ROSAT Observations G. HASINGER Max-Planck-Institut flir extraterrestrische Physik, D-85740 Garching, Germany Abstract. This review describes the most recent advances in the study of the extragalactic soft X-ray background and what we can learn about its constituents. The deepest pointed observations with the ROSAT PSPC are discussed. The logN-logS relation is presented, which reaches to the faintest X-ray fluxes and to the highest AGN surface densities ever achieved. The N(>S) relation shows a 2 density in excess of 400 deg- at the faintest fluxes and a flattening below the Einstein Deep Survey limit. About 60% of the extragalactic background has been resolved in the deepest field. Detailed source spectra and first optical and radio identifications will be discussed. The results are put into perspective of the higher energy X -ray background. Key words: X-rays, background radiations, active galactic nuclei. 1. Introduction The extragalactic X-ray background (XRB), discovered about 30 years ago, has been studied extensively with many X-ray experiments, in particular with the satel lites HEAO I and II (see ego Boldt 1987) and with ROSAT (e. g. Hasinger et aI. , 1993). Figure 1 shows a compilation of some of the most recent spectral measure ments for the X-ray background. Over the energy range from 3 to about 100 keY its spectrum can be well approximated by an optically thin thermal bremsstrahlung model with kT ~ 40 keY, while at lower X-ray energies a steepening into a new component has been observed observed (e. g.

This book provides the first comprehensive historical account of the evolution of scientific traditions in astronomy, astrophysics, and the space sciences within the Max Planck Society. Structured with in-depth archival research, interviews with protagonists, unpublished photographs, and an extensive bibliography, it follows a unique history: from the post-war relaunch of physical sciences in West Germany, to the spectacular developments and successes of cosmic sciences in the second half of the 20th century, up to the emergence of multi-messenger astronomy. It reveals how the Society acquired national and international acclaim in becoming one of the world’s most productive research organizations in these fields.

Charge-Coupled Devices (CCDs) are the state-of-the-art detector in many fields of observational science. Updated to include all of the latest developments in CCDs, this second edition of the Handbook of CCD Astronomy is a concise and accessible reference on all practical aspects of using CCDs. Starting with their electronic workings, it discusses their basic characteristics and then gives methods and examples of how to determine these values. While the book focuses on the use of CCDs in professional observational astronomy, advanced amateur astronomers, and researchers in physics, chemistry, medical imaging, and remote sensing will also find it very valuable. Tables of useful and hard-to-find data, key practical equations, and new exercises round off the book and ensure that it provides an ideal introduction to the practical use of CCDs for graduate students, and a handy reference for more experienced users.

The ability of storing, managing, and giving access to the huge quantity of data collected by astronomical observatories is one of the major challenges of modern astronomy. At the same time, the growing complexity of data systems implies a change of concepts: the scientist has to manipulate data as well as information. Recent developments of the `WorldWideWeb' bring interesting answers to these problems. The book presents a wide selection of databases, archives, data centers, and information systems. Clear and up-to-date descriptions are included, together with their scientific context and motivations. Audience: This volume provides an essential tool for astronomers, librarians, data specialists and computer engineers.

**The Cosmic Frontier Embark on an Extraordinary Journey Beyond Our Solar System** Unlock the mysteries of the universe and explore the vast expanse beyond our solar system with "The Cosmic Frontier." This compelling eBook offers an in-depth look at the fascinating world of exoplanets and the groundbreaking techniques used to study them. Whether you're a seasoned astronomy enthusiast or new to the subject, this comprehensive guide is your gateway to understanding the latest discoveries in exoplanet science. Discover the allure of exoplanets, planets that orbit stars beyond our Sun, beginning with their captivating history and the reasons why their study is paramount in modern astronomy. Dive into the various methods scientists use to detect these distant worlds, from the Transit Method to Gravitational Microlensing, each unveiling secrets hidden in the cosmos. With detailed chapters on the Kepler Space Telescope and its monumental discoveries, "The Cosmic Frontier" highlights how this mission has shaped our understanding of space and what lies ahead. Explore the concept of the Goldilocks Zone, identifying conditions necessary for life and examining potentially habitable exoplanets that have captured worldwide attention. Beyond gas giants and super-Earths, the book introduces an array of diverse exoplanets, including rogue planets and water worlds. Learn about the ongoing search for extraterrestrial life and the role of SETI in this intriguing quest, while examining how exoplanets have permeated popular culture. Future prospects in exoplanet research appear bright, with upcoming missions, technological advances, and international collaboration paving the way. Take a closer look at spectroscopy and ground-based telescopes that have revolutionized the study of exoplanetary atmospheres. "The Cosmic Frontier" delves into the formation of exoplanets, comparative planetology, citizen science, and the ethical implications of discovering life. Engage with visionary chapters that ask the big questions in exoplanet science and provide practical tools for aspiring astronomers. Immerse yourself in captivating case studies of iconic exoplanets, from the TRAPPIST-1 system to Proxima Centauri b, and gain insights into current trends and future challenges in this ever-evolving field. Journey through "The Cosmic Frontier" and inspire the next generation of explorers with the wonders of the universe.