WISEA J064750.85-154616.4: a new nearby L/T transition dwarf

Aims: Our aim is to detect and classify previously overlooked brown dwarfs in the solar neighbourhood. Methods: We performed a proper motion search among bright sources observed with the Wide-field Infrared Survey Explorer (WISE) that are also seen in the Two Micron All Sky Survey (2MASS). Our candidates appear according to their red $J$$-$$K_s$ colours as nearby late-L dwarf candidates. Low-resolution near-infrared (NIR) classification spectroscopy in the $HK$ band allowed us to get spectroscopic distance and tangential velocity estimates. Results: We have discovered a new L9.5 dwarf, WISEA J064750.85-154616.4, at a spectroscopic distance of about 14 pc and with a tangential velocity of about 11 km/s, typical of the Galactic thin disc population. We have confirmed another recently found L/T transition object at about 10 pc, WISEA J140533.13+835030.7, which we classified as L8 (NIR).Comment: Research Note accepted for publication in Astronomy and Astrophysics, 5 pages, 3 figure

An overlooked brown dwarf neighbour (T7.5 at d~5pc) of the Sun and two additional T dwarfs at about 10pc

Although many new brown dwarf (BD) neighbours have recently been discovered thanks to new sky surveys in the mid- and near-infrared (MIR, NIR), their numbers are still more than five times lower than those of stars in the same volume. Our aim is to detect and classify new BDs to eventually complete their census in the immediate Solar neighbourhood. We combined multi-epoch data from sky surveys at different wavelengths to detect BD neighbours of the Sun by their high proper motion (HPM). We concentrated at relatively bright MIR (w2<13.5) BD candidates from WISE expected to be so close to the Sun that they may also be seen in older NIR (2MASS, DENIS) or even red optical (SDSS i- and z-band, SSS I-band) surveys. With low-resolution NIR spectroscopy we classified the new BDs and estimated their distances and velocities. We have discovered the HPM (pm~470mas/yr) T7.5 dwarf, WISE J0521+1025, which is at d=5.0+-1.3pc from the Sun the nearest known T dwarf in the northern sky, and two early-T dwarfs, WISE J0457-0207 (T2) and WISE J2030+0749 (T1.5), with proper motions of ~120 and ~670mas/yr and distances of 12.5+-3.1pc and 10.5+-2.6pc, respectively. The last one was independently discovered and also classified as a T1.5 dwarf by Mace and coworkers. All three show thin disk kinematics. They may have been overlooked in the past owing to overlapping images and because of problems with matching objects between different surveys and measuring their proper motions.Comment: 7 pages, incl. 6 figures and 1 table, accepted for publication in Astronomy and Astrophysics, minor changes in title, abstract, and conclusion

The unevenly distributed nearest brown dwarfs

To address the questions of how many brown dwarfs there are in the Milky Way, how do these objects relate to star formation, and whether the brown dwarf formation rate was different in the past, the star-to-brown dwarf number ratio can be considered. While main sequence stars are well known components of the solar neighborhood, lower mass, substellar objects increasingly add to the census of the nearest objects. The sky projection of the known objects at <6.5 pc shows that stars present a uniform distribution and brown dwarfs a non-uniform distribution, with about four times more brown dwarfs behind than ahead of the Sun relative to the direction of rotation of the Galaxy. Assuming that substellar objects distribute uniformly, their observed configuration has a probability of 0.1 %. The helio- and geocentricity of the configuration suggests that it probably results from an observational bias, which if compensated for by future discoveries, would bring the star-to-brown dwarf ratio in agreement with the average ratio found in star forming regions

Stellar rotation, binarity, and lithium in the open cluster IC4756

An important aspect in the evolutionary scenario of cool stars is their rotation and the rotationally induced magnetic activity and interior mixing. Stars in open clusters are particularly useful tracers for these aspects because of their known ages. We aim to characterize the open cluster IC4756 and measure stellar rotation periods and surface differential rotation for a sample of its member stars. Thirty-seven cluster stars were observed continuously with the CoRoT satellite for 78 days in 2010. Follow-up high-resolution spectroscopy of the CoRoT targets and deep Str\"omgren $uvby\beta$ and H$\alpha$ photometry of the entire cluster were obtained with our robotic STELLA facility and its echelle spectrograph and wide-field imager, respectively. We determined high-precision photometric periods for 27 of the 37 CoRoT targets and found values between 0.155 and 11.4 days. Twenty of these are rotation periods. Twelve targets are spectroscopic binaries of which 11 were previously unknown; orbits are given for six of them. Six targets were found that show evidence of differential rotation with $\Delta\Omega/\Omega$ in the range 0.04-0.15. Five stars are non-radially pulsating stars with fundamental periods of below 1d, two stars are semi-contact binaries, and one target is a micro-flaring star that also shows rotational modulation. Nine stars in total were not considered members because of much redder color(s) and deviant radial velocities with respect to the cluster mean. H$\alpha$ photometry indicates that the cluster ensemble does not contain magnetically over-active stars. The cluster average metallicity is -0.08$\pm$0.06 (rms) and its logarithmic lithium abundance for 12 G-dwarf stars is 2.39$\pm$0.17 (rms). [...]Comment: A&A, in pres

QUÍMICA NA WEB E NA PRÁTICA: DIVULGANDO A QUÍMICA NAS ESCOLAS E NAS REDES SOCIAIS

A inserção e divulgação da Universidade com as escolas tem como objetivo promover o encontro entre a ciência, a metodologia científica e alunos, no sentido de auxiliar o processo de ensino/aprendizagem visando à integração entre diferentes áreas da química e o currículo regular. Neste contexto, abre a possibilidade de contribuir para a formação interdisciplinar de alunos e professores de Ciências, Química e Biologia de escolas de ensino fundamental e médio. Assim, o presente projeto tem como objetivo realizar a divulgação da Química e do Curso de Química Ambiental da Universidade Federal do Tocantins (UFT) Campus Gurupi, na forma de exposições e divulgação nas redes sociais, ainda realizando ações que aproximam a comunidade científica da comunidade externa. Para tal, foi utilizado a rede social do Instagram para tais exposições, tendo aumento significativo de seguidores e publicações desde abril/2021; um alcance de mais de três mil visualizações; ações como rodas de conversa, que promoveram a interação e divulgação do curso de Química Ambiental com alunos do ensino médio. Mostrando assim, que as redes sociais são ferramentas, aos quais além de ajudarem na propagação da ciência produzida no meio científico, colaboram de forma abrangente a aproximação da população com a Universidad

GTC/CanariCam Deep Mid-infrared Imaging Survey of Northern Stars within 5 pc

© 2021. The Author(s). Published by the American Astronomical Society. This is an open access article distributed under the Creative Commons Attribution License, to view a copy of the license, see: https://creativecommons.org/licenses/by/4.0/In this work we present the results of a direct imaging survey for brown dwarf companions around the nearest stars at the mid-infrared 10 micron range (λ c = 8.7 μm, Δλ = 1.1 μm) using the CanariCam instrument on the 10.4 m Gran Telescopio Canarias (GTC). We imaged the 25 nearest stellar systems within 5 pc of the Sun at declinations δ > −25° (at least half have planets from radial-velocity studies), reaching a mean detection limit of 11.3 ± 0.2 mag (1.5 mJy) in the Si-2 8.7 μm band over a range of angular separations from 1″ to 10″. This would have allowed us to uncover substellar companions at projected orbital separations between ∼2 and 50 au, with effective temperatures down to 600 K and masses greater than 30 M Jup assuming an average age of 5 Gyr and masses down to the deuterium-burning mass limit for objects with ages <1 Gyr. From the nondetection of such companions, we determined upper limits on their occurrence rate at depths and orbital separations yet unexplored by deep imaging programs. For the M dwarfs, the main component of our sample, we found with a 90% confidence level that fewer than 20% of these low-mass stars have L- and T-type brown dwarf companions with m ≳ 30 MJup and Teff ≳ 600 K at ∼3.5–35 au projected orbital separations.Peer reviewedFinal Published versio