The principal components analysis (PCA) technique is used to develop an extremely fast and stable Stokes inversion code, suitable for application to large data sets from instruments that operate under standard conditions. This paper provides some tips on reducing the dimensionality of the problem, which are then used to develop a practical

We present RIJHK imaging of seven radio galaxies from the 7C Redshift Survey (7CRS) which lack strong emission lines and we use these data to investigate their spectral energy distributions (SEDs) with models that constrain their redshifts. Six of these seven galaxies have extremely red colours (R-K>5.5) and we find that almost all of them lie in

We present new infrared photometry of the WC7-type Wolf-Rayet star HD 192641 (WR137) from 1985 to 1999. These data track the cooling of the dust cloud formed in the 1982-84 dust-formation episode from 1985 to 1991, the increase of the infrared flux from 1994.5 to a new dust-formation maximum in 1997 and its subsequent fading. From these and earlier

We discuss the mechanism for the oscillatory behavior of the static interparticle potential in a degenerate electron plasma. This behavior, observed in metallic alloys, is commonly referred to as 'Friedel oscillations', and its origin associated to the Kohn singularity. We show that, although this interpretation is adequate for large distances, the

The IRIS network has accumulated full disk helioseismological data since July 1989, i.e. a complete 11-year solar cycle. Since the last paper publishing a frequency list [A&A 317 (1997) L71], not only has the network acquired new data, but has also developed new co-operative programs with compatible instruments [Abstr. SOHO 6/GONG 98 Workshop (1998

After a brief description of how spectral emission lines can be studied by the self-absorption-curve method, we show what happens when it is used to examine the FeIII and NII lines of P Cygni. An extremely surprising result is obtained; more highly-excited pure-emission lines without blueshifted absorption appear to be optically thicker than less