Aneides hardii

Number of pages=23Geological SciencesIntegrative Biolog

The High Chromospheres of the Late A Stars

We report the detection of N V 1239 A transition region emission in HST/GHRS spectra of the A7 V stars, Alpha Aql and Alpha Cep. Our observations provide the first direct evidence of 1-3 x 10^5 K material in the atmospheres of normal A-type stars. For both stars, and for the mid-A--type star Tau3 Eri, we also report the detection of chromospheric emission in the Si III 1206 A line. At a B-V color of 0.16 and an effective temperature of 8200 K, Tau3 Eri becomes the hottest main sequence star known to have a chromosphere and thus an outer convection zone. We see no firm evidence that the Si III line surface fluxes of the A stars are any lower than those of moderately active, solar-type, G and K stars. This contrasts sharply with their coronal X-ray emission, which is >100 times weaker than that of the later-type stars. Given the strength of the N V emission observed here, it now appears unlikely that the X-ray faintness of the A stars is due to their forming very cool, <= 1 MK coronae. An alternative explanation in terms of mass loss in coronal winds remains a possibility, though we conclude from moderate resolution spectra of the Si III lines that such winds, if they exist, do not penetrate into the chromospheric Si III--forming layers of the star, since the profiles of these lines are *not* blueshifted, and may well be redshifted with respect to the star.Comment: LaTex, 12 pages, 3 Postscript figures, uses aaspp4, accepted by Ap

Rank one perturbations and the zeros of paraorthogonal polynomials on the unit circle

We prove several results about zeros of paraorthogonal polynomials using the theory of rank one perturbations of unitary operators. In particular, we obtain new details on the interlacing of zeros for successive POPUC.Comment: 8 page

SO(3)-Structures on 8-manifolds

We study Riemannian 8-manifolds with an infinitesimal action of SO(3) by which each tangent space breaks into irreducible spaces of dimensions 3 and 5. The relationship with quaternionic, almost product- and PSU-geometry is thoroughly explained using representation-theoretical arguments.Comment: 19 pages, 2 figure

Complex homothetic foliations on K\"ahler manifolds

We obtain a local classification of complex homothetic foliations on Kaehler manifolds by complex curves. This is used to construct almost Kaehler, Ricci-flat metrics subject to additional curvature properties.Comment: Final version, up to typos. To appear in BLM