Inhomogeneous distribution of mercury on the surfaces of rapidly rotating HgMn stars

Starspots are usually associated with the action of magnetic fields at the stellar surfaces. However, recently an inhomogeneous chemical distribution of mercury was found for the mercury-manganese (HgMn) star alpha And -- a well-established member of a non-magnetic subclass of the chemically peculiar stars of the upper main sequence. In this study we present first results of the high-resolution survey of the HgII 3984 resonance line in the spectra of rapidly rotating HgMn stars with atmospheric parameters similar to those of alpha And. We use spectrum synthesis modelling and take advantage of the Doppler resolution of the stellar surfaces to probe horizontal structure of mercury distribution. Clear signatures of spots are found in the HgII 3984 line profiles of HR 1185 and HR 8723. Two observations of the latter star separated by two days give evidence for the line profile variability. We conclude that inhomogeneous distribution of Hg is a common phenomenon for the rapidly rotating HgMn stars in the 13000--13800 K effective temperature range independently of the stellar evolutionary stage. These results establish existence of a new class of spectrum variable spotted B-type stars. It is suggested that the observed Hg inhomogeneities arise from dynamical instabilities in the chemical diffusion processes and are unrelated to magnetic phenomena.Comment: 6 pages, 3 figures, accepted by Astronomy & Astrophysic

Inverse problems for Jacobi operators II: Mass perturbations of semi-infinite mass-spring systems

We consider an inverse spectral problem for infinite linear mass-spring systems with different configurations obtained by changing the first mass. We give results on the reconstruction of the system from the spectra of two configurations. Necessary and sufficient conditions for two real sequences to be the spectra of two modified systems are provided.Comment: 25 pages, 2 figures. Typos were corrected, two remarks were added, material added to Sec.

Role of the electromagnetic processes in the high-energy muon production

The muon pair production by gammas in the atmosphere is discussed as a mechanism of “prompt” muon production at very high energies. It is shown that this process dominates over the conventional muon production through pion and kaon decay at energies greater than several PeV

Muon pair production by muons and narrow muon bundles underground

We consider the process of muon pair production by high-energy muons and its consequences for the characteristics of muon flux underground. It is shown that the accounting of this process in the muon propagation through the rock results in an additional flux of narrow double- and triple-muon events which is comparable to the conventional flux of narrow muon bundles with low multiplicity

The Largest Russian Optical Telescope BTA: Current Status and Modernization Prospects

The Russian 6-m telescope (BTA), once the largest telescope in the world and now the largest optical telescope in Russia, has been successfully operating for almost 45 years. In this paper we briefly overview the observing methods the facility can currently provide, the ongoing projects on the development of scientific equipment, the status of the telescope among the world's and Russian astronomical communities, our ambitions to attract new users, and the prospects the observatory wishes to realize in the near future.Comment: To be published in: I.I. Romanyuk, I.A. Yakunin, A.F. Valeev, and D.O. Kudryavtsev (eds), Ground-Based Astronomy in Russia. 21st Century, Proceedings of the All-Russian Conference, ISBN: 978-5-6045062-0-