We study the effect that the temperature structure has on the determination of the primordial helium abundance, Yp. We provide an equation linking T(O III), the temperature derived from the [O III] lines, and T(He II), the temperature of the He I lines, both for H II regions with O++ only and for H II regions where a fraction of O+ is present. By

IAUC 7821 available at Central Bureau for Astronomical Telegrams.

The results of the tenth multi-site campaign of the STEPHI network are reported. The delta Scuti stars V624 Tau (HD 23156) and HD 23194, belonging to the Pleiades cluster, were observed photometrically for 34 days on three continents during 1999 November-December. An overall run of 343 hours of data was collected. Seven frequencies for V624 Tau and

We present a general procedure for obtaining the present density fluctuation probability distribution given the statistics of the initial conditions. The main difficulties faced with regard to this problem are those related to the nonlinear evolution of the density fluctuations and those posed by the fact that the fields we are interested in are

We show that SBS1150+599A is most probably a planetary nebula located in the Galactic halo (becoming PN G135.9+55.9). Our photoionization models indicate that its oxygen abundance is lower than 1/100 solar.

Planetary nebulae (PNe) have been used to trace the chemical evolution of galaxies, not only in the Milky Way (Esteban & Peimbert 1995 and references therein) but also in nearby galaxies (Dopita et al. 1997; Richer et al. 1999; Jacoby & Ciardullo 1999). Extragalactic PNe have also been used as secondary distance indicators by means of the planetary