bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interstellar medium simulations
Authors: Breitschwerdt D. , de Avillez M.A. , Feige J. , Dettbarn C. 
Published: October 2014

AbstractIn this review we critically assess numerical simulations of the interstellar medium (ISM), and argue that 3D high resolution calculations are the most promising method to determine the structure of the interstellar gas and follow its evolution well into the nonlinear regime. Based on a Riemann solver adaptive mesh refinement code, we present a model, which fulfills the basic requirements of running it sufficiently long in order to erase memory effects of the initial conditions, set up a disk‐halo fountain flow cycle, for converging solutions with increasing mesh refinement. We obtain the following results: (i) in a supernova driven ISM, high Reynolds number turbulence generates structures on all scales, (ii) the volume filling factor of the hot gas is substantially reduced due to the fountain flow, (iii) gas clouds are transient shock compressed layers, (iv) more than half of the gas mass resides in thermally unstable regimes, (v) O VI is distributed in patchy mixing layers, with the derived column densities being in agreement with FUSE and Copernicus observations, (vi) the electron density distribution up to distances of 8 kpc in the disk is consistent with pulsar dispersion measure observations, provided that the electron and ionization structure are not in equilibrium, (vii) the interstellar cooling function depends both on space and time (and not only on temperature and metallicity), (viii) the Local Bubble has been produced by 14–20 supernovae about 14 Myr ago, exploding in a moving group on its path through the local ISM, (ix) the nearest supernova explosion to Earth occurred 2.2 × 106 yr ago at a distance of ∼85 pc, in agreement with measurements of the radionuclide 60Fe found in the ferromanganese crust on the ocean floor (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Measuring the mass accretion rates of Herbig Ae/Be stars with X‐shooter
Authors: Pogodin M.A. , Hubrig S. , Yudin R.V. , Schöller M. , Gonzälez J.F. , Stelzer B. 
Published: October 2014

AbstractWe present the results of our observations of eight magnetic Herbig Ae/Be stars obtained with the X‐shooter spectrograph mounted on UT2 at the VLT. X‐shooter provides a simultaneous, medium‐resolution and high‐sensitivity spectrum over the entire wavelength range from 300 to 2500 nm. We estimate the mass accretion rates (Ṁacc) of the targets from 13 different spectral diagnostics using empiric calibrations derived previously for T Tauri‐type stars and brown dwarfs. We have estimated the mass accretion rates of our targets, which range from 2 × 10–9 to 2 × 10–7 M⊙ yr–1. Furthermore, we have found accretion rate variability with amplitudes of 0.10–0.40 dex taking place on time scales from one day to tens of days. Additional future night‐to‐night observations need to be carried out to investigate the character of Ṁacc variability in details. Our study shows that the majority of the calibration relations can be applied to Herbig Ae/Be stars, but several of them need to be re‐calibrated on the basis of new spectral data for a larger number of Herbig Ae/Be stars (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Relative astrometric and photometric measurements of visual binaries made with the Nice 76‐cm refractor in 2008
Authors: Gili R. , Prieur J.‐L. 
Published: October 2014

AbstractWe present relative astrometric and photometric measurements of visual binaries made in 2008, with the 76‐cm refractor of Côte d'Azur Observatory. Our observing list contains orbital couples as well as binaries whose motion is still uncertain. Three different techniques were used for obtaining measurements: Lucky imaging, speckle interferometry and the Direct Vector Autocorrelation method. We obtained 2420 new measurements of the relative position of 2225 objects, with angular separations in the range 0″.07‐11″.5, and an average accuracy of 0″.02. The mean error on the position angles is 0°.6. We managed to observe faint systems (mV ≈ 12) with large magnitude difference (up to ΔmV ≈ 5). We have thus been able to measure many systems containing red dwarf stars that had been poorly monitored since their discovery. We also measured the difference of magnitude of the two components of 376 objects with an estimated error of 0.1 mag. Finally, we provide a list of 33 newly discovered components of multiple or binary systems, which is a significant complement to our GII catalog (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical design of the new solar telescope GREGOR
Authors: Soltau D. , Volkmer R. , von der Lühe O. , Berkefeld Th. 
Published: October 2014

AbstractThis article describes the considerations which led to the current optical design of the new 1.5 m solar telescope GREGOR. The result is Gregorian design with two real foci in the optical train. The telescope includes a relay optic with a pupil image used by a high order adaptive optics system (AO). The optical design is described in detail and performance characteristics are given. Finally we show some verification results which prove that – without atmospheric effects – the completed telescope reaches a diffraction limited performance (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Open‐foldable domes with high‐tension textile membranes: The GREGOR dome
Authors: Hammerschlag R.H. , Kommers J.N. , Visser S. , Bettonvil F.C.M. , van Schie A.G.M. , van Leverink S.J. , Sliepen G. , Jägers A.P.L. , Schmidt W. , Volkmer R. 
Published: October 2014

AbstractDouble layers of high‐tensioned textile membranes were applied to the completely open‐foldable dome for the GREGOR telescope for the first time. Simultaneous climate measurements inside and outside the dome have proven the thermalinsulating capability of this double‐layer construction. The GREGOR dome is the result of the continuation of the ESO research on open‐foldable domes with textile structures, followed by the research for the DOT dome with high‐tensioned textile membranes. It cleared the way to extreme stability required for astronomical practice on high mountain sites with heavy storms and ice formation. The storm Delta with 245 km/h 1‐minute mean maximum at the location of the GREGOR caused no problems, nor did other storms afterwards. Opening and closing experiences up to wind speeds of 90 km/h were without problems. New technical developments were implemented and tested at the GREGOR dome, opening the way for application to much larger domes up to the 30 m diameter‐class range (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The GREGOR polarimetric calibration unit
Authors: Hofmann A. , Arlt K. , Balthasar H. , Bauer S.M. , Bittner W. , Paschke J. , Popow E. , Rendtel J. , Soltau D. , Waldmann T. 
Published: October 2014

AbstractThe new Solar telescope GREGOR is designed to observe small‐scale dynamic magnetic structures below a size of 70 km on the Sun with high spectral resolution and polarimetric accuracy. For this purpose, the polarimetric concept of GREGOR is based on a combination of post‐focus polarimeters with pre‐focus equipment for high precision calibration. The Leibniz‐Institute for Astrophysics Potsdam developed the GREGOR calibration unit which is an integral part of the telescope. We give an overview of the function and design of the calibration unit and present the results of extensive testing series done in the Solar Observatory “Einsteinturm” and at GREGOR (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Using the Sun to study the impact of stellar activity on exoplanet detectability
Authors: Meunier N. , Lagrange A.M. 
Published: October 2014

AbstractStellar activity induced by spots and plages, even at a low level of activity, affects the radial velocity signatures. It is therefore crucial to determine how it impacts our ability to detect small planetary signals such as those produced by Earth‐mass planets in the habitable zone of stars. We focus on the solar case: thanks to the wealth of accurate data available, the Sun gives us a unique opportunity to test the impact of stellar activity on such detections. We use the Sun as a template and investigate in details the impact of spots and plages as well as the role played by the attenuation of convection due to the presence of magnetic activity. We present the detection limits obtained in various conditions. We find that the plage contribution due to the convective blueshift attenuation dominates the total signal, with a peak‐to‐peak amplitude over the solar cycle of about 8 m s–1, and show that this contribution would prevent the detection of the Earth around the Sun, even with forthcoming high precision radial velocity instruments, unless ways to correct the signal are found. We therefore propose practical ways to correct for the activity on various timescales from days to years, and use again the Sun to estimate the ultimate detection limits achievable once the signal is corrected from the Sun's activity. Estimations will be briefly presented. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Disks, accretion and outflows of brown dwarfs
Authors: Joergens V. , Herczeg G. , Liu Y. , Pascucci I. , Whelan E. , Alcalá J. , Biazzo K. , Costigan G. , Gully‐Santiago M. , Henning Th. , Natta A. , Rigliaco E. , Rodríguez‐Ledesma M.V. , Sicilia‐Aguilar A. , Tottle J. , Wolf S. 
Published: October 2014

AbstractCharacterization of the properties of young brown dwarfs are important to constraining the formation of objects at the extreme low‐mass end of the initial mass function. While young brown dwarfs share many properties with solar‐mass T Tauri stars, differences may be used as tests of how the physics of accretion/outflow and disk chemistry/dissipation depend on the mass of the central object. This article summarizes the presentations and discussions during the splinter session on “Disks, accretion and outflows of brown dwarfs” held at the CoolStars17 conference in Barcelona in June 2012. Recent results in the field of brown dwarf disks and outflows include the determination of brown dwarf disk masses and geometries based on Herschel far‐IR photometry (70–160 µm), accretion properties based on X‐Shooter spectra, and new outflow detections in the very low‐mass regime. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison between accretion‐related properties of Herbig Ae/Be and T Tauri stars
Authors: Mendigutía I. 
Published: October 2014

AbstractThis paper summarizes several results concerning the comparison between accretion‐related properties of cool (T Tauri; T < 7000 K, M < 1 M⊙) and hot (Herbig Ae/Be; 7000 K < T < 13000 K; 1 M⊙ < M < 6 M⊙) pre‐main sequence (PMS) stars. This comparison gives insight into the analogies/differences in the physics of the star‐disk interaction and in the physical mechanisms driving disk dissipation.Several optical and near‐IR line luminosities used for low‐mass objects are also valid to estimate typical accretion rates for intermediate‐mass stars under similar empirical expressions. In contrast, the Hα width at 10 % of peak intensity is used as an accretion tracer for T Tauris, but is not reliable to estimate accretion rates for Herbig Ae/Bes. This can be explained as a consequence of the different stellar rotation rates that characterize both types of stars. In addition, there are similar trends when the accretion rate is related to the near‐IR colours and disk masses, suggesting that viscous accretion disk models are able to explain these trends for both T Tauri and Herbig Ae/Be stars. However, there are two major differences between cool and hot PMS objects. First, the inner gas dissipation timescale, as estimated by relating the accretion rates and the stellar ages, is slightly faster for Herbig Ae/Be stars. This could have implications on the physical mechanism able to form planets around objects more massive than the Sun. Second, the relative position of Herbig Ae/Bes with disks showing signs of inner dust clearing in the accretion rate‐disk mass plane contrasts with that of transitional T Tauri stars, when both samples are compared with “classical”, non‐evolved disks. This latter difference could be pointing to a different physical mechanism driving disk evolution, depending on the stellar regime
New insights: The accretion process and variable wind from TW Hya
Authors: Dupree A.K. 
Published: October 2014

AbstractFor the first time in a classical T Tauri star, we are able to trace an accretion event signaled by an hour‐long enhancement of X‐rays from the accretion shock and revealed through substantial sequential changes in optical emission line profiles. Downflowing turbulent material appears in Hα and Hβ emission. He D3 (5876 Å) broadens, coupled with an increase in flux. Two hours after the X‐ray accretion event, the optical veiling increases due to continuum emission from the hot splashdown region. The response of the stellar coronal emission to the heated photosphere follows about 2.4 hours later, giving direct evidence that the stellar corona is heated in part by accretion. Then, the stellar wind becomes re‐established. A model that incorporates the dynamics of this sequential series of events includes: an accretion shock, a cooling downflow in a supersonically turbulent region, followed by photospheric and later, coronal heating. This model naturally explains the presence of broad optical and ultraviolet lines, and affects the mass accretion rates currently determined from emission line profiles. These results, coupled with the large heated coronal region revealed from X‐ray diagnostics, suggest that current models are not adequate to explain the accretion process in young stars. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of the four catalogues by pairs, the Hipparcos, new Hipparcos, EOC‐2 and IL, by using μδ for the common 1120 stars
Authors: Damljanović G. , Cvetković Z. 
Published: October 2014

AbstractWe present comparison results of our Independent Latitude (IL) catalogue of μδ determinations for 1120 bright stars with the Hipparcos, new Hipparcos and Earth Orientation Catalogue (EOC‐2) values. Also, we took into consideration the EOC3 and EOC4 (recent versions of EOC catalogues). Our μδ values are based on zenith telescope observations from seven Independent Latitude (IL) observatories. The IL measures are spanning a time baseline of up to 90 years which is the key advantage to the accurate determination of μδ. The short interval of the Hipparcos satellite observations is a disadvantage for a good accuracy of stellar proper motion, especially in the case of double and multiple stars. For this reason many astrometric catalogues have appeared after the publication of the Hipparcos including our IL catalogue. These catalogues are an appropriate combination of the Hipparcos satellite and ground‐based data which yields more accurate stellar coordinates and/or their proper motions. Among various types of ground‐based observations the latitude and universal time variations obtained from several million observations of stars reduced to the Hipparcos reference system were used for this purpose. These observations were obtained during almost the entire last century and were originally used to determine the Earth Orientation Parameters. It is also possible to use these data in the inverse task of checking the accuracy of stellar coordinates and/or their proper motions listed in the Hipparcos Catalogue. Such latitude and universal time variations data are the basis of the EOC and IL catalogues. In this paper, we computed the differences in μδ values between pairs of catalogues and analyzed the results to characterize the μδ errors for the four catalogues with a special focus on our IL catalogue. The standard errors of μδ for IL stars observed over more than 20 years are mostly smaller than or equal to the Hipparcos errors, and close to the accuracy level of the EOC‐2 (EOC‐3, EOC‐4) and the new Hipparcos. The resulting investigations of errors of differences of μδ, show that all four catalogues have relatively small random and systematic errors which are close to each other meaning that the corresponding μδ values have a high accuracy. Our sample also contains detected double and multiple stars for which the effects of the orbital and proper motions are difficult to separate. The differences of μδ values for these stars generally exceed those obtained for single stars. Also, these discrepancies could be attributed to effect of possible, still unrecognized, astrometric binaries. These investigations about the proper motions and double stars are in line with the activity of the IAU Working Group on Astrometry by Small Ground‐Based Telescopes. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Evolution of solar‐type stellar winds
Authors: Suzuki T.K. 
Published: October 2014

AbstractBy extending our self‐consistent MHD simulations for the solar wind, we study the evolution of stellar winds of solar‐type stars from early main sequence stage to red giant phase. Young solar‐type stars are active and the mass loss rates are larger by up to ∼100 times than that of the present‐day sun. We investigate how the stellar wind is affected when the magnetic field strength and fluctuation amplitude at the photosphere increase. While the mass loss rate sensitively depends on the input energy from the surface because of the global instability related to the reflection and nonlinear dissipation of Alfvén waves, it saturates at ∼100 times because most of the energy is used up for the radiative losses rather than the kinetic energy of the wind. After the end of the main sequence phase when the stellar radius expands by ∼10 times, the steady hot corona with temperature 106 K, suddenly disappears. Chromospheric materials, with hot bubbles embedded owing to thermal instability, directly stream out; the red giant wind is not a steady stream but a structured outflow. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Solar irradiance variability
Authors: Solanki S.K. , Unruh Y.C. 
Published: October 2014

AbstractThe Sun has long been considered a constant star, to the extent that its total irradiance was termed the solar constant. It required radiometers in space to detect the small variations in solar irradiance on timescales of the solar rotation and the solar cycle. A part of the difficulty is that there are no other constant natural daytime sources to which the Sun's brightness can be compared. The discovery of solar irradiance variability rekindled a long‐running discussion on how strongly the Sun affects our climate. A non‐negligible influence is suggested by correlation studies between solar variability and climate indicators. The mechanism for solar irradiance variations that fits the observations best is that magnetic features at the solar surface, i.e. sunspots, faculae and the magnetic network, are responsible for almost all variations (although on short timescales convection and p‐mode oscillations also contribute). In spite of significant progress important questions are still open. Thus there is a debate on how strongly irradiance varies on timescales of centuries (i.e. how much darker the Sun was during the Maunder minimum than it is today). It is also not clear how the solar spectrum changes over the solar cycle. Both these questions are of fundamental importance for working out just how strongly the Sun influences our climate. Another interesting question is how solar irradiance variability compares with that of other cool dwarfs, particularly now that observations from space are available also for stars. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Furthering our knowledge of the solar neighborhood using WISE
Authors: Cushing M.C. , Kirkpatrick J.D. , Gelino C.R. , Wright E.L. , Gizis J.E. , Gomes J.I. , Leggett S.K. , Lodieu N. , Mace G.N. , Dupuy T.J. 
Published: October 2014

AbstractThe launch of NASA's Wide‐field Infrared Survey Explorer (WISE) in late 2009 ushered in an new era in the study of the solar neighborhood. Its mid‐infrared capabilities have proven critical to the discovery of the bulk of the coolest (Teff < 1000 K) brown dwarfs, including the new Y dwarfs, and its all‐sky coverage lends itself to searches for high proper motions stars using other infrared surveys such as the Two Micron All Sky Survey (2MASS), UKIRT Infrared Deep Sky Survey (UKIDSS), and Visible and Infrared Survey Telescope for Astronomy (VISTA) surveys. This splinter session of the 17th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun was organized to bring together researchers working with WISE data to both identify brown dwarfs and characterize their properties. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Non‐thermal processes in coronae and beyond
Authors: Poppenhaeger K. , Günther H. M. , Beiersdorfer P. , Brickhouse N. S. , Carter J. A. , Hudson H. S. , Kowalski A. , Lalitha S. , Miceli M. , Wolk S. J. 
Published: October 2014

AbstractThis contribution summarizes the splinter session “Non‐thermal processes in coronae and beyond” held at the Cool Stars 17 workshop in Barcelona in 2012. It covers new developments in high energy non‐thermal effects in the Earth's exosphere, solar and stellar flares, the diffuse emission in star forming regions and reviews the state and the challenges of the underlying atomic databases. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
M dwarf stars in the light of (future) exoplanet searches
Authors: Rojas‐Ayala B. , Hilton E.J. , Mann A.W. , Lépine S. , Gaidos E. , Bonfils X. , Helling Ch. , Henry T.J. , Rogers L. A. , von Braun K. , Youdin A. 
Published: October 2014

AbstractWe present a brief overview of a splinter session on M dwarf stars as planet hosts that was organized as part of the Cool Stars 17 conference. The session was devoted to reviewing our current knowledge of M dwarf stars and exoplanets in order to prepare for current and future exoplanet searches focusing in low mass stars. We review the observational and theoretical challenges to characterize M dwarf stars and the importance of accurate fundamental parameters for the proper characterization of their exoplanets and our understanding on planet formation. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The kinematics of very low mass dwarfs: Splinter session summary
Authors: Burgasser A.J. , Faherty J.K. , Schmidt S. , West A.A. , Zapatero Osorio M.R. , Pineda J.S. , Burningham B. , Nicholls C. , Sanderson R. , Shkolnik E. , Rodriguez D. , Riedel A. , Joergens V. 
Published: October 2014

AbstractKinematic investigations are being increasingly deployed in studies of the lowest mass stars and brown dwarfs to investigate their origins, characterize their atmospheres, and examine the evolution of their physical parameters. This article summarizes the contributions made at the “Kinematics of Very Low Mass Dwarfs” splinter session. Results discussed include analysis of kinematic distributions of M, L, and T dwarfs; theoretical tools for interpreting these distributions; identifications of very low mass halo dwarfs and wide companions to nearby stars; radial velocity variability among young and very cool brown dwarfs; and the search and identification of M dwarfs in young moving groups. A summary of discussion points at the conclusion of the splinter sesseion is also presented. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)