bluuebunny/crossref_metadata_2025 huggingface dataset:
CN rotational excitation
Authors: Krełowski J. , Galazutdinov G. , Gnaciński P.
Published: October 2014

We demonstrate, using a sample of high quality spectra, that the average equivalent width ratio of the unsaturated R(0) and R(1) lines of the CN B2Σ+ – X2Σ+ (0, 0) band near 3875 Å equals π instead of 3.73 – calculated for the CMBR temperature T = 2.725 K and the already published oscillator strengths of both transitions, i.e. the excitation temperature of CN is slightly higher than it should be expected if CMBR is the only excitation mechanism. Taking into account the saturation effects by means of profile fitting during the column density calculations does not remove the revealed temperature excess. Possible interpretations of the effect are discussed (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The significance of the Hansen Ideal space frame
Authors: Jochim E.F.M.
Published: October 2014

Known and unknown properties of Hansen Ideal coordinates are summarized. It is shown that the ideal space frame is a general and necessary component of basic celestial mechanics and astrodynamics, as well as of any theory of motion. A typical consequence is the intimate correlation of the Hansen frame with the Lagrange constraint within the method of the variation of the parameters. The use of observations in the ideal frame may allow conclusions on the intergalactic fundamental coordinate system (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The hemispheric variation of the flare index during solar cycles 20–23
Authors: Deng L.H. , Qu Z.Q. , Liu T. , Wang K.R.
Published: October 2014

In this paper, the monthly counts of flare index in the northern and southern hemispheres are used to investigate the hemispheric variation of the flare index in each of solar cycles 20–23. It is found that, (1) the flare index is asymmetrically distributed in each solar cycle and its asymmetry is a real phenomenon; (2) the flare index in the northern hemisphere begins earlier than that in the southern hemisphere in each of solar cycles 20–23, and the phase shifts between the two hemispheres show an odd‐even pattern; (3) although the flare index dominating in a hemisphere does not mean that it leads in phase in this hemisphere in individual solar cycle, these two features have an intrinsic relationship. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cosmic Flows surveys and CLUES simulations
Authors: Courtois H.M. , Tully R.B.
Published: October 2014

‘Cosmic Flows’ is a program to determine galaxy distances for 30000 galaxies with systematic errors below 2%, almost ten times the number currently known and a five‐fold improvement in systematics. The resultant velocity field will provide input for constrained local universe simulations: CLUES (www.clues‐project.org). The observed and the simulated universe are then comparatively studied. This synergy of observations and theory distinguishes the program, and should lead to fundamental discoveries regarding the sources of deviations from the expansion of the universe. Specifically, the program should give a definitive answer to one of the most outstanding unsolved problem in cosmology: the cause of the motion of 630 km s–1 of our Galaxy manifested in the microwave background dipole. This paper presents current results with particular emphasis on the “great attractor” reconstruction (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Milky Way simulations: The Galaxy, its stellar halo and its satellites – insights from a hybrid cosmological approach
Authors: De Lucia G.
Published: October 2014

Our home galaxy – the Milky Way – is a fairly large spiral galaxy, prototype of the most common morphological class in the local Universe. Although being only a galaxy, it is the only one that can be studied in unique detail: for the Milky Way and for a number of members of the Local Group, a wealth of observational data is available about the ages and chemical abundances of their stars. Much more information is expected to come in the next few years, from ongoing and planned spectroscopic and astrometric surveys, providing a unique benchmark for modern theories of galaxy formation. In this review, I will summarize recent results on the formation of our Milky Way, its stellar halo, and its satellite galaxies. I will focus, in particular, on results obtained in the framework of hybrid models of galaxy formation, and refer to other reviews in this issue for studies based on hydrodynamical simulations (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Gamma‐ray burst host galaxies at low and high redshift
Authors: Savaglio S.
Published: October 2014

The galaxies hosting the most energetic explosions in the universe, the gamma‐ray bursts (GRBs), are generally found to be low‐mass, metal poor, blue and star forming galaxies. However, the majority of the targets investigated so far (less than 100) are at relatively low redshift, z < 2. We know that at low redshift, the cosmic star formation is predominantly in small galaxies. Therefore, at low redshift, long‐duration GRBs, which are associated with massive stars, are expected to be in small galaxies. Preliminary investigations of the stellar mass function of z < 1.5 GRB hosts does not indicate that these galaxies are different from the general population of nearby star‐forming galaxies. At high‐z, it is still unclear whether GRB hosts are different. Recent results indicate that a fraction of them might be associated with dusty regions in massive galaxies. Remarkable is the a super‐solar metallicity measured in the interstellar medium of a z = 3.57 GRB host (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New results from Galactic ISM surveys: The frothy ISM
Authors: McClure‐Griffiths N.M.
Published: October 2014

The past 10 years have seen a resurgence in studies of the Milky Way's interstellar medium (ISM) driven by new surveys of the Galactic plane at wavelengths from 4 microns to 20 cm. These surveys, which include the H I International Galactic Plane Survey, the Spitzer GLIMPSE and MIPSGAL surveys, the recently commenced Herschel HI‐GAL survey, and several surveys of CO J = 1–0, are allowing us to trace the evolution of the ISM on scales of parsecs and sub‐parsecs from warm and diffuse through to cold, dusty molecular gas. Together with hydrodynamical simulations of ever‐increasing sophistication our understanding of the ISM in the disk of the Milky Way has evolved from the 1970's simplistic models of cold clouds surrounded by warm gas to a complex mixture of phases intertwined and interconnected, whose cooling is driven by colliding flows. Here I focus on the “frothy” ISM, where structure and evolution is impacted by bubbles, shells and supershells. I discuss the role of these objects in cooling, the formation of molecules and even the transfer of matter out of the disk of the Galaxy (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The extinction curve in the visible and the value of RV: Addendum to AN 333, 160
Authors: Zagury F. , Turner D.G.
Published: October 2014

This paper corrects and completes a previous study of the shape of the extinction curve in the visible and the value of RV. A continuous visible/infrared extinction law proportional to 1/λp with p close to 1 (± 0.4) is indistinguishable from a perfectly linear law (p = 1) in the visible within observational precision, but the shape of the curve in the infrared can be substantially modified. Values of p slightly larger than 1 would account for the increase of extinction (compared to the p = 1 law) reported for λ > 1 μ m and deeply affect the value of RV. In the absence of gray extinction RV must be 4.04 if p = 1. It becomes 3.14 for p = 1.25, 3.00 for p = 1.30, and 2.76 for p = 1.40. Values of p near 1.3 are also attributed to extinction by atmospheric aerosols, which indicates that both phenomena may be governed by similar particle size distributions. A power extinction law may harmonize visible and infrared data into a single, continuous, and universal interstellar extinction law (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Larger, faster, better: Current trends in cosmological simulations
Authors: Springel V.
Published: October 2014

Numerical simulations of galaxy formation provide a powerful technique for calculating the non‐linear evolution of cosmic structure formation. In fact, they have played an instrumental role in establishing the current standard cosmological model known as ΛCDM. In this brief review, I highlight some of largest calculations carried out recently in the field, and I discuss the challenges involved in making further progress with simulations in the future. These entail the need to scale up the simulations to ever larger sizes and much better resolution, the need to develop more comprehensive numerical models of the physics of galaxy formation, and the need to improve the accuracy of the numerical techniques currently employed. The present epoch of petaflop supercomputers, and the exaflop machines that are foreseen towards the end of the decade, demand novel types of simulation codes that yet have tobe developed (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
GJ 581 update: Additional evidence for a Super‐Earth in the habitable zone
Authors: Vogt S.S. , Butler R.P. , Haghighipour N.
Published: October 2014

We present an analysis of the significantly expanded HARPS 2011 radial velocity data set for GJ 581 that was presented by Forveille et al. (2011). Our analysis reaches substantially different conclusions regarding the evidence for a Super‐Earth‐mass planet in the star's Habitable Zone. We were able to reproduce their reported χ2ν and RMS values only after removing some outliers from their models and refitting the trimmed down RV set. A suite of 4000 N‐body simulations of their Keplerian model all resulted in unstable systems and revealed that their reported 3.6σ detection of e = 0.32 for the eccentricity of GJ 581e is manifestly incompatible with the system's dynamical stability. Furthermore, their Keplerian model, when integrated only over the time baseline of the observations, significantly increases the χ2ν and demonstrates the need for including non‐Keplerian orbital precession when modeling this system. We find that a four‐planet model with all of the planets on circular or nearly circular orbits provides both an excellent self‐consistent fit to their RV data and also results in a very stable configuration. The periodogram of the residuals to a 4‐planet all‐circular‐orbit model reveals significant peaks that suggest one or more additional planets in this system. We conclude that the present 240‐point HARPS data set, when analyzed in its entirety, and modeled with fully self‐consistent stable orbits, by and of itself does offer significant support for a fifth signal in the data with a period near 32 days. This signal has a false alarm probability of <4% and is consistent with a planet of minimum mass 2.2 M⊕, orbiting squarely in the star's habitable zone at 0.13 AU, where liquid water on planetary surfaces is a distinct possibility (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The opacity of spiral galaxy disks: IX. Dust and gas surface densities
Authors: Holwerda B.W. , Allen R.J. , de Blok W.J.G. , Bouchard A. , González‐Lópezlira R.A. , van der Kruit P.C. , Leroy A.
Published: October 2014

Our aim is to explore the relation between gas, atomic and molecular, and dust in spiral galaxies. Gas surface densities are from atomic hydrogen and CO line emission maps. To estimate the dust content, we use the disk opacity as inferred from the number of distant galaxies identified in twelve HST/WFPC2 fields of ten nearby spiral galaxies. The observed number of distant galaxies is calibrated for source confusion and crowding with artificial galaxy counts and here we verify our results with sub‐mm surface brightnesses from archival Herschel ‐SPIRE data. We find that the opacity of the spiral disk does not correlate well with the surface density of atomic (H I) or molecular hydrogen (H2) alone implying that dust is not only associated with the molecular clouds but also the diffuse atomic disk in these galaxies. Our result is a typical dust‐to‐gas ratio of 0.04, with some evidence that this ratio declines with galactocentric radius, consistent with recent Herschel results. We discuss the possible causes of this high dust‐to‐gas ratio; an over‐estimate of the dust surface‐density, an under‐estimate of the molecular hydrogen density from CO maps or a combination of both. We note that while our value of the mean dust‐to‐gas ratio is high, it is consistent with the metallicity at the measured radii if one assumes the Pilyugin & Thuan (2005) calibration of gas metallicity. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New classification and basic stellar parameter of SW Equulei
Authors: Behre O. , Hünsch M.
Published: October 2014

We review the classification of the variable star SW Equulei, formerly classified as a close binary of the W UMa type with a period of 0.83632 d and components of spectral types O–A or F–G and later. New observations indicate that the light curve is not that of an eclipsing binary but of a pulsating star with a period half of the old value. Further examination shows that SW Equulei is a double mode star of the RRd Lyrae type with a fundamental period of P = 0.560727 d and an overtone of P = 0.4181777 d at a distance of ≈ 7.1 kpc. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
CSS091109:035759+102943: A candidate polar
Authors: Schwope A.D. , Thinius B.
Published: October 2014

We report optical time‐resolved photometry of the CRTS transient CSS091109:035759+102943. Pronounced orbital variability with a 114 min period, large X‐ray variability and the IR to X‐ray spectral energy distribution suggest a classification as a magnetic cataclysmic binary, a likely AM Herculis star or polar (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Rotation, activity, and lithium abundance in cool binary stars
Authors: Strassmeier K. G. , Weber M. , Granzer T. , Järvinen S.
Published: October 2014

We have used two robotic telescopes to obtain time‐series high‐resolution optical echelle spectroscopy and VI and/or by photometry for a sample of 60 active stars, mostly binaries. Orbital solutions are presented for 26 double‐lined systems and for 19 single‐lined systems, seven of them for the first time but all of them with unprecedented phase coverage and accuracy. Eighteen systems turned out to be single stars. The total of 6609 R = 55000 échelle spectra are also used to systematically determine effective temperatures, gravities, metallicities, rotational velocities, lithium abundances and absolute Hα‐core fluxes as a function of time. The photometry is used to infer unspotted brightness, V – I and/or b – y colors, spot‐induced brightness amplitudes and precise rotation periods. An extra 22 radial‐velocity standard stars were monitored throughout the science observations and yield a new barycentric zero point for our STELLA/SES robotic system. Our data are complemented by literature data and are used to determine rotation‐temperature‐activity relations for active binary components. We also relate lithium abundance to rotation and surface temperature. We find that 74% of all known rapidly‐rotating active binary stars are synchronized and in circular orbits but 26% (61 systems) are rotating asynchronously of which half have Prot > Porb and e > 0. Because rotational synchronization is predicted to occur before orbital circularization active binaries should undergo an extra spin‐down besides tidal dissipation. We suspect this to be due to a magnetically channeled wind with its subsequent braking torque. We find a steep increase of rotation period with decreasing effective temperature for active stars, Prot α T–7eff, for both single and binaries, main sequence and evolved. For inactive, single giants with Prot > 100 d, the relation is much weaker, Prot α T‐1.12eff. Our data also indicate a period‐activity relation for Hα of the form RHα α P0.24rot for binaries and RHα α P‐0.14rot for singles. Its power‐law difference is possibly significant. Lithium abundances in our (field‐star) sample generally increase with effective temperature and are paralleled with an increase of the dispersion. The dispersion for binaries can be 1–2 orders of magnitude larger than for singles, peaking at an absolute spread of 3 orders of magnitude near Teff ≈ 5000 K. On average, binaries of comparable effective temperature appear to exhibit 0.25 dex less surface lithium than singles, as expected if the depletion mechanism is rotation dependent. We also find a trend of increased Li abundance with rotational period of form log n (Li) α –0.6 log Prot but again with a dispersion of as large as 3‐4 orders of magnitude (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mining the ESO WFI and INT WFC archives for known Near Earth Asteroids. Mega‐Precovery software
Authors: Vaduvescu O. , Popescu M. , Comsa I. , Paraschiv A. , Lacatus D. , Sonka A. , Tudorica A. , Birlan M. , Suciu O. , Char F. , Constantinescu M. , Badescu T. , Badea M. , Vidican D. , Opriseanu C.
Published: October 2014

The ESO/MPG WFI and the INT WFC wide field archives comprising 330 000 images were mined to search for serendip‐itous encounters of known Near Earth Asteroids (NEAs) and Potentially Hazardous Asteroids (PHAs). A total of 152 as‐teroids (44 PHAs and 108 other NEAs) were identified using the PRECOVERY software, their astrometry being measured on 761 images and sent to the Minor Planet Centre. Both recoveries and precoveries were reported, including prolonged orbital arcs for 18 precovered objects and 10 recoveries. We analyze all new opposition data by comparing the orbits fitted before and after including our contributions. We conclude the paper presenting “Mega‐Precovery”, a new online service focused on data mining of many instrument archives simultaneously for one or a few given asteroids. A total of 28 instrument archives have been made available for mining using this tool, adding together about 2.5 million images forming the “Mega‐Archive”
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

We 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

This 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

We 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

Age 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

Astrophysical 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

Low 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

he 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

A 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

Variability 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

We 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

Young 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

We 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

The 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

Following 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

Brown 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

In 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

We 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

Recovering 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)
Preliminary results on γ Dor and δ Sct‐γ Dor hybrids in the CoRoT exo‐field of LRa01
Authors: Hareter M.
Published: October 2014

The 131 days long, high‐precision light curves observed in the CoRoT exo‐field during LRa01 were investigated for γ Dor and δ Sct‐γ Dor hybrid stars. In total 418 γ Dor and 274 δ Sct‐γ Dor hybrid candidates were identified. For a fraction of these candidates spectra are available obtained at the Anglo‐Australian Observatory. Effective temperatures and surface gravity were derived by fitting synthetic spectra of three Balmer lines, i.e. Hα, Hβ, and Hγ, as well as of the Ca K line at 3933 °A. The bona fide γ Dor and hybrid stars were plotted in an Teff‐ log g diagram that shows the expected concentration of γ Dor stars at the cool border of the δ Sct strip. In contrast, the hybrids fill the whole δ Sct instability strip without a noticeable concentration. Remarkably, the fraction of constant stars, with no signal above 3 times the noise level, is smallest in the same temperature regime (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spectroscopic frequencies of 4 CVn in 2010 and 2011
Authors: Schmid V.S. , Themessl N. , Breger M. , Aerts C. , Beck P.G. , Castanheira B.G. , Fritz V. , Papics P.I. , Debosscher J. , Falcon R.E.
Published: October 2014

Numerous high‐resolution spectra of the δ Scuti star 4 CVn were gathered at McDonald Observatory in Texas, USA. They were prepared for interpretation using standard IRAF routines for a subsequent frequency analysis and mode identification with the software FAMIAS. After the reduction process a clear trend in the first moment of the line profile (radial velocity) remained, indicating the signature of binary motion. This was corrected for by fitting a Keplerian orbit, followed by a detailed analysis of the data in the reference frame of the primary. The results of the frequency analysis are in good agreement with previous photometric studies. This paper presents thirteen pulsation modes that were detected in the data sets for the years 2010 and/or 2011. Future work involves spectroscopic mode identification and subsequent seismic modeling (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Do we see the simultaneous occurrence of stellar rotational effects and short‐period pulsations in some A‐type Kepler stars?
Authors: Lampens P. , Tkachenko A. , Lehmann H. , Debosscher J. , Aerts C. , Beck P.G. , Bloemen S. , Kochiashvili N. , Derekas A.
Published: October 2014

We used high‐quality Kepler photometry and recent spectroscopic data to investigate the Kepler target KIC 005988140 considering three possible scenario’s: (1) binarity, (2) co‐existence of δ Scuti‐ and γ Doradus‐type oscillations, and (3) rotational modulation with spots over the stellar surface. Using spectrum synthesis, we derived improved atmospheric parameters from high‐resolution, high signal‐to‐noise spectra. The star is of spectral type A7.5 IV–III with a metallicity slightly lower than that of the Sun. The Fourier analyses of both the photometric and the spectroscopic data reveal two dominant frequencies – with an integer ratio equal to two – in the low frequency regime. Nine more frequencies located in the typical δ Scuti range were also detected. The mean light and radial velocity curves which are not exactly in antiphase, show a similar double‐wave shape. We therefore suggest on a preliminary basis that the physical cause of the observed light and radial velocity variations is the simultaneous occurrence of (δ Sct‐type) pressure modes and stellar rotation coupled to inhomogeneities on the surface of this late A‐type star (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The current state‐of‐the‐art in active region seismology
Authors: Moradi H.
Published: October 2014

Helioseismology is the study of the variations in the internal structure and properties of the dynamics of the Sun from measurements of its surface oscillations. With the 2010 launch of the Solar Dynamics Observatory (SDO) we are undoubtedly approaching a new dawn for local helioseismology, as the extent and quality of raw surface oscillation data has never been better. However, advances in theory and modelling are still required to fully utilise these data, especially in magnetic active regions and sunspots, where the physics is poorly understood (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Kepler Fourier concepts: The performance of the Kepler data pipeline
Authors: Murphy S.J.
Published: October 2014

Given the extreme precision attainable with the Kepler Space Telescope, the mitigation of instrumental artefacts is very important. In an earlier paper (Murphy 2012), the characteristics of Kepler data were discussed in light of their effect on asteroseismology. We continue this discussion now that data processed with the new PDC‐MAP pipeline are publicly available; users should use the latest data reductions available at the Mikulski Archive for Space Telescopes (MAST), not just for PDC, but also for improvements in the attached meta‐data. We discuss the injection of noise in the frequency range 0–24 d−1 (up to ∼277 µHz) by the PDC‐LS pipeline into ∼15% of light‐curves (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The puzzle of combination frequencies found in heat‐driven pulsators
Authors: Pápics P.I.
Published: October 2014

Searching for combinations in the frequency spectra of variable stars is a commonly used method within the asteroseismological community, as harmonics and linear combinations of individual frequencies are expected to appear not only by chance, but also as a characteristic signature linked to different physical phenomena, e.g., nonlinear oscillations, binarity, and rotation. Furthermore it is very important to identify independent frequencies for modelling purposes. We show that using high precision data sets delivered by recent space missions, the distinction between combinations having a real physical meaning and spurious combinations which only appear by chance gets more and more difficult. We demonstrate how careful one should be with the interpretation of such combination frequencies by presenting the statistical distributions derived from artificial data sets. Based on comparisons to observations, we find that, despite the high statistical probability of finding combinations in random data sets (having similar properties to the ones of real stars), there is a significant difference in the number of the lowest order combinations between stars with and starts without real combination frequencies. This way, a search for frequency combinations is very useful when interpreted properly, and when results are compared to simulations (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)