Chi sta uccidendo gli ammassi giovani? Un nuovo caso per la Gaia-ESO Survey

La maggior parte delle stelle si formano in ammassi che rapidamente si disperdono lasciando isolati i loro membri. Quale sia il processo fisico che governa la loro evoluzione e dissipazione non è ancora chiaro. Alcuni recenti risultati, ottenuti dalla Survey Spettroscopica Gaia-ESO, stanno dando nuovi interessanti indizi che chiariscono alcuni aspetti del problema, ma che pongono anche nuove domande.We know that most stars form in clusters that very quickly disperse, leaving their members isolated. However, the process driving the early evolution of star clusters and their dissipation is not yet clear. Recent results obtained with the large spectroscopic survey Gaia-ESO are providing new interesting clues that can shed more light but also raise new questions

Nearby Young, Active, Late-type Dwarfs in Gaia's First Data Release

The Galex Nearby Young Star Survey (GALNYSS) has yielded a sample of $\sim$2000 UV-selected objects that are candidate nearby ($D \stackrel{<}{\sim}$150 pc), young (age $\sim$10--100 Myr), late-type stars. Here, we evaluate the distances and ages of the subsample of (19) GALNYSS stars with Gaia Data Release 1 (DR1) parallax distances $D \le 120$ pc. The overall youth of these 19 mid-K to early-M stars is readily apparent from their positions relative to the loci of main sequence stars and giants in Gaia-based color-magnitude and color-color diagrams constructed for all Galex- and WISE-detected stars with parallax measurements included in DR1. The isochronal ages of all 19 stars lie in the range $\sim$10--100 Myr. Comparison with Li-based age estimates indicates a handful of these stars may be young main-sequence binaries rather than pre-main sequence stars. Nine of the 19 objects have not previously been considered as nearby, young stars, and all but one of these are found at declinations north of $+$30$^\circ$. The Gaia DR1 results presented here indicate that the GALNYSS sample includes several hundred nearby, young stars, a substantial fraction of which have not been previously recognized as having ages $\stackrel{<}{\sim}$100 Myr.Comment: 30 pages, 4 tables, 7 figures; to appear in The Astrophysical Journal; 1st replacement to correct typos/omissions in Table 3 and acknowledgments; 2nd replacement to incorporate corrections to ApJ proof

A Combined Spitzer and Herschel Infrared Study of Gas and Dust in the Circumbinary Disk Orbiting V4046 Sgr

We present results from a spectroscopic Spitzer and Herschel mid-to-far-infrared study of the circumbinary disk orbiting the evolved (age ~12-23 Myr) close binary T Tauri system V4046 Sgr. Spitzer IRS spectra show emission lines of [Ne II], H_2 S(1), CO_2 and HCN, while Herschel PACS and SPIRE spectra reveal emission from [O I], OH, and tentative detections of H_2O and high-J transitions of CO. We measure [Ne III]/[Ne II] < 0.13, which is comparable to other X-ray/EUV luminous T Tauri stars that lack jets. We use the H_2 S(1) line luminosity to estimate the gas mass in the relatively warm surface layers of the inner disk. The presence of [O I] emission suggests that CO, H_2O, and/or OH is being photodissociated, and the lack of [C I] emission suggests any excess C may be locked up in HCN, CN and other organic molecules. Modeling of silicate dust grain emission features in the mid-infrared indicates that the inner disk is composed mainly of large (r~5 um) amorphous pyroxene and olivine grains (~86% by mass) with a relatively large proportion of crystalline silicates. These results are consistent with other lines of evidence indicating that planet building is ongoing in regions of the disk within ~30 AU of the central, close binary.Comment: 33 pages, 9 figures, 3 tables. Accepted for publication in Ap

Menos mulheres, menos jovens, mais incertezas. A transição demográfica no Brasil Rural Meridional

http://dx.doi.org/10.5902/2318179610453Este artigo analisa o processo de masculinização e de envelhecimento da população rural dos estados meridionais do Brasil (Rio Grande do Sul, Santa Catarina e Paraná)a partir dos dados dos dois últimos censos demográficos. A ênfase dos autores está em discutir algumas de suas possíveis causas, demonstrar a importância destes fenômenos, assim como do debate em torno ao futuro da ruralidade nessa parte do país

The role of radial migration in open cluster and field star populations with Gaia dr3

The survival time of a star cluster depends on its total mass, density, and thus size, as well as on the environment in which it was born and in which lies. Its dynamical evolution is influenced by various factors such as gravitational effects of the Galactic bar, spiral structures, and molecular clouds. Overall, the factors that determine the longevity of a cluster are complex and not fully understood. This study aims to investigate if open clusters and field stars respond differently to the perturbations that cause radial migration. In particular, we aim at understanding the nature of the oldest surviving clusters. We compared the time evolution of the kinematic properties of two Gaia DR3 samples: the first sample is composed of $\sim$40 open clusters and the second one of $\sim$66,000 MSTO field stars. Both selected samples are composed of stars selected with the same quality criterion, belonging to the thin disc, in a similar metallicity range, located in the same Galactocentric region [7.5-9 kpc] and with ages >1 Gyr. We performed a statistical analysis comparing the properties of the samples of field stars and of open clusters. A qualitative comparison of kinematic and orbital properties reveals that clusters younger than 2-3 Gyr are more resistant to perturbations than field stars and they move along quasi-circular orbits. Conversely, clusters older than approximately 3 Gyr have more eccentric and inclined orbits than isolated stars in the same age range. Such orbits lead them to reach higher elevations on the Galactic plane, maximising their probability to survive several Gyr longer. A formal statistical analysis reveals that there are differences among the time evolution of most of the kinematic and orbital properties of field stars and open clusters. Our results suggest that oldest survived clusters are usually more massive and move on orbits with higher eccentricity.Comment: 13 pages, 20 figures, 2 tables. Article accepted for publication in A&

Kinematics of young star clusters with the Gaia-ESO Survey

Studying the kinematical properties of young star clusters and star forming regions may help to understand the physical mechanisms driving their dynamical evolution and dissipation into the field. However, due to the lack of high quality data this kind of studies has been carried out only for a small sample of regions. The scenario is rapidly changing thanks to the Gaia-ESO Survey that is observing high resolution spectra of a large sample of clusters in the 1 to 100 Myr age range. In this proceeding we summarize the first results of this project in the field of cluster kinematics

Desafios à institucionalização das indicações geográficas no Brasil

O artigo analisa os desafios existentes, no Brasil, com relação à institucionalização das indicações geográficas de produtos agroalimentares, tomando por base, a experiência europeia. A recente expansão no número de experiências de diferenciação não tem sido capaz de engendrar mudanças requeridas para estabilizar um sistema que, atualmente, mostra-se extremamente frágil e carente de coordenação. O estudo baseia-se em entrevistas realizadas com atores sociais ligados a diversas iniciativas de indicações geográficas da Espanha (Andaluzia) e do Rio Grande do Sul (Serra Gaúcha)

Investigating Star-disk Interactions During Late-stage Circusmtellar Disk Evolution in the Nearby Pre-MS Stars T Cha and TWA 30

We investigate, via contemporaneous X-ray and optical/IR observations, the nearby, pre-main sequence star/disk systems T Chamaeleontis (T Cha; D ~ 110 pc, age 3-5 Myr) and TWA 30A and 30B (D ~ 40 pc; age ~ 8 Myr). All three of these systems present opportunities to probe pre-main sequence (pre-MS) star-disk interactions during late-stage circumstellar disk evolution. The classical T Tauri star T Cha is the closest known example of a highly inclined, actively accreting, solar-mass star/disk system; furthermore, T Cha may be orbited by a low-mass companion or massive planet that has cleared an inner hole in its disk. We analyze near-simultaneous Chandra high-resolution X-ray and optical H-alpha spectroscopy observations of T Cha and find a correlation between X-ray and optical extinction resulting from variable photospheric obscuration from a disk warp/clump. We search for signatures of accretion and infer the X-ray absorbing properties of the T Cha circumstellar disk.We also present contemporaneous XMM-Newton X-ray and optical/IR spectroscopic observations of the nearby, actively accreting, very low-mass (mid-M) pre-MS star/disk/jet systems TWA 30A and 30B. Like T Cha, each component of this wide binary is viewed through a nearly edge-on circumstellar disk. We investigate potential X-ray accretion signatures, and compare the levels of magnetic activity in TWA 30A and 30B to those of other nearby, low-mass pre-MS stars near the H-burning limit. Both TWA 30A and 30B display large near-IR variability, suggestive of (respectively) variable obscuration of the stellar photosphere and a possible disk-rim warp. We detect only TWA 30A in X-rays and, similar to the case of T Cha, find a correlation between optical/IR and X-ray extinction associated with variable photospheric obscuration. The proximity and highly-inclined viewing geometries of the TWA 30 pair and T Cha, combined with contemporaneous optical/IR and X-ray observations, afford a unique opportunity to investigate the composition of late-stage circumstellar disks orbiting pre-MS stars