Examinando por Autor "Cáceres, C."

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    A qualitative classification of extraterrestrial civilizations
    (EDP Sciences, 2020-07) Ivanov, V.D.; Beamín, J.C.; Cáceres, C.; Minniti, D.
    Context. Interest in searches for extraterrestrial civilizations (ETCs) has been boosted in recent decades by the discovery of thousands of exoplanets. Aims. We turn to the classification of ETCs for new considerations that may help to design better strategies for searching for ETCs. Methods. This study is based on analogies with our own biological, historical, technological, and scientific development. We took a basic taxonomic approach to ETCs and investigated the implications of the new classification on ETC evolution and observational patterns. Finally, we used the quantitative scheme of Kardashev and considered its implications on the searches for ETCs as a counter example to our qualitative classification. Results. We propose a classification based on the abilities of ETCs to modify and integrate with their environments: Class 0 uses the environment as it is, Class 1 modifies the environment to fit its needs, Class 2 modifies itself to fit the environment, and a Class 3 ETC is fully integrated with the environment. Combined with the classical Kardashev scale, our scheme forms a two-dimensional method for interpreting ETC properties. Conclusions. The new framework makes it obvious that the available energy is not a unique measure of ETC progress: it may not even correlate with how well that energy is used. The possibility for progress without increased energy consumption implies a lower detectability, so in principle the existence of a Kardashev Type III ETC in the Milky Way cannot be ruled out. This reasoning weakens the Fermi paradox, allowing for the existence of advanced, yet not energy hungry, low-detectability ETCs. The integration of ETCs with the environment will make it impossible to tell technosignatures and natural phenomena apart. Therefore, the most likely opportunity for SETI searches to find advanced ETCs is to look for beacons, specifically set up by them for young civilizations like ours (if they would want to do that remains a matter of speculation). The other SETI window of opportunity is to search for ETCs at technological level similar to ours. To rephrase the famous saying of Arthur Clarke, sufficiently advanced civilizations are indistinguishable from nature. © ESO 2020.
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    Ítem
    WISE J061213.85-303612.5: A new T-dwarf binary candidate
    (EDP Sciences, 2015-06) Huélamo, N.; Ivanov V.D., Kurtev R.; Girard, J.H.; Borissova, J.; Mawet, D.; Mužić, K.; Cáceres, C.; Melo, C.H.F.; Sterzik, M.F.; Minniti, D.
    Context. T and Y dwarfs are among the coolest and least luminous objects detected, and they can help to understand the properties of giant planets. Up to now, there are more than 350 T dwarfs that have been identified thanks to large imaging surveys in the infrared, and their multiplicity properties can shed light on the formation process. Aims. The aim of this work is to look for companions around a sample of seven ultracoool objects. Most of them have been discovered by the WISE observatory and have not been studied before for multiplicity. Methods. We observed a sample six T dwarfs and one L9 dwarf with the Laser Guide Star (LGS) and NAOS-CONICA, the adaptive optics (AO) facility, and the near infrared camera at the ESO Very Large Telescope.We observed all the objects in one or more near-IR filters (JHKs). Results. From the seven observed objects, we have identified a subarcsecond binary system, WISE J0612-3036, composed of two similar components with spectral types of T6. We measure a separation of ρ = 350 ± 5 mas and a position angle of PA = 235 ± 1°. Using the mean absolute magnitudes of T6 dwarfs in the 2MASS JHKs bands, we estimate a distance of d = 31 ± 6 pc and derive a projected separation of ρ ∼ 11 ± 2 au. Another target, WISE J2255-3118, shows a very faint object at 1″. 3 in the Ks image. The object is marginally detected in H, and we derive a near infrared color of H - Ks > 0.1mag. HST/WFC3 public archival data reveals that the companion candidate is an extended source. Together with the derived color, this suggests that the source is most probably a background galaxy. The five other sources are apparently single, with 3-σ sensitivity limits between H = 19-21 for companions at separations >0″.5. Conclusions. WISE 0612-3036 is probably a new T-dwarf binary composed of two T6 dwarfs. As in the case of other late T-dwarf binaries, it shows a mass ratio close to 1, although its projected separation, ∼11 au, is larger than the average (∼5 au). Additional observations are needed to confirm that the system is bound. © 2015 ESO.