108 research outputs found
Constraining the Nordtvedt parameter with the BepiColombo Radioscience experiment
BepiColombo is a joint ESA/JAXA mission to Mercury with challenging
objectives regarding geophysics, geodesy and fundamental physics. The Mercury
Orbiter Radioscience Experiment (MORE) is one of the on-board experiments,
including three different but linked experiments: gravimetry, rotation and
relativity. The aim of the relativity experiment is the measurement of the
post-Newtonian parameters. Thanks to accurate tracking between Earth and
spacecraft, the results are expected to be very precise. However, the outcomes
of the experiment strictly depends on our "knowledge" about solar system:
ephemerides, number of bodies (planets, satellites and asteroids) and their
masses. In this paper we describe a semi-analytic model used to perform a
covariance analysis to quantify the effects, on the relativity experiment, due
to the uncertainties of solar system bodies parameters. In particular, our
attention is focused on the Nordtvedt parameter used to parametrize the
strong equivalence principle violation. After our analysis we estimated
which is about 1~order of magnitude
larger than the "ideal" case where masses of planets and asteroids have no
errors. The current value, obtained from ground based experiments and lunar
laser ranging measurements, is .
Therefore, we conclude that, even in presence of uncertainties on solar system
parameters, the measurement of by MORE can improve the current precision
of about 1~order of magnitude
The first search for variable stars in the open cluster NGC 6253 and its surrounding field
This work presents the first high-precision variability survey in the field
of the intermediate-age, metal--rich open cluster NGC 6253. Clusters of this
type are benchmarks for stellar evolution models. Continuous photometric
monitoring of the cluster and its surrounding field was performed over a time
span of ten nights using the Wide Field Imager mounted at the ESO-MPI 2.2m
telescope. High-quality timeseries, each composed of about 800 datapoints, were
obtained for 250,000 stars using ISIS and DAOPHOT packages. Candidate members
were selected by using the colour-magnitude diagrams and
period-luminosity-colour relations. Membership probabilities based on the
proper motions were also used. The membership of all the variables discovered
within a radius of 8 arcmin from the centre is discussed by comparing the
incidence of the classes in the cluster direction and in the surrounding field.
We discovered 595 variables and we also characterized most of them providing
their variability classes, periods, and amplitudes. The sample is complete for
short periods: we classified 20 pulsating variables, 225 contact systems, 99
eclipsing systems (22 Beta Lyr type, 59 Beta Per type, 18 RS CVn type), and 77
rotational variables. The time-baseline hampered the precise characterization
of 173 variables with periods longer than 4-5 days. Moreover, we found a
cataclysmic system undergoing an outburst of about 2.5 mag. We propose a list
of 35 variable stars (8 contact systems, 2 eclipsing systems, 15 rotational
variables, 9 long-period variables and the cataclysmic variable) as probable
members of NGC 6253.Comment: Astronomy and Astrophysics, in press. Extended version with tables
and light curve
Space tests of the strong equivalence principle:BepiColombo and the Sun-Earth Lagrangian points opportunity
The validity of General Relativity, after 100 years, is supported by solid
experimental evidence. However, there is a lot of interest in pushing the
limits of precision by other experiments. Here we focus our attention on the
equivalence principle, in particular the strong form. The results of ground
experiments and lunar laser ranging have provided the best upper limit on the
Nordtvedt parameter {\eta} that models deviations from the strong equivalence
principle. Its uncertainty is currently {\sigma}[{\eta}] =4.4
. In the first part of this paper we will describe the experiment, to
measure {\eta}, that will be done by the future mission BepiColombo. The
expected precision on {\eta} is . In the second part we will
consider the ranging between the Earth and a spacecraft orbiting near the
Sun-Earth Lagrangian points to get an independent measurement of {\eta}. In
this case, we forecast a constraint similar to that achieved by lunar laser
ranging.Comment: 11 pages, 2 figure
A quasi-complete mechanical model for a double torsion pendulum
We present a dynamical model for the double torsion pendulum nicknamed PETER,
where one torsion pendulum hangs in cascade, but off-axis, from the other. The
dynamics of interest in these devices lies around the torsional resonance, that
is at very low frequencies (mHz). However, we find that, in order to properly
describe the forced motion of the pendulums, also other modes must be
considered, namely swinging and bouncing oscillations of the two suspended
masses, that resonate at higher frequencies (Hz). Although the system has
obviously 6+6 Degrees of Freedom, we find that 8 are sufficient for an accurate
description of the observed motion. This model produces reliable estimates of
the response to generic external disturbances and actuating forces or torques.
In particular, we compute the effect of seismic floor motion (tilt noise) on
the low frequency part of the signal spectra and show that it properly accounts
for most of the measured low frequency noise.Comment: 15 pages, 6 figure
ESASky v.2.0: all the skies in your browser
With the goal of simplifying the access to science data to scientists and
citizens, ESA recently released ESASky (http://sky.esa.int), a new open-science
easy-to-use portal with the science-ready Astronomy data from ESA and other
major data providers. In this presentation, we announced version 2.0 of the
application, which includes access to all science-ready images, catalogues and
spectra, a feature to help planning of future JWST observations, the
possibility to search for data of all (targeted and serendipitously observed)
Solar System Objects in Astronomy images, a first support to mobile devices and
several other smaller usability features. We also discussed the future
evolution of the portal and the lessons learnt from the 1+ year of operations
from the point of view of access, visualization and manipulation of big
datasets (all sky maps, also called HiPS) and large catalogues (like e.g. the
Gaia DR1 catalogues or the Hubble Source Catalogue) and the design and
validation principles for the development of friendly GUIs for thin layer web
clients aimed at scientists.Comment: 4 pages, 2 figures, ADASS 2017 conference proceeding
Testing the gravitational redshift with an inner Solar System probe: the VERITAS case
The NASA Discovery-class mission VERITAS, selected in June 2021, will be
launched towards Venus after 2027. In addition to the science instrumentation
that will build global foundational geophysical datasets, VERITAS proposed to
conduct a technology demonstration for the Deep Space Atomic Clock (DSAC-2). A
first DSAC successfully operated in low-Earth orbit for more than two years,
demonstrated the trapped ion atomic clock technology, and established a new
level of performance for clocks in space. DSAC-2 would have further
improvements in size, power, and performance. It would host a
grade USO to produce a frequency output with short-term
stability of less than (where is the
averaging time). However, due to funding shortfalls, DSAC-2, had to be
canceled. The initially foreseen presence of an atomic clock on board the
probe, however, raised the question whether this kind of instrumentation could
be useful not only for navigation and time transfer but also for fundamental
physics tests. In this work, we consider the DSAC-2 atomic clock and VERITAS
mission as a specific example to measure possible discrepancies in the redshift
predicted by General Relativity by using an atomic clock onboard an
interplanetary spacecraft. In particular we investigate the possibility of
measuring possible violations of the Local Lorentz Invariance and Local
Position Invariance principles. We perform accurate simulations of the
experiment during the VERITAS cruise phase. We consider different
parametrizations of the possible violations of the General Relativity,
different operational conditions, and several different assumptions on the
expected measurement performance. Our analysis shows the scientific value of
atomic clocks like DSAC-2 hosted onboard interplanetary spacecraft.Comment: 15 pages, 9 figure
Optimizing the Earth-LISA "rendez-vous"
We present a general survey of heliocentric LISA orbits, hoping it might help
in the exercise of rescoping the mission. We try to semi-analytically optimize
the orbital parameters in order to minimize the disturbances coming from the
Earth-LISA interaction. In a set of numerical simulations we include
nonautonomous perturbations and provide an estimate of Doppler shift and
breathing as a function of the trailing angle.Comment: 18 pages, 16 figures. Submitted on CQ
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