Ilya Ilyin

Context. Abundance ratios between elements synthesized on different nucleosynthetic timescales provide the empirical chemical clocks needed to estimate stellar ages, but robust calibrations require homogeneous samples with precise stellar parameters and elemental abundances. Aims. We investigate whether the presence of planets modifies empirical chemical clock relations. Methods. We present high-precision stellar parameters and elemental abundances for 52 new planet-hosting targets observed with Keck/HIRES, LBT/PEPSI, and Subaru/HDS. The full sample, i.e., the sample presented here combined with those from Papers I and II, comprises 94 stars, of which 81 are identified as planet-hosting solar twins and analogs. We used this sample to characterize the Galactic chemical evolution and derive empirical chemical clock relations. Results. We recover the expected Galactic chemical evolution trends, with α -elements such as Mg and S increasing with stellar age, while s -process elements such as Y, Ba, and Sr show negative age correlations. In contrast, Fe-peak elements and the r -process element Eu show little or no significant age dependence. These trends give rise to tight chemical clock relations based on [Y/Mg], [Y/Al], [Ba/Mg], [Ba/Al], and [Sr/Mg], with [Y/Mg] and [Y/Al] providing the strongest correlations. [Ba/Al] shows the steepest age dependence, and the Ba-based ratios are generally more sensitive to age than their Y-based counterparts. Conclusions. Planet-hosting solar analogs follow chemical clock relations consistent with those of nearby solar twins, with no evidence of a significant planet-related effect. The derived relations are primarily applicable to local solar twins and analogs in the Galactic thin disk.

Interaction in massive binary stars is expected to produce a large population of intermediate-mass (2 − 8 M _⊙ ) envelope-stripped stars, yet such objects have remained elusive in the Milky Way. We report the identification of an unambiguous Galactic example in a short-period ( P = 5.94 d), double-lined spectroscopic binary, discovered in the SDSS-V Milky Way Mapper survey. The system consists of a rapidly rotating O-type star and a hotter, lower-mass companion, which shows He II and N IV emission lines with large radial velocity variations, revealing its binary nature. Combined orbital constraints and joint spectroscopic and photometric modelling show that the companion is a hot ( T _* ≈ 60 kK), helium-rich star with a mass of 3.2 − 5.8 M _⊙ , placing it squarely in the intermediate-mass regime and below values typically inferred for classical Wolf–Rayet (WR) stars. Its spectral properties are inconsistent with accretion-powered emission and instead indicate a stripped star that formed through binary mass transfer. The system’s short period, negligible eccentricity, and rapidly rotating O-star point to a post-interaction configuration following efficient mass transfer and spin-up of the accretor. Comparison with binary evolution models suggests that the stripped star is observed in a brief inflated phase following mass transfer, which increases its optical flux contribution and facilitates its detection. The inferred mass-loss rate log Ṁ /(M _⊙ yr ⁻¹ ) = −6.3 ± 0.1 is in line with mass-loss rates observed for classical WR stars in the Milky Way and exceeds those measured for intermediate-mass stripped stars in the Magellanic Clouds, with the caveat that our target selection is biased towards systems with stronger emission features. As an unambiguous and well-characterised intermediate-mass stripped star, this system provides a key benchmark for models of binary evolution at solar metallicity, stripped-envelope supernova progenitors, and the formation of compact-object binaries.

Massive stars are predominantly found in binary and multiple systems that interact over the course of their lifetime. As several studies suggest that the origin of magnetic fields in massive stars involves a merging event, mass transfer, or a common envelope evolution, magnetic field measurements in stripped star systems, blue supergiants (BSGs), and Be stars, all previously suggested as binary interaction products, are of special interest. We present new magnetic field measurements for three systems, the stripped star system HR 6819, the BSG k Sco, and the Be star o Aqr, and discuss the appearance of the Zeeman features frequently observed in complex systems.

We present results from a spectroscopic survey of 32 FGK stars hosting brown dwarfs, using high-resolution optical spectra ( R = 130,000 and 50,000) obtained with the Potsdam Echelle Polarimetric and Spectroscopic Instrument spectrograph on the Large Binocular Telescope. The primary goal of this survey is to determine precise stellar parameters and abundances for 11 elements (C, O, Mg, Si, Ca, Al, Ti, Fe, Y, S, and N) in these systems. We employ spectral synthesis within the BACCHUS framework to derive precise stellar properties and elemental abundance ratios. For our data with average signal-to-noise ratio > 200, we achieve a typical error of 42 K in T _eff and ∼0.03 dex for [Fe/H]. We observe a significant dispersion from a solar C/O ratio among the sample of brown dwarf host stars that host primarily wide-orbit brown dwarfs. Using established theoretical chemical frameworks, we discuss the implications of the observed Mg/Si and Ca/Al ratios for cloud properties in the brown dwarf companions. Finally, we evaluate the applicability of the [Y/Mg] stellar clock for our sample and discuss the broader implications of our results. This work provides a timely and uniform abundance analysis of host stars, supporting extended wavelength brown dwarf observations in the era of JWST.

Magnetic fields are considered to be key components of massive stars, with a far-reaching impact on their evolution and ultimate fate. A magnetic mechanism was suggested for the collimated explosion of massive stars, relevant for long-duration gamma-ray bursts, X-ray flashes, and asymmetric core collapse supernovae. However, the origin of the observed stable, globally organized magnetic fields in massive stars is still a matter of debate: it has been argued that they can be fossil, dynamo generated, or generated by strong binary interactions or merging events. Taking into account that multiplicity is a fundamental characteristic of massive stars, observational evidence is accumulating that the magnetism originates through interaction between the system components, both during the initial mass transfer or when the stellar cores merge.

The question of whether genuinely young high- α stars exist has been discussed for more than a decade since their discovery from asteroseismology of giant stars, as it is challenging to break the degeneracy between the binary interaction and the genuinely young scenarios. Young high- α stars are hard to explain with a traditional chemical evolution model, as the high- α disk is typically associated with the early epoch of star formation in the Milky Way. Combined with recent advances of gyrochronology, and that ⁷ Li can serve as an unambiguous indicator for identifying merger products in dwarfs (thanks to its low burning temperature), we identified young high- α dwarf candidate stars through their fast rotation in a previous study. For this paper, we performed high-resolution spectroscopic follow-up on these candidates using the Potsdam Echelle Polarimetric and Spectroscopic Instrument, and confirm three additional stars that are most likely genuinely young. Together with the star from the earlier paper, we find three out of four of them center around [Fe/H] = −0.5 dex, are ∼5 Gyr old, and have a similar amount of elevated Li (∼0.5 dex) and Al (∼0.1 dex) compared to stars with matching log g , T _eff , Mg, and Fe within observational uncertainties, hinting at their common formation pathway.

Context. While about two dozen Herbig Ae/Be stars have been reported to be magnetic, only two of them, HD 101412 and HD 190073, have had their magnetic field geometries studied in the past. The knowledge of the magnetic field structure is important to understanding how magnetospheric accretion works in these stars. Aims. We aim to study in detail the spectral and magnetic variability of HD 179218, which is necessary to put constraints on its magnetic field geometry. Methods. We measured the mean longitudinal magnetic field, ⟨ B _z ⟩, from newly acquired and archival high-resolution spectropolarimetric observations of HD 179218 using the least-squares deconvolution technique. Additionally, we studied the spectral variability of the hydrogen lines using dynamical spectra. Results. Based on our analysis of the Stokes V spectra of HD 179218, we report for the first time the definite detection of a magnetic field. Using a slightly refined rotation period of P _rot = 1.34102 d, we constrained its geometry as follows: an estimated magnetic obliquity angle of β = 79.9 ± 0.7° and a dipole strength of B _d = 2142 ± 52 G. The ⟨ B _z ⟩ variation is best fitted by the superposition of a sine wave and of its first harmonic, but more spectropolarimetric observations are necessary to test the impact of the limited measurement precision and the uneven coverage of the rotation cycle. The strongest emission in the H α and H β line profiles in the medium-resolution spectra acquired in 2025 was detected close to the phases of the best visibility of the magnetic poles. HD 179218 is the second Herbig Ae/Be star after HD 190073 for which a first snapshot of a magnetosphere is presented.

Context. Recent observational studies suggest that Be stars most likely are formed through the process of mass transfer in binary systems. In view of the wide consensus that the origin of the magnetic field in stars with radiative envelopes involves binary interaction processes, searching for magnetic fields in Be stars appears especially promising. Aims. As a pilot project, we searched for the presence of magnetic fields in a sample of seven well-known Be stars. Methods. We used high-resolution HARPSpol spectra to measure the mean longitudinal magnetic field, employing the least squares deconvolution technique. A dedicated measurement procedure introduced by our group in recent years was applied. Results. Opposite to previous spectropolarimetric studies reporting that magnetic fields in Be stars are weak and usually below 100 G, our study presents the first observational evidence that magnetic fields in Be stars can be as strong as a few hundred gauss. Magnetic fields are detected in all studied Be stars, with the strongest magnetic field being about −460 G for the B0.5 III star HD 184915. Magnetic fields in the range between 338 and 380 G (in absolute values) are detected in three other Be stars, HD 209409, HD 209522, and HD 224686. Due to the fact that magnetic fields in Be stars are stronger than previously believed, we must re-evaluate our understanding of the initial conditions of massive binaries to be able to determine the origin of such systems.

We present the abundances of 23 elements, including 11 heavy elements (Cu, Zn, Sr, Y, Zr, Ba, La, Ce, Nd, Sm, and Eu) for up to 86 metal-poor (−2 ≲ [Fe/H] ≲ −1) subgiants. We use KORG, a state of the art spectral synthesis package, to derive 1D-LTE abundances from high-SNR and high-resolution spectra taken by the Large Binocular Telescope with the Potsdam Echelle Polarimetric and Spectroscopic Instrument. These precise spectra and abundance measurements minimize the impact of photon noise (≲0.06 dex), allowing us to robustly measure the intrinsic abundance scatter in [X/Fe]. After removing two stars with exceptional s -process enhancement, we find that the intrinsic scatter among the s - and r -process elements tends to be larger than for the lighter elements, with heavy element scatter ranging from 0.11 (Zn) to 0.27 (Eu) dex. Intrinsic abundance scatter could have multiple origins, including star-to-star variations in the ratios of nucleosynthetic sources as well as stochastic sampling of the progenitor supernovae properties, such as mass, rotation, and magnetic field strength. We explore the expected abundance scatter signature caused by stochastic sampling, finding that a fraction of both rapidly rotating core-collapse supernovae and magnetorotationally driven supernova are needed to reach the observed abundances and intrinsic scatter. This analysis is limited by the restrictive parameter spaces spanned by existing yield sets. A diverse, finely sampled grid of supernovae yields is needed to robustly model stochastic abundance scatter.