References of "Astronomische Nachrichten"
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See detailDebris disks as seen by Herschel/DUNES
Löhne, T.; Eiroa, C.; Augereau, J.-C. et al

in Astronomische Nachrichten (2012), 333

The far-infrared excesses produced by debris disks are common features of stellar systems. These disks are thought to contain solids ranging from micron-sized dust to planetesimals. Naturally, their ... [more ▼]

The far-infrared excesses produced by debris disks are common features of stellar systems. These disks are thought to contain solids ranging from micron-sized dust to planetesimals. Naturally, their formation and evolution are linked to those of potential planets. With this motivation, the Herschel open time key programme DUNES (DUst around NEarby Stars) aims at further characterising known debris disks and discovering new ones in the regime explored by the Herschel space observatory. On the one hand, in their survey of 133 nearby FGK stars, DUNES discovered a class of extremely cold and faint debris disks, different from well-known disks such as the one around Vega in that their inferred typical grain sizes are rather large, indicating low dynamical excitation and low collision rates. On the other hand, for the more massive disk around the sun-like star HD 207129, well-resolved PACS images confirmed the ring-liked structure seen in HST images and provided valuable information for an in-depth study and benchmark for models. Employing both models for power-law fitting and collisional evolution we found the disk around HD 207129 to feature low collision rates and large grains, as well. Transport by means of Poynting-Robertson drag likely plays a role in replenishing the dust seen closer to the star, inside of the ring. The inner edge is therefore rather smooth and the contribution from the extended halo of barely bound grains is small. Both slowly self-stirring and planetary perturbations could potentially have formed and shaped this disk. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. [less ▲]

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See detailMagnetic field studies of massive main sequence stars
Schöller, M.; Hubrig, S.; Ilyin, I. et al

in Astronomische Nachrichten (2011), 332

We report on the status of our spectropolarimetric observations of massive stars. During the last years, we have discovered magnetic fields in many objects of the upper main sequence, including Be stars ... [more ▼]

We report on the status of our spectropolarimetric observations of massive stars. During the last years, we have discovered magnetic fields in many objects of the upper main sequence, including Be stars, β Cephei and Slowly Pulsating B stars, and a dozen O stars. Since the effects of those magnetic fields have been found to be substantial by recent models, we are looking into their impact on stellar rotation, pulsation, stellar winds, and chemical abundances. Accurate studies of the age, environment, and kinematic characteristics of the magnetic stars are also promising to give us new insight into the origin of the magnetic fields. Furthermore, longer time series of magnetic field measurements allow us to observe the temporal variability of the magnetic field and to deduce the stellar rotation period and the magnetic field geometry. Studies of the magnetic field in massive stars are indispensable to understand the conditions controlling the presence of those fields and their implications on the stellar physical parameters and evolution. [less ▲]

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See detailSpectroscopic variability and magnetic fields of HgMn stars
Hubrig, S.; González, J. F.; Ilyin, I. et al

in Astronomische Nachrichten (2011), 332

The discovery of exotic abundances, chemical inhomogeneities, and weak magnetic fields on the surface of late B-type primaries in spectroscopic binaries has important implications not only for our ... [more ▼]

The discovery of exotic abundances, chemical inhomogeneities, and weak magnetic fields on the surface of late B-type primaries in spectroscopic binaries has important implications not only for our understanding of the formation mechanisms of stars with Hg and Mn peculiarities themselves, but also for the general understanding of B-type star formation in binary systems. The origin of the abundance anomalies observed in late B-type stars with HgMn peculiarity is still poorly understood. The connection between HgMn peculiarity and membership in binary and multiple systems is supported by our observations during the last decade. The important result achieved in our studies of a large sample of HgMn stars is the finding that most HgMn stars exhibit spectral variability of various chemical elements, proving that the presence of an inhomogeneous distribution on the surface of these stars is a rather common characteristic and not a rare phenomenon. Further, in the studied systems, we found that all components are chemically peculiar with different abundance patterns. Generally, He and Si variable Bp stars possess large-scale organised magnetic fields that in many cases appear to occur essentially in the form of a single large dipole located close to the centre of the star. The presence of magnetic fields in the atmospheres of HgMn stars has been demonstrated in several studies. In addition to the measurements of longitudinal and quadratic magnetic fields, this work also showed evidence for a relative magnetic intensification of Fe II lines produced by different magnetic desaturations induced by different Zeeman-split components. Based on ESO Archival data, from ESO programme 083.D-1000(A). [less ▲]

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See detailAsteroseismology of OB stars with CoRoT
Degroote, P.; Aerts, C.; Samadi, R. et al

in Astronomische Nachrichten (2010), 331

The CoRoT satellite is revolutionizing the photometric study of massive O-type and B-type stars. During its long runs, CoRoT observed the entire main sequence B star domain, from typical hot β Cep stars ... [more ▼]

The CoRoT satellite is revolutionizing the photometric study of massive O-type and B-type stars. During its long runs, CoRoT observed the entire main sequence B star domain, from typical hot β Cep stars, via cooler hybrid p- and g-mode pulsators to the SPB stars near the edge of the instability strip. CoRoT lowers the sensitivity barrier from the typical mmag-precision reached from the ground, to the μmag-level reached from space. Within the wealth of detected and identified pulsation modes, relations have been found in the form of multiplets, combination of frequencies, and frequency- and period spacings. This wealth of observational evidence is finally providing strong constraints to test current models of the internal structure and pulsations of hot stars. Aside from the expected opacity driven modes with infinite lifetime, other unexpected types of variability are detected in massive stars, such as modes of stochastic nature. The simultaneous observation of all these light curve characteristics implies a challenge for both observational asteroseismology and stellar modelling. The CoRoT space mission was developed and is operated by the French space agency CNES, with participation of ESA's RSSD and Science Programmes, Austria, Belgium, Brazil, Germany, and Spain. [less ▲]

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See detailInference from adiabatic analysis of solar-like oscillations in red giants
Montalban Iglesias, Josefa ULg; Miglio, Andrea ULg; Noels-Grötsch, Arlette ULg et al

in Astronomische Nachrichten (2010), 331

The clear detection with CoRoT and Kepler of radial and non-radial solar-like oscillations in many red giants paves the way to seismic inferences on the structure of such stars. We present an overview of ... [more ▼]

The clear detection with CoRoT and Kepler of radial and non-radial solar-like oscillations in many red giants paves the way to seismic inferences on the structure of such stars. We present an overview of the properties of the adiabatic frequencies and frequency separations of radial and non-radial oscillation modes, highlighting how their detection allows a deeper insight into the properties of the internal structure of red giants. In our study we consider models of red giants in different evolutionary stages, as well as of different masses and chemical composition. We describe how the large and small separations computed with radial modes and with non-radial modes mostly trapped in the envelope depend on the stellar global parameters and evolutionary state, and we compare our theoretical predictions and first Kepler data.Finally, we find that the properties of dipole modes constitute a promising seismic diagnostic of the evolutionary state of red-giant stars. [less ▲]

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See detailGround-based follow-up in relation to Kepler asteroseismic investigation
Uytterhoeven, K.; Briquet, Maryline ULg; Bruntt, H. et al

in Astronomische Nachrichten (2010), 331

The Kepler space mission, successfully launched in March 2009, is providing continuous and high-precision photometry of thousands of stars simultaneously. The uninterrupted time-series of stars of all ... [more ▼]

The Kepler space mission, successfully launched in March 2009, is providing continuous and high-precision photometry of thousands of stars simultaneously. The uninterrupted time-series of stars of all known pulsation types are a precious source for asteroseismic studies. The Kepler data do not provide information on the physical parameters, such as T_eff, log g, metallicity, and v sin i, which are crucial for successful asteroseismic modelling. Additional ground-based time-series data are needed to characterize mode parameters in several types of pulsating stars. Therefore, ground-based multi-colour photometry and mid/high-resolution spectroscopy are needed to complement the space data. We present ground-based activities within KASC on selected asteroseismic Kepler targets of several pulsation types. Based on observations made with the Isaac Newton Telescope and William Herschel Telescope operated by the Isaac Newton Group, with the Nordic Optical Telescope, operated jointly by Denmark, Finland, Iceland, Norway, and Sweden, with the Italian Telescopio Nazionale Galileo (TNG) operated by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica), and with the Mercator telescope, operated by the Flemish Community, all on the island of La Palma at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias (IAC). Based on observations made with the IAC-80 operated on the island of Tenerife by the IAC at the Spanish Observatorio del Teide. Also based on observations taken at the observatories of Sierra Nevada, San Pedro Mártir, Vienna, Xinglong, Apache Point, Lulin, Tautenburg, McDonald, Skinakas, Pic du Midi, Mauna Kea, Steward Observatory, Mt. Wilson, Białków Observatory of the Wrocław University, Piszkésteto Mountain Station, and Observatoire de Haute Provence. Based on spectra taken at the Loiano (INAF - OA Bologna), Serra La Nave (INAF - OA Catania) and Asiago (INAF - OA Padova) observatories. Also based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck-Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC). We acknowledge with thanks the variable star observations from the AAVSO International Database contributed by observers worldwide and used in this research. Funding for the Kepler mission is provided by NASA's Science Mission Directorate. We thank the entire Kepler team for the development and operations of this outstanding mission. [less ▲]

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See detailTowards ensemble asteroseismology of the young open clusters χ Persei and NGC 6910
Saesen, S.; Pigulski, A.; Carrier, F. et al

in Astronomische Nachrichten (2010), 331

As a result of the variability survey in χ Persei and NGC 6910, the number of β Cep stars that are members of these two open clusters is increased to twenty stars, nine in NGC 6910 and eleven in χ Persei ... [more ▼]

As a result of the variability survey in χ Persei and NGC 6910, the number of β Cep stars that are members of these two open clusters is increased to twenty stars, nine in NGC 6910 and eleven in χ Persei. We compare pulsational properties, in particular the frequency spectra, of β Cep stars in both clusters and explain the differences in terms of the global parameters of the clusters. We also indicate that the more complicated pattern of the variability among B-type stars in χ Persei is very likely caused by higher rotational velocities of stars in this cluster. We conclude that the sample of pulsating stars in the two open clusters constitutes a very good starting point for the ensemble asteroseismology of β Cep-type stars and maybe also for other B-type pulsators. [less ▲]

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See detailAsteroseismology of solar-type stars with Kepler: III. Ground-based data
Molenda-Żakowicz, J.; Bruntt, H.; Sousa, S. et al

in Astronomische Nachrichten (2010), 331

We report on the ground-based follow-up program of spectroscopic and photometric observations of solar-like asteroseismic targets for the Kepler space mission. These stars constitute a large group of more ... [more ▼]

We report on the ground-based follow-up program of spectroscopic and photometric observations of solar-like asteroseismic targets for the Kepler space mission. These stars constitute a large group of more than a thousand objects which are the subject of an intensive study by the Kepler Asteroseismic Science Consortium Working Group 1 (KASC WG-1). In the current work we will discuss the methods we use to determine the fundamental stellar atmospheric parameters using high-quality stellar spectra. These provide essential constraints for the asteroseismic modelling and make it possible to verify the parameters in the Kepler Input Catalogue (KIC). [less ▲]

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See detailOscillations in rapidly rotating stars
Reese, Daniel ULg

in Astronomische Nachrichten (2010, December 01), 331

Spurred by the spectroscopic and interferometric observations of rapidly rotating stars and the highly accurate pulsation data coming from asteroseismology space missions, theoreticians have spent many ... [more ▼]

Spurred by the spectroscopic and interferometric observations of rapidly rotating stars and the highly accurate pulsation data coming from asteroseismology space missions, theoreticians have spent many years developing models for such stars and studying their oscillations. This has led to the discovery of new phenomena and new types of pulsation modes. In what follows, a review is given of the different methods used to model the effects of rotation on stellar pulsations, as well as a description of these effects on inertial, gravito-inertial, r and acoustic modes. [less ▲]

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See detailCan an underestimation of opacity explain B-type pulsators in the SMC?
Salmon, Sébastien ULg; Montalban Iglesias, Josefa ULg; Miglio, Andrea ULg et al

in Astronomische Nachrichten (2010, October 09), 331(9-10),

Slowly Pulsating B and ß Cephei are ĸ mechanism driven pulsating B stars. That ĸ mechanism works since a peak in the opacity due to a high number of atomic transitions from iron-group elements occurs in ... [more ▼]

Slowly Pulsating B and ß Cephei are ĸ mechanism driven pulsating B stars. That ĸ mechanism works since a peak in the opacity due to a high number of atomic transitions from iron-group elements occurs in the area of log T ~ 5.3. Theoretical results predict very few SPBs and no ß Cep to be encountered in low metallicity environments such as the Small Magellanic Cloud. However recent variability surveys of B stars in the SMC reported the detection of a significant number of SPB and ß Cep candidates. Though the iron content plays a major role in the excitation of ß Cep and SPB pulsations, the chemical mixture representative of the SMC B stars such as recently derived does not leave room for a significant increase of the iron abundance in these stars. Whilst abundance of iron-group elements seems reliable, is the opacity in the iron-group elements bump underestimated? We determine how the opacity profile in B-type stars should change to excite SPB and ß Cep pulsations in early-type stars of the SMC. [less ▲]

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See detailThe PLATO End-to-End CCD Simulator -- Modelling space-based ultra-high precision CCD photometry for the assessment study of the PLATO Mission
Zima, W.; Arentoft, T.; De Ridder, J. et al

in Astronomische Nachrichten (2010, October 09), 331(9-10),

The PLATO satellite mission project is a next generation ESA Cosmic Vision satellite project dedicated to the detection of exo-planets and to asteroseismology of their host-stars using ultra-high ... [more ▼]

The PLATO satellite mission project is a next generation ESA Cosmic Vision satellite project dedicated to the detection of exo-planets and to asteroseismology of their host-stars using ultra-high precision photometry. The main goal of the PLATO mission is to provide a full statistical analysis of exo-planetary systems around stars that are bright and close enough for detailed follow-up studies. Many aspects concerning the design trade-off of a space-based instrument and its performance can best be tackled through realistic simulations of the expected observations. The complex interplay of various noise sources in the course of the observations made such simulations an indispensable part of the assessment study of the PLATO Payload Consortium. We created an end-to-end CCD simulation software-tool, dubbed PLATOSim, which simulates photometric time-series of CCD images by including realistic models of the CCD and its electronics, the telescope optics, the stellar field, the pointing uncertainty of the satellite (or Attitude Control System [ACS] jitter), and all important natural noise sources. The main questions that were addressed with this simulator were the noise properties of different photometric algorithms, the selection of the optical design, the allowable jitter amplitude, and the expected noise budget of light-curves as a function of the stellar magnitude for different parameter conditions. The results of our simulations showed that the proposed multi-telescope concept of PLATO can fulfil the defined scientific goal of measuring more than 20000 cool dwarfs brighter than mV =11 with a precision better than 27 ppm/h which is essential for the study of earth-like exo-planetary systems using the transit method. [less ▲]

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See detailTheoretical study of γ Doradus pulsations in pre-main sequence stars
Bouabid, M*-P; Montalban Iglesias, Josefa ULg; Miglio, Andrea ULg et al

in Astronomische Nachrichten (2010), 331

The question of the existence of the pre-main sequence (PMS) γ Doradus (γ Dor) pulsators has been raised by observations of young clusters such as NGC 884 hosting γ Dor members. We have explored the ... [more ▼]

The question of the existence of the pre-main sequence (PMS) γ Doradus (γ Dor) pulsators has been raised by observations of young clusters such as NGC 884 hosting γ Dor members. We have explored the properties of γ Dor-type pulsations with a grid of PMS models covering the mass range {1.2 < M_*/M_ȯ < 2.5} and we derive the theoretical instability strip (IS) for the PMS γ Dor pulsators. We explore the possibility of distinguishing between PMS and MS γ Dor by the behaviour of the period spacing of their high order gravity modes (g-modes). [less ▲]

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See detailKepler observations: Light shed on the hybrid γ Doradus - δ Scuti pulsation phenomenon
Grigahcène, A.; Uytterhoeven, K.; Antoci, V. et al

in Astronomische Nachrichten (2010), 331

Through the observational study of stellar pulsations, the internal structure of stars can be probed and theoretical models can be tested. The main sequence γ Doradus (Dor) and δ Scuti (Sct) stars with ... [more ▼]

Through the observational study of stellar pulsations, the internal structure of stars can be probed and theoretical models can be tested. The main sequence γ Doradus (Dor) and δ Scuti (Sct) stars with masses 1.2-2.5 M[SUB]ȯ[/SUB] are particularly interesting for asteroseismic study. The γ Dor stars pulsate in high-order gravity (g) modes, with pulsational periods of order of one day. The δ Sct stars, on the other hand, show low-order g and pressure (p) modes with periods of order of 2 hours. Theory predicts the existence of `hybrid' stars, i.e. stars pulsating in both types of modes, in an overlap region between the instability strips of γ Dor and δ Sct stars in the Hertzsprung-Russell diagram. Hybrid stars are particularly interesting as the two types of modes probe different regions of the stellar interior and hence provide complementary model constraints. Before the advent of Kepler, only a few hybrid stars had been confirmed. The {{Kepler}} satellite is providing a true revolution in the study of and search for hybrid stars. Analysis of the first 50 days of {{Kepler}} data of hundreds of γ Dor and δ Sct candidates reveals extremely rich frequency spectra, with most stars showing frequencies in both the δ Sct and γ Dor frequency range. As these results show that there are practically no pure δ Sct or γ Dor pulsators, a new observational classification scheme is proposed by \cite{Grig10}. We present their results and characterize 234 stars in terms of δ Sct, γ Dor, δ Sct/γ Dor or γ Dor/δ Sct hybrids. [less ▲]

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See detailAsteroseismology of solar-type stars with Kepler I: Data analysis
Karoff, C.; Chaplin, W. J.; Appourchaux, T. et al

in Astronomische Nachrichten (2010), 331

We report on the first asteroseismic analysis of solar-type stars observed by Kepler. Observations of three G-type stars, made at one-minute cadence during the first 33.5 days of science operations ... [more ▼]

We report on the first asteroseismic analysis of solar-type stars observed by Kepler. Observations of three G-type stars, made at one-minute cadence during the first 33.5 days of science operations, reveal high signal-to-noise solar-like oscillation spectra in all three stars: About 20 modes of oscillation can clearly be distinguished in each star. We discuss the appearance of the oscillation spectra, including the presence of a possible signature of faculae, and the presence of mixed modes in one of the three stars. [less ▲]

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See detailTowards the asteroseismology analysis of the Herbig Ae star HD 104237
Fumel, Aurélie ULg; Böhm, Torsten

in Astronomische Nachrichten (2010), 331(9-10),

Understanding the internal structure of pulsating Herbig Ae stars by the aim of an asteroseismological study will help us to constrain the origin of the tremendous activity, wind and variability observed ... [more ▼]

Understanding the internal structure of pulsating Herbig Ae stars by the aim of an asteroseismological study will help us to constrain the origin of the tremendous activity, wind and variability observed in this group of pre-main sequence stars. The time-series analysis of the equivalent photospheric profiles of HD 104237 has revealed non-radial pulsations of low-degree (ℓ = 0 or 1). We present a preliminary mode identification corresponding to the main detected frequency f1 = 33.289 c/d. In addition, as we need to constrain a stellar atmosphere model in order to simulate the pulsations of HD 104237, our aim is to determine accurately its fundamental parameters (Teff, log g, abundances); as this study is still in progress, we present our strategy. [less ▲]

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See detailRealisation of a fully-deterministic microlensing observing strategy for inferring planet populations
Dominik, M.; Jørgensen, U. G.; Rattenbury, N. J. et al

in Astronomische Nachrichten (2010), 331

Within less than 15 years, the count of known planets orbiting stars other than the Sun has risen from none to more than 400 with detections arising from four successfully applied techniques: Doppler ... [more ▼]

Within less than 15 years, the count of known planets orbiting stars other than the Sun has risen from none to more than 400 with detections arising from four successfully applied techniques: Doppler-wobbles, planetary transits, gravitational microlensing, and direct imaging. While the hunt for twin Earths is on, a statistically well-defined sample of the population of planets in all their variety is required for probing models of planet formation and orbital evolution so that the origin of planets that harbour life, like and including ours, can be understood. Given the different characteristics of the detection techniques, a complete picture can only arise from a combination of their respective results. Microlensing observations are well-suited to reveal statistical properties of the population of planets orbiting stars in either the Galactic disk or bulge from microlensing observations, but a mandatory requirement is the adoption of strictly-deterministic criteria for selecting targets and identifying signals. Here, we describe a fully-deterministic strategy realised by means of the ARTEMiS (Automated Robotic Terrestrial Exoplanet Microlensing Search) system at the Danish 1.54-m telescope at ESO La Silla between June and August 2008 as part of the MiNDSTEp (Microlensing Network for the Detection of Small Terrestrial Exoplanets) campaign, making use of immediate feedback on suspected anomalies recognized by the SIGNALMEN anomaly detector. We demonstrate for the first time the feasibility of such an approach, and thereby the readiness for studying planet populations down to Earth mass and even below, with ground-based observations. While the quality of the real-time photometry is a crucial factor on the efficiency of the campaign, an impairment of the target selection by data of bad quality can be successfully avoided. With a smaller slew time, smaller dead time, and higher through-put, modern robotic telescopes could significantly outperform the 1.54-m Danish, whereas lucky-imaging cameras could set new standards for high-precision follow-up monitoring of microlensing events. Based on data collected by the MiNDSTEp consortium with the Danish 1.54-m telescope at the ESO La Silla Observatory. [less ▲]

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See detailSolar-like oscillations in cluster stars
Stello, D.; Basu, S.; Bedding, T. R. et al

in Astronomische Nachrichten (2010), 331

This article summaries a talk given at the HELAS IV international meeting We present a brief overview of the history of attempts to obtain a clear detection of solar-like oscillations in cluster stars ... [more ▼]

This article summaries a talk given at the HELAS IV international meeting We present a brief overview of the history of attempts to obtain a clear detection of solar-like oscillations in cluster stars, and discuss the results on the first clear detection, which was made by the Kepler Asteroseismic Science Consortium (KASC) Working Group 2. Data from Kepler. [less ▲]

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See detailNew magnetic field measurements of beta Cephei stars and slowly pulsating B stars
Hubrig, S.; Briquet, Maryline ULg; De Cat, P. et al

in Astronomische Nachrichten (2009), 330

We present the results of the continuation of our magnetic survey with FORS 1 at the VLT of a sample of B-type stars consisting of confirmed or candidate β Cephei stars and Slowly Pulsating B (hereafter ... [more ▼]

We present the results of the continuation of our magnetic survey with FORS 1 at the VLT of a sample of B-type stars consisting of confirmed or candidate β Cephei stars and Slowly Pulsating B (hereafter SPB) stars, along with a small number of normal B-type stars. A weak mean longitudinal magnetic field of the order of a few hundred Gauss was detected in three β Cephei stars and two stars suspected to be β Cephei stars, in five SPB stars and eight stars suspected to be SPB stars. Additionally, a longitudinal magnetic field at a level larger than 3Ï has been diagnosed in two normal B-type stars, the nitrogen-rich early B-type star HD 52089 and in the B5 IV star HD 153716. Roughly one third of β Cephei stars have detected magnetic fields: Out of 13 β Cephei stars studied to date with FORS 1, four stars possess weak magnetic fields, and out of the sample of six suspected β Cephei stars two show a weak magnetic field. The fraction of magnetic SPBs and candidate SPBs is found to be higher: Roughly half of the 34 SPB stars have been found to be magnetic and among the 16 candidate SPBs eight stars possess magnetic fields. In an attempt to understand why only a fraction of pulsating stars exhibit magnetic fields, we studied the position of magnetic and non-magnetic pulsating stars in the H-R diagram. We find that their domains in the H-R diagram largely overlap, and no clear picture emerges as to the possible evolution of the magnetic field across the main sequence. It is possible that stronger fields tend to be found in stars with lower pulsating frequencies and smaller pulsating amplitudes. A somewhat similar trend is found if we consider a correlation between the field strength and the v sin i-values, i.e. stronger magnetic fields tend to be found in more slowly rotating stars. Based on observations obtained at the European Southern Observatory, Paranal, Chile (ESO programmes 078.D-0140(A), 078.D-0330(A), 079.D-0241(A), and 080.D-0383(A)). [less ▲]

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See detailMorphological properties of isolated galaxies vs. isolation criteria
Vavilova, I. B.; Melnyk, Olga ULg; Elyiv, Andrii ULg

in Astronomische Nachrichten (2009), 330

We studied the morphological properties of isolated galaxies samples in dependence on the isolation parameter and properties of primary catalogs. With this aim we identified the samples of single and ... [more ▼]

We studied the morphological properties of isolated galaxies samples in dependence on the isolation parameter and properties of primary catalogs. With this aim we identified the samples of single and isolated galaxies from SDSS DR5 (Single and QIsol) with the 3D Voronoi tessellation method (Elyiv et al. 2009). We found that in comparison with other samples of isolated galaxies, the QIsol sample contains an excess of late-type galaxies, especially with a low luminosity and BCG/Im/Irr morphology. We also showed that the fractions of early type galaxies in QIsol SDSS DR5 sample and samples 2MIG (Karachentseva et al. 2010) and CIG (Karachentseva et al. 1973; Hernandez-Toledo et al. 2008) are in a good agreement (16-19 %), but Allam's (Allam et al. 2005) and Prada's (Prada et al. 2003) SDSS DR1 samples show a higher excess of the early type galaxies that can be explained by the selection criteria and morphology definition method. We found a weak relation between isolation parameter and color index for the Single sample that may indicate that even in the low dense environment the morphology density relation is observed. We conclude that morphological properties of the resulting sample of isolated galaxies are highly dependent on the primary catalogue from which the galaxies were selected. Moreover, the selection criterion is also important but plays a secondary role in the resulting morphological content, color indices distribution and other parameters of the isolated galaxy samples. Only four galaxies are common in the 2MIG, QIsol, and CIG samples, namely UGC5184, UGC6121, UGC8495, and UGC9598, that allows to consider them as really most isolated galaxies. [less ▲]

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See detailA procedure for modelling asymptotic g-mode pulsators: The case of gamma Doradus stars
Moya, A.; Suárez, J. C.; Martín-Ruiz, S. et al

in Astronomische Nachrichten (2008), 329

Mode identification is one of the first and main problems we encounter in trying to develop the complete potential of asteroseismology. In the particular case of {g}-mode pulsators, this is still an ... [more ▼]

Mode identification is one of the first and main problems we encounter in trying to develop the complete potential of asteroseismology. In the particular case of {g}-mode pulsators, this is still an unsolved problem, from both the observational and theoretical points of view. Nevertheless, in recent years, some observational and theoretical efforts have been made to find a solution. In this work we use the latest theoretical and computational tools to understand asymptotic {g}-mode pulsators: 1) the Frequency Ratio Method, and 2) Time Dependent Convection. With these tools, a self-consistent procedure for mode identification and modelling of these {g}-mode pulsators can be constructed. This procedure is illustrated using observational information available for the gamma Doradus star 9 Aurigae. [less ▲]

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