We use the results of a new, multi-epoch, multi-wavelength, near-infrared census of the Trapezium Cluster in Orion to construct and to analyze the structure of its infrared (K band) luminosity function. Specifically, we employ an improved set of model luminosity functions to derive this cluster’s underlying Initial Mass Function (IMF) across the entire range of mass from OB stars to sub-stellar...

Measuring the build-up of stellar mass is one of the main objectives of studies of galaxy evolution. Traditionally, the mass in stars and the star formation rates have been measured by different indicators, such as photometric colours, emission lines, and the UV and IR emission. We intend to show that it is possible to derive the physical parameters of galaxies from their broad-band spectral en...

We build a stellar-dynamical model of the Milky Way barred bulge and disk, using a newly implemented adaptive particle method. The underlying mass model has been previously shown to match the Galactic near-infrared surface brightness as well as gas-kinematic observations. Here we show that the new stellar-dynamical model also matches the observed stellar kinematics in several bulge fields, and ...

We present a simple physical mechanism that can account for the observed stellar mass spectrum for masses M∗>∼ 0.5M⊙. The model depends solely on the competitive accretion that occurs in stellar clusters where each star’s accretion rate depends on the local gas density and the square of the accretion radius. In a stellar cluster, there are two different regimes depending on whether the gas or t...

An approach is introduced for incorporating the concept of stellar pollution into stellar evolution models. The approach involves enhancing the metal content of the surface layers of stellar models. In addition, the surface layers of stars in the mass range of 0.5 − 2.0M⊙ are mixed to an artificial depth motivated by observations of lithium abundance. The behavior of polluted stellar evolution ...

We use high signal-to-noise spectroscopy for a sample of 232 quiescent galaxies in the Shapley Supercluster, to investigate how their stellar populations depend on velocity dispersion (σ), luminosity and stellar mass. The sample spans a large range in velocity dispersion (30– 300 km s) and in luminosity (MR from –18.7 to –23.2). Estimates of age, total metallicity (Z/H) andα-element abundance r...

The optical and H I properties for a sample of low surface brightness (LSB) dwarf galaxies, cataloged from the Second Palomar Sky Survey, is presented. Gas mass fractions for LSB dwarfs reach the highest levels of any know galaxy type (fg =95%) confirming that their low stellar densities are due to inefficient conversion of gas mass into stellar mass. Comparison with star formation models indic...

We present stellar mass measurements for a sample of 36 luminous compact blue galaxies (LCBGs) at redshifts in the flanking fields around the Hubble Deep Field–North. The technique is based on fitting a twoz p 0.4–1.2 component galaxy population model to multi-broadband photometry. Best-fit models are found to be largely independent of the assumed values for the initial mass function (IMF) and ...

Do " isolated " planetary mass objects orbit invisible stellar mass companions? Abstract We propose that the " isolated " planetary mass objects observed by Zapa-tero Osorio et al in the σ Orionis cluster might actually be in orbit around invisible stellar mass companions such as mirror stars. The existence of such objects can be motivated by the dark matter problem and the observation of MACHO...