Browsing Research publications by Author "Geier, S."
Now showing items 1-13 of 13
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Binaries discovered by the MUCHFUSS project SDSS J08205+0008 - An eclipsing subdwarf B binary with brown dwarf companion
Geier, S.; Schaffenroth, V.; Drechsel, H.; Heber, U.; Kupfer, T.; Tillich, A.; Ostensen, R.; Smolders, K.; Degroote, P.; Maxted, P.F.L.; Barlow, B.N.; Gansicke, B.T.; Marsh, T.R.; Napiwotzki, R. (2011)Hot subdwarf B stars (sdBs) are extreme horizontal branch stars believed to originate from close binary evolution. Indeed about half of the known sdB stars are found in close binaries with periods ranging from a few hours ... -
Binaries discovered by the SPY project: V. GD 687 – a massive double degenerate binary progenitor that will merge within a Hubble time
Geier, S.; Heber, U.; Kupfer, T.; Napiwotzki, R. (2010)The ESO SN Ia Progenitor Survey (SPY) aims at finding merging double degenerate binaries as candidates for supernova type Ia (SN Ia) explosions. A white dwarf merger has also been suggested to explain the formation of rare ... -
Binaries discovered by the SPY survey VI : Discovery of a low mass companion to the hot subluminous planetary nebula central star EGB5-a recently ejected common envelope?
Geier, S.; Napiwotzki, R.; Heber, U.; Nelemans, G. (2011)Hot subdwarf B stars (sdBs) in close binary systems are assumed to be formed via common envelope ejection. According to theoretical models, the amount of energy and angular momentum deposited in the common envelope scales ... -
Binary sdB Stars with Massive Compact Companions
Geier, S.; Karl, C.; Edelmann, H.; Heber, U.; Napiwotzki, R. (Astronomical Society of the Pacific, 2008)The masses of compact objects like white dwarfs, neutron stars and black holes are fundamental to astrophysics, but very difficult to measure. We present the results of an analysis of subluminous B (sdB) stars in close ... -
Hot subdwarf stars in close-up view. I. Rotational properties of subdwarf B stars in close binary systems and nature of their unseen companions
Geier, S.; Heber, U.; Podsiadlowski, P.; Edelmann, H.; Napiwotzki, R.; Kupfer, T.; Muller, S. (2010)The origin of hot subdwarf B stars (sdBs) is still unclear. About half of the known sdBs are in close binary systems for which common envelope ejection is the most likely formation channel. Little is known about this dynamic ... -
The Hyper-MUCHFUSS project : probing the Galactic halo with sdB stars
Tillich, A.; Heber, U.; Geier, S.; Hirsch, H.; Maxted, P.F.L.; Gansicke, B.T.; Marsh, T.R.; Napiwotzki, R.; Ostensen, R.; Scholz, R.D. (2011)Context. High-velocity stars in the Galactic halo, e. g. the so-called hyper-velocity stars (HVS), are important tracers of the properties of the dark matter halo, in particular its mass. Aims. A search for the fastest ... -
Massive unseen companions to hot faint underluminous stars from SDSS (MUCHFUSS) - Analysis of seven close subdwarf B binaries
Geier, S.; Maxted, P.F.L.; Napiwotzki, R.; Ostensen, R.; Heber, U.; Hirsch, H.; Kupfer, T.; Muller, S.; Tillich, A.; Barlow, B.N.; Oreiro, R.; Ottosen, T.A.; Copperwheat, C.; Gansicke, B.T.; Marsh, T.R. (2011)The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims at finding hot subdwarf stars with massive compact companions like massive white dwarfs (M > 1.0 ), neutron stars or stellar ... -
Metal Abundances of Subdwarf B Stars from SPY - a Pattern Emerges
Geier, S.; Heber, U.; Napiwotzki, R. (Astronomical Society of the Pacific, 2008)The formation of sdBs is still puzzling, as is the chemical compo- sition of their atmospheres. While helium and other light elements are depleted relative to solar values, heavy elements are highly enriched. Diffusion ... -
MUCHFUSS - massive unseen companions to hot faint underluminous stars from SDSS
Geier, S.; Schaffenroth, V.; Hirsch, H.; Tillich, A.; Heber, U.; Maxted, P. F. L.; Ostensen, R. H.; Barlow, B. N.; O'Toole, S. J.; Kupfer, T.; Marsh, T.; Gaensicke, B.; Napiwotzki, R.; Cordes, O.; Mueller, S.; Classen, L.; Ziegerer, E.; Drechsel, H. (2012-06)The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims at finding hot subdwarf stars with massive compact companions (white dwarfs with masses M > 1.0 M?, neutron stars or black ... -
The MUCHFUSS project - Searching for hot subdwarf binaries with massive unseen companions : survey, target selection and atmospheric parameters
Geier, S.; Hirsch, H.; Tillich, A.; Maxted, P.F.L.; Bentley, S.J.; Ostensen, R.; Heber, U.; Gansicke, B.T.; Marsh, T.R.; Napiwotzki, R.; Barlow, B.N.; O'Toole, S. (2011)The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims at finding sdBs with compact companions like supermassive white dwarfs (M > 1.0M⊙), neutron stars or black holes. The existence ... -
Radial Velocity Variable sdO/Bs from SPY - Preliminary Orbits of Three New Short Period Binaries
Geier, S.; Heber, U.; Napiwotzki, R. (Astronomical Society of the Pacific, 2008)We present new results from follow-up time-resolved spectroscopy of radial velocity variable hot subdwarfs from the SPY project. Medium resolu- tion spectra were taken at the ESO NTT. Preliminary orbital solutions are ... -
Spectroscopic Analysis of Subluminous B Stars in Binaries with Compact Companions
Geier, S.; Karl, C.; Edelmann, H.; Heber, U.; Napiwotzki, R. (Astronomical Society of the Pacific, 2007)The masses of compact objects like white dwarfs, neutron stars and black holes are fundamental to astrophysics, but very difficult to measure. We present the results of an analysis of subluminous B (sdB) stars in close ... -
The Subdwarf B + White Dwarf Binary KPD 1930+2752, a Supernova Type Ia Progenitor Candidate
Geier, S.; Nesslinger, S.; Heber, U.; Przybilla, N.; Napiwotzki, R.; Kudritzki, R-P. (Astronomical Society of the Pacific, 2007)The nature of the progenitors of type Ia supernovae is still under controversial debate. KPD 1930+2752 is one of the best SN Ia progenitor can- didates known today. The object is a double degenerate system consisting of a ...