24,967 research outputs found
Fe XIII coronal line emission in cool M dwarfs
We report on a search for the Fe xiii forbidden coronal line at 3388.1 \AA in
a sample of 15 M-type dwarf stars covering the whole spectral class as well as
different levels of activity. A clear detection was achieved for LHS 2076
during a major flare and for CN Leo, where the line had been discovered before.
For some other stars the situation is not quite clear. For CN Leo we
investigated the timing behaviour of the Fe xiii line and report a high level
of variability on a timescale of hours which we ascribe to microflare heating.Comment: 13 pages, 10 figure
New Indicators for AGN Power: The Correlation Between [O IV] lambda 25.89 micron and Hard X-ray Luminosity for Nearby Seyfert Galaxies
We have studied the relationship between the [O IV] lambda 25.89 micron
emission line luminosities, obtained from Spitzer spectra, the X-ray continua
in the 2-10 keV band, primarily from ASCA, and the 14-195 keV band obtained
with the SWIFT/Burst Alert Telescope (BAT), for a sample of nearby (z < 0.08)
Seyfert galaxies. For comparison, we have examined the relationship between the
[O III] 5007, the 2-10 keV and the 14-195 keV luminosities for the same set of
objects. We find that both the [O IV] and [O III] luminosities are
well-correlated with the BAT luminosities. On the other hand, the [O III]
luminosities are better-correlated with 2-10 keV luminosities than are those of
[O IV]. When comparing [O IV] and [O III] luminosities for the different types
of galaxies, we find that the Seyfert 2's have significantly lower [O III] to
[O IV] ratios than the Seyfert 1's. We suggest that this is due to more
reddening of the narrow line region (NLR) of the Seyfert 2's. Assuming Galactic
dust to gas ratios, the average amount of extra reddening corresponds to a
hydrogen column density of ~ few times 10^21 cm^-2, which is a small fraction
of the X-ray absorbing columns in the Seyfert 2's. The combined effects of
reddening and the X-ray absorption are the probable reason why the [O III]
versus 2-10 keV correlation is better than the [O IV] versus 2-10 keV, since
the [O IV] emission line is much less affected by extinction. Overall, we find
the [O IV] to be an accurate and truly isotropic indicator of the power of the
AGN. This suggests that it can be useful in deconvolving the contribution of
the AGN and starburst to the spectrum of Compton-thick and/or X-ray weak
sources.Comment: Accepted for publication in the Astrophysical Journal. 31 pages, 6
figures, 4 table
Correlated and zonal errors of global astrometric missions: a spherical harmonic solution
We propose a computer-efficient and accurate method of estimation of
spatially correlated errors in astrometric positions, parallaxes and proper
motions obtained by space and ground-based astrometry missions. In our method,
the simulated observational equations are set up and solved for the
coefficients of scalar and vector spherical harmonics representing the output
errors, rather than for individual objects in the output catalog. Both
accidental and systematic correlated errors of astrometric parameters can be
accurately estimated. The method is demonstrated on the example of the JMAPS
mission, but can be used for other projects of space astrometry, such as SIM or
JASMINE.Comment: Accepted by AJ, to be published in 201
Disentangling the near infrared continuum spectral components of the inner 500 pc of Mrk 573: two-dimensional maps
We present a near infrared study of the spectral components of the continuum
in the inner 500500 pc of the nearby Seyfert galaxy Mrk573 using
adaptive optics near-infrared integral field spectroscopy with the instrument
NIFS of the Gemini North Telescope at a spatial resolution of 50 pc. We
performed spectral synthesis using the {\sc starlight} code and constructed
maps for the contributions of different age components of the stellar
population: young ( Myr), young-intermediate (
Myr), intermediate-old ( Myr Gyr) to the
near-IR K-band continuum, as well as their contribution to the total stellar
mass. We found that the old stellar population is dominant within the inner 250
pc, while the intermediate age components dominate the continuum at larger
distances. A young stellar component contributes up to 20% within the
inner 70 pc, while hot dust emission and featureless continuum components
are also necessary to fit the nuclear spectrum, contributing up to 20% of the
K-band flux there. The radial distribution of the different age components in
the inner kiloparsec of Mrk573 is similar to those obtained by our group for
the Seyfert galaxies Mrk1066, Mrk1157 and NGC1068 in previous works using a
similar methodology. Young stellar populations (100 Myr) are seen in the
inner 200-300 pc for all galaxies contributing with 20% of the K-band
flux, while the near-IR continuum is dominated by the contribution of
intermediate-age stars (100 Myr-2 Gyr) at larger distances. Older stellar
populations dominate in the inner 250 pc
Complex Dynamics and Synchronization of Delayed-Feedback Nonlinear Oscillators
We describe a flexible and modular delayed-feedback nonlinear oscillator that
is capable of generating a wide range of dynamical behaviours, from periodic
oscillations to high-dimensional chaos. The oscillator uses electrooptic
modulation and fibre-optic transmission, with feedback and filtering
implemented through real-time digital-signal processing. We consider two such
oscillators that are coupled to one another, and we identify the conditions
under which they will synchronize. By examining the rates of divergence or
convergence between two coupled oscillators, we quantify the maximum Lyapunov
exponents or transverse Lyapunov exponents of the system, and we present an
experimental method to determine these rates that does not require a
mathematical model of the system. Finally, we demonstrate a new adaptive
control method that keeps two oscillators synchronized even when the coupling
between them is changing unpredictably.Comment: 24 pages, 13 figures. To appear in Phil. Trans. R. Soc. A (special
theme issue to accompany 2009 International Workshop on Delayed Complex
Systems
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