arXiv subjects

J. Nuspl

Publications and source records attributed to J. Nuspl.

21 records · Page 2Linked to original sources

arXiv2006

Multi-site campaign on the open cluster M67. I. Observations and photometric reductions

We report on an ambitious multi-site campaign aimed at detecting stellar variability, particularly solar-like oscillations, in the red giant stars in the open cluster M67 (NGC 2682). During the six-week observing run, which comprised 164 telescope nights, we used nine 0.6-m to 2.1-m class telescopes located around the world to obtain uninterrupted time-series photometry. We outline here the data acquisition and reduction, with emphasis on the optimisation of the signal-to-noise of the low amplitude (50-500 micromag) solar-like oscillations. This includes a new and efficient method for obtaining the linearity profile of the CCD response at ultra high precision (~10 parts per million). The noise in the final time series is 0.50 mmag per minute integration for the best site, while the noise in the Fourier spectrum of all sites combined is 20 micromag. In addition to the red giant stars, this data set proves to be very valuable for studying high-amplitude variable stars such as eclipsing binaries, W UMa systems and delta Scuti stars.

astro-ph↗

arXiv2006

Multicolour CCD photometry of the variable stars in globular cluster M3

We present time series data on the variable stars of the galactic globular cluster Messier 3 (M3). We give BVI light curves for 226 RR Lyrae, 2 SX Phe and 1 W Vir type variables, along with estimated fundamental photometric parameters such as intensity and magnitude-averaged brightness and pulsation periods. In some cases the periods we have found significantly differ from the previously published ones. This is the first published light curve and period determination for variable V266. The I-band light curve has not been observed previously for numerous (76) variables. Three new RR Lyrae variables have been discovered. Groups of RR Lyrae variables that belong to different evolutionary stages and have been separated previously on the basis of V data were found here for all colours and colour indices by cluster analysis. The I-band period -- luminosity relation is also discussed. From the 66 modulated (Blazhko type) RR Lyrae stars we investigated, six are newly identified and two of them are first overtone pulsators. In the case of 13 RR Lyrae, the period of Blazhko cycle has been estimated for the first time. V252 is identified as a new RRd variable. Amplitude ratio of RRd stars have been investigated to search possible mode content changes. In contrast to previous publications no changes have been found. Problems with the sampling of the time series of typical cluster variability surveys is demonstrated.

astro-ph↗

arXiv2005

Indirect evidence for short period magnetic cycles in W UMa stars

Complex period variations of five W UMa type binaries (AB And, OO Aql, DK Cyg, V566 Oph, U Peg) were investigated by analyzing their O--C diagrams, and several common features were found. Four of the five systems show secular period variations at a constant rate on the order of |dP / dt 1/P | ~ 10E-7 1/yr. In the case of AB And, OO Aql, and U Peg a high-amplitude, nearly one-century long quasi-sinusoidal pattern was also found. It might be explained as light-time effect, or by some magnetic phenomena, although the mathematical, and consequently the physical, parameters of these fits are very problematic, as the obtained periods are very close to the length of the total data range. The most interesting feature of the studied O--C diagrams is a low amplitude (2-4 x 10E-3 d) modulation with a period around 18--20 yr in four of the five cases. This phenomenon might be indirect evidence of some magnetic cycle in late-type overcontact binaries as an analog to the observed activity cycles in RS CVn systems.

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