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Grant
Agency: Cordis | Branch: H2020 | Program: IA | Phase: GALILEO-1-2014 | Award Amount: 4.37M | Year: 2015

DEMETRA aims to demonstrate the feasibility of delivering early EGNSS timing services to end users by utilising an operational demonstrator and conducting tests with pilot applications. Based on the current practice of national metrological laboratories, DEMETRA will define and develop a prototype of a European time disseminator, based on EGNSS., An array of important service features that are necessary for a wide variety of users will be added. These will include: high accuracy calibrated time transfer to a monitored and certified remote time stamping. Nine different time services are proposed for demonstration by consortium partners. These will be established at INRIM premises for two validation test campaigns: a closed loop test, aiming to validate the performances and the second test will be with user terminals located in a real user environment, integrated into the user application to test the real advantages and feasibility of the new proposed services. Envisaged end users are telecoms, power transmission, banks, and TV broadcasting networks. The DEMETRA partnership, including Scientific Institutions, GNSS Industries, and a service provider cover the different facets of the project, including an analysis of commercial potential in terms of market and business development. DEMETRA fits perfectly the objectives of the work program in relation to: innovation, demonstration of pilot applications, use of EGNOS and Galileo Early Services, intention to commercialise the developed service, certification, legal and societal acceptance fostering EGNSS adoption and Long term potential to set common standards in the field of GNSS applications. The proposed services could become the basis for European timing standards, facilitating the independence from GPS for the timing of critical European infrastructure and fostering the dissemination through Europe of common standardised time services, based on EGNSS.


Grant
Agency: Cordis | Branch: FP7 | Program: CP-FP | Phase: SPA.2013.2.1-01 | Award Amount: 3.17M | Year: 2014

The advent of wide-angle imaging of the inner heliosphere has revolutionised the study of the solar wind and, in particular, transient solar wind structures such as Coronal Mass Ejections (CMEs) and Co-rotating Interaction Regions (CIRs). CMEs comprise enormous plasma and magnetic field structures that are ejected from the Sun and propagate at what can be immense speeds through interplanetary space, while CIRs are characterised by extensive swathes of compressed plasma/magnetic field that form along flow discontinuities of solar origin that permeate the inner heliosphere. With Heliospheric Imaging came the unique ability to track the evolution of these features as they propagate through the inner heliosphere. Prior to the development of wide-angle imaging of the inner heliosphere, signatures of such solar wind transients could only be observed within a few solar radii of the Sun, and in the vicinity of a few near-Earth and interplanetary probes making in-situ measurements of the solar wind. Heliospheric Imaging has, for the first time, filled that vast and crucial observational gap. HELCATS provides an unprecedented focus for world-leading European expertise in the novel and revolutionary, European-led field of Heliospheric Imaging, in terms of instrumentation, data analysis, modelling and science. HELCATS is a strategic programme that aims to empower the wider scientific community, in Europe and beyond, by providing access to advanced catalogues - validated and augmented through the use of techniques and models - for the analysis of solar wind transients, based on observations from European-led space instrumentation. All participant groups are at the forefront of heliospheric research and bring distinct, yet highly complementary, skills to the project. HELCATS will add significant value to the exploitation of existing European space instrumentation, providing a strong foundation for enhanced exploitation and advancement of the heliospheric research in Europe.


Groenewegen M.A.T.,Koninklijke Sterrenwacht Van Belgie
Astronomy and Astrophysics | Year: 2012

For the best-studied nearby Galactic asymptotic giant branch (AGB) stars a wealth of observational data is typically available in the form of photometry, often extending into the sub-mm, spectra covering a wide wavelength range, and often also visibility curves. Almost 100 AGB stars and red super giants have been imaged as part of the MESS Herschel guaranteed time key program. This does not only add photometry points between 60 and 500 micron, but also intensity profiles at these wavelengths. Dust radiative transfer models are often used to analyse these types of datasets, but there are very many input parameters and therefore it is not straightforward how to derive a best fit. In order to facilitate this, the publicly available one-dimensional (1D) dust radiative transfer code DUSTY was modified and extended, and included as a subroutine in a minimazation code. The code allows a certain parameter set (typically luminosity, dust optical depth, dust temperature at the inner radius and slope of the density law) to be minimised against photometric and spectroscopic data, visibility curves and 1D intensity profiles as constraints. The code is described and first results are presented on the MESS targets OH 26.5 and TT Cyg. For OH26.5 previous findings regarding a two-component wind are confirmed, but with a smaller drop in mass loss (a factor of 5) than previously suggested. For TT Cyg it proved difficult to fit the Herschel intensity profiles and spectral energy distribution simultaneously. The best fits are obtained for density profiles that deviate strongly from r-2 and are more like r+3-+3.5. This is qualitatively consistent with hydrodynamical models that simulate the interaction of the stellar wind with the interstellar medium. © 2012 ESO. Source


Groenewegen M.A.T.,Koninklijke Sterrenwacht Van Belgie
Astronomy and Astrophysics | Year: 2012

Context. Mass loss is one of the fundamental properties of asymptotic giant branch (AGB) stars, but for stars with initial masses below ∼1 M ⊙, the mass loss on the first red giant branch (RGB) actually dominates mass loss on the AGB. Nevertheless, mass loss on the RGB is still often parameterised by a simple Reimers law in stellar evolution models. Aims. We study the infrared excess and mass loss of a sample of nearby RGB stars with reliably measured Hipparcos parallaxes and compare the mass loss to that derived for luminous stars in clusters. Methods. The spectral energy distributions of a well-defined sample of 54 RGB stars are constructed, and fitted with the dust radiative transfer model DUSTY. The central stars are modelled by MARCS model atmospheres. In a first step, the best-fit MARCS model is derived, basically determining the effective temperature. In a second step, models with a finite dust optical depth are fitted and it is determined whether the reduction in χ2 in such models with one additional free parameter is statistically significant. Results. Among the 54 stars, 23 stars are found to have a significant infrared excess, which is interpreted as mass loss. The most luminous star with L = 1860 L̇ is found to undergo mass loss, while none of the 5 stars with L < 262 L⊙ display evidence of mass loss. In the range 265 < L < 1500 L⊙, 22 stars out of 48 experience mass loss, which supports the notion of episodic mass loss. It is the first time that excess emission is found in stars fainter than ∼600 L⊙. The dust optical depths are translated into mass-loss rates assuming a typical expansion velocity of 10 km s-1 and a dust-to-gas ratio of 0.005. In this case, fits to the stars with an excess result in log Ṁ (M⊙ yr-1) = (1.4 ± 0.4)log L + (-13.2 ± 1.2) and log Ṁ (M⊙ yr-1) = (0.9 ± 0.3) log (L R/M) + (-13.4 ± 1.3) assuming a mass of 1.1 M ⊙ for all objects. We caution that if the expansion velocity and dust-to-gas ratio have different values from those assumed, the constants in the fit will change. If these parameters are also functions of luminosity, then this would affect both the slopes and the offsets. The mass-loss rates are compared to those derived for luminous stars in globular clusters, by fitting both the infrared excess, as in the present paper, and the chromospheric lines. There is excellent agreement between these values and the mass-loss rates derived from the chromospheric activity. There is a systematic difference with the literature mass-loss rates derived from modelling the infrared excess, and this has been traced to technical details on how the DUSTY radiative transfer model is run. If the present results are combined with those from modelling the chromospheric emission lines, we obtain the fits log Ṁ (M⊙ yr-1) = (1.0 ± 0.3)log L + (-12.0 ± 0.9) and log Ṁ (M⊙ yr-1) = (0.6 ± 0.2)log (L R/M) + (-11.9 ± 0.9), and find that the metallicity dependence is weak at best. The predictions of these mass-loss rate formula are tested against the recent RGB mass loss determination in NGC 6791. Using a scaling factor of ∼10 ± ∼ 5, both relations can fit this value. That the scaling factor is larger than unity suggests that the expansion velocity and/or dust-to-gas ratio, or even the dust opacities, are different from the values adopted. Angular diameters are presented for the sample. They may serve as calibrators in interferometric observations. © 2012 ESO. Source


Groenewegen M.A.T.,Koninklijke Sterrenwacht Van Belgie
Astronomy and Astrophysics | Year: 2013

Context. The metallicity dependence of the Cepheid period-luminosity (PL) relation is of importance in establishing the extragalactic distance scale. Aims. The aim of this paper is to investigate the metallicity dependence of the PL relation in V and K, based on a sample of 128 Galactic, 36 Large Magellanic Cloud (LMC), and 6 Small Magellanic Cloud (SMC) Cepheids with individual Baade-Wesselink (BW) distances (some of the stars also have an Hubble Space Telescope (HST) based and Hipparcos parallax or are in clusters) and individually determined metallicities from high-resolution spectroscopy. Methods. Literature values of the V-band, K-band, and radial velocity data were collected for the sample of Cepheids. Based on a (V-K) surface-brightness relation and a projection factor, distances were derived from a BW analysis. Results. The p-relation finally adopted is 1.50-0.24log P. The slope of this relation is based on the condition that the distance to the LMC does not depend on period or (V-K) colour and that the slope of the PL relation based on the BW distances agrees with that based on apparent magnitude. The zero point of the relation is tight to the Cepheids with HST and revised Hipparcos parallaxes as well as to Cepheids in clusters. The slope of the Galactic and LMC K-band relation formally agrees within the errors, and combining all Cepheids (including the SMC) results in a negligible metallicity dependence and a relation of MK = (-2.50 ± 0.08) + (-3.06 ± 0.06)log P. A similar conclusion is found for the reddening-free Wesenheit relation (W(VK) = K-0.13(V-K)), with MWVK = (-2.68 ± 0.08) + (-3.12 ± 0.06)log P. In the V-band the situation is more complex. The slope of the LMC and the Galactic PL relation differ at the 3σ level. Combining the sample nevertheless results in a metallicity term significant at the 2σ level: MV = (-1.55 ± 0.09) + (-2.33 ± 0.07)log P + (+0.23 ± 0.11)[Fe/H]. Taking only the Galactic Cepheids, the metallicity term is no longer significant, namely (+ 0.17 ± 0.25). Compared to the recent works by Storm et al. (2011a, A&A, 534, A94; 2011b, A&A, 534, A95), there is both agreement and disagreement. A similar dependence of the p-factor on period is found, but the zero point found here implies a shorter distance scale. The distance modulus (DM) to the LMC and SMC found here are 18.29 ± 0.02 and 18.73 ± 0.06 (statistical error on the mean), respectively. Systematic differences in reddening could have an effect of order +0.05 in DM. The details of the comparison of BW-based distances and Cepheids with HST and revised Hipparcos parallaxes also play a role. The method used by Storm et al. would lead to larger DM of 18.37 and 18.81 for the LMC and SMC, respectively. The LMC DM is shorter than the currently accepted value, which is in the range 18.42 to 18.55, and it is speculated that the p-factor may depend on metallicity. This is not predicted by theoretical investigations, but these same investigations do not predict a steep dependence on period either, indicating that additional theoretical work is warranted. © 2013 ESO. Source

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