Polaris, the nearest and brightest classical Cepheid, is a member of at least a triple system. It has a wide (18″) physical companion, the F-type dwarf Polaris B. Polaris itself is a single-lined spectroscopic binary with an orbital period of ∼30 years (Kamper 1996). By combining Hipparcos measurements of the instantaneous proper motion with long-term measurements and the Kamper radial-velocity orbit, Wielen et al (2000) have predicted the astrometric orbit of the close companion. Using the Hubble Space Telescope and the Advanced Camera for Surveys' High-Resolution Channel with an ultraviolet (F220W) filter, we have now directly detected the close companion. Based on the Wielen et al orbit, the Hipparcos parallax, and our measurement of the separation (0″.176 ± 0″.002), we find a preliminary mass of 5.0 ± 1.5 M⊙ for the Cepheid and 1.38 ± 0.61 M⊙ for the close companion. These values will be refined by additional HST observations scheduled for the next 3 years.

We have also obtained a Chandra ACIS-I image of the Polaris field. Two distant companions C and D are not X-rays sources and hence are not young enough to be physical companions of the Cepheid. There is one additional stellar X-ray source in the field, located 253″ from Polaris A, which is a possible companion. Further investigation of such a distant companion is valuable to confirm the full extent of the system.

We report the results from an homogeneous analysis of the X-ray (ACIS-S/Chandra) data available for a sample of 52 LINER galaxies. The X-ray morphology has been classified attending to their nuclear compactness in the hard band (4.5–8.0 keV), into 2 categories: AGN-like nuclei (with a clearly identified unresolved nuclear source) and Starburst-like nuclei (without a clear nuclear source). 60% of the total sample are classified as AGNs, with a median luminosity of $\rm{L_{X}(2.0\hbox{-}10.0 keV)=2.5\times 10^{40} erg s^{-1}}$, which is an order of magnitude higher than that for SB-like nuclei. The spectral fitting allows to conclude that most of the objects need a non-negligible thermal contribution. When no spectral fitting can be performed (low signal-to-noise ratio), the Color-Color diagrams allow us to compute physical parameters such as density column, temperature of the thermal model or spectral index and therefore to analyze the origin of the X-ray emission. All X-ray morphology, spectral fitting and Color-Color diagrams allow conclude that a high percentage of LINER galaxies host AGN nuclei.