Recent discoveries of supersoft X‐ray sources in M 31     

M. Henze  W. Pietsch  F. Haberl  G. Sala  M. Hernanz  D. Hatzidimitriou  A. Rau  D.H. Hartmann  J. Greiner  M. Orio  H. Stiele  M.J. Freyberg 《Astronomische Nachrichten》2010,331(2):193-196

Classical novae (CNe) have recently been reported to represent the major class of supersoft X‐ray sources (SSSs) in the central area of our neighbouring galaxy M 31. This paper presents a review of results from recent X‐ray observations of M 31 with XMM‐Newton and Chandra. We carried out a dedicated optical and X‐ray monitoring program of CNe and SSSs in the central area ofM 31. We discovered the first SSSs in M 31 globular clusters (GCs) and their connection to the very first discovered CN in a M 31 GC. This result may have an impact on the CN rate in GCs. Furthermore, in our optical and X‐ray monitoring data we discovered the CN M3 1N 2007‐11a, which shows a very short SSS phase of 29–52 days. Short SSS states (durations ≤ 100 days) of CNe indicate massive white dwarfs (WDs) that are candidate progenitors of supernovae type Ia. In the case of M31N 2007‐11a, the optical and X‐ray light curves suggest a binary containing a WD with M_WD > 1.0 M_⊙. Finally, we present the discovery of the SSS counterpart of the CN M31N 2006‐04a. The X‐ray light curve of M31N 2006‐04a shows short‐time variability, which might indicate an orbital period of about 2 hours (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

SIMS U-Pb dating of micro-zircons in the lunar meteorites Dhofar 1528 and Dhofar 1627     

Bidong Zhang  Yangting Lin  Jialong Hao  Devin L. Schrader  Meenakshi Wadhwa  Randy L. Korotev  William K. Hartmann  Audrey Bouvier 《Meteoritics & planetary science》2023,58(10):1540-1551

About half of the lunar meteorites in our collections are feldspathic breccias. Acquiring geochronologic information from these breccias is challenging due to their low radioactive-element contents and their often polymict nature. We used high-spatial-resolution (5 μm) NanoSIMS (nanoscale secondary ion mass spectrometry) U-Pb dating technique to date micro-zircons in the lunar feldspathic meteorites Dhofar 1528 and Dhofar 1627. Three NanoSIMS dating spots of two zircon grains from Dhofar 1528 show a discordia with an upper intercept at 4354 ± 76 Ma and a lower intercept at 332 ± 1407 Ma (2σ, MSWD = 0.01, p = 0.91). Three spots of two zircon grains in Dhofar 1627 define a discordia with an upper intercept at 3948 ± 30 Ma and a lower intercept at 691 ± 831 Ma (2σ, MSWD = 0.40, p = 0.53). Both samples likely experienced shock metamorphism caused by impacts. Based on the clastic nature, lack of recrystallization and the consistent U-Pb and Pb-Pb dates of the zircons in Dhofar 1528, the U-Pb date of 4354 Ma is interpreted as the crystallization age of its Mg-suite igneous precursor. Some of the Dhofar 1627 zircons show poikilitic texture, a crystallization from the matrix impact melt, so the U-Pb date of 3948 Ma corresponds to an impact event, likely the Imbrium basin-forming event. These data are the first radiometric ages for these two meteorites and demonstrate that in situ (high spatial resolution) U-Pb dating has potential for extracting geochronological information about igneous activities and impact events from lunar feldspathic and polymict breccias.  相似文献   

Chemistry of the heavily urbanized Bagmati River system in Kathmandu Valley, Nepal: export of organic matter, nutrients, major ions, silica, and metals     

Maya P. Bhatt  William H. McDowell  Kevin H. Gardner  Jens Hartmann 《Environmental Earth Sciences》2014,71(2):911-922

Water quality in less-developed countries is often subject to substantial degradation, but is rarely studied in a systematic way. The concentration and flux of major ions, carbon, nitrogen, silicon, and trace metals in the heavily urbanized Bagmati River within Kathmandu Valley, Nepal, are reported. The concentrations of all chemical species increased with distance downstream with the exceptions of protons and nitrate, and showed strong relationships with population density adjacent to the river. Total dissolved nitrogen (TDN), dominated by NH₄, was found in high concentrations along the Bagmati drainage system. The export of dissolved organic carbon (DOC) and TDN were 23 and 33 tons km^?2 year^?1, respectively, at the outlet point of the Kathmandu Valley, much higher than in relatively undeveloped watersheds. The cationic and silica fluxes were 106 and 18 tons km^?2 year^?1 at the outlet of the Bagmati within Kathmandu Valley, and 36 and 32 tons km^?2 year^?1 from the relatively pristine headwater area. The difference between headwaters and the urban site suggests that the apparent weathering flux is three times higher than the actual weathering rate in the heavily urbanized Bagmati basin. Fluxes of cations and silica are above the world average, as well as fluxes from densely populated North American and European watersheds. End-member composition of anthropogenic sources like sewage or agricultural runoff is needed to understand the drivers of this high rate of apparent weathering.  相似文献   

Turbulence in Class 0 and I protostellar envelopes     

D. Ward-Thompson  L. Hartmann  D. J. Nutter 《Monthly notices of the Royal Astronomical Society》2005,357(2):687-690

We estimate the levels of turbulence in the envelopes of class 0 and I protostars using a model based on measurements of the peak separation of double-peaked asymmetric line profiles. We use observations of 20 protostars of both class 0 and I taken in the  HCO⁺(J = 3 → 2)  line that show the classic double-peaked profile. We find that some class 0 sources show high levels of turbulence, whilst others demonstrate much lower levels. In class I protostars, we find predominantly low levels of turbulence. The observations are consistent with a scenario in which class 0 protostars form in a variety of environments and subsequently evolve into class I protostars. The data do not appear to be consistent with a recently proposed scenario in which class 0 protostars can only form in extreme environments.  相似文献   

Gamma-rays from neutron stars     

D. H. Hartmann 《Astronomy and Astrophysics Review》1995,6(3):225-270

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Blocky craters: Implications about the lunar megaregolith     

T. W. Thompson  W. J. Roberts  W. K. Hartmann  R. W. Shorthill  S. H. Zisk 《Earth, Moon, and Planets》1979,21(3):319-342

Radar, infrared, and photogeologic properties of lunar craters have been studied to determine whether there is a systematic difference in blocky craters between the maria and terrae and whether this difference may be due to a deep megaregolith of pulverized material forming the terra surface, as opposed to a layer of semi-coherent basalt flows forming the mare surface. Some 1310 craters from about 4 to 100 km diameter have been catalogued as radar and/or infrared anomalies. In addition, a study of Apollo Orbital Photography confirmed that the radar and infrared anomalies are correlated with blocky rubble around the crater.Analysis of the radar and infrared data indicated systematic terra—mare differences. Fresh terra craters smaller than 12 km were less likely to be infrared and radar anomalies than comparable mare craters: but terra and mare craters larger than 12 km had similar infrared and radar signatures. Also, there are many terra craters which are radar bright but not infrared anomalies.Our interpretation of these data is that while the maria are rock layers (basaltic flow units) where craters eject boulder fields, the terrae are covered by relatively pulverized megaregolith at least 2 km deep, where craters eject less rocky rubble. Blocky rubble, either in the form of actual rocks or partly consolidated blocks, contributes to the radar and infrared signatures of the crater. However, aging by impacts rapidly destroys these effects, possibly through burial by secondary debris or by disintegration of the blocks themselves, especially in terra regions.PSI Contribution No. 110.  相似文献   

Paleocratering of the Moon: Review of post-Apollo data   总被引：1，自引：0，他引：1  

William K. Hartmann 《Astrophysics and Space Science》1972,17(1):48-64

As a result of the dating of lunar samples, we are in a position to utilize the lunar surface as a recorder of environmental conditions in the Earth-Moon neighborhood in the past. Plots of crater density vs rock age at different lunar landing sites can be used to date unexplored lunar provinces. These plots also demonstrate evolution in the population of planetesimals that struck the Moon. Prior to 4.1 aeons ago, the cratering rate on the Moon was at least 10³ times the present rate, and the rate declined with a half-life less than 8×10⁷ yr. During the interval from 4.1 to 3.2 aeons ago, the number of planetesimals showed an exponential decay with a half-life about 3×10⁸ yr, corresponding to sweep-up of particles from solar orbits somewhat similar to those of Apollo asteroids. A more nearly constant cratering rate applied in the last three aeons. These data indicate that the Moon displays at least the final stages of an ancient accretion process; they also set certain conditions on possible capture processes relating to the Moon's origin. Pre-Apollo expectations that the Moon would provide a Rosetta Stone for interpreting solar system history and planet formation thus appear justified.Paper given at Philadelphia meeting of American Association for Advancement of Science, December, 1971.  相似文献   

‘A Case Study on a Polar Cold Air Outbreak over Fram Strait using a Mesoscale Weather Prediction Model’     

Ulrike?WackerEmail author  K.?V.?Jayaraman?Potty  Christof?Lüpkes  J?rg?Hartmann  Matthias?Raschendorfer 《Boundary-Layer Meteorology》2005,117(2):301-336

The mesoscale weather prediction model ’Lokal-Modell’ (LM) of the Deutscher Wetterdienst is applied to the situation of an Arctic cold air outbreak in the Fram Strait region in April 1998. Observations are available from a flight along 5⁰E carried out during the ARTIST campaign. Initial and time-dependent boundary data for the simulation are taken from a larger scale operational model system. Using the standard configuration of LM, the simulation reproduced the propagation of cold air and the characteristic structure of the atmospheric boundary layer (ABL) in fair agreement with the observations. However, a detailed comparison revealed three basic problems. Firstly, there is evidence that the available data on sea-ice conditions were insufficient approximations to the true state for several reasons. A modification of the sea-ice data towards observations revealed that parts of the discrepancies were due to the original sea-ice data. Secondly, a control run with the model in its standard configuration shows an insufficient warming of the ABL downstream of the ice edge due to underestimation of surface heat fluxes. A simple modification of the approach for the scalar roughness length resulted in the strongest benefit, while comparative studies showed only a slight sensitivity to different types of parametrisation of turbulent mixing or the inclusion of an additional moist convection parametrisation. Thirdly, in all the simulations the deepening of the convective ABL downstream of the ice edge is weaker than observed. This may be partly due to the thermal stratification above the ABL in the analysis data, which is more stable than observed; but it may also be a hint to the fact that processes near the inversion are insufficiently parametrised in mesoscale models with resolutions as used in LM. The simulated cloud layer in the convective ABL is similar to that observed with respect to condensate content, a sharply defined cloud top, a diffuse lower bound, and continuous light precipitation.  相似文献   

Moon: Origin and evolution of multi-ring basins   总被引：2，自引：0，他引：2  

W. K. Hartmann  C. A. Wood 《Earth, Moon, and Planets》1971,3(1):3-78

This paper summarizes current data and new observations on lunar basin systems. Parts 1–4 review earlier literature and give new crater-counts used to reconstruct basin histories. Among the results are: basin rings are defined by faults, hills, craters, and/or wrinkle ridges; all of these are inter-related; 2 plays a special role in the ratios of ring diameters; flooding occurred in many basins prior to the formation of the familiar front-side maria; 3 km is a typical depth of lava flooding in basins. Parts 5–11 interpret these results in terms of origin and evolution of basins. Polar concentrations of basins and old, large craters are found (Figures 28 and 29). Basins originated by impacts of very early planetesimals left over from or created during formation of the Moon (6). Concentric fractures were produced by the impacts. Concentric rings developed along fractures during subsequent sagging of the basin into partially melted substrata, along the lines of theory and experiments by Lance and Onat (1962) (Figures 36 and 37). There is marginal empirical evidence that some rings formed significantly after their basins (8). The structure of specific rings depended on the nature of volcanic products extruded. Wrinkle ridges, peak-rings, rings of craters, concentric graben, and central peaks are all consequences of basin-forming evolutionary processes (9, Figure 41), Flooding by lava was a final stage in basin evolution. Lava extruded from concentric ring-faults, wrinkle ridges, and crater and basin rims (10). Mascons are directly correlated with the amount of mare lava, but not correlated with basin age or morphology (11). Section 12 summarizes the results and compares them to those of other authors.  相似文献   

Does crater “saturation equilibrium” occur in the solar system?     

William K. Hartmann 《Icarus》1984,60(1):56-74

Similarity is found in crater densities on the most heavily cratered surfaces throughout the solar system. This is hypothesized to result from a steady-state “saturation equilibrium” being approached or achieved by cratering processes. This hypothesis conflicts with some recent interpretations. However, it accounts for (1) a similarity in maximum relative crater density, below certain theoretically predicted values, on all heavily cratered surfaces; (2) a leveling off at this same relative density among 100-m scale (secondary?) craters in populations on lunar maria and other sparsely cratered lunar surfaces; (3) the approximate uniformity of maximum relative densities on Saturn satellites (in spite of dramatic variations predicted from nonsaturation models assuming heliocentric impactors). The lunar frontside upland crater population, sometimes described as a well-preserved production function useful for interpreting other planetary surfaces, is found not to be a production function. It was modified by intercrater plains formed (at least partly) by early upland basaltic lava flooding, recently confirmed spectrophotometrically. Consistent with this, counts in “pure uplands” (those lacking intercrater plains) match the proposed saturation equilibrium density. Variations among large (D > 64 km) crater populations are found, but these may involve several hypothesized mechanisms that rapidly obliterate large craters, especially on icy surfaces. Recent models, in which different populations of interplanetary bodies hit different planets, need further appraisal.  相似文献