88 research outputs found
Updating Standard Solar Models
We present an updated version of our standard solar model (SSM) where helium
and heavy elements diffusion is included and the improved OPAL equation of
state (Rogers 1994, Rogers Swenson \& Iglesias 1996) is used. In such a way the
EOS is consistent with the adopted opacity tables, from the same Livermore
group, an occurrence which should further enhance the reliability of the model.
The results for the physical characteristics and the neutrino production of our
SSM are discussed and compared with previous works on the matter.Comment: compress uuencoded postscript file of 8 pages and two figures; for
any problem please write to [email protected]
The Cosmic-Ray Proton and Helium Spectra measured with the CAPRICE98 balloon experiment
A new measurement of the primary cosmic-ray proton and helium fluxes from 3
to 350 GeV was carried out by the balloon-borne CAPRICE experiment in 1998.
This experimental setup combines different detector techniques and has
excellent particle discrimination capabilities allowing clear particle
identification. Our experiment has the capability to determine accurately
detector selection efficiencies and systematic errors associated with them.
Furthermore, it can check for the first time the energy determined by the
magnet spectrometer by using the Cherenkov angle measured by the RICH detector
well above 20 GeV/n. The analysis of the primary proton and helium components
is described here and the results are compared with other recent measurements
using other magnet spectrometers. The observed energy spectra at the top of the
atmosphere can be represented by (1.27+-0.09)x10^4 E^(-2.75+-0.02) particles
(m^2 GeV sr s)^-1, where E is the kinetic energy, for protons between 20 and
350 GeV and (4.8+-0.8)x10^2 E^(-2.67+-0.06) particles (m^2 GeV nucleon^-1 sr
s)^-1, where E is the kinetic energy per nucleon, for helium nuclei between 15
and 150 GeV nucleon^-1.Comment: To be published on Astroparticle Physics (44 pages, 13 figures, 5
tables
Tracing mixing in stars: new beryllium observations of the open clusters NGC 2516, Hyades, and M67
Determinations of beryllium abundance in stars, together with lithium,
provide a key tool to investigate the so far poorly understood extra-mixing
processes at work in stellar interiors. We measured Be in three open
clusters,complementing existing Be surveys, and aiming at gathering a more
complete empirical scenario of the evolution of Be as a function of stellar age
and temperature. Specifically, we analyzed VLT/UVES spectra of members of NGC
2516, the Hyades, and M 67 to determine their Be and Li abundances. In the
first two clusters we focused on stars cooler than 5400 K, while the M 67
sample includes stars warmer than 6150 K, as well as two subgiants and two blue
stragglers. We also computed the evolution of Be for a 0.9 Mo star based on
standard evolutionary models. We find different emprical behaviours for stars
in different temperature bins and ages. Stars warmer than 6150 K show Be
depletion and follow a Be vs. Li correlation while Be is undepleted in stars in
the ~6150-5600 K range. NGC 2516 members cooler than 5400 K have not depleted
any Be, but older Hyades of similar temperature do show some depletion. Be is
severely depleted in the subgiants and blue stragglers. The results for warm
stars are in agreement with previous studies, supporting the hypothesis that
mixing in this temperature regime is driven by rotation. The same holds for the
two subgiants that have evolved from the "Li gap". This mechanism is instead
not the dominant one for solar-type stars. We show that Be depletion of cool
Hyades cannot simply be explained by the effect of increasing depth of the
convective zone. Finally, the different Be content of the two blue stragglers
suggests that they have formed by two different processes (i.e., collisions vs.
binary merging).Comment: 19 pages, 10 figures, accepted for publication in Astronomy &
Astrophysic
Extreme Energy Cosmic Rays (EECR) Observation Capabilities of an "Airwatch from Space'' Mission
The longitudinal development and other characteristics of the EECR induced
atmospheric showers can be studied from space by detecting the fluorescence
light induced in the atmospheric nitrogen. According to the Airwatch concept a
single fast detector can be used for measuring both intensity and time
development of the streak of fluorescence light produced by the atmospheric
shower induced by an EECR. In the present communication the detection
capabilities for the EECR observation from space are discussed.Comment: 3 pages (LaTeX). To appear in the Proceedings of TAUP'9
Does Solar Physics Provide Constraints to Weakly Interacting Massive Particles?
We investigate whether present data on helioseismology and solar neutrino
fluxes may constrain WIMP--matter interactions in the range of WIMP parameters
under current exploration in WIMP searches. We find that, for a WIMP mass of 30
GeV, once the effect of the presence of WIMPs in the Sun's interior is
maximized, the squared isothermal sound speed is modified, with respect to the
standard solar model, by at most 0.4% at the Sun's center. The maximal effect
on the Boron-8 solar neutrino flux is a reduction of 4.5%. Larger masses lead
to smaller effects. These results imply that present sensitivities in the
measurements of solar properties, though greatly improved in recent years, do
not provide information or constraints on WIMP properties of relevance for dark
matter. Furthermore, we show that, when current bounds from direct WIMP
searches are taken into account, the effect induced by WIMPs with dominant
coherent interactions are drastically reduced as compared to the values quoted
above. The case of neutralinos in the minimal supersymmetric standard model is
also discussed.Comment: 31 pages, 2 tables and 9 figures, typeset with ReVTeX4. The paper may
also be found at http://www.to.infn.it/~fornengo/papers/helio.ps.gz or
through http://www.to.infn.it/astropart/index.htm
Neutrino masses: From fantasy to facts
Theory suggests the existence of neutrino masses, but little more. Facts are
coming close to reveal our fantasy: solar and atmospheric neutrino data
strongly indicate the need for neutrino conversions, while LSND provides an
intriguing hint. The simplest ways to reconcile these data in terms of neutrino
oscillations invoke a light sterile neutrino in addition to the three active
ones. Out of the four neutrinos, two are maximally-mixed and lie at the LSND
scale, while the others are at the solar mass scale. These schemes can be
distinguished at neutral-current-sensitive solar & atmospheric neutrino
experiments. I discuss the simplest theoretical scenarios, where the lightness
of the sterile neutrino, the nearly maximal atmospheric neutrino mixing, and
the generation of & all follow
naturally from the assumed lepton-number symmetry and its breaking. Although
the most likely interpretation of the present data is in terms of
neutrino-mass-induced oscillations, one still has room for alternative
explanations, such as flavour changing neutrino interactions, with no need for
neutrino mass or mixing. Such flavour violating transitions arise in theories
with strictly massless neutrinos, and may lead to other sizeable flavour
non-conservation effects, such as , conversion in
nuclei, unaccompanied by neutrino-less double beta decay.Comment: 33 pages, latex, 16 figures. Invited Talk at Ioannina Conference,
Symmetries in Intermediate High Energy Physics and its Applications, Oct.
1998, to be published by Springer Tracts in Modern Physics. Festschrift in
Honour of John Vergados' 60th Birthda
The small satellite NINA-MITA to study galactic and solar cosmic rays in low-altitude polar orbit
Abstract The satellite MITA, carrying on board the scientific payload NINA-2, was launched on July the 15th, 2000 from the cosmodrome of Plesetsk (Russia) with a Cosmos-3M rocket. The satellite and the payload are currently operating within nominal parameters. NINA-2 is the first scientific payload for the technological flight of the Italian small satellite MITA. The detector used in this mission is identical to the one already flying on the Russian satellite Resurs-O1 n.4 in a 840-km sun-synchronous orbit, but makes use of the extensive computer and telemetry capabilities of MITA bus to improve the active data acquisition time. NINA physics objectives are to study cosmic nuclei from hydrogen to iron in the energy range between 10 MeV/n and 1 GeV/n during the years 2000–2003, that is the solar maximum period. The device is capable of charge identification up to iron with isotope sensitivity up to oxigen. The 87.3 degrees, 460 km altitude polar orbit allows investigations of cosmic rays of solar and galactic origin, so to study long and short term solar transient phenomena, and the study of the trapped radiation at higher geomagnetic cutoff
Measurements of cosmic-ray electrons and positrons by the Wizard/CAPRICE collaboration
Two recent ballon-borne experiments have been performed by the WiZard/CAPRICE collaboration in order to study the electron and positron components in the cosmic radiation.
On 1994 August 8–9 the CAPRICE94 experiment flew from norther Canada and on 1998 May 28–29 the CAPRICE98 experiment flew from New Mexico, USA at altitudes corresponding to 3.9 and 5.5 g/cm2 of average residual atmosphere respectively. The apparatus were equipped with a Ring Imaging Cherenkov (RICH) detector, a time-of-flight system, a superconducting magnet spectrometer with a tracking system and a 7-radiation-length silicon-tungsten imaging calorimeter. The RICH used in 1994 had a solid NaF radiator while in 1998 the RICH had a C4F10 gaseous radiator.
We report on the electron and positron spectra and positron fraction at the top of the atmosphere from few hundred MeV to 40 GeV measured by these two experiments
THE SPACE TELESCOPE NINA: RESULTS OF A BEAM TEST CALIBRATION
Abstract In June 1998 the telescope NINA will be launched in space on board of the Russian satellite Resource-01 n.4. The main scientific objective of the mission is the study of the anomalous, galactic and solar components of the cosmic rays in the energy interval 10–200 MeV/n. The core of the instrument is a silicon detector whose performances have been tested with a particle beam at the GSI Laboratory in Germany in 1997; we report here on the results obtained during the beam calibration
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