Prospects for asteroseismology

The observational basis for asteroseismology is being dramatically strengthened, through more than two years of data from the CoRoT satellite, the flood of data coming from the Kepler mission and, in the slightly longer term, from dedicated ground-based facilities. Our ability to utilize these data depends on further development of techniques for basic data analysis, as well as on an improved understanding of the relation between the observed frequencies and the underlying properties of the stars. Also, stellar modelling must be further developed, to match the increasing diagnostic potential of the data. Here we discuss some aspects of data interpretation and modelling, focussing on the important case of stars with solar-like oscillations.Comment: Proc. HELAS Workshop on 'Synergies between solar and stellar modelling', eds M. Marconi, D. Cardini & M. P. Di Mauro, Astrophys. Space Sci., in the press Revision: correcting abscissa labels on Figs 1 and

TESS Cycle 1 observations of roAp stars with 2-min cadence data

We present the results of a systematic search for new rapidly oscillating Ap (roAp) stars using the 2-min cadence data collected by the Transiting Exoplanet Survey Satellite (TESS) during its Cycle 1 observations. We identify 12 new roAp stars. Amongst these stars we discover the roAp star with the longest pulsation period, another with the shortest rotation period, and six with multiperiodic variability. In addition to these new roAp stars, we present an analysis of 44 known roAp stars observed by TESS during Cycle 1, providing the first high-precision and homogeneous sample of a significant fraction of the known roAp stars. The TESS observations have shown that almost 60 per cent (33) of our sample of stars are multiperiodic, providing excellent cases to test models of roAp pulsations, and from which the most rewarding asteroseismic results can be gleaned. We report four cases of the occurrence of rotationally split frequency multiplets that imply different mode geometries for the same degree modes in the same star. This provides a conundrum in applying the oblique pulsator model to the roAp stars. Finally, we report the discovery of non-linear mode interactions in $\alpha$ Cir (TIC 402546736, HD 128898) around the harmonic of the principal mode -- this is only the second case of such a phenomenon...

TOI-257b (HD 19916b): A warm sub-saturn orbiting an evolved F-type star

We report the discovery of a warm sub-Saturn, TOI-257b (HD 19916b), based on data from NASA's Transiting Exoplanet Survey Satellite (TESS). The transit signal was detected by TESS and confirmed to be of planetary origin based on radial velocity observations. An analysis of the TESS photometry, the Minerva-Australis, FEROS, and HARPS radial velocities, and the asteroseismic data of the stellar oscillations reveals that TOI-257b has a mass of MP = 0.138 ± 0.023 M J (43.9 ± 7.3, M⊕), a radius of RP = 0.639 ± 0.013 R J (7.16 ± 0.15, R ⊕), bulk density of 0.65+0.12-0.11 (cgs), and period 18.38818 +0.00085 -0.00084 days. TOI-257b orbits a bright (V = 7.612 mag) somewhat evolved late F-type star with M∗ = 1.390 ± 0.046 rm M sun, R∗ = 1.888 ± 0.033 Rsun, Teff = 6075 ± 90 rm K, and vsin i = 11.3 ± 0.5 km s-1. Additionally, we find hints for a second non-transiting sub-Saturn mass planet on a ∼71 day orbit using the radial velocity data. This system joins the ranks of a small number of exoplanet host stars (∼100) that have been characterized with asteroseismology. Warm sub-Saturns are rare in the known sample of exoplanets, and thus the discovery of TOI-257b is important in the context of future work studying the formation and migration history of similar planetary systems

Variability Among B Stars Observed with WIRE

Item does not contain fulltextFollowing the failure of the main experiment on board the Wide-Field Infrared Explorer satellite (WIRE), the on-board star camera was used as the first space-based asteroseismology experiment. From May 1999 through November 2006, well over 200 targets were observed for periods ranging up to 40+ days. The typical noise level (measured at a frequency of 10 mHz) of these observations was <5 ppm for a 3rd magnitude star. More than 35 Beta Cep and SPB stars have been observed with WIRE, and analysis has been ongoing for some time. New oscillation modes have been observed for targets such as Beta Cru (Cuypers et al. 2002), Kappa Sco (Cuypers et al. 2004), and Lambda Sco (Bruntt & Buzasi 2006). Lambda Sco in particular comprises two B type stars in a wide orbit (P = 1083 d), and one of these components has a low mass companion (P = 5.95 d). After subtracting the Beta Cep pulsation Bruntt & Buzasi (2006) could clearly see the primary and secondary eclipses in the close system. From their preliminary light curve analysis they constrained the mass and radius of the component stars. Until now, however, the majority of the B stars observed with WIRE have not been analyzed. Here we begin this process, presenting light curves and power spectra, and reporting frequencies and amplitudes for the B stars in the WIRE collection

Properties of 42 solar-type Kepler targets from the asteroseismic modeling portal

Recently the number of main-sequence and subgiant stars exhibiting solar-like oscillations that are resolved into individual mode frequencies has increased dramatically. While only a few such data sets were available for detailed modeling just a decade ago, the Kepler mission has produced suitable observations for hundreds of new targets. This rapid expansion in observational capacity has been accompanied by a shift in analysis and modeling strategies to yield uniform sets of derived stellar properties more quickly and easily. We use previously published asteroseismic and spectroscopic data sets to provide a uniform analysis of 42 solar-type Kepler targets from the Asteroseismic Modeling Portal. We find that fitting the individual frequencies typically doubles the precision of the asteroseismic radius, mass, and age compared to grid-based modeling of the global oscillation properties, and improves the precision of the radius and mass by about a factor of three over empirical scaling relations. We demonstrate the utility of the derived properties with several applications. © 2014. The American Astronomical Society. All rights reserved.

Linguistic Situation in Twenty sub-Saharan African Countries: A Survey-based Approach

Data on second languages in sub-Saharan Africa are hard to come by. Consequently, any source that contributes to our knowledge beyond the level of primary languages should be appreciated and exploited. This article utilises Round 4 of the Afrobarometer Survey that collects information on ethnicity, home, and additional languages in 20 sub-Saharan African countries. The study has three main contributions. First, it overviews and compares some widely used sources that contain linguistic data and investigates why they show such a diverse picture on language use patterns. Second, it applies the ICP which, according to the author’s knowledge, is the first linguistic measure that takes multilingualism into account. Third, it shows how a simple graphic representation of the ICP can be used to visualise the most important dimensions of a country’s linguistic situation including the order of languages according to their size, the presence of monolingual speakers, and the relation between vernaculars and the former colonisers’ languages. The study findings are expected to be of interest to scholars engaged in language policy and planning and language-related development issues