Multiple scattering in plane atmosphere

Studies on multiple scattering and radiative transfer began early in this century by the work of Schwarzschild, Miln e, and Eddington. In the 1950's the important books of Chandrasekhar, Kourganoff and Sobolev on this subject appeared. In spite of the fact that almost all important questions in this very classical problem have now been solved, it often takes long to obtain the numerical answer to a simple question. For that reason I stated some years ago to prepare a book which should contain many tables and graphs together with a condensed text. In the course of this work it was found useful to deviate from normal usage in some respects, which I shall briefly review.Asociación Argentina de Astronomí

Radio astronomy at Leiden University

The radiotelescope of 25-meter diameter at Dwingeloo is now 10 years in almost continuous operation. The Observatories of Leiden and Groningen share the observing time. A doctor's thesis is often based on several thousand hours of observation, not all taken by the man himself. A good part of the registration and reduction is automatic. In the following a selection of some recent results is presented.Asociación Argentina de Astronomí

Observing the interstellar magnetic field

Before coming to a more detailed discussion, let us see what ways exist to establish the presence of a magnetic field In the galaxy at all. (Table 1). We shall briefly review these methods one by one.Asociación Argentina de Astronomí

Multiple scattering in plane atmosphere

Studies on multiple scattering and radiative transfer began early in this century by the work of Schwarzschild, Miln e, and Eddington. In the 1950's the important books of Chandrasekhar, Kourganoff and Sobolev on this subject appeared. In spite of the fact that almost all important questions in this very classical problem have now been solved, it often takes long to obtain the numerical answer to a simple question. For that reason I stated some years ago to prepare a book which should contain many tables and graphs together with a condensed text. In the course of this work it was found useful to deviate from normal usage in some respects, which I shall briefly review.Asociación Argentina de Astronomí

Radio astronomy at Leiden University

The radiotelescope of 25-meter diameter at Dwingeloo is now 10 years in almost continuous operation. The Observatories of Leiden and Groningen share the observing time. A doctor's thesis is often based on several thousand hours of observation, not all taken by the man himself. A good part of the registration and reduction is automatic. In the following a selection of some recent results is presented.Asociación Argentina de Astronomí

Radio astronomy at Leiden University

The radiotelescope of 25-meter diameter at Dwingeloo is now 10 years in almost continuous operation. The Observatories of Leiden and Groningen share the observing time. A doctor's thesis is often based on several thousand hours of observation, not all taken by the man himself. A good part of the registration and reduction is automatic. In the following a selection of some recent results is presented.Asociación Argentina de Astronomí

Observing the interstellar magnetic field

Before coming to a more detailed discussion, let us see what ways exist to establish the presence of a magnetic field In the galaxy at all. (Table 1). We shall briefly review these methods one by one.Asociación Argentina de Astronomí

Neutral hydrogen in extragalactic systems

Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe

Streamer Wave Events Observed in Solar Cycle 23

In this paper we conduct a data survey searching for well-defined streamer wave events observed by the Large Angle and Spectrometric Coronagraph (LASCO) on-board the Solar and Heliospheric Observatory (SOHO) throughout Solar Cycle 23. As a result, 8 candidate events are found and presented here. We compare different events and find that in most of them the driving CMEs ejecta are characterized by a high speed and a wide angular span, and the CME-streamer interactions occur generally along the flank of the streamer structure at an altitude no higher than the bottom of the field of view of LASCO C2. In addition, all front-side CMEs have accompanying flares. These common observational features shed light on the excitation conditions of streamer wave events. We also conduct a further analysis on one specific streamer wave event on 5 June 2003. The heliocentric distances of 4 wave troughs/crests at various exposure times are determined; they are then used to deduce the wave properties like period, wavelength, and phase speeds. It is found that both the period and wavelength increase gradually with the wave propagation along the streamer plasma sheet, and the phase speed of the preceding wave is generally faster than that of the trailing ones. The associated coronal seismological study yields the radial profiles of the Alfv\'en speed and magnetic field strength in the region surrounding the streamer plasma sheet. Both quantities show a general declining trend with time. This is interpreted as an observational manifestation of the recovering process of the CME-disturbed corona. It is also found that the Alfv\'enic critical point is at about 10 R$_\odot$ where the flow speed, which equals the Alfv\'en speed, is $\sim$ 200 km s$^{-1}$