bluuebunny/crossref_metadata_2025_split huggingface dataset:
The L dwarf/T dwarf transition: Multiplicity, magnetic activity and mineral meteorology across the hydrogen burning limit
Authors: Burgasser A.J. 
Published: October 2014

AbstractThe transition between the L dwarf and T dwarf spectral classes is one of the most remarkable along the stellar/brown dwarf main sequence, separating sources with photospheres containing mineral condensate clouds from those containing methane and ammonia gases. Unusual characteristics of this transition include a 1 µm brightening between late Land early T dwarfs observed in both parallax samples and coeval binaries; a spike in the multiplicity fraction; evidence of increased photometric variability, possibly arising from patchy cloud structures; and a delayed transition for young, planetary‐mass objects. All of these features can be explained if this transition is governed by the “rapid” (nonequlibrium) rainout of clouds from the photosphere, triggered by temperature, surface gravity, metallicity and (perhaps) rotational effects. While the underlying mechanism of this rainout remains under debate, the transition is now being exploited to discover and precisely characterize tight (<1 AU) very low‐mass binaries that can be used to test brown dwarf evolutionary and atmospheric theories, and resolved binaries that further constrain the properties of this remarkable transition. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Starspots and spin‐orbit alignment for Kepler cool host stars
Authors: Sanchis‐Ojeda R. , Winn J.N. , Fabrycky D.C. 
Published: October 2014

AbstractThe angle between the spin axis of the host star and the orbit of its planets (i.e., the stellar obliquity) is precious information about the formation and evolution of exoplanetary systems. Measurements of the Rossiter‐McLaughlin effect revealed that many stars that host a hot‐Jupiter have high obliquities, suggesting that hot‐Jupiter formation involves excitation of orbital inclinations. In this contribution we show how the passage of the planet over starspots can be used to measure the obliquity of exoplanetary systems. This technique is used to obtain – for the first time – the obliquity of a system with several planets that lie in a disk, Kepler‐30, with the result that the star has an obliquity smaller than 10 degrees. The implications for the formation of exoplanetary systems, in particular the hot‐Jupiter population, are also discussed. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determining distances using asteroseismic methods
Authors: Silva Aguirre V. , Casagrande L. , Basu S. , Campante T. L. , Chaplin W. J. , Huber D. , Miglio A. , Serenelli A. M. , KASC WG#1  
Published: October 2014

AbstractAsteroseismology has been extremely successful in determining the properties of stars in different evolutionary stages with a remarkable level of precision. However, to fully exploit its potential, robust methods for estimating stellar parameters are required and independent verification of the results is needed. In this talk, I present a new technique developed to obtain stellar properties by coupling asteroseismic analysis with the infrared flux method. Using two global seismic observables and multi‐band photometry, the technique determines masses, radii, effective temperatures, bolometric fluxes, and thus distances for field stars in a self‐consistent manner. Applying our method to a sample of solar‐like oscillators in the Kepler field that have accurate Hipparcos parallaxes, we find agreement in our distance determinations to better than 5 %. Comparison with measurements of spectroscopic effective temperatures and interferometric radii also validate our results, and show that our technique can be applied to stars evolved beyond the main‐sequence phase. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Angular momentum evolution of cool stars: Toward a synthesis of observations and theory before and after the ZAMS
Authors: Meibom S. , Barnes S.A. , Covey K. , Jeffries R.D. , Matt S. , Morin J. , Palacios A. , Reiners A. , Sicilia‐Aguilar A. , Irwin J. 
Published: October 2014

AbstractThe coexistence of fast and slowly rotating cool stars in ZAMS clusters – forming distinct sequences in the color vs. rotation period plane – is providing clues to differences in their pre main‐sequence angular momentum evolution. This Cool Stars 17 splinter was dedicated to a discussion of new observational and theoretical results that may help discriminate between proposed mechanisms for early angular momentum regulation and help us explain the observed ZAMS dichotomy
Angular momentum evolution of low‐mass pre‐main sequence stars via extreme coronal mass ejections
Authors: Aarnio A.N. , Matt S.P. , Stassun K.G. 
Published: October 2014

AbstractThe angular momentum evolution of cool stars during the pre‐main sequence phase of stellar evolution remains a major outstanding problem. Multiple processes are likely involved in the transfer of mass and angular momentum within and out of the star+disk system. The role of coronal mass ejections (CMEs), energetic events which shed mass and magnetic flux in the Sun, has yet to be fully explored in the context of pre‐main sequence stars. It is well established that young, solar‐type stars exhibit X‐ray activity levels up to four orders of magnitude higher than the present‐day Sun, suggesting that CMEs associated with these extreme X‐ray flares could be an important process for expelling mass and angular momentum. We present a novel approach to modeling the CMEs of low‐mass pre‐main sequence stars that uses a solar‐calibrated CME model and observed X‐ray flare rates for young stars. We derive mass loss rates via stellar CMEs and calculate their attendant angular momentum losses during the pre‐main sequence phase. While we find the mass loss rates to be modest, ∼10 % of steady‐state stellar wind values from the literature, the angular momentum losses can be substantial, potentially counteracting the effects of initial stellar spin‐up due to contraction in tens of Myr. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Volatile and refractory abundances of F‐ and G‐type stars
Authors: González Hernández J.I. , Delgado‐Mena E. , Sousa S. G. , Israelian G. , Santos N.C. , Udry S. 
Published: October 2014

AbstractWe present a detailed chemical abundance analysis of a sample of F‐ and G‐type stars. We investigate the possibility that the presence of terrestrial planets could affect the volatile‐to‐refractory abundance ratios. Stars with and without planets exhibit very similar abundance behaviours, either for solar twins or even when considering the whole sample of 95 solar analogs, 33 with and 62 without detected planets, in the metallicity range –0.3 < [Fe/H] < 0.5. After removing the Galactic chemical evolution effects, the small differences in the abundance patterns of stars with and without planets practically disappear and the mean volatile‐to‐refractory abundance ratios of the two samples are very close to solar values. If the depletion signature depends on the size of the convective zone, then stars hotter than the Sun should, in principle, show enhanced volatile‐to‐refractory abundance differences. Thus, we have also selected a sample of late F‐ and early G‐type main‐sequence stars with high‐quality spectra. We have in total 29 planet‐host stars and 32 stars without planets in the Teff range 5950–6400 K. We find very accurate Galactic chemical trends of these hotter stars that match those of solar analogs. Finally, we compare the abundance ratios of volatile and refractory elements versus the condensation temperature of this sample of main‐sequence stars hotter than the Sun with respect to those of solar analogs, paying special attention to those stars containing super‐Earth‐like planets. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Radii and temperatures of cool stars with interferometry
Authors: Boyajian T.S. 
Published: October 2014

AbstractThis proceeding reviews the results of our survey to measure the fundamental properties of nearby, main‐sequence, K– and M–type stars, specifically reported in Boyajian et al. (2012a). The results presented double the number of precise measurements obtained for stars of this type. We use observations of the stellar angular diameter obtained through interferometry coupled with the distance and bolometric flux to determine the stellar linear radius, effective temperature, and luminosity. These data are used to derive empirical relations to the fundamental properties of stars. We highlight the challenges these data bring to current stellar atmospheric and evolutionary models. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Constraining the core‐rotation rate in red‐giant stars from Kepler space photometry
Authors: Beck P.G. , De Ridder J. , Aerts C. , Kallinger T. , Hekker S. , García R.A. , Mosser B. , Davies G.R. 
Published: October 2014

AbstractRotation plays a key role in stellar structure and its evolution. Through transport processes which induce rotational mixing of chemical species and the redistribution of angular momentum, internal stellar rotation influences the evolutionary tracks in the Hertzsprung‐Russell diagram. In turn, evolution influences the rotational properties. Therefore, information on the rotational properties of the deep interior would help to better understand the stellar evolution. However, as the internal rotational profile cannot be measured directly, it remains a major unknown leaving this important aspect of models unconstrained. We can test for nonrigid rotation inside the stars with asteroseismology. Through the effect of rotational splitting of non‐radial oscillation modes, we investigate the internal rotation profile indirectly. Red giants have very slow rotation rates leading to a rotational splitting on the level of a few tenth of a μHz. Only from more than 1.5 years of consecutive data from the NASA Kepler space telescope, these tiny variations could be resolved. A qualitative comparison to theoretical models allowed constraining the core‐to‐surface rotation rate for some of these evolved stars. In this paper, we report on the first results of a large sample study of splitting of individual dipole modes (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the surface structure of sunspots
Authors: Franz M. 
Published: October 2014

AbstractA precise knowledge of the surface structure of sunspots is essential to construct adequate input models for helioseismic inversion tools. We summarize our recent findings about the velocity and magnetic field in and around sunspots using HINODE observation. To this end we quantize the horizontal and vertical component of the penumbral velocity field at different levels of precision and study the moat flow around sunspot. Furthermore, we find that a significant amount of the penumbral magnetic fields return below the surface within the penumbra. Finally, we explain why the related opposite polarity signals remain hidden in magnetograms constructed from measurements with limited spectral resolution (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Brite‐Constellation: A status report
Authors: Kaiser A. , Kuschnig R. , Weiss W.W. , BRITE‐Constellation team  
Published: October 2014

AbstractThe BRITE‐Constellation, short for “BRIght Target Explorer” Constellation, is a group of six nanosatellites from Austria, Poland and Canada carrying thirty millimeter aperture optical telescopes with a CCD camera. The goal of the mission is to photometrically measure low‐level oscillations and temperature variations of the brightest stars in the sky down to a visual magnitude of 4.0, with unprecedented precision and time coverage not achievable from ground in two colors. The improved three‐axis pointing performance which is a critical element that makes this high precision photometry mission feasible is a recent development by the University of Toronto’s Space Flight Laboratory. The University of Vienna and the FFG/ALR (Austria’s space agency) are financing the development of two satellites. The Polish Academy of Sciences is funding two additional satellites as well as the Canadian Space Agency resulting in six components for the constellation (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
EXOTIME: Searching for planets and measuring $ \dot P $ in sdB pulsators
Authors: Lutz R. , Schuh S. , Silvotti R. 
Published: October 2014

AbstractWe 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 Lynb (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Presentation of the reduction pipeline of the SONG échelle spectrograph
Authors: Triviño A. , Uytterhoeven K. , Grundahl F. , Pallé P.L. , the SONG team  
Published: October 2014

AbstractWe give an overview of the spectral reduction pipeline that will be used to process the data of the échelle spectrograph of the SONG‐OT telescope node of the SONG (Stellar Observations Network Group) network on Tenerife. In particular, we focus on the iodine absorption cell technique to derive precise radial velocity measurements. The telescope and dome of SONG‐OT were installed on 23 April 2012, and first light is foreseen this autumn. The reduction pipeline will be tested, optimized and improved when real stellar data will become available (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ground‐based photometric support for the CoRoT mission by the CoRoT‐Hungarian Asteroseismology Group
Authors: Bognár Zs. , Paparó M. 
Published: October 2014

AbstractThe CoRoT–Hungarian Asteroseismology Group was established in 2005 and joined the preparatory work of the CoRoT Mission via an ESA PECS project. After the successful launch of the telescope, we have continued our work of groundbased multi‐colour photometric observations and contributed to the analyses of CoRoT data. Our observations were focused on δ Scuti, γ Doradus, and RR Lyrae stars. The follow‐up of some selected targets’ pulsations in different wavelengths has provided valuable information for mode identification. We provided additional support by the confirmation of relatively faint variables’ spectral types. We proved that our ground‐based observations can help in the interpretation of a target with a contaminated CoRoT light curve. In this paper, we summarize our most important results of the photometric support for the CoRoT Mission (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
RR Lyrae stars seen from space
Authors: Guggenberger E. 
Published: October 2014

AbstractRR Lyrae stars for a long time had the reputation of being rather simple pulsators, but the advent of high‐precision space photometry has meanwhile changed this picture dramatically. This article summarizes the results obtained for two remarkable Blazhko RR Lyrae stars and discusses how our view of RR Lyrae stars has changed since the availability of ultra‐precise satellite photometry as it is obtained by CoRoT and Kepler. Both stars, CoRoT 105288363 and V445 Lyrae, show a multitude of phenomena that were impossible to observe from the ground, either because of the small amplitude of the effect, or because uninterrupted long‐term monitoring was required for a detection. Not only was it found that strong and irregular cycle‐to‐cycle changes of the Blazhko effect can occur, and that seemingly chaotic phenomena need to be accounted for when modeling the Blazhko effect, but also a rich spectrum of low‐amplitude frequencies was detected in addition to the fundamental radial pulsation in RRab stars. The so‐called period doubling phenomenon, higher radial overtones and possibly also non‐radial modes make RR Lyrae stars more multifaceted than previously thought. This article presents the various aspects of irregularity of the Blazhko effect, questioning its long‐standing definition as a “periodic modulation”, and also discusses the low‐amplitude pulsation signatures that had been hidden in the noise of observations for centuries (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New results in RR Lyrae modeling: Convective cycles, additional modes and more
Authors: Molnár L. , Kolláth Z. , Szabó R. , Plachy E. 
Published: October 2014

AbstractRecent theoretical and observational findings breathed new life into the field of RRLyrae stars. The ever more precise and complete measurements of the space asteroseismology missions revealed new details, such as the period doubling and the presence of the additional modes in the stars. Theoretical work also flourished: period doubling was explained and an additional mode has been detected in hydrodynamic models as well. Although the most intriguing mystery, the Blazhko‐effect has remained unsolved, new findings indicate that the convective cycle model can be effectively ruled out for short‐ and medium‐period modulations. On the other hand, the plausibility of the radial resonance model is increasing, as more and more resonances are detected both in models and stars (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Red giant oscillations: Stellar models and mode frequency calculations
Authors: Jendreieck A. , Weiss A. , Silva Aguirre V. , Christensen‐Dalsgaard J. , Handberg R. , Ruchti G. , Jiang C. , Thygesen A. 
Published: October 2014

AbstractWe present preliminary results on modelling KIC 7693833, the so far most metal‐poor red giant star observed by Kepler. From time series spanning several months, global oscillation parameters and individual frequencies were obtained and compared to theoretical calculations. Evolution models are calculated taking into account spectroscopic and asteroseismic constraints. The oscillation frequencies of the models were computed and compared to the Kepler data. In the range of mass computed, there is no preferred model, giving an uncertainty of about 30 K in Teff, 0.02 dex in log g, 0.7R⊙ in radius, and of about 2.5 Gyrs in age (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Seismic comparison of the 11‐ and 2‐year cycle signatures in the Sun
Authors: Simoniello R. , Jain K. , Tripathy S.C. , Turck‐Chiéze S. , Finsterle W. , Roth M. 
Published: October 2014

AbstractThe solar magnetic activity consists of two periodic components: the main cycle with a period of 11 yr and a shorter cycle with a period of ≈2 yr. The origin of this second periodicity is still not well understood. We use almost 15 years of long high‐quality resolved data provided by the Global Oscillation Network Group (GONG) to investigate the solar cycle changes in p‐mode oscillations with spherical degree Ł = 0–120 and in the range of 1600 µHz ≤ ν ≤ 3500 µHz. For both periodic components of solar magnetic activity our findings locate the origin of the frequency shift in the subsurface layers with a sudden enhancement in the amplitude of the shift in the last few hundred kilometers. We also show that the size of the shift increases towards equatorial latitudes and from minimum to maximum of solar activity. On the other hand, the signatures of the 2‐yr cycle differ from the one of the 11‐yr cycle in the magnitude of the shift, as the 2‐yr cycle causes a weaker shift in mode frequencies and a slower enhancement in the last few hundred kilometers. Based on these findings we speculate that a possible physical mechanism behind the quasi biennial periodicity (QBP) could be the beating between different dynamo modes (dipole and quadrupole mode) (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Measuring the solar meridional flow from perturbations of eigenfunctions of global oscillations
Authors: Schad A. , Timmer J. , Roth M. 
Published: October 2014

AbstractWe present a new concept to infer the meridional flow in the deep solar interior from global oscillation data. This concept is based on the estimation of the coupling strengths of p‐mode eigenfunctions mediated by the meridional flow. We illustrate the performance of the method using simulations and present first inversion results of a large‐scale flow component of the meridional flow obtained from MDI data (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hydrodynamical comparison test of solar models
Authors: Bach K. , Kim Y.‐C. 
Published: October 2014

AbstractWe present three dimensional radiation‐hydrodynamical (RHD) simulations for solar surface convection based on three most recent solar mixtures: Grevesse & Sauval (1998), Asplund, Grevesse & Sauval (2005), and Asplund, Grevesse, Sauval & Scott (2009). The outer convection zone of the Sun is an extremely turbulent region composed of partly ionized compressible gases at high temperature. The super‐adiabatic layer (SAL) is the transition region where the transport of energy changes drastically from convection to radiation. In order to describe physical processes accurately, a realistic treatment of radiation should be considered as well as convection. However, newly updated solar mixtures that are established from radiation‐hydrodynamics do not generate properly internal structures estimated by helioseismology. In order to address this fundamental problem, solar models are constructed consistently based on each mixture and used as initial configurations for radiation‐hydrodynamical simulations. From our simulations, we find that the turbulent flows in each model are statistically similar in the SAL (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Asteroseismology and magnetic cycles
Authors: Santos A.R.G. , Cunha M.S. , Lima J.J.G. 
Published: October 2014

AbstractSmall cyclic variations in the frequencies of acoustic modes are expected to be a common phenomenon in solar‐like pulsators, as a result of stellar magnetic activity cycles. The frequency variations observed throughout the solar and stellar cycles contain information about structural changes that take place inside the stars as well as about variations in magnetic field structure and intensity. The task of inferring and disentangling that information is, however, not a trivial one. In the sun and solar‐like pulsators, the direct effect of the magnetic field on the oscillations might be significantly important in regions of strong magnetic field (such as solar/stellar spots), where the Lorentz force can be comparable to the gas‐pressure gradient. Our aim is to determine the sun‐/starspot effect on the oscillation frequencies and attempt to understand if this effect contributes strongly to the frequency changes observed along the magnetic cycle. The total contribution of the spots to the frequency shifts results from a combination of direct and indirect effects of the magnetic field on the oscillations. In this first work we considered only the indirect effect associated with changes in the stratification within the starspot. Based on the solution of the wave equation and the variational principal we estimated the impact of these stratification changes on the oscillation frequencies of global modes in the sun and found that the induced frequency shifts are about two orders of magnitude smaller than the frequency shifts observed over the solar cycle (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Constraints on stellar parameters of the slowly pulsating B star HD 182255 from complex asteroseismology
Authors: Walczak P. , Szewczuk W. , Daszyńska‐Daszkiewicz J. 
Published: October 2014

AbstractSeismic modeling of the slowly pulsating B‐type star HD182255 yields strong constraints on the radial orders of the two dominant modes. For these frequencies, we derive also the empirical values of the complex nonadiabatic parameter f. These two seismic tools, i.e., pulsational frequencies and the associated values of f, allow to test available opacity data, chemical composition, and overshooting effciency (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)