Orbit determination of Transneptunian objects and Centaurs for the prediction of stellar occultations

The prediction of stellar occultations by Transneptunian objects and Centaurs is a difficult challenge that requires accuracy both in the occulted star position as for the object ephemeris. Until now, the most used method of prediction involving tens of TNOs/Centaurs was to consider a constant offset for the right ascension and for the declination with respect to a reference ephemeris. This offset is determined as the difference between the most recent observations of the TNO and the reference ephemeris. This method can be successfully applied when the offset remains constant with time. This paper presents an alternative method of prediction based on a new accurate orbit determination procedure, which uses all the available positions of the TNO from the Minor Planet Center database plus sets of new astrometric positions from unpublished observations. The orbit determination is performed through a numerical integration procedure (NIMA), in which we develop a specific weighting scheme. The NIMA method was applied for 51 selected TNOs/Centaurs. For this purpose, we have performed about 2900 new observations during 2007-2014. Using NIMA, we succeed in predicting the stellar occultations of 10 TNOs and 3 Centaurs between 2013 and 2015. By comparing the NIMA and JPL ephemerides, we highlighted the variation of the offset between them with time. Giving examples, we show that the constant offset method could not accurately predict 6 out of the 13 observed positive occultations successfully predicted by NIMA. The results indicate that NIMA is capable of efficiently refine the orbits of these bodies. Finally, we show that the astrometric positions given by positive occultations can help to further refine the orbit of the TNO and consequently the future predictions. We also provide the unpublished observations of the 51 selected TNOs and their ephemeris in a usable format by the SPICE library.Comment: 12 pages, 9 figures, accepted in A&

Alterações nas características químicas de um Cambissolo Háplico cultivado com melão

O presente trabalho avaliou alterações nas propriedades químicas em Cambissolo, em função do tempo de cultivo com melão, em Baraúna-RN. Selecionaram-se 4 áreas: mata nativa e áreas com um, dois e três anos de cultivo, com amostras coletadas nas camadas de 0-20 e 20-40 cm de profundidade. Foram determinados os teores de carbono orgânico, nitrogênio total, nitrato, fósforo disponível e bases trocáveis, a acidez potencial, pH, condutividade elétrica, soma de bases, capacidade de troca de cátions, saturação por bases e sódio e atividade da fração argila. Os dados foram submetidos à análise de variância e ajustados à equação de regressão com médias comparadas por Tukey a 5% de probabilidade. O tempo de cultivo influenciou todas as características químicas, exceto nitrogênio total. Os teores de cálcio e a CTC reduziram com o tempo de cultivo, tendo as demais características químicas apresentado tendência ao incremento. A camada superficial apresentou valores mais elevados para a maioria das características químicas, exceto nitrato e magnésio

Astrometry of the main satellites of Uranus: 18 years of observations

We determine accurate positions of the main satellites of Uranus: Miranda, Ariel, Umbriel, Titania, and Oberon. Positions of Uranus, as derived from those of these satellites, are also determined. The observational period spans from 1992 to 2011. All runs were made at the Pico dos Dias Observatory, Brazil. We used the software called Platform for Reduction of Astronomical Images Automatically (PRAIA) to minimise (digital coronography) the influence of the scattered light of Uranus on the astrometric measurements and to determine accurate positions of the main satellites. The positions of Uranus were then indirectly determined by computing the mean differences between the observed and ephemeris positions of these satellites. A series of numerical filters was applied to filter out spurious data. These filters are mostly based on the comparison between the positions of Oberon with those of the other satellites and on the offsets as given by the differences between the observed and ephemeris positions of all satellites. We have, for the overall offsets of the five satellites, -29 (+/-63) mas in right ascension and -27 (+/-46) mas in declination. For the overall difference between the offsets of Oberon and those of the other satellites, we have +3 (+/-30) mas in right ascension and -2 (+/-28) mas in declination. Ephemeris positions for the satellites were determined from DE432+ura111. Comparisons using other modern ephemerides for the solar system -INPOP13c- and for the motion of the satellites -NOE-7-2013- were also made. They confirm that the largest contribution to the offsets we find comes from the motion of the barycenter of the Uranus system around the barycenter of the solar system, as given by the planetary ephemerides. Catalogues with the observed positions are provided.Comment: 13 pages, 21 figure

Irrigação na cultura do chuchu.

A presente publicação tem por objetivo orientar produtores e técnicos ligados à produção de chuchu sobre procedimentos e informações técnicas simples e atuais sobre os principais sistemas de irrigação e métodos de manejo da água que podem ser usados com sucesso na cultura.bitstream/item/127635/1/CT-139X.pd

Astrometric positions for 18 irregular satellites of giant planets from 23 years of observations

The irregular satellites of the giant planets are believed to have been captured during the evolution of the solar system. Knowing their physical parameters, such as size, density, and albedo is important for constraining where they came from and how they were captured. The best way to obtain these parameters are observations in situ by spacecrafts or from stellar occultations by the objects. Both techniques demand that the orbits are well known. We aimed to obtain good astrometric positions of irregular satellites to improve their orbits and ephemeris. We identified and reduced observations of several irregular satellites from three databases containing more than 8000 images obtained between 1992 and 2014 at three sites (Observat\'orio do Pico dos Dias, Observatoire de Haute-Provence, and European Southern Observatory - La Silla). We used the software PRAIA (Platform for Reduction of Astronomical Images Automatically) to make the astrometric reduction of the CCD frames. The UCAC4 catalog represented the International Celestial Reference System in the reductions. Identification of the satellites in the frames was done through their ephemerides as determined from the SPICE/NAIF kernels. Some procedures were followed to overcome missing or incomplete information (coordinates, date), mostly for the older images. We managed to obtain more than 6000 positions for 18 irregular satellites: 12 of Jupiter, 4 of Saturn, 1 of Uranus (Sycorax), and 1 of Neptune (Nereid). For some satellites the number of obtained positions is more than 50\% of what was used in earlier orbital numerical integrations. Comparison of our positions with recent JPL ephemeris suggests there are systematic errors in the orbits for some of the irregular satellites. The most evident case was an error in the inclination of Carme.Comment: 9 pages, with 3 being online materia

Parâmetros genéticos estimados sob um modelo multicaracterística para características reprodutivas de ovelhas da raça Morada Nova.

Resumo: O objetivo do presente estudo foi estimar parâmetros genéticos para características reprodutivas de ovelhas da raça Morada Nova. Utilizou-se, neste estudo, dados pertencentes ao núcleo de conservação da Embrapa Caprinos e Ovinos localizada na cidade de Sobral-CE e gerenciados pelo Programa de Melhoramento Genético de Caprinos e Ovinos de Corte (GENECOC). As características avaliadas foram intervalo de partos (IEP), dias para o parto (DP), período de gestação (PG) e número de serviços por concepção (NSC). As estimativas dos parâmetros genéticos e fenotípicos foram obtidas pelo método da Máxima Verossimilhança Restrita Livre de Derivadas (REML), sob modelo animal multicaracterística, usando o aplicativo MTDFREML. As estimativas de herdabilidades foram próximas de zero para IEP e DP, baixa para PG e moderada para NSC. As estimativas indicam que as características estudadas estão sobre maior influência ambiental do que genética. [Estimated genetic parameters for reproductive traits in Morada Nova breed sheep under a multi-trait model]. Abstract: The aim of the present study was to estimate genetic parameters for reproductive traits of ewes of Morada Nova breed sheep. Data from the conservation flock of Embrapa Caprinos e Ovinos, located in Sobral - CE, controlled by the ?Programa de Melhoramento Genético de Caprinos e Ovinos de Corte? (GENECOC), were used in this study. The traits evaluated were lambing interval (IEP), lambing day (DP), gestation length (PG) and number of service per conception number (NSC). The estimative of phenotypic and genetic parameters were obtained by Derivative Free Restricted Maximum Likelihood method, utilizing a multi-trait animal model and the MTDFREML software. The heritabilities estimates were next to zero for IEP and DP, low for PG and moderate for NSC. The estimates indicate that traits are under higher influence of the environment than genetic. Keywords: genetic correlations, heritability, mixed models, varianc

Results of two multi-chord stellar occultations by dwarf planet (1) Ceres

We report the results of two multi-chord stellar occultations by the dwarf planet (1) Ceres that were observed from Brazil on 2010 August 17, and from the USA on 2013 October 25. Four positive detections were obtained for the 2010 occultation, and nine for the 2013 occultation. Elliptical models were adjusted to the observed chords to obtain Ceres' size and shape. Two limb fitting solutions were studied for each event. The first one is a nominal solution with an indeterminate polar aspect angle. The second one was constrained by the pole coordinates as given by Drummond et al. Assuming a Maclaurin spheroid, we determine an equatorial diameter of 972 $\pm$ 6 km and an apparent oblateness of 0.08 $\pm$ 0.03 as our best solution. These results are compared to all available size and shape determinations for Ceres made so far, and shall be confirmed by the NASA's Dawn space mission.Comment: 9 pages, 6 figures. Accepted for publication in MNRA

The first observed stellar occultations by the irregular satellite Phoebe (Saturn IX) and improved rotational period

peer reviewedWe report six stellar occultations by Phoebe (Saturn IX), an irregular satellite of Saturn, obtained between mid-2017 and mid-2019. The 2017 July 6 event was the first stellar occultation by an irregular satellite ever observed. The occultation chords were compared to a 3D shape model of the satellite obtained from Cassini observations. The rotation period available in the literature led to a sub-observer point at the moment of the observed occultations where the chords could not fit the 3D model. A procedure was developed to identify the correct sub-observer longitude. It allowed us to obtain the rotation period with improved precision compared to the currently known value from literature. We show that the difference between the observed and the predicted sub-observer longitude suggests two possible solutions for the rotation period. By comparing these values with recently observed rotational light curves and single- chord stellar occultations, we can identify the best solution for Phoebe's rotational period as 9.27365 ± 0.00002 h. From the stellar occultations, we also obtained six geocentric astrometric positions in the ICRS as realized by the Gaia DR2 with uncertainties at the 1-mas level

Influência da carbonização na anatomia da madeira Dinizia excelsa Ducke.

Esse trabalho caracteriza as estruturas anatômicas da madeira e carvão vegetal de Dinizia excelsa Ducke e avalia as alterações anatômicas consequentes do processo de carbonização. Foi realizada a descrição anatômica para madeira e carvão, os parâmetros anatômicos foram submetidos à estatística descritiva para caracterização anatômica do lenho e do carvão. O efeito da carbonização sobre as características anatômicas da madeira foi verificado utilizando "modelos lineares generalizados - GLM para medidas repetidas". Maior parte das características anatômicas qualitativas foi mantida. Porém, algumas sofreram alterações de forma ou foram rompidas após a carbonização. A forma dos vasos foi afetada pela carbonização. O diâmetro tangencial do lume dos vasos (-32,93%) e a altura dos raios (+ 10,41%) variaram significativamente