New Astronomy Reviews最新文献

Circumstellar disks of planetary debris are now known or suspected to closely orbit hundreds of white dwarf stars. To date, both data and theory support disks that are entirely contained within the preceding giant stellar radii, and hence must have been produced during the white dwarf phase. This picture is strengthened by the signature of material falling onto the pristine stellar surfaces; disks are always detected together with atmospheric heavy elements. The physical link between this debris and the white dwarf host abundances enables unique insight into the bulk chemistry of extrasolar planetary systems via their remnants. This review summarizes the body of evidence supporting dynamically active planetary systems at a large fraction of all white dwarfs, the remnants of first generation, main-sequence planetary systems, and hence provide insight into initial conditions as well as long-term dynamics and evolution.

Radioactive power for several delayed optical displays of core-collapse supernovae is commonly described as having been provided by decays of ⁵⁶Ni nuclei. This review analyses the provenance of that energy more deeply: the form in which that energy is stored; what mechanical work causes its storage; what conservation laws demand that it be stored; and why its release is fortuitously delayed for about 10⁶ s into a greatly expanded supernova envelope. We call the unifying picture of those energy transfers the secondary supernova machine owing to its machine-like properties; namely, mechanical work forces storage of large increases of nuclear Coulomb energy, a positive energy component within new nuclei synthesized by the secondary machine. That positive-energy increase occurs despite the fusion decreasing negative total energy within nuclei. The excess of the Coulomb energy can later be radiated, accounting for the intense radioactivity in supernovae. Detailed familiarity with this machine is the focus of this review. The stored positive-energy component created by the machine will not be reduced until roughly 10⁶ s later by radioactive emissions (EC and $\beta +$) owing to the slowness of weak decays. The delayed energy provided by the secondary supernova machine is a few × 10⁴⁹ erg, much smaller than the one percent of the 10⁵³ erg collapse that causes the prompt ejection of matter; however, that relatively small stored energy is vital for activation of the late displays. The conceptual basis of the secondary supernova machine provides a new framework for understanding the energy source for late SNII displays. We demonstrate the nuclear dynamics with nuclear network abundance calculations, with a model of sudden compression and reexpansion of the nuclear gas, and with nuclear energy decompositions of a nuclear-mass law. These tools identify excess Coulomb energy, a positive-energy component of the total negative nuclear energy, as the late activation energy. If the value of fundamental charge e were smaller, SNII would not be so profoundly radioactive. Excess Coulomb energy has been carried within nuclei radially for roughly 10⁹ km before being radiated into greatly expanded supernova remnants. The Coulomb force claims heretofore unacknowledged significance for supernova physics.

This is the third of a series of four papers, the goal of which is to identify the overcontact eclipsing binary star systems for which a solid case can be made for mass exchange. To reach this goal, it is necessary first to identify those systems for which there is a strong case for period change. We have identified 60 candidate systems; in the first two papers (Nelson et al., 2014, Nelson et al., 2016) we discussed 40 individual cases; this paper continues with the last 20. For each system, we present a detailed discussion and evaluation concerning the observational and interpretive material presented in the literature. At least one eclipse timing (ET) diagram, commonly referred to as an “O–C diagram”, that includes the latest available data, accompanies each discussion. In paper 4, we will discuss the mechanisms that can cause period change and which of the 60 systems can be reliably concluded to exhibit mass exchange; we will also provide a list of marginal and rejected cases – suitable for future work.

This is the second of a series of four papers, the goal of which is to identify the overcontact eclipsing binary star systems for which a solid case can be made for mass exchange. To reach this goal, it is necessary first to identify those systems for which there is a strong case for period change. We have identified 60 candidate systems; in the first paper (Nelson et al., 2014) we discussed 20 individual cases; this paper continues with the next 20. For each system, we present a detailed discussion and evaluation concerning the observational and interpretive material presented in the literature. An eclipse timing (ET) diagram (or diagrams), commonly referred to as an "O–C diagram", that includes the latest available data accompanies each discussion. In paper 4, we will discuss the mechanisms that can effect period change and which of the 60 systems can be reliably concluded to exhibit mass exchange; we will also provide a list of marginal and rejected cases suitable for future work.

I review the current state of numerical simulations of stellar feedback in the context of star formation at scales ranging from the formation of individual stars to models of galaxy formation including cosmic reionisation. I survey the wealth of algorithms developed recently to solve the radiative transfer problem and to simulate stellar winds, supernovae and protostellar jets. I discuss the results of these simulations with regard to star formation in molecular clouds, the interaction of different feedback mechanisms with each other and with magnetic fields, and in the wider context of galactic- and cosmological-scale simulations.

Compact Astronomical Low-frequency, Low-cost Instrument for Spectroscopy in Transportable Observatories (CALLISTO) is a global network of spectrometer system with the purpose to observe the Sun's activities. There are 37 stations (using 68 instruments) forming this network from more than 96 countries. We investigate the radio frequency interference (RFI) affecting CALLISTO at these stations. We found that the RFI severely affecting CALLISTO within radio astronomical windows below 870 MHz are in the ranges of 80–110 MHz and 460–500 MHz. We also found that all stations are relatively free from RFI at 270–290 MHz. We investigate the general effect of RFI on detection of solar bursts. We considered type III solar bursts on 10th May, 28th June, 6th July and 8th July, type II on 24th April and type IV on 9th March (all in 2012) in order to measure the percentage of RFI level during solar burst in general. The SNR of the strong solar bursts in for these detections have maxima reaching up to 46.20 (for 6th July).

Gamma-ray bursts (GRBs) are the most luminous electromagnetic explosions in the Universe, which emit up to 8.8 × 10⁵⁴ erg isotropic equivalent energy in the hard X-ray band. The high luminosity makes them detectable out to the largest distances yet explored in the Universe. GRBs, as bright beacons in the deep Universe, would be the ideal tool to probe the properties of high-redshift universe: including the cosmic expansion and dark energy, star formation rate, the reionization epoch and the metal enrichment history of the Universe. In this article, we review the luminosity correlations of GRBs, and implications for constraining the cosmological parameters and dark energy. Observations show that the progenitors of long GRBs are massive stars. So it is expected that long GRBs are tracers of star formation rate. We also review the high-redshift star formation rate derived from GRBs, and implications for the cosmic reionization history. The afterglows of GRBs generally have broken power-law spectra, so it is possible to extract intergalactic medium (IGM) absorption features. We also present the capability of high-redshift GRBs to probe the pre-galactic metal enrichment and the first stars.

The majority of known Galactic black holes reside in low-mass X-ray binaries. They are rare and fascinating objects, providing unique information on strong gravity, accretion disc physics, and stellar and binary evolution. There is no doubt that our understanding of the formation of black hole low-mass X-ray binaries has significantly advanced in the past decade. However, some key issues are still unresolved. In this paper we briefly summarize the observational clues and theoretical progress on the formation of black hole low-mass X-ray binaries.

In April 2013, a workshop entitled “What Regulates Galaxy Evolution?” was held at the Lorentz Center. The aim of the workshop was to bring together the observational and theoretical community working on galaxy evolution, and to discuss in depth of the current problems in the subject, as well as to review the most recent observational constraints. A total of 42 astrophysicists attended the workshop. A significant fraction of the time was devoted to identifying the most interesting “open questions” in the field, and to discuss how progress can be made. This review discusses the four questions (one for each day of the workshop) that, in our opinion, were the focus of the most intense debate. We present each question in its context, and close with a discussion of what future directions should be pursued in order to make progress on these problems.

Although Type Ia supernovae (SNe Ia) are a major tool in cosmology and play a key role in the chemical evolution of galaxies, the nature of their progenitor systems (apart from the fact that they must content at least one white dwarf, that explodes) remains largely unknown. In the last decade, considerable efforts have been made, both observationally and theoretically, to solve this problem. Observations have, however, revealed a previously unsuspected variety of events, ranging from very underluminous outbursts to clearly overluminous ones, and spanning a range well outside the peak luminosity-decline rate of the light curve relationship, used to make calibrated candles of the SNe Ia. On the theoretical side, new explosion scenarios, such as violent mergings of pairs of white dwarfs, have been explored. We review those recent developments, emphasizing the new observational findings, but also trying to tie them to the different scenarios and explosion mechanisms proposed thus far.