Orion

A very large field of the sky that includes the Perseus molecular cloud complex (upper right), the Taurus-Auriga molecular cloud complex (upper left), and the Orion star-forming region (lower center), as observed with IRAS in the combined wavelength bands. where t is the optical depth and dfi the solid angle subtended by the source. Fv may be obtained by fitting some regression function to the data. IRAS found over 250,000 sources, which to a large extent are identified as emissions...

The Xray Account of YSOs

The first extraterrestrial X-rays were detected from the Sun by H. Friedman in 1949 in a V2 rocket flight. It took another 25 years to take the first X-ray image during a SKYLAB mission in 1973. Plate 2.1 shows a more modern soft X-ray image of the Sun as seen with the YOHKOH soft X-ray telescope 64 giving a stunning view of a corona. Modern telecopes are not yet powerful enough to image coronae from other stars, but Plate 2.1 could give a small-scale impression of coronal activity in young...

Abbreviations

This appendix contains short explanations of the acronyms and abbreviations used throughout the book. the descriptions given are minimal and only designed for look-up purposes. In the book acronyms are spelled out only once when they appear for the first time. there are no references or other referrals attached to these explanations with the exception of links to websites in some cases (where a fuller explanation is given). In all other cases, the main text of this book or a standard textbook...

CTTS versus WTTS

The issue of a predominantly coronal origin in young PMS stars is currently extensively debated. So far the question whether CTTS and WTTS have distinguished differences in their X-ray emission remains unclear. Specifically the statistical account in major star-forming clusters, such as the ONC and IC 348, do not support major X-ray differences between WTTS and CTTS other than that the former have somewhat enhanced fluxes (see Sect. 8.4). To date this manifests the assumption that in both cases...

The Conqest of the Electromagnetic Spectrum

Newton, in the middle of the 17th century, found out that light is composed of a whole range of colors and that this spectrum spans from violet to blue, green, yellow, orange and red. It implies a wavelength range from about 400 to about 750 nanometers. Not much was known about the nature of light until 1690 when C. Huygens showed that light has a wave character. Over 100 years later this scale rapidly expanded at both ends. F.W. Herschel found in 1800 that the largest amount of heat from the...