Constraints on the structure and seasonal variations of Triton’s atmosphere from the 5 October 2017 stellar occultation and previous observations⋆

Context. A stellar occultation by Neptune's main satellite, Triton, was observed on 5 October 2017 from Europe, North Africa, and the USA. We derived 90 light curves from this event, 42 of which yielded a central flash detection. Aims. We aimed at constraining Triton's atmospheric structure and the seasonal variations of its atmospheric pressure since the Voyager 2 epoch (1989). We also derived the shape of the lower atmosphere from central flash analysis. Methods. We used Abel inversions and direct ray-tracing code to provide the density, pressure, and temperature profiles in the altitude range ∼8 km to ∼190 km, corresponding to pressure levels from 9 μbar down to a few nanobars. Results. (i) A pressure of 1.18 ± 0.03 μbar is found at a reference radius of 1400 km (47 km altitude). (ii) A new analysis of the Voyager 2 radio science occultation shows that this is consistent with an extrapolation of pressure down to the surface pressure obtained in 1989. (iii) A survey of occultations obtained between 1989 and 2017 suggests that an enhancement in surface pressure as reported during the 1990s might be real, but debatable, due to very few high S/N light curves and data accessible for reanalysis. The volatile transport model analysed supports a moderate increase in surface pressure, with a maximum value around 2005-2015 no higher than 23 μbar. The pressures observed in 1995-1997 and 2017 appear mutually inconsistent with the volatile transport model presented here. (iv) The central flash structure does not show evidence of an atmospheric distortion. We find an upper limit of 0.0011 for the apparent oblateness of the atmosphere near the 8 km altitude

The Dark Energy Survey: Prospects for Resolved Stellar Populations

Wide angle and deep surveys, regardless of their primary purpose, always sample a large number of stars in the Galaxy and in its satellite system. We here make a forecast of the expected stellar sample resulting from the Dark Energy Survey and the perspectives that it will open for studies of Galactic structure and resolved stellar populations in general. An estimated 1.2x10^8 stars will be sampled in DES grizY filters. This roughly corresponds to 20% of all DES sources. Most of these stars belong to the stellar thick disk and halo of the Galaxy. DES will probe low-mass stellar and sub-stellar objects at depths from 3 to 8 times larger than SDSS. The faint end of the main-sequence will be densely sampled beyond 10 kpc. The slope of the low mass end of the stellar IMF will be constrained to within a few hundredth dex, even in the thick disk and halo. In the sub-stellar mass regime, the IMF slope will be potentially constrained to within dlog ____phi(m) / dlog m ~ 0.1$. About 3x10^4 brown dwarf and at least 7.6x10^5 white dwarf candidates will be selected, the latter embedded into the thick disk and halo. The stellar halo flattening will also be constrained to within a few percent. DES will probe the main sequence of new Milky Way satellites and halo clusters for distances out to ~ 120 kpc, therefore yielding stellar surface density contrasts 1.6-1.7 times larger than those attainable with SDSS. It will also allow detection of these objects in the far reaches of the stellar halo, substantially increasing the number and quality of probes to the Galactic potential. Combined with northern samples, such as the SDSS, the DES stellar sample will yield constraints on the structure and stellar populations of Galactic components in unprecedented detail. In particular, the combined sample from both hemispheres will allow detailed studies of halo and thick disk asymmetries and triaxiality

PreCam, a Precursor Observational Campaign for Calibration of the Dark Energy Survey

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

A ring system detected around the Centaur (10199) Chariklo

Hitherto, rings have been found exclusively around the four giant planets in the Solar System. Rings are natural laboratories in which to study dynamical processes analogous to those that take place during the formation of planetary systems and galaxies. Their presence also tells us about the origin and evolution of the body they encircle. Here we report observations of a multichord stellar occultation that revealed the presence of a ring system around (10199) Chariklo, which is a Centaur-that is, one of a class of small objects orbiting primarily between Jupiter and Neptune-with an equivalent radius of 124â â 9â kilometres (ref. 2). There are two dense rings, with respective widths of about 7 and 3 kilometres, optical depths of 0.4 and 0.06, and orbital radii of 391 and 405 kilometres. The present orientation of the ring is consistent with an edge-on geometry in 2008, which provides a simple explanation for the dimming of the Chariklo system between 1997 and 2008, and for the gradual disappearance of ice and other absorption features in its spectrum over the same period. This implies that the rings are partly composed of water ice. They may be the remnants of a debris disk, possibly confined by embedded, kilometre-sized satellites. © 2014 Macmillan Publishers Limited.Fil: Braga Ribas, F.. Observatório Nacional; BrasilFil: Sicardy, B.. Universite Pierre et Marie Curie; FranciaFil: Ortiz, J.L.. Consejo Superior de Investigaciones Científicas; EspañaFil: Snodgrass, C.. Max Planck Institute for Solar System Research; AlemaniaFil: Roques, F.. Universite Pierre et Marie Curie; FranciaFil: Vieira Martins, R.. Centre National de la Recherche Scientifique; Francia. Universidade Federal do Rio de Janeiro; BrasilFil: Camargo, J.I.B.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Assafin, M.. Universidade Federal do Rio de Janeiro; BrasilFil: Duffard, R.. Consejo Superior de Investigaciones Científicas; EspañaFil: Jehin, E.. Université de Liège; BélgicaFil: Pollock, J.. Appalachian State University; Estados UnidosFil: Leiva, R.. Pontificia Universidad Católica de Chile; Chile. Universidad Católica de Chile; ChileFil: Emilio, M.. Universidade Estadual de Ponta Grossa; BrasilFil: MacHado, D.I.. Universidade Estadual Do Oeste Do Pará; BrasilFil: Colazo, C.. Universidad Nacional de Córdoba; Argentina. Ministerio de Educación de la Provincia de Córdoba; ArgentinaFil: Lellouch, E.. Universite Pierre et Marie Curie; FranciaFil: Skottfelt, J.. University of Copenhagen; Dinamarca. Geological Museum; DinamarcaFil: Gillon, M.. Université de Liège; BélgicaFil: Ligier, N.. Universite Pierre et Marie Curie; FranciaFil: Maquet, L.. Universite Pierre et Marie Curie; FranciaFil: Benedetti Rossi, G.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Gomes, A. Ramos. Universidade Federal do Rio de Janeiro; BrasilFil: Kervella, P.. Universite Pierre et Marie Curie; FranciaFil: Monteiro, H.. Instituto de Física e Química; BrasilFil: Sfair, R.. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Moutamid, M. El. Universite Pierre et Marie Curie; Francia. Centre National de la Recherche Scientifique; FranciaFil: Tancredi, G.. Observatorio Astronómico Los Molinos; Uruguay. Universidad de la República; UruguayFil: Spagnotto, J.. Observatorio El Catalejo la Pampa; ArgentinaFil: Maury, A.. San Pedro de Atacama Celestial Explorations; ChileFil: Morales, N.. Consejo Superior de Investigaciones Científicas; EspañaFil: Gil Hutton, Ricardo Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico ; ArgentinaFil: Roland, S.. Observatorio Astronómico Los Molinos; UruguayFil: Ceretta, A.. Universidad de la República; Uruguay. Observatorio del IPA; UruguayFil: Gu, S.-H.. Chinese Academy of Sciences; República de ChinaFil: Wang, X.-B.. Chinese Academy of Sciences; República de ChinaFil: Harpsøe, K.. University of Copenhagen; Dinamarca. Geological Museum; DinamarcaFil: Rabus, M.. Universidad Católica de Chile; Chile. Pontificia Universidad Católica de Chile; Chile. Max Planck Institute for Astronomy; AlemaniaFil: Manfroid, J.. Université de Liège; BélgicaFil: Opitom, C.. Université de Liège; BélgicaFil: Vanzi, L.. Pontificia Universidad Católica de Chile; Chile. Universidad Católica de Chile; ChileFil: Mehret, L.. Universidade Estadual de Ponta Grossa;Fil: Lorenzini, L.. Polo Astronômico Casimiro Montenegro Filho; BrasilFil: Schneiter, E.M.. Universidad Nacional de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Iate-conicet; ArgentinaFil: Melia, R.. Universidad Nacional de Córdoba; ArgentinaFil: Lecacheux, J.. Universite Pierre et Marie Curie; FranciaFil: Colas, F.. Centre National de la Recherche Scientifique; FranciaFil: Vachier, F.. Centre National de la Recherche Scientifique; FranciaFil: Widemann, T.. Universite Pierre et Marie Curie; FranciaFil: Almenares, L.. Universidad de la República; Uruguay. Observatorio Astronomico Los Molinos; UruguayFil: Sandness, R.G.. San Pedro de Atacama Celestial Explorations; ChileFil: Char, F.. Universidad de Antofagasta; ChileFil: Perez, V.. Universidad de la República; Uruguay. Observatorio Astronomico Los Molinos; UruguayFil: Lemos, P.. Universidad de la República; Uruguay. Observatorio Astronomico Los Molinos; UruguayFil: Martinez, N.. Universidad de la República; Uruguay. Observatorio Astronomico Los Molinos; UruguayFil: Jørgensen, U.G.. Universidad de Copenhagen; DinamarcaFil: Dominik, M.. University of St. Andrews; Reino UnidoFil: Roig, F.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Reichart, D.E.. University of North Carolina; Estados UnidosFil: Lacluyze, A.P.. University of North Carolina; Estados UnidosFil: Haislip, J.B.. University of North Carolina; Estados UnidosFil: Ivarsen, K.M.. University of North Carolina; Estados UnidosFil: Moore, J.P.. University of North Carolina; Estados UnidosFil: Frank, N.R.. University of North Carolina; Estados UnidosFil: Garcia Lambas, Diego Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; Argentin