To analyze the SACY (Search for Associations Containing Young stars) survey we developed a method to find young associations and to define their high probability members. These bona fide members enable to obtain the kinematical and the physical properties of each association in a proper way. Recently we noted a concentration in the UV plane and we found a new association we are calling ASYA (All Sky Young Association) for its overall distribution in the sky with a total of 38 bonafide members and an estimated age of 110 Myr, the oldest young association found in the SACY survey. We present here its kinematical, space and Li distributions and its HR diagram.

The primary goal of the sacy project (Search for Associations Containing Young Stars) was to identify possible associations of stars younger than the Pleiades association among optical counterparts of ROSAT X-ray-bright sources. The study of the chemical abundance in stars located in regions of stellar formation is extremely important to understand stellar nucleo-synthesis, the physical mechanisms controlling mixing in stellar interiors, and chemical enrichment in the Galaxy. The present work highights the first results of a chemical-abundance study of evolved stars identified in the sacy survey. For this, we performed a detailed spectroscopic analysis for the determination of atmospheric parameters and Li abundance for a sample of giant and subgiant stars. The observations were carried out with high resolution using the FEROS (R = 48 000) échelle spectrograph. We measured the stellar parameters (Teff, log g, vmic, [Fe/H]) from LTE analysis in the complete range of 420-1100 nm. Li abundance was derived from the region around the lithium line at 6707.78 Å for the entire sample of stars.

We present the stellar parameters and lithium abundance for 23 stars of the young stellar association AB Doradus, determined by photometry and spectroscopy. The photometric data was obtained at OPD/LNA and/or from the literature and the spectroscopic data was obtained at La silla/ESO and at OPD/LNA. The parameters were determined using photometric calibrations, line ratios, curves of growth and spectral synthesis. Our results confirm that the selected stars are probably association members, showing an uniform metallicity and lithium depletion consistent with 50 Myears

In recent years. we have spectroscopically observed thousands of counterparts of selected ROSAT bright sources in the sacy project (Search for Associations Containing Young stars). We demonstrated that hundreds of the young stars found this way belong to nearby young, loose associations, some detected only in sacy, with ages in the range from 5 to 100 Myr. For their ages, these associations show no trace of their primitive nurseries, which poses some difficulties as to their origins. Nevertheless, there are some associations clearly associated with young open clusters, such as the ϵ Cha association (6 Myr) with the η Cha cluster, and the Argus association with IC 2391 (40 Myr). There seem to exist also more subtle connections, such as the AB Dor association (75 Myr) with the Pleiades. Here, we present evidence of the connections of young associations to open clusters, to understand their origin and their possible insertion in the cluster infant-mortality and Gould Belt scenarios.

Verification of theoretical predictions of an oscillating behavior of the fine-structure constant, $\alpha$, with cosmic time requires high precision measurements at individual redshifts, while in earlier studies the mean $\Delta\alpha/\alpha$ values averaged over wide redshift intervals were usually reported. This requirement can be met via the Single Ion Differential $\alpha$ Measurement (SIDAM) procedure. We apply SIDAM to the FeII lines associated with the damped Ly$\alpha$ system observed at $z = 1.15$ in the spectrum of HE0515–4414. The weighted mean calculated on the base of carefully selected 34 FeII pairs is $\langle \Delta\alpha/\alpha \rangle = (-0.07\,{\pm}\,0.84)\times10^{-6}$. The precision of this estimate represents a large improvement over previous measurements of $\Delta\alpha/\alpha$.

We present stellar parameters, Li abundances for 21 stars of the young ($\sim$50 Myears) AB Dor association, based on high-resolution spectra obtained with FEROS at the ESO 1.52m telescope, the Coudé Spectrograph at the OPD 1.6m telescope. These results are part of an ongoing project for the determination of stellar parameters, abundances for a large sample of T Tauri, post-T Tauri stars in PMS associations identified on the Search for Associations Containing Young Stars survey. The sample consists of G, K, M stars counterparts of ROSAT bright sources.

Since we expect Li depletion for the K, M stars, but small Li depletion for the G stars, we can compare the upper values of Li abundances for these stars with the one of the Galactic disk interstellar mean, at the same time provide constrains for the study of Li depletion on a chemically homogeneous high metallicity sample.

In the Pico dos Dias Survey (PDS), devised to search for young stellar objects, we found also K giants presenting moderate to strong Lithium lines associated with IRAS sources. But there are some gK with weak or absent Li lines too. There is a dichotomy in the distribution of the IRAS spectral indices between both kinds of K stars. A model of an expanding shell with a mass-dependent velocity may explain this behavior, if the photospheric Li depletion takes only ˜2500 yrs.

We analyze the Li depletion in the PTT-gap proposed by Martin (1997) using the young stars, with ages between 10 and 100 Myr, recently discovered by us during a survey around isolated T Tau stars.

Our knowledge of the distribution of low mass stars (T-associations) in the Galaxy, as an indicator of star forming regions (SFR), is badly known due to an observational bias. A correlation with high-mass stars (OB-associations) will not solve the problem, because some well known SFR as Taurus and Chamaleonis seem to preferentially form low mass stars. One way to tackle this question is by invoking the distribution of known T Tauri stars (TTS) and the distribution of selected IRAS sources that are potential candidates to be new TTS. We must be aware, however, that an important number of TTS are not IRAS sources. Considering these distributions, we have found a smooth distribution of SFR along the local galactic plane. The number of TTS in each SFR is very variable probably due to a variable efficiency of star formation. Also there are some isolated TTS from SFR which could indicate the dissipation of old SFR or that some TTS can be formed from isolated very small clouds.