Search Publications

Halo stars in the immediate solar neighbourhood

Jahreiß, H.; Fuchs, B.

We have searched the Fourth Catalogue of Nearby Stars for halo stars and identified 15 subdwarfs and a high velocity white dwarf in the solar neighbourhood. This search was motivated mainly by the recent determinations of MACHO masses of about 0.5cal M_sun, which are typical for halo dwarfs. The local mass density of these stars is 1.5*10(-4) cal …

Bar-driven evolution of S0s: the edge-on galaxy NGC 4570

van den Bosch, Frank C.; Emsellem, Eric

We present circumstantial evidence that the central region of the edge-on S0 galaxy NGC 4570, which harbours a 150-pc scale nuclear disc in addition to its main outer disc, has been shaped under the influence of a small (~500 pc) bar. This is based on the discovery of two edge-on rings, the locations of which are consistent with the inner Lindblad…

A New Analysis of RR Lyrae Kinematics in the Solar Neighborhood

Martin, John C.; Morrison, Heather L.

Full space velocities are computed for a sample of 130 nearby RR Lyrae variables using both ground-based and Hipparcos proper motions. In many cases proper motions for the same star from multiple sources have been averaged to produce approximately a factor of 2 improvement in the transverse space velocity errors. In most cases, this exceeds the ac…

Clouds of High Contrast on Uranus

Karkoschka, Erich

Cosmological Parameters from Multiple-Arc Gravitational Lensing Systems. I. Smooth Lensing Potentials

Link, Robert; Pierce, Michael J.

We describe a new approach for the determination of cosmological parameters using gravitational lensing systems with multiple arcs. We exploit the fact that a given cluster can produce multiple arcs from sources over a broad range in redshift. The coupling between the critical radius of a single arc and the projected mass density of the lensing cl…

Seismic Holography of Solar Activity

Braun, D. C.; Lindsey, C.; Fan, Y. +1 more

Helioseismic images of sunspots show a remarkable acoustic anomaly surrounding the sunspot. We applied the computational formalism of ``helioseismic holography'' to SOHO-MDI observations to render acoustic images of NOAA AR 7973, an active region containing a moderately large sunspot. The results of this study are based on simple ``acoustic power …

Small-scale structures in the far-infrared background

Laureijs, R. J.; Klaas, Ulrich; Herbstmeier, Uwe +6 more

Four fields with areas ranging from 80 to 2000 arcmin(2) have been mapped with the photometer on board of the Infrared Space Observatory (ISO) at 90 and around 180mu m in regions of bright and faint cirrus. We examined the spatial characteristics of the infrared background emission with high spatial resolution and found that the fluctuations in th…

A Possible Mechanism for the Origin of Emerging Flux in the Sunspot Moat

Title, A.; Shine, R.; Sakai, J. I. +1 more

Mass and energy flow near sunspots are associated with the emergence of magnetic flux, which then moves outward in the sunspot moat. We present results of analytical and numerical studies of the interaction of horizontal magnetic flux and plasma flows in three-dimensional geometry. We show that nonlinear coupling of flux and plasma flows in the pr…

The Ultracompact H II Region G5.97-1.17: an Evaporating Circumstellar Disk in M8

Henning, T.; Stecklum, B.; Hayward, T. L. +4 more

We present new high spatial resolution optical, infrared, and radio observations of G5.97-1.17, an ultracompact H ii region 2.7" distant from the O7 star Herschel 36 in the center of M8, the Lagoon Nebula. Infrared imaging was obtained using the adaptive optics system ADONIS on the ESO 3.6 m telescope and a thermal-IR camera on the Hale 5 m; optic…

Kinematic signatures of violent formation of galactic OB associations from HIPPARCOS measurements

Torra, J.; Comeron, F.; Gomez, A. E.

Proper motions measured by Hipparcos confirm the large anomalous velocities of the OB associations located around the Cygnus Superbubble (Cygnus OB1, OB3, OB7, and OB9), and reveal a clearly organized expanding pattern in Canis Major OB1. At the distances of these associations, the organized velocity patterns imply LSR velocities of up to ~ 60 km …