Related papers: Variable rotational line broadening in the Be star…

Observations of circumstellar disks around stars as a function of stellar properties such as mass, metallicity, multiplicity, and age, provide constraints on theories concerning the formation and evolution of planetary systems. Utilizing…

Context: Rotationally supported disks are critical in the star formation process. The questions of when do they form and what factors influence or hinder their formation have been studied but are largely unanswered. Observations of early…

We present rotation periods for thousands of active stars in the Kepler field derived from Q3 data. In most cases a second period close to the rotation period was detected, which we interpreted as surface differential rotation (DR). Active…

In the group of B stars with spectroscopic peculiarities, we can find the Be and the B[e] stars. The Be stars are early-type rapid rotators that present, as their principal characteristic, emission lines of hydrogen and singly ionized…

The spectra of stars with the B[e] phenomenon are dominated by features that are related to physical conditions of circumstellar material around these objects and are not intrinsic to the stars. Previous studies have shown that emission…

Spectroscopic, polarimetric, and high spectral resolution interferometric data covering the period 1995-2011 are analyzed to document the transition into a new phase of circumstellar disk activity in the classical Be-shell star 48 Lib. The…

The non-axisymmetric structure of accretion disks around the neutron star in Be/X-ray binaries is studied by analyzing the results from three dimensional (3D) Smoothed Particle Hydrodynamics (SPH) simulations. It is found that ram pressure…

Spectroscopic observations of stars in young open clusters have revealed evidence for a dichotomous distribution of stellar rotational velocities, with 10-30% of stars rotating slowly and the remaining 70-90% rotating fairly rapidly. At the…

Be stars possess gaseous circumstellar decretion disks, which are well described using standard $\alpha$-disk theory. The Be star 28 CMa recently underwent a long outburst followed by a long period of quiescence, during which the disk…

The work is aimed at a study of the circumstellar disk of the bright classical binary Be star {\pi} Aqr. We analysed variations of a double-peaked profile of the H{\alpha} emission line in the spectrum of {\pi} Aqr that was observed in many…

Disks of bodies orbiting a much more massive central object are extremely common in astrophysics. When the orbits comprising such disks are eccentric, we show they are susceptible to a new dynamical instability. Gravitational forces between…

(abridged) As the favoured progenitors of long-duration gamma-ray bursts, massive stars may represent our best signposts of individual objects in the early Universe, but special conditions seem required to make these bursters, which might…

We present high resolution Na I D spectroscopy of the beta Pic disk, and the resonantly scattered sodium emission can be traced from less than 30 AU to at least 140 AU from the central star. This atomic gas is co-existent with the dust…

We report on the successful science verification phase of a new observing mode at the Keck interferometer, which provides a line-spread function width and sampling of 150km/s at K'-band, at a current limiting magnitude of K'~7mag with…

In binary systems with a strongly misaligned disk, the central binary stars can travel a significant vertical distance above and below the disk's orbital plane. This can cause large changes in illumination of the disk over the course of the…

Emission-line stars are typically surrounded by dense circumstellar material, often in form of rings or disc-like structures. Line emission from forbidden transitions trace a diversity of density and temperature regimes. Of particular…

The purpose of this work is to review the observational properties of Be/X-ray binaries. The open questions in Be/X-ray binaries include those related to the Be star companion, that is, the so-called "Be phenomenon", such as, timescales…

Here we present observational evidence that the broad emission line region (BELR) of active galactic nuclei (AGN) generally has an outer boundary. This was already clear for sources with an obvious transition between the broad and narrow…

The effect of gravitational darkening on models of the thermal structure of Be star disks is systematically studied for a wide range of Be star spectral types and rotation rates. Gravitational darkening causes a reduction of the stellar…

Classical Be stars are well known to eject mass, but the details governing the initial distribution and evolution of this matter into a disk are poorly constrained by observations. By combining high-cadence spectroscopy with contemporaneous…