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Measuring Plasma Parameters With Thermal Noise Spectroscopy

Moncuquet, Michel; Issautier, Karine; Meyer-Vernet, Nicole +4 more

This paper describes the basic principles, the unique features and the limitations of thermal noise spectroscopy as a tool for in situ diagnostics in space plasmas. This technique is based on the analysis of the electrostatic field spectrum produced by the quasi-thermal fluctuations of the electrons and ions, which can be measured with a sensitive…

The Opacity of Nearby Galaxies from Colors and Counts of Background Galaxies. I. The Synthetic Field Method and Its Application to NGC 4536 and NGC 3664

Ferguson, Henry C.; Calzetti, Daniela; Panagia, Nino +3 more

We describe a new direct method for determining the opacity of foreground galaxies that does not require any a priori assumptions about the spatial distribution or the reddening law of the obscuring material. The method is to measure the colors and counts of background galaxies that can be identified through the foreground system. The method is ca…

Mass determination of astrometric binaries with Hipparcos. III. New results for 28 systems

Mignard, F.; Martin, C.; McAlister, H. A. +1 more

This paper is the third of a series devoted to the determination of stellar masses from Hipparcos data. This is a continuation of Martin et al. (1997), who introduced the theory and assessed the performance of the method from simulated data, and of a second paper with the first results for 46 systems, ( te[Martin & Mignard 1998]{Mar98}). The o…

On Chromospheric Heating Mechanisms of ``Basal Flux'' Stars

Judge, P. G.; Carpenter, K. G.

Several pieces of evidence have been pieced together over recent years to support the notion that the chromospheric emission measured from stars with convection zones results in part from the upward propagation and dissipation of acoustic waves. One argument, based on a statistical analysis of available UV data of such stars across the H-R diagram…

Alfven wave transmission and particle acceleration in parallel shock waves

Vainio, R.; Schlickeiser, R.

We study Alfven wave transmission through parallel shocks. First, the paper corrects for mistakes made in a previous study by Campeanu & Schlickeiser on the same subject. It is shown, contrary to CS, that first-order Fermi acceleration by multiple shock crossings is generally more effective than stochastic acceleration in the downstream region…

The interstellar extinction in the solar neighbourhood. I. Statistical approach

Egret, D.; Vergely, J. -L.; Koeppen, J. +1 more

Assuming some specific distribution of the interstellar clouds, we interpret the projected stellar extinction in terms of mean extinction by cloud as well as cloud density on the line of sight. Individual stellar extinctions are derived from Stroemgren photometry and from accurate distances based on Hipparcos parallaxes. Extinction profiles as a f…

Emission Line and Ultraviolet to X-Ray Continuum Correlations: Constraints on the Anisotropy of the Ionizing Continuum in Active Galactic Nuclei

Wang, Ting-Gui; Zhou, You-Yuan; Lu, You-Jun

Anisotropic emission of the ionizing continuum is a general prediction of accretion disk models. In this paper, we present the results of correlation analysis of the UV emission line and UV to X-ray continuum properties for a large sample of broad emission line AGNs observed with ROSAT, IUE, and HST. We find strong correlations between the C IV/Ly…

Hubble Space Telescope Imaging of the Circumstellar Nebulosity of T Tauri

Ballester, Gilda E.; Krist, John E.; Crisp, David +14 more

Short-exposure Planetary Camera images of T Tauri have been obtained using broadband filters spanning the wavelength range 0.55-0.80 µm. The optically visible star lies very close to an arc of reflection nebulosity. The arc's northern arm extends approximately 5" from the star, while its southwestern arm appears brighter and extends only 2".…

Induced Massive Star Formation in the Trifid Nebula?

Acosta-Pulido, J.; Cernicharo, J.; Cox, P. +7 more

The discovery of new gamma Doradus stars from the HIPPARCOS mission

Eyer, L.; Aerts, C.; Kestens, E.

We present a classification of 39 new variable stars with spectral type between A2 and F8 discovered by Hipparcos with the aim to find new gamma Doradus stars. We have used a multivariate classification scheme and report the discovery of 14 new gamma Doradus variables among this unbiased sample. Our results point out the biased nature towards hot …