Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy

We review HB stars in a broad astrophysical context, including both variable and non-variable stars. A reassessment of the Oosterhoff dichotomy is presented, which provides unprecedented detail regarding its origin and systematics. We show that the Oosterhoff dichotomy and the distribution of globular clusters (GCs) in the HB morphology-metallicity plane both exclude, with high statistical significance, the possibility that the Galactic halo may have formed from the accretion of dwarf galaxies resembling present-day Milky Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the second-parameter problem is presented. A technique is proposed to estimate the HB types of extragalactic GCs on the basis of integrated far-UV photometry. The relationship between the absolute V magnitude of the HB at the RR Lyrae level and metallicity, as obtained on the basis of trigonometric parallax measurements for the star RR Lyrae, is also revisited, giving a distance modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are studied. Finally, the conductive opacities used in evolutionary calculations of low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and Space Scienc

Cation activation of pyrophosphatases from soil microorganisms

The intracellular inorganic pyrophosphatases obtained from mixed cultures of soil microorganisms were characterised in terms of the activating cation and pH-activity profile. Microorganisms were grown in an initial culture 10 mm in tetrasodium pyrophosphate, a nutritionally non-specific aqueous medium, buffered at pH 7.0 with an organic buffer and inoculated with soil. The intracellular pyrophosphatases in a desalted, cell-free enzyme preparation were examined for activity in assays using 1 mM tetrasodium pyrophosphate and nine cations (Mg, Zn, Co, Mn, Fe, Ca, Cu, Al and Fe) over the pH range 2-10, with appropriate buffers. Only the first 5 cations activated the enzymes. The pH-activity profiles for each cation were different and each displayed only one pH optimum. The pH optima were not greatly affected by cation concentration or kind of buffer. The specific activities at the optimum pH and cation concentration for each culture decreased in order Mg > Zn > Co > Mn > Fe. The results indicate the production of functionally similar enzymes by diverse microorganisms