We report our analysis of the stability of pulsation periods in the DAV star (pulsating hydrogen atmosphere white dwarf) ZZ Ceti, also called R548. On the basis of observations that span 31 years, we conclude that the period 213.13 s observed in ZZ Ceti drifts at a rate dP/dt=1.2 Gyr, comparable to the theoretical cooling timescale for the star

We present Heinrich Hertz Telescope CO (3-2) observations of a sample of 10 early-type galaxies detected both in far-infrared (IRAS) and in CO (1-0). Six of the objects (i.e., 60% of the sample) were detected in the CO (3-2) transition. Comparison of the beam-matched CO (3-2)/CO (1-0) and CO (2-1)/CO (1-0) intensity ratios with simple large

The faint end of the differential galaxy number counts n(m) in the Hubble Deep Field-North (HDF-N) has been determined for the F450W, F606W, and F814W filters by means of surface brightness fluctuation measurements. This technique allows us to explore n(m) beyond the limiting magnitude of the HDF, providing new, stronger constraints on the faint

We describe a Fourier-based method of separating bars from spirals in near-infrared images. The method takes advantage of the fact that a bar is typically a feature with a relatively fixed position angle and uses the simple assumption that the relative Fourier amplitudes due to the bar decline with radius past a maximum in the same or a similar

The ROSAT X-ray observations were carried out at three different epochs between 1992 and 1996. Two PSPC (called "A" and "B") and one HRI ("H") observations were scheduled on NGC 2451. (3 data files).

In this paper we discuss the reason for the widely found discrepancy between Sérsic brightness law fitted along major and minor axes of elliptical galaxies. We show that this difference is a natural consequence of the isophotes eccentricity law. We present a mathematical transformation that allows to obtain the minor axis Sérsic's law from that of