12 research outputs found
Dynamical constraints on some orbital and physical properties of the WD0137-349 A/B binary system
In this paper I deal with the WD0137-349 binary system consisting of a white
dwarf (WD) and a brown dwarf (BD) in a close circular orbit of about 116 min.
I, first, constrain the admissible range of values for the inclination i by
noting that, from looking for deviations from the third Kepler law, the
quadrupole mass moment Q would assume unlikely large values, incompatible with
zero at more than 1-sigma level for i 43 deg. Then, by
conservatively assuming that the most likely values for i are those that
prevent such an anomalous behavior of Q, i.e. those for which the third Kepler
law is an adequate modeling of the orbital period, I obtain i=39 +/- 2 deg.
Such a result is incompatible with the value i=35 deg quoted in literature by
more than 2 sigma. Conversely, it is shown that the white dwarf's mass range
obtained from spectroscopic measurements is compatible with my experimental
range, but not for i=35 deg. As a consequence, my estimate of yields an
orbital separation of a=(0.59 +/- 0.05)R_Sun and an equilibrium temperature of
BD of T_eq=(2087 +/- 154)K which differ by 10% and 4%, respectively, from the
corresponding values for i=35 deg.Comment: LaTex2e, 11 pages, 3 figures, no tables. It refers to gr-qc/0611126
and better clarify the result obtained there. Accepted by Astrophysics and
Space Scienc
The Physical Role of Gravitational and Gauge Degrees of Freedom in General Relativity - II: Dirac versus Bergmann observables and the Objectivity of Space-Time
(abridged)The achievements of the present work include: a) A clarification of
the multiple definition given by Bergmann of the concept of {\it (Bergmann)
observable. This clarification leads to the proposal of a {\it main conjecture}
asserting the existence of i) special Dirac's observables which are also
Bergmann's observables, ii) gauge variables that are coordinate independent
(namely they behave like the tetradic scalar fields of the Newman-Penrose
formalism). b) The analysis of the so-called {\it Hole} phenomenology in strict
connection with the Hamiltonian treatment of the initial value problem in
metric gravity for the class of Christoudoulou -Klainermann space-times, in
which the temporal evolution is ruled by the {\it weak} ADM energy. It is
crucial the re-interpretation of {\it active} diffeomorphisms as {\it passive
and metric-dependent} dynamical symmetries of Einstein's equations, a
re-interpretation which enables to disclose their (nearly unknown) connection
to gauge transformations on-shell; this is expounded in the first paper
(gr-qc/0403081). The use of the Bergmann-Komar {\it intrinsic
pseudo-coordinates} allows to construct a {\it physical atlas} of 4-coordinate
systems for the 4-dimensional {\it mathematical} manifold, in terms of the
highly non-local degrees of freedom of the gravitational field (its four
independent {\it Dirac observables}), and to realize the {\it physical
individuation} of the points of space-time as {\it point-events} as a
gauge-fixing problem, also associating a non-commutative structure to each
4-coordinate system.Comment: 41 pages, Revtex
Application of Time Transfer Function to McVittie Spacetime: Gravitational Time Delay and Secular Increase in Astronomical Unit
We attempt to calculate the gravitational time delay in a time-dependent
gravitational field, especially in McVittie spacetime, which can be considered
as the spacetime around a gravitating body such as the Sun, embedded in the
FLRW (Friedmann-Lema\^itre-Robertson-Walker) cosmological background metric. To
this end, we adopt the time transfer function method proposed by Le
Poncin-Lafitte {\it et al.} (Class. Quant. Grav. 21:4463, 2004) and Teyssandier
and Le Poncin-Lafitte (Class. Quant. Grav. 25:145020, 2008), which is
originally related to Synge's world function and enables to
circumvent the integration of the null geodesic equation. We re-examine the
global cosmological effect on light propagation in the solar system. The
round-trip time of a light ray/signal is given by the functions of not only the
spacial coordinates but also the emission time or reception time of light
ray/signal, which characterize the time-dependency of solutions. We also apply
the obtained results to the secular increase in the astronomical unit, reported
by Krasinsky and Brumberg (Celest. Mech. Dyn. Astron. 90:267, 2004), and we
show that the leading order terms of the time-dependent component due to
cosmological expansion is 9 orders of magnitude smaller than the observed value
of , i.e., ~[m/century]. Therefore, it is not possible
to explain the secular increase in the astronomical unit in terms of
cosmological expansion.Comment: 13 pages, 2 figures, accepted for publication in General Relativity
and Gravitatio
Parametrized Post-Newtonian Orbital Effects in Extrasolar Planets
Perturbative Post-Newtonian variations of the standard osculating orbital
elements are obtained by using the two-body equations of motion in the
Parameterized Post-Newtonian theoretical framework. The results obtained are
applied to the Einstein and. Brans - Dicke theories. As a results, the
semi-major axis and eccentricity exhibit periodic variation, but no secular
changes.. The longitude of periastron and mean longitude at epoch experience
both secular and periodic shifts. The Post-Newtonian effects are calculated and
discussed for six extrasolar planets.Comment: Accepted for publication in Astrophys. Space Sc
Phenomenology of the Lense-Thirring effect in the Solar System
Recent years have seen increasing efforts to directly measure some aspects of
the general relativistic gravitomagnetic interaction in several astronomical
scenarios in the solar system. After briefly overviewing the concept of
gravitomagnetism from a theoretical point of view, we review the performed or
proposed attempts to detect the Lense-Thirring effect affecting the orbital
motions of natural and artificial bodies in the gravitational fields of the
Sun, Earth, Mars and Jupiter. In particular, we will focus on the evaluation of
the impact of several sources of systematic uncertainties of dynamical origin
to realistically elucidate the present and future perspectives in directly
measuring such an elusive relativistic effect.Comment: LaTex, 51 pages, 14 figures, 22 tables. Invited review, to appear in
Astrophysics and Space Science (ApSS). Some uncited references in the text
now correctly quoted. One reference added. A footnote adde
Galaxy bulges and their massive black holes: a review
With references to both key and oft-forgotten pioneering works, this article
starts by presenting a review into how we came to believe in the existence of
massive black holes at the centres of galaxies. It then presents the historical
development of the near-linear (black hole)-(host spheroid) mass relation,
before explaining why this has recently been dramatically revised. Past
disagreement over the slope of the (black hole)-(velocity dispersion) relation
is also explained, and the discovery of sub-structure within the (black
hole)-(velocity dispersion) diagram is discussed. As the search for the
fundamental connection between massive black holes and their host galaxies
continues, the competing array of additional black hole mass scaling relations
for samples of predominantly inactive galaxies are presented.Comment: Invited (15 Feb. 2014) review article (submitted 16 Nov. 2014). 590
references, 9 figures, 25 pages in emulateApJ format. To appear in "Galactic
Bulges", E. Laurikainen, R.F. Peletier, and D.A. Gadotti (eds.), Springer
Publishin
The g305 star-forming complex: Embedded massive star formation discovered by herschel hi-gal
We present a Herschel far-infrared study towards the rich massive star-forming complex G305, utilizing PACS 70, 160 ?m and SPIRE 250, 350, and 500 ?m observations from the Hi-GAL survey of the Galactic plane. The focus of this study is to identify the embedded massive star-forming population within G305, by combining far-infrared data with radio continuum, H2O maser, methanol maser, MIPS and Red MSX Source survey data available from previous studies. By applying a frequentist technique we are able to identify a sample of the most likely associations within our multiwavelength data set, which can then be identified from the derived properties obtained from fitted spectral energy distributions (SEDs). By SED modelling using both a simple modified blackbody and fitting to a comprehensive grid of model SEDs, some 16 candidate associations are identified as embedded massive star-forming regions. We derive a two-selection colour criterion from this sample of log (F70/F500)=1 and log (F160/F350)=1.6 to identify an additional 31 embedded massive star candidates with no associated star formation tracers. Using this result we can build a picture of the presentday star formation of the complex, and by extrapolating an initial mass function, suggest a current population of 2×104 young stellar objects (YSOs) present, corresponding to a star formation rate (SFR) of 0.01-0.02M yr-1. Comparing this resolved SFR, to extragalactic SFR tracers (based on the Kennicutt-Schmidt relation), we find that the star formation activity is underestimated by a factor of?2 in comparison to the SFR derived from the YSO population. © 2012 The Authors