19 research outputs found
The POINT-AGAPE Survey I: The Variable Stars in M31
The POINT-AGAPE collaboration has been monitoring M31 for three seasons with
the Wide Field Camera on the Isaac Newton Telescope. In each season, data are
taken for one hour per night for roughly sixty nights during the six months
that M31 is visible. The two fields of view straddle the central bulge,
northwards and southwards. We have calculated the locations, periods and
amplitudes of 35414 variable stars in M31 as a by-product of our microlensing
search. The variables are classified according to their period and amplitude of
variation. They are classified into population I and II Cepheids, Miras and
semi-regular long-period variables. The population I Cepheids are associated
with the spiral arms, while the central concentration of the Miras and
long-period variables varies noticeably, the stars with brighter (and shorter)
variations being much more centrally concentrated. A crucial role in the
microlensing experiment is played by the asymmetry signal. It was initially
assumed that the variable stars would not be a serious problem as their
distributions would be symmetric. We demonstrate that this assumption is not
correct. We find that differential extinction associated with the dust lanes
causes the variable star distributions to be asymmetric. The size and direction
of the asymmetry of the variable stars is measured as a function of period and
amplitude of variation. The implications of this discovery for the successful
completion of the microlensing experiments towards M31 are discussed.
(Abridged)Comment: To appear in MNRAS. Revised version including additional discussion
on color of variables. Additional data table will be available once the paper
is publishe
Design concepts for the Cherenkov Telescope Array CTA: an advanced facility for ground-based high-energy gamma-ray astronomy
Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA
Rotating Stars in Relativity
Rotating relativistic stars have been studied extensively in recent years,
both theoretically and observationally, because of the information one could
obtain about the equation of state of matter at extremely high densities and
because they are considered to be promising sources of gravitational waves. The
latest theoretical understanding of rotating stars in relativity is reviewed in
this updated article. The sections on the equilibrium properties and on the
nonaxisymmetric instabilities in f-modes and r-modes have been updated and
several new sections have been added on analytic solutions for the exterior
spacetime, rotating stars in LMXBs, rotating strange stars, and on rotating
stars in numerical relativity.Comment: 101 pages, 18 figures. The full online-readable version of this
article, including several animations, will be published in Living Reviews in
Relativity at http://www.livingreviews.org
Measurement of Z0 decays to hadrons, and a precise determination of the number of neutrino species
We have made a precise measurement of the cross section for e+e--->Z0-->hadrons with the L3 detector at LEP, covering the range from 88.28 to 95.04 GeV. From a fit to the Z0 mass, total width, and the hadronic cross section to be MZ0=91.160 +/- 0.024 (experiment) +/-0.030(LEP) GeV, [Gamma]Z0=2.539+/-0.054 GeV, and [sigma]h(MZ0)=29.5+/-0.7 nb. We also used the fit to the Z0 peak cross section and the width todetermine [Gamma]invisible=0.548+/-0.029 GeV, which corresponds to 3.29+/-0.17 species of light neutrinos. The possibility of four or more neutrino flavors is thus ruled out at the 4[sigma] confidence level.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28683/3/0000500.pd
A measurement of the Z0 leptonic partial widths and the vector and axial vector coupling constants
We have measured the partial widths of the Z0 into lepton pairs, and the forward-backward charge asymmetry for the process e+e--->[mu]+[mu]- using the L3 detector at LEP. We obtain an average [Gamma]ll of 83.0+/-2.1+/-1.1 MeV.From this result and the asymmetry measurement, we extract the values of the vector and axial vector couplings of the Z0 to leptons: grmv=-0.066-0.027+0.046 and grmA= -0.495-0.007+0.007.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28666/3/0000483.pd