Stelios Kleidis

The unique frequency spectrum of the Blazhko RRc Star LS Her

The Blazhko effect in RR Lyrae stars is still poorly understood theoretically. Stars with multiple Blazhko periods or in which the Blazhko effect itself varies are particularly challenging. This study investigates the Blazhko effect in the RRc star LS Her. Detailed CCD photometry in the V, R c and I c band has been performed on 63 nights during six months. LS Her is confirmed to have a Blazhko period of 12.75 ± 0.02 d. However, where normally the side frequencies of the Blazhko triplet are expected, an equidistant group of three frequencies is found on both sides of the main pulsation frequency. As a consequence, the period and amplitude of the Blazhko effect itself vary in a cycle of 109 ± 4 d. LS Her is a unique object turning out to be very important in the verification of the theories for the Blazhko effect.

V371 Per ― A thick-disc, short-period F/1O Cepheid

V371 Per was found to be a double-mode Cepheid with a fundamental mode period of 1.738 days, the shortest among Galactic beat Cepheids, and an unusually high period ratio of 0.731, while the other Galactic beat Cepheids have period ratios between 0.697 and 0.713. The latter suggests that the star has a metallicity [Fe/H] between −1 and −0.7. The derived distance from the Galactic plane places it in the thick disc or the Halo, while all other Galactic beat Cepheids belong to the thin disc. There are indications from historical data that both the fundamental and first overtone periods have lengthened.

Photometry of GSC 762-110, a new triple-mode radially pulsating star

Context. Stars pulsating in three radial modes are very rare; only three examples are known in the Galaxy. These stars are very useful since their periods may be measured very precisely, and this will constrain the global stellar parameters and the models of the stars interior. Aims. The purpose of this paper is to present a new example of the class of triple-mode radial pulsators. Methods. A search for candidate multi-mode pulsators was carried out in public survey data. Time-series photometry of one of the candidates, GSC 762-110, was performed. Results. GSC 762-110 was found to be a triple-mode radial pulsator, with a fundamental period of 0.1945 d and period ratios of 0.7641 and 0.8012. In addition two non-radial modes were found, for which the amplitude has diminished considerably over the last few years.

Search for pulsation among suspected A-type binaries and the new multiperiodic Delta Scuti star HD217860

We have explored a sample of suspected A-type binaries in a systematic way, both spectroscopically and photometrically. Due to their location in the H-R diagram, indications of pulsation and/or chemical peculiarities among these suspected binary (or multiple) systems may be found. High-resolution spectroscopy obtained with the ELODIE and MUSICOS spectrographs was used in combination with a few nights of differential CCD photometry in order to search for pulsation(s). Of the 32 investigated targets, eight are spectroscopic binaries, one of which is a close binary also showing eclipses, and three have been identified as Delta Scuti pulsators with rapid line-profile variations. Among the latter stars, HD 217860 reveals interesting multiperiodic photometric and spectroscopic variations, with up to eight frequencies common to two large photometric data sets. We suggest that at least one radial overtone mode is excited among the two most dominant frequencies. We furthermore found evidence for a strong modulation of the amplitude(s) and/or the (radial) frequency content of this intriguing Delta Scuti star.