The Astronomy and Astrophysics Review最新文献

{"title":"Multiple populations in massive star clusters under the magnifying glass of photometry: theory and tools","authors":"Santi Cassisi,&nbsp;Maurizio Salaris","doi":"10.1007/s00159-020-00127-y","DOIUrl":"https://doi.org/10.1007/s00159-020-00127-y","url":null,"abstract":"<p>The existence of star-to-star light-element abundance variations in massive Galactic and extragalactic star clusters has fairly recently superseded the traditional paradigm of individual clusters hosting stars with the same age, and uniform chemical composition. Several scenarios have been put forward to explain the origin of this multiple stellar population phenomenon, but so far all have failed to reproduce the whole range of key observations. Complementary to high-resolution spectroscopy, which has first revealed and characterized chemically the presence of multiple populations in Galactic globular clusters, photometry has been instrumental in investigating this phenomenon in much larger samples of stars—adding a number of crucial observational constraints and correlations with global cluster properties—and in the discovery and characterization of multiple populations also in Magellanic Clouds’ intermediate-age clusters. The purpose of this review is to present the theoretical underpinning and application of the photometric techniques devised to identify and study multiple populations in resolved star clusters. These methods have played and continue to play a crucial role in advancing our knowledge of the cluster multiple population phenomenon, and promise to extend the scope of these investigations to resolved clusters even beyond the Local Group, with the launch of the James Webb Space Telescope.</p>","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"28 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2020-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1007/s00159-020-00127-y","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4302080","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Nuclear star clusters","authors":"Nadine Neumayer,&nbsp;Anil Seth,&nbsp;Torsten Böker","doi":"10.1007/s00159-020-00125-0","DOIUrl":"https://doi.org/10.1007/s00159-020-00125-0","url":null,"abstract":"<p>We review the current knowledge about nuclear star clusters (NSCs), the spectacularly dense and massive assemblies of stars found at the centers of most galaxies. Recent observational and theoretical works suggest that many NSC properties, including their masses, densities, and stellar populations, vary with the properties of their host galaxies. Understanding the formation, growth, and ultimate fate of NSCs, therefore, is crucial for a complete picture of galaxy evolution. Throughout the review, we attempt to combine and distill the available evidence into a coherent picture of NSC evolution. Combined, this evidence points to a clear transition mass in galaxies of <span>(sim 10^9,M_odot)</span> where the characteristics of nuclear star clusters change. We argue that at lower masses, NSCs are formed primarily from globular clusters that inspiral into the center of the galaxy, while at higher masses, star formation within the nucleus forms the bulk of the NSC. We also discuss the co-existence of NSCs and central black holes, and how their growth may be linked. The extreme densities of NSCs and their interaction with massive black holes lead to a wide range of unique phenomena including tidal disruption and gravitational-wave events. Finally, we review the evidence that many NSCs end up in the halos of massive galaxies stripped of the stars that surrounded them, thus providing valuable tracers of the galaxies’ accretion histories.</p>","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"28 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2020-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1007/s00159-020-00125-0","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4253778","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Observations of galactic and extragalactic novae","authors":"Massimo Della Valle,&nbsp;Luca Izzo","doi":"10.1007/s00159-020-0124-6","DOIUrl":"https://doi.org/10.1007/s00159-020-0124-6","url":null,"abstract":"<p>The recent GAIA DR2 measurements of distances to galactic novae have allowed to re-analyse some properties of nova populations in the Milky Way and in external galaxies on new and more solid empirical bases. In some cases, we have been able to confirm results previously obtained, such as the concept of nova populations into two classes of objects, that is <i>disk</i> and <i>bulge</i> novae and their link with the Tololo spectroscopic classification in Fe II and He/N novae. The recent and robust estimates of nova rates in the Magellanic Clouds galaxies provided by the OGLE team have confirmed the dependence of the normalized nova rate (i.e., the nova rate per unit of luminosity of the host galaxy) with the colors and/or class of luminosity of the parent galaxies. The nova rates in the Milky Way and in external galaxies have been collected from literature and critically discussed. They are the necessary ingredient to asses the contribution of novae to the nucleosynthesis of the respective host galaxies, particularly to explain the origin of the overabundance of lithium observed in young stellar populations. A direct comparison between distances obtained via GAIA DR2 and maximum magnitude vs. rate of decline (MMRD) relationship points out that the MMRD can provide distances with an uncertainty better than 30%. Multiwavelength observations of novae along the whole electromagnetic spectrum, from radio to gamma rays, have revealed that novae undergo a complex evolution characterized by several emission phases and a non-spherical geometry for the nova ejecta.</p>","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"28 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2020-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1007/s00159-020-0124-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4086209","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Cool outflows in galaxies and their implications","authors":"Sylvain Veilleux,&nbsp;Roberto Maiolino,&nbsp;Alberto D. Bolatto,&nbsp;Susanne Aalto","doi":"10.1007/s00159-019-0121-9","DOIUrl":"https://doi.org/10.1007/s00159-019-0121-9","url":null,"abstract":"<p>Neutral-atomic and molecular outflows are a common occurrence in galaxies, near and far. They operate over the full extent of their galaxy hosts, from the innermost regions of galactic nuclei to the outermost reaches of galaxy halos. They carry a substantial amount of material that would otherwise have been used to form new stars. These cool outflows may have a profound impact on the evolution of their host galaxies and environments. This article provides an overview of the basic physics of cool outflows, a comprehensive assessment of the observational techniques and diagnostic tools used to characterize them, a detailed description of the best-studied cases, and a more general discussion of the statistical properties of these outflows in the local and distant universe. The remaining outstanding issues that have not yet been resolved are summarized at the end of the review to inspire new research directions.</p>","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"28 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2020-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1007/s00159-019-0121-9","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4108644","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Molecular jets from low-mass young protostellar objects","authors":"Chin-Fei Lee","doi":"10.1007/s00159-020-0123-7","DOIUrl":"https://doi.org/10.1007/s00159-020-0123-7","url":null,"abstract":"<p>Molecular jets are seen coming from the youngest protostars in the early phase of low-mass star formation. They are detected in CO, SiO, and SO at (sub)millimeter wavelengths down to the innermost regions, where their associated protostars and accretion disks are deeply embedded and where they are launched and collimated. They are not only the fossil records of accretion history of the protostars but also are expected to play an important role in facilitating the accretion process. Studying their physical properties (e.g., mass-loss rate, velocity, rotation, radius, wiggle, molecular content, shock formation, periodical variation, magnetic field, etc) allows us to probe not only the jet launching and collimation, but also the disk accretion and evolution, and potentially binary formation and planetary formation in the disks. Here, the recent exciting results obtained with high-spatial and high-velocity resolution observations of molecular jets in comparison to those obtained in the optical jets in the later phase of star formation are reviewed. Future observations of molecular jets with a large sample at high spatial and velocity resolution with ALMA are expected to lead to a breakthrough in our understanding of jets from young stars.</p>","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"28 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2020-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1007/s00159-020-0123-7","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"5181985","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"What is a globular cluster? An observational perspective","authors":"Raffaele Gratton,&nbsp;Angela Bragaglia,&nbsp;Eugenio Carretta,&nbsp;Valentina D’Orazi,&nbsp;Sara Lucatello,&nbsp;Antonio Sollima","doi":"10.1007/s00159-019-0119-3","DOIUrl":"https://doi.org/10.1007/s00159-019-0119-3","url":null,"abstract":"<p>Globular clusters are large and dense agglomerate of stars. At variance with smaller clusters of stars, they exhibit signs of some chemical evolution. At least for this reason, they are intermediate between open clusters and massive objects such as nuclear clusters or compact galaxies. While some facts are well established, the increasing amount of observational data are revealing a complexity that has so far defied the attempts to interpret the whole data set in a simple scenario. We review this topic focusing on the main observational features of clusters in the Milky Way and its satellites. We find that most of the observational facts related to the chemical evolution in globular clusters are described as being primarily a function of the initial mass of the clusters, tuned by further dependence on the metallicity—that mainly affects specific aspects of the nucleosynthesis processes involved—and on the environment, that likely determines the possibility of independent chemical evolution of the fragments or satellites, where the clusters form. We review the impact of multiple populations on different regions of the colour–magnitude diagram and underline the constraints related to the observed abundances of lithium, to the cluster dynamics, and to the frequency of binaries in stars of different chemical composition. We then re-consider the issues related to the mass budget and the relation between globular cluster and field stars. Any successful model of globular cluster formation should explain these facts.</p>","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"27 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2019-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1007/s00159-019-0119-3","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4183336","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Pulsating white dwarfs: new insights","authors":"Alejandro H. Córsico,&nbsp;Leandro G. Althaus,&nbsp;Marcelo M. Miller Bertolami,&nbsp;S. O. Kepler","doi":"10.1007/s00159-019-0118-4","DOIUrl":"https://doi.org/10.1007/s00159-019-0118-4","url":null,"abstract":"<p>Stars are extremely important astronomical objects that constitute the pillars on which the Universe is built, and as such, their study has gained increasing interest over the years. White dwarf stars are not the exception. Indeed, these stars constitute the final evolutionary stage for more than 95% of all stars. The Galactic population of white dwarfs conveys a wealth of information about several fundamental issues and are of vital importance to study the structure, evolution and chemical enrichment of our Galaxy and its components—including the star formation history of the Milky Way. Several important studies have emphasized the advantage of using white dwarfs as reliable clocks to date a variety of stellar populations in the solar neighborhood and in the nearest stellar clusters, including the thin and thick disks, the Galactic spheroid and the system of globular and open clusters. In addition, white dwarfs are tracers of the evolution of planetary systems along several phases of stellar evolution. Not less relevant than these applications, the study of matter at high densities has benefited from our detailed knowledge about evolutionary and observational properties of white dwarfs. In this sense, white dwarfs are used as laboratories for astro-particle physics, being their interest focused on physics beyond the standard model, that is, neutrino physics, axion physics and also radiation from “extra dimensions”, and even crystallization. The last decade has witnessed a great progress in the study of white dwarfs. In particular, a wealth of information of these stars from different surveys has allowed us to make meaningful comparison of evolutionary models with observations. While some information like surface chemical composition, temperature and gravity of isolated white dwarfs can be inferred from spectroscopy, and the total mass and radius can be derived as well when they are in binaries, the internal structure of these compact stars can be unveiled only by means of asteroseismology, an approach based on the comparison between the observed pulsation periods of variable stars and the periods predicted by appropriate theoretical models. The asteroseismological techniques allow us to infer details of the internal chemical stratification, the total mass, and even the stellar rotation profile. In this review, we first revise the evolutionary channels currently accepted that lead to the formation of white-dwarf stars, and then, we give a detailed account of the different sub-types of pulsating white dwarfs known so far, emphasizing the recent observational and theoretical advancements in the study of these fascinating variable stars.</p>","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"27 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2019-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1007/s00159-019-0118-4","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4486342","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Small Solar System Bodies as granular media","authors":"D. Hestroffer,&nbsp;P. Sánchez,&nbsp;L. Staron,&nbsp;A. Campo Bagatin,&nbsp;S. Eggl,&nbsp;W. Losert,&nbsp;N. Murdoch,&nbsp;E. Opsomer,&nbsp;F. Radjai,&nbsp;D. C. Richardson,&nbsp;M. Salazar,&nbsp;D. J. Scheeres,&nbsp;S. Schwartz,&nbsp;N. Taberlet,&nbsp;H. Yano","doi":"10.1007/s00159-019-0117-5","DOIUrl":"https://doi.org/10.1007/s00159-019-0117-5","url":null,"abstract":"<p>Asteroids and other Small Solar System Bodies (SSSBs) are of high general and scientific interest in many aspects. The origin, formation, and evolution of our Solar System (and other planetary systems) can be better understood by analysing the constitution and physical properties of small bodies in the Solar System. Currently, two space missions (Hayabusa2, OSIRIS-REx) have recently arrived at their respective targets and will bring a sample of the asteroids back to Earth. Other small body missions have also been selected by, or proposed to, space agencies. The threat posed to our planet by near-Earth objects (NEOs) is also considered at the international level, and this has prompted dedicated research on possible mitigation techniques. The DART mission, for example, will test the kinetic impact technique. Even ideas for industrial exploitation have risen during the last years. Lastly, the origin of water and life on Earth appears to be connected to asteroids. Hence, future space mission projects will undoubtedly target some asteroids or other SSSBs. In all these cases and research topics, specific knowledge of the structure and mechanical behaviour of the surface as well as the bulk of those celestial bodies is crucial. In contrast to large telluric planets and dwarf planets, a large proportion of such small bodies is believed to consist of gravitational aggregates (‘rubble piles’) with no—or low—internal cohesion, with varying macro-porosity and surface properties (from smooth regolith covered terrain, to very rough collection of boulders), and varying topography (craters, depressions, ridges). Bodies with such structure can sustain some plastic deformation without being disrupted in contrast to the classical visco-elastic models that are generally valid for planets, dwarf planets, and large satellites. These SSSBs are hence better described through granular mechanics theories, which have been a subject of intense theoretical, experimental, and numerical research over the last four decades. This being the case, it has been necessary to use the theoretical, numerical and experimental tools developed within soil mechanics, granular dynamics, celestial mechanics, chemistry, condensed matter physics, planetary and computer sciences, to name the main ones, in order to understand the data collected and analysed by observational astronomy (visible, thermal, and radio), and different space missions. In this paper, we present a review of the multi-disciplinary research carried out by these different scientific communities in an effort to study SSSBs.</p>","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"27 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2019-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1007/s00159-019-0117-5","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4975667","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The astrophysics of nanohertz gravitational waves","authors":"Sarah Burke-Spolaor,&nbsp;Stephen R. Taylor,&nbsp;Maria Charisi,&nbsp;Timothy Dolch,&nbsp;Jeffrey S. Hazboun,&nbsp;A. Miguel Holgado,&nbsp;Luke Zoltan Kelley,&nbsp;T. Joseph W. Lazio,&nbsp;Dustin R. Madison,&nbsp;Natasha McMann,&nbsp;Chiara M. F. Mingarelli,&nbsp;Alexander Rasskazov,&nbsp;Xavier Siemens,&nbsp;Joseph J. Simon,&nbsp;Tristan L. Smith","doi":"10.1007/s00159-019-0115-7","DOIUrl":"https://doi.org/10.1007/s00159-019-0115-7","url":null,"abstract":"<p>Pulsar timing array (PTA) collaborations in North America, Australia, and Europe, have been exploiting the exquisite timing precision of millisecond pulsars over decades of observations to search for correlated timing deviations induced by gravitational waves (GWs). PTAs are sensitive to the frequency band ranging just below 1?nanohertz to a few tens of microhertz. The discovery space of this band is potentially rich with populations of inspiraling supermassive black hole binaries, decaying cosmic string networks, relic post-inflation GWs, and even non-GW imprints of axionic dark matter. This article aims to provide an understanding of the exciting open science questions in cosmology, galaxy evolution, and fundamental physics that will be addressed by the detection and study of GWs through PTAs. The focus of the article is on providing an understanding of the mechanisms by which PTAs can address specific questions in these fields, and to outline some of the subtleties and difficulties in each case. The material included is weighted most heavily toward the questions which we expect will be answered in the near-term with PTAs; however, we have made efforts to include most currently anticipated applications of nanohertz GWs.</p>","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"27 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2019-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1007/s00159-019-0115-7","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4723707","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Fast radio bursts","authors":"E. Petroff,&nbsp;J. W. T. Hessels,&nbsp;D. R. Lorimer","doi":"10.1007/s00159-019-0116-6","DOIUrl":"https://doi.org/10.1007/s00159-019-0116-6","url":null,"abstract":"<p>The discovery of radio pulsars over a half century ago was a seminal moment in astronomy. It demonstrated the existence of neutron stars, gave a powerful observational tool to study them, and has allowed us to probe strong gravity, dense matter, and the interstellar medium. More recently, pulsar surveys have led to the serendipitous discovery of fast radio bursts (FRBs). While FRBs appear similar to the individual pulses from pulsars, their large dispersive delays suggest that they originate from far outside the Milky Way and hence are many orders-of-magnitude more luminous. While most FRBs appear to be one-off, perhaps cataclysmic events, two sources are now known to repeat and thus clearly have a longer lived central engine. Beyond understanding how they are created, there is also the prospect of using FRBs—as with pulsars—to probe the extremes of the Universe as well as the otherwise invisible intervening medium. Such studies will be aided by the high-implied all-sky event rate: there is a detectable FRB roughly once every minute occurring somewhere on the sky. The fact that less than a hundred FRB sources have been discovered in the last decade is largely due to the small fields-of-view of current radio telescopes. A new generation of wide-field instruments is now coming online, however, and these will be capable of detecting multiple FRBs per day. We are thus on the brink of further breakthroughs in the short-duration radio transient phase space, which will be critical for differentiating between the many proposed theories for the origin of FRBs. In this review, we give an observational and theoretical introduction at a level that is accessible to astronomers entering the field.</p>","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"27 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2019-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1007/s00159-019-0116-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4948890","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}