Impact of stellar companions on precise radial velocities

Context: With the announced arrival of instruments such as ESPRESSO one can expect that several systematic noise sources on the measurement of precise radial velocity will become the limiting factor instead of photon noise. A stellar companion within the fiber is such a possible noise source. Aims: With this work we aim at characterizing the impact of a stellar companion within the fiber to radial velocity measurements made by fiber-fed spectrographs. We consider the contaminant star either to be part of a binary system whose primary star is the target star, or as a background/foreground star. Methods: To carry out our study, we used HARPS spectra, co-added the target with contaminant spectra, and then compared the resulting radial velocity with that obtained from the original target spectrum. We repeated this procedure and used different tunable knobs to reproduce the previously mentioned scenarios. Results: We find that the impact on the radial velocity calculation is a function of the difference between individual radial velocities, of the difference between target and contaminant magnitude, and also of their spectral types. For the worst-case scenario in which both target and contaminant star are well centered on the fiber, the maximum contamination for a G or K star may be higher than 10 cm/s, on average, if the difference between target and contaminant magnitude is $\Delta m$ < 10, and higher than 1 m/s if $\Delta m$ < 8. If the target star is of spectral type M, $\Delta m$ < 8 produces the same contamination of 10 cm/s, and a contamination may be higher than 1 m/sComment: Accepted for publication in A&A on 29/12/2019 - 14 page

Is Λ\LambdaCDM an effective CCDM cosmology?

We show that a cosmology driven by gravitationally induced particle production of all non-relativistic species existing in the present Universe mimics exactly the observed flat accelerating $\Lambda$CDM cosmology with just one dynamical free parameter. This kind of scenario includes the creation cold dark matter (CCDM) model [Lima, Jesus & Oliveira, JCAP 011(2010)027] as a particular case and also provides a natural reduction of the dark sector since the vacuum component is not needed to accelerate the Universe. The new cosmic scenario is equivalent to $\Lambda$CDM both at the background and perturbative levels and the associated creation process is also in agreement with the universality of the gravitational interaction and equivalence principle. Implicitly, it also suggests that the present day astronomical observations cannot be considered the ultimate proof of cosmic vacuum effects in the evolved Universe because $\Lambda$CDM may be only an effective cosmology.Comment: 6 pages, 2 figures, changes in the abstract, introduction, new references and typo correction

Impact of micro-telluric lines on precise radial velocities and its correction

Context: In the near future, new instruments such as ESPRESSO will arrive, allowing us to reach a precision in radial-velocity measurements on the order of 10 cm/s. At this level of precision, several noise sources that until now have been outweighed by photon noise will start to contribute significantly to the error budget. The telluric lines that are not neglected by the masks for the radial velocity computation, here called micro-telluric lines, are one such noise source. Aims: In this work we investigate the impact of micro-telluric lines in the radial velocities calculations. We also investigate how to correct the effect of these atmospheric lines on radial velocities. Methods: The work presented here follows two parallel lines. First, we calculated the impact of the micro-telluric lines by multiplying a synthetic solar-like stellar spectrum by synthetic atmospheric spectra and evaluated the effect created by the presence of the telluric lines. Then, we divided HARPS spectra by synthetic atmospheric spectra to correct for its presence on real data and calculated the radial velocity on the corrected spectra. When doing so, one considers two atmospheric models for the synthetic atmospheric spectra: the LBLRTM and TAPAS. Results: We find that the micro-telluric lines can induce an impact on the radial velocities calculation that can already be close to the current precision achieved with HARPS, and so its effect should not be neglected, especially for future instruments such as ESPRESSO. Moreover, we find that the micro-telluric lines' impact depends on factors, such as the radial velocity of the star, airmass, relative humidity, and the barycentric Earth radial velocity projected along the line of sight at the time of the observation.Comment: Accepted in A&

Efeito de cobertura verde com leguminosa perene na supressão da infestação de plantas daninhas do café em produção.

O objetivo deste trabalho foi avaliar o potencial de controle de espécies leguminosas perenes sobre as plantas daninhas do café (Coffea arabica) em produção. O experimento foi instalado em Patrocínio-MG, utilizando-se uma lavoura de café com idade de 8 anos, variedade catuaí, linhagem IAC-99, tendo espaçamento de 3,80 x 0,70m. Foram aplicados 10 tratamentos em esquema fatorial 4x2+2: 4 espécies de leguminosas perenes: (Arachis pintoi, Macrotyloma axillare, Neonotonia wightii e Calopogonium mucunoides); 2 espaçamentos de plantio das leguminosas (2 linhas de 0,50 m e 3 linhas entre 0,25 m) e 2 tratamentos adicionais de controle das plantas daninhas (capina manual e controle químico). O delineamento foi de blocos casualizados com 4 repetições. Não houve efeito do espaçamento de plantio das leguminosas na cobertura do solo, na infestação de plantas daninhas e no índice produtivo do café. No geral as leguminosas proporcionaram menor infestação das plantas daninhas, comparadas à capina manual e controle químico, sendo que no primeiro ano as espécies Macrotyloma axillare, Calopogonium mucunoides e Arachis pintoi obtiveram menores infestações, porém no segundo ano de condução do experimento, as espécies Macrotyloma axillare e Neonotonia wightii seguida pelo Arachis pintoi foram as que apresentaram menores infestações de plantas daninhas. Na cobertura do solo pelas leguminosas, inicialmente no primeiro ano, a espécie Arachis pintoi apresentou uma taxa de cobertura inferior às demais, porém no segundo ano essa espécie foi superior. Dentre as espécies de plantas daninhas identificadas, independente do tratamento utilizado, o picão-preto (Bidens pilosa) foi o mais freqüente, tanto no primeiro como no segundo ano. Não houve interferência das espécies leguminosas no índice produtivo do café

New Constraints on the Variable Equation of State Parameter from X-Ray Gas Mass Fractions and SNe Ia

Recent measurements are suggesting that we live in a flat Universe and that its present accelerating stage is driven by a dark energy component whose equation of state may evolve in time. Assuming two different parameterizations for the function $\omega(z)$, we constrain their free parameters from a joint analysis involving measurements from X-Ray luminosity of galaxy clusters and SNe type Ia data.Comment: paper, 6 pages, 1 figure Accepted by Int. Journal of Modern Physics D (IJPMD

New domestic processing methods: effect on potato nutritional composition

Background and objectives: Potatoes nutritional and bioactive features are influenced by thermal processing conditions, defining its nutritional composition and health impact. Consumers seek increasingly for faster domestic cooking methods, such as microwave cooking in alternative to current frying or baking. Also, several devices are being commercialized for healthier frying simulation, without a documented characterization of the final processed food nutritional data. Thus, this study aimed to assess and compare the influence of these domestic processing methods on the quality of potatoes processed with olive oil. Methods: Potatoes were processed by frying, baking, microwave and a low-fat frying device, with equivalent shape and olive oil amounts, except frying. Samples were evaluated for crude fat, fatty acid composition, vitamin E, total carotenoids and total phenols. Results: Microwave cooked potatoes presented similar fat contents as standard frying, higher than those achieved by baking or with the low-fat frying device tested, but the fatty acid composition was similar. Vitamin E loss was comparatively higher after frying but no significant differences were found for total carotenoids. Potatoes phenolic compounds were partially loss during cooking, being apparently higher after baking. Conclusions: The distinct nutritional features obtained highlight for the importance of detailing the food compositional tables regarding each processing method, including the “new” domestic methodologies, increasingly used by consumers