Wavelength dependence of angular diameters of M giants: an observational perspective     

A. P. Jacob  T. R. Bedding  J. G. Robertson  M. Scholz 《Monthly notices of the Royal Astronomical Society》2000,312(4):733-746

We discuss the wavelength dependence of angular diameters of M giants from an observational perspective. Observers cannot directly measure an optical-depth radius for a star, despite this being a common theoretical definition. Instead, they can use an interferometer to measure the square of the fringe visibility. We present new plots of the wavelength-dependent centre-to-limb variation (CLV) of intensity of the stellar disc as well as visibility for Mira and non-Mira M giant models. We use the terms 'CLV spectra' and 'visibility spectra' for these plots. We discuss a model-predicted extreme limb-darkening effect (also called the narrow-bright-core effect) in very strong TiO bands which can lead to a misinterpretation of the size of a star in these bands. We find no evidence as yet that this effect occurs in real stars. Our CLV spectra can explain the similarity in visibilities of R Dor (M8IIIe) that have been observed recently, despite the use of two different passbands. We compare several observations with models, and find that the models generally underestimate the observed variation in visibility with wavelength. We present CLV and visibility spectra for a model that is applicable to the M supergiant α Ori.  相似文献   

Programme of the Galactic meridian: Star counts and Galactic models 2. Distribution of absolute proper motions     

V. Andruk  N. Kharchenko  E. Schilbach  R.-D. Scholz 《Astronomische Nachrichten》1996,317(1):19-28

A comparison of the observed distribution of absolute proper motions with a kinematical model of the Galaxy is presented. Proper motions with respect to galaxies were obtained for about 40 000 stars along the main Galactic meridian and in two fields near the North Galactic pole (programme MEGA). The Galaxy is considered as composed of the disk (main sequence and disk red giants), the thick disk and spheroid populations. For each subsystem, spatial velocity components and their dispersions were computed. The distribution of kinematical parameters were modelled for stars located in different directions of the Galaxy.  相似文献   

Investigation of the kinematics and structure of the Galaxy in the vicinity of the North galactic pole     

N. Kharchenko  E. Schilbach  R.-D. Scholz 《Astronomische Nachrichten》1994,315(4):291-301

In the framework of the programme of studying the meridional section of the Galaxy (MEGA) the absolute proper motions of more than 11000 stars with respect to 3000 galaxies and their stellar magnitudes in the B, V Johnson system are determined in two sky regions near the North Galactic Pole (NGP) by means of Tautenburg Schmidt plates. The limiting and completing apparent stellar magnitudes are B = 20.4 and 18.3 mag, the overall and the investigated sky areas are 16.4 and 14.6 square degrees, respectively. Distances have been determined using the stellar magnitudes, colours, proper motions and reduced proper motions. Stellar kinematics, eccentricities of Galactic orbits, spatial distribution and changes of these characteristics with Z-distance from the Galactic plane are obtained up to 15 kpc. Four subsystems distinguished in the NGP direction, respectively with semithicknesses of 0.25, 0.38, 0.67, 1.48 kpc and density ellipsoid axial ratios of 0.09, 0.20, 0.28, 0.49 show mean velocities in the Galactic rotation direction relative to the LSR of 5.6 ± 0.6, − 11.0 ± 0.6, − 62.5 ± 1.2, − 181.6 ± 4.4 km/s, and ages of 0.1, 0.4, 0.9, 1 of the Galaxy age.  相似文献   

Density profiles and luminosity functions of the globular clusters M3 and M92     

R.-D. Scholz  K.-H. Schmidt 《Astronomische Nachrichten》1992,313(1):45-52

Tautenburg Schmidt plates with the globular clusters M3 and M92 were measured on the APM facility in Cambridge, mainly for astrometric purposes. The data were used to derive the radial density profiles and the luminosity functions of these clusters. There is a good agreement of our results with formerly ones derived by other authors. In both clusters effects of mass segregation are observed.  相似文献   

Active mud volcanoes on the upper slope of the western Nile deep-sea fan—first results from the P362/2 cruise of R/V Poseidon   总被引：1，自引：0，他引：1  

Tomas Feseker  Kevin R. Brown  Cecile Blanchet  Florian Scholz  Marianne Nuzzo  Anja Reitz  Mark Schmidt  Christian Hensen 《Geo-Marine Letters》2010,30(3-4):169-186

In February 2008, cruise P362/2 was undertaken aboard R/V Poseidon to the Giza and North Alex mud volcanoes (MVs) on the upper slope of the western Nile deep-sea fan. Emitted fluids were strongly depleted in chloride and rich in hydrocarbons, predominantly of thermogenic origin. In-situ sediment temperature measurements indicate extremely high and moderate levels of activity for the North Alex MV and Giza MV, respectively, and suggest rapid changes from dormant to active stages. Both the physical properties of core sediments (e.g., color and magnetic susceptibility), and their assemblages of micro- and nannofossils point to different sources for the two mud volcanoes. Biostratigraphic dating suggests source depths of 2,100–2,450 mbsf for the Giza MV and 1,150–1,550 mbsf for the North Alex MV. Very high temperatures of up to 70°C in shallow sediments at the North Alex MV can be explained only if the fluid source were warmer and deeper than the sediment source.  相似文献   

Positions of extragalactic objects in the vicinity of M3 and M31 (5C3 radio field) and in the 5C1 radio field     

W. R. Dick  H. Lorenz  P. Notni  E. Schilbach  R.-D. Scholz  G. A. Richter 《Astronomische Nachrichten》1986,307(2):85-88

We have determined the positions of 65 compact extragalactic objects with magnitudes between 16^m and 21^m.7. The mean error of one position is about 0″.3 in α cos δ and in δ. Some hitherto unpublished redshifts are also listed.  相似文献   

Photometric and Spectroscopic Study of the Variable Star ET And     

E. Gerth  G. Scholz  K. P. Panov 《Astronomische Nachrichten》1984,305(2):79-86

The short-periodic spectroscopic and photometric variations and the frequency ratio of 1:2 suggest the existence of a triple system for ET And, though some serious difficulties continue to exist in explaining all observational facts. Assuming a triple, the observable star is the primary of a very close, ellipsoidal binary system. Under this assumption the star cannot be a main-sequence B9 star as usually assumed. It should be a star located in the domain of the horizontal branch stars in the HR diagram possessing a thin and expanding envelope. Spektroskopische und photometrische Beobachtungen des variablen Sterns ET And wurden in den Jahren 1981/82 ausgeführt. Zusätzlich zu der bekannten periodischen Variation der Radialgeschwindigkeit von 48.308 Tagen, hervorgerufen durch einen Begleiter und der wahrscheinlich von der Rotation des Sterns herrührenden photometrischen Periode von 1.61883 Tagen, existieren weitere periodische Variationen. So variieren die Radialgeschwindigkeiten mit einer Periode von 0.1989 Tagen und die photometrischen Werte mit der Hälfte dieses Wertes, d. h. mit 0.0994 Tagen. Die Minima der Helligkeit koinzidieren mit den Extrema der Radialgeschwindigkeiten. Die Radialgeschwindigkeitskurve weicht etwas von der Harmonischen ab; die Werte steigen rascher an, als sie abfallen. Das gleiche Verhalten liegt auch für den entsprechenden Teil der Lichtkurve vor. Die kurzperiodischen spektroskopischen und photometrischen Variationen und das Frequenzverhältnis 1:2 legen die Existenz eines Dreifachsystems für ET And nahe, obwohl für die Erklärung aller Beobachtungswerte einige ernste Schwierigkeiten fortbestehen. Vorausgesetzt der Stern sei ein Dreifachsystem, dann ist der beobachtete Stern die Hauptkomponente eines sehr engen ellipsoidalen Systems und kann nicht ein Hauptsequenz-B9-Stern sein, wie allgemein angenommen wird. Vermutlich handelt es sich bei ET And um einen Vertreter der Gruppe der Horizontalsterne im HR-Diagramm, welcher noch eine dünne, expandierende Hülle besitzt.  相似文献   

M. JASCHEK and H.-G. GROTH: Be Stafs. (IAU SymposiumN. 98). D. Reidel Publishing Company,Dordrecht-Holland/Boston USA, 1982, 523 Seiten,Preis 65, - Dfl.     

G. Scholz 《Astronomische Nachrichten》1983,304(2):95-95

  相似文献   

Preliminary reconstruction of sediment-source linkages for the past 6000 yr at the Petit Lac d'Annecy, France, based on mineral magnetic data   总被引：1，自引：0，他引：1  

John Dearing  Yuquan Hu  Pippa Doody  Peter A. James  Achim Brauer 《Journal of Paleolimnology》2001,25(2):245-258

An 8 m core from the central plain of the Petit Lac d'Annecy, France, two floodplain cores, river bedload sediments and several hundred soil samples from the catchment have been studied using magnetic techniques. The soils, mainly developed on limestones and local glacial tills, show widespread magnetic enhancement with higher ferrimagnetic concentrations and contents of SP grains than found in the lake sediments. Some soils show significant concentrations of canted antiferromagnetic minerals (mainly haematite). Using magnetic quotient parameters the surface soils are classified into four mineralogical types. The lake and floodplain sediment properties over the past 6000 yrs can largely be explained by the erosion and deposition of these sources, with a smaller superimposed biogenic (magnetosomes) signal. Derived sediment-source linkages allow the construction of several hypotheses about geomorphological changes in the catchment system: (i) the long-term erosion of high altitude unweathered substrates has gradually increased towards the present day; (ii) the erosion of high altitude soils has increased within the last 1000 yrs, possibly during the period of the 'Little Ice Age'; (iii) shifts towards an increased erosion of surface lowland soil occurred ~2000 and 1000 yrs ago and may be linked to an accelerated accretion of floodplain overbank deposits; (iv) there has been a significant storage of surface soil within floodplains, which leads to an underestimation of the importance of soil erosion in the lake sediment records; (v) the sediment transported by high magnitude, low frequency flood events has shifted in source from high altitude soils before ~1000 cal. yr BP to lowland and mid-altitude free draining soils after ~1000 cal. yr BP.  相似文献   

High-resolution sea ice in long-term global ocean GCM integrations     

Achim Stssel  Marion M. Stssel  Joong-Tae Kim 《Ocean Modelling》2007,16(3-4):206-223

The resolution of the sea-ice component of a coarse-resolution global ocean general circulation model (GCM) has been enhanced to about 22 km in the Southern Ocean. The ocean GCM is designed for long-term integrations suitable for investigations of the deep-ocean equilibrium response to changes in southern hemisphere high-latitude processes. The space and time scales of the high-resolution sea-ice component are commensurate with those of the resolution of satellite passive-microwave sea-ice data. This provides the opportunity for a rigorous evaluation of simulated sea-ice characteristics. It is found that the satellite-derived continuous high ice concentration of the interior winter ice pack can only be captured when vertical oceanic mixing is modified in a way that less local, intermittent convection occurs. Furthermore, the width and the variability of the coastal polynyas around the Antarctic continent and its ice shelves are best captured when some form of ice-shelf melting is accounted for. The width of the wintertime ice edge is reasonably reproduced, while its variability remains underestimated, closely following the coarse-grid pattern of the ocean model due to its high dependence on ocean temperature. Additional variability besides daily winds, e.g. in form of idealized tidal currents, improves the temporal and spatial ice-edge variability, while leads in the interior ice pack become more abundant, more in line with the fine-scale satellite-derived texture. The coast- or ice-shelf line is described on the fine grid based on satellite passive-microwave data. This method requires parts of a coarse coastal ocean grid cell to be covered by an inert layer of “fast ice” or “ice shelf”. Reasonable long-term global deep-ocean properties can only be achieved when these areas are not inert, i.e. are exposed to heat flux and ice growth, or when the vertical mixing parameterization allows for excessive open-ocean convection. The model area exposed to cold high-latitude atmospheric conditions thus being most decisive for a realistic representation of the long-term deep-ocean properties, suggests that high-latitude coastlines are definitely in need of being represented at high resolution, including ice sheets and their effects on the heat and freshwater flux for the ocean.  相似文献