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Search Results: 1 - 10 of 1377 matches for " Sonja Schuh "
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Pulsations and planets: the asteroseismology-extrasolar-planet connection
Sonja Schuh
Physics , 2010, DOI: 10.1002/asna.201011366
Abstract: The disciplines of asteroseismology and extrasolar planet science overlap methodically in the branch of high-precision photometric time series observations. Light curves are, amongst others, useful to measure intrinsic stellar variability due to oscillations, as well as to discover and characterize those extrasolar planets that transit in front of their host stars, periodically causing shallow dips in the observed brightness. Both fields ultimately derive fundamental parameters of stellar and planetary objects, allowing to study for example the physics of various classes of pulsating stars, or the variety of planetary systems, in the overall context of stellar and planetary system formation and evolution. Both methods typically also require extensive spectroscopic follow-up to fully explore the dynamic characteristics of the processes under investigation. In particularly interesting cases, a combination of observed pulsations and signatures of a planet allows to characterize a system's components to a very high degree of completeness by combining complementary information. The planning of the relevant space missions has consequently converged with respect to science cases, where at the outset there was primarily a coincidence in instrumentation and techniques. Whether space- or ground-based, a specific type of stellar pulsations can themselves be used in an innovative way to search for extrasolar planets. Results from this additional method at the interface of stellar pulsation studies and exoplanet hunts in a beyond-mainstream area are presented.
Acoustic and buoyancy modes throughout stellar evolution - Seismic properties of stars at different stellar ages and masses
Sonja Schuh
Physics , 2012, DOI: 10.1002/asna.201211812
Abstract: Parameter regions in which stars can become pulsationally unstable are found throughout the Hertzsprung-Russel diagram. Stars of high, intermediate, low and very low masses may cross various instability regions along their paths of evolutionary sequences. In describing them, I give special consideration to hybrid pulsational characteristics that are particularly valuable for asteroseismic investigations, to Pdot measurements that allow us to directly follow the stellar evolutionary changes in some stars, and to new research results that stand out with respect to previous consensus.
Amplitude variation and multiplet structures: Is PG1605+072 a slow rotator?
Jan Langfellner,Sonja Schuh,the MSST,WET teams
Physics , 2012,
Abstract: The subdwarf B star PG1605+072, with an unusually low log g ~ 5.3, shows a high number of non-radial pulsation modes, making it a promising candidate for asteroseismology. This could allow probing the star's interior to gain important insights in its structure and evolution. Comparison of previous work conducted over the last decade shows clear amplitude variation and hints of frequency variation. We analyse white light photometric data of the Multi-Site Spectroscopic Telescope (MSST) and Whole Earth Telescope (WET) XCov22 campaigns using prewhitening techniques and O-C diagrams. A total of 85 significant frequencies are identified, among them more than 20 frequency sums and harmonics. Moreover, it is shown that the main mode's amplitude varies like a sine with a period of ~630 d, indicative of long-term beating. Strong hints for the existence of frequency multiplets support the hypothesis that PG1605+072 is a slow rotator with V_eq < 0.9 km/s, contrary to previous claims. Existing asteroseismic models mainly suggest that the star possesses a high mass of ~0.7 M_Sun, presuming the main pulsation mode to be radial. This calls for an alternate formation channel.
Preface: Planetary Systems Beyond the Main Sequence 2010
Ulrich Heber,Horst Drechsel,Sonja Schuh
Physics , 2010, DOI: 10.1063/1.3570974
Abstract: Preface of Planetary Systems Beyond the Main Sequence including conference scope and summary, short overview of programme, acknowledgements of patronage, sponsors, the scientific organising committee, and the local organising committee.
The EXOTIME targets HS0702+6043 and HS0444+0458
Ronny Lutz,Sonja Schuh,Roberto Silvotti
Physics , 2010, DOI: 10.1063/1.3570968
Abstract: Pulsations in subdwarf B (sdB) stars are an important tool to constrain the evolutionary status of these evolved objects. Interestingly, the same data used for this asteroseismological approach can also be used to search for substellar companions around these objects by analyzing the timing of the pulsations by means of a so-called O-C diagram. Substellar objects around sdB stars are important for two different reasons: they are suspected to be able to influence the evolution of their host-star and they are an ideal test case to examine the properties of exoplanets which have survived the red giant expansion of their host stars.
Table of Contents: Planetary Systems Beyond the Main Sequence 2010
Sonja Schuh,Ulrich Heber,Horst Drechsel
Physics , 2010,
Abstract: We give here the Table of Contents page for the Proceedings of "Planetary Systems beyond the Main Sequence", held in August 2010 at Bamberg, Germany. This conference was the first to discuss the fate of a planet and its host star when the star evolves into a red giant and finally ends its life as a white dwarf. Scientists specialised in stellar evolution met experts from the exoplanet field to discuss this interplay.
EXOTIME: searching for planets and measuring Pdot in sdB pulsators
Ronny Lutz,Sonja Schuh,Roberto Silvotti
Physics , 2013, DOI: 10.1002/asna.201211793
Abstract: We review the status of the EXOTIME project (EXOplanet search with the TIming MEthod). The two main goals of EXOTIME are to search for sub-stellar companions to sdB stars in wide orbits, and to measure the secular variation of the pulsation periods, which are related to the evolutionary change of the stellar structure. Now, after four years of dense monitoring, we start to see some results and present the brown dwarf and exoplanet candidates V1636 Ori b and DW Lyn b.
The Nature of the Hyper-Runaway Candidate HIP 60350
Andreas Irrgang,Norbert Przybilla,Ulrich Heber,M. Fernanda Nieva,Sonja Schuh
Physics , 2010, DOI: 10.1088/0004-637X/711/1/138
Abstract: Young, massive stars in the Galactic halo are widely supposed to be the result of an ejection event from the Galactic disk forcing some stars to leave their place of birth as so-called runaway stars. Here, we present a detailed spectroscopic and kinematic analysis of the runaway B-star HIP 60350 to determine which runaway scenario - a supernova explosion disrupting a binary system or dynamical interaction in star clusters - may be responsible for HIP 60350's peculiar orbit. Based on a non-local thermodynamic equilibrium approach, a high-resolution optical echelle spectrum was examined to revise spectroscopic quantities and for the first time to perform a differential chemical abundance analysis with respect to the B-type star 18 Peg. The results together with proper motions from the Hipparcos Catalog further allowed the three-dimensional kinematics of the star to be studied numerically. The abundances derived for HIP 60350 are consistent with a slightly supersolar metallicity agreeing with the kinematically predicted place of birth ca. 6 kpc away from the Galactic center. However, they do not exclude the possibility of an alpha-enhanced abundance pattern expected in the case of the supernova scenario. Its outstanding high Galactic rest frame velocity of 530 plus-minus 35 km/s is a consequence of ejection in the direction of Galactic rotation and slightly exceeds the local Galactic escape velocity in a standard Galactic potential. Hence HIP 60350 may be unbound to the Galaxy.
The Potential of the Timing Method to Detect Evolved Planetary Systems
Roberto Silvotti,Robert Szabo,Pieter Degroote,Roy H. Ostensen,Sonja Schuh
Physics , 2010, DOI: 10.1063/1.3570966
Abstract: The timing method, using either stellar pulsations or eclipse timing of close binaries as a clock, is proving to be an efficient way to detect planets around stars that have evolved beyond the red giant branch. In this article we present a short review of the recent discoveries and we investigate the potential of the timing method using data both from ground-based facilities as well as from the Kepler and CoRoT space missions.
V391 Peg: identification of the two main pulsation modes from ULTRACAM u'g'r' amplitudes
Roberto Silvotti,Suzanna Randall,Vik S. Dhillon,Tom R. Marsh,Chris D. Savoury,Sonja Schuh,Gilles Fontaine,Pierre Brassard
Physics , 2010, DOI: 10.1002/asna.201011451
Abstract: V391 Peg (HS2201+2610) is an extreme horizontal branch subdwarf B (sdB) star, it is an hybrid pulsator showing p- and g-mode oscillations, and hosts a 3.2/sini M_Jup planet at an orbital distance of about 1.7 AU. In order to improve the characterization of the star, we measured the pulsation amplitudes in the u'g'r' SLOAN photometric bands using ULTRACAM at the William Herschel 4.2 m telescope and we compared them with theoretical values. The preliminary results presented in this article conclusively show that the two main pulsation periods at 349.5 and 354.1 s are a radial and a dipole mode respectively. This is the first time that the degree index of multiple modes has been uniquely identified for an sdB star as faint as V391 Peg (B=14.4), proving that multicolor photometry is definitely an efficient technique to constrain mode identification, provided that the data have a high enough quality.
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