The luminosities and periods of obscured AGB stars in the LMC are discussed using a combination of ISO and ground-based infrared photometry. The bolometric luminosities of these stars fall close to an extrapolation of the period-luminosity relation derived for oxygen-rich Mira variables, with both oxygenand carbon-rich stars falling close to the same relation. It has been known for many years t...

The variability of gamma-ray burst (GRB) is thought to be correlated with its absolute peak luminosity, and this relation had been used to derive an estimate of the redshifts of GRBs. Recently Amati et al. present the results of spectral and energetic properties of several GRBs with know redshifts. Here we analyse the properties of two group GRBs, one group with known redshift from afterglow ob...

Aims. We investigate the dependence of the luminosity-diameter relation of galaxies on the environment. Methods. This study is based on a comparison between the 80 galaxies in the Shapley-Ames Catalog that are located within a distance of 10 Mpc, and the luminosity-diameter relation for galaxies in great clusters such as Virgo and Coma. Results. A relatively tight linear correlation is observed...

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 versu...

Based on updated nonlinear, convective pulsation models computed for several values of stellar mass, luminosity and metallicity, theoretical constraints on the K−band Period-Luminosity (P L K) relation of RR Lyrae stars are presented. We show that for each given metal content the predicted P L K is marginally dependent on uncertainties of the stellar mass and/or luminosity. Then, by considering...