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Suppression of cooling by strong magnetic fields in white dwarf stars
Valyavin, G.,Shulyak, D.,Wade, G. A.,Antonyuk, K.,Zharikov, S. V.,Galazutdinov, G. A.,Plachinda, S.,Bagnulo, S.,Machado, L. Fox,Alvarez, M.,Clark, D. M.,Lopez, J. M.,Hiriart, D.,Han, Inwoo,Jeon, Young Nature Publishing Group, a division of Macmillan P 2014 Nature Vol.515 No.7525
Isolated cool white dwarf stars more often have strong magnetic fields than young, hotter white dwarfs, which has been a puzzle because magnetic fields are expected to decay with time but a cool surface suggests that the star is old. In addition, some white dwarfs with strong fields vary in brightness as they rotate, which has been variously attributed to surface brightness inhomogeneities similar to sunspots, chemical inhomogeneities and other magneto-optical effects. Here we describe optical observations of the brightness and magnetic field of the cool white dwarf WD 1953-011 taken over about eight years, and the results of an analysis of its surface temperature and magnetic field distribution. We find that the magnetic field suppresses atmospheric convection, leading to dark spots in the most magnetized areas. We also find that strong fields are sufficient to suppress convection over the entire surface in cool magnetic white dwarfs, which inhibits their cooling evolution relative to weakly magnetic and non-magnetic white dwarfs, making them appear younger than they truly are. This explains the long-standing mystery of why magnetic fields are more common amongst cool white dwarfs, and implies that the currently accepted ages of strongly magnetic white dwarfs are systematically too young.
Maritime Navigation Systems: Role And Place In The Safety Of Navigation
Tkachenko, Valeriy,Voloshyna, Olha,Marukhnenko, Оleksandr,Slobodanyuk, Mykola,Zharikov, Volodymyr,Yatsenko, Sergiy International Journal of Computer ScienceNetwork S 2021 International journal of computer science and netw Vol.21 No.9
The article assesses the level of navigation safety, in theoretical terms, defines the complexity of managing navigational risks in practice. The issues of assessing the navigational safety have been studied due to the importance and relevance of the issue in question, however, due to the great complexity of the problem under consideration, the article considers and indicates the directions for the development of the solution of the given direction, where, first of all, it became necessary to analyze the issue of assessing the levels of navigation risks when navigating vessels of various types in difficult navigation conditions.
A STUDY OF THE PHOTOMETRIC VARIABILITY OF THE PECULIAR MAGNETIC WHITE DWARF WD 1953-011
Valyavin, G.,Antonyuk, K.,Plachinda, S.,Clark, D. M.,Wade, G. A.,Machado, Lester Fox,Alvarez, M.,Lopez, J. M.,Hiriart, D.,Han, Inwoo,Jeon, Young-Beom,Bagnulo, S.,Zharikov, S. V.,Zurita, C.,Mujica, R. IOP Publishing 2011 The Astrophysical journal Vol.734 No.1
<P>We present and interpret simultaneous new photometric and spectroscopic observations of the peculiar magnetic white dwarf WD 1953-011. The flux in the V-band filter and intensity of the Balmer spectral lines demonstrate variability with the rotation period of about 1.45 days. According to previous studies, this variability can be explained by the presence of a dark spot having a magnetic nature, analogous to a sunspot. Motivated by this idea, we examine possible physical relationships between the suggested dark spot and the strong-field magnetic structure (magnetic 'spot' or 'tube') recently identified on the surface of this star. Comparing the rotationally modulated flux with the variable spectral observables related to the magnetic 'spot,' we establish their correlation and therefore their physical relationship. Modeling the variable photometric flux assuming that it is associated with temperature variations in the stellar photosphere, we argue that the strong-field area and dark, low-temperature spot are comparable in size and located at the same latitudes, essentially overlapping each other with a possible slight longitudinal shift. In this paper, we also present a new, improved value of the star's rotational period and constrain the characteristics of the thermal inhomogeneity over the degenerate's surface.</P>