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We attempt to determine the molecular composition of disks around young low-mass stars in the $\rho$ Oph region and to compare our results with a similar study performed in the Taurus-Auriga region. We used the IRAM 30 m telescope to…

Close binary interactions may play a critical role in the formation of the rapidly rotating Be stars. Mass transfer can result in a mass gainer star spun up by the accretion of mass and angular momentum, while the mass donor is stripped of…

(Abridged) We performed a deep infrared imaging survey of 63 embedded young stellar objects (YSOs) located in the Taurus and Ophiuchus clouds to search for companions. The sample includes Class I and flat infrared spectrum protostellar…

Observations at various wavelengths of late B-type stars exhibiting strong overabundances of the chemical elements Hg and Mn in their atmospheres indicate that these stars are frequently found in binary and multiple systems. We intend to…

The optical to near-infrared (300 - 2500 nm) spectrum of the candidate massive Young Stellar Object (YSO) B275, embedded in the star forming region M17, has been observed with X-shooter on the ESO Very Large Telescope. The spectrum includes…

Herbig-Haro flows are signposts of recent major accretion and outflow episodes. We aim to determine the nature and properties of the little-known outflow source HH 250-IRS, which is embedded in the Aquila clouds. We have obtained adaptive…

BM Orionis, eclipsing binary system that located in the center of Orion Nebula Cluster posses several enigmatic problems. Its intrinsic nature and nebular environment make it harder to measure the physical parameters of the system, but it…

We report the discovery of twelve faint Herbig-Haro (HH) objects in LDN 673 found using a novel color-composite imaging method that reveals faint H{\alpha} emission in complex environments. Follow-up observations in [S II] confirmed their…

Evidence is presented that 2MASS J03202839-0446358, a late-type dwarf with discrepant optical (M8:) and near-infrared (L1) spectral types, is an as-yet unresolved stellar/brown dwarf binary with late-type M dwarf and T dwarf components.…

We present a detailed investigation of the radial distribution of blue straggler star and binary populations in the Galactic globular cluster NGC 5466, over the entire extension of the system. We used a combination of data acquired with the…

Given that a majority of stars form in multiple systems, in order to fully understand the star- and planet-formation processes we must seek to understand them in multiple stellar systems. With this in mind, we present an analysis of the…

Observations of binaries have traditionally provided the means for ascertaining stellar masses. Here, we use the published data on 8 pre-main-sequence pairs to gauge the accuracy of our own, recently calculated, evolutionary tracks (Palla &…

This paper describes our study of the astrophysics of individual components in close pre-main-sequence binaries. We observed both stars in 17 systems, located in 4 nearby star forming regions, using low-resolution (R=760), infrared…

New spectroscopic observations of the halo hyper-velocity star candidate SDSS J121150.27+143716.2 ($V=17.92$ mag) revealed a cool companion to the hot subdwarf primary. The components have a very similar radial velocity and their absolute…

Our general understanding of multiple star and planet formation is primarily based on observations of young multiple systems in low density regions like Tau-Aur and Oph. Since many, if not most, of the stars are born in clusters,…

Early Herbig Be (HBe) stars are massive, young stars accreting through the Boundary Layer mechanism. However, given the rapid ($<$ 2 Myr) evolution of early Herbig stars to the main-sequence phase, studying the evolution of the…

We observed high-resolution optical spectra of 11 RV Tauri stars without IR excess, with the primary goal of searching for chemical depletion patterns. Using equivalent widths of absorption lines, we calculated photospheric parameters and…

We report centimeter continuum observations with the VLA and the VLBA as well as mid-infrared observations with COMICS/SUBARU toward the components of the YLW 15 very young binary system, VLA 1 and VLA 2. The centimeter emission of the two…

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…

We present the orbital and physical parameters of a newly discovered low-mass detached eclipsing binary from the All-Sky Automated Survey (ASAS) database: ASAS J011328-3821.1 A - a member of a visual binary system with the secondary…