General Seminar
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General Seminar takes place every Monday at 11.15 in Piwnice, radioastronomy seminar room.
Remote participation via the BigBlueButton (BBB).
19 May 2025
“Probing the magnetospheres of a sample of the CP stars through the dips in their TESS light curves”
dr Martin Vanko
Astronomical Institute, Slovak Academy of Sciences, Tatranska Lomnica, Slovakia
Abstract:
The light curves of chemically peculiar stars typically show periodic variability due to surface spots, which a low-order harmonic expansion can model in most cases. However, high-precision satellite photometry reveals tiny complex features (called dips) in the light curves of some of these stars that are difficult to explain as surface phenomena under reasonable assumptions. An analysis of the dips in the light curves, together with spectroscopic observations of several CP stars, will be presented.
“Binarity of iconic magnetic CP star CU Virginis”
dr Jan Janik
Department of Theoretical Physics and Astrophysics, Masaryk University, Brno, Czech Republic
Abstract:
Magnetic chemically peculiar (mCP) stars are valuable for studying the rotation of upper main sequence stars due to their stable chemical inhomogeneities on the surface. These features cause periodic variations in brightness, spectral lines, and polarization as the stars rotate, enabling precise measurements of rotational periods and their changes. CU Virginis, a rapidly rotating silicon mCP star, also known as the first hot stellar radio and X-ray pulsar, has shown variable rotational periods since 1984. Studies have revealed quasi-cyclic period oscillations, with increases until 2005 followed by decreases. We analyzed over 50,000 observations from 1955–2022, finding stable phase curve shapes across all data types. The observed O–C variations suggest possible binary motion, implying an unseen companion – potentially a black hole. However, expected radial velocity changes (∼12 km/s) are not observed. CU Virginis’ radial velocity appears constant, contradicting the binary hypothesis. Therefore, the rotational period variations are likely due to internal stellar processes. Secular changes in differential rotation within the star’s outer layers offer the most plausible explanation.