Showing papers by "Julio Camargo published in 2013"
Pierre-and-Marie-Curie University1, Spanish National Research Council2, Federal University of Rio de Janeiro3, Ponta Grossa State University4, Universidade Federal de Santa Catarina5, University of Antofagasta6, National Institute for Space Research7, Pontifical Catholic University of Chile8, University of Liège9, Centre national de la recherche scientifique10, University of Toulouse11, Appalachian State University12, University of North Carolina at Chapel Hill13
TL;DR: Braga Ribas et al. as discussed by the authors proposed a method to improve the quality of the data collected by the data collection system of the government of Brazil, using data from the Ministerio de Ciencia, Tecnologia e Innovacao.
Abstract: Fil: Braga Ribas, F.. Ministerio de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; Brasil; . Laboratoire d;
103 citations
TL;DR: In this paper, the authors investigated the possible causes for the observed non-coincidence between the optical and ICRF2 positions and found an analytical relation that describes the resulting centroid shift, as a function of the atmospheric seeing, the brightness ratio and the relative distance between the two contributing flux sources.
Abstract: We obtained improved optical positions for 300 ICRF2 sources - the Rio survey. We compared the Rio survey with 10 other selected optical astrometric surveys and studied the link between the Hipparcos Catalogue Reference Frame (HCRF) and the International Celestial Reference Frame, Second Realization (ICRF2). We investigated the possible causes for the observed non-coincidence between the optical and ICRF2 positions. The Rio survey positions were referred to the second version of the United States Naval Observatory CCD Astrograph Catalog (UCAC2), currently the best tested HCRF densification. The sources are between -90 degrees < delta < +30 degrees. We used two telescopes with suitable diameters and focal lengths to properly link the observed ICRF2 sources with the UCAC2, using intermediate brightness stars. We certified the astrometry done with many statistical tests. The average 'optical minus ICRF2' offsets and respective standard deviations in (alpha, delta) were -3 mas (41 mas) and +4 (45 mas). The Rio survey represents well the zero-point offset of the other surveys. The standard error of 3.5 mas found for the HCRF/ICRF2 link indicates an error excess that can be originated by a non-coincidence between the observed optical/VLBI positions. We thus discussed the influence of the errors from the UCAC2. Then, we searched for correlations with the source morphology, represented by structure indices defined in the radio and in the optical domain. Finally, we studied how the position offsets could originate from the perturbation of the optical point spread function (PSF) of the source's core, by a second source of flux. We found an analytical relation that describes the resulting centroid shift, as a function of the atmospheric seeing, the brightness ratio and the relative distance between the two contributing flux sources. Two scenarios, modelled by this relation, are discussed: an extinction window in the dust torus nearby the core, and a Galactic star near the line of sight.
20 citations
TL;DR: In this article, the authors used the Oren-Nayar reflexive model to map the inhomogeneous light scattering on the surface of the satellites of the Earth and fitted the occultation and eclipse light curves using semi-analytical models that take into account the gradual decrease of light over the shadow, the solar limb darkening and the solar phase angle.
Abstract: The light curves of mutual eclipses and occultations between the natural satellites of a planet allow us to obtain high-precision position and relative motion from differential photometry, enough to detect weak orbital disturbing forces, such as tidal forces. The observations are made during the equinoxes of the planet.
We studied 25 light curves observed in Brazil during the 2009 campaign of the Galilean satellites’ mutual phenomena. A narrow-band filter centred at 890 nm was used, strongly attenuating the Jupiter's scattered light. We fitted the occultation and eclipse light curves using semi-analytical models that take into account the gradual decrease of light over the shadow, the solar limb darkening and the solar phase angle. The Oren–Nayar reflexive model was used to map the inhomogeneous light scattering on the surface of the satellites. For the first time it is used in a work about mutual events. Here, we include the study that made us decide for this model.
We measured the impact parameter, relative velocity and central instant with average precisions of 7.46 km (2.2 mas), 0.08 km s−1 (0.02 mas s−1) and 0.42 s (6.13 km), respectively. The fit precision of the normalized light-curve fluxes ranged between 0.4 and 4.4 per cent.
13 citations
24 Oct 2013
TL;DR: PreCam as mentioned in this paper is a precursor observational campaign supporting the Dark Energy Survey (DES), which produces a photometric and astrometric catalog of nearly a hundred thousand standard stars within the DES footprint, while the PreCam instrument also serves as a prototype testbed for the DECam.
Abstract: PreCam, a precursor observational campaign supporting the Dark Energy Survey (DES), is designed to produce a photometric and astrometric catalog of nearly a hundred thousand standard stars within the DES footprint, while the PreCam instrument also serves as a prototype testbed for the Dark Energy Camera (DECam)'s hardware and software. This catalog represents a potential 100-fold increase in Southern Hemisphere photometric standard stars, and therefore will be an important component in the calibration of the Dark Energy Survey. We provide details on the PreCam instrument's design, construction and testing, as well as results from a subset of the 51 nights of PreCam survey observations on the University of Michigan Department of Astronomy's Curtis-Schmidt telescope at Cerro Tololo Inter-American Observatory. We briefly describe the preliminary data processing pipeline that has been developed for PreCam data and the preliminary results of the instrument performance, as well as astrometry and photometry of a sample of stars previously included in other southern sky surveys.
5 citations
TL;DR: PreCam as discussed by the authors is a precursor observational campaign supporting the Dark Energy Survey (DES), which produces a photometric and astrometric catalog of nearly a hundred thousand standard stars within the DES footprint, while the PreCam instrument also serves as a prototype testbed for the DECam.
Abstract: PreCam, a precursor observational campaign supporting the Dark Energy Survey (DES), is designed to produce a photometric and astrometric catalog of nearly a hundred thousand standard stars within the DES footprint, while the PreCam instrument also serves as a prototype testbed for the Dark Energy Camera (DECam)'s hardware and software. This catalog represents a potential 100-fold increase in Southern Hemisphere photometric standard stars, and therefore will be an important component in the calibration of the Dark Energy Survey. We provide details on the PreCam instrument's design, construction and testing, as well as results from a subset of the 51 nights of PreCam survey observations on the University of Michigan Department of Astronomy's Curtis-Schmidt telescope at Cerro Tololo Inter-American Observatory. We briefly describe the preliminary data processing pipeline that has been developed for PreCam data and the preliminary results of the instrument performance, as well as astrometry and photometry of a sample of stars previously included in other southern sky surveys.
4 citations
16 Sep 2013
3 citations