910 research outputs found
Empirical Uncertainty Estimators for Astrometry from Digital Databases
In order to understand the positional uncertainties of arbitrary objects in
several of the current major databases containing astrometric information, a
sample of extragalactic radio sources with precise positions in the
International Celestial Reference Frame (ICRF) is compared with the available
positions of their optical counterparts. The discrepancies between the radio
and various optical positions are used to derive empirical uncertainty
estimators for the USNO-A2.0, USNO-A1.0, Guide Star Selection System (GSSS)
images, and the first and second Digitized Sky Surveys (DSS-I and DSS-II). In
addition, an estimate of the uncertainty when the USNO-A2.0 catalog is
transferred to different image data is provided. These optical astrometric
frame uncertainties can in some cases be the dominant error term when
cross-identifying sources at different wavelengths.Comment: 12 pages including 2 figures and 1 table. Accepted for publication in
The Astronomical Journal, October 1999. Values in Table 1 for DSS I corrected
99-07-1
Host Galaxies of low z Radio-loud Quasars: A search of HST archives
We searched the HST archives for unpublished WFPC2 images of low redshift
(z<0.5) radio loud quasars (RLQ). This led to the identification of 11 objects.
We present here the results of the analysis of these images from which we
derive the properties of their host galaxies. All objects are clearly resolved
and their surrounding nebulosity is consistent with an elliptical galaxy model.
These new data, together with previous published HST observations, form a
sample of 34 sources which significantly expands all previous studies of low
redshift RLQ based on HST data. For this full sample we derive the average
absolute magnitude of the host galaxies =-24.01+/-0.48, and the effective
radius =10.5+/-3.7kpc. No significant correlation is found between the
nucleus and the host galaxy luminosity. Using the relationship between black
hole mass (M_BH) and bulge luminosity we investigate the relation between M_BH
and total radio power for RLQ and compare with other classes of radio sources.
The overall distribution of AGN in the plane M_BH-P(radio) exhibits a trend for
increasing M_BH with increasing P(radio) but with a substantial spread. RLQ
occupy the region of most powerful sources and most massive BH. The quasars
appear to emit over a wide range of power with respect to their Eddington
luminosity as deduced by the estimated M_BH.Comment: 23 pages, 8 figures, ApJ in pres
The 7-channel FIR HCN Interferometer on J-TEXT Tokamak
A seven-channel far-infrared hydrogen cyanide (HCN) laser interferometer has
been established aiming to provide the line integrated plasma density for the
J-TEXT experimental scenarios. A continuous wave glow discharge HCN laser
designed with a cavity length 3.4 m is used as the laser source with a
wavelength of 337 {\mu}m and an output power up to 100 mW. The system is
configured as a Mach-Zehnder type interferometer. Phase modulation is achieved
by a rotating grating, with a modulation frequency of 10 kHz which corresponds
to the temporal resolution of 0.1 ms. The beat signal is detected by TGS
detector. The phase shift induced by the plasma is derived by the comparator
with a phase sensitivity of 0.06 fringe. The experimental results measured by
the J-TEXT interferometer are presented in details. In addition, the inversed
electron density profile done by a conventional approach is also given. The
kinematic viscosity of dimethyl silicone and vibration control is key issues
for the system performance. The laser power stability under different kinematic
viscosity of silicone oil is presented. A visible improvement of measured
result on vibration reduction is shown in the paper.Comment: conference (15th-International Symposium on Laser-Aided Plasma
Diagnostics
IRAS observations of active galaxies
The IRAS survey gives an unbiased view of the infrared properties of the active galaxies. Seyfert galaxies occupy much the same area in color-color plots as to normal infrared bright galaxies, but extend the range towards flatter 60 to 25 mm slopes. Statistically the Seyfert 1 galaxies can be distinguished from the Seyfert 2 galaxies, lying predominantly closer to the area with constant slopes between 25 and 200 mm. The infrared measurements of the Seyfert galaxies cannot distinguish between the emission mechanisms in these objects although they agree with the currently popular ideas; they do provide a measure of the total luminosity of the Seyferts. The quasar's position in the color-color diagrams continue the trend of the Seyferts. The quasar 3C48 is shown to be exceptional among the radio loud quasars in that it has a high infrared luminosity which dominates the power output of the quasar and is most likely associated with the underlying host galaxy
Fabry Perot Halpha Observations of the Barred Spiral NGC 3367
We report the gross properties of the velocity field of the barred spiral
galaxy NGC 3367. The following values were found: inclination with respect to
the plane of the sky, i=30 deg; position angle (PA) of receding semi major axis
PA=51 and systemic velocity V(sys)=3032 km/s. Large velocity dispersion are
observed of upt o 120 km/s in the nuclear region, of up to 70 km/s near the
eastern bright sources just beyond the edge of the stellar bar where three
spiral arms seem to start and in the western bright sources at about 10 kpc.
Deviations from normal circular velocities are observed from all the disk but
mainly from the semi circle formed by the string of south western Halpha
sources. An estimate of the dynamical mass is M(dyn)=2x10^11 Msolar.Comment: Accepted to be published in May 2001 issue in the A.J. 19 pages, 7
figure
Comment on "Correlation of the Highest-Energy Cosmic Rays with Nearby Extragalactic Objects"
We argue that the data published by the Pierre Auger Collaboration
(arXiv:0711.2256) disfavor at 99% confidence level their hypothesis that most
of the highest-energy cosmic rays are protons from nearby astrophysical
sources, either Active Galactic Nuclei or other objects with a similar spatial
distribution.Comment: 1000 words, 2 figures, scicite.st
Classification of Static Charged Black Holes in Higher Dimensions
The uniqueness theorem for static charged higher dimensional black hole
containing an asymptotically flat spacelike hypersurface with compact interior
and with both degenerate and non-degenerate components of event horizon is
proposed. By studies of the near-horizon geometry of degenerate horizons one
was able to eliminate the previous restriction concerning the inequality
fulfilled by the charges of the adequate components of the aforementioned
horizons.Comment: 9 pages, RevTex, to be published in Phys.Rev. D1
Semantic annotations on heritage models: 2D/3D approaches and future research challenges
Research in the field of Cultural Heritage is increasingly moving towards the creation of digital information systems, in which the geometric representation of an artifact is linked to some external information, through meaningful tags. The process of attributing additional and structured information to various elements in a given digital model is customarily identified with the term semantic annotation; the added contextual information is associated, for instance, to analysis and conservation terms. Starting from the existing literature, aim of this work is to discuss how semantic annotations are used, in digital architectural heritage models, to link the geometrical representation of an artefact with knowledge-related information. Most consolidated methods -such as traditional mapping on 2D media, are compared with more recent approaches making the most of 3D representation. Reference is made, in particular, to Heritage-BIM techniques and to collaborative reality-based platforms, such as AĂŻoli (http://aioli.cloud). Potentialities and limits of the different solutions proposed in literature are critically discussed, also addressing future research challenges in Cultural Heritage application fields
A Robust Method for Drilling Monitoring using Acoustic Emission
Acoustic Emission (AE) is considered an efficient tool for monitoring of machining operations, for both tool condition and working piece integrity. However, the use of AE is more challenging in case of drilling, due to heavy dependence of AE signals to process parameters. Monitoring drilling using AE thus requires robust methods to extract useful information in signals. The paper describes such a method that adapts itself to AE signals obtained during drilling, allowing the automatic set-up of an adaptive threshold to perform AE count rate. Experiments have been conducted that show the robustness of the method and its usefulness in drilling monitoring.International audienceAcoustic Emission (AE) is considered an efficient tool for monitoring of machining operations, for both tool condition and working piece integrity. However, the use of AE is more challenging in case of drilling, due to heavy dependence of AE signals to process parameters. Monitoring drilling using AE thus requires robust methods to extract useful information in signals. The paper describes such a method that adapts itself to AE signals obtained during drilling, allowing the automatic set-up of an adaptive threshold to perform AE count rate. Experiments have been conducted that show the robustness of the method and its usefulness in drilling monitoring
The last Gift of BeppoSAX: PDS Observations of the two Blazars 1ES 0507-040 and PKS 1229-021
Towards the end of the BeppoSAX mission, the only operated Narrow Field
Instrument was the PDS, which covers the energy range 13-300 keV. Two blazars,
1ES 0507-040 (z=0.304) and PKS 1229-021 (z= 1.045), suitably located in the sky
for BeppoSAX pointing, were observed for about 2 days each in Spring 2002 with
the PDS and detected up to 50 keV. 1ES0507-040 had been already observed by the
BeppoSAX NFIs at an earlier epoch for a much shorter time. We have re-analysed
those data as well, and identified a possible contamination problem in the PDS
spectrum. We present our recent PDS data on both sources, combined with the
previous BeppoSAX data and with non-simultaneous observations at other
frequencies. The derived Spectral Energy Distributions allow us to discuss the
origin of the high energy component.Comment: 4 pages, 6 figures, poster presented at the symposium: The Restless
High-Energy Universe, Amsterdam, May 200
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