Interpretation of the solar-like pulsational behaviour of η Bootis     

Maria Pia Di Mauro  JØrgen Christensen-Dalsgaard  Lucio Paternò  Francesca D'Antona 《Solar physics》2004,220(2):185-198

HR 5235, better known as η Bootis, is a bright and well-known star for which very accurate observations have recently enabled Kjeldsen et al. (2003) and Carrier, Bouchy, and Eggenberger (2003) not only to confirm the presence of solar-like oscillations, but also to identify the excitation in the oscillation spectrum of several p-mode frequencies with harmonic degrees l = 0 – 2. Here we show how such observational success, through the calculation and the investigation of theoretical structure models and the comparison of the observed oscillation spectra with the predicted p-mode frequencies of oscillations, permits one to draw conclusions about the actual evolutionary state of this star and on the physical properties of its internal structure. The computation of the structure models is based on the use of updated global parameters and includes overshooting from the convective core. In particular, we consider the effect on the stellar structure, and hence on the theoretical frequencies, of employing different equations of state and different formalisms to describe the convective energy transport.  相似文献   

Preliminary results of the multisite time-series campaign on the sdB pulsator PG 1325+101     

R. Silvotti  A. Bonanno  A. Frasca  S. Bernabei  R. Janulis  R. Østensen  S.-L. Kim  B.-G. Park  J. Xiaojun  J. Guo  Z. Liu  M.D. Reed  R.S. Patterson  K.M. Gietzen  P.J. Clark  G.W. Wolf  Y. Lipkin  L. Formiggini  E. Leibowitz  T.D. Oswalt  M. Rudkin  K. Johnston 《Astrophysics and Space Science》2004,289(3-4):445-448

I present a model for the formation and evolution of a massive disk galaxy, within a growing dark halo whose mass evolves according to cosmological simulations of structure formation. The galactic evolution is simulated with a new 3D chemo-dynamical code, including dark matter, stars and a multi-phase ISM. We follow the evolution from redshift z = 4.85 until the present epoch. The energy release by massive stars and supernovae prevents a rapid collapse of the baryonic matter and delays the maximum star formation until redshift z ≈ 1. The galaxy forms radially from inside-out and vertically from top-to-bottom. The feedback of stars leads to turbulent motions and large-scale flows in the ISM. As one result the galactic disk is significantly enriched by chemical elements synthesized in bulge stars.  相似文献   

Solar isotopic composition and abundance of europium     

Øivind Hauge 《Solar physics》1972,27(2):286-293

High resolution spectra of six photospheric Eu ii lines have been studied using the method of spectrum synthesizing. The isotope ratio is found to be Eu₁₅₃/Eu₁₅₁ = (48 ± 6)/(52 6) and the solar abundance of europium equals log _Eu = 0.7 ± 0.2 in the log _H = 12.00 scale.  相似文献   

Cirque glacier activity in arctic Norway during the last deglaciation     

yvind Paasche  Svein Olaf Dahl  Jostein Bakke  Reidar Lvlie  Atle Nesje 《Quaternary Research》2007,68(3):387-399

Numerous cirques of the Lofoten–Vesterålen archipelago in northern Norway have distinct moraine sequences that previously have been assigned to the Allerød-Younger Dryas ( 13,400 to 11,700 yr BP) interval, constraining the regional distribution of the equilibrium-line altitude (ELA) of cirque and valley glaciers. Here we present evidence from a once glacier-fed lake on southern Andøya that contests this view. Analyses of radiocarbon dated lacustrine sediments including rock magnetic parameters, grain size, organic matter, dry bulk density and visual interpretation suggest that no glacier was present in the low-lying cirque during the Younger Dryas-Allerød. The initiation of the glacial retreat commenced with the onset of the Bølling warming ( 14,700 yr BP) and was completed by the onset of Allerød Interstade ( 13,400 yr BP). The reconstructed glacier stages of the investigated cirque coincide with a cool and dry period from  17,500 to 14,700 yr BP and a somewhat larger Last Glacial Maximum (LGM) advance possibly occurring between  21,050 and 19,100 yr BP.  相似文献   

The HYPER-MUCHFUSS project—the constant high-velocity population     

A. Tillich  S. Geier  U. Heber  H. Hirsch  P. F. L. Maxted  T. Marsh  B. Gänsicke  R. Napiwotzki  R. Østensen  R.-D. Scholz 《Astrophysics and Space Science》2010,329(1-2):69-76

The HYPER-MUCHFUSS (HYPER-velocity stars or Massive Unseen Companions of Hot Faint Underluminous Stars from SDSS) project targets a population of high-velocity subluminous B stars to discover either close binaries with massive unseen companions or hyper-velocity stars. We re-observed high-velocity subdwarf selected candidates from the SDSS spectroscopic Data Release 6. Starting in 2007 we used several instruments and have now reached a completion level of 33% (from 265 targets), whereas we found at least 16 close binaries. Here we present results for two of our 39 hyper-velocity star candidates. From the available Digitized Sky Surveys photographic plates we measured a significant proper motion for 14 stars. Combining this information with a detailed spectroscopic analysis allows for the first time a complete determination of the 3D-trajectories for a high-velocity sample. We present our preliminary results for the two subdwarfs J1644+4523 and J1211+1437. Assuming the Standard Allen and Santillan (Rev. Mex. Astron. Astrofis. 22:255, 1991) potential the first one is bound and originates in the central region of the Galaxy. The subdwarf B star J1211+1437 is possibly unbound and seems to originate in the Galactic rim. We also performed numerical kinematical experiments with increased dark matter halo mass. and found that the origin of J1644+4523 in the central region is not changed but the time-of-flight is drastically shortened. J1211+1437 would be bound and probably belongs to population II.  相似文献   

Radial velocity and line-profile variations in the sdBV star PG 1325+101     

Roy H. Østensen  John H. Telting 《Astrophysics and Space Science》2004,290(3-4):449-456

Historically, any newly discovered object needed to be “confirmed” with optical observations. Catalogs were published, such as the PKS (Parkes Catalog), with stamp-sized photographs that allowed us to “see” what was just found. This is still somewhat true, although far less than in the past. We are probably reaching an information overload with more efficient instruments, larger detectors, multiple wavelength coverage and an increasing number of ground and space-based facilities. At the same time, information technology is catching up and is allowing us to use the data regardless of where they reside. An increasing need of multi-wavelength observations to understand the underlying physics of the observed phenomena and the challenge to mine petabyte databases is leading to a federation of archives and cooperation among computer scientists and astronomers. These are the seeds of a virtual observatory, a cyberspace entity where the data are ready to be found and analyzed. In the United States, the National Science Foundation (NSF) and the National Aeronautics and Space Administration (NASA) are funding initiatives that will lead to the creation of this entity. This paper describes these projects.  相似文献   

Implicit Treatment of Compositional Flow     

I. Garrido  E. Øian  M. Chaib  G.E. Fladmark  M.S. Espedal 《Computational Geosciences》2004,8(1):1-19

In basin modeling the thermodynamics of a multicomponent multiphase fluid flux are computationally too expensive when derived from a cubic equation of state and the Gibbs equality constraints. In this article we present an alternative implicit molar mass formulation technique using binary mixture thermodynamics. The two proposed solution methods are based on a hybrid smoother, Gauss–Seidel–Galerkin at each time-step with analytical computation of the derivatives. The new algorithm overcomes the difficulty of choosing an optimal relaxation parameter and reduce significantly the numerical effort for the computation of the molar masses. Numerical results are presented which show significant improvements with respect to previous methods.  相似文献   

The radiological environment of Svalbard   总被引：1，自引：0，他引：1  

Justin P. Gwynn  Mark Dowdall  Corine Davids  Øyvind G. Selnæs  Bjørn Lind 《Polar research》2004,23(2):167-180

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Environmental changes in an alpine lake (Gossenköllesee, austria) over the last two centuries – the influence of air temperature on biological parameters     

Karin A. Koinig  Christian Kamenik  Roland Schmidt  Anna Agustí-Panareda  Peter Appleby  Andrea Lami  Miroslava Prazakova  Neil Rose  Øyvind A. Schnell  Richard Tessadri  Roy Thompson  Roland Psenner 《Journal of Paleolimnology》2002,28(1):147-160

Changes in microfossils (diatoms, chrysophytes, chironomids and cladocera remains), geochemistry and deposition of atmospheric pollutants have been investigated in the sediment records of the alpine lake Gossenköllesee (Tyrol, Austria) spanning the last two centuries. The sediment records were compared with seasonal and annual air temperature trends calculated for the elevation (2417 m a.s.l.) and the geographical position (47° 1346N, 11° 0051E) of the lake, and with precipitation records available since 1866 from Innsbruck. Temperature trends followed a 20–30 year oscillation between cold and warm periods. Regarding long-term changes, temperature trends showed a U-shaped trend between 1780 and 1950, followed by a steep increase since 1975.Physical, geochemical, and organic parameters were not controlled by air temperature. Among the biological records only diatoms and chrysophytes reacted to air temperature changes: the relative abundance of planktonic diatoms increased during warm periods and changes in mean annual alpine air temperature explained 36.5% of their variation. The relation between abundance of seasonal stomatocyst types and air temperature varied on two different time scales: while summer stomatocysts were influenced by short term temperature fluctuations, the autumn stomatocysts were affected only by the long term changes. Other biological parameters exhibited a constant species composition (chironomids, pigments) or changes were small and independent of temperature (cladocera). Spheroidal carbonaceous fly-ash particles, and trends in Pb and Cr indicated increasing deposition of atmospheric pollutants but had no detectable effects on the biological parameters either. In respect to temperature variations over the last 200 years, this alpine lake is much less sensitive than expected and has thus to be regarded as a well buffered site. However, temperature alone is not sufficient to understand changes in species composition and other biogeochemical processes with unknown historical patterns might have affected species composition more strongly.  相似文献   

Numerical modelling of organic waste dispersion from fjord located fish farms     

Alfatih Ali  Øyvind Thiem  Jarle Berntsen 《Ocean Dynamics》2011,61(7):977-989

In this study, a three-dimensional particle tracking model coupled to a terrain following ocean model is used to investigate the dispersion and the deposition of fish farm particulate matter (uneaten food and fish faeces) on the seabed due to tidal currents. The particle tracking model uses the computed local flow field for advection of the particles and random movement to simulate the turbulent diffusion. Each particle is given a settling velocity which may be drawn from a probability distribution according to settling velocity measurements of faecal and feed pellets. The results show that the maximum concentration of organic waste for fast sinking particles is found under the fish cage and continue monotonically decreasing away from the cage area. The maximum can split into two maximum peaks located at both sides of the centre of the fish cage area in the current direction. This process depends on the sinking time (time needed for a particle to settle at the bottom), the tidal velocity and the fish cage size. If the sinking time is close to a multiple of the tidal period, the maximum concentration point will be under the fish cage irrespective of the tide strength. This is due to the nature of the tidal current first propagating the particles away and then bringing them back when the tide reverses. Increasing the cage size increases the likelihood for a maximum waste accumulation beneath the fish farm, and larger farms usually means larger biomasses which can make the local pollution even more severe. The model is validated by using an analytical model which uses an exact harmonic representation of the tidal current, and the results show an excellent agreement. This study shows that the coupled ocean and particle model can be used in more realistic applications to help estimating the local environmental impact due to fish farms.  相似文献