arXiv subjects

M. Pritzkuleit

Publications and source records attributed to M. Pritzkuleit.

7 recordsLinked to original sources

arXiv2026

A 500 pc volume-limited sample of hot subluminous stars III. The short-period binary population

Hot subdwarf stars of spectral types O and B (sdO/B) in binaries form as products of substantial mass loss near the tip of the red giant branch and offer powerful constraints on binary-star evolutionary models. However, details of some formation channels remain missing. We present a comprehensive analysis of the short-period binary population in the 500 pc volume-limited sample of hot subdwarfs, enabled by precise Gaia DR3 parallaxes. Besides 45 known binaries within 500 pc, this work identifies 50 new single-lined radial-velocity variable systems, 34 with orbital solutions with periods between 0.07 and 22 days. We derive an overall short-period binary fraction of 34.7 (+2.8/-2.9)% for the full sample of 301 hot subdwarfs within 500 pc, corrected for orbital inclination and detection efficiency. The newly solved binaries predominantly occupy the 1-20 day range, a parameter space previously under-represented in the literature. We identify five new reflection-effect systems, three ellipsoidal modulation systems, a newly solved HW Vir system, and a new triple candidate. The sdB and sdO binary fractions are similar, while the sdOB class shows a fraction roughly half that of sdB/sdO stars, with periods over one day, suggesting a different evolutionary pathway. Underluminous hot subdwarfs below the canonical extreme horizontal branch show a binary fraction comparable to other sdB/sdO stars but host only white dwarf companions, which are more massive and mainly found at periods under one day. We provide the first volume-complete birthrate estimates for sub-populations, determining a Galactic merger rate of 2.5+-1.5x10^-5 yr^-1 for sdO/B binaries, explaining no more than ~12% of the eHe-sdO population. We also derive birthrates for two SN Ia progenitor channels, finding hot subdwarf binaries could account for up to 2.5 (+0.7/-0.5)% of the observed Galactic SN Ia rate.

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arXiv2026

Stars on the ascending helium giant branch I. From white dwarf merger to helium giant: the evolutionary state of the rapidly rotating hot subdwarf HE 1518-0948

Hot subdwarf stars with masses above $0.8 M_\odot$ ascend the helium giant branch after the end of core helium burning, before entering the white dwarf cooling track or exploding as type Ib/c supernovae. Such massive helium stars are typically expected to form through the stripping of an intermediate mass star by a binary companion after which some hydrogen is still expected to be retained. However, the subclass of extreme helium rich hot subdwarfs (He-sdOs) shows no or very weak hydrogen traces, and their low binary fraction suggests that they are either created through single-star evolution triggered by a late hot flash in a low-mass red giant or the merger of two helium white dwarfs. Most He-sdOs are located close to the helium zero-age main sequence, while a small number exhibit much lower surface gravities, indicating inflated radii. Whether these objects are evolutionarily connected to the main He-sdO population remains unclear. In this work, we analyse the luminous, extreme helium-rich, low-surface-gravity sdO HE 1518-0948 (HE 1518) through a detailed spectroscopic study of optical and ultraviolet data. A comparison with evolutionary models indicates that HE 1518 is the product of a massive double helium white dwarf merger and is currently undergoing helium shell burning while ascending the helium giant branch. This makes HE 1518 one of only a few known objects located in this sparsely populated region of the Hertzsprung-Russell diagram. Such stars provide valuable laboratories for studying the evolution of massive hot subdwarfs beyond core helium burning, and their high luminosities allow them to be detected at large distances.

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arXiv2026

The massive hot subdwarf binary LAMOST J065816.72+094343.1

Massive short-period binaries involving hot subdwarf stars (sdO/Bs) are rare but important to constraining pathways for binary star evolution. Moreover, some of the most promising candidate progenitor systems leading to Type Ia supernovae (SNe Ia) involve sdO/Bs. LAMOST J065816.72+094343.1 has been identified as such a candidate. To explore the nature and evolutionary future of LAMOST J065816.72+094343.1, we complemented archival spectroscopic data with additional time series spectra and high-resolution spectroscopy of the object. After combining these with photometric data, we determined the orbital parameters of the system and the mass of the companion. We solved the orbit of the system by analyzing 68 low- and medium-resolution spectra using state-of-the-art mixed local thermodynamic equilibrium (LTE) and non-LTE model atmospheres. Additionally, we gathered nine high-resolution spectra to determine atmospheric parameters and the projected rotational velocity of the sdOB. The inclination angle of the system was constrained assuming tidal synchronization of the sdOB, which was verified via analysis of the ellipsoidal variations in the TESS light curve. We determine LAMOSTJ065816.72+094343.1 to be a binary consisting of a massive $0.82 \pm 0.17 \mathrm{M}_{\odot}$ sdOB component with a $1.30^{+0.31}_{-0.26} \mathrm{M}_{\odot}$ unseen companion. Due to the companion's mass being very close to the Chandrasekhar mass limit and high for a white dwarf, it is unclear whether it is a white dwarf or a neutron star. We find the system to be in a close orbit, with a period of $P=0.31955193 \mathrm{d}$ and an inclination angle of $i = 49.6^{+5.2}_{-4.2} \mathrm{deg}$. While the exact nature of the companion remains unknown, we determine the system to either lead to a SN Ia or an intermediate mass binary pulsar, potentially after a phase as an intermediate-mass X-ray binary.

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arXiv2026

A 500 pc volume-limited sample of hot subluminous stars II. Atmospheric parameters, mass distribution, and kinematics

We present a quantitative spectroscopic and kinematic analysis of a volume-complete sample of hot subluminous stars within 500 pc of the Sun, assembled using accurate parallax measurements from Gaia Data Release 3 (DR3). In total, 3226 spectra of 253 hot subdwarf stars were analysed to derive atmospheric parameters (effective temperature, surface gravity, and helium abundance) and radial velocities. Spectral energy distributions (SEDs) combined with Gaia parallaxes were used to measure stellar radii, luminosities, and masses. The derived atmospheric parameters reveal a consistent alignment between sdB and sdO stars in the Kiel diagram when compared to theoretical evolutionary models. We identify a population (about 10%) of hot subdwarfs located below the 0.45 Msun zero-age EHB in both the Kiel and Hertzsprung-Russell diagrams, which likely originate from intermediate-mass progenitors (1.8-8 Msun). The overall mass distribution peaks at 0.48 pm 0.12 Msun, while hot subdwarfs below the EHB peak at 0.43 pm 0.10 Msun, supporting non- or semi-degenerate helium ignition characteristic of intermediate-mass stars. Interpolation of EHB and post-EHB tracks yields mass distributions consistent with those derived from SEDs and parallaxes. Assuming a mass range between 0.40 and 0.50 Msun, we find that the post-EHB birthrate is 2-3 times higher than the EHB birthrate, suggesting overestimated EHB lifetimes or contamination from additional formation channels. Our kinematic analysis shows that 86 pm 2% of the stars belong to the Galactic thin disk, with 13 pm 1% and 1 pm 1% associated with the thick disk and halo. The below-EHB population is found exclusively in the thin disk, the only Galactic component young enough to host intermediate-mass progenitors. Its absence from other large samples suggests that non-degenerate formation channels play a more prominent role in the Galactic disk.

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arXiv2025

The twin red giant branch system BD+20 5391 A case study of low-mass double-core evolution

Understanding interactions of binary systems on the red giant branch is crucial to understanding the formation of compact stellar remnants such as helium-core white dwarfs (He-WDs) and hot subdwarfs. However, the detailed evolution of such systems, particularly those with nearly identical components, remains under-explored. We aim to analyse the double-lined spectroscopic binary system BD+20 5391, composed of two red giant stars, in order to characterise its orbital and stellar parameters and to constrain its evolution. Spectroscopic data were collected between 2020 and 2025 using the Ond\v{r}ejov Echelle Spectrograph and the Mercator \'Echelle Spectrograph. The time-resolved spectra were fitted with models to determine the radial velocity curve and derive the system's parameters. We then used the position of both stars in the Hertzsprung-Russell diagram to constrain the system's current evolutionary state, and we discuss potential outcomes of future interactions between the binary components. We find that the two stars in BD+20 5391 will likely initiate Roche lobe overflow (RLOF) simultaneously, leading to a double-core evolution scenario. The stars' helium core masses at RLOF onset will be almost identical, at 0.33 $\mathrm{M}_{\odot}$. This synchronised evolution suggests two possible outcomes: common envelope ejection, resulting in a short-period double He-WD binary, or a merger without envelope ejection. In the former case, the resulting double He-WD may merge later and form a hot subdwarf star. This study provides a valuable benchmark example for understanding the evolution of interacting red giant binaries, which will be discovered in substantial numbers in upcoming large-scale spectroscopic surveys.

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arXiv2025

Where are the binaries? -- Searching for blue horizontal-branch stars in binary systems in the inner Galactic Halo

Blue horizontal-branch (BHB) stars are evolved low-mass objects that have completed their core hydrogen burning main-sequence (MS) stage and have lost significant mass during the red giant phase culminating in the helium flash. We determine the fraction of BHBs in binary systems over a wide range of separations in the inner Galactic Halo to constrain mass-loss mechanisms and evolutionary pathways. Using a catalog of 22,336 BHB candidates from Gaia DR3, we analysed radial velocity variations found in spectra (263 spectra of 89 targets) acquired using the Ondrejov Echelle spectrograph at the Astronomical Institute of the Czech Academy of Sciences together with archival spectra from the Ultraviolet and Visual Echelle Spectrograph (UVES) and Fiber-fed Extended Range Optical Spectrograph (FEROS). We searched for wide common proper motion pairs, binary candidates with enhanced astrometric noise, and binaries with astrometric orbital solutions in Gaia DR3. Archival light curves from Gaia DR3 and the Zwicky Transient Facility (ZTF) were checked for binary induced variations. Synthetic SEDs and binary detection probabilities were modelled to account for selection effects. We find a binary fraction of <2.2%, far lower than the rates for their main-sequence (MS) and red-giant branch (RGB) progenitors (30-50%). This suggests that BHBs are either not descendants of binary systems, or that existing companions do not survive the BHB formation process. The negligible binary fraction implies single-star evolution could dominate BHB formation, contrasting with EHB stars where binarity is critical. Our results challenge models of mass loss on the RGB and highlight the need for alternative mechanisms.

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arXiv2024

A 500 pc volume-limited sample of hot subluminous stars I. Space density, scale height, and population properties

We present the first volume-limited sample of spectroscopically confirmed hot subluminous stars out to 500 pc, defined using the accurate parallax measurements from the {\em Gaia} space mission data release 3 (DR3). The sample comprises a total of 397 members, with 305 ($\sim 77\%$) identified as hot subdwarf stars, including 83 newly discovered systems. Of these, we observe that 178 ($\sim58\%$) are hydrogen-rich sdBs, 65 are sdOBs ($\sim 21\%$), 32 are sdOs ($\sim 11\%$), and 30 are He-sdO/Bs ($\sim 10\%$). Among them, 48 ($\sim 16\%$) exhibit an infrared excess in their spectral energy distribution fits, suggesting a composite binary system. The hot subdwarf population is estimated to be 90\% complete, assuming that most missing systems are these composite binaries located within the main sequence (MS) in the \emph{Gaia} colour-magnitude diagram (CMD). The remaining sources in the sample include cataclysmic variables (CVs), blue horizontal branch stars (BHBs), hot white dwarfs (WDs), and MS stars. We derived the mid-plane density $\rho_{0}$ and scale height $\mathrm{h}_{z}$ for the non-composite hot subdwarf star population using a hyperbolic sechant profile (sech$^2$). The best-fit values are $\rho_{0}\,=\,5.17\pm 0.33 \times10^{-7}$ stars/pc$^{3}$ and $\mathrm{h}_{z} = 281 \pm 62$ pc. When accounting for the composite-colour hot subdwarfs and their estimated completeness, the mid-plane density increases to $\rho_{0}\,=\,6.15^ {+1.16}_{-0.53} \times10^{-7}$ stars/pc$^{3}$. This corrected space density is an order of magnitude lower than predicted by population synthesis studies, supporting previous observational estimates.

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