New systemic radial velocities of suspected RR Lyrae binary stars

Among the tens of thousands of known RR Lyrae stars there are only a handful that show indications of possible binarity. The question why this is the case is still unsolved, and has recently sparked several studies dedicated to the search for additional RR Lyraes in binary systems. Such systems are particularly valuable because they might allow to constrain the stellar mass. Most of the recent studies, however, are based on photometry by finding a light time effect in the timings of maximum light. This approach is a very promising and successful one, but it has a major drawback: by itself, it cannot serve as a definite proof of binarity, because other phenomena such as the Blazhko effect or intrinsic period changes could lead to similar results. Spectroscopic radial velocity measurements, on the other hand, can serve as definite proof of binarity. We have therefore started a project to study spectroscopically RR Lyrae stars that are suspected to be binaries. We have obtained radial velocity (RV) curves with the 2.1m telescope at McDonald observatory. From these we derive systemic RVs which we will compare to previous measurements in order to find changes induced by orbital motions. We also construct templates of the RV curves that can facilitate future studies. We also observed the most promising RR Lyrae binary candidate, TU UMa, as no recent spectroscopic measurements were available. We present a densely covered pulsational RV curve, which will be used to test the predictions of the orbit models that are based on the O-C variations.Comment: 4 pages, 1 figure, to appear in the No. 105 issue of the Communications from the Konkoly Observatory of the Hungarian Academy of Science

A search for binary candidates among the fundamental mode RR Lyrae stars observed by Kepler

Although roughly half of all stars are considered to be part of binary or multiple systems, there are only two confirmed cases of RR Lyrae pulsators with companions. One of them is TU Uma (Wade et al 1999) - a classical RR Lyrae star in a very eccentric orbit - and the other is OGLE-BLG-RRLYR-02792 (Pietrzynski et al 2012). Considering the wealth of well-studied RR Lyrae stars, this number is astoundingly low. Having more RR Lyrae stars in binary systems at hand would be extremely valuable to get independent measurements of the masses. The data from the Kepler mission with their unprecedented precision and the long time span of about four years offer a unique possibility to systematically search for the signatures of binarity in RR Lyrae stars. Using the pulsation as a clock, we studied the variations in the timing of maximum light to hunt for possible binary systems in the sample.Comment: CoRoT Symposium 3 / Kepler KASC-7 joint meeting, Toulouse, July 2014. To be published by EPJ Web of Conference

Stellar cycles

Das Phänomen der Amplituden- und Phasenmodulation in pulsierenden Sternen ist seit mehr als einem Jahrhundert bekannt. Es war Sergei Nikolaevich Blazhko (1907), der es im Stern RW Draconis bemerkte und als erster beschrieb. Seitdem wurde der so genannte Blazhko Effekt in vielen Sternen nachgewiesen. Diese Arbeit behandelte das Phänomen des Blazhko Effektes bei RR Lyrae Sternen im Hinblick auf photometrische Beobachtungen. Das erste Kapitel gibt einen Überblick über die allgemeinen Eigenschaften de Klasse der RR Lyrae Sterne. Im zweiten Kapitel wird die Phänomenologie des Blazhko Effektes besprochen wie sie in der Photometrie zu sehen ist. Der aktuelle Stand der Forschungen und Beobachtungen zu diesem Thema wird zusammengefasst. Behandelte Aspekte sind unter anderem die Länge des Modulationszyklus, die Stärke des Blazhko Effektes, seine Abhängigkeit von der Metallizität der betroffen Sterne und die Rate seines Auftretens in verschiedenen Sternsystemen. Im dritten Kapitel werden die Daten präsentiert die im Rahmen dieser Diplomarbeit gesammelt wurden, und Beobachtungsmethoden sowie die Vorgehensweise bei der Datenreduktion werden erklärt. Die Analysen wurden die mit den neuen Daten durchgeführt wurden, werden im vierten Kapitel behandelt. Zwei südliche Blazhko-Sterne wurden im Rahmen dieser Diplomarbeit mehrere Wochen lang photometrisch beobachtet. Eine Fourieranalyse ermöglichte die präzise Bestimmung sowohl der Pulsations- als auch der Modulationsperiode. Auch die Eigenschaften der Lichtkurve sowie ihre Veränderungen im Lauf des Modulationszyklus wurden untersucht. Weiters wurde die Metallizität der untersuchten Sterne aus den Parametern ihrer Lichtkurve berechnet, und auf diese Weise ein Test durchgeführt, in welcher Blazhkophase die Sterne am ehesten einem "normalen", d.h. nicht modulierten, Stern gleichen.Amplitude and also phase variability in pulsating stars has been known for more than a century. The first to report it was Sergei Nikolaevich Blazhko (1907) on the star RW Draconis. Since then, the so-called Blazhko effect has been found in many stars of RR Lyrae type, for a long time the most often cited incidence rate was 20-30% for RRab stars and about 5% for RRc, recent estimates even give values around 50% and higher. In this thesis the properties of the Blazhko phenomenon have been discussed from an observational point of view, and new photometric results have been presented. Chapter 1 provides some basic information about RR Lyrae stars in general and explained some important terms and diagrams. In Chapter 2 the current knowledge about the photometric phenomenology of the Blazhko effect is summarized. The data obtained in the framework of the Blazhko project centered in Vienna are presented in Chapter 3 together with the data reduction methods and observational techniques which were used. The Analyses which were performed are described in Chapter 4. High precision photomultiplier photometry was obtained for two southern Blazhko stars. A Fourier analysis was performed for both stars, and the pulsation as well as the Blazhko period could be determined with good accuracy. Also, various features of the light curve and its changes during the modulation cycle were studied in detail

Mitigating the mass dependence in the Δν\Delta\nu scaling relation of red-giant stars

The masses and radii of solar-like oscillators can be estimated through the asteroseismic scaling relations. These relations provide a direct link between observables, i.e. effective temperature and characteristics of the oscillation spectra, and stellar properties, i.e. mean density and surface gravity (thus mass and radius). These scaling relations are commonly used to characterize large samples of stars. Usually, the Sun is used as a reference from which the structure is scaled. However, for stars that do not have a similar structure as the Sun, using the Sun as a reference introduces systematic errors as large as 10\% in mass and 5\% in radius. Several alternatives for the reference of the scaling relation involving the large frequency separation (typical frequency difference between modes of the same degree and consecutive radial order) have been suggested in the literature. In a previous paper, we presented a reference function with a dependence on both effective temperature and metallicity. The accuracy of predicted masses and radii improved considerably when using reference values calculated from our reference function. However, the residuals indicated that stars on the red-giant branch possess a mass dependence that was not accounted for. Here, we present a reference function for the scaling relation involving the large frequency separation that includes the mass dependence. This new reference function improves the derived masses and radii significantly by removing the systematic differences and mitigates the trend with $\nu_{\rm max}$ (frequency of maximum oscillation power) that exists when using the solar value as a reference.Comment: 12 pages, 7 figures, accepted for publication in MNRA

Collagen VI-Related Myopathy Caused by Compound Heterozygous Mutations of COL6A3 in a Consanguineous Kurdish Family

Collagen VI-related myopathies are caused by mutations of COL6A1, COL6A2, and COL6A3 and present with a wide phenotypic spectrum ranging from severe Ulrich congenital muscular dystrophy to mild Bethlem myopathy. Here, we report a consanguineous Kurdish family with 3 siblings affected by autosomal-recessive Bethlem myopathy caused by compound heterozygous mutations of COL6A3. We found the previously described missense mutation c.7447A > G/p.(Lys2483Glu) and a novel large deletion encompassing the exon 1-39 of the COL6A3 gene. Apart from the classical clinical symptoms, all patients had keratoconus, which expands the phenotype of the collagen VI-related myopathies

Describing complex interactions of social-ecological systems for tipping point assessments: an analytical framework

Humans play an interconnecting role in social-ecological systems (SES), they are part of these systems and act as agents of their destruction and regulation. This study aims to provide an analytical framework, which combines the concept of SES with the concept of tipping dynamics. As a result, we propose an analytical framework describing relevant dynamics and feedbacks within SES based on two matrixes: the “tipping matrix” and the “cross-impact matrix.” We take the Southwestern Amazon as an example for tropical regions at large and apply the proposed analytical framework to identify key underlying sub-systems within the study region: the soil ecosystem, the household livelihood system, the regional social system, and the regional climate system, which are interconnected through a network of feedbacks. We consider these sub-systems as tipping elements (TE), which when put under stress, can cross a tipping point (TP), resulting in a qualitative and potentially irreversible change of the respective TE. By systematically assessing linkages and feedbacks within and between TEs, our proposed analytical framework can provide an entry point for empirically assessing tipping point dynamics such as “tipping cascades,” which means that the crossing of a TP in one TE may force the tipping of another TE. Policy implications: The proposed joint description of the structure and dynamics within and across SES in respect to characteristics of tipping point dynamics promotes a better understanding of human-nature interactions and critical linkages within regional SES that may be used for effectively informing and directing empirical tipping point assessments, monitoring or intervention purposes. Thereby, the framework can inform policy-making for enhancing the resilience of regional SES

Describing complex interactions of social-ecological systems for tipping point assessments: an analytical framework

Humans play an interconnecting role in social-ecological systems (SES), they are part of these systems and act as agents of their destruction and regulation. This study aims to provide an analytical framework, which combines the concept of SES with the concept of tipping dynamics. As a result, we propose an analytical framework describing relevant dynamics and feedbacks within SES based on two matrixes: the “tipping matrix” and the “cross-impact matrix.” We take the Southwestern Amazon as an example for tropical regions at large and apply the proposed analytical framework to identify key underlying sub-systems within the study region: the soil ecosystem, the household livelihood system, the regional social system, and the regional climate system, which are interconnected through a network of feedbacks. We consider these sub-systems as tipping elements (TE), which when put under stress, can cross a tipping point (TP), resulting in a qualitative and potentially irreversible change of the respective TE. By systematically assessing linkages and feedbacks within and between TEs, our proposed analytical framework can provide an entry point for empirically assessing tipping point dynamics such as “tipping cascades,” which means that the crossing of a TP in one TE may force the tipping of another TE. Policy implications: The proposed joint description of the structure and dynamics within and across SES in respect to characteristics of tipping point dynamics promotes a better understanding of human-nature interactions and critical linkages within regional SES that may be used for effectively informing and directing empirical tipping point assessments, monitoring or intervention purposes. Thereby, the framework can inform policy-making for enhancing the resilience of regional SES