3,147 research outputs found
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-
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