We present the results of a search for young stellar objects around the two isolated T Tauri stars (TTSs) TW Hya and CoD−29◦8887. From the spectroscopic properties of these two objects, it is obvious that they are T Tauri stars, although they are not associated with a star-forming region as it is the case for most of the known TTSs. Especially TW Hya is the only classical TTS that is not locate...

Origin and evolution of tetraploid Elymus fibrosus (Schrenk) Tzvelev were characterized using low-copy nuclear gene Rpb2 (the second largest subunit of RNA polymerase II), and chloroplast region trnL-trnF (spacer between the tRNA Leu (UAA) gene and the tRNA-Phe (GAA) gene). Ten accessions of E. fibrosus along with 19 Elymus species with StH genomic constitution and diploid species in the tribe ...

We present Hα spectropolarimetry observations of a sample of 10 bright T Tauri stars, supplemented with new Herbig Ae/Be star data. A change in the linear polarisation across Hα is detected in most of the T Tauri (9/10) and Herbig Ae (9/11) objects, which we interpret in terms of a compact source of line photons that is scattered off a rotating accretion disk. We find consistency between the po...

We construct a protostellar disk model that takes into account the combined effect of viscous evolution, photoevaporation and the differential radial motion of dust grains and gas. For T Tauri disks, the lifetimes of dust disks that are mainly composed of millimeter sized grains are always shorter than the gas disks’ lifetimes, and become similar only when the grains are fluffy (density . 0.1 g...

Residual gas in disks around young stars can spin down stars, circularize the orbits of terrestrial planets, and whisk away the dusty debris that is expected to serve as a signpost of terrestrial planet formation. We have carried out a sensitive search for residual gas and dust in the terrestrial planet region surrounding young stars ranging in age from a few to ∼10Myr. Using high-resolution 4....

We present long-slit spectroscopy and spectroastrometry of He i 1.083 mm emission in the T Tauri star DG Tauri. We identify three components in the He i feature: (1) a blueshifted emission component at km s , 1 v 200 (2) a bright emission component at zero velocity with a FWZI of ∼500 km s , and (3) a blueshifted absorption 1 feature at velocities between 250 and 500 km s . The position and vel...

We construct models for the rotation rates of T Tauri stars whose spin is regulated by magnetic linkage between the star and a surrounding accretion disc. Our models utilise a time-dependent disc code to follow the accretion process and include the eeects of pre-main-sequence stellar evolution. We nd that the initial disc mass controls the evolution of the star-disc system. For suuciently massi...