Time Analysis of the CO+ COMA OF COMET P/HALLEY BY IMAGE PROCESSING TECHNIQUES     

Voelzke  Marcos Rincon  Schlosser  Wolfgang  Schmidt-Kaler  Theodor 《Astrophysics and Space Science》1997,250(1):35-51

Photographic and photoelectric observations of comet P/Halley's ion gas coma from CO⁺ at 4250 ? were part of the Bochum Halley Monitoring Program, conducted from 1986 February 17, to April 17 at the European Southern Observatory on La Silla (Chile). In this spectral range it is possible to watch the continuous formation, motion and expansion of plasma structures. To observe the morphology of these structures 32CO⁺ photos (glass plates) from P/Halley's comet have been analysed. They have a field of view of 28°.6× 28°.6 and were obtained from 1986 March 29, to April 17 with exposure times between 20 and120 minutes. All photos were digitized with a PDS 2020 GM (Photometric Data System) microdensitometer at the Astronomisches Institut derWestf?lischen Wilhelms-Universit?t in Münster (one pixel= 25 μm × 25 μm ≈ 46′.88×46′.88). After digitization the data were reduced to relative intensities, and the part with proper calibrations were also converted to absolute intensities, expressed in terms of column densities using the image data systems MIDAS (Munich Image Data Analysis System; ESO – Image Processing Group, 1988) and IHAP (Image Handling And Processing; Middleburg, 1983). With the help of the Stellingwerf-Theta-Minimum-Method (Stellingwerf, 1978) a period of (2.22 ± 0.09) days results from analysis of structures in the plasma-coma by subtracting subsequent images. This method is also compared with the Fourier method. There may be a second cycle with a period of about 3.6 days. The idea behind subtracting subsequent images is that rotation effects are only 10% phenomena on gas distribution. Difference images are than used to suppress the static component of the gas cloud. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The distribution of atomic gas and dust in nearby galaxies – II. Further matched-resolution Very Large Array H i and SCUBA 850-μm images     

H. C. Thomas  L. Dunne  D. A. Green †  M. S. Clemens  P. Alexander  S. Eales 《Monthly notices of the Royal Astronomical Society》2004,348(4):1197-1207

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The unusual distribution of molecular gas and star formation in Arp 140     

H. Cullen  P. Alexander  D. A. Green  M. Clemens  K. Sheth 《Monthly notices of the Royal Astronomical Society》2007,374(4):1185-1197

We investigate the atomic and molecular interstellar medium and star formation of NGC 275, the late-type spiral galaxy in Arp 140, which is interacting with NGC 274, an early-type system. The atomic gas (H  i ) observations reveal a tidal tail from NGC 275 which extends many optical radii beyond the interacting pair. The H  i morphology implies a prograde encounter between the galaxy pair approximately ∼1.5 × 10⁸ yr ago. The Hα emission from NGC 275 indicates clumpy irregular star formation, clumpiness which is mirrored by the underlying mass distribution as traced by the K _s-band emission. The molecular gas distribution is striking in its anticorrelation with the H  ii regions. Despite the evolved nature of NGC 275's interaction and its barred potential, neither the molecular gas nor the star formation is centrally concentrated. We suggest that this structure results from stochastic star formation leading to preferential consumption of the gas in certain regions of the galaxy. In contrast to the often-assumed picture of interacting galaxies, NGC 275, which appears to be close to merger, does not display enhanced or centrally concentrated star formation. If the eventual merger is to lead to a significant burst of star formation it must be preceded by a significant conversion of atomic to molecular gas as at the current rate of star formation all the molecular gas will be exhausted by the time the merger is complete.  相似文献   

Gas in early-type galaxies: cross-fuelling in late-type–early-type pairs?     

H. Cullen  P. Alexander  M. Clemens 《Monthly notices of the Royal Astronomical Society》2006,366(1):49-57

We present  ¹²CO ( J = 1–0)  and  ¹²CO ( J = 2–1)  observations of eight early-type galaxies, forming part of a sample of interacting galaxies, each consisting of one late- and one early-type system. All of the early-type galaxies observed are undetected in CO to low levels, allowing us to place tight constraints on their molecular gas content. Additionally, we present H  i absorption data for one system. The implications for possible gas transfer from the late- to the early-type galaxy during the interaction are discussed.  相似文献   

RAM-Pressure Stripping of a Galaxy's ISM     

M. Clemens  P. Alexander  D. Green 《Astrophysics and Space Science》2001,276(2-4):451-458

NGC 4485 is a late-type galaxy moving through the very extended HI envelope of its companion, NGC 4490. NGC 4485 is undetected in HI,CO and IRAS wavebands, but a peak at all of these frequencies is seen displaced from the optical disk. HI data show a prominent bow-shock ahead of this displaced gas. It is argued that almost the entire ISM, including molecular clouds, has been stripped from this galaxy byram-pressure, and that it will emerge from the encounter with very little star forming potential. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Observation of a variable,ZZ Ceti white dwarf: GD154     

B. Pfeiffer  G. Vauclair  N. Dolez  M. Chevreton  J. R. Fremy  G. Herpe  M. Barstow  S. J. Kleinman  T. K. Watson  J. A. Belmonte  S. O Kepler  A. Kanaan  O. Giovannini  R. E. Nather  D. E. Winget  J. Provencal  J. C. Clemens  P. Bradley  J. Dixson  A. D. Grauer  G. Fontaine  P. Bergeron  F. Wesemael  C. F. Claver  T. Matzeh  E. Leibowitz  P. Moskalik 《Astrophysics and Space Science》1993,210(1-2):201-204

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Quaternary palaeoceanographic changes in the northern South China Sea (ODP Site 1146): radiolarian evidence     

Rujian Wang  Steven Clemens  Baoqi Huang  Muhong Chen 《第四纪科学杂志》2003,18(8):745-756

The abundance and accumulation rates of siliceous microfossils in the northern South China Sea, including radiolarians, diatoms and sponge spicules, increased during most glacial intervals within the past 1100 kyr. Similar trends are observed in the index of thermocline surface radiolarians (TSR), diatom accumulation rates (DAR), charcoal accumulation rates (CAR) and the abundance of radiolarian species Cycladophora davisiana davisiana. Decreasing sea‐surface temperature accompanied by increased seasonality since 900 ka is indicated by a decline in the tropical radiolarian assemblage, including Tetrapyle octacantha and Octopyle stenozona, and by an increase in the subtropical assemblage, including Pterocorys zancleus, Peromelissa phalacra and Ommatartuts tetrathalamus tetrathalamus. Rapid increases at about 800 to 700 ka of siliceous microfossils, charcoal, subsurface and intermediate radiolarians, as well as the TSR index and the DAR, imply a fundamental shift in climate and a shoaling thermocline. Although these fundamental changes in the silicious fauna and flora of the South China Sea take place within the context of a developing 100‐kyr cycle, they do not change in step with changing sea‐level as indicated by marine δ¹⁸O. This is most clearly illustrated by the step‐like increase in silica accumulation (radiolaria, diatoms and sponge spicules) at 680 ka. Rather, these fundamental changes probably reflect intensified surface productivity associated with enhanced East Asian winter‐monsoon circulation. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

A sequential ensemble prediction system at convection-permitting scales     

Marco Milan  Dirk Schüttemeyer  Theresa Bick  Clemens Simmer 《Meteorology and Atmospheric Physics》2014,123(1-2):17-31

A sequential data assimilation approach (SAM) that incorporates elements of particle filtering with resampling (SIR, Sequential Importance Resampling) is introduced. SAM is applied to the COSMO-DE-EPS, which is an ensemble prediction system for weather forecasting on convection-permitting scales. At the convective scale and beyond, the atmosphere increasingly exhibits non-linear state space evolutions. For an ensemble-based data assimilation system, this requires both an adequate metric that quantifies the distance between the observed atmospheric state and the states simulated by the ensemble members, and a methodology to counteract filter degeneracy, i.e. the collapse of the simulated state space. We, therefore, propose a combination of resampling, which accounts for simulated state space clustering, and nudging. SAM differs from the classical SIR approach mainly in the weighting applied to the ensemble members. By keeping cluster representatives during resampling, the method maintains the potential for non-linear system state development. With three convective case studies, we demonstrate that SAM improves forecast quality compared with the control EPS (EPS without data assimilation) for the first 5–6 h of forecast.  相似文献   

Temperature-dependent leaching of chemical elements from mineral water bottle materials     

Clemens Reimann  Manfred Birke  Peter Filzmoser 《Applied Geochemistry》2012

It is well established that minute amounts of chemical elements will leach from bottle materials (glass or PET – polyethylene terephthalate) to water stored in such bottles. This study investigated whether leaching increases with storage temperature. For glass bottles this is clearly the case for a long list of elements: Ag, Al, As, B, Ba, Ca, Co, Cr, Cs, Cu, Fe, Ga, Ge, K, La, Li, Mg, Mo, Na, Ni, Pb, Rb, Sb, Se, Sn, Sr, Ti, U, V, W and Zr. However, for glass bottles drinking water maximum admissible concentration values as defined by European authorities are not exceeded even after 1 week of leaching at 80 °C. The critical temperature limit where leaching substantially increases for many elements appears to be 45 °C. For PET bottles, Sb is the only element where leaching is observed at all temperatures and again leaching strongly increases at 45 °C. For PET bottles Sb concentrations observed in water after 1 week storage at 80 °C reach almost four times the maximum admissible concentration values for drinking water but do not exceed the relevant higher limit for food (including water) packaged in PET.  相似文献   

Quaternary clay mineralogy in the northern South China Sea (ODP Site 1146)     

Zhifei?LiuEmail author  Trentesaux?Alain  Steven?C.?Clemens  Pinxian?Wang 《中国科学D辑(英文版)》2003,46(12):1223-1235

Measurement of clay mineralogy at ODP Site 1146 in the northern South China Sea (SCS) indicates that illite, chlorite, and kaolinite contents increased during glacials and smectite content increased during interglacials. The smectite/(illite+chlorite) ratio and the smectite abundance were determined as mineralogical indicators for the East Asian monsoon evolution. At a 10 ka timescale, prevailing southeasterly surface oceanic currents during interglacials transported more smectite from the south and east areas to the north, showing a strengthened summer monsoon circulation, whereas dominated counter-clockwise surface currents during glacials carried more illite and chlorite from Taiwan as well as from the Yangtze River via the Luzon Strait to the northern SCS, indicating a strongly intensified winter monsoon. Based on a 100 ka timescale, a linear correlation between the smectite/(illite+chlorite) ratio and the sedimentation rate reflects that the winter monsoon has prevailed in the northern SCS in the intervals 2000–1200 ka and 400–0 ka and the summer monsoon did the same in the interval 1200–400 ka. The evolution of the summer monsoon provides an almost linear response to the summer insolation of Northern Hemisphere, implying an astronomical forcing of the East Asian monsoon evolution.  相似文献