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The study reports photometric and spectroscopic observations of two recently recognised contact binary systems. Both systems show total eclipses and analysis of the light curves indicate both have a very low mass ratios of less than 0.3. We…
PSR J1306--40 is a millisecond pulsar binary with a non-degenerate companion in an unusually long $\sim$1.097 day orbit. We present new optical photometry and spectroscopy of this system, and model these data to constrain fundamental…
We present the characterization of the low-gravity M6 dwarf 2MASS J0619-2903 previously identified as an unusual field object based on its strong IR excess and variable near-IR spectrum. Multiple epochs of low-resolution (R~150) near-IR…
During the study of a large set of late-type stellar X-ray sources, we discovered a large fraction of multiple systems. In this paper we investigate the orbital elements and kinematic properties of three new spectroscopic triple systems as…
PSR J1618-3921 is one of five known millisecond pulsars (MSPs) in eccentric orbits (eMPSs) located in the Galactic plane, whose formation is poorly understood. Earlier studies of these objects revealed significant discrepancies between…
The young, low-mass, triple system NTTS 155808-2219 (ScoPMS 20) was previously identified as a ~17-day period single-lined spectroscopic binary with a tertiary component at 0.21 arcseconds. Using high-resolution infrared spectra, acquired…
(abridged) PSR J1903+0327, a millisecond pulsar in an eccentric (e = 0.44) 95-day orbit with a (~ 1Msun) companion poses a challenge to our understanding of stellar evolution in binary and multiple-star systems. Here we describe optical and…
The millisecond pulsar J1903+0327 is accompanied by an ordinary G-dwarf star in an unusually wide ($P_{\rm orb} \simeq 95.2$\,days) and eccentric ($e \simeq 0.44$) orbit. The standard model for producing MSPs fails to explain the orbital…
We present observations of a new low-mass double-lined eclipsing binary system discovered using repeat observations of the celestial equator from the Sloan Digital Sky Survey II. Using near-infrared photometry and optical spectroscopy we…
The young system RX J0529.3+1210 was initially identified as a single-lined spectroscopic binary. Using high-resolution infrared spectra, acquired with NIRSPEC on Keck II, we measured radial velocities for the secondary. The method of using…
We present updated results of a high-resolution, magnitude limited (Ks<12 mag) imaging survey of nearby low-mass M6.0-M7.5 field stars. The observations were carried out using adaptive optics at the Gemini North, VLT, Keck II, and Subaru…
Abundances of Li, heavy elements and carbon isotope ratios have been measured in 12 J-type galactic carbon stars. The abundance analysis shows that in these stars the abundances of s-process elements with respect to the metallicity are…
We present photometric, astrometric and spectroscopic observations of the nearby (9.8 pc) low-mass binary Gl 569Bab (in turn being a companion to the early-M star Gl 569A), made with the Keck adaptive optics facility. Having observed Gl…
GJ 367 is a bright (V $\approx$ 10.2) M1 V star that has been recently found to host a transiting ultra-short period sub-Earth on a 7.7 hr orbit. With the aim of improving the planetary mass and radius and unveiling the inner architecture…
PSR J1024$-$0719 is a millisecond pulsar that was long thought to be isolated. However, puzzling results concerning its velocity, distance, and low rotational period derivative have led to reexamination of its properties. We present updated…
We report the detection of three small transiting planets around the young K3 dwarf K2-233 (2MASS J15215519-2013539) from observations during Campaign 15 of the K2 mission. The star is relatively nearby ($d$ = 69 pc) and bright ($V$ = 10.7…
The star HD 28363 in the Hyades cluster has been known for over a century as a visual binary with a period of 40 yr. The secondary is, in turn, a single-lined spectroscopic binary with a 21-day period. Here we report extensive spectroscopic…
We present very accurate orbital parameters and mass measurements (2.4% accuracy) for the well known very low mass triple system Gl 866. We obtain first orbital elements for the short-period orbit and greatly improve the long period orbit.…
An accident of misidentification has brought to light the interesting system HD 191588, a new RS CVn-type spectroscopic binary. A radial-velocity study of the primary star, the only seen component, carried out at the Observatoire de…
We report the results of high spectral and angular resolution infrared observations of the multiple system GL 569 A and B that were intended to measure the dynamical masses of the brown dwarf binary believed to comprise GL 569 B. Our…