bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relative astrometry and near‐infrared differential photometry of nearby southern orbital binaries with adaptive optics
Authors: Lampens P. , Prieur J.‐L. , Argyle R.W. , Cuypers J. 
Published: October 2014

AbstractWe present relative astrometry and differential photometry measurements for a sample of nearby southern orbital binaries making use of the technique of Adaptive Optics. The observations were made in December 2000, with the ADONIS camera mounted at the 3.6‐m ESO telescope from La Silla Observatory, equipped with the broad‐band near‐infrared filters (J ‐, H ‐, K ‐passbands). Our sample contains stars which do not fit very well the empirical mean mass‐luminosity relation (according to our previous study), but for which accurate parallaxes (determined by the Hipparcos satellite) and high‐quality orbits were available thanks to many previous efforts. We derived accurate positions and J, H, K magnitudes of the individual components of those binaries. The individual stellar components have near‐infrared colour indices well grouped in those plots and are comparable to standard single stars. The data reduction procedure used for deriving those results is described in detail. It is based on a least‐squares fit of Moffat‐Lorentz profiles in direct imaging for well‐resolved systems and on Fourier analysis for very close pairs. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hopes and expectations with GREGOR
Authors: Kneer F. 
Published: October 2014

AbstractThis contribution to the series of GREGOR inauguration articles addresses the history of the GREGOR telescope. It was obvious since a long time that the study of the atmospheric dynamics on the Sun needs telescopes with a large aperture. So the first plans to replace the 40 years old Gregory‐Coudé Telescope, with its 45 cm primary mirror, by a large, 1.5‐meter telescope date back to 1997. After a positive review of the project by the Deutsche Forschungsgemeinschaft in 2000, the large financial support started in 2000. Unfortunately, the new technology of the Cesic mirrors was not yet ripe to produce the large primary mirror with this light‐weight material. So, the project was much delayed. After recollecting for the reader several dates, I also go through some properties of GREGOR. I recall the aims of the project and discuss difficulties and ways to realise the intentions (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
One of the first members of RS CVn‐type systems: MM Herculis
Authors: Taş G. , Evren S. 
Published: October 2014

AbstractWe present the long‐term multi‐colour photometry of MM Her which is one of the first members of the RS CVn‐type of eclipsing binary systems. We took advantage of its photometry‐spanning 33 years to evaluate its long‐term variation, which is caused by the evolution of the activity structures located on the surface of the cooler component. In this study we found that the long‐term variation in the brightness, colour, and amplitude of seasonal light curves over the years could be represented by two periods: one of which is of around 22.5 years, and is similar to all in this regard, but the other is a period value of about 9.5 years for the brightness variation, and of about 7.5 years for the variation in colour and amplitude. The analysis of the spot minimum phases gives a migration period of approximately 7.8 years. We also presented a new light curve analysis solution, and improved its light elements in this study. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Measuring the ages of low‐mass stars and brown dwarfs
Authors: Bochanski J.J. , Hawley S.L. , Covey K.R. , Agüeros M.A. , Baraffe I. , Catalán S. , Mohanty S. , Rice E.L. , West A.A. 
Published: October 2014

AbstractAge is among the most elusive, yet important, fundamental properties of low–mass stars and brown dwarfs. M dwarfs have main‐sequence lifetimes that are estimated to be trillions of years, with little change in luminosity. In contrast, brown dwarfs cool and dim with time, resulting in a significant degeneracy between mass, age, and luminosity. Despite these inherent challenges, there have been recent efforts on both observational and theoretical fronts that may yield precise ages for low‐mass stars and brown dwarfs. We feature some current observational efforts focused on estimating ages of these objects as presented in our Cool Stars 17 splinter session. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Polarisation and magnetic fields in cool stars and the Sun
Authors: Martínez González M.J. , Marsden S.C. 
Published: October 2014

AbstractAstrophysical plasmas and magnetic fields are inextricably coupled to each other. But magnetic fields are elusive; they cannot be fully characterized with standard (spectroscopic) observational techniques. Fortunately, polarisation, the third fundamental property of light, encodes all the quantitative information on the magnetism of the objects we observe. This splinter session brought together the solar and stellar spectropolarimetric communities to discuss some of the fundamental unsolved questions of solar and stellar magnetism and the future of spectropolarimetric observations. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Li‐enrichment in red giant rapid rotators: Planet engulfment versus extra mixing
Authors: Carlberg J.K. , Cunha K. , Smith V.V. , Majewski S.R. 
Published: October 2014

AbstractLow mass stars undergo dramatic changes during the post main sequence evolution as the nuclear energy source shifts from the stellar core to a thin shell of active hydrogen burning. The outer convection zones of these stars deepen, dredging up nuclear‐processed material and altering the stellar surface abundances. Some light elements, such as lithium, are easily destroyed in the stellar interior, and dredge‐up depletes the surface abundances of these elements. The red giant stars' expanding radii also pose a threat to the stability of close orbiting planets, which can be tidally engulfed by the star. Planet engulfment may be able to account for two of the well known classes of atypical red giant stars: the rapid rotators and Li‐rich red giants. Alternatively, internal Li regeneration combined with “extra‐mixing” in red giants may account for Li‐rich giants, but this mechanism may not be able to explain rapid rotation. We have recently completed an observational study of field red giant stars, targeting both slow and rapid rotators, to compare the light element distribution between these two classes of rotators. We find that the rapid rotators have enriched Li abundances compared to the slow rotators; however, both classes of stars have similar distributions of12C/13C – a proxy for mixing. Lower12C/13C ratios are expected in stars that have regenerated Li internally. The peculiar red giant stars in our sample (both Li‐rich and rapid rotators) are not easily explained with either planet engulfment or Li regeneration alone. Both processes are likely at work. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Full metal bracket: A calibration of infrared and optical spectroscopic metallicities of M dwarfs over 1.5 dex
Authors: Mann A.W. , Brewer J.M. , Gaidos E. , Lépine S. , Hilton E.J. 
Published: October 2014

Abstracthe determination of metallicities in late‐type stars is particularly difficult because their cool atmospheres enable the formation of complex molecules. Instead, most studies use wide binaries that include a solar‐type primary and an M dwarf companion. However, most previous studies utilize only a small number (15–25) of binaries, limiting the effective range of their calibrations. We present our observations and analysis of a sample of 105 FGK‐M wide binary systems with metallicities of –1.04 < [Fe/H] < +0.56 and companion spectral types from K5.5 to M6. We obtain moderate resolution (1300 < R < 2000) visible and near‐infrared spectra for each late‐type companion, and high‐resolution spectra for the 44 primary stars that lack published metallicities. We use our sample to determine, empirically, which spectral features are best correlated with the metallicity of the primary. We find over 80 features in K and M dwarf visible and near‐infrared spectra that are useful for predicting metallicity. We use a subset of these features to derive metallicity calibrations for different wavelength regimes, and show that it is possible to get metallicities reliable to < 0.10 dex using either visible, J, H, or K band spectra, however, when using visible spectra this requires the use of different calibrations for early‐type (K5.5 to M2) and late‐type (M2 to M6) dwarfs. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The stratified evolution of a cool star
Authors: Michaud G. , Richer J. , Richard O. 
Published: October 2014

AbstractA low mass star usually experiences stratification and abundance anomalies during its evolution. A 0.95 M⊙ star with a metallicity Z = 0.004 is followed from the main–sequence to the horizontal branch (HB). On the main sequence the larger effects of stratification may come from accretion as was suggested in relation to metallicity and planet formation. As it evolves through the giant branch, stratification appears around the hydrogen burning shell. It may create hydrodynamic instabilities and be related to abundance anomalies on the giant branch. After the helium flash the star evolves to the HB. If it loses enough mass, it ends up a hot HB star (or in the field an sdB star) with effective temperatures larger than 11000 K. All sdB stars are observed to have approximately solar iron abundance whatever their original metallicity, implying overabundances by factors of up to 100. So should the 0.95 solar mass star. How its internal hydrodynamic properties on the main sequence may influence its fate on the HB is currently uncertain. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A multiwavelength view of star‐disk interaction in NGC 2264
Authors: Cody A.M. , Stauffer J.R. , Micela G. , Baglin A. , the CSI 2264 team  
Published: October 2014

AbstractVariability is a signature property of cool young stars, particularly for those surrounded by disks. Traditional single‐band time series display complex features associated with accretion, disk structure, and accompanying stellar activity, but these processes are challenging to model. To make progress in connecting observed time domain properties with the underlying physics of young stars and their disks, we have embarked on an unprecedented multiwavelength monitoring campaign: the Coordinated Synoptic Investigation of NGC 2264 (“CSI 2264”). Beginning in December 2011, CSI 2264 has acquired 30 continuous days of mid‐infrared time series from Spitzer, simultaneous optical monitoring from CoRoT and MOST, X‐ray observations with Chandra, as well as complementary data from a number of ground‐based telescopes. The extraordinary photometric precision, cadence, and time baseline of these observations enable detailed correlation of variability properties at different wavelengths, corresponding to locations from the stellar surface to the inner AU of the disk. We present the early results of the program, and discuss the need for further modeling efforts into young stars and their disks. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The northern census of M dwarfs within 100 pc, and its potential for exoplanet surveys
Authors: Lépine S. , Gaidos E. 
Published: October 2014

AbstractWe present a new census of ∼ 100000 M dwarfs located within 100 pc of the Sun, identified in the SUPERBLINK proper motion survey. We show the new census to be >95 % complete to 50 pc, and >70 % complete to 100 pc. We discuss various subsamples which should be considered high‐priority targets for exoplanet surveys. These include: (1) very bright M dwarfs amenable to high‐precision radial velocity surveys, (2) young M dwarfs making promising targets for direct/coronagraphic imaging programs, and (3) late‐type M dwarfs with small radii, which have strong potential for the detection of Earth‐mass planets in transit surveys. We show that all three subsamples are well‐represented in the census, and discuss magnitude and color ranges of possible targets, and additional observations which may be required to validate the targets for exoplanet surveys and filter out possible contaminants. We present results from an ongoing followup program, which has so far gathered low‐resolution optical spectra for ∼ 8000 M dwarfs (including all within 20 pc, and those brighter than J = 9 mag), and already provides formal spectral classification and metallicity estimates for a significant number of high‐priority targets. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Accretion, winds and outflows in young stars
Authors: Günther H.M. 
Published: October 2014

AbstractYoung stars and planetary systems form in molecular clouds. After the initial radial infall an accretion disk develops. For classical T Tauri stars (CTTS, F‐K type precursors) the accretion disk does not reach down to the central star, but it is truncated near the co‐rotation radius by the stellar magnetic field. The inner edge of the disk is ionized by the stellar radiation, so that the accretion stream is funneled along the magnetic field lines. On the stellar surface an accretion shock develops, which is observed over a wide wavelength range as X‐ray emission, UV excess, optical veiling and optical and IR emission lines. Some of the accretion tracers, e.g. Hα, can be calibrated to measure the accretion rate. This accretion process is variable on time scales of hours to years due to changing accretion rates, stellar rotation and reconfiguration of the magnetic field. Furthermore, many (if not all) accreting systems also drive strong outflows which are ultimately powered by accretion. However, the exact driving mechanism is still unclear. Several components could contribute to the outflows: slow, wide‐angle disk winds, X‐winds launched close to the inner disk rim, and thermally driven stellar winds. In any case, the outflows contain material of very different temperatures and speeds. The disk wind is cool and can have a molecular component with just a few tens of km s–1, while the central component of the outflow can reach a few 100 km s–1. In some cases the inner part of the outflow is collimated to a small‐angle jet. These jets have an onion‐like structure, where the inner components are consecutively hotter and faster. The jets can contain working surfaces, which show up as Herbig‐Haro knots. Accretion and outflows in the CTTS phase do not only determine stellar parameters like the rotation rate on the main‐sequence, they also can have a profound impact on the environment of young stars. This review concentrates on CTTS in near‐by star forming regions where observations of high spatial and spectral resolution are available. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The SLoWPoKES catalog of low‐mass ultra–wide binaries: A cool stars resource for testing fundamental properties and for constraining binary formation theory
Authors: Dhital S. , West A.A. , Stassun K.G. , Law N.M. 
Published: October 2014

AbstractWe present results from the Sloan Low‐mass Wide Pairs of Kinematically Equivalent Stars (SLoWPoKES) catalog of ultra‐wide (103–105.5 AU), low‐mass (K5–M7) common proper motion binaries. We constructed a Galactic model, based on empirical stellar number density and 3D velocity distributions, to select bona fide pairs with probability of chance alignment <5 %, making SLoWPoKES an efficient sample for followup observations. Our initial catalog contains 1342 disk dwarf, subdwarf, and white dwarf‐red dwarf systems and is the largest collection of low‐mass, wide binaries ever assembled. The diversity – in mass, metallicity, age, and evolutionary states – of SLoWPoKES pairs makes it a valuable resource of coeval laboratories to examine and constrain the physical properties of low‐mass stars. SLoWPoKES pairs show signatures of two (or more) formation modes in the distribution of the physical separation and higher‐order multiplicity. Neither dynamical dissipation of primordial triples/quadruples or dynamical capture of ejected stars can explain the observed populations by itself. We use follow‐up spectroscopic observations to recalibrate the metallicity‐sensitive ζTiO/CaH index by assuming that both members of the binary system have the same composition. Our new formulation is a significantly better tracer of absolute metallicity, particularly for the early‐type M dwarfs. The catalogs are publicly available on a custom data visualization portal. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Surfing the photon noise: New techniques to find low‐mass planets around M dwarfs
Authors: Anglada‐Escudé G. , Butler R.P. , Reiners A. , Jones H.R.A. , Tuomi M. , Jenkins J.S. , Barnes J.R. , Vogt S.S. , Zechmeister M. 
Published: October 2014

AbstractThe current precision radial velocities techniques to detect low mass planets in M dwarf are quickly reviewed. This includes high resolution spectroscopic observations made both in the optical and in the near infrared. We discuss that, given the current instrumental performance, optical RVs are still far ahead over other approaches. However, this situation might change soon with the advent of new spectrographs with red/nIR capabilities. We review a newly developed method to obtain precision RV measurements on stabilized spectrographs and how it is implemented to archival HARPS observations. In addition to get much closer to the photon noise, this approach allows us to identify and filter out wavelength dependent noise sources achieving unprecedented accuracy on G, K and specially M dwarfs. We show how including red/infrared observations is of paramount importance to efficiently and unambiguously detect very low mass planets around cool spectral types. As examples, we show new measurements on Barnard's star indicating that the star is stable down to 0.9 cm s–1over a time‐span of 4 years and how RV signals correlated with activity indices disappear when using the reddest half of the HARPS wavelength range. To conclude, we present new results, detections and describe the implications in terms of planet/multi‐planet abundances around cool stars. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dust production and mass loss in cool evolved stars
Authors: Boyer M.L. 
Published: October 2014

AbstractFollowing the red giant branch phase and the subsequent core He‐burning phase, the low‐ to intermediate‐mass stars (0.8 < M /M⊙ < 8) begin to ascend the asymptotic giant branch (AGB). Pulsations levitate material from the stellar surface and provide density enhancements and shocks, which can encourage dust formation and re‐processing. The dust composition depends on the atmospheric chemistry (abundance of carbon relative to oxygen), which is altered by dredging up newly formed carbon to the surface of the star. I will briefly review the current status of models that include AGB mass loss and relate them to recent observations of AGB stars from the Surveying the Agents of Galaxy Evolution (SAGE) Spitzer surveys of the Small and Large Magellanic Clouds, including measures of the total dust input to the interstellar medium from AGB stars. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Protoplanetary disks and planet formation around brown dwarfs and very low‐mass stars
Authors: Apai D. 
Published: October 2014

AbstractBrown dwarfs and very low‐mass stars are very common in the Galaxy, yet we know little about the planetary systems they may host. Here we review observational evidence emerging from comparative studies of disks around brown dwarfs and sun‐like stars. These studies show that very young brown dwarfs and very low mass stars have disks as frequently as sun‐like stars do, arguing for the same formation processes. There are indications, but no conclusive evidence yet, for a longer disk lifetime around the lowest‐mass stars and brown dwarfs. At the same time, evidence for faster dust processing and more strongly reduced disk scale heights is found, demonstrating that the first steps of planet formation also take place around brown dwarfs. With increasingly sensitive infrared instruments a new window is opening on gas‐phase chemistry in these disks and the first surveys indicate a different gas‐phase chemistry and, perhaps, a suppressed nitrogen chemistry. Sub‐millimeter surveys reveal disk masses of a few Jupiter mass, which core accretion models show is enough to form few Earth‐mass and smaller planets, but not gas giant planets. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The solar‐stellar connection: Insights from helioseismology
Authors: Chaplin W.J. 
Published: October 2014

AbstractIn this review we discuss helioseismology as a probe of the solar activity cycle, highlighting in particular results on studies of the recent, unusual solar minimum. We then discuss the solar‐stellar connection, in the context of the potential for performing asteroseismic studies of stellar activity cycles of solar‐type stars using data from Kepler, CoRoT and groundbased observations. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Infrared parallaxes of young field brown dwarfs and connections to directly imaged gas‐giant exoplanets
Authors: Liu M.C. , Dupuy T.J. , Allers K.N. 
Published: October 2014

AbstractWe have measured high‐precision infrared parallaxes with the Canada‐France‐Hawaii Telescope for a large sample of candidate young (≈10–100 Myr) and intermediate‐age (≈ 100–600 Myr) ultracool dwarfs, with spectral types ranging from M8 to T2.5. These objects are compelling benchmarks for substellar evolution and ultracool atmospheres at lower surface gravities (i.e., masses) than most of the field population. We find that the absolute magnitudes of our young sample can be systematically offset from ordinary (older) field dwarfs, with the young late‐M objects being brighter and the young/dusty mid‐L (L3–L6.5) objects being fainter, especially at J band. Thus, we conclude the “underluminosity” of the young planetary‐mass companions HR 8799b and 2MASS J1207–39b compared to field dwarfs is also manifested in young free‐floating brown dwarfs, though the effect is not as extreme. At the same time, some young objects over the full spectral type range of our sample are similar to field objects, and thus a simple correspondence between youth and magnitude offset relative to the field population appears to be lacking. Comparing the kinematics of our sample to nearby stellar associations and moving groups, we identify several new moving group members, including the first free‐floating L dwarf in the AB Dor moving group, 2MASS J0355+11. Altogether, the effects of surface gravity (age) and dust content on the magnitudes and colors of substellar objects appear to be degenerate. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Example inversion for a new generalized local helioseismology pipeline
Authors: DeGrave K. , Jackiewicz J. 
Published: October 2014

AbstractRecovering information about solar sub‐surface perturbations with helioseismology requires many time‐consuming steps. A small number of pipelines have already been established to speed the processing of data, though these only focus on data obtained from a single source (i.e. GONG, HMI) and are not necessarily modifiable by external users. To take advantage of the full range of solar data available today and to facilitate the necessary testing of helioseismic methods, a time‐distance helioseismology pipeline is being constructed at New Mexico State University. This will aid in the processing of data from multiple sources including GONG, MDI, HMI, and numerical simulations, and will serve to speed data analysis to produce science products. Using this pipeline, two example inversions are performed on an eight hour time‐series from GONG as a proof of concept, and the preliminary results are described herein (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)