (sdBV) stars, implying that they are gravity modes rather than pressure modes. As such, they represent a new class of variable star.