New Astronomy Reviews最新文献

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.

We examine the performance of standard pre-main-sequence (PMS) stellar evolution models against the accurately measured properties of a benchmark sample of 26 PMS stars in 13 eclipsing binary (EB) systems having masses 0.04–4.0 M_⊙ and nominal ages ≈1–20 Myr. We provide a definitive compilation of all fundamental properties for the EBs, with a careful and consistent reassessment of observational uncertainties. We also provide a definitive compilation of the various PMS model sets, including physical ingredients and limits of applicability. No set of model isochrones is able to successfully reproduce all of the measured properties of all of the EBs. In the H–R diagram, the masses inferred for the individual stars by the models are accurate to better than 10% at ≳1 M_⊙, but below 1 M_⊙ they are discrepant by 50–100%. Adjusting the observed radii and temperatures using empirical relations for the effects of magnetic activity helps to resolve the discrepancies in a few cases, but fails as a general solution. We find evidence that the failure of the models to match the data is linked to the triples in the EB sample; at least half of the EBs possess tertiary companions. Excluding the triples, the models reproduce the stellar masses to better than ∼10% in the H–R diagram, down to 0.5 M_⊙, below which the current sample is fully contaminated by tertiaries. We consider several mechanisms by which a tertiary might cause changes in the EB properties and thus corrupt the agreement with stellar model predictions. We show that the energies of the tertiary orbits are comparable to that needed to potentially explain the scatter in the EB properties through injection of heat, perhaps involving tidal interaction. It seems from the evidence at hand that this mechanism, however it operates in detail, has more influence on the surface properties of the stars than on their internal structure, as the lithium abundances are broadly in good agreement with model predictions. The EBs that are members of young clusters appear individually coeval to within 20%, but collectively show an apparent age spread of ∼50%, suggesting true age spreads in young clusters. However, this apparent spread in the EB ages may also be the result of scatter in the EB properties induced by tertiaries.

This is the first 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 present paper and in two succeeding papers we will discuss the individual cases. For each system, we will present a detailed discussion and evaluation concerning the observational and interpretive material presented in the literature. An eclipse timing diagram (or diagrams), commonly referred to as an “O–C diagram”, using the latest available data will accompany each discussion. In paper 3, we will also present a table of marginal and rejected cases. In paper 4, we will present a discussion of the mechanisms that can effect period change and which of the systems presented can be reliably concluded to exhibit mass exchange.