8,227 research outputs found
The effect of tides on the Sculptor dwarf spheroidal galaxy
Dwarf spheroidal galaxies (dSphs) appear to be some of the most dark matter
dominated objects in the Universe. Their dynamical masses are commonly derived
using the kinematics of stars under the assumption of equilibrium. However,
these objects are satellites of massive galaxies (e.g.\ the Milky Way) and thus
can be influenced by their tidal fields. We investigate the implication of the
assumption of equilibrium focusing on the Sculptor dSph by means of ad-hoc
-body simulations tuned to reproduce the observed properties of Sculptor
following the evolution along some observationally motivated orbits in the
Milky Way gravitational field. For this purpose, we used state-of-the-art
spectroscopic and photometric samples of Sculptor's stars. We found that the
stellar component of the simulated object is not directly influenced by the
tidal field, while the mass of the more diffuse DM halo is
stripped. We conclude that, considering the most recent estimate of the
Sculptor proper motion, the system is not affected by the tides and the stellar
kinematics represents a robust tracer of the internal dynamics. In the
simulations that match the observed properties of Sculptor, the present-day
dark-to-luminous mass ratio is within the stellar half-light radius
( kpc) and within the maximum radius of the analysed dataset
( kpc).Comment: 19 pages, 10 figures, accepted for publication in MNRAS. V3: updated
after editor comments See our playlist for simulation videos:
https://av.tib.eu/series/633/supplemental+videos+of+the+paper+the+effect+of+tides+on+the+sculptor+dwarf+spheroidal+galax
The impact of tidal errors on the determination of the Lense-Thirring effect from satellite laser ranging
The general relativistic Lense-Thirring effect can be detected by means of a
suitable combination of orbital residuals of the laser-ranged LAGEOS and LAGEOS
II satellites. While this observable is not affected by the orbital
perturbation induced by the zonal Earth solid and ocean tides, it is sensitive
to those generated by the tesseral and sectorial tides. The assessment of their
influence on the measurement of the parameter mu, with which the
gravitomagnetic effect is accounted for, is the goal of this paper. After
simulating the combined residual curve by calculating accurately the
mismodeling of the more effective tidal perturbations, it has been found that,
while the solid tides affect the recovery of mu at a level always well below
1%, for the ocean tides and the other long-period signals Delta mu depends
strongly on the observational period and the noise level: Delta mu(tides)
amounts to almost 2% after 7 years. The aliasing effect of K1 l=3 p=1 tide and
SRP(4241) solar radiation pressure harmonic, with periods longer than 4 years,
on the perigee of LAGEOS II yield to a maximum systematic uncertainty on
\m_{LT} of less than 4% over different observational periods. The zonal
18.6-year tide does not affect the combined residuals.Comment: 24 pages, 4 tables, 6 figures, submitted to Int. Journal of Mod.
Phys. D. Changes in auctorship, references and conten
Super-ASTROD: Probing primordial gravitational waves and mapping the outer solar system
Super-ASTROD (Super Astrodynamical Space Test of Relativity using Optical
Devices or ASTROD III) is a mission concept with 3-5 spacecraft in 5 AU orbits
together with an Earth-Sun L1/L2 spacecraft ranging optically with one another
to probe primordial gravitational-waves with frequencies 0.1 microHz - 1 mHz,
to test fundamental laws of spacetime and to map the outer solar system. In
this paper we address to its scientific goals, orbit and payload selection, and
sensitivity to gravitational waves.Comment: 7 pages, 1 figure, presented to 7th International LISA Symposium,
16-20 June 2008, Barcelona; submitted to Classical and Quantum Gravity;
presentation improve
On the perspectives of testing the Dvali-Gabadadze-Porrati gravity model with the outer planets of the Solar System
The multidimensional braneworld gravity model by Dvali, Gabadadze and Porrati
was primarily put forth to explain the observed acceleration of the expansion
of the Universe without resorting to dark energy. One of the most intriguing
features of such a model is that it also predicts small effects on the orbital
motion of test particles which could be tested in such a way that local
measurements at Solar System scales would allow to get information on the
global properties of the Universe. Lue and Starkman derived a secular
extra-perihelion \omega precession of 5\times 10^-4 arcseconds per century,
while Iorio showed that the mean longitude \lambda is affected by a secular
precession of about 10^-3 arcseconds per century. Such effects depend only on
the eccentricities e of the orbits via second-order terms: they are, instead,
independent of their semimajor axes a. Up to now, the observational efforts
focused on the dynamics of the inner planets of the Solar System whose orbits
are the best known via radar ranging. Since the competing Newtonian and
Einsteinian effects like the precessions due to the solar quadrupole mass
moment J2, the gravitoelectric and gravitomagnetic part of the equations of
motion reduce with increasing distances, it would be possible to argue that an
analysis of the orbital dynamics of the outer planets of the Solar System, with
particular emphasis on Saturn because of the ongoing Cassini mission with its
precision ranging instrumentation, could be helpful in evidencing the predicted
new features of motion. In this note we investigate this possibility in view of
the latest results in the planetary ephemeris field. Unfortunately, the current
level of accuracy rules out this appealing possibility and it appears unlikely
that Cassini and GAIA will ameliorate the situation.Comment: LaTex, 22 pages, 2 tables, 10 figures, 27 references. Reference [17]
added, reference [26] updated, caption of figures changed, small change in
section 1.
LAGEOS-type Satellites in Critical Supplementary Orbit Configuration and the Lense-Thirring Effect Detection
In this paper we analyze quantitatively the concept of LAGEOS--type
satellites in critical supplementary orbit configuration (CSOC) which has
proven capable of yielding various observables for many tests of General
Relativity in the terrestrial gravitational field, with particular emphasis on
the measurement of the Lense--Thirring effect.Comment: LaTex2e, 20 pages, 7 Tables, 6 Figures. Changes in Introduction,
Conclusions, reference added, accepted for publication in Classical and
Quantum Gravit
A uniform treatment of the orbital effects due to a violation of the Strong Equivalence Principle in the gravitational Stark-like limit
We analytically work out several effects which a violation of the Strong
Equivalence Principle (SEP) induces on the orbital motion of a binary system
constituted of self-gravitating bodies immersed in a constant and uniform
external field. We do not restrict to the small eccentricity limit. Moreover,
we do not select any specific spatial orientation of the external polarizing
field. We explicitly calculate the SEP-induced mean rates of change of all the
osculating Keplerian orbital elements of the binary, the perturbation of the
projection of the binary orbit onto the line-of-sight, the shift of the radial
velocity, and the range and range-rate signatures and as well. We find that the
ratio of the SEP precessions of the node and the inclination of the binary
depends only on and the pericenter of the binary itself, being independent on
both the magnitude and the orientation of the polarizing field, and on the
semimajor axis, the eccentricity and the node of the binary. Our results, which
do not depend on any particular SEP-violating theoretical scheme, can be
applied to quite general astronomical and astrophysical scenarios. They can be
used to better interpret present and future SEP experiments, especially when
several theoretical SEP mechanisms may be involved, and to suitably design new
dedicated tests.Comment: LaTex2e, 14 pages, no figures, no tables, 42 references. To appear in
Classical and Quantum Gravity (CQG
Porosity and Inclusion Detection in CFRP by Infrared Thermography
The ever wide use of composite materials in the aeronautical industry has evidenced the need for development of ever more effective nondestructive evaluation methodologies in order to reduce rejected parts and to optimize production costs. Infrared thermography has been recently enclosed amongst the standardized non destructive testing techniques, but its usefulness needs still complete assessment since it can be employed in several different arrangements and for many purposes. In this work, the possibility to detect slag inclusions and porosity is analyzed with both lock-in themography and pulse thermography in the transmission mode. To this end, carbon-fiber-peinforced polymers different specimens are specifically fabricated of several different stacking sequences and with embedded slag inclusions and porosity percentages. As main results, both of the techniques are found definitely able to reveal the presence of the defects above mentioned. Moreover, these techniques could be considered complementary in order to better characterize the nature of the detected defects
Evidence for supernova feedback sustaining gas turbulence in nearby star-forming galaxies
HI and CO observations indicate that the cold gas in galaxies is very
turbulent. However, the turbulent energy is expected to be quickly dissipated,
implying that some energy source is needed to explain the observations. The
nature of such turbulence was long unclear, as even the main candidate,
supernova (SN) feedback, seemed insufficient. Other mechanisms have been
proposed, but without reaching a general consensus. The key novelty of our work
is considering that the gas disc thickness and flaring increase the dissipation
timescale of turbulence, thus reducing the energy injection rate required to
sustain it. In excellent agreement with the theoretical expectations, we found
that the fraction of the SN energy (a.k.a. SN coupling efficiency) needed to
maintain the cold gas turbulence is %, solving a long-standing
conundrum.Comment: 3 pages, 1 figure, Proceedings IAU Symposium 373, accepte
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