Publications (38)
The bright blue side of the night sky: Spectroscopic survey of bright and hot (pre-) white dwarfs
Nicole Reindl, Ramazan Islami, Klaus Werner +10
We report on the spectroscopic confirmation of 68 new bright ( mag) and blue (pre-)white dwarfs (WDs). This finding has allowed us to almost double the number of the h…
EVR-CB-001: An evolving, progenitor, white dwarf compact binary discovered with the Evryscope
Jeffrey K. Ratzloff, Brad N. Barlow, Thomas Kupfer +7
We present EVR-CB-001, the discovery of a compact binary with an extremely low mass () helium core white dwarf progenitor (pre-He WD) and an unseen low mass…
Discovery of a double detonation thermonuclear supernova progenitor
Thomas Kupfer, Evan B. Bauer, Jan van Roestel +12
We present the discovery of a new double detonation progenitor system consisting of a hot subdwarf B (sdB) binary with a white dwarf companion with an P=76.34179(2) min orbital per…
Mysterious, Variable, and Extremely Hot: White Dwarfs Showing Ultra-High Excitation Lines I. Photometric Variability
Nicole Reindl, Veronika Schaffenroth, Semih Filiz +3
About 10% of all stars exhibit absorption lines of ultra-high excited (UHE) metals (e.g. OVIII) in their optical spectra when entering the white dwarf cooling sequence. The recent…
Stratospheric balloons as a platform for the next large far infrared observatory
Philipp Maier, Jürgen Wolf, Alfred Krabbe +21
Observations that require large physical instrument dimensions and/or a considerable amount of cryogens, as it is the case for high spatial resolution far infrared (FIR) astronomy,…
Probing the inner Galactic Halo with blue horizontal branch stars: Gaia DR3 based catalogue with atmospheric and stellar parameters
Richard Culpan, Matti Dorsch, Stephan Geier +4
Context. Stars that are found on the blue horizontal-branch (BHB) have evolved from low-mass stars that have completed their core hydrogen burning main sequence stage and have unde…
SHOTGLAS I: The ultimate spectroscopic census of extreme horizontal branch stars in Centauri
Marilyn Latour, Suzanna K. Randall, Annalisa Calamida +2
The presence of extreme horizontal branch (EHB) and blue hook stars in some Galactic globular clusters (GGCs) constitutes one of the remaining mysteries of stellar evolution. In th…
AA Doradus and its Cool Companion - The Influence of Enhanced Metal Line Blanketing and the Reflection Effect
Sebastian Müller, Stephan Geier, Ulrich Heber
This paper has been withdrawn by the author due to a crucial error with the analysis of the He II 4686 line.
A stripped helium star in the potential black hole binary LB-1
Andreas Irrgang, Stephan Geier, Simon Kreuzer +2
The recently claimed discovery of a massive () black hole in the Galactic solar neighborhood has led to controversial discussions because it…
The population of hot subdwarf stars studied with Gaia -- IV. Catalogues of hot subluminous stars based on Gaia EDR3
Richard Culpan, Stephan Geier, Ingrid Pelisoli +3
In light of substantial new discoveries of hot subdwarfs by ongoing spectroscopic surveys and the availability of the Gaia mission Early Data Release 3 (EDR3), we compiled new rele…
Stellar archaeology with Gaia: the Galactic white dwarf population
Boris Gaensicke, Pier-Emmanuel Tremblay, Martin Barstow +23
Gaia will identify several 1e5 white dwarfs, most of which will be in the solar neighborhood at distances of a few hundred parsecs. Ground-based optical follow-up spectroscopy of t…
Towards a European Stratospheric Balloon Observatory -- The ESBO Design Study
Philipp Maier, Jürgen Wolf, Thomas Keilig +18
This paper presents the concept of a community-accessible stratospheric balloon-based observatory that is currently under preparation by a consortium of European research institute…
Confirming new white dwarf-ultracool dwarf binary candidates
Miriam Hogg, Sarah Casewell, Graham Wynn +8
We present the results of a study to discover prospective new white dwarf-L dwarf binaries as identified by their near-infrared excesses in the UKIDSS catalogue. We obtained optica…
Discovery of two bright DO-type white dwarfs
Nicole Reindl, Stephan Geier, Roy H. Ãstensen
We discovered two bright DO-type white dwarfs, GALEXJ053628.3+544854 (J0536+5448) and GALEX231128.0+292935(J2311+2929), which rank among the eight brightest DO-type white dwarfs kn…
Discovery of hot subdwarfs with extremely high carbon and oxygen abundances
Klaus Werner, Nicole Reindl, Stephan Geier +1
Helium rich subdwarf O stars (sdOs) are hot compact stars in a pre-white dwarf evolutionary state. Most of them have effective temperatures and surface gravities in the range Teff…
A Data Release 2 catalogue of white dwarfs and a comparison with SDSS
Nicola Pietro Gentile Fusillo, Pier-Emmanuel Tremblay, Boris T. Gänsicke +11
We present a catalogue of white dwarf candidates selected from the second data release of (DR2). We used a sample of spectroscopically confirmed white dwarfs from the Sloan…
Studying hot evolved stars with ultraviolet spectroscopy
Stephan Geier, Nicole Reindl, Matti Dorsch +7
Hot evolved stars are key objects to reconstruct the various evolutionary pathways of Sun-like stars, to probe binary interactions and the physics of supernovae. They serve as powe…
The ORCA-TWIN qCMOS Experiment I. Science case and commissioning at Calar Alto Observatory
Martin M. Roth, Pasko Roje, Stella Vjesnica +18
We describe a pilot study to explore a new generation of fast and low noise CMOS image sensors for time domain astronomy, using two remote telescopes with a baseline of 1635 km. Th…
Experiments in binary evolution
Stephan Geier, Thomas Kupfer, Pierre Maxted +1
The majority of stars more massive than the Sun is found in binary or multiple star systems and many of them will interact during their evolution. Specific interactions, where prog…
Hot subdwarf binaries - Masses and nature of their heavy compact companions
Stephan Geier, Uli Heber, Heinz Edelmann +3
Neutron stars and stellar-mass black holes are the remnants of massive stars, which ended their lives in supernova explosions. These exotic objects can only be studied in relativel…
A proto-helium white dwarf stripped by a substellar companion via common-envelope ejection -- Uncovering the true nature of a candidate hypervelocity B-type star
Andreas Irrgang, Stephan Geier, Ulrich Heber +3
In the past, SDSS J160429.12+100002.2 was spectroscopically classified as a blue horizontal branch (BHB) star. Assuming a luminosity that is characteristic of BHB stars, the object…
Meet the family - the catalog of known hot subdwarf stars
Stephan Geier, Roy H. Ãstensen, Peter Nemeth +6
In preparation for the upcoming all-sky data releases of the Gaia mission, we compiled a catalog of known hot subdwarf stars and candidates drawn from the literature and yet unpubl…
A comprehensive search for hot subdwarf stars using Gaia and TESS I. Pulsating hot subdwarf B stars
Murat Uzundag, Jurek Krzesinski, Ingrid Pelisoli +4
Hot subdwarf B (sdB) stars are evolved, subluminous, helium-burning stars, most likely formed when red-giant stars lose their hydrogen envelope via interactions with close companio…
PTF1 J082340.04+081936.5: A hot subdwarf B star with a low mass white dwarf companion in an 87 minute orbit
Thomas Kupfer, Jan van Roestel, Jared Brooks +19
We present the discovery of the hot subdwarf B star (sdB) binary PTF1 J082340.04+081936.5. The system has an orbital period P min (0.060761584(10) days), ma…
Hot subluminous Stars: Highlights from the MUCHFUSS and Kepler missions
Ulrich Heber, Stephan Geier, Boris Gaensicke
Research into hot subdwarf stars is progressing rapidly. We present recent important discoveries. First we review the knowledge about magnetic fields in hot subdwarfs and highlight…
Spectral analysis of the binary nucleus of the planetary nebula Hen 2-428 - first results
Nicolle L. Finch, Nicole Reindl, Martin A. Barstow +4
Identifying progenitor systems for the double-degenerate scenario is crucial to check the reliability of type Ia super-novae as cosmological standard candles. Santander-Garcia et a…
Three new hot hydrogen-deficient pre-white dwarfs
Klaus Werner, Nicole Reindl, Max Pritzkuleit +1
We have detected three new hydrogen-deficient (H < 0.001 mass fraction) pre-white dwarfs (WDs) with helium-dominated atmospheres. The first object is a relatively cool PG1159 star…
Looking into the cradle of the grave: J22564-5910, a young post-merger hot subdwarf?
Joris Vos, Ingrid Pelisoli, Jan Budaj +10
We present the discovery of J22564-5910, a new type of hot subdwarf (sdB) which shows evidence of gas present in the system and has shallow, multi-peaked hydrogen and helium lines…
Non-local thermodynamic equilibrium spectral analysis of five hot, hydrogen-deficient pre-white dwarfs
Klaus Werner, Nicole Reindl, Matti Dorsch +3
Hot, compact, hydrogen-deficient pre-white dwarfs (pre-WDs) with effective temperatures of Teff > 70,000 K and a surface gravity of 5.0 < log g < 7.0 are rather rare objects despit…
White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 14
S. O. Kepler, Ingrid Pelisoli, Detlev Koester +6
White dwarfs carry information on the structure and evolution of the Galaxy, especially through their luminosity function and initial-to-final mass relation. Very cool white dwarfs…
Hot subdwarf stars from the Hamburg Quasar Survey
Ulrich Heber, Lennard Kufleitner, Matti Dorsch +4
Hot subluminous stars (sdO/B) are evolved low mass stars originating from red giants that lost their envelope almost entirely. The multitude of observed phenomena imply that severa…
Alone but not lonely: Observational evidence that binary interaction is always required to form hot subdwarf stars
Ingrid Pelisoli, Joris Vos, Stephan Geier +2
Hot subdwarfs are core-helium burning stars that show lower masses and higher temperatures than canonical horizontal branch stars. They are believed to be formed when a red giant s…
The HYPERMUCHFUSS Campaign -- an undiscovered high velocity population
Alfred Tillich, Stephan Geier, Uli Heber +7
We present an overview and a status report of HYPERMUCHFUSS (HYPER velocity or Massive Unseen Companions of Hot Faint Underluminious Stars Survey) aiming at the detection of a popu…
An extremely fast halo hot subdwarf star in a wide binary system
Péter Németh, Eva Ziegerer, Andreas Irrgang +4
New spectroscopic observations of the halo hyper-velocity star candidate SDSS J121150.27+143716.2 ( mag) revealed a cool companion to the hot subdwarf primary. The compone…
V407 Vul: a triple star system with an AM CVn detectable by gravitational wave observatories
James Munday, Antonio C. Rodriguez, Nicole Reindl +23
The AM CVn class includes mass transferring, ultra-compact double white dwarf binaries with orbital periods on the timescale of minutes. A long-standing puzzle is that none of the…
PG 1610062: a runaway B star challenging classical ejection mechanisms
Andreas Irrgang, Stephan Geier, Ulrich Heber +2
Hypervelocity stars are rare objects, mostly main-sequence (MS) B stars, traveling so fast that they will eventually escape from the Milky Way. Recently, it has been shown that the…
Clean catalogues of blue horizontal-branch stars using Gaia EDR3
Richard Culpan, Ingrid Pelisoli, Stephan Geier
Context: Blue horizontal-branch stars are very old objects that can be used as markers in studies of the Galactic structure and formation history. To create a clean sky catalogue o…
Revealing the True Nature of Hen 2-428
Nicole Reindl, Nicolle L. Finch, Veronika Schaffenroth +5
The nucleus of Hen 2-428 is a short orbital period (4.2 h) spectroscopic binary, whose status as potential supernovae type Ia progenitor has raised some controversy in the literatu…