Received ; accepted – 2 – ABSTRACT The Trifid nebula (M20) is a well-known prominent optical HII region trisected by bands of obscuring dust lanes and excited by an O7.5 star HD 164492A. Previous near-IR, mid-IR and radio continuum observations of the cluster of stars at the center of the Trifid nebula indicated circumstellar disks associated with hot stars with envelopes that are photoionized ...

Context. It is still debated whether star formation process depends on environment. In particular it is yet unclear whether star formation in the outer Galaxy, where the environmental conditions are, theoretically, less conducive, occurs in the same way as in the inner Galaxy. Aims. We investigate the population of NGC 1893, a young cluster (∼3−4 Myr) in the outer part of the Galaxy (RG ≥ 11 kp...

We report the discovery of two spectroscopic binaries in the field of the old open cluster M67 – S 1063 and S 1113 – whose positions in the color-magnitude diagram place them ≈ 1 mag below the subgiant branch. A ROSAT study of M67 independently discovered these stars to be X-ray sources. Both have propermotion membership probabilities greater than 97%; precise center-of-mass velocities are cons...

A simple model is constructed to evaluate the change of star formation rate of a disk galaxy due to environmental e†ects in clusters of galaxies. Three e†ects are investigated : (1) tidal force from the potential well of the cluster, (2) increase of external pressure when the galaxy plows into the intracluster medium, and (3) high-speed encounters between galaxies. General analysis indicates th...

We discuss HST FOS ultraviolet spectroscopy and NICMOS near-infrared photometry of four young super star clusters in the central region of the irregular starburst galaxy NGC 1569. The new observations coupled with previous HST WFPC2 photometry and ground-based optical spectroscopy allow us to isolate and age-date the hot and cool stellar components of these massive clusters. We analyze the two ...

We use the ages, masses and metallicities of the rich young star cluster systems in the nearby starburst galaxies NGC 3310 and NGC 6745 to derive their cluster formation histories and subsequent evolution. We further expand our analysis of the systematic uncertainties involved in the use of broad-band observations to derive these parameters (Paper I) by examining the effects of a priori assumpt...

We identified star clusters in archived HST/WFPC2 images of the merger and ultra-luminous infrared galaxy NGC 6240, with the aim of investigating whether star cluster properties (luminosity, age and mass) in such an extreme environment differ from those of clusters in less luminous starburst galaxies. We found 54 star clusters in all of the F450W, F547M and F814W exposures, of which 41 are loca...

We have developed a new parallel supercomputer code based on Hénon’s Monte Carlo method for simulating the dynamical evolution of globular clusters. This new code allows us to calculate the evolution of a cluster containing a realistic number of stars (N ∼ 10 − 10) in about a day of computing time. The discrete, star-by-star representation of the cluster in the simulation allows us to treat nat...

We report on BV I CCD photometry of a field centered in the region of the Galactic star cluster Whiting 1 down to V = 23.0. This cluster has never been studied insofar, and we provide for the first time estimates of its fundamental parameters, namely, radial extent, age, distance and reddening. Whiting 1 turns out to be a compact star cluster with a diameter of about 1. We find that the cluster...

We present new results from deep GALEX UV imaging of the cluster Cl 0024+17 at z ∼ 0.4. Rest-frame far UV emission is detected from a large fraction of so-called “passive spiral galaxies” –a significant population which exhibits spiral morphology with little or no spectroscopic evidence for ongoing star formation. This population is thought to represent infalling galaxies whose star formation h...