Black holes in binary stellar systems and galactic nuclei

Science.gov (United States)

Cherepashchuk, A. M.

2014-04-01

In the last 40 years, following pioneering papers by Ya B Zeldovich and E E Salpeter, in which a powerful energy release from nonspherical accretion of matter onto a black hole (BH) was predicted, many observational studies of black holes in the Universe have been carried out. To date, the masses of several dozen stellar-mass black holes (M_BH = (4{-}20) M_\\odot) in X-ray binary systems and of several hundred supermassive black holes (M_BH = (10^{6}{-}10^{10}) M_\\odot) in galactic nuclei have been measured. The estimated radii of these massive and compact objects do not exceed several gravitational radii. For about ten stellar-mass black holes and several dozen supermassive black holes, the values of the dimensionless angular momentum a_* have been estimated, which, in agreement with theoretical predictions, do not exceed the limiting value a_* = 0.998. A new field of astrophysics, so-called black hole demography, which studies the birth and growth of black holes and their evolutionary connection to other objects in the Universe, namely stars, galaxies, etc., is rapidly developing. In addition to supermassive black holes, massive stellar clusters are observed in galactic nuclei, and their evolution is distinct from that of supermassive black holes. The evolutionary relations between supermassive black holes in galactic centers and spheroidal stellar components (bulges) of galaxies, as well as dark-matter galactic haloes are brought out. The launch into Earth's orbit of the space radio interferometer RadioAstron opened up the real possibility of finally proving that numerous discovered massive and highly compact objects with properties very similar to those of black holes make up real black holes in the sense of Albert Einstein's General Relativity. Similar proofs of the existence of black holes in the Universe can be obtained by intercontinental radio interferometry at short wavelengths \\lambda \\lesssim 1 mm (the international program, Event Horizon Telescope).

Compact stellar object: the formation and structure

Energy Technology Data Exchange (ETDEWEB)

Duarte, S.B. [Centro Brasileiro de Pesquisas Fisicas (CBPF/MCT), Rio de Janeiro, RJ (Brazil)

2012-07-01

Full text: The formation of compact objects is viewed at the final stages of stellar evolution. The supernova explosion events are then focalized to explain the formation of pulsars, hybrid neutron star and the limit case of the latter, the quark stars. We discuss the stability and structure of these objects in connection with the properties of the hadron and quark-gluon plasma equation of state. The hadron-quark phase transition in deep interior of these objects is discussed taking into account the implications on the density distribution of matter along the radial direction. The role of neutrinos confinement in the ultradense stellar medium in the early stages of pulsar formation is another interesting aspect to be mentioned in this presentation. Recent results for maximum mass of compact stellar objects for different forms of equations of state will be shown, presenting some theoretical predictions for maximum mass of neutron stars allowed by different equations of state assigned to dense stellar medium. Although a density greater than few times the nuclear equilibrium density appears in deep interior of the core, at the crust the density decreases by several orders of magnitude where a variety of hadronic states appears, the 'pasta'-states of hadrons. More externally, a lattice of nuclei can be formed permeated not only by electrons but also by a large amount of free neutrons and protons. These are possible structure of neutron star crust to have the density and pressures with null values at the neutron star surface. The ultimate goal of this talk is to give a short view of the compact star area for students and those who are introducing in this subject. (author)

Analysis Of Ultra Compact Ionized Hydrogen Regions Within The Northern Half Of The Galactic Disk

Science.gov (United States)

Bruce, John

2011-01-01

From a catalog of 199 candidate ultra compact (UC) HII regions 123 sources included in the the intersection of the GLIMPSE (8 μm),Cornish (6 cm), and Bolocam ( 1.1 mm) galactic plane surveys (BGPS) were analyzed. The sources were sorted based on 6 cm morphology and coincidence with 8 μm bubbles. The 1.1 mm flux attributes were measured and calculations were performed to determine the ionized hydrogen contributions to the 1.1 mm flux. The category averages and frequencies were obtained as well. Significant differences in HII percentages were present among the morphology groups but ranged widely, without apparent distinction, between the bubble forming and triggered source categories.

Galactic structure

International Nuclear Information System (INIS)

1989-01-01

The occurrence of hot, apparently normal, massive stars far from the galactic plane has been a major puzzle in an understanding of galactic structure and evolution. Such stars have been discovered and studied at the South African Astronomical Observatory (SAAO) over a number of years. During 1989 further evidence has been obtained indicating that these stars are normal, massive objects. Other studies of galactic structure conducted by the SAAO have included research on: the central bulge region of our galaxy; populations of M giants in the galaxy; a faint blue object survey; a survey of the galactic plane for distant Cepheid variables; interstellar reddening, and K-type dwarfs as tracers for the gravitational force perpendicular to the galactic plane. 1 fig

Compact Objects in Astrophysics White Dwarfs, Neutron Stars and Black Holes

CERN Document Server

Camenzind, Max

2007-01-01

Compact objects are an important class of astronomical objects in current research. Supermassive black holes play an important role in the understanding of the formation of galaxies in the early Universe. Old white dwarfs are nowadays used to calibrate the age of the Universe. Mergers of neutron stars and black holes are the sources of intense gravitational waves which will be measured in the next ten years by gravitational wave detectors. Camenzind's Compact Objects in Astrophysics gives a comprehensive introduction and up-to-date overview about the physical processes behind these objects, covering the field from the beginning to most recent results, including all relevant observations. After a presentation of the taxonomy of compact objects, the basic principles of general relativity are given. The author then discusses in detail the physics and observations of white dwarfs and neutron stars (including the most recent equations of state for neutron star matter), the gravitational field of rapidly rotating c...

DOUBLE COMPACT OBJECTS. I. THE SIGNIFICANCE OF THE COMMON ENVELOPE ON MERGER RATES

International Nuclear Information System (INIS)

Dominik, Michal; Belczynski, Krzysztof; Bulik, Tomasz; Fryer, Christopher; Holz, Daniel E.; Berti, Emanuele; Mandel, Ilya; O'Shaughnessy, Richard

2012-01-01

The last decade of observational and theoretical developments in stellar and binary evolution provides an opportunity to incorporate major improvements to the predictions from population synthesis models. We compute the Galactic merger rates for NS-NS, BH-NS, and BH-BH mergers with the StarTrack code. The most important revisions include updated wind mass-loss rates (allowing for stellar-mass black holes up to 80 M ☉ ), a realistic treatment of the common envelope phase (a process that can affect merger rates by 2-3 orders of magnitude), and a qualitatively new neutron star/black hole mass distribution (consistent with the observed m ass gap ) . Our findings include the following. (1) The binding energy of the envelope plays a pivotal role in determining whether a binary merges within a Hubble time. (2) Our description of natal kicks from supernovae plays an important role, especially for the formation of BH-BH systems. (3) The masses of BH-BH systems can be substantially increased in the case of low metallicities or weak winds. (4) Certain combinations of parameters underpredict the Galactic NS-NS merger rate and can be ruled out. (5) Models incorporating delayed supernovae do not agree with the observed NS/BH 'mass gap', in accordance with our previous work. This is the first in a series of three papers. The second paper will study the merger rates of double compact objects as a function of redshift, star formation rate, and metallicity. In the third paper, we will present the detection rates for gravitational-wave observatories, using up-to-date signal waveforms and sensitivity curves.

Manifestations of a cosmological density of compact objects in quasar light

International Nuclear Information System (INIS)

Canizares, C.R.

1982-01-01

The gravitational lens effects of a cosmological density of compact objects with masses in the range 0.01 0 and quasar redshift. Comparison of the expected manifestations with a variety of quasar data suggests that the density of compact objects in the 0.01--10 5 M/sub sun/ range is not sufficient to close the universe if quasar continuum emission comes from a region -3 pc. This would exclude nuclear burning stars and their remnants. This conclusion is based on several scant and heterogeneous data sets, but it can be refined and strengthened with further data. As gravitational lensing predicts a minimum scatter in various observed quantities, upper limits to the cosmological density of compact objects are not invalidated by the unknown evolution of intrinsic quasar properties

Black holes, white dwarfs and neutron stars: The physics of compact objects

International Nuclear Information System (INIS)

Shapiro, S.L.; Teukolsky, S.A.

1983-01-01

The contents include: Star deaths and the formation of compact objects; White dwarfs; Rotation and magnetic fields; Cold equation of state above neutron drip; Pulsars; Accretion onto black holes; Supermassive stars and black holes; Appendices; and Indexes. This book discusses one aspect, compact objects, of astronomy and provides information of astrophysics or general relativity

Gravitationally compact objects as nucleation sites for first-order vacuum phase transitions

International Nuclear Information System (INIS)

Samuel, D.A.; Hiscock, W.A.

1992-01-01

A characteristic of first-order phase transitions is their ability to be initiated by nucleation sites. In this paper we consider the role that gravitationally compact objects may play as nucleation sites for first-order phase transitions within quantum fields. As the presence of nucleation sites may prevent the onset of supercooling, the existence of nucleation sites for phase transitions within quantum fields may play an important role in some inflationary models of the Universe, in which the Universe is required to exist in a supercooled state for a period of time. In this paper we calculate the Euclidean action for an O(3) bubble nucleating about a gravitationally compact object, taken to be a boson star for simplicity. The gravitational field of the boson star is taken to be a small perturbation on flat space, and the O(3) action is calculated to linear order as a perturbation on the O(4) action. The Euclidean bubble profile is found by solving the (Higgs) scalar field equation numerically; the thin-wall approximation is not used. The gravitationally compact objects are found to have the effect of reducing the Euclidean action of the nucleating bubble, as compared to the Euclidean action for the bubble in flat spacetime. The effect is strongest when the size of the gravitationally compact object is comparable to the size of the nucleating bubble. Further, the size of the decrease in action increases as the nucleating ''star'' is made more gravitationally compact. Thus, gravitationally compact objects may play the role of nucleation sites. However, their importance to the process of false-vacuum decay is strongly dependent upon their number density within the Universe

Formalism for testing theories of gravity using lensing by compact objects. II. Probing post-post-Newtonian metrics

International Nuclear Information System (INIS)

Keeton, Charles R.; Petters, A.O.

2006-01-01

We study gravitational lensing by compact objects in gravity theories that can be written in a post-post-Newtonian (PPN) framework: i.e., the metric is static and spherically symmetric, and can be written as a Taylor series in m /r, where m is the gravitational radius of the compact object. Working invariantly, we compute corrections to standard weak-deflection lensing observables at first and second order in the perturbation parameter ε=θ/θ E , where θ is the angular gravitational radius and θ E is the angular Einstein ring radius of the lens. We show that the first-order corrections to the total magnification and centroid position vanish universally for gravity theories that can be written in the PPN framework. This arises from some surprising, fundamental relations among the lensing observables in PPN gravity models. We derive these relations for the image positions, magnifications, and time delays. A deep consequence is that any violation of the universal relations would signal the need for a gravity model outside the PPN framework (provided that some basic assumptions hold). In practical terms, the relations will guide observational programs to test general relativity, modified gravity theories, and possibly the cosmic censorship conjecture. We use the new relations to identify lensing observables that are accessible to current or near-future technology, and to find combinations of observables that are most useful for probing the spacetime metric. We give explicit applications to the galactic black hole, microlensing, and the binary pulsar J0737-3039

Probing the Galactic Structure of the Milky Way with H II Regions

Science.gov (United States)

Red, Wesley Alexander; Wenger, Trey V.; Balser, Dana; Anderson, Loren; Bania, Thomas

2018-01-01

Mapping the structure of the Milky Way is challenging since we reside within the Galactic disk and distances are difficult to determine. Elemental abundances provide important constraints on theories of the formation and evolution of the Milky Way. HII regions are the brightest objects in the Galaxy at radio wavelengths and are detected across the entire Galactic disk. We use the Jansky Very Large Array (VLA) to observe the radio recombination line (RRL) and continuum emission of 120 Galactic HII regions located across the Galactic disk. In thermal equilibrium, metal abundances are expected to set the nebular electron temperature with high abundances producing low temperatures. We derive the metallicity of HII regions using an empirical relation between an HII region's radio recombination line-to-continuum ratio and nebular metallicity. Here we focus on a subset of 20 HII regions from our sample that have been well studied with the Green Bank Telescope (GBT) to test our data reduction pipeline and analysis methods. Our goal is to expand this study to the Southern skies with the Australia Telescope Compact Array and create a metallicity map of the entire Galactic disk.

A family of charged compact objects with anisotropic pressure

Energy Technology Data Exchange (ETDEWEB)

Maurya, S.K. [University of Nizwa, Department of Mathematical and Physical Sciences, College of Arts and Science, Nizwa (Oman); Govender, M. [Durban University of Technology, Department of Mathematics, Durban (South Africa)

2017-06-15

Utilizing an ansatz developed by Maurya et al. we present a class of exact solutions of the Einstein-Maxwell field equations describing a spherically symmetric compact object. A detailed physical analysis of these solutions in terms of stability, compactness and regularity indicates that these solutions may be used to model strange star candidates. In particular, we model the strange star candidate Her X-1 and show that our solution conforms to observational data to an excellent degree of accuracy. An interesting and novel phenomenon which arises in this model is the fact that the relative difference between the electromagnetic force and the force due to the pressure anisotropy changing sign within the stellar interior. This may be an additional mechanism required for stability against cracking of the stellar object. (orig.)

Evolution of binaries with compact objects in globular clusters

OpenAIRE

Ivanova, Natalia

2017-01-01

Dynamical interactions that take place between objects in dense stellar systems lead to frequent formation of exotic stellar objects, unusual binaries, and systems of higher multiplicity. They are most important for the formation of binaries with neutron stars and black holes, which are usually observationally revealed in mass-transferring binaries. Here we review the current understanding of compact object's retention, of the metallicity dependence on the formation of low-mass X-ray binaries...

Evolution of Supernova Remnants Near the Galactic Center

Energy Technology Data Exchange (ETDEWEB)

Yalinewich, A.; Piran, T.; Sari, R. [Racah Institute of Physics, the Hebrew University, 91904, Jerusalem (Israel)

2017-03-20

Supernovae near the Galactic center (GC) evolve differently from regular Galactic supernovae. This is mainly due to the environment into which the supernova remnants (SNRs) propagate. SNRs near the GC propagate into a wind swept environment with a velocity directed away from the GC, and a graded density profile. This causes these SNRs to be non-spherical, and to evolve faster than their Galactic counterparts. We develop an analytic theory for the evolution of explosions within a stellar wind, and verify it using a hydrodynamic code. We show that such explosions can evolve in one of three possible morphologies. Using these results we discuss the association between the two SNRs (SGR East and SGR A’s bipolar radio/X-ray lobes) and the two neutron stars (the Cannonball and SGR J1745-2900) near the GC. We show that, given the morphologies of the SNR and positions of the neutron stars, the only possible association is between SGR A’s bipolar radio/X-ray lobes and SGR J1745-2900. If a compact object was created in the explosion of SGR East, it remains undetected, and the SNR of the supernova that created the Cannonball has already disappeared.

Binding Energy and Equilibrium of Compact Objects

Directory of Open Access Journals (Sweden)

Germano M.

2014-04-01

Full Text Available The theoretical analysis of the existence of a limit mass for compact astronomic ob- jects requires the solution of the Einstein’s equations of g eneral relativity together with an appropriate equation of state. Analytical solutions exi st in some special cases like the spherically symmetric static object without energy sou rces that is here considered. Solutions, i.e. the spacetime metrics, can have a singular m athematical form (the so called Schwarzschild metric due to Hilbert or a nonsingula r form (original work of Schwarzschild. The former predicts a limit mass and, conse quently, the existence of black holes above this limit. Here it is shown that, the origi nal Schwarzschild met- ric permits compact objects, without mass limit, having rea sonable values for central density and pressure. The lack of a limit mass is also demonst rated analytically just imposing reasonable conditions on the energy-matter densi ty, of positivity and decreas- ing with radius. Finally the ratio between proper mass and to tal mass tends to 2 for high values of mass so that the binding energy reaches the lim it m (total mass seen by a distant observer. As it is known the negative binding energ y reduces the gravitational mass of the object; the limit of m for the binding energy provides a mechanism for stable equilibrium of any amount of mass to contrast the gravitatio nal collapse.

Gravitational effects of condensate dark matter on compact stellar objects

International Nuclear Information System (INIS)

Li, X.Y.; Wang, F.Y.; Cheng, K.S.

2012-01-01

We study the gravitational effect of non-self-annihilating dark matter on compact stellar objects. The self-interaction of condensate dark matter can give high accretion rate of dark matter onto stars. Phase transition to condensation state takes place when the dark matter density exceeds the critical value. A compact degenerate dark matter core is developed and alter the structure and stability of the stellar objects. Condensate dark matter admixed neutron stars is studied through the two-fluid TOV equation. The existence of condensate dark matter deforms the mass-radius relation of neutron stars and lower their maximum baryonic masses and radii. The possible effects on the Gamma-ray Burst rate in high redshift are discussed

The diversity of neutron stars: Nearby thermally emitting neutron stars and the compact central objects in supernova remnants

Science.gov (United States)

Kaplan, David L.

Neutron stars are invaluable tools for exploring stellar death, the physics of ultra-dense matter, and the effects of extremely strong magnetic fields. The observed population of neutron stars is dominated by the > 1000 radio pulsars, but there are distinct sub-populations that, while fewer in number, can have significant impact on our understanding of the issues mentioned above. These populations are the nearby isolated neutron stars discovered by ROSAT, and the central compact objects in supernova remnants. The studies of both of these populations have been greatly accelerated in recent years through observations with the Chandra X-ray Observatory and the XMM-Newton telescope. First, we discuss radio, optical, and X-ray observations of the nearby neutron stars aimed at determining their relation to the Galactic neutron star population and at unraveling their complex physical processes by determining the basic astronomical parameters that define the population -- instances, ages, and magnetic fields -- the uncertainties in which limit any attempt to derive basic physical parameters for these objects. We conclude that these sources are 10^6 year-old cooling neutron stars with magnetic fields above 10^13 G. Second, we describe the hollow supernova remnant problem: why many of the supernova remnants in the Galaxy have no indication central neutron stars. We have undertaken an X-ray census of neutron stars in a volume-limited sample of Galactic supernova remnants, and from it conclude that either many supernovae do not produce neutron stars contrary to expectation, or that neutron stars can have a wide range in cooling behavior that makes many sources disappear from the X-ray sky.

XMM-NEWTON MEASUREMENT OF THE GALACTIC HALO X-RAY EMISSION USING A COMPACT SHADOWING CLOUD

International Nuclear Information System (INIS)

Henley, David B.; Shelton, Robin L.; Cumbee, Renata S.; Stancil, Phillip C.

2015-01-01

Observations of interstellar clouds that cast shadows in the soft X-ray background can be used to separate the background Galactic halo emission from the local emission due to solar wind charge exchange (SWCX) and/or the Local Bubble (LB). We present an XMM-Newton observation of a shadowing cloud, G225.60–66.40, that is sufficiently compact that the on- and off-shadow spectra can be extracted from a single field of view (unlike previous shadowing observations of the halo with CCD-resolution spectrometers, which consisted of separate on- and off-shadow pointings). We analyzed the spectra using a variety of foreground models: one representing LB emission, and two representing SWCX emission. We found that the resulting halo model parameters (temperature T h ≈ 2 × 10 6 K, emission measure E h ≈4×10 −3  cm −6  pc) were not sensitive to the foreground model used. This is likely due to the relative faintness of the foreground emission in this observation. However, the data do favor the existence of a foreground. The halo parameters derived from this observation are in good agreement with those from previous shadowing observations, and from an XMM-Newton survey of the Galactic halo emission. This supports the conclusion that the latter results are not subject to systematic errors, and can confidently be used to test models of the halo emission

Workshop I – Black holes and compact objects

Indian Academy of Sciences (India)

This is a summary of the papers presented in session W1 on the papers submitted to the workshop I on the classical aspects of black holes and compact objects were classified into three categories: (i) theoretical aspects; (ii) astrophysical aspects; (iii) gravitational radiation. The three sessions were devoted each to one of ...

MHD Flows in Compact Astrophysical Objects Accretion, Winds and Jets

CERN Document Server

Beskin, Vasily S

2010-01-01

Accretion flows, winds and jets of compact astrophysical objects and stars are generally described within the framework of hydrodynamical and magnetohydrodynamical (MHD) flows. Analytical analysis of the problem provides profound physical insights, which are essential for interpreting and understanding the results of numerical simulations. Providing such a physical understanding of MHD Flows in Compact Astrophysical Objects is the main goal of this book, which is an updated translation of a successful Russian graduate textbook. The book provides the first detailed introduction into the method of the Grad-Shafranov equation, describing analytically the very broad class of hydrodynamical and MHD flows. It starts with the classical examples of hydrodynamical accretion onto relativistic and nonrelativistic objects. The force-free limit of the Grad-Shafranov equation allows us to analyze in detail the physics of the magnetospheres of radio pulsars and black holes, including the Blandford-Znajek process of energy e...

Hot super-dense compact object with particular EoS

Science.gov (United States)

Tito, E. P.; Pavlov, V. I.

2018-03-01

We show the possibility of existence of a self-gravitating spherically-symmetric equilibrium configuration for a neutral matter with neutron-like density, small mass M ≪ M_{⊙}, and small radius R ≪ R_{⊙}. We incorporate the effects of both the special and general theories of relativity. Such object may be formed in a cosmic cataclysm, perhaps an exotic one. Since the base equations of hydrostatic equilibrium are completed by the equation of state (EoS) for the matter of the object, we offer a novel, interpolating experimental data from high-energy physics, EoS which permits the existence of such compact system of finite radius. This EoS model possesses a critical state characterized by density ρc and temperature Tc. For such an object, we derive a radial distribution for the super-dense matter in "liquid" phase using Tolman-Oppenheimer-Volkoff equations for hydrostatic equilibrium. We demonstrate that a stable configuration is indeed possible (only) for temperatures smaller than the critical one. We derive the mass-radius relation (adjusted for relativistic corrections) for such small (M ≪ M_{⊙}) super-dense compact objects. The results are within the constraints established by both heavy-ion collision experiments and theoretical studies of neutron-rich matter.

Casimir potential of a compact object enclosed by a spherical cavity

International Nuclear Information System (INIS)

Zaheer, Saad; Rahi, Sahand Jamal; Emig, Thorsten; Jaffe, Robert L.

2010-01-01

We study the electromagnetic Casimir interaction of a compact object contained inside a closed cavity of another compact object. We express the interaction energy in terms of the objects' scattering matrices and translation matrices that relate the coordinate systems appropriate to each object. When the enclosing object is an otherwise empty metallic spherical shell, much larger than the internal object, and the two are sufficiently separated, the Casimir force can be expressed in terms of the static electric and magnetic multipole polarizabilities of the internal object, which is analogous to the Casimir-Polder result. Although it is not a simple power law, the dependence of the force on the separation of the object from the containing sphere is a universal function of its displacement from the center of the sphere, independent of other details of the object's electromagnetic response. Furthermore, we compute the exact Casimir force between two metallic spheres contained one inside the other at arbitrary separations. Finally, we combine our results with earlier work on the Casimir force between two spheres to obtain data on the leading-order correction to the proximity force approximation for two metallic spheres both outside and within one another.

OPTICAL/NEAR-INFRARED SELECTION OF RED QUASI-STELLAR OBJECTS: EVIDENCE FOR STEEP EXTINCTION CURVES TOWARD GALACTIC CENTERS?

Energy Technology Data Exchange (ETDEWEB)

Fynbo, J. P. U.; Krogager, J.-K.; Vestergaard, M.; Geier, S. [Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen O (Denmark); Venemans, B. [Max-Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany); Noterdaeme, P. [CNRS-UPMC, UMR7095, Institut d' Astrophysique de Paris, 98bis Bd. Arago, F-75014 Paris (France); Moller, P. [European Southern Observatory, Karl-Schwarzschildstrasse 2, D-85748 Garching bei Muenchen (Germany); Ledoux, C. [European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago 19 (Chile)

2013-01-15

We present the results of a search for red QSOs using a selection based on optical imaging from the Sloan Digital Sky Survey (SDSS) and near-infrared imaging from UKIDSS. Our main goal with the selection is to search for QSOs reddened by foreground dusty absorber galaxies. For a sample of 58 candidates (including 20 objects fulfilling our selection criteria that already have spectra in the SDSS), 46 (79%) are confirmed to be QSOs. The QSOs are predominantly dust-reddened except for a handful at redshifts z {approx}> 3.5. However, the dust is most likely located in the QSO host galaxies (and for two, the reddening is primarily caused by Galactic dust) rather than in the intervening absorbers. More than half of the QSOs show evidence of associated absorption (BAL absorption). Four (7%) of the candidates turned out to be late-type stars, and another four (7%) are compact galaxies. We could not identify the remaining four objects. In terms of their optical spectra, these QSOs are similar to the QSOs selected in the FIRST-2MASS Red Quasar Survey except they are on average fainter, more distant, and only two are detected in the FIRST survey. As per the usual procedure, we estimate the amount of extinction using the SDSS QSO template reddened by Small-Magellanic-Cloud-(SMC) like dust. It is possible to get a good match to the observed (rest-frame ultraviolet) spectra, but it is not possible to match the observed near-IR photometry from UKIDSS for nearly all the reddened QSOs. The most likely reasons are that the SDSS QSO template is too red at optical wavelengths due to contaminating host galaxy light and because the assumed SMC extinction curve is too shallow. Three of the compact galaxies display old stellar populations with ages of several Gyr and masses of about 10{sup 10} M{sub Sun} (based on spectral energy distribution modeling). The inferred stellar densities in these galaxies exceed 10{sup 10} M{sub Sun} kpc{sup -2}, which is among the highest measured for early

Compact objects in pure Lovelock theory

Science.gov (United States)

Dadhich, Naresh; Hansraj, Sudan; Chilambwe, Brian

For static fluid interiors of compact objects in pure Lovelock gravity (involving only one Nth order term in the equation), we establish similarity in solutions for the critical odd and even d = 2N + 1, 2N + 2 dimensions. It turns out that in critical odd d = 2N + 1 dimensions, there cannot exist any bound distribution with a finite radius, while in critical even d = 2N + 2 dimensions, all solutions have similar behavior. For exhibition of similarity, we would compare star solutions for N = 1, 2 in d = 4 Einstein and d = 6 in Gauss-Bonnet theory, respectively. We also obtain the pure Lovelock analogue of the Finch-Skea model.

The Chandra Dust-scattering Halo of Galactic Center Transient Swift J174540.7–290015

Energy Technology Data Exchange (ETDEWEB)

Corrales, L. R. [Einstein Fellow, University of Wisconsin-Madison, 475 North Charter Street, Madison, WI, 53706 (United States); Mon, B.; Haggard, D. [McGill Space Institute, McGill University, 3550 University Street, Montreal, QC, H3A 2A7 (Canada); Baganoff, F. K. [MIT Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue, Cambridge, MA, 02139 (United States); Garmire, G. [Huntingdon Institute for X-ray Astronomy, 10677 Franks Road Huntingdon, PA, 16652 (United States); Degenaar, N. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 OHA (United Kingdom); Reynolds, M. [University of Michigan, 1085 S. University, 311 West Hall, Ann Arbor, MI 48109 (United States)

2017-04-20

We report the detection of a dust-scattering halo around a recently discovered X-ray transient, Swift J174540.7–290015, which in early 2016 February underwent one of the brightest outbursts ( F {sub X} ≈ 5 × 10{sup −10} erg cm{sup −2} s{sup −1}) observed from a compact object in the Galactic Center field. We analyze four Chandra images that were taken as follow-up observations to Swift discoveries of new Galactic Center transients. After adjusting our spectral extraction for the effects of detector pile-up, we construct a point-spread function for each observation and compare it to the GC field before the outburst. We find residual surface brightness around Swift J174540.7–290015, which has a shape and temporal evolution consistent with the behavior expected from X-rays scattered by foreground dust. We examine the spectral properties of the source, which shows evidence that the object transitioned from a soft to hard spectral state as it faded below L {sub X} ∼ 10{sup 36} erg s{sup −1}. This behavior is consistent with the hypothesis that the object is a low-mass X-ray binary in the Galactic Center.

New Galactic Candidate Luminous Blue Variables and Wolf-Rayet Stars

Science.gov (United States)

Stringfellow, Guy S.; Gvaramadze, Vasilii V.; Beletsky, Yuri; Kniazev, Alexei Y.

2012-04-01

We have undertaken a near-infrared spectral survey of stars associated with compact mid-IR shells recently revealed by the MIPSGAL (24 μm) and GLIMPSE (8 μm) Spitzer surveys, whose morphologies are typical of circumstellar shells produced by massive evolved stars. Through spectral similarity with known Luminous Blue Variable (LBV) and Wolf-Rayet (WR) stars, a large population of candidate LBVs (cLBVs) and a smaller number of new WR stars are being discovered. This significantly increases the Galactic cLBV population and confirms that nebulae are inherent to most (if not all) objects of this class.

Properties of BL Lac objects

International Nuclear Information System (INIS)

Wolfe, A.M.; Pittsburgh, University, Pittsburgh, Pa.)

1980-01-01

The properties of BL Lacertae objects are examined in light of their recently realized similarities to quasars and associations with galactic radiation. The criteria typically used to define BL Lac objects are analyzed, with attention given to radio spectra, optical continual, radio and optical variability, optical polarization and emission lines, and evidence that BL Lac objects and optically violent variables represent the most compact and strongly variable sources among the general class of quasars is discussed. Connections between BL Lac objects and the galaxies in which they have been observed to be embedded are discussed and it is pointed out that no low-luminosity quasars have been found to be associated with first-ranked giant ellipticals. Future observations which may clarify the properties and relationships of BL Lac objects are indicated

Supermassive dark-matter Q-balls in galactic centers?

Energy Technology Data Exchange (ETDEWEB)

Troitsky, Sergey [Institute for Nuclear Research of the Russian Academy of Sciences,60th October Anniversary Prospect 7a, Moscow 117312 (Russian Federation); Moscow Institute for Physics and Technology,Institutskii per. 9, 141700, Dolgoprudny, Moscow Region (Russian Federation)

2016-11-11

Though widely accepted, it is not proven that supermassive compact objects (SMCOs) residing in galactic centers are black holes. In particular, the Milky Way’s SMCO can be a giant nontopological soliton, Q-ball, made of a scalar field: this fits perfectly all observational data. Similar but tiny Q-balls produced in the early Universe may constitute, partly or fully, the dark matter. This picture explains in a natural way, why our SMCO has very low accretion rate and why the observed angular size of the corresponding radio source is much smaller than expected. Interactions between dark-matter Q-balls may explain how SMCOs were seeded in galaxies and resolve well-known problems of standard (non-interacting) dark matter.

Improving a real-time object detector with compact temporal information

DEFF Research Database (Denmark)

Ahrnbom, Martin; Jensen, Morten Bornø; Åström, Kalle

2017-01-01

Neural networks designed for real-time object detection have recently improved significantly, but in practice, look- ing at only a single RGB image at the time may not be ideal. For example, when detecting objects in videos, a foreground detection algorithm can be used to obtain compact temporal......, a problem this approach is well suited for. The ac- curacy was found to improve significantly (up to 66%), with a roughly 40% increase in computational time....

Compact objects for everyone: I. White dwarf stars

Energy Technology Data Exchange (ETDEWEB)

Jackson, C B; Taruna, J; Pouliot, S L; Ellison, B W; Lee, D D; Piekarewicz, J [Department of Physics, Florida State University, Tallahassee, FL 32306 (United States)

2005-09-01

Based upon previous discussions on the structure of compact stars geared towards undergraduate physics students, a real experiment involving two upper-level undergraduate physics students, a beginning physics graduate and two advanced graduate students was conducted. A recent addition to the physics curriculum at Florida State University, The Physics of Stars, sparked quite a few students' interests in the subject matter involving stellar structure. This, coupled with Stars and statistical physics by Balian and Blaizot (1999 Am. J. Phys. 67 1189) and Neutron stars for undergraduates by Silbar and Reddy (2004 Am. J. Phys. 72 892), is the cornerstone of this small research group who tackled solving the structure equations for compact objects in the summer of 2004. Through the use of a simple finite-difference algorithm coupled to Microsoft Excel and Maple, solutions to the equations for stellar structure are presented in the Newtonian regime appropriate to the physics of white dwarf stars.

Compact objects for everyone: I. White dwarf stars

International Nuclear Information System (INIS)

Jackson, C B; Taruna, J; Pouliot, S L; Ellison, B W; Lee, D D; Piekarewicz, J

2005-01-01

Based upon previous discussions on the structure of compact stars geared towards undergraduate physics students, a real experiment involving two upper-level undergraduate physics students, a beginning physics graduate and two advanced graduate students was conducted. A recent addition to the physics curriculum at Florida State University, The Physics of Stars, sparked quite a few students' interests in the subject matter involving stellar structure. This, coupled with Stars and statistical physics by Balian and Blaizot (1999 Am. J. Phys. 67 1189) and Neutron stars for undergraduates by Silbar and Reddy (2004 Am. J. Phys. 72 892), is the cornerstone of this small research group who tackled solving the structure equations for compact objects in the summer of 2004. Through the use of a simple finite-difference algorithm coupled to Microsoft Excel and Maple, solutions to the equations for stellar structure are presented in the Newtonian regime appropriate to the physics of white dwarf stars

On the number of light rings in curved spacetimes of ultra-compact objects

Science.gov (United States)

Hod, Shahar

2018-01-01

In a very interesting paper, Cunha, Berti, and Herdeiro have recently claimed that ultra-compact objects, self-gravitating horizonless solutions of the Einstein field equations which have a light ring, must possess at least two (and, in general, an even number of) light rings, of which the inner one is stable. In the present compact paper we explicitly prove that, while this intriguing theorem is generally true, there is an important exception in the presence of degenerate light rings which, in the spherically symmetric static case, are characterized by the simple dimensionless relation 8 πrγ2 (ρ +pT) = 1 [here rγ is the radius of the light ring and { ρ ,pT } are respectively the energy density and tangential pressure of the matter fields]. Ultra-compact objects which belong to this unique family can have an odd number of light rings. As a concrete example, we show that spherically symmetric constant density stars with dimensionless compactness M / R = 1 / 3 possess only one light ring which, interestingly, is shown to be unstable.

Planck 2013 results. XXVIII. The Planck Catalogue of Compact Sources

DEFF Research Database (Denmark)

Planck Collaboration,; Ade, P. A. R.; Aghanim, N.

2013-01-01

The Planck Catalogue of Compact Sources (PCCS) is the catalogue of sources detected in the Planck nominal mission data. It consists of nine single-frequency catalogues of compact sources containing reliable sources, both Galactic and extragalactic, detected over the entire sky. The PCCS covers th...

Binary compact object inspiral: Detection expectations

Indian Academy of Sciences (India)

... events/yr. These predictions, for the first time, bring the expectations for DNS detections by initial LIGO .... our galactic event rate out to the local group. ..... VK thanks her collaborators in the work reviewed here: C Kim, P Grandclément,. C Ihm ...

New Evidence for a Black Hole in the Compact Binary Cygnus X-3

Science.gov (United States)

Shrader, Chris R.; Titarchuk, Lev; Shaposhnikov, Nikolai

2010-01-01

The bright and highly variable X-ray and radio source known as Cygnus X-3 was among the first X-ray sources discovered, yet it remains in many ways an enigma. Its known to consist of a massive. Wolf-Rayet primary in an extremely tight orbit with a compact object. Yet one of the most basic of pa.ranietern the mass of the compact object - is not known. Nor is it even clear whether its is a neutron star or a black hole. In this Paper we present our analysis of the broad-band high-energy continua covering a substantial range in luminosity and spectral morphology. We apply these results to a recently identified scaling relationship which has been demonstrated to provide reliable estimates of the compact object mass in a number of accretion powered binaries. This analysis leads us to conclude that the compact object in Cygnus X-3 has a mass greater than 4.2 solar mass thus clearly indicative of a black hole and as such resolving a longstanding issue. The full range of uncertainty in our analysis and from using a. range of recently published distance estimates constrains the compact object mass to lie between 4.2 solar mass and 14.4 solar mass. Our favored estimate, based on a 9.0 kpc distance estimate is approx. l0 solar mass, with the. error margin of 3.2 solar masses. This result may thus pose challenges to shared-envelope evolutionary models of compact binaries. as well as establishing Cygnus X-3 as the first confirmed accretion-powered galactic gamma: ray source.

Monitoring the Galactic Centre with the Australia Telescope Compact Array

Czech Academy of Sciences Publication Activity Database

Borkar, A.; Eckart, A.; Straubmeier, C.; Kunneriath, Devaky; Jalali, B.; Sabha, N.; Shahzamanian, B.; García-Marín, M.; Valencia-S, M.; Sjouwerman, L.; Britzen, S.; Karas, Vladimír; Dovčiak, Michal; Donea, A.; Zensus, A.

2016-01-01

Roč. 458, č. 3 (2016), s. 2336-2349 ISSN 0035-8711 R&D Projects: GA ČR(CZ) GC13-00070J Institutional support: RVO:67985815 Keywords : galactic Centre * black hole Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.961, year: 2016

Black holes, white dwarfs, and neutron stars the physics of compact objects

CERN Document Server

Shapiro, Stuart Louis

1983-01-01

This self-contained textbook brings together many different branches of physics--e.g. nuclear physics, solid state physics, particle physics, hydrodynamics, relativity--to analyze compact objects. The latest astronomical data is assessed

Planck 2015 results: XXVIII. The Planck Catalogue of Galactic cold clumps

DEFF Research Database (Denmark)

Ade, P. A R; Aghanim, N.; Arnaud, M.

2016-01-01

We present the Planck Catalogue of Galactic Cold Clumps (PGCC), an all-sky catalogue of Galactic cold clump candidates detected by Planck. This catalogue is the full version of the Early Cold Core (ECC) catalogue, which was made available in 2011 with the Early Release Compact Source Catalogue (E...

Gravitational-wave signatures of exotic compact objects and of quantum corrections at the horizon scale

CERN Document Server

Cardoso, Vitor; Macedo, Caio F. B.; Palenzuela, Carlos; Pani, Paolo

2016-01-01

Gravitational waves from binary coalescences provide one of the cleanest signatures of the nature of compact objects. It has been recently argued that the post-merger ringdown waveform of exotic ultracompact objects is initially identical to that of a black-hole, and that putative corrections at the horizon scale will appear as secondary pulses after the main burst of radiation. Here we extend this analysis in three important directions: (i)~we show that this result applies to a large class of exotic compact objects with a photon sphere for generic orbits in the test-particle limit; (ii)~we investigate the late-time ringdown in more detail, showing that it is universally characterized by a modulated and distorted train of "echoes" of the modes of vibration associated with the photon sphere; (iii)~we study for the first time equal-mass, head-on collisions of two ultracompact boson stars and compare their gravitational-wave signal to that produced by a pair of black-holes. If the initial objects are compact eno...

Positrons annihilation and the Galactic center

International Nuclear Information System (INIS)

Wallyn, Pierre

1992-01-01

The Galactic center has been observed in gamma rays, many times since more than two decades and we do not still have a full comprehensive picture of this region. It is fairly well established that the 511 keV annihilation line has two origins: a steady diffuse emission, which follows more or less the type I supernovae distribution along the Galactic plane and a variable emission coming from the positrons emitted by (at least) one compact object and annihilating in a nearby cold molecular cloud. We present here an analysis of the profiles and intensifies of the 511 keV annihilation line observed in the direction of the Galactic center. We find that a warm medium (temperature of 8000 K) can describe the annihilation of positrons from the diffuse component of the line. The high state observations of the 511 keV line can be explained if the time-variable component is coming from the annihilation of the positrons in a cold medium (temperature around 80 K). This constraint on the annihilation medium temperature supports the association with the molecular cloud G-0.86-0.08 in the direction of 1E1740.7-2942. On may 22, 1989, HEXAGONE detected a narrow 511 keV line and also a broad emission around 170 keV in the direction of the Galactic center. Two weeks before, EXITE observed in the same direction a new transient source EXS 1737.9-2952 which showed a bump around 102 keV. We propose a simple semi-quantitative model which can mimic the bumps as well as its time variations and emphasize the strong similarities between EXS1737.9-2952 and Nova Muscae. We study the behaviour of positron annihilation by charge exchange in the cold phase of the interstellar medium. We calculate formula for the slowing-down time before thermalization of positrons of a given initial energy, for different medium densities. Our scenario explains the lack of detection of the recombination lines from positronium and gives new constraints on their possible observation. (author) [fr

An asymmetric distribution of positrons in the Galactic disk revealed by γ-rays

International Nuclear Information System (INIS)

Weidenspointner, G.; Skinner, G.; Jean, P.; Knoedlseder, J.; Von Ballmoos, P.; Bignami, G.; Weidenspointner, G.; Diehl, R.; Strong, A.; Weidenspointner, G.; Skinner, G.; Skinner, G.; Skinner, G.; Cordier, B.; Schanne, S.; Winkler, Ch.; Bignami, G.

2008-01-01

Gamma-ray line radiation at 511 keV is the signature of electron positron annihilation. Such radiation has been known for 30 years to come from the general direction of the Galactic Centre, but the origin of the positrons has remained a mystery. Stellar nucleosynthesis, accreting compact objects, and even the annihilation of exotic dark-matter particles have all been suggested. Here we report a distinct asymmetry in the 511 keV line emission coming from the inner Galactic disk (∼ 10-50 degrees from the Galactic Centre). This asymmetry resembles an asymmetry in the distribution of low mass X-ray binaries with strong emission at photon energies ≥20 keV ('hard' LMXBs), indicating that they may be the dominant origin of the positrons. Although it had long been suspected that electron-positron pair plasmas may exist in X-ray binaries, it was not evident that many of the positrons could escape to lose energy and ultimately annihilate with electrons in the interstellar medium and thus lead to the emission of a narrow 511 keV line. For these models, our result implies that up to a few times 10 41 positrons escape per second from a typical hard LMXB. Positron production at this level from hard LMXBs in the Galactic bulge would reduce (and possibly eliminate) the need for more exotic explanations, such as those involving dark matter. (authors)

An asymmetric distribution of positrons in the Galactic disk revealed by {gamma}-rays

Energy Technology Data Exchange (ETDEWEB)

Weidenspointner, G; Skinner, G; Jean, P; Knoedlseder, J; Von Ballmoos, P; Bignami, G [UPS, CNRS, Ctr Etud Spatiale Rayonnements, Toulouse 4, (France); Weidenspointner, G; Diehl, R; Strong, A [Max Planck Inst Extraterr Phys, D-85741 Garching, (Germany); Weidenspointner, G [MPI Halbleiterlab, D-81739 Munich, (Germany); Skinner, G [NASA, CRESST, Greenbelt, MD 20771 (United States); Skinner, G [NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 (United States); Skinner, G [Univ Maryland, Dept Astron, College Pk, MD 20742 (United States); Cordier, B; Schanne, S [CEA Saclay, DSM, DAPNIA, SAp, F-91191 Gif Sur Yvette, (France); Winkler, Ch [ESA, ESTEC, SCI SA, NL-2201 AZ Noordwijk, (Netherlands); Bignami, G [IUSS, I-27100 Pavia, (Italy)

2008-07-01

Gamma-ray line radiation at 511 keV is the signature of electron positron annihilation. Such radiation has been known for 30 years to come from the general direction of the Galactic Centre, but the origin of the positrons has remained a mystery. Stellar nucleosynthesis, accreting compact objects, and even the annihilation of exotic dark-matter particles have all been suggested. Here we report a distinct asymmetry in the 511 keV line emission coming from the inner Galactic disk ({approx} 10-50 degrees from the Galactic Centre). This asymmetry resembles an asymmetry in the distribution of low mass X-ray binaries with strong emission at photon energies {>=}20 keV ('hard' LMXBs), indicating that they may be the dominant origin of the positrons. Although it had long been suspected that electron-positron pair plasmas may exist in X-ray binaries, it was not evident that many of the positrons could escape to lose energy and ultimately annihilate with electrons in the interstellar medium and thus lead to the emission of a narrow 511 keV line. For these models, our result implies that up to a few times 10{sup 41} positrons escape per second from a typical hard LMXB. Positron production at this level from hard LMXBs in the Galactic bulge would reduce (and possibly eliminate) the need for more exotic explanations, such as those involving dark matter. (authors)

The Einstein objective grating spectrometer survey of galactic binary X-ray sources

Science.gov (United States)

Vrtilek, S. D.; Mcclintock, J. E.; Seward, F. D.; Kahn, S. M.; Wargelin, B. J.

1991-01-01

The results of observations of 22 bright Galactic X-ray point sources are presented, and the most reliable measurements to date of X-ray column densities to these sources are derived. The results are consistent with the idea that some of the objects have a component of column density intrinsic to the source in addition to an interstellar component. The K-edge absorption due to oxygen is clearly detected in 10 of the sources and the Fe L and Ne K edges are detected in a few. The spectra probably reflect emission originating in a collisionally excited region combined with emission from a photoionized region excited directly by the central source.

The MACHO Project Sample of Galactic Bulge High-Amplitude Scuti Stars: Pulsation Behavior and Stellar Properties

International Nuclear Information System (INIS)

Bennett, D.P.; Cook, K.H.; Freeman, K.C.; Geha, M.; Griest, K.; Lehner, M.J.; Marshall, S.L.; McNamara, B.J.; Minniti, D.; Nelson, C.; Peterson, B.A.; Popowski, P.; Pratt, M.R.; Quinn, P.J.; Rodgers, A.W.; Sutherland, W.; Templeton, M.R.; Vandehei, T.; Welch, D.L.

1999-01-01

We have detected 90 objects with periods and lightcurve structure similar to those of field(delta) Scuti stars, using the Massive Compact Halo Object (MACHO) Project database of Galactic bulge photometry. If we assume similar extinction values for all candidates and absolute magnitudes similar to those of other field high-amplitude(delta) Scuti stars (HADS), the majority of these objects lie in or near the Galactic bulge. At least two of these objects are likely foreground(delta) Scuti stars, one of which may be an evolved nonradial pulsator, similar to other evolved, disk-population(delta) Scuti stars. We have analyzed the light curves of these objects and find that they are similar to the light curves of field(delta) Scuti stars and the(delta) Scuti stars found by the Optical Gravitational Lens Experiment (OGLE). However, the amplitude distribution of these sources lies between those of low- and high-amplitude(delta) Scuti stars, which suggests that they may be an intermediate population. We have found nine double-mode HADS with frequency ratios ranging from 0.75 to 0.79, four probable double- and multiple-mode objects, and another four objects with marginal detections of secondary modes. The low frequencies (5-14 cycles d(sup -1)) and the observed period ratios of(approx)0.77 suggest that the majority of these objects are evolved stars pulsating in fundamental or first overtone radial modes

Planck 2015 results. XXVIII. The Planck Catalogue of Galactic Cold Clumps

CERN Document Server

Ade, P.A.R.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Banday, A.J.; Barreiro, R.B.; Bartolo, N.; Battaner, E.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bonaldi, A.; Bonavera, L.; Bond, J.R.; Borrill, J.; Bouchet, F.R.; Boulanger, F.; Bucher, M.; Burigana, C.; Butler, R.C.; Calabrese, E.; Catalano, A.; Chamballu, A.; Chiang, H.C.; Christensen, P.R.; Clements, D.L.; Colombi, S.; Colombo, L.P.L.; Combet, C.; Couchot, F.; Coulais, A.; Crill, B.P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R.D.; Davis, R.J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Désert, F.-X.; Dickinson, C.; Diego, J.M.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Ducout, A.; Dupac, X.; Efstathiou, G.; Elsner, F.; Enßlin, T.A.; Eriksen, H.K.; Falgarone, E.; Fergusson, J.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A.A.; Franceschi, E.; Frejsel, A.; Galeotta, S.; Galli, S.; Ganga, K.; Giard, M.; Giraud-Héraud, Y.; Gjerløw, E.; González-Nuevo, J.; Górski, K.M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J.E.; Hansen, F.K.; Hanson, D.; Harrison, D.L.; Helou, G.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S.R.; Hivon, E.; Hobson, M.; Holmes, W.A.; Hornstrup, A.; Hovest, W.; Huffenberger, K.M.; Hurier, G.; Jaffe, A.H.; Jaffe, T.R.; Jones, W.C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kisner, T.S.; Knoche, J.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lamarre, J.-M.; Lasenby, A.; Lattanzi, M.; Lawrence, C.R.; Leonardi, R.; Lesgourgues, J.; Levrier, F.; Liguori, M.; Lilje, P.B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P.M.; Macías-Pérez, J.F.; Maggio, G.; Maino, D.; Mandolesi, N.; Mangilli, A.; Marshall, D.J.; Martin, P.G.; Martínez-González, E.; Masi, S.; Matarrese, S.; Mazzotta, P.; McGehee, P.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mitra, S.; Miville-Deschênes, M.-A.; Moneti, A.; Morgante, G.; Mortlock, D.; Moss, A.; Munshi, D.; Murphy, J.A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C.B.; Nørgaard-Nielsen, H.U.; Noviello, F.; Novikov, D.; Novikov, I.; Oxborrow, C.A.; Paci, F.; Pagano, L.; Pajot, F.; Paladini, R.; Paoletti, D.; Pasian, F.; Patanchon, G.; Pearson, T.J.; Pelkonen, V.-M.; Perdereau, O.; Perotto, L.; Perrotta, F.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Pratt, G.W.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J.P.; Reach, W.T.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Renzi, A.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rossetti, M.; Roudier, G.; Rubiño-Martín, J.A.; Rusholme, B.; Sandri, M.; Santos, D.; Savelainen, M.; Savini, G.; Scott, D.; Seiffert, M.D.; Shellard, E.P.S.; Spencer, L.D.; Stolyarov, V.; Sudiwala, R.; Sunyaev, R.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J.A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Tuovinen, J.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Wade, L.A.; Wandelt, B.D.; Wehus, I.K.; Yvon, D.; Zacchei, A.

2016-01-01

We present the Planck Catalogue of Galactic Cold Clumps (PGCC), an all-sky catalogue of Galactic cold clump candidates detected by Planck. This catalogue is the full version of the Early Cold Core (ECC) catalogue, which was made available in 2011 with the Early Release Compact Source Catalogue (ERCSC) and contained 915 high S/N sources. It is based on the Planck 48 months mission data that are currently being released to the astronomical community. The PGCC catalogue is an observational catalogue consisting exclusively of Galactic cold sources. The three highest Planck bands (857, 545, 353 GHz) have been combined with IRAS data at 3 THz to perform a multi-frequency detection of sources colder than their local environment. After rejection of possible extragalactic contaminants, the PGCC catalogue contains 13188 Galactic sources spread across the whole sky, i.e., from the Galactic plane to high latitudes, following the spatial distribution of the main molecular cloud complexes. The median temperature of PGCC so...

VERITAS Galactic Observations

Energy Technology Data Exchange (ETDEWEB)

Hughes, Gareth

2013-06-15

We report on recent Galactic results and discoveries made by the VERITAS collaboration. The Very Energetic Radiation Imaging Telescope Array System (VERITAS) is a ground-based gamma-ray observatory, located in southern Arizona, able to detect gamma rays of energies from 100 GeV up to 30 TeV. VERITAS has been fully operational since 2007 and its current sensitivity enables the detection of a 1% Crab Nebula flux at 5 sigma in under 30 hours. The observatory is well placed to view large parts of the galactic plane including its center, resulting in a strong galactic program. Objects routinely observed include Pulsars, Pulsar Wind Nebula, X-ray binaries and sources with unidentified counterparts in other wavelengths.

A new direction for dark matter research: intermediate-mass compact halo objects

Energy Technology Data Exchange (ETDEWEB)

Chapline, George F. [Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA (United States); Frampton, Paul H., E-mail: george.chapline@gmail.com, E-mail: paul.h.frampton@gmail.com [15 Summerheights, 29 Water Eaton Road, Oxford OX2 7PG (United Kingdom)

2016-11-01

The failure to find evidence for elementary particles that could serve as the constituents of dark matter brings to mind suggestions that dark matter might consist of massive compact objects (MACHOs). In particular, it has recently been argued that MACHOs with masses > 15 M {sub ⊙} may have been prolifically produced at the onset of the big bang. Although a variety of astrophysical signatures for primordial MACHOs with masses in this range have been discussed in the literature, we favor a strategy that uses the potential for magnification of stars outside our galaxy due to gravitational microlensing of these stars by MACHOs in the halo of our galaxy. We point out that the effect of the motion of the Earth on the shape of the micro-lensing brightening curves provides a promising approach to testing over the course of next several years the hypothesis that dark matter consists of massive compact objects.

The galactic distribution of pulsars

International Nuclear Information System (INIS)

Lyne, A.G.

1981-01-01

The galactic distribution of pulsars follows the general form of many population I objects in galactocentric radius, but has a wide distribution above and below the galactic plane due to high space velocities imparted to the pulsars at birth. The evidence for this model is described and the various factors involved in estimating the total galactic population and the galactic birthrate of pulsars are discussed. The various estimates of the galactic population which cluster around 5 x 10 5 are seen to be critically dependent upon the cut-off at low luminosities and upon the value of the mean electron density within 500 pc of the Earth. Estimates of the lifetimes of pulsars are available from both the characteristic ages and proper motion measurements and both give values of about 5 million years. The implied birthrate of one in every 10 years is barely compatible with most estimates of the galactic supernova rate. (Auth.)

Where Have All the Central Compact Objects Gone?

Science.gov (United States)

Gotthelf, Eric

2017-09-01

The central compact object (CCO) class of young neutron stars in supernova remnants (SNRs) are detected only as thermal X-ray sources. Characterized by weak magnetic fields, a fundamental puzzle of their evolution is the absence of any evidence for their numerous descendants in X-ray or radio surveys. We know that their true ages are much younger than their inferred timing ages, which implies that some apparently old radio pulsars may actually be evolved CCOs in dispersed SNRs, young enough to be detected as still hot thermal X-ray sources. Here we propose a complete volume limited survey of apparently old radio pulsars to search for descendants of CCOs, providing important constraints on neutron star evolution.

Probing the Large Faraday Rotation Measure Environment of Compact Active Galactic Nuclei

Directory of Open Access Journals (Sweden)

Alice Pasetto

2018-03-01

Full Text Available Knowing how the ambient medium in the vicinity of active galactic nuclei (AGNs is shaped is crucial to understanding generally the evolution of such cosmic giants as well as AGN jet formation and launching. Thanks to the new broadband capability now available at the Jansky Very Large Array (JVLA, we can study changes in polarization properties, fractional polarization, and polarization angles, together with the total intensity spectra of a sample of 14 AGNs, within a frequency range from 1 to 12 GHz. Depolarization modeling has been performed by means of so-called “qu-fitting” to the polarized data, and a synchrotron self absorption model has been used for fitting to the total intensity data. We found complex behavior both in the polarization spectra and in the total intensity spectra, and several Faraday components with a large rotation measure (RM and several synchrotron components were needed to represent these spectra. Here, results for three targets are shown. This new method of analyzing broadband polarization data through qu-fitting successfully maps the complex surroundings of unresolved objects.

Accreting Compact Object at the Center of the Supernova Remnant RCW 103.

Science.gov (United States)

Sanwal, D.; Garmire, G. P.; Garmire, A.; Pavlov, G. G.; Mignani, R.

2002-05-01

We observed the radio-quiet central compact object of the supernova remnant RCW 103 with the Chandra ACIS during 13.8 hours on 2002 March 3, when the source was in high state, with a time-averaged flux of 8*E-12 erg cm-2 s-1 in the 0.5--8.0 keV band. The complex light curve of the source shows a period of about 6.4 hours and two partial eclipses or dips per period, separated by 180o in phase. The variability of the source proves that it is powered by accretion, likely from a low-mass companion in a binary system. Deep near-IR observations of the source with VLT suggest a potential counterpart of the compact object about 2'' from the nominal Chandra position. The magnitudes of the potential counterpart are J ≈ 22.3, H ≈ 19.6, and Ks ≈ 18.5, with an uncertainty of about 0.5 mag. We will discuss possible interpretations of the observational results. This work was partially supported by NASA grants NAS8-01128 and NAG5-10865.

The MACHO Project Sample of Galactic Bulge High-Amplitude {delta} Scuti Stars: Pulsation Behavior and Stellar Properties

Energy Technology Data Exchange (ETDEWEB)

Alcock, C.; Allsman, R. A.; Alves, D. R.; Axelrod, T. S.; Becker, A. C.; Bennett, D. P.; Cook, K. H.; Freeman, K. C.; Geha, M.; Griest, K. (and others)

2000-06-20

We have detected 90 objects with periods and light-curve structures similar to those of field {delta} Scuti stars using the Massive Compact Halo Object (MACHO) Project database of Galactic bulge photometry. If we assume similar extinction values for all candidates and absolute magnitudes similar to those of other field high-amplitude {delta} Scuti stars (HADS), the majority of these objects lie in or near the Galactic bulge. At least two of these objects are likely foreground {delta} Scuti stars, one of which may be an evolved nonradial pulsator, similar to other evolved, disk-population {delta} Scuti stars. We have analyzed the light curves of these objects and find that they are similar to the light curves of field {delta} Scuti stars and the {delta} Scuti stars found by the Optical Gravitational Lens Experiment (OGLE). However, the amplitude distribution of these sources lies between those of low- and high-amplitude {delta} Scuti stars, which suggests that they may be an intermediate population. We have found nine double-mode HADS with frequency ratios ranging from 0.75 to 0.79, four probable double- and multiple-mode objects, and another four objects with marginal detections of secondary modes. The low frequencies (5-14 cycles day-1) and the observed period ratios of {approx}0.77 suggest that the majority of these objects are evolved stars pulsating in fundamental or first overtone radial modes. (c) 2000 The American Astronomical Society.

HI Clouds Near the Galactic Center: Possible Tracers of the Nuclear Wind

Science.gov (United States)

Lockman, Felix J.; McClure-Griffiths, Naomi; DiTeodoro, Enrico

2017-01-01

We have used the Green Bank Telescope to discover more than one hundred neutral hydrogen clouds that appear to be embedded in the Fermi Bubble -- the Milky Way’s nuclear wind. With the other members of this population that were previously found with the Australia Telescope Compact Array, we now have a sample of about 200 such clouds. They are identified by their peculiar velocities. The cloud kinematics show no trace of Galactic rotation or association with the Galactic bar. Near longitude zero the clouds can have values of VLSR = +-200 km/s. No clouds have been detected with |VLSR| > 350 km/s. The clouds are concentrated toward the Galactic plane, but some are still found to |b|=10 degrees, or z > 1 kpc at the Galactic Center, where the current surveys end. These clouds are important tracers of conditions in the nuclear wind of the Milky Way.

Searching for axion-like particles with active-galactic nuclei

International Nuclear Information System (INIS)

Burrage, Clare; Davis, Anne-Christine; Shaw, Douglas J.

2009-12-01

Strong mixing between photons and axion-like particles in the magnetic fields of clusters of galaxies induces a scatter in the observed luminosities of compact sources in the cluster. This is used to construct a new test for axion-like particles; applied to observations of active galactic nuclei it is strongly suggestive of the existence of a light axion-like particle. (orig.)

Searching for axion-like particles with active-galactic nuclei

Energy Technology Data Exchange (ETDEWEB)

Burrage, Clare [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Davis, Anne-Christine [Centre for Mathematical Sciences, Cambridge (United Kingdom). Dept. of Applied Mathematics and Theoretical Physics; Shaw, Douglas J. [Queen Mary Univ. of London (United Kingdom). Astronomy Unit, School of Mathematical Sciences

2009-12-15

Strong mixing between photons and axion-like particles in the magnetic fields of clusters of galaxies induces a scatter in the observed luminosities of compact sources in the cluster. This is used to construct a new test for axion-like particles; applied to observations of active galactic nuclei it is strongly suggestive of the existence of a light axion-like particle. (orig.)

H I absorption in nearby compact radio galaxies

Science.gov (United States)

Glowacki, M.; Allison, J. R.; Sadler, E. M.; Moss, V. A.; Curran, S. J.; Musaeva, A.; Deng, C.; Parry, R.; Sligo, M. C.

2017-05-01

H I absorption studies yield information on both active galactic nucleus (AGN) feeding and feedback processes. This AGN activity interacts with the neutral gas in compact radio sources, which are believed to represent the young or recently re-triggered AGN population. We present the results of a survey for H I absorption in a sample of 66 compact radio sources at 0.040 100 km s-1) features, indicative of disturbed gas kinematics. Such broad, shallow and offset features are also found within low-excitation radio galaxies which is attributed to disturbed circumnuclear gas, consistent with early-type galaxies typically devoid of a gas-rich disc. Comparing mid-infrared colours of our galaxies with H I detections indicates that narrow and deep absorption features are preferentially found in late-type and high-excitation radio galaxies in our sample. These features are attributed to gas in galactic discs. By combining XMM-Newton archival data with 21-cm data, we find support that absorbed X-ray sources may be good tracers of H I content within the host galaxy. This sample extends previous H I surveys in compact radio galaxies to lower radio luminosities and provides a basis for future work exploring the higher redshift universe.

The Galactic Distribution of Massive Star Formation from the Red MSX Source Survey

Science.gov (United States)

Figura, Charles C.; Urquhart, J. S.

2013-01-01

Massive stars inject enormous amounts of energy into their environments in the form of UV radiation and molecular outflows, creating HII regions and enriching local chemistry. These effects provide feedback mechanisms that aid in regulating star formation in the region, and may trigger the formation of subsequent generations of stars. Understanding the mechanics of massive star formation presents an important key to understanding this process and its role in shaping the dynamics of galactic structure. The Red MSX Source (RMS) survey is a multi-wavelength investigation of ~1200 massive young stellar objects (MYSO) and ultra-compact HII (UCHII) regions identified from a sample of colour-selected sources from the Midcourse Space Experiment (MSX) point source catalog and Two Micron All Sky Survey. We present a study of over 900 MYSO and UCHII regions investigated by the RMS survey. We review the methods used to determine distances, and investigate the radial galactocentric distribution of these sources in context with the observed structure of the galaxy. The distribution of MYSO and UCHII regions is found to be spatially correlated with the spiral arms and galactic bar. We examine the radial distribution of MYSOs and UCHII regions and find variations in the star formation rate between the inner and outer Galaxy and discuss the implications for star formation throughout the galactic disc.

Casimir forces between compact objects: The scalar case

International Nuclear Information System (INIS)

Emig, T.; Graham, N.; Jaffe, R. L.; Kardar, M.

2008-01-01

We have developed an exact, general method to compute Casimir interactions between a finite number of compact objects of arbitrary shape and separation. Here, we present details of the method for a scalar field to illustrate our approach in its most simple form; the generalization to electromagnetic fields is outlined in Ref. [T. Emig, N. Graham, R. L. Jaffe, and M. Kardar, Phys. Rev. Lett. 99, 170403 (2007).]. The interaction between the objects is attributed to quantum fluctuations of source distributions on their surfaces, which we decompose in terms of multipoles. A functional integral over the effective action of multipoles gives the resulting interaction. Each object's shape and boundary conditions enter the effective action only through its scattering matrix. Their relative positions enter through universal translation matrices that depend only on field type and spatial dimension. The distinction of our method from the pairwise summation of two-body potentials is elucidated in terms of the scattering processes between three objects. To illustrate the power of the technique, we consider Robin boundary conditions φ-λ∂ n φ=0, which interpolate between Dirichlet and Neumann cases as λ is varied. We obtain the interaction between two such spheres analytically in a large separation expansion, and numerically for all separations. The cases of unequal radii and unequal λ are studied. We find sign changes in the force as a function of separation in certain ranges of λ and see deviations from the proximity force approximation even at short separations, most notably for Neumann boundary conditions

ATOMIC HYDROGEN IN A GALACTIC CENTER OUTFLOW

Energy Technology Data Exchange (ETDEWEB)

McClure-Griffiths, N. M.; Green, J. A.; Hill, A. S. [Australia Telescope National Facility, CSIRO Astronomy and Space Science, Marsfield, NSW 2122 (Australia); Lockman, F. J. [National Radio Astronomy Observatory, Green Bank, WV 24944 (United States); Dickey, J. M. [School of Physics and Mathematics, University of Tasmania, TAS 7001 (Australia); Gaensler, B. M.; Green, A. J., E-mail: naomi.mcclure-griffiths@csiro.au [Sydney Institute for Astronomy, School of Physics, The University of Sydney, NSW 2006 (Australia)

2013-06-10

We describe a population of small, high-velocity, atomic hydrogen clouds, loops, and filaments found above and below the disk near the Galactic center. The objects have a mean radius of 15 pc, velocity widths of {approx}14 km s{sup -1}, and are observed at |z| heights up to 700 pc. The velocity distribution of the clouds shows no signature of Galactic rotation. We propose a scenario where the clouds are associated with an outflow from a central star-forming region at the Galactic center. We discuss the clouds as entrained material traveling at {approx}200 km s{sup -1} in a Galactic wind.

ATOMIC HYDROGEN IN A GALACTIC CENTER OUTFLOW

International Nuclear Information System (INIS)

McClure-Griffiths, N. M.; Green, J. A.; Hill, A. S.; Lockman, F. J.; Dickey, J. M.; Gaensler, B. M.; Green, A. J.

2013-01-01

We describe a population of small, high-velocity, atomic hydrogen clouds, loops, and filaments found above and below the disk near the Galactic center. The objects have a mean radius of 15 pc, velocity widths of ∼14 km s –1 , and are observed at |z| heights up to 700 pc. The velocity distribution of the clouds shows no signature of Galactic rotation. We propose a scenario where the clouds are associated with an outflow from a central star-forming region at the Galactic center. We discuss the clouds as entrained material traveling at ∼200 km s –1 in a Galactic wind.

Magnetic braking in galactic flows

International Nuclear Information System (INIS)

Sparke, L.S.

1982-01-01

The nuclear fireworks of active galaxies are believed to derive their power from the kinetic energy of gas falling onto a massive central objects; mass shed from evolving galactic stars is an obvious source of fuel for this process. But this ejected material shares the galactic rotation, and a centrifugal barrier will prevent it from reaching the nucleus, if its angular momentum is not removed. This paper shows that, if the large-scale galactic magnetic field has a strong enough radial component, magnetic torques can act to spin down the infalling matter. Rotation of the interstellar gas induces a toroidal magnetic field, and Maxwell stresses remove angular momentum from the flow; gas can then fall inward to the galactic center. In this way, the monster in the nucleus can be fed on gas from a galaxy's own stars. The magnetic fields in M87 and NGC 1275, giant elliptical galaxies which are accreting from an intracluster medium, appear to be strong enough to allow magnetic braking

The galactic distribution of pulsars

International Nuclear Information System (INIS)

Lyne, A.G.

1982-01-01

The galactic distribution of pulsars follows the general form of many population I objects in galactocentric radius, but has a wide distribution above and below the plane due to high space velocities imparted to the pulsars at birth. Statistical studies of the properties of large numbers of pulsars and proper motion measurements demonstrate that the effective magnetic dipole moments decay on a timescale of about 8 million years. This work provides a better knowledge of pulsar evolution and ages and shows that a birthrate of one pulsar every 20 to 50 years is required to sustain the observed galactic population of 300,000. This rate is comparable with most recent estimates of the galactic supernova rate, but requires nearly all supernovae to produce active pulsars. (orig.)

The origin of interstellar asteroidal objects like 1I/2017 U1 'Oumuamua

Science.gov (United States)

Zwart, S. Portegies; Torres, S.; Pelupessy, I.; Bédorf, J.; Cai, Maxwell X.

2018-05-01

We study the origin of the interstellar object 1I/2017 U1 'Oumuamua by juxtaposing estimates based on the observations with simulations. We speculate that objects like 'Oumuamua are formed in the debris disc as left over from the star and planet formation process, and subsequently liberated. The liberation process is mediated either by interaction with other stars in the parental star-cluster, by resonant interactions within the planetesimal disc or by the relatively sudden mass loss when the host star becomes a compact object. Integrating 'Oumuamua backward in time in the Galactic potential together with stars from the Gaia-TGAS catalogue we find that about 1.3 Myr ago 'Oumuamua passed the nearby star HIP 17288 within a mean distance of 1.3 pc. By comparing nearby observed L-dwarfs with simulations of the Galaxy we conclude that the kinematics of 'Oumuamua is consistent with relatively young objects of 1.1-1.7 Gyr. We just met 'Oumuamua by chance, and with a derived mean Galactic density of ˜3 × 105 similarly sized objects within 100 au from the Sun or ˜1014 per cubic parsec we expect about 2 to 12 such visitors per year within 1 au from the Sun.

arXiv Light Primordial Exotic Compact Objects as All Dark Matter

CERN Document Server

Raidal, Martti; Vaskonen, Ville; Veermäe, Hardi

2018-06-13

The radiation emitted by horizonless exotic compact objects (ECOs), such as wormholes, 2-2-holes, fuzzballs, gravastars, boson stars, collapsed polymers, superspinars etc., is expected to be strongly suppressed when compared to the radiation of black holes. If large primordial curvature fluctuations collapse into such objects instead of black holes, they do not evaporate or evaporate much slower than black holes and could thus constitute all of the dark matter with masses below $M < 10^{-16}M_\\odot.$ We reevaluate the relevant experimental constraints for light ECOs in this mass range and show that very large new parameter space down to ECO masses $M\\sim 10\\,{\\rm TeV}$ opens up for light primordial dark matter. A new dedicated experimental program is needed to test this mass range of primordial dark matter.

On optical spectra of the NGC 6677 galaxy and the adjacent bright compact object

International Nuclear Information System (INIS)

Chuvaev, K.K.

1987-01-01

Spectral observations of NGC 6677 galaxy and the adjacent object carried out during six nights on the spectrograph with the image tube of 2.6-m Shain telescope showed, that the bright compact object is a star belonging to our galaxy but not an active galaxy. The NGC 6677 galaxy has sufficiently rich emission spectrum. On the basis of measured values of red shift Z, the inclination and the extent of emission lines, the mass of the galaxy has been estimated (M=7x10 9 M Sun )

Do massive compact objects without event horizon exist in infinite derivative gravity?

Science.gov (United States)

Koshelev, Alexey S.; Mazumdar, Anupam

2017-10-01

Einstein's general theory of relativity is plagued by cosmological and black-hole type singularities Recently, it has been shown that infinite derivative, ghost free, gravity can yield nonsingular cosmological and mini-black hole solutions. In particular, the theory possesses a mass-gap determined by the scale of new physics. This paper provides a plausible argument, not a no-go theorem, based on the Area-law of gravitational entropy that within infinite derivative, ghost free, gravity nonsingular compact objects in the static limit need not have horizons.

Compact objects in relativistic theories of gravity

Science.gov (United States)

Okada da Silva, Hector

2017-05-01

In this dissertation we discuss several aspects of compact objects, i.e. neutron stars and black holes, in relativistic theories of gravity. We start by studying the role of nuclear physics (encoded in the so-called equation of state) in determining the properties of neutron stars in general relativity. We show that low-mass neutron stars are potentially useful astrophysical laboratories that can be used to constrain the properties of the equation of state. More specifically, we show that various bulk properties of these objects, such as their quadrupole moment and tidal deformability, are tightly correlated. Next, we develop a formalism that aims to capture how generic modifications from general relativity affect the structure of neutron stars, as predicted by a broad class of gravity theories, in the spirit of the parametrized post-Newtonian formalism (PPN). Our "post-Tolman-Oppenheimer-Volkoff" formalism provides a toolbox to study both stellar structure and the interior/exterior geometries of static, spherically symmetric relativistic stars. We also apply the formalism to parametrize deviations from general relativity in various astrophysical observables related with neutron stars, including surface redshift, apparent radius, Eddington luminosity. We then turn our attention to what is arguably the most well-motivated and well-investigated generalization of general relativity: scalar-tensor theory. We start by considering theories where gravity is mediated by a single extra scalar degree of freedom (in addition to the metric tensor). An interesting class of scalar-tensor theories passes all experimental tests in the weak-field regime of gravity, yet considerably deviates from general relativity in the strong-field regime in the presence of matter. A common assumption in modeling neutron stars is that the pressure within these object is spatially isotropic. We relax this assumption and examine how pressure anisotropy affects the mass, radius and moment of inertia

Broad-Band Variability in Accreting Compact Objects

Directory of Open Access Journals (Sweden)

S. Scaringi

2015-02-01

Full Text Available Cataclysmic variable stars are in many ways similar to X-ray binaries. Both types of systems possess an accretion disk, which in most cases can reach the surface (or event horizon of the central compact object. The main difference is that the embedded gravitational potential well in X-ray binaries is much deeper than those found in cataclysmic variables. As a result, X-ray binaries emit most of their radiation at X-ray wavelengths, as opposed to cataclysmic variables which emit mostly at optical/ultraviolet wavelengths. Both types of systems display aperiodic broad-band variability which can be associated to the accretion disk. Here, the properties of the observed X-ray variability in XRBs are compared to those observed at optical wavelengths in CVs. In most cases the variability properties of both types of systems are qualitatively similar once the relevant timescales associated with the inner accretion disk regions have been taken into account. The similarities include the observed power spectral density shapes, the rms-flux relation as well as Fourier-dependant time lags. Here a brief overview on these similarities is given, placing them in the context of the fluctuating accretion disk model which seeks to reproduce the observed variability.

Stellar structure and compact objects before 1940: Towards relativistic astrophysics

Science.gov (United States)

Bonolis, Luisa

2017-06-01

Since the mid-1920s, different strands of research used stars as "physics laboratories" for investigating the nature of matter under extreme densities and pressures, impossible to realize on Earth. To trace this process this paper is following the evolution of the concept of a dense core in stars, which was important both for an understanding of stellar evolution and as a testing ground for the fast-evolving field of nuclear physics. In spite of the divide between physicists and astrophysicists, some key actors working in the cross-fertilized soil of overlapping but different scientific cultures formulated models and tentative theories that gradually evolved into more realistic and structured astrophysical objects. These investigations culminated in the first contact with general relativity in 1939, when J. Robert Oppenheimer and his students George Volkoff and Hartland Snyder systematically applied the theory to the dense core of a collapsing neutron star. This pioneering application of Einstein's theory to an astrophysical compact object can be regarded as a milestone in the path eventually leading to the emergence of relativistic astrophysics in the early 1960s.

Phenomenological aspects of new gravitational forces. I. Rapidly rotating compact objects

International Nuclear Information System (INIS)

Nieto, M.M.; Goldman, T.; Hughes, R.J.

1987-01-01

A general phenomenological feature of theories of quantum gravity is the existence of spin-1 and spin-0 partners of the graviton, which are expected to be massive (have finite ranges). In the static limit, the forces associated with these partners could almost cancel for particle-particle interactions and yet still produce dramatic effects for antiparticle-particle interactions (such as the gravitational attraction of antiprotons to Earth). However, at relativistic velocities the new forces could become significant even for particle-particle interactions. In this paper we show how these partners could modify the dynamics of particles at the surface of rotating, compact objects, specifically, rapidly rotating pulsars

THE BOLOCAM GALACTIC PLANE SURVEY. II. CATALOG OF THE IMAGE DATA

International Nuclear Information System (INIS)

Rosolowsky, Erik; Dunham, Miranda K.; Evans, Neal J.; Harvey, Paul; Ginsburg, Adam; Bally, John; Battersby, Cara; Glenn, Jason; Stringfellow, Guy S.; Bradley, E. Todd; Aguirre, James; Cyganowski, Claudia; Dowell, Darren; Drosback, Meredith; Walawender, Josh; Williams, Jonathan P.

2010-01-01

We present a catalog of 8358 sources extracted from images produced by the Bolocam Galactic Plane Survey (BGPS). The BGPS is a survey of the millimeter dust continuum emission from the northern Galactic plane. The catalog sources are extracted using a custom algorithm, Bolocat, which was designed specifically to identify and characterize objects in the large-area maps generated from the Bolocam instrument. The catalog products are designed to facilitate follow-up observations of these relatively unstudied objects. The catalog is 98% complete from 0.4 Jy to 60 Jy over all object sizes for which the survey is sensitive ( -2.4±0.1 and that the mean Galactic latitude for sources is significantly below the midplane: (b) = (-0. 0 095 ± 0. 0 001).

ARE ALL SHORT-HARD GAMMA-RAY BURSTS PRODUCED FROM MERGERS OF COMPACT STELLAR OBJECTS?

International Nuclear Information System (INIS)

Virgili, Francisco J.; Zhang Bing; O'Brien, Paul; Troja, Eleonora

2011-01-01

The origin and progenitors of short-hard gamma-ray bursts (GRBs) remain a puzzle and a highly debated topic. Recent Swift observations suggest that these GRBs may be related to catastrophic explosions in degenerate compact stars, denoted as 'Type I' GRBs. The most popular models include the merger of two compact stellar objects (NS-NS or NS-BH). We utilize a Monte Carlo approach to determine whether a merger progenitor model can self-consistently account for all the observations of short-hard GRBs, including a sample with redshift measurements in the Swift era (z-known sample) and the CGRO/BATSE sample. We apply various merger time delay distributions invoked in compact star merger models to derive the redshift distributions of these Type I GRBs, and then constrain the unknown luminosity function of Type I GRBs using the observed luminosity-redshift (L-z) distributions of the z-known sample. The best luminosity function model, together with the adopted merger delay model, is then applied to confront the peak flux distribution (log N-log P distribution) of the BATSE and Swift samples. We find that for all the merger models invoking a range of merger delay timescales (including those invoking a large fraction of 'prompt mergers'), it is difficult to reconcile the models with all the data. The data are instead statistically consistent with the following two possible scenarios. First, that short/hard GRBs are a superposition of compact-star-merger-origin (Type I) GRBs and a population of GRBs that track the star formation history, which are probably related to the deaths of massive stars (Type II GRBs). Second, the entire short/hard GRB population is consistent with a typical delay of 2 Gyr with respect to the star formation history with modest scatter. This may point toward a different Type I progenitor than the traditional compact star merger models.

Evolution of the accretion structure of the compact object in the symbiotic binary BF Cygni during outburst in 2009-2014

Science.gov (United States)

Tomov, N. A.; Tomova, M. T.; Bisikalo, D. V.

2017-12-01

The eclipsing symbiotic binary BF Cyg has had five orbital minima during its last optical outburst after 2006. The second minimum is much shallower than the first one and after that the minimum get deeper again. We determined the parameters of the accretion structure surrounding the compact object in two minima and traced its evolution until 2014. Moreover, we analysed the continuum of the system in the region of the UBVRCIC photometric bands to derive the parameters of its components at two times orbital maximum and calculated the mass-loss rate of the compact object. The results obtained allow us to conclude about the mechanism of fading of the optical light of the system until 2014. These results show that the optical flux of the outbursted compact object decreases because of "contraction" of its observed photosphere (pseudophotosphere) which, on its side, is due to increase of the velocity of its stellar wind, and the optical flux of the circumbinary nebula decreases mainly because of reduction of its mean density, which, on its side, is due to destruction of the accretion structure.

An Active Black Hole in a Compact Dwarf

Science.gov (United States)

Kohler, Susanna

2016-05-01

A new type of galaxy has just been added to the galaxy zoo: a small, compact, and old elliptical galaxy that shows signs of a monster black hole actively accreting material in its center. What can this unusual discovery tell us about how compact elliptical galaxies form?A New Galactic BeastCompact elliptical galaxies are an extremely rare early-type dwarf galaxy. Consistent with their name, compact ellipticals are small, very compact collections of ancient stars; these galaxies exhibit a high surface brightness and arent actively forming stars.Optical view of the ancient compact elliptical galaxy SDSS J085431.18+173730.5 (center of image) in an SDSS color composite image. [Adapted from Paudel et al. 2016]Most compact ellipticals are found in dense environments, particularly around massive galaxies. This has led astronomers to believe that compact ellipticals might form via the tidal stripping of a once-large galaxy in interactions with another, massive galaxy. In this model, once the original galaxys outer layers are stripped away, the compact inner bulge component would be left behind as a compact elliptical galaxy. Recent discoveries of a few isolated compact ellipticals, however, have strained this model.Now a new galaxy has been found to confuse our classification schemes: the first-ever compact elliptical to also display signs of an active galactic nucleus. Led by Sanjaya Paudel (Korea Astronomy and Space Science Institute), a team of scientists discovered SDSS J085431.18+173730.5 serendipitously in Sloan Digital Sky Survey data. The team used SDSS images and spectroscopy in combination with data from the Canada-France-Hawaii Telescope to learn more about this unique galaxy.Puzzling CharacteristicsSDSS J085431.18+173730.5 presents an interesting conundrum. Ancient compact ellipticals are supposed to be devoid of gas, with no fuel left to trigger nuclear activity. Yet SDSS J085431.18+173730.5 clearly shows the emission lines that indicate active accretion onto

Head-on infall of two compact objects: Third post-Newtonian energy flux

International Nuclear Information System (INIS)

Mishra, Chandra Kant; Iyer, Bala R.

2010-01-01

Head-on infall of two compact objects with arbitrary mass ratio is investigated using the multipolar post-Minkowskian approximation method. At the third post-Newtonian order the energy flux, in addition to the instantaneous contributions, also includes hereditary contributions consisting of the gravitational-wave tails, tails-of-tails, and the tail-squared terms. The results are given both for infall from infinity and also for infall from a finite distance. These analytical expressions should be useful for the comparison with the high accuracy numerical relativity results within the limit in which post-Newtonian approximations are valid.

THE BOLOCAM GALACTIC PLANE SURVEY. VIII. A MID-INFRARED KINEMATIC DISTANCE DISCRIMINATION METHOD

Energy Technology Data Exchange (ETDEWEB)

Ellsworth-Bowers, Timothy P.; Glenn, Jason; Battersby, Cara; Ginsburg, Adam; Bally, John [CASA, University of Colorado, UCB 389, University of Colorado, Boulder, CO 80309 (United States); Rosolowsky, Erik [Department of Physics and Astronomy, University of British Columbia Okanagan, 3333 University Way, Kelowna, BC V1V 1V7 (Canada); Mairs, Steven [Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 1A1 (Canada); Evans, Neal J. II [Department of Astronomy, University of Texas, 1 University Station C1400, Austin, TX 78712 (United States); Shirley, Yancy L., E-mail: timothy.ellsworthbowers@colorado.edu [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

2013-06-10

We present a new distance estimation method for dust-continuum-identified molecular cloud clumps. Recent (sub-)millimeter Galactic plane surveys have cataloged tens of thousands of these objects, plausible precursors to stellar clusters, but detailed study of their physical properties requires robust distance determinations. We derive Bayesian distance probability density functions (DPDFs) for 770 objects from the Bolocam Galactic Plane Survey in the Galactic longitude range 7. Degree-Sign 5 {<=} l {<=} 65 Degree-Sign . The DPDF formalism is based on kinematic distances, and uses any number of external data sets to place prior distance probabilities to resolve the kinematic distance ambiguity (KDA) for objects in the inner Galaxy. We present here priors related to the mid-infrared absorption of dust in dense molecular regions and the distribution of molecular gas in the Galactic disk. By assuming a numerical model of Galactic mid-infrared emission and simple radiative transfer, we match the morphology of (sub-)millimeter thermal dust emission with mid-infrared absorption to compute a prior DPDF for distance discrimination. Selecting objects first from (sub-)millimeter source catalogs avoids a bias towards the darkest infrared dark clouds (IRDCs) and extends the range of heliocentric distance probed by mid-infrared extinction and includes lower-contrast sources. We derive well-constrained KDA resolutions for 618 molecular cloud clumps, with approximately 15% placed at or beyond the tangent distance. Objects with mid-infrared contrast sufficient to be cataloged as IRDCs are generally placed at the near kinematic distance. Distance comparisons with Galactic Ring Survey KDA resolutions yield a 92% agreement. A face-on view of the Milky Way using resolved distances reveals sections of the Sagittarius and Scutum-Centaurus Arms. This KDA-resolution method for large catalogs of sources through the combination of (sub-)millimeter and mid-infrared observations of molecular

Constraints on Galactic populations from the unidentified EGRET sources

International Nuclear Information System (INIS)

Siegal-Gaskins, Jennifer M.; Pavlidou, Vasiliki; Brown, Carolyn; Olinto, Angela V.; Fields, Brian D.

2007-01-01

A significant fraction of the sources in the third EGRET catalog have not yet been identified with a low-energy counterpart. We evaluate the plausibility of a Galactic population accounting for some or all of the unidentified EGRET sources by making the simple assumption that galaxies similar to the Milky Way host comparable populations of gamma-ray emitters. Rather than focusing on the properties of a specific candidate emitter, we constrain the abundance and spatial distribution of proposed Galactic populations. We find that it is highly improbable that the unidentified EGRET sources contain more than a handful of members of a Galactic halo population, but that current observations are consistent with all of these sources being Galactic objects if they reside entirely in the disk and bulge. We discuss the additional constraints and new insights into the nature of Galactic gamma-ray emitting populations that GLAST is expected to provide

THE GALFA-H I COMPACT CLOUD CATALOG

Energy Technology Data Exchange (ETDEWEB)

Saul, Destry R.; Peek, J. E. G.; Grcevich, J.; Putman, M. E.; Brown, A. R. H.; Hamden, E. T. [Department of Astronomy, Columbia University, New York, NY 10027 (United States); Douglas, K. A. [Physics and Astronomy, University of Calgary/Dominion Radio Astrophysical Observatory, P.O. Box 248, Penticton, BC V2A 6J9 (Canada); Korpela, E. J. [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States); Stanimirovic, S.; Lee, M.; Burkhart, B.; Pingel, N. M. [Department of Astronomy, University of Wisconsin, Madison, 475 N Charter St, Madison, WI 53703 (United States); Heiles, C. [Radio Astronomy Lab, UC Berkeley, 601 Campbell Hall, Berkeley, CA 94720 (United States); Gibson, S. J. [Department of Physics and Astronomy, Western Kentucky University, Bowling Green, KY 42101 (United States); Begum, A. [Indian Institute of Science Education and Research, ITI Campus (Gas Rahat) Building, Govindpura, Bhopal-23 (India); Tonnesen, S. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

2012-10-10

We present a catalog of 1964 isolated, compact neutral hydrogen clouds from the Galactic Arecibo L-Band Feed Array Survey Data Release One. The clouds were identified by a custom machine-vision algorithm utilizing the difference of Gaussian kernels to search for clouds smaller than 20'. The clouds have velocities typically between |V{sub LSR}| =20 and 400 km s{sup -1}, line widths of 2.5-35 km s{sup -1}, and column densities ranging from 1 to 35 Multiplication-Sign 10{sup 18} cm{sup -2}. The distances to the clouds in this catalog may cover several orders of magnitude, so the masses may range from less than a solar mass for clouds within the Galactic disk, to greater than 10{sup 4} M{sub Sun} for high-velocity clouds (HVCs) at the tip of the Magellanic Stream. To search for trends, we separate the catalog into five populations based on position, velocity, and line width: HVCs; galaxy candidates; cold low-velocity clouds (LVCs); warm, low positive-velocity clouds in the third Galactic quadrant; and the remaining warm LVCs. The observed HVCs are found to be associated with previously identified HVC complexes. We do not observe a large population of isolated clouds at high velocities as some models predict. We see evidence for distinct histories at low velocities in detecting populations of clouds corotating with the Galactic disk and a set of clouds that is not corotating.

G2 and Sgr A *: A Cosmic Fizzle at the Galactic Center

Energy Technology Data Exchange (ETDEWEB)

Morsony, Brian J. [Dept. of Astronomy, University of Maryland, 1113 Physical Sciences Complex, College Park, MD, 20742-2421 (United States); Gracey, Brandon T.; Workman, Jared C. [Dept. of Physical and Environmental Sciences, Colorado Mesa University, Grand Junction, CO, 81501 (United States); Yoon, DooSoo [Dept. of Astronomy, University of Wisconsin-Madison, 2535 Sterling Hall, 475 N. Charter Street, Madison, WI, 53706-1582 (United States)

2017-07-01

We carry out a series of simulations of G2-type clouds interacting with the black hole at the galactic center, to determine why no large changes in the luminosity of Sgr A * were seen, and to determine the nature of G2. We measure the accretion rate from the gas cloud onto Sgr A * for a range of simulation parameters, such as cloud structure, background structure, background density, grid resolution, and accretion radius. For a broad range of parameters, the amount of cloud material accreted is small relative to the amount of background material accreted. The total accretion rate is not significantly effected for at least 30 yr after periapsis. We find that reproducing observations of G2 likely requires two components for the object: an extended, cold gas cloud responsible for the Br- γ emission, and a compact core or dusty stellar object dominating the bolometric luminosity. In simulations, the bolometric and X-ray luminosity have a peak lasting from about one year before to one year after periapsis, a feature not detected in observations. Our simulated Br- γ emission is largely consistent with observations leading up to periapsis, with a slight increase in luminosity and a large increase in the FWHM of the line velocity. All emission from a gaseous component of G2 should fade rapidly after periapsis and be undetectable after one year, due to shock heating and expansion of the cloud. Any remaining emission should be from the compact component of G2.

The Smith Cloud: surviving a high-speed transit of the Galactic disc

Science.gov (United States)

Tepper-García, Thor; Bland-Hawthorn, Joss

2018-02-01

The origin and survival of the Smith high-velocity H I cloud has so far defied explanation. This object has several remarkable properties: (i) its prograde orbit is ≈100 km s-1 faster than the underlying Galactic rotation; (ii) its total gas mass (≳ 4 × 106 M⊙) exceeds the mass of all other high-velocity clouds (HVCs) outside of the Magellanic Stream; (iii) its head-tail morphology extends to the Galactic H I disc, indicating some sort of interaction. The Smith Cloud's kinetic energy rules out models based on ejection from the disc. We construct a dynamically self-consistent, multi-phase model of the Galaxy with a view to exploring whether the Smith Cloud can be understood in terms of an infalling, compact HVC that has transited the Galactic disc. We show that while a dark-matter (DM) free HVC of sufficient mass and density can reach the disc, it does not survive the transit. The most important ingredient to survival during a transit is a confining DM subhalo around the cloud; radiative gas cooling and high spatial resolution (≲ 10pc) are also essential. In our model, the cloud develops a head-tail morphology within ∼10 Myr before and after its first disc crossing; after the event, the tail is left behind and accretes on to the disc within ∼400 Myr. In our interpretation, the Smith Cloud corresponds to a gas 'streamer' that detaches, falls back and fades after the DM subhalo, distorted by the disc passage, has moved on. We conclude that subhaloes with MDM ≲ 109 M⊙ have accreted ∼109 M⊙ of gas into the Galaxy over cosmic time - a small fraction of the total baryon budget.

Galactic radio astronomy

CERN Document Server

Sofue, Yoshiaki

2017-01-01

This book is a concise primer on galactic radio astronomy for undergraduate and graduate students, and provides wide coverage of galactic astronomy and astrophysics such as the physics of interstellar matter and the dynamics and structure of the Milky Way Galaxy and galaxies. Radio astronomy and its technological development have led to significant progress in galactic astronomy and contributed to understanding interstellar matter and galactic structures. The book begins with the fundamental physics of radio-wave radiation, i.e., black body radiation, thermal emission, synchrotron radiation, and HI and molecular line emissions. The author then gives overviews of ingredients of galactic physics, including interstellar matter such as the neutral (HI), molecular hydrogen, and ionized gases, as well as magnetic fields in galaxies. In addition, more advanced topics relevant to the Galaxy and galaxies are also contained here: star formation, supernova remnants, the Galactic Center and black holes, galactic dynamics...

Transition from galactic to extra-galactic cosmic rays

International Nuclear Information System (INIS)

Aloisio, Roberto

2006-01-01

In this paper we review the main features of the observed Cosmic Rays spectrum in the energy range 10 17 eV to 10 20 eV. We present a theoretical model that explains the main observed features of the spectrum, namely the second Knee and Dip, and implies a transition from Galactic to Extra-Galactic cosmic rays at energy E ≅ 10 18 eV, with a proton dominated Extra-Galactic spectrum

The galactic X-ray sources

International Nuclear Information System (INIS)

Gursky, H.; Schreier, E.

1975-01-01

The current observational evidence on galactic X-ray sources is presented both from an astrophysical and astronomical point of view. The distributional properties of the sources, where they appear in the Galaxy, and certain average characteristics are discussed. In this way, certain properties of the X-ray sources can be deduced which are not apparent in the study of single objects. The properties of individual X-ray sources are then described. The hope is that more can be learnt about neutron stars and black holes, their physical properties, their origin and evolution, and their influence on other galactic phenomena. Thus attention is paid to those elements of data which appear to have the most bearing on these questions. (Auth.)

Recent Results on Central Compact Objects

Science.gov (United States)

Halpern, Jules P.; Gotthelf, E. V.

2011-09-01

We will review the latest observational results and theoretical puzzles about the class of central compact objects (CCOs) in supernova remnants (SNRs), 10 isolated neutron stars (NSs) with steady, thermal X-ray emission and absence of a surrounding pulsar wind nebula. Three CCOs have detected X-ray pulsations, with periods of 0.105, 0.112, and 0.424 s. X-ray timing studies reveal that their spin-down rates are extremely small, implying dipole magnetic fields of only 3.e10-1.e11 G, which is unprecedented among the population of young pulsars. In the absence of a stronger magnetic field, it is difficult to explain the high temperatures of their surface hot spots, which may instead require a magnetic field configuration that is different from a centered dipole. While CCOs are inconspicuous relative to ordinary young pulsars and active magnetars, that they are found in SNRs in comparable numbers to other classes of NSs implies that they must represent a significant fraction of NS births. Nevertheless, they fall in a region of the P,P-dot diagram for radio pulsars that is underpopulated, so it is not clear if CCOs are intrinsically radio quiet, and what happens to their descendants, the "orphaned CCOs" whose SNRs have dissipated. It has been speculated that if their magnetic fields were initially strong but were buried by prompt fall-back of supernova debris, then the dipole field may eventually diffuse back to the surface, and CCOs could join the main population of ordinary pulsars. We will also discuss how the absence of detected pulsations from the majority of CCOs makes them difficult to distinguish from magnetars in quiescence, which have X-ray spectra and luminosities similar to those of CCOs. However, they can be distinguished with long-term monitoring, since magnetars are eventually variable, while CCOs are steady X-ray emitters.

Galactic planetary nebulae and evolution of their nuclei

International Nuclear Information System (INIS)

Khromov, G.S.

1980-01-01

The galactic system of planetary nebulae is investigated using previously constructed distance scale and kinematics data. A strong effect of observational selection is established, which has the consequence that with increasing distance, ever brighter and younger objects are observed. More accurate determinations of the spatial and surface densities of the planetary nebulae system are obtained as well as a new estimate of their total number in the Galaxy, which is approximately 200,000. New estimates are also made of the masses of the nebulae, the absolute magnitudes of the nebulae and their nuclei, and other physical parameters of these objects. The spatial and kinematic characteristics of the planetary nebulae indicate that they are objects of the old type I population. It is possible that their remote ancestors are main sequence stars of the type B8-A5-F or as yet unidentified objects of the same galactic subsystem

Constraints on baryonic dark matter in the Galactic halo and Local Group

Science.gov (United States)

Richstone, Douglas; Gould, Andrew; Guhathakurta, Puragra; Flynn, Chris

1992-01-01

A four-color method and deep CCD data are used to search for very faint metal-poor stars in the direction of the south Galactic pole. The results make it possible to limit the contribution of ordinary old, metal-poor stars to the dynamical halo of the Galaxy or to the Local Group. The ratio of the mass of the halo to its ordinary starlight must be more than about 2000, unless the halo is very small. For the Local Group, this ratio is greater than about 400. If this local dark matter is baryonic, the process of compact-object formation must produce very few 'impurities' in the form of stars similar to those found in globular clusters. The expected number of unbound stars with MV not greater than 6 within 100 pc of the sun is less than 1 based on the present 90-percent upper limit to the Local Group starlight.

DOUBLE COMPACT OBJECTS. III. GRAVITATIONAL-WAVE DETECTION RATES

Energy Technology Data Exchange (ETDEWEB)

Dominik, Michal; Belczynski, Krzysztof; Bulik, Tomasz [Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warsaw (Poland); Berti, Emanuele [Department of Physics and Astronomy, The University of Mississippi, University, MS 38677 (United States); O’Shaughnessy, Richard [Center for Gravitation, Cosmology, and Astrophysics, University of Wisconsin-Milwaukee, Milwaukee, WI (United States); Mandel, Ilya [School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT (United Kingdom); Fryer, Christopher [CCS-2, MSD409, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Holz, Daniel E. [Enrico Fermi Institute, Department of Physics, and Kavli Institute for Cosmological Physics University of Chicago, Chicago, IL 60637 (United States); Pannarale, Francesco [School of Physics and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA (United Kingdom)

2015-06-20

The unprecedented range of second-generation gravitational-wave (GW) observatories calls for refining the predictions of potential sources and detection rates. The coalescence of double compact objects (DCOs)—i.e., neutron star–neutron star (NS–NS), black hole–neutron star (BH–NS), and black hole–black hole (BH–BH) binary systems—is the most promising source of GWs for these detectors. We compute detection rates of coalescing DCOs in second-generation GW detectors using the latest models for their cosmological evolution, and implementing inspiral-merger-ringdown gravitational waveform models in our signal-to-noise ratio calculations. We find that (1) the inclusion of the merger/ringdown portion of the signal does not significantly affect rates for NS–NS and BH–NS systems, but it boosts rates by a factor of ∼1.5 for BH–BH systems; (2) in almost all of our models BH–BH systems yield by far the largest rates, followed by NS–NS and BH–NS systems, respectively; and (3) a majority of the detectable BH–BH systems were formed in the early universe in low-metallicity environments. We make predictions for the distributions of detected binaries and discuss what the first GW detections will teach us about the astrophysics underlying binary formation and evolution.

THE GALACTIC POPULATION OF YOUNG γ-RAY PULSARS

International Nuclear Information System (INIS)

Watters, Kyle P.; Romani, Roger W.

2011-01-01

We have simulated a Galactic population of young pulsars and compared with the Fermi LAT sample, constraining the birth properties, beaming and evolution of these spin-powered objects. Using quantitative tests of agreement with the distributions of observed spin and pulse properties, we find that short birth periods P 0 ∼ 50 ms and γ-ray beams arising in the outer magnetosphere, dominated by a single pole, are strongly preferred. The modeled relative numbers of radio-detected and radio-quiet objects agrees well with the data. Although the sample is local, extrapolation to the full Galaxy implies a γ-ray pulsar birthrate 1/(59 yr). This is shown to be in good agreement with the estimated Galactic core collapse rate and with the local density of OB star progenitors. We give predictions for the numbers of expected young pulsar detections if Fermi LAT observations continue 10 years. In contrast to the potentially significant contribution of unresolved millisecond pulsars, we find that young pulsars should contribute little to the Galactic γ-ray background.

Interstellar scattering, the North Polar Spur, and a possible new class of compact galactic radio sources

International Nuclear Information System (INIS)

Rickard, J.J.; Cronyn, W.M.

1979-01-01

A reanalysis of the Cambridge interplanetary scintillation (IPS) catalog of angular sizes of radio sources reveals that there is no statistically significant evidence for increased interstellar angular broadening in the galactic plane, in conflict with previous studies. There is a significant contribution to the decrease in the ratios of scintillators/nonscintillators and strong/weak scintillators near the plane from galactic supernova remnants which were included in previous studies of source counts. Using the catalog angular sizes, we show there is no lack of small sources of any size in the plane. However, we do find a 500 deg 2 region near the North Polar Spur (NPS) radio feature, a suspected supernova remnant, where there seems to be a true deficit of small sources. This deficit may be caused by enhanced broadening associated with the NPS. Our conclusion about the apparent absence of angular broadening in the plane conflicts with estimates of broadening based upon the geometrical relationship between time delay and angular size applied to pulsar coherence bandwidths and pulse decay times. To explain this discrepancy, we suggest two alternatives: (1) Large angular broadening of extragalactic sources in the plane may indeed exist so that sources exhibiting IPS (i.e., of small angular diameter) must be galactic in nature. Properties of this possible new class of sources--called scintars--are discussed, and 42 scintar candidates are identified. (2) There is little angular broadening of extragalactic sources, and the pulsar data are being misinterpreted

Sound speeds, cracking and the stability of self-gravitating anisotropic compact objects

International Nuclear Information System (INIS)

Abreu, H; Hernandez, H; Nunez, L A

2007-01-01

Using the concept of cracking we explore the influence that density fluctuations and local anisotropy have on the stability of local and non-local anisotropic matter configurations in general relativity. This concept, conceived to describe the behavior of a fluid distribution just after its departure from equilibrium, provides an alternative approach to consider the stability of self-gravitating compact objects. We show that potentially unstable regions within a configuration can be identified as a function of the difference of propagations of sound along tangential and radial directions. In fact, it is found that these regions could occur when, at a particular point within the distribution, the tangential speed of sound is greater than the radial one

Uniaxial backfill block compaction

International Nuclear Information System (INIS)

Koskinen, V.

2012-05-01

The main parts of the project were: to make a literature survey of the previous uniaxial compaction experiments; do uniaxial compaction tests in laboratory scale; and do industrial scale production tests. Object of the project was to sort out the different factors affecting the quality assurance chain of the backfill block uniaxial production and solve a material sticking to mould problem which appeared during manufacturing the blocks of bentonite and cruched rock mixture. The effect of mineralogical and chemical composition on the long term functionality of the backfill was excluded from the project. However, the used smectite-rich clays have been tested for mineralogical consistency. These tests were done in B and Tech OY according their SOPs. The objective of the Laboratory scale tests was to find right material- and compaction parameters for the industrial scale tests. Direct comparison between the laboratory scale tests and industrial scale tests is not possible because the mould geometry and compaction speed has a big influence for the compaction process. For this reason the selected material parameters were also affected by the previous compaction experiments. The industrial scale tests were done in summer of 2010 in southern Sweden. Blocks were done with uniaxial compaction. A 40 tons of the mixture of bentonite and crushed rock blocks and almost 50 tons of Friedland-clay blocks were compacted. (orig.)

Hard X-ray balloon observations of compact galactic and extragalactic X-ray sources

International Nuclear Information System (INIS)

Staubert, R.; Kendziorra, E.; Pietsch, W.; Proctor, R.J.; Reppin, C.; Steinle, H.; Truemper, J.; Voges, W.

1981-01-01

A balloon program in hard X-ray astronomy (20-200 keV) is jointly pursued by the Astronomisches Institut der Universitaet Tuebingen (AIT) and the Max Planck-Institut fuer Extraterrestrische Physik in Garching (MPE). Since 1973 nine succussful balloon flights have been performed from Texas and Australia. Here results on Centaurus A and on several galactic binary X-ray sources are summarized. In particular the high energy photon spectrum of Hercules X-1 and the evidence for the cyclotron line feature which was discovered by us in 1976 is reviewed. (orig.)

Relativistic models of a class of compact objects

Indian Academy of Sciences (India)

describe compact stars in hydrostatic equilibrium are discussed. The stellar ... [2] and examine the physical plausibility of several models of a class of neutron stars ... the physical space. However, for k = 0, the space-time metric (12) degenerates into that of Einstein's static Universe filled with matter of uniform density.

A compact small-beam XRF instrument for in-situ analysis of objects of historical and/or artistic value

Science.gov (United States)

Vittiglio, G.; Janssens, K.; Vekemans, B.; Adams, F.; Oost, A.

1999-11-01

The analytical characteristics, possibilities and limitations of a compact and easily transportable small-beam XRF instrument are described. The instrument consists of a compact, mini-focus Mo X-ray tube that is collimated to produce a sub-mm beam and a peltier-cooled PIN diode detector. Relative MDLs in highly scattering matrices are situated in the 10-100-ppm range; for metallic matrices featuring strong matrix lines, the MDLs of the instrument are approximately a factor 2 higher. Since only a small irradiation area is required, a simple micro-polishing technique that may be performed in situ in combination with the measurements is shown to be effective for the determination of the bulk composition of corroded bronze objects. As an example, a series of Egyptian bronze objects date from XXII nd Egyptian Dynasty (ca. 1090 BC) to the Roman era (30 BC to 640 AD) was analyzed in order to contribute to the very limited database on Cu-alloy compositions from this period.

Ruprecht 106 - A young metal-poor Galactic globular cluster

International Nuclear Information System (INIS)

Buonanno, R.; Buscema, G.; Fusi Pecci, F.; Richer, H.B.; Fahlman, G.G.

1990-01-01

The first CCD photometric survey in the Galactic globular cluster Ruprecht 106 has been performed. The results show that Ruprecht 106 is a metal-poor cluster with (Fe/H) about -2 located at about 25 kpc from the Galactic center. A sizable, high centrally concentrated population of blue stragglers was detected. Significant differences in the positions of the turnoffs in the color-magnitude diagram are found compared to those in metal-poor clusters. The cluster appears younger than other typical metal-poor Galactic globulars by about 4-5 Gyr; if true, this object would represent the first direct proof of the existence of a significant age spread among old, very metal-poor clusters. 51 refs

A MID-INFRARED CENSUS OF STAR FORMATION ACTIVITY IN BOLOCAM GALACTIC PLANE SURVEY SOURCES

International Nuclear Information System (INIS)

Dunham, Miranda K.; Robitaille, Thomas P.; Evans, Neal J. II; Schlingman, Wayne M.; Cyganowski, Claudia J.; Urquhart, James

2011-01-01

We present the results of a search for mid-infrared signs of star formation activity in the 1.1 mm sources in the Bolocam Galactic Plane Survey (BGPS). We have correlated the BGPS catalog with available mid-IR Galactic plane catalogs based on the Spitzer Space Telescope GLIMPSE legacy survey and the Midcourse Space Experiment (MSX) Galactic plane survey. We find that 44% (3712 of 8358) of the BGPS sources contain at least one mid-IR source, including 2457 of 5067 (49%) within the area where all surveys overlap (10 deg. s tarlessBGPS sources which were not matched to any mid-IR sources. The mean 1.1 mm flux of each group increases with increasing probability of active star formation. We also find that the 'starless' BGPS sources are the most compact, while the sources with the highest probability of star formation activity are on average more extended with large skirts of emission. A subsample of 280 BGPS sources with known distances demonstrates that mass and mean H 2 column density also increase with probability of star formation activity.

Galactic dynamics

CERN Document Server

Binney, James

2008-01-01

Since it was first published in 1987, Galactic Dynamics has become the most widely used advanced textbook on the structure and dynamics of galaxies and one of the most cited references in astrophysics. Now, in this extensively revised and updated edition, James Binney and Scott Tremaine describe the dramatic recent advances in this subject, making Galactic Dynamics the most authoritative introduction to galactic astrophysics available to advanced undergraduate students, graduate students, and researchers. Every part of the book has been thoroughly overhauled, and many section

Planck 2013 results. XXVIII. The Planck Catalogue of Compact Sources

CERN Document Server

Ade, P.A.R.; Armitage-Caplan, C.; Arnaud, M.; Ashdown, M.; Atrio-Barandela, F.; Aumont, J.; Baccigalupi, C.; Banday, A.J.; Barreiro, R.B.; Bartlett, J.G.; Battaner, E.; Benabed, K.; Benoit, A.; Benoit-Levy, A.; Bernard, J.P.; Bersanelli, M.; Bielewicz, P.; Bobin, J.; Bock, J.J.; Bonaldi, A.; Bonavera, L.; Bond, J.R.; Borrill, J.; Bouchet, F.R.; Bridges, M.; Bucher, M.; Burigana, C.; Butler, R.C.; Cardoso, J.F.; Carvalho, P.; Catalano, A.; Challinor, A.; Chamballu, A.; Chen, X.; Chiang, L.Y.; Chiang, H.C.; Christensen, P.R.; Church, S.; Clemens, M.; Clements, D.L.; Colombi, S.; Colombo, L.P.L.; Couchot, F.; Coulais, A.; Crill, B.P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R.D.; Davis, R.J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Delouis, J.M.; Desert, F.X.; Dickinson, C.; Diego, J.M.; Dole, H.; Donzelli, S.; Dore, O.; Douspis, M.; Dupac, X.; Efstathiou, G.; Ensslin, T.A.; Eriksen, H.K.; Finelli, F.; Forni, O.; Frailis, M.; Franceschi, E.; Galeotta, S.; Ganga, K.; Giard, M.; Giardino, G.; Giraud-Heraud, Y.; Gonzalez-Nuevo, J.; Gorski, K.M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Hansen, F.K.; Hanson, D.; Harrison, D.; Henrot-Versille, S.; Hernandez-Monteagudo, C.; Herranz, D.; Hildebrandt, S.R.; Hivon, E.; Hobson, M.; Holmes, W.A.; Hornstrup, A.; Hovest, W.; Huffenberger, K.M.; Jaffe, T.R.; Jaffe, A.H.; Jones, W.C.; Juvela, M.; Keihanen, E.; Keskitalo, R.; Kisner, T.S.; Kneissl, R.; Knoche, J.; Knox, L.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lahteenmaki, A.; Lamarre, J.M.; Lasenby, A.; Laureijs, R.J.; Lawrence, C.R.; Leahy, J.P.; Leonardi, R.; Leon-Tavares, J.; Leroy, C.; Lesgourgues, J.; Liguori, M.; Lilje, P.B.; Linden-Vornle, M.; Lopez-Caniego, M.; Lubin, P.M.; Macias-Perez, J.F.; Maffei, B.; Maino, D.; Mandolesi, N.; Maris, M.; Marshall, D.J.; Martin, P.G.; Martinez-Gonzalez, E.; Masi, S.; Matarrese, S.; Matthai, F.; Mazzotta, P.; McGehee, P.; Meinhold, P.R.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mitra, S.; Miville-Deschenes, M.A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Naselsky, P.; Nati, F.; Natoli, P.; Negrello, M.; Netterfield, C.B.; Norgaard-Nielsen, H.U.; Noviello, F.; Novikov, D.; Novikov, I.; O'Dwyer, I.J.; Osborne, S.; Oxborrow, C.A.; Paci, F.; Pagano, L.; Pajot, F.; Paladini, R.; Paoletti, D.; Partridge, B.; Pasian, F.; Patanchon, G.; Pearson, T.J.; Perdereau, O.; Perotto, L.; Perrotta, F.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Popa, L.; Poutanen, T.; Pratt, G.W.; Prezeau, G.; Prunet, S.; Puget, J.L.; Rachen, J.P.; Reach, W.T.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Ricciardi, S.; Riller, T.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Roudier, G.; Rowan-Robinson, M.; Rubino-Martin, J.A.; Rusholme, B.; Sandri, M.; Santos, D.; Savini, G.; Schammel, M.P.; Scott, D.; Seiffert, M.D.; Shellard, E.P.S.; Spencer, L.D.; Starck, J.L.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sunyaev, R.; Sureau, F.; Sutton, D.; Suur-Uski, A.S.; Sygnet, J.F.; Tauber, J.A.; Tavagnacco, D.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Tuovinen, J.; Turler, M.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Varis, J.; Vielva, P.; Villa, F.; Vittorio, N.; Wade, L.A.; Walter, B.; Wandelt, B.D.; Yvon, D.; Zacchei, A.; Zonca, A.

2014-01-01

The Planck Catalogue of Compact Sources (PCCS) is the catalogue of sources detected in the first 15 months of Planck operations, the "nominal" mission. It consists of nine single-frequency catalogues of compact sources, both Galactic and extragalactic, detected over the entire sky. The PCCS covers the frequency range 30--857\\,GHz with higher sensitivity (it is 90% complete at 180 mJy in the best channel) and better angular resolution (from ~33' to ~5') than previous all-sky surveys in this frequency band. By construction its reliability is >80% and more than 65% of the sources have been detected at least in two contiguous Planck channels. In this paper we present the construction and validation of the PCCS, its contents and its statistical characterization.

The Galactic magnetic fields

International Nuclear Information System (INIS)

Han Jinlin

2006-01-01

A good progress has been made on studies of Galactic magnetic fields in last 10 years. I describe what we want to know about the Galactic magnetic fields, and then review we current knowledge about magnetic fields in the Galactic disk, the Galactic halo and the field strengths. I also listed many unsolved problems on this area

Planck 2015 results. XXVI. The Second Planck Catalogue of Compact Sources

CERN Document Server

Ade, P.A.R.; Argueso, F.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Banday, A.J.; Barreiro, R.B.; Bartolo, N.; Battaner, E.; Beichman, C.; Benabed, K.; Benoit, A.; Benoit-Levy, A.; Bernard, J.P.; Bersanelli, M.; Bielewicz, P.; Bock, J.J.; Bohringer, H.; Bonaldi, A.; Bonavera, L.; Bond, J.R.; Borrill, J.; Bouchet, F.R.; Boulanger, F.; Bucher, M.; Burigana, C.; Butler, R.C.; Calabrese, E.; Cardoso, J.F.; Carvalho, P.; Catalano, A.; Challinor, A.; Chamballu, A.; Chary, R.R.; Chiang, H.C.; Christensen, P.R.; Clemens, M.; Clements, D.L.; Colombi, S.; Colombo, L.P.L.; Combet, C.; Couchot, F.; Coulais, A.; Crill, B.P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R.D.; Davis, R.J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Desert, F.X.; Dickinson, C.; Diego, J.M.; Dole, H.; Donzelli, S.; Dore, O.; Douspis, M.; Ducout, A.; Dupac, X.; Efstathiou, G.; Elsner, F.; Ensslin, T.A.; Eriksen, H.K.; Falgarone, E.; Fergusson, J.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A.A.; Franceschi, E.; Frejsel, A.; Galeotta, S.; Galli, S.; Ganga, K.; Giard, M.; Giraud-Heraud, Y.; Gjerlow, E.; Gonzalez-Nuevo, J.; Gorski, K.M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J.E.; Hansen, F.K.; Hanson, D.; Harrison, D.L.; Helou, G.; Henrot-Versille, S.; Hernandez-Monteagudo, C.; Herranz, D.; Hildebrandt, S.R.; Hivon, E.; Hobson, M.; Holmes, W.A.; Hornstrup, A.; Hovest, W.; Huffenberger, K.M.; Hurier, G.; Jaffe, A.H.; Jaffe, T.R.; Jones, W.C.; Juvela, M.; Keihanen, E.; Keskitalo, R.; Kisner, T.S.; Kneissl, R.; Knoche, J.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lahteenmaki, A.; Lamarre, J.M.; Lasenby, A.; Lattanzi, M.; Lawrence, C.R.; Leahy, J.P.; Leonardi, R.; Leon-Tavares, J.; Lesgourgues, J.; Levrier, F.; Liguori, M.; Lilje, P.B.; Linden-Vornle, M.; Lopez-Caniego, M.; Lubin, P.M.; Macias-Perez, J.F.; Maggio, G.; Maino, D.; Mandolesi, N.; Mangilli, A.; Maris, M.; Marshall, D.J.; Martin, P.G.; Martinez-Gonzalez, E.; Masi, S.; Matarrese, S.; McGehee, P.; Meinhold, P.R.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mitra, S.; Miville-Deschenes, M.A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Moss, A.; Munshi, D.; Murphy, J.A.; Naselsky, P.; Nati, F.; Natoli, P.; Negrello, M.; Netterfield, C.B.; Norgaard-Nielsen, H.U.; Noviello, F.; Novikov, D.; Novikov, I.; Oxborrow, C.A.; Paci, F.; Pagano, L.; Pajot, F.; Paladini, R.; Paoletti, D.; Partridge, B.; Pasian, F.; Patanchon, G.; Pearson, T.J.; Perdereau, O.; Perotto, L.; Perrotta, F.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Pratt, G.W.; Prezeau, G.; Prunet, S.; Puget, J.L.; Rachen, J.P.; Reach, W.T.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Renzi, A.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rossetti, M.; Roudier, G.; Rowan-Robinson, M.; Rubino-Martin, J.A.; Rusholme, B.; Sandri, M.; Sanghera, H.S.; Santos, D.; Savelainen, M.; Savini, G.; Scott, D.; Seiffert, M.D.; Shellard, E.P.S.; Spencer, L.D.; Stolyarov, V.; Sudiwala, R.; Sunyaev, R.; Sutton, D.; Suur-Uski, A.S.; Sygnet, J.F.; Tauber, J.A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tornikoski, M.; Tristram, M.; Tucci, M.; Tuovinen, J.; Turler, M.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Wade, L.A.; Walter, B.; Wandelt, B.D.; Wehus, I.K.; Yvon, D.; Zacchei, A.; Zonca, A.

2016-01-01

The Second Planck Catalogue of Compact Sources is a catalogue of sources detected in single-frequency maps from the full duration of the Planck mission and supersedes previous versions of the Planck compact source catalogues. It consists of compact sources, both Galactic and extragalactic, detected over the entire sky. Compact sources detected in the lower frequency channels are assigned to the PCCS2, while at higher frequencies they are assigned to one of two sub-catalogues, the PCCS2 or PCCS2E, depending on their location on the sky. The first of these catalogues covers most of the sky and allows the user to produce subsamples at higher reliabilities than the target 80% integral reliability of the catalogue. The PCCS2E contains sources detected in sky regions where the diffuse emission makes it difficult to quantify the reliability of the detections. Both the PCCS2 and PCCS2E include polarization measurements, in the form of polarized flux densities, or upper limits, and orientation angles for all seven pol...

Active galactic nuclei cores in infrared-faint radio sources. Very long baseline interferometry observations using the Very Long Baseline Array

Science.gov (United States)

Herzog, A.; Middelberg, E.; Norris, R. P.; Spitler, L. R.; Deller, A. T.; Collier, J. D.; Parker, Q. A.

2015-06-01

Context. Infrared-faint radio sources (IFRS) form a new class of galaxies characterised by radio flux densities between tenths and tens of mJy and faint or absent infrared counterparts. It has been suggested that these objects are radio-loud active galactic nuclei (AGNs) at significant redshifts (z ≳ 2). Aims: Whereas the high redshifts of IFRS have been recently confirmed based on spectroscopic data, the evidence for the presence of AGNs in IFRS is mainly indirect. So far, only two AGNs have been unquestionably confirmed in IFRS based on very long baseline interferometry (VLBI) observations. In this work, we test the hypothesis that IFRS contain AGNs in a large sample of sources using VLBI. Methods: We observed 57 IFRS with the Very Long Baseline Array (VLBA) down to a detection sensitivity in the sub-mJy regime and detected compact cores in 35 sources. Results: Our VLBA detections increase the number of VLBI-detected IFRS from 2 to 37 and provide strong evidence that most - if not all - IFRS contain AGNs. We find that IFRS have a marginally higher VLBI detection fraction than randomly selected sources with mJy flux densities at arcsec-scales. Moreover, our data provide a positive correlation between compactness - defined as the ratio of milliarcsec- to arcsec-scale flux density - and redshift for IFRS, but suggest a decreasing mean compactness with increasing arcsec-scale radio flux density. Based on these findings, we suggest that IFRS tend to contain young AGNs whose jets have not formed yet or have not expanded, equivalent to very compact objects. We found two IFRS that are resolved into two components. The two components are spatially separated by a few hundred milliarcseconds in both cases. They might be components of one AGN, a binary black hole, or the result of gravitational lensing.

Relativistic simulations of compact object mergers for nucleonic matter and strange quark matter

International Nuclear Information System (INIS)

Bauswein, Andreas Ottmar

2010-01-01

Under the assumption that the energy of the ground state of 3-flavor quark matter is lower than the one of nucleonic matter, the compact stellar remnants of supernova explosions are composed of this quark matter. Because of the appearance of strange quarks, such objects are called strange stars. Considering their observational features, strange stars are very similar to neutron stars made of nucleonic matter, and therefore observations cannot exclude the existence of strange stars. This thesis introduces a new method for simulating mergers of compact stars and black holes within a general relativistic framework. The main goal of the present work is the investigation of the question, whether the coalescence of two strange stars in a binary system yields observational signatures that allow one to distinguish them from colliding neutron stars. In this context the gravitational-wave signals are analyzed. It is found that in general the characteristic frequencies in the gravitational-wave spectra are higher for strange stars. Moreover, the amount of matter that becomes gravitationally unbound during the merging is determined. The detection of ejecta of strange star mergers as potential component of cosmic ray flux could serve as a proof of the existence of strange quark matter. (orig.)

Relativistic simulations of compact object mergers for nucleonic matter and strange quark matter

Energy Technology Data Exchange (ETDEWEB)

Bauswein, Andreas Ottmar

2010-01-29

Under the assumption that the energy of the ground state of 3-flavor quark matter is lower than the one of nucleonic matter, the compact stellar remnants of supernova explosions are composed of this quark matter. Because of the appearance of strange quarks, such objects are called strange stars. Considering their observational features, strange stars are very similar to neutron stars made of nucleonic matter, and therefore observations cannot exclude the existence of strange stars. This thesis introduces a new method for simulating mergers of compact stars and black holes within a general relativistic framework. The main goal of the present work is the investigation of the question, whether the coalescence of two strange stars in a binary system yields observational signatures that allow one to distinguish them from colliding neutron stars. In this context the gravitational-wave signals are analyzed. It is found that in general the characteristic frequencies in the gravitational-wave spectra are higher for strange stars. Moreover, the amount of matter that becomes gravitationally unbound during the merging is determined. The detection of ejecta of strange star mergers as potential component of cosmic ray flux could serve as a proof of the existence of strange quark matter. (orig.)

A transient, flat spectrum radio pulsar near the Galactic Centre

Science.gov (United States)

Dexter, J.; Degenaar, N.; Kerr, M.; Deller, A.; Deneva, J.; Lazarus, P.; Kramer, M.; Champion, D.; Karuppusamy, R.

2017-06-01

Recent studies have shown possible connections between highly magnetized neutron stars ('magnetars'), whose X-ray emission is too bright to be powered by rotational energy, and ordinary radio pulsars. In addition to the magnetar SGR J1745-2900, one of the radio pulsars in the Galactic Centre (GC) region, PSR J1746-2850, had timing properties implying a large magnetic field strength and young age, as well as a flat spectrum. All characteristics are similar to those of rare, transient, radio-loud magnetars. Using several deep non-detections from the literature and two new detections, we show that this pulsar is also transient in the radio. Both the flat spectrum and large amplitude variability are inconsistent with the light curves and spectral indices of three radio pulsars with high magnetic field strengths. We further use frequent, deep archival imaging observations of the GC in the past 15 yr to rule out a possible X-ray outburst with a luminosity exceeding the rotational spin-down rate. This source, either a transient magnetar without any detected X-ray counterpart or a young, strongly magnetized radio pulsar producing magnetar-like radio emission, further blurs the line between the two categories. We discuss the implications of this object for the radio emission mechanism in magnetars and for star and compact object formation in the GC.

Elusive active galactic nuclei

Science.gov (United States)

Maiolino, R.; Comastri, A.; Gilli, R.; Nagar, N. M.; Bianchi, S.; Böker, T.; Colbert, E.; Krabbe, A.; Marconi, A.; Matt, G.; Salvati, M.

2003-10-01

A fraction of active galactic nuclei do not show the classical Seyfert-type signatures in their optical spectra, i.e. they are optically `elusive'. X-ray observations are an optimal tool to identify this class of objects. We combine new Chandra observations with archival X-ray data in order to obtain a first estimate of the fraction of elusive active galactic nuclei (AGN) in local galaxies and to constrain their nature. Our results suggest that elusive AGN have a local density comparable to or even higher than optically classified Seyfert nuclei. Most elusive AGN are heavily absorbed in the X-rays, with gas column densities exceeding 1024 cm-2, suggesting that their peculiar nature is associated with obscuration. It is likely that in elusive AGN the nuclear UV source is completely embedded and the ionizing photons cannot escape, which prevents the formation of a classical narrow-line region. Elusive AGN may contribute significantly to the 30-keV bump of the X-ray background.

Are baryonic galactic halos possible

International Nuclear Information System (INIS)

Olive, K.A.; Hegyi, D.J.

1986-01-01

There is little doubt from the rotation curves of spiral galaxies that galactic halos must contain large amounts of dark matter. In this contribution, the authors review arguments which indicate that it is very unlikely that galactic halos contain substantial amounts of baryonic matter. While the authors would like to be able to present a single argument which would rule out baryonic matter, at the present time they are only able to present a collection of arguments each of which argues against one form of baryonic matter. These include: 1) snowballs; 2) gas; 3) low mass stars and Jupiters; 4) high mass stars; and 5) high metalicity objects such as rooks or dust. Black holes, which do not have a well defined baryon number, are also a possible candidate for halo matter. They briefly discuss black holes

Molecular clouds and galactic spiral structure

International Nuclear Information System (INIS)

Dame, T.M.

1984-02-01

Galactic CO line emission at 115 GHz was surveyed in order to study the distribution of molecular clouds in the inner galaxy. Comparison of this survey with similar H1 data reveals a detailed correlation with the most intense 21 cm features. To each of the classical 21 cm H1 spiral arms of the inner galaxy there corresponds a CO molecular arm which is generally more clearly defined and of higher contrast. A simple model is devised for the galactic distribution of molecular clouds. The modeling results suggest that molecular clouds are essentially transient objects, existing for 15 to 40 million years after their formation in a spiral arm, and are largely confined to spiral features about 300 pc wide

Towards a formalism for mapping the spacetimes of massive compact objects: Bumpy black holes and their orbits

International Nuclear Information System (INIS)

Collins, Nathan A.; Hughes, Scott A.

2004-01-01

Astronomical observations have established that extremely compact, massive objects are common in the Universe. It is generally accepted that these objects are, in all likelihood, black holes. As observational technology has improved, it has become possible to test this hypothesis in ever greater detail. In particular, it is or will be possible to measure the properties of orbits deep in the strong field of a black hole candidate (using x-ray timing or future gravitational-wave measurements) and to test whether they have the characteristics of black hole orbits in general relativity. Past work has shown that, in principle, such measurements can be used to map the spacetime of a massive compact object, testing in particular whether the object's multipolar structure satisfies the rather strict constraints imposed by the black hole hypothesis. Performing such a test in practice requires that we be able to compare against objects with the 'wrong' multipole structure. In this paper, we present tools for constructing the spacetimes of bumpy black holes: objects that are almost black holes, but that have some multipoles with the wrong value. In this first analysis, we focus on objects with no angular momentum. Generalization to bumpy Kerr black holes should be straightforward, albeit labor intensive. Our construction has two particularly desirable properties. First, the spacetimes which we present are good deep into the strong field of the object--we do not use a 'large r' expansion (except to make contact with weak field intuition). Second, our spacetimes reduce to the exact black hole spacetimes of general relativity in a natural way, by dialing the 'bumpiness' of the black hole to zero. We propose that bumpy black holes can be used as the foundation for a null experiment: if black hole candidates are indeed the black holes of general relativity, their bumpiness should be zero. By comparing the properties of orbits in a bumpy spacetime with those measured from an

Wolf-Rayet stars and galactic structure

International Nuclear Information System (INIS)

Stenholm, B.

1975-01-01

A 15 0 wide strip along the galactic equator between longitudes 250 0 and 360 0 has been searched for Wolf-Rayet stars. Six new WR stars and four new planetary nebulae have been found. Seven stars earlier listed as WR stars have been rejected as such. The new WR stars in the 'Luminous Stars in the Southern Milky Way' are discussed. A sample of 154 WR stars has been treated statistically. For the distribution in longitude, comparisons are made with OB stars and classical cepheids. The differences in distribution are thought to be an age effect. An effort to explain the empty interval towards the anticentre is made. The distribution in latitude is compared with young clusters and long-period cepheids. The physical plane formed by these objects is tilted about one degree to the galactic plane and the tilt is upwards in the Cygnus direction. This result is also received by a least squares solution of the objects when given in rectangular coordinates. The WR star sample is regarded as fairly complete up to a distance of 5 kpc. (orig.) [de

Direct evidence for a massive galactic halo

International Nuclear Information System (INIS)

Hawkins, M.R.S.

1983-01-01

The discovery of a very distant galactic RR Lyrae star, R15 is reported. Spectroscopic observations of the object show that it has a high negative radial velocity, implying a lower limit to the mass of the galaxy of 1.4 x 10 12 Msun. (author)

Strong gravitational lensing by a Konoplya-Zhidenko rotating non-Kerr compact object

Energy Technology Data Exchange (ETDEWEB)

Wang, Shangyun; Chen, Songbai; Jing, Jiliang, E-mail: shangyun_wang@163.com, E-mail: csb3752@hunnu.edu.cn, E-mail: jljing@hunnu.edu.cn [Institute of Physics and Department of Physics, Hunan Normal University, Changsha, Hunan 410081 (China)

2016-11-01

Konoplya and Zhidenko have proposed recently a rotating non-Kerr black hole metric beyond General Relativity and make an estimate for the possible deviations from the Kerr solution with the data of GW 150914. We here study the strong gravitational lensing in such a rotating non-Kerr spacetime with an extra deformation parameter. We find that the condition of existence of horizons is not inconsistent with that of the marginally circular photon orbit. Moreover, the deflection angle of the light ray near the weakly naked singularity covered by the marginally circular orbit diverges logarithmically in the strong-field limit. In the case of the completely naked singularity, the deflection angle near the singularity tends to a certain finite value, whose sign depends on the rotation parameter and the deformation parameter. These properties of strong gravitational lensing are different from those in the Johannsen-Psaltis rotating non-Kerr spacetime and in the Janis-Newman-Winicour spacetime. Modeling the supermassive central object of the Milk Way Galaxy as a Konoplya-Zhidenko rotating non-Kerr compact object, we estimated the numerical values of observables for the strong gravitational lensing including the time delay between two relativistic images.

Galactic sprinklers

International Nuclear Information System (INIS)

Vandeusen, W.

1984-01-01

It is believed by many astronomers that gravitation is responsible for holding a strong whirlpool of hot, dense material together at the center of the Milky Way galaxy. However, the galactic-sprinkler model suggests that the whirlpool is not being held together, and that the stars, gas and dust within the spirals are being thrown outward. It is also suggested that much of the ejected material eventually returns to the galactic center, as do stars within our stellar neighborhood. The material is believed to be subjected to extreme changes in the gravitational time rate which may cause it to follow an inbound spiral that is basically similar to the outbound spiral. Radio studies also indicate that the galactic arms on either side of the galactic center move at different velocities and in different directions with respect to our location and that the whole group of stars in the vicinity of the solar system may be moving outward from the galactic center at a velocity of about 40 kps. Through the use of velocity data in kps, and distance data in light years, the radial component of the sun's trajectory can be estimated with respect to time by a parabola. The spiral trajectory of the sun can be calculated and plotted on polar coordinates by combining both the radial component and tangential component (230 kps)

Search for macroscopic dark matter in the halo of the milky way through microlensing. A feasibility study

International Nuclear Information System (INIS)

Moniez, M.

1990-05-01

The possibility of searching for non-visible massive compact objects in the galactic halo is discussed here. The discovery of such objects would solve the problem of the missing mass in the galaxies, and the experiments which investigate for weakly interacting particles assuming a diffuse cloud of dark matter would have to revise their limits. The non-discovery of these objects would exclude the last possibility left for baryonic dark matter, providing good evidence that the galactic halo has to be made of new particles. The description of the general-relativistic microlensing effect and its application to the search of massive compact objects are given here. A feasibility study shows that it is possible to monitor the luminosity of several million stars in the Large Magellanic Cloud with the required precision, in order to detect a possible microlensing phenomenon induced by heavy compact objects (10 -4 - 10 -1 solar mass units). A CCD-based experimental setup is described, which would make it possible to search for compact objects in the 10 -6 - 10 -4 solar mass unit domain

Evidence for accreted component in the Galactic discs

Science.gov (United States)

Xing, Q. F.; Zhao, G.

2018-06-01

We analyse the distribution of [Mg/Fe] abundance in the Galactic discs with F- and G-type dwarf stars selected from the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) archive. The sample stars are assigned into different stellar populations by using kinematic criteria. Our analysis reveals the chemical inhomogeneities in the Galactic thick disc. A few of metal-poor stars in the thick disc exhibit relatively low [Mg/Fe] abundance in respect to the standard thick-disc sample. The orbital eccentricities and maximum Galactocentric radii of low-α metal-poor stars are apparently greater than that of high-α thick-disc stars. The orbital parameters and chemical components of low-α stars in the thick disc suggest that they may have been formed in regions with low star formation rate that were located at large distances from the Galactic centre, such as infalling dwarf spheroidal galaxies.

Study of the high energy emission of accreting compact objects with SPI/INTEGRAL

International Nuclear Information System (INIS)

Droulans, R.

2011-01-01

The study of the high energy emission is essential for understanding the radiative processes inherent to accretion flows onto compact objects (black holes and neutron stars). The X/γ-ray continuum of these systems is successfully interpreted in terms of two components. The first component corresponds to blackbody emission from a geometrically thin optically thick accretion disk while the second component is generally associated to Compton scattering of the thermal disk flux off hot electrons. Despite considerable advances throughout the years, the heating mechanisms as well as the structure of the hot Comptonizing plasma remain poorly understood. In order to shed light on the physical processes that govern the innermost regions of the accretion flow, we take advantage of the data archive accumulated by the SPI instrument, a high energy spectrometer (20 keV - 8 MeV) developed at the CESR (now IRAP, Toulouse, France) for the INTEGRAL mission. Above 150 keV, SPI combines a unique spectral resolution with unequalled sensitivity, being thus an ideal tool to study the high energy emission of accreting compact objects. The thesis manuscript reports on the results of timing and spectral studies of three particular systems. First, I address the high energy emission of the enigmatic micro-quasar GRS 1915+105, a source characterized by colossal luminosity and strong chaotic variability in X-rays. On a timescale of about one day, the photon index of the 20 - 200 keV spectrum varies between 2.7 and 3.5; at higher energies (≥150 keV), SPI unveils the systematic presence of an additional emission component, extending without folding energy up to ∼ 500 keV. Second, I study the high energy emission of GX 339-4, a source whose spectral properties are representative of black hole transients. The spectrum of the luminous hard state of this system shows a variable high energy tail (≥150 keV), with significant flux changes on a short timescale (several hours). I explain the

Galactic chemical evolution: perspectives and prospects

International Nuclear Information System (INIS)

Trimble, V.

1987-01-01

The first modern, quantitative models of galactic chemical evolution appeared exactly 20 years ago in the PhD dissertation of the late Beatrice M. Tinsley. Such models represent a synthesis of the behavior of the 10 11 or more stars that form over the 10 10 year age of a galaxy like their Milky Way and are vital both for understanding how and why galaxies have the luminosities, colors, and chemical compositions they see now and for interpreting observations of distant galaxies to answer cosmological questions about the size, age, density, inhomogeneities, and geometry of the universe. Since my last status report on the subject, some issues have become much clearer (the distinctness of nucleosynthesis in Type I, low mass, supernovae, from that in Type II's that make pulsars; the importance of galaxy mergers and interactions in triggering bursts of star formation), while others have remained puzzling (the sites of the r and p processes) or newly-surfaced (the nucleosynthetic contributions of pre-galactic massive objects; the nature and roll of dark matter in galaxies). The talk will touch briefly on the past, present, and future of galactic evolution studies

H II REGION DRIVEN GALACTIC BUBBLES AND THEIR RELATIONSHIP TO THE GALACTIC MAGNETIC FIELD

Energy Technology Data Exchange (ETDEWEB)

Pavel, Michael D.; Clemens, D. P., E-mail: pavelmi@bu.edu, E-mail: clemens@bu.edu [Institute for Astrophysical Research, Boston University, 725 Commonwealth Ave., Boston, MA 02215 (United States)

2012-12-01

The relative alignments of mid-infrared traced Galactic bubbles are compared to the orientation of the mean Galactic magnetic field in the disk. The orientations of bubbles in the northern Galactic plane were measured and are consistent with random orientations-no preferential alignment with respect to the Galactic disk was found. A subsample of H II region driven Galactic bubbles was identified, and as a single population they show random orientations. When this subsample was further divided into subthermal and suprathermal H II regions, based on hydrogen radio recombination linewidths, the subthermal H II regions showed a marginal deviation from random orientations, but the suprathermal H II regions showed significant alignment with the Galactic plane. The mean orientation of the Galactic disk magnetic field was characterized using new near-infrared starlight polarimetry and the suprathermal H II regions were found to preferentially align with the disk magnetic field. If suprathermal linewidths are associated with younger H II regions, then the evolution of young H II regions is significantly affected by the Galactic magnetic field. As H II regions age, they cease to be strongly linked to the Galactic magnetic field, as surrounding density variations come to dominate their morphological evolution. From the new observations, the ratios of magnetic-to-ram pressures in the expanding ionization fronts were estimated for younger H II regions.

Galactic bulge preferred over dark matter for the Galactic centre gamma-ray excess

Science.gov (United States)

Macias, Oscar; Gordon, Chris; Crocker, Roland M.; Coleman, Brendan; Paterson, Dylan; Horiuchi, Shunsaku; Pohl, Martin

2018-05-01

An anomalous gamma-ray excess emission has been found in the Fermi Large Area Telescope data1 covering the centre of the Galaxy2,3. Several theories have been proposed for this `Galactic centre excess'. They include self-annihilation of dark-matter particles4, an unresolved population of millisecond pulsars5, an unresolved population of young pulsars6, or a series of burst events7. Here, we report on an analysis that exploits hydrodynamical modelling to register the position of interstellar gas associated with diffuse Galactic gamma-ray emission. We find evidence that the Galactic centre excess gamma rays are statistically better described by the stellar over-density in the Galactic bulge and the nuclear stellar bulge, rather than a spherical excess. Given its non-spherical nature, we argue that the Galactic centre excess is not a dark-matter phenomenon but rather associated with the stellar population of the Galactic bulge and the nuclear bulge.

Evolution and merging of binaries with compact objects

International Nuclear Information System (INIS)

Bethe, Hans A.; Brown, Gerald E.; Lee, Chang-Hwan

2007-01-01

In the light of recent observations in which short γ-ray bursts are interpreted as arising from black-hole(BH), neutron-star(NS) or NS-NS mergings we would like to review our research on the evolution of compact binaries, especially those containing NS's. These were carried out with predictions for LIGO in mind, but are directly applicable to short γ-ray bursts in the interpretation above. Most important in our review is that we show that the standard scenario for evolving NS-NS binaries always ends up with a low-mass BH (LMBH), NS binary. Bethe and Brown [1998, Astrophys. J. 506, 780] showed that this fate could be avoided if the two giants in the progenitor binary burned He at the same time, and that in this way the binary could avoid the common envelope evolution of the NS with red giant companion which sends the first born NS into a BH in the standard scenario. The burning of He at the same time requires, for the more massive giants such as the progenitors of the Hulse-Taylor binary NS that the two giants be within 4% of each other in zero age main sequence (ZAMS) mass. Applying this criterion to all binaries results in a factor ∼5 of LMBH-NS binaries as compared with NS-NS binaries. Although this factor is substantially less than the originally claimed factor of 20 which Bethe and Brown (1998) estimated, largely because a careful evolution has been carried through here, our factor 5 is augmented by a factor of ∼8 arising from the higher rate of star formation in the earlier Galaxy from which the BH-NS binaries came from. Furthermore, here we calculate the mergers for short-hard gamma-ray bursts, whereas Bethe and Brown's factor 20 included a factor of 2 for the higher chirp masses in a BH-NS binary as compared with NS-NS one. In short, we end up with an estimate of factor ∼40 over that calculated with NS-NS binary mergers in our Galaxy alone. Our total rate is estimated to be about one merging of compact objects per year. Our scenario of NS-NS binaries

The Galactic O-Star Catalog (GOSC) and the Galactic O-Star Spectroscopic Survey (GOSSS): current status

Science.gov (United States)

Maíz Apellániz, J.; Alonso Moragón, A.; Ortiz de Zárate Alcarazo, L.; The Gosss Team

2017-03-01

We present the updates of the Galactic O-Star Catalog (GOSC) that we have undertaken in the last two years: new spectral types, more objects, additional information, and coordination with CDS. We also present updates for the Galactic O-Star Spectroscopic Survey (GOSSS). A new paper (GOSSS-III) has been published and ˜ 1000 targets have been observed since 2014. Four new setups have been added to our lineup and for two of them we have already obtained over 100 spectra: with OSIRIS at the 10.4 m GTC we are observing northern dim stars and with FRODOspec at the 2.0 m Liverpool Telescope we are observing northern bright stars. Finally, we also make available new versions of MGB, the spectral classification tool associated with the project, and of the GOSSS grid of spectroscopic standards.

The Galactic 511 keV line: analysis and interpretation of Integral observations

International Nuclear Information System (INIS)

Lonjou, V.

2005-09-01

Ever since the discovery of the 511 keV annihilation line emission from the galactic center region in the late seventies, the origin of galactic positrons has been the topic of a vivid scientific debate. It is also one of the prime scientific objectives of the imaging spectrometer SPI on board ESA's INTEGRAL observatory. In this thesis first a description of the most important SPI sub-system is given - the detector plane. Procedures for detector energy calibration and detector degradation analysis are developed. The determination of instrumental background models, a crucial aspect of data analysis, is elaborated. These background models are then applied to deriving sky maps and spectra of unprecedented quality of the Galactic positron annihilation radiation. The emission is centered on the galactic center with a spatial resolution of 8 degrees (FWHM), a second spatial component appears clearly: the galactic disc. The ray energy has been measured with unprecedented accuracy: 511.0 ± 0.03 keV for a full width at half maximum (FWHM) of 2.07 ± 0.1 keV. The total galactic flux ranges from 1.09 to 2.43 10 -3 ph.cm -2 .s -1 including uncertainties on spatial distribution. Finally, the implications of these observations for the production of positrons by various Galactic populations are discussed

Candidate high-z protoclusters among the Planck compact sources, as revealed by Herschel-SPIRE

Science.gov (United States)

Greenslade, J.; Clements, D. L.; Cheng, T.; De Zotti, G.; Scott, D.; Valiante, E.; Eales, S.; Bremer, M. N.; Dannerbauer, H.; Birkinshaw, M.; Farrah, D.; Harrison, D. L.; Michałowski, M. J.; Valtchanov, I.; Oteo, I.; Baes, M.; Cooray, A.; Negrello, M.; Wang, L.; van der Werf, P.; Dunne, L.; Dye, S.

2018-05-01

By determining the nature of all the Planck compact sources within 808.4 deg2 of large Herschel surveys, we have identified 27 candidate protoclusters of dusty star-forming galaxies (DSFGs) that are at least 3σ overdense in either 250, 350, or 500 μm sources. We find roughly half of all the Planck compact sources are resolved by Herschel into multiple discrete objects, with the other half remaining unresolved by Herschel. We find a significant difference between versions of the Planck catalogues, with earlier releases hosting a larger fraction of candidate protoclusters and Galactic cirrus than later releases, which we ascribe to a difference in the filters used in the creation of the three catalogues. We find a surface density of DSFG candidate protoclusters of (3.3 ± 0.7) × 10-2 sources deg-2, in good agreement with previous similar studies. We find that a Planck colour selection of S857/S545 1. Our candidate protoclusters are a factor of 5 times brighter at 353 GHz than expected from simulations, even in the most conservative estimates. Further observations are needed to confirm whether these candidate protoclusters are physical clusters, multiple protoclusters along the line of sight, or chance alignments of unassociated sources.

THE GALACTIC O-STAR SPECTROSCOPIC SURVEY (GOSSS). II. BRIGHT SOUTHERN STARS

International Nuclear Information System (INIS)

Sota, A.; Apellániz, J. Maíz; Alfaro, E. J.; Morrell, N. I.; Barbá, R. H.; Arias, J. I.; Walborn, N. R.; Gamen, R. C.

2014-01-01

We present the second installment of GOSSS, a massive spectroscopic survey of Galactic O stars, based on new homogeneous, high signal-to-noise ratio, R ∼ 2500 digital observations from both hemispheres selected from the Galactic O-Star Catalog (GOSC). In this paper we include bright stars and other objects drawn mostly from the first version of GOSC, all of them south of δ = –20°, for a total number of 258 O stars. We also revise the northern sample of Paper I to provide the full list of spectroscopically classified Galactic O stars complete to B = 8, bringing the total number of published GOSSS stars to 448. Extensive sequences of exceptional objects are given, including the early Of/WN, O Iafpe, Ofc, ON/OC, Onfp, Of?p, and Oe types, as well as double/triple-lined spectroscopic binaries. The new spectral subtype O9.2 is also discussed. The magnitude and spatial distributions of the observed sample are analyzed. We also present new results from OWN, a multi-epoch high-resolution spectroscopic survey coordinated with GOSSS that is assembling the largest sample of Galactic spectroscopic massive binaries ever attained. The OWN data combined with additional information on spectroscopic and visual binaries from the literature indicate that only a very small fraction (if any) of the stars with masses above 15-20 M ☉ are born as single systems. In the future we will publish the rest of the GOSSS survey, which is expected to include over 1000 Galactic O stars

Testing the Binary Black Hole Nature of a Compact Binary Coalescence.

Science.gov (United States)

Krishnendu, N V; Arun, K G; Mishra, Chandra Kant

2017-09-01

We propose a novel method to test the binary black hole nature of compact binaries detectable by gravitational wave (GW) interferometers and, hence, constrain the parameter space of other exotic compact objects. The spirit of the test lies in the "no-hair" conjecture for black holes where all properties of a Kerr black hole are characterized by its mass and spin. The method relies on observationally measuring the quadrupole moments of the compact binary constituents induced due to their spins. If the compact object is a Kerr black hole (BH), its quadrupole moment is expressible solely in terms of its mass and spin. Otherwise, the quadrupole moment can depend on additional parameters (such as the equation of state of the object). The higher order spin effects in phase and amplitude of a gravitational waveform, which explicitly contains the spin-induced quadrupole moments of compact objects, hence, uniquely encode the nature of the compact binary. Thus, we argue that an independent measurement of the spin-induced quadrupole moment of the compact binaries from GW observations can provide a unique way to distinguish binary BH systems from binaries consisting of exotic compact objects.

SECULAR EVOLUTION OF COMPACT BINARIES NEAR MASSIVE BLACK HOLES: GRAVITATIONAL WAVE SOURCES AND OTHER EXOTICA

International Nuclear Information System (INIS)

Antonini, Fabio; Perets, Hagai B.

2012-01-01

The environment near supermassive black holes (SMBHs) in galactic nuclei contains a large number of stars and compact objects. A fraction of these are likely to be members of binaries. Here we discuss the binary population of stellar black holes and neutron stars near SMBHs and focus on the secular evolution of such binaries, due to the perturbation by the SMBH. Binaries with highly inclined orbits with respect to their orbit around the SMBH are strongly affected by secular Kozai processes, which periodically change their eccentricities and inclinations (Kozai cycles). During periapsis approach, at the highest eccentricities during the Kozai cycles, gravitational wave (GW) emission becomes highly efficient. Some binaries in this environment can inspiral and coalesce at timescales much shorter than a Hubble time and much shorter than similar binaries that do not reside near an SMBH. The close environment of SMBHs could therefore serve as a catalyst for the inspiral and coalescence of binaries and strongly affect their orbital properties. Such compact binaries would be detectable as GW sources by the next generation of GW detectors (e.g., advanced-LIGO). Our analysis shows that ∼0.5% of such nuclear merging binaries will enter the LIGO observational window while on orbits that are still very eccentric (e ∼> 0.5). The efficient GW analysis for such systems would therefore require the use of eccentric templates. We also find that binaries very close to the SMBH could evolve through a complex dynamical (non-secular) evolution, leading to emission of several GW pulses during only a few years (though these are likely to be rare). Finally, we note that the formation of close stellar binaries, X-ray binaries, and their merger products could be induced by similar secular processes, combined with tidal friction rather than GW emission as in the case of compact object binaries.

Accretion disks in active galactic nuclei

International Nuclear Information System (INIS)

Shields, G.A.

1989-01-01

Active galactic nuclei (AGN) have taunted astrophysicists for a quarter century. How do these objects produce huge luminosities---in some cases, far outshining our galaxy---from a region perhaps no larger than the solar system? Accretion onto supermassive black holes has been widely considered the best buy in theories of AGN. Much work has gone into accretion disk theory, searches for black holes in galactic nuclei, and observational tests. These efforts have not proved the disk model, but there is progress. Evidence for black holes in the nuclei of nearby galaxies is provided by observations of stellar velocities, and radiation from the disk's hot surface may be observed in the ultraviolet (UV) and neighboring spectral bands. In the review, the author describe some of the recent work on accretion disks in AGN, with an emphasis on points of contact between theory and observation

Population studies - evidence for accretion of the galactic halo

International Nuclear Information System (INIS)

Norris, J.E.; Ryan, S.G.

1989-01-01

While there are comparatively few prograde-orbit dwarf stars in advance of the sun's motion of the type of which 510, selected kinematically, are presented, it is noted that there are significant numbers of objects on retrograde orbits that move with a speed greater than the sun's, relative to a nonrotating system, in the opposite direction about the Galactic center. It is suggested that this asymmetry is explainable in terms of the Searle and Zinn (1978) and Rodgers and Paltoglou (1984) models of halo formation by accretion; in these, fragments experience dynamical friction from an already-formed Galactic disk. 21 references

Galactic models

International Nuclear Information System (INIS)

Buchler, J.R.; Gottesman, S.T.; Hunter, J.H. Jr.

1990-01-01

Various papers on galactic models are presented. Individual topics addressed include: observations relating to galactic mass distributions; the structure of the Galaxy; mass distribution in spiral galaxies; rotation curves of spiral galaxies in clusters; grand design, multiple arm, and flocculent spiral galaxies; observations of barred spirals; ringed galaxies; elliptical galaxies; the modal approach to models of galaxies; self-consistent models of spiral galaxies; dynamical models of spiral galaxies; N-body models. Also discussed are: two-component models of galaxies; simulations of cloudy, gaseous galactic disks; numerical experiments on the stability of hot stellar systems; instabilities of slowly rotating galaxies; spiral structure as a recurrent instability; model gas flows in selected barred spiral galaxies; bar shapes and orbital stochasticity; three-dimensional models; polar ring galaxies; dynamical models of polar rings

A SCALING RELATION BETWEEN MEGAMASER DISK RADIUS AND BLACK HOLE MASS IN ACTIVE GALACTIC NUCLEI

International Nuclear Information System (INIS)

Wardle, Mark; Yusef-Zadeh, Farhad

2012-01-01

Several thin, Keplerian, sub-parsec megamaser disks have been discovered in the nuclei of active galaxies and used to precisely determine the mass of their host black holes. We show that there is an empirical linear correlation between the disk radius and the black hole mass. We demonstrate that such disks are naturally formed by the partial capture of molecular clouds passing through the galactic nucleus and temporarily engulfing the central supermassive black hole. Imperfect cancellation of the angular momenta of the cloud material colliding after passing on opposite sides of the hole leads to the formation of a compact disk. The radial extent of the disk is determined by the efficiency of this process and the Bondi-Hoyle capture radius of the black hole, and naturally produces the empirical linear correlation of the radial extent of the maser distribution with black hole mass. The disk has sufficient column density to allow X-ray irradiation from the central source to generate physical and chemical conditions conducive to the formation of 22 GHz H 2 O masers. For initial cloud column densities ∼ 23.5 cm –2 the disk is non-self-gravitating, consistent with the ordered kinematics of the edge-on megamaser disks; for higher cloud columns the disk would fragment and produce a compact stellar disk similar to that observed around Sgr A* at the galactic center.

Limits on compact halo objects as dark matter from gravitational microlensing

Directory of Open Access Journals (Sweden)

Jetzer Philippe

2014-04-01

Full Text Available Microlensing started with the seminal paper by Paczyński in 1986 [1], first with observations towards the Large Magellanic Cloud and the galactic bulge. Since then many other targets have been observed and new applications have been found. In particular, it turned out to be a powerful method to detect planets in our galaxy and even in the nearby M31. Here, we will present some results obtained so far by microlensing without being, however, exhaustive.

Examining Sites of Recent Star Formation in the Galactic Center: A Closer Look at the Arched Filaments and H HII Regions

Science.gov (United States)

Hankins, Matthew; Herter, Terry; Lau, Ryan; Morris, Mark; Mills, Elisabeth

2018-01-01

In this dissertation presentation, we analyze mid-infrared imaging of the Arched Filaments and H HII regions in the Galactic center taken with the Faint Object Infrared Camera for the SOFIA Telescope (FORCAST). Examining these regions are of great interest because they provide insights on star formation in the Galactic center and the interactions massive stars have with the ISM. The Arched Filaments are a collection of molecular cloud ridges which are ionized by the nearby Arches star cluster, and give the appearance of large (~25 pc) arch-like structures. The H HII regions are a collection of HII regions just to the west of the Arches cluster (~5-15 pc). The origin of the stars powering the H HII regions is uncertain, as they may have formed in a nearby molecular cloud or could be ejected members of the Arches cluster. FORCAST observations of these regions were used to study the morphology and heating structure of the HII regions, as well as constrain their luminosities.Color-temperature maps of the Arched Filaments created with the FORCAST data reveals fairly uniform dust temperatures (~70-100 K) across the length filaments. The temperature uniformity of the clouds can be explained if they are heated by the Arches cluster but are located at a larger distance from the cluster than they appear. The density of the Arched Filaments clouds was estimated from the FORCAST data and was found to be below the threshold for tidal shearing, indicating that that the clouds will be destroyed by the strong tidal field near the Galactic center. To the west of the Arched Filaments, there is an interesting collection of HII regions, referred to as the H HII regions. These regions are likely heated by massive O/B type stars, and the morphology of the dust emission associated with these objects indicate a mixture of potential in situ formation mechanisms and interlopers. Interestingly, FORCAST imaging of the H HII regions also reveal several compact sources, which may be young

Multiwavelength observations of Active Galactic Nuclei from the radio to the hard X-rays

Science.gov (United States)

Beuchert, Tobias

2017-07-01

Active Galaxies form a peculiar type of galaxies. Their cores, the so-called "Active Galactic Nuclei" (AGN), are the most persistent luminous objects in the universe. Accretion of several solar masses per year onto black holes of Millions to Billions of solar masses drive the immense energy output of these systems, which can exceed that of the entire galaxy. The compact energy source, however, only measures about one over a Billion times that of the entire galaxy. Subject of my thesis are observations of the two main channels of energy release of selected AGN systems, both of which are encompassed by profound and yet unanswered questions. These channels are on the one hand the pronounced X-ray emission of the hot and compact accreting environment in close vicinity of the black hole, and on the other hand the radio synchrotron emission of magnetically collimated jets that are fed by portions of the accreted matter. These jets also function as effective accelerators and drive the injected matter deep into the intergalactic medium. As the circumnuclear environment of AGN is too compact to be spatially resolved in the X-rays, I show how X-ray spectroscopy can be used to: (1) understand the effects of strong gravity to trace the geometry and physics of the X-ray source and (2) more consistently quantify matter that surrounds and dynamically absorbs our direct line of sight towards the X-ray source. Second, I unveil the valuable information contained in the polarized radio light being emitted from magnetized jet outflows. In contrast to the X-ray emitting region, I am able to spatially resolve the inner parts of the jet of a prominent galaxy with help of the Very Long Baseline Array, a large network of radio telescopes. The resulting polarization maps turn out to be exceptionally promising in answering fundamental questions related to jet physics.

Very fast optical flaring from a possible new Galactic magnetar.

Science.gov (United States)

Stefanescu, A; Kanbach, G; Słowikowska, A; Greiner, J; McBreen, S; Sala, G

2008-09-25

Highly luminous rapid flares are characteristic of processes around compact objects like white dwarfs, neutron stars and black holes. In the high-energy regime of X-rays and gamma-rays, outbursts with variabilities on timescales of seconds or less are routinely observed, for example in gamma-ray bursts or soft gamma-ray repeaters. At optical wavelengths, flaring activity on such timescales has not been observed, other than from the prompt phase of one exceptional gamma-ray burst. This is mostly due to the fact that outbursts with strong, fast flaring are usually discovered in the high-energy regime; most optical follow-up observations of such transients use instruments with integration times exceeding tens of seconds, which are therefore unable to resolve fast variability. Here we show the observation of extremely bright and rapid optical flaring in the Galactic transient SWIFT J195509.6+261406. Our optical light curves are phenomenologically similar to high-energy light curves of soft gamma-ray repeaters and anomalous X-ray pulsars, which are thought to be neutron stars with extremely high magnetic fields (magnetars). This suggests that similar processes are in operation, but with strong emission in the optical, unlike in the case of other known magnetars.

2MASS Identifications for Galactic OB Stars

OpenAIRE

Reed, B. Cameron

2007-01-01

Cross-identifications for 14,574 intrinsically luminous galactic stars (mostly OB stars) to objects in the 2MASS survey have been determined using a search box of +/-0.0015 degrees (+/- 5.4 arcsec) in both RA and Dec. Instructions on obtaining the relevant files can be obtained at othello.alma.edu/~reed/OB-2MASS.doc.

A systematic search for dwarf counterparts to ultra compact high velocity clouds

Science.gov (United States)

Bennet, Paul; Sand, David J.; Crnojevic, Denija; Strader, Jay

2015-01-01

Observations of the Universe on scales smaller than typical, massive galaxies challenge the standard Lambda Cold Dark Matter paradigm for structure formation. It is thus imperative to discover and characterize the faintest dwarf galaxy systems, not just within the Local Group, but in relatively isolated environments as well in order to properly connect them with models of structure formation. Here we report on a systematic search of public ultraviolet and optical archives for dwarf galaxy counterparts to so-called Ultra Compact High Velocity Clouds (UCHVCs), which are compact, isolated HI sources recently found in the Galactic Arecibo L-band Feed Array-HI (GALFA-HI) and Arecibo Legacy Fast ALFA (ALFALFA-HI) surveys. Our search has uncovered at least three strong dwarf galaxy candidates, and we present their inferred star formation rate and structural properties here.

Planets in other universes: habitability constraints on density fluctuations and galactic structure

Energy Technology Data Exchange (ETDEWEB)

Adams, Fred C.; Coppess, Katherine R. [Physics Department, University of Michigan, Ann Arbor, MI 48109 (United States); Bloch, Anthony M., E-mail: fca@umich.edu, E-mail: kcoppess@umich.edu, E-mail: abloch@umich.edu [Mathematics Department, University of Michigan, Ann Arbor, MI 48109 (United States)

2015-09-01

Motivated by the possibility that different versions of the laws of physics could be realized within other universes, this paper delineates the galactic structure parameters that allow for habitable planets and revisits constraints on the amplitude Q of the primordial density fluctuations. Previous work indicates that large values of Q lead to galaxies so dense that planetary orbits cannot survive long enough for life to develop. Small values of Q lead to delayed star formation, loosely bound galaxies, and compromised heavy element retention. This work generalizes previous treatments in the following directions: [A] We consider models for the internal structure of the galaxies, including a range of stellar densities, and find the fraction of the resulting galactic real estate that allows for stable, long-lived planetary orbits. [B] For high velocity encounters, we perform a large ensemble of numerical simulations to estimate cross sections for the disruption of planetary orbits due to interactions with passing stars. [C] We consider the background radiation fields produced by the galaxies: if a galaxy is too compact, the night sky seen from a potentially habitable planet can provide more power than the host star. [D] One consequence of intense galactic background radiation fields is that some portion of the galaxy, denoted as the Galactic Habitable Zone, will provide the right flux levels to support habitable planets for essentially any planetary orbit including freely floating bodies (but excluding close-in planets). As the value of Q increases, the fraction of stars in a galaxy that allow for (traditional) habitable planets decreases due to both orbital disruption and the intense background radiation. However, the outer parts of the galaxy always allow for habitable planets, so that the value of Q does not have a well-defined upper limit (due to scattering or radiation constraints). Moreover, some Galactic Habitable Zones are large enough to support more

Planets in other universes: habitability constraints on density fluctuations and galactic structure

International Nuclear Information System (INIS)

Adams, Fred C.; Coppess, Katherine R.; Bloch, Anthony M.

2015-01-01

Motivated by the possibility that different versions of the laws of physics could be realized within other universes, this paper delineates the galactic structure parameters that allow for habitable planets and revisits constraints on the amplitude Q of the primordial density fluctuations. Previous work indicates that large values of Q lead to galaxies so dense that planetary orbits cannot survive long enough for life to develop. Small values of Q lead to delayed star formation, loosely bound galaxies, and compromised heavy element retention. This work generalizes previous treatments in the following directions: [A] We consider models for the internal structure of the galaxies, including a range of stellar densities, and find the fraction of the resulting galactic real estate that allows for stable, long-lived planetary orbits. [B] For high velocity encounters, we perform a large ensemble of numerical simulations to estimate cross sections for the disruption of planetary orbits due to interactions with passing stars. [C] We consider the background radiation fields produced by the galaxies: if a galaxy is too compact, the night sky seen from a potentially habitable planet can provide more power than the host star. [D] One consequence of intense galactic background radiation fields is that some portion of the galaxy, denoted as the Galactic Habitable Zone, will provide the right flux levels to support habitable planets for essentially any planetary orbit including freely floating bodies (but excluding close-in planets). As the value of Q increases, the fraction of stars in a galaxy that allow for (traditional) habitable planets decreases due to both orbital disruption and the intense background radiation. However, the outer parts of the galaxy always allow for habitable planets, so that the value of Q does not have a well-defined upper limit (due to scattering or radiation constraints). Moreover, some Galactic Habitable Zones are large enough to support more

Applications of machine-learning algorithms for infrared colour selection of Galactic Wolf-Rayet stars

Science.gov (United States)

Morello, Giuseppe; Morris, P. W.; Van Dyk, S. D.; Marston, A. P.; Mauerhan, J. C.

2018-01-01

We have investigated and applied machine-learning algorithms for infrared colour selection of Galactic Wolf-Rayet (WR) candidates. Objects taken from the Spitzer Galactic Legacy Infrared Midplane Survey Extraordinaire (GLIMPSE) catalogue of the infrared objects in the Galactic plane can be classified into different stellar populations based on the colours inferred from their broad-band photometric magnitudes [J, H and Ks from 2 Micron All Sky Survey (2MASS), and the four Spitzer/IRAC bands]. The algorithms tested in this pilot study are variants of the k-nearest neighbours approach, which is ideal for exploratory studies of classification problems where interrelations between variables and classes are complicated. The aims of this study are (1) to provide an automated tool to select reliable WR candidates and potentially other classes of objects, (2) to measure the efficiency of infrared colour selection at performing these tasks and (3) to lay the groundwork for statistically inferring the total number of WR stars in our Galaxy. We report the performance results obtained over a set of known objects and selected candidates for which we have carried out follow-up spectroscopic observations, and confirm the discovery of four new WR stars.

A full-sky, high-resolution atlas of galactic 12 μm dust emission with WISE

International Nuclear Information System (INIS)

Meisner, Aaron M.; Finkbeiner, Douglas P.

2014-01-01

We describe our custom processing of the entire Wide-field Infrared Survey Explorer (WISE) 12 μm imaging data set, and present a high-resolution, full-sky map of diffuse Galactic dust emission that is free of compact sources and other contaminating artifacts. The principal distinctions between our resulting co-added images and the WISE Atlas stacks are our removal of compact sources, including their associated electronic and optical artifacts, and our preservation of spatial modes larger than 1.°5. We provide access to the resulting full-sky map via a set of 430 12.°5 × 12.°5 mosaics. These stacks have been smoothed to 15'' resolution and are accompanied by corresponding coverage maps, artifact images, and bit-masks for point sources, resolved compact sources, and other defects. When combined appropriately with other mid-infrared and far-infrared data sets, we expect our WISE 12 μm co-adds to form the basis for a full-sky dust extinction map with angular resolution several times better than Schlegel et al.

Nonconformally flat initial data for binary compact objects

International Nuclear Information System (INIS)

Uryu, Koji; Limousin, Francois; Gourgoulhon, Eric; Friedman, John L.; Shibata, Masaru

2009-01-01

A new method is described for constructing initial data for a binary neutron-star system in quasiequilibrium circular orbit. Two formulations for nonconformally flat data, waveless and near-zone helically symmetric, are introduced; in each formulation, the Einstein-Euler system, written in 3+1 form on an asymptotically flat spacelike hypersurface, is exactly solved for all metric components, including the spatially nonconformally flat potentials, and for irrotational flow. A numerical method applicable to both formulations is explained with an emphasis on the imposition of a spatial gauge condition. Results are shown for solution sequences of irrotational binary neutron-stars with matter approximated by parametrized equations of state that use a few segments of polytropic equations of state. The binding energy and total angular momentum of solution sequences computed within the conformally flat--Isenberg-Wilson-Mathews--formulation are closer to those of the third post-Newtonian (3PN) two point particles up to the closest orbits, for the more compact stars, whereas sequences resulting from the waveless/near-zone helically symmetric formulations deviate from the 3PN curve even more for the sequences with larger compactness. We think it likely that this correction reflects an overestimation in the Isenberg-Wilson-Mathews formulation as well as in the 3PN formula, by ∼1 cycle in the gravitational-wave phase during the last several orbits. The work suggests that imposing spatial conformal flatness results in an underestimate of the quadrupole deformation of the components of binary neutron-star systems in the last few orbits prior to merger.

DENSITY OF WARM IONIZED GAS NEAR THE GALACTIC CENTER: LOW RADIO FREQUENCY OBSERVATIONS

International Nuclear Information System (INIS)

Roy, Subhashis

2013-01-01

We have observed the Galactic center (GC) region at 0.154 and 0.255 GHz with the Giant Metrewave Radio Telescope. A total of 62 compact likely extragalactic (EG) sources are detected. Their scattering sizes decrease linearly with increasing angular distance from the GC up to about 1°. The apparent scattering sizes of the sources are more than an order of magnitude less than predicted earlier by the NE2001 model of Galactic electron distribution within 359.°5 e is ∼10 cm –3 , which matches the NE2001 model. This model predicts the EG sources to be resolved out from 1.4 GHz interferometric surveys. However, out of 10 EG sources expected in the region, 8 likely EG are present in the 1.4 GHz catalog. Ionized interfaces of dense molecular clouds to the ambient medium are most likely responsible for strong scattering and low radio frequency absorption. However, dense GC clouds traced by CS J = 1-0 emission are found to have a narrow distribution of ∼0.°2 across the Galactic plane. Angular distribution of most EG sources seen through the so-called Hyperstrong Scattering Region are random in b, and typically ∼7 out of 10 sources will not be seen through the dense molecular clouds, which explains why most of them are not scatter broadened at 1.4 GHz

Radiography with cosmic-ray and compact accelerator muons; Exploring inner-structure of large-scale objects and landforms.

Science.gov (United States)

Nagamine, Kanetada

2016-01-01

Cosmic-ray muons (CRM) arriving from the sky on the surface of the earth are now known to be used as radiography purposes to explore the inner-structure of large-scale objects and landforms, ranging in thickness from meter to kilometers scale, such as volcanic mountains, blast furnaces, nuclear reactors etc. At the same time, by using muons produced by compact accelerators (CAM), advanced radiography can be realized for objects with a thickness in the sub-millimeter to meter range, with additional exploration capability such as element identification and bio-chemical analysis. In the present report, principles, methods and specific research examples of CRM transmission radiography are summarized after which, principles, methods and perspective views of the future CAM radiography are described.

Galactically inertial space probes for the direct measurement of the metric expansion of the universe

International Nuclear Information System (INIS)

Cagnani, Ivan

2011-01-01

Astrometric data from the future GAIA and OBSS missions will allow a more precise calculation of the local galactic circular speed, and better measurements of galactic movements relative to the CMB will be obtained by post-WMAP missions (ie Planck). Contemporary development of high specific impulse electric propulsion systems (ie VASIMIR) will enable the development of space probes able to properly compensate the galactic circular speed as well as the resulting attraction to the centre of our galaxy. The probes would appear immobile to an ideal observer fixed at the centre of the galaxy, in contrast of every other galactic object, which would appear moving according to their local galactic circular speed and their proper motions. Arranging at least three of these galactically static probes in an extended formation and measuring reciprocal distances of the probes over time with large angle laser ranges could allow a direct measurement of the metric expansion of the universe. Free-drifting laser-ranged targets released by the spacecrafts could also be used to measure and compensate solar system's induced local perturbations. For further reducing local effects and increase the accuracy of the results, the distance between the probes should be maximized and the location of the probes should be as far as possible from the Sun and any massive object (ie Jupiter, Saturn). Gravitational waves could also induce random errors but data from GW observatories like the planned LISA could be used to correct them.

The population of planetary nebulae near the Galactic Centre: chemical abundances

Science.gov (United States)

Mollá, M.; Cavichia, O.; Costa, R. D. D.; Maciel, W. J.

2017-10-01

In this work, we report physical parameters and abundances derived for a sample of 15 high extinction planetary nebulae located in the inner 2° of the Galactic bulge, based on low dispersion spectroscopy secured at the SOAR telescope using the Goodman spectrograph. The new data allow us to extend our database including older, weaker objects that are at the faint end of the planetary nebulae luminosity function. The data provide chemical compositions for PNe located in this region of the bulge to explore the chemical enrichment history of the central region of the Galactic bulge. The results show that the abundances of our sample are skewed to higher metallicities than previous data in the outer regions of the bulge. This can indicate a faster chemical enrichment taking place at the Galactic centre.

Detection of extended galactic sources with an underwater neutrino telescope

International Nuclear Information System (INIS)

Leisos, A.; Tsirigotis, A. G.; Tzamarias, S. E.; Lenis, D.

2014-01-01

In this study we investigate the discovery capability of a Very Large Volume Neutrino Telescope to Galactic extended sources. We focus on the brightest HESS gamma rays sources which are considered also as very high energy neutrino emitters. We use the unbinned method taking into account both the spatial and the energy distribution of high energy neutrinos and we investigate parts of the Galactic plane where nearby potential neutrino emitters form neutrino source clusters. Neutrino source clusters as well as isolated neutrino sources are combined to estimate the observation period for 5 sigma discovery of neutrino signals from these objects

The KMOS3D Survey: Rotating Compact Star-forming Galaxies and the Decomposition of Integrated Line Widths

Science.gov (United States)

Wisnioski, E.; Mendel, J. T.; Förster Schreiber, N. M.; Genzel, R.; Wilman, D.; Wuyts, S.; Belli, S.; Beifiori, A.; Bender, R.; Brammer, G.; Chan, J.; Davies, R. I.; Davies, R. L.; Fabricius, M.; Fossati, M.; Galametz, A.; Lang, P.; Lutz, D.; Nelson, E. J.; Momcheva, I.; Rosario, D.; Saglia, R.; Tacconi, L. J.; Tadaki, K.; Übler, H.; van Dokkum, P. G.

2018-03-01

Using integral field spectroscopy, we investigate the kinematic properties of 35 massive centrally dense and compact star-forming galaxies (SFGs; {log}{\\overline{M}}* [{M}ȯ ]=11.1, {log}({{{Σ }}}1{kpc}[{M}ȯ {kpc}}-2])> 9.5, {log}({M}* /{r}e1.5[{M}ȯ {kpc}}-1.5])> 10.3) at z ∼ 0.7–3.7 within the KMOS3D survey. We spatially resolve 23 compact SFGs and find that the majority are dominated by rotational motions with velocities ranging from 95 to 500 km s‑1. The range of rotation velocities is reflected in a similar range of integrated Hα line widths, 75–400 km s‑1, consistent with the kinematic properties of mass-matched extended galaxies from the full KMOS3D sample. The fraction of compact SFGs that are classified as “rotation-dominated” or “disklike” also mirrors the fractions of the full KMOS3D sample. We show that integrated line-of-sight gas velocity dispersions from KMOS3D are best approximated by a linear combination of their rotation and turbulent velocities with a lesser but still significant contribution from galactic-scale winds. The Hα exponential disk sizes of compact SFGs are, on average, 2.5 ± 0.2 kpc, 1–2× the continuum sizes, in agreement with previous work. The compact SFGs have a 1.4× higher active galactic nucleus (AGN) incidence than the full KMOS3D sample at fixed stellar mass with an average AGN fraction of 76%. Given their high and centrally concentrated stellar masses, as well as stellar-to-dynamical mass ratios close to unity, the compact SFGs are likely to have low molecular gas fractions and to quench on a short timescale unless replenished with inflowing gas. The rotation in these compact systems suggests that their direct descendants are rotating passive galaxies. Based on observations obtained at the Very Large Telescope (VLT) of the European Southern Observatory (ESO), Paranal, Chile (ESO program IDs 092A-0091, 093.A-0079, 094.A-0217, 095.A-0047, 096.A-0025, 097.A-0028, and 098.A-0045).

UNDERSTANDING COMPACT OBJECT FORMATION AND NATAL KICKS. II. THE CASE OF XTE J1118 + 480

International Nuclear Information System (INIS)

Fragos, T.; Willems, B.; Kalogera, V.; Ivanova, N.; Rockefeller, G.; Fryer, C. L.; Young, P. A.

2009-01-01

In recent years, an increasing number of proper motions have been measured for Galactic X-ray binaries. When supplemented with accurate determinations of the component masses, orbital period, and donor effective temperature, these kinematical constraints harbor a wealth of information on the system's past evolution. Here, we consider all this available information to reconstruct the full evolutionary history of the black hole X-ray binary XTE J1118 + 480, assuming that the system originated in the Galactic disk and the donor has solar metallicity. This analysis accounts for four evolutionary phases: mass transfer through the ongoing X-ray phase, tidal evolution before the onset of Roche lobe overflow, motion through the Galactic potential after the formation of the black hole, and binary orbital dynamics due to explosive mass loss and possibly a black hole natal kick at the time of core collapse. We find that right after black hole formation, the system consists of a ≅6.0-10.0 M sun black hole and a ≅1.0-1.6 M sun main-sequence star. We also find that that an asymmetric natal kick is not only plausible but required for the formation of this system, and derive a lower and upper limit on the black hole natal kick velocity magnitude of 80 km s -1 and 310 km s -1 , respectively.

PROPERTIES OF THE COMPACT H II REGION COMPLEX G-0.02-0.07

International Nuclear Information System (INIS)

Mills, E.; Morris, M. R.; Lang, C. C.; Dong, H.; Wang, Q. D.; Cotera, A.; Stolovy, S. R.

2011-01-01

We present new extinction maps and high-resolution Paschen-alpha images of G-0.02-0.07, a complex of compact H II regions located adjacent to the M-0.02-0.07 giant molecular cloud, 6 pc in projection from the center of the Galaxy. These H II regions, which lie in projection just outside the boundary of the Sgr A East supernova remnant, represent one of the most recent episodes of star formation in the central parsecs of the Galaxy. The 1.87 μm extinctions of regions A, B, and C are almost identical, approximately 3.7 mag. Region D, in contrast, has a peak extinction of A 1.87 = 5.9 mag. Adopting an extinction law specific to the Galactic center, we find that these extinctions correspond to visual extinctions of A V = 45 and A V = 71. The similar and uniform extinctions of regions A, B, and C are consistent with that expected for foreground extinction in the direction of the Galactic center, suggesting that they lie at the front side of the M-0.02-0.07 molecular cloud. Region D is more compact, has a higher extinction, and is thus suspected to be younger and embedded in a dense core in a compressed ridge on the western edge of this cloud.

Thermal evolution of massive compact objects with dense quark cores

International Nuclear Information System (INIS)

Hess, Daniel; Sedrakian, Armen

2011-01-01

We examine the thermal evolution of a sequence of compact objects containing low-mass hadronic and high-mass quark-hadronic stars constructed from a microscopically motivated equation of state. The dependence of the cooling tracks in the temperature versus age plane is studied on the variations of the gaplessness parameter (the ratio of the pairing gap for red-green quarks to the electron chemical potential) and the magnitude of blue quark gap. The pairing in the red-green channel is modeled assuming an inhomogeneous superconducting phase to avoid tachionic instabilities and anomalies in the specific heat; the blue colored condensate is modeled as a Bardeen-Cooper-Schrieffer (BCS)-type color superconductor. We find that massive stars containing quark matter cool faster in the neutrino-cooling era if one of the colors (blue) is unpaired and/or the remaining colors (red-green) are paired in a inhomogeneous gapless superconducting state. The cooling curves show significant variations along the sequence, as the mass (or the central density) of the models is varied. This feature provides a handle for fine-tuning the models to fit the data on the surface temperatures of same-age neutron stars. In the late-time photon cooling era we observe inversion in the temperature arrangement of models, i.e., stars experiencing fast neutrino cooling are asymptotically hotter than their slowly cooling counterparts.

OBSERVATIONAL UPPER BOUND ON THE COSMIC ABUNDANCES OF NEGATIVE-MASS COMPACT OBJECTS AND ELLIS WORMHOLES FROM THE SLOAN DIGITAL SKY SURVEY QUASAR LENS SEARCH

Energy Technology Data Exchange (ETDEWEB)

Takahashi, Ryuichi; Asada, Hideki [Faculty of Science and Technology, Hirosaki University, Hirosaki 036-8561 (Japan)

2013-05-01

The latest result in the Sloan Digital Sky Survey Quasar Lens Search (SQLS) has set the first cosmological constraints on negative-mass compact objects and Ellis wormholes. There are no multiple images lensed by the above two exotic objects for {approx}50, 000 distant quasars in the SQLS data. Therefore, an upper bound is put on the cosmic abundances of these lenses. The number density of negative-mass compact objects is n < 10{sup -8}(10{sup -4}) h {sup 3} Mpc{sup -3} at the mass scale |M| > 10{sup 15}(10{sup 12}) M{sub Sun }, which corresponds to the cosmological density parameter |{Omega}| < 10{sup -4} at the galaxy and cluster mass range |M| = 10{sup 12-15} M{sub Sun }. The number density of the Ellis wormhole is n < 10{sup -4} h {sup 3} Mpc{sup -3} for a range of the throat radius a = 10-10{sup 4} pc, which is much smaller than the Einstein ring radius.

Opacity in compact extragalactic radio sources and the core shift effect

International Nuclear Information System (INIS)

Kovalev, Y Y; Lobanov, A P; Pushkarev, A B; Zensus, J A

2008-01-01

The apparent position of the 'core' in a parsec-scale radio jet (a compact, bright emitting region at the narrow end of the jet) depends on the observing frequency, owing to synchrotron self-absorption and external absorption. This dependency both provides a tool to probe physical conditions in the vicinity of the core and poses problems for astrometric studies using compact radio sources. We investigate the frequency-dependent shift of the positions of the cores (core shift) observed with very long baseline interferometry (VLBI) in parsec-scale jets. We present results for 29 selected active galactic nuclei (AGN). In these AGN, the magnitude of the measured core shift between 2.3 and 8.6 GHz reaches 1.4 mas, with a median value for the sample of 0.44 mas. We discuss related physics as well as astrometry applications and plans for further studies.

Angular Spectra of Polarized Galactic Foregrounds

OpenAIRE

Cho, Jung; Lazarian, A.

2003-01-01

It is believed that magnetic field lines are twisted and bend by turbulent motions in the Galaxy. Therefore, both Galactic synchrotron emission and thermal emission from dust reflects statistics of Galactic turbulence. Our simple model of Galactic turbulence, motivated by results of our simulations, predicts that Galactic disk and halo exhibit different angular power spectra. We show that observed angular spectra of synchrotron emission are compatible with our model. We also show that our mod...

Version 2000 of the Catalogue of Galactic Planetary Nebulae

Science.gov (United States)

Kohoutek, L.

2001-11-01

The ``Catalogue of Galactic Planetary Nebulae (Version 2000)'' appears in Abhandlungen aus der Hamburger Sternwarte, Band XII in the year 2001. It is a continuation of CGPN(1967) and contains 1510 objects classified as galactic PNe up to the end of 1999. The lists of possible pre-PNe and possible post-PNe are also given. The catalogue is restricted only to the data belonging to the location and identification of the objects. It gives identification charts of PNe discovered since 1965 (published in the supplements to CGPN) and those charts of objects discovered earlier, which have wrong or uncertain identification. The question ``what is a planetary nebula'' is discussed and the typical values of PNe and of their central stars are summarized. Short statistics about the discoveries of PNe are given. The catalogue is also available in the Centre de Données, Strasbourg and at Hamburg Observatory via internet. The Catalogue is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/378/843

Planetary nebulae and Wolf-Rayet stars in the galactic-centre field

Energy Technology Data Exchange (ETDEWEB)

Allen, D A [Anglo-Australian Observatory, Epping (Australia)

1979-06-01

A UK Schmidt objective-prism plate of the Galactic-centre field has been examined. Of the 74 objects in the field which have been catalogued as planetary nebulae, only half appear correctly classified; the others include Be stars, symbiotic stars, and stars without emission lines. A further 19 planetary nebulae and two Wolf-Rayet stars have been discovered.

VizieR Online Data Catalog: Catalogue of Galactic Planetary Nebulae (Kohoutek, 2001)

Science.gov (United States)

Kohoutek, L.

2001-05-01

The "Catalogue of Galactic Planetary Nebulae (Version 2000)" appears in Abhandlungen aus der Hamburger Sternwarte, Band XII in the year 2001. It is a continuation of CGPN(1967) and contains 1510 objects classified as galactic PNe up to the end of 1999. The lists of possible pre-PNe and possible post-PNe are also given. The catalogue is restricted only to the data belonging to the location and identification of the objects. It gives identification charts of PNe discovered since 1965 (published in the supplements to CGPN) and those charts of objects discovered earlier, which have wrong or uncertain identification. The question "what is a planetary nebula" is discussed and the typical values of PNe and of their central stars are summarized. Short statistics about the discoveries of PNe are given. The catalogue is also available in the Centre de Donnees, Strasbourg and at Hamburg Observatory via internet. (15 data files).

TeV Gamma Rays From Galactic Center Pulsars

Energy Technology Data Exchange (ETDEWEB)

Hooper, Dan [Fermilab; Cholis, Ilias [Johns Hopkins U.; Linden, Tim [Ohio State U., CCAPP

2017-05-25

Measurements of the nearby pulsars Geminga and B0656+14 by the HAWC and Milagro telescopes have revealed the presence of bright TeV-emitting halos surrounding these objects. If young and middle-aged pulsars near the Galactic Center transfer a similar fraction of their energy into TeV photons, then these sources could dominate the emission that is observed by HESS and other ground-based telescopes from the innermost ~10^2 parsecs of the Milky Way. In particular, both the spectral shape and the angular extent of this emission is consistent with TeV halos produced by a population of pulsars. The overall flux of this emission requires a birth rate of ~100-1000 neutron stars per Myr near the Galactic Center, in good agreement with recent estimates.

Studies of relativistic jets in active galactic nuclei with SKA

NARCIS (Netherlands)

Agudo, I.; Bottcher, M.; Falcke, H.; Georganopoulos, M.; Ghisellini, G.; Giovannini, G.; Giroletti, M.; Gomez, J.L.; Gurvits, L.; Laing, R.; Lister, M.; Marti, J.M.; Meyer, E.T.; Mizuno, Y.; O'Sullivan, S.; Padovani, P.; Paragi, Z.; Perucho, M.; Schleicher, D.; Stawarz, L.; Vlahakis, N.; Wardle, J.

2014-01-01

Relativistic jets in active galactic nuclei (AGN) are among the most powerful astrophysical objects discovered to date. Indeed, jetted AGN studies have been considered a prominent science case for SKA, and were included in several different chapters of the previous SKA Science Book (Carilli &

Polarization of stellar, nebular, and galactic radiation

Energy Technology Data Exchange (ETDEWEB)

Shulov, O.S.

1981-01-01

The history of polarimetric investigations at the Astronomical Observatory of Leningrad State University is reviewed. Instruments, facilities, and methods used are described, and various studies of lasting importance are summarized. Some results are presented for observations and studies of interstellar polarization and of polarization in close binaries, high-luminosity red and ir stars, several nebulae in the Galaxy, galaxies, galactic nuclei, quasars, N galaxies, and BL Lac objects.

Compact stars

Science.gov (United States)

Estevez-Delgado, Gabino; Estevez-Delgado, Joaquin

2018-05-01

An analysis and construction is presented for a stellar model characterized by two parameters (w, n) associated with the compactness ratio and anisotropy, respectively. The reliability range for the parameter w ≤ 1.97981225149 corresponds with a compactness ratio u ≤ 0.2644959374, the density and pressures are positive, regular and monotonic decrescent functions, the radial and tangential speed of sound are lower than the light speed, moreover, than the plausible stability. The behavior of the speeds of sound are determinate for the anisotropy parameter n, admitting a subinterval where the speeds are monotonic crescent functions and other where we have monotonic decrescent functions for the same speeds, both cases describing a compact object that is also potentially stable. In the bigger value for the observational mass M = 2.05 M⊙ and radii R = 12.957 Km for the star PSR J0348+0432, the model indicates that the maximum central density ρc = 1.283820319 × 1018 Kg/m3 corresponds to the maximum value of the anisotropy parameter and the radial and tangential speed of the sound are monotonic decrescent functions.

Correlating non-linear properties with spectral states of RXTE data: possible observational evidences for four different accretion modes around compact objects

Science.gov (United States)

Adegoke, Oluwashina; Dhang, Prasun; Mukhopadhyay, Banibrata; Ramadevi, M. C.; Bhattacharya, Debbijoy

2018-05-01

By analysing the time series of RXTE/PCA data, the non-linear variabilities of compact sources have been repeatedly established. Depending on the variation in temporal classes, compact sources exhibit different non-linear features. Sometimes they show low correlation/fractal dimension, but in other classes or intervals of time they exhibit stochastic nature. This could be because the accretion flow around a compact object is a non-linear general relativistic system involving magnetohydrodynamics. However, the more conventional way of addressing a compact source is the analysis of its spectral state. Therefore, the question arises: What is the connection of non-linearity to the underlying spectral properties of the flow when the non-linear properties are related to the associated transport mechanisms describing the geometry of the flow? This work is aimed at addressing this question. Based on the connection between observed spectral and non-linear (time series) properties of two X-ray binaries: GRS 1915+105 and Sco X-1, we attempt to diagnose the underlying accretion modes of the sources in terms of known accretion classes, namely, Keplerian disc, slim disc, advection dominated accretion flow and general advective accretion flow. We explore the possible transition of the sources from one accretion mode to others with time. We further argue that the accretion rate must play an important role in transition between these modes.

Local Swift-BAT active galactic nuclei prefer circumnuclear star formation

Science.gov (United States)

Lutz, D.; Shimizu, T.; Davies, R. I.; Herrera-Camus, R.; Sturm, E.; Tacconi, L. J.; Veilleux, S.

2018-01-01

We use Herschel data to analyze the size of the far-infrared 70 μm emission for z BAT selected active galactic nuclei (AGN), and 515 comparison galaxies that are not detected by BAT. For modest far-infrared luminosities 8.5 BAT hosts that is only half that of comparison galaxies of same far-infrared luminosity. The result mostly reflects a more compact distribution of star formation (and hence gas) in the AGN hosts, but compact AGN heated dust may contribute in some extremely AGN dominated systems. Our findings are in support of an AGN-host coevolution where accretion onto the central black hole and star formation are fed from the same gas reservoir, with more efficient black hole feeding if that reservoir is more concentrated. The significant scatter in the far-infrared sizes emphasizes that we are mostly probing spatial scales much larger than those of actual accretion, and that rapid accretion variations can smear the distinction between the AGN and comparison categories. Large samples are hence needed to detect structural differences that favor feeding of the black hole. No size difference between AGN host and comparison galaxies is observed at higher far-infrared luminosities log(LFIR [L⊙]) > 10.5 (star formation rates ≳6 M⊙ yr-1), possibly because these are typically reached in more compact regions. Full Table A.1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/609/A9

On planetary nebulae and Wolf-Rayet stars in the galactic-centre field

International Nuclear Information System (INIS)

Allen, D.A.

1979-01-01

A UK Schmidt objective-prism plate of the Galactic-centre field has been examined. Of the 74 objects in the field which have been catalogued as planetary nebulae, only half appear correctly classified; the others include Be stars, symbiotic stars, and stars without emission lines. A further 19 planetary nebulae and two Wolf-Rayet stars have been discovered. (author)

THE EVOLUTION OF GAS CLOUDS FALLING IN THE MAGNETIZED GALACTIC HALO: HIGH-VELOCITY CLOUDS (HVCs) ORIGINATED IN THE GALACTIC FOUNTAIN

International Nuclear Information System (INIS)

Kwak, Kyujin; Shelton, Robin L.; Raley, Elizabeth A.

2009-01-01

In the Galactic fountain scenario, supernovae and/or stellar winds propel material into the Galactic halo. As the material cools, it condenses into clouds. By using FLASH three-dimensional magnetohydrodynamic simulations, we model and study the dynamical evolution of these gas clouds after they form and begin to fall toward the Galactic plane. In our simulations, we assume that the gas clouds form at a height of z = 5 kpc above the Galactic midplane, then begin to fall from rest. We investigate how the cloud's evolution, dynamics, and interaction with the interstellar medium (ISM) are affected by the initial mass of the cloud. We find that clouds with sufficiently large initial densities (n ≥ 0.1 H atoms cm -3 ) accelerate sufficiently and maintain sufficiently large column densities as to be observed and identified as high-velocity clouds (HVCs) even if the ISM is weakly magnetized (1.3 μG). However, the ISM can provide noticeable resistance to the motion of a low-density cloud (n ≤ 0.01 H atoms cm -3 ) thus making it more probable that a low-density cloud will attain the speed of an intermediate-velocity cloud rather than the speed of an HVC. We also investigate the effects of various possible magnetic field configurations. As expected, the ISM's resistance is greatest when the magnetic field is strong and perpendicular to the motion of the cloud. The trajectory of the cloud is guided by the magnetic field lines in cases where the magnetic field is oriented diagonal to the Galactic plane. The model cloud simulations show that the interactions between the cloud and the ISM can be understood via analogy to the shock tube problem which involves shock and rarefaction waves. We also discuss accelerated ambient gas, streamers of material ablated from the clouds, and the cloud's evolution from a sphere-shaped to a disk- or cigar-shaped object.

A COMPACT GROUP OF GALAXIES AT Z = 2.48 HOSTING AN AGN-DRIVEN OUTFLOW

Energy Technology Data Exchange (ETDEWEB)

Shih, Hsin-Yi [Gemini Observatory, 670 N Aohoku Place, Hilo, HI 96720 (United States); Stockton, Alan, E-mail: jshih@gemini.edu, E-mail: stockton@ifa.hawaii.edu [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)

2015-12-10

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 × 10{sup 11}M{sub ⊙} 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 active galactic nucleus (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.

A radio continuum and infrared study of Galactic HII regions

NARCIS (Netherlands)

Martin-Hernandez, NL; van der Hulst, JM; Tielens, AGGM

We present observations of the 4.8 and 8.6 GHz continuum emission towards 11 southern H II regions made with the Australian Telescope Compact Array. The observed objects were selected from the Infrared Space Observatory (ISO) spectral catalogue of compact H II regions (Peeters et al. 2002b). The

X-Ray Timing and Spectral Observations of Galactic Black Hole Candidate XTE J1550--564 During Outburst

Energy Technology Data Exchange (ETDEWEB)

Reilly, Kaice T

2002-12-11

Soft X-ray transients (SXTs), a sub-class of low-mass X-ray binaries (LMXBs), provide a unique opportunity to test General Relativity and to probe fundamental physics under conditions terrestrially unattainable. SXT outbursts are of great interest because they allow the study of LMXBs under a wide range of accretion rates. The majority of known SXTs contain black holes, therefore SXT outbursts are key to understanding accretion physics around black holes and in active galactic nuclei, which are thought to contain supermassive, M {approx} 10{sup 6} - 10{sup 10} M{circle_dot}, where M{circle_dot} is one solar mass, central compact objects. These compact objects are most likely black holes, which exhibit, on a much larger scale, accretion physics similar to that around black holes in SXTs. In this work, the timing and spectral properties of the SXT and microquasar XTE J1550-564 during outburst are studied. Observations made by the Unconventional Stellar Aspect (USA) Experiment on board the Advanced Research and Global Observation Satellite (ARGOS) are emphasized. USA data show a low-frequency quasi-periodic oscillation (LFQPO) with a centroid frequency that tends to increase with increasing USA flux and a fractional rms amplitude which is correlated with the USA hardness ratio (4-16 keV/1-4 keV). Several high-frequency quasi-periodic oscillations (HFQPOs) were detected by the Rossi X-ray Timing Explorer (RXTE), during periods where the LFQPO is seen to be weakening or not detectable at all. The evolution of the USA hardness ratio with time and source flux is examined. The hardness-intensity diagram shows counterclockwise cyclical evolution and possibly indicates the presence of two independent accretion flows: a geometrically thin, optically thick accretion disk and a hot sub-Keplerian flow.

Modelling of anisotropic compact stars of embedding class one

Energy Technology Data Exchange (ETDEWEB)

Bhar, Piyali [Government General Degree College, Department of Mathematics, Singur, Hooghly, West Bengal (India); Maurya, S.K. [University of Nizwa, Department of Mathematical and Physical Sciences, College of Arts and Science, Nizwa (Oman); Gupta, Y.K. [Raj Kumar Goel Institute of Technology, Department of Mathematics, Ghaziabad, U.P. (India); Manna, Tuhina [St. Xavier' s College, Department of Commerce (Evening), Kolkata, West Bengal (India)

2016-10-15

In the present article, we have constructed static anisotropic compact star models of Einstein field equations for the spherical symmetric metric of embedding class one. By assuming the particular form of the metric function ν, we have solved the Einstein field equations for anisotropic matter distribution. The anisotropic models represent the realistic compact objects such as SAX J 1808.4-3658 (SS1), Her X-1, Vela X-12, PSR J1614-2230 and Cen X-3. We have reported our results in details for the compact star Her X-1 on the ground of physical properties such as pressure, density, velocity of sound, energy conditions, TOV equation and red-shift etc. Along with these, we have also discussed about the stability of the compact star models. Finally we made a comparison between our anisotropic stars with the realistic objects on the key aspects as central density, central pressure, compactness and surface red-shift. (orig.)

Impact of Distance Determinations on Galactic Structure. I. Young and Intermediate-Age Tracers

Science.gov (United States)

Matsunaga, Noriyuki; Bono, Giuseppe; Chen, Xiaodian; de Grijs, Richard; Inno, Laura; Nishiyama, Shogo

2018-06-01

Here we discuss impacts of distance determinations on the Galactic disk traced by relatively young objects. The Galactic disk, ˜40 kpc in diameter, is a cross-road of studies on the methods of measuring distances, interstellar extinction, evolution of galaxies, and other subjects of interest in astronomy. A proper treatment of interstellar extinction is, for example, crucial for estimating distances to stars in the disk outside the small range of the solar neighborhood. We'll review the current status of relevant studies and discuss some new approaches to the extinction law. When the extinction law is reasonably constrained, distance indicators found in today and future surveys are telling us stellar distribution and more throughout the Galactic disk. Among several useful distance indicators, the focus of this review is Cepheids and open clusters (especially contact binaries in clusters). These tracers are particularly useful for addressing the metallicity gradient of the Galactic disk, an important feature for which comparison between observations and theoretical models can reveal the evolution of the disk.

Exploring the 13CO/C18O abundance ratio towards Galactic young stellar objects and HII regions

Science.gov (United States)

Areal, M. B.; Paron, S.; Celis Peña, M.; Ortega, M. E.

2018-05-01

Aims: Determining molecular abundance ratios is important not only for the study of Galactic chemistry, but also because they are useful to estimate physical parameters in a large variety of interstellar medium environments. One of the most important molecules for tracing the molecular gas in the interstellar medium is CO, and the 13CO/C18O abundance ratio is usually used to estimate molecular masses and densities of regions with moderate to high densities. Nowadays isotope ratios are in general indirectly derived from elemental abundances ratios. We present the first 13CO/C18O abundance ratio study performed from CO isotope observations towards a large sample of Galactic sources of different natures at different locations. Methods: To study the 13CO/C18O abundance ratio, we used 12CO J = 3 - 2 data obtained from the CO High-Resolution Survey, 13CO and C18O J = 3 - 2 data from the 13CO/C18O (J = 3 - 2) Heterodyne Inner Milky Way Plane Survey, and some complementary data extracted from the James Clerk Maxwell Telescope database. We analyzed a sample of 198 sources composed of young stellar objects (YSOs), and HII and diffuse HII regions as catalogued in the Red MSX Source Survey in 27.°5 ≤ l ≤ 46.°5 and |b|0.°5. Results: Most of the analyzed sources are located in the galactocentric distance range 4.0-6.5 kpc. We found that YSOs have, on average, lower 13CO/C18O abundance ratios than HII and diffuse HII regions. Taking into account that the gas associated with YSOs should be less affected by the radiation than in the case of the others sources, selective far-UV photodissociation of C18O is confirmed. The 13CO/C18O abundance ratios obtained in this work are systematically lower than those predicted from the known elemental abundance relations. These results will be useful in future studies of molecular gas related to YSOs and HII regions based on the observation of these isotopes.

Differences in the size-internal velocity relation of galactic and extragalactic HII regions

International Nuclear Information System (INIS)

Odell, C.R.

1990-01-01

The nature of the size-internal velocity relation in extragalactic HII regions is examined in order to improve their use as distance determinants. The relation between the linear size and the internal velocity was compared for HII regions in the Galaxy and in external galaxies. Data for the former are from the researcher's own studies at high spatial resolution, while the latter have been the subject of spectroscopy that includes almost the entire objects. The Galactic HII regions are corrected to values of the internal velocity that would be observed if they were at extragalactic distances. A very different size-internal velocity relation was found for the two types of objects in the sense that the extragalactic objects are some ten times larger at the same internal velocity. This is interpreted to mean that the extragalactic HII regions are actually complexes of small HII regions comparable in size to their Galactic counterparts

DIRECT IMAGING OF A COMPACT MOLECULAR OUTFLOW FROM A VERY LOW LUMINOSITY OBJECT: L1521F-IRS

Energy Technology Data Exchange (ETDEWEB)

Takahashi, Satoko [Joint ALMA Observatory, Alonso de Cordova 3107, Vitacura, Santiago (Chile); Ohashi, Nagayoshi [Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617, Taiwan (China); Bourke, Tyler L., E-mail: satoko.takahashi@nao.ac.jp [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2013-09-01

Studying the physical conditions of very low luminosity objects (VeLLOs; L{sub bol} < 0.1 L{sub Sun }) is important for understanding the earliest evolutionary stage of protostars and brown dwarfs. We report interferometric observations of the VeLLO L1521F-IRS, in {sup 12}CO (2-1) line emission and the 1.3 mm continuum emission, using the Submillimeter Array. With the {sup 12}CO (2-1) high-resolution observations, we have spatially resolved a compact but poorly collimated molecular outflow associated with L1521F-IRS for the first time. The blueshifted and redshifted lobes are aligned along the east and west side of L1521F-IRS with a lobe size of Almost-Equal-To 1000 AU. The estimated outflow mass, maximum outflow velocity, and outflow force are (9.0-80) Multiplication-Sign 10{sup -4} M{sub Sun }, 7.2 km s{sup -1}, and (7.4-66) Multiplication-Sign 10{sup -7} M{sub Sun} km s{sup -1} yr{sup -1}, respectively. The estimated outflow parameters such as size, mass, and momentum rate are similar to values derived for other VeLLOs, and are located at the lower end of values compared to previously studied outflows associated with low- to high-mass star-forming regions. Low-velocity less collimated (1.5 km s{sup -1}/1200 AU) and higher-velocity compact (4.0 km s{sup -1}/920 AU) outflow components are suggested by the data. These velocity structures are not consistent with those expected in the jet-driven or wind-driven outflow models, perhaps suggesting a remnant outflow from the first hydrostatic core as well as an undeveloped outflow from the protostar. Detection of an infrared source and compact millimeter continuum emission suggests the presence of the protostar, while its low bolometric luminosity (0.034-0.07 L{sub Sun }) and small outflow suggests that L1521F is in the earliest protostellar stage (<10{sup 4} yr) and contains a substellar mass object. The bolometric (or internal) luminosity of L1521F-IRS suggests that the current mass accretion rate is an order of

The H.E.S.S. Galactic plane survey

Science.gov (United States)

H. E. S. S. Collaboration; Abdalla, H.; Abramowski, A.; Aharonian, F.; Benkhali, F. Ait; Angüner, E. O.; Arakawa, M.; Arrieta, M.; Aubert, P.; Backes, M.; Balzer, A.; Barnard, M.; Becherini, Y.; Tjus, J. Becker; Berge, D.; Bernhard, S.; Bernlöhr, K.; Blackwell, R.; Böttcher, M.; Boisson, C.; Bolmont, J.; Bonnefoy, S.; Bordas, P.; Bregeon, J.; Brun, F.; Brun, P.; Bryan, M.; Büchele, M.; Bulik, T.; Capasso, M.; Carrigan, S.; Caroff, S.; Carosi, A.; Casanova, S.; Cerruti, M.; Chakraborty, N.; Chaves, R. C. G.; Chen, A.; Chevalier, J.; Colafrancesco, S.; Condon, B.; Conrad, J.; Davids, I. D.; Decock, J.; Deil, C.; Devin, J.; deWilt, P.; Dirson, L.; Djannati-Ataï, A.; Domainko, W.; Donath, A.; Drury, L. O.'C.; Dutson, K.; Dyks, J.; Edwards, T.; Egberts, K.; Eger, P.; Emery, G.; Ernenwein, J.-P.; Eschbach, S.; Farnier, C.; Fegan, S.; Fernandes, M. V.; Fiasson, A.; Fontaine, G.; Förster, A.; Funk, S.; Füßling, M.; Gabici, S.; Gallant, Y. A.; Garrigoux, T.; Gast, H.; Gaté, F.; Giavitto, G.; Giebels, B.; Glawion, D.; Glicenstein, J. F.; Gottschall, D.; Grondin, M.-H.; Hahn, J.; Haupt, M.; Hawkes, J.; Heinzelmann, G.; Henri, G.; Hermann, G.; Hinton, J. A.; Hofmann, W.; Hoischen, C.; Holch, T. L.; Holler, M.; Horns, D.; Ivascenko, A.; Iwasaki, H.; Jacholkowska, A.; Jamrozy, M.; Jankowsky, D.; Jankowsky, F.; Jingo, M.; Jouvin, L.; Jung-Richardt, I.; Kastendieck, M. A.; Katarzyński, K.; Katsuragawa, M.; Katz, U.; Kerszberg, D.; Khangulyan, D.; Khélifi, B.; King, J.; Klepser, S.; Klochkov, D.; Kluźniak, W.; Komin, Nu.; Kosack, K.; Krakau, S.; Kraus, M.; Krüger, P. P.; Laffon, H.; Lamanna, G.; Lau, J.; Lees, J.-P.; Lefaucheur, J.; Lemière, A.; Lemoine-Goumard, M.; Lenain, J.-P.; Leser, E.; Lohse, T.; Lorentz, M.; Liu, R.; López-Coto, R.; Lypova, I.; Marandon, V.; Malyshev, D.; Marcowith, A.; Mariaud, C.; Marx, R.; Maurin, G.; Maxted, N.; Mayer, M.; Meintjes, P. J.; Meyer, M.; Mitchell, A. M. W.; Moderski, R.; Mohamed, M.; Mohrmann, L.; Morå, K.; Moulin, E.; Murach, T.; Nakashima, S.; de Naurois, M.; Ndiyavala, H.; Niederwanger, F.; Niemiec, J.; Oakes, L.; O'Brien, P.; Odaka, H.; Ohm, S.; Ostrowski, M.; Oya, I.; Padovani, M.; Panter, M.; Parsons, R. D.; Paz Arribas, M.; Pekeur, N. W.; Pelletier, G.; Perennes, C.; Petrucci, P.-O.; Peyaud, B.; Piel, Q.; Pita, S.; Poireau, V.; Poon, H.; Prokhorov, D.; Prokoph, H.; Pühlhofer, G.; Punch, M.; Quirrenbach, A.; Raab, S.; Rauth, R.; Reimer, A.; Reimer, O.; Renaud, M.; de los Reyes, R.; Rieger, F.; Rinchiuso, L.; Romoli, C.; Rowell, G.; Rudak, B.; Rulten, C. B.; Safi-Harb, S.; Sahakian, V.; Saito, S.; Sanchez, D. A.; Santangelo, A.; Sasaki, M.; Schandri, M.; Schlickeiser, R.; Schüssler, F.; Schulz, A.; Schwanke, U.; Schwemmer, S.; Seglar-Arroyo, M.; Settimo, M.; Seyffert, A. S.; Shafi, N.; Shilon, I.; Shiningayamwe, K.; Simoni, R.; Sol, H.; Spanier, F.; Spir-Jacob, M.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Steppa, C.; Sushch, I.; Takahashi, T.; Tavernet, J.-P.; Tavernier, T.; Taylor, A. M.; Terrier, R.; Tibaldo, L.; Tiziani, D.; Tluczykont, M.; Trichard, C.; Tsirou, M.; Tsuji, N.; Tuffs, R.; Uchiyama, Y.; van der Walt, D. J.; van Eldik, C.; van Rensburg, C.; van Soelen, B.; Vasileiadis, G.; Veh, J.; Venter, C.; Viana, A.; Vincent, P.; Vink, J.; Voisin, F.; Völk, H. J.; Vuillaume, T.; Wadiasingh, Z.; Wagner, S. J.; Wagner, P.; Wagner, R. M.; White, R.; Wierzcholska, A.; Willmann, P.; Wörnlein, A.; Wouters, D.; Yang, R.; Zaborov, D.; Zacharias, M.; Zanin, R.; Zdziarski, A. A.; Zech, A.; Zefi, F.; Ziegler, A.; Zorn, J.; Żywucka, N.

2018-04-01

We present the results of the most comprehensive survey of the Galactic plane in very high-energy (VHE) γ-rays, including a public release of Galactic sky maps, a catalog of VHE sources, and the discovery of 16 new sources of VHE γ-rays. The High Energy Spectroscopic System (H.E.S.S.) Galactic plane survey (HGPS) was a decade-long observation program carried out by the H.E.S.S. I array of Cherenkov telescopes in Namibia from 2004 to 2013. The observations amount to nearly 2700 h of quality-selected data, covering the Galactic plane at longitudes from ℓ = 250° to 65° and latitudes |b|≤ 3°. In addition to the unprecedented spatial coverage, the HGPS also features a relatively high angular resolution (0.08° ≈ 5 arcmin mean point spread function 68% containment radius), sensitivity (≲1.5% Crab flux for point-like sources), and energy range (0.2-100 TeV). We constructed a catalog of VHE γ-ray sources from the HGPS data set with a systematic procedure for both source detection and characterization of morphology and spectrum. We present this likelihood-based method in detail, including the introduction of a model component to account for unresolved, large-scale emission along the Galactic plane. In total, the resulting HGPS catalog contains 78 VHE sources, of which 14 are not reanalyzed here, for example, due to their complex morphology, namely shell-like sources and the Galactic center region. Where possible, we provide a firm identification of the VHE source or plausible associations with sources in other astronomical catalogs. We also studied the characteristics of the VHE sources with source parameter distributions. 16 new sources were previously unknown or unpublished, and we individually discuss their identifications or possible associations. We firmly identified 31 sources as pulsar wind nebulae (PWNe), supernova remnants (SNRs), composite SNRs, or gamma-ray binaries. Among the 47 sources not yet identified, most of them (36) have possible

AN ULTRA-DEEP NEAR-INFRARED SPECTRUM OF A COMPACT QUIESCENT GALAXY AT z = 2.2

International Nuclear Information System (INIS)

Kriek, Mariska; Van Dokkum, Pieter G.; Marchesini, Danilo; Labbe, Ivo; Franx, Marijn; Quadri, Ryan F.; Illingworth, Garth D.

2009-01-01

Several recent studies have shown that about half of the massive galaxies at z ∼ 2 are in a quiescent phase. Moreover, these galaxies are commonly found to be ultra-compact with half-light radii of ∼1 kpc. We have obtained a ∼29 hr spectrum of a typical quiescent, ultra-dense galaxy at z = 2.1865 with the Gemini Near-Infrared Spectrograph. The spectrum exhibits a strong optical break and several absorption features, which have not previously been detected in z > 2 quiescent galaxies. Comparison of the spectral energy distribution with stellar population synthesis models implies a low star formation rate (SFR) of 1-3 M sun yr -1 , an age of 1.3-2.2 Gyr, and a stellar mass of ∼2 x 10 11 M sun . We detect several faint emission lines, with emission-line ratios of [N II]/Hα, [S II]/Hα, and [O II]/[O III] typical of low-ionization nuclear emission-line regions. Thus, neither the stellar continuum nor the nebular emission implies active star formation. The current SFR is <1% of the past average SFR. If this galaxy is representative of compact quiescent galaxies beyond z = 2, it implies that quenching of star formation is extremely efficient and also indicates that low luminosity active galactic nuclei (AGNs) could be common in these objects. Nuclear emission is a potential concern for the size measurement. However, we show that the AGN contributes ∼<8% to the rest-frame optical emission. A possible post-starburst population may affect size measurements more strongly; although a 0.5 Gyr old stellar population can make up ∼<10% of the total stellar mass, it could account for up to ∼40% of the optical light. Nevertheless, this spectrum shows that this compact galaxy is dominated by an evolved stellar population.

The influence of crushed rock salt particle gradation on compaction

International Nuclear Information System (INIS)

Ran, C.; Daemen, J.J.K.

1994-01-01

This paper presents results of laboratory compaction testing to determine the influence of particle size, size gradation and moisture-content on compaction of crushed rock salt. Included is a theoretical analysis of the optimum size gradation. The objective is to evaluate the relative densities that can be achieved with tamping techniques. Initial results indicate that compaction increases with maximum particle size and compaction energy, and varies significantly with article size gradation and water content

Gamma-ray evidence for a stellar-mass black hole near the Galatic Center

International Nuclear Information System (INIS)

Ramaty, R.; Lingenfelter, R.E.

1989-01-01

Observations at 511 keV and higher energies have provided evidence for a variable, compact source of annihilation radiation and >511-keV continuum emission at the Galactic Center or in its vicinity. The authors have reviewed this evidence. The strongest argument for the existence of this compact source is the time variation of the 511-keV line flux, inferred from observations at different times for over a decade. These observations include a recent detection of the 511-keV line showing that the compact source, after not being seen for nine years, has become active again. In addition to this compact source, there also is evidence for a distributed source of galactic 511-keV line emission. This is based on the comparison of observations with broad and narrow field- of-view detectors, as well as on a direct observation with a narrow field-of-view instrument pointing in the galactic plane away from the Galactic Center. Much remains to be learned about this emission from observations with improved angular and energy resolution. Such observations will provide new information on nucleosynthesis, supernovae, galactic structure, and the interstellar medium. However, in the present paper, the authors deal mainly with the compact source in an attempt to clarify the arguments that have led us to suggest that this object is a stellar-mass black hole. The authors review the technique that they have used to separate the compact and distributed sources, emphasizing the uncertainties caused by data obtained with very poor angular resolution. They show the time dependence of the 511-keV line emission and the >511-keV continuum and summarize the evidence that these two emissions are correlated

First results from the INTEGRAL galactic plane scans

DEFF Research Database (Denmark)

Winkler, C.; Gehrels, N.; Schonfelder, V.

2003-01-01

Scans of the Galactic plane performed at regular intervals constitute a key element of the guaranteed time observations of the INTEGRAL observing programme. These scans are done for two reasons: frequent monitoring of the Galactic plane in order to detect transient sources, and time resolved mapp...... mapping of the Galactic plane in continuum and diffuse line emission. This paper describes first results obtained from the Galactic plane scans executed so far during the early phase (Dec. 2002-May 2003) of the nominal mission.......Scans of the Galactic plane performed at regular intervals constitute a key element of the guaranteed time observations of the INTEGRAL observing programme. These scans are done for two reasons: frequent monitoring of the Galactic plane in order to detect transient sources, and time resolved...

Cosmic ray acceleration by large scale galactic shocks

International Nuclear Information System (INIS)

Cesarsky, C.J.; Lagage, P.O.

1987-01-01

The mechanism of diffusive shock acceleration may account for the existence of galactic cosmic rays detailed application to stellar wind shocks and especially to supernova shocks have been developed. Existing models can usually deal with the energetics or the spectral slope, but the observed energy range of cosmic rays is not explained. Therefore it seems worthwhile to examine the effect that large scale, long-lived galactic shocks may have on galactic cosmic rays, in the frame of the diffusive shock acceleration mechanism. Large scale fast shocks can only be expected to exist in the galactic halo. We consider three situations where they may arise: expansion of a supernova shock in the halo, galactic wind, galactic infall; and discuss the possible existence of these shocks and their role in accelerating cosmic rays

A newly-recognized galactic supernova remnant with shell-type and filled-center features

International Nuclear Information System (INIS)

Barnes, D.J.; Turtle, A.J.

1988-01-01

While the number of galactic supernova remnants (SNRs) now known is fairly large (>150), the subset among these that are known to resemble the Crab Nebula is still distressingly small, about 15 or so. Thus any object that can be unambiguously included in this exclusive club forms a valuable addition to knowledge of this class. The authors report observations of a newly recognized nonthermal galactic object, G18.94-1.06, having all the hallmarks of the classical shell-type SNRs, while also appearing to have a filled-centre component located inside the shell. Among the known Crab-like remnants, about one third show this dual nature. This diagnosis of G18.94-1.06 is supported mainly by the variations in spectral index across the source, as seen between the two observation frequencies, 408 MHz and 5.0 GHz

Structure and content of the galaxy and galactic gamma rays

International Nuclear Information System (INIS)

1976-01-01

The conference included papers on γ-ray pulsars, galactic diffuse flux and surveys, radio surveys of external galaxies, galactic distribution of pulsars, and galactic gamma emission. Galactic structure drawing on all branches of galactic astronomy is discussed. New and unpublished material is included

The classification of p-compact groups for p odd

DEFF Research Database (Denmark)

Andersen, Kasper K. S.; Grodal, Jesper Kragh; Møller, Jesper Michael

2008-01-01

A p-compact group, as defined by Dwyer and Wilkerson, is a purely homotopically defined p-local analog of a compact Lie group. It has long been the hope, and later the conjecture, that these objects should have a classification similar to the classification of compact Lie groups. In this paper we...... groups are uniquely determined as p-compact groups by their Weyl groups seen as finite reflection groups over the p-adic integers. Our approach in fact gives a largely self-contained proof of the entire classification theorem for p odd....

Structure and content of the galaxy and galactic gamma rays

Energy Technology Data Exchange (ETDEWEB)

1976-01-01

The conference included papers on ..gamma..-ray pulsars, galactic diffuse flux and surveys, radio surveys of external galaxies, galactic distribution of pulsars, and galactic gamma emission. Galactic structure drawing on all branches of galactic astronomy is discussed. New and unpublished material is included. (JFP)

THE NUCLEAR INFRARED EMISSION OF LOW-LUMINOSITY ACTIVE GALACTIC NUCLEI

Energy Technology Data Exchange (ETDEWEB)

Mason, R. E. [Gemini Observatory, Northern Operations Center, 670 N. A' ohoku Place, Hilo, HI 96720 (United States); Lopez-Rodriguez, E.; Packham, C. [Department of Astronomy, University of Florida, 211 Bryant Space Science Center, P.O. Box 112055, Gainesville, FL 32611 (United States); Alonso-Herrero, A. [Instituto de Fisica de Cantabria, CSIC-UC, Avenida de los Castros s/n, 39005 Santander (Spain); Levenson, N. A.; Radomski, J. [Gemini Observatory, Southern Operations Center, c/o AURA, Casilla 603, La Serena (Chile); Ramos Almeida, C. [Instituto de Astrofisica de Canarias, C/Via Lactea, s/n, E-38205, La Laguna, Tenerife (Spain); Colina, L. [Departamento de Astrofisica, Centro de Astrobiologia (CSIC/INTA), Instituto Nacional de Tecnica Aeroespacial, Crta de Torrejon a Ajalvir, km 4, 28850 Torrejon de Ardoz, Madrid (Spain); Elitzur, M. [Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506 (United States); Aretxaga, I. [Instituto Nacional de Astrofisica, Optica y Electronica (INAOE), Aptdo. Postal 51 y 216, 72000 Puebla (Mexico); Roche, P. F. [Astrophysics, Department of Physics, University of Oxford, DWB, Keble Road, Oxford OX1 3RH (United Kingdom); Oi, N. [Department of Astronomy, School of Science, Graduate University for Advanced Studies (SOKENDAI), Mitaka, Tokyo 181-8588 (Japan)

2012-07-15

We present high-resolution mid-infrared (MIR) imaging, nuclear spectral energy distributions (SEDs), and archival Spitzer spectra for 22 low-luminosity active galactic nuclei (LLAGNs; L{sub bol} {approx}< 10{sup 42} erg s{sup -1}). Infrared (IR) observations may advance our understanding of the accretion flows in LLAGNs, the fate of the obscuring torus at low accretion rates, and, perhaps, the star formation histories of these objects. However, while comprehensively studied in higher-luminosity Seyferts and quasars, the nuclear IR properties of LLAGNs have not yet been well determined. We separate the present LLAGN sample into three categories depending on their Eddington ratio and radio emission, finding different IR characteristics for each class. (1) At the low-luminosity, low-Eddington-ratio (log L{sub bol}/L{sub Edd} < -4.6) end of the sample, we identify 'host-dominated' galaxies with strong polycyclic aromatic hydrocarbon bands that may indicate active (circum-)nuclear star formation. (2) Some very radio-loud objects are also present at these low Eddington ratios. The IR emission in these nuclei is dominated by synchrotron radiation, and some are likely to be unobscured type 2 AGNs that genuinely lack a broad-line region. (3) At higher Eddington ratios, strong, compact nuclear sources are visible in the MIR images. The nuclear SEDs of these galaxies are diverse; some resemble typical Seyfert nuclei, while others lack a well-defined MIR 'dust bump'. Strong silicate emission is present in many of these objects. We speculate that this, together with high ratios of silicate strength to hydrogen column density, could suggest optically thin dust and low dust-to-gas ratios, in accordance with model predictions that LLAGNs do not host a Seyfert-like obscuring torus. We anticipate that detailed modeling of the new data and SEDs in terms of accretion disk, jet, radiatively inefficient accretion flow, and torus components will provide further

INVISIBLE ACTIVE GALACTIC NUCLEI. II. RADIO MORPHOLOGIES AND FIVE NEW H i 21 cm ABSORPTION LINE DETECTORS

Energy Technology Data Exchange (ETDEWEB)

Yan, Ting; Stocke, John T.; Darling, Jeremy [Center for Astrophysics and Space Astronomy, UCB 389, University of Colorado, Boulder, CO 80309-0389 (United States); Momjian, Emmanuel [National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801 (United States); Sharma, Soniya [Research School of Astronomy and Astrophysics, The Australian National University, Mt Stromlo Observatory, ACT 2611 (Australia); Kanekar, Nissim [National Centre for Radio Astrophysics, TIFR, Post Bag 3, Ganeshkhind, Pune 411 007 (India)

2016-03-15

This is the second paper directed toward finding new highly redshifted atomic and molecular absorption lines at radio frequencies. To this end, we selected a sample of 80 candidates for obscured radio-loud active galactic nuclei (AGNs) and presented their basic optical/near-infrared (NIR) properties in Paper I. In this paper, we present both high-resolution radio continuum images for all of these sources and H i 21 cm absorption spectroscopy for a few selected sources in this sample. A-configuration 4.9 and 8.5 GHz Very Large Array continuum observations find that 52 sources are compact or have substantial compact components with size <0.″5 and flux densities >0.1 Jy at 4.9 GHz. The 36 most compact sources were then observed with the Very Long Baseline Array at 1.4 GHz. One definite and 10 candidate Compact Symmetric Objects (CSOs) are newly identified, which is a detection rate of CSOs ∼three times higher than the detection rate previously found in purely flux-limited samples. Based on possessing compact components with high flux densities, 60 of these sources are good candidates for absorption-line searches. Twenty-seven sources were observed for H i 21 cm absorption at their photometric or spectroscopic redshifts with only six detections (five definite and one tentative). However, five of these were from a small subset of six CSOs with pure galaxy optical/NIR spectra (i.e., any AGN emission is obscured) and for which accurate spectroscopic redshifts place the redshifted 21 cm line in a radio frequency intereference (RFI)-free spectral “window” (i.e., the percentage of H i 21 cm absorption-line detections could be as high as ∼90% in this sample). It is likely that the presence of ubiquitous RFI and the absence of accurate spectroscopic redshifts preclude H i detections in similar sources (only 1 detection out of the remaining 22 sources observed, 13 of which have only photometric redshifts); that is, H i absorption may well be present but is masked by

Peat compaction in deltas : implications for Holocene delta evolution

NARCIS (Netherlands)

van Asselen, S.

2010-01-01

Many deltas contain substantial amounts of peat, which is the most compressible soil type. Therefore, peat compaction potentially leads to high amounts of subsidence in deltas. The main objective of this research was to quantify subsidence due to peat compaction in Holocene fluvial-deltaic settings

Galactic structure and gamma radiation

International Nuclear Information System (INIS)

Casse, Michel; Cesarsky, Catherine; Paul Jacques

1977-01-01

A model of spiral structure of the Galaxy is outlined from radiosynchrotron and gamma observations. The most interesting observations in the galactic context, obtained by the SAS II American satellite are concerned with the distribution of the γ photoemission at energies higher than 10 8 eV, along the galactic equator. The model proposed is in quantitative agreement with the present ideas on the spiral structure of the Galaxy, the galactic magnetic field, and the confinement of cosmic rays by the magnetic field and of the magnetic field by matter. Following the American era, the European COS-B satellite opens the European phase towards an identification of the discrete gamma radiation sources [fr

HUBBLE SPACE TELESCOPE WFC3 GRISM SPECTROSCOPY AND IMAGING OF A GROWING COMPACT GALAXY AT z = 1.9

International Nuclear Information System (INIS)

Van Dokkum, Pieter G.; Brammer, Gabriel

2010-01-01

We present HST/WFC3 grism near-IR spectroscopy of the brightest galaxy at z > 1.5 in the GOODS-South WFC3 ERS grism pointing. The spectrum is of remarkable quality and shows the redshifted Balmer lines Hβ, Hγ, and Hδ in absorption at z = 1.902 ± 0.002. The absorption lines can be produced by a post-starburst stellar population with a luminosity-weighted age of ∼0.5 Gyr. The mass-to-light ratio inferred from the spectrum implies a stellar mass of (4 ± 1) x 10 11 M sun . We determine the morphology of the galaxy from a deep WFC3 H 160 image. Similar to other massive galaxies at z ∼ 2 the galaxy is compact, with an effective radius of 2.1 ± 0.3 kpc. Although most of the light is in a compact core, the galaxy has two red, smooth spiral arms that appear to be tidally induced. The spatially resolved spectroscopy demonstrates that the center of the galaxy is quiescent whereas the surrounding disk is forming stars, as it shows Hβ in emission. The galaxy interacts with a companion at a projected distance of 18 kpc, which also shows prominent tidal features. The companion is a factor of ∼10 fainter than the primary galaxy and may have a lower metallicity. It is tempting to interpret these observations as evidence for the growth of compact, quiescent high-redshift galaxies through minor mergers, which has been proposed by several recent observational and theoretical studies. Interestingly both objects host luminous active galactic nuclei, which implies that these mergers can be accompanied by significant black hole growth.

Massive Young Stellar Objects in the Galactic Center. 1; Spectroscopic Identification from Spitzer/IRS Observations

Science.gov (United States)

An, Deokkeun; Ramirez, Solange V.; Sellgren, Kris; Arendt, Richard G.; Boogert, A. C. Adwin; Robitaille, Thomas P.; Schultheis, Mathias; Cotera, Angela S.; Smith, Howard A.; Stolovy, Susan R.

2011-01-01

We present results from our spectroscopic study, using the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope, designed to identify massive young stellar objects (YSOs) in the Galactic Center (GC). Our sample of 107 YSO candidates was selected based on IRAC colors from the high spatial resolution, high sensitivity Spitzer/IRAC images in the Central Molecular Zone (CMZ), which spans the central approximately 300 pc region of the Milky Way Galaxy. We obtained IRS spectra over 5 micron to 35 micron using both high- and low-resolution IRS modules. We spectroscopically identify massive YSOs by the presence of a 15.4 micron shoulder on the absorption profile of 15 micron CO2 ice, suggestive of CO2 ice mixed with CH30H ice on grains. This 15.4 micron shoulder is clearly observed in 16 sources and possibly observed in an additional 19 sources. We show that 9 massive YSOs also reveal molecular gas-phase absorption from C02, C2H2, and/or HCN, which traces warm and dense gas in YSOs. Our results provide the first spectroscopic census of the massive YSO population in the GC. We fit YSO models to the observed spectral energy distributions and find YSO masses of 8 - 23 solar Mass, which generally agree with the masses derived from observed radio continuum emission. We find that about 50% of photometrically identified YSOs are confirmed with our spectroscopic study. This implies a preliminary star formation rate of approximately 0.07 solar mass/yr at the GC.

A new model for spherically symmetric anisotropic compact star

Energy Technology Data Exchange (ETDEWEB)

Maurya, S.K.; Dayanandan, Baiju [University of Nizwa, Department of Mathematical and Physical Sciences, College of Arts and Science, Nizwa (Oman); Gupta, Y.K. [Raj Kumar Goel Institute of Technology, Department of Mathematics, Ghaziabad, UP (India); Ray, Saibal [Government College of Engineering and Ceramic Technology, Department of Physics, Kolkata, West Bengal (India)

2016-05-15

In this article we obtain a new anisotropic solution for Einstein's field equations of embedding class one metric. The solution represents realistic objects such as Her X-1 and RXJ 1856-37. We perform a detailed investigation of both objects by solving numerically the Einstein field equations with anisotropic pressure. The physical features of the parameters depend on the anisotropic factor i.e. if the anisotropy is zero everywhere inside the star then the density and pressures will become zero and the metric turns out to be flat. We report our results and compare with the above mentioned two compact objects as regards a number of key aspects: the central density, the surface density onset and the critical scaling behaviour, the effective mass and radius ratio, the anisotropization with isotropic initial conditions, adiabatic index and red shift. Along with this we have also made a comparison between the classical limit and theoretical model treatment of the compact objects. Finally we discuss the implications of our findings for the stability condition in a relativistic compact star. (orig.)

Numerical relativity reaching into post-Newtonian territory: a compact-object binary simulation spanning 350 gravitational-wave cycles

Science.gov (United States)

Scheel, Mark; Szilagyi, Bela; Blackman, Jonathan; Chu, Tony; Kidder, Lawrence; Pfeiffer, Harald; Buonanno, Alessandra; Pan, Yi; Taracchini, Andrea; SXS Collaboration

2015-04-01

We present the first numerical-relativity simulation of a compact-object binary whose gravitational waveform is long enough to cover the entire frequency band of advanced gravitational-wave detectors such as LIGO, Virgo and KAGRA, for mass ratio 7 and total mass as low as 45 . 5M⊙ . We find that effective-one-body models, either uncalibrated or calibrated against substantially shorter numerical-relativity waveforms at smaller mass ratios, reproduce our new waveform remarkably well, with a loss in detection rate due to modeling error smaller than 0 . 3 % . In contrast, post-Newtonian inspiral waveforms and existing phenomenological inspiral-merger-ringdown waveforms display much greater disagreement with our new simulation. The disagreement varies substantially depending on the specific post-Newtonian approximant used.

X-ray spectral models of Galactic bulge sources - the emission-line factor

International Nuclear Information System (INIS)

Vrtilek, S.D.; Swank, J.H.; Kallman, T.R.

1988-01-01

Current difficulties in finding unique and physically meaningful models for the X-ray spectra of Galactic bulge sources are exacerbated by the presence of strong, variable emission and absorption features that are not resolved by the instruments observing them. Nine Einstein solid state spectrometer (SSS) observations of five Galactic bulge sources are presented for which relatively high resolution objective grating spectrometer (OGS) data have been published. It is found that in every case the goodness of fit of simple models to SSS data is greatly improved by adding line features identified in the OGS that cannot be resolved by the SSS but nevertheless strongly influence the spectra observed by SSS. 32 references

INFERRING THE GALACTIC POTENTIAL WITH GAIA AND FRIENDS: SYNERGIES WITH OTHER SURVEYS

Energy Technology Data Exchange (ETDEWEB)

Sanderson, Robyn E., E-mail: robyn@astro.columbia.edu [Department of Astronomy, Columbia University, New York, NY 10027 (United States)

2016-02-10

In the coming decade, the Gaia satellite will precisely measure the positions and velocities of millions of stars in the Galactic halo, including stars in many tidal streams. These streams, the products of hierarchical accretion of satellite galaxies by the Milky Way (MW), can be used to infer the Galactic gravitational potential thanks to their initial compactness in phase space. Plans for observations to extend Gaia’s radial velocity (RV) measurements to faint stars, and to determine precise distances to RR Lyrae in streams, would further extend the power of Gaia’s kinematic catalog to characterize the MW’s potential at large Galactocentric distances. In this work I explore the impact of these extra data on the ability to fit the potential using the method of action clustering, which statistically maximizes the information content (clumpiness) of the action space of tidal streams, eliminating the need to determine stream membership for individual stars. Using a mock halo in a toy spherical potential, updated post-launch error models for Gaia, and estimates for RV and distance errors for the tracers to be followed up, I show that combining either form of additional information with the Gaia catalog greatly reduces the bias in determining the scale radius and total mass of the Galaxy compared to the use of Gaia data alone.

Monitoring the Dusty S-cluster Object (DSO/G2) on its Orbit toward the Galactic Center Black Hole

Czech Academy of Sciences Publication Activity Database

Valencia-S, M.; Eckart, A.; Zajaček, Michal; Peissker, F.; Parsa, M.; Grosso, N.; Mossoux, E.; Porquet, D.; Jalali, B.; Karas, Vladimír; Yazici, S.; Shahzamanian, B.; Sabha, N.; Saalfeld, R.; Smajic, S.; Grellmann, R.; Moser, L.; Horrobin, M.; Borkar, A.; García-Marín, M.; Dovčiak, Michal; Kunneriath, Devaky; Karssen, G.; Bursa, Michal; Straubmeier, C.; Bushouse, H.

2015-01-01

Roč. 800, č. 2 (2015), 125/1-125/21 ISSN 0004-637X R&D Projects: GA ČR(CZ) GC13-00070J Grant - others:EU(XE) COST Action MP0905 Institutional support: RVO:67985815 Keywords : black holes * galactic center * Milky way Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.909, year: 2015

Observation of galactic gamma radiation

International Nuclear Information System (INIS)

Paul, J.A.

1982-09-01

A complete and deep survey of the galactic high-energy gamma radiation is now available, thanks to the gamma-ray telescopes on board of the SAS-2 and COS-B spacecrafts. A comparison of the COS-B gamma-ray survey with a fully sampled CO survey together with an Hsub(I) survey is used to show that a simple model, in which uniformly distributed cosmic rays interact with the interstellar gas, can account for almost all the gamma-ray emission observed in the first galactic quadrant. At medium galactic latitudes, it is shown that a relationship exists between the gamma radiation and the interstellar absorption derived from galaxy counts. Therefore gamma rays from the local galactic environment can be used as a valuable probe of the content and structure of the local interstellar medium. The large scale features of the local interstellar gas are revealed, in particular wide concentrations of nearby molecular hydrogen. On a smaller scale, the detection of numerous localized gamma-ray sources focuses the attention on some particular phases of clusters of young and massive stars where diffuse processes of gamma-ray emission may also be at work

Multi-objective optimization of a compact pressurized water nuclear reactor computational model for biological shielding design using innovative materials

Energy Technology Data Exchange (ETDEWEB)

Tunes, M.A., E-mail: matheus.tunes@usp.br [Department of Metallurgical and Materials Engineering, Escola Politécnica da Universidade de São Paulo, Av. Prof. Mello Moraes, 2463 – CEP 05508 – 030 São Paulo (Brazil); Oliveira, C.R.E. de, E-mail: cassiano@unm.edu [Department of Nuclear Engineering, The University of New Mexico, Farris Engineering Center, 221, Albuquerque, NM 87131-1070 (United States); Schön, C.G., E-mail: schoen@usp.br [Department of Metallurgical and Materials Engineering, Escola Politécnica da Universidade de São Paulo, Av. Prof. Mello Moraes, 2463 – CEP 05508 – 030 São Paulo (Brazil)

2017-03-15

Highlights: • Use of two n-γ transport codes leads to optimized model of compact nuclear reactor. • It was possible to safely reduce both weight and volume of the biological shielding. • Best configuration obtained by using new composites for both γ and n attenuation. - Abstract: The aim of the present work is to develop a computational model of a compact pressurized water nuclear reactor (PWR) to investigate the use of innovative materials to enhance the biological shielding effectiveness. Two radiation transport codes were used: the first one – MCNP – for the PWR design and the GEM/EVENT to simulate (in a 1D slab) the behavior of several materials and shielding thickness on gamma and neutron radiation. Additionally MATLAB Optimization Toolbox was used to provide new geometric configurations of the slab aiming at reducing the volume and weight of the walls by means of a cost/objective function. It is demonstrated in the reactor model that the dose rate outside biological shielding has been reduced by one order of magnitude for the optimized model compared with the initial configuration. Volume and weight of the shielding walls were also reduced. The results indicated that one-dimensional deterministic code to reach an optimized geometry and test materials, combined with a three-dimensional model of a compact nuclear reactor in a stochastic code, is a fast and efficient procedure to test shielding performance and optimization before the experimental assessment. A major outcome of this research is that composite materials (ECOMASS 2150TU96) may replace (with advantages) traditional shielding materials without jeopardizing the nuclear power plant safety assurance.

Galactic distribution of X-ray burst sources

International Nuclear Information System (INIS)

Lewin, W.H.G.; Hoffman, J.A.; Doty, J.; Clark, G.W.; Swank, J.H.; Becker, R.H.; Pravdo, S.H.; Serlemitsos, P.J.

1977-01-01

It is stated that 18 X-ray burst sources have been observed to date, applying the following definition for these bursts - rise times of less than a few seconds, durations of seconds to minutes, and recurrence in some regular pattern. If single burst events that meet the criteria of rise time and duration, but not recurrence are included, an additional seven sources can be added. A sky map is shown indicating their positions. The sources are spread along the galactic equator and cluster near low galactic longitudes, and their distribution is different from that of the observed globular clusters. Observations based on the SAS-3 X-ray observatory studies and the Goddard X-ray Spectroscopy Experiment on OSO-9 are described. The distribution of the sources is examined and the effect of uneven sky exposure on the observed distribution is evaluated. It has been suggested that the bursts are perhaps produced by remnants of disrupted globular clusters and specifically supermassive black holes. This would imply the existence of a new class of unknown objects, and at present is merely an ad hoc method of relating the burst sources to globular clusters. (U.K.)

Interpretation of astrophysical neutrinos observed by IceCube experiment by setting Galactic and extra-Galactic spectral components

CERN Document Server

Marinelli, Antonio; Grasso, Dario; Urbano, Alfredo; Valli, Mauro

2016-01-01

The last IceCube catalog of High Energy Starting Events (HESE) obtained with a livetime of 1347 days comprises 54 neutrino events equally-distributed between the three families with energies between 25 TeV and few PeVs. Considering the homogeneous flavors distribution (1:1:1) and the spectral features of these neutrinos the IceCube collaboration claims the astrophysical origin of these events with more than $5\\sigma$. The spatial distribution of cited events does not show a clear correlation with known astrophysical accelerators leaving opened both the Galactic and the extra-Galactic origin interpretations. Here, we compute the neutrino diffuse emission of our Galaxy on the basis of a recently proposed phenomenological model characterized by radially-dependent cosmic-ray (CR) transport properties. We show that the astrophysical spectrum measured by IceCube experiment can be well explained adding to the diffuse Galactic neutrino flux (obtained with this new model) a extra-Galactic component derived from the as...

Can we constrain the maximum value for the spin parameter of the super-massive objects in galactic nuclei without knowing their actual nature?

International Nuclear Information System (INIS)

Bambi, Cosimo

2011-01-01

In 4-dimensional General Relativity, black holes are described by the Kerr solution and are subject to the bound |a * |≤1, where a * is the black hole spin parameter. If current black hole candidates are not the black holes predicted in General Relativity, this bound does not hold and a * might exceed 1. In this Letter, I relax the Kerr black hole hypothesis and I find that the value of the spin parameter of the super-massive black hole candidates in galactic nuclei cannot be higher than about 1.2. A higher spin parameter would not be consistent with a radiative efficiency η>0.15, as observed at least for the most luminous AGN. While a rigorous proof is lacking, I conjecture that the bound |a * |≤1.2 is independent of the exact nature of these objects.

Optical observations of binary X-ray sources

International Nuclear Information System (INIS)

Charles, P.

1982-01-01

Here I shall consider only those systems where the compact object is a neutron star (or in a few cases perhaps a black hole). Since van Paradijs (1982) has recently produced an excellent and comprehensive review of optical observations of compact galactic X-ray sources I shall summarise the basic properties of the optical counterparts and discuss a few representative systems in some detail. (orig./WL)

Compact stellar X-ray sources

NARCIS (Netherlands)

Lewin, W.H.G.; van der Klis, M.

2006-01-01

X-ray astronomy is the prime available window on astrophysical compact objects: black holes, neutron stars and white dwarfs. In the last ten years new observational opportunities have led to an explosion of knowledge in this field. This book provides a comprehensive overview of the astrophysics of

The galactic distribution of Wolf-Rayet stars

International Nuclear Information System (INIS)

Hidayat, B.; Supelli, K.; Hucht, K.A. van der

1982-01-01

On the basis of the most recent compilation of narrow-band photometry and absolute visual magnitudes of Wolf-Rayet stars, and adopting a normal interstellar extinction law in all directions, the galactic distribution of 132 of the 159 known galactic WR stars is presented and discussed. The spiral structure is found to be more clearly pronounced than in earlier studies. Furthermore the authors find an indication of two spiral arms at r=4 and 6 kpc. There appears to be an asymmetry of the z-distribution of single stars with respect to galactic longitude. The location of the WC8.5 and WC9 stars between 4.5 and 9 kpc from the galactic center is discussed in the context of Maeder's red supergiant to WR star scenario. (Auth.)

Formation of Compact Ellipticals in the merging star cluster scenario

Science.gov (United States)

Urrutia Zapata, Fernanda Cecilia; Theory and star formation group

2018-01-01

In the last years, extended old stellar clusters have been observed. They are like globular clusters (GCs) but with larger sizes(a limit of Re=10 pc is currently seen as reasonable). These extended objects (EOs) cover a huge range of mass. Objects at the low mass end with masses comparable to normal globular clusters are called extended clusters or faint fuzzies Larsen & Brodie (2000) and objects at the high-mass end are called ultra compact dwarf galaxies (UCDs). Ultra compact dwarf galaxies are compact object with luminositys above the brigtest known GCs. UCDs are more compact than typical dwarf galaxies but with comparable luminosities. Usually, a lower mass limit of 2 × 10^6 Solar masses is applied.Fellhauer & Kroupa (2002a,b) demostrated that object like ECs, FFs and UCDs can be the remnants of the merger of star clusters complexes, this scenario is called the Merging Star Cluster Scenario. Amore concise study was performed by Bruens et al. (2009, 2011).Our work tries to explain the formation of compact elliptical(cE). These objects are a comparatively rare class of spheroidal galaxies, possessing very small Re and high central surface brightnesses (Faber 1973). cEs have the same parameters as extended objects but they are slightly larger than 100 pc and the luminosities are in the range of -11 to -12 Mag.The standard formation sceanrio of these systems proposes a galaxy origin. CEs are the result of tidal stripping and truncation of nucleated larger systems. Or they could be a natural extension of the class of elliptical galaxies to lower luminosities and smaller sizes.We want to propose a completely new formation scenario for cEs. In our project we try to model cEs in a similar way that UCDs using the merging star cluster scenario extended to much higher masses and sizes. We think that in the early Universe we might have produced sufficiently strong star bursts to form cluster complexes which merge into cEs. So far it is observationally unknown if cEs are

Spitzer Digs Up Galactic Fossil

Science.gov (United States)

2004-01-01

[figure removed for brevity, see original site] Figure 1 [figure removed for brevity, see original site] Figure 2 This false-color image taken by NASA's Spitzer Space Telescope shows a globular cluster previously hidden in the dusty plane of our Milky Way galaxy. Globular clusters are compact bundles of old stars that date back to the birth of our galaxy, 13 or so billion years ago. Astronomers use these galactic 'fossils' as tools for studying the age and formation of the Milky Way. Most clusters orbit around the center of the galaxy well above its dust-enshrouded disc, or plane, while making brief, repeated passes through the plane that each last about a million years. Spitzer, with infrared eyes that can see into the dusty galactic plane, first spotted the newfound cluster during its current pass. A visible-light image (inset of Figure 1) shows only a dark patch of sky. The red streak behind the core of the cluster is a dust cloud, which may indicate the cluster's interaction with the Milky Way. Alternatively, this cloud may lie coincidentally along Spitzer's line of sight. Follow-up observations with the University of Wyoming Infrared Observatory helped set the distance of the new cluster at about 9,000 light-years from Earth - closer than most clusters - and set the mass at the equivalent of 300,000 Suns. The cluster's apparent size, as viewed from Earth, is comparable to a grain of rice held at arm's length. It is located in the constellation Aquila. Astronomers believe that this cluster may be one of the last in our galaxy to be uncovered. This image composite was taken on April 21, 2004, by Spitzer's infrared array camera. It is composed of images obtained at four wavelengths: 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange) and 8 microns (red). Galactic Fossil Found Behind Curtain of Dust In Figure 2, the image mosaic shows the same patch of sky in various wavelengths of light. While the visible-light image (left) shows a dark sky speckled

G25.5 + 0.2: a very young supernova remnant or a galactic planetary nebula?

International Nuclear Information System (INIS)

White, R.L.; Becker, R.H.

1990-01-01

G25.5 + 0.2, a radio source suggested by previous authors to be a very young galactic supernova remnant, is more likely to be a planetary nebula. Its IRAS colours and fluxes and its radio spectrum and morphology are all consistent with the properties of planetary nebulae; its radio flux and distance imply a large mass of ionized gas, which is expected from a Type I planetary nebula lying in the galactic plane. We suggest some definitive observations which should be able to determine whether this interesting object is a planetary nebula or a supernova remnant. (author)

Galactic Winds and the Role Played by Massive Stars

Science.gov (United States)

Heckman, Timothy M.; Thompson, Todd A.

Galactic winds from star-forming galaxies play at key role in the evolution of galaxies and the intergalactic medium. They transport metals out of galaxies, chemically enriching the intergalactic medium and modifying the chemical evolution of galaxies. They affect the surrounding interstellar and circumgalactic media, thereby influencing the growth of galaxies though gas accretion and star formation. In this contribution we first summarize the physical mechanisms by which the momentum and energy output from a population of massive stars and associated supernovae can drive galactic winds. We use the prototypical example of M 82 to illustrate the multiphase nature of galactic winds. We then describe how the basic properties of galactic winds are derived from the data, and summarize how the properties of galactic winds vary systematically with the properties of the galaxies that launch them. We conclude with a brief discussion of the broad implications of galactic winds.

Constraining jet physics in weakly accreting black holes

NARCIS (Netherlands)

Markoff, S.

2007-01-01

Outflowing jets are observed in a variety of astronomical objects such as accreting compact objects from X-ray binaries (XRBs) to active galactic nuclei (AGN), as well as at stellar birth and death. Yet we still do not know exactly what they are comprised of, why and how they form, or their exact

Limits on the cosmological abundance of supermassive compact objects from a millilensing search in gamma-ray burst data.

Science.gov (United States)

Nemiroff, R J; Marani, G F; Norris, J P; Bonnell, J T

2001-01-22

A new search for the gravitational lens effects of a significant cosmological density of supermassive compact objects (SCOs) on gamma-ray bursts (GRBs) has yielded a null result. We inspected the timing data of 774 BATSE-triggered GRBs for evidence of millilensing: repeated peaks similar in light-curve shape and spectra. Our null detection leads us to conclude that, in all candidate universes simulated, Omega(SCO)<0.1 is favored for SCO masses in the range 10(5)

Approaching the Post-Newtonian Regime with Numerical Relativity: A Compact-Object Binary Simulation Spanning 350 Gravitational-Wave Cycles.

Science.gov (United States)

Szilágyi, Béla; Blackman, Jonathan; Buonanno, Alessandra; Taracchini, Andrea; Pfeiffer, Harald P; Scheel, Mark A; Chu, Tony; Kidder, Lawrence E; Pan, Yi

2015-07-17

We present the first numerical-relativity simulation of a compact-object binary whose gravitational waveform is long enough to cover the entire frequency band of advanced gravitational-wave detectors, such as LIGO, Virgo, and KAGRA, for mass ratio 7 and total mass as low as 45.5M_{⊙}. We find that effective-one-body models, either uncalibrated or calibrated against substantially shorter numerical-relativity waveforms at smaller mass ratios, reproduce our new waveform remarkably well, with a negligible loss in detection rate due to modeling error. In contrast, post-Newtonian inspiral waveforms and existing calibrated phenomenological inspiral-merger-ringdown waveforms display greater disagreement with our new simulation. The disagreement varies substantially depending on the specific post-Newtonian approximant used.

Formation and Evolution of X-ray Binaries

Science.gov (United States)

Fragkos, Anastasios

X-ray binaries - mass-transferring binary stellar systems with compact object accretors - are unique astrophysical laboratories. They carry information about many complex physical processes such as star formation, compact object formation, and evolution of interacting binaries. My thesis work involves the study of the formation and evolution of Galactic and extra-galacticX-ray binaries using both detailed and realistic simulation tools, and population synthesis techniques. I applied an innovative analysis method that allows the reconstruction of the full evolutionary history of known black hole X-ray binaries back to the time of compact object formation. This analysis takes into account all the available observationally determined properties of a system, and models in detail four of its evolutionary evolutionary phases: mass transfer through the ongoing X-ray phase, tidal evolution before the onset of Roche-lobe overflow, motion through the Galactic potential after the formation of the black hole, and binary orbital dynamics at the time of core collapse. Motivated by deep extra-galactic Chandra survey observations, I worked on population synthesis models of low-mass X-ray binaries in the two elliptical galaxies NGC3379 and NGC4278. These simulations were targeted at understanding the origin of the shape and normalization of the observed X-ray luminosity functions. In a follow up study, I proposed a physically motivated prescription for the modeling of transient neutron star low-mass X-ray binary properties, such as duty cycle, outburst duration and recurrence time. This prescription enabled the direct comparison of transient low-mass X-ray binary population synthesis models to the Chandra X-ray survey of the two ellipticals NGC3379 and NGC4278. Finally, I worked on population synthesismodels of black holeX-ray binaries in the MilkyWay. This work was motivated by recent developments in observational techniques for the measurement of black hole spin magnitudes in

MODIFIED GRAVITY SPINS UP GALACTIC HALOS

Energy Technology Data Exchange (ETDEWEB)

Lee, Jounghun [Astronomy Program, Department of Physics and Astronomy, FPRD, Seoul National University, Seoul 151-747 (Korea, Republic of); Zhao, Gong-Bo [National Astronomy Observatories, Chinese Academy of Science, Beijing 100012 (China); Li, Baojiu [Institute of Computational Cosmology, Department of Physics, Durham University, Durham DH1 3LE (United Kingdom); Koyama, Kazuya, E-mail: jounghun@astro.snu.ac.kr [Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, PO1 3FX (United Kingdom)

2013-01-20

We investigate the effect of modified gravity on the specific angular momentum of galactic halos by analyzing the halo catalogs at z = 0 from high-resolution N-body simulations for a f(R) gravity model that meets the solar-system constraint. It is shown that the galactic halos in the f(R) gravity model tend to acquire significantly higher specific angular momentum than those in the standard {Lambda}CDM model. The largest difference in the specific angular momentum distribution between these two models occurs for the case of isolated galactic halos with mass less than 10{sup 11} h {sup -1} M {sub Sun }, which are likely least shielded by the chameleon screening mechanism. As the specific angular momentum of galactic halos is rather insensitive to other cosmological parameters, it can in principle be an independent discriminator of modified gravity. We speculate a possibility of using the relative abundance of low surface brightness galaxies (LSBGs) as a test of general relativity given that the formation of the LSBGs occurs in fast spinning dark halos.

OGLE-III MICROLENSING EVENTS AND THE STRUCTURE OF THE GALACTIC BULGE

Energy Technology Data Exchange (ETDEWEB)

Wyrzykowski, Łukasz; Rynkiewicz, Alicja E.; Skowron, Jan; Kozłowski, Szymon; Udalski, Andrzej; Szymański, Michał K.; Kubiak, Marcin; Soszyński, Igor; Pietrzyński, Grzegorz; Poleski, Radosław; Pietrukowicz, Paweł; Pawlak, Michał, E-mail: lw@astrouw.edu.pl [Warsaw University Astronomical Observatory, Al. Ujazdowskie 4, 00-478 Warszawa (Poland)

2015-01-01

We present and study the largest and most comprehensive catalog of microlensing events ever constructed. The sample of standard microlensing events comprises 3718 unique events from 2001-2009 with 1409 events that had not been detected before in real-time by the Early Warning System of the Optical Gravitational Lensing Experiment. The search pipeline uses machine learning algorithms to help find rare phenomena among 150 million objects and to derive the detection efficiency. Applications of the catalog can be numerous, from analyzing individual events to large statistical studies of the Galactic mass, kinematics distributions, and planetary abundances. We derive maps of the mean Einstein ring crossing time of events spanning 31 deg{sup 2} toward the Galactic center and compare the observed distributions with the most recent models. We find good agreement within the observed region and we see the signature of the tilt of the bar in the microlensing data. However, the asymmetry of the mean timescales seems to rise more steeply than predicted, indicating either a somewhat different orientation of the bar or a larger bar width. The map of events with sources in the Galactic bulge shows a dependence of the mean timescale on the Galactic latitude, signaling an increasing contribution from disk lenses closer to the plane relative to the height of the disk. Our data present a perfect set for comparing and enhancing new models of the central parts of the Milky Way and creating a three-dimensional picture of the Galaxy.

The distances of the Galactic Novae

Science.gov (United States)

Ozdonmez, Aykut; Guver, Tolga; Cabrera-Lavers, Antonio; Ak, Tansel

2016-07-01

Using location of the RC stars on the CMDs obtained from the UKIDSS, VISTA and 2MASS photometry, we have derived the reddening-distance relations towards each Galactic nova for which at least one independent reddening measurement exists. We were able to determine the distances of 72 Galactic novae and set lower limits on the distances of 45 systems. The reddening curves of the systems are presented. These curves can be also used to estimate reddening or the distance of any source, whose location is close to the position of the nova in our sample. The distance measurement method in our study can be easily applicable to any source, especially for ones that concentrated along the Galactic plane.

Analysis of laboratory compaction methods of roller compacted concrete

Science.gov (United States)

Trtík, Tomáš; Chylík, Roman; Bílý, Petr; Fládr, Josef

2017-09-01

Roller-Compacted Concrete (RCC) is an ordinary concrete poured and compacted with machines typically used for laying of asphalt road layers. One of the problems connected with this technology is preparation of representative samples in the laboratory. The aim of this work was to analyse two methods of preparation of RCC laboratory samples with bulk density as the comparative parameter. The first method used dynamic compaction by pneumatic hammer. The second method of compaction had a static character. The specimens were loaded by precisely defined force in laboratory loading machine to create the same conditions as during static rolling (in the Czech Republic, only static rolling is commonly used). Bulk densities obtained by the two compaction methods were compared with core drills extracted from real RCC structure. The results have shown that the samples produced by pneumatic hammer tend to overestimate the bulk density of the material. For both compaction methods, immediate bearing index test was performed to verify the quality of compaction. A fundamental difference between static and dynamic compaction was identified. In static compaction, initial resistance to penetration of the mandrel was higher, after exceeding certain limit the resistance was constant. This means that the samples were well compacted just on the surface. Specimens made by pneumatic hammer actively resisted throughout the test, the whole volume was uniformly compacted.

THE GALACTIC O-STAR SPECTROSCOPIC SURVEY (GOSSS). III. 142 ADDITIONAL O-TYPE SYSTEMS

International Nuclear Information System (INIS)

Apellániz, J. Maíz; Sota, A.; Alfaro, E. J.; Arias, J. I.; Barbá, R. H.; Walborn, N. R.; Simón-Díaz, S.; Herrero, A.; Negueruela, I.; Marco, A.; Leão, J. R. S.; Gamen, R. C.

2016-01-01

This is the third installment of the Galactic O-Star Spectroscopic Survey (GOSSS), a massive spectroscopic survey of Galactic O stars, based on new homogeneous, high signal-to-noise ratio, R  ∼ 2500 digital observations selected from the Galactic O-Star Catalog. In this paper, we present 142 additional stellar systems with O stars from both hemispheres, bringing the total of O-type systems published within the project to 590. Among the new objects, there are 20 new O stars. We also identify 11 new double-lined spectroscopic binaries, 6 of which are of O+O type and 5 of O+B type, and an additional new tripled-lined spectroscopic binary of O+O+B type. We also revise some of the previous GOSSS classifications, present some egregious examples of stars erroneously classified as O-type in the past, introduce the use of luminosity class IV at spectral types O4-O5.5, and adapt the classification scheme to the work of Arias et al.

THE GALACTIC O-STAR SPECTROSCOPIC SURVEY (GOSSS). III. 142 ADDITIONAL O-TYPE SYSTEMS

Energy Technology Data Exchange (ETDEWEB)

Apellániz, J. Maíz [Centro de Astrobiología, CSIC-INTA, campus ESAC, camino bajo del castillo s/n, E-28 692 Madrid (Spain); Sota, A.; Alfaro, E. J. [Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomía s/n, E-18 008 Granada (Spain); Arias, J. I.; Barbá, R. H. [Departamento de Física, Universidad de La Serena, Av. Cisternas 1200 Norte, La Serena (Chile); Walborn, N. R. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21 218 (United States); Simón-Díaz, S.; Herrero, A. [Instituto de Astrofísica de Canarias, E-38 200 La Laguna, Tenerife (Spain); Negueruela, I.; Marco, A. [DFISTS, EPS, Universidad de Alicante, carretera San Vicente del Raspeig s/n, E-03 690 Alicante (Spain); Leão, J. R. S. [Univ. Federal do Rio Grande do Norte—UFRN, Caixa Postal 1524, CEP 59 078-970, Natal—RN (Brazil); Gamen, R. C., E-mail: jmaiz@cab.inta-csic.es [Instituto de Astrofísica de La Plata (CONICET, UNLP), Paseo del Bosque s/n, 1900 La Plata (Argentina)

2016-05-01

This is the third installment of the Galactic O-Star Spectroscopic Survey (GOSSS), a massive spectroscopic survey of Galactic O stars, based on new homogeneous, high signal-to-noise ratio, R  ∼ 2500 digital observations selected from the Galactic O-Star Catalog. In this paper, we present 142 additional stellar systems with O stars from both hemispheres, bringing the total of O-type systems published within the project to 590. Among the new objects, there are 20 new O stars. We also identify 11 new double-lined spectroscopic binaries, 6 of which are of O+O type and 5 of O+B type, and an additional new tripled-lined spectroscopic binary of O+O+B type. We also revise some of the previous GOSSS classifications, present some egregious examples of stars erroneously classified as O-type in the past, introduce the use of luminosity class IV at spectral types O4-O5.5, and adapt the classification scheme to the work of Arias et al.

Palomar 13: An Unusual Stellar System in the Galactic Halo

Science.gov (United States)

Côté, Patrick; Djorgovski, S. G.; Meylan, G.; Castro, Sandra; McCarthy, J. K.

2002-08-01

We report the first results of a program to study the internal kinematics of globular clusters in the outer halo of the Milky Way. Using the Keck telescope and High Resolution Echelle Spectrometer, we have measured precise radial velocities for 30 candidate red giants in the direction of Palomar 13, an object traditionally cataloged as a compact, low-luminosity globular cluster. We have combined these radial velocities with published proper motion membership probabilities and new CCD photometry from the Keck and Canada-France-Hawaii telescopes to isolate a sample of 21 probable members. We find a systemic velocity of s=24.1+/-0.5 km s-1 and a projected, intrinsic velocity dispersion of σp=2.2+/-0.4 km s-1. Although modest, this dispersion is nevertheless several times larger than that expected for a globular cluster of this luminosity and central concentration. Taken at face value, it implies a mass-to-light ratio of ΥV=40+24-17 based on the best-fit King-Michie model. The surface density profile of Palomar 13 also appears unusual compared to most Galactic globular clusters; depending upon the details of background subtraction and model-fitting, Palomar 13 either contains a substantial population of ``extratidal'' stars, or is considerably more spatially extended than previously suspected. The full surface density profile is equally well fitted by a King-Michie model having a high concentration and large tidal radius, or by a Navarro-Frenk-White model. We examine-and tentatively reject-a number of possible origins for the observed characteristics of Palomar 13 (e.g., velocity ``jitter'' among the red giant branch stars, spectroscopic binary stars, nonstandard mass functions, modified Newtonian dynamics) and conclude that the two leading explanations are either catastrophic heating during a recent perigalacticon passage or the presence of a dark matter halo. The available evidence therefore suggests that Palomar 13 is either a globular cluster that is now in the

Habitable Evaporated Cores and the Occurrence of Panspermia Near the Galactic Center

Science.gov (United States)

Chen, Howard; Forbes, John C.; Loeb, Abraham

2018-03-01

Black holes growing via the accretion of gas emit radiation that can photoevaporate the atmospheres of nearby planets. Here, we couple planetary structural evolution models of sub-Neptune-mass planets to the growth of the Milky Way’s central supermassive black hole, Sgr A*, and investigate how planetary evolution is influenced by quasar activity. We find that, out to ∼20 pc from Sgr A*, the XUV flux emitted during its quasar phase can remove several percent of a planet’s H/He envelope by mass; in many cases, this removal results in bare rocky cores, many of which are situated in the habitable zones of G-type stars. Near the Galactic Center, the erosion of sub-Neptune-sized planets may be one of the most prevalent channels by which terrestrial super-Earths are created. As such, the planet population demographics may be quite different close to Sgr A* than in the galactic outskirts. The high stellar densities in this region (about seven orders of magnitude greater than the solar neighborhood) imply that the distance between neighboring rocky worlds is short (500–5000 au). The proximity between potentially habitable terrestrial planets may enable the onset of widespread interstellar panspermia near the nuclei of our galaxy. More generally, we predict these phenomena to be ubiquitous for planets in nuclear star clusters and ultra-compact dwarfs. Globular clusters, on the other hand, are less affected by the central black holes.

The Galactic Club or Galactic Cliques? Exploring the limits of interstellar hegemony and the Zoo Hypothesis

Science.gov (United States)

Forgan, Duncan H.

2017-10-01

The Zoo solution to Fermi's Paradox proposes that extraterrestrial intelligences (ETIs) have agreed to not contact the Earth. The strength of this solution depends on the ability for ETIs to come to agreement, and establish/police treaties as part of a so-called `Galactic Club'. These activities are principally limited by the causal connectivity of a civilization to its neighbours at its inception, i.e. whether it comes to prominence being aware of other ETIs and any treaties or agreements in place. If even one civilization is not causally connected to the other members of a treaty, then they are free to operate beyond it and contact the Earth if wished, which makes the Zoo solution `soft'. We should therefore consider how likely this scenario is, as this will give us a sense of the Zoo solution's softness, or general validity. We implement a simple toy model of ETIs arising in a Galactic Habitable Zone, and calculate the properties of the groups of culturally connected civilizations established therein. We show that for most choices of civilization parameters, the number of culturally connected groups is >1, meaning that the Galaxy is composed of multiple Galactic Cliques rather than a single Galactic Club. We find in our models for a single Galactic Club to establish interstellar hegemony, the number of civilizations must be relatively large, the mean civilization lifetime must be several millions of years, and the inter-arrival time between civilizations must be a few million years or less.

Galactic Habitable Zone and Astrobiological Complexity

Science.gov (United States)

Vukotic, B.

2012-12-01

This is a short thesis description and for the sake of brevity most things are left out. For more details, those interested are further directed to the thesis related papers in this article reference list. Thesis itself is available at the University of Belgrade library "Svetozar Markovic" (Serbian version only). In this thesis we study the astrobiological history of the Galactic habitable zone through the means of numerical modeling. First group of simulations are unidimensional (time-axis) toy models examine the influence of global regulation mechanisms (gamma-ray bursts and supernovae) on temporal evolution of Galactic astrobiological complexity. It is shown that under the assumption of global regulation classical anti SETI arguments can be undermined. Second group of simulations are more complex bidimensional probabilistic cellular automata models of the Galactic thin disk. They confirm the findings of the toy models and give some insights into the spatial clustering of astrobiological complexity. As a new emerging multidisciplinary science the basic concepts of astrobiology are poorly understood and although all the simulations present here do not include some basic physics (such as Galactic kinematics and dynamics), the input parameters are somewhat arbitrary and could use a future refinement (such as the boundaries of the Galactic habitable zone). This is the cause for low weight and high uncertainty in the output results of the simulations. However, the probabilistic cellular automata has shown as a highly adaptable modeling platform that can simulate various class of astrobiological models with great ease.

FORMATION OF ULTRA-COMPACT BLUE DWARF GALAXIES AND THEIR EVOLUTION INTO NUCLEATED DWARFS

International Nuclear Information System (INIS)

Bekki, Kenji

2015-01-01

We propose that there is an evolutionary link between ultra-compact blue dwarf galaxies (UCBDs) with active star formation and nucleated dwarfs based on the results of numerical simulations of dwarf–dwarf merging. We consider the observational fact that low-mass dwarfs can be very gas-rich, and thereby investigate the dynamical and chemical evolution of very gas-rich, dissipative dwarf–dwarf mergers. We find that the remnants of dwarf–dwarf mergers can be dominated by new stellar populations formed from the triggered starbursts and consequently can have blue colors and higher metallicities (Z ∼ [0.2–1]Z ⊙ ). We also find that the remnants of these mergers can have rather high mass densities (10 4 M ⊙ pc −3 ) within the central 10 pc and small half-light radii (40−100 pc). The radial stellar structures of some merger remnants are similar to those of nucleated dwarfs. Star formation can continue in nuclear gas disks (R < 100 pc) surrounding stellar galactic nuclei (SGNs) so that the SGNs can finally have multiple stellar populations with different ages and metallicities. These very compact blue remnants can be identified as UCBDs soon after merging and as nucleated dwarfs after the young stars fade. We discuss these results in the context of the origins of metal-rich ultra-compact dwarfs and SGNs

FORMATION OF ULTRA-COMPACT BLUE DWARF GALAXIES AND THEIR EVOLUTION INTO NUCLEATED DWARFS

Energy Technology Data Exchange (ETDEWEB)

Bekki, Kenji [ICRAR, M468, The University of Western Australia 35 Stirling Highway, Crawley Western Australia, 6009 (Australia)

2015-10-10

We propose that there is an evolutionary link between ultra-compact blue dwarf galaxies (UCBDs) with active star formation and nucleated dwarfs based on the results of numerical simulations of dwarf–dwarf merging. We consider the observational fact that low-mass dwarfs can be very gas-rich, and thereby investigate the dynamical and chemical evolution of very gas-rich, dissipative dwarf–dwarf mergers. We find that the remnants of dwarf–dwarf mergers can be dominated by new stellar populations formed from the triggered starbursts and consequently can have blue colors and higher metallicities (Z ∼ [0.2–1]Z{sub ⊙}). We also find that the remnants of these mergers can have rather high mass densities (10{sup 4} M{sub ⊙} pc{sup −3}) within the central 10 pc and small half-light radii (40−100 pc). The radial stellar structures of some merger remnants are similar to those of nucleated dwarfs. Star formation can continue in nuclear gas disks (R < 100 pc) surrounding stellar galactic nuclei (SGNs) so that the SGNs can finally have multiple stellar populations with different ages and metallicities. These very compact blue remnants can be identified as UCBDs soon after merging and as nucleated dwarfs after the young stars fade. We discuss these results in the context of the origins of metal-rich ultra-compact dwarfs and SGNs.

Supernovae-generated high-velocity compact clouds

Science.gov (United States)

Yalinewich, A.; Beniamini, P.

2018-05-01

Context. A previous study claimed the discovery of an intermediate-mass black hole (IMBH). This hypothetical black hole was invoked in order to explain the high-velocity dispersion in one of several dense molecular clouds near the Galactic center. The same study considered the possibility that this cloud was due to a supernova explosion, but disqualified this scenario because no X-rays were detected. Aims: We here check whether a supernova explosion could have produced that cloud, and whether this explanation is more likely than an IMBH. More specifically, we wish to determine whether a supernova inside a dense molecular cloud would emit in the X-rays. Methods: We have approached this problem from two different directions. First, we performed an analytic calculation to determine the cooling rate by thermal bremsstrahlung and compared this time to the lifetime of the cloud. Second, we estimated the creation rate of these dense clouds in the central molecular zone (CMZ) region near the Galactic center, where they were observed. Based on this rate, we can place lower bounds on the total mass of IMBHs and clouds and compare this to the masses of the components of the CMZ. Results: We find that the cooling time of the supernova remnant inside a molecular cloud is shorter than its dynamical time. This means that the temperature in such a remnant would be much lower than that of a typical supernova remnant. At such a low temperature, the remnant is not expected to emit in the X-rays. We also find that to explain the rate at which such dense clouds are created requires fine-tuning the number of IMBHs. Conclusions: We find the supernova model to be a more likely explanation for the formation of high-velocity compact clouds than an IMBH.

Hot stars in young massive clusters: Mapping the current Galactic metallicity

Science.gov (United States)

de la Fuente, Diego; Najarro, Francisco; Davies, Ben; Trombley, Christine; Figer, Donald F.; Herrero, Artemio

2013-06-01

Young Massive Clusters (YMCs) with ages guarantee that these objects present the same chemical composition than the surrounding environment where they are recently born. Finally, the YMCs host very massive stars whose extreme luminosities allow to accomplish detailed spectroscopic analyses even in the most distant regions of the Milky Way. Our group has carried out ISAAC/VLT spectroscopic observations of hot massive stars belonging to several YMCs in different locations around the Galactic disk. As a result, high signal-to-noise, near-infrared spectra of dozens of blue massive stars (including many OB supergiants, Wolf-Rayet stars and a B hypergiant) have been obtained. These data are fully reduced, and NLTE spherical atmosphere modeling is in process. Several line diagnostics will be combined in order to calculate metal abundances accurately for each cluster. The diverse locations of the clusters will allow us to draw a two-dimensional chemical map of the Galactic disk for the first time. The study of the radial and azimuthal variations of elemental abundances will be crucial for understanding the chemical evolution of the Milky Way. Particularly, the ratio between Fe-peak and alpha elements will constitute a powerful tool to investigate the past stellar populations that originated the current Galactic chemistry.

CANDELS: THE PROGENITORS OF COMPACT QUIESCENT GALAXIES AT z ∼ 2

International Nuclear Information System (INIS)

Barro, Guillermo; Faber, S. M.; Koo, David C.; Kocevski, Dale D.; Trump, Jonathan R.; Mozena, Mark; McGrath, Elizabeth; Cheung, Edmond; Fang, Jerome; Pérez-González, Pablo G.; Williams, Christina C.; Van der Wel, Arjen; Wuyts, Stijn; Bell, Eric F.; Croton, Darren J.; Ceverino, Daniel; Dekel, Avishai; Ashby, M. L. N.; Ferguson, Henry C.; Fontana, Adriano

2013-01-01

We combine high-resolution Hubble Space Telescope/WFC3 images with multi-wavelength photometry to track the evolution of structure and activity of massive (M * > 10 10 M ☉ ) galaxies at redshifts z = 1.4-3 in two fields of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey. We detect compact, star-forming galaxies (cSFGs) whose number densities, masses, sizes, and star formation rates (SFRs) qualify them as likely progenitors of compact, quiescent, massive galaxies (cQGs) at z = 1.5-3. At z ∼> 2, cSFGs present SFR = 100-200 M ☉ yr –1 , yet their specific star formation rates (sSFR ∼ 10 –9 yr –1 ) are typically half that of other massive SFGs at the same epoch, and host X-ray luminous active galactic nuclei (AGNs) 30 times (∼30%) more frequently. These properties suggest that cSFGs are formed by gas-rich processes (mergers or disk-instabilities) that induce a compact starburst and feed an AGN, which, in turn, quench the star formation on dynamical timescales (few 10 8 yr). The cSFGs are continuously being formed at z = 2-3 and fade to cQGs down to z ∼ 1.5. After this epoch, cSFGs are rare, thereby truncating the formation of new cQGs. Meanwhile, down to z = 1, existing cQGs continue to enlarge to match local QGs in size, while less-gas-rich mergers and other secular mechanisms shepherd (larger) SFGs as later arrivals to the red sequence. In summary, we propose two evolutionary tracks of QG formation: an early (z ∼> 2), formation path of rapidly quenched cSFGs fading into cQGs that later enlarge within the quiescent phase, and a late-arrival (z ∼< 2) path in which larger SFGs form extended QGs without passing through a compact state.

The pulsar contribution to the diffuse galactic gamma-ray emission

DEFF Research Database (Denmark)

Pohl, M.; Kanbach, G.; Hunter, S.D.

1997-01-01

There is active interest in the extent to which unresolved gamma-ray pulsars contribute to the Galactic diffuse emission, and in whether unresolved gamma-ray pulsars could be responsible for the excess of diffuse Galactic emission above 1 GeV that has been observed by EGRET. The diffuse gamma......-ray intensity due to unresolved pulsars is directly linked to the number of objects that should be observed in the EGRET data. We can therefore use our knowledge of the unidentified EGRET sources to constrain model parameters like the pulsar birthrate and their beaming angle. This analysis is based only...... on the properties of the six pulsars that have been identified in the EGRET data and is independent of choice of a pulsar emission model. We find that pulsars contribute very little to the diffuse emission at lower energies, whereas above 1 GeV they can account for 18% of the observed intensity in selected regions...

Galactic binaries with eLISA

OpenAIRE

Nelemans, G.

2013-01-01

I review what eLISA will see from Galactic binaries -- double stars with orbital periods less than a few hours and white dwarf (or neutron star/black hole) components. I discuss the currently known binaries that are guaranteed (or verification) sources and explain why the expected total number of eLISA Galactic binaries is several thousand, even though there are large uncertainties in our knowledge of this population, in particular that of the interacting AM CVn systems. I very briefly sketch...

The sixth catalogue of galactic Wolf-Rayet stars, their past and present

International Nuclear Information System (INIS)

Hucht, K.A. van der; Conti, P.S.; Lundstroem, I.; Stenholm, B.

1981-01-01

This paper presents the Sixth Catalogue of galactic Wolf-Rayet stars (Pop I), a short history on the five earlier WR catalogues, improved spectral classification, finding charts, a discussion on related objects, and a review of the current statur of Wolf-Rayet star research. The appendix presents a bibliography on most of the Wolf-Rayet literature published since 1867. (orig.)

Study of potential applications of compact ECRIS to analytical system

International Nuclear Information System (INIS)

Kidera, M.; Takahashi, K.; Seto, Y.; Kishi, S.; Enomoto, S.; Nagamatsu, T.; Tanaka, T.

2012-01-01

The objective of this study is to develop a desktop-sized system of element mass analysis (element analysis system) with a compact electron cyclotron resonance (ECR) ion source in the ionization section. This system is different from other element analysis systems in terms of the effective use of ionization by ECR plasma. A compact ECR ion source is required to fit in the desktop-sized element analysis system. This paper reporting the development of the compact ECR ion source, is followed by the associated poster. (authors)

AN ABSENCE OF FAST RADIO BURSTS AT INTERMEDIATE GALACTIC LATITUDES

Energy Technology Data Exchange (ETDEWEB)

Petroff, E.; Van Straten, W.; Bailes, M.; Barr, E. D.; Coster, P.; Flynn, C.; Keane, E. F. [Centre for Astrophysics and Supercomputing, Swinburne University of Technology, P.O. Box 218, Hawthorn, VIC 3122 (Australia); Johnston, S. [CSIRO Astronomy and Space Science, Australia Telescope National Facility, P.O. Box 76, Epping, NSW 1710 (Australia); Bates, S. D.; Keith, M. J.; Kramer, M.; Stappers, B. W. [Jodrell Bank Centre for Astrophysics, University of Manchester, Alan Turing Building, Oxford Road, Manchester M13 9PL (United Kingdom); Bhat, N. D. R. [ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), 44 Rosehill Street, Redfern, NSW 2016 (Australia); Burgay, M.; Possenti, A.; Tiburzi, C. [INAF—Osservatorio Astronomico di Cagliari, Via della Scienza, I-09047 Selargius (Italy); Burke-Spolaor, S. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91104 (United States); Champion, D.; Ng, C. [Max Planck Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany); Levin, L., E-mail: epetroff@astro.swin.edu.au [Department of Physics, West Virginia University, Morgantown, WV 26506 (United States); and others

2014-07-10

Fast radio bursts (FRBs) are an emerging class of bright, highly dispersed radio pulses. Recent work by Thornton et al. has revealed a population of FRBs in the High Time Resolution Universe (HTRU) survey at high Galactic latitudes. A variety of progenitors have been proposed, including cataclysmic events at cosmological distances, Galactic flare stars, and terrestrial radio frequency interference. Here we report on a search for FRBs at intermediate Galactic latitudes (–15° Galactic models—must be included to ease the discrepancy between the detection rates at high and low Galactic latitudes. A revised rate estimate or another strong and heretofore unknown selection effect in Galactic latitude would provide closer agreement between the surveys' detection rates. The dearth of detections at low Galactic latitude disfavors a Galactic origin for these bursts.