TY - THES A1 - Gruner, David T1 - New frontiers in gyrochronology T1 - Neue Horizonte in Gyrochronologie BT - exploring the evolution of stellar rotation in open clusters and wide binaries BT - eine Untersuchung der Entwicklung von Sternrotation in offenen Sternhaufen und weiten Doppelsternsystemen N2 - Late-type stars are by far the most frequent stars in the universe and of fundamental interest to various fields of astronomy – most notably to Galactic archaeology and exoplanet research. However, such stars barely change during their main sequence lifetime; their temperature, luminosity, or chemical composition evolve only very slowly over the course of billions of years. As such, it is difficult to obtain the age of such a star, especially when it is isolated and no other indications (like cluster association) can be used. Gyrochronology offers a way to overcome this problem. Stars, just like all other objects in the universe, rotate and the rate at which stars rotate impacts many aspects of their appearance and evolution. Gyrochronology leverages the observed rotation rate of a late-type main sequence star and its systematic evolution to estimate their ages. Unlike the above-mentioned parameters, the rotation rate of a main sequence star changes drastically throughout its main sequence lifetime; stars spin down. The youngest stars rotate every few hours, whereas much older stars rotate only about once a month, or – in the case of some late M-stars – once in a hundred days. Given that this spindown is systematic (with an additional mass dependence), it gave rise to the idea of using the observed rotation rate of a star (and its mass or a suitable proxy thereof) to estimate a star’s age. This has been explored widely in young stellar open clusters but remains essentially unconstrained for stars older than the sun, and K and M stars older than 1 Gyr. This thesis focuses on the continued exploration of the spindown behavior to assess, whether gyrochronology remains applicable for stars of old ages, whether it is universal for late-type main sequence stars (including field stars), and to provide calibration mileposts for spindown models. To accomplish this, I have analyzed data from Kepler space telescope for the open clusters Ruprecht 147 (2.7 Gyr old) and M 67 (4 Gyr). Time series photometry data (light curves) were obtained for both clusters during Kepler’s K2 mission. However, due to technical limitations and telescope malfunctions, extracting usable data from the K2 mission to identify (especially long) rotation periods requires extensive data preparation. For Ruprecht 147, I have compiled a list of about 300 cluster members from the literature and adopted preprocessed light curves from the Kepler archive where available. They have been cleaned of the gravest of data artifacts but still contained systematics. After correcting them for said artifacts, I was able to identify rotation periods in 31 of them. For M 67 more effort was taken. My work on Ruprecht 147 has shown the limitations imposed by the preselection of Kepler targets. Therefore, I adopted the time series full frame image directly and performed photometry on a much higher spatial resolution to be able to obtain data for as many stars as possible. This also means that I had to deal with the ubiquitous artifacts in Kepler data. For that, I devised a method that correlates the artificial flux variations with the ongoing drift of the telescope pointing in order to remove it. This process was a large success and I was able to create light curves whose quality match and even exceede those that were created by the Kepler mission – all while operating on higher spatial resolution and processing fainter stars. Ultimately, I was able to identify signs of periodic variability in the (created) light curves for 31 and 47 stars in Ruprecht 147 and M 67, respectively. My data connect well to bluer stars of cluster of the same age and extend for the first time to stars redder than early-K and older than 1 Gyr. The cluster data show a clear flattening in the distribution of Ruprecht 147 and even a downturn for M 67, resulting in a somewhat sinusoidal shape. With that, I have shown that the systematic spindown of stars continues at least until 4 Gyr and stars continue to live on a single surface in age-rotation periods-mass space which allows gyrochronology to be used at least up to that age. However, the shape of the spindown – as exemplified by the newly discovered sinusoidal shape of the cluster sequence – deviates strongly from the expectations. I then compiled an extensive sample of rotation data in open clusters – very much including my own work – and used the resulting cluster skeleton (with each cluster forming a rip in color-rotation period-mass space) to investigate if field stars follow the same spindown as cluster stars. For the field stars, I used wide binaries, which – with their shared origin and coevality – are in a sense the smallest possible open clusters. I devised an empirical method to evaluate the consistency between the rotation rates of the wide binary components and found that the vast majority of them are in fact consistent with what is observed in open clusters. This leads me to conclude that gyrochronology – calibrated on open clusters – can be applied to determine the ages of field stars. N2 - Sterne mit späten Spektraltypen sind mit Abstand die Häufigsten im Universum und von großem Interesse für verschiedene Bereiche der Astronomie. Dabei sind insbesondere galaktische Archäologie und die Erforschung von Exoplanten zu nennen. Das Problem ist jedoch, dass sich diese Sterne nur sehr langsam entwickeln; ihre Temperatur, Helligkeit und chemische Zusammensetzung ändern kaum während ihrer langen Hauptreihenphase. Daher ist es schwierig für solche Sterne ein Alter zu bestimmen – vorallem wenn sie isoliert sind und es keine anderne Indikatoren (z.B. die Zugehörigkeit zu einem Sternhaufen) gibt. Eine Möglichkeit dieses Problem zu umgehen ist Gyrochronologie. Sterne, wie alle anderen Objekte im Universum, rotieren und die Rate, mit der sie rotieren, beeinflusst viele Aspekte ihrer Evolution. Gyrochronologie nutzt die beobachtete Rotation und ihre Änderung mit der Zeit als ein Mittel zur Altersbestimmung. Anders als zuvor genannte Parameter ändert sich die Rate, mit der Sterne rotieren, deutlich im Laufe ihrer Hauptreihenentwicklung. Sie verlangsamt sich. Junge Sterne rotieren in wenigen Stunden einmal um sich selbst – ältere brauchen dafür schon einen Monat oder gar bis zu über hundert Tage. Die Tatsache, dass das Abbremsen systematischen Gesetzmäßigkeiten unterliegt, gebar die Idee dies zu nutzen um das Alter eines Sternes zu bestimmen. Das Verhalten junger Sterne wurde ausführlich erfoscht, jedoch für die meisten Sterne älter als 1 Gyr nicht bekannt, wie sich die Rotationsraten entwickeln. Diese Arbeit fokussiert sich auf die fortgesetzte Erforschung des Abbremsens; insbesondere ob Gyrochronologie auch für ältere Sterne nutzbar ist, ob es universell für alle Sterne (inklusive Feldsterne) ist und darauf weitere Kalibrationspunkte für Abbrems-Modelle bereitzustellen. Dafür habe ich, basierend auf photometrischen Zeitserien (Lichtkurven) von Keplers K2 Programm, die offenen Sternhaufen Ruprecht 147 (2.7 Gyr alt) and M 67 (4 Gyr) untersucht. Es sind jedoch umfangreiche Schritte in der Datenverarbeitung notwendig um Fehlfunktionen und technischen Limitationen des Teleskops zu begegnen. Für Ruprecht 147 habe ich aus Literaturdaten eine Liste von 300 Haufen-zugehörigen Sternen erstellt und mit fertigreduzierte Lichtkurven aus dem Kepler Archiv kombiniert. Die gröbsten Datensystematiken wurden in diesen bereinigt, denoch sind problematische Artefakte weiterhin vorhanden. Die Arbeit an Ruprecht 147 hat die Limitationen von archivierten Kepler Daten gezeigt. Daher wurde für M 67 mehr Aufwand betrieben. Direkt basierend auf den photometrischen Auffnahmen habe ich eigene Lichtkurven erzeugt, was eine deutlich höhere räumliche Auflösung erlaubt hat. Das hieß jedoch auch, dass ich mich mit all Systematiken in Kepler Daten befassen musste. Dafür habe ich eine Methodik konzipiert, die die künstlichen Variation im aufgezeichneten Fluss mit der Position eines Sterns auf dem Detektor korreliert und daraus eine Korrektur bestimmt. Dieser Prozess war so erfolgreich, dass ich Lichtkurven kreiert habe, die in ihrer Qualität an die archivierten Daten heran kommen oder sie gar übersteigen. Nach entsprechender Korrektur der Artefakte konnte ich Rotationsperioden für 31 (in Ruprecht 147) und 47 (in M 67) Sterne identifizieren. Genau wie zuvor in jüngeren Sternhaufen gesehen, folgen auch die äelteren Sternhaufen einer klaren Sequenz im Farb-Rotations-Raum. Meine Daten schließen direkt an Ergebnisse gleichaltriger Haufen an und erweitern diese zum ersten Mal zu Sternen älter als 1 Gyr und röter als frühe K-Sterne. Meine Ergebnisse zeigen eine deutliche Abweichung von der erwarteten Entwicklung, verkörpert durch eine klare Abflachung der Sequenz für Ruprecht 147, die für M 67 eine sinusförmige Struktur annimmt. Dennoch konnte ich damit zeigen, dass sich das systematische Abbremsen der Rotation von Sterne auch bis 4 Gyr fortsetzt und Sterne sich weiterhin auf eine wohldefinierten Ebene im Farb-Rotations-Alters-Raum befinden. Das heißt auch, Gyrochronologie kann mindestens für bis zu 4 Gyr alte Sterne genutzt werden. Basierend auf meinen eigenen Ergebnissen und Literaturdaten für jüngere Sternhaufen habe ich einen Vergleich mit Feldsternen durchgeführt. Die Feldsterne für diesen Vergleich entstammen weiten Doppelsternsystemen. Deren gemeinsamer Ursprung erlaubt eine Evaluierung der inneren Konsistenz beider Sterne. Mein Vergleich hat gezeigt, dass Doppelsternsysteme mit sich selbst aber auch mit den Sternhaufen konsistent sind. Ich habe damit erstmalig gezeigt, dass sich die Rotation von Feldsternen und Haufensternen gleich entwickelt. In Konsequenz bedeutet dies auch, dass Gyrochronologie angewandt werden kann, um das Alter von Feldsternen zu bestimmen. KW - Gyrochronologie KW - gyrochronology KW - spindown KW - rotation KW - Rotation Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-615268 ER - TY - JOUR A1 - Gruner, David A1 - Barnes, Sydney A. T1 - Rotation periods for cool stars in the open cluster Ruprecht 147 (NGC 6774) Implications for gyrochronology JF - Astronomy and astrophysics : an international weekly journal N2 - Context: 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. Aims: We study the 2.7 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. Methods: 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. We placed them in the cluster color-magnitude diagram and checked the related information against appropriate isochrones. The light curves were then corrected for data systematics using Principal Component Analysis on all observed K2 C07 stars and subsequently subjected to periodicity analysis. Results: Periodic signals are found for 32 stars, 21 of which are considered to be both highly reliable and to represent single, or effectively single, Ru 147 stars. These stars cover the spectral types from late-F to mid-M stars, and they have periods ranging from 6 d - 33 d, allowing for a comparison of Ruprecht 147 to both 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. Conclusions: 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 Ru 147 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. KW - stars: late-type KW - stars: low-mass KW - stars: rotation KW - stars: solar-type Y1 - 2020 U6 - https://doi.org/10.1051/0004-6361/202038984 SN - 0004-6361 SN - 1432-0746 VL - 644 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Gruner, David A1 - Hainich, Rainer A1 - Sander, Andreas Alexander Christoph A1 - Shenar, Tomer A1 - Todt, Helge Tobias A1 - Oskinova, Lidia M. A1 - Ramachandran, Varsha A1 - Ayres, T. A1 - Hamann, Wolf-Rainer T1 - The extreme O-type spectroscopic binary HD 93129A A quantitative, multiwavelength analysis JF - Astronomy and astrophysics : an international weekly journal N2 - 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 spectrum 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-circle dot) = 6.15, T-eff = 52 kK, and log (M)over dot = -4.7[M-circle dot yr(-1)] for the primary Aa, and log(L/L-circle dot) = 5.58, T-eff = 45 kK, and log (M)over dot = -5.8 [M(circle dot)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. KW - stars: individual: HD 93129A KW - stars: atmospheres KW - stars: fundamental parameters KW - stars: early-typeP Y1 - 2018 U6 - https://doi.org/10.1051/0004-6361/201833178 SN - 1432-0746 VL - 621 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Hainich, Rainer A1 - Ramachandran, Varsha A1 - Shenar, Tomer A1 - Sander, Andreas Alexander Christoph A1 - Todt, Helge Tobias A1 - Gruner, David A1 - Oskinova, Lidia M. A1 - Hamann, Wolf-Rainer T1 - PoWR grids of non-LTE model atmospheres for OB-type stars of various metallicities JF - Astronomy and astrophysics : an international weekly journal N2 - 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. KW - stars: massive KW - stars: early-type KW - stars: atmospheres KW - stars: winds KW - outflows KW - stars: mass-loss KW - radiative transfer Y1 - 2019 U6 - https://doi.org/10.1051/0004-6361/201833787 SN - 1432-0746 VL - 621 PB - EDP Sciences CY - Les Ulis ER -