Related papers: X rays from old open clusters: M 67 and NGC 188
We present results of a search for variable stars in the intermediate-age open cluster NGC 7044. We found 23 variable stars in the observed field. One star turned out to be of the delta Sct type with two pulsational modes excited. From the…
We present new multi-wavelength observations of two ultraluminous X-ray sources (ULXs) hosted by globular clusters (GCs) in the giant elliptical NGC 1399, focusing on CXO J0338318-352604 (GCU7), only the second GC ULX known to have luminous…
A combination of two unsupervised machine learning algorithms, DBSCAN and GMM are used to find members with a high probability of twelve open clusters, M38, NGC2099, Coma Ber, NGC752, M67, NGC2243, Alessi01, Bochum04, M34, M35, M41, and…
The formation of hot subdwarf stars (sdBs), which are core helium-burning stars located on the extended horizontal branch, is still not understood. Many of the known hot subdwarf stars reside in close binary systems with short orbital…
Chandra observations of the X-ray faint elliptical galaxy NGC 4697 resolve much of the X-ray emission (61% within one effective radius) into ~80 point sources, of which most are low mass X-ray binaries (LMXBs). These LMXBs provide the bulk…
A correlation of X-ray source and Halpha emission-line object catalogues in the Small Magellanic Cloud (SMC) shows that more than two thirds of the optically identified Be stars in Be/X-ray binaries are found as emission-line objects in the…
We use deep Chandra observations to measure the emissivity of the unresolved X-ray emission in the elliptical galaxy NGC 3379. After elimination of bright, low-mass X-ray binaries with luminosities >10^{36 erg/sec, we find that the…
We report on our search for distant clusters of galaxies based on optical and X-ray follow up observations of X-ray candidates from the SHARC survey. Based on the assumption that the absence of bright optical or radio counterparts to…
We present the surface photometry of star clusters in the nearby dwarf elliptical galaxies NGC 185 and NGC 205, obtained from deep HST WFPC2 F555W (V) and F814W (I) images. We have obtained surface brightness and color profiles of six star…
New HST observations show that the bright X-ray source in the face-on spiral galaxy NGC 1073 is located near a ring of recent star formation with an age of 8-16 Myr. This strengthens the association of X-ray sources in spiral galaxies…
We describe the results of a search for transit-like events caused by giant planets occulting stars in the old, metal-rich open cluster NGC 6791 based on BVI-colour photometry from eight nights of observations with the 2.54m Nordic Optical…
We report the discovery of a remarkable concentration of massive galaxies with extended X-ray emission at $z_{spec} = 2.506$, which contains 11 massive ($M_{*} \gtrsim 10^{11} M_{\odot}$) galaxies in the central 80kpc region (11.6$\sigma$…
We present a new independent determination for the age of one of the oldest open clusters, NGC 188: $6.41 \pm 0.33$ Gyr. We utilize a novel approach where we jointly fit the radial velocities (RVs) and spectral energy distributions (SED) of…
We present a study of X-ray source populations in M87, the cD galaxy of the Virgo cluster, using 12 archival {\it Chandra} observations with a total exposure of $\sim$680 ks spanning about a decade. A total of 346 point-like sources are…
Recent evolutionary computations predict that a few percent of massive OB stars in binary systems should have a dormant BH companion. Despite several reported X-ray quiet OB+BH systems over the last couple of years, finding them with…
It has been suggested that most Be/X-ray binaries are low X-ray luminosity nearby objects, containing white dwarfs (Chevalier & Ilovaisky 1998). We show that existing evidence indicates that all known Be/X-ray binaries are relatively bright…
The results of CCD photometric survey performed with the 90/180 cm Schmidt-Cassegrain Telescope of the Nicolaus Copernicus University Astronomical Observatory in Piwnice (Poland) and the 70/172 cm Schmidt Telescope of the National…
We report the results of XMM-Newton observations of HD49798/RXJ0648.0-4418, the only known X-ray binary consisting of a hot sub-dwarf and a white dwarf. The white dwarf rotates very rapidly (P=13.2 s) and has a dynamically measured mass of…
We present the results of a search for X-ray variability in the galactic open cluster NGC 2516. This cluster has been observed on 8 occasions using XMM-Newton making it an excellent target for such a study. We find 4 sources which show…
The core of the galactic globular cluster M13 (NGC 6205) has been observed with WFPC2 on the Hubble Space Telescope through visual, blue and mid- and far-UV filters in a programme devoted to study the UV population in a sample of Galactic…