24,316 research outputs found
Task force on applied mathematics
Tomas Garza relates how the Research Center for Applied Mathematics Systems and Services in Mexico became the Research Institute for Applied Mathematics and Systems and what the type of work performed is
Extended Coronal Emission Lines in Active Galactic Nuclei
VLT and NTT spectra are used to examine the nuclear and extended coronal line
emission in a sample of well-known Seyfert 1 and 2 galaxies. The excellent
spatial resolution obtained with VLT allowed us to map [SiVI] 1.963 m and
[SiVII] 2.48 m on scales of up to 20 pc. Coronal line emission, extended
to distances of 100 pc, is detected in some of the lines analyzed,
particularly in [FeX] 6374\AA, [FeXI] 7891\AA, and [SiVII] 2.48m. Most
coronal lines are strongly asymmetric towards the blue and broader than
low-ionization lines. This result is particularly important for Circinus, where
previous observations had failed at detecting larger widths for high-ionization
lines. Photoionization models are used to investigate the physical conditions
and continuum luminosities necessary to produced the observed coronal emission.
We found that an ionization parameter U> 0.10 is necessary to reproduce the
observations, although the clouds should be located at distances < 30 pc.Comment: 4 pages, 6 figures, to appear in proceedings of IAU Symposium No.
222, The Interplay Among Black Holes, Stars and ISM in Galacti Nucle
Near-infrared spectroscopy of nearby Seyfert galaxies - II. Molecular content and coronal emission
We present sub-arcsec near-infrared 1.5 - 2.5 micron moderate resolution
long-slit spectra of eight nearby Seyfert galaxies (z<0.01), both parallel to
the ionization cone and perpendicular to it. These spectra complement similar
data on six Seyferts, presented in Reunanen, Kotilainen & Prieto (2002). Large
concentrations of molecular gas (H2) are present in the nucleus regardless of
the Seyfert type. The spatial extent of the H2 emission is larger perpendicular
to the cone than parallel to it in 6/8 (75 %) galaxies, in agreement with the
unified models of Active Galactic Nuclei. Broad BrGamma was detected in nearly
half of the optically classified Seyfert 2 galaxies, including two objects with
no evidence for hidden polarized Broad Line Region. Nuclear [FeII] emission is
generally blueshifted which together with high BrGamma/[FeII] ratios suggests
shocks as the dominant excitation mechanism in Seyfert galaxies. Bright coronal
emission lines [SiVI] and [SiVII] are common in Seyferts, as they are detected
in ~60 % of the galaxies. In three galaxies the coronal lines are extended only
in the direction parallel to the cone. This could be explained by shock
excitation due to the jet or superwind interacting with the interstellar
medium.Comment: 19 pages, accepted for publication in MNRA
Chemical Abundances from the Continuum
The calculation of solar absolute fluxes in the near-UV is revisited,
discussing in some detail recent updates in theoretical calculations of
bound-free opacity from metals. Modest changes in the abundances of elements
such as Mg and the iron-peak elements have a significant impact on the
atmospheric structure, and therefore self-consistent calculations are
necessary. With small adjustments to the solar photospheric composition, we are
able to reproduce fairly well the observed solar fluxes between 200 and 270 nm,
and between 300 and 420 nm, but find too much absorption in the 270-290 nm
window. A comparison between our reference 1D model and a 3D time-dependent
hydrodynamical simulation indicates that the continuum flux is only weakly
sensitive to 3D effects, with corrections reaching <10% in the near-UV, and <2%
in the optical.Comment: 10 pages, 5 figures, to appear in the proceedings of the conference A
Stellar Journey, a symposium in celebration of Bengt Gustafsson's 65th
birthday, June 23-27, 2008, Uppsal
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