Publications (31)
The impact of rotation on the line profiles of Wolf-Rayet stars
Tomer Shenar, Wolf-Rainer Hamann, Helge Todt
Massive Wolf-Rayet stars are recognized today to be in a very common, but short, evolutionary phase of massive stars. While our understanding of Wolf-Rayet stars has increased dram…
Correlated X-ray and optical variability in the O-type supergiant zeta Puppis
Joy S. Nichols, Yael Naze, David P. Huenemoerder +11
Analysis of the recent long exposure Chandra X-ray observation of the early-type O star zeta Pup shows clear variability with a period previously reported in optical photometric st…
X-rays, clumping and stellar wind structures
Lidia Oskinova, Wolf-Rainer Hamann, Richard Ignace +1
X-ray emission is ubiquitous among massive stars. In the last decade, X-ray observations revolutionized our perception of stellar winds but opened a Pandora's box of urgent problem…
The donor star of the X-ray pulsar X1908+075
Silvia MartÃnez-Núñez, Andreas Sander, Ãngel GÃmenez-GarcÃa +4
High-mass X-ray binaries (HMXBs) consist of a massive donor star and a compact object. While several of those systems have been well studied in X-rays, little is known for most of…
The most luminous stars in the Galaxy and the Magellanic Clouds
Wolf-Rainer Hamann, Andreas Barniske, Adriane Liermann +3
Some of the Wolf-Rayet stars are found to have very high bolometric luminosities (more than 1000000 solar). We employ the Potsdam Wolf-Rayet (PoWR) model atmospheres for their spec…
Coupling hydrodynamics with comoving frame radiative transfer: II. Stellar wind stratification in the high-mass X-ray binary Vela X-1
Andreas A. C. Sander, Felix Fürst, Peter Kretschmar +5
CONTEXT: Vela X-1, a prototypical high mass X-ray binary (HMXB), hosts a neutron star (NS) in a close orbit around an early-B supergiant donor star. Accretion of the donor star's w…
Coupling hydrodynamics with comoving frame radiative transfer: I. A unified approach for OB and WR stars
Andreas A. C. Sander, Wolf-Rainer Hamann, Helge Todt +2
CONTEXT: For more than two decades, stellar atmosphere codes have been used to derive the stellar and wind parameters of massive stars. Although they have become a powerful tool an…
Expansion of hydrogen-poor knots in the born-again planetary nebulae A30 and A78
Xuan Fang, Martin A. Guerrero, Ramon A. Marquez-Lugo +8
We analyze the expansion of hydrogen-poor knots and filaments in the born-again planetary nebulae A30 and A78 based on Hubble Space Telescope (HST) images obtained almost 20 yr apa…
WR 120bb and WR 120bc: a pair of WN9h stars with possibly interacting circumstellar shells
Sonja Burgemeister, Vasilii V. Gvaramadze, Guy S. Stringfellow +3
Two optically obscured Wolf-Rayet (WR) stars have been recently discovered by means of their infrared (IR) circumstellar shells, which show signatures of interaction with each othe…
3-D radiative transfer in clumped hot star winds I. Influence of clumping on the resonance line formation
Brankica Å urlan, Wolf-Rainer Hamann, JiÅà Kubát +2
The true mass-loss rates from massive stars are important for many branches of astrophysics. For the correct modeling of the resonance lines, which are among the key diagnostics of…
3-D Monte Carlo radiative transfer calculation of resonance line formation in the inhomogeneous expanding stellar wind
Brankica Å urlan, Wolf-Rainer Hamann, JiÅà Kubát +2
We study the effects of optically thick clumps, non-void inter-clump medium, variation of the onset of clumping, and velocity dispersion inside clumps on the formation of resonance…
The origin and impact of Wolf-Rayet-type mass loss
Andreas A. C. Sander, Jorick S. Vink, Erin R. Higgins +3
Classical Wolf-Rayet (WR) stars mark an important stage in the late evolution of massive stars. As hydrogen-poor massive stars, these objects have lost their outer layers, while st…
A new outburst in LMC-N66
Miriam Pena, M. Teresa Ruiz, Patricio Rojo +2
This is the first report on the new outburst presented by the central star of the LMC-N66 nebula. This object was classified as a planetary nebula, however, its true nature is unde…
Runaway Acceleration of Line-Driven Winds: the Role of the Outer Boundary
Achim Feldmeier, Isaac Shlosman, Wolf-Rainer Hamann
Observations and theory suggest that line driven winds from hot stars and luminous accretion disks adopt a unique, critical solution which corresponds to maximum mass loss rate. We…
A Deep Exposure in High Resolution X-Rays Reveals the Hottest Plasma in the Puppis Wind
David P. Huenemoerder, Richard Ignace, Nathan A. Miller +9
We have obtained a very deep exposure (813 ks) of Puppis (O4 supergiant) with the Chandra/HETG Spectrometer. Here we report on analysis of the 1-9 Ã region, especially well s…
Dynamically consistent analysis of Galactic WN4b stars
Roel R. Lefever, Andreas A. C. Sander, Matheus Bernini-Peron +6
Many Wolf-Rayet (WR) stars have optically thick winds that cloak the hydrostatic layers of the underlying star. In these cases, traditional spectral analysis methods are plagued by…
Phase-dependent study of near-infrared disk emission lines in LB-1
Jifeng Liu, Zheng Zheng, Roberto Soria +19
The mass, origin and evolutionary stage of the binary system LB-1 has been the subject of intense debate, following the claim that it hosts an 70 black hole, in st…
The Galactic WC stars: Stellar parameters from spectral analyses indicate a new evolutionary sequence
Andreas Sander, Wolf-Rainer Hamann, Helge Todt
[Abridged] [...] AIMS: We aim to establish the stellar parameters and mass-loss rates of the Galactic WC stars. These data provide the empirical basis of studies of (i) the role of…
Moving inhomogeneous envelopes of stars
Lidia M. Oskinova, Brankica Kubatova, Wolf-Rainer Hamann
Massive stars are extremely luminous and drive strong winds, blowing a large part of their matter into the galactic environment before they finally explode as a supernova. Quantita…
First JWST/NIRSpec Spectroscopy of O Stars in the Small Magellanic Cloud
Armin Mang Román, Peter Zeidler, Wolf-Rainer Hamann +10
Determining how much mass is removed by stellar winds is crucial to understanding massive star evolution and feedback. However, traditional spectroscopic diagnostics in the UV and…
The Galactic WC and WO stars: The impact of revised distances from Gaia DR2 and their role as massive black hole progenitors
Andreas A. C. Sander, Wolf-Rainer Hamann, Helge Todt +4
Wolf-Rayet stars of the carbon sequence (WC stars) are an important cornerstone in the late evolution of massive stars before their core collapse. As core-helium burning, hydrogen-…
The cooling-down central star of the planetary nebula SwSt\,1: a late thermal pulse in a massive post-AGB star?
Marcin Hajduk, Helge Todt, Wolf-Rainer Hamann +3
SwSt 1 (PN G001.5-06.7) is a bright and compact planetary nebula containing a late [WC]-type central star. Previous studies suggested that the nebular and stellar lines are slowly…
Massive stars in advanced evolutionary stages, and the progenitor of GW150914
Wolf-Rainer Hamann, Lidia Oskinova, Helge Todt +4
The recent discovery of a gravitational wave from the merging of two black holes of about 30 solar masses each challenges our incomplete understanding of massive stars and their ev…
A new type of X-ray pulsar
Lidia M. Oskinova, Yael Naze, Helge Todt +4
X-ray emission from stars much more massive than the Sun was discovered only 35 years ago. Such stars drive fast stellar winds where shocks can develop, and it is commonly assumed…
Probing Wolf-Rayet Winds: Chandra/HETG X-Ray Spectra of WR 6
David P. Huenemoerder, Kenneth G. Gayley, Wolf-Rainer Hamann +6
With a deep Chandra/HETGS exposure of WR 6, we have resolved emission lines whose profiles show that the X-rays originate from a uniformly expanding spherical wind of high X-ray-co…
X-ray line emission from a fragmented stellar wind
Achim Feldmeier, Lida Oskinova, Wolf-Rainer Hamann
We discuss X-ray line formation in dense O star winds. A random distribution of wind shocks is assumed to emit X-rays that are partially absorbed by cooler wind gas. The cool gas r…
A Coordinated X-ray and Optical Campaign of the Nearest Massive Eclipsing Binary, delta Orionis Aa: III. Analysis of Optical Photometric MOST and Spectroscopic (Ground Based) Variations
Herbert Pablo, Noel D. Richardson, Anthony F. J. Moffat +44
We report on both high-precision photometry from the MOST space telescope and ground-based spectroscopy of the triple system delta Ori A consisting of a binary O9.5II+early-B (Aa1…
The Wolf-Rayet stars in M31: I. Analysis of the late-type WN stars
Andreas Sander, Helge Todt, Rainer Hainich +1
Context: Comprehensive studies of Wolf-Rayet stars were performed in the past for the Galactic and the LMC population. The results revealed significant differences, but also unexpe…
Discovery of a new transitional type of evolved massive stars with hard ionizing flux
Andreas A. C. Sander, Roel R. Lefever, Joris Josiek +12
Wolf-Rayet (WR) stars are the evolved descendants of the most massive stars and show emission-line dominated spectra formed in their powerful stellar winds. Marking the final evolu…
On the consistent treatment of the quasi-hydrostatic layers in hot star atmospheres
Andreas Sander, Tomer Shenar, Rainer Hainich +3
CONTEXT: Spectroscopic analysis remains the most common method to derive masses of massive stars, the most fundamental stellar parameter. While binary orbits and stellar pulsations…
Testing massive star evolution, star-formation history, and feedback at low metallicity: Photometric analysis of OB stars in the SMC Wing
Leah M. Fulmer, John S. Gallagher, Wolf-Rainer Hamann +2
The supergiant ionized shell SMC-SGS 1 (DEM 167), located in the outer Wing of the Small Magellanic Cloud (SMC), resembles structures that originate from an energetic star-formatio…