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- ItemChemical composition of the RS CVn-type star lambda andromedae(Berlin : de Gruyter, 2010) Tautvaišiené, G.; Barisevičius, G.; Berdyugina, Svetlana V.; Chorniy, Yuriy; Ilyin, Ilya V.Photospheric parameters and chemical composition are determined for the single-lined chromospherically active RS CVn-type star λ And (HD 222107). From the high resolution spectra obtained on the Nordic Optical Telescope, abundances of 22 chemical elements and isotopes, including such key elements as 12C, 13C, N and O, were investigated. The differential line analysis with the MARCS model atmospheres gives Teff = 4830 K, log g = 2.8, [Fe/H] = -0.53, [C/Fe] = 0.09, [N/Fe] = 0.35, [O/Fe] = 0.45, C/N = 2.21, 12C/13C = 14. The 12C/13C ratio for a star of the RS CVn-type is determined for the first time, and its low value gives a hint that extra-mixing processes may start acting in low-mass chromospherically active stars below the bump of the luminosity function of red giants.
- ItemDiscovery of magnetic fields in five DC white dwarfs(Les Ulis : EDP Sciences, 2023) Berdyugin, Andrei V.; Piirola, Vilppu; Bagnulo, Stefano; Landstreet, John D.; Berdyugina, Svetlana V.About half of white dwarfs (WDs) evolve to the DC state as they cool; the others become DQ or (temporarily?) DZ WDs. The recent magnetic survey of the local 20 pc volume has established a high frequency of magnetic fields among WDs older than 2-3 Gyr, demonstrating that in low-and average-mass WDs, the effects of magnetism become more common as they age, and the fields on average become stronger. However, the available statistics of WDs older than about 5 Gyr do not clearly establish how fields evolve beyond this age. We are carrying out a survey to clarify the occurrence of magnetism in DC-type WDs in order to better understand this late evolution. We use broadband filter polarimetry, arguably the most efficient way to detect magnetic fields in featureless WDs via continuum circular polarization. Here we report the discovery of a magnetic field in five DC WDs (of 23 observed), almost doubling the total sample of known magnetic WDs belonging to the DC spectral class.
- ItemStochastic entropy production in the quite Sun magnetic fields(Oxford : Oxford Univ. Press, 2019) Gorobets, Andriy Y.; Berdyugina, Svetlana V.The second law of thermodynamics imposes an increase of macroscopic entropy with time in an isolated system. Microscopically, however, the entropy production can be negative for a single, microscopic realization of a thermodynamic process. The so-called fluctuation theorems provide exact relations between the stochastic entropy consumption and generation. Here, we analyse pixel-to-pixel fluctuations in time of small-scale magnetic fields (SSMF) in the quiet Sun observed with the SDO/HMI instrument. We demonstrate that entropy generated by SSMF obeys the fluctuation theorems. In particular, the SSMF entropy consumption probability is exactly exponentially smaller than the SSMF entropy generation probability. This may have fundamental implications for the magnetic energy budget of the Sun. © The Author(s) 2018. Published by Oxford University Press on behalf of The Royal Astronomical Society.
- ItemRemote sensing of life: Polarimetric signatures of photosynthetic pigments as sensitive biomarkers(Cambridge : Cambridge University Press, 2015) Berdyugina, Svetlana V.; Kuhn, Jeff R.; Harrington, David M.; Šantl-Temkiv, Tina; Messersmith, E. JohnWe develop a polarimetry-based remote-sensing method for detecting and identifying life forms in distant worlds and distinguishing them from non-biological species. To achieve this we have designed and built a bio-polarimetric laboratory experiment BioPol for measuring optical polarized spectra of various biological and non-biological samples. Here we focus on biological pigments, which are common in plants and bacteria that employ them either for photosynthesis or for protection against reactive oxygen species. Photosynthesis, which provides organisms with the ability to use light as a source of energy, emerged early in the evolution of life on Earth. The ability to harvest such a significant energy resource could likely also develop on habited exoplanets. Thus, we investigate the detectability of biomolecules that can capture photons of particular wavelengths and contribute to storing their energy in chemical bonds. We have carried out laboratory spectropolarimetric measurements of a representative sample of plants containing various amounts of pigments such as chlorophyll, carotenoids and others. We have also measured a variety of non-biological samples (sands, rocks). Using our lab measurements, we have modelled intensity and polarized spectra of Earth-like planets having different surface coverage by photosynthetic organisms, deserted land and ocean, as well as clouds. Our results demonstrate that linearly polarized spectra provide very sensitive and rather unambiguous detection of photosynthetic pigments of various kinds. Our work paves the path towards analogous measurements of microorganisms and remote sensing of microbial ecology on the Earth and of extraterrestrial life on other planets and moons.
- ItemGlobal warming as a detectable thermodynamic marker of Earth-like extrasolar civilizations: The case for a telescope like Colossus(Cambridge : Cambridge University Press, 2015) Kuhn, Jeff R.; Berdyugina, Svetlana V.Earth-like civilizations generate heat from the energy that they utilize. The thermal radiation from this heat can be a thermodynamic marker for civilizations. Here we model such planetary radiation on Earth-like planets and propose a strategy for detecting such an alien unintentional thermodynamic electromagnetic biomarker. We show that astronomical infrared (IR) civilization biomarkers may be detected within an interestingly large cosmic volume using a 70 m-class or larger telescope. In particular, the Colossus telescope with achievable coronagraphic and adaptive optics performance may reveal Earth-like civilizations from visible and IR photometry timeseries’ taken during an exoplanetary orbit period. The detection of an alien heat signature will have far-ranging implications, but even a null result, given 70 m aperture sensitivity, could also have broad social implications.
- ItemInfrared Dual-Line Hanle Diagnostic of the Coronal Vector Magnetic Field(Lausanne : Frontiers Media, 2016) Dima, Gabriel I.; Kuhn, Jeffrey R.; Berdyugina, Svetlana V.Measuring the coronal vector magnetic field is still a major challenge in solar physics. This is due to the intrinsic weakness of the field (e.g., ~4G at a height of 0.1R⊙ above an active region) and the large thermal broadening of coronal emission lines. We propose using concurrent linear polarization measurements of near-infrared forbidden and permitted lines together with Hanle effect models to calculate the coronal vector magnetic field. In the unsaturated Hanle regime both the direction and strength of the magnetic field affect the linear polarization, while in the saturated regime the polarization is insensitive to the strength of the field. The relatively long radiative lifetimes of coronal forbidden atomic transitions implies that the emission lines are formed in the saturated Hanle regime and the linear polarization is insensitive to the strength of the field. By combining measurements of both forbidden and permitted lines, the direction and strength of the field can be obtained. For example, the SiX 1.4301 μm line shows strong linear polarization and has been observed in emission over a large field-of-view (out to elongations of 0.5 R⊙). Here we describe an algorithm that combines linear polarization measurements of the SiX 1.4301 μm forbidden line with linear polarization observations of the HeI 1.0830 μm permitted coronal line to obtain the vector magnetic field. To illustrate the concept we assume that the emitting gas for both atomic transitions is located in the plane of the sky. The further development of this method and associated tools will be a critical step toward interpreting the high spectral, spatial and temporal infrared spectro-polarimetric measurements that will be possible when the Daniel K. Inouye Solar Telescope (DKIST) is completed in 2019.
- ItemChemical composition of the RS CVn-type star 33 Piscium(Berlin : de Gruyter, 2011) Barisevičius, G.; Tautvaišiené, Gražina G.; Berdyugina, Svetlana V.; Chorniy, Yuriy; Ilyin, Ilya V.Abundances of 22 chemical elements, including the key elements and isotopes such as 12C, 13C, N and O, are investigated in the spectrum of 33 Psc, a single-lined RS CVn-type binary of low magnetic activity. The high resolution spectra were observed on the Nordic Optical Telescope and analyzed with the MARCS model atmospheres. The following main parameters have been determined: Teff = 4750 K, log g = 2.8, [Fe/H] = -0.09, [C/Fe] = -0.04, [N/Fe] = 0.23, [O/Fe] = 0.05, C/N = 2.14, 12C/13C = 30, which show the first-dredge-up mixing signatures and no extra-mixing.
- ItemChemical composition of the RS CVn-type star 29 Draconis(Berlin : de Gruyter, 2010) Barisevičius, G.; Tautvaišiené, Gražina G.; Berdyugina, Svetlana V.; Chorniy, Yuriy; Ilyin, Ilya V.Abundances of 22 chemical elements, including the key elements and isotopes such as 12C, 13C, N and O, are investigated in the spectrum of 33 Psc, a single-lined RS CVn-type binary of low magnetic activity. The high resolution spectra were observed on the Nordic Optical Telescope and analyzed with the MARCS model atmospheres. The following main parameters have been determined: Teff = 4750 K, log g = 2.8, [Fe/H] = -0.09, [C/Fe] = -0.04, [N/Fe] = 0.23, [O/Fe] = 0.05, C/N = 2.14, 12C/13C = 30, which show the first-dredge-up mixing signatures and no extra-mixing.