Luminosity Function of the Cluster of Galaxies Abell 566

We investigate the Luminosity Function(LF)of the cluster of galaxies Abell 566.The photometric data of 15 intermediate-bands are obtained from the Beijing-Arizona- Taiwan-Connecticut(BATC)photometric sky survey.For each of the 15 wavebands,the LF of cluster galaxies is well modelled by the Schechter function,with characteristic luminosi- ties from-18.0 to-21.9 magnitude,from the a- to the p-band.Morphological dependence of the LF is investigated by separating the cluster members into‘red’and‘blue’subsamples. It is clear that late type galaxies have a steeper shape of LF than the early type galaxies.We also divided the sample galaxies by their local environment.It was found that galaxies in the sparser region have steeper shape of LF than galaxies in the denser region.Combining the results of morphological and environmental dependence of LFs,we show that Abell 566 is a well relaxed cluster with positive evidence of galaxy interaction and merger,and excess number of bright early type galaxies located in its denser region.     

The formation of neutron star systems through accretion-induced collapse in white-dwarf binaries

The accretion-induced collapse(AIC) scenario was proposed 40 years ago as an evolutionary end state of oxygen-neon white dwarfs(ONe WDs), linking them to the formation of neutron star(NS) systems.However, there has been no direct detection of any AIC event so far, even though there exists a lot of indirect observational evidence. Meanwhile, the evolutionary pathways resulting in NS formation through AIC are still not thoroughly investigated. In this article, we review recent studies on the two classic progenitor models of AIC events, i.e., the single-degenerate model(including the ONe WD+MS/RG/He star channels and the CO WD+He star channel) and the double-degenerate model(including the double CO WD channel,the double ONe WD channel and the ONe WD+CO WD channel). Recent progress on these progenitor models is reviewed, including the evolutionary scenarios leading to AIC events, the initial parameter space for producing AIC events and the related objects(e.g., the pre-AIC systems and the post-AIC systems).For the single-degenerate model, the pre-AIC systems(i.e., the progenitor systems of AIC events) could potentially be identified as supersoft X-ray sources, symbiotics and cataclysmic variables(such as classical novae, recurrent novae, Ne novae and He novae) in the observations, whereas the post-AIC systems(i.e.,NS systems) could potentially be identified as low-/intermediate-mass X-ray binaries, and the resulting low-/intermediate-mass binary pulsars, most notably millisecond pulsars. For the double-degenerate model,the pre-AIC systems are close double WDs with short orbital periods, whereas the post-AIC systems are single isolated NSs that may correspond to a specific kind of NS with peculiar properties. We also review the predicted rates of AIC events, the mass distribution of NSs produced via AIC and the gravitational wave(GW) signals from double WDs that are potential GW sources in the Galaxy in the context of future spacebased GW detectors, such as LISA, TianQin, Taiji, etc. Recent theoretical and observational constraints on the detection of AIC events are summarized. In order to confirm the existence of the AIC process, and resolve this long-term issue presented by current stellar evolution theories, more numerical simulations and observational identifications are required.     

Combining asteroid models derived by lightcurve inversion with asteroidal occultation silhouettes

Asteroid sizes can be directly measured by observing occultations of stars by asteroids. When there are enough observations across the path of the shadow, the asteroid’s projected silhouette can be reconstructed. Asteroid shape models derived from photometry by the lightcurve inversion method enable us to predict the orientation of an asteroid for the time of occultation. By scaling the shape model to fit the occultation chords, we can determine the asteroid size with a relative accuracy of typically ∼10%. We combine shape and spin state models of 44 asteroids (14 of them are new or updated models) with the available occultation data to derive asteroid effective diameters. In many cases, occultations allow us to reject one of two possible pole solutions that were derived from photometry. We show that by combining results obtained from lightcurve inversion with occultation timings, we can obtain unique physical models of asteroids.     

The luminosity function around isolated spiral galaxies

We determine the companion galaxy luminosity function (LF) for regions around isolated spiral galaxies. If we assume that any excess in the galaxy number counts in the vicinity of a spiral galaxy is due to galaxies at the same distance, then a system LF can be determined from the variation of excess numbers with apparent magnitude. By studying the excess over many field 'centre' galaxies, a good statistical accuracy can be obtained for the companion galaxy LF. Since redshift information is not required for the faint galaxies, it is possible to sample further down the LF as compared with redshift surveys. For 23 primary galaxies of known redshift, we find a dwarf satellite Schechter LF with a characteristic magnitude M _V *( D )≃−19 and a faint-end slope α=−1.7, down to M_V =−14 ( H ₀=50 km s⁻¹ Mpc⁻¹).     

Constraining Coronal Heating: Employing Bayesian Analysis Techniques to Improve the Determination of Solar Atmospheric Plasma Parameters

One way of revealing the nature of the coronal heating mechanism is by comparing simple theoretical one-dimensional hydrostatic loop models with observations at the temperature and/or density structure along these features. The most well-known method for dealing with comparisons like that is the χ ² approach. In this paper we consider the restrictions imposed by this approach and present an alternative way for making model comparisons using Bayesian statistics. In order to quantify our beliefs we use Bayes factors and information criteria such as AIC and BIC. Two datasets (Ugarte-Urra et al. 2005; Priest et al. 2000) are reanalyzed using the method described above. For the dataset of Ugarte-Urra et al. (2005), we conclude to apex dominant heating as the likely heating candidate, whereas the dataset of Priest et al. (2000) implies basal heating. Note that these new results are different from those obtained using the chi-squared statistic. For this we suggest that proper usage of Classical and Bayesian statistics should be applied in order to make safe assumptions about the nature of the coronal heating mechanisms.     

Identification of emission sources of umbral flashes using phase congruency

The emission sources of umbral flashes(UFs) are believed to be closely related to running umbral and penumbral waves,and are concluded to be associated with umbral dots in the solar photosphere. Accurate identification of emission sources of UFs is crucial for investigating these physical phenomena and their inherent relationships. A relatively novel model of shape perception,namely phase congruency(PC),uses phase information in the Fourier domain to identify the geometrical shape of the region of interest in different intensity levels,rather than intensity or gradient.Previous studies indicate that the model is suitable for identifying features with low contrast and low luminance. In the present paper,we applied the PC model to identify the emission sources of UFs and to locate their positions. For illustrating the high performance of our proposed method,two time sequences of Ca II H images derived from the Hinode/SOT on 2010 August 10 and 2013 August 20 were used. Furthermore,we also compared these results with the analysis results that are identified by the traditional/classical identification methods,including the gray-scale adjusted technique and the running difference technique. The result of our analysis demonstrates that our proposed method is more accurate and effective than the traditional identification methods when applied to identifying the emission sources of UFs and to locating their positions.     

Spurious contribution to cosmic ray scattering calculations

The quasi-linear theory for cosmic ray propagation is a well-known and widely accepted theory. In this paper, we discuss the different contributions to the pitch-angle Fokker–Planck coefficient from large and small scales for slab geometry using the damping model of dynamical turbulence. These examinations will give us a hint on the limitation range where the quasi-linear approximation is a good approximation.     

Determination of 3D Trajectories of Knots in Solar Prominences Using MSDP Data

In this paper we present a new method of restoration of the true three-dimensional (3D) trajectories of prominence knots using ground-based observations taken with a single telescope that is equipped with a Multi-Channel Subtractive Double Pass imaging spectrograph. Our method allows us to evaluate the true 3D trajectories of the prominence knots without any assumptions concerning the shape of the trajectories or the dynamics of the motion. The reconstructed trajectories of several knots observed in three prominences are presented.     

Evidence for luminosity evolution of long gamma-ray bursts in Swift data

We compute the luminosity function (LF) and the formation rate of long gamma-ray bursts (GRBs) by fitting the observed differential peak flux distribution obtained by the Burst and Transient Source Experiment (BATSE) in two different scenarios: (i) the GRB luminosity evolves with redshift and (ii) GRBs form preferentially in low-metallicity environments. In both cases, model predictions are consistent with the Swift number counts and with the number of detections at   z > 2.5  and >3.5. To discriminate between the two evolutionary scenarios, we compare the model results with the number of luminous bursts (i.e. with isotropic peak luminosity in excess of 10⁵³ erg s⁻¹) detected by Swift in its first 3 yr of mission. Our sample conservatively contains only bursts with good redshift determination and measured peak energy. We find that pure luminosity evolution models can account for the number of sure identifications. In the case of a pure density evolution scenario, models with   Z _th > 0.3 Z_⊙  are ruled out with high confidence. For lower metallicity thresholds, the model results are still statistically consistent with available lower limits. However, many factors can increase the discrepancy between model results and data, indicating that some luminosity evolution in the GRB LF may be needed also for such low values of Z _th. Finally, using these new constraints, we derive robust upper limits on the bright end of the GRB LF, showing that this cannot be steeper than ∼2.6.     

Large-scale bias in the Universe — II. Redshift-space bispectrum

The determination of the density parameter Ω₀ from the large-scale distribution of galaxies is one of the major goals of modern cosmology. However, if galaxies are biased tracers of the underlying mass distribution, linear perturbation theory leads to a degeneracy between Ω₀ and the linear bias parameter b , and the density parameter cannot be estimated. In Matarrese, Verde &38; Heavens we developed a method based on second-order perturbation theory to use the bispectrum to lift this degeneracy by measuring the bias parameter in an Ω₀-independent way. The formalism was developed assuming that one has perfect information on the positions of galaxies in three dimensions. In galaxy redshift surveys, the three-dimensional information is imperfect, because of the contaminating effects of peculiar velocities, and the resulting clustering pattern in redshift space is distorted. In this paper we combine second-order perturbation theory with a model for collapsed, virialized structures, to extend the method to redshift space, and demonstrate that the method should be successful in determining with reasonable accuracy the bias parameter from state-of-the-art surveys such as the Anglo-Australian 2 degree Field Survey and the Sloan Digital Sky Survey.     

On the jet contribution to the active galactic nuclei cosmic energy budget

Black holes release energy via the production of photons in their accretion discs but also via the acceleration of jets. We investigate the relative importance of these two paths over cosmic time by determining the mechanical luminosity function (LF) of radio sources and by comparing it to a previous determination of the bolometric LF of active galactic nuclei (AGN) from X-ray, optical and infrared observations. The mechanical LF of radio sources is computed in two steps: the determination of the mechanical luminosity as a function of the radio luminosity and its convolution with the radio LF of radio sources. Even with the large uncertainty deriving from the former, we can conclude that the contribution of jets is unlikely to be much larger than ∼10 per cent of the AGN energy budget at any cosmic epoch.     

Influence of environment on the luminosity function of galaxies

The luminosity function (LF) of galaxies in different environments is studied. A method proposed by the author is used to determine the LF of galaxies. It is found that the luminosity functions of galaxies of different morphological types in single galaxies and small groups do not differ greatly. The luminosity functions of galactic clusters differ greatly from the analogous functions for other systems. A relatively large number of faint galaxies is observed in clusters. Groups with low dispersions in their radial velocities and with small average pairwise distances between the members contain relatively many faint galaxies and relatively few bright galaxies compared to groups with large dispersions in their radial velocities and large average pairwise distances between members. This applies to elliptical and lenticular galaxies, as well as to spiral and irregular galaxies.     

Effects of the Triaxiality on the Rotation of Celestial Bodies: Application to the Earth,Mars and Eros

In this paper we discuss the influence of the triaxiality of a celestialbody on its free rotation, i.e. in absence of any external gravitationalperturbation. We compare the results obtained through two different analytical formalisms, one established from Andoyer variables by usingHamiltonian theory, the other one from Euler's variables by usingLagrangian equations. We also give a very accurate formulation of thepolar motion (polhody) in the case of a small amplitude of this motion.Then, we carry out a numerical integration of the problem, with aRunge–Kutta–Felberg algorithm, and for the two kinds of methods above, that we apply to three different celestial bodies considered as rigid : the Earth, Mars, and Eros. The reason of this choice is that each of this body corresponds to a more or less triaxial shape.In the case of the Earth and Mars we show the good agreement betweenanalytical and numerical determinations of the polar motion, and theamplitude of the effect related to the triaxial shape of the body, whichis far from being negligible, with some influence on the polhody of theorder of 10 cm for the Earth, and 1 m for Mars. In the case of Eros, weuse recent output data given by the NEAR probe, to determine in detailthe nature of its free rotational motion, characterized by the presence ofimportant oscillations for the Euler angles due to the particularly largetriaxial shape of the asteroid.     

A two-dimensional model for a solar prominence: Effect of an external magnetic field

Using analytical approximations we study the effects of different external magnetic configurations on the half-width, mass, and internal magnetic structure of a quiescent solar prominence, modelled as a thin vertical sheet of cool plasma. Firstly, we build up a zeroth-order model and analyse the effects produced by a potential coronal field or a constant- force-free field. This model allows us to obtain the half-width and mass of the prominence for different values of the external field, pressure and shear angle. Secondly, the effects of these external magnetic configurations on a two-dimensional model proposed by Ballester and Priest (1987) are studied. The main effects are a change of the half-width with height, an increase of the mass, a decrease of the magnetic field strength with height and a change in the shape of the magnetic field lines.     

Source dependency of exospheric sodium on Mercury

Due to a large solar radiation effect, the sodium exosphere exhibits many interesting effects, including the formation of an extended corona and a tail-like structure. The current suite of observations allows us to study some physical properties of the sodium exosphere, such as the source rates and the interaction with the surface, both experimentally and theoretically. In order to quantify the complex variations in the sodium exosphere in more detail, we use an exospheric model with the Monte-Carlo method to examine the surface interactions of a sodium atom, including the surface thermal accommodation rate and the sticking coefficient. The source rates from different components, such as the photon stimulated desorption (PSD), the meteoroid impact vaporization (MIV), and the solar wind ion sputtering (IS), can be constrained by comparing our exospheric model calculations with the published observational data. The detected terminator to limb (TL) ratio on the disk and the tail production rate can be explained with no sticking effect and small thermal accommodation rates. We also examine the best fit of the MIV source evolution, through comparison with the disk-averaged emission. The resultant discrepancy between the observations and the model fit may reflect the surface variation in the sodium abundance. A comprehensive mapping of the surface geochemical composition of the surface by the MESSENGER and Bepi-Colombo missions should give us more information about the nature of this surface-bound exosphere.     

The formation of submillisecond pulsars and the possibility of detection

Pulsars have been recognized to be normal neutron stars, but sometimes have been argued to be quark stars. Submillisecond pulsars, if detected, would play an essential and important role in distinguishing quark stars from neutron stars. We focus on the formation of such submillisecond pulsars in this paper. A new approach to the formation of a submillisecond pulsar (quark star) by means of the accretion-induced collapse (AIC) of a white dwarf is investigated. Under this AIC process, we found that: (i) almost all newborn quark stars could have an initial spin period of ∼0.1 ms; (ii) nascent quark stars (even with a low mass) have a sufficiently high spin-down luminosity and satisfy the conditions for pair production and sparking process and appear as submillisecond radio pulsars; (iii) in most cases, the times of newborn quark stars in the phase with spin period <1 (or <0.5) ms are long enough for the stars to be detected.
As a comparison, an accretion spin-up process (for both neutron and quark stars) is also investigated. It is found that quark stars formed through the AIC process can have shorter periods (≤0.5 ms), whereas the periods of neutron stars formed in accretion spin-up processes must be longer than 0.5 ms. Thus, if a pulsar with a period shorter than 0.5 ms is identified in the future, it could be a quark star.     

The K-band luminosity function of nearby field galaxies

We present a measurement of the K -band luminosity function (LF) of field galaxies obtained from near-infrared imaging of a sample of 345 galaxies selected from the Stromlo-APM Redshift Survey. The LF is reasonably well fitted over the 10-mag range −26 M _K −16 by a Schechter function with parameters α =−1.16±0.19, M *=−23.58±0.42 and φ *=0.012±0.008 Mpc⁻³, assuming a Hubble constant of H ₀=100 km s⁻¹ Mpc⁻¹. We have also estimated the LF for two subsets of galaxies subdivided by the equivalent width of the H α emission line at EW(H α )=10 Å. There is no significant difference in LF shape between the two samples, although there is a hint (∼1 σ significance) that emission-line galaxies (ELGs) have M * roughly 1 mag fainter than non-ELGs. Contrary to the optical LF, there is no difference in faint-end slope α between the two samples.     

On turbulence in the quasi-perpendicular bow shock

In this paper we propose to review the fundamental aspects of turbulence theories and their relevance to particle distribution functions observed by the cluster satellites in the quasi-perpendicular shock. The paper focusses on the hierarchical model describing the different levels of plasma turbulence; from the linear theory, through the quasi-linear remedy, to strong turbulence theories in the context of the earth's bow shock. We will discuss very briefly the validity of these approximations, and their relevance as far as satellite observations are concerned. In particular, we will discuss the development of non-Gaussian features in the ion distribution functions through the evaluation of higher order moments such as the kurtosis or flatness and the skewness. We have found that the profile of the kurtosis versus skewness tends to collapse to a parabolic line. This in turn allows us to draw analogies with neutral fluid turbulence where such a collapse of the kurtosis-skewness profile has been observed.