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1.
Under the combination effect of recommencement heating due to the spin-down of strange stars (SSs) and heat preservation due to the weak conduction heat of the crust, Cooper pair breaking and formation (PBF) in colour superconducting quark matter arises. We investigate the cooling of SSs with a crust in the colour superconductivity phase including both deconfinement heating (DH) and the PBF process. We find that DH can delay the thermal evolution of SSs and the PBF process suppresses the early temperature rise of the stars. The cooling SSs behave within the brightness constraint of young compact objects when the colour superconductivity gap is small enough.  相似文献   

2.
Interpretations of visible/near-infrared reflectance spectra of Mars are often complicated by the effects of dust coatings that obscure the underlying materials of interest. The ability to separate the spectral reflectance signatures of coatings and substrates requires an understanding of how their individual and combined reflectance properties vary with phase angle. Toward this end, laboratory multispectral observations of rocks coated with different amounts of Mars analog dust were acquired under variable illumination and viewing geometries using the Bloomsburg University Goniometer (BUG). These bidirectional reflectance distribution function (BRDF) data were fit with a two-layer radiative transfer model, which replicated BUG observations of dust-coated basaltic andesite substrates relatively well. Derived single scattering albedo and phase function parameters for the dust were useful in testing the model's ability to derive the spectrum of a “blind” substrate (unknown to the modeler) coated with dust. Subsequent tests were run using subsets of the BUG data restricted by goniometric or coating thickness coverage. Using the entire data set provided the best constraints on model parameters, although some reductions in goniometric coverage could be tolerated without substantial degradation. Predictably, the most thinly coated samples provided the best information on the substrate, whereas the thickest coatings best replicated the dust. Dust zenith optical thickness values ∼0.6-0.8 best constrain the substrate and coating simultaneously, particularly for large ranges of incidence or emission angles. The lack of sufficient angles can be offset by having a greater number and range of coatings thicknesses. Given few angles and thicknesses, few constraints can be placed concurrently on the spectral properties of the coating and substrate.  相似文献   

3.
A broadband anti-reflective(AR) coating design for astronomical large-aperture telescopes is proposed. We give simulations of two-, three-and four-layer silica sol-gel on fused silica and finally get the optimal optical constants. As a comparison, we discuss the traditional dielectric material that has been applied to broadband AR coatings. To better guide the following experiment, we also conduct error analysis and feasibility analysis, combining with the technological characteristics of sol-gel. The analytical method is suitable for other wavebands and substrates. It is also instructive for large area AR coatings in the field of solar cells.  相似文献   

4.
One of the most puzzling features of the Kuiper Belt, which has been confirmedby numerous surveys, is the optical colour diversity that seems to prevail among the observed TNOs. TNOs and Centaurs have surfaces showing dramaticallydifferent colours and spectral reflectances, from neutral to very red. With therelatively few visible-NIR colour datasets available, the colour diversity seemsalso to extend to the near infrared wavelengths. Relevant statistical analyses havebeen performed and several studies have pointed out strong correlations betweenoptical colours and some orbital parameters (i, e, q) for the Classical KuiperBelt objects. On the other hand, no clear trend is obvious for Plutinos, Scatteredobjects or Centaurs. Another important result is the absence of correlation of colourswith size or heliocentric distance for any of the populations of outer Solar Systemobjects. The strong colour anisotropy found is important because it is a diagnosticof some physical effects processing the surfaces of TNOs and/or some possiblecomposition diversity. In this paper, we will review the current knowledge of thecolour properties of TNOs, describe the observed colour distribution within theEdgeworth–Kuiper belt, and address the problem of their possible origin.  相似文献   

5.
Surface photometry of 18 Virgo cluster dwarf elliptical (dE) and dwarf lenticular (dS0) galaxies, made by Gavazzi et al. in the H band (1.65 μm) and in the B band (0.44 μm), shows that the ratio of the effective radii of these stellar systems in the B and H bands,   r e B / r e H   , ranges between 0.7 and 2.2. In particular, dwarf ellipticals and lenticulars with a red total colour index   B - H   (i.e. with  3.2< B - H <4)  have equal effective radii in these two passbands. By contrast, blue (i.e. with  2.5< B - H <3.1)  dEs and dS0s have B -band effective radii about 50 per cent larger than the H -band ones, on average. Consistently, strong negative gradients in   B - H   along the galactocentric radius are found to be associated with blue total colours. This trend is not found in a sample of 29 giant E and S0 galaxies of the Coma cluster with analogous data available in the literature. These early-type giants span a broad range in    r e B / r e H    (0.2–2.2)  , with a mean   r e B / r e H ∼1.1  , but a narrow range in (red) colour  (3.3< B - H <4.2)  . In these stellar systems, colour gradients are usually interpreted as arising either from age/metallicity gradients along the radial coordinate or from dust attenuation, whatever the total colour of the system is. Assuming each of these three distinct interpretations of the origin of colour gradients, we discuss the origin of the association of strong negative colour gradients with blue colours found in the early-type dwarfs under study, in relation with current scenarios of formation and evolution of dE and dS0 galaxies.  相似文献   

6.
In the present work we have presented and analysedB andV light curves and the (B-V)-colour curve of the short period (RS CVn type) binary system UV Psc, and derived absolute information from the available data.x 2 minimization procedures were utilized to a large extent in fitting light and colour curves.The solutions show the binary to be at a distance of about 90 pc with two detached components which are close to the main sequence (G2 and K0). The inclination of the orbit is close to 90°Photometric irregularities present in the light curve are briefly considered in relation to current ideas on RS CVn systems, and the colour information indicates a locally hotter (rather than cooler) region is responsible for the irregularities.  相似文献   

7.
The nature of the starburst phenomenon in galaxies is investigated using a narrow-band colour system designed to study colour evolution in distant clusters. Work on zero redshift, luminous far-IR galaxies, calibrated by starburst models, demonstrates the usefulness of this colour system in isolating starburst from normal star-forming colours, and also demonstrates a strong correlation with far-IR colours despite reddening effects. The same colour system applied to distant clusters finds that a majority of the faint blue cluster population are starburst dwarf galaxies, probably the progenitors of the current population of dwarf ellipticals in nearby clusters. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

8.
We extend the mass-halo formalism for analytically generating power spectra to allow for the different clustering behaviour observed in galaxy subpopulations. Although applicable to other separations, we concentrate our methods on a simple separation by rest-frame colour into 'red' and 'blue' subpopulations through modifications to the 〈 N 〉( M ) relations and halo distribution functions for each of the subpopulations. This sort of separation is within the capabilities of the current generations of simulations as well as galaxy surveys, suggesting a potentially powerful observational constraint for current and future simulations. In anticipation of this, we demonstrate the sensitivity of the resulting power spectra to the choice of model parameters.  相似文献   

9.
Detecting colour changes of a gravitational microlensing event induced by the limb-darkened extended source effect is important for obtaining useful information about both the lens and the source star. However, precise measurements of the colour changes are hampered by blending, which also causes colour changes of the event. In this paper, we show that although the colour change measured from the subtracted image by using the recently developed photometric method of the 'difference image analysis' (DIA) differs from the colour change measured by using the conventional method based on the extraction of the individual source stars' point spread functions, the curve of the colour changes (colour curve) constructed by using the DIA method enables one to obtain the same information about the lens and source star, but with significantly reduced uncertainties due to the absence of blending. We investigate the patterns of the DIA colour curves for both single lens and binary lens events by constructing colour change maps.  相似文献   

10.
In this paper, we investigate the colour changes of gravitational microlensing events caused by the two different mechanisms of differential amplification for a limb-darkened extended source and blending. From this investigation, we find that the colour changes of limb-darkened extended source events (colour curves) have dramatically different characteristics depending on whether the lens transits the source star or not. We show that for a source transit event, the lens proper motion can be determined by simply measuring the turning time of the colour curve instead of fitting the overall colour or light curves. We also find that even for a very small fraction of blended light, the colour changes induced by blending are equivalent to those induced by limb darkening, causing serious distortion in the observed colour curve. Therefore, to obtain useful information about the lens and source star from the colour curve of an event, it will be essential to correct for blending. We discuss various methods of blending correction .  相似文献   

11.
We present optical and near-infrared (NIR) surface brightness and colour profiles, in bands ranging from U to K, for the disk and bulge components of a complete sample of 30 nearby S0 to Sbc galaxies with inclinations larger than 50 °. We describe in detail the observations and the determination of colour parameters. Calibrated monochromatic and real-colour images are presented, as well as colour index maps. This data set, tailored for the study of the population characteristics of galaxy bulges, provides useful information on the colours of inner disks as well. In related papers, we have used them to quantify colour gradients in bulges, and age differentials between bulge and inner disk.  相似文献   

12.
In order to investigate the hypothesis that dust aggregates were transformed to meteoritic chondrules by nebular lightning, we exposed silicatic and metallic dust samples to electrical discharges with energies of 120 to 500 J in air at pressures between 10 and 105 Pa. The target charges consisted of powders of micrometer-sized particles and had dimensions of mm. The dust samples generally fragmented leaving the major fraction thermally unprocessed. A minor part formed sintered aggregates of 50 to 500 μm. In a few experiments melt spherules having sizes ?180 μm in diameter (and, generally, interior voids) were formed; the highest spherule fraction was obtained with metallic Ni. Our experiments indicate that chondrule formation by electric current or by particle bombardment inside a discharge channel is unlikely.  相似文献   

13.
The evolution of number density, size and intrinsic colour is determined for a volume-limited sample of visually classified early-type galaxies selected from the Hubble Space Telescope /Advanced Camera for Surveys images of the Great Observatories Origins Deep Survey (GOODS) North and South fields (version 2). The sample comprises 457 galaxies over 320 arcmin2 with stellar masses above  3 × 1010 M⊙  in the redshift range  0.4 < z < 1.2  . Our data allow a simultaneous study of number density, intrinsic colour distribution and size. We find that the most massive systems  (≳3 × 1011 M⊙)  do not show any appreciable change in comoving number density or size in our data. Furthermore, when including the results from 2dF galaxy redshift survey, we find that the number density of massive early-type galaxies is consistent with no evolution between   z = 1.2  and 0, i.e. over an epoch spanning more than half of the current age of the Universe. We find large discrepancies between the predictions of semi-analytic models. Massive galaxies show very homogeneous intrinsic colour distributions, with nearly flat radial colour gradients, but with a significant negative correlation between stellar mass and colour gradient, such that red cores appear predominantly in massive galaxies. The distribution of half-light radii – when compared to   z ∼ 0  and   z > 1  samples – is compatible with the predictions of semi-analytic models relating size evolution to the amount of dissipation during major mergers.  相似文献   

14.
郑广生  张力 《天文学进展》2001,19(2):184-196
利用三维脉冲星磁层模型研究了磁层外隙的几何结构,首先用自治模型确定“外隙”的垂直尺度,在该模型中外隙尺度受回流的外隙流（带有隙加速的带电粒子发射的曲率光子）加热极帽而产生的热光子的碰撞而成对生成所限,外隙的横向尺度也受本地对生成所限,在脉冲星的磁层中,原则上有两个拓扑分离的外隙,允许同时进入和流出粒子,不过,流入粒子流产生的辐射形态受隙了本地对生成和恒星附近的磁对生成的严格制约,根据外隙及其本地结构的三维模型计算了类Crab脉冲星的辐射和相位分解谱。  相似文献   

15.
We investigate a stationary particle acceleration zone in the outer magnetosphere of an obliquely rotating neutron star. The charge depletion as a result of global current causes a large electric field along the magnetic field lines. Migratory electrons and/or positrons are accelerated by this field to radiate curvature gamma-rays, some of which collide with the X-rays to materialize as pairs in the gap. As a result of this pair-production cascade, the replenished charges partially screen the electric field, which is self-consistently solved together with the distribution of particles and gamma-rays. If no current is injected at either of the boundaries of the accelerator, the gap is located around the so-called null surface, where the local Goldreich–Julian charge density vanishes. However, we find that the gap position shifts outwards (or inwards) when particles are injected at the inner (or outer) boundary. We apply the theory to the seven pulsars whose X-ray fields are known from observations. We show that the gap should be located near to or outside of the null surface for the Vela pulsar and PSR B1951+32, so that their expected GeV spectrum may be consistent with observations. We then demonstrate that the intrinsically large TeV flux from the outer gap of PSR B0540–69 is absorbed by the magnetospheric infrared photons, causing it to be undetectable. We also point out that the electrodynamic structure and the resultant GeV emission properties of millisecond pulsars are similar to young pulsars.  相似文献   

16.
In hierarchical models, where spheroidal galaxies are primarily produced via a continuous merging of disc galaxies, the number of intrinsically red systems at faint limits will be substantially lower than in 'traditional' models where the bulk of star formation was completed at high redshifts. In this paper we analyse the optical–near-infrared colour distribution of a large flux-limited sample of field spheroidal galaxies identified morphologically from archival Hubble Space Telescope data. The I 814− HK ' colour distribution for a sample jointly limited at I 814<23 mag and HK '<19.5 mag is used to constrain their star formation history. We compare visual and automated methods for selecting spheroidals from our deep HST images and, in both cases, detect a significant deficit of intrinsically red spheroidals relative to the predictions of high-redshift monolithic-collapse models. However, the overall space density of spheroidals (irrespective of colour) is not substantially different from that seen locally. Spectral synthesis modelling of our results suggests that high-redshift spheroidals are dominated by evolved stellar populations polluted by some amount of subsidiary star formation. Despite its effect on the optical–infrared colour, this star formation probably makes only a modest contribution to the overall stellar mass. We briefly discuss the implications of our results in the context of earlier predictions based on models where spheroidals assemble hierarchically.  相似文献   

17.
We discuss the dispersion relation of linearly-polarized waves, propagating along a strong background magnetic field embedded in an electron-positron plasma. The results are then applied to the study of the propagation conditions of coherent curvature radio radiation inside neutron stars magnetospheres, as produced by electric discharges following current pulsar models.  相似文献   

18.
An open issue in pulsar's models is the current adjustment between the gap current and the global current that depends on the global structure of the pulsar's magnetosphere. Here I propose a mechanism for the global return current in pulsars.  相似文献   

19.
Radial and 2D colour properties of E+A galaxies   总被引：1，自引：0，他引：1  
We investigated the radial colour gradient and two-dimensional (2D) colour properties of 22 E+A galaxies with  5.5 < Hδ equivalent width(EW) < 8.5 Å  and 49 normal early-type galaxies as a control sample at a redshift of <0.2 in the Second Data Release of the Sloan Digital Sky Survey. We found that a substantial number of E+A galaxies exhibit positive slopes of radial colour gradient (bluer gradients toward the centre) which are seldom seen in normal early-type galaxies. We found irregular 'colour morphologies'– asymmetrical and clumpy patterns – at the centre of g − r and r − i 2D colour maps of E+A galaxies with positive slopes of colour gradient. Kolomogorov–Smirnov two-sample tests show that g − r and r − i colour gradient distributions of E+A galaxies differ from those of early-type galaxies with a more than 99.99 per cent significance level. We also found a tight correlation between radial colour gradients and colours, and between radial colour gradients and the 4000-Å break in the E+A sample; E+A galaxies which exhibit bluer colour or weaker D 4000 tend to have positive slopes of radial colour gradient. We compared the GISSEL model and E+A observational quantities,  Hδ EW, D 4000  and u − g colour, and found that almost all our E+A galaxies are situated along a single evolutionary track. Therefore, these results are interpreted as E+A galaxies evolving from  Hδ EW ∼ 8 Å  to  Hδ EW ∼ 5 Å  , with colour gradients changing from positive to negative, and with the irregular 2D colour map becoming smoother, during a time-scale of ∼300 Myr. Our results favour the hypothesis that E+A galaxies are post-starburst galaxies caused by merger/interaction, having undergone a centralized violent starburst.  相似文献   

20.
A statistical study of global galaxy parameters can help to improve our understanding of galaxy formation processes. In this paper we present the analysis of global galaxy parameters based on optical and near-infrared observations of a large sample of edge-on disc galaxies. We found a correlation between the ratio of the radial to vertical scale parameter and galaxy type: galaxies become systematically thinner when going from type S0 to type Sc, whereas the distribution seems to level off for later types. The observed scalelength ratios (and thus the radial colour gradients) largely represent the dust content of the galaxies. On average, the colour gradients indicated by the scalelength ratios increase from type Sa to at least type Sc. For galaxy types later than Sc, the average colour gradient seems to decrease again. The distribution of K -band (edge-on) disc central surface brightnesses is rather flat, although with a large scatter. However, the latest-type sample galaxies ( T  > 6) show an indication that their average disc central surface brightnesses may be fainter than those of the earlier types. This effect is probably not the result of dust extinction.  相似文献   

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