Post T Tauri stars in the solar neighborhood: isolated or members of young associations and moving groups

Post T Tauri stars (PTTS) are late-type stars in the age range between 10 and 100 Myr filling the gap between T Tauri (TTs) and zero-age: main sequence phases. This period of evolution remains ambiguous and until now different studies of young stars have failed to find the numbers of PTTS that are expected. In the last years, some PTTS have been identified among the X-ray detected pre-main sequence stars in some star-forming regions. More recently, additional PTTS have been identified in young associations and moving groups (β Pic, TW Hya, Tucana/Horologium, and the AB Dor). However, many isolated PTTS still remain undiscovered. In this contribution, we compiled the PTTS previously identified in the literature, and identified new candidates using the information provided by the high resolution spectra obtained during our surveys of late-type stars possible members to young moving groups, FGK stars in the solar neighborhood, and RasTyc sample. To identify PTTS we applied an age-oriented definition using relative age indicators (Li abundance, chromospheric and coronal emission and the kinematics) as well as color-magnitude diagrams and pre-main sequence isochrones.

Madurez sintáctica: influencia de las TIC en sus índices y estudio comparativo entre las generaciones pre y post-internet

There is a growing concern about the poor quality of the writing of children and teenagers because of the continuous and constant exposure to the new technologies. Increasingly parents complain that their children spend too much time with their phones, tablets, computers, video games, etc. There is also an increase in the number of teachers who complain about their students’ writing skills. Some of the most prominent criticisms are loss of vocabulary, simplified syntax and the poor spelling of the compositions. To verify if these criticisms are motivated or not by the use of information and communication technologies (ICT) is what moved us to initiate this doctoral dissertation entitled “The influence of ICT on ratings of syntactic maturity: a comparative study between pre- and post-internet generations”. We aim to know if a daily and constant exposure to the ICT can affect the syntactic maturity rates of children and teenagers. We also want to find out if there are differences between the levels of syntactic maturity of today’s students and those of the 1990s, when there were no ICT and internet. In order to do this, we have carried out a quantitative analysis taking as a reference previous studies by generativist researchers in the Anglo-Saxon and Hispanic world and we have used the same units of measure (T-unit and clause). We collected a corpus of 382 essays, half argumentative and half descriptive, from 191 individuals. We have analyzed them according to ten dependent variables or syntactic maturity rates and other independent variables (Hours in internet, Course, Sex, Location, Type of school) by applying techniques of descriptive and inferential statistics...