173 research outputs found
Disk tracing for B[e] supergiants in the Magellanic Clouds
B[e] supergiants are evolved massive stars with a complex circumstellar
environment. A number of important emission features probe the structure and
the kinematics of the circumstellar material. In our survey of Magellanic Cloud
B[e] supergiants we focus on the [OI] and [CaII] emission lines, which we
identified in four more objects.Comment: 2 pages; 1 figure; submitted to the proceedings of the Physics of
Evolved Stars - A conference dedicated to the memory of Olivier Chesneau,
Nice, France, June 8-12, 201
A Pan-Spectral Method of Abundance Determination
We propose a new method for determination of element abundances in stellar
atmospheres aimed for the automatic processing of high-quality stellar spectra.
The pan-spectral method is based on weighted cumulative line-widths Q of
studied element. Difference in quantities Q found from synthetic and observed
spectra gives a correction to the initial abundance. Final abundances are then
found by rapidly converging iterations. Calculations can be made for many
elements simultaneously and do not demand supercomputers.Comment: 4 pages, 2 figures, contribution presented at the ESO/Lisbon/Aveiro
Workshop on Precision Spectroscopy in Astrophysics held in Aveiro, Portugal,
11-15 September 200
Macroclumping as solution of the discrepancy between H{\alpha} and P v mass loss diagnostics for O-type stars
Recent studies of O-type stars demonstrated that discrepant mass-loss rates
are obtained when different diagnostic methods are employed - fitting the
unsaturated UV resonance lines (e.g. P v) gives drastically lower values than
obtained from the H{\alpha} emission. Wind clumping may be the main cause for
this discrepancy. In a previous paper, we have presented 3-D Monte-Carlo
calculations for the formation of scattering lines in a clumped stellar wind.
In the present paper we select five O-type supergiants (from O4 to O7) and test
whether the reported discrepancies can be resolved this way. In the first step,
the analyses start with simulating the observed spectra with Potsdam Wolf-Rayet
(PoWR) non-LTE model atmospheres. The mass-loss rates are adjusted to fit best
to the observed H{\alpha} emission lines. For the unsaturated UV resonance
lines (i.e. P v) we then apply our 3-D Monte-Carlo code, which can account for
wind clumps of any optical depths, a non-void inter-clump medium, and a
velocity dispersion inside the clumps. The ionization stratifications and
underlying photospheric spectra are adopted from the PoWR models. From fitting
the observed resonance line profiles, the properties of the wind clumps are
constrained. Our results show that with the mass-loss rates that fit H{\alpha}
(and other Balmer and He II lines), the UV resonance lines (especially the
unsaturated doublet of P v) can also be reproduced without problem when
macroclumping is taken into account. There is no need to artificially reduce
the mass-loss rates, nor to assume a sub-solar phosphorus abundance or an
extremely high clumping factor, contrary to what was claimed by other authors.
These consistent mass-loss rates are lower by a factor of 1.3 to 2.6, compared
to the mass-loss rate recipe from Vink et al. Macroclumping resolves the
previously reported discrepancy between H{\alpha} and P v mass-loss
diagnostics.Comment: 18 pages, 14 figures, 5 tables, accepted for publication in
Astrononomy & Astrophysic
Praktiline põllumajanduslik kõrgharidus ja ühiskonnale suunatud tegevused
Esitlus toimus visioonikonverentsil "Tarkus toidab. 100 aastat emakeelset põllumajanduslikku kõrgharidust" 18.10.2019 Eesti Rahva Muuseumis
Lühike Põltsamaa ajalugu
Digiteeritud Euroopa Regionaalarengu Fondi rahastusel, projekti "Eesti teadus- ja õppekirjandus" (2014-2020.12.03.21-0848) raames.https://www.ester.ee/record=b1190400*es
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