The ratios of hydrogen Balmer emission line intensities in cataclysmic variables are signatures of the physical processes that produce them. To quantify those signatures relative to classifications of cataclysmic variable types, we applied the multivariate statistical analysis methods of principal components analysis and discriminant function analysis to the spectroscopic emission data set of Williams (1983). The two analysis methods reveal two different sources of variation in the ratios of the emission lines. The source of variation seen in the principal components analysis was shown to be correlated with the binary orbital period. The source of variation seen in the discriminant function analysis was shown to be correlated with the equivalent width of the Hβ line. Comparison of the data scatterplot with scatterplots of theoretical models shows that Balmer line emission from T CrB systems is consistent with the photoionization of a surrounding nebula. Otherwise, models that we considered do not reproduce the wide range of Balmer decrements, including ‘inverted’ decrements, seen in the data.

We present images of Mars obtained in the 2.0 μm CO2 band with the United Kingdom Infrared Telescope (UKIRT). The images reveal topographic features of the Martian surface that are usually invisible in direct albedo images at visible or IR wavelengths, but agree remarkably well with the topography of the planet as mapped by the MOLA instrument on Mars Global Surveyor. The CO2 band depth is a measure of the absorbing column of CO2 and hence determined primarily by the surface atmospheric pressure. The surface pressure variations are detected with a sensitivity of 4–5 Pa. We compare our data with radiative transfer models and find that the measured CO2 variation with pressure is consistent with the models. We discuss the possibility that similar observations might be used to observe atmospheric pressure changes due to Martian weather systems.

When analyzing dark matter halos forming in cosmological n-body simulations, it is common practice to obtain the density profile utilizing spherical shells. However, it is also known that the systems under investigation are far from spherically symmetric but, rather, follow a triaxial mass distribution. In this study we present an estimator for the error introduced by spherically averaging an elliptical mass distribution. We systematically investigate the differences arising when using a triaxial density profile under the assumption of spherical symmetry. We show that the variance in the density can be as large as 50% in the outer parts of dark matter halos for extreme (but still credible) axis ratios of 0.55: 0.67: 1. The inner parts are less affected but still show a scatter at the 16% level for these prolate systems. For more moderate ellipticities, i.e. axis ratios of 0.73: 0.87: 1, the error is smaller but still as large as 10–20% depending on distance. We further provide a simple formula that allows estimation of this variance as a function of radius for arbitrary axis ratios. We conclude that highly prolate and/or oblate systems are better fit by analytical profiles that take into account the triaxial nature of cosmological objects.

We have monitored multi-TeV cosmic rays by a small air shower array in Tehran (35°43′ N, 51°20′ E, 1200 m = 890 g cm−2). More than 1.1 × 106 extensive air shower events were recorded. These observations enabled us to analyse sidereal variation of the galactic cosmic ray intensity. The observed sidereal daily variation is compared to the expected variation which includes the Compton–Getting effect due to the motion of the earth in the Galaxy. In addition to the Compton–Getting effect, an anisotropy has been observed which is due to a unidirectional anisotropy of cosmic ray flow along the Galactic arms.