We investigate the dependence of physical properties of galaxies brighter than Mr = −18.0 + 5logh in the Sloan Digital Sky Survey (SDSS) on environment, as measured by local density using an adaptive smoothing kernel. We find that variations of galaxy properties with environment are almost entirely due to the dependence of morphology and luminosity on environment. Because galaxy properties depe...

We present a new model atmosphere analysis of nine central stars of planetary nebulae. This study is based on a new generation of realistic stellar model atmospheres for hot stars; state-of-the-art, hydrodynamically consistent, spherically symmetric model atmospheres that have been shown to correctly reproduce the observed UV spectra of massive Population I O-type stars. The information provide...

The aim of this talk is to review the methodology required to translate the observed luminosity function of a stellar sample into the mass function of the stars constituting the sample. Emphasis is given to the stellar models which necessarily underlie this operation, as the mass function is proportional to the derivative of the mass{luminosity relation, and this latter quantity can not be deri...

Photon-axion conversion induced by intergalactic magnetic fields causes an apparent dimming of distant sources, notably of cosmic standard candles such as supernovae of type Ia (SNe Ia). We review the impact of this mechanism on the luminosity-redshift relation of SNe Ia, on the dispersion of quasar spectra, and on the spectrum of the cosmic microwave background. The original idea of explaining...

We present a robust method to derive the duty cycle of QSO activity based on the empirical QSO luminosity function and on the present-day linear relation between the masses of supermassive black holes and those of their spheroidal host stellar systems. It is found that the duty cycle is substantially less than unity, with characteristic values in the range 3− 6× 10. Finally, we tested the expec...

We investigate the variation of galaxy clustering with luminosity using the recently completed SSRS2 sample. Clustering measurements based on the two-point correlation function and the variance of counts in cells reveal a strong dependence of clustering on luminosity for galaxies brighter than L∗, while no significant variation is detected for fainter galaxies. We derive a relative bias versus ...

GRB 060218 is a watershed event. Statistically, its detection suggests that there is likely a distinct low-luminosity (LL) population of gamma-ray bursts (GRBs) whose event rate is much higher than that of conventional high-luminosity GRBs. This LL population may give significant contribution to the diffuse neutrino background flux at energies higher than 1016eV. The spectral lag of this burst ...

We present the results of non-linear pulsation modeling of bump Cepheids in the LMC and SMC. By obtaining an optimal fit to the observed MACHO V and R lightcurves we can determine the fundamental parameters of each Cepheid, namely mass, luminosity, effective temperature, distance modulus and reddening. We are able to describe the mass-luminosity relation for core-He burning intermediate mass st...