We examine how accretion on to T Tauri stars may be modulated by a time-dependent ‘magnetic gate’ where the inner edge of the accretion disc is disrupted by a varying stellar field. We show that magnetic field variations on time-scales ≪ 10 yr can modulate the accretion flow, thus providing a possible mechanism both for the marked photometric variability of T Tauri stars and for the possible co...

We present accurate radial velocity measurements on the pulsating extremely iron-deficient post-AGB object HD 52961 and the RV Tauri star EN TrA (HD 131356) proving them to be binaries. Our long-term photometric monitoring campaign shows that the RV Tauri photometric class “b” phenomenon in HD 52961 is due to variable circumstellar extinction during orbital motion. By comparing carefully the ob...

We have analyzed GHRS data of eight Classical T Tauri stars (CTTSs) and one Weak T Tauri star (WTTS). The GHRS data consist of an spectral range 40 Å wide centered on 2800 Å. For 4 of the CTTS we have nearly simultaneous optical observations which contain Hα, Hβ, He I, NaD, and the Ca II infrared triplet. The Mg II resonance doublet is the strongest feature in the 2800 Å range. This line has a ...

Context. Recent photospheric abundance studies of galactic field RV Tauri stars show that depletion of refractory elements is rather common in these evolved objects. Aims. The process that creates this chemical anomaly is not understood well, but it probably requires the presence of gravitationally bound dust in a binary system. We test for the presence of depletion in extra-galactic objects. M...

Microalgal-bacterial interactions are commonly found in marine environments and are well known in diatom cultures maintained in laboratory. These interactions also exert strong effects on bacterial and algal diversity in the oceans. Small green eukaryote algae of the class Mamiellophyceae (Chlorophyta) are ubiquitous and some species, such as Ostreococcus spp., are particularly important in Med...

The effects of water stress on leaf water relations and growth are reported for three perennial tussock grass genotypes under glasshouse conditions. Studies were performed in genotypes El Palmar INTA and Selección Anguil of Agropyron scabrifolium (Döell) Parodi, and El Vizcachero of A. elongatum (Host) Beauv. Agropyron scabrifolium El Palmar INTA is native to a region with warm-temperate and hu...

This article addressed effective agronomic practices used to cultivate promising varieties of desert forage plants suitable for soil-climatic conditions in order improve the condition and increase productivity degraded pastures. The results field research on selection, collection, reproduction seeds perennial plant species with high productivity, resistant drought saline soils desert, restorati...