8,834 research outputs found
Spectral Variations in Early-Type Galaxies as a Function of Mass
We report on the strengths of three spectral indicators - Mg_2, Hbeta, and
Hn/Fe - in the integrated light of a sample of 100 field and cluster E/S0
galaxies. The measured indices are sensitive to age and/or and metallicity
variations within the galaxy sample. Using linear regression analysis for data
with non-uniform errors, we determine the intrinsic scatter present among the
spectral indices of our galaxy sample as a function of internal velocity
dispersion. Our analysis indicates that there is significantly more intrinsic
scatter in the two Balmer line indices than in the Mg_2 index, indicating that
the Balmer indices provide more dynamic range in determining the age of a
stellar population than does the Mg_2 index. Furthermore, the scatter is much
larger for the low velocity dispersion galaxies, indicating that star formation
has occurred more recently in the lower mass galaxies.Comment: 4 pages, 1 figure, 1 table, to appear in the Astrophysical Journal
Letter
Plasma Wakefield Acceleration with a Modulated Proton Bunch
The plasma wakefield amplitudes which could be achieved via the modulation of
a long proton bunch are investigated. We find that in the limit of long bunches
compared to the plasma wavelength, the strength of the accelerating fields is
directly proportional to the number of particles in the drive bunch and
inversely proportional to the square of the transverse bunch size. The scaling
laws were tested and verified in detailed simulations using parameters of
existing proton accelerators, and large electric fields were achieved, reaching
1 GV/m for LHC bunches. Energy gains for test electrons beyond 6 TeV were found
in this case.Comment: 9 pages, 7 figure
Symbiotic stars in the Local Group of Galaxies
Preliminary results of the ongoing search for symbiotic binary stars in the
Local Group of Galaxies are presented and discussed.Comment: Proceedings of Physics of Evolved Stars 2015: A Conference Dedicated
to the Memory of Olivier Chesneau, Nice, 8-12 June 201
The luminosity function of Palomar 5 and its tidal tails
We present the main sequence luminosity function of the tidally disrupted
globular cluster Palomar 5 and its tidal tails. For this work we analyzed
imaging data obtained with the Wide Field Camera at the INT (La Palma) and data
from the Wide Field Imager at the MPG/ESO 2.2 m telescope at La Silla down to a
limiting magnitude of approximately 24.5 mag in B. Our results indicate that
preferentially fainter stars were removed from the cluster so that the LF of
the cluster's main body exhibits a significant degree of flattening compared to
other GCs. This is attributed to its advanced dynamical evolution. The LF of
the tails is, in turn, enhanced with faint, low-mass stars, which we interpret
as a consequence of mass segregation in the cluster.Comment: 4 pages, 3 figures, to be published in the proceedings of the
conference "Satellites and tidal streams" held at La Palma, Canary Islands,
May 26 - 30, 200
A fluorescent mutant of the phosphorus-solubilizing fungus Penicillium bilaiae to image rhizosphere growth
Non-Peer ReviewedNovozymes manufactures and markets a phosphate inoculant, JumpStart®, based on the
phosphorus-solubilizing fungus Penicillium bilaiae. We are developing a mutant of this fungus
that expresses the DsRed-Express fluorescent protein, which will be used as a research tool to
allow us to see where and how P. bilaiae interacts with plant roots
Electron Neutrino Mass Measurement by Supernova Neutrino Bursts and Implications on Hot Dark Matter
We present a new strategy for measuring the electron neutrino mass (\mnue)
by future detection of a Galactic supernova in large underground detectors such
as the Super-Kamiokande (SK). This method is nearly model-independent and one
can get a mass constraint in a straightforward way from experimental data
without specifying any model parameters for profiles of supernova neutrinos. We
have tested this method using virtual data generated from a numerical model of
supernova neutrino emission by realistic Monte-Carlo simulations of the SK
detection. It is shown that this method is sensitive to \mnue of 3 eV
for a Galactic supernova, and this range is as low as the prediction of the
cold+hot dark matter scenario with a nearly degenerate mass hierarchy of
neutrinos, which is consistent with the current observations of solar and
atmospheric neutrino anomalies and density fluctuations in the universe.Comment: 4 pages including 1 figure, accepted by Phys. Rev. Let
Cosmological milestones and energy conditions
Until recently, the physically relevant singularities occurring in FRW
cosmologies had traditionally been thought to be limited to the "big bang", and
possibly a "big crunch". However, over the last few years, the zoo of
cosmological singularities considered in the literature has become considerably
more extensive, with "big rips" and "sudden singularities" added to the mix, as
well as renewed interest in non-singular cosmological events such as "bounces"
and "turnarounds". In this talk, we present an extensive catalogue of such
cosmological milestones, both at the kinematical and dynamical level. First,
using generalized power series, purely kinematical definitions of these
cosmological events are provided in terms of the behaviour of the scale factor
a(t). The notion of a "scale-factor singularity" is defined, and its relation
to curvature singularities (polynomial and differential) is explored. Second,
dynamical information is extracted by using the Friedmann equations (without
assuming even the existence of any equation of state) to place constraints on
whether or not the classical energy conditions are satisfied at the
cosmological milestones. Since the classification is extremely general, and
modulo certain technical assumptions complete, the corresponding results are to
a high degree model-independent.Comment: 8 pages, 1 table, conference proceedings for NEB XII conference in
Nafplio, Greec
Large Extra Dimensions, Sterile neutrinos and Solar Neutrino Data
Solar, atmospheric and LSND neutrino oscillation results require a light
sterile neutrino, , which can exist in the bulk of extra dimensions.
Solar , confined to the brane, can oscillate in the vacuum to the zero
mode of and via successive MSW transitions to Kaluza-Klein states of
. This new way to fit solar data is provided by both low and
intermediate string scale models. From average rates seen in the three types of
solar experiments, the Super-Kamiokande spectrum is predicted with 73%
probability, but dips characteristic of the 0.06 mm extra dimension should be
seen in the SNO spectrum.Comment: 4 pages, 2 figure
Hubble Space Telescope Imaging of the Ultra-Compact High Velocity Cloud AGC 226067: A stripped remnant in the Virgo Cluster
We analyze the optical counterpart to the ultra-compact high velocity cloud
AGC 226067, utilizing imaging taken with the Advanced Camera for Surveys (ACS)
on the Hubble Space Telescope. The color magnitude diagram of the main body of
AGC 226067 reveals an exclusively young stellar population, with an age of
7--50 Myr, and is consistent with a metallicity of [Fe/H]0.3 as
previous work has measured via HII region spectroscopy. Additionally, the color
magnitude diagram is consistent with a distance of 17 Mpc,
suggesting an association with the Virgo cluster. A secondary stellar system
located 1.6' (8 kpc) away in projection has a similar stellar
population. The lack of an old red giant branch (5 Gyr) is contrasted
with a serendipitously discovered Virgo dwarf in the ACS field of view (Dw
J122147+132853), and the total diffuse light from AGC~226067 is consistent with
the luminosity function of the resolved 7--50 Myr stellar population. The
main body of AGC~226067 has a =11.30.3, or
=5.41.310 given the stellar population.
We searched 20 deg of imaging data adjacent to AGC~226067 in the Virgo
Cluster, and found two similar stellar systems dominated by a blue stellar
population, far from any massive galaxy counterpart -- if this population has
similar star formation properties as AGC~226067, it implies 0.1
yr in Virgo intracluster star formation. Given its unusual
stellar population, AGC~226067 is likely a stripped remnant and is plausibly
the result of compressed gas from the ram pressure stripped M86 subgroup
(350 kpc away in projection) as it falls into the Virgo Cluster.Comment: 9 pages, 4 figures, 1 table. Accepted by the Astrophysical Journa
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