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HD 98800 is a nearby hierarchical quadruple system comprising two binaries orbiting each other. Surprisingly, despite its $\sim$ 10 Myr age and dynamic environment, the Ba-Bb component is surrounded by a compact gas-rich disc in a polar…
BA-type supergiants are amongst the most optically-bright stars. They are observable in extragalactic environments, hence potential accurate distance indicators. Emission activity in the Halpha line of the BA supergiants Rigel (B8Ia) and…
HD~5501, a hitherto little studied eclipsing binary with an early A-type primary, has been caught in a short-lived, astrophysically interesting phase of its binary evolution. Recent photometric and spectroscopic observations, including…
A crucial issue in star formation is to understand the physical mechanism by which mass is accreted onto and ejected by a young star. The visible spectrometer VEGA on the CHARA array can be an efficient means of probing the structure and…
To characterize the mechanisms of planet formation it is crucial to investigate the properties and evolution of protoplanetary disks around young stars, where the initial conditions for the growth of planets are set. Our goal is to study…
We present high spatial resolution maps of ro-vibrational molecular hydrogen emission from the environment of the GG Tau A binary component in the GG Tau quadruple system. The H2 v= 1-0 S(1) emission is spatially resolved and encompasses…
Binary post-AGB stars are interesting laboratories to study both the evolution of binaries as well as the structure of circumstellar disks. A multiwavelength high angular resolution study of the prototypical object 89 Herculis is performed…
HS0907+1902 was recently discovered to be one of a handful of deeply eclipsing dwarf novae with periods longward of the 2 -- 3 hr `gap'. This paper presents orbit-resolved spectra and time series photometry of an eclipse. The apparent…
The recent findings of gas giant planets around young A-type stars suggest that disks surrounding Herbig Ae/Be stars will develop planetary systems. An interesting case is HD142527, for which previous observations revealed a complex…
Our current understanding is that intermediate- to high-mass stars form in a way similar to low-mass stars, that is, through disk accretion. However, the physical conditions that play a role in disk formation, evolution, and the possibility…
Context: Stellar evolution models are highly dependent on accurate mass estimates, especially for high-mass stars in the early stages of evolution. The most direct method for obtaining model-independent masses is derivation from the orbit…
We present intermediate- and low-resolution optical spectra around Halpha and LiI 6708 A for a sample of 25 low mass stars and 2 brown dwarfs with confirmed membership in the pre-main sequence stellar sigma Orionis cluster. Our observations…
We conducted a 12-month monitoring campaign of 33 T Tauri stars (TTS) in Taurus. Our goal was to monitor objects that possess a disk but have a weak Halpha line, a common accretion tracer for young stars, to determine whether they host a…
We present ALMA observations of the 0.88 millimeter dust continuum, 13CO, and C18O J=3-2 line emission of the circumbinary disk HD142527 at a spatial resolution of about 0.25". This system is characterized by a large central cavity of…
We present high-resolution optical spectra of 15 objects near or below the sub-stellar limit in the Upper Scorpius and $\rho$ Ophiuchus star-forming regions. These spectra, obtained with the HIRES instrument on the Keck I telescope, are…
Certain lines in spectra of the Galactic microquasar SS 433, in particular the brilliant H alpha line, have been interpreted as emission from a circumbinary disk. In this interpretation the orbital speed of the glowing material is in excess…
In a previous study, we found that the detached post-common-envelope binary LTT 560 displays an Halpha emission line consisting of two anti-phased components. While one of them was clearly caused by stellar activity from the secondary…
We present phase-resolved optical spectra of the low mass X-ray binary system V801 Ara. The spectra, obtained in 2014 with IMACS on the Magellan/Baade telescope at Las Campanas Observatory, cover the full binary orbit of 3.8 hours. They…
We present near-infrared H and K-band spectro-interferometric observations of the gaseous disk around the primary Be star in the delta Sco binary system, obtained in 2007 (between periastron passages in 2000 and 2011). Observations using…
The majority of the pre-main-sequence Herbig Ae/Be stars reside in binary systems. As these systems are young, their properties may contain an imprint of the star formation process at intermediate masses. However, these systems are…