arXiv subjects

Max Pritzkuleit

Publications and source records attributed to Max Pritzkuleit.

5 recordsLinked to original sources

arXiv2026

Two hot pre-white dwarfs inside the red-giant-branch planetary nebula Pa 13 -- Double core evolution or common envelope-induced rejuvenation?

Close binary central stars of PNe offer a unique window for investigating the conditions immediately following the ejection of a common envelope (CE). Double eclipsing and double-lined double systems are particularly valuable as they provide minimally model-dependent constraints on fundamental binary parameters. We report that the nucleus of Pa13 (P=0.3988d) belongs to this rare class of systems and present a comprehensive analysis of its double-degenerate binary. We performed a two-component NLTE spectral analysis based on phase-resolved X-Shooter spectroscopy, multi-band light-curve modeling, SED fitting, as well as a kinematic analysis. Both stars are found to be hot pre-white dwarfs, with Star1 being cooler but larger (Teff=50kK, R=0.40Rsol) than Star2 (Teff=75kK, R=0.16Rsol). The weakness of spectral lines of Star2 made both the atmospheric and RV analyses challenging, and we uncovered a strong sensitivity of the assumed surface ratio to its derived RV curve. Yet, the RV curve and Kiel mass of Star1 (M1=0.41+/-0.02Msol) could be determined precisely, allowing for a dynamical mass determination of Star2 (M2=0.39+/-0.04Msol). We uncovered that Pa13 exhibits a small but significant orbital eccentricity (e=0.02+/-0.01), making it only the second post-CE binary nucleus with a measured eccentricity. We conclude that Pa13 provides hitherto the strongest evidence that PNe can be observed around post-RGB stars. Immediately after the CE-ejection, Star1 likely still filled its Roche lobe, suggesting that Pa13 is a more evolved, detached descendant of over-contact double-degenerate systems such as Hen2-428. Since the mass ratio of Pa13 is close to unity the system may have formed through double-core CE evolution. Alternatively, there must exist an efficient CE-induced rejuvenation mechanism capable of reheating the cool white dwarf in the binary, as already indicated by Hen2-428. (abbreviated)

astro-ph.SR↗

arXiv2025

Discovery of a new transitional type of evolved massive stars with hard ionizing flux

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 evolution stage before core collapse, the standard picture of WR stars has been that they evolve through three well-defined spectral subtypes known as WN, WC, and WO. Here, we present a detailed analysis of five objects that defy this scheme, demonstrating that WR stars can also evolve directly from the WN to the WO stage. Our study reveals that this direct transition is connected to low metallicity and weaker winds. The WN/WO stars and their immediate WN precursors are hot and emit a high flux of photons capable of fully ionizing helium. The existence of these stages unveil that high mass stars which manage to shed off their outer hydrogen layers in a low-metallicity environment can spend a considerable fraction of their lifetime in a stage that is difficult to detect in integrated stellar populations, but at the same time yields hard ionizing flux. The identification of the WN to WO evolution path for massive stars has significant implications for understanding the chemical enrichment and ionizing feedback in star-forming galaxies, in particular at earlier cosmic times.

astro-ph.SR↗

arXiv2024

Three new hot hydrogen-deficient pre-white dwarfs

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 (effective temperature Teff = 72,000 K) that has the lowest surface gravity of any PG1159 star known (log g = 4.8). It is a PG1159 star in the earliest pre-WD phase. The second object is a hot subdwarf O (sdO) star (Teff = 50,000 K, log g = 5.3) with high carbon and oxygen abundances. It is only the third known member of the recently established CO-sdO spectral class, which comprises stars that are thought to be formed by a merger of a disrupted low-mass CO WD with a higher-mass He WD. The third object is one of the rare stars of spectral type O(He) (Teff = 90,000 K, log g = 5.5).

astro-ph.SR↗

arXiv2023

The bright blue side of the night sky: Spectroscopic survey of bright and hot (pre-) white dwarfs

We report on the spectroscopic confirmation of 68 new bright ($G=13.5-17.2$ mag) and blue (pre-)white dwarfs (WDs). This finding has allowed us to almost double the number of the hottest ($T_{\mathrm{eff}} \geq 60$kK) known WDs brighter than $G=16$ mag. We increased the number of known ultra-high excitation (UHE) WDs by 20%, found one unambiguous close binary system consisting of one DA WD with an irradiated low-mass companion, one DAO, and one DOA WD that are likely in their transformation phase of becoming pure DA WDs, one rare, naked O(H) star, two DA and two DAO WDs with $T_{\mathrm{eff}}$ possibly in excess of 100kK, three new DOZ WDs, and three of our targets are central stars of (possible) planetary nebulae. Using non-local thermodynamic equilibrium models, we derived the atmospheric parameters of these stars and by fitting their spectral energy distribution we derived their radii, luminosities, and gravity masses. In addition, we derived their masses in the Kiel and Hertzsprung-Russell diagram (HRD). We find that Kiel, HRD, and gravity mass agree only in half of the cases. This is not unexpected and we attribute this to the neglect of metal opacities, possibly stratified atmospheres, as well as possible uncertainties of the parallax zero point determination. Furthermore, we carried out a search for photometric variability in our targets using archival data, finding that 26% of our targets are variable. This includes 15 new variable stars, with only one of them being clearly an irradiation effect system. Strikingly, the majority of the variable stars exhibit non-sinusoidal light-curve shapes, which are unlikely explained in terms of close binary systems. We propose that a significant fraction of all (not just UHE) WDs develop spots when entering the WD cooling phase. We suggest that this could be related to the on-set of weak magnetic fields and possibly diffusion.

astro-ph.SR↗

arXiv2022

Discovery of hot subdwarfs with extremely high carbon and oxygen abundances

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 = 40,000-50,000 K and log g = 5.5-6.0. Their atmospheres are helium dominated. If present at all, C, N, and O are trace elements. The abundance patterns are explained in terms of nucleosynthesis during single star evolution (late helium core flash) or a binary He-core white dwarf merger. Here we announce the discovery of two hot hydrogen-deficient sdOs (PG1654+322 and PG1528+025) that exhibit unusually strong carbon and oxygen lines. A non-LTE model atmosphere analysis of spectra obtained with the Large Binocular Telescope and by the LAMOST survey reveals astonishingly high abundances of C (~20%) and O (~20%) and that the two stars are located close to the helium main sequence. Both establish a new spectroscopic class of hot H-deficient subdwarfs (CO-sdO) and can be identified as the remnants of a He-core white dwarf that accreted matter of a merging low-mass CO-core white dwarf. We conclude that the CO-sdOs represent an alternative evolutionary channel creating PG1159 stars besides the evolution of single stars that experience a late helium-shell flash.

astro-ph.SR↗