199 research outputs found
Integral Field Spectroscopy of a peculiar Supernova Remnant MF16 in NGC6946
We present a study of a peculiar Supernova Remnant MF16, associated with the
Ultraluminous X-ray Source (ULX) NGC6946 ULX-1. Observations were taken with
the MultiPupil Fiber Spectrograph (MPFS) with 6-m telescope on January 2005.
The nebula is found to be highly asymmetric, one of the parts being much denser
and colder. The two-component structure of the emission lines and radial
velocity gradient argue for a non-spherical nebula, expanding with a velocity
of about 100 km/s. Neither shock models nor the X-ray emission can adequately
explain the actual emission line spectrum of MF16, so we suggest an additional
ultraviolet source with a luminosity of about 10E40 erg/s. We confirm
coincidence of the ULX with the central star, and identify radio emission
observed by VLA with the most dense part of the nebula.Comment: Proceedings of the ESO and Euro3D Workshop "Science Perspectives for
3D Spectroscopy", Garching (Germany), October 10-14, 2005. M. Kissler-Patig,
M.M. Roth and J.R. Walsh (eds.
Solving the Sports League Scheduling Problem with Tabu Search
In this paper we present a tabu approach for a version of the Sports League Scheduling Problem. The approach adopted is based on a formulation of the problem as a Constraint Satisfaction Problem (CSP). Tests were carried out on problem instances of up to 40 teams representing 780 integer variables with 780 values per variable. Experimental results show that this approach outperforms some existing methods and is one of the most promising methods for solving problems of this type
Active Galaxies in the UV
In this article we present different aspects of AGN studies demonstrating the
importance of the UV spectral range. Most important diagnostic lines for
studying the general physical conditions as well as the metalicities in the
central broad line region in AGN are emitted in the UV. The UV/FUV continuum in
AGN excites not only the emission lines in the immediate surrounding but it is
responsible for the ionization of the intergalactic medium in the early stages
of the universe. Variability studies of the emission line profiles of AGN in
the UV give us information on the structure and kinematics of the immediate
surrounding of the central supermassive black hole as well as on its mass
itself.Comment: 29 pages, 13 figures, Ap&SS in pres
The Planetary Nebula Luminosity Function at the Dawn of Gaia
The [O III] 5007 Planetary Nebula Luminosity Function (PNLF) is an excellent
extragalactic standard candle. In theory, the PNLF method should not work at
all, since the luminosities of the brightest planetary nebulae (PNe) should be
highly sensitive to the age of their host stellar population. Yet the method
appears robust, as it consistently produces < 10% distances to galaxies of all
Hubble types, from the earliest ellipticals to the latest-type spirals and
irregulars. It is therefore uniquely suited for cross-checking the results of
other techniques and finding small offsets between the Population I and
Population II distance ladders. We review the calibration of the method and
show that the zero points provided by Cepheids and the Tip of the Red Giant
Branch are in excellent agreement. We then compare the results of the PNLF with
those from Surface Brightness Fluctuation measurements, and show that, although
both techniques agree in a relative sense, the latter method yields distances
that are ~15% larger than those from the PNLF. We trace this discrepancy back
to the calibration galaxies and argue that, due to a small systematic error
associated with internal reddening, the true distance scale likely falls
between the extremes of the two methods. We also demonstrate how PNLF
measurements in the early-type galaxies that have hosted Type Ia supernovae can
help calibrate the SN Ia maximum magnitude-rate of decline relation. Finally,
we discuss how the results from space missions such as Kepler and Gaia can help
our understanding of the PNLF phenomenon and improve our knowledge of the
physics of local planetary nebulae.Comment: 12 pages, invited review at the conference "The Fundamental Cosmic
Distance Scale: State of the Art and Gaia Perspective", to appear in
Astrophysics and Space Scienc
The Seyfert-LINER Galaxy NGC 7213: An XMM-Newton Observation
We examine the XMM X-ray spectrum of the LINER-AGN NGC 7213, which is best
fit with a power law, K-alpha emission lines from Fe I, Fe XXV and Fe XXVI and
a soft X-ray collisionally ionised thermal plasma with kT=0.18 +0.03/-0.01 keV.
We find a luminosity of 7x10^(-4) L_Edd, and a lack of soft X-ray excess
emission, suggesting a truncated accretion disc. NGC 7213 has intermediate
X-ray spectral properties, between those of the weak AGN found in the LINER M81
and higher luminosity Seyfert galaxies. This supports the notion of a
continuous sequence of X-ray properties from the Galactic Centre through LINER
galaxies to Seyferts, likely determined by the amount of material available for
accretion in the central regions.Comment: 7 pages, 2 figures. To appear in From X-ray Binaries to Quasars:
Black Hole Accretion on All Mass Scales, ed. T. J. Maccarone, R. P. Fender,
and L. C. Ho (Dordrecht: Kluwer
Supermassive Binaries and Extragalactic Jets
Some quasars show Doppler shifted broad emission line peaks. I give new
statistics of the occurrence of these peaks and show that, while the most
spectacular cases are in quasars with strong radio jets inclined to the line of
sight, they are also almost as common in radio-quiet quasars. Theories of the
origin of the peaks are reviewed and it is argued that the displaced peaks are
most likely produced by the supermassive binary model. The separations of the
peaks in the 3C 390.3-type objects are consistent with orientation-dependent
"unified models" of quasar activity. If the supermassive binary model is
correct, all members of "the jet set" (astrophysical objects showing jets)
could be binaries.Comment: 31 pages, PostScript, missing figure is in ApJ 464, L105 (see
http://www.aas.org/ApJ/v464n2/5736/5736.html
Fitting the integrated Spectral Energy Distributions of Galaxies
Fitting the spectral energy distributions (SEDs) of galaxies is an almost
universally used technique that has matured significantly in the last decade.
Model predictions and fitting procedures have improved significantly over this
time, attempting to keep up with the vastly increased volume and quality of
available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of
multiwavelength data sets, and the methods used to fit model SEDs to observed
galaxy data sets. We touch upon the achievements and challenges in the major
ingredients of SED fitting, with a special emphasis on describing the interplay
between the quality of the available data, the quality of the available models,
and the best fitting technique to use in order to obtain a realistic
measurement as well as realistic uncertainties. We conclude that SED fitting
can be used effectively to derive a range of physical properties of galaxies,
such as redshift, stellar masses, star formation rates, dust masses, and
metallicities, with care taken not to over-interpret the available data. Yet
there still exist many issues such as estimating the age of the oldest stars in
a galaxy, finer details ofdust properties and dust-star geometry, and the
influences of poorly understood, luminous stellar types and phases. The
challenge for the coming years will be to improve both the models and the
observational data sets to resolve these uncertainties. The present review will
be made available on an interactive, moderated web page (sedfitting.org), where
the community can access and change the text. The intention is to expand the
text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics &
Space Scienc
NP-hardness of Deciding Convexity of Quartic Polynomials and Related Problems
We show that unless P=NP, there exists no polynomial time (or even
pseudo-polynomial time) algorithm that can decide whether a multivariate
polynomial of degree four (or higher even degree) is globally convex. This
solves a problem that has been open since 1992 when N. Z. Shor asked for the
complexity of deciding convexity for quartic polynomials. We also prove that
deciding strict convexity, strong convexity, quasiconvexity, and
pseudoconvexity of polynomials of even degree four or higher is strongly
NP-hard. By contrast, we show that quasiconvexity and pseudoconvexity of odd
degree polynomials can be decided in polynomial time.Comment: 20 page
Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment
This paper describes an analysis of the angular distribution of W->enu and
W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with
the ATLAS detector at the LHC in 2010, corresponding to an integrated
luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and
the missing transverse energy, the W decay angular distribution projected onto
the transverse plane is obtained and analysed in terms of helicity fractions
f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV
and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw
> 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour,
are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017
+/- 0.030, where the first uncertainties are statistical, and the second
include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables,
revised author list, matches European Journal of Physics C versio
Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS
The chi_b(nP) quarkonium states are produced in proton-proton collisions at
the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS
detector. Using a data sample corresponding to an integrated luminosity of 4.4
fb^-1, these states are reconstructed through their radiative decays to
Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks
corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new
structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is
also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes.
This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table,
corrected author list, matches final version in Physical Review Letter
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