Suchergebnisse

In 2 experiments, a 12-min computerized vigilance task was demonstrated to reproduce the vigilance decrement, high workload (NASA-TLX), and stressful character (Dundee Stress State Questionnaire) of vigilance tasks lasting 30 min or more. In Experiment 1, the abbreviated task was also shown to duplicate the signal salience effect, a major finding associated with long-duration vigilance tasks. Moreover, Experiment 2 showed that performance on the abbreviated task can be enhanced by caffeine - a drug that benefits long-duration tasks. This enhancement effect was limited to performance, however, suggesting that caffeine influences factors that control signal detection but not those that control task-induced stress. The results parallel those obtained with long-duration tasks and support a resource-depletion model of the vigilance decrement. The abbreviated task might be useful in situations in which long-duration tasks are precluded (e.g., performance assessment batteries, neuropsychological testing, and brain imaging).

Context. We initiated a deep-imaging survey of Scorpius-Centaurus A-F stars in 2015. These stars are predicted to host warm inner and cold outer belts of debris reminiscent of the architecture of emblematic systems such as HR 8799. Aims. We present resolved images of a ring of debris around the F5-type star HD 141011 that was observed as part of our survey. We aim to set constraints on the properties of the disk, compare them to those of other resolved debris disks in Sco-Cen, and detect companions. Methods. We obtained high-contrast coronagraphic observations of HD 141011 in 2015, 2016, and 2019 with VLT/SPHERE. We removed the stellar halo using angular differential imaging. We searched for scattered light emission from a disk in the residuals and applied a forward-modeling approach to retrieve its morphological and photometric properties. We combined our radial velocity and imaging data to derive detection probabilities for companions co-planar with the disk orientation. Results. We resolve a narrow ring of debris that extends up to ∼1.100 (∼141 au) from the star in the IRDIS and IFS data obtained in 2016 and 2019. The disk is not detected in the 2015 data which are of poorer quality. The disks is best reproduced by models of a noneccentric ring centered on the star with an inclination of 69.1 ± 0.9 ◦ , a position angle of −24.6 ± 1.7 ◦ , and a semimajor axis of 127.5 ± 3.8 au. The combination of radial velocity and imaging data excludes brown-dwarf (M > 13.6 MJup) companions coplanar with the disk from 0.1 to 0.9 au and from 20 au up to 500 au (90% probability). Conclusions. HD 141011 adds to the growing list of debris disks that are resolved in Sco-Cen. It is one of the faintest disks that are resolved from the ground and has a radial extent and fractional width (∼12.5%) reminiscent of Fomalhaut. Its moderate inclination and large semimajor axis make it a good target for the James Webb Space Telescope and should allow a deeper search for putative companions shaping the dust distribution. ; French National Research Agency (ANR) ANR-14-CE33-0018 ANR-20-CE31-0012 France from the CNRS-D2P PICS grant France from the Programmes Nationaux de Planetologie et de Physique Stellaire (PNP) France from the Programmes Nationaux de Planetologie et de Physique Stellaire (PNPS) European Research Council (ERC) 885 593 Istituto Nazionale Astrofisica (INAF) Agenzia Spaziale Italiana (ASI) 2018-16-HH.0 PRIN-INAF 2019 "Planetary systems at young ages (PLATEA)" Australian Research Council FT170100040 DP180104235 ANID, -Millennium Science Initiative Program NCN19_171 Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) CONICYT FONDECYT 1180395 French National Research Agency (ANR) ANR10 LABX56 Spanish Government AyA2017-84089 European Commission 776403 Universidad de Valparaiso ; Versión publicada - versión final del editor

Context. Proxima Centauri is the closest star to the Sun and it is known to host an Earth-like planet in its habitable zone; very recently a second candidate planet was proposed based on radial velocities. At quadrature, the expected projected separation of this new candidate is larger than 1 arcsec, making it a potentially interesting target for direct imaging.Aims. While identification of the optical counterpart of this planet is expected to be very difficult, successful identification would allow for a detailed characterization of the closest planetary system.Methods. We searched for a counterpart in SPHERE images acquired over four years through the SHINE survey. In order to account for the expected large orbital motion of the planet, we used a method that assumes the circular orbit obtained from radial velocities and exploits the sequence of observations acquired close to quadrature in the orbit. We checked this with a more general approach that considers Keplerian motion, called K-stacker.Results. We did not obtain a clear detection. The best candidate has signal-to-noise ratio (S/N) = 6.1 in the combined image. A statistical test suggests that the probability that this detection is due to random fluctuation of noise is away from the astrometric motion of Proxima as measured from early Gaia data. This, together with the unexpectedly high flux associated with our direct imaging detection, means we cannot confirm that our candidate is indeed Proxima c.Conclusions. On the other hand, if confirmed, this would be the first observation in imaging of a planet discovered from radial velocities and the second planet (after Fomalhaut b) of reflecting circumplanetary material. Further confirmation observations should be done as soon as possible. ; Progetto Premiale 2015 FRONTIERA of the Italian Ministry of Education, University, and Research OB.FU. 1.05.06.11 CONICYT + PAI/Convocatoria nacional subvención a la instalación en la academia, convocatoria 2017 + Folio PAI77170087 European Union (EU) 664931 Swiss National Science Foundation (SNSF) PZ00P2180098 Ministry of Education, Universities and Research (MIUR) Research Projects of National Relevance (PRIN) Programme National de Planetologie (PNP) Programme National de Physique Stellaire (PNPS) of CNRS-INSU French National Research Agency (ANR) ANR10 LABX56 Centre National de la Recherche Scientifique (CNRS) French National Research Agency (ANR) ANR-14-CE330018 ESO Centre National de la Recherche Scientifique (CNRS) MPIA (Germany) Istituto Nazionale Astrofisica (INAF) FINES (Switzerland) NOVA (Netherlands) European Union (EU) RII3-Ct-2004-001566 226604 312430 European Union (EU) RII3-Ct-2004-001566 226604 312430 French National Research Agency (ANR) ANR-15-IDEX-02