A search for evidence of irradiation in Centaurus X-4 during quiescence

We present a study of the neutron star X-Ray Transient Cen X-4. Our aim is to look for any evidence of irradiation of the companion with a detailed analysis of its radial velocity curve, relative contribution of the donor star and Doppler tomography of the main emission lines. To improve our study all our data are compared with a set of simulations that consider different physical parameters of the system, like the disc aperture angle and the mass ratio. We conclude that neither the radial velocity curve nor the orbital variation of the relative donor's contribution to the total flux are affected by irradiation. On the other hand, we do see emission from the donor star at H${\alpha}$ and HeI 5876 which we tentatively attribute to irradiation effects. In particular, the H${\alpha}$ emission from the companion is clearly asymmetric and we suggest is produced by irradiation from the hot-spot. Finally, from the velocity of the HeI 5876 spot we constrain the disc opening angle to alpha=7-14 deg.Comment: 4 pages, 5 figures, accepted for publication in A&A as a R

The 1989 and 2015 outbursts of V404 Cygni: a global study of wind-related optical features

The black hole transient V404 Cygni exhibited a bright outburst in June 2015 that was intensively followed over a wide range of wavelengths. Our team obtained high time resolution optical spectroscopy (~90 s), which included a detailed coverage of the most active phase of the event. We present a database consisting of 651 optical spectra obtained during this event, that we combine with 58 spectra gathered during the fainter December 2015 sequel outburst, as well as with 57 spectra from the 1989 event. We previously reported the discovery of wind-related features (P-Cygni and broad-wing line profiles) during both 2015 outbursts. Here, we build diagnostic diagrams that enable us to study the evolution of typical emission line parameters, such as line fluxes and equivalent widths, and develop a technique to systematically detect outflow signatures. We find that these are present throughout the outburst, even at very low optical fluxes, and that both types of outflow features are observed simultaneously in some spectra, confirming the idea of a common origin. We also show that the nebular phases depict loop patterns in many diagnostic diagrams, while P-Cygni profiles are highly variable on time-scales of minutes. The comparison between the three outbursts reveals that the spectra obtained during June and December 2015 share many similarities, while those from 1989 exhibit narrower emission lines and lower wind terminal velocities. The diagnostic diagrams presented in this work have been produced using standard measurement techniques and thus may be applied to other active low-mass X-ray binaries.Comment: Accepted for publication in MNRAS. 23 pages paper, plus a 9 pages appendix with extra tables and figures. 18 figures are included in the paper and 8 in the appendi

A population-based controlled experiment assessing the epidemiological impact of digital contact tracing

While Digital contact tracing (DCT) has been argued to be a valuable complement to manual tracing in the containment of COVID-19, no empirical evidence of its effectiveness is available to date. Here, we report the results of a 4-week population-based controlled experiment that took place in La Gomera (Canary Islands, Spain) between June and July 2020, where we assessed the epidemiological impact of the Spanish DCT app Radar Covid. After a substantial communication campaign, we estimate that at least 33% of the population adopted the technology and further showed relatively high adherence and compliance as well as a quick turnaround time. The app detects about 6.3 close-contacts per primary simulated infection, a significant percentage being contacts with strangers, although the spontaneous follow-up rate of these notified cases is low. Overall, these results provide experimental evidence of the potential usefulness of DCT during an epidemic outbreak in a real population

Black hole accretion disks in the canonical low-hard state

Stellar-mass black holes in the low-hard state may hold clues to jet formation and basic accretion disk physics, but the nature of the accretion flow remains uncertain. A standard thin disk can extend close to the innermost stable circular orbit, but the inner disk may evaporate when the mass accretion rate is reduced. Blackbody-like continuum emission and dynamically-broadened iron emission lines provide independent means of probing the radial extent of the inner disk. Here, we present an X-ray study of eight black holes in the low-hard state. A thermal disk continuum with a colour temperature consistent with $L \propto T^{4}$ is clearly detected in all eight sources, down to $\approx5\times10^{-4}L_{Edd}$. In six sources, disk models exclude a truncation radius larger than 10rg. Iron-ka fluorescence line emission is observed in half of the sample, down to luminosities of $\approx1.5\times10^{-3}L_{Edd}$. Detailed fits to the line profiles exclude a truncated disk in each case. If strong evidence of truncation is defined as (1) a non-detection of a broad iron line, {\it and} (2) an inner disk temperature much cooler than expected from the ${\rm L} \propto {\rm T}^{4}$ relation, none of the spectra in this sample offer strong evidence of disk truncation. This suggests that the inner disk may evaporate at or below $\approx1.5\times10^{-3}L_{Edd}$.Comment: Accepted for publication in MNRAS, 20 pages, 18 figure

BlackCAT: A catalogue of stellar-mass black holes in X-ray transients

During the last ~50 years, the population of black hole candidates in X-ray binaries has increased considerably with 59 Galactic objects detected in transient low-mass X-ray binaries, plus a few in persistent systems (including ~5 extragalactic binaries). We collect near-infrared, optical and X-ray information spread over hundreds of references in order to study the population of black holes in X-ray transients as a whole. We present the most updated catalogue of black hole transients, which contains X-ray, optical and near-infrared observations together with their astrometric and dynamical properties. It provides new useful information in both statistical and observational parameters providing a thorough and complete overview of the black hole population in the Milky Way. Analysing the distances and spatial distribution of the observed systems, we estimate a total population of ~1300 Galactic black hole transients. This means that we have already discovered less than ~5% of the total Galactic distribution. The complete version of this catalogue will be continuously updated online and in the Virtual Observatory, including finding charts and data in other wavelengths.Comment: http://www.astro.puc.cl/BlackCAT - Accepted for publication in Astronomy & Astrophysics. 20 pages, 8 figures, 5 Table

Furiously fast and red: sub-second optical flaring in V404 Cyg during the 2015 outburst peak

We present observations of rapid (sub-second) optical flux variability in V404 Cyg during its 2015 June outburst. Simultaneous three-band observations with the ULTRACAM fast imager on four nights show steep power spectra dominated by slow variations on ∼100–1000 s time-scales. Near the peak of the outburst on June 26, a dramatic change occurs and additional, persistent sub-second optical flaring appears close in time to giant radio and X-ray flaring. The flares reach peak optical luminosities of ∼ few × 1036 erg s−1. Some are unresolved down to a time resolution of 24 ms. Whereas the fast flares are stronger in the red, the slow variations are bluer when brighter. The redder slopes, emitted power and characteristic time-scales of the fast flares can be explained as optically thin synchrotron emission from a compact jet arising on size scales ∼140–500 Gravitational radii (with a possible additional contribution by a thermal particle distribution). The origin of the slower variations is unclear. The optical continuum spectral slopes are strongly affected by dereddening uncertainties and contamination by strong Hα emission, but the variations of these slopes follow relatively stable loci as a function of flux. Cross-correlating the slow variations between the different bands shows asymmetries on all nights consistent with a small red skew (i.e. red lag). X-ray reprocessing and non-thermal emission could both contribute to these. These data reveal a complex mix of components over five decades in time-scale during the outburst

Avanços recentes em nutrição de larvas de peixes

Os requisitos nutricionais de larvas de peixes são ainda mal compreendidos, o que leva a altas mortalidades e problemas de qualidade no seu cultivo. Este trabalho pretende fazer uma revisão de novas metodologias de investigação, tais como estudos com marcadores, genómica populacional, programação nutricional, génomica e proteómica funcionais, e fornecer ainda alguns exemplos das utilizações presentes e perspectivas futuras em estudos de nutrição de larvas de peixes

First light with HiPERCAM on the GTC

HiPERCAM is a quintuple-beam imager that saw first light on the 4.2 m William Herschel Telescope (WHT) in October 2017 and on the 10.4 m Gran Telescopio Canarias (GTC) in February 2018. The instrument uses re- imaging optics and 4 dichroic beamsplitters to record ugriz (300–1000 nm) images simultaneously on its five CCD cameras. The detectors in HiPERCAM are frame-transfer devices cooled thermo-electrically to 90°C, thereby allowing both long-exposure, deep imaging of faint targets, as well as high-speed (over 1000 windowed frames per second) imaging of rapidly varying targets. In this paper, we report on the as-built design of HiPERCAM, its first-light performance on the GTC, and some of the planned future enhancements

Development, nutrition, and rearing practices of relevant catfish species (Siluriformes) at early stages

Catfish (Siluriformes) are important species for aquaculture worldwide, with an annual production in 2018 of ca. 6 million t. This review focuses on reassessing larval development, first feeding, and early rearing practices of the most important farmed catfish species, along with some candidate species for aquaculture diversification: Pangasianodon hypophthalmus (Pangasiidae), Clarias gariepinus (Clariidae), Ictalurus punctatus (Ictaluridae), Pseudoplatystoma spp. (Pimelodidae), Heteropneustes fossilis (Heteropneustidae), Rhamdia quelen (Heptapteridae), Ompok bimaculatus (Siluridae), and Lophiosilurus alexandri (Pseudopimelodidade). These species are initially reared indoors from one day to two weeks and are then transferred to fertilised outdoor ponds where they either feed on natural zooplankton or compound feeds. With the exception of C. gariepinus, I. punctatus, R. quelen and P. hypophthalmus, consistent and reliable fry production is a bottleneck that limits the expansion of farming of other species, such as Pseudoplatystoma spp., H. fossilis, O. bimaculatus, and L. alexandri. Rearing systems (extensive, semi-extensive, intensive) and feeding protocols vary with species and geographical regions. Cannibalism and size heterogeneity are common, and these features create problems for larval and fry rearing of catfish species. Information about their nutritional requirements is required for the formulation of compound feeds that can guarantee high survival and good growth of catfish fries. However, such knowledge for most species is scarce, although some data are available for I. punctatus. Further genomic resources might allow fine-tuning rearing success. This review describes some successes in this field, and also highlights gaps in knowledge to guide future research that can promote the development of catfish aquaculture

Development, nutrition, and rearing practices of relevant catfish species (Siluriformes) at early stages

WOS:000662174500001International audienceCatfish (Siluriformes) are important species for aquaculture worldwide, with an annual production in 2018 of ca. 6 million t. This review focuses on reassessing larval development, first feeding, and early rearing practices of the most important farmed catfish species, along with some candidate species for aquaculture diversification: Pangasianodon hypophthalmus (Pangasiidae), Clarias gariepinus (Clariidae), Ictalurus punctatus (Ictaluridae), Pseudoplatystoma spp. (Pimelodidae), Heteropneustes fossilis (Heteropneustidae), Rhamdia quelen (Heptapteridae), Ompok bimaculatus (Siluridae), and Lophiosilurus alexandri (Pseudopimelodidade). These species are initially reared indoors from one day to two weeks and are then transferred to fertilised outdoor ponds where they either feed on natural zooplankton or compound feeds. With the exception of C. gariepinus, I. punctatus, R. quelen and P. hypophthalmus, consistent and reliable fry production is a bottleneck that limits the expansion of farming of other species, such as Pseudoplatystoma spp., H. fossilis, O. bimaculatus, and L. alexandri. Rearing systems (extensive, semi-extensive, intensive) and feeding protocols vary with species and geographical regions. Cannibalism and size heterogeneity are common, and these features create problems for larval and fry rearing of catfish species. Information about their nutritional requirements is required for the formulation of compound feeds that can guarantee high survival and good growth of catfish fries. However, such knowledge for most species is scarce, although some data are available for I. punctatus. Further genomic resources might allow fine-tuning rearing success. This review describes some successes in this field, and also highlights gaps in knowledge to guide future research that can promote the development of catfish aquaculture