863 research outputs found
Star Formation History of a Young Super-Star Cluster in NGC 4038/39: Direct Detection of Low Mass Pre-Main Sequence Stars
We present an analysis of the near-infrared spectrum of a young massive star
cluster in the overlap region of the interacting galaxies NGC 4038/39 using
population synthesis models. Our goal is to model the cluster population as
well as provide rough constraints on its initial mass function (IMF). The
cluster shows signs of youth such as thermal radio emission and strong hydrogen
emission lines in the near-infrared. Late-type absorption lines are also
present which are indicative of late-type stars in the cluster. The strength
and ratio of these absorption lines cannot be reproduced through either
late-type pre-main sequence (PMS) stars or red supergiants alone. Thus we
interpret the spectrum as a superposition of two star clusters of different
ages, which is feasible since the 1" spectrum encompasses a physical region of
~90 pc and radii of super-star clusters are generally measured to be a few
parsecs. One cluster is young (<= 3 Myr) and is responsible for part of the
late-type absorption features, which are due to PMS stars in the cluster, and
the hydrogen emission lines. The second cluster is older (6 Myr - 18 Myr) and
is needed to reproduce the overall depth of the late-type absorption features
in the spectrum. Both are required to accurately reproduce the near-infrared
spectrum of the object. Thus we have directly detected PMS objects in an
unresolved super-star cluster for the first time using a combination of
population synthesis models and pre-main sequence tracks. This analysis serves
as a testbed of our technique to constrain the low-mass IMF in young super-star
clusters as well as an exploration of the star formation history of young UC
HII regions.Comment: 26 pages, 5 figures, accepted for publication in the Astrophysical
Journa
VLT/SPHERE deep insight of NGC 3603's core: Segregation or confusion?
We present new near-infrared photometric measurements of the core of the
young massive cluster NGC 3603 obtained with extreme adaptive optics. The data
were obtained with the SPHERE instrument mounted on ESO Very Large Telescope,
and cover three fields in the core of this cluster. We applied a correction for
the effect of extinction to our data obtained in the J and K broadband filters
and estimated the mass of detected sources inside the field of view of
SPHERE/IRDIS, which is 13.5"x13.5". We derived the mass function (MF) slope for
each spectral band and field. The MF slope in the core is unusual compared to
previous results based on Hubble space telescope (HST) and very large telescope
(VLT) observations. The average slope in the core is estimated as
-1.06^{+0.26}_{-0.26} for the main sequence stars with 3.5 Msun < M < 120
Msun.Thanks to the SPHERE extreme adaptive optics, 814 low-mass stars were
detected to estimate the MF slope for the pre-main sequence stars with 0.6
Msun< M < 3.5 Msun , Gamma = -0.54^{+0.11}_{-0.11} in the K-band images in two
fields in the core of the cluster. For the first time, we derive the mass
function of the very core of the NGC 3603 young cluster for masses in the range
0.6 - 120 Msun. Previous studies were either limited by crowding, lack of
dynamic range, or a combination of both
Giant birefringence in optical antenna arrays with widely tailorable optical anisotropy
The manipulation of light by conventional optical components such as a
lenses, prisms and wave plates involves engineering of the wavefront as it
propagates through an optically-thick medium. A new class of ultra-flat optical
components with high functionality can be designed by introducing abrupt phase
shifts into the optical path, utilizing the resonant response of arrays of
scatters with deeply-subwavelength thickness. As an application of this
concept, we report a theoretical and experimental study of birefringent arrays
of two-dimensional (V- and Y-shaped) optical antennas which support two
orthogonal charge-oscillation modes and serve as broadband, anisotropic optical
elements that can be used to locally tailor the amplitude, phase, and
polarization of light. The degree of optical anisotropy can be designed by
controlling the interference between the light scattered by the antenna modes;
in particular, we observe a striking effect in which the anisotropy disappears
as a result of destructive interference. These properties are captured by a
simple, physical model in which the antenna modes are treated as independent,
orthogonally-oriented harmonic oscillators
Mid-Infrared Spectroscopic Properties of Ultra-Luminous Infrared Quasars
We analyse mid-infrared (MIR) spectroscopic properties for 19 ultra-luminous
infrared quasars (IR QSOs) in the local universe based on the spectra from the
Infrared Spectrograph on board the Spitzer Space Telescope. The MIR properties
of IR QSOs are compared with those of optically-selected Palomar-Green QSOs (PG
QSOs) and ultra-luminous infrared galaxies (ULIRGs). The average MIR spectral
features from ~ 5 to 30um, including the spectral slopes, 6.2um PAH emission
strengths and [NeII] 12.81um luminosities of IR QSOs, differ from those of PG
QSOs. In contrast, IR QSOs and ULIRGs have comparable PAH and [NeII]
luminosities. These results are consistent with IR QSOs being at a transitional
stage from ULIRGs to classical QSOs. We also find that the colour index
alpha(30, 15) is a good indicator of the relative contribution of starbursts to
AGNs for all QSOs. Correlations between the [NeII] 12.81um and PAH 6.2um
luminosities and those between the [NeII], PAH with 60um luminosities for
ULIRGs and IR QSOs indicate that both [NeII] and PAH luminosities are
approximate star formation rate indicators for IR QSOs and starburst-dominated
galaxies; the scatters are, however, quite large (~ 0.7 to 0.8 dex). Finally
the correlation between the EW(PAH 6.2um) and outflow velocities suggests that
star formation activities are suppressed by feedback from AGNs and/or
supernovae.Comment: 19 pages, 8 figures, 6 tables, accepted for publication in MNRA
Assembly of α-Glucan by GlgE and GlgB in Mycobacteria and Streptomycetes
Actinomycetes, such as mycobacteria and streptomycetes, synthesize α-glucan with α-1,4 linkages and α-1,6 branching to help evade immune responses and to store carbon. α-Glucan is thought to resemble glycogen except for having shorter constituent linear chains. However, the fine structure of α-glucan and how it can be defined by the maltosyl transferase GlgE and branching enzyme GlgB were not known. Using a combination of enzymolysis and mass spectrometry, we compared the properties of α-glucan isolated from actinomycetes with polymer synthesized in vitro by GlgE and GlgB. We now propose the following assembly mechanism. Polymer synthesis starts with GlgE and its donor substrate, α-maltose 1-phosphate, yielding a linear oligomer with a degree of polymerization (∼16) sufficient for GlgB to introduce a branch. Branching involves strictly intrachain transfer to generate a C chain (the only constituent chain to retain its reducing end), which now bears an A chain (a nonreducing end terminal branch that does not itself bear a branch). GlgE preferentially extends A chains allowing GlgB to act iteratively to generate new A chains emanating from B chains (nonterminal branches that themselves bear a branch). Although extension and branching occur primarily with A chains, the other chain types are sometimes extended and branched such that some B chains (and possibly C chains) bear more than one branch. This occurs less frequently in α-glucans than in classical glycogens. The very similar properties of cytosolic and capsular α-glucans from Mycobacterium tuberculosis imply GlgE and GlgB are sufficient to synthesize them both
A Study of B0 -> J/psi K(*)0 pi+ pi- Decays with the Collider Detector at Fermilab
We report a study of the decays B0 -> J/psi K(*)0 pi+ pi-, which involve the
creation of a u u-bar or d d-bar quark pair in addition to a b-bar -> c-bar(c
s-bar) decay. The data sample consists of 110 1/pb of p p-bar collisions at
sqrt{s} = 1.8 TeV collected by the CDF detector at the Fermilab Tevatron
collider during 1992-1995. We measure the branching ratios to be BR(B0 -> J/psi
K*0 pi+ pi-) = (8.0 +- 2.2 +- 1.5) * 10^{-4} and BR(B0 -> J/psi K0 pi+ pi-) =
(1.1 +- 0.4 +- 0.2) * 10^{-3}. Contributions to these decays are seen from
psi(2S) K(*)0, J/psi K0 rho0, J/psi K*+ pi-, and J/psi K1(1270)
An integrated pan-European research infrastructure for validating smart grid systems
A driving force for the realization of a sustainable energy supply in Europe is the integration of distributed, renewable energy resources. Due to their dynamic and stochastic generation behaviour, utilities and network operators are confronted with a more complex operation of the underlying distribution grids. Additionally, due to the higher flexibility on the consumer side through partly controllable loads, ongoing changes of regulatory rules, technology developments, and the liberalization of energy markets, the system’s operation needs adaptation. Sophisticated design approaches together with proper operational concepts and intelligent automation provide the basis to turn the existing power system into an intelligent entity, a so-called smart grid. While reaping the benefits that come along with those intelligent behaviours, it is expected that the system-level testing will play a significantly larger role in the development of future solutions and technologies. Proper validation approaches, concepts, and corresponding tools are partly missing until now. This paper addresses these issues by discussing the progress in the integrated Pan-European research infrastructure project ERIGrid where proper validation methods and tools are currently being developed for validating smart grid systems and solutions.This work is supported by the European Community’s Horizon 2020
Program (H2020/2014-2020) under project “ERIGrid” (Grant Agreement
No. 654113). Further information is available at the corresponding
website www.erigrid.eu
Diffractive Dijet Production at sqrt(s)=630 and 1800 GeV at the Fermilab Tevatron
We report a measurement of the diffractive structure function of
the antiproton obtained from a study of dijet events produced in association
with a leading antiproton in collisions at GeV at the
Fermilab Tevatron. The ratio of at GeV to
obtained from a similar measurement at GeV is compared with
expectations from QCD factorization and with theoretical predictions. We also
report a measurement of the (-Pomeron) and ( of parton in
Pomeron) dependence of at GeV. In the region
, GeV and , is
found to be of the form , which obeys
- factorization.Comment: LaTeX, 9 pages, Submitted to Phys. Rev. Letter
Search for Narrow Diphoton Resonances and for gamma-gamma+W/Z Signatures in p\bar p Collisions at sqrt(s)=1.8 TeV
We present results of searches for diphoton resonances produced both
inclusively and also in association with a vector boson (W or Z) using 100
pb^{-1} of p\bar p collisions using the CDF detector. We set upper limits on
the product of cross section times branching ratio for both p\bar
p\to\gamma\gamma + X and p\bar p\to\gamma\gamma + W/Z. Comparing the inclusive
production to the expectations from heavy sgoldstinos we derive limits on the
supersymmetry-breaking scale sqrt{F} in the TeV range, depending on the
sgoldstino mass and the choice of other parameters. Also, using a NLO
prediction for the associated production of a Higgs boson with a W or Z boson,
we set an upper limit on the branching ratio for H\to\gamma\gamma. Finally, we
set a lower limit on the mass of a `bosophilic' Higgs boson (e.g. one which
couples only to \gamma, W, and Z$ bosons with standard model couplings) of 82
GeV/c^2 at 95% confidence level.Comment: 30 pages, 11 figure
Search for Gluinos and Scalar Quarks in Collisions at TeV using the Missing Energy plus Multijets Signature
We have performed a search for gluinos (\gls) and squarks (\sq) in a data
sample of 84 pb of \ppb collisions at = 1.8 TeV, recorded by
the Collider Detector at Fermilab, by investigating the final state of large
missing transverse energy and 3 or more jets, a characteristic signature in
R-parity-conserving supersymmetric models. The analysis has been performed
`blind', in that the inspection of the signal region is made only after the
predictions from Standard Model backgrounds have been calculated. Comparing the
data with predictions of constrained supersymmetric models, we exclude gluino
masses below 195 \gev (95% C.L.), independent of the squark mass. For the case
\msq \approx \mgls, gluino masses below 300 \gev are excluded.Comment: 7 pages, 3 figure
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