Astronomical Review最新文献

{"title":"Cosmological consequences of gravity with spin and torsion","authors":"N. Popławski","doi":"10.1080/21672857.2013.11519725","DOIUrl":"https://doi.org/10.1080/21672857.2013.11519725","url":null,"abstract":"Abstract The consistency of the gravitational field with the quantum-mechanical, spin angular momentum of matter requires space time to be endowed with curvature and torsion. The Einstein-Cartan-Sciama-Kibble theory of gravity, which extends general relativity to include torsion, may eliminate the singularity at the big bang and replace it with a nonsingular bounce. Gravity with spin and torsion may also solve several major problems in cosmology : singularities in black holes, the origin of the Universe, the flatness and horizon poblems, the arrow of time, the matter-antimatter asymmetry in the Universe, the nature of dark matter and dark energy, and the p referred axis in the Universe.","PeriodicalId":204186,"journal":{"name":"Astronomical Review","volume":"49 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125589893","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Cosmic Gamma-Ray Spectroscopy","authors":"R. Diehl","doi":"10.1080/21672857.2013.11519722","DOIUrl":"https://doi.org/10.1080/21672857.2013.11519722","url":null,"abstract":"Abstract Penetrating gamma- rays require complex instrumentation for astronomical spectroscopy measurements of gamma-rays from cosmic sources. A combination of multiple-interaction detectors in space and post-processing of detector events on ground have lead to a spectroscopy performance which is now capable to provide new astrophysical insights. Spectral signatures in the MeV regime originate from transitions in atomic nuclei, stimulated by either radioactive decays or high-energy nuclear collisions such as with cosmic rays. Lines have been detected from radioactive isotopes produced in stellar and supernova nuclear burning, and from energetic-particle interactions in solar flares. Radioactive-decay gamma-rays from 56Ni directly reflect the power source of supernova light. 44Ti is produced in core-collapse supernova interiors and the largely unknown and dynamical conditions herein. From 26Al and 60Fe which are distributed in interstellar space from massive-star nucleosynthesis over millions of years. Additionally, nuclear de-excitation lines have been measured in solar-flare events, and convey information a b out energetic particle production in these outbursts, and t heir interaction in the solar atmosphere. Annihilating posit rons add another very special astrophysical source, which has been puzzling so far, with its characteristic gamma-rays at 511 keV; it has been measured both in such solar flares, and throughout the interstellar medium of our Milky Way galaxy. - We discuss instrumentation and data processing for cosmic gamma-ray spectroscopy, and the astrophysical issues and insights from these measurements.","PeriodicalId":204186,"journal":{"name":"Astronomical Review","volume":"72 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129386253","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Optimization of a large correlator array configuration to maximize the coverage of υ-ν plane and minimize the sidelobes","authors":"Shahideh Kiehbadroudinezhad, N. Noordin","doi":"10.1080/21672857.2013.11519723","DOIUrl":"https://doi.org/10.1080/21672857.2013.11519723","url":null,"abstract":"Abstract The synthesized array is commonly used in radio astronomy and the Giant Metrewave Radio Telescope (GMRT) is one of the world’s foremost telescopes of this kind. The aim of this paper is to optimize an array of antennas, similar to GMRT, by changing the position of antennas. The effect of only changing the configuration was studied and the results of circular and spiral arrangements are discussed. The results are shown, the spiral combined with a circle configuration which is able to cover the #x03C5;-ν plane very well and decreases sidelobes. The results and observations are discussed in this report.","PeriodicalId":204186,"journal":{"name":"Astronomical Review","volume":"65 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131408477","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Occurrence of Non-pulsating Stars in the gamma Doradus/delta Scuti Pulsation Instability Region","authors":"J. Guzik, P. Bradley, Jason Jackiewiecz, K. Uytterhoeven, K. Kinemuchi","doi":"10.1080/21672857.2013.11519724","DOIUrl":"https://doi.org/10.1080/21672857.2013.11519724","url":null,"abstract":"Abstract As part of the NASA KeplerGuest Observer program, we requested and obtained long-cadence data on about 2700 faint (Kepler magnitude 14-16) stars with effective temperatures and surface gravities that lie near or within the pulsation instability region for main-sequence gamma Doradus and delta Scuti pulsating variables. These variables are of spectral type A-F with masses 1.4 to 2.5 solar masses. The delta Scuti stars pulsate in radial and non-radial acoustic modes, with periods of a few hours (frequencies ~10 cycles/day), while gamma Doradus variables pulsate in nonradial gravity modes with periods 0.3 to 3 days (frequencies ~1 cycle/day). Here we consider the light curves and Fourier transforms of 633 stars in an unbiased sample observed by Kepler in Quarters 6-13 (June 201 0-June 2012). We show the location of these stars in the log surface gravity-effective temperature diagram compared to the instability region limits established from ground-based observations, and taking into account uncertainties and biases in the KeplerInput Catalog Teff values. While hundreds of variables have been discovered in the Keplerdata, about 60% of the stars in our sample do not show any frequencies between 0.2 and 24.4 cycles/day with amplitude above 20 parts per million. We find that six of these apparently constant stars lie within the instability region. We discuss some possible reasons that these stars do not show photometric variability in the Keplerdata. We also comment on the ‘nonconstant’ stars, and find 26 variable star candidates, many of which also do not lie within the expected instability region.","PeriodicalId":204186,"journal":{"name":"Astronomical Review","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129549689","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Occurrence of Non-pulsating Stars in the gamma Doradus/delta Scuti Pulsation Instability Region","authors":"J. Guzik, P. Bradley, Jason Jackiewiecz, K. Uytterhoeven, K. Kinemuchi","doi":"10.1080/21672857.2014.11519730","DOIUrl":"https://doi.org/10.1080/21672857.2014.11519730","url":null,"abstract":"Abstract As part of the NASA Kepler Guest Observer program, we requested and obtained long-cadence data on about 2700 faint (Kepler magnitude 14-16) stars with effective temperatures and surface gravities that lie near or within the pulsation instability region for main-sequence gamma Doradus and delta Scuti pulsating variables. These variables are of spectral type A-F with masses 1.4 to 2.5 solar masses. The delta Scuti stars pulsate in radial and non-radial acoustic modes, with periods of a few hours (frequencies ~10 cycles/day), while gamma Doradus variables pulsate in nonradial gravity modes with periods 0.3 to 3 days (frequencies ~1 cycle/day). Here we consider the light curves and Fourier transforms of 633 stars in an unbiased sample observed by Kepler in Quarters 6-13 (June 201 0-June 2012). We show the location of these stars in the log surface gravity-effective temperature diagram compared to the instability region limits established from ground-based observations, and taking into account uncertainties and biases in the Kepler Input Catalog TettValues. While hundreds of variables have been discovered in the Kepler data, about 60% of the stars in our sample do not show any frequencies between 0.2 and 24.4 cycles/day with amplitude above 20 parts per million. We find that six of these apparently constant stars lie within the instability region. We discuss some possible reasons that these stars do not show photometric variability in the Kepler data. We also comment on the 'nonconstant' stars, and find 26 variable star candidates, many of which also do not lie within the expected instability region.","PeriodicalId":204186,"journal":{"name":"Astronomical Review","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125421391","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Connection between Gravity and Electromagnetism","authors":"Octavian Balaci","doi":"10.1080/21672857.2014.11519728","DOIUrl":"https://doi.org/10.1080/21672857.2014.11519728","url":null,"abstract":"Abstract A new interpretation of electrodynamics and gravity is presented, based on the idea that the electromagnetic and gravitational properties of vacuum are connected. The space and time are treated as imaginary concepts. With this, the electrodynamics and gravitational phenomena can be explained with a Galilean invariant vacuum. Also a new way to explain the gravitational attraction will result.","PeriodicalId":204186,"journal":{"name":"Astronomical Review","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123611935","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Cosmic Gamma-Ray Spectroscopy","authors":"R. Diehl","doi":"10.1080/21672857.2013.11519720","DOIUrl":"https://doi.org/10.1080/21672857.2013.11519720","url":null,"abstract":"Abstract Penetrating gamma-rays require complex instrumentation for astronomical spectroscopy measurements of gamma-rays from cosmic sources. A combination of multiple-interaction detectors in space and post-processing of detector events on ground have lead to a spectroscopy performance which is now capable to provide new astrophysical insights. Lines have been detected from radioactive isotopes produced in stellar and supernova nuclear burning. These are lines from 56Ni as it powers supernova light, from 44Ti which is produced in core-collapse supernova interiors, and from 26Al and 60Fe which are disctributed in interstellar space from massive-star nucleosynthesis over millions of years. Additionally, nuclear de-excitation lines have been measured in solar-flare events, and convey information about energetic-particle production in these outbursts, and their interaction in the solar atmosphere. Annihilation of positrons leads to gamma-rays at 511 keV characteristic energy, and has been measured both in such solar flares, and throughout the interstellar medium of our Milky Way galaxy. -- We discuss instrumentation and data processing for cosmic gamma-ray spectroscopy, and the astrophysical issues and insights from these measurements.","PeriodicalId":204186,"journal":{"name":"Astronomical Review","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132122994","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Overview of photometric galaxy cluster surveys at optical wavelengths","authors":"S. Desai","doi":"10.1080/21672857.2013.11519719","DOIUrl":"https://doi.org/10.1080/21672857.2013.11519719","url":null,"abstract":"Abstract The first galaxy cluster catalog was constructed by Abell in the 50s. Since then, with the advent of multi-megapixel digital cameras mounted on telescopes all over the world there have been a variety of optical photometric surveys with the ambituous goal to map out the large scale structure of the universe to larger and larger redshifts. One goal of these large scale structure surveys has been the discovery of thousands of galaxy clusters which have been used for a variety of cosmological and astrophysical studies. We shall review the salient features of these galaxy cluster surveys in the past two decades and provide a brief snapshot of some of the upcoming surveys in the next decade.","PeriodicalId":204186,"journal":{"name":"Astronomical Review","volume":" 8","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"113950360","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Conformal Singularity as a Cosmological Mirror: Classical Theory","authors":"M. Ibison","doi":"10.1080/21672857.2013.11519718","DOIUrl":"https://doi.org/10.1080/21672857.2013.11519718","url":null,"abstract":"In Robertson-Walker coordinates the cosmological scale factor asymptotes to an exponential as the evolution becomes dominated by dark energy. The singularity, which in the Robertson-Walker system is characterized by the red-shift of all radiation to nothing, is at infinity therefore. Since the Robertson-Walker time is the proper time of a co-moving observer the Robertson-Walker chart is geodesicallycomplete in the future time direction complete that is from the perspective of matter geodesics. Yet when the metric is expressed in conformal coordinates electromagnetic radiation can be made to appear to be completely insensitive to the scale factor including the singularity, which presents no barrier to its passage therefore. The conformal chart extends beyond the singularity and under reasonable assumptions the conformal Friedmann equation predicts a development of the scale factor that is anti-symmetric about the time of the singularity.","PeriodicalId":204186,"journal":{"name":"Astronomical Review","volume":"35 48","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131501040","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Super-Renormalizable Multidimensional Gravity: Theory and Applications","authors":"L. Modesto","doi":"10.1080/21672857.2013.11519717","DOIUrl":"https://doi.org/10.1080/21672857.2013.11519717","url":null,"abstract":"Abstract In this paper we introduce a perturbatively super-renormalizable and unitary theory of quantum gravity in any dimension D. In four dimensions the theory is an extension of the Stelle higher derivative gravity that involves an infinite number of derivative terms characterized by two entire functions, a.k .a. “form factors”. In dimension D we preserve two entire functions and we implement a finite number of local operators required by the quantum consistency of the theory. The main reason to introduce the entire functions is to avoid ghosts (states of negative norm) like the one in the four-dimensional Stelle's theory. The new theory is indeed ghost-free since the two entire functions have the property to generalize the Einstein-Hilbert action without introducing new poles in the propagator. By expanding the form factors to the lowest order in a mass scale we introduce, the local high derivative theory is recovered. Any truncation of the entire functions gives rise to the unitarity violation and it is only by keeping all the infinite series that we overcome similar issues. The theory is renormalizable at one loop and finite from two loops upward. More precisely, the theory turns out to be super-renormalizable because the covariant counter-terms have less derivatives then the classical action and the coefficients of the terms with more derivatives do not need any kind of infinity renormalization. In this paper we essentially study three classes of form factors, systematically showing the tree-level unitarity. We prove that the gravitation potential is regular in r = 0 for all the choices of form factors compatible with renormalizability and unitarity. We also include Black hole spherical symmetric solutions omitting higher curvature corrections to the equation of motions. For two out of three form factors the solutions are regular and the classical singularity is replaced by a “de Sitter-like core” in r = 0. For one particular choice of the form factors, we prove that the D-dimensional “Newtonian cosmology” is singularity-free and the Universe spontaneously follows a de Sitter evolution at the “Planck scale” for any matter content (either dust or radiation). We conclude the article providing an extensive analysis of the spectral dimension for any D and for the three classes of theories. In the ultraviolet regime the spectral dimension takes on different values for the three cases: less than or equal to “1” for the first case, “0” for the second one and “2” for the third one. Once the class of t heories compatible with renormalizability and unitarity is defined, the spectral dimension has the same short distance “critical value” or “accumulation point” for any value of the topological dimension D.","PeriodicalId":204186,"journal":{"name":"Astronomical Review","volume":"66 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117347738","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}