First detection of thermal radio jets in a sample of proto-brown dwarf candidates

We observed with the JVLA at 3.6 and 1.3 cm a sample of 11 proto-brown dwarf candidates in Taurus in a search for thermal radio jets driven by the most embedded brown dwarfs. We detected for the first time four thermal radio jets in proto-brown dwarf candidates. We compiled data from UKIDSS, 2MASS, Spitzer, WISE and Herschel to build the Spectral Energy Distribution (SED) of the objects in our sample, which are similar to typical Class~I SEDs of Young Stellar Objects (YSOs). The four proto-brown dwarf candidates driving thermal radio jets also roughly follow the well-known trend of centimeter luminosity against bolometric luminosity determined for YSOs, assuming they belong to Taurus, although they present some excess of radio emission compared to the known relation for YSOs. Nonetheless, we are able to reproduce the flux densities of the radio jets modeling the centimeter emission of the thermal radio jets using the same type of models applied to YSOs, but with corresponding smaller stellar wind velocities and mass-loss rates, and exploring different possible geometries of the wind or outflow from the star. Moreover, we also find that the modeled mass outflow rates for the bolometric luminosities of our objects agree reasonably well with the trends found between the mass outflow rates and bolometric luminosities of YSOs, which indicates that, despite the "excess" centimeter emission, the intrinsic properties of proto-brown dwarfs are consistent with a continuation of those of very low mass stars to a lower mass range. Overall, our study favors the formation of brown dwarfs as a scaled-down version of low-mass stars.Comment: 18 pages, 8 figures, 14 tables, accepted by the Astrophysical Journa

Radio-loud Quasars above Redshift 4: VLBI Imaging of an Extended Sample

High-redshift radio sources provide plentiful opportunities for studying the formation and evolution of early galaxies and supermassive black holes. However, the number of known radio-loud active galactic nuclei (AGN) above redshift 4 is rather limited. At high redshifts, it appears that blazars, with relativistically beamed jets pointing towards the observer, are in majority compared to radio-loud sources with jets misaligned with respect to the line of sight. To find more of these misaligned AGN, milliarcsec-scale imaging studies carried out with very long baseline interferometry (VLBI) are needed, as they allow us to distinguish between compact core--jet radio sources and those with more extended emission. Previous high-resolution VLBI studies revealed that some of the radio sources among blazar candidates in fact show unbeamed radio emission on milliarcsecond scales. The most accurate optical coordinates determined with the Gaia astrometric space mission are also useful in the classification process. Here, we report on dual-frequency imaging observations of 13 high-redshift (4 < z < 4.5) quasars at 1.7 and 5 GHz with the European VLBI Network. This sample increases the number of z>4 radio sources for which VLBI observations are available by about a quarter. Using structural and physical properties, such as radio morphology, spectral index, variability, brightness temperature, as well as optical coordinates, we identified six blazars and six misaligned radio AGNs, with the remaining one tentatively identified as blazar

Very long baseline interferometry observations of the high-redshift blazar candidate J0141-5427

Active galactic nuclei (AGN) have been observed as far as redshift z~7. They are crucial in investigating the early Universe as well as the growth of supermassive black holes at their centres. Radio-loud AGN with their jets seen at a small viewing angle are called blazars and show relativistic boosting of their emission. Thus, their apparently brighter jets are easier to detect in the high-redshift Universe. DES J014132.4-542749.9 is a radio-luminous but X-ray weak blazar candidate at z = 5. We conducted high-resolution radio interferometric observations of this source with the Australian Long Baseline Array at 1.7 and 8.5 GHz. A single, compact radio emitting feature was detected at both frequencies with a flat radio spectrum. We derived the milliarcsecond-level accurate position of the object. The frequency dependence of its brightness temperature is similar to that of blazar sources observed at lower redshifts. Based on our observations, we can confirm its blazar nature. We compared its radio properties with those of two other similarly X-ray-weak and radio-bright AGN, and found that they show very different relativistic boosting characteristics.Comment: 8 pages, 4 figures, accepted for publication in PAS

The CARMENES search for exoplanets around M dwarfs: Nine new double-line spectroscopic binary stars

Context. The CARMENES spectrograph is surveying ~300 M dwarf stars in search for exoplanets. Among the target stars, spectroscopic binary systems have been discovered, which can be used to measure fundamental properties of stars. Aims. Using spectroscopic observations, we determine the orbital and physical properties of nine new double-line spectroscopic binary systems by analysing their radial velocity curves. Methods. We use two-dimensional cross-correlation techniques to derive the radial velocities of the targets, which are then employed to determine the orbital properties. Photometric data from the literature are also analysed to search for possible eclipses and to measure stellar variability, which can yield rotation periods. Results. Out of the 342 stars selected for the CARMENES survey, 9 have been found to be double-line spectroscopic binaries, with periods ranging from 1.13 to ~8000 days and orbits with eccentricities up to 0.54. We provide empirical orbital properties and minimum masses for the sample of spectroscopic binaries. Absolute masses are also estimated from mass-luminosity calibrations, ranging between ~0.1 and ~0.6 Msol . Conclusions. These new binary systems increase the number of double-line M dwarf binary systems with known orbital parameters by 15%, and they have lower mass ratios on average.Comment: Accepted for publication in A&A. 17 pages, 4 figure

Elastic and vibrational properties of alpha and beta-PbO

The structure, electronic and dynamic properties of the two layered alpha (litharge) and beta (massicot) phases of PbO have been studied by density functional methods. The role of London dispersion interactions as leading component of the total interaction energy between layers has been addressed by using the Grimme's approach, in which new parameters for Pb and O atoms have been developed. Both gradient corrected and hybrid functionals have been adopted using Gaussian-type basis sets of polarized triple zeta quality for O atoms and small core pseudo-potential for the Pb atoms. Basis set superposition error (BSSE) has been accounted for by the Boys-Bernardi correction to compute the interlayer separation. Cross check with calculations adopting plane waves that are BSSE free have also been performed for both structures and vibrational frequencies. With the new set of proposed Grimme's type parameters structures and dynamical parameters for both PbO phases are in good agreement with experimental data.Comment: 8 pages, 5 figure

Three little radio galaxies in the early Universe

Volonteri et al. (2011) found that the number of radio-loud quasars above redshift 4 calculated from the luminosity function (based upon Swift/BAT observations) is much smaller than the number estimated from the known high-redshift beamed sources, blazars, assuming that for every beamed source with a Lorentz factor of $\Gamma$, statistically $2 \Gamma^2$ non-beamed sources should exist. To explain the missing misaligned (non-beamed) population of high-redshift sources, they proposed various explanations, involving heavy optical obscuration and significantly different Lorentz factors at early cosmological epochs. Our EVN observations targeting high-redshift ($z>4$) blazar candidates revealed 3 sources not showing relativistic beaming, but rather kpc-scale double structures. These three sources have significant radio emission resolved out with the EVN, while they are compact on $\sim 5-10$ arcsec scale. Our dual-frequency ($1.5$ and $5$ GHz) e-MERLIN observations of these three sources revealed a rich morphology, bending jets, and hot spots with possible sites of interaction between the jets and the surrounding medium at intermediate scales.Comment: 6 pages, 3 figures, 1 table, accepted for the Proceedings of the 14th European VLBI Network Symposium & Users Meetin

Downgrading Recent Estimates of Land Available for Biofuel Production

Recent estimates of additional land available for bioenergy production range from 320 to 1411 million ha. These estimates were generated from four scenarios regarding the types of land suitable for bioenergy production using coarse-resolution inputs of soil productivity, slope, climate, and land cover. In this paper, these maps of land availability were assessed using high-resolution satellite imagery. Samples from these maps were selected and crowdsourcing of Google Earth images was used to determine the type of land cover and the degree of human impact. Based on this sample, a set of rules was formulated to downward adjust the original estimates for each of the four scenarios that were previously used to generate the maps of land availability for bioenergy production. The adjusted land availability estimates range from 56 to 1035 million ha depending upon the scenario and the ruleset used when the sample is corrected for bias. Large forest areas not intended for biofuel production purposes were present in all scenarios. However, these numbers should not be considered as definitive estimates but should be used to highlight the uncertainty in attempting to quantify land availability for biofuel production when using coarse-resolution inputs with implications for further policy development

The effect of bean origin and temperature on grinding roasted coffee

Coffee is prepared by the extraction of a complex array of organic molecules from the roasted bean, which has been ground into fine particulates. The extraction depends on temperature, water chemistry and also the accessible surface area of the coffee. Here we investigate whether variations in the production processes of single origin coffee beans affects the particle size distribution upon grinding. We find that the particle size distribution is independent of the bean origin and processing method. Furthermore, we elucidate the influence of bean temperature on particle size distribution, concluding that grinding cold results in a narrower particle size distribution, and reduced mean particle size. We anticipate these results will influence the production of coffee industrially, as well as contribute to how we store and use coffee daily