Yazar "Lampens, P." seçeneğine göre listele

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    High-resolution spectroscopy and abundance analysis of ? Scuti stars near the ? Doradus instability strip
    (Oxford Univ Press, 2017) Kahraman Alicavus, F.; Niemczura, E.; Polinska, M.; Helminiak, K. G.; Lampens, P.; Molenda-Zakowicz, J.; Ukita, N.
    delta Scuti stars are remarkable objects for asteroseismology. In spite of decades of investigations, there are still important questions about these pulsating stars to be answered, such as their positions in log T-eff-log g diagram, or the dependence of the pulsation modes on atmospheric parameters and rotation. Therefore, we performed a detailed spectroscopic study of 41 delta Scuti stars. The selected objects are located near the gamma Doradus instability strip to make a reliable comparison between both types of variables. Spectral classification, stellar atmospheric parameters T-eff, log g, xi) and v sin i values were determined. The spectral types and luminosity classes of stars were found to be A1-F5 and III-V, respectively. The T-eff ranges from 6600 to 9400 K, whereas the obtained log g values are from 3.4 to 4.3. The v sin i values were found between 10 and 222 km s(-1). The derived chemical abundances of delta Scuti stars were compared to those of the non-pulsating stars and gamma Doradus variables. It turned out that both delta Scuti and gamma Doradus variables have similar abundance patterns, which are slightly different from the non-pulsating stars. These chemical differences can help us to understand why there are non-pulsating stars in classical instability strip. Effects of the obtained parameters on pulsation period and amplitude were examined. It appears that the pulsation period decreases with increasing T-eff. No significant correlations were found between pulsation period, amplitude and v sin i.
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    Study of chemically peculiar stars - I. High-resolution spectroscopy and K2 photometry of Am stars in the region of M44
    (Oxford Univ Press, 2022) Joshi, Santosh; Trust, Otto; Semenko, E.; Williams, P. E.; Lampens, P.; De Cat, P.; Vermeylen, L.
    We present a study based on the high-resolution spectroscopy and K2 space photometry of five chemically peculiar stars in the region of the open cluster M44. The analysis of the high-precision photometric K2 data reveals that the light variations in HD 73045 and HD 76310 are rotational in nature and caused by spots or cloud-like co-rotating structures, which are non-stationary and short-lived. The time-resolved radial velocity measurements, in combination with the K2 photometry, confirm that HD 73045 does not show any periodic variability on time-scales shorter than 1.3 d, contrary to previous reports in the literature. In addition to these new rotational variables, we discovered a new heartbeat system, HD 73619, where no pulsational signatures are seen. The spectroscopic and spectropolarimetric analyses indicate that HD 73619 belongs to the peculiar Am class, with either a weak or no magnetic field, considering the 200-G detection limit of our study. The least-squares deconvolution profiles for HD 76310 indicate a complex structure in its spectra, suggesting that this star is either part of a binary system or surrounded by a cloud shell. When placed in the Hertzsprung-Russell diagram, all studied stars are evolved from the main sequence and situated in the delta Scuti instability strip. This work is relevant for further detailed studies of chemically peculiar stars, for example on inhomogeneities (including spots) in the absence of magnetic fields and the origin of the pulsational variability in heartbeat systems.
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    The Algol-type eclipsing binaries RW CrB and VZ Leo: new RI photometric study and search for pulsations
    (Springer, 2009) Ulas, B.; Niarchos, P. G.; Lampens, P.; Liakos, A.
    In this study we present the new R and I light curve solutions for the eclipsing binary systems RW CrB and VZ Leo, which for VZ Leo is the first one in the literature. Our new observations have been analyzed using the Wilson-Devinney code from which new geometric and photometric elements are derived. The geometry of both stars is that of a semi-detached binary system where the secondary component fills its Roche lobe while the primary component is well inside. In the case of RW CrB, asymmetry in the light curve was explained by a spot model. The orbital period changes of both systems were studied and the results indicated a period decrease which can be explained by angular momentum loss. We also investigated the possibility of pulsations of the primary components since these systems are mentioned as candidates of delta Sct type pulsation. However, a time-series analysis of the residual curves in the filter I does not indicate any evidence of periodic light variation for both systems. Finally, we compared the results obtained for both binary stars to those of similar systems.