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Gamma-ray burst host galaxies are deficient in molecular gas, and show anomalous metal-poor regions close to GRB positions. Using recent Australia Telescope Compact Array (ATCA) Hi observations we show that they have substantial atomic gas reservoirs. This suggests that star formation in these galaxies may be fuelled by recent inflow of metal-poor atomic gas. While this process is debated, it can happen in low-metallicity gas near the onset of star formation because gas cooling (necessary for star formation) is faster than the Hi-to-H2 conversion.
The Sun drives most events of space weather in the vicinity of the Earth. Because the activities of the Sun are complicated, a visualized chart with key objects of solar activities is needed for space weather forecast. This work investigates the key objects in research during the past forty years and surveys a variety of solar observational data. We design the solar synoptic chart (SSC) that covers the key objects of solar activities, i.e., active regions, coronal holes, filaments/prominences, flares and coronal mass ejections, and synthesizes images from different heights and temperatures of solar atmosphere. The SSC is used to analyze the condition of the Sun in March 2012 and October 2014 as examples. The result shows that the SSC is timely, comprehensive, concise and easy to understand. It has the potentiality for space weather forecast and can help in improving the public education.
Based on the Bayesian Inference (BI) method, the Mixture-Model approach is improved to combine all kinematic data, including the coordinative position($\vec{x}$), proper motion ($\vec{\mu}$) and radial velocity(v), to separate the motion of the cluster from field stars, as well as to determine the intrinsic kinematic status and dynamical effects of the cluster, such as the mass segregation, anisotropy etc.. Meanwhile, the membership probability of individual stars are estimated as by product results. This method has been testified by simulation of toy models and also successfully used for well studied open clusters, such as M67 and NGC188. It is expected to largely help the studies of open clusters while combine the coming GAIA data.
The star formation rate (SFR) is a fundamental property of galaxies and it is crucial to understand the build-up of their stellar content, their chemical evolution, and energetic feedback. The SFR of galaxies is typically obtained by observing the emission by young stellar populations directly in the ultraviolet, the optical nebular line emission from gas ionized by newly-formed massive stars, the reprocessed emission by dust in the infrared range, or by combining observations at different wavelengths and fitting the full spectral energy distributions of galaxies. In this brief review we describe the assumptions, advantages and limitations of different SFR indicators, and we discuss the most promising SFR indicators for high-redshift studies.
We present observations of a remarkable compact group of galaxies at z = 2.48. Four galaxies, all within 40 kpc of each other, surround a powerful high redshift radio source. This group comprises two compact red passive galaxies and a pair of merging galaxies. One of the red galaxies, with an apparent stellar mass of 3.6×1011 M⊙ and an effective radius of 470 pc, is one of the most extreme examples of a massive quiescent compact galaxy found so far. One of the pair of merging galaxies hosts the AGN producing the large powerful radio structure. The merger is massive and enriched, consistent with the mass-metallicity relation expected at this redshift. Close to the merging nuclei, the emission lines exhibit broad and asymmetric profiles that suggest outflows powered either by a very young expanding radio jet or by AGN radiation. At ≳ 50 kpc from the system, we found a fainter extended-emission region that may be a part of a radio jet-driven outflow.
We review nonlinear force-free field (NLFFF) modeling of magnetic fields in active regions. The NLFFF model (in which the electric current density is parallel to the magnetic field) is often adopted to describe the coronal magnetic field, and numerical solutions to the model are constructed based on photospheric vector magnetogram boundary data. Comparative tests of NLFFF codes on sets of boundary data have revealed significant problems, in particular associated with the inconsistency of the model and the data. Nevertheless NLFFF modeling is often applied, in particular to flare-productive active regions. We examine the results, and discuss their reliability.
The gravitational wave radiation will release the energy momentum, which will dissipate the rotation of neutron star while in the accretion process. If the deformation of star is known, then we can estimate the maximum spin frequency of pulsar, based on which we can interpret why the spin periods of all millisecond pulsars cannot be less than one millisecond.
The mass and cumulative mass profile of the Galaxy are its most fundamental properties. Estimating these properties, however, is not a trivial problem. We rely on the kinematic information from Galactic satellites such as globular clusters and dwarf galaxies, and this data is incomplete and subject to measurement uncertainty. In particular, the complete 3D velocity vectors of objects are sometimes unavailable, and there may be selection biases due to both the distribution of objects around the Galaxy and our measurement position. On the other hand, the uncertainties of these data are fairly well understood. Thus, we would like to incorporate these uncertainties and the incomplete data into our estimate of the Milky Way's mass. The Bayesian paradigm offers a way to deal with both the missing kinematic data and measurement errors using a hierarchical model. An application of this method to the Milky Way halo mass profile, using the kinematic data for globular clusters and dwarf satellites, is shown.
Planck scanned the entire sky every six months at nine frequencies bands from 28 to 857 GHz with enough sensitivity to detect over a thousand radio sources. It thus provided measurements of the mm and sub-mm spectra of these sources in a regular cadence, even at wavelengths hard to observe from the ground. Polarization measurements (or upper limits) are provided for brighter sources at 28-353 GHz. Finally, Planck is calibrated to <1% accuracy in most of its frequency bands. I briefly introduce the valuable data set Planck provides on extragalactic sources, then describe some of the scientific conclusions drawn from the Planck measurements.
We report progresses of a joint project on searching for extremely metal-poor (EMP) stars based on LAMOST survey and Subaru follow-up observation. Follow-up high-resolution snapshot spectra have been obtained for 70 objects, resulting in 42 EMP stars. A number of chemically interesting objects have already been identified, including (1) Two UMP (ultra metal-poor) stars with [Fe/H] ~ −4.0. One of them is the second UMP turnoff star with Li detection. (2) A super Li-rich (A(Li) ~ 3.1) EMP giant. This is the most metal-poor and extreme example of Li enhancement in giants known to date, and will shed light on Li production during the evolution of red giants. (3) A few EMP stars showing extreme overabundance in heavy elements. Detailed abundances of these extreme objects and statistics obtained by the large sample of EMP stars will provide important constraints on the Galactic halo formation.
Studying the internal dynamics of stellar clusters is conducted primarily through N-Body simulations. One of the major inputs into N-Body simulations is the binary star frequency and mass distribution, which is currently constrained by relations derived from field binary stars. However to truly understand how clustered environments evolve, binary data from within star clusters is needed including masses. Detailed information on binaries masses, primary and secondary, in star clusters has been limited to date. The primary technique currently available has been radial velocity surveys that are limited in depth. Using previous two-band photometry-based studies that may cover different mass ranges produce potentially discrepant interpretations of the observed binary population. We introduce a new binary detection method, Binary INformation from Open Clusters Using SEDs (BINOCS) that covers the wide mass range needed to improve cluster N-body simulation inputs and comparisons. Using newly-observed multi-wavelength photometric catalogs (0.3 - 8 microns) of the key open clusters with a range of ages, we can show that the BINOCS method determines accurate binary component masses for unresolved cluster binaries through comparison to available RV-based studies. Using this method, we present results on the dynamical evolution of binaries from 0.4 - 2.5 solar masses within five prototypical clusters, spaning 30 Myr to 3.5 Gyr, and how the binary populations evolve as a function of mass.
Research on the structure and dynamics of the Galactic System covers a large field of research, from formation scenarios to long-term evolution and secular processes. Today we speak of near-field cosmology where the oldest parts of the Galaxy are used to probe back to early times, e.g. studying the chemical signatures of the oldest star clusters and dwarf galaxies to learn about the byproducts of the first stars. Some of the most detailed work relates to the structure of the dark matter and baryons in order to compare with expectation from N-body models. Secular processes have been identified (e.g. stellar migration) where material within the Galaxy is being reorganized by dynamical resonances and feedback processes.
Commission 22 (Meteors, Meteorites and Interplanetary Dust) was established at the first IAU General Assembly held in Rome in 1922, with William Frederick Denning as its first President. Denning was an accountant by profession, but as an amateur astronomer he contributed extensively to meteor science. Commission 22 thus established a pattern that has continued to this day that non-professional astronomers were welcomed and valued and could play a significant role in its affairs. The field of meteors, meteorites and interplanetary dust has played a disproportional role in the astronomical perception of the general public through the majestic displays of our annual meteor showers. Those in the field deployed many techniques uncommon in other fields of astronomy, studying the “vermin of space”, the small solid bodies that pervade interplanetary space and impact Earth's atmosphere, the surface of the Moon, and that of our satellites in orbit. Over time, the field has tackled a wide array of problems, from predicting the encounter with meteoroid streams, to the origin of our meteorites and the nature of the zodiacal cloud. Commission 22 has played an important role in organizing the field through dedicated meetings, a data centre, and working groups that developed professional-amateur relationships and that organized the nomenclature of meteor showers. The contribution of Commission 22 to the field is perhaps most readily seen in the work of the presidents that followed in the footsteps of Denning.
We present a set of time dependent chemical evolution models (based on the UMIST† astrochemistry 2012 code, McElroy et al. (2013) for a range of initial physical cloud parameters: 10 K < T < 20 K; 103 cm−3 < n(H2) < 5 ⋅ 104 cm−3; 1 < AV < 10 and with estimated values of scaled interstellar ultraviolet radiation field. We compare our chemical model results with the relative abundances of: CO, CH, OH, HCO+, HCN, HNC, NH3, N2H+ and H2CO molecules. We find significant time dependent variations of the chemical ratios of: X(NH3/H2); X(HCO+/H2) and X(HCO+/NH3). The input physical conditions were taken from Fehér O. et al. (2015) at 16 positions along the TMC-1 dark cloud. The NH3 and HCO+ relative densities based on the observations of Fehér O. et al. (2015) help to find the “chemical age” of the given position in the evolution curves.
This communication presents the situation regarding astronomical and archaeoastronomical heritage related to the World Heritage Convention through recent years up until today. Some parallel events and works were promoted strongly within the IAU–UNESCO Initiative during the International Year of Astronomy (2009). This was followed by a joint program by the IAU and ICOMOS—an official advisory body assisting the World Heritage Committee in the evaluation of nomination dossiers. The result of that work is an important publication by around 40 authors from 20 different countries all around the world: Heritage Sites of Astronomy and Archaeoastronomy in the Context of the UNESCO World Heritage Convention (Ruggles & Cotte 2010). A second volume is under preparation (2015). It was also accompanied by some initiatives such as the “Windows to the Universe" organisation and the parallel constitution of local “Starlight Reserves”. Some regional meetings studying specific facets or regional heritage in the field giving significant knowledge progresses also accompanied the global trend for astronomical heritage.
WH assessment is defined by a relatively strict format and methodology. A key phrase is “demonstration of Outstanding Universal Value” to justify the WH Listing by the Committee. This communication first examines the requirements and evaluation practices about of demonstrating OUV for a given place in the context of astronomical or archaeoastronomical heritage. That means the examination of the tangible attributes, an inventory of the property in terms of immoveable and moveable components and an inventory of intangible issues related to the history (history of the place in the context of the history of astronomy and cultural history). This is also related to the application to the site of the concept of integrity and authenticity, as regards the place itself and in comparison with other similar places (WH sites already listed, sites on national WH Tentative Lists, or other similar places in the region). The second issue of the communication is to give a glimpse of today's WH List, including some difficulties with listing and occasional failures, and trends and promising approaches.
Massive black holes (MBHs) are nowadays recognized as integral parts of galaxy evolution. Both the approximate proportionality between MBH and galaxy mass, and the expected importance of feedback from active MBHs in regulating star formation in their host galaxies point to a strong interplay between MBHs and galaxies. MBHs must form in the first galaxies and be fed by gas in these galaxies, with continuous or intermittent inflows that, at times, can be larger than the Eddington rate. Feedback from supernovae and from the MBHs themselves modulates the growth of the first MBHs. While current observational data only probe the most massive and luminous MBHs, the tip of the iceberg, we will soon be able to test theoretical models of MBH evolution on more “normal” MBHs: the MBHs that are indeed relevant in building the population that we observe in local galaxies, including our own Milky Way.
Continuous and precise space-based photometry has made it possible to measure the orbital frequency modulation of pulsating stars in binary systems with extremely high precision over long time spans. We present the phase modulation (PM) method for finding binaries among pulsating stars. We demonstrate how the orbital elements of a pulsating binary star can be obtained analytically from photometry alone, without spectroscopic radial velocity measurement. Frequency modulation (FM) caused by binary orbital motion also manifests itself in the Fourier transform, as a multiplet with equal spacing of the orbital frequency. The orbital parameters can also be extracted by analysing the amplitudes and phases of the peaks in these multiplets. We derive analytically the theoretical relations between the multiplet properties and the orbital parameters, and present a method for determining these parameters, including the eccentricity and the argument of periapsis. This, too, is achievable with the photometry alone, without spectroscopic radial velocity measurements. We apply these two methods to Kepler mission data and demonstrate that the results are in good agreement with each other. These methods are used to search for invisible binary companions, including planets and invisible massive objects such as neutron stars and stellar-mass black holes.
Since 2011, Oukaimeden Observatory (OUCA) has become one of the active NEO search facilities in the word. Its discovery statistics shows that the MOSS (Morocco Oukaimeden Sky Survey) project received credits for more than 2,145 new designations, including 3 NEOs and 4 comets. Its excellent astro-climactic characteristics are partly behind the success. The average number of observable nights is around 280 nights per year, while median seeing is 0.8-0.9 arcsec. We completed construction of a new telescope at the site in March 2015. It is Optical Wide-field Patrol (OWL) facility designed and built by Korea Space Science Institute (KASI). The primary objective of this facility is to monitor national space assets of Korea; either wide-field imaging- or fast data acquisition- capabilities enable the 0.5m telescope to conduct observation programs to catalog and follow-up various transient events in the night sky. We present the seeing condition, the OWL system and preliminary results obtained at OWL@Oukaimeden during the past several months.