2,896 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
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-
The variation of the magnetic field of the Ap star HD~50169 over its 29 year rotation period
Context. The Ap stars that rotate extremely slowly, with periods of decades
to centuries, represent one of the keys to the understanding of the processes
leading to the differentiation of stellar rotation.
Aims. We characterise the variations of the magnetic field of the Ap star HD
50169 and derive constraints about its structure.
Methods. We combine published measurements of the mean longitudinal field
of HD 50169 with new determinations of this field moment from circular
spectropolarimetry obtained at the 6-m telescope BTA of the Special
Astrophysical Observatory of the Russian Academy of Sciences. For the mean
magnetic field modulus , literature data are complemented by the analysis of
ESO spectra, both newly acquired and from the archive. Radial velocities are
also obtained from these spectra.
Results. We present the first determination of the rotation period of HD
50169, Prot = (29.04+/-0.82) y. HD 50169 is currently the longest-period Ap
star for which magnetic field measurements have been obtained over more than a
full cycle. The variation curves of both and have a significant degree
of anharmonicity, and there is a definite phase shift between their respective
extrema. We confirm that HD 50169 is a wide spectroscopic binary, refine its
orbital elements, and suggest that the secondary is probably a dwarf star of
spectral type M.
Conclusions. The shapes and mutual phase shifts of the derived magnetic
variation curves unquestionably indicate that the magnetic field of HD 50169 is
not symmetric about an axis passing through its centre. Overall, HD 50169
appears similar to the bulk of the long-period Ap stars.Comment: 10 pages, 3 figures, accepted for publication in A&
HD 178892 - a cool Ap star with extremely strong magnetic field
We report a discovery of the Zeeman resolved spectral lines, corresponding to
the extremely large magnetic field modulus =17.5 kG, in the cool Ap star HD
178892. The mean longitudinal field of this star reaches 7.5 kG, and its
rotational modulation implies the strength of the dipolar magnetic component
Bp>=23 kG. We have revised rotation period of the star using the All Sky
Automated Survey photometry and determined P=8.2478 d. Rotation phases of the
magnetic and photometric maxima of the star coincide with each other. We
obtained Geneva photometric observation of HD 178892 and estimated
Teff=7700+/-250 K using photometry and the hydrogen Balmer lines. Preliminary
abundance analysis reveals abundance pattern typical of rapidly oscillating Ap
stars.Comment: Accepted by Astronomy & Astrophysics; 4 pages, 4 figure
The Laser Ion Source Trap (LIST) coupled to a gas cell catcher
The proof of principle of the Laser Ion Source Trap (LIST) coupled to a gas
cell catcher system has been demonstrated at the Leuven Isotope Separator
On-Line (LISOL). The experiments were carried out by using the modified gas
cell-based laser ion source and the SextuPole Ion Guide (SPIG). Element
selective resonance laser ionization of neutral atoms was taking place inside
the cold jet expanding out of the gas cell catcher. The laser path was oriented
in longitudinal as well as transverse geometries with respect to the atoms
flow. The enhancement of beam purity and the feasibility for in-source laser
spectroscopy were investigated in off-line and on-line conditions.Comment: 11 pages, 13 figure
Spectral and localization properties of the Dirichlet wave guide with two concentric Neumann discs
Bound states of the Hamiltonian describing a quantum particle living on three
dimensional straight strip of width are investigated. We impose the Neumann
boundary condition on the two concentric windows of the radii and
located on the opposite walls and the Dirichlet boundary condition on the
remaining part of the boundary of the strip. We prove that such a system
exhibits discrete eigenvalues below the essential spectrum for any .
When and tend to the infinity, the asymptotic of the eigenvalue is
derived. A comparative analysis with the one-window case reveals that due to
the additional possibility of the regulating energy spectrum the anticrossing
structure builds up as a function of the inner radius with its sharpness
increasing for the larger outer radius. Mathematical and physical
interpretation of the obtained results is presented; namely, it is derived that
the anticrossings are accompanied by the drastic changes of the wave function
localization. Parallels are drawn to the other structures exhibiting similar
phenomena; in particular, it is proved that, contrary to the two-dimensional
geometry, at the critical Neumann radii true bound states exist.Comment: 25 pages, 7 figure
Raman fingerprints of ultrasmall nanodiamonds produced from adamantane
The synthesis of ultrasmall (2-5 nm) nanodiamonds purely from adamantane at
pressure of 12 GPa is reported. Their structural features have been studied by
Raman spectroscopy. The unusual vibration band containing a number of
pronounced maxima at about 1147, 1245, 1344, and 1456 cm-1 was detected in
Raman spectra. The band is confidently identified with the bending vibrational
modes of CHx groups terminating the nanodiamonds surface. Excessively intense
mode at 1344 cm-1 is explained by its coupling with the 1328 cm-1 diamond
phonons. The Raman band found is proposed to be used for express recognition of
ultrasmall nanodiamonds produced from adamantane and other hydrocarbons with a
high hydrogen content. Moreover, polarized CH bonds on a diamond surface are
sensitive to environmental conditions. This opens up opportunities for using
the diamond produced from adamantane as ultrasmall nanosensors in biology,
chemistry, and medicineComment: 12 pages, 6 figure
- …