- Hot Subdwarf Stars in Close-Up View: Orbits, Rotation, Abundances and Masses of their Unseen Companions (2009)
- Hot underluminous stars, also called hot subdwarfs or sdBs, are evolved stars, which already went through the giant-phase and lost most of their envelope. About half of the known sdBs are in close binary systems with usually invisible companions. This work mostly deals with such close binary systems and contains a detailed analysis of more than 100 sdB stars. Not only the elemental abundances and rotational velocities have been measured, but also the orbital parameters of binaries. Masses and nature of the unseen companions were constrained. The most important result of this work was the discovery that at least 4% of the analysed sdBs could have massive and compact companions: Neutron stars or even black holes. A dark population of these exotic objects would have been discovered in this case.
- Radial Velocity Survey of Low‐Mass Companions to sdB Stars (2011)
- The origin of subdwarf B (sdB) stars is not fully understood yet since it requires high mass loss at the red giant stage. SdBs in close binary systems are formed via common envelope ejection, but the origin of apparently single sdB stars remains unclear. Substellar companions may be able to trigger common envelope ejection and help forming sdBs that appear to be single. Using a sample of high resolution spectra we aim at detecting small radial velocity (RV) shifts caused by such low mass (sub‐)stellar companions. The RVs are measured with high accuracy using sharp metal lines. Our goal is to test the theoretical predictions and put constraints on the population of the lowest mass companions to sdB stars.
- Radial Velocity Search for Substellar Companions to sdB Stars (2011)
- After the discovery of a substellar companion to the hot subdwarf HD 149382, we have started a radial velocity search for similar objects around other bright sdB stars using the Anglo‐Australian Telescope. Our aim is to test the hypothesis that close substellar companions can significantly affect the post‐main sequence evolution of solar‐type stars. It has previously been proposed that binary interactions in this scenario could lead to the formation of hot subdwarfs. The detection of such objects will provide strong evidence that Jupiter‐mass planets can survive the interaction with a solar‐type star as it evolves up the Red Giant Branch. We present the first results of our search here.
- Analysis of Two Eclipsing Hot Subdwarf Binaries with a Low Mass Stellar and a Brown Dwarf Companion (2011)
- The formation of hot subdwarf stars (sdBs), which are core helium‐burning stars located on the extended horizontal branch, is still not understood. Many of the known hot subdwarf stars reside in close binary systems with short orbital periods between a few hours and a few days with either M star or white dwarf companions. Common envelope ejection is the most probable formation channel. Among these, eclipsing systems are of special importance because it is possible to constrain the parameters of both components tightly by combining spectroscopic and light curve analyses. We report the discovery of two eclipsing binaries with a brown dwarf (<0.07 M☉) and a 0.15 M☉ late main sequence star companion in close orbits around sdB stars.
- Schwellenmacht - Kernenergie und Außenpolitik der Bundesrepublik Deutschland von 1949 bis 1980 (2011)
- Die Proliferation von Nuklearwaffen gehört zu den drängendsten Problemfeldern auf dem Gebiet der internationalen Sicherheitspolitik. Seit dem Ende des Kalten Krieges testeten Staaten wie Indien, Pakistan und Nordkorea Atomwaffen. Der Iran wiederum betont die friedliche Ausrichtung seines mit Ehrgeiz vorangetriebenen und umstrittenen Atomprogramms. Das internationale Regelwerk, das einen Missbrauch von Kernenergie verhindern und die Verbreitung von Kernwaffen eindämmen soll, basiert im Wesentlichen auf dem Nichtverbreitungsvertrag von 1970. Während rechtliche Aspekte dieses Vertragswerks, das im Kalten Krieg formuliert wurde, gut untersucht sind, wurde der Entstehungsgeschichte bisher wenig Aufmerksamkeit geschenkt. Besonders die Rolle der nichtnuklearen Staaten in diesem Prozeß blieb unklar. In dieser Arbeit wird der Einfluss der Bundesrepublik Deutschland, als einer der wichtigsten nuklearen Schwellenmächte, auf die Formulierung des internationalen Regelwerks zur Vermeidung von Proliferation im Speziellen sowie die Bedeutung der Kernenergie für die deutsche Außenpolitik im Allgemeinen untersucht.
- Substellar Companions and the Formation of Hot Subdwarf Stars (2011)
- We give a brief review over the observational evidence for close substellar companions to hot subdwarf stars. The formation of these core helium‐burning objects requires huge mass loss of their red giant progenitors. It has been suggested that besides stellar companions substellar objects in close orbits may be able to trigger this mass loss. Such objects can be easily detected around hot subdwarf stars by medium or high resolution spectroscopy with an RV accuracy at the km s−1‐level. Eclipsing systems of HW Vir type stick out of transit surveys because of their characteristic light curves. The best evidence that substellar objects in close orbits around sdBs exist and that they are able to trigger the required mass loss is provided by the eclipsing system SDSS J0820+0008, which was found in the course of the MUCHFUSS project. Furthermore, several candidate systems have been discovered.