Article
Astronomy & Astrophysics
Klaus Werner, Nicole Reindl, Matti Dorsch, Stephan Geier, Ulisse Munari, Roberto Raddi
Summary: Hot, compact, hydrogen-deficient pre-white dwarfs are rare objects that are believed to be the outcome of either single star evolution or binary star evolution. Their study is important for understanding the physics of thermonuclear flashes and merger events. Spectroscopically, they are divided into three different classes, namely PG1159, O(He), or He-sdO. This study presents a spectroscopic analysis of five such stars and found that some of them have hydrogen content that cannot be explained by current evolution models.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
Michela Rigoselli, Davide De Grandis, Sandro Mereghetti, Christian Malacaria
Summary: We investigated the hot subdwarf 49798 on a 1.55 day orbit using data from LAXA. We found that the compact object is steadily spinning up and determined the inclination and masses of the system through optical observations. Additionally, we studied possible variations in the soft X-ray pulsed flux.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Jiangdan Li, Christopher A. Onken, Christian Wolf, Peter Nemeth, Mike Bessell, Zhenwei Li, Xiaobin Zhang, Jiao Li, Luqian Wang, Lifang Li, Yangping Luo, Hailiang Chen, Kaifan Ji, Xuefei Chen, Zhanwen Han
Summary: A hot subdwarf O (sdO) star and a white dwarf (WD) binary system, which has the capability of emitting low-frequency gravitational waves and possibly being the progenitor of Type Ia supernovae, has been discovered. Spectroscopy and light curve analysis provide information about the system, such as temperature, mass ratio, and disc characteristics. The binary system is believed to have originated from a common envelope ejection channel and might result in an R Coronae Borealis (R CrB) star.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
T. Ryabchikova, S. Zvyagintsev, A. Tkachenko, V Tsymbal, Yu Pakhomov, E. Semenko
Summary: The study on the SB2 system HD 60803 involved a detailed spectroscopic analysis using different methods to determine the fundamental parameters of the components, revealing consistent results. While the chemical composition of the components showed no significant difference, the abundance of lithium exhibited a slight variance. The estimated age of the system was concluded to be 5.5 +/- 0.5 billion years.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
P. Nemeth, J. Vos, F. Molina, A. Bastian
Summary: This study aims to investigate the chemical composition and Galactic kinematics of the spectroscopic binary SB 744, revealing it as an old Population II system with a heavy-metal subclass hot subdwarf star and super-solar lead abundances. The presence of fluorine suggests a past hierarchical triple system or single-star evolution through late core helium flash and atmospheric mixing to explain the observed abundances.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
T. Ryabchikova, Yu Pakhomov, L. Mashonkina, T. Sitnova
Summary: This study presents a comparative analysis of two wide binary systems - 16 Cyg and HD 219542. The results show a small difference in chemical abundance between the A and B components in both systems, suggesting a weak influence of giant gas planets on the chemical composition of the host star's atmosphere. Additionally, the behavior of chemical elements with respect to the condensation temperature differs between 16 Cyg and HD 219542, indicating different chemical environments during their formation.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Simon Blouin, Siyi Xu
Summary: Recent studies show that the mass accretion rates of cool, old white dwarfs do not significantly decrease over several billion years of cooling time, indicating the need for mechanisms to consistently deliver planetesimals inside the Roche radius of white dwarfs.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Simon Blouin, Antoine Bedard, Pier-Emmanuel Tremblay
Summary: The Gaia colour-magnitude diagram shows a clear separation between hydrogen-atmosphere white dwarfs and helium-atmosphere white dwarfs during the cooling process. However, the magnitudes of pure-helium atmospheres are too similar to those of pure-hydrogen atmospheres to explain this bifurcation. To explain the observed split, it has been suggested that there must be trace amounts of hydrogen and/or metals in the helium-dominated atmospheres of hydrogen-deficient white dwarfs. This study aims to provide a comprehensive explanation by considering population synthesis simulations, model atmospheres, and evolutionary calculations along with element transport in white dwarf envelopes. The simulations successfully reproduce the bifurcation and highlight the importance of convective dredge-up of carbon in explaining the observations.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
A. Claret
Summary: There are currently no specific calculations of gravity-darkening exponents for white dwarfs in the literature, but theoretical approaches to the distribution of temperatures on the surfaces of white dwarfs distorted by rotation and/or tides are being developed. Discrepancies were found between the gravity-darkening exponents calculated using different methods, with physical connections identified between these exponents and convective efficiency. Generalisations of the von Zeipel theorem for hot white dwarfs were made, predicting that gravity-darkening exponents may be smaller than 1.0 under certain circumstances.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
J. Krticka, A. Kawka, Z. Mikulasek, L. Fossati, I. Krtickova, M. Prvak, J. Janik, R. Liptaj, M. Zejda, E. Paunzen
Summary: This study investigates the nature of the periodic light variability of the white dwarf EPIC 206197016, which is found to be caused by surface spots or binarity. The spectroscopic analysis reveals periodic radial velocity variations, indicating gravitational interaction with an invisible red dwarf companion. The white dwarf shows the Balmer line problem, possibly due to the presence of heavy elements or a circumstellar cloud.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
Abbigail K. Elms, Pier-Emmanuel Tremblay, Boris T. Gansicke, Detlev Koester, Mark A. Hollands, Nicola Pietro Gentile Fusillo, Tim Cunningham, Kevin Apps
Summary: We have identified two ultra-cool metal-polluted white dwarfs, WD J2147-4035 and WD J1922+0233, which are the coolest and second coolest DZ stars known to date. These stars have unusually blue and red colors, respectively, given their low temperatures. They are likely members of the Galactic disc and could be crucial objects in future studies on the age limit of the Milky Way disc.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Wen-Cong Chen
Summary: Based on the study of HD49798/RX J0648.0C4418, we propose an alternative model to explain the observed X-ray luminosity and interpret it from the perspective of a debris disk. Further observations can help confirm or rule out the existence of a debris disk.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
Yangyang Zhang, Hailiang Chen, Xuefei Chen, Zhanwen Han
Summary: The study demonstrates that the mass transfer scheme can significantly influence the evolution of red giant binaries, resulting in differences in final donor masses and orbital periods. Models using the 'Kolb' scheme show larger orbital periods compared to the 'classical' scheme under the same donor mass conditions.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Alexander Venner, Simon Blouin, Antoine Bedard, Andrew Vanderburg
Summary: The observational signature of core crystallization of white dwarfs has been discovered, but it requires additional mechanisms of energy release in white dwarf interiors. In this work, a newly discovered white dwarf is confirmed to be undergoing crystallization, making it the first one with externally constrained total age. However, the age determination is not precise enough to make strong constraints to models of white dwarf crystallization, but the results support the hypothesis of Ne-22 phase separation causing the excess cooling delay.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Nicole Reindl, Ramazan Islami, Klaus Werner, S. O. Kepler, Max Pritzkuleit, Harry Dawson, Matti Dorsch, Alina Istrate, Ingrid Pelisoli, Stephan Geier, Murat Uzundag, Judith Provencal, Stephen Justham
Summary: We report on the spectroscopic confirmation of 68 new bright and blue white dwarfs, which nearly doubles the number of the hottest known white dwarfs. We also discovered new types of white dwarfs and found that a significant fraction of them exhibit photometric variability. These findings are important for understanding the formation and evolution of white dwarfs.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
Miroslav D. Filipovic, J. L. Payne, R. Z. E. Alsaberi, R. P. Norris, P. J. Macgregor, L. Rudnick, B. S. Koribalski, D. Leahy, L. Ducci, R. Kothes, H. Andernach, L. Barnes, I. S. Bojicic, L. M. Bozzetto, R. Brose, J. D. Collier, E. J. Crawford, R. M. Crocker, S. Dai, T. J. Galvin, F. Haberl, U. Heber, T. Hill, A. M. Hopkins, N. Hurley-Walker, A. Ingallinera, T. Jarrett, P. J. Kavanagh, E. Lenc, K. J. Luken, D. Mackey, P. Manojlovic, P. Maggi, C. Maitra, C. M. Pennock, S. Points, S. Riggi, G. Rowell, S. Safi-Harb, H. Sano, M. Sasaki, S. Shabala, J. Stevens, J. Th van Loon, N. F. H. Tothill, G. Umana, D. Urosevic, V. Velovic, T. Vernstrom, J. L. West, Z. Wan
Summary: We report the discovery of J0624-6948, a low-surface brightness radio ring located between the Galactic Plane and the Large Magellanic Cloud (LMC). This source shares similarities with odd radio circles (ORCs) but also exhibits significant differences, suggesting it may be a different type of object. The most plausible explanation is that it is an intergalactic supernova remnant resulting from a single-degenerate type Ia supernova in the outskirts of the LMC.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Todd C. Hillwig, Nicole Reindl, Hannah M. Rotter, Adam W. Rengstorf, Ulrich Heber, Andreas Irrgang
Summary: In the survey of central stars of planetary nebulae, two newly discovered binary systems were identified. Physical parameters and the possibility of true planetary nebula for these systems were discussed based on spectral modeling and observational data.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
A. Bhat, A. Irrgang, U. Heber
Summary: Runaway stars are ejected from their place of birth in the Galactic disk through violent ejection processes. They may originate from young open clusters and be ejected either through N-body interactions or binary supernova explosions. With the help of Gaia astrometry, the kinematics of young runaway stars can be studied with high precision, allowing for the identification of their origin in open stellar clusters even when they are far away. A minimization method has been developed to determine whether objects come from the same place, which has been tested on samples of Orion runaways. Trajectories of known runaway stars have been calculated using this fitting procedure based on Gaia data and updated radial velocities. The study also investigates the ejection mechanisms for the runaway stars by identifying parent clusters based on their trajectories and analyzing cluster age and flight time.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
S. Geier, M. Dorsch, I Pelisoli, N. Reindl, U. Heber, A. Irrgang
Summary: Hot subdwarf stars are likely formed by close binary interactions and represent a late stage in the evolution of low-mass stars. A study of radial velocity variability reveals completely different behavior between He-poor and He-rich hot subdwarfs. There is likely no evolutionary connection between these subtypes, and the majority of hot subdwarf stars are formed through binary merger channels.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
Gavin Ramsay, Patrick A. Woudt, Thomas Kupfer, Jan van Roestel, Kerry Paterson, Brian Warner, David A. H. Buckley, Paul J. Groot, Ulrich Heber, Andreas Irrgang, C. Simon Jeffery, Mokhine Motsoaledi, Martinus J. Schwartz, Thomas Wevers
Summary: Blue Large-Amplitude Pulsators (BLAPs) are a new class of blue variable stars that show periodic variations in their light curves with short periods and high amplitudes. Nine blue variable stars were identified in the OmegaWhite survey, showing a periodic modulation with periods ranging from 7 to 37 minutes and amplitudes ranging from 0.11 to 0.28 mag. Follow-up observations using SALT and telescopes at SAAO revealed four stars that are identified as BLAPs. One star belongs to the V361 Hya class of pulsating stars and is located near an extended nebula. Another star shows characteristics similar to sdAV pulsators. In contrast, one binary star system contains an sdB and a white dwarf with an orbital period of 73.7 minutes, which is one of only six white dwarf-sdB binaries with a period shorter than 80 minutes. High cadence photometry of four candidate BLAPs shows features that resemble notch-like features seen in longer period Cepheid pulsators.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Yaotian Zeng, Zheng-Wei Liu, Alexander Heger, Curtis McCully, Friedrich K. Ropke, Zhanwen Han
Summary: Supernovae of Type Iax are a faint subclass of hydrogen-free supernovae. Recent studies suggest that they could originate from a weak deflagration explosion of a near-Chandrasekhar-mass white dwarf in a binary system with a helium-star donor. We investigate the postimpact evolution of the surviving helium companion stars and find that their luminosities increase significantly after the impact. We also find that they evolve into O-type hot subdwarf stars after reaching thermal equilibrium.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
D. Sebastian, E. W. Guenther, M. Deleuil, M. Dorsch, U. Heber, C. Heuser, D. Gandolfi, S. Grziwa, H. J. Deeg, R. Alonso, F. Bouchy, Sz Csizmadia, F. Cusano, M. Fridlund, S. Geier, A. Irrgang, J. Korth, D. Nespral, H. Rauer, L. Tal-Or
Summary: The theories of planet formation have conflicting results regarding the frequency of close-in giant planets around intermediate mass stars (IMSs). In this study, the CoRoT survey is used to determine the absolute frequency of IMSs with close-in gas giants and compare it to solar-like stars. The results show that the frequency of close-in giant planets around IMSs is significantly lower than that around solar-mass stars.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
G. Leidi, C. Birke, R. Andrassy, J. Higl, P. V. F. Edelmann, G. Wiest, C. Klingenberg, F. K. Roepke
Summary: Fully compressible magnetohydrodynamic (MHD) simulations are essential for studying magnetic field generation in deep convective layers of stars. However, traditional methods become inefficient due to the strict time step constraints. This study presents a new method that efficiently simulates low Mach number compressible MHD flows in strongly stratified setups.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
R. Pakmor, F. P. Callan, C. E. Collins, S. E. de Mink, A. Holas, W. E. Kerzendorf, M. Kromer, P. G. Neunteufel, John T. O'Brien, F. K. Roepke, A. J. Ruiter, I. R. Seitenzahl, Luke J. Shingles, S. A. Sim, S. Taubenberger
Summary: The progenitor systems and explosion mechanism of Type Ia supernovae are still unknown. Currently favoured progenitors include double-degenerate systems consisting of two carbon-oxygen white dwarfs with thin helium shells. In this study, the fate of the secondary white dwarf in such a system is investigated, and it is found that the outer ejecta and observables of the explosion are similar regardless of whether the secondary explodes or survives. However, the inner ejecta differ significantly, resulting in a slower decline rate of the bolometric light curve in the model with a secondary explosion.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Christine E. Collins, Sabrina Gronow, Stuart A. Sim, Friedrich K. Roepke
Summary: Double detonation explosion of sub-Chandrasekhar mass white dwarfs is a potential scenario for Type Ia supernovae, but the simulations show red colors not observed in normal SNe Ia. The model spectra exhibit peculiar features and line blanketing of certain elements. Future simulations may improve the agreement with observations of normal SNe Ia.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Engineering, Civil
Henriette Triebke, Markus Kromer, Peter Vortisch
Summary: The study finds that MATSim and SUMO behave differently in different traffic dynamic test cases, which has implications on our tool-coupling efforts.
TRANSPORTATION RESEARCH RECORD
(2023)
Article
Astronomy & Astrophysics
V. Schaffenroth, B. N. Barlow, I. Pelisoli, S. Geier, T. Kupfer
Summary: Hot subdwarfs in close binaries with different companions show unique light variations, such as reflection effect, ellipsoidal modulation, and Doppler beaming. Analyzing these light variations allows us to derive the mass and radius of the companion, determine its nature, and estimate the rotation period of the hot subdwarf. High-quality space-based light curves provide better observations and help in analyzing a large sample of hot subdwarf binaries. The study has successfully constrained the parameters of companion stars and determined the rotation period of some short-period sdBs.
ASTRONOMY & ASTROPHYSICS
(2023)