Testing Asteroseismic Radii of Dwarfs and Subgiants with Kepler and Gaia

We test asteroseismic radii of Kepler main-sequence and subgiant stars by deriving their parallaxes which are compared with those of the first Gaia data release. We compute radii based on the asteroseismic scaling relations as well as by fitting observed oscillation frequencies to stellar models for a subset of the sample, and test the impact of using effective temperatures from either spectroscopy or the infrared flux method. An offset of 3%, showing no dependency on any stellar parameters, is found between seismic parallaxes derived from frequency modelling and those from Gaia. For parallaxes based on radii from the scaling relations, a smaller offset is found on average; however, the offset becomes temperature dependent which we interpret as problems with the scaling relations at high stellar temperatures. Using the hotter infrared flux method temperature scale, there is no indication that radii from the scaling relations are inaccurate by more than about 5%. Taking the radii and masses from the modelling of individual frequencies as reference values, we seek to correct the scaling relations for the observed temperature trend. This analysis indicates that the scaling relations systematically overestimate radii and masses at high temperatures, and that they are accurate to within 5% in radius and 13% in mass for main-sequence stars with temperatures below 6400 K. However, further analysis is required to test the validity of the corrections on a star-by-star basis and for more evolved stars.Comment: 12 pages, 9 figures. Accepted for publication in MNRA

'Rapid fire' spectroscopy of Kepler solar-like oscillators

The NASA Kepler mission has been continuously monitoring the same field of the sky since the successful launch in March 2009, providing high-quality stellar lightcurves that are excellent data for asteroseismology, far superior to any other observations available at the present. In order to make a meaningful analysis and interpretation of the asteroseismic data, accurate fundamental parameters for the observed stars are needed. The currently available parameters are quite uncertain as illustrated by e.g. Thygesen et al. (A&A 543, A160, 2012), who found deviations as extreme as 2.0 dex in [Fe/H] and log g, compared to catalogue values. Thus, additional follow-up observations for these targets are needed in order to put firm limits on the parameter space investigated by the asteroseismic modellers. Here, we propose a metod for deriving accurate metallicities of main sequence and subgiant solar-like oscillators from medium resolution spectra with a moderate S/N. The method takes advantage of the additional constraints on the fundamental parameters, available from asteroseismology and multi-color photometry. The approach enables us to reduce the analysis overhead significantly when doing spectral synthesis, which in turn will increases the efficiency of follow-up observations.Comment: 3 pages, 2 figures. Proceedings from Asteroseismology of Stellar Populations in the Milky Way 2013 to appear in 'Astrophysics and Space Science Proceedings

The Swiss Tropical and Public Health Institute: past, present and future

Compared internationally, the history of the Swiss Tropical and Public Health Institute (Swiss TPH) is unusual. Founded in 1944, at a time of utmost isolation, it was a response to specific needs of the government of Switzerland during the Second World War. In 1943, the Swiss Federal Council approached universities in Switzerland and asked them to submit project proposal that had the potential to mitigate possible post-war unemployment and threatening economic isolation. Members of the University of Basel proposed to establish a Swiss Tropical Institute (today: Swiss TPH). With its harbour at the River Rhine, Basel was an important international transport hub. The city was and still is the headquarters of important pharmaceutical companies, such as Novartis Pharma AG and F. Hoffmann-La Roche AG, which were looking for new markets overseas. Last but not least, scientific expeditions to Africa were rather common in the 19(th) and the beginning of the 20(th) century for members of Basel's bourgeoisie. Initially, Swiss TPH focused primarily on basic research into diseases of poverty, but over the years it has developed into an important player in public, international and global health. This article sees the development of the institute as a reflection of the visions of its directors from the founder Professor Rudolf Geigy to Professor Jurg Utzinger, who is the current Swiss TPH director. It includes interviews with the four latest of them, discussing their experiences and attempts to adapt the institute to an ever changing global environment. From these lessons learnt we hope to gain insights that could be relevant for today's leaders of scientific institutes; foster public-private partnerships and contribute to solve some of the most pressing global health challenges

The dissimilar chemical composition of the planet-hosting stars of the XO-2 binary system

Using high-quality spectra of the twin stars in the XO-2 binary system, we have detected significant differences in the chemical composition of their photospheres. The differences correlate strongly with the elements' dust condensation temperature. In XO-2N, volatiles are enhanced by about 0.015 dex and refractories are overabundant by up to 0.090 dex. On average, our error bar in relative abundance is 0.012 dex. We present an early metal-depletion scenario in which the formation of the gas giant planets known to exist around these stars is responsible for a 0.015 dex offset in the abundances of all elements while 20 M_Earth of non-detected rocky objects that formed around XO-2S explain the additional refractory-element difference. An alternative explanation involves the late accretion of at least 20 M_Earth of planet-like material by XO-2N, allegedly as a result of the migration of the hot Jupiter detected around that star. Dust cleansing by a nearby hot star as well as age or Galactic birthplace effects can be ruled out as valid explanations for this phenomenon.Comment: ApJ, in press. Complete linelist (Table 3) available in the "Other formats -> Source" downloa

The Solar Twin Planet Search II. A Jupiter twin around a solar twin

Through our HARPS radial velocity survey for planets around solar twin stars, we have identified a promising Jupiter twin candidate around the star HIP11915. We characterize this Keplerian signal and investigate its potential origins in stellar activity. Our analysis indicates that HIP11915 hosts a Jupiter-mass planet with a 3800-day orbital period and low eccentricity. Although we cannot definitively rule out an activity cycle interpretation, we find that a planet interpretation is more likely based on a joint analysis of RV and activity index data. The challenges of long-period radial velocity signals addressed in this paper are critical for the ongoing discovery of Jupiter-like exoplanets. If planetary in nature, the signal investigated here represents a very close analog to the solar system in terms of both Sun-like host star and Jupiter-like planet.Comment: 8 pages, 5 figures; A&A accepted; typos corrected in this versio