Star collisions may easily occur in a cluster of stars orbiting around a massive black hole. Such collisions can transform part of the star kinetic energy in observable radiating energy. In this paper we derive the star collision rate and the resulting highly variable luminosity for the case of a cluster containing stars of different masses. The variability of the derived light curves is comput...

We are conducting a large program to classify newly discovered Milky Way star cluster candidates from the list of Froebrich, Scholz & Raftery (2007b). Here we present deep NIR follow-up observations from ESO/NTT of 14 star cluster candidates. We show that the combined analysis of star density maps and colour-colour/magnitude diagrams derived from deep near-infrared imaging is a viable tool to r...

We present a spectroscopic analysis of two galaxy clusters at z≈ 0.2, out to ∼ 4 Mpc. The two clusters VMF73 and VMF74 as identified by Vikhlinin et al. (1998) were observed with multiple object spectroscopy using MOSCA at the Calar Alto 3.5 m telescope. Both clusters lie in the ROSAT Position Sensitive Proportional Counter field R285 and were selected from the X-ray Dark Cluster Survey (Gilban...

We present observations of a massive star cluster near the nuclear region of the nearby starburst galaxy NGC 253. The peak of near-infrared emission, which is spatially separated by 4 from the kinematic center of the galaxy, is coincident with a super star cluster whose properties we examine with low-resolution (R ∼ 1,200) infrared CTIO spectroscopy and optical/near-infrared HST imaging. Extinc...

We present a photometric and spectroscopic study of the compact H ii region Sh 138 and its associated stellar cluster. The positions and BVRIJHK magnitudes are obtained for more than 400 stars over a field of about 4′ square centred on the H ii region. Sh 138 is excited by a cluster of young massive stars. At the cluster’s very centre are at least four O–B2 stars separated by less than 4′′. The...

With the help of a statistical parameter derived from optical spectra, we show that the current star formation rate of a galaxy, falling into a cluster along a supercluster filament, is likely to undergo a sudden enhancement before the galaxy reaches the virial radius of the cluster. From a sample of 52 supercluster-scale filaments of galaxies joining a pair of rich clusters of galaxies within ...

IEEE 802.15.4 protocols are gaining interests in both industrial and research fields as candidate technologies for (WPAN) Wireless Personal Area Networks, (WSN) Wireless Sensor Network and control Wireless Networks applications. This paper analyzes multiple topologies such as Cluster-Tree, Mesh and Star in various scenarios to compare different performance metrics (Throughput, traffic sent, tra...

We use HST/ACS imaging of 100 early-type galaxies in the ACS Virgo Cluster Survey to investigate the nature of diffuse star clusters (DSCs). Compared to globular clusters (GCs), these star clusters have moderately low luminosities (MV > −8) and a broad distribution of sizes (3 < rh < 30 pc), but they are principally characterized by their low mean surface brightnesses which can be more than thr...

We show that the rapid evolution in the fraction of blue, star-forming galaxies seen in clusters as a function of redshift (the Butcher-Oemler effect) can be explained very simply if structure formation in the universe proceeeds hierarchically. We show that a rich cluster observed at high redshift has had a significantly different evolutionary history to a cluster of the same richness observed ...