Possible chromospheric activity cycles in AD Leo

AD Leo (GJ 388) is an active dM3 flare star extensively observed both in the quiescent and flaring states. Since this active star is near the fully-convective boundary, to study in detail its long-term chromospheric activity could be an appreciable contribution for the dynamo theory. Here, we analyze with the Lomb-Scargle periodogram the Ca II K line-core fluxes derived from CASLEO spectra obtained between 2001 and 2013 and the V magnitude from the ASAS database between 2004 and 2010. From both totally independent time-series, we obtain a possible activity cycle of period $\sim7$ years and a less-significant shorter one of $\sim2$ years. A tentative interpretation is that a dynamo operating near the surface could be generating the longer cycle, while a second dynamo operating in the deep convection zone could be responsible for the shorter one. Based on the long duration of our observing program at CASLEO and the fact that we observe simultaneously different spectral features, we also analyze the relation between simultaneous measurements of the Na I index ($R^{\prime}_D$), H$\alpha$ and Ca II K fluxes at different activity levels of AD Leo, including flares.Comment: 21 pages, 3 figures.Accepted for publication in ApJ

Gaia FGK Benchmark Stars: Effective temperatures and surface gravities

Large Galactic stellar surveys and new generations of stellar atmosphere models and spectral line formation computations need to be subjected to careful calibration and validation and to benchmark tests. We focus on cool stars and aim at establishing a sample of 34 Gaia FGK Benchmark Stars with a range of different metallicities. The goal was to determine the effective temperature and the surface gravity independently from spectroscopy and atmospheric models as far as possible. Fundamental determinations of Teff and logg were obtained in a systematic way from a compilation of angular diameter measurements and bolometric fluxes, and from a homogeneous mass determination based on stellar evolution models. The derived parameters were compared to recent spectroscopic and photometric determinations and to gravity estimates based on seismic data. Most of the adopted diameter measurements have formal uncertainties around 1%, which translate into uncertainties in effective temperature of 0.5%. The measurements of bolometric flux seem to be accurate to 5% or better, which contributes about 1% or less to the uncertainties in effective temperature. The comparisons of parameter determinations with the literature show in general good agreements with a few exceptions, most notably for the coolest stars and for metal-poor stars. The sample consists of 29 FGK-type stars and 5 M giants. Among the FGK stars, 21 have reliable parameters suitable for testing, validation, or calibration purposes. For four stars, future adjustments of the fundamental Teff are required, and for five stars the logg determination needs to be improved. Future extensions of the sample of Gaia FGK Benchmark Stars are required to fill gaps in parameter space, and we include a list of suggested candidates.Comment: Accepted by A&A; 34 pages (printer format), 14 tables, 13 figures; language correcte

KIC~8975515: a fast-rotating (γ\gamma Dor - δ\delta Sct) hybrid star with Rossby modes and a slower δ\delta Sct companion in a long-period orbit

{KIC~8975515 is a \emph{Kepler} double-lined spectroscopic binary system with hybrid pulsations. Two components have similar atmospheric properties (T$_{\rm eff}$ $\sim$ 7400~K), and one of them is a fast rotator ($v\sin i = 162$ versus 32 km/s). Our aim is to study the \emph {Kepler} light curve in great detail in order to determine the frequencies of the pulsations, to search for regular spacing patterns in the Fourier spectrum, if any, and to discuss their origin in the context of binarity and fast rotation. In this paper, we study the properties of the stellar pulsations based on a careful analysis in the low-, intermediate- and high-frequency regions of the Fourier spectrum. This is done by performing repeated frequency-search analyses with successive prewhitenings of all the significant frequencies detected in the spectrum. Moreover, we searched for regular period spacings among the $g$ modes, as well as frequency splitting among the $g$ and $p$ modes. In the low-frequency regime, five regular period spacing patterns including one series of prograde $g$ modes and four series of retrograde $r$ modes were detected. The $r$ modes are well-distributed with respect to the harmonics of the rotational frequency of the fast-rotating star $f_{\rm rot}$ = 1.647 d$^{-1}$. The dominant $g$ mode is $f_{2}$ = 2.37 d$^{-1}$. The strongest p mode, at $f_{1}$ = 13.97 d$^{-1}$, forms a singlet. In the high-frequency region, we identified two multiplets of regularly split $p$ modes with mean frequency spacings of 0.42 d$^{-1}$ and 1.65 d$^{-1}$. We detected some series of retrograde $r$ and prograde $g$ modes as well as two multiplets of $p$ modes with frequency spacings related to the stellar rotation of both components of the twin system KIC~8975515. We identified the fast-rotating component as a hybrid pulsator with $r$ modes and the slowly-rotating component as a $\delta$ Sct pulsator.Comment: Accepted to publish on A \&

Amphibiomorphic modeled and painted pottery from argentine patagonia and Central-Southern Chile. Functional interpretation and identification of species based on mimetic and aposematic traits

This work aims to identify attributes or features related to endemic amphibians in modeled and painted pottery from central-southern Chile and north-western Argentina. From this work, we were able to identify four species of amphibians represented in certain types of modeled and painted pottery, and we also complemented this data with modern references and ethnohistorical chronicles of the potential use given to this pottery in particular. This contribution postulates that some elements of the black-onred pottery of the Early Ceramic Period of Araucaniá in central-southern Chile and of Patagonia in northwestern Argentina, seek to highlight amphibiomorphic characteristics such as exophthalmia (protruding eyes) and aposematism (brilliant coloring and brightness of the vessel by using an engobe decoration). Based on the ethnohistorical data of the area, it is also proposed that these vessels could be linked to the exclusive use of highly toxic substances. Finally, the results allowed us to explore the close ecological interaction between human groups and woodlands.Fil: Perez, Alberto Enrique. Universidad Católica de Temuco; ChileFil: Schuster, Veronica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Diversidad y Evolución Austral; ArgentinaFil: Jofré, Daniella P.. Universidad Católica de Temuco; Chil

Revisiting the 16 Cygni planet host at unprecedented precision and exploring automated tools for precise abundances

The binary system 16 Cygni is key in studies of the planet-star chemical composition connection, as only one of the stars is known to host a planet. This allows us to better assess the possible influence of planet interactions on the chemical composition of stars that are born from the same cloud and thus, should have a similar abundance pattern. In our previous work, we found clear abundance differences for elements with Z$\leq30$ between both components of this system, and a trend of these abundances as a function of the condensation temperature (T$_{c}$), which suggests a spectral chemical signature related to planet formation. In this work we show that our previous findings are still consistent even if we include more species, like the volatile N and neutron capture elements (Z $>$ 30). We report a slope with T$_{c}$ of $1.56 \pm 0.24 \times 10^{-5}$ dex K$^{-1}$, that is good agreement with both our previous work and recent results by Nissen and collaborators. We also performed some tests using ARES and iSpec to automatic measure the equivalent width and found T$_c$ slopes in reasonable agreement with our results as well. In addition, we determine abundances for Li and Be by spectral synthesis, finding that 16 Cyg A is richer not only in Li but also in Be, when compared to its companion. This may be evidence of planet engulfment, indicating that the T$_{c}$ trend found in this binary system may be a chemical signature of planet accretion in the A component, rather than a imprint of the giant planet rocky core formation on 16 Cyg B.Comment: 11 pages, 5 figures, accepted for publication in A&

Constraining a possible time-variation of the gravitational constant through "gravitochemical heating" of neutron stars

A hypothetical time-variation of the gravitational constant $G$ would cause neutron star matter to depart from beta equilibrium, due to the changing hydrostatic equilibrium. This forces non-equilibrium beta processes to occur, which release energy that is invested partly in neutrino emission and partly in heating the stellar interior. Eventually, the star arrives at a stationary state in which the temperature remains nearly constant, as the forcing through the change of $G$ is balanced by the ongoing reactions. Comparing the surface temperature of the nearest millisecond pulsar, PSR J0437-4715, inferred from ultraviolet observations, with our predicted stationary temperature, we estimate two upper limits for this variation: (1) $|\dot G/G| < 2 \times 10^{-10}$ yr$^{-1}$, if we allow direct Urca reactions operating in the neutron star core, and (2) $|\dot G/G| < 4 \times 10^{-12}$ yr$^{-1}$, considering only modified Urca reactions. Both results are competitive with those obtained by other methods, with (2) being among the most restrictive.Comment: 4 pages, including 2 figures. Accepted for publication in Phys. Rev. Lett. Revised version includes minor changes in the wording, and more substantial changes in the last 2 paragraphs (Discussion and Conclusions). Equations, figures, and results are unchange

Fundamental stellar parameters of benchmark stars from CHARA interferometry. I. Metal-poor stars

Benchmark stars are crucial as validating standards for current as well as future large stellar surveys of the Milky Way. However, the number of suitable metal-poor benchmarks is currently limited. We aim to construct a new set of metal-poor benchmarks, based on reliable interferometric effective temperature ($T_\text{eff}$) determinations and a homogeneous analysis with a desired precision of $1\%$ in $T_\text{eff}$. We observed ten late-type metal-poor dwarf and giants: HD2665, HD6755, HD6833, HD103095, HD122563, HD127243, HD140283, HD175305, HD221170, and HD224930. Only three of the ten stars (HD103095, HD122563, and HD140283) have previously been used as benchmarks. For the observations, we used the high angular resolution optical interferometric instrument PAVO at the CHARA array. We modelled angular diameters using 3D limb darkening models and determined $T_\text{eff}$ directly from the Stefan-Boltzmann relation, with an iterative procedure to interpolate over tables of bolometric corrections. Surface gravities ($\log(g)$) were estimated from comparisons to Dartmouth stellar evolution model tracks. We collected spectroscopic observations from the ELODIE and FIES spectrographs and estimated metallicities ($\mathrm{[Fe/H]}$) from a 1D non-LTE abundance analysis of unblended lines of neutral and singly ionized iron. We inferred $T_\text{eff}$ to better than $1\%$ for five of the stars (HD103095, HD122563, HD127243, HD140283, and HD224930). The $T_\text{eff}$ of the other five stars are reliable to between $2-3\%$; the higher uncertainty on the $T_\text{eff}$ for those stars is mainly due to their having a larger uncertainty in the bolometric fluxes. We also determined $\log(g)$ and $\mathrm{[Fe/H]}$ with median uncertainties of $0.03\,\mathrm{dex}$ and $0.09\,\mathrm{dex}$, respectively. These ten stars can, therefore, be adopted as a new, reliable set of metal-poor benchmarks.Comment: 13 pages, 7 figures, 8 tables + 10 online tables, abstract shortened to meet arXiv requirements, accepted in A&

Magnetoencephalographic assessment of changes in brain activity in normal aging when performing a task under interference conditions

Determinar si la realización de una tarea de reconocimiento con interferencia activa, producía cambios en los patrones de activación cerebral con respecto a la presentación de otra con interferencia pasiva. Población y metodología: en veinte ancianos sanos se midió con magnetoencefalografía. Se realizó a cada uno de ellos la escala de Memoria de Wechsler-III (WMS-III), la escala de Inteligencia de Wechsler, el Boston Naming Test, el test de fluidez verbal, el test de clasificación de tarjetas de Wisconsin, el trail Making Test y el test de colores y palabras (STROOP). Los registros se llevaron a cabo mediante un magnetoencefalógrafo de 148 canales capaz de medir la actividad magnética generada en toda la convexidad craneal. Resultados: encontramos una mayor activación en la condición de interferencia activa en las regiones mediales temporales, corteza visual, y región ventral anterior durante los primeros 400 milisegundos en el hemisferio izquierdo y únicamente en el derecho para la corteza visual, mientras que en la condición de interferencia pasiva, se obtuvo una mayor activación en la región ventral anterior durante los 700-800 milisegundos en el hemisferio izquierdo. Conclusión: la presentación de estos dos tipos de interferencia, activa y pasiva, modula los patrones de activación fronto-temporales en el envejecimiento normalTo determine whether performing a recognition task under interference conditions produces changes in brain activity pattern compared with the activity seen under conditions of passive interference. Population and methods: Twenty healthy elderly subjects were subjected to magnetoencephalography. In each patient we applied the Wechsler Memory Scale-III (WMS-III), the Wechsler Intelligence Scale, the Boston Naming Test, the verbal fluency test, the Wisconsin card classification test, the Trail Making Test and the colors and words test (STROOP). The recordings were made using a 148-channel magnetoencephalograph capable of measuring the magnetic activity generated within the entire cranial convexity. Results: Greater activation was recorded under active interference conditions in the medial temporal regions, visual cortex and anterior ventral area in the first 400 ms in the left hemisphere and only in the right hemisphere for the visual cortex, while under passive interference conditions, increased activation was obtained in the anterior ventral region during the 700-800 ms in the left hemisphere. Conclusion: The presentation of both types of interference, active and passive, modulates the fronto-temporal activation patterns in normal agin

Energy production in varying {\alpha} theories

Aims. On the basis the theoretical model proposed by Bekenstein for {\alpha}'s variation, we analyze the equations that describe the energy exchange between matter and both the electromagnetic and the scalar fields. Methods. We determine how the energy flow of the material is modified by the presence of a scalar field. We estimate the total magnetic energy of matter from the "sum rules techniques". We compare the results with data obtained from the thermal evolution of the Earth and other planets. Results. We obtain stringent upper limits to the variations in {\alpha} that are comparable with those obtained from atomic clock frequency variations. Conclusions. Our constraints imply that the fundamental length scale of Bekenstein's theory "lB" cannot be larger than Planck's length "lP"