2,821 research outputs found
A method of determining combustion gas flow
Zirconium oxide coating enables the determination of hot gas flow patterns on liquid rocket injector face and baffle surfaces to indicate modifications that will increase performance and improve combustion stability. The coating withstands combustion temperatures and due to the coarse surface and coloring of the coating, shows the hot gas patterns
The First Spectroscopically Resolved Sub-parsec Orbit of a Supermassive Binary Black Hole
One of the most intriguing scenarios proposed to explain how active galactic
nuclei are triggered involves the existence of a supermassive binary black hole
system in their cores. Here we present an observational evidence for the first
spectroscopically resolved sub-parsec orbit of a such system in the core of
Seyfert galaxy NGC 4151. Using a method similar to those typically applied for
spectroscopic binary stars we obtained radial velocity curves of the
supermassive binary system, from which we calculated orbital elements and made
estimates about the masses of components. Our analysis shows that periodic
variations in the light and radial velocity curves can be accounted for an
eccentric, sub-parsec Keplerian orbit of a 15.9-year period. The flux maximum
in the lightcurve correspond to the approaching phase of a secondary component
towards the observer. According to the obtained results we speculate that the
periodic variations in the observed H{\alpha} line shape and flux are due to
shock waves generated by the supersonic motion of the components through the
surrounding medium. Given the large observational effort needed to reveal this
spectroscopically resolved binary orbital motion we suggest that many such
systems may exist in similar objects even if they are hard to find. Detecting
more of them will provide us with insight into black hole mass growth process.Comment: 29 pages, 10 figures, published in ApJ, 759, 11
Exploring possible relations between optical variability time scales and broad emission line shapes in AGN
Here we investigate the connection of broad emission line shapes and
continuum light curve variability time scales of type-1 Active Galactic Nuclei
(AGN). We developed a new model to describe optical broad emission lines as an
accretion disk model of a line profile with additional ring emission. We
connect ring radii with orbital time scales derived from optical light curves,
and using Kepler's third law, we calculate mass of central supermassive black
hole (SMBH). The obtained results for central black hole masses are in a good
agreement with {other methods. This indicates that the variability time scales
of AGN may not be stochastic, but rather connected to the orbital time scales
which depend on the central SMBH mass.Comment: 13 pages, 3 figures, Accepted on 11 May 2018 Front. Astron. Space Sc
Quasars: from the Physics of Line Formation to Cosmology
Quasars accreting matter at very high rates (known as extreme Population A
[xA] or super-Eddington accreting massive black holes) provide a new class of
distance indicators covering cosmic epochs from the present-day Universe up to
less than 1 Gyr from the Big Bang. The very high accretion rate makes it
possible that massive black holes hosted in xA quasars radiate at a stable,
extreme luminosity-to-mass ratio. This in turns translates into stable physical
and dynamical conditions of the mildly ionized gas in the quasar low-ionization
line emitting region. In this contribution, we analyze the main optical and UV
spectral properties of extreme Population A quasars that make them easily
identifiable in large spectroscopic surveys at low-z (z < 1) and intermediate-z
(2 < z < 2.6), and the physical conditions that are derived for the formation
of their emission lines. Ultimately, the analysis supports the possibility of
identifying a virial broadening estimator from low-ionization line widths, and
the conceptual validity of the redshift-independent luminosity estimates based
on virial broadening for a known luminosity-to-mass ratio.Comment: 13 pages, 5 figures. Invited lecture at SPIG 2018, Belgrade. To
appear in Ato
Black hole mass estimates in quasars - A comparative analysis of high- and low-ionization lines
The inter-line comparison between high- and low-ionization emission lines has
yielded a wealth of information on the quasar broad line region (BLR) structure
and dynamics, including perhaps the earliest unambiguous evidence in favor of a
disk + wind structure in radio-quiet quasars. We carried out an analysis of the
CIV 1549 and Hbeta line profiles of 28 Hamburg-ESO high luminosity quasars and
of 48 low-z, low luminosity sources in order to test whether the
high-ionization line CIV 1549 width could be correlated with Hbeta and be used
as a virial broadening estimator. We analyze intermediate- to high-S/N,
moderate resolution optical and NIR spectra covering the redshifted CIV and
H over a broad range of luminosity log L ~ 44 - 48.5 [erg/s] and
redshift (0 - 3), following an approach based on the quasar main sequence. The
present analysis indicates that the line width of CIV 1549 is not immediately
offering a virial broadening estimator equivalent to H. At the same time
a virialized part of the BLR appears to be preserved even at the highest
luminosities. We suggest a correction to FWHM(CIV) for Eddington ratio (using
the CIV blueshift as a proxy) and luminosity effects that can be applied over
more than four dex in luminosity. Great care should be used in estimating
high-L black hole masses from CIV 1549 line width. However, once corrected
FWHM(CIV) values are used, a CIV-based scaling law can yield unbiased MBH
values with respect to the ones based on H with sample standard
deviation ~ 0.3 dex.Comment: 43 pages, 15 Figures, submitted to A&
Detailed Analysis of Balmer Lines in a Sloan Digital Sky Survey Sample of 90 Broad Line Active Galactic Nuclei
In order to contribute to the general effort aiming at the improvement of our
knowledge about the physical conditions within the Broad Line Region (BLR) of
Active Galactic Nuclei (AGN), here we present the results achieved by our
analysis of the spectral properties of a sample of 90 broad line emitting
sources, collected at the Sloan Digital Sky Survey (SDSS) database. By focusing
our attention mainly onto the Balmer series of hydrogen emission lines, which
is the dominant feature in the optical wavelength range of many BLR spectra, we
extracted several flux and profile measurements, which we related to other
source properties, such as optical continuum luminosities, inferred black hole
masses, and accretion rates. Using the Boltzmann Plot method to investigate the
Balmer line flux ratios as a function of the line profiles, we found that
broader line emitting AGN typically have larger H_alpha / H_beta and smaller
H_gamma / H_beta and H_delta / H_beta line ratios. With the help of some recent
investigations, we model the structure of the BLR and we study the influence of
the accretion process on the properties of the BLR plasma.Comment: 14 pages, 11 figures, fixes the wrong names of 4 objects; published
on Ap
Mehun-sur-Yèvre – Le Château
Date de l'opération : 1989 (FP) ; 1986 (SD) ; 1985 (SD) ; 1984 (SU) Inventeur(s) : Delmarre P ; Bon Philippe En 1984, la fouille a porté sur une fosse de plan rectangulaire (1,70 m x 1,80 m), construite en appareil cyclopéen dont le mur nord-est a servi de fondation au mur de la courtine édifié au XIe s., tandis que le mur nord-ouest a été incorporé à la base du donjon édifié au XIIIe s. Dans un premier temps, cette fosse a pu servir de puits, par l'utilisation d'une source résurgente à fleur..
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