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81.
J. M. Oliveira R. D. Jeffries J. Th. van Loon M. T. Rushton 《Monthly notices of the Royal Astronomical Society》2006,369(1):272-280
We present new K - and L '-band imaging observations for members of the young (3–5 Myr) σ Orionis cluster, obtained at the United Kingdom Infrared Telescope (UKIRT) with the UKIRT 1–5 micron Imager Spectrometer (UIST). We determine ( K − L ') colour excesses with respect to the photospheres, finding evidence for warm circumstellar dust around 27 out of 83 cluster members that have masses between 0.04 and 1.0 M⊙ . This indicates a circumstellar disc frequency of at least (33 ± 6) per cent for this cluster, consistent with previous determinations from smaller samples and also consistent with the 3-Myr disc half-life suggested by Haisch et al. There is marginal evidence that the disc frequency declines towards lower masses, but the data are also consistent with no mass dependence at all. There is no evidence for spatial segregation of objects with and without circumstellar discs. 相似文献
82.
Results of the DEKORP 1 (BELCORP-DEKORP) deep seismic reflection studies in the western part of the Rhenish Massif 总被引:1,自引:0,他引:1
DEKORP Research GroupH.-J. Anderle R. Bittner R. Bortfeld J. Bouckaert G. Büchel G. Dohr H.-J. Dürbaum H. Durst W. Fielitz E. Flüh T. Gundlach L. Hance A. Henk F. Jordan D. Kläschen M. Klöckner R. Meissner W. Meyer O. Oncken C. Reichert K.-H. Ribbert P. Sadowiak H.-U. Schmincke J. Schmoll R. Walter K. Weber U. Weihrauch Th. Wever 《Geophysical Journal International》1991,106(1):203-227
83.
M. den Heijer G. I. G. Jzsa J. Kerp P. Serra Th. van der Hulst G. Kauffmann J. Wang F. Bigiel J. Brinchmann D. Carton D. Cormier M.‐L. Huang 《Astronomische Nachrichten》2015,336(3):284-311
We examine the H I kinematics of the “Bluedisk” ensemble of 48 galaxies selected from the Sloan Digital Sky Survey and observed in H I with the Westerbork Synthesis Radio Telescope. The sample consists of 25 galaxies with a high H I mass fraction and a comparatively large control sample comprising 23 galaxies of comparable stellar mass, stellar mass surface density, redshift, and inclination. By studying the H I velocity fields of these galaxies, we investigate whether there are signatures of ongoing gas accretion: i.e. global asymmetries and indications for warping and kinematical lopsidedness. We find no enhanced kinematical asymmetries between the H I‐rich sample and the control sample galaxies, indicating no significant difference in kinematical signatures such as warping and lopsidedness. Furthermore, we find no difference in position angle and systemic velocity offset with respect to the optical between both sub‐samples. We therefore do not find compelling evidence for enhanced global asymmetry of the H I‐excess galaxies ensemble properties in comparison to the control sample galaxies. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
84.
Summary. The first DEKORP profile, DEKORP 2-S, a 250 km long line perpendicular to the Variscan strike direction, has provided evidence of major crustal shortening during the Variscan orogeny. Sporadic dipping events in a generally transparent upper crust are interpreted as thrust faults, while the highly reflective lower crust fits into the general picture of Palaeozoic provinces. Correlations are established between certain reflectivity patterns and rheology. Moho depths and reflecting lamellae are considered to be post-Variscan. 相似文献
85.
86.
The formation of a weak shock at the interaction of the solar wind with the cometary neutral gas is confirmed in a non-stationary gasdynamic model. No shocks will be detectable along the ICE path and if the VEGA/GIOTTO spacecraft enter the cometary atmosphere. A shock can only be expected at an exit from the Halley atmosphere. 相似文献
87.
88.
Hydrogen peroxide (H2O2) has been suggested as a possible oxidizer of the martian surface. Photochemical models predict a mean column density in the range of 1015-1016 cm−2. However, a stringent upper limit of the H2O2 abundance on Mars (9×1014 cm−2) was derived in February 2001 from ground-based infrared spectroscopy, at a time corresponding to a maximum water vapor abundance in the northern summer (30 pr. μm, Ls=112°). Here we report the detection of H2O2 on Mars in June 2003, and its mapping over the martian disk using the same technique, during the southern spring (Ls=206°) when the global water vapor abundance was ∼10 pr. μm. The spatial distribution of H2O2 shows a maximum in the morning around the sub-solar latitude. The mean H2O2 column density (6×1015 cm−2) is significantly greater than our previous upper limit, pointing to seasonal variations. Our new result is globally consistent with the predictions of photochemical models, and also with submillimeter ground-based measurements obtained in September 2003 (Ls=254°), averaged over the martian disk (Clancy et al., 2004, Icarus 168, 116-121). 相似文献
89.
L. Kaper N.R. Trams P. Barr J.Th. Van Loon L.B.F.M. Waters 《Astrophysics and Space Science》1997,255(1-2):199-204
We present the first results of our ISO program on High-Mass X-ray Binaries (HMXBs). Infrared photometry, obtained at different
aspect angles of the systems, is used to investigate the massive star's disrupted stellar wind and the accretion flow towards
the compact X-ray source.
Scenarios for massive binary evolution predict that HMXBs receive a large kick velocity during the supernova explosion of
the compact star's progenitor. One might, therefore, expect to observe wind bow shocks around these systems such as observed
around many OB-runaway stars. Such a wind bow shock has recently been discovered around the system Vela X-1.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
90.
A. C.Fabian D. R.Ballantyne A.Merloni S.Vaughan K.Iwasawa Th.Boller 《Monthly notices of the Royal Astronomical Society》2002,331(3):L35-L39
A model for the inner regions of accretion flows is presented where, owing to disc instabilities, cold and dense material is clumped into deep sheets or rings. Surrounding these density enhancements is hot, tenuous gas where coronal dissipation processes occur. We expect this situation to be most relevant when the accretion rate is close to Eddington and the disc is radiation-pressure-dominated, and so may apply to narrow-line Seyfert 1 (NLS1) galaxies. In this scenario, the hard X-ray source is obscured for most observers, and so the detected X-ray emission would be dominated by reflection off the walls of the sheets. A simple Comptonization calculation shows that the large photon-indices characteristic of NLS1s would be a natural outcome of two reprocessors closely surrounding the hard X-ray source. We test this model by fitting the XMM-Newton spectrum of the NLS1 1H 0707–495 between 0.5 and 11 keV with reflection-dominated ionized disc models. A very good fit is found with three different reflectors each subject to the same Γ=2.35 power law. An iron overabundance is still required to fit the sharp drop in the spectrum at around 7 keV. We note that even a small corrugation of the accretion disc may result in Γ>2 and a strong reflection component in the observed spectrum. Therefore, this model may also explain the strength and the variability characteristics of the MCG–6-30-15 Fe K α line. The idea needs to be tested with further broad-band XMM-Newton observations of NLS1s. 相似文献