Probing the circumstellar structures of T Tauri stars and their relationship to those of Herbig stars     

Jorick S. Vink  Janet E. Drew  Tim J. Harries  René D. Oudmaijer  Yvonne Unruh 《Monthly notices of the Royal Astronomical Society》2005,359(3):1049-1064

We present Hα spectropolarimetry observations of a sample of 10 bright T Tauri stars, supplemented with new Herbig Ae/Be star data. A change in the linear polarization across Hα is detected in most of the T Tauri (9/10) and Herbig Ae (9/11) objects, which we interpret in terms of a compact source of line photons that is scattered off a rotating accretion disc. We find consistency between the position angle (PA) of the polarization and those of imaged disc PAs from infrared and millimetre imaging and interferometry studies, probing much larger scales. For the Herbig Ae stars AB Aur, MWC 480 and CQ Tau, we find the polarization PA to be perpendicular to the imaged disc, which is expected for single scattering. On the other hand, the polarization PA aligns with the outer disc PA for the T Tauri stars DR Tau and SU Aur and FU Ori, conforming to the case of multiple scattering. This difference can be explained if the inner discs of Herbig Ae stars are optically thin, whilst those around our T Tauri stars and FU Ori are optically thick. Furthermore, we develop a novel technique that combines known inclination angles and our recent Monte Carlo models to constrain the inner rim sizes of SU Aur, GW Ori, AB Aur and CQ Tau. Finally, we consider the connection of the inner disc structure with the orientation of the magnetic field in the foreground interstellar medium: for FU Ori and DR Tau, we infer an alignment of the stellar axis and the larger magnetic field direction.  相似文献   

The copper-nickel concentration log: A tool for stratigraphic interpretation within the ultramafic and basal zones of the stillwater complex, Montana     

L.J. Drew  W.J. Bawiec  N.J Page  J.H. Schuenemeyer 《Journal of Geochemical Exploration》1985,23(2):117-137

An analogue to the electric well log was devised for copper-nickel concentration drill-hole data from the Basal and lower part of the Ultramafic zones of the Stillwater Complex using automated data processing. The copper-nickel concentration logs graphically represent intensity (concentration) values that reflect the distribution of the elements in sulfide and silicate minerals. Four major patterns are recognized by their characteristic variations in copper and nickel intensity: (1) relatively flat, low-level copper-intensity signatures associated with arcuate nickel-intensity patterns that correlate with rocks in the Peridotite member of the Ultramafic zone; (2) arcuate or bulb-like patterns of copper and nickel intensity that correlate closely with the Basal bronzite cumulate member of the Basal zone; (3) complex patterns consisting of intervals of low-intensity copper and moderate-intensity nickel, spikes of high nickel and copper intensity, and high copper intensity associated with low nickel intensity that correlate respectively with cordierite-pyroxene hornfels, massive sulfide, norites and mineralized diabase dikes in the Basal norite member; and (4) large intervals of extremely low copper and nickel intensity that correlate with quartz-orthopyroxene hornfels. The recognition and interpretation of these patterns allow two- and three-dimensional stratigraphic and lithologic reconstructions to be done by means of concentration-log correlations instead of variable quality lithologic logging.  相似文献   

Book reviews     

Crimes  Peter B.  Roseboom  Eugene H.  Drew  Lawrence J. 《Natural Resources Research》1994,3(3):250-252

Natural Resources Research -  相似文献   

Zipf’s Law: A Viable Geological Paradigm?     

Daniel?F.?MerriamEmail author  Lawrence?J.?Drew  John?H.?Schuenemeyer 《Natural Resources Research》2004,13(4):265-271

Zipfs Law originally was proposed as a guide to a statistical distribution in social studies. The law describes a relationship between size and rank of discrete phenomena. It is a variant of Paretos 1927 Law known as the 80/20 rule and is similar to Bodes Law in concept. The relationship described by Zipfs Law is a succession of order data with the largest followed by half the size for the next largest, which in turn, the next is half that size, and so on. In geology, it has been used with moderate success in resource assessment of mining and petroleum. In essence, it predicts how many entities of a certain size may be left in a sequence of decreasing size assuming the largest has been ascertained. Examples of applications would be plotting the rank and size of ore deposits or oil fields to determine how many deposits remained undiscovered and their size. After a flurry of papers in the 1970s and 1980s, application of the law apparently either was successful and thus not reported in way the literature or was determined to be ineffectual and its use discontinued, but either way the law lapsed into obscurity. Examples of oil- and gas-field size in Kansas, the occurrence of historic earthquakes that affected the state, and size of anticlines (plains-type folds) are presented to illustrate application and limits of Zipfs Law.  相似文献   

Characteristics of Water-Well Yields in Part of the Blue Ridge Geologic Province in Loudoun County,Virginia     

Sutphin  David M.  Drew  Lawrence J.  Schuenemeyer  John H.  Burton  William C. 《Natural Resources Research》2001,10(1):1-19

Loudoun County, Virginia, which is located about 50 km to the west of Washington, DC, was the site of intensive suburban development during the 1980s and 1990s. In the western half of the county, the source of water for domestic use has been from wells drilled into the fractured crystalline bedrock of the Blue Ridge Geologic Province. A comprehensive digital database that contains information on initial yield, location, depth, elevation, and other data for 3651 wells drilled in this 825.5-km² area was combined with a digital geologic map to form the basis for a study of geologic and temporal controls on water-well yields. Statistical modeling procedures were used to determine that mean yields for the wells were significantly different as a function of structural setting, genetic rock type, and geologic map unit. The Bonferroni procedure then was used to determine which paired comparisons contributed to these significant differences. The data were divided into 15 temporal drilling increments to determine if the time-dependent trends that exist for the Loudoun County data are similar to those discovered in a previous study of water-well yields in the Pinardville 7.5-min quadrangle, New Hampshire. In both regions, trends, which include increasing proportions of very low yield wells and increasing well depths through time, and the counterintuitive result of increasing mean well yields through time, were similar. In addition, a yield-to-depth curve similar tothat discovered in the Pinardville quadrangle was recognized in this study. Thus, the temporal model with a feed-forward-loop mechanism to explain the temporal trends in well characteristics proposed for the New Hampshire study appears to apply to western Loudoun County.  相似文献   

Hydrogeologic Significance of the Association Between Well-Yield Variography and Bedrock Geologic Structures,Pinardville Quadrangle,New Hampshire     

Drew  Lawrence J.  Karlinger  Michael R.  Schuenemeyer  John H.  Armstrong  Thomas R. 《Natural Resources Research》2003,12(1):79-91

The spatial continuity of water-well yields is associated with the fracture properties of the crystalline basement rocks in the Pinardville quadrangle, New Hampshire. The analysis reported in this paper expands upon previous work of a study of 939 wells in the quadrangle. This expanded analysis was performed on updated and new geologic map data, new fracture-set data and analyses, and a set of water-well yields that was expanded by 752 newly located wells. Variogram mapping of the water-well yields formed the basis for the synthesis of the spatial continuity in well yield with the geological data. A variety of associations were determined that directly relate the spatial properties of well yields to the characteristics and structure of the crystalline bedrocks in the quadrangle.  相似文献   

Radiation-driven winds from luminous accretion discs     

Daniel Proga  James M. Stone  & Janet E. Drew 《Monthly notices of the Royal Astronomical Society》1998,295(3):595-617

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The evolved B[e] star HD 87643: observations and a radiation-driven disc wind model for B[e] stars     

René D. Oudmaijer  Daniel Proga  Janet E. Drew  & Dolf de Winter 《Monthly notices of the Royal Astronomical Society》1998,300(1):170-182

New high-resolution spectroscopic and medium-resolution spectropolarimetric data of the B[e] star HD 87643 are presented, complemented with optical broad- and narrow-band imaging. The spectrum of HD 87643 exhibits the hybrid characteristics well known to be representative of the group of B[e] stars; a fast wind with an expansion velocity in excess of 1000 km s⁻¹ is measured in the hydrogen and helium lines, while a slower component is traced by lower excitation lines and forbidden lines. Clues to the geometry of the rapidly expanding circumstellar shell are provided by the startling polarization changes across Hα. Comparison with published schematic calculations indicates that the polarizing material is located in a slowly rotating, expanding disc structure. A hydrodynamical model is then presented, the results of which are consistent with the original two-wind concept for B[e] stars, and which exhibits kinematic properties that may well explain the observed spectral features in HD 87643. The model calculations use as input a B star undergoing mass loss, surrounded by an optically thick disc. The resulting configuration consists of a fast polar wind from the star and a slowly expanding disc wind. The model also predicts that the stellar wind at intermediate latitudes is slower and denser than in the polar region.  相似文献   

Oil and gas forecasting. Reflections of a petroleum geologist: L. J. Drew Oxford University Press; ISBN 019 5061705; Price: £40.00     

L. J. Drew 《Marine and Petroleum Geology》1991,8(4)

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Photosynthesis, Respiration and other Factors Influencing the Growth of Laminar/a ochroleuca PYL below 50 Metres in the Straits of Messina     

Edward A.  Drew  John F.  Ireland  Colin  Muir  William A. A.  Robertson John D.  Robinson 《Marine Ecology》1982,3(4):335-355

Abstract. The population of Laminaria ochroleuca in the current swept Straits of Messina was investigated regarding its age structure and photosynthesis. Age structure appears to be determined by sporadic recruitment and the limitation of growth due to peak currents decapitating older plants, which is corroborated by drag force resistance calculations. The calculation of a carbon budget from measurements of photosynthesis and dark respiration both in the laboratory and in situ shows that L. ochroleuca cannot satisfy its carbon demands for growth and respiration at 50 m depth and no satisfactory explanation can be given for its rapid growth between 50 and 100 m.  相似文献