New upper limits on Jovian X rays     

L.E. Peterson  H.S. Hudson  V. Tsikoudi 《Icarus》1976,29(3):419-425

The UCSD X-ray telescope on OSO-3 scanned Jupiter for 33 days during February and March 1968. We have searched the data for a steady Jovian flux, and for a burst component at times of decametric radio bursts. Neither component was detected at a sensitivity of ～0.1 photon (cm²sec)^?1 for hv > 7.7 keV. At 4.4AU, the 3σ upper limits correspond to X-ray luminosities of 7.4 × 10¹⁹ ergs sec^?1 for the steady component, and 2 × 10²⁰ ergs sec^?1 for the burst component. The observations occurred during a period of high solar activity, during which three sudden-commencement magnetic storms were observed at Earth. We compare the upper limits with several different calculations of the expected flux levels, and conclude that major improvements in X-ray detection techniques will be required before Jovian X rays can be detected with near-Earth observations.  相似文献   

Origin and evolution of the solar system,II     

Hannes Alfvén  Gustaf Arrhenius 《Astrophysics and Space Science》1970,9(1):3-33

(7)Formation of celestial bodies. The basic concepts of the accretional process are discussed, and the inadequacy of the contractional model is pointed out. A comparison is made between the general pre-planetary state on the one hand and the present state in the asteroidal region on the other. A model for accretion of resonance-captured grains leading to the formation of resonance-captured planets and satellites is suggested.(8)Spin and accretion. The relation between the accretional process and the spin of planets is analyzed.(9)Accretion of planets and satellites. It is shown that jet streams are a necessary intermediate stage in the formation of celestial bodies. The time sequence of planet formation is analyzed, and it is shown that the newly accreted bodies have a characteristic internal heat structure; the cases of the Earth and the Moon are considered in detail. A region of high initial temperature is found at 0.4 of the present Earth radius, whereas the culminating temperature of the Moon is near its present surface. An accretional heat wave is found to proceed outwards, and may produce the observed differentiation features.  相似文献   

Distribution,Abundance, and Habitat Characterization of the Saltmarsh Topminnow, <Emphasis Type="Italic">Fundulus jenkinsi</Emphasis> (Everman 1892)     

John D. Lopez  Mark S. Peterson  Jake Walker  Gretchen L. Grammer  Mark S. Woodrey 《Estuaries and Coasts》2011,34(1):148-158

The saltmarsh topminnow (Fundulus jenkinsi) is federally listed as a Species of Concern due to a its rarity, impacts from human activities, and lack of information on its biology and ecology. From 2007 through 2008, we used Breder traps to fish the marsh edge on a falling tide in four regions from Louisiana through the Florida panhandle during winter, spring, and summer periods. Out of 2,108 Breder traps deployed, 661 F. jenkinsi were collected as far east as Escambia Bay, Florida, with Weeks Bay, National Estuarine Research Reserve (NERR), Alabama, yielding the highest F. jenkinsi abundance. Principal component analysis (PCA) was used to ordinate physical–chemical data into two meaningful components: a geomorphic axis (water depth, bank slope, and plant stem density) and a seasonal/spatial axis of species occurrence (water temperature, salinity, and turbidity). PCA showed a higher mean catch-per-unit-effort (CPUE) in environments comprised of low to moderate stem density (<25 stems/0.25 m⁻²), depth (<25 cm), bank slope (<15°), turbidity (<30 NTU), and salinity (<16) coupled with spring and early summer water temperatures (>15°C). F. jenkinsi CPUE was significantly higher in Spartina cynosuroides marsh edge compared with five other habitat types, even though it was one of the least sampled habitats. This species appears to be collected more frequently and in higher CPUE in small dendritic creeks off of main channels than suggested by our previous work in main channel edge habitat. This suggests that small creeks are important vectors for marsh access and supports the value of the dendritic nature of salt marshes to marsh residents.  相似文献   

Differences in top-down and bottom-up regulation of macroalgal communities between a reef crest and back reef habitat in Zanzibar     

Gustaf Lillieskld Sj  Erik Mrk  Simon Andersson  Inger Melander 《Estuarine, Coastal and Shelf Science》2011,91(4):331

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Long-lived spiral structure inN-body simulations: work in progress     

Alessandro B. Romeo  Gustaf Rydbeck  Mauri J. Valtonen 《Astrophysics and Space Science》1994,216(1-2):359-359

Work is in progress for constructing physically consistentN-body models capable of supporting a long-lived spiral structure. Such models would represent a missing link between theory and observations of disc galaxies.  相似文献   

First results from the arcminute cosmology bolometer array receiver     

M. C. Runyan  P. A. R. Ade  J. J. Bock  J. R. Bond  C. Cantalupo  C. R. Contaldi  M. D. Daub  J. H. Goldstein  P. L. Gomez  W. L. Holzapfel  C. L. Kuo  A. E. Lange  M. Lueker  M. Newcomb  J. B. Peterson  D. Pogosyan  A. K. Romer  J. Ruhl  E. Torbet  D. Woolsey 《New Astronomy Reviews》2003,47(11-12):915

We review the first science results from the Arcminute Cosmology Bolometer Array Receiver (ACBAR); a multi-frequency millimeter-wave receiver optimized for observations of the Cosmic Microwave Background (CMB) and the Sunyaev–Zel’dovich (SZ) effect in clusters of galaxies. ACBAR was installed on the 2 m Viper telescope at the South Pole in January 2001 and the results presented here incorporate data through July 2002. We present the power spectrum of the CMB at 150 GHz over the range ℓ=150–3000 measured by ACBAR as well as estimates for the values of the cosmological parameters within the context of ΛCDM models. We find that the inclusion of Ω_Λ greatly improves the fit to the power spectrum. We also observe a slight excess of small-scale anisotropy at 150 GHz; if interpreted as power from the SZ effect of unresolved clusters, the measured signal is consistent with CBI and BIMA within the context of the SZ power spectrum models tested.  相似文献   

The 2dF Galaxy Redshift Survey: galaxy luminosity functions per spectral type     

Darren S. Madgwick  Ofer Lahav  Ivan K. Baldry  Carlton M. Baugh  Joss Bland-Hawthorn  Terry Bridges  Russell Cannon  Shaun Cole  Matthew Colless  Chris Collins  Warrick Couch  Gavin Dalton  Roberto De Propris  Simon P. Driver  George Efstathiou  Richard S. Ellis  Carlos S. Frenk  Karl Glazebrook  Carole Jackson  Ian Lewis  Stuart Lumsden  Steve Maddox  Peder Norberg  John A. Peacock  Bruce A. Peterson  Will Sutherland  Keith Taylor 《Monthly notices of the Royal Astronomical Society》2002,333(1):133-144

We calculate the optical b _J luminosity function (LF) of the 2dF Galaxy Redshift Survey (2dFGRS) for different subsets defined by their spectral properties. These spectrally selected subsets are defined using a new parameter, η , which is a linear combination of the first two projections derived from a Principal Component Analysis. This parameter η identifies the average emission- and absorption-line strength in the galaxy rest frame spectrum, and hence is a useful indicator of the present star formation. We use a total of 75 000 galaxies in our calculations, chosen from a sample of high signal-to-noise ratio, low-redshift galaxies observed before 2001 January. We find that there is a systematic steepening of the faint-end slope ( α ) as one moves from passive  ( α =-0.54)  to active  ( α =-1.50)  star-forming galaxies, and that there is also a corresponding faintening of the rest frame characteristic magnitude   M *-5 log₁₀( h )  (from −19.6 to −19.2). We also show that the Schechter function provides a poor fit to the quiescent (Type 1) LF for very faint galaxies  [ M _{b J}-5 log₁₀( h )  fainter than −16.0], perhaps suggesting the presence of a significant dwarf population. The LFs presented here give a precise confirmation of the trends seen previously in a much smaller preliminary 2dFGRS sample, and in other surveys. We also present a new procedure for determining self-consistent k -corrections, and investigate possible fibre-aperture biases.  相似文献   

Parameter constraints for flat cosmologies from cosmic microwave background and 2dFGRS power spectra     

Will J. Percival  Will Sutherland  John A. Peacock  Carlton M. Baugh  Joss Bland-Hawthorn  Terry Bridges  Russell Cannon  Shaun Cole  Matthew Colless  Chris Collins  Warrick Couch  Gavin Dalton  Roberto De Propris  Simon P. Driver  George Efstathiou  Richard S. Ellis  Carlos S. Frenk  Karl Glazebrook  Carole Jackson  Ofer Lahav  Ian Lewis  Stuart Lumsden  Steve Maddox  Stephen Moody  Peder Norberg  Bruce A. Peterson  Keith Taylor 《Monthly notices of the Royal Astronomical Society》2002,337(3):1068-1080

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The 2dF Galaxy Redshift Survey: the dependence of galaxy clustering on luminosity and spectral type   总被引：1，自引：0，他引：1  

Peder Norberg  Carlton M. Baugh  Ed Hawkins  Steve Maddox  Darren Madgwick  Ofer Lahav  Shaun Cole  Carlos S. Frenk  Ivan Baldry  Joss Bland-Hawthorn  Terry Bridges  Russell Cannon  Matthew Colless  Chris Collins  Warrick Couch  Gavin Dalton  Roberto De Propris  Simon P. Driver  George Efstathiou  Richard S. Ellis  Karl Glazebrook  Carole Jackson  Ian Lewis  Stuart Lumsden  John A. Peacock  Bruce A. Peterson  Will Sutherland  Keith Taylor 《Monthly notices of the Royal Astronomical Society》2002,332(4):827-838

We investigate the dependence of galaxy clustering on luminosity and spectral type using the 2dF Galaxy Redshift Survey (2dFGRS). Spectral types are assigned using the principal-component analysis of Madgwick et al. We divide the sample into two broad spectral classes: galaxies with strong emission lines ('late types') and more quiescent galaxies ('early types'). We measure the clustering in real space, free from any distortion of the clustering pattern owing to peculiar velocities, for a series of volume-limited samples. The projected correlation functions of both spectral types are well described by a power law for transverse separations in the range  2<( σ / h ^-1 Mpc)<15  , with a marginally steeper slope for early types than late types. Both early and late types have approximately the same dependence of clustering strength on luminosity, with the clustering amplitude increasing by a factor of ∼2.5 between L * and 4 L *. At all luminosities, however, the correlation function amplitude for the early types is ∼50 per cent higher than that of the late types. These results support the view that luminosity, and not type, is the dominant factor in determining how the clustering strength of the whole galaxy population varies with luminosity.  相似文献   

The 2dF Galaxy Redshift Survey: the blue galaxy fraction and implications for the Butcher–Oemler effect     

Roberto De Propris  Matthew Colless  John A. Peacock  Warrick J. Couch  Simon P. Driver  Michael L. Balogh  Ivan K. Baldry  Carlton M. Baugh  Joss Bland-Hawthorn  Terry Bridges  Russell Cannon  Shaun Cole  Chris Collins  Nicholas Cross  Gavin Dalton  George Efstathiou  Richard S. Ellis  Carlos S. Frenk  Karl Glazebrook  Edward Hawkins  Carole Jackson  Ofer Lahav  Ian Lewis  Stuart Lumsden  Steve Maddox  Darren Madgwick  Peder Norberg  Will Percival  Bruce A. Peterson  Will Sutherland  Keith Taylor 《Monthly notices of the Royal Astronomical Society》2004,351(1):125-132

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