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Time-series data taken with the Hubble Space Telescope of a field six core radii (~5') from the center of the globular cluster Messier 4, and covering a period of about 10 weeks in early 2001, have been analyzed in search of variable…
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…
We present the first spectrum of the most luminous infrared star in M33, and use it to demonstrate that the object is almost certainly a binary composed of a massive O star and a dust-enshrouded Red Hypergiant. This is the most luminous…
The existence of strange quark stars has been proposed many years ago. More recently, the possible co-existence of a first family composed of "normal" neutron stars with a second family of strange quark stars has been proposed as a solution…
During the last 25 years, hundreds of binary stars and planets have been discovered towards the Galactic Bulge by microlensing surveys. Thanks to a new generation of large-sky surveys, it is now possible to regularly detect microlensing…
Since the release of the Hipparcos catalog in 1997, the distance to the Pleiades open cluster has been heavily debated. The distance obtained from Hipparcos and those by alternative methods differ by 10 to 15 %. As accurate stellar…
This is a brief note to comment on some recent papers addressing the Monoceros ring. In our view, nothing new was delivered on the matter: No new evidence or arguments are presented which lead to think that the over-densities in Monoceros…
Anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) are enigmatic pulsar-like objects. The energy budget is the fundamental problem in their studies. In the magnetar model, they are supposed to be powered by the extremely…
Planetary nebulae (PNe) are circumstellar gas ejected during an intense mass-losing phase in the the lives of asymptotic giant branch stars. PNe have a stunning variety of shapes, most of which are not spherically symmetric. The debate over…
It is a pity that the real state of matter in pulsar-like stars is still not determined confidently because of the uncertainty about cold matter at supranuclear density, even 40 years after the discovery of pulsar. Nuclear matter (related…
We summarize results of a search for X-ray-emitting binary stars in the massive globular cluster Omega Centauri (NGC 5139) using Chandra and HST. ACIS-I imaging reveals 180 X-ray sources, of which we estimate that 45-70 are associated with…
The Galactic Center (GC) is dominated by the gravity of a super-massive black hole (SMBH), Sagittarius A$^*$, and is suspected to contain a sizable population of binary stars. Such binaries form hierarchical triples with the SMBH,…
Stars in globular clusters are generally believed to have all formed at the same time, early in the Galaxy's history. 'Blue stragglers' are stars massive enough that they should have evolved into white dwarfs long ago. Two possible…
In this paper we report on the follow-up of five potential exoplanets detected with Gaia astrometry and provide an overview of what is currently known about the nature of the entire Gaia astrometric exoplanet candidate sample, 72 systems in…
Symbiotic binaries are putative progenitors of type Ia supernovae. The census of Galactic symbiotic binaries is so incomplete that we cannot reliably estimate the total population of these stars, and use it to check whether that number is…
The three objects have been identified as members of the recently recognized class of Gamma Doradus stars, which exhibit multi-periodic photometric variations that are thought to arise from non-radial pulsation. The particular objects…
Eclipses of the single-line spectroscopic binary star, epsilon Aurigae, provide an opportunity to study the poorly-defined companion. We used the MIRC beam combiner on the CHARA array to create interferometric images during eclipse ingress.…
Binary F stars exhibit large brightness anomaly, which is defined here as the difference between the absolute magnitude from the uvby photometry and the actual absolute magnitude of the star. We have found that the anomaly inversely…
We report the serendipitous discovery of a previously unknown quasar at 10.5" from Q2225-403 (z=2.410). The observation of the broad emission line of MgII_2798 and of the surrounding FeII multiplets indicates that the companion quasar is at…
A combination of high-resolution and wide-field imaging reveals two binary stars and one triple star system among the sample of the first 11 stars with planets detected by radial velocity variations. High resolution speckle or adaptive…