Isochrones, equal-age curves, are widely used in astrophysics to estimate stellar ages. Classical stellar parameters are, however, very limited in their usability for main sequence stars because of their weak age-dependence. Here, rotation period measurements provide complementary information. We construct and present a set of rotational isochrones, named the Potsdam Empirical Rotational Isochrones from CLustEr Stars (Pericles), that leverage rotation periods. They are constructed empirically using stars in well-studied open clusters and a small number of complementary field stars. The rotational isochrones span the main sequence stars from late-F type near the Kraft break to the fully-convective boundary around M3 stars, and are available for ages <= 6 Gyr. We also discuss a limitation to such color- or temperature based rotational isochrones, together with ideas to overcome it.

We quantify the effect of starspots for the orbital elements of the spotted RS CVn binary λ Andromedae (λ And) and present an empirical correction. The aim is to obtain a more precise orbital solution that can be used to better study the system's severe orbital-rotational asynchronism. Phase-resolved high-resolution optical spectra were recorded over the course of 522 days in 2021-2022. We employed two facilities with medium and high resolution spectroscopy for the multiple activity analyses. Doppler imaging is used to reconstruct λ And's starspots with a high resolution (R= 250 000) and high signal-to-noise ratio spectra. Optimized cross-correlation functions were used to measure precise radial velocities at a level of a few ten's of m/s. The spot-corrected radial velocities enable, on average, a threefold increase in precision of the individual orbital elements. The residual velocity jitter with a full range of 500 m/s is modulated by the rotation period of λ And of 54.4±0.3 days. Our logarithmic gravity from spectrum synthesis of 2.8±0.2 together with the interferometrically determined stellar radius suggest a most-likely mass of the primary of ≈1.4 Msun. The small orbital mass function then implies a secondary mass of just ≈0.1 Msun, which is appropriate for an L-class brown dwarf. The Doppler image reconstructs a dominating cool spot with an umbral temperature difference of ≈1000 K with respect to the photosphere of 4660 K and is likely surrounded by a moat-like velocity field. Three more weaker spots add to the total surface spottedness, which is up to 25 visible surface. Seven optical chromospheric tracers show rotational modulation of their emission line fluxes in phase with the cool spots. This surface configuration appears to have been stable for the 522 days of our observations.

Gyrochronology allows the derivation of ages for cool main sequence stars from their observed rotation periods and masses, or a suitable proxy of the latter. It is increasingly well explored for FGK stars, but requires further measurements for older ages and K-M-type stars. Recent work has shown that the behavior of stellar spindown differs significantly from prior expectations for late-type stars. We study the 4Gyr-old benchmark open cluster M67 to explore this behavior further. We combined a Gaia DR3 sample with the Kepler K2 superstamp of Campaign 5 around M67 and created new light curves from aperture photometry. The light curves are subjected to an extensive correction process to remove instrumental systematics and trending, followed by period analysis to measure stellar rotation. We identify periodic signals in 136 light curves, 47 of which are from the rotation of effectively single main-sequence stars that span from early-G to mid-M type. These results connect well to prior work on M67 and extend it to much later spectral types. We find that the rotation periods of single stars of age 4Gyr define a tight relationship with color, ranging from spectral types F through M. The corresponding surface of rotation period against age and mass is therefore well-defined to an older age than was previously known. However, the deviations from prior expectations of the stellar spindown behavior are even more pronounced at 4Gyr. The binary cluster members do not follow the single star relationship. The majority are widely scattered below the single star sequence. Consequently, they do not seem to be suitable for gyrochronology at present.

We embarked on a high-resolution optical spectroscopic survey of bright Transiting Exoplanet Survey Satellite (TESS) stars around the Northern Ecliptic Pole (NEP), dubbed the Vatican-Potsdam-NEP (VPNEP) survey. Our NEP coverage comprises 1067 stars, of which 352 are bona fide dwarf stars and 715 are giant stars, all cooler than spectral type F0 and brighter than V=8. m 5. Our aim is to characterize these stars for the benefit of future studies in the community. We analyzed the spectra via comparisons with synthetic spectra. Particular line profiles were analyzed by means of eigen-profiles, equivalent widths, and relative emission-line fluxes (when applicable). Two R=200 000 spectra were obtained for each of the dwarf stars with the Vatican Advanced Technology Telescope (VATT) and the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI), with typically three R=55 000 spectra obtained for the giant stars with STELLA and the STELLA Echelle Spectrograph (SES). Combined with V-band magnitudes, Gaia eDR3 parallaxes, and isochrones from the Padova and Trieste Stellar Evolutionary Code, the spectra can be used to obtain radial velocities, effective temperatures, gravities, rotational and turbulence broadenings, stellar masses and ages, and abundances for 27 chemical elements, as well as isotope ratios for lithium and carbon, line bisector spans, convective blue-shifts (when feasible), and levels of magnetic activity from Hα, Hβ, and the Ca ii infrared triplet. In this initial paper, we discuss our analysis tools and biases, presenting our first results from a pilot sub-sample of 54 stars (27 bona-fide dwarf stars observed with VATT+PEPSI and 27 bona-fide giant stars observed with STELLA+SES) and making all reduced spectra available to the community.

Context. Gyrochronology enables the derivation of ages of late-type main sequence stars based on their rotation periods and a mass proxy, such as color. It has been explored in open clusters, but a connection to field stars has yet to be successfully established.Aims. We explore the rotation rates of wide binaries, representing enlightening intermediaries between clusters and field stars, and their overlap with those of open cluster stars.Methods. We investigated a recently created catalog of wide binaries, matched the cataloged binaries to observations by the Kepler mission (and its K2 extension), validated or re-derived their rotation periods, identified 283 systems where both stars are on the main sequence and have vetted rotation periods, and compared the systems with open cluster data.Results. We find that the vast majority of these wide binaries (236) line up directly along the curvilinear ribs defined by open clusters in color-period diagrams or along the equivalent interstitial gaps between successive open clusters. The parallelism in shape is remarkable. Twelve additional systems are clearly rotationally older. The deviant systems, a minority, are mostly demonstrably hierarchical. Furthermore, the position of the evolved component in the color-magnitude diagram for the additional wide binary systems that contain one is consistent with the main sequence component's rotational age.Conclusions. We conclude that wide binaries, despite their diversity, follow the same spindown relationship as observed in open clusters, and we find that rotation-based age estimates yield the same ages for both components in a wide binary. This suggests that cluster and field stars spin down in the same way and that gyrochronology can be applied to field stars to determine their ages, provided that they are sufficiently distant from any companions to be considered effectively single. The results also suggest that the impact of metallicity variations on the spindown is likely not to be a major concern.

Gyrochronology is the study of stellar rotational evolution with time. Open clusters provide ideal candidates to calibrate the dependence of rotation rates on stellar mass and age due to their mostly homogeneous nature. NGC 6709 is about 150 Myrs and at a distance of 1kpc away with solar metallicity. Observations are taken with STELLA1 at the Izana Observatory in Tenerife, Spain. The cluster is observed over sev-eral months to search for rotation periods of up to 30 days. EDR3 for mass. Sample of light curves of four stars and two statistical methods. The phase

Gyrochronology allows the derivation of ages for cool main sequence stars based on their observed rotation periods and masses, or a suitable proxy thereof. It is increasingly well-explored for FGK stars, but requires further measurements for older ages and K-M-type stars. We study the nearby, 3 Gyr-old open cluster Ruprecht 147 to compare it with the previously-studied, but far more distant, NGC 6819 cluster, and especially to measure cooler stars than was previously possible there. We constructed an inclusive list of 102 cluster members from prior work, including Gaia DR2, and for which light curves were also obtained during Campaign 7 of the Kepler/K2 space mission. [...] Periodic signals are found for 32 stars, 21 of which are considered to be both highly reliable and to represent single, or effectively single, Ru147 stars. These stars cover the spectral types from late-F to mid-M stars, and they have periods ranging from 6d-32d, allowing for a comparison of Ruprecht 147 to both of the other open clusters and to models of rotational spindown. The derived rotation periods connect reasonably to, overlap with, and extend to lower masses the known rotation period distribution of the 2.5 Gyr-old cluster NGC 6819. The data confirm that cool stars lie on a single surface in rotation period-mass-age space, and they simultaneously challenge its commonly assumed shape. The shape at the low mass region of the color-period diagram at the age of Ru147 favors a recently-proposed model, which requires a third mass-dependent timescale in addition to the two timescales required by a former model, suggesting that a third physical process is required to model rotating stars effectively.

The study of massive stars in different metallicity environments is a central topic of current stellar research. The spectral analysis of massive stars requires adequate model atmospheres. The computation of such models is difficult and time-consuming. Therefore, spectral analyses are greatly facilitated if they can refer to existing grids of models. Here we provide grids of model atmospheres for OB-type stars at metallicities corresponding to the Small and Large Magellanic Clouds, as well as to solar metallicity. In total, the grids comprise 785 individual models. The models were calculated using the state-of-the-art Potsdam Wolf-Rayet (PoWR) model atmosphere code. The parameter domain of the grids was set up using stellar evolution tracks. For all these models, we provide normalized and flux-calibrated spectra, spectral energy distributions, feedback parameters such as ionizing photons, Zanstra temperatures, and photometric magnitudes. The atmospheric structures (the density and temperature stratification) are available as well. All these data are publicly accessible through the PoWR website.

Context. HD 93129A was classified as the earliest O-type star in the Galaxy (O2 If*) and is considered as the prototype of its spectral class. However, interferometry shows that this object is a binary system, while recent observations even suggest a triple configuration. None of the previous spectral analyses of this object accounted for its multiplicity. With new high-resolution UV and optical spectra, we have the possibility to reanalyze this key object, taking its binary nature into account for the first time.Aims. We aim to derive the fundamental parameters and the evolutionary status of HD 93129A, identifying the contributions of both components to the composite spectrumMethods. We analyzed UV and optical observations acquired with the Hubble Space Telescope and ESO’s Very Large Telescope. A multiwavelength analysis of the system was performed using the latest version of the Potsdam Wolf-Rayet model atmosphere code.Results. Despite the similar spectral types of the two components, we are able to find signatures from each of the components in the combined spectrum, which allows us to estimate the parameters of both stars. We derive log(L∕L⊙) = 6.15, Teff = 52 kK, and log Ṁ = −4.7 [M⊙ yr−1] for the primary Aa, and log(L∕L⊙) = 5.58, Teff = 45 kK, and log Ṁ = −5.8 [M⊙yr−1] for the secondary Ab.Conclusions. Even when accounting for the binary nature, the primary of HD 93129A is found to be one of the hottest and most luminous O stars in our Galaxy. Based on the theoretical decomposition of the spectra, we assign spectral types O2 If* and O3 III(f*) to components Aa and Ab, respectively. While we achieve a good fit for a wide spectral range, specific spectral features are not fully reproduced. The data are not sufficient to identify contributions from a hypothetical third component in the system.