Additional spectra of asteroid 1996 FG3, backup target of the ESA MarcoPolo-R mission

Near-Earth binary asteroid (175706) 1996 FG3 is the current backup target of the ESA MarcoPolo-R mission, selected for the study phase of ESA M3 missions. It is a primitive (C-type) asteroid that shows significant variation in its visible and near-infrared spectra. Here we present new spectra of 1996 FG3 and we compare our new data with other published spectra, analysing the variation in the spectral slope. The asteroid will not be observable again over the next three years at least. We obtained the spectra using DOLORES and NICS instruments at the Telescopio Nazionale Galileo (TNG), a 3.6m telescope located at El Roque de los Muchachos Observatory in La Palma, Spain. To compare with other published spectra of the asteroid, we computed the spectral slope S', and studied any plausible correlation of this quantity with the phase angle (alpha). In the case of visible spectra, we find a variation in spectral slope of Delta S' = 0.15 +- 0.10 %/10^3 A/degree for 3 < alpha < 18 degrees, in good agreement with the values found in the literature for the phase reddening effect. In the case of the near-infrared, we find a variation in the slope of Delta S' = 0.04 +- 0.08 %/10^3 A/degree for 6 < alpha < 51 degrees. Our computed variation in S' agrees with the only two values found in the literature for the phase reddening in the near-infrared. The variation in the spectral slope of asteroid 1996 FG3 shows a trend with the phase angle at the time of the observations, both in the visible and the near-infrared. It is worth noting that, to fully explain this spectral variability we should take into account other factors, like the position of the secondary component of the binary asteroid 1999 FG3 with respect to the primary, or the spin axis orientation at the time of the observations. More data are necessary for an analysis of this kind.Comment: 4 pages, 3 figures, Accepted in A&A 25 June 201

Effective spacetime from multi-dimensional gravity

We study the effective spacetimes in lower dimensions that can be extracted from a multidimensional generalization of the Schwarzschild-Tangherlini spacetimes derived by Fadeev, Ivashchuk and Melnikov ({\it Phys. Lett,} {\bf A 161} (1991) 98). The higher-dimensional spacetime has $D = (4 + n + m)$ dimensions, where $n$ and $m$ are the number of "internal" and "external" extra dimensions, respectively. We analyze the effective $(4 + n)$ spacetime obtained after dimensional reduction of the $m$ external dimensions. We find that when the $m$ extra dimensions are compact (i) the physics in lower dimensions is independent of $m$ and the character of the singularities in higher dimensions, and (ii) the total gravitational mass $M$ of the effective matter distribution is less than the Schwarzshild mass. In contrast, when the $m$ extra dimensions are large this is not so; the physics in $(4 + n)$ does explicitly depend on $m$, as well as on the nature of the singularities in high dimensions, and the mass of the effective matter distribution (with the exception of wormhole-like distributions) is bigger than the Schwarzshild mass. These results may be relevant to observations for an experimental/observational test of the theory.Comment: A typo in Eq. (24) is fixe

Transition from decelerated to accelerated cosmic expansion in braneworld universes

Braneworld theory provides a natural setting to treat, at a classical level, the cosmological effects of vacuum energy. Non-static extra dimensions can generally lead to a variable vacuum energy, which in turn may explain the present accelerated cosmic expansion. We concentrate our attention in models where the vacuum energy decreases as an inverse power law of the scale factor. These models agree with the observed accelerating universe, while fitting simultaneously the observational data for the density and deceleration parameter. The redshift at which the vacuum energy can start to dominate depends on the mass density of ordinary matter. For Omega = 0.3, the transition from decelerated to accelerated cosmic expansion occurs at z approx 0.48 +/- 0.20, which is compatible with SNe data. We set a lower bound on the deceleration parameter today, namely q > - 1 + 3 Omega/2, i.e., q > - 0.55 for Omega = 0.3. The future evolution of the universe crucially depends on the time when vacuum starts to dominate over ordinary matter. If it dominates only recently, at an epoch z < 0.64, then the universe is accelerating today and will continue that way forever. If vacuum dominates earlier, at z > 0.64, then the deceleration comes back and the universe recollapses at some point in the distant future. In the first case, quintessence and Cardassian expansion can be formally interpreted as the low energy limit of our model, although they are entirely different in philosophy. In the second case there is no correspondence between these models and ours.Comment: In V2 typos are corrected and one reference is added for section 1. To appear in General Relativity and Gravitatio

Stars in five dimensional Kaluza Klein gravity

In the five dimensional Kaluza Klein (KK) theory there is a well known class of static and electromagnetic--free KK--equations characterized by a naked singularity behavior, namely the Generalized Schwarzschild solution (GSS). We present here a set of interior solutions of five dimensional KK--equations. These equations have been numerically integrated to match the GSS in the vacuum. The solutions are candidates to describe the possible interior perfect fluid source of the exterior GSS metric and thus they can be models for stars for static, neutral astrophysical objects in the ordinary (four dimensional) spacetime.Comment: 15 pages, 8 figures. To be published in EPJ

Efficient fiber-optical interface for nanophotonic devices

We demonstrate a method for efficient coupling of guided light from a single mode optical fiber to nanophotonic devices. Our approach makes use of single-sided conical tapered optical fibers that are evanescently coupled over the last ~10 um to a nanophotonic waveguide. By means of adiabatic mode transfer using a properly chosen taper, single-mode fiber-waveguide coupling efficiencies as high as 97(1)% are achieved. Efficient coupling is obtained for a wide range of device geometries which are either singly-clamped on a chip or attached to the fiber, demonstrating a promising approach for integrated nanophotonic circuits, quantum optical and nanoscale sensing applications.Comment: 7 pages, 4 figures, includes supplementary informatio

Exclusive measurement of coherent eta photoproduction from the deuteron

Coherent photoproduction of eta mesons from the deuteron has been measured from threshold up to incident photon energies of 750 MeV using the photon spectrometer TAPS at the tagged photon facility at the Mainz microtron MAMI. For the first time, differential coherent cross sections have been deduced from the coincident detection of the eta meson and the recoil deuteron. A missing energy analysis was used for the suppression of background events so that a very clean identification of coherent eta-photoproduction was achieved. The resulting cross sections agree with previous experimental results except for angles around 90 deg in the photon-deuteron cm-system where they are smaller. They are compared to various model calculations.Comment: 4 pages, 4 figure

The internal structure and formation of early-type galaxies: the gravitational--lens system MG2016+112 at z=1.004

[Abridged] We combine our measurements of the velocity dispersion and the surface brightness profile of the lens galaxy D in the system MG2016+112 (z=1.004) with constraints from gravitational lensing to study its internal mass distribution. We find that: (i) dark matter accounts for >50% of the total mass within the Einstein radius (99% CL), excluding at the 8-sigma level that mass follows light inside the Einstein radius with a constant mass-to-light ratio (M/L). (ii) the total mass distribution inside the Einstein radius is well-described by a density profile ~r^-gamma' with an effective slope gamma'=2.0+-0.1+-0.1, including random and systematic uncertainties. (iii) The offset of galaxy D from the local Fundamental Plane independently constrains the stellar M/L, and matches the range derived from our models, leading to a more stringent lower limit of >60% on the fraction of dark matter within the Einstein radius (99%CL). Under the assumption of adiabatic contraction, the inner slope of the dark matter halo before the baryons collapsed is gamma_i<1.4 (68 CL), marginally consistent with the highest-resolution cold dark matter simulations that indicate gamma_i~1.5. This might indicate that either adiabatic contraction is a poor description of E/S0 formation or that additional processes play a role as well. Indeed, the apparently isothermal density distribution inside the Einstein radius, is not a natural outcome of adiabatic contraction models, where it appears to be a mere coincidence. By contrast, we argue that isothermality might be the result of a stronger coupling between luminous and dark-matter, possibly the result of (incomplete) violent relaxation processes. Hence, we conclude that galaxy D appears already relaxed 8 Gyr ago.Comment: 8 pages, 4 figures, ApJ, in press, minor change

SO(n + 1) Symmetric Solutions of the Einstein Equations in Higher Dimensions

A method of solving the Einstein equations with a scalar field is presented. It is applied to find higher dimensional vacuum metrics invariant under the group SO(n + 1) acting on n-dimensional spheres.Comment: 11 page

The visible and near-infrared spectra of asteroids in cometary orbits

We study the visible and near-infrared (NIR) spectral properties of different ACO populations and compare them to the independently determined properties of comets. We select our ACOs sample based on published dynamical criteria and present our own observational results obtained using the 10.4m Gran Telescopio Canarias (GTC), the 4.2m William Herschel Telescope (WHT), the 3.56m Telescopio Nazionale Galileo (TNG), and the 2.5m Isaac Newton Telescope (INT), all located at the El Roque de los Muchachos Observatory (La Palma, Spain), and the 3.0m NASA Infrared Telescope Facility (IRTF), located at the Mauna Kea Observatory, in Hawaii. We include in the analysis the spectra of ACOs obtained from the literature. We derive the spectral class and the visible and NIR spectral slopes. We also study the presence of hydrated minerals by studying the 0.7 $\mu$m band and the UV-drop below 0.5 $\mu$m associated with phyllosilicates. We present new observations of 17 ACOs, 11 of them observed in the visible, 2 in the NIR and 4 in the visible and NIR. We also discuss the spectra of 12 ACOs obtained from the literature. All but two ACOs have a primitive-like class spectrum (X or D-type). Almost 100\% of the ACOs in long-period cometary orbits (Damocloids) are D-types. Those in Jupiter family comet orbits (JFC-ACOs) are $\sim$ 60\% D-types and $\sim$ 40\% X-types. The mean spectral slope $S'$ of JFC-ACOs is 9.7 $\pm$ 4.6 \%/1000 \AA \ and for the Damocloids this is 12.2 $\pm$ 2.0 \%/1000 \AA . No evidence of hydration on the surface of ACOs is found from their visible spectra. The slope and spectral class distribution of ACOs is similar to that of comets. The spectral classification, the spectral slope distribution of ACOs, and the lack of spectral features indicative of the presence of hydrated minerals on their surface, strongly suggest that ACOs are likely dormant or extinct comets.Comment: 11 pages, 10 Figures, published in A&

Visible and near-infrared observations of asteroid 2012 DA14 during its closest approach of February 15, 2013

Near-Earth asteroid 2012 DA14 made its closest approach on February 15, 2013, when it passed at a distance of 27,700 km from the Earth's surface. It was the first time an asteroid of moderate size was predicted to approach that close to the Earth, becoming bright enough to permit a detailed study from ground-based telescopes. Asteroid 2012 DA14 was poorly characterized before its closest approach. We acquired data using several telescopes on four Spanish observatories: the 10.4m Gran Telescopio Canarias (GTC) and the 3.6m Telescopio Nazionale Galileo (TNG), both in the El Roque de los Muchachos Observatory (ORM, La Palma); the 2.2m CAHA telescope, in the Calar Alto Observatory (Almeria); the f/3 0.77m telescope in the La Hita Observatory (Toledo); and the f/8 1.5m telescope in the Sierra Nevada Observatory (OSN, Granada). We obtained visible and near-infrared color photometry, visible spectra and time-series photometry. Visible spectra together with color photometry of 2012 DA14 show that it can be classified as an L-type asteroid, a rare spectral type with a composition similar to that of carbonaceous chondrites. The time-series photometry provides a rotational period of 8.95 +- 0.08 hours after the closest approach, and there are indications that the object suffered a spin-up during this event. The large amplitude of the light curve suggests that the object is very elongated and irregular, with an equivalent diameter of around 18m. We obtain an absolute magnitude of H_R = 24.5 +- 0.2, corresponding to H_V = 25.0 +- 0.2. The GTC photometry also gives H_V = 25.29 +- 0.14. Both values agree with the value listed at the Minor Planet Center shortly after discovery. From the absolute photometry, together with some constraints on size and shape, we compute a geometric albedo of p_V = 0.44 +- 0.20, which is slightly above the range of albedos known for L-type asteroids (0.082 - 0.405).Comment: 7 pages, 4 figures, 1 table. Accepted in A&A (June 17 2013