Incidence of debris discs around FGK stars in the solar neighbourhood

Debris discs are a consequence of the planet formation process and constitute the fingerprints of planetesimal systems. Their solar system's counterparts are the asteroid and Edgeworth-Kuiper belts. The aim of this paper is to provide robust numbers for the incidence of debris discs around FGK stars in the solar neighbourhood. The full sample of 177 FGK stars with d<20 pc proposed for the DUNES survey is presented. Herschel/PACS observations at 100 and 160 micron complemented with data at 70 micron, and at 250, 350 and 500 micron SPIRE photometry, were obtained. The 123 objects observed by the DUNES collaboration were presented in a previous paper. The remaining 54 stars, shared with the DEBRIS consortium and observed by them, and the combined full sample are studied in this paper. The incidence of debris discs per spectral type is analysed and put into context together with other parameters of the sample, like metallicity, rotation and activity, and age. The subsample of 105 stars with d<15 pc containing 23 F, 33 G and 49 K stars, is complete for F stars, almost complete for G stars and contains a substantial number of K stars to draw solid conclusions on objects of this spectral type. The incidence rates of debris discs per spectral type 0.26 (6 objects with excesses out of 23 F stars), 0.21 (7 out of 33 G stars) and 0.20 (10 out of 49 K stars), the fraction for all three spectral types together being 0.22 (23 out of 105 stars). Uncertainties corresponding to a 95% confidence level are given in the text for all these numbers. The medians of the upper limits of L_dust/L_* for each spectral type are 7.8E-7 (F), 1.4E-6 (G) and 2.2E-6 (K); the lowest values being around 4.0E-7. The incidence of debris discs is similar for active (young) and inactive (old) stars. The fractional luminosity tends to drop with increasing age, as expected from collisional erosion of the debris belts.Comment: 31 pages, 15 figures, 10 tables, 2 appendice

A peculiar class of debris disks from Herschel/DUNES - A steep fall off in the far infrared

Aims. We present photometric data of debris disks around HIP 103389 (HD 199260), HIP 107350 (HN Peg, HD206860), and HIP 114948 (HD 219482), obtained in the context of our Herschel Open Time Key Program DUNES (DUst around NEarby Stars). Methods. We used Herschel/PACS to detect the thermal emission of the three debris disks with a 3 sigma sensitivity of a few mJy at 100 um and 160 um. In addition, we obtained Herschel/PACS photometric data at 70 um for HIP 103389. Two different approaches are applied to reduce the Herschel data to investigate the impact of data reduction on the photometry. We fit analytical models to the available spectral energy distribution (SED) data. Results. The SEDs of the three disks potentially exhibit an unusually steep decrease at wavelengths > 70 um. We investigate the significance of the peculiar shape of these SEDs and the impact on models of the disks provided it is real. Our modeling reveals that such a steep decrease of the SEDs in the long wavelength regime is inconsistent with a power-law exponent of the grain size distribution -3.5 expected from a standard equilibrium collisional cascade. In contrast, a very distinct range of grain sizes is implied to dominate the thermal emission of such disks. However, we demonstrate that the understanding of the data of faint sources obtained with Herschel is still incomplete and that the significance of our results depends on the version of the data reduction pipeline used. Conclusions. A new mechanism to produce the dust in the presented debris disks, deviations from the conditions required for a standard equilibrium collisional cascade (grain size exponent of -3.5), and/or significantly different dust properties would be necessary to explain the potentially steep SED shape of the three debris disks presented. (abridged)Comment: 14 pages, 4 figures, accepted by A&

DUst Around NEarby Stars. The survey observational results

Context. Debris discs are a consequence of the planet formation process and constitute the fingerprints of planetesimal systems. Their solar system's counterparts are the asteroid and Edgeworth-Kuiper belts. Aims. The DUNES survey aims at detecting extra-solar analogues to the Edgeworth-Kuiper belt around solar-type stars, putting in this way the solar system into context. The survey allows us to address some questions related to the prevalence and properties of planetesimal systems. Methods. We used Herschel/PACS to observe a sample of nearby FGK stars. Data at 100 and 160 μm were obtained, complemented in some cases with observations at 70 μm, and at 250, 350 and 500 μm using SPIRE. The observing strategy was to integrate as deep as possible at 100 μm to detect the stellar photosphere. Results. Debris discs have been detected at a fractional luminosity level down to several times that of the Edgeworth-Kuiper belt. The incidence rate of discs around the DUNES stars is increased from a rate of ∼ 12.1% ± 5% before Herschel to ∼ 20.2% ± 2%. A significant fraction (∼ 52%) of the discs are resolved, which represents an enormous step ahead from the previously known resolved discs. Some stars are associated with faint far-IR excesses attributed to a new class of cold discs. Although it cannot be excluded that these excesses are produced by coincidental alignment of background galaxies, statistical arguments suggest that at least some of them are true debris discs. Some discs display peculiar SEDs with spectral indexes in the 70–160 μm range steeper than the Rayleigh-Jeans one. An analysis of the debris disc parameters suggests that a decrease might exist of the mean black body radius from the F-type to the K-type stars. In addition, a weak trend is suggested for a correlation of disc sizes and an anticorrelation of disc temperatures with the stellar age

ALMA observations of <i>α</i> Centauri: first detection of main-sequence stars at 3 mm wavelength

Context. The precise mechanisms that provide the non-radiative energy for heating the chromosphere and the corona of the Sun and those of other stars constitute an active field of research. By studying stellar chromospheres one aims at identifying the relevant physical processes. Defining the permittable extent of the parameter space can also serve as a template for the Sun-as-a-star. This feedback will probably also help identify stars that potentially host planetary systems that are reminiscent of our own. Aims. Earlier observations with Herschel and APEX have revealed the temperature minimum of α Cen, but these were unable to spatially resolve the binary into individual components. With the data reported in this Letter, we aim at remedying this shortcoming. Furthermore, these earlier data were limited to the wavelength region between 100 and 870 μm. In the present context, we intend to extend the spectral mapping (SED) to longer wavelengths, where the contrast between stellar photospheric and chromospheric emission becomes increasingly evident. Methods. The Atacama Large Millimeter/submillimeter Array (ALMA) is particularly suited to point sources, such as unresolved stars. ALMA provides the means to achieve our objectives with both its high sensitivity of the collecting area for the detection of weak signals and the high spatial resolving power of its adaptable interferometer for imaging close multiple stars. Results. This is the first detection of main-sequence stars at a wavelength of 3 mm. Furthermore, the individual components of the binary α Cen AB are clearly detected and spatially well resolved at all ALMA wavelengths. The high signal-to-noise ratios of these data permit accurate determination of their relative flux ratios, i.e., SyB / SyA = 0.54 ± 0.04 at 440 μm, = 0.46 ± 0.01 at 870 μm, and = 0.47 ± 0.006 at 3.1 mm, respectively. Conclusions. The previously obtained flux ratio of 0.44±0.18, which was based on measurements in the optical and at 70 μm, is consistent with the present ALMA results, albeit with a large error bar. The observed 3.1 mm emission greatly exceeds what is predicted from the stellar photospheres, and undoubtedly arises predominantly as free-free emission in the ionized chromospheric plasmas of both stars. Given the distinct difference in their cyclic activity, the similarity of their submm SEDs appears surprising

How dusty is <i>α</i> Centauri? Excess or non-excess over the infrared photospheres of main-sequence stars

Context. Debris discs around main-sequence stars indicate the presence of larger rocky bodies. The components of the nearby, solar-type binary α Centauri have metallicities that are higher than solar, which is thought to promote giant planet formation. Aims. We aim to determine the level of emission from debris around the stars in the α Cen system. This requires knowledge of their photospheres. Having already detected the temperature minimum, Tmin, of α Cen A at far-infrared wavelengths, we here attempt to do the same for the more active companion α Cen B. Using the α Cen stars as templates, we study the possible effects that Tmin may have on the detectability of unresolved dust discs around other stars. Methods. We used Herschel-PACS, Herschel-SPIRE, and APEX-LABOCA photometry to determine the stellar spectral energy distributions in the far infrared and submillimetre. In addition, we used APEX-SHeFI observations for spectral line mapping to study the complex background around α Cen seen in the photometric images. Models of stellar atmospheres and of particulate discs, based on particle simulations and in conjunction with radiative transfer calculations, were used to estimate the amount of debris around these stars. Results. For solar-type stars more distant than α Cen, a fractional dust luminosity fd ≡ Ldust/Lstar ~ 2 × 10-7 could account for SEDs that do not exhibit the Tmin effect. This is comparable to estimates of fd for the Edgeworth-Kuiper belt of the solar system. In contrast to the far infrared, slight excesses at the 2.5σ level are observed at 24 μm for both α Cen A and B, which, if interpreted as due to zodiacal-type dust emission, would correspond to fd ~ (1-3) × 10-5, i.e. some 102 times that of the local zodiacal cloud. Assuming simple power-law size distributions of the dust grains, dynamical disc modelling leads to rough mass estimates of the putative Zodi belts around the α Cen stars, viz. ≲4 × 10-6 M☾of 4 to 1000 μm size grains, distributed according to n(a) ∝ a-3.5. Similarly, for filled-in Tmin emission, corresponding Edgeworth-Kuiper belts could account for ~ 10-3 M☾ of dust. Conclusions Our far-infrared observations lead to estimates of upper limits to the amount of circumstellar dust around the stars α Cen A and B. Light scattered and/or thermally emitted by exo-Zodi discs will have profound implications for future spectroscopic missions designed to search for biomarkers in the atmospheres of Earth-like planets. The far-infrared spectral energy distribution of α Cen B is marginally consistent with the presence of a minimum temperature region in the upper atmosphere of the star. We also show that an α Cen A-like temperature minimum may result in an erroneous apprehension about the presence of dust around other, more distant stars. Based on observations with Herschel which is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Also based on observations with APEX, which is a 12 m diameter submillimetre telescope at 5100 m altitude on Llano Chajnantor in Chile. The telescope is operated by Onsala Space Observatory, Max-Planck-Institut für Radioastronomie (MPIfR), and European Southern Observatory (ESO)

A Compact Dication Source for Ba2+^{2+} Tagging and Heavy Metal Ion Sensor Development

We present a tunable metal ion beam that delivers controllable ion currents in the picoamp range for testing of dry-phase ion sensors. Ion beams are formed by sequential atomic evaporation and single or multiple electron impact ionization, followed by acceleration into a sensing region. Controllability of the ionic charge state is achieved through tuning of electrode potentials that influence the retention time in the ionization region. Barium, lead, and cobalt samples have been used to test the system, with ion currents identified and quantified using a quadrupole mass analyzer. Realization of a clean $\mathrm{Ba^{2+}}$ ion beam within a bench-top system represents an important technical advance toward the development and characterization of barium tagging systems for neutrinoless double beta decay searches in xenon gas. This system also provides a testbed for investigation of novel ion sensing methodologies for environmental assay applications, with dication beams of Pb$^{2+}$ and Cd$^{2+}$ also demonstrated for this purpose

Autonomías y autogobierno en la América diversa

Los activismos globales de los pueblos indígenas y afrodescendientes han puesto en la arena de los debates el reclamo de autodeterminación, autonomía y autogobierno, logrando avances relevantes en las normas internacionales. Sin embargo, estos logros se enfrentan a políticas y realidades de los gobiernos nacionales y los intereses económicos de todo tipo en sus países, que los amenazan y pretenden profundizar el despojo. En este libro concebimos a la autonomía como una variedad de prácticas, procesos y mecanismos de auto-gobernanza a través de los cuales se expresan y se dotan de sentido los derechos inherentes y aspiraciones soberanas de los pueblos indígenas y afrodescendientes alrededor del mundo. El derecho a la libre determinación es una parte consustancial de la vida sociopolítica contemporánea y, su ejercicio en sus territorios es hoy, probablemente, uno de los únicos caminos para la persistencia de la vida en el planeta. Las contribuciones que integran este volumen, muchas de ellas de autoría indígena, colocan debates que abordan esos desafíos y enlazan las voces ancestrales con las luchas de hoy y la defensa del futuro

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

DUNES: survey observational results

The on-line tabular material contains a complete description of the DUNES objects, providing absolute parameters of the stars, the photometry used to build their spectral energy distributions, the Herchel/PACS fluxes, the photospheric predictions at the PACS wavelengths, the significance of the potential excesses and additional information concerning the stars with extended emission, the offsets of the stellar positions as measured in the optical and in the PACS100 images, the AORs (Astronomical Observation Request number) of the observations and the on-source integration times