Related papers: Statistics of wide pre-main sequence binaries in t…

We present first results of a survey for companions among X-ray selected pre-main sequence stars, most of them being weak-line T Tauri stars (WTTS). These T Tauri stars have been identified in the course of optical follow-up observations of…

The third data release of Gaia introduced a large catalog of astrometric binaries, out of which about 3,200 are likely main-sequence stars with a white-dwarf (WD) companion. These binaries are typically found with orbital separations of ~1…

We present the first statistical analysis of exoplanet direct imaging surveys combining adaptive optics imaging at small separations with deep seeing-limited observations at large separations allowing us to study the entire orbital…

Using proper motion data for 894 stars in the Orion Nebula Cluster (ONC) compiled by Jones & Walker in 1988, we search for binaries with apparent separations in the range 1000-5000 AU, and find an upper limit of three. Using a Monte Carlo…

A detailed spectroscopic survey of chemically peculiar (CP) stars in the Orion OB1 association is the most comprehensive observational program in the field of stellar magnetism that has been carried out at SAO so far. As at the end of 2018,…

$\delta$ Orionis is the closest massive multiple stellar system and one of the brightest members of the Orion OB association. The primary (Aa1) is a unique evolved O star. In this work, we applied a two-step disentangling method to a series…

Context. Only a few open clusters are as important for the study of stellar and substellar objects, and their formation and evolution, as the young sigma Orionis cluster. However, a complete spectroscopic characterisation of its whole…

Aims. Having established the binary status of nineteen O-type stars located in four Cygnus OB associations, we now determine their fundamental parameters to constrain their properties and their evolutionary status. We also investigate their…

Observations over the last decade have indicated that a large fraction of the stars are part of a binary or multiple system. For our understanding of star formation it is therefore of crucial importance to characterise the outcome of the…

We present the results of a high-resolution imaging survey of 22 brown dwarfs and very low mass stars in the nearby (~145 pc) young (~1-2 Myr) low-density star-forming region Taurus-Auriga. We obtained images with the Advanced Camera for…

We present an extensive search in the literature and Gaia DR2 for visual co-moving binary companions to stars hosting exoplanets and brown dwarfs within 200 pc. We found 218 planet hosts out of 938 to be part of multiple-star systems, with…

From Very Long Baseline Array (VLBA) observations we previously identified a population of 123 young stellar systems with nonthermal radio emission toward the core of the Orion Nebula Cluster (ONC). We find optical sources in the Gaia DR2…

We examine the spectroscopic binary population for two massive nearby regions of clustered star formation, the Orion Nebula Cluster and NGC 2264, supplementing the data presented by Tobin et al. (2009, 2015) with more recent observations…

We present results from a large, high-spatial-resolution near-infrared imaging search for stellar and sub-stellar companions in the Taurus-Auriga star-forming region. The sample covers 64 stars with masses between those of the most massive…

We present new Spitzer Space Telescope observations of two fields in the Orion OB1 association. We report here IRAC/MIPS observations for 115 confirmed members and 41 photometric candidates of the ~10 Myr 25 Orionis aggregate in the OB1a…

Context. Establishing the multiplicity of O-type stars is the first step towards accurately determining their stellar parameters. Moreover, the distribution of the orbital parameters provides observational clues to the way that O-type stars…

The first Gaia Data Release presents an opportunity to characterise the low-mass population of OB associations, providing larger statistical samples and better constraints on the formation and evolution of clusters and associations. Using…

Deep optical imaging is used to study time-domain properties of young brown dwarfs in sigma Orionis over typical rotational time-scales and to search for new substellar and planetary-mass cluster members. We used VIMOS at the VLT to monitor…

Massive binaries play significant roles in many fields. Identification of massive stars, particularly massive binaries, is of great importance. In this paper, by adopting the technique of measuring the equivalent widths of several spectral…

We conducted a radial velocity survey of the Cygnus OB2 Association over a 6 year (1999 - 2005) time interval to search for massive close binaries. During this time we obtained 1139 spectra on 146 OB stars to measure mean systemic radial…