bluuebunny/crossref_metadata_2025 huggingface dataset:
On velocity and reactive scalar spectra in turbulent premixed flames
Authors: Kolla H. , Hawkes E. R. , Kerstein A. R. , Swaminathan N. , Chen J. H.
Published: August 2014

Kinetic energy and reactive scalar spectra in turbulent premixed flames are studied from compressible three-dimensional direct numerical simulations (DNS) of a temporally evolving rectangular slot-jet premixed flame, a statistically one-dimensional configuration. The flames correspond to a lean premixed hydrogen–air mixture at an equivalence ratio of 0.7, preheated to 700 K and at 1 atm, and three DNS are considered with a fixed jet Reynolds number of 10 000 and a jet Damköhler number varying between 0.13 and 0.54. For the study of spectra, motivated by the need to account for density change, which can be locally strong in premixed flames, a new density-weighted definition for two-point velocity/scalar correlations is proposed. The density-weighted two-point correlation tensor retains the essential properties of its constant-density (incompressible) counterpart and recovers the density-weighted Reynolds stress tensor in the limit of zero separation. The density weighting also allows the derivation of balance equations for velocity and scalar spectrum functions in the wavenumber space that illuminate physics unique to combusting flows. Pressure–dilatation correlation is a source of kinetic energy at high wavenumbers and, analogously, reaction rate–scalar fluctuation correlation is a high-wavenumber source of scalar energy. These results are verified by the spectra constructed from the DNS data. The kinetic energy spectra show a distinct inertial range with a $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}-5/3$ scaling followed by a ‘diffusive–reactive’ range at higher wavenumbers. The exponential drop-off in this range shows a distinct inflection in the vicinity of the wavenumber corresponding to a laminar flame thickness, $\delta _L$, and this is attributed to the contribution from the pressure–dilatation term in the energy balance in wavenumber space. Likewise, a clear spike in spectra of major reactant species (hydrogen) arising from the reaction-rate term is observed at wavenumbers close to $\delta _L$. It appears that in the inertial range classical scaling laws for the spectra involving the Kolmogorov scale are applicable, but in the high-wavenumber range where chemical reactions have a strong signature the laminar flame thickness produces a better collapse. It is suggested that a full scaling should perhaps involve the Kolmogorov scale, laminar flame thickness, Damköhler number and Karlovitz number.
The relationships among network ties, organizational agility, and organizational performance: A study of the flat glass industry in Taiwan
Authors: Lee Yu-Muo , Yang Chyan
Published: August 2014

Firms face a rapidly changing market environment under the pressure of difficult challenges such as limited resources and increasing costs. Organizations may actively seek to cooperate with other members for benefits from knowledge sharing. Establishing quality network ties among suppliers and customers is a significant study subject. Here, we assessed the impact of the signing of the Economic Cooperation Framework Agreement on Taiwan flat glass industry and study measures adopted by the manufacturers. The effective sample size is 250. We found that through the intermediary of organizational agility and strong network ties, a firm can enhance its organizational performance.
Lichen communities in two old-growth pine (Pinus) forests
Authors: WAGNER Christopher , SCHRAM Lyndsay J. , McMULLIN Richard Troy , HUNT Shelley L. , ANAND Madhur
Published: August 2014

Many lichen species have specific environmental requirements for colonization. Old-growth forests contain microhabitats required by a particular suite of lichens. In Ontario, Canada, old-growth forests are increasingly uncommon and the lichen communities within some of these forests are not well known. To better understand the lichen communities that inhabit old-growth forests in the province, we examined the lichen biota on coarse woody debris (CWD) and trees in a red pine (Pinus resinosa) and a white pine (Pinus strobus) dominated stand in northern Ontario. Lichen diversity was assessed on different forms of CWD and trees in each forest. Lichen diversity did not differ significantly between CWD types in the red pine forest, but was significantly different in the white pine forest. There was no significant difference in lichen diversity amongst different decay stages of CWD in either forest. In both forests, lichen communities on stumps, logs, and snags differed from lichen communities present on trees. A variety of CWD types is important for overall lichen species richness in the red pine forest. Our results demonstrate to land managers that different types of old-growth forests are ecologically unique, even those dominated by tree species in the same genus. Management of an old-growth forest should suit its individual ecology.
Quantifying the loss of lichen epiphyte diversity from the pre-industrial Exmoor landscape (south-west England)
Authors: YAHR Rebecca , COPPINS Brian J. , ELLIS Christopher J.
Published: August 2014

Across much of lowland Britain, lichen diversity has been dramatically affected by the Industrial Revolution, including the lasting legacy of pollution, and changes in land use including the loss, intensification, or abandonment of traditional woodland management. We sampled preserved epiphytes on historical timbers in vernacular buildings to reconstruct pre-industrial lichen species occurrence for a site in Exmoor, south-west England, and used these data to quantify biodiversity loss that appears related to shifts in woodland composition. A total of 33 lichen epiphyte species were collected from pre-industrial structural timbers, and these were compared with modern lichen occurrence. Based on a direct comparison with species presence-absence in the same 10 km target grid-square,c. 31% of species recorded from the pre-industrial landscape had disappeared from the post-1960 landscape. Based on statistical inference comparing historical records with present-day biogeographical distributions, up to 38% of species could be inferred to be lost. This study presents a surprisingly high figure for these losses for a region in Britain usually recognized as having a relatively unpolluted environment and a diverse set of lichens. Of 12 species that were inferred to be lost, nine are predominantly found on nutrient-rich bark, and in our study onUlmus, the dominant timber in the archaeological samples. We conclude that shifts in phorophyte distribution and abundance may be more important in this region than previously understood.
Scott and Shackleton in the media: a response to Ben Macintyre
Authors: May Karen , Lewis George
Published: August 2014

An opinion piece by Ben Macintyre entitled ‘Sorry, Scott fans: noble death is so last century’ appeared inThe Times(London) on 20 September 2013. In this, Macintyre argued not only that Ernest Shackleton should be explicitly contrasted against his contemporary and rival Robert Falcon Scott, but that Shackleton should be found superior to Scott in virtually every way. It was a dispiriting piece, strongly suggesting that that the media's understanding of Scott has not greatly advanced since the savage, cod-psychological and often unsubstantiated attacks upon Scott's character and reputation in the 1970s–1990s. Sadly, all too often polar history is reduced to a zero-sum game where praise for Shackleton is directly proportional to insults directed at Scott.
Assessing Grounding Frequency using Ship Traffic and Waterway Complexity
Authors: Mazaheri Arsham , Montewka Jakub , Kotilainen Pentti , Edvard Sormunen Otto-Ville , Kujala Pentti
Published: August 2014

Ship traffic is the factor that presents in almost all of the existing grounding risk models. It is considered to be one of the main factors affecting the expected frequency of ship groundings. This is mostly accepted by experts as common sense. However, there is no research available on the actual dependency between ship traffic and grounding accidents. In this paper, we conduct a study aimed at determining the statistical dependency between the density and distribution of traffic, the number and frequency of grounding accidents and the dependency between the complexity of waterways and an actual accident. For this purpose we utilise statistical analysis of maritime traffic, obtained from Automatic Identification System (AIS) data and grounding accidents, enhanced with the expert elicitation techniques delivering the waterway complexity index. The sea area under investigation is the Gulf of Finland. The results show statistical dependency between frequency of grounding and waterway complexity as well as the traffic distribution. However, the study does not reveal any significant dependency between grounding and traffic density.
RECONSTRUCTING AN ANCIENT AQUATIC LIFEWAY IN THE LAKE CUITZEO BASIN, MICHOACAN, MEXICO
Authors: Williams Eduardo
Published: August 2014

This study of subsistence activities (fishing, hunting, gathering, and manufacture) in the Lake Cuitzeo Basin underscores the value of ethnoarchaeology as a tool for reconstructing the ancient aquatic lifeway in the territory of the ancient Tarascan state, which flourished in an environment dominated by lakes, rivers, marshes, and other wetlands. Mesoamerica was the only civilization in the ancient world that lacked major domesticated sources of animal protein, such as cattle, pigs, and sheep. Therefore, the abundant wild aquatic species (fish, birds, reptiles, amphibians, insects, and plants, among others) played a strategic role in the diet and economy of most Mesoamerican cultures, including the Tarascans. Most of the activities, artifacts, and features linked with aquatic lifeways throughout Mesoamerica are difficult to detect in the archaeological record. As a result, we must rely on ethnographic and ethnohistorical perspectives like the ones discussed here to formulate analogies, in order to understand this important aspect of the ancient past.
THE LATE AND TERMINAL CLASSIC CERAMIC SEQUENCE AT LA MILPA, BELIZE: IMPLICATIONS FOR ITS OCCUPATION HISTORY
Authors: Sagebiel Kerry Lynn
Published: August 2014

Previous interpretations of the occupation history of La Milpa, Belize, which were based on preliminary ceramic data, suggested that occupation of the site fluctuated dramatically from the Late Preclassic to the Terminal Classic (400b.c.–a.d.850). It was determined that the modest Late Preclassic village became a large Early Classic city with regal-ritual architecture and carved monuments. In Late Classic I, it appeared the site was nearly abandoned. Its reoccupation and exponential growth in Late Classic II was followed by rapid abandonment before the end of the Late Classic III/Terminal Classic. New ceramic analyses utilizing attribute analysis with an emphasis on formal modes has clarified the sequence and, in turn, softened the occupation curves. This article provides descriptions of the Late Classic I, II, and III ceramics, along with revised percentage frequency graphs of La Milpa's occupation history based primarily on the work of the La Milpa Archaeological Project (1992–2002).
MAYA COASTAL PRODUCTION, EXCHANGE, LIFE STYLE, AND POPULATION MOBILITY: A VIEW FROM THE PORT OF XCAMBO, YUCATAN, MEXICO
Authors: Sosa Thelma Sierra , Cucina Andrea , Price T. Douglas , Burton James H. , Tiesler Vera
Published: August 2014

Anchored in archaeological, bioarchaeological, and chemical research conducted at the coastal enclave of Xcambo, this paper examines Classic period Maya coastal saline economic production and exchange, along with the lifestyle, ethnicity, and mobility of the traders. Nestled in the coastal marshlands of the northern Yucatan, Mexico, Xcambo functioned as a salt production center and port during its occupation, maintaining long-reaching ties with other parts of the Maya world and Veracruz. Considered together, the different data sets document a reorientation in Xcambo's exchange routes and connections, which are echoed by increasingly diverse cultural affiliations and an increasing geographic mobility of Xcambo's merchants. This new information confirms the known pattern of gradually intensifying, though still relatively independent, trade dynamics along the Maya coast in the centuries leading up to the so-called “Maya collapse” and the rise of a new merchant league under the control of Chichen Itza. It was this new order that probably led to the swift end of Xcambo soon aftera.d.700.
FORMATIVE OBSIDIAN PROCUREMENT AT TRES ZAPOTES, VERACRUZ, MEXICO: IMPLICATIONS FOR OLMEC AND EPI-OLMEC POLITICAL ECONOMY
Authors: Pool Christopher A. , Knight Charles L. F. , Glascock Michael D.
Published: August 2014

We report the results of chemical sourcing of obsidian artifacts from Tres Zapotes using X-ray fluorescence analysis. This is the first obsidian sourcing study for this major Olmec and Epi-Olmec center in which samples are drawn from secure archaeological proveniences specifically assigned to Early, Middle, Late Formative, and Protoclassic periods. We employed a stratified random sampling strategy to select 180 obsidian artifacts from excavated assemblages, supplementing the random sample with another 24 specimens drawn from rare visual categories. Consequently, we are able to characterize changes in the relative importance of different obsidian sources in the political economy of Tres Zapotes across the critical transition from Olmec to Epi-Olmec society with greater confidence than has been possible for the Gulf lowlands while extending our observations to the full sample of 5,713 visually characterized obsidian artifacts—2,695 of which come from the well-dated Formative contexts examined in this article. Our study confirms the absence of obsidian from Otumba and from Guatemalan sources in the excavated Olmec assemblage in favor of sources from eastern Puebla and Veracruz, supporting a model of overlapping autonomous networks for obsidian procurement at Gulf Olmec sites. Presence of the Guatemalan San Martín Jilotepeque source in Epi-Olmec contexts may relate to the reestablishment of trans-Isthmian contacts, while increasing prevalence of Zaragoza-Oyameles obsidian from eastern Puebla marks the beginning of a long-term trend. Although more even representation of obsidian sources in Epi-Olmec contexts is consistent with the hypothesized transition from an exclusionary Olmec political economy toward a more “corporate” system associated with power sharing among factional leaders at Tres Zapotes, neither Olmec nor Epi-Olmec elites monopolized a particular obsidian source or technology.
PRODUCCIONES PALACIEGAS TENOCHCAS EN OBJETOS DE CONCHA Y LAPIDARIA
Authors: Velázquez Castro Adrián , Melgar Tísoc Emiliano Ricardo
Published: August 2014

Investigaciones recientes han mostrado que un buen número de objetos procedentes de las ofrendas del recinto sagrado de Tenochtitlan son producciones locales y no piezas foráneas, obtenidas por tributo, intercambio o saqueo. En el caso de los objetos de concha y lapidaria, sus características formales permiten identificar a un importante grupo no solamente como propio del centro de México, sino como exclusivo de Tenochtitlan e incluso de su templo principal, ya que elementos idénticos no han sido recuperados en otros emplazamientos o en las edificaciones aledañas alHuey Teocallitenochca. El estudio de las técnicas de manufactura de estas piezas ha permitido confirmar esta suposición e incluso proponer la existencia de un estilo tecnológico tenochca. La gran estandarización morfológica y tecnológica de los objetos y su restringida distribución, permiten proponer que su producción se llevaba a cabo en un contexto dependiente, probablemente en el palacio mismo del gobernante mexica.
Associations between socio-economic status and school-day dietary intake in a sample of grade 5–8 students in Vancouver, Canada
Authors: Ahmadi Naseam , Black Jennifer L , Velazquez Cayley E , Chapman Gwen E , Veenstra Gerry
Published: August 2014

Objective

To examine associations between students’ socio-economic status (SES) and school-day dietary intake, and the roles of parents and peers in shaping these associations.

Design

A cross-sectional survey measured school-day intake of vegetables, whole grains, low-fat milk, packaged snack foods and sugar-sweetened beverages. Logistic regression models examined associations between SES (parental education and food insecurity status) and dietary outcomes during or en route to or from school, and examined whether peer modelling or parental norms potentially mediated the associations between SES and dietary outcomes.

Setting

Twenty-six public schools in Vancouver, Canada in 2012.

Subjects

Nine hundred and fifty students in grades 5–8.

Results

Students whose parents completed some college, compared with those completing high school or less, were significantly more likely to consume vegetables daily (unadjusted OR=1·85; 95 % CI 1·06, 3·22) and students whose parents completed college or university were significantly less likely to consume sugar-sweetened beverages daily (unadjusted OR=0·67; 95 % CI 0·47, 0·94). Food secure students were also significantly less likely to consume sugar-sweetened beverages daily compared with food insecure students (unadjusted OR=0·52; 95 % CI 0·29, 0·92). Parental norms, but not peer modelling, emerged as a potential mediator of the association between SES and vegetable intake. SES was not significantly associated with the remaining dietary outcomes.

Conclusions

Higher SES was significantly associated with two of five school-day dietary outcomes and predicted higher likelihood of daily nutritious food choices at school. The present study suggests that there is room for improvement in school-day dietary quality for students from all SES backgrounds in Vancouver.
(E)RACING SLAVERY
Authors: Weiner Melissa F.
Published: August 2014

Textbooks are explicitly racial texts that offer important insights into national memories of slavery and colonialism. The Dutch have long engaged in the social forgetting of slavery even as race served as an organizing principal during centuries of colonial domination of the Dutch West Indies and Suriname. While the Dutch have recently begun to address their history of enslavement, they have yet to sufficiently address how the discursive legacies of slavery continue to impact the lives of Afro-Dutch descendants of enslaved2AfricansandWhite Dutch in The Netherlands today. This paper uses qualitative content and discourse analytic methods to examine the depiction of slavery, The Netherlands’ role in the slave trade and enslavement, and the commemoration of slavery in all Dutch primary school history textbooks published since 1980 to address questions of whether textbooks feature scientific colonialism to perpetuate The Netherlands’ social forgetting of slavery in a nation that denies the existence of race even as racialized socioeconomic inequalities persist. A Eurocentric master narrative of racial Europeanization perpetuates Dutch social forgetting of slavery and scientific colonialism to both essentialize Afro-Dutch and position their nation squarely within Europe’s history of enslavement even while attempting to minimize their role within it. Findings have important implications for both The Netherlands and all nations with histories of enslavement as the discourses and histories presented in textbooks impact generations of students, who shape local and national policy regarding racial minorities, racial identities, and ideologies.
Magnetic field dispersion in the neighbourhood of Bok Globules
Authors: Rodrigues C. V. , Magalhães V. de S. , Vilas-Boas J. W. , Racca G. , Pereyra A.
Published: August 2014

We performed an observational study of the relation between the interstellar magnetic field alignment and star formation in twenty (20) sky regions containing Bok Globules. The presence of young stellar objects in the globules is verified by a search of infrared sources with spectral energy distribution compatible with a pre main-sequence star. The interstellar magnetic field direction is mapped using optical polarimetry. These maps are used to estimate the dispersion of the interstellar magnetic field direction in each region from a Gaussian fit, σB. In addition to the Gaussian dispersion, we propose a new parameter, η, to measure the magnetic field alignment that does not rely on any function fitting. Statistical tests show that the dispersion of the magnetic field direction is different in star forming globules relative to quiescent globules. Specifically, the less organised magnetic fields occur in regions having young stellar objects.
The magnetosphere of the close accreting PMS binary V4046 Sgr AB
Authors: Gregory S. G. , Holzwarth V. R. , Donati J.-F. , Hussain G. A. J. , Montmerle T. , Alecian E. , Alencar S. H. P. , Argiroffi C. , Audard M. , Bouvier J. , Damiani F. , Güdel M. , Huenemoerder D. P. , Kastner J. H. , Maggio A. , Sacco G. G. , Wade G. A.
Published: August 2014

We present a preliminary 3D potential field extrapolation model of the joint magnetosphere of the close accreting PMS binary V4046 Sgr. The model is derived from magnetic maps obtained as part of a coordinated optical and X-ray observing program.
Magnetospheric Accretions and the Inner Winds of Classical T Tauri Stars
Authors: Kurosawa Ryuichi , Romanova M. M.
Published: August 2014

Recent spectropolarimetric observations suggest that young low-mass stars such as classical T Tauri stars (CTTSs) possess relatively strong (~kG) magnetic field. This supports a scenario in which the final accretion onto the stellar surface proceeds through a magnetosphere, and the winds are formed in magnetohydrodynamics (MHD) processes. We examine recent numerical simulations of magnetospheric accretions via an inclined dipole and a complex magnetic fields. The difference between a stable accretion regime, in which accretion occurs in ordered funnel streams, and an unstable regime, in which gas penetrates through the magnetosphere in several unstable streams due to the magnetic Rayleigh-Taylor instability, will be discussed. We describe how MHD simulation results can be used in separate radiative transfer (RT) models to predict observable quantiles such as line profiles and light curves. The plausibility of the accretion flows and outflows predicted by MHD simulations (via RT models) can be tested against observations. We also address the issue of outflows/winds that arise from the innermost part of CTTSs. First, we discuss the line formations in a simple disk wind and a stellar wind models. We then discuss the formation of the conically shaped magnetically driven outflow that arises from the disk-magnetosphere boundary when the magnetosphere is compressed into an X-type configuration.
Magnetic higher-mass stars in the early stages of their evolution
Authors: Grunhut Jason H. , Alecian E.
Published: August 2014

Over the past decade, significant investigations have been made through the use of high-resolution spectropolarimetry to probe the surface magnetic field characteristics of young higher-mass (M ≳ 1.5 M⊙) stars from pre-main sequence to zero-age main sequence evolutionary phases. The results of these observational campaigns suggest that these young higher-mass stars host similar magnetic properties to their main sequence descendants - strong, stable, globally-ordered fields that are detected in approximately 10 percent of all stars. This strongly contrasts with lower-mass stars, where it is generally accepted that a solar-like dynamo is in operation that generates more complex, globally-weak fields that are ubiquitous. The consensus is magnetic fields in higher-mass stars are fossil remnants of a magnetic field present in the molecular cloud, or generated very early during stellar formation. This review discusses the spectropolarimetric observations of higher-mass stars and how these observations have guided our current understanding of the magnetic characteristics of young higher-mass stars.
The Effects of Magnetic Activity on Lithium-Inferred Ages of Stars
Authors: Juarez Aaron J. , Cargile Phillip A. , James David J. , Stassun Keivan G.
Published: August 2014

In this project, we investigate the effects of magnetic activity on the Lithium Depletion Boundary (LDB) to recalibrate the measured ages for star clusters, using the open cluster Blanco 1 as a pilot study. We apply the LDB technique on low-mass Pre-Main-Sequence (PMS) stars to derive an accurate age for Blanco 1, and we consider the effect of magnetic activity on this inferred age. Although observations have shown that magnetic activity directly affects stellar radius and temperature, most PMS models do not include the effects of magnetic activity on stellar properties. Since the lithium abundance of a star depends on its radius and temperature, we expect that LDB ages are affected by magnetic activity. After empirically accounting for the effects of magnetic activity, we find the age of Blanco 1 to be ~100 Myr, which is ~30 Myr younger than the standard LDB age of ~130 Myr.
X-ray emission regimes and rotation sequences in the M34 open cluster
Authors: Gondoin Philippe
Published: August 2014

I report on a correlation between the saturated and non-saturated regimes of X-ray emission and the rotation sequences that have been observed in the M34 open cluster. An interpretation of this correlation in term of magnetic activity evolution in the early stage of evolution on the main sequence is presented.
Probing the structure of local magnetic field of solar features with helioseismology
Authors: Daiffallah Khalil
Published: August 2014

Motivated by the problem of local solar subsurface magnetic structure, we have used numerical simulations to investigate the propagation of waves through monolithic magnetic flux tubes of different sizes. A cluster model can be a good approximation to simulate sunspots as well as solar plage regions which are composed of an ensemble of compactly packed thin flux tubes. Simulations of this type are powerful tools to probe the structure and the dynamics of various solar features which are directly related to solar magnetic field activity.
Hanle and Zeeman effects: from solar to stellar diagnostics
Authors: Ariste A. López
Published: August 2014

We suggest the use of the area asymmetries of the Stokes V profile of a line sensitive to the Zeeman effect to diagnose variatios of the magnetic field along the line of sight in stellar atmospheres. This tool could allow to disentangle the magnetic topology of the observed stellar features in analogy to the solar case: a fibril topology as in plage and netwrok magnetic fields vs. a homogeneous and strong field as in sunspots. We also suggest the use of the Hanle effect as a means to observe weak global dipoles.
A Bcool spectropolarimetric survey of over 150 solar-type stars
Authors: Marsden Stephen , Petit Pascal , Jeffers Sandra , do Nascimento Jose-Dias , Carter Bradley , Brown Carolyn
Published: August 2014

As part of the Bcool project, over 150 solar-type stars chosen mainly from planet search databases have been observed between 2006 and 2013 using the NARVAL and ESPaDOnS spectropolarimeters on the Telescope Bernard Lyot (Pic du Midi, France) and the Canada France Hawaii Telescope (Mauna Kea, USA), respectively. These single “snapshot” observations have been used to detect the presence of magnetic fields on 40% of our sample, with the highest detection rates occurring for the youngest stars. From our observations we have determined the mean surface longitudinal field (or an upper limit for stars without detections) and the chromospheric surface fluxes, and find that the upper envelope of the absolute value of the mean surface longitudinal field is directly correlated to the chromospheric emission from the star and increases with rotation rate and decreases with age.
Magnetic Fields in Low-Mass Stars: An Overview of Observational Biases
Authors: Reiners Ansgar
Published: August 2014

Stellar magnetic dynamos are driven by rotation, rapidly rotating stars produce stronger magnetic fields than slowly rotating stars do. The Zeeman effect is the most important indicator of magnetic fields, but Zeeman broadening must be disentangled from other broadening mechanisms, mainly rotation. The relations between rotation and magnetic field generation, between Doppler and Zeeman line broadening, and between rotation, stellar radius, and angular momentum evolution introduce several observational biases that affect our picture of stellar magnetism. In this overview, a few of these relations are explicitly shown, and the currently known distribution of field measurements is presented.
On the spectropolarimetric signature of FeH in the laboratory and in sunspots
Authors: Crozet Patrick , Ross Amanda J. , Alleq Nathalie , Ariste Arturo López , Le Men Claude , Gelly Bernard
Published: August 2014

Laboratory spectra showing Zeeman patterns in some FeH lines susceptible to be used as magnetic probes in cool stellar atmostpheres have been recorded in the laboratory, and molecular Landé factors obtained from analysis. These Landé factors have been used to model some lines recorded in Stokes V polarisation in sunspot spectra at the solar telescope THEMIS.
Magnetic fields in M-dwarfs from high-resolution infrared spectroscopy
Authors: Shulyak D. , Reiners A. , Seemann U. , Kochukhov O. , Piskunov N.
Published: August 2014

Accurate spectroscopic measurements of magnetic fields in low mass stars remain challenging because of their cool temperatures, strong line blending, and often fast rotation. This is why previous estimates were based either on the analysis of only a few lines or made use of some indirect techniques. This frequently led to noticeable scatter in obtained results. In this talk I will present and discuss new results on the determination of the intensity and geometry of the magnetic fields in M-dwarfs using IR observations obtained with CRIRES@VLT. The instrument provides unprecedented data of high resolution (R = 100 000) which is crucial for resolving individual magnetically broadened molecular and atomic lines. Such an in-depth analysis based on direct magnetic spectral synthesis opens a possibility to deduce both field intensity and geometry avoiding most of the limitation and assumptions made in previous studies.
Stellar Magnetic Dynamos and Activity Cycles
Authors: Wright Nicholas J.
Published: August 2014

Using a new uniform sample of 824 solar and late-type stars with measured X-ray luminosities and rotation periods we have studied the relationship between rotation and stellar activity that is believed to be a probe of the underlying stellar dynamo. Using an unbiased subset of the sample we calculate the power law slope of the unsaturated regime of the activity – rotation relationship as LX / Lbol ∝ Roβ, where β = − 2.70 ± 0.13. This is inconsistent with the canonical β = − 2 slope to a confidence of 5σ and argues for an interface-type dynamo. We map out three regimes of coronal emission as a function of stellar mass and age, using the empirical saturation threshold and theoretical super-saturation thresholds. We find that the empirical saturation timescale is well correlated with the time at which stars transition from the rapidly rotating convective sequence to the slowly rotating interface sequence in stellar spin-down models. This may be hinting at fundamental changes in the underlying stellar dynamo or internal structure. We also present the first discovery of an X-ray unsaturated, fully convective M star, which may be hinting at an underlying rotation - activity relationship in fully convective stars hitherto not observed. Finally we present early results from a blind search for stellar X-ray cycles that can place valuable constraints on the underlying ubiquity of solar-like activity cycles.
Differential rotation and meridional flows in stellar convection zones
Authors: Küker Manfred , Rüdiger Günther
Published: August 2014

Differential rotation and meridional flow are key ingredients in flux transport dynamo models of the solar activity cycle. As the subsurface flow pattern is not sufficiently constrained by observations, it is a major source of uncertainty in solar and stellar dynamo models. We discuss the current mean field theory of stellar differential rotation and meridional flows and its predicitons for the Sun and stars on the lower main sequence.
Hyper X-ray Flares on Active Stars Detected with MAXI
Authors: Higa Masaya , Tsuboi Yohko , Negoro Hitoshi , Nakahira Satoshi , Tomida Hiroshi , Matsuoka Masaru ,   The MAXI team
Published: August 2014

MAXI started its operation in 2009 August. Owing to its unprecedentedly high sensitivity as an all-sky X-ray monitor and to its capability of real-time data transfer, we have detected 56 strong flares from twenty-one active stars (eleven RS CVn systems, one Algol system, seven dMe stars, one dKe star and one Young Stellar Object). These flares have large X-ray luminosity of 6 × 1030 –5 × 1033 ergs s−1 in the 2–20 keV band. The flares can be thought to be high ends among their own categories. During the flare from AT Mic on 2012 April 18th, one of the largest X-ray luminosities was recorded as a dMe star, 6 × 1032 ergs s−1 in the 2–20 keV band. It is larger than its bolometric luminosity by 4 times. The total energy emitted during the flare is 1036 ergs in the same band. Such total energy can be obtained on large flares from RS CVn system, but not on any other flares from dMe stars. In this proceeding, we report on the present situation in characteristics of hyper X-ray flares on each stellar categories.
Rotation & differential rotation of the active Kepler stars
Authors: Reinhold Timo , Reiners Ansgar , Basri Gibor
Published: August 2014

Stellar rotation is a well-known quantity for tens of thousands of stars. In contrast, differential rotation (DR) is only known for a handful of stars because DR cannot be measured directly. We present rotation periods for more than 24,000 active stars in the Kepler field. Thereof, more than 18,000 stars show a second period, which we attribute to surface differential rotation. Our rotation periods are consistent with previous measurements and the theory of magnetic braking. Our results on DR paint a rather different picture: The temperature dependence of the absolute shear δΩ is split into two groups separated around 6000 K. For the cooler stars δΩ only slightly increases with temperature, whereas stars hotter than 6000 K show large scatter. This is the first time that DR has been measured for such a large number of stars.
Investigating magnetic activity of F stars with the Kepler mission
Authors: Mathur S. , García R. A. , Ballot J. , Ceillier T. , Salabert D. , Metcalfe T. S. , Régulo C. , Jiménez A. , Bloemen S.
Published: August 2014

The dynamo process is believed to drive the magnetic activity of stars like the Sun that have an outer convection zone. Large spectroscopic surveys showed that there is a relation between the rotation periods and the cycle periods: the longer the rotation period is, the longer the magnetic activity cycle period will be. We present the analysis of F stars observed by Kepler for which individual p modes have been measure and with surface rotation periods shorter than 12 days. We defined magnetic indicators and proxies based on photometric observations to help characterise the activity levels of the stars. With the Kepler data, we investigate the existence of stars with cycles (regular or not), stars with a modulation that could be related to magnetic activity, and stars that seem to show a flat behaviour.
The effects of stellar winds and magnetic fields on exoplanets
Authors: Vidotto A. A.
Published: August 2014

The great majority of exoplanets discovered so far are orbiting cool, low-mass stars whose properties are relatively similar to the Sun. However, the stellar magnetism of these stars can be significantly different from the solar one, both in topology and intensity. In addition, due to the present-day technology used in exoplanetary searches, most of the currently known exoplanets are found orbiting at extremely close distances to their host stars (< 0.1 au). The dramatic differences in stellar magnetism and orbital radius can make the interplanetary medium of exoplanetary systems remarkably distinct from that of the Solar System. To constrain interactions between exoplanets and their host-star's magnetised winds and to characterise the interplanetary medium that surrounds exoplanets, more realistic stellar wind models, which account for factors such as stellar rotation and the complex stellar magnetic field configurations of cool stars, must be employed. Here, I briefly review the latest progress made in data-driven modelling of magnetised stellar winds. I also show that the interaction of the stellar winds with exoplanets can lead to several observable signatures, some of which that are absent in our own Solar System.
Stellar Magnetism and starspots: the implications for exoplanets
Authors: Vilela Conrad , Southworth John , del Burgo Carlos
Published: August 2014

Stellar variability induced by starspots can hamper the detection of exoplanets and bias planet property estimations. These features can also be used to study star-planet interactions as well as inferring properties from the underlying stellar dynamo. However, typical techniques, such as ZDI, are not possible for most host-stars. We present a robust method based on spot modelling to map the surface of active star allowing us to statistically study the effects and interactions of stellar magnetism with transiting exoplanets. The method is applied to the active Kepler-9 star where we find small evidence for a possible interaction between planet and stellar magnetosphere which leads to a 2:1 resonance between spot rotation and orbital period.
On the effects of stellar winds on exoplanetary magnetospheres
Authors: See V. , Jardine M. , Vidotto A. A. , Petit P. , Marsden S. C. , Jeffers S. V.
Published: August 2014

The habitable zone is the range of orbital distances from a host star in which an exoplanet would have a surface temperature suitable for maintaining liquid water. This makes the orbital distance of exoplanets an important variable when searching for extra-solar Earth analogues. However, the orbital distance is not the only important factor determining whether an exoplanet is potentially suitable for life. The ability of an exoplanet to retain an atmosphere is also vital since it helps regulate surface temperatures. One mechanism by which a planetary atmosphere can be lost is erosion due to a strong stellar wind from the host star. The presence of a magnetosphere can help to shield a planetary atmosphere from this process. Using a simple stellar wind model, we present the impact that stellar winds might have on magnetospheric sizes of exoplanets. This is done with the aim of further constraining the parameter space in which we look for extra-solar Earth analogues.
The magnetic characteristics of Galactic OB stars from the MiMeS survey of magnetism in massive stars
Authors: Wade G. A. , Grunhut J. , Alecian E. , Neiner C. , Aurière M. , Bohlender D. A. , David-Uraz A. , Folsom C. , Henrichs H. F. , Kochukhov O. , Mathis S. , Owocki S. , Petit V. ,   the MiMeS Collaboration
Published: August 2014

The Magnetism in Massive Stars (MiMeS) project represents the largest systematic survey of stellar magnetism ever undertaken. Based on a sample of over 550 Galactic B and O-type stars, the MiMeS project has derived the basic characteristics of magnetism in hot, massive stars. Herein we report preliminary results.
The analysis of Li i 6708A line through the rotational period of HD166473 taking into account Paschen-Back magnetic splitting
Authors: Shavrina A. V. , Khalack V. , Glagolevskij Y. , Lyashko D. , Landstreet J. , Leone F. , Giarrusso M.
Published: August 2014

The analysis of Li i 6708 Å line was performed for 6 rotational phases distributed over the whole rotational period (~9.5 years) of HD166473. The magnetic field model was constructed based on the polarimetric measurements from Mathys et al. (2007). For each observed phase the modulus of the magnetic field was also estimated from simulation of the Fe ii 6147 Å, 6149 Å and Pr iii 6706.7 Å line profiles taking into account Zeeman magnetic splitting. The lithium abundance in each phase was obtained from fitting the observed Li i 6708 Å profile with the synthetic one calculated assuming Paschen-Back splitting and estimated magnetic field characteristics from Pr iii 6706.7 Å line profile.
Magnetic fields of Ap stars from full Stokes vector spectropolarimetric observations
Authors: Rusomarov N. , Kochukhov O. , Piskunov N.
Published: August 2014

Current knowledge about stellar magnetic fields relies almost entirely on circular polarization observations, with very few objects having been observed in all four Stokes parameters. We are investigating a sample of Ap stars in all four Stokes parameters using the HARPSpol instrument at the 3.6-m ESO telescope. In the context of this project we recently observed the magnetic Ap star HD 24712 (DO Eri, HR 1217). The resulting spectra have dense phase coverage, resolving power > 105, and S/N ratio of 300–600. These are the highest quality full Stokes observations obtained for any star other than the Sun. Furthermore, we have achieved good phase coverage for HD 125248 and HD 119419. Typical four Stokes parameters HARPSpol spectra are shown in Fig. 1. An analysis of the full Stokes vector spectropolarimetric data set of HD 24712 has been published in Rusomarov et al. (2013).
Magnetic Doppler Imaging of He-strong star HD 184927
Authors: Yakunin I. , Wade G. , Bohlender D. , Kochukhov O. , Tsymbal V. ,   MiMeS Collaborators
Published: August 2014

We have employed an extensive new timeseries of Stokes I and V spectra obtained with the ESPaDOnS spectropolarimeter at the 3.6-m Canada-France-Hawaii Telescope to investigate the physical parameters, chemical abundance distributions and magnetic field topology of the slowly-rotating He-strong star HD 184927. We infer a rotation period of 9d .53071 ± 0.00120 from Hα, Hβ, LSD magnetic measurements and EWs of helium lines. We used an extensive NLTE TLUSTY grid along with the SYNSPEC code to model the observed spectra and find a new value of luminosity. In this poster we present the derived physical parameters of the star and the results of Magnetic Doppler Imaging analysis of the Stokes I and V profiles. Wide wings of helium lines can be described only under the assumption of the presence of a large, very helium-rich spot.
The unusual binary HD 83058 in the region of the Scorpius-Centaurus OB association
Authors: Pogodin M. A. , Drake N. A. , Jilinski E. G. , Pereira C. B.
Published: August 2014

We present the results of high-resolution spectroscopy of the binary system HD 83058 situated in the region of the Sco-Cen OB association. On the base of the radial-curve solution we have determined the elements of the orbit and determined the period P = 2.365102 days. We have disentangled the spectra of the two components of the system and derived the basic parameters of both components. We have shown that moving features in the Si iii line profiles seen in the spectra of the primary can be interpreted in the frame of the assumption of the rotation of local spot-like inhomogeneities on the stellar surface. We have also found that the lines in the spectrum of the secondary show another type of variability.
X-rays from magnetic massive OB stars
Authors: Petit V. , Cohen D. H. , Nazé Y. , Gagné M. , Townsend R. H. D. , Leutenegger M. A. , ud-Doula A. , Owocki S. P. , Wade G. A.
Published: August 2014

The magnetic activity of solar-type and low-mass stars is a well known source of coronal X-ray emission. At the other end of the main sequence, X-rays emission is instead associated with the powerful, radiatively driven winds of massive stars. Indeed, the intrinsically unstable line-driving mechanism of OB star winds gives rise to shock-heated, soft emission (~0.5 keV) distributed throughout the wind. Recently, the latest generation of spectropolarimetric instrumentation has uncovered a population of massive OB-stars hosting strong, organized magnetic fields. The magnetic characteristics of these stars are similar to the apparently fossil magnetic fields of the chemically peculiar ApBp stars. Magnetic channeling of these OB stars' strong winds leads to the formation of large-scale shock-heated magnetospheres, which can modify UV resonance lines, create complex distributions of cooled Halpha emitting material, and radiate hard (~2-5 keV) X-rays. This presentation summarizes our coordinated observational and modelling efforts to characterize the manifestation of these magnetospheres in the X-ray domain, providing an important contrast between the emission originating in shocks associated with the large-scale fossil fields of massive stars, and the X-rays associated with the activity of complex, dynamo-generated fields in lower-mass stars.
Investigating the origin of cyclical spectral variations in hot, massive stars
Authors: David-Uraz Alexandre , Wade Gregg A. , Petit Véronique , ud-Doula Asif
Published: August 2014

OB stars are known to exhibit various types of wind variability, as detected in their ultraviolet spectra, amongst which are the ubiquitous discrete absorption components (DACs). These features have been associated with large-scale azimuthal structures extending from the base of the wind to its outer regions: corotating interaction regions (CIRs). There are several competing hypotheses as to which physical processes may perturb the star's surface and generate CIRs, including magnetic fields and non radial pulsations (NRPs), the subjects of this paper with a particular emphasis on the former. Although large-scale magnetic fields are ruled out, magnetic spots deserve further investigation, both on the observational and theoretical fronts.
UVMag: a UV and optical spectropolarimeter for stellar physics
Authors: Neiner Coralie , Petit Pascal , Parès Laurent ,   the UVMag consortium
Published: August 2014

UVMag is a space project currently under R&D study. It consists in a medium-size telescope equipped with a spectropolarimeter to observe in the UV and optical wavelength domains simultaneously. Its first goal is to obtain time series of selected magnetic stars over their rotation period, to study them from their surface to their environment, in particular their wind and magnetospheres. As the star rotates it will be possible to reconstruct 3D maps of the star and its surroundings. The second goal of UVMag is to obtain two observations of a large sample of stars to construct a new database of UV and optical spectropolarimetric measurements.
Surface magnetism of cool giant and supergiant stars
Authors: Korhonen Heidi
Published: August 2014

The existence of starspots on late-type giant stars in close binary systems, that exhibit rapid rotation due to tidal locking, has been known for more than five decades. Photometric monitoring spanning decades has allowed studying the long-term magnetic activity in these stars revealing complicated activity cycles. The development of observing and analysis techniques that has occurred during the past two decades has also enabled us to study the detailed starspot and magnetic field configurations on these active giants. In the recent years magnetic fields have also been detected on slowly rotating giants and supergiant stars. In this paper I review what is known of the surface magnetism in the cool giant and supergiant stars.
On dynamo action in the giant star Pollux: first results
Authors: Palacios Ana , Brun Allan Sacha
Published: August 2014

We present preliminary results of a 3D MHD simulation of the convective envelope of the giant star Pollux for which the rotation period and the magnetic field intensity have been measured from spectroscopic and spectropolarimetric observations. This giant is one of the first single giants with a detected magnetic field, and the one with the weakest field so far. Our aim is to understand the development and the action of the dynamo in its extended convective envelope.