Comet Hale-Bopp is, without doubt, one of the most important objects for cometary science which has ever been observed. The light curve is well-observed from a heliocentric distance 7.2 AU and some information is available at distances as great as 17 AU. This allows the photometric evolution of the comet to be studied as different volatiles

A comprehensive study of the planetary nebula K4-55 is presented. In addition to CCD narrowband images, spatially resolved low-dispersion and high-resolution spectra were obtained. This has allowed the different morphological features in the images to be connected with the kinematics and with the physical information, leading to the establishment

The first X-ray observation of the Seyfert 2 galaxy NGC 5252 is reported. ASCA Astro-D collected approximately 4000 photons per detector, enough to perform an accurate spectral analysis of this source. The luminosity of NGC 5252 is LX(0.7-10 keV) ≌ 2.6 × 1043 ergs s-1, typical of a Seyfert 1 galaxy. A simple description of the spectrum with a

We propose a method to classify faint objects from digital astronomical images based on a layered feedforward neural network which has been trained by the backpropagation procedure (Werbos 1974). An "academic" example showing that artificial neural network method behaves as a Bayesian classifier is discussed. A comparison of the classification

We have applied the InfraRed Flux Method (IRFM) to a sample of 475 dwarfs and subdwarfs in order to derive their effective temperatures with a mean accuracy of about 1.5%. We have used the new homogeneous grid of theoretical model atmosphere flux distributions developed by Kurucz (1991, 1993) for the application of the IRFM. The atmospheric

A large monitoring project, OJ-94, was set up with the aim of monitoring the blazar OJ 287 during the predicted optical outburst (in fall 1994, Sillanpaa et al. 1988) and simultaneously to collect a large data base for a small sample of blazars. Through this campaign we have obtained the best ever obtained optical light curve for any extragalactic