The determination of the solar oxygen abundance remains a central problem in astrophysics, as its accuracy is limited not only by models but also by systematics. While many of these factors have been thoroughly characterized, the effect of the solar activity cycle has so far remained unexplored. Due to its relative strength and accessibility, the O I infrared triplet is typically the primary choice for abundance studies. However, previous investigations have shown that abundances inferred from this triplet tend to be higher than expected on active stars, whereas such an overabundance effect is not observed for the much weaker forbidden O I 6300 Å line. This raises the question of whether a similar trend can be found for the Sun. To address this question, we analyze two decades’ worth of synoptic disk-integrated Sun-as-a-star datasets from the FEROS, HARPS-N, PEPSI, and NEID spectrographs, focusing on the infrared triplet (7772, 7774, 7775 Å) and the forbidden O I 6300 Å line. The excellent signal-to-noise ratio of the PEPSI observations allows us to detect a weak but significant variation in the equivalent widths of the infrared triplet, corresponding to about 0.01 dex difference in abundance between activity minimum and maximum. This value is significantly smaller than the typical uncertainties on the solar oxygen abundance. Due to higher scatter, no comparable trend is found in the other data sets. Based on these results, we conclude that within the typical uncertainties presented in other works, we can assume the inferred solar oxygen abundance to be stable across the solar cycle, but that this effect may be significant for other, more active stars.

Read more: Pietrow et al. 2026, A&A, in press. arXiv:2601.15919

Quantifying stellar parameters and magnetic activity for cool stars in double-lined spectroscopic binaries (SB2) is not straightforward, as both stars contribute to the observed composite spectra and are likely variable. Disentangled component spectra allow a detailed analysis of a component’s magnetic activity. We aim at separating the spectra of the two stellar components of the HR7275 SB2 system. Our further aim is a more accurate orbital solution by cleaning the observed radial velocities (RV) from activity perturbations of the spotted primary (“RV jitter”) and obtain a surface image of this component. We provide time-series high- and ultra-high resolution optical spectra and apply two different disentangling methods. RV residuals are modeled with three-sine function fits. The primary’s spectral-line profiles are modeled with the Doppler imaging code iMAP. Magnetic fields are measured for the primary based on least-square deconvolved Stokes-V line profiles. Chromospheric emission is determined from the line-cores of Ca II H&K, Ca II IRT 8542 Å, and Balmer Hα. Before applying those analyses, we provide a disentangling technique to determine the system properties more accurately. The Doppler image of the primary shows two large cool spots of size ≈20% of the visible hemisphere plus three smaller spots, each still ≈13% in size. In total, HR7275a exhibited an impressive spottedness of ≈40% of its entire surface in May-June 2022. The RV is modulated by the rotation of the primary with maximum amplitudes of 320 ms⁻¹ and 650 ms⁻¹ for two different modulation behaviors during the 250 d of our observations. This jitter is primarily caused by the varying asymmetries of the apparent disk brightness due to the cool spots. Its removal resulted in roughly ten times higher precision of the orbital elements. Our snapshot magnetic-field measurements reveal phase dependent (large-scale) surface fields between +0.6±2.0G at phase 0.1 and −15.2±2.7G at phase 0.6, indicating a complex magnetic morphology related to the location of the photospheric spots. We also obtain a logarithmic lithium abundance of 0.58±0.1 for HR7275a, indicating considerable mixing, and 0.16 for HR7275b, which is an extremely low value.

Read more: Adebali, Weber, Strassmeier, et al. 2026, A&A, in press. arXiv:2512.09521

We present the abundances of 23 elements, including 11 heavy elements (Cu, Zn, Sr, Y, Zr, Ba, La, Ce, Nd, Sm, 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 starto-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 CCSN and magnetorotationally driven SN 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.

Read more: Griffith, E. J. et al. 2026, ApJ, in press. arXiv:2512.02122

We observed the dayside thermal emission spectrum of UHJ HAT-P-70b using the high-resolution spectrographs CARMENES and PEPSI. Through our cross-correlation analysis, we detected emission signals for Al I, AlH, Ca II, Cr I, Fe I, Fe II, Mg I, Mn I, and Ti I, marking the first detection of Al I and AlH in an exoplanetary atmosphere. Tentative signals of C I, Ca I, Na I, NaH, and Ni I were also identified. Based on those detections, we were able to perform atmospheric retrievals to constrain the thermal profile and elemental abundances of the planet’s dayside hemisphere. The retrieved temperature-pressure profile reveals a strong temperature inversion layer. The chemical free retrieval yielded a metallicity of [Fe/H] = 0.38, while the chemical equilibrium retrieval resulted in [Fe/H] = 0.23, with both values consistent with the solar metallicity. We also tentatively found an enriched abundance of Ni, which could result from the accretion of Ni-rich planetesimals during the planet’s formation.

Read more: B. Guo, F. Yan, Th. Henning, et al. 2026, A&A, in press. arXiv:2512.21470

We present quantitative surface-activity information for a sequence of 21 Hyades dwarf stars with effective temperatures all cooler than the red edge of the lithium dip and Rossby (Ro) numbers between 0.14 to 0.54 with respect to the Sun (Ro(Sun)=1). High-resolution high-S/N PEPSI Stokes-IV spectra and least-squares deconvolution of thousands of spectral lines per spectrum are employed for measuring surface magnetic fields, rotational velocities, lithium abundances, and chromospheric CaII IRT fluxes. Lithium abundances A(Li) range from 95 times solar on the warm end of the sample to 1/25 solar on the cool end. We confirm the tight relation with T(eff)  and extent it to K-M stars. A formal relation with rotational period and velocity in the sense higher A(Li) for faster rotators is present. Targets rotating faster than vsini of 6 km/s appear Li saturated. CaII IRT fluxes also show a relation with T(eff), P(rot) and vsini, but opposite to A(Li), in an inverse sense with higher radiative losses for the slower=cooler rotators. Disk-integrated, unsigned, magnetic-field strengths of 15.4±3.6(rms)G are measured for targets warmer than 5000K and 91±61(rms)G for targets cooler than this. These field strengths relate to P(rot), vsini, and Ro, but in a bi-modal fashion. We conclude that the Rossby-number dependency of the surface activity tracers on our Hyades dwarf sequence primarily originates from convective motions, expressed by its turnover time, and only to a smaller and sometimes inverse extent from surface rotation and its related extra mixing.

Read more: Strassmeier et al. 2025, A&A, in press; e-print arXiv:2510.21456

We present five datasets of high-resolution optical emission spectra of the ultra-hot Jupiter KELT-20 b with the PEPSI spectrograph. Using a Bayesian retrieval framework, we constrain its dayside pressure-temperature profile and abundances of Fe, Ni, and Ca, providing the first measurements for Ni and Ca for KELT-20 b in emission. We retrieve the pre- and post-eclipse datasets separately (corresponding to the evening and morning sides, respectively), and compare the constraints on their thermal structures and chemical abundances. We constrain lower abundances in the pre-eclipse datasets compared to the post-eclipse datasets. We interpret these results with an equilibrium chemistry model which suggests ∼ 10 − 30× supersolar refractory abundances. Due to the well-known degeneracy between absolute abundances and continuum opacities, the abundance ratios are more precise probes of the planetary abundances. Therefore we measure the abundance ratios [Ni/Fe] and [Ca/Fe] across these datasets and find they agree within 1σ. We constrain [Ni/Fe] to be consistent with solar within 2σ, and [Ca/Fe] to be 0.001-0.01× solar, not accounting for ionization.

Read more: Bonidie et al. 2025, AJ, in press.  eprint arXiv:2511.09720

ELT-20b is a well-studied exoplanet within the highly observable ultra hot Jupiter (UHJ) regime, yet its multidimensional atmospheric structure remains largely unconstrained. Recent advances in instrumentation and increased general circulation model (GCM) complexity have enabled observers to resolve the imprints of more intricate physical mechanisms in time-resolved data. We performed high-resolution cross-correlation transmission spectroscopy (HRCCTS) on a single transit time series of KELT-20b, observed with PEPSI on the LBT. We detect Fe I (11.9σ) and Fe II (23.7σ) and tentatively detect Na I (3.4σ) and Cr I (3.3σ) upon combining nineteen in-transit exposures.

Read more: Lenhart et al. 2025, AJ, in press. eprint arXiv:2503.07719

Ultra-hot Jupiters (UHJs) orbit close to their host stars and experience extreme conditions, making them important laboratories to explore atmospheric composition and dynamics. Transmission spectroscopy is a useful tool to reveal chemical species and their vertical and longitudinal distribution in the atmosphere. We use transmission spectra from the PEPSI (Potsdam Echelle Polarimetric and Spectroscopic Instrument) spectrograph on the Large Binocular Telescope to search for species and measure their time-resolved wind velocities in the atmosphere of TOI-1518 b. We detect Fe I at 7.8 σ and Fe II at 8.9 σ, and tentatively detect Cr I at 4.4 σ and Ni I at 4.0 σ. The time-resolved wind velocities of Fe I show a velocity pattern that is consistent with the velocity pattern of Fe II . TOI-1518 b joins a small sample of UHJs for which time-resolved wind velocities have been measured.

Read more: Basinger et al. (2025), MNRAS, 543, 4136

Read more: Järvinen & Strassmeier 2025, A&A, 698, A93;  arXiv

We present high-resolution optical emission spectroscopy observations of the ultra hot Jupiters (UHJs) TOI-1431b and TOI-1518b using the PEPSI spectrograph on the LBT. We detect emission lines from Fe I with a significance of 5.68σ and 7.68σ for TOI 1431b and TOI-1518b, respectively. We also tentatively detect Cr I emission from TOI-1431b at 4.32σ. For TOI-1518 b, we tentatively detect Ni I, Fe II, and Mg I at significance levels ranging from 3−4σ. Detection of emission lines indicates that both planets possess temperature inversions in their atmospheres, providing further evidence of the ubiquity of stratospheres among UHJs. By analyzing the population of hot Jupiters, we compare models that predict the distribution of planets in the temperature-gravity space, and find a recent global circulation model suite from Roth et al. (2024) provides a reasonable match to the observed onset of inversions at Teq∼2000 K. The ubiquity of strong Fe I emission lines among UHJs, together with the paucity of detections of TiO, suggest that atomic iron is the dominant optical opacity source in their atmospheres and can be responsible for the inversions.

Read more: Petz et al. 2025, AJ, in press; arXiv