We use the formalism of constrained Gaussian random field to compute a precise large scale simulation of the 60 Mpc/h volume of our Local Universe. We derive the constraints from the reconstructed peculiar velocities of the 2MASS Redshift Survey. We obtain a correlation of 0.99 between the log-density field of the dark matter distribution of the simulation and the log-density of observed galaxies of the Local Universe. We achieve a good comparison of the simulated velocity field to the observed velocity field obtained from the galaxy distances of the NBG-3k. At the end, we compare the two-point correlation function of both the 2MRS galaxies and of the dark matter particles of the simulation. We conclude that this method is a very promising technique of exploring the dynamics and the particularities the Universe in our neighbourhood.
Cold fronts - density and temperature plasma discontinuities - are ubiquitous in cool cores of galaxy clusters, where they appear as X-ray brightness edges in the intracluster medium, near-concentric with the cluster center. For several well-observed core cold fronts from the literature, we analyze the thermodynamic profiles above and below the front. While the pressure appears continuous across most of the cold fronts, we find that all of them require significant centripetal acceleration inside (beneath) the front. This is naturally explained by tangential bulk flow just below the cold fronts, nearly sonic in most cases, and tangential shear flow involving a fair fraction of the plasma beneath the front. Such shear should generate near-equipartition magnetic fields on scales <~50 pc from the front, and could magnetize the entire core. Such fields would explain the apparent stability of cool-core cold fronts and the cold front-radio minihalo association reported recently.
The merger dynamics of a black hole-neutron star (BHNS) binary is influenced by the neutron star equation of state (EoS) through the latter's effect on the neutron star's radius and on the character of the mass transfer onto the black hole. We study these effects by simulating a number of BHNS binaries in full general relativity using a mixed pseudospectral/finite difference code. We consider several models of the neutron star matter EoS, including Gamma=2 and Gamma=2.75 polytropes and the nuclear-theory based Shen EoS. For models using the Shen EoS, we consider two limits for the evolution of the composition: source-free advection and instantaneous beta-equilibrium. To focus on EoS effects, we fix the mass ratio to 3:1 and the initial aligned black hole spin to a/m=0.5 for all models. We confirm earlier studies which found that more compact stars create a stronger gravitational wave signal but a smaller postmerger accretion disk. We also vary the EoS while holding the compaction fixed. All mergers are qualitatively similar, but we find signatures of the EoS in the waveform and in the tail and disk structures.
We review the current status of attempts to numerically model the merger of neutron star-neutron star (NSNS) and black hole-neutron star (BHNS) binary systems, and we describe the understanding of such events that is emerging from these calculations. To accurately model the physics of NSNS and BHNS mergers is a difficult task. It requires solving Einstein's equations for dynamic spacetimes containing black holes. It also requires evolving the hot, supernuclear-density neutron star matter together with the magnetic and radiation fields that can influence the post-merger dynamics. Older studies concentrated on either one or the other of these challenges, but now efforts are being made to model both relativity and microphysics accurately together. These NSNS and BHNS simulations are then used to characterize the gravitational wave signals of such events and to address their potential for generating short-duration gamma ray bursts.
Distortions in the primordial cosmic microwave background (CMB) along the line-of-sight can be modeled and described using 11 fields. These distortion fields correspond to various cosmological signals such as weak gravitational lensing of the CMB by large-scale structure, screening from patchy reionization, rotation of the plane of polarization due to magnetic fields or parity violating physics. Various instrumental systematics such as gain fluctuations, pixel rotation, differential gain, pointing, differential ellipticity are also described by the same distortion model. All these distortions produce B-mode that contaminate the primordial tensor B-modes signal. In this paper we show that apart from generating B-modes, each distortion uniquely couples different modes $(\bfl_1\ne \bfl_2)$ of the CMB anisotropies, generating $<EB>$ correlations which for the primordial CMB are zero. We describe and implement unbiased minimum variance quadratic estimators which using the off diagonal correlations in the CMB can extract the map of distortions. We perform Monte-Carlo simulations to characterize the estimators and illustrate the level of distortions that can be detected with current and future experiments. The estimators can be used to look for cosmological signals, or to check for any residual systematics in the data. As a specific example of primordial tensor B-mode diagnostics we compare the level of minimum detectable distortions using our method with maximum allowed distortion level for the B-modes detection. We show that for any experiment, the distortions will be detected at high significance using correlations before they would show up as spurious B-modes in the power spectrum.
We present high angular resolution (down to 0.3" = 13 AU in diameter) Submillimeter Array observations of the 880 micron (340 GHz) thermal continuum emission from circumstellar dust disks in the nearby HD 98800 and Hen 3-600 multiple star systems. In both cases, the dust emission is resolved and localized around one stellar component - the HD 98800 B and Hen 3-600 A spectroscopic binaries - with no evidence for circum-system material. Using two-dimensional Monte Carlo radiative transfer calculations, we compare the SMA visibilities and broadband spectral energy distributions with truncated disk models to empirically locate the inner and outer edges of both disks. The HD 98800 B disk appears to be aligned with the spectroscopic binary orbit, is internally truncated at a radius of 3.5 AU, and extends to only 10-15 AU from the central stars. The Hen 3-600 A disk is slightly larger, with an inner edge at 1 AU and an outer radius of 15-25 AU. These inferred disk structures compare favorably with theoretical predictions of their truncation due to tidal interactions with the stellar companions.
We present results of our pulsar population synthesis of normal pulsars from the Galactic disk using our previously developed Monte-Carlo code. From our studies of observed radio pulsars that have clearly identifiable core and cone components, in which we fit the polarization sweep as well as the pulse profiles in order to constrain the viewing geometry, we develop a model describing the luminosity and ratio of radio core-to-cone peak fluxes. In this model, short period pulsars are more cone-dominated. We explore models of neutron star evolution with and without magnetic field decay, and with different initial period distributions. We present preliminary results including simulated population statistics that are compared with the observed radio pulsar population. The evolved neutron star populations resulting from this simulation can be used to model distributions of gamma-ray pulsars for comparison to Fermi results.
Wide-field deep gri images obtained with the Megacam of the Canada-France-Hawaii Telescope (CFHT) are used to investigate the spatial configuration of stars around five metal-poor globular cluster M15, M30, M53, NGC 5053, and NGC 5466, in a field-of-view ~3 degree. Applying a mask filtering algorithm to the color-magnitude diagrams of the observed stars, we sorted cluster's member star candidates that are used to examine the characteristics of the spatial stellar distribution surrounding the target clusters. The smoothed surface density maps and the overlaid isodensity contours indicate that all of the five metal-poor globular clusters exhibit strong evidence of extratidal overdensity features over their tidal radii, in the form of extended tidal tails around the clusters. The orientations of the observed extratidal features show signatures of tidal tails tracing the clusters' orbits, inferred from their proper motions, and effects of dynamical interactions with the Galaxy. Our findings include detections of a tidal bridge-like feature and an envelope structure around the pair of globular clusters M53 and NGC 5053. The observed radial surface density profiles of target clusters have a deviation from theoretical King models, for which the profiles show a break at 0.5~0.7r_t, extending the overdensity features out to 1.5~2r_t. Both radial surface density profiles for different angular sections and azimuthal number density profiles confirm the overdensity features of tidal tails around the five metal-poor globular clusters. Our results add further observational evidence that the observed metal-poor halo globular clusters originate from an accreted satellite system, indicative of the merging scenario of the formation of the Galactic halo.
We present an analysis of Spitzer IRS spectroscopy of 83 active galaxies from the extended 12 micron sample. We find rank correlations between several tracers of star formation which suggest that (1) the PAH feature is a reliable tracer of star formation, (2) there is a significant contribution to the heating of the cool dust by stars, (3) the H$_2$ emission is also primarily excited by star formation. The 55-90 vs. 20-30 spectral index plot is also a diagnostic of the relative contribution of Starburst to AGN. We see there is a large change in spectral index across the sample. Thus, the contribution to the IR spectrum from the AGN and starburst components can be comparable in magnitude but the relative contribution also varies widely across the sample. We find rank correlations between several AGN tracers. We search for correlations between AGN and Starburst tracers and we conclude that the AGN and Starburst tracers are not correlated. This is consistent with our conclusion that the relative strength of the AGN and Starburst components varies widely across the sample. Thus, there is no simple link between AGN fueling and Black Hole Growth and star formation in these galaxies. The distribution of Sil 10 micron and 18 micron strengths is consistent with the clumpy torus models of Sirocky et al. We find a rank correlation between the [NeV] 14 micron line and the 6.7 micron continuum which may be due to an extended component of hot dust. The Sy 2s with a Hidden Broad Line Region (HBLR) have a higher ratio of AGN to Starburst contribution to the SED than Sy 2s without an HBLR. This may contribute to the detection of the HBLR in polarized light. The Sy 2s with an HBLR are more similar to the Sy 1s than they are to the Sy 2s without an HBLR.
We report the first results from deep X-ray observations of the Wolf-Rayet binary system WR147 with the Chandra HETG. Analysis of the zeroth order data reveals that WR147 is a double X-ray source. The northern counterpart is likely associated with the colliding wind region, while the southern component is certainly identified with the WN star in this massive binary. The latter is the source of high energy X-rays (including the Fe K_alpha complex at 6.67 keV) whose production mechanism is yet unclear. For the first time, X-rays are observed directly from a WR star in a binary system.
We report the discovery of an unusually blue L5 dwarf within 10 pc of the Sun from a search of Sloan Digital Sky Survey (SDSS) spectra. A spectrophotometric distance estimate of 8.0+/-1.6 pc places SDSS J141624.08+134826.7 among the six closest known L dwarfs. SDSS 1416+13 was overlooked in infrared color-based searches because of its unusually blue J-K_S color, which also identifies it as the nearest member of the blue L dwarf subclass. We present additional infrared and optical spectroscopy from the IRTF/SpeX and Magellan/MagE spectrographs and determine UVW motions that indicate old/thick disk kinematics. The inclusion of SDSS 1416+13 in the 20 pc sample of L dwarfs increases the number of L5 dwarfs by 20% suggesting that the L dwarf luminosity function may be far from complete.
We present our numerical results of two-dimensional hydrodynamic (HD) simulations and magnetohydrodynamic (MHD) simulations of the collapse of rotating massive stars in light of the collapsar model of gamma-ray bursts (GRBs). Pushed by recent evolution calculations of GRB progenitors, we focus on lower angular momentum of the central core than the ones taken mostly in previous studies. By performing special relativistic simulations including both realistic equation of state and neutrino cooling, we follow a long-term evolution of the slowly rotating collapsars up to 10 s, accompanied by the formation of jets and accretion disks. We find such outfows can be launched both by MHD process and neutrino process. We investigeate the properties of these jets whether it can become GRBs or remains primary weak outflow.
We present a comprehensive survey of B abundances in diffuse interstellar clouds from HST/STIS observations along 56 Galactic sight lines. Our sample is the result of a complete search of archival STIS data for the B II resonance line at 1362 angstroms, with each detection confirmed by the presence of absorption from other dominant ions at the same velocity. The data probe a range of astrophysical environments including both high-density regions of massive star formation as well as low-density paths through the Galactic halo, allowing us to clearly define the trend of B depletion onto interstellar grains as a function of gas density. Many extended sight lines exhibit complex absorption profiles that trace both local gas and gas associated with either the Sagittarius-Carina or Perseus spiral arm. Our analysis indicates a higher B/O ratio in the inner Sagittarius-Carina spiral arm than in the vicinity of the Sun, which may suggest that B production in the current epoch is dominated by a secondary process. The average gas-phase B abundance in the warm diffuse ISM is consistent with the abundances determined for a variety of Galactic disk stars, but is depleted by 60 percent relative to the solar system value. Our survey also reveals sight lines with enhanced B abundances that potentially trace recent production of B-11 either by cosmic-ray or neutrino-induced spallation. Such sight lines will be key to discerning the relative importance of the two production routes for B-11 synthesis.
Recent observations in X-ray and Gamma-ray suggest that the emission region
of the pulsar magnetosphere can be multifold. In particular, the open-close
boundary of the magnetic field, so-called the Y-point, can be the new candidate
place where magnetic field energy converts into the plasma heat and/or flow
energy. Here, we present a new Particle-in-Cell code, which can be applied to
the Y-point of the pulsar magnetosphere in axisymmetric geometry. The
electromagnetic solver is used in the two-dimensional grid points with the
cylindrical coordinate (R, z), while the particle solver operates in the
three-dimensional Cartesian coordinate (x, y, z), where the Buneman-Boris
method is used. The particle motion is treated in special relativity. The inner
boundary conditions are set up to generate rotation of the magnetosphere by use
of the force-free semi-analytic solution given by Uzdensky (2003, ApJ, 598,
446).
The code has been verified by dispersion relations of all the wave modes in
electron-positron plasmas.
The initial test run is also presented to demonstrate the Y-shaped structure
at the top of the dead zone on the light cylinder. We suggest that the
structure is variable with quasi-periodicity associated with magnetic
reconnection and that plasma will be accelerated and/or heated. In a
time-averaged point of view, break up of the ideal-MHD condition takes place in
the vicinity of the Y-point.
We study the detectability of the gravitational waves (GWs) from the Q-ball formation associated with the Affleck-Dine (AD) mechanism, taking into account both of the dilution effect due to Q-ball domination and of finite temperature effects. The AD mechanism predicts the formation of non-topological solitons, Q-balls, from which GWs are generated. Q-balls with large conserved charge $Q$ can produce a large amount of GWs. On the other hand, the decay rate of such Q-balls is so small that they may dominate the energy density of the universe, which implies that GWs are significantly diluted and that their frequencies are redshifted during Q-ball dominated era. Thus, the detectability of the GWs associated with the formation of Q-balls is determined by these two competing effects. We find that there is a finite but small parameter region where such GWs may be detected by future detectors such as DECIGO or BBO, only in the case when the thermal logarithmic potential dominates the potential of the AD field. Otherwise GWs from Q-balls would not be detectable even by these futuristic detectors: $\Omega_{\rm GW}^0<10^{-21}$. Unfortunately, for such parameter region the present baryon asymmetry of the universe can hardly be explained unless one fine-tunes A-terms in the potential. However the detection of such a GW background may give us an information about the early universe, for example, it may suggest that the flat directions with $B-L=0$ are favored.
We report results from a blind analysis of the final data taken with the Cryogenic Dark Matter Search experiment (CDMS II) at the Soudan Underground Laboratory, Minnesota, USA. A total raw exposure of 612 kg-days was analyzed for this work. We observed two events in the signal region; based on our background estimate, the probability of observing two or more background events is 23%. These data set an upper limit on the Weakly Interacting Massive Particle (WIMP)-nucleon elastic-scattering spin-independent cross-section of 7.0x10^{-44} cm^2 for a WIMP of mass 70 GeV/c^2 at the 90% confidence level. Combining this result with all previous CDMS II data gives an upper limit on the WIMP-nucleon spin-independent cross-section of 3.8x10^{-44} cm^2 for a WIMP of mass 70 GeV/c^2. We also exclude new parameter space in recently proposed inelastic dark matter models.
We revisit the vertical structure of neutrino-dominated accretion flows in spherical coordinates. We stress that the flow should be geometrically thick when advection becomes dominant. In our calculation, the luminosity of neutrino annihilation is enhanced by one or two orders of magnitude. The empty funnel along the rotation axis can naturally explain the neutrino annihilable ejection.
The TeV radio galaxy M87 is the first radio galaxy detected in the TeV regime. The structure of its jet, which is not pointing towards our line of sight, is spatially resolved in X-ray (by Chandra), optical and radio observations. In 2008, the three main Atmospheric Cherenkov Telescope observatories VERITAS, MAGIC and H.E.S.S. coordinated their observations in a joint campaign from January to May with a total observation time of approx. 120 hours. In February, strong and rapid day-scale TeV flares were detected. VLBA monitoring observations during the same period showed that the 43 GHz radio flux density of the unresolved core began to rise at the time of the TeV flares and eventually reached levels above any previously seen with VLBI. New jet components appeared during the flare. The localization accuracy of the TeV instruments of many arcseconds, even for strong sources, is inadequate to constrain the origin of the emission in the inner jets of AGNs. For M87, with a 6 billion solar mass black hole and a distance of 16.7 Mpc, the VLBA resolution instead corresponds to 30 by 60 Schwarzschild radii. This is starting to resolve the jet collimation region. The temporal coincidence of the TeV and radio flares indicates that they are related and provides the first direct evidence that the TeV radiation from this source is produced within a few tens of RS of the radio core, thought to be coincident to within the VLBA resolution with the black hole.
We explore the noiseless Burgers dynamics in the inviscid limit, the so
called ``adhesion model'' in cosmology, in a regime where (almost) all the
fluid particles are embedded within point-like massive halos. Taking advantage
of the formulation of the dynamics in terms of Legendre transforms and convex
hulls, for a properly taken inviscid limit, we study the evolution with time of
the distribution of matter and the associated partitions of the Lagrangian and
Eulerian spaces. We describe how the halo mass distribution derives from a
triangulation in Lagrangian space, while the dual Voronoi-like tessellation in
Eulerian space gives the boundaries of empty regions with shock nodes at their
vertices.
We then show that, at variance with the common lore, the adhesion model leads
to halo fragmentations for space dimensions greater or equal to 2. This is most
easily seen from the properties of the Lagrangian-space triangulation and we
illustrate this process in the 2D case. In particular, we explain how
point-like halos only merge through three-body collisions while two-body
collisions always give rise to two new massive shock nodes (in 2D). This
generalizes to higher dimensions and we briefly illustrate the 3D case. This
leads to an original picture for the continuous formation of massive halos
through successive halo fragmentations and mergings.
These lecture notes cover some of the theoretical topics associated with cosmic acceleration. Plausible explanations to cosmic acceleration include dark energy, modified gravity and a violation of the Copernican principle. Each of these possibilities are briefly described.
Launched on the 11th of June 2008, the Fermi Large Area Telescope (LAT) has made several outstanding scientific contributions to the high energy astrophysics community. One of these contributions was the high statistics measurement of the Galactic Cosmic Ray (GCR) electron + positron spectrum from 20 GeV to 1 TeV. The Fermi satellite is in a nearly circular orbit with an inclination of 25.6 degrees at an altitude of 565 km. Given this orbit it is possible to measure the GCR electrons + positrons down to roughly 5 GeV. However, this lower limit in energy is highly dependent on the orbital position of the LAT in geomagnetic coordinates due to the rigidity cutoff. In order to measure the spectrum down to these energies it is necessary to sample the population of electrons + positrons in several different geomagnetic positions. In this poster we present the analysis performed to extend the lower limit in energy of the GCR electron + positron spectrum measured by the Fermi LAT.
We present the analysis of the interstellar gamma-ray emission measured by the Fermi Large Area Telescope toward a region in the second Galactic quadrant at 100 deg < l < 145 deg and -15 deg < b < +30 deg. This region encompasses the prominent Gould-Belt clouds of Cassiopeia, Cepheus and the Polaris flare, as well as atomic and molecular complexes at larger distances, like that associated with NGC 7538 in the Perseus arm. The good kinematic separation in velocity between the local, Perseus, and outer arms, and the presence of massive complexes in each of them make this region well suited to probe cosmic rays and the interstellar medium beyond the solar circle. The gamma-ray emissivity spectrum of the gas in the Gould Belt is consistent with expectations based on the locally measured cosmic-ray spectra. The gamma-ray emissivity decreases from the Gould Belt to the Perseus arm, but the measured gradient is flatter than expectations for cosmic-ray sources peaking in the inner Galaxy as suggested by pulsars. The Xco=N(H2)/W(CO) conversion factor is found to increase from (0.87 +- 0.05) 10^20 cm^-2 (K km s^-1)^-1 in the Gould Belt to (1.9 +- 0.2) 10^20 cm^-2 (K km s^-1)^-1 in the Perseus arm. We derive masses for the molecular clouds under study. Dark gas, not properly traced by radio and microwave surveys, is detected in the Gould Belt through a correlated excess of dust and gamma-ray emission: its mass amounts to ~50% of the CO-traced mass.
We describe the optical spectropolarimetric monitoring program at Steward Observatory centered around gamma-ray-bright blazars and the LAT Monitored Source List planned for Fermi Cycles 2-4. The large number of measurements made during Cycle 1 of the Fermi mission are available to the research community and the data products are summarized (see this http URL). The optical data include spectropolarimetry at a resolution of ~20 A, broad-band polarization and flux measurements, and flux-calibrated spectra spanning 4000-7600 A. These data provide a comprehensive view of the optical variability of an important sample of objects during the Fermi Era. In addition to broad-band flux and linear polarization monitoring, the spectra allow for the tracking of changes to the spectral index of the synchrotron continuum, importance of non-synchrotron emission features, and how and when the polarization varies with wavelength, an important clue as to the structure of the emission region or the identification of multiple nonthermal components. As an illustration, we present observations of 3C 454.3 obtained in 2009 September during an exceptionally bright gamma-ray flare. The blazar was optically bright during the flare, but except for a few short periods, it showed surprisingly low polarization (P < 5%). Opportunities exist within the Fermi research community to coordinate with our long-term optical monitoring program toward the goal of maximum scientific value to both the Fermi and associated radio VLBI monitoring of blazars.
Ionizing UV radiation and supernova flows amidst clustered minihalos at high redshift regulated the rise of the first stellar populations in the universe. Previous studies have addressed the effects of very massive primordial stars on the collapse of nearby halos into new stars, but the absence of the odd-even nucleosynthetic signature of pair-instability supernovae in ancient metal-poor stars suggests that Population III stars may have been less than 100 M$_{\odot}$. We extend our earlier survey of local UV feedback on star formation to 25 - 80 M$_{\odot}$ stars and include kinetic feedback by supernovae for 25 - 40 M$_{\odot}$ stars. We find radiative feedback to be relatively uniform over this mass range, primarily because the larger fluxes of more massive stars are offset by their shorter lifetimes. Our models demonstrate that prior to the rise of global UV backgrounds, Lyman-Werner photons from nearby stars cannot prevent halos from forming new stars. These calculations also reveal that violent dynamical instabilities can erupt in the UV radiation front enveloping a primordial halo but that they ultimately have no effect on the formation of a star. Finally, our simulations suggest that relic H II regions surrounding partially evaporated halos may expel Lyman-Werner backgrounds at lower redshifts, allowing stars to form that were previously suppressed. We provide fits to radiative and kinetic feedback on star formation for use in both semianalytic models and numerical simulations.
We acquired and analyzed adaptive-optics imaging observations of asteroid (2)
Pallas from Keck II and the Very Large Telescope taken during four Pallas
oppositions between 2003 and 2007, with spatial resolution spanning 32-88 km
(image scales 13-20 km/pix). We improve our determination of the size, shape,
and pole by a novel method that combines our AO data with 51 visual
light-curves spanning 34 years of observations as well as occultation data.
The shape model of Pallas derived here reproduces well both the projected
shape of Pallas on the sky and light-curve behavior at all the epochs
considered. We resolved the pole ambiguity and found the spin-vector
coordinates to be within 5 deg. of [long, lat] = [30 deg., -16 deg.] in the
ECJ2000.0 reference frame, indicating a high obliquity of ~84 deg., leading to
high seasonal contrast. The best triaxial-ellipsoid fit returns radii of a=275
km, b= 258 km, and c= 238 km. From the mass of Pallas determined by
gravitational perturbation on other minor bodies [(1.2 +/- 0.3) x 10-10 Solar
Masses], we derive a density of 3.4 +/- 0.9 g.cm-3 significantly different from
the density of C-type (1) Ceres of 2.2 +/- 0.1 g.cm-3. Considering the spectral
similarities of Pallas and Ceres at visible and near-infrared wavelengths, this
may point to fundamental differences in the interior composition or structure
of these two bodies.
We define a planetocentric longitude system for Pallas, following IAU
guidelines. We also present the first albedo maps of Pallas covering ~80% of
the surface in K-band. These maps reveal features with diameters in the 70-180
km range and an albedo contrast of about 6% wrt the mean surface albedo.
Vesta, the second largest Main Belt asteroid, will be the first to be
explored in 2011 by NASA's Dawn mission. It is a dry, likely differentiated
body with spectrum suggesting that is has been resurfaced by basaltic lava
flows, not too different from the lunar maria.
Here we present the first disk-resolved spectroscopic observations of an
asteroid from the ground. We observed (4) Vesta with the ESO-VLT adaptive
optics equipped integral-field near-infrared spectrograph SINFONI, as part of
its science verification campaign. The highest spatial resolution of ~90 km on
Vesta's surface was obtained during excellent seeing conditions (0.5") in
October 2004.
We observe spectral variations across Vesta's surface that can be interpreted
as variations of either the pyroxene composition, or the effect of surface
aging. We compare Vesta's 2 micron absorption band to that of
howardite-eucrite-diogenite (HED) meteorites that are thought to originate from
Vesta, and establish particular links between specific regions and HED
subclasses. The overallcomposition is found to be mostly compatible with
howardite meteorites, although a small area around 180 deg. East longitude
could be attributed to a diogenite-rich spot. We finally focus our spectral
analysis on the characteristics of Vesta's bright and dark regions as seen from
Hubble Space Telescope's visible and Keck-II's near-infrared images.
We report the first systematic survey of molecular lines (including HCO+ (1-0) and 12CO, 13CO, C18O (1-0) lines at 3 mm band) towards a new sample of 88 massive young stellar object (MYSO) candidates associated with ongoing outflows (known as extended green objects or EGOs) identified from the Spitzer GLIMPSE survey in the northern hemisphere with the PMO-13.7 m radio telescope. By analyzing the asymmetries of the optically thick line HCO+ for 69 of 72 EGOs with HCO+ detection, we found 29 sources with blue asymmetric profiles and 19 sources with red asymmetric profiles. This results in a blue excess of 0.14, seen as a signature of collapsing cores in the observed EGO sample. The relatively small blue excess measured in our full sample due to that the observed EGOs are mostly dominated by outflows and at an earlier evolutionary phase associated with IRDCs and 6.7 GHz methanol masers. The physical properties of clouds surrounding EGOs derived from CO lines are similar to those of massive clumps wherein the massive star forming cores associated with EGOs possibly embedded. The infall velocities and mass infall rates derived for 20 infall candidates are also consistent with the typical values found in MYSOs. Thus our observations further support the speculation of Cyganowski et al. (2008) that EGOs trace a population with ongoing outflow activity and active rapid accretion stage of massive protostellar evolution from a statistical view, although there maybe have limitations due to single-pointing survey with a large beam.
New CCD photometric observations of the eclipsing binary V566 Oph have been obtained. The light curves are analyzed with the Wilson-Devinney code and new geometric and photometric elements are derived. A new O-C analysis of the system is presented and apparent period changes are discussed with respect to possible Light-Time Effect in the system.
We present an observation of the Rossiter-McLaughlin effect for the planetary system WASP-3. Radial velocity measurements were made during transit using the SOPHIE spectrograph at the 1.93m telescope at Haute-Provence Observatory. The shape of the effect shows that the sky-projected angle between the stellar rotation axis and planetary orbital axis (lambda) is small and consistent with zero within 2 sigma; lambda = 15 +10/-9 deg. WASP-3b joins the ~two-thirds of planets with measured spin-orbit angles that are well aligned and are thought to have undergone a dynamically-gentle migration process such as planet-disc interactions. We find a systematic effect which leads to an anomalously high determination of the projected stellar rotational velocity (vsini = 19.6 +2.2/-2.1 km/s) compared to the value found from spectroscopic line broadening (vsini = 13.4 +/- 1.5 km/s). This is thought to be caused by a discrepancy in the assumptions made in the extraction and modelling of the data. Using a model developed by Hirano et al. (2009) designed to address this issue, we find vsini to be consistent with the value obtained from spectroscopic broadening measurements (vsini = 15.7 +1.4/-1.3 km/s).
Transverse oscillations of coronal loops are often observed and have been theoretically interpreted as kink magnetohydrodynamic (MHD) modes. Numerical simulations by Terradas et al. (2008, ApJ 687, L115) suggest that shear flows generated at the loop boundary during kink oscillations could give rise to a Kelvin-Helmholtz instability (KHI). Here, we investigate the linear stage of the KHI in a cylindrical magnetic flux tube in the presence of azimuthal shear motions. We consider the basic, linearized MHD equations in the beta = 0 approximation, and apply them to a straight and homogeneous cylindrical flux tube model embedded in a coronal environment. Azimuthal shear flows with a sharp jump of the velocity at the cylinder boundary are included in the model. We obtain an analytical expression for the dispersion relation of the unstable MHD modes supported by the configuration, and compute analytical approximations of the critical velocity shear and the KHI growth rate in the thin tube limit. A parametric study of the KHI growth rates is performed by numerically solving the full dispersion relation. We find that fluting-like modes can develop a KHI in time-scales comparable to the period of kink oscillations of the flux tube. The KHI growth rates increase with the value of the azimuthal wavenumber and decrease with the longitudinal wavenumber. However, the presence of a small azimuthal component of the magnetic field can suppress the KHI. Azimuthal motions related to kink oscillations of untwisted coronal loops may trigger a KHI, but this phenomenon has not been observed to date. We propose that the azimuthal component of the magnetic field is responsible for suppressing the KHI in a stable coronal loop. The required twist is small enough to prevent the development of the pinch instability.
We present the results of modelling the subgiant star $\beta$ Hydri using the seismic observational constraints. We have computed several grids of stellar evolutionary tracks using Aarhus STellar Evolution Code (ASTEC, Christensen-Dalsgaard, 2008a), with and without helium diffusion and settling. For those models on each track that are located at the observationally determined position of $\beta$ Hydri in the HR diagram, we have calculated the oscillation frequencies using Aarhus adiabatic pulsation package (ADIPLS, Christensen-Dalsgaard, 2008b). Applying the near-surface corrections to the calculated frequencies using the empirical law presented by Kjeldsen et al. (2008), we have compared the corrected model frequencies with the observed frequencies of the star. We show that after correcting the frequencies for the near-surface effects, we have a fairly good fit for both $l$=0 and $l$=2 frequencies. We also have good agreement between the observed and calculated $l$=1 mode frequencies although there is room for improvement in order to fit all the observed mixed modes simultaneously.
The non-linear evolution of the energy density of the radiation is shown to induce spectral distortions of the cosmic microwave background both at recombination and during the reionization era. This distortion has the same spectral signature as the one produced by the re-scattering of photons by non-relativistic hot electrons, the thermal Sunyaev-Zeldovich effect, whose amplitude is quantified by a Compton y parameter. A diffuse y-sky is then expected to emerge from mode couplings in the non-linear evolution of the cosmological perturbations and to superimpose to the point source contributions of galaxy clusters. The equations describing the evolution of the y field and a hierarchy governing its angular multipoles are derived from the second order Boltzmann equation. These equations are then integrated numerically to obtain the first predicted power spectrum of the diffuse y-sky. It is found to be a remarkable tracer of the reionization history of the Universe.
New CCD photometric observations in V, R and I filters of the eclipsing binary AV CMi have been obtained. The complete light curves are analyzed with the Wilson-Devinney code and new geometric and photometric elements are derived. Moreover, 2-year systematic observations of the system revealed the existence of a third body orbiting around one of the components with an approximate period of 0.52 days. The first light elements for this additional component are given and its nature is discussed.
Many sunspots are surrounded by a radial outflow called the moat flow. We investigate the moat flow at two different heights of the solar atmosphere for a sunspot whose magnetic properties were reported in the first paper of this series. We use two simultaneous time series taken with the Transition Region And Coronal Explorer (TRACE) in white light and in the UV at 170 nm. The field-of-view is centered on the small sunspot NOAA 10886 located near disk center. Horizontal velocities are derived by applying two different local correlation tracking techniques. Outflows are found everywhere in the moat. In the inner moat, the velocities from the UV series are larger than those from white light, whereas in the outer part of the moat we find the converse result. The results imply that the white light velocities represent a general outflow of the quiet sun plasma in the moat, while UV velocities are dominated by small bright points that move faster than the general plasma flow.
We report two different types of backflow from jets by performing 2D special relativistic hydrodynamical simulations. One is anti-parallel and quasi-straight to the main jet (quasi-straight backflow), and the other is bent path of the backflow (bent backflow). We find that the former appears when the head advance speed is comparable to or higher than the local sound speed at the hotspot while the latter appears when the head advance speed is slower than the sound speed bat the hotspot. Bent backflow collides with the unshocked jet and laterally squeezes the jet. At the same time, a pair of new oblique shocks are formed at the tip of the jet and new bent fast backflows are generated via these oblique shocks. The hysteresis of backflow collisions is thus imprinted in the jet as a node and anti-node structure. This process also promotes broadening of the jet cross sectional area and it also causes a decrease in the head advance velocity. This hydrodynamic process may be tested by observations of compact young jets.
Blazars are a kind of active galactic nuclei (AGN) in which a relativistic jet is considered to be directed along the line of sight. They are characterized by strong and rapid variability of the flux and high polarization. We performed a monitoring of 41 blazars in the optical and near-infrared regions from 2008 to 2009 using TRISPEC attached to the "Kanata" 1.5-m telescope. In this paper, we report the correlation of the flux, color and polarization using our data, and discuss universal features for blazars, which have not fully been established. Three blazars (3C 454.3, QSO 0454$-$234, and PKS 1510$-$089) tended to be redder when they were brighter, only during their faint states. This color behavior suggests that the contribution of a thermal component is strong in the faint states for those objects. Excluding this "redder-when-brighter" phase, we found that 24 blazars tended to be bluer when they were brighter. This number corresponds to 83% among well-observed objects which we observed for $>10$ nights. Thus, we conclude that the "bluer-when-brighter" trend is a universal feature for blazars. On the other hand, the correlation of the flux and the polarization degree is relatively weak; only 10 objects showed a significant positive correlation. We also investigated the luminosity-dependence of the color and polarization, and found that lower luminosity objects have smaller variation amplitudes both in the flux, color, and polarization degree.
A year after \emph{Fermi} was launched, the number of known gamma-ray pulsars has increased dramatically. For the first time, a sizable population of pulsars has been discovered in gamma-ray data alone. For the first time, millisecond pulsars have been confirmed as powerful sources of gamma-ray emission, and a whole population of these objects is seen with the LAT. The remaining gamma-ray pulsars are young pulsars, discovered via an efficient collaboration with radio and X-ray telescopes. It is now clear that a large fraction of the nearby energetic pulsars are gamma-ray emitters, whose luminosity grows with the spin-down energy loss rate. Many previously unidentified EGRET sources turn out to be pulsars. Many of the detected pulsars are found to be powering pulsar wind nebulae, and some are associated with TeV sources. The \emph{Fermi} LAT is expected to detect more pulsars in gamma rays in the coming years, while multi-wavelength follow ups should detect \emph{Fermi}-discovered pulsars. The data already revealed that gamma-ray pulsars generally emit fan-like beams sweeping over a large fraction of the sky and produced in the outer magnetosphere.
The MAGIC telescope is the largest single-dish Imaging Atmospheric Cherenkov Telescope (IACT) with the lowest energy threshold among the current generation of IACTs as low as 25 GeV. Therefore, the MAGIC telescope is a perfect instrument to study the galactic sources especially in the context of observations with the satellite observatories Fermi and AGILE. This paper will give an overview of the MAGIC results on the galactic sources including detailed observations of binary systems, supernova remnants and the first detection of the Crab pulsar above 25 GeV .
A status report of the second phase of the MAGIC ground-based gamma-ray facility (as of October 2009) is presented. MAGIC became recently a stereoscopic Cherenkov observatory with the inauguration of its second telescope, MAGIC-II, which is currently approaching the end of its commissioning stage.
We study how direct detection of the inflationary gravitational wave background constrains inflationary parameters and complements CMB polarization measurements. The error ellipsoids calculated using the Fisher information matrix approach with Planck and the direct detection experiment, BBO (Big Bang Observer), show different directions of parameter degeneracy, and the degeneracy is broken when they are combined. For a slow-roll parameterization, we show that BBO could significantly improve the constraints on the tensor-to-scalar ratio compared with Planck alone. We also look at a quadratic and a natural inflation model. In both cases, if the temperature of reheating is also treated as a free parameter, then the addition of BBO can significantly improve the error bars. In the case of natural inflation, we find that the addition of BBO could even partially improve the error bars of a cosmic variance-limited CMB experiment.
The CRESST experiment aims for a detection of dark matter in the form of WIMPs. These particles are expected to scatter elastically off the nuclei of a target material, thereby depositing energy on the recoiling nucleus. CRESST uses scintillating CaWO4 crystals as such a target. The energy deposited by an interacting particle is primarily converted to phonons which are detected by transition edge sensors. In addition, a small fraction of the interaction energy is emitted from the crystals in the form of scintillation light which is measured in coincidence with the phonon signal by a separate cryogenic light detector for each target crystal. The ratio of light to phonon energy permits the discrimination between the nuclear recoils expected from WIMPs and events from radioactive backgrounds which primarily lead to electron recoils. CRESST has shown the success of this method in a commissioning run in 2007 and, since then, further investigated possibilities for an even better suppression of backgrounds. Here, we report on a new class of background events observed in the course of this work. The consequences of this observation are discussed and we present the current status of the experiment.
We re-examine the stellar kinematics of the Solar neighbourhood in terms of the velocity of the Sun with respect to the local standard of rest. We show that the classical determination of its component V_sun in the direction of Galactic rotation via Stroemberg's relation is undermined by the metallicity gradient in the disc, which introduces a correlation between the colour of a group of stars and the radial gradients of its properties. Comparing the local stellar kinematics to a chemodynamical model which accounts for these effects, we obtain (U,V,W)_sun = (11.1 +/- 0.74, 12.24 +/- 0.47, 7.25 +/-0.37) km/s, with additional systematic uncertainties of ~ (1,2,0.5) km/s. In particular, V_sun is 7 km/s larger than previously estimated. The new values of solar motion are extremely insensitive to the metallicity gradient within the disc.
The Large Area Telescope (LAT) onboard the Fermi satellite is observing the gamma-ray sky in the high energy region, above 20 MeV. We have developed a method to reconstruct the energy spectra of the gamma-rays detected by the Fermi LAT instrument based on a Bayesian unfolding approach, that takes into account the energy dispersion introduced by the instrument response. The method has been successfully applied to reconstruct the energy spectra of both steady and pulsating point sources. The analysis technique will be illustrated and the results obtained in some significant test cases will be discussed.
The Fermi Large Area Telescope (LAT) has been surveying the sky in gamma rays from 30 MeV to more than 300 GeV since August 2008. Fermi is the only mission able to detect high energy > few hundreds MeV emission from the Sun during the new solar cycle 24: the Solar System Science Group of the Fermi team is continuously monitoring high energy emission from the Sun searching for flare events. Preliminary upper limits (E>100 MeV) have been derived for all solar flares detected so far by other missions and experiments (RHESSI, Fermi, GBM, GOES). Upper limit for flaring Sun emission (integrated over one year of data) has also been derived. Here we present the analysis techniques as well as the details of this search and the preliminary results obtained so far.
We report the results of an analysis to identify candidates for very high energy (VHE; E > 100 GeV) emission from high-latitude (|b|>10) unassociated sources in the year-1 catalog under development by the Fermi large area telescope (LAT) team. These are sources with no known counterparts at other wavelengths. Since VHE instruments are pointed instruments with small fields of view and low duty cycles, their observing programs need to be planned carefully to identify the most promising targets for observation. The scientific potential of combined Fermi and VHE observations has already been demonstrated with a number of joint VHE-Fermi papers. The goal of this work is to select the most promising unassociated Fermi sources for joint observations with Fermi and the VHE instruments.
We present the first detailed spectral and timing analysis of the High Mass X-ray Binary (HMXB) 4U 1909+07 with INTEGRAL and RXTE. 4U 1909+07 is detected with an average of 2.4cps in ISGRI, but shows flares up to ~50cps. The system shows a pulse period of 605s, but we found that the period changes erratically around this value. The pulse profile is extremely energy dependent: while it shows a double peaked structure at low energies, the secondary pulse decreases rapidly with increasing energy and above 20keV only the primary pulse is visible. This evolution is consistent between PCA, HEXTE and ISGRI. We find that the phase averaged spectrum can be well fitted with a photoabsorbed power law with a cutoff at high energies and a blackbody component. To investigate the peculiar pulse profile, we performed phase resolved spectral analysis. We find that a change in the cutoff energy is required to fit the changing spectrum of the different pulse phases.
We measure the neutral absorption towards the black hole X-ray binary system LMC X-1 from six archival soft X-ray spectra obtained with the gratings and/or CCD detectors on Chandra, XMM-Newton, and Swift. Four spectral models for the soft continuum have been investigated. While the powerlaw model may overestimate NH considerably, the others give consistent results. Taking the lower metalicity of the Large Magellanic Cloud into account, we find equivalent hydrogen column densities of N_H = (1.0-1.3)*10^22 cm^-2, with a systematic dependence on the orbital phase. This variation of the neutral absorption can nearly explain the orbital modulation of the soft X-ray flux recently detected with the All Sky Monitor (ASM) on the Rossi X-ray Timing Explorer (RXTE).
Gamma-ray binaries are orbital modulated gamma-ray sources in the Galaxy detected both at GeV and TeV energies. The high-energy radiation may come from the interaction of energetic electrons injected by a young pulsar and photons from the massive companion star. We present a model for the production of high-energy radiation where emission, absorption and pair cascading are considered. New observations of LS I +61 303 by the Fermi Space Telescope revealed an exponential cut-off in the spectrum at a few GeV, inconsistent with gamma-gamma absorption. Electrons radiating at GeV and TeV have probably two different origins. We investigate whether the emission from the unshocked pulsar wind explains the GeV component in LS I +61 303.
Two classes of gamma-ray bursts were identified in the BATSE catalogs characterized by their durations. There were also some indications for the existence of a third type of gamma-ray bursts. Swift satellite detectors have different spectral sensitivity than pre-Swift ones for GRBs. Therefore in this paper we analyze the bursts' duration distribution and also the duration-hardness bivariate distribution, published in The First BAT Catalog. Similarly to the BATSE data, to explain the BAT GRBs' duration distribution three components are needed. Although, the relative frequencies of the groups are different than they were in the BATSE GRB sample, the difference in the instrument spectral sensitivities can explain this bias in a natural way. This means theoretical models may have to explain three different type of gamma-ray bursts.
We report the detection of the lunar gamma-ray emission during the first year of Fermi-LAT observations. Such emission is produced by cosmic ray nuclei interacting with the lunar surface. Thanks to the solar minimum conditions and the reduced effects of heliospheric modulation, the lunar flux was at its maximum due to the increased flux of Galactic cosmic rays hitting the lunar surface. Fermi-LAT instrument has a superior sensitivity, angular resolution, and observes the whole sky every two orbits. It is the only gamma-ray mission capable of detecting the lunar emission with high confidence and to monitor it over the full 24th solar cycle. We also report the status of a search of the gamma-ray emission from major planets and asteroid populations in the ecliptic plane.
The uncertainties which still plague our understanding of the evolution of the light nuclides D, 3He and 4He in the Galaxy are described. Measurements of the local abundance of deuterium range over a factor of 3. The observed dispersion can be reconciled with the predictions on deuterium evolution from standard Galactic chemical evolution models, if the true local abundance of deuterium proves to be high, but not too high, and lower observed values are due to depletion onto dust grains. The nearly constancy of the 3He abundance with both time and position within the Galaxy implies a negligible production of this element in stars, at variance with predictions from standard stellar models which, however, do agree with the (few) measurements of 3He in planetary nebulae. Thermohaline mixing, inhibited by magnetic fields in a small fraction of low-mass stars, could in principle explain the complexity of the overall scenario. However, complete grids of stellar yields taking this mechanism into account are not available for use in chemical evolution models yet. Much effort has been devoted to unravel the origin of the extreme helium-rich stars which seem to inhabit the most massive Galactic globular clusters. Yet, the issue of 4He evolution is far from being fully settled even in the disc of the Milky Way.
The spectral energy distribution (SED) of high-frequency peaked BL Lac objects (HBL) is characterized by two peaks: one in the UV-X-ray and one in the GeV-TeV regime. An interesting object for analyzing these broadband characteristics is PKS 2005-489, which in 2004 showed the softest TeV spectrum ever measured. In 2009, a multi-wavelength campaign has been conducted with, for the first time, simultaneous observations by H.E.S.S. (TeV), Fermi/LAT (GeV), RXTE (keV), Swift (keV, UV, optical) and ATOM (optical) to cover the two peaks of the SED. During this campaign PKS 2005-489 underwent a high state in all wavebands which gives the opportunity to study in detail the emission processes of a high state of this interesting HBL.
In recent years, ground-based very-high-energy (VHE; E>100 GeV) gamma-ray astronomy has experienced a major breakthrough with the impressive astrophysical results obtained mainly by the current generation experiments like H.E.S.S., MAGIC, MILAGRO and VERITAS. The ground-based Imaging Air Cherenkov Technique for detecting VHE gamma-rays has matured, and a fast assembly of inexpensive and robust telescopes is possible. The goal for the next generation of instruments is to increase their sensitivity by a factor >10 compared to current facilities, to extend the accessible gamma-ray energies from a few tens of GeV to a hundred TeV, and to improve on other parameters like the energy and angular resolution (improve the point-spread function by a factor 4-5 w.r.t. current instruments). The Cherenkov Telescope Array (CTA) project is an initiative to build the next generation ground-based gamma-ray instrument, will serve as an observatory to a wide astrophysics community. I discuss the key physics goals and resulting design considerations for CTA, the envisaged technical solutions chosen, and the organizational and operational requirements for operating such a large-scale facility as well as the specific needs of VHE gamma-ray astronomy.
Using a detailed model of the internal shock phase, we discuss the origin of the prompt emission in gamma-ray bursts. We focus on the identification of the dominant radiative process (Fermi-GBM range) and propose an explanation for some features observed by Fermi-LAT at high energy in some GRB lightcurves.
In this contribution we discuss the origin of the extreme helium-rich stars which inhabit the blue main sequence (bMS) of the Galactic globular cluster Omega Centauri. In a scenario where the cluster is the surviving remnant of a dwarf galaxy ingested by the Milky Way many Gyr ago, the peculiar chemical composition of the bMS stars can be naturally explained by considering the effects of strong differential galactic winds, which develop owing to multiple supernova explosions in a shallow potential well.
We investigate the scale-locality of cascades of conserved invariants at high kinetic and magnetic Reynolds numbers in the ``inertial-inductive range'' of magnetohydrodynamic (MHD) turbulence, where velocity and magnetic field increments exhibit suitable power-law scaling. We prove that fluxes of total energy and cross-helicity--or, equivalently, fluxes of Els\"asser energies--are dominated by the contributions of local triads. Corresponding spectral transfers are also scale-local when defined using octave wavenumber bands. Flux and transfer of magnetic helicity may be dominated by non-local triads. The magnetic stretching term also may be dominated by non-local triads but we prove that it can convert energy only between velocity and magnetic modes at comparable scales. We explain the disagreement with numerical studies that have claimed conversion nonlocally between disparate scales. We present supporting data from a $1024^3$ simulation of forced MHD turbulence.
An updated model for the synchrotron and inverse Compton emission from a population of high energy electrons of the Crab Nebula is used to reproduce the measured spectral energy distribution from radio to high energy gamma-rays. By comparing the predicted inverse Compton component with recent Fermi measurements of the nebula's emission, it is possible to determine the average magnetic field in the nebula and to derive the underlying electron energy distribution. The model calculation can then be used to cross calibrate the Fermi observations with ground based air shower measurements. The resulting energy calibration factors are derived and can be used for combining broad energy measurements taken with Fermi in conjunction with ground based measurements.
Blazars are a small fraction of all extragalactic sources but, unlike other objects, they are strong emitters across the entire electromagnetic spectrum. Recent data in the microwave region of the electromagnetic spectrum have become available to allow for systematic studies of blazars over large cosmological volumes. This frequency band is indeed particularly suited for the selection of blazars since at these frequencies the contamination from radio extended components with steep spectra is no longer present and the emission from the accretion process is negligible. During the first 3 months of scientific operations Fermi-LAT detected 106 bright, high-galactic latitude (| b |> 10 deg) AGNs with high significance. In this study we investigate the possible relations between the microwave and the gamma-ray emissions for Fermi-LAT detected AGNs belonging to WMAP 5th year bright source catalog.
We present the main characteristics of the proposed location for the
Javalambre Astrophysical Observatory. The measurements have been obtained from
spectrophotometric, photometric and seeing data obtained with different
monitors and instruments on the site and publicly accessible meteorological
satellite data.
The night-sky optical spectrum observed in a moonless night shows very little
contamination by the typical pollution lines. Their contribution to the
sky-brightness is ~0.06 mag in B, ~0.09 mag in V and ~0.06 mag in R. In
particular, the comparison of the strengths of the Sodium artificial and
natural lines indicates that the site satisfies the IAU recommendations for a
dark site. The zenith-corrected values of the moonless night-sky surface
brightness are B = 22.8 mag arcsec^-2, V = 22.1 mag arcsec^-2, R = 21.5 mag
arcsec^-2, I = 20.4 mag arcsec^-2, which indicates that the site is very dark.
The extinction has been measured for the summer period, with a typical value of
0.22 mag in the V-Band, with the best measured value of 0.18 mag in a totally
photometric night. The median value of the seeing in the V-band for the last
two years (2008-9) is 0.71", with a mode of 0.58". The seeing values present a
seasonal pattern, being smaller in summer (~0.69") than in winter time (0.77").
For 68% of the analyzed nights the seeing was better than 0.8" during the
entire night. The seeing is found to be stable for rather long periods, in
particular for the nights with good seeing values. The typical scale, for
nights with the seeing below 0.8", is about 5 hours for variations within 20%
of the reference value. The fraction of totally clear nights is ~53%, while the
fraction of nights with at least a 30% of the night clear is ~74%.
We study the quasi-simultaneous Spectral Energy Distributions (SED) of 48 LBAS blazars, collected within three months of the Fermi LAT Bright AGN Sample (LBAS) data taking period, combining Fermi and Swift data with radio NIR-Optical and hard-X/gamma-ray data. We have used these SEDs to characterize the peak position and intensity of both the low and the high-energy features of blazar spectra. The results have been used to derive empirical relationships that estimate the position of the two peaks from the broad-band colors (i.e. the radio to optical, alpha_ro, and optical to X-ray, alpha_ox, spectral slopes) and from the gamma-ray spectral index. Our data show that the synchrotron peak frequency is positioned between 10^(12.5) and 10^(14.5) Hz in broad-lined FSRQs and between 10^(13) and 10^(17) Hz in featureless BL Lacertae objects. We find that the gamma-ray spectral slope is strongly correlated with the synchrotron peak energy and with the X-ray spectral index, as expected at first order in synchrotron - inverse Compton scenarios. However, simple homogeneous, one-zone, Synchrotron Self Compton (SSC) models cannot explain most of our SEDs, especially in the case of FSRQs and low energy peaked (LBL) BL Lacs. More complex models involving External Compton Radiation or multiple SSC components are required to reproduce the overall SEDs and the observed spectral variability.
Blazars are a small fraction of all extragalactic sources but, unlike other objects, they are strong emitters across the entire electromagnetic spectrum. In this study we have conducted a detailed investigation of the broad-band spectral properties of the gamma-ray selected blazars of the Fermi-LAT Bright AGN Sample (LBAS). By combining the accurately estimated Fermi gamma-ray spectra with Swift, radio, NIR-Optical and hard-X/gamma-ray data, collected within three months of the LBAS data taking period, we were able to assemble high-quality and quasi-simultaneous Spectral Energy Distributions (SED) for 48 LBAS blazars.
VERITAS is the high-sensitivity instrument of latest generation. It is often used for the short AGN monitoring exposures evenly distributed over entire observational season of a source of interest. Each of these exposures is long enough to detect the source at the flux level of about 1 Crab. During the 2009 observing season a number of exposures of Mkn 501 with VERITAS revealed variable TeV gamma-ray emission at the flux level eventually exceeding 2 Crab. The spectral and flux variability measurements in TeV gamma rays for the 2009 data sample of Mkn 501 are summarized in this paper.
We report the discovery of a young planetary-mass brown dwarf in the rho Oph cloud core. The object was identified as such with the aid of a 1.5-2.4 micron low-resolution spectrum obtained using the NIRC instrument on the Keck I telescope. Based on the COND model, the observed spectrum is consistent with a reddened (Av ~ 15-16) brown dwarf whose effective temperature is in the range 1200-1800 K. For an assumed age of 1 Myr, comparison with isochrones further constrains the temperature to ~ 1400 K and suggests a mass of ~ 2-3 Jupiter masses. The inferred temperature is suggestive of an early T spectral type, which is supported by spectral morphology consistent with weak methane absorption. Based on its inferred distance (~ 100 pc) and the presence of overlying visual absorption, it is very likely to be a rho Oph cluster member. In addition, given the estimated spectral type, it may be the youngest and least massive T dwarf found so far. Its existence suggests that the initial mass function for the rho Oph star-forming region extends well into the planetary-mass regime.
The Large Area Telescope (LAT) on board Fermi has detected high-energy gamma rays from the quiet Sun produced by interactions of cosmic-ray nucleons with the solar surface and cosmic-ray electrons with solar photons in the heliosphere. Such observations provide a probe of the extreme conditions near the solar atmosphere and photosphere and permit the study of the modulation of cosmic rays over the inner heliosphere. For the first year of Fermi observations the solar modulation was at its minimum corresponding to a maximum cosmic-ray flux and, hence, maximum gamma-ray emission from the Sun. We discuss the study of the quiescent solar emission, including spectral analysis of its two components, disk and inverse Compton, using the first-year data of the mission and models using the electron spectrum measured by Fermi.
The Fermi Gamma-Ray Space Telescope was launched in June 2008 and the onboard Large Area Telescope (LAT) has been collecting data since August of that same year. The LAT is currently being used to study a wide range of science topics in high-energy astrophysics, one of which is the study of high-energy cosmic rays. The LAT has recently demonstrated its ability to measure cosmic-ray electrons, and the Fermi LAT Collaboration has published a measurement of the high-energy cosmic-ray electron spectrum in the 20 GeV to 1 TeV energy range. Some methods for performing a similar analysis to measure the cosmic-ray proton spectrum using the LAT will be presented with emphasis on unfolding the reconstructed proton energy.
We present results from the first two years of our fast-cadence 15 GHz gamma-ray blazar monitoring program, part of the F-GAMMA radio monitoring project. Our sample includes the 1158 blazars north of -20 degrees declination from the Candidate Gamma-Ray Blazar Survey (CGRaBS), which encompasses a significant fraction of the extragalactic sources detected by the Fermi Gamma-ray Space Telescope. We introduce a novel likelihood analysis for computing a time series variability amplitude statistic that separates intrinsic variability from measurement noise and produces a quantitative error estimate. We use this method to characterize our radio light curves. We also present results indicating a statistically significant correlation between simultaneous average 15 GHz radio flux density and gamma-ray photon flux.
We present a review about the relevance of the paper by Peimbert and Costero (1969), on the chemical abundance determinations of H II regions. We analize the observational evidence in favor of the presence of temperature variations inside gaseous nebulae. We make a brief mention of the methods used to estimate the contribution of the unobserved ions to the total chemical abundances.
We present a complex radio burst, associated with the January 20, 2005 extreme event, recorded by the ARTEMIS-IV radio spectrograph at Thermopylae, Greece. The radio observations are combined with HXR & Gamma-Ray recordings from the SONG/CORONAS-F. The emission in the decimetric to decametric range consisted of two distinct type II lanes in close succession, each lane was followed by a flare continuum-like burst (FCII) and accompanied by groups of bursts of the type III family. These were superposed on an extended type IV continuum with rich fine structure. A number of energetic particle acceleration episodes associated with HXR and Gamma-Ray peaks, the latter being a result of pion decay, were recorded. The high time and spectral resolution observations of bidirectional and reverse drift type III groups suggest a reconnection front as the origin of the metric-decametric flare continuum (FCII). The interpretation of the two metric type II bands presents certain ambiguities as they may be the signatures of reconnection shocks or reverse CME shocks or they may be piston driven by flare ejected plasmoids; furthermore they cannot be positively associated with the CME bow shock. The same holds for the hectometric type II which was recorded by the WIND/WAVES; it cannot be identified with certainty as the extension of the type II into the interplanetary space or the CME bow shock.
Diffuse gamma-ray emission arising from interactions of cosmic rays with the interstellar gas traces the densities of both of them throughout the Milky Way. We discuss the results obtained from the analysis of Fermi LAT observations in the region of Cassiopeia and Cepheus, towards the Perseus spiral arm. We find that the gamma-ray emissivity of local gas is consistent with expectations based on the cosmic-ray spectra measured at the Earth. The emissivity decreases from the Gould Belt to the Perseus arm, but the measured gradient is flatter than predictions by a propagation model based on a cosmic-ray source distribution peaking in the inner Galaxy as suggested by pulsars. The Xco=N(H2)/W(CO) conversion factor moderately increases by a factor ~2 from the Gould Belt to the Perseus arm. The presence of additional gas not properly traced by HI and CO surveys in the Gould Belt is suggested by the correlation between gamma rays and thermal emission from cold interstellar dust.
Scalar Dark Matter (DM) can have dimensionful coupling to the Higgs boson - the "soft" portal into DM - which is predicted to be unsuppressed by underlying SO(10) GUT. The dimensionful coupling can be large, \mu/v >> 1, without spoiling perturbativity of low energy theory up to the GUT scale. We show that the soft portal into DM naturally triggers radiative EWSB via large 1-loop DM corrections to the effective potential. In this scenario EWSB, DM thermal freeze-out cross section and DM scattering on nuclei are all dominated by the same coupling, predicting DM mass range to be 700 GeV< M_{DM} < 2 TeV. The spin-independent direct detection cross section is predicted to be just at the present experimental sensitivity and can explain the observed CDMS II recoil events.
There are three observables related to neutrino mass, namely the kinematic mass in direct searches, the effective mass in neutrino-less double beta decay, and the sum of neutrino masses in cosmology. In the limit of exactly degenerate neutrinos there are very simple relations between those observables, and we calculate corrections due to non-zero mass splitting. We discuss how the possible non-unitarity of the lepton mixing matrix may modify these relations and find in particular that corrections due to non-unitarity can exceed the corrections due to mass splitting. We furthermore investigate constraints from neutrino-less double beta decay on mass and mixing parameters of heavy neutrinos in the type I see-saw mechanism. There are constraints from assuming that heavy neutrinos are exchanged, and constraints from assuming light neutrino exchange, which arise from an exact see-saw relation. The latter has its origin in the unitarity violation arising in see-saw scenarios. We illustrate that the limits from the latter approach are much stronger. The drastic impact on inverse neutrino-less double beta decay (e e -> W W) is studied. We furthermore discuss neutrino mixing in case there is one or more light sterile neutrino. Neutrino oscillation probabilities for long baseline neutrino oscillation experiments are considered, and the analogy to general non-unitarity phenomenology, such as zero-distance effects, is pointed out.
We study the representations of tensor random fields on the sphere basing on the theory of representations of the rotation group. Introducing specific components of a tensor field and imposing the conditions of weak isotropy and mean square continuity, we derive their spectral decompositions in terms of generalized spherical functions. The properties of random coefficients of the decompositions are characterized, including such an important question as conditions of Gaussianity.
The dynamics of TeVeS in a homogeneous and isotropic universe is shown to be equivalent to the dynamics of an interacting two-component system, consisting of a scalar field and a "fluid", related to the matter part, with explicitly given coupling term. Scaling solutions (solutions with a constant ratio of the energy densities of both components) in the "Einstein frame" are found which are exponentially expanding or contracting with no remaining freedom for Bekenstein's $F$ function. In the "physical frame" these solutions are of the power-law type. An equivalent General Relativity (GR) picture of the dynamics suggests that it is the scalar field which plays the role of dark matter, while the "matter" has to mimic (phantom-type) dark energy.
We investigate different neutrino signals from the decay of dark matter particles to determine the prospects for their detection, and more specifically if any spectral signature can be disentangled from the background in present and future neutrino observatories. If detected, such a signal could bring an independent confirmation of the dark matter interpretation of the dramatic rise in the positron fraction above 10 GeV recently observed by the PAMELA satellite experiment and offer the possibility of distinguishing between astrophysical sources and dark matter decay or annihilation. In combination with other signals, it may also be possible to distinguish among different dark matter decay channels.
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As very-high--energy photons propagate through the extragalactic background light (EBL), they interact with the soft photons and initiate electromagnetic cascades of lower energy photons and electrons. The collective intensity of a cosmological population emitting at very-high energies (VHE) will be attenuated at the highest energies through interactions with the EBL and enhanced at lower energies by the resulting cascade. We calculate the cascade radiation created by VHE photons produced by blazars and investigate the effects of cascades on the collective intensity of blazars and the resulting effects on the extragalactic gamma-ray background. We find that cascade radiation greatly enhances the collective intensity from blazars at high energies before turning over due to attenuation. The prominence of the resulting features depends on the blazar gamma-ray luminosity function, spectral index distribution, and the model of the EBL. We additionally calculate the cascade radiation from the distinct spectral sub-populations of blazars, BL Lacertae objects (BL Lacs) and flat-spectrum radio quasars (FSRQs), finding that the collective intensity of BL Lacs is considerably more enhanced by cascade radiation than that of the FSRQs due to their harder spectra. As such, studies of the blazar contribution to the EGRB by Fermi will have profound implications for the nature of the EBL, the evolution of blazars, and blazar spectra.
We present the discovery of a bright (J = 13.1 mag) nearby L6 dwarf found in a search for L-type ultracool subdwarfs in the Sloan Digital Sky Survey (SDSS) Data Release 7. SDSS J141624.08+134826.7 exhibits blue near-infrared colors compared to other optically-typed L6 objects, but its optical and near-infrared spectra do not show metal-poor features characteristic of known L-type ultracool subdwarfs. Instead, SDSS J141624.08+134826.7 is probably a nearby example of the class of L dwarfs with low condensate opacities which exhibit unusually blue near-infrared colors for a given spectral type. Its deep 1.4 and 1.9 um H2O absorption bands, weak 2.3 um CO feature, strong 0.99 um FeH band, and shallow optical TiO and CaH bands resemble the spectra of other blue L dwarfs which are believed to have unusually thin or large-grained cloud structure. The luminosity of SDSS J141624.08+134826.7 implies that it is either a high-mass brown dwarf or a low mass star, depending on its age, and its UVW space motion suggests a thin-disk membership. With a spectrophotometric distance of 8.4 +/- 1.9 pc, SDSS J141624.08+134826.7 is one of the nearest L dwarfs to the Sun and is therefore an excellent target for high resolution imaging, spectroscopic, and astrometric follow-up observations.
The galaxy M82 has long been considered a promising target for VHE gamma-ray observations because of the compact starburst region in its core. Theoretical predictions have suggested it should be detectable by ground-based imaging Cherenkov telescopes like VERITAS and that a detection would have implications for the understanding of the origin of cosmic rays. M82 was observed with the VERITAS array during the 2007-2009 observing seasons. With an exposure of 137 hours, VERITAS was able to detect a gamma-ray signal at the 5 sigma level. This marks the discovery of gamma rays not only from M82 but also from the new source class of starburst galaxies. The observed flux from M82 is 3.7\pm 0.8(stat)\pm 0.7(syst)x10^-13 photons cm^-2 s^-1 above an energy threshold of 700 GeV, which corresponds to 0.9% of the Crab Nebula flux. The differential energy spectrum is a power law with a photon index Gamma=2.5\pm 0.6(stat)\pm 0.2(syst). Both the flux and the photon index is close to recent theoretical predictions. The VERITAS data places a strong correlation between the star-formation activity and the cosmic-ray production in M82.
We report the identification of 17 candidate brown dwarf binaries whose components straddle the L dwarf/T dwarf transition. These sources were culled from a large near-infrared spectral sample of L and T dwarfs observed with the Infrared Telescope Facility SpeX spectrograph. Candidates were selected on the basis of spectral ratios which segregate known (resolved) L dwarf/T dwarf pairs from presumably single sources. Composite templates, constructed by combining 13581 pairs of absolute flux-calibrated spectra, are shown to provide statistically superior fits to the spectra of our seventeen candidates as compared to single templates. Ten of these candidates appear to have secondary components that are significantly brighter than their primaries over the 1.0-1.3 micron band, indicative of rapid condensate depletion at the L dwarf/T dwarf transition. Our results support prior indications of enhanced multiplicity amongst early-type T dwarfs; 53+/-7% of the T0-T4 dwarfs in our spectral sample are found to be either resolved or unresolved (candidate) pairs, although this is consistent with an intrinsic (volume complete) brown dwarf binary fraction of only 15%. If verified, this sample of spectral binaries more than doubles the number of known L dwarf/T dwarf transition pairs, enabling a broader exploration of this poorly-understood phase of brown dwarf atmospheric evolution.
Recent X-ray observations by Fermi/GBM discovered a new torque reversal of 4U 1626-67 after 18 years of steady spinning down. Using Swift/BAT observations we were able to center this new torque reversal on Feb 4 2008, lasting approximately 150 days. From 2004 up to the end of 2007, the spin-down rate averaged at a mean rate of ~dnu/dt=-4.8e-13 Hz s-1 until the torque reversal reported here. Since then it has been following a steady spin-up at a mean rate of ~dnu/dt= 4e-13 Hz s-1. The properties of this torque reversal, as well as the lack of correlation between the X-ray flux and the torque applied to the neutron star before this transition, challenges our understanding of the physical mechanisms operating in this system.
We present a summary of the observation strategy of TANAMI (Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry), a monitoring program to study the parsec-scale structure and dynamics of relativistic jets in active galactic nuclei (AGN) of the Southern Hemisphere with the Australian Long Baseline Array (LBA) and the trans-oceanic antennas Hartebeesthoek, TIGO, and O'Higgins. TANAMI is focusing on extragalactic sources south of -30 degrees declination with observations at 8.4 GHz and 22 GHz every ~2 months at milliarcsecond resolution. The initial TANAMI sample of 43 sources has been defined before the launch of the Fermi Gamma Ray Space Telescope to include the most promising candidates for bright gamma-ray emission to be detected with its Large Area Telescope (LAT). Since November 2008, we have been adding new sources to the sample, which now includes all known radio- and gamma-ray bright AGN of the Southern Hemisphere. The combination of VLBI and gamma-ray observations is crucial to understand the broadband emission characteristics of AGN and the nature of relativistic jets.
H.E.S.S. is one of the most sensitive instruments in the very high energy (VHE; > 100 GeV) gamma-ray domain and has revealed many new sources along the Galactic Plane. After the successful first VHE Galactic Plane Survey of 2004, H.E.S.S. has continued and extended that survey in 2005-2008, discovering a number of new sources, many of which are unidentified. Some of the unidentified H.E.S.S. sources have several positional counterparts and hence several different possible scenarios for the origin of the VHE gamma-ray emission; their identification remains unclear. Others have so far no counterparts at any other wavelength. Particularly, the lack of an X-ray counterpart puts serious constraints on emission models. Several newly discovered and still unidentified VHE sources are reported here.
The Vela pulsar is one of the most exciting gamma-ray sources and has been at the forefront of high-energy pulsar science since the detection of gamma-ray pulsations at the radio period by SAS-2 in 1975. With the unprecedented angular resolution, effective area, field of view, and timing resolution, in the GeV band, of the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope, the light curve of the Vela pulsar can be studied in greater detail than ever before. Using a timing solution derived solely from the LAT data, phase aligned with the radio emission, the spectrum of the Vela pulsar has been fit in intervals as small as 0.0016 in phase. Significant variation is seen in the cutoff energy and photon index across the light curve, strongly supporting curvature radiation as the source of the high-energy gamma-rays from the Vela pulsar.
We describe an improved method of mapping the gamma-ray sky by applying the Linear Radon Transform to data from BATSE on NASA's CGRO. Based on a method similar to that used in medical imaging, we use the relatively sharp (~0.25 deg) limb of the Earth to collimate BATSE's eight Large Area Detectors (LADs). Coupling this to the ~51-day precession cycle of the CGRO orbit, we can complete a full survey of the sky, localizing point sources to < 1 deg accuracy. This technique also uses a physical model for removing many sources of gamma-ray background, which allows us to image strong gamma-ray sources such as the Crab up to ~2 MeV with only a single precession cycle. We present the concept of the Radon Transform technique as applied to the BATSE data for imaging the gamma-ray sky and show sample images in three broad energy bands (23-98 keV, 98-230 keV, and 230-595 keV) centered on the positions of selected sources from the catalog of 130 known sources used in our Enhanced BATSE Occultation Package (EBOP) analysis system. Any new sources discovered during the sky survey will be added to the input catalog for EBOP allowing daily light curves and spectra to be generated. We also discuss the adaptation of tomographic imaging to the Fermi GBM occultation project.
Given a class of dark energy models, constraints from one set of cosmic acceleration observables make predictions for other observables. Here we present the allowed ranges for the expansion rate H(z), distances D(z), and the linear growth function G(z) (as well as other, derived growth observables) from the current combination of cosmological measurements of supernovae, the cosmic microwave background, baryon acoustic oscillations, and the Hubble constant. With a cosmological constant as the dark energy and assuming near-minimal neutrino masses, the growth function is already predicted to better than 2% precision at any redshift, with or without spatial curvature. Direct measurements of growth that match this precision offer the opportunity to stringently test and potentially rule out a cosmological constant. While predictions in the broader class of quintessence models are weaker, it is remarkable that they are typically within a factor of 2-3 of forecasts for future space-based supernovae and Planck CMB measurements. In particular, measurements of growth at any redshift, or the Hubble constant H_0, that exceed LambdaCDM predictions by substantially more than 2% would rule out not only a cosmological constant but also the whole quintessence class, with or without curvature and early dark energy. Barring additional systematic errors hiding in the data, such a discovery would require more exotic explanations of cosmic acceleration such as phantom dark energy, dark energy clustering, or modifications of gravity.
A large sample of blazar from the Candidate Gamma Ray Blazar Survey (CGRaBS) has been observed with the Owens Valley Radio Observatory (OVRO) 40-Meter Telescope at 15GHz. Using these quasi-simultaneous observations, we study the connection between the gamma-ray behavior of blazars as detected by Fermi-LAT and the cm band as observed by the F-GAMMA project with the OVRO 40-Meter Telescope. Comparing the light curves for a large number of sources, it is possible to study in detail the relation between the gamma-ray and radio activity of Fermi-LAT detected gamma-ray blazars. We present first results for correlations between Fermi-LAT and our 15 ~GHz observations.
We investigate the effect of heating by luminosity sources in a simulation of clustered star formation. Our heating method involves a simplified continuum radiative transfer method that calculates the dust temperature. The gas temperature is set by the dust temperature. We present the results of four simulations, two simulations assume an isothermal equation of state and the two other simulations include dust heating. We investigate two mass regimes, i.e., 84 Msun and 671 Msun, using these two different energetics algorithms. The mass functions for the isothermal simulations and simulations which include dust heating are drastically different. In the isothermal simulation, we do not form any objects with masses above 1 Msun. However, the simulation with dust heating, while missing some of the low-mass objects, forms high-mass objects (~20 Msun) which have a distribution similar to the Salpeter IMF. The envelope density profiles around the stars formed in our simulation match observed values around isolated, low-mass star-forming cores. We find the accretion rates to be highly variable and, on average, increasing with final stellar mass. By including radiative feedback from stars in a cluster-scale simulation, we have determined that it is a very important effect which drastically affects the mass function and yields important insights into the formation of massive stars.
We discuss Fermi observations of gamma-ray loud binaries. We show that within hadronic model of activity of LSI +61 303, detection of cut-off in the GeV spectrum constrains maximal energy of the primary protons. In this way, the GeV gamma-ray data impose constraint on the expected neutrino signal (spectrum and lightcurve) from the source. We also briefly discuss perspectives of GeV band detection of PSR B1259-63 during the 2010 periastron passage.
We show that kicks generated by topological currents may be responsible for the large velocities seen in a number of pulsars. The majority of the kick builds up within the first second of the star's birth and generates a force about two orders of magnitude larger than a neutrino kick in the same temperature and magnetic field regime. Because of the nature of the topological currents the star's cooling is not affected until it reaches 10^9 K; thereafter the current replaces neutrino emission as the dominant cooling process. A requirement for the kick to occur is a suitably thin crust on the star; this leads us to speculate that pulsars with large kicks are quark stars and those with small kicks are neutron stars. If true this would be an elegant way to distinguish quark stars from neutron stars.
The Galactic Center region is expected to host the largest density of Dark Matter (DM) particles within the Milky Way. Then a relatively large gamma-ray signal would be expected from the possible DM particles annihilation (or decay). We are searching for the DM gamma-ray signal from the Galactic Center, which is also rich in bright discrete gamma-ray sources. Furthermore intense diffuse gamma-ray emission due to cosmic-ray interactions with interstellar gas and radiation is detected from the same direction. A preliminary analysis of the data, taken during the first 11 months of the Fermi satellite operations, is reported. The diffuse gamma-ray backgrounds and discrete sources, as we know them today, can account for the large majority of the detected gamma-ray emission from the Galactic Center. Nevertheless a residual emission is left, not accounted for by the above models. An improved model of the Galactic diffuse emission and a careful evaluation of new (possibly unresolved) sources (or source populations) will improve the sensitivity for a DM search.
In the last couple of years the Magic air Cherenkov telescope has made significant contributions to very high energy $\gamma$-ray astronomy. These include the detection of the galactic binary system LSI +61 303 and the observation of pulsed emission from the Crab pulsar. Extragalactic objects like the famous FSRQ 3C 279 and the LBL S5 0716+714 have both been detected during optical high states, and the radio galaxy M87 could be observed during an unexpected strong $\gamma$-ray outburst. Given its low energy trigger threshold (~50 GeV) and fast repositioning time of less than 30s the Magic air Cherenkov telescope is particularly well suited for the observation of fast transient objects like AGN or GRBs. So far no GRB could be detected with Magic, however. In this paper we present selected highlights from recent MAGIC observations of extragalactic objects.
Using the Gamma Ray Burst Monitor (GBM) on-board Fermi, we are monitoring the hard X-ray/soft gamma ray sky using the Earth occultation technique. Each time a source in our catalog enters or exits occultation by the Earth, we measure its flux using the change in count rates due to the occultation. Currently we are using CTIME data with 8 energy channels spanning 8 keV to 1 MeV for the GBM NaI detectors and spanning 150 keV to 40 MeV for the GBM BGO detectors. Our preliminary catalog consists of galactic X-ray binaries, the Crab Nebula, and active galactic nuclei. In addition, to Earth occultations, we have observed numerous occultations with Fermi's solar panels. We will present early results. Regularly updated results can be found on our website this http URL
A very small dispersion in the speed of light may be observable in Fermi time- and energy-tagged data on variable sources, such as gamma-ray bursts (GRB) and active galactic nuclei (AGN). We describe a method to compute the size of this effect by applying the Feynman sum-over-histories formalism for relativistic quantum electrodynamics to a discrete model of space-time called \emph{causal set theory}.
The first VERITAS telescope was installed in 2002-2003 at the Fred Lawrence Whipple Observatory and was originally operated as a prototype instrument. Subsequently the decision was made to locate the full array at the same site, resulting in an asymmetric array layout. As anticipated, this resulted in less than optimal sensitivity due to the loss in effective area and the increase in background due to local muon initiated triggers. In the summer of 2009, the VERITAS collaboration relocated Telescope 1 to improve the overall array layout. This has provided a 30% improvement in sensitivity corresponding to a 60% change in the time needed to detect a source.
We present the topometric MST method to search for clusters of photons in the LAT sky, which was used to obtain the seed list for the compilation of the First LAT catalog. This method works well in non-dense field and can be profitably used at energies higher than a few GeV. We describe the particular techniques developed by us to improve the cluster selection criteria and the estimate of the astronomical coordinates of the possibly associated gamma-ray sources. A simulation technique to evaluate the confidence level of the source detectionis presented.
We demonstrate a method for quantitatively comparing gamma-ray pulsar light curves with magnetosphere beaming models. With the Fermi LAT providing many pulsar discoveries and high quality pulsar light curves for the brighter objects, such comparison allows greatly improved constraints on the emission zone geometry and the magnetospheric physics. Here we apply the method to Fermi LAT light curves of a set of bright pulsars known since EGRET or before. We test three approximate models for the magnetosphere structure and two popular schemes for the location of the emission zone, the Two Pole Caustic (TPC) model and the Outer Gap (OG) model. We find that OG models and relatively physical B fields approximating force-free dipole magnetospheres are preferred at high statistical significance. An application to the full LAT pulsar sample will allow us to follow the emission zone's evolution with pulsar spindown.
Using the Gamma ray Burst Monitor (GBM) on Fermi we are monitoring accreting pulsar systems. We use the rates from GBM's 12 NaI detectors in the 8-50 keV range to detect and monitor pulsations with periods between 0.5 and 1000 seconds. After discussing our analysis approach we present results for individual sources from the first year of monitoring. Updated figures for these and other sources are available at this http URL .
Radio galaxies are the only non-blazar AGN detected in the VHE (E > 100 GeV) band. These objects enable the investigation of the main substructures of the AGN, in particular the core, the jet and its interaction with the intergalactic environment. VERITAS observations have included exposures on a number of radio galaxies. Recently, the discovery by Fermi of GeV emission from the radio galaxy NGC 1275 triggered VERITAS observations of this source. Results from the VERITAS observations of radio galaxies and future plans are presented.
We present results of a study of the localization capability of Fermi-LAT, using a large set of blazars with precise radio locations. Since the width of the PSF decreases with energy, the performance is typically dominated by a few high energy photons, so it is important to properly characterize the high-energy PSF. Using such data, we have found a need to modify the pre-launch high-energy (greater than a few GeV) PSF derived from extensive Monte Carlo simulations of particle interactions in the LAT; the resulting data-based PSF is shown
The Large Area Telescope (LAT), Fermi's main instrument, is providing a new view of the local energetic pulsar population. In addition to identifying a pulsar origin of a large fraction of the bright unidentified Galactic EGRET sources, the LAT results provide a great opportunity to study a sizable population of high-energy pulsars. Correlations of their physical properties, such as the trend of the luminosity versus the rotational energy loss rate, help identify global features of the gamma-ray pulsar population. Several lines of evidence, including the light curve and spectral features, suggest that gamma-ray emission from the brightest pulsars arises largely in the outer magnetosphere.
We report on a preliminary analysis of the diffuse gamma-ray observations of local giant molecular clouds Orion A and B with the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope. The gamma-ray emission of the clouds is well explained by hadronic and electromagnetic interactions between cosmic rays and nuclei in the clouds. In consequence, we obtain the total masses of the Orion A and B clouds to be (80.6 +/- 7.5 +/- 4.8) x 10^3 Msun and (39.5 +/- 5.2 +/- 2.6) x 10^3 Msun, respectively, for the distance to the clouds of 400 pc and the Galactic CR spectrum predicted by GALPROP on the local observations of CRs. The structure of molecular clouds have been extensively studied by radio telescopes, especially using the line intensity of CO molecules (WCO) and a constant conversion factor from Wco to N (H_2) (= Xco). However, this factor is found to be significantly different for Orion A and B: 1.76 +/- 0.04 +/- 0.02 and 1.27 +/- 0.06 +/- 0.01, respectively.
Using hydrodynamic approach, it is shown that the properties of a marginally stable collisionless stellar disc resemble those of a thermodynamic system undergoing a gas--liquid phase transition. The maximum in Toomre's stability diagram, which separates gravitationally stable and unstable states with respect to axisymmetric perturbations, can be treated as a critical point for this transition. Static perturbations of stellar density are explored and the mean perturbation amplitude is considered as the order parameter of the theory. The disc's state is assumed to change as the disc passes through the critical point. Since the disc tends to retain hydrostatic equilibrium, structures can be formed spontaneously, identifiable with a seed spiral structure. A power-law scaling of the order parameter in the vicinity of the critical point has been found. The susceptibility and other Landau--Weiss exponents similar to those in the Van der Waals theory are calculated. The critical behaviour of marginally stable discs at the initial stage of their evolution occurs in numerical simulations where snapshots of stellar positions reveal stellar splinters and crescents diverging from the disc centre. These structures can be a result of the phase transition. In numerical simulations, these structures eventually reduce to decaying worm-type features because of the `heating' most likely resulting from instability of stellar orbits due to resonances. Under favourable conditions the critical behaviour leading to the establishment of order in a stellar disc can result in the generation of a spiral structure.
Until now the known sources in the Galactic center with sufficiently smooth spectra and of sufficient brightness to be suitable for high resolution infrared absorption spectroscopy of interstellar gas occupied a narrow range of longitudes, from the central cluster of hot stars to approximately 30 pc east of the center. In order to more fully characterize the gas within the r ~ 180 pc Central Molecular Zone it is necessary to find additional such sources that cover a much wider longitudinal range of sightlines. We are in the process of identifying luminous dust-embedded objects suitable for spectroscopy within 1.2 deg in longitude and 0.1 deg in latitude of Sgr A* using the Spitzer GLIMPSE and the 2MASS catalogues. Here we present spectra of H3+ and CO towards two such objects, one located 140 pc west of Sgr A*, and the other located on a line of sight to the Sgr B molecular cloud complex 85 pc to the east of Sgr A*. The sightline to the west passes through two dense clouds of unusually high negative velocities and also appears to sample a portion of the Expanding Molecular Ring. The spectra toward Sgr B reveal at least ten absorption components covering over 200 km/s and by far the largest equivalent width ever observed in an interstellar H3+line; they appear to provide the first near-infrared view into that hotbed of star formation.
The Fermi Large Area Telescope (LAT) has provided the measurement of the high energy cosmic ray electrons plus positrons (CRE) spectrum with unprecedented accuracy form 20 GeV to 1 TeV. Recently this range has been extended down to ~ 7 GeV. The spectrum shows no prominent features and it is significantly harder than that inferred from several previous experiments. While the reported Fermi-LAT data alone may be interpreted in terms of a single (electron dominated) Galactic component, when combined with other complementary experimental results, specifically the CRE spectrum measured by H.E.S.S., and especially the positron fraction measured by PAMELA, an additional electron and positron component seems to be required. We show that the acceleration of electron-positron pairs in Galactic pulsars may offer a natural (though not unique) interpretation of all those results.
The clustering properties of a well-defined sample of 734 H-alpha emitters at z=0.84 obtained as part of the Hi-z Emission Line Survey (HiZELS) are investigated. The spatial correlation function is very well-described by (r/r_0)^-1.8, with r_0=2.7+-0.3Mpc/h. The correlation length r_0 increases strongly with H-alpha luminosity, L_H-alpha, from r_0~2Mpc/h for the most quiescent galaxies (star-formation rates of ~4M_sun/yr), up to r_0>5Mpc/h for the brightest galaxies in H-alpha. The correlation length also increases with increasing rest-frame K-band luminosity (M_K), but the r_0-L_H-alpha correlation maintains its full statistical significance at fixed M_K. At z=0.84, star-forming galaxies classified as irregulars or mergers are much more clustered than discs and non-mergers, but once the samples are matched in L_H-alpha and M_K, the differences vanish, implying that the clustering is independent of morphological type at z~1. The typical H-alpha emitters found at z=0.84 reside in dark-matter haloes of ~10^12M_sun, but those with the highest SFRs reside in more massive haloes of ~10^13M_sun. Comparing the results with those of H-alpha surveys at different redshifts, it is seen that although the break of the H-alpha luminosity function, L*, evolves by a factor of ~30 from z=0.24 to z=2.23, galaxies with the same L_H-alpha/L*(z) are found in dark matter haloes of similar masses, independently of cosmic time. This not only confirms that star-formation is more efficient at higher redshift, but also suggests a fundamental connection between the strong decrease of L* since z=2.23 and the quenching of star-formation in galaxies residing within dark-matter haloes significantly more massive than 10^12M_sun at any given epoch. (Abridged).
Z CMa is a binary system which consists of two young stars: A Herbig AeBe component "Z CMa NW" embedded in a dust cocoon and a less massive component "Z CMa SE", which is classified as a FU Orionis type star. Recently, the system showed the largest outburst reported during the almost 90 years of available observations. During the recent outburst we detect that the Z CMa system is polarized by 2.6% in the continuum and emission line spectrum, with a position angle still perpendicular to the jet. From the high level of polarization we conclude that the outburst is associated with the dust embedded Herbig AeBe NW component. The main result of our studies is that the bolometric luminosity of Z CMa remained surprisingly constant during the recent "outburst". We conclude that either the geometry of the cavity through which the light escapes from the cocoon has opened a new path, or that the screen of dust, which reflects the light toward the observer became more efficient causing the observed increase of the visual brightness by about 2.5 magnitudes.
A simple phenomenological formula is developed relating one ion energy, the collision energy of an ion and a nucleus at rest in the Earth's atmosphere, to another ion energy, the trajectory energy of the ion before the collision. The resulting formula realizes the possibility that ultra-high energy cosmic rays are products of the supernovae in our Galaxy while recognizing that terrestrial experiments have not yet detected any effect. If the collision-trajectory energy difference is one or two percent for 1 TeV protons at the Tevatron, then a readily apparent difference should occur with a 7 TeV trajectory at the LHC.
We report on recently derived improved versions of the relations between supermassive black hole mass (M_BH) and host-galaxy bulge velocity dispersion (sigma) and luminosity (L) (the M-sigma and M-L relations), based on ~50 M_BH measurements and ~20 upper limits. Particular attention is paid to recovery of the intrinsic scatter (epsilon_0) in both relations. The scatter was found to be significantly larger than estimated in most previous studies. The large scatter requires revision of the local black hole mass function, and it implies that there may be substantial selection bias in studies of the evolution of the M-sigma and M-L relations. When only considering ellipticals, the scatter appears to decrease. These results appear to be insensitive to a wide range of assumptions about the measurement errors and the distribution of intrinsic scatter. We also report on the effects on the fits of culling the sample according to the resolution of the black hole's sphere of influence.
We report the discovery of a large-amplitude oscillation in the hot subdwarf B star CS 1246 and present multi-colour photometry and time-resolved spectroscopy supporting this discovery. We used the 0.41-m PROMPT array to acquire data in the u', g', r', and i' filters simultaneously over 3 consecutive nights in 2009 April. These data reveal a single oscillation mode with a period of 371.707 +/- 0.002 s and an amplitude dependent upon wavelength, with a value of 34.5 +/- 1.6 mma in the u' filter. We detected no additional frequencies in any of the light curves. Subsequently, we used the 4.1-m SOAR telescope to acquire a time-series of 248 low-resolution spectra spanning 6 hrs to look for line profile variations. Models fits to the spectra give mean atmospheric values of Teff = 28450 +/- 700 K and log g = 5.46 +/- 0.11 undergoing variations with semi-amplitudes of 507 +/- 55 K and 0.034 +/- 0.009 dex, respectively. We also detect a radial velocity oscillation with an amplitude of 8.8 +/- 1.1 km/s. The relationship between the angular and physical radii variations shows the oscillation is consistent with a radial mode. Under the assumption of a radial pulsation, we compute the stellar distance, radius, and mass as d = 460 +/- 140 pc, R = 0.19 +/- 0.08 Rsun, and M = 0.39 +/- 0.22 Msun, respectively, using the Baade-Wesselink method.
We present the first description of mode trapping for sdO models. Mode trapping of gravity modes caused by the He/H chemical transition is found for a particular model, providing a selection effect for high radial order trapped modes. Low- and intermediate-radial order {\em p}-modes (mixed modes with a majority of nodes in the P-mode region) are found to be trapped by the C-O/He transition, but with no significant effects on the driving. This region seems to have also a subtle effect on the trapping of low radial order {\em g}-modes (mixed modes with a majority of nodes in the G-mode region), but again with no effect on the driving. We found that for mode trapping to have an influence on the driving of sdO modes (1) the mode should be trapped in a way that the amplitude of the eigenfunctions is lower in a damping region and (2) in this damping region significant energy interchange has to be produced.
The power spectra of 457 short BATSE bursts were analyzed, focusing on the 64 ms lightcurves' tails in the low energy bands. Using MC simulations, 22 GRBs were identified with unusually high harmonic power above 0.03 Hz. The sky distribution of these bursts shows an extraordinarily strong dipole moment with a 99.994% significance.
The direct images of giant extrasolar planets recently obtained around several main sequence stars represent a major step in the study of planetary systems. These high-dynamic range images are among the most striking results obtained by the current generation of high angular resolution instruments, which will be superseded by a new generation of instruments in the coming years. It is therefore an appropriate time to review the contributions of high angular resolution visible/infrared techniques to the rapidly growing field of extrasolar planetary science. During the last 20 years, the advent of the Hubble Space Telescope, of adaptive optics on 4- to 10-m class ground-based telescopes, and of long-baseline infrared stellar interferometry has opened a new viewpoint on the formation and evolution of planetary systems. By spatially resolving the optically thick circumstellar discs of gas and dust where planets are forming, these instruments have considerably improved our models of early circumstellar environments and have thereby provided new constraints on planet formation theories. High angular resolution techniques are also directly tracing the mechanisms governing the early evolution of planetary embryos and the dispersal of optically thick material around young stars. Finally, mature planetary systems are being studied with an unprecedented accuracy thanks to single-pupil imaging and interferometry, precisely locating dust populations and putting into light a whole new family of long-period giant extrasolar planets.
GRB 080319B is one of the brightest and most extensively sampled bursts. It has good coverage at many wavelengths. Here we present the optical observations of the Palomar 60 inch telescope, which spans a long time interval after the burst. We augment the optical dataset with freely available Swift BAT and XRT observations reduced by us. We also compare our conclusions with the published parameters from the rich literature about this burst.
The performance of nine RHESSI germanium detectors has been gradually deteriorating since its launch in 2002 because of radiation damage caused by passing through the Earth's radiation belts. To restore its former sensitivity, the spectrometer underwent an annealing procedure in November 2007. It, however, changed the RHESSI response and affected gamma-ray burst measurements, e.g., the hardness ratios and the spectral capabilities bellow approximately 100 keV.
As GRBs trace the high-z Universe, there is a non-negligible probability of a lensing effect being imprinted on the lightcurves of the bursts. We propose to search for lensed candidates with a cross-correlation method, by looking at bursts days to years apart coming from the same part of the sky. We look for similarities and hypothesize a Singular Isothermal Sphere (SIS) model for the lens. A lensed pair would enable us to constrain the mass of the lensing object. Our search did not reveal any gravitationally lensed events.
We develop a novel maximum a posterior method to measure magnetic power spectra from Faraday rotation data and implement it in the REALMAF code. Using a sophisticated model for the magnetic autocorrelation in real space permits us to alleviate previously required simplifying assumptions in the processing. We also introduce a way to treat the divergence relation of the magnetic field with a multiplicative factor in Fourier space, which allows us to model the magnetic autocorrelation as a spherically symmetric function. Applied to the dataset of Hydra A north, we find a power law power spectrum between spatial scales of 0.3 kpc to 8 kpc, with no visible turnover at large scales within this range and a spectral index consistent with a Kolmogorov-like power law regime. The magnetic field strength profile seems to follow the electron density profile with an index alpha=1. A variation of alpha from 0.5 to 1.5 would lead to a spectral index between 1.55 and 2.05. The extrapolated magnetic field strength in the cluster center highly depends on the assumed projection angle of the jet. For an angle of 45 degree we get 36 muG in the center and directly probed 16 muG at 50 kpc radius.
A sample of almost 400 Gamma-ray bursts (GRBs) detected by the RHESSI satellite is studied statistically. We focus on GRB duration and hardness ratio and use the statistical chi^2 test and the F-test to compare the number of GRB subgroups in the RHESSI database with that of the BATSE database. Although some previous articles based on the BATSE catalog claim the existence of an intermediate GRB subgroup, besides long and short, we have not found a statistically significant intermediate subgroup in the RHESSI data.
The Gamma-ray burst (GRB) database based on the data by the RHESSI satellite provides a unique and homogeneous database for future analyses. Here we present preliminary results on the duration and hardness ratio distributions for a sample of 228 GRBs observed with RHESSI.
Some articles based on the BATSE gamma-ray burst (GRB) catalog claim the existence of a third population of GRBs, besides long and short. In this contribution we wanted to verify these claims with an independent data source, namely the RHESSI GRB catalog. Our verification is based on the statistical analysis of duration and hardness ratio of GRBs. The result is that there is no significant third group of GRBs in our RHESSI GRB data-set.
Galaxies are composed of baryonic stars and gas embedded in dark matter halos. Here I briefly review two aspects of the connection between baryons and their halos. (1) The observed baryon content of galaxies falls short of the cosmic baryon fraction by an amount that varies systematically with mass. Where these missing baryons now reside is unclear. (2) The characteristic acceleration in disk galaxies correlates strongly with their baryonic mass surface density. This implies a close coupling between the gravitational dynamics, which is presumably dominated by dark matter, and the purely baryonic components of galaxies.
To constrain the giant pulse (GP) emission mechanism and test the model of Lyutikov (2007) of GP emission, we are carrying out a campaign of simultaneous observations of the Crab pulsar between gamma-rays (Fermi) and radio wavelengths. The correlation between times of arrival of radio GPs and high-energy photons, whether it exists or not, will allow us to choose between different origins of GP emission and further constrain the emission physics. Our foremost goal was testing whether radio GPs are due to changes in the coherence of the radio emission mechanism, variations in the pair creation rate in the pulsar magnetosphere, or changes in the beaming direction. Accomplishing this goal requires an enormous number of simultaneous radio GPs and gamma-photons. Thus, we organized a radio observations campaign using the 42-ft telescope at the Jodrell Bank Observatory (UK), the 140-ft telescope, and the 100-m Richard C. Byrd Green Bank Telescope (GBT) at the Green Bank Observatory (WV). While the observations with the two first ones are ongoing, here we present the preliminary results of 20 hrs of observations with the GBT at the high frequency of 8.9 GHz. These particular observations were aimed to probe the model of GP emission by Lyutikov (2007) which predicts that GPs at frequencies > 4 GHz should be accompanied by gamma -ray photons of energies of 1-100 GeV.
A sample of 286 gamma-ray bursts (GRBs) detected by the Swift satellite and 358 GRBs detected by the RHESSI satellite are studied statistically. Previously published articles, based on the BATSE GRB Catalog, claimed the existence of an intermediate subgroup of GRBs with respect to duration. We use the statistical chi^2 test and the F-test to compare the number of GRB subgroups in our databases with the earlier BATSE results. Similarly to the BATSE database, the short and long subgroups are well detected in the Swift and RHESSI data. However, contrary to the BATSE data, we have not found a statistically significant intermediate subgroup in either Swift or RHESSI data.
Since its launch in June 2008, the Large Area Telescope (LAT), onboard the \emph{Fermi} Gamma-ray Space Telescope, has greatly added to our understanding of gamma-ray pulsars. Its fine point spread function and large effective area, combined with the time-differencing method, make it the first gamma-ray instrument capable of discovering a new population of gamma-ray pulsars. We will present the recent discovery of the youngest (~4600 yr) radio-quiet gamma-ray pulsar discovered in a blind frequency search so far: PSR J1022-5746, a pulsar associated with an extended TeV source. We also present multiwavelength observations of the source, including X-ray observations.
Some of the very high energy gamma rays observed from distant Active Galactic Nuclei (AGN) could be the secondary photons produced in the interactions of cosmic ray protons emitted by the AGN with the photon background along the line of sight. We discuss the predictions of this model for the upcoming observations of ultrahigh-energy neutrino sources with IceCube and other neutrino telescopes, which can help distinguish between the primary and secondary photons and can help improve understanding of intergalactic magnetic fields, extragalactic background light, and the acceleration mechanisms of cosmic rays.
In this paper, we compare some popular dark energy models with the assumption of a flat universe by using the latest observational data including the type Ia supernovae Constitution compilation, the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey and the Two Degree Field Galaxy Redshift Survey, and the cosmic microwave background measurement given by the five-year Wilkinson Microwave Anisotropy Probe observations. Model comparison statistics such as the Bayesian and Akaike information criteria are applied to assess the worth of the models. These statistics favor models that give a good fit with fewer parameters. Based on this analysis, we find that the simplest cosmological constant model that has only one free parameter is still preferred by the current data. For other dynamical dark energy models, we find that some of them, such as the $\alpha$ dark energy, constant $w$, generalized Chaplygin gas, and holographic dark energy models, can provide good fits to the current data, and three of them, namely, the agegraphic dark energy, Dvali-Gabadadze-Porrati, and Ricci dark energy models, are clearly disfavored by the data.
I show that the 17th century eruption of the massive luminous blue variable (LBV) star P Cygni can be explained by mass transfer to a B-type binary companion in an eccentric orbit, under the assumption that the luminosity peaks occurred at periastron passages. The mass was accreted by the companion and liberated gravitational energy, part of which went to an increase in luminosity. I find that mass transfer of ~0.1 solar masses to a B-type binary companion of ~3-6 solar masses can account for the energy of the eruption, and for the decreasing time interval between the observed peaks in the visual light curve of the eruption. Such a companion is predicted to have an orbital period of ~7 years, and its Doppler shift should be possible to detect with high spectral resolution observations. Explaining the eruption of P Cygni by mass transfer further supports the idea that all major LBV eruptions are triggered by interaction of an unstable LBV with a stellar companion.
Chandra [1] made an attempt to show that the work of Dwivedi and Srivastava [2] (hereinafter DS) can be investigated even analytically and their results are erroneous. Dwivedi and Srivastava [3] picked up some values of Chandra [1] and tried to show that they are not physically acceptable. Some results of Chandra [1] are not physically acceptable, as these are the outcome of the wrong approach of DS. However, the results are numerically correct whereas the results of DS are numerically wrong.
Pandey & Dwivedi (2007) again tried to claim that the dispersion relation for the given set of equations must be a sixth degree polynomial. Through a series of papers, they are unnecessarily creating confusion. In the present communication, we have shown how Pandey & Dwivedi (2007) are introducing an additional root, which is insignificant. Moreover, five roots of both the polynomials are common and they are sufficient for the discussion of propagation of slow-mode and fast-mode waves.
(Abridged) Turbulence in the solar wind is believed to generate an energy cascade that is supported primarily by Alfv\'en waves or Alfv\'enic fluctuations at MHD scales and by kinetic Alfv\'en waves (KAWs) at kinetic scales $k_\perp \rho_i\gtrsim 1$. Linear Landau damping of KAWs increases with increasing wavenumber and at some point the damping becomes so strong that the energy cascade is completely dissipated. A model of the energy cascade process that includes the effects of linear collisionless damping of KAWs and the associated compounding of this damping throughout the cascade process is used to determine the wavenumber where the energy cascade terminates. It is found that this wavenumber occurs approximately when $|\gamma/\omega|\simeq 0.25$, where $\omega(k)$ and $\gamma(k)$ are, respectively, the real frequency and damping rate of KAWs and the ratio $\gamma/\omega$ is evaluated in the limit as the propagation angle approaches 90 degrees relative to the direction of the mean magnetic field.
The Large Area Telescope (LAT) on board the \textit{Fermi} Gamma-ray Space Telescope discovered a rapid (about 5 days duration), high-energy (E >100 MeV) gamma-ray outburst from a source identified with the blazar PKS 1502+106 (OR 103, S3 1502+10, z=1.839) starting on August 05, 2008 and followed by bright and variable flux over the next few months. Results on the gamma-ray localization and identification, as well as spectral and temporal behavior during the first months of the Fermi all-sky survey are reported here in conjunction with a multi-waveband characterization as a result of one of the first Fermi multi-frequency campaigns. The campaign included a Swift ToO (followed up by 16-day observations on August 07-22, MJD 54685-54700), VLBA (within the MOJAVE program), Owens Valley (OVRO) 40m, Effelsberg-100m, Metsahovi-14m, RATAN-600 and Kanata-Hiroshima radio/optical observations. Results from the analysis of archival observations by INTEGRAL, XMM-Newton and Spitzer space telescopes are reported for a more complete picture of this new gamma-ray blazar.
Since VLBI techniques give microarcsecond position accuracy of celestial objects, tests of GR using radio sources as probes of a gravitational field have been made. We present the results from two recent tests using the VLBA: In 2005, the measurement of the classical solar deflection; and in 2002, the measurement of the retarded gravitational deflection associated with Jupiter. The deflection experiment measured PPN-gamma to an accuracy of 0.0003; the Jupiter experiment measured the retarded term to 20% accuracy. The controversy over the interpretation of the retarded term is summarized.
We investigate the most plausible stellar Initial Mass Function (IMF) and the main origin of the tilt of the Fundamental Plane (FP) for old, massive early-type galaxies. We consider a sample of 13 bright galaxies of the Coma cluster and combine our results with those obtained from a sample of 57 lens galaxies in the same luminous mass range. We estimate the luminous mass and stellar mass-to-light ratio values of the sample galaxies by fitting their SDSS multi-band photometry with composite stellar population models computed with different dust-free, solar-metallicity templates and IMFs. We compare these measurements and those derived from two-component orbit-based dynamical modelling. The photometric and dynamical luminous mass estimates of the galaxies in our sample are consistent, within the errors, if a Salpeter IMF is adopted. On the contrary, with a Kroupa or Chabrier IMF the two luminous mass diagnostics differ at a more than 4 \sigma level. For the massive Coma galaxies, their stellar mass-to-light ratio scales with luminous mass as the corresponding effective quantities are observed to scale on the FP. This indicates that the tilt of the FP is primarily caused by stellar population properties. We conclude that old, massive lens and non-lens early-type galaxies obey the same luminous and dynamical scaling relations, favour a Salpeter IMF, and suggest a stellar population origin for the tilt of the FP. The validity of these results for samples of early-type galaxies with different age and mass properties still remains to be tested.
We report unfiltered CCD observations of the first confirmed superoutburst of the dwarf nova RX J1715.6+6856 in August 2009. At quiescence the star was magnitude 18.3 (CCD, clear). The outburst amplitude was at least 2.4 magnitudes and it lasted at least 6 days, although the first part of the outburst was probably missed. Analysis of the light curve revealed superhumps with peak-to-peak amplitude of 0.1 magnitude, thereby showing it to be a member of the SU UMa family. The mean superhump period was Psh = 0.07086(78) d with a superhump period excess of epsilon = 0.038 and an estimated mass ratio q = 0.167. In the final stages of the outburst, as the star approached quiescence, the superhumps disappeared to be replaced by a modulation corresponding to the orbital period. The star was regularly monitored between August 2007 and September 2009 revealing a total of 12 outbursts, with an outburst frequency of approximately once per month.
We develop the XFaster Cosmic Microwave Background (CMB) temperature and polarization anisotropy power spectrum and likelihood technique for the Planck CMB satellite mission. We give an overview of this estimator and its current implementation and present the results of applying this algorithm to simulated Planck data. We show that it can accurately extract the power spectrum of Planck data for the high-l multipoles range. We compare the XFaster approximation for the likelihood to other high-l likelihood approximations such as Gaussian and Offset Lognormal and a low-l pixel-based likelihood. We show that the XFaster likelihood is not only accurate at high-l, but also performs well at moderately low multipoles. We also present results for cosmological parameter Markov Chain Monte Carlo estimation with the XFaster likelihood. As long as the low-l polarization and temperature power are properly accounted for, e.g., by adding an adequate low-l likelihood ingredient, the input parameters are recovered to a high level of accuracy.
We comment on the recent paper by Srivastava and Dwivedi (J. Astrophs. Astr. {\bf 28}, 1, 2007). In the said paper the derived dispersion relation $\nu \eta \cos^4 \theta k^4 + [v_A^2 - i \omega (\nu + \eta)] \cos^2 \theta k^2 - \omega^2 = 0$ seems to be in error. Consequently, the conclusion drawn in their paper are not reliable.
We present the mass-X-ray observable scaling relationships for clusters of galaxies using the XMM-Newton cluster catalog of Snowden et al. Our results are roughly consistent with previous observational and theoretical work, with one major exception. We find 2-3 times the scatter around the best fit mass scaling relationships as expected from cluster simulations or seen in other observational studies. We suggest that this is a consequence of using hydrostatic mass, as opposed to virial mass, and is due to the explicit dependence of the hydrostatic mass on the gradients of the temperature and gas density profiles. We find a larger range of slope in the cluster temperature profiles at r_{500} than previous observational studies. Additionally, we find only a weak dependence of the gas mass fraction on cluster mass, consistent with a constant. Our average gas mass fraction results argue for a closer study of the systematic errors due to instrumental calibration and analysis method variations. We suggest that a more careful study of the differences between various observational results and with cluster simulations is needed to understand sources of bias and scatter in cosmological studies of galaxy clusters.
We present multiwavelength linear polarimetric observations of 104 stars towards the region of young open cluster NGC 6823. The polarization towards NGC 6823 is dominated by foreground dust grains and we found the evidence for the presence of several layers of dust towards the line of sight. The first layer of dust is located approximately within 200 pc towards the cluster, which is much closer to the Sun than the cluster (~ 2.1 kpc). The radial distribution of the position angles for the member stars are found to show a systematic change while the polarization found to reduce towards the outer parts of the cluster and the average position angle of coronal region of the cluster is very close to the inclination of the Galactic parallel (~ 32 degree). The size distribution of the grains within NGC 6823 is similar to those in general interstellar medium. The patchy distribution of foreground dust grains are suggested to be mainly responsible for the both differential reddening and polarization towards NGC 6823. The majority of the observed stars do not show the evidence of intrinsic polarization in their light.
Recent accurate abundance analyses of B-type main sequence stars in the solar vicinity has shown that abundances derived from these stellar objects are more homogeneous and metal-rich than previously thought. We investigate whether the inhomogeneity of abundances previously found in B-type stars in the Ori OB1 association is real (hence a signature of enrichment of the newly formed stars in an induced star formation scenario) or a consequence of intrinsic errors induced by the use of photometric indices to establish the stellar parameters prior to the abundance analysis. We obtained a new (improved) spectroscopic data set comprising 13 B-type stars in the various Ori OB1 associations, and performed a detailed, self-consistent spectroscopic abundance analysis by means of the modern stellar atmosphere code FASTWIND. We detect systematic errors in the stellar parameters determined previously which affect the derived abundances. Once these errors are accounted for, we find a high degree of homogeneity in the O and Si abundances for stars in the four Ori OB1 subgroups. The derived abundances are in very good agreement with recent determinations in other B-type stars in the solar vicinity. We also compare our results with those obtained for the Sun during the epoch of the "solar crisis", and the Orion nebula.
Thanks to the high multiplex and efficiency of Giraffe at the VLT we have been able for the first time to observe the Li I doublet in the Main Sequence (MS) stars of a Globular Cluster. At the same time we observed Li in a sample of Sub-Giant (SG) stars of the same B-V colour. Our final sample is composed of 84 SG stars and 79 MS stars. In spite of the fact that SG and MS span the same temperature range we find that the equivalent widths of the Li I doublet in SG stars are systematically larger than those in MS stars, suggesting a higher Li content among SG stars. This is confirmed by our quantitative analysis. We derived the effective temperatures, from H$\alpha$ fitting, and NLTE Li abundances of the stars in our the sample, using 3D and 1D models. We find that SG stars have a mean Li abundance higher by 0.1dex than MS stars, using both 1D and 3D models. We also detect a positive slope of Li abundance with effective temperature. These results provide an unambiguous evidence that the Li abundance changes with evolutionary status. The physical mechanisms responsible for this behaviour are not yet clear, and none of the existing models seems to describe accurately these observations. Based on these conclusions, we believe that the cosmological lithium problem still remains an open question.
As an alternative to dark energy it has been suggested that we may be at the
center of an inhomogeneous isotropic universe described by a
Lemaitre-Tolman-Bondi (LTB) solution of Einstein's field equations. We
calculate the low redshift expansion of the luminosity distance $D_L(z)$ and
the redshift spherical shell mass density $mn(z)$ for a central observer in a
LTB space without cosmological constant and show how they can fit the
observations implied by a $\Lambda CDM $ model if the conditions to avoid a
central singularity are not imposed. Our results are in agreement with
numerical attempts to solve the inversion problem, where clear signs of the
presence of singularities have emerged.
Another important consequence of our calculation is that it is impossible to
solve the inversion problem for both $mn(z)$ and $D_L(z)$ setting one the two
functions $k(r)$ or $t^b(r)$ to zero, even allowing singularities, since we
would then have only five independent parameters, and six equations to solve.
This analytical form of the local solution of the inversion problem provides a
useful tool to better interpret the results of numerical calculations, and to
make a general statement about how many independent observables can be
reproduced.
We computed the power spectrum of weak cosmic shear in models with non-Gaussian primordial density fluctuations. Cosmological initial conditions deviating from Gaussianity have recently attracted much attention in the literature, especially with respect to their effect on the formation of non-linear structures and because of the bounds that they can put on the inflationary epoch. The fully non-linear matter power spectrum was evaluated with the use of the physically motivated, semi-analytic halo model, where the mass function and linear halo bias were suitably corrected for non-Gaussian cosmologies. In agreement with previous work, we found that a level of non-Gaussianity compatible with CMB bounds and with positive skewness produces an increase in power of the order of a few percent at intermediate scales. We then used the matter power spectrum, together with observationally motivated background source redshift distributions in order to compute the cosmological weak lensing power spectrum. We found that the degree of deviation from the power spectrum of the reference Gaussian model is small compared to the statistical error expected from even future weak lensing surveys. However, summing the signal over a large range of multipoles can beat down the noise, bringing to a significant detection of non-Gaussianity at the level of $|f_\mathrm{NL}| \simeq $ few tens, when all other cosmological parameters are held fixed. Finally, we have shown that the constraints on the level of non-Gaussianity can be improved by $\sim 20%$ with the use of weak lensing tomography.
Rapid Oscillations in the Solar Atmosphere (ROSA) is a synchronized, six camera high cadence solar imaging instrument developed by Queen's University Belfast. The system is available on the Dunn Solar Telescope at the National Solar Observatory in Sunspot, New Mexico, USA as a common-user instrument. Consisting of six 1k x 1k Peltier-cooled frame-transfer CCD cameras with very low noise (0.02-15 e/s/pixel), each ROSA camera is capable of full-chip readout speeds in excess of 30 Hz, or 200 Hz when the CCD is windowed. Combining multiple cameras and fast readout rates, ROSA will accumulate approximately 12 TB of data per 8 hours observing. Following successful commissioning during August 2008, ROSA will allow multi-wavelength studies of the solar atmosphere at high temporal resolution.
The determination of ages of central stars of planetary nebulae (CSPN) is a complex problem, and there is presently no single method that can be generally applied. We have developed several methods to estimate the ages of CSPN, based both on the observed nebular properties and in some properties of the stars themselves.Our aim is to estimate the ages and the age distribution of CSPN and to compare the derived results with mass and age determinations of CSPN and white dwarfs based on empirical determinations of these quantities. We discuss several methods to derive the age distribution of CSPN, namely, (i) the use of an age-metallicity relation that also depends on the galactocentric distance, (ii) the use of an age-metallicity relation obtained for the galactic disk, and (iii) the determination of ages from the central star masses obtained from the observed nitrogen abundances. We consider a sample of planetary nebulae in the galactic disk, most of which ($\sim$ 69%) are located in the solar neighbourhood, within 3 kpc from the Sun. We estimate the age distribution of CSPN with average uncertainties of 1-2 Gyr, and compare our results with the expected distribution based both on the observed mass distribution of white dwarfs and on the age distribution derived from available mass distributions of CSPN. We conclude most CSPN in the galactic disk have ages under 6 Gyr, and that the age distribution is peaked around 2-4 Gyr.
RT-2 Experiment (RT - Roentgen Telescope) is a low energy gamma-ray
instrument which is designed and developed as a part of Indo-Russian
collaborative project of CORONAS-PHOTON Mission to study the Solar flares in
wide energy band of electromagnetic spectrum ranging from UV to high-energy
gamma-rays (~2000 MeV).
RT-2 instruments will cover the energy range of 15 keV to 150 keV extendable
up to ~1 MeV. It consists of three detectors (two Phoswich detectors, namely,
RT-2/S, RT-2/G and one solid-state imaging detector RT-2/CZT) and one
processing electronic device (RT-2/E). Both Phoswich detectors will have time
resolved spectrum, whereas the solid-state imaging detector will have high
resolved image of the solar flares in hard X-rays. We have used Co-57 (122 keV)
radio-active source for onboard calibration of all three detectors. In this
paper, we briefly discuss the in-flight performance of RT-2 instruments and
present initial flight data from the instruments.
This mission was launched into polar LEO (Low Earth Orbit) (~550 km) on 30th
January 2009 from Plesetsk Cosmodrome, Russia.
Combination of Fresnel Zone Plates (FZP) can make excellent telescopes for imaging in X-rays. We present the results of our experiments with such telescopes with an X-ray source kept at a distance of 45 feet. We compare the patterns obtained from experiments with those obtained by our Monte-Carlo simulations. In simulations, we allow the sources to be at finite distances (diverging beam) as well as at infinite distances (parallel beam) and show that the resolution is worsened when the source is nearby. We also present simulated results for the observation of the galactic center and show that the sources may be reconstructed with accuracy. We compare the performance of such a telescope with other X-ray imaging devices used in space-astronomy. The Zone Plate based instrument has been sent for the first time in a recently launched KORONAS-FOTON satellite.
Rotation and magnetic activity are intimately linked in main-sequence stars of G or later spectral types. The presence and level of magnetic activity depend on stellar rotation, and rotation itself is strongly influenced by strength and topology of the magnetic fields. Open clusters represent especially useful targets to investigate the rotation/activity/age connection. The open cluster M11 has been studied as a part of the RACE-OC project (Rotation and ACtivity Evolution in Open Clusters), which is aimed at exploring the evolution of rotation and magnetic activity in the late-type members of open clusters with different ages. Photometric observations of the open cluster M11 were carried out in June 2004 using LOAO 1m telescope. The rotation periods of the cluster members are determined by Fourier analysis of photometric data time series. We further investigated the relations between the surface activity, characterized by the light curve amplitude, and rotation. We have discovered a total of 75 periodic variables in the M11 FoV, of which 38 are candidate cluster members. Specifically, among cluster members we discovered 6 early-type, 2 eclipsing binaries and 30 bona-fide single periodic late-type variables. Considering the rotation periods of 16 G-type members of the almost coeval 200-Myr M34 cluster, we could determine the rotation period distribution from a more numerous sample of 46 single G stars at an age of about 200-230 Myr and determine a median rotation period P=4.8d. A comparison with the younger M35 cluster (~150 Myr) and with the older M37 cluster (~550 Myr) shows that G stars rotate slower than younger M35 stars and faster than older M37 stars. The measured variation of the median rotation period is consistent with the scenario of rotational braking of main-sequence spotted stars as they age.
We test cosmological models of structure formation using the rotation curve of the nearest spiral galaxy, M31, determined using a recent deep, full-disk 21-cm imaging survey smoothed to 466 pc resolution. We fit a tilted ring model to the HI data from 8 to 37 kpc. The disk of M31 warps from 25 kpc outwards and becomes more inclined with respect to our line of sight. Newtonian dynamics without a dark matter halo provide a very poor fit to the rotation curve derived using the warp model. In the framework of modified Newtonian dynamic however the 21-cm rotation curve is well fitted by the gravitational potential traced by the baryonic matter density alone. The inclusion of a dark matter halo with a density profile as predicted by structure formation in a hierarchical clustering LambdaCDM cosmology makes the mass model in newtonian dynamic compatible with the rotation curve data. The dark halo concentration for the best fit is C=12 and its total mass is 1.2 10^{12} Msun. If a dark halo model with a constant density core is considered, the core radius has to be larger than 20 kpc in order for the model to fit to the data. We extrapolate the best-fit LambdaCDM and constant-density core mass models to very large galactocentric radii, comparable to the size of the dark matter halo. A comparison of the predicted mass with the M31 mass determined at such large radii using other dynamical tracers, confirms the validity of our results. In particular the LambdaCDM dark halo model which best fits the 21-cm data well reproduces the M31 mass traced out to 560 kpc. Our estimated total mass of M31 is 1.3 10^{12} Msun, with 12% baryonic fraction and only 6% of the baryons in neutral gas.
The most promising mechanism acting towards damping the kink oscillations of coronal loops is resonant absorption. In this context most of previous studies neglected the effect of the obvious equilibrium flow along magnetic field lines. The flows are in general sub-Alfv\'enic and hence comparatively slow. Here we investigate the effect of an equilibrium flow on the resonant absorption of linear kink MHD waves in a cylindrical magnetic flux tube with the aim of determining the changes in the frequency of the forward and backward propagating waves and in the modification of the damping times due to the flow. A loop model with both the density and the longitudinal flow changing in the radial direction is considered. We use the thin tube thin boundary (TTTB) approximation in order to calculate the damping rates. The full resistive eigenvalue problem is also solved without assuming the TTTB approximation. Using the small ratio of flow and Alfv\'en speeds we derive simple analytical expressions to the damping rate. The analytical expressions are in good agreement with the resistive eigenmode calculations. Under typical coronal conditions the effect of the flow on the damped kink oscillations is small when the characteristic scale of the density layer is similar or smaller than the characteristic width of the velocity layer. However, in the opposite situation the damping rates can be significantly altered, specially for the backward propagating wave which is undamped while the forward wave is overdamped.
The study of short-duration gamma-ray bursts (GRBs) has undergone a revolution in recent years thanks to the discovery of the first afterglows and host galaxies in May 2005. In this review we summarize our current knowledge of the galactic and sub-galactic environments of short GRBs, and the implications for the progenitor population. The most crucial results are: (i) some short GRBs occur in elliptical galaxies; (ii) the majority of short GRBs occur in star forming galaxies; (iii) the star forming hosts of short GRBs are distinct from the host galaxies of long GRBs in terms of star formation rates, luminosities, and metallicities, and instead appear to be drawn from the general field galaxy population; (iv) the physical offsets of short GRBs relative to their host galaxy centers are significantly larger than for long GRBs; (v) the observed offset distribution agrees well with predictions for the locations of NS-NS binary mergers; and (vi) unlike long GRBs, which tend to occur in the brightest regions of their hosts, the environments of short GRBs generally under-represent the light distribution of their host galaxies. Taken together, these observations suggest that short GRB progenitors have a wide age distribution and generally track stellar mass rather than star formation activity. These results are fully consistent with NS-NS binary mergers, but partial contribution from prompt or delayed magnetar formation is also consistent with the data.
Current models of galaxy formation lack an efficient and physically constrained mechanism to regulate star formation (SF) in low and intermediate mass galaxies. We argue that the missing ingredient could be the effect of photoionization by local sources on the gas cooling. We show that the soft X-ray and EUV flux generated by SF is able to efficiently remove the main coolants (e.g., HeII, OV and FeIX) from the halo gas via direct photoionization. As a consequence, the cooling and accretion time of the gas surrounding star-forming galaxies may increase by one or two orders of magnitude. For a given halo mass and redshift, the effect is directly related to the value of the star formation rate (SFR). Our results suggest the existence of a critical SFR above which "cold" mode accretion is stopped, even for haloes with virial masses well below the critical shock-heating mass suggested by previous studies.The evolution of the critical SFR with redshift, for a given halo mass, resembles the respective steep evolution of the observed SFR for z<1. This suggests that photoionization by local sources would be able to regulate gas accretion and star formation, without the need for additional, strong feedback processes.
Cosmic-ray energy densities in central regions of starburst galaxies, as inferred from radio and gamma-ray measurements of, respectively, non-thermal synchrotron and neutral pion decay emission, are typically U_p = O(100)eV/cm3, i.e. typically at least an order of magnitude larger than near the Galactic center and in other non-very-actively star-forming galaxies. We first show that these very different energy-density levels reflect a similar disparity in the respective supernova rates in the two environments, which is not unexpected given the supernova origin of (Galactic) energetic particles. As a consequence of this correspondence, we then demonstrate that there is partial quantitative evidence that the stellar initial mass function (IMF) in starburst nuclei has a low-mass truncation at ~2M_sun, as predicted by theoretical models of turbulent media, in contrast with the much smaller value of 0.1M_sun that characterizes the low-mass cutoff of the stellar IMF in `normal' galactic environments.
Recent work on the luminosities of type II Cepheids (CephIIs) and RR Lyrae variables is reviewed.In the near infrared (JHKs) the CephIIs in globular clusters show a narrow, linear, period-luminosity relation over their whole period range (about 1 to 100 days). The CephIIs in the general field of the LMC follow this relation for periods shorter than about 20 days. At longer period (the region of the RV Tau stars), the LMC field stars have a significant scatter and in the mean are more luminous than the PL relation. The OGLEIII optical data for the LMC field variables show similar trends. Infrared colours of stars in the RV Tau period range show marked mean differences between three groupings; the Galactic field, the LMC field, and globular clusters. In the case of the Galactic field, at least, this may be strongly influenced by selection effects. In the period range about 4 to 20 days (the W Vir range) there are stars lying above the PL relation which may be recognized by their light curves and are all likely to be binaries. The bright Galactic variable, kappa Pav probably belongs to this group. There is evidence that CephIIs in the general field (LMC and Galaxy) have a wider range of masses than those in globular clusters. At present the CephII PL zero-point depends on the pulsation parallaxes of two stars. Zero-points of RR Lyrae M(V)-[Fe/H] and Ks-log P relations can be obtained from trigonometrical, statistical and pulsation parallaxes. These zero-points are compared with those for CephIIs and with the classical Cepheid scale using variables of these three types in the LMC. Within the uncertainties (about 0.1mag) the various scales are in agreement.
We report on observations of the Large Magellanic Cloud with the Fermi Gamma-Ray Space Telescope. The LMC is clearly detected with the Large Area Telescope (LAT) and for the first time the emission is spatially well resolved in gamma-rays. Our observations reveal the massive star forming region 30 Doradus as a bright source of gamma-ray emission in the LMC. The observations furthermore show that the gamma-ray emission correlates little with the gas density of the LMC. Implications of this finding will be discussed.
Current mass-loss rate estimates imply that main sequence winds are not sufficient to strip away the H-rich envelope to yield Wolf-Rayet (WR) stars. The rich transitional population of Westerlund 1 (Wd 1) provides an ideal laboratory to observe mass-loss processes throughout the transitional phase of stellar evolution. An analysis of deep radio continuum observations of Wd 1 is presented. We detect 18 cluster members. The radio properties of the sample are diverse, with thermal, non-thermal and composite thermal/non-thermal sources present. Mass-loss rates are ~10^{-5} solar mass/year across all spectral types, insufficient to form WRs during a massive star lifetime, and the stars must undergo a period of enhanced mass loss. The sgB[e] star W9 may provide an example, with a mass-loss rate an order of magnitude higher than the other cluster members, and an extended nebula of density ~3 times the current wind. This structure is reminiscent of luminous blue variables, and one with evidence of two eras of high, possibly eruptive, mass loss. Three OB supergiants are detected, implying unusually dense winds. They also may have composite spectra, suggesting binarity. Spatially resolved nebulae are associated with three of the four RSGs and three of the six YHGs in the cluster, which are due to quiescent mass loss rather than outbursts. For some of the cool star winds, the ionizing source may be a companion star though the cluster radiation density is sufficiently high to provide the necessary ionizing radiation. Five WR stars are detected with composite spectra, interpreted as arising in colliding-wind binaries.
We present a study of the X-ray to optical properties of a sample of 545 X-ray selected Type 1 AGN, from the XMM-COSMOS survey, over a wide range of redshifts ($0.04<\z<4.25$) and X-ray luminosities ($40.6 \leq \Log \Lhard \leq 45.3$). About 60% of them are spectroscopically identified Type 1 AGN, while the others have a reliable photometric redshift and are classified as Type 1 AGN on the basis of their multi-band Spectral Energy Distributions. We discuss the relationship between UV and X-ray luminosity, as parameterized by the $\alphaox$ spectral slope, and its dependence on redshift and luminosity. We compare our findings with previous investigations of optically selected broad-line AGN (mostly from SDSS). A highly significant correlation between $\alphaox$ and $\lo$ is found, in agreement with previous investigations of optically selected samples. We calculate bolometric corrections, $\kbol$, for the whole sample using hard X-ray luminosities ($\Lhard$), and the Eddington ratios for a subsample of 150 objects for which black hole mass estimates are available. We confirm the trend of increasing bolometric correction with increasing Eddington ratio as proposed in previous works. A tight correlation is found between $\alphaox$ and $\kbol$, which can be used to estimate accurate bolometric corrections using only optical and X-ray data. We find a significant correlation between $\alphaox$ and Eddington ratio, in which $\alphaox$ increases for increasing Eddington ratios.
The new release of the SPECFIND radio cross-identification catalogue,
SPECFIND V2.0, is presented. It contains 107488 cross-identified objects with
at least three radio sources observed at three independent frequencies.
Compared to the previous release the number of entry radio catalogues is
increased from 20 to 97 containing 115 tables. This large increase was only
made possible by the development of four tools at CDS which use the standards
and infrastructure of the Virtual Observatory (VO). This was done in the
framework of the VO-TECH European Design Study of the Sixth Framework Program.
We give an overview of the different classes of radio sources that a user can
encounter. Due to the increase of frequency coverage of the input radio
catalogues, this release demonstrates that the SPECFIND algorithm is able to
detect spectral breaks around a frequency of ~1 GHz.
We investigate the shear viscosity of neutron star matter in the presence of an antikaon condensate. The electron and muon number densities are reduced due to the appearance of a $K^-$ condensate in neutron star matter, whereas the proton number density increases. Consequently the shear viscosity due to scatterings of electrons and muons with themselves and protons is lowered compared to the case without the condensate. On the other hand, the contribution of proton-proton collisions to the proton shear viscosity through electromagnetic and strong interactions, becomes important and comparable to the neutron shear viscosity.
The globular cluster $\omega$ Centauri (NGC 5139) is a puzzling stellar system harboring several distinct stellar populations whose origin still represents a unique astrophysical challenge. Current scenarios range from primordial chemical inhomogeneities in the mother cloud to merging of different sub-units and/or subsequent generations of enriched stars - with a variety of different pollution sources- within the same potential well. In this paper we study the chemical abundance pattern in the outskirts of Omega Centauri, half-way to the tidal radius (covering the range of 20-30 arcmin from the cluster center), and compare it with chemical trends in the inner cluster regions, in an attempt to explore whether the same population mix and chemical compositions trends routinely found in the more central regions is also present in the cluster periphery.We extract abundances of many elements from FLAMES/UVES spectra of 48 RGB stars using the equivalent width method and then analyze the metallicity distribution function and abundance ratios of the observed stars. We find, within the uncertainties of small number statistics and slightly different evolutionary phases, that the population mix in the outer regions cannot be distinguished from the more central regions, although it is clear that more data are necessary to obtain a firmer description of the situation. From the abundance analysis, we did not find obvious radial gradients in any of the measured elements.
A long-range force acting only between nonbaryonic particles would be associated with a large violation of the weak equivalence principle. We explore cosmological consequences of this idea, which we label ReBEL (daRk Breaking Equivalence principLe). A high resolution hydrodynamical simulation of the distributions of baryons and dark matter confirms our previous findings that a ReBEL force of comparable strength to gravity on comoving scales of about 1 Mpc/h causes voids between the concentrations of large galaxies to be more nearly empty, suppresses accretion of intergalactic matter onto galaxies at low redshift, and produces an early generation of dense dark matter halos. A preliminary analysis indicates the ReBEL scenario is consistent with the one-dimensional power spectrum of the Lyman-Alpha forest and the three-dimensional galaxy auto-correlation function. Segregation of baryons and DM in galaxies and systems of galaxies is a strong prediction of ReBEL. ReBEL naturally correlates the baryon mass fraction in groups and clusters of galaxies with the system mass, in agreement with recent measurements.
The TANAMI program has been monitoring the parsec-scale radio jets of southern gamma-ray bright AGN with VLBI techniques simultaneously with Fermi/LAT monitoring of their gamma-ray emission. Here we present the gamma-ray properties of the TANAMI sources based on an analysis of the preliminary 1-year LAT source list. We present upper limits on the gamma-ray flux for TANAMI sources not detected by LAT.
In an attempt to understand the extraordinarily small mass-loss rates of
late-type O dwarfs, mass fluxes in the relevant part of (Teff, g)-space are
derived from first principles using a previously-described code for
constructing moving reversing layers. From these mass fluxes, a weak-wind
domain is identified within which a star's rate of mass loss by a
radiatively-driven wind is less than that due to nuclear burning. The five
weak-wind stars recently analysed by Marcolino et al. (2009) fall within or at
the edge of this domain. But although the theoretical mass fluxes for these
stars are approximately 1.4 dex lower than those derived with the formula of
Vink et al. (2000), the observed rates are still not matched, a failure that
may reflect our poor understanding of low-density supersonic outflows.
Mass fluxes are also computed for two strong-wind O4 stars analysed by Bouret
et al. (2005). The predictions agree with the sharply reduced mass loss rates
found when wind clumping is taken into account.
We present the Geodesic Deviation Equation (GDE) for the Friedmann-Robertson-Walker(FRW) universe and we compare it with the equation for Bianchi type I model. We justify consider this cosmological model due to the recent importance the Bianchi Models have as alternative models in cosmology. The main property of these models, solutions of Einstein Field Equations (EFE) is that they are homogeneous as the FRW model but they are not isotropic. We can see this because they have a non-null Weyl tensor in the GDE.
We present the results of a multiwavelength campaign searching for young objects in the intragroup medium of seven compact groups of galaxies: HCG 2, 7, 22, 23, 92, 100 and NGC 92. We used Fabry-Perot velocity fields and rotation curves together with GALEX NUV and FUV images, optical R-band and HI maps to evaluate the stage of interaction of each group. We conclude that groups (i) HCG 7 and HCG 23 are in an early stage of interaction, (ii) HCG 2 and HCG 22 are mildly interacting, and (iii) HCG 92, HCG 100 and NGC 92 are in a late stage of evolution. Evolved groups have a population of young objects in their intragroup medium while no such population is found within the less evolved groups. We also report the discovery of a tidal dwarf galaxy candidate in the tail of NGC 92. These three groups, besides containing galaxies which have peculiar velocity fields, also show extended HI tails. Our results indicate that the advanced stage of evolution of a group together with the presence of intragroup HI clouds may lead to star formation in the intragroup medium.
Galactic very high energy (VHE, > 100 GeV) gamma ray sources in the inner Galaxy H.E.S.S. survey tend to cluster within 1 degree in latitude around the Galactic plane. HESS J1507-622 instead is unique, since it is located at latitude of ~3.5 degrees. HESS J1507-622 is slightly extended over the PSF of the instrument and hence its Galactic origin is clear. The search for counterparts in other wavelength regimes (radio, infrared and X-rays) failed to show any plausible counterparts; and given its position off the Galactic plane and hence the absorption almost one order of magnitude lower, it is very surprising to not see any counterparts especially at X-rays wavelengths (by ROSAT, XMM Newton and Chandra). Its latitude implies that it is either rather close, within about 1 kpc, or is located well off the Galactic plane. And also the models reflect the uniqueness of this object: a leptonic PWN scenario would place this source due to its quite small extension to multi-kpc distance whereas a hadronic scenario would preferentially locate this object at distances of < 1 kpc where the density of target material is higher.
It is shown that the curvature of space-time induced by vacuum fluctuations of quantum fields should be proportional to the square of Newton's constant $G$. This offers a possible explanation for the success of the approximation $G m^6 c^2 h^{-4}$ for the dark energy density, with $m$ being a typical mass of elementary particles.
We study physical properties and global structures of a time-dependent, spherically symmetric solution obtained via the dimensional reduction of intersecting M-branes. We find that the spacetime describes a maximally charged black hole which asymptotically tends to the Friedmann-Lema\^itre-Robertson-Walker (FLRW) universe filled by a stiff matter. The metric solves the field equations of Einstein-Maxwell-dilaton system, in which four Abelian gauge fields couple to the dilation with different coupling constants. The spacetime satisfies the dominant energy condition and is characterised by two parameters, $Q$ and $\tau$, related to the Maxwell charge and the relative ratio of black-hole horizon radii, respectively. In spite of the nontrivial time-dependence of the metric, it turns out that the black hole event horizon is a Killing horizon. This unexpected symmetry may be ascribed to the fact that the 11-dimensional (11D) brane configurations are supersymmetric in the static limit. Finally, combining with laws of trapping horizon, we discuss the thermodynamic properties of the black hole. It is shown that the horizon possesses a nonvanishing temperature, contrary to the extremal Reissner-Nordstr{\o}m (RN) solution.
A variety of detectors has been proposed for dark matter direct detection, but most of them -- by the fact -- are still at R&D stage. In many cases, it is claimed that the lack of an adequate detectors' radio-purity might be compensated through heavy uses of MonteCarlo simulations, subtractions and handlings of the measured counting rates, in order to claim higher sensitivity (just for a particular scenario). The relevance of a correct evaluation of systematic effects in the use of MonteCarlo simulations at very low energy (which has always been safely discouraged in the field so far) and of multiple subtractions and handling procedures applied to the measured counting rate is shortly addressed here at some extent. Many other aspects would also deserve suitably deep investigations.
We describe an efficient implementation of a coherent statistic for continuous gravitational wave searches from neutron stars. The algorithm works by transforming the data taken by a gravitational wave detector from a moving Earth bound frame to one that sits at the Solar System barycenter. Many practical difficulties arise in the implementation of this algorithm, including constraints of small computer memory, discreteness of the data, losses due to interpolation and gaps in real data. This implementation is considerably more efficient than previous implementations of these kinds of searches.
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In a volume-limited sample of 63 ultracool dwarfs of spectral type M7-M9.5, we have obtained high-resolution spectroscopy with UVES at the Very Large Telescope and HIRES at Keck Observatory. In this second paper, we present projected rotation velocities, average magnetic field strengths, and chromospheric emission from the Halpha line. We confirm earlier results that the mean level of normalized Halpha luminosity decreases with lower temperature, and we find that the scatter among Halpha luminosities is larger at lower temperature. We measure average magnetic fields between 0 and 4kG with no indication for a dependence on temperature between M7 and M9.5. For a given temperature, Halpha luminosity is related to magnetic field strength, consistent with results in earlier stars. A few very slowly rotating stars show very weak magnetic fields and Halpha emission, all stars rotating faster than our detection limit show magnetic fields of at least a few hundred Gauss. In contrast to earlier-type stars, we observe magnetic fields weaker than 1kG in stars rotating faster than ~3km/s, but we find no correlation between rotation and magnetic flux generation among them. We interpret this as a fundamental change in the dynamo mechanism; in ultracool dwarfs, magnetic field generation is predominantly achieved by a turbulent dynamo, while other mechanisms can operate more efficiently at earlier spectral type.
We present a non-parametric measure of the ellipticity and the alignment of the dark matter halos in Abell 901/902 supercluster. This super-cluster is a system of four separate peaks in a $0.5^{\circ}\times0.5^{\circ}$ field of view. We map the mass distribution of each individual peak using an improved version of Particle Based Lensing (PBL) and measure the ellipticity of the dark matter halos associated with two of the peaks directly from the mass map and by fitting them to a singular isothermal ellipse. The parametric and non-parametric measurements are consistent for A901b while the position angle for the Southwest Group is different for the two techniques. We account for this discrepancy to substructure present in the Southwest Peak. We estimate an axis ratio of $0.37\pm 0.1$ for A901b and $0.54^{+0.08}_{-0.09}$ for the Southwest Group.
Observations of distant bright quasars suggest that billion solar mass supermassive black holes (SMBHs) were already in place less than a billion years after the Big Bang. Models in which light black hole seeds form by the collapse of primordial metal-free stars cannot explain their rapid appearance due to inefficient gas accretion. Alternatively, these black holes may form by direct collapse of gas at the center of protogalaxies. However, this requires metal-free gas that does not cool efficiently and thus is not turned into stars, in contrast with the rapid metal enrichment of protogalaxies. Here we use a numerical simulation to show that mergers between massive protogalaxies naturally produce the required central gas accumulation with no need to suppress star formation. Merger-driven gas inflows produce an unstable, massive nuclear gas disk. Within the disk a second gas inflow accumulates more than 100 million solar masses of gas in a sub-parsec scale cloud in one hundred thousand years. The cloud undergoes gravitational collapse, which eventually leads to the formation of a massive black hole. The black hole can grow to a billion solar masses in less than a billion years by accreting gas from the surrounding disk.
The first galaxies likely formed a few hundred million years after the Big Bang. Until recently, it has not been possible to detect galaxies earlier than ~750 million years after the Big Bang. The new HST WFC3/IR camera changed this when the deepest-ever, near-IR image of the universe was obtained with the HUDF09 program. Here we use this image to identify three redshift z~10 galaxy candidates in the heart of the reionization epoch when the universe was just 500 million years old. These would be the highest redshift galaxies yet detected, higher than the recent detection of a GRB at z~8.2. The HUDF09 data previously revealed galaxies at z~7 and z~8. Galaxy stellar population models predict substantial star formation at z>9-10. Verification by direct observation of the existence of galaxies at z~10 is the next step. Our conservative search and extensive testing for contamination and spurious images suggests that we can set reliable constraints based upon our 3 z~10 candidates, unlike a recent claim of 20 z~10 sources which appear to be spurious. The detection of galaxies at z>8 is further enhanced by our detailed analysis of 2 other faint sources likely at z~8.4 and z~8.7. Our z~10 sample suggests that the luminosity function and star formation rate density evolution found at lower redshifts continues to z~10, and pushes back the timescale for early galaxy buildup to z>10, increasing the likely role of galaxies in providing the UV flux needed to reionize the universe. The true nature of these galaxies, at just 4% of the age of the universe, will remain hidden until JWST is launched.
Understanding the astrophysical processes acting within galaxy groups and their effects on the evolution of the galaxy population is one of the crucial topic of modern cosmology, as almost 60% of galaxies in the Local Universe are found in groups. We imaged in the far (FUV 1539 A) and near ultraviolet (NUV 2316 A) with GALEX three nearby groups, namely LGG93, LGG127 and LGG225. We obtained the UV galaxy surface photometry and, for LGG225, the only group covered by the SDSS, the photometry in u, g, r, i, z bands. We discuss galaxy morphologies looking for interaction signatures and we analyze the SED of galaxies to infer their luminosity-weighted ages. The UV and optical photometry was also used to perform a kinematical and dynamical analysis of each group and to evaluate the stellar mass. A few member galaxies in LGG225 show a distorted UV morphology due to ongoing interactions. (FUV-NUV) colors suggest that spirals in LGG93 and LGG225 host stellar populations in their outskirts younger than that of M31 and M33 in the LG or with less extinction. The irregular interacting galaxy NGC3447A has a significantly younger stellar population (few Myr old) than the average of the other irregular galaxies in LGG225 suggesting that the encounter triggered star formation. The early-type members of LGG225, NGC3457 and NGC3522, have masses of the order of a few 10^9 Mo, comparable to the Local Group ellipticals. For the most massive spiral in LGG225, we estimate a stellar mass of ~4x10$^{10}$ Mo, comparable to M33 in the LG. Ages of stellar populations range from a few to ~7 Gyr for the galaxies in LGG225. The kinematical and dynamical analysis indicates that LGG127 and LGG225 are in a pre-virial collapse phase, i.e. still undergoing dynamical relaxation, while LGG93 is likely virialized. (Abridged)
We report X-ray constraints for 20 of 52 high-z ULIRGs identified in the Spitzer xFLS to constrain their obscuration. Notably, decomposition of Spitzer-IRS spectra for the 52 objects already indicates that most are weak-PAH ULIRGs dominated by hot-dust continua, characteristic of AGN. Given their redshifts, they have AGN bolometric luminosities of ~1e45-1e47 erg/s comparable to powerful QSOs. This, coupled with their high IR-to-optical ratios and often significant silicate absorption, strongly argues in favor of these mid-IR objects being heavily obscured QSOs. At X-ray energies, we marginally detect two ULIRGs, while the rest have only upper limits. Using the IRS-derived 5.8um AGN continuum luminosity as a proxy for the expected X-ray luminosities, we find that all of the observed sources must individually be highly obscured, while X-ray stacking limits on the undetected sources suggest that the majority, if not all, are likely to be at least mildly Compton-thick (NH>1e24 cm-2). With a space density of ~1.4e-7 Mpc-3 at z~2, such objects imply a lower limit on the obscured AGN fraction (i.e., the ratio of AGN above and below NH=1e22 cm-2) of >~1.7:1 even among luminous QSOs. Our findings, which are based on extensive multi-wavelength constraints including Spitzer IRS spectra, should aid in the interpretation of similar objects from larger or deeper mid-IR surveys, where considerable uncertainty about the source properties remains and comparable follow-up is not yet feasible.
We present an improved version of the SimpleX method for radiative transfer on an unstructured Delaunay grid. The grid samples the medium through which photons are transported in an optimal way for fast radiative transfer calculations. In this paper we study the detailed working of SimpleX in test problems and show improvements over the previous version of the method. We have applied a direction conserving transport scheme that correctly transports photons in the optically thin regime, a regime where the original SimpleX algorithm lost its accuracy. In addition, a scheme of dynamic grid updates is employed to ensure correct photon transport when the optical depth changes during a simulation. For the application to large data sets, the method is parallellised for distributed memory machines using MPI. To test the new method, we have performed standard tests for cosmological radiative transfer. We show excellent correspondence with both the analytical solution (when available) and to the results of other codes compared to the former version of SimpleX, without sacrificing the benefits of the high computational speed of the method.
We apply the time-renormalization group approach to study the effect of primordial non-Gaussianities in the non-linear evolution of cosmological dark matter density perturbations. This method improves the standard perturbation approach by solving renormalization group-like equations governing the dynamics of gravitational instability. The primordial bispectra constructed from the dark matter density contrast and the velocity fields represent initial conditions for the renormalization group flow. We consider local, equilateral and folded shapes for the initial non-Gaussianity and analyze as well the case in which the non-linear parameter f_{NL} parametrizing the strength of the non-Gaussianity depends on the momenta in Fourier space through a power-law relation, the so-called running non-Gaussianity. For the local model of non-Gaussianity we compare our findings for the power-spectrum with those of recent N-body simulations and find that they accurately fit the N-body data up to wave-numbers k \sim 0.25 h/Mpc at z=0. We also present predictions for the (reduced) matter bispectra for the various shapes of non-Gaussianity.
We demonstrate that the output of a cosmological N-body simulation can, to remarkable accuracy, be scaled to represent the growth of large-scale structure in a cosmology with parameters similar to but different from those originally assumed. Our algorithm involves three steps: a reassignment of length, mass and velocity units, a relabelling of the time axis, and a rescaling of the amplitudes of individual large-scale fluctuation modes. We test it using two matched pairs of simulations. Within each pair, one simulation assumes parameters consistent with analyses of the first-year WMAP data. The other has lower matter and baryon densities and a 15% lower fluctuation amplitude, consistent with analyses of the three-year WMAP data. The pairs differ by a factor of a thousand in mass resolution, enabling performance tests on both linear and nonlinear scales. Our scaling reproduces the mass power spectra of the target cosmology to better than 0.5% on large scales (k < 0.1 h/Mpc) both in real and in redshift space. In particular, the BAO features of the original cosmology are removed and are correctly replaced by those of the target cosmology. Errors are still below 3% for k < 1 h/Mpc. Power spectra of the dark halo distribution are even more precisely reproduced, with errors below 1% on all scales tested. A halo-by-halo comparison shows that centre-of-mass positions and velocities are reproduced to better than 90 kpc/h and 5%, respectively. Halo masses, concentrations and spins are also reproduced at about the 10% level, although with small biases. Halo assembly histories are accurately reproduced, leading to central galaxy magnitudes with errors of about 0.25 magnitudes and a bias of about 0.13 magnitudes for a representative semi-analytic model.
Advances in laser and Z-pinch technology, coupled with the development of
plasma diagnostics and the availability of high-performance computers, have
recently stimulated the growth of high-energy density laboratory astrophysics.
In particular a number of experiments have been designed to study radiative
shocks and jets with the aim of shedding new light on physical processes linked
to the ejection and accretion of mass by newly born stars.
Although general scaling laws are a powerful tools to link laboratory
experiments with astrophysical plasmas, the phenomena modelled are often too
complicated for simple scaling to remain relevant. Nevertheless, the
experiments can still give important insights into the physics of astrophysical
systems and can be used to provide the basic experimental validation of
numerical simulations in regimes of interest to astrophysics.
We will illustrate the possible links between laboratory experiments,
numerical simulations and astrophysics in the context of stellar jets. First we
will discuss the propagation of stellar jets in a cross-moving interstellar
medium and the scaling to Z-pinch produced jets. Our second example focuses on
slab-jets produced at the PALS (Prague Asterix Laser System) laser installation
and their practical applications to astrophysics. Finally, we illustrate the
limitations of scaling for radiative shocks, which are found at the head of the
most rapid stellar jets.
The simulation of the optical turbulence (OT) for astronomical applications obtained with non-hydrostatic atmospherical models at meso-scale presents, with respect to measurements, some advantages. The future of the ground-based astronomy relies upon the potentialities and feasibility of the ELTs. Our ability in knowing, controlling and 'managing' the effects of the turbulence on such a new generation telescopes and facilities are determinant to assure their competitiveness with respect to the space astronomy. In the past several studies have been carried out proving the feasibility of the simulation of realistic Cn2 profiles above astronomical sites. The European Community (FP6 Program) decided recently to fund a Project aiming, from one side, to prove the feasibility of the OT forecasts and the ability of meso-scale models in discriminating astronomical sites from optical turbulence point of view and, from the other side, to boost the development of this discipline at the borderline between the astrophysics and the meteorology. In this contribution I will present the scientific and technological goals of this project, the challenges for the ground-based astronomy that are related to the success of such a project and the international synergies that have been joint to optimize the results.
We are integrating the Fermi Gamma-Ray Burst Monitor (GBM) into the Interplanetary Network (IPN) of Gamma-Ray Burst (GRB) detectors. With the GBM, the IPN will comprise 9 experiments. This will 1) assist the Fermi team in understanding and reducing their systematic localization uncertainties, 2) reduce the sizes of the GBM and Large Area Telescope (LAT) error circles by 1 to 4 orders of magnitude, 3) facilitate the identification of GRB sources with objects found by ground- and space-based observatories at other wavelengths, from the radio to very high energy gamma-rays, 4) reduce the uncertainties in associating some LAT detections of high energy photons with GBM bursts, and 5) facilitate searches for non-electromagnetic GRB counterparts, particularly neutrinos and gravitational radiation. We present examples and demonstrate the synergy between Fermi and the IPN. This is a Fermi Cycle 2 Guest Investigator project.
We present numerical simulations aimed at exploring the effects of varying the sub-grid physics parameters on the evolution and the properties of the galaxy formed in a low-mass dark matter halo (~7 times 10^10 Msun/h at redshift z=0). The simulations are run within a cosmological setting with a nominal resolution of 218 pc comoving and are stopped at z = 0.43. In all of our simulations, an extended old/intermediate-age stellar halo and a more compact younger stellar disk are formed. We found that a non negligible fraction of the halo stars are formed in situ in a spheroidal distribution. Changes in the sub-grid physics parameters affect significantly and in a complex way the evolution and properties of the galaxy: (i) Lower threshold densities nsf produce larger stellar effective radii Re, less peaked circular velocity curves V_c(R), and greater amounts of low-density and hot gas in the disk mid-plane; (ii) When stellar feedback is modeled by temporarily switching off radiative cooling in the star forming regions, Re increases (by a factor of ~ 2 in our particular model), the circular velocity curve becomes flatter, and a complex multi-phase gaseous disk structure develops; (iii) A more efficient local conversion of gas mass to stars, measured by a stellar particle mass distribution biased toward larger values, increases the strength of the feedback energy injection -driving outflows and inducing burstier SF histories; iv) If feedback is too strong, gas loss by galactic outflows -which are easier to produce in low-mass galaxies- interrupts SF, whose history becomes episodic. The simulations exhibit two important shortcomings: the baryon fractions are higher, and the specific SF rates are much smaller, than observationally inferred values for redshifts ~ 0.4-1.
Our observations of the quiet Sun with the NST have yielded unanticipated
results on smal-scale solar dynamic. Althought small-scale solar dynamic have
been well-studied, the NST is enabling us to probe finer scale dynamic
exploiting higher spatial resolution. We discuss NST resutls from data taken
29th July 2009 using an broadband filter centered on TiO 705.7nm spectral line.
Data are from the center of the solar disk where we observed quiet Sun.
We registered bright-point like structures in most of the intergranular
lanes. They vary in behaviour and evolution. Co-registered solar oscillations
tend to congregate near certain types of bright-point like structures. The
oscillations with maximum power tend to appear only above or near these
structures.
The image quality from Ground-Layer Adaptive Optics (GLAO) can be gradually increased with decreased contiguous field of view. This trade-off is dependent on the vertical profile of the optical turbulence (Cn2 profiles). It is known that the accuracy of the vertical distribution measured by existing Cn2 profiling techniques is currently quite uncertain for wide field performance predictions 4 to 20 arcminutes. With assumed uncertainties in measurements from Generalized-SCIDAR (GS), SODAR plus MASS we quantify the impact of this uncertainty on the trade-off between field of view and image quality for photometry of science targets at the resolution limit. We use a point spread function (PSF) model defined analytically in the spatial frequency domain to compute the relevant photometry figure of merit at infrared wavelengths. Statistics of this PSF analysis on a database of Cn2 measurements are presented for Mt. Graham, Arizona and Dome C, Antarctica. This research is part of the activities of ForOT (3D Forecasting of Optical Turbulence above astronomical sites).
Supernova remnants (SNRs) are among the strongest candidates to explain the flux of cosmic rays below the knee around 10^15 eV. Pulsar wind nebulae (PWNe), synchrotron nebulae powered by the spin-down of energetic young pulsars, comprise one of the most populous VHE gamma-ray source classes. Gamma-ray studies in the GeV and TeV bands probe the nature (ions vs. electrons), production, and diffusion of high-energy particles in SNRs and PWNe. For sources that are visible across both the GeV and TeV bands, such as IC 443, the spatial and spectral distribution of gamma rays can be studied over an unprecedented energy range. This presentation will review recent VERITAS results, including studies of Cassiopeia A, IC 443, PSR J1930+1852, and the SNR G106.3+2.7/Boomerang region, and discuss prospects for complementary studies of SNRs and PWNe in the Fermi and VHE gamma-ray bands.
[abridged] From a sample of Ly-alpha emitters in the GOODS-S field with uncontaminated photometry and optical (red) spectroscopy, we select a spatially compact object at a redshift of 5.563 (Ly-alpha) that shows a second emission line, identified as N IV] 1486 A. The SED is modelled in a way that accounts for both the N IV] line emission and the photometry in a self-consistent way. The photoionization code CLOUDY is used to calculate a range of nebular models as a function of stellar ionizing source temperature, ionization parameter, density and nebular metallicity. We compare the theoretical and observed magnitudes and search for the model parameters that also reproduce the observed N IV] luminosity and equivalent width. A nebular model with a hot blackbody ionizing source of around 100 kK and a nebular metallicity of ~5% of solar is able to fit the observed SED and, in particular, explain the large apparent Balmer break which is inferred from the pure stellar population model fitting conventionally applied to multi-band photometric observations. In our model, an apparent spectral break is produced by strong [O III] 4959, 5007 A emission falling in one of the IR bands (IRAC1 in this case). A lower limit on the total baryonic mass of a model of this type is 3.2 x 10^8 Msun . It is argued that objects with Ly-alpha emission at high redshift that show an apparent Balmer break may have their SED dominated by nebular emission and so could possibly be identified with very young starbursting galaxies rather than massive evolved stellar populations. Detailed studies of these emission nebulae with large telescopes will provide a unique insight into very early chemical evolution.
We explore the properties of the H_beta emission line profile in a large, homogeneous and bright sample of N~470 low redshift quasars extracted from Sloan Digital Sky Survey (DR5). We approach the investigation from two complementary directions: composite/median spectra and a set of line diagnostic measures (asymmetry index, centroid shift and kurtosis) in individual quasars. The project is developed and presented in the framework of the so-called 4D Eigenvector 1 (4DE1) Parameter Space, with a focus on its optical dimensions, FWHM(H_beta) and the relative strength of optical FeII (R_FeII=W(FeII4434-4684)/W(H_beta)). We reenforce the conclusion that not all quasars are alike and spectroscopically they do not distribute randomly about an average typical optical spectrum. Our results give further support to the concept of two populations A and B (narrower and broader than 4000 km/s FWHM(H_beta), respectively) that emerged in the context of 4DE1 space. The broad H_beta profiles in composite spectra of Population A sources are best described by a Lorentzian and in Population B by a double Gaussian model. Moreover, high and low accretion sources (an alternative view of the Population A/B concept) not only show significant differences in terms of Black Hole (BH) mass and Eddington ratio L_bol/L_Edd, but they also show distinct properties in terms of line asymmetry, shift and shapes. We finally suggest that a potential refinement of the 4DE1 space can be provided by separating two populations of quasars at R_FeII~0.50 rather than at FWHM(H_beta)=4000 km/s. Concomitantly, the asymmetry and centroid shift profile measures at 1/4 fractional intensity can be reasonable surrogates for the FWHM(H_beta) dimension of the current 4DE1.
We consider the physical conditions and origin of the z = 0.0777 absorption system observed in C III, C II, Si III, C IV, O VI, and H I absorption along the line of sight towards the quasar PHL 1811. We analysed the HST/STIS and FUSE spectra of this quasar and compared the results to Cloudy photoionization and collisional ionization models in order to derive densities, temperatures, and metallicities of the absorbing gas. The absorption can be explained by two C III clouds, offset by 35 km/s in velocity, with metallicities of ~one-tenth the solar value. One cloud has a density of order n_H = 1.2 +0.9 -0.5 * 10^-3 cm^-3 (thickness 0.4 +0.3 -0.2 kpc) and produces the observed C II and Si III absorption, while the other has a density of order n_H = 1.2 +0.9 -0.5 * 10^-5 cm^-3 (thickness 80 +70 -40 kpc) and gives rise to the observed weak C IV absorption. Cloud temperatures are ~14,000 +3000 -2000 K and ~34,000 -4000 +2000 K for photoionized models. Although collisionally ionized clouds with T ~ 70,000 K are possible, they are less likely because of the short cooling time-scales involved. Previous studies revealed no luminous galaxy at the absorber's redshift, so it is probably related to tidal debris, ejected material, a dwarf galaxy, or other halo material in a galaxy group. Our models also indicate that one of the two clouds would produce detectable weak Mg II absorption if spectral coverage of that transition existed. We predict what the system would look like at z ~ 1 when the ionizing background radiation was more intense. We find that at z ~ 1 the denser component resembles a C IV absorber. The second C III cloud in this z = 0.0777 absorber may be analogous to a subset of the more diffuse O VI absorbers at higher redshift.
The model of dark matter is presented where the dark matter is a \emph{classical} gauge field. A spherical symmetric solution of Yang-Mills equation is obtained. The asymptotic behavior of the gauge fields and matter density is investigated. It is shown that the distribution of the matter density allows us interpret it as the dark matter. The fitting of a typical rotational curve with the rotational curve created by the spherical solution of SU(3) Yang-Mills equation is made.
We use data from the first 100 square-degree field observed by the South Pole Telescope (SPT) in 2008 to measure the angular power spectrum of temperature anisotropies contributed by the background of dusty star-forming galaxies at millimeter wavelengths. From the auto and cross correlation of 150 and 220 GHz SPT maps, we significantly detect both Poisson distributed and, for the first time at millimeter wavelengths, clustered components of power from a background of dusty star-forming galaxies. The spectral indices between 150 and 220 GHz of the Poisson and clustered components are found to be 3.86 +- 0.26 and 3.8 +- 1.2 respectively, implying a steep scaling of the dust emissivity index beta ~ 2. The Poisson and clustered power detected in SPT, BLAST (at 600, 860, and 1200 GHz), and Spitzer (1900 GHz) data can be understood in the context of a simple model in which all galaxies have the same grey body spectrum with dust emissivity index of beta = 2 and dust temperature T_d = 34 K. In this model, half of the 150 GHz background light comes from redshifts greater than 3.2. We also use the SPT data to place an upper limit on the amplitude of the kinetic Sunyaev-Zel'dovich power spectrum at l = 3000 of 13 uK^2 at 95% confidence.
The origin of the solar wind is one of the most important unresolved prob- lems in space and solar physics. We report here the first spectroscopic signatures of the nascent fast solar wind on the basis of observations made by the EUV Imaging Spectrometer (EIS) on Hinode in a polar coronal hole, in which patches of blueshift are clearly present on dopplergrams of coronal emission lines with a formation temperature of lg(T/K)=6.0. The corresponding upflow is associated with open field lines in the coronal hole, and seems to start in the solar transition region and becomes more prominent with increasing temperature. This temperature-dependent plasma outflow is interpreted as evidence of the nascent fast solar wind in the polar coronal hole. The patches with significant upflows are still isolated in the upper transition region but merge in the corona, in agreement with the scenario of solar wind outflow being guided by expanding magnetic funnels.
We report cosmic microwave background (CMB) power spectrum measurements from the first 100 sq. deg. field observed by the South Pole Telescope (SPT) at 150 and 220 GHz. On angular scales where the primary CMB anisotropy is dominant, ell ~< 3000, the SPT power spectrum is consistent with the standard LambdaCDM cosmology. On smaller scales, we see strong evidence for a point source contribution, consistent with a population of dusty, star-forming galaxies. After we mask bright point sources, anisotropy power on angular scales of 3000 < ell < 9500 is detected with a signal-to-noise > 50 at both frequencies. We combine the 150 and 220 GHz data to remove the majority of the point source power, and use the point source subtracted spectrum to detect Sunyaev-Zel'dovich (SZ) power at 2.6 sigma. At ell=3000, the SZ power in the subtracted bandpowers is 4.2 +/- 1.5 uK^2, which is significantly lower than the power predicted by a fiducial model using WMAP5 cosmological parameters. This discrepancy may suggest that contemporary galaxy cluster models overestimate the thermal pressure of intracluster gas. Alternatively, this result can be interpreted as evidence for lower values of sigma8. When combined with an estimate of the kinetic SZ contribution, the measured SZ amplitude shifts sigma8 from the primary CMB anisotropy derived constraint of 0.794 +/- 0.028 down to 0.773 +/- 0.025. The uncertainty in the constraint on sigma8 from this analysis is dominated by uncertainties in the theoretical modeling required to predict the amplitude of the SZ power spectrum for a given set of cosmological parameters.
We report the observation of a new dwarf nova, OT J055717+683226, during its first-ever recorded superoutburst in December 2006. Our observation shows that this object is an SU UMa-type dwarf nova having a very short superhump period of 76.67+/- 0.03 min (0.05324+/-0.00002 d). The next superoutburst was observed in March 2008. The recurrence time of superoutbursts (supercycle) is, hence, estimated to be ~480 d. The supercycle is much shorter than those of WZ Sge-type dwarf novae having supercycles of >~ 10 yr, which are a major population of dwarf novae in the shortest orbital period regime (<~85 min). Using a hierarchical cluster analysis, we identified seven groups of dwarf novae in the shortest orbital period regime. We identified a small group of objects that have short supercycles, small outburst amplitudes, and large superhump period excesses, compared with those of WZ Sge stars. OT J055717+683226 probably belongs to this group.
RAT0455+1305 was discovered during the Rapid Temporal Survey which aims in finding any variability on timescales of a few minutes to several hours. The star was found to be another sdBV star with one high amplitude mode and relatively long period. These features along with estimation of T_eff and log g makes this star very similar to Balloon 090100001. Encouraged by prominent results obtained for the latter star we have decided to perform white light photometry on RAT0455+1305. In 2009 we used the 1.5m telescope located in San Pedro Martir Observatory in Mexico. Fourier analysis confirmed the dominant mode found in the discovery data, uncovered another peak close to the dominant one, and three peaks in the low frequency region. This shows that RAT0455+1305 is another hybrid sdBV star pulsating in both p- and g-modes.
The recent analyses of the light curves provided by CoRoT have revealed
pulsation spectra of unprecedented richness and precision, in particular,
thousands of pulsating modes, and a clear distribution of amplitudes with
frequency. In the community, some scientists have started doubting about the
validity of the classical tools to analyze these very accurate light curves.
This work provides the asteroseismic community with answers to this question
showing that (1) it is physically possible for a star to excite at a time and
with the observed amplitudes such a large number of modes; and (2) that the
kinetic energy accumulated in all those modes does not destroy the equilibrium
of the star. Consequently, mathematical tools presently applied in the analyses
of light curves can a priori be trusted. This conclusion is even more important
now, when a large amount of space data coming from Kepler are currently being
analyzed.
The power spectrum of different stellar cases, and the non-adiabatic code
GraCo have been used to estimate the upper limit of the energy per second
required to excite all the observed modes, and their total kinetic energy. A
necessary previous step for this study is to infer the relative radial
pulsational amplitude from the observed photometric amplitude, scaling our
linear pulsational solutions to absolute values. The derived upper limits for
the required pulsational energy were compared with 1) the luminosity of the
star; and 2) the gravitational energy. We obtained that both upper energy
limits are orders of magnitude smaller.
CH stars form a distinct class of objects with characteristic properties like iron deficiency, enrichment of carbon and overabundance in heavy elements. These properties can provide strong observational constraints for theoretical computation of nucleosynthesis at low-metallicity. An important question is the relative surface density of CH stars which can provide valuable inputs to our understanding on the role of low to intermediate-mass stars in the early Galactic chemical evolution. Spectroscopic characterization provides an effective way of identifying CH stars. The present analysis is aimed at a quantitative assessment of the fraction of CH stars in a sample of stars using a set of spectral classification criteria. The sample consists of 92 objects selected from a collection of candidate Faint High Latitude Carbon stars from the Hamburg/ESO survey. Medium resolution (R ~ 1300) spectra for these objects were obtained using OMR at VBO, Kavalur and HFOSC at HCT, IAO, Hanle, during 2007 - 2009 spanning a wavelength range 3800 - 6800 A. Spectral analysis shows 36 of the 92 objects to be potential CH stars; combined with our earlier studies (Goswami 2005, Goswami et al. 2007) this implies ~ 37% (of 243) objects as the CH fraction. We present spectral descriptions of the newly identified CH star candidates. Estimated effective temperatures, 12C/13C isotopic ratios and their locations on the two colour J-H vs H-K plot are used to support their identification.
We present preliminary results from a multi-wavelength study of a merger candidate, NGC3801, hosting a young FR I radio galaxy, with a Z-shaped structure. Analysing archival data from the VLA, we find two HI emission blobs on either side of the host galaxy, suggesting a 30 kpc sized rotating gas disk aligned with stellar rotation, but rotating significantly faster than the stars. Broad, faint, blue-shifted absorption wing and an HI absorption clump associated with the shocked shell around the eastern lobe are also seen, possibly due to an jet-driven outflow. While 8.0 um dust and PAH emission, from Spitzer and near and far UV emission from GALEX is seen on a large scale in an S-shape, partially coinciding with the HI emission blobs, it reveals a ~2 kpc radius ring-like, dusty, starforming structure in the nuclear region, orthogonal to the radio jet axis. Its similarities with Kinematically Decoupled Core galaxies and other evidences have been argued for a merger origin of this young, bent jet radio galaxy.
Due to its location and climate, Antarctica offers unique conditions for long-period observations across a broad wavelength regime, where important diagnostic lines for molecules and ions can be found, that are essential to understand the chemical properties of the interstellar medium. In addition to the natural benefits of the site, new technologies, resulting from astrophotonics, may allow miniaturised instruments, that are easier to winterise and advanced filters to further reduce the background in the infrared.
We present the first detailed analysis of the rest-frame UV spectrum of the gravitationally lensed Lyman break galaxy (LBG), the `8 o'clock arc'. The spectrum of the 8 o'clock arc is rich in stellar and interstellar medium (ISM) features, and presents several similarities to the well-known MS1512-cB58 LBG. The stellar photospheric absorption lines allowed us to constrain the systemic redshift, z_sys = 2.7350+/-0.0003, of the galaxy, and derive its stellar metallicity, Z=0.82 Z_sol. With a total stellar mass of ~4.2x10^{11} M_sol, the 8 o'clock arc agrees with the mass-metallicity relation found for z>2 star-forming galaxies. The 31 ISM absorption lines detected led to the abundance measurements of 9 elements. The metallicity of the ISM, Z=0.65 Z_sol (Si), is very comparable to the metallicity of stars and ionized gas, and suggests that the ISM of the 8 o'clock arc has been rapidly polluted and enriched by ejecta of OB stars. The ISM lines extend over ~1000 km/s and have their peak optical depth blueshifted relative to the stars, implying gas outflows of about -120 km/s. The Ly-alpha line is dominated by a damped absorption profile on top of which is superposed a weak emission, redshifted relative to the ISM lines by about +690 km/s and resulting from multiply backscattered Ly-alpha photons emitted in the HII region surrounded by the cold, expanding ISM shell. A homogeneous spherical radiation transfer shell model with a constant outflow velocity, determined by the observations, is able to reproduce the observed Ly-alpha line profile and dust content. These results fully support the scenario proposed earlier, where the diversity of Ly-alpha line profiles in LBGs and Ly-alpha emitters, from absorption to emission, is mostly due to variations of HI column density and dust content (abridged).
Lithium is made up in the envelopes of massive Asymptotic Giant Branch (AGB) stars through the process of Hot Bottom Burning. In Globular Clusters, this processing is one possible source of the hot-CNO burning whose nuclear products are then ejected into the intracluster medium and take part in the formation of a second stellar generation, explaining the peculiar distribution of chemical elements among the cluster stars. We discuss the lithium yields from AGB stars in the mass range 3-6.3 Msun, and from super-AGB stars of masses in the range 6.5-9 Msun for metallicity Z=0.001. The qualitative behaviour of these yields is discussed in terms of the physical structure of the different masses. Although many uncertainties affect the other yields of these stars (e.g. O, Na and Mg), even larger uncertainties affect the lithium yield, as it depends dramatically on the adopted description of mass loss. When we adopt our standard mass loss formulation, very large yields are obtained especially for the super-AGB stars, and we discuss their possible role on the lithium abundance of second generation stars in globular clusters.
We discuss pulsations of the rapidly oscillating Ap (roAp) star HD 24712 (HR
1217) based on nonadiabatic analyses taking into account the effect of dipole
magnetic fields. We have found that all the pulsation modes appropriate for HD
24712 are damped; i.e., the kappa-mechanism excitation in the hydrogen
ionization layers is not strong enough to excite high-order p-modes with
periods consistent with observed ones, all of which are found to be above the
acoustic cut-off frequencies of our models.
The main (2.721 mHz) and the highest (2.806 mHz) frequencies are matched with
modified $l=2$ and $l=3$ modes, respectively. The large frequency separation
($\approx 68 \mu$Hz) is reproduced by models which lay within the error box of
HD 24712 on the HR diagram. The nearly equally spaced frequencies of HD 24712
indicate the small frequency separation to be as small as $\approx 0.5\mu$Hz.
However, the small separation derived from theoretical $l=1$ and 2 modes are
found to be larger than $\sim 3\mu$Hz. The problem of equal spacings could be
resolved by assuming that the spacings correspond to pairs of $l=2$ and $l=0$
modes. The amplitude distribution on the stellar surface is strongly affected
by the magnetic field resulting in the predominant concentration at the polar
regions.
Amplitudes and phases of radial-velocity variations for various spectral
lines are converted to relations of amplitude/phase versus optical depth in the
atmosphere. Oscillation phase delays gradually outward in the outermost layers
indicating the presence of waves propagating outward. The phase changes steeply
around $\log\tau\sim-3.5$, which supports a $T-\tau$ relation having a small
temperature inversion there.
The dark matter content of galaxies is usually determined from galaxies in dynamical equilibrium, mainly from rotationally supported galactic components. Such determinations restrict measurements to special regions in galaxies, e.g. the galactic plane(s), whereas other regions are not probed at all. Interacting galaxies offer an alternative, because extended tidal tails often probe outer or off-plane regions of galaxies. However, these systems are neither in dynamical equilibrium nor simple, because they are composed of two or more galaxies, by this increasing the associated parameter space.We present our genetic algorithm based modeling tool which allows to investigate the extended parameter space of interacting galaxies. From these studies, we derive the dynamical history of (well observed) galaxies. Among other parameters we constrain the dark matter content of the involved galaxies. We demonstrate the applicability of this strategy with examples ranging from stellar streams around theMilkyWay to extended tidal tails, from proto-typical binary galaxies (like M51 or the Antennae system) to small group of galaxies.
Two types of data sets for investigation of solar- modulated cycles in the climate of Bulgaria during the last ~ 200 years has been used in this study: 1. Instrumental data for the rainfalls and temperatures in 26 stations during the period AD 1899-1994; A smoothing dendrochronological data series of the tree rings width of a beech sample (Fagus) for the period of AD 1780-1982. The data proceedings has been provided separately for the "winter" (November-April) and "summer" (May-October) half- years. A well expressed quasi-20-22 and 54 yr cycles in the rains and temperature instrumental "summer" series as well as quasi 11yr cycle for the "winter" temeperature data has been established for the studied period 1899-1994. However there are also very serious variations of the 11 and 22 yr cycle magnitudes. The quasi 20-22 yr ("summer") cycle is weak expressed before AD 1930, while the 11 yr (winter) cycle is faded rapidly after ~AD 1975/76. The existence of 20-22 yr climatic cycle could be traced since the end of the supercenturial solar Dalton minimum (AD 1795-1830) in the beech tree ring width series. Strong cycles by duration of 54, 67 and 115 years are also found in this series. All they have solar analogs (in the coronal activity as well as in the "cosmogenic" 10Be and aurora activity data series). Extreme little tree ring widths during the Dalton minimum has been detected.
We present results from the spectral analysis of a long XMM-Newton observation of the radio-loud NLS1 galaxy PKS0558-504. The source is highly variable, on all sampled time scales. We did not observe any absorption features in either the soft or hard X-ray band. We found weak evidence for the presence of an iron line at ~6.8 keV, which is indicative of emission from highly ionized iron. The 2-10 keV band spectrum is well fitted by a simple power law model, whose slope steepens with increasing flux, similar to what is observed in other Seyferts as well. The soft excess is variable both in flux and shape, and it can be well described by a low-temperature Comptonisation model, whose slope flattens with increasing flux. The soft excess flux variations are moderately correlated with the hard band variations, and we found weak evidence that they are leading them by ~20 ksec. Our results rule out a jet origin for the bulk of the X-ray emission in this object. The observed hard band spectral variations suggest intrinsic continuum slope variations, caused by changes in the "heating/cooling" ratio of the hot corona. The low-temperature Comptonising medium, responsible for the soft excess emission, could be a hot layer in the inner disc of the source, which appears due to the fact that the source is accreting at a super-Eddington rate. The soft excess flux and spectral variations could be caused by random variations of the accretion rate.
Alternative cosmologies, based on extensions of General Relativity, predict modified thermal histories in the Early Universe in the pre Big Bang Nucleosynthesis (BBN) era, epoch which is not directly constrained by cosmological observations. When the expansion rate is enhanced with respect to the standard case, thermal relics typically decouple with larger relic abundances. The correct value of the relic abundance is therefore obtained for larger annihilation cross sections, as compared to standard cosmology. A direct consequence is that indirect detection rates are enhanced. Extending previous analyses of ours, we derive updated astrophysical bounds on the dark matter annihilation cross sections and use them to constrain alternative cosmologies in the pre-BBN era. We also determine the characteristics of these alternative cosmologies in order to provide the correct value of relic abundance for a thermal relic for the (large) annihilation cross section required to explain the PAMELA results on the positron fraction, therefore providing a "cosmological boost" solution to the dark matter interpretation of the PAMELA data.
I collect virtually all photometry of the ten known galactic recurrent novae (RNe) and their 37 known eruptions. This consists of my modern measures of nearly all archival plates (providing the only data for half of 37 known eruptions), my own 10,000 CCD magnitudes from 1987 to present (providing virtually all of the magnitudes in quiescence for seven RNe), over 140,000 visual magnitude estimates recorded by amateur astronomers (who discovered half the known eruptions), and the small scattering of magnitudes from all the literature. From this, I produce various uniform products; (1) BVRIJHK comparison star magnitudes and BV comparison star sequences to cover the entire range of eruption, (2) complete light curves for all eruptions, (3) best fit B and V light curve templates, (4) orbital periods for all-but-one RN, (5) exhaustive searches for all missed eruptions, (6) measured discovery efficiencies since 1890, (7) true recurrence time scales, (8) predicted next eruption dates, (9) variations on time scales of minutes, hours, days, months, years, decades, and century, (10) uniform distances and extinctions to all RNe, (11) BV colors at peak and UBVRIJHK colors at minimum all with extinction corrections, and (12) the spectral energy distributions over UBVRIJHK. Highlights of this work include the discoveries of one new RN, six previously-undiscovered eruptions, and the discovery of the orbital periods for half the RNe. The goal of this work is to provide uniform demographics for answering questions like the `What is the death rate of RNe in our galaxy?' and `Are the white dwarfs gaining or losing mass over each eruption cycle?'. An important use of this work is for the question of whether RNe can be the progenitors of Type Ia supernovae.
The large-scale curvature perturbations induced by spectator anisotropic stresses are analyzed across the matter-radiation transition. It is assumed that the anisotropic stress is associated with a plasma component whose energy density is subdominant both today and prior to photon decoupling. The enforcement of the momentum constraint and the interplay with the neutrino anisotropic stress determine the regular initial conditions of the Einstein-Boltzmann hierarchy. The Cosmic Microwave Background observables have shapes and phases which differ both from the ones of the conventional adiabatic mode as well as from their non-adiabatic counterparts.
We present a new data set of transit observations of the TrES-2b exoplanet taken in spring 2009, using the 1.2m Oskar-Luhning telescope (OLT) of Hamburg Observatory and the 2.2m telescope at Calar Alto Observatory using BUSCA (Bonn University Simultaneous CAmera). Both the new OLT data, taken with the same instrumental setup as our data taken in 2008, as well as the simultaneously recorded multicolor BUSCA data confirm the low inclination values reported previously, and in fact suggest that the TrES-2b exoplanet has already passed the first inclination threshold (i_min,1 = 83.417) and is not eclipsing the full stellar surface any longer. Using the multi-band BUSCA data we demonstrate that the multicolor light curves can be consistently fitted with a given set of limb darkening coefficients without the need to adjust these coefficients, and further, we can demonstrate that wavelength dependent stellar radius changes must be small as expected from theory. Our new observations provide further evidence for a change of the orbit inclination of the transiting extrasolar planet TrES-2b reported previously. We examine in detail possible causes for this inclination change and argue that the observed change should be interpreted as nodal regression. While the assumption of an oblate host star requires an unreasonably large second harmonic coefficient, the existence of a third body in the form of an additional planet would provide a very natural explanation for the observed secular orbit change. Given the lack of clearly observed short-term variations of transit timing and our observed secular nodal regression rate, we predict a period between approximately 50 and 100 days for a putative perturbing planet of Jovian mass. Such an object should be detectable with present-day radial velocity (RV) techniques.
The discovery of cosmic radio emission by Karl Jansky in the course of searching for the source of interference to telephone communications and the instrumental advances which followed, have led to a series of new paradigm changing astronomical discoveries. These discoveries, which to a large extent define much of modern astrophysical research were the result of the right people being in the right place at the right time using powerful new instruments, which in many cases they had designed and built. They were not the result of trying to test any particular theoretical model or trying to answer previously posed questions, but they opened up whole new areas of exploration and discovery. Rather many important discoveries came from military or communications research; others while looking for something else; and yet others from just looking. Traditionally, the designers of big telescopes invariably did not predict what the telescopes would ultimately be known for. The place in history of the next generation of telescopes will not likely be found in the science case created to justify their construction, but in the unexpected new phenomena, new theories, and new ideas which will emerge from these discoveries. It is important that those who are in a position to filter research proposals and plans not dismiss as butterfly collecting, investigations which explore new areas without having predefined the result they are looking for. Progress must also allow for new discoveries, as well as for the explanation of old discoveries. New telescopes need to be designed with the flexibility to make new discoveries which will invariably raise new questions and new problems.
Magnetic reconnection in the low atmosphere, e.g. chromosphere, is investigated in various physical environments. Its implications for the origination of explosive events (small--scale jets) are discussed. A 2.5-dimensional resistive magnetohydrodynamic (MHD) model in Cartesian coordinates is used. It is found that the temperature and velocity of the outflow jets as a result of magnetic reconnection are strongly dependent on the physical environments, e.g. the magnitude of the magnetic field strength and the plasma density. If the magnetic field strength is weak and the density is high, the temperature of the jets is very low (~10,000 K) as well as its velocity (~40 km/s). However, if environments with stronger magnetic field strength (20 G) and smaller density (electron density Ne=2x10^{10} cm^{-3}) are considered, the outflow jets reach higher temperatures of up to 600,000 K and a line-of-sight velocity of up to 130 km/s which is comparable with the observational values of jet-like events.
XMM-Newton successfully detected the minimum state of PG 2112+059 during a
short snapshot observation and performed a long follow-up observation. The high
signal-to-noise spectra are modelled assuming different emission scenarios and
compared with archival spectra taken by XMM-Newton and Chandra.
The PG 2112+059 X-ray spectra acquired in May 2007 allowed the detection of a
weak iron fluorescent line, which is interpreted as being caused by reflection
from neutral material at some distance from the primary X-ray emitting source.
The X-ray spectra of PG 2112+059 taken at five different epochs during
different flux states can be interpreted within two different scenarios. The
first consists of two layers of ionised material with column densities of N_H
~5 x 10^22 cm^-2 and N_H ~3.5 x 10^23 cm^-2, respectively. The first layer is
moderately ionised and its ionisation levels follow the flux changes, while the
other layer is highly ionised and does not show any correlation with the flux
of the source. The spectra can also be interpreted assuming reflection by an
ionised accretion disk seen behind a warm absorber. The warm absorber
ionisation is consistent with being correlated with the flux of the source,
which provides an additional degree of self-consistency with the overall
reflection-based model. We explain the spectral variability with light bending
according to the models of Miniutti and Fabian and constrain the black hole
spin to be a/M > 0.86. Both scenarios also assume that a distant cold reflector
is responsible for the Fe K \alpha emission line.
Light bending provides an attractive explanation of the different states of
PG 2112+059 and may also describe the physical cause of the observed properties
of other X-ray weak quasars.
The large-scale structure of the Universe, as traced by the distribution of galaxies, is now being revealed by large-volume cosmological surveys. The structure is characterized by galaxies distributed along filaments, the filaments connecting in turn to form a percolating network. Our objective here is to quantitatively specify the underlying mechanisms that drive the formation of the cosmic network: By combining percolation-based analyses with N-body simulations of gravitational structure formation, we elucidate how the network has its origin in the properties of the initial density field (nature) and how its contrast is then amplified by the nonlinear mapping induced by the gravitational instability (nurture).
An analytic theory of the waves in colliding ring galaxies was presented some years ago, but the observations where not of sufficient quality then to make quantitative comparisons. Well-resolved observations of a few systems are now available to make such comparisons, and structure imaged in several dozen systems, derived from the recent compilation of Madore, Nelson and Petrillo and the Galaxy Zoo project, can further constrain the theory. Systems with two rings are especially useful for deriving such constraints. After examining the implications of recent observations of ring sizes and structure, I extend the analytic theory, investigate limiting cases, and present several levels of approximation. The theory is especially simple in the case of nearly flat rotation curves. I present observational comparisons for a few systems, including: Arp 10, the Cartwheel and AM2136-492. The fit is quite good over a large range of cases. For the Cartwheel there are discrepancies, but the areas of disagreement are suggestive of additional factors, such as multiple collisions. A specific prediction of the theory in the case of nearly flat rotation curves is that the ratio of the outward velocity of successive rings approximately equals the ratio of ring sizes. Ring velocities are also shown to scale simply with local circular velocities in this limit.
Many of the most exciting questions in astrophysics and cosmology, including the majority of observational probes of dark energy, rely on an understanding of the nonlinear regime of structure formation. In order to fully exploit the information available from this regime and to extract cosmological constraints, accurate theoretical predictions are needed. Currently such predictions can only be obtained from costly, precision numerical simulations. This paper is the third in a series aimed at constructing an accurate calibration of the nonlinear mass power spectrum on Mpc scales for a wide range of currently viable cosmological models, including dark energy. The first two papers addressed the numerical challenges, and the scheme by which an interpolator was built from a carefully chosen set of cosmological models. In this paper we introduce the ``Coyote Universe'' simulation suite which comprises nearly 1,000 N-body simulations at different force and mass resolutions, spanning 38 wCDM cosmologies. This large simulation suite enables us to construct a prediction scheme, or emulator, for the nonlinear matter power spectrum accurate at the percent level out to k~1 h/Mpc. We describe the construction of the emulator, explain the tests performed to ensure its accuracy, and discuss how the central ideas may be extended to a wider range of cosmological models and applications. A power spectrum emulator code is released publicly as part of this paper.
We investigate the transverse oscillations of a line-tied multi-stranded coronal loop composed of several parallel cylindrical strands. First, the collective fast normal modes of the loop are found with the T-matrix theory. There is a huge quantity of normal modes with very different frequencies and a complex structure of the associated magnetic pressure perturbation and velocity field. The modes can be classified as bottom, middle, and top according to their frequencies and spatial structure. Second, the temporal evolution of the velocity and magnetic pressure perturbation after an initial disturbance are analyzed. We find complex motions of the strands. The frequency analysis reveals that these motions are a combination of low and high frequency modes. The complexity of the strand motions produces a strong modulation of the whole tube movement. We conclude that the presumed internal fine structure of a loop influences its transverse oscillations and so its transverse dynamics cannot be properly described by those of an equivalent monolithic loop.
The VERITAS IACT observatory has carried out an extensive survey of the Cygnus region between 67 and 82 degrees in galactic longitude and between -1 and 4 degrees in galactic latitude. This region is a natural choice for a Very High Energy (VHE) gamma-ray survey in the Northern Hemisphere, as it contains a substantial number of potential VHE gamma-ray emitters such as supernova remnants, pulsar wind nebulae, high-mass X-ray binaries, and massive star clusters, in addition to a few previously detected VHE gamma-ray sources. It is also home to a number of GeV gamma-ray sources, including no less than four new high-significance sources detected in the first six months of Fermi data. The VERITAS survey, comprising more than 140 hours of observations, reaches an average VHE point-source flux sensitivity of better than 4% of the Crab Nebula flux at energies above 200 GeV. Here we report on preliminary results from this survey, including two source detections, and discuss the prospects for further studies that would exploit the joint coverage provided by VERITAS and Fermi data in this region.
High energy electrons and positrons from decaying dark matter can produce a significant flux of gamma rays by inverse Compton off low energy photons in the interstellar radiation field. This possibility is inevitably related with the dark matter interpretation of the observed PAMELA and FERMI excesses. The aim of this paper is providing a simple and universal method to constraint dark matter models which produce electrons and positrons in their decay by using the Fermi LAT gamma-ray observations in the energy range between 0.5 GeV and 300 GeV. We provide a set of universal response functions that, once convolved with a specific dark matter model produce the desired constraint. Our response functions contain all the astrophysical inputs such as the electron propagation in the galaxy, the dark matter profile, the gamma-ray fluxes of known origin, and the Fermi LAT data. We study the uncertainties in the determination of the response functions and apply them to place constraints on some specific dark matter decay models that can well fit the positron and electron fluxes observed by PAMELA and Fermi LAT. To this end we also take into account prompt radiation from the dark matter decay. We find that with the available data decaying dark matter cannot be excluded as source of the PAMELA positron excess.
The Minimal Supersymmetric Standard Model has several flat directions, which can naturally be excited during inflation. If they have a slow (perturbative) decay, they may affect the thermalization of the inflaton decay products. In the present paper, we consider the system of udd and QLd flat directions, which breaks the U(1)xSU(2)xSU(3) symmetry completely. In the unitary gauge and assuming a general soft breaking mass configuration, we show that for a range of parameters, the background condensate of flat directions can undergo a fast non-perturbative decay, due to non-adiabatic evolution of the eigenstates. We find that both the background evolution and part of the decay can be described accurately by previously studied gauged toy models of flat direction decay.
In usual particle models, sterile neutrinos can account for the dark matter of the Universe only if they have masses in the keV range and are warm dark matter. Stringent cosmological and astrophysical bounds, in particular imposed by X-ray observations, apply to them. We point out that in a particular variation of the inert doublet model, sterile neutrinos can account for the dark matter in the Universe and may be either cold or warm dark matter candidates, even for masses much larger than the keV range. These Inert-Sterile neutrinos, produced non-thermally in the early Universe, would be stable and have very small couplings to Standard Model particles, rendering very difficult their detection in either direct or indirect dark matter searches. They could be, in principle, revealed in colliders by discovering other particles in the model.
The requirements of electroweak symmetry breaking (EWSB) and correct relic density of thermal Dark Matter (DM) predict large spin-independent direct detection cross section in scalar DM models based on underlying SO(10) non-supersymmetric GUT. Interpreting the CDMS signal events as DM recoil on nuclei, we study implications of this assumption on EWSB, Higgs boson mass and direct production of scalar DM at LHC experiments. We show that this interpretation indicates relatively light DM, M_DM ~ O(100) GeV, with large pair production cross section at LHC in correlation with the spin-independent direct DM detection cross section. The next-to-lightest dark scalar S_NL is predicted to be long-lived, providing distinctive experimental signatures of displaced vertex of two leptons or jets plus missing transverse energy.
We develop a fully covariant, well-posed 5D effective action for the 6D cascading gravity brane-world model, and use this to study cosmological solutions. We obtain this effective action through the 6D decoupling limit, in which an additional scalar degree mode, \pi, called the brane-bending mode, determines the bulk-brane gravitational interaction. The 5D action obtained this way inherits from the sixth dimension an extra \pi self-interaction kinetic term. We compute appropriate boundary terms, to supplement the 5D action, and hence derive fully covariant junction conditions and the 5D Einstein field equations. Using these, we derive the cosmological evolution induced on a 3-brane moving in a static bulk. We study the strong- and weak-coupling regimes analytically in this static ansatz, and perform a complete numerical analysis of our solution. Although the cascading model can generate an accelerating solution in which the \pi field comes to dominate at late times, the presence of a critical singularity prevents the \pi field from dominating entirely. Our results open up the interesting possibility that a more general treatment of degravitation in a time-dependent bulk may lead to an accelerating universe without a cosmological constant.
The CDMS Collaboration has presented its results for the final exposure of the CDMS II experiment and reports that two candidate events for dark matter would survive after application of the various discrimination and subtraction procedures inherent in their analysis. We show that a population of relic neutralinos, which was already proved to fit the DAMA/LIBRA data on the annual modulation effect, could naturally explain the two candidate CDMS II events, if these are actually due to a dark matter signal.
High energy cosmic neutrino fluxes can be produced inside relativistic jets under the envelopes of collapsing stars. In the energy range E ~ (0.3 - 1e5) GeV, flavor conversion of these neutrinos is modified by various matter effects inside the star and the Earth. We present a comprehensive (both analytic and numerical) description of the flavor conversion of these neutrinos which includes: (i) oscillations inside jets, (ii) flavor-to-mass state transitions in an envelope, (iii) loss of coherence on the way to observer, and (iv) oscillations of the mass states inside the Earth. We show that conversion has several new features which are not realized in other objects, in particular interference effects ("L- and H- wiggles") induced by the adiabaticity violation. The neutrino-neutrino scattering inside jet and inelastic neutrino interactions in the envelope may produce some additional features at E > 1e4 GeV. We study dependence of the probabilities and flavor ratios in the matter-affected region on angles theta13 and theta23, on the CP-phase delta, as well as on the initial flavor content and density profile of the star. We show that measurements of the energy dependence of the flavor ratios will, in principle, allow to determine independently the neutrino and astrophysical parameters.
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The adhesion approximation is a simple analytical model suggested for explanation of the major geometrical features of the observed structure in the galaxy distribution on scales from 1 to (a few)x100/h Mpc. It is based on Burgers' equation and therefore allows analysis in considerable detail. A particular version of the model that assumes the infinitesimal viscosity naturally results in irregular tessellation of the universe. Generic elements of the tessellation: vertices, edges, faces and three-dimensional tiles can be associated with astronomical objects of different kinds: clusters, superclusters and voids of galaxies. Point-like vertices contain the most of the mass and one-dimensional edges (filaments) are the second massive elements. The least massive are the two-dimensional faces and tiles (voids). The evolution of the large-scale structure can be viewed as a continuous process that transports mass predominantly from the high- to low-dimensional elements of the tessellation. For instance, the mass from the cells flows into faces, edges and vertices, in turn the mass from faces flows into edges and vertices, etc. At the same time, the elements of the tessellation themselves are in continuous motion resulting in mergers of some vertices, growth of some tiles and shrinking and disappearance of the others as well as other metamorphoses.
We present observations of the Class 0 protostar L1157-mm using the Combined Array for Research in Millimeter-wave Astronomy (CARMA) in 3 mm dust continuum and N2H+ line emission. In the N2H+ line, we detect a large-scale envelope extended over a linear size of ~20,000AU flattened in the direction perpendicular to the outflow. This N2H+ feature coincides with the outer envelope seen in the 8 micron extinction by Looney et al. Meanwhile, the dust continuum traces the compact, nearly spherical structure of the inner envelope, where N2H+ becomes depleted. This highly flattened N2H+ envelope also shows dynamical signatures consistent with gravitational infall in the inner region, but a slow, solid-body rotation at large scales. This flattened structure is not a rotationally supported circumstellar disk; instead, it resembles a prestellar core both morphologically and kinematically, representing the early phase of a Class 0 system. In this paper, we construct a simple model to interpret both the dust continuum and N2H+ emission and suggest a possible dynamical scenario for the overall properties of the envelope.
We address the problem of angular momentum transport in stellar radiative interiors with a novel semi-analytic spectral technique, using an eigenfunction series expansion, that can be used to derive benchmark solutions in hydromagnetic regimes with very high Reynolds number (10^7 - 10^8). The error arising from the truncation of the series is evaluated analytically. The main simplifying assumptions are the neglect of meridional circulation and of non-axisymmetric magnetic fields. The advantages of our approach are shown by applying it to a spin-down model for a 1 M_sun main-sequence star. The evolution of the coupling between core and envelope is investigated for different values of the viscosity and different geometries and values of the poloidal field. We confirm that a viscosity enhancement by 10^4 with respect to the molecular value is required to attain a rigid rotation in the core of the Sun within its present age. We suggest that a quadrupolar poloidal field may explain the short coupling time-scale needed to model the observed rotational evolution of fast rotators on the ZAMS, while a dipolar geometry is indicated in the case of slow rotators. Our novel semi-analytic spectral method provides a conceptually simple and rigorous treatment of a classic MHD problem and allows us to explore the influence of various parameters on the rotational history of radiative interiors.
We provide an analysis of timing irregularities observed for 366 pulsars. Observations were obtained using the 76-m Lovell radio telescope at the Jodrell Bank Observatory over the past 36 years. These data sets have allowed us to carry out the first large-scale analysis of pulsar timing noise over time scales of > 10yr, with multiple observing frequencies and for a large sample of pulsars. Our sample includes both normal and recycled pulsars. The timing residuals for the pulsars with the smallest characteristic ages are shown to be dominated by the recovery from glitch events, whereas the timing irregularities seen for older pulsars are quasi-periodic. We emphasise that previous models that explained timing residuals as a low-frequency noise process are not consistent with observation.
G54.1+0.3 is a young pulsar wind nebula (PWN), closely resembling the Crab, for which no thermal shell emission has been detected in X-rays. Recent Spitzer observations revealed an infrared (IR) shell containing a dozen point sources arranged in a ring-like structure, previously proposed to be young stellar objects. An extended knot of emission located in the NW part of the shell appears to be aligned with the pulsar's X-ray jet, suggesting a possible interaction with the shell material. Surprisingly, the IRS spectrum of the knot resembles the spectrum of freshly formed dust in Cas A, and is dominated by an unidentified dust emission feature at 21 microns. The spectra of the shell also contain various emission lines and show that some are significantly broadened, suggesting that they originate in rapidly expanding supernova (SN) ejecta. We present the first evidence that the PWN is driving shocks into expanding SN ejecta and we propose an alternative explanation for the origin of the IR emission in which the shell is composed entirely of SN ejecta. In this scenario, the freshly formed SN dust is being heated by early-type stars belonging to a cluster in which the SN exploded. Simple dust models show that this interpretation can give rise to the observed shell emission and the IR point sources.
We derive the evolution equations for a plasma comprising multiple species of charged fluids with relativistic bulk and thermal motion. We show that a minimal fluid coupling model allows a natural casting of the evolution equations in terms of generalized vorticity which treats the fluid motion and electromagnetic fields equally. Equilibria can be found using a variational principle based on minimizing the total enstrophy subject to energy and helicity constraints. A subset of these equilibria correspond to minimum energy. We present the equations for these states, and give an example showing the structure of the relaxed states.
This is the first paper of a series presenting a Spheroid's Panchromatic Investigation in Different Environmental Regions (SPIDER). The sample of spheroids consists of 5,080 bright (Mr<-20) Early-Type galaxies (ETGs), in the redshift range of 0.05 to 0.095, with optical (griz) photometry and spectroscopy from SDSS-DR6 and Near-Infrared (YJHK) photometry from UKIDSS-LAS (DR4). We describe how homogeneous photometric parameters (galaxy colors and structural parameters) are derived using grizYJHK wavebands. We find no systematic steepening of the CM relation when probing the baseline from g-r to g-K, implying that internal color gradients drive most of the mass-metallicity relation in ETGs. As far as structural parameters are concerned we find that the mean effective radius of ETGs smoothly decreases, by ~30%, from g through K, while no significant dependence on waveband is detected for the axis ratio, Sersic index, and a4 parameters. Also, velocity dispersions are re-measured for all the ETGs using STARLIGHT and compared to those obtained by SDSS. We compare our (2DPHOT) measurements of total magnitude, effective radius, and mean surface brightness with those obtained as part of the SDSS pipeline (Photo). Significant differences are found and reported, including comparisons with a third and independent part. A full characterization of the sample completeness in all wavebands is presented, establishing the limits of application of the characteristic parameters presented here for the analysis of the global scaling relations of ETGs.
We present a complete analysis of the Fundamental Plane of early-type galaxies (ETGs) in the nearby universe. The sample, as defined in paper I, comprises 39,993 ETGs located in environments covering the entire domain in local density (from field to cluster). We derive the FP of ETGs in the grizYJHK wavebands with a detailed discussion on fitting procedure, bias due to selection effects and bias due to correlated errors on r_e and mue as key factors in obtaining meaningful FP coefficients. Studying the Kormendy relation we find that its slope varies from g (3.44+-0.04) to K (3.80+-0.02) implying that smaller size ETGs have a larger ratio of optical/NIR radii than galaxies with larger re. We also examine the Faber-Jackson relation and find that its slope is similar for all wavebands, within the uncertainties, with a mean value of 0.198+-0.007. The variation of the FP coefficients for the magnitude selected sample from g through K amounts to 11%, negligible, and 10%, respectively. We find that the tilt of the FP becomes larger for higher Sersic index and larger axis ratios, independent of the waveband we measured the FP variables. This suggests that these variations are likely related to structural and dynamical differences of galaxian properties. We also show that the current semi-analytical models of galaxy formation reproduce very well the variation of age and metallicity of the stellar populations present in massive ETGs as a function of the stellar mass in these systems. In particular, we find that massive ETGs have coeval stellar pops with age varying only by a few % per decade in mass, while metallicity increases with stellar mass by 23% per mass decade.
The asteroid (21) Lutetia is the target of a planned close encounter by the Rosetta spacecraft in July 2010. To prepare for that flyby, Lutetia has been extensively observed by a variety of astronomical facilities. We used the Hubble Space Telescope (HST) to determine the albedo of Lutetia over a wide wavelength range, extending from ~150 nm to ~700 nm. Using data from a variety of HST filters and a ground-based visible light spectrum, we employed synthetic photometry techniques to derive absolute fluxes for Lutetia. New results from ground-based measurements of Lutetia's size and shape were used to convert the absolute fluxes into albedos. We present our best model for the spectral energy distribution of Lutetia over the wavelength range 120-800 nm. There appears to be a steep drop in the albedo (by a factor of ~2) for wavelengths shorter than ~300 nm. Nevertheless, the far ultraviolet albedo of Lutetia (~10%) is considerably larger than that of typical C-chondrite material (~4%). Lutetia's reflectivity is not consistent with a metal-dominated surface at infrared or radar wavelengths, and its albedo at all wavelengths (UV-visibile-IR-radar) is larger than observed for typical primitive, chondritic material. We derive a relatively high FUV albedo of ~10%, a result that will be tested by observations with the Alice spectrograph during the Rosetta flyby of Lutetia in July 2010.
We combined two-dimensional kinematic and morphology information on the Halpha emission, obtained using near-infrared integral field spectroscopy, with broad-band photometry to investigate the dynamical structure and the physical properties of a sample of ten late-type galaxies at 1.0 < z < 1.5. The sample displays a range of kinematical types which include one merger, one face-on galaxy, and eight objects showing evidence of rotation. Among these eight objects, half are rotation-dominated galaxies, while the rest are dispersion-dominated. We found also that two galaxies out of the rotation-dominated galaxies are pure rotationally supported disks. They achieve a maximum velocity of ~180-290 km/s within ~0.5-1 kpc, similar to local spirals with thin disks. The galaxies of our sample have relatively young stellar populations (< 1.5 Gyr) and possess a range of stellar mass of 0.6-5 X10^10 Msun. In addition, most of them have not yet converted the majority of their gas into stars (six galaxies have their gas fraction >50 per cent). Therefore, those of them which already have a stable disk will probably have their final stellar mass similar to the present-day spirals, to which these rotating systems can be seen as precursors. We conclude our study by investigating the stellar mass Tully-Fisher relation at 1.2 < z < 1.5.
What do we mean by neutrino astronomy? Which information is it able to provide us and which is its potential? To address these questions, we discuss three among the most relevant sources of neutrinos: the Sun; the core collapse supernovae; the supernova remnants. For each of these astronomical objects, we describe the state of the art, we present the expectations and we outline the most actual problems from the point of view of neutrino astronomy.
Giant planets orbiting main-sequence stars closer than 0.1 AU are called hot Jupiters. They interact with their stars affecting their angular momentum. Recent observations provide suggestive evidence of excess angular momentum in stars with hot Jupiters in comparison to stars with distant and less massive planets. This has been attributed to tidal interaction, but needs to be investigated in more detail considering also other possible explanations because in several cases the tidal synchronization time scales are much longer than the ages of the stars. We select stars harbouring transiting hot Jupiters to study their rotation and find that those with an effective temperature greater than 6000 K and a rotation period shorter than 10 days are synchronized with the orbital motion of their planets or have a rotation period approximately twice that of the planetary orbital period. Stars with an effective temperature lower than 6000 K and a rotation period longer than 10 days show a general trend toward synchronization with increasing effective temperature or decreasing orbital period. We propose a model for the angular momentum evolution of stars with hot Jupiters to interpret these observations. It is based on the hypothesis that a close-in giant planet affects the coronal field of its host star leading to a topology with predominantly closed field lines. Our model can be tested observationally and has relevant consequences for the relationship between stellar rotation and close-in giant planets as well as for the application of gyrochronology to estimate the age of planet-hosting stars.
We present JHK near-infrared photometric study for the old open cluster (OC) Trumpler 5 (Tr 5), based on the 2MASS data. From the color-magnitude diagrams of Tr 5, we have located the position of the red giant clump (RGC) stars, and used the mean magnitude of the RGC stars in K-band to estimate the distance to Tr 5, d = 3.1 +/- 0.1 kpc ((m-M)_0 = 12.46 +/- 0.04). From fitting the theoretical isochrones of Padova group, we have estimated the reddening, metallicity, and age : E(B-V) = 0.64 +/- 0.05, [Fe/H] = -0.4 +/- 0.1 dex, and t =2.8 +/- 0.2 Gyr (log t=9.45 +/- 0.04), respectively. These parameters generally agree well with those obtained from the previous studies on Tr 5 and confirms that this cluster is an old OC with metallicity being metal-poorer than solar abundance, located in the anti-Galactic center region.
Semi-analytic models of galaxy formation typically form the spheroidal components of galaxies ("bulges"), solely through galactic major mergers. However, it is possible that non-merger events (e.g. a "fly-by" by a smaller halo) can perturb a galaxy--halo system sufficiently to form a bulge. We present a preliminary investigation into the frequency of major changes in halo and galaxy spin direction, which could be signatures of such events.
We report on observations of TeV-selected AGN made during the first 5.5 months of observations with the Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope (Fermi). In total, 28 TeV AGN were selected for study. The Fermi observations show clear detections of 21 of these TeV-selected objects. Most can be described with a power law of spectral index harder than 2, with a spectral break generally required to accommodate the TeV measurements. Evidence for systematic evolution of the gamma-ray spectrum with redshift is presented and discussed in the context of the EBL.
CONTEXT: Most current radial velocity planet search programs have concentrated on stars of one solar mass. Our knowledge on the frequency of giant planets and brown dwarf companions to more massive stars is thus rather limited. In the case of solar-like stars, the frequency of short-period brown dwarf companions and very massive planets seems to be low. AIMS: Here we present evidence for a substellar companion to 30 Ari B, an F-star of 1.16 $\pm$ 0.04 $\rm M_\odot$ that is a member of a hierarchical triple system. METHODS: The companion was detected by means of precise radial velocity measurements using the 2-m Alfred-Jensch telescope and its 'echelle spectrograph. An iodine absorption cell provided the wavelength reference for precise stellar radial velocity measurements. RESULTS: We analyzed our radial velocity measurements and derived an orbit to the companion with period, P= 335.1+/-2.5 days, eccentricity e = 0.289+/-0.092, and mass function f(m) = (6.1+/-1.7)*10E-7 Modot. CONCLUSIONS: We conclude that the radial velocity variations of 30 Ari B are due to a companion with $m$ sin $i$ of $9.88\pm0.94$ $\rm M_{Jup}$ that is either a massive planet or a brown dwarf. {The object thus belongs to the rare class of massive planets and brown dwarfs orbiting main- sequence stars.
The rich acoustic oscillation spectrum in solar-type variables make these stars particularly interesting for studying fluid-dynamical aspects of the stellar interior. I present a summary of the properties of solar-like oscillations, how they are excited and damped and discuss some of the recent progress in using asteroseismic diagnostic techniques for analysing low-degree acoustic modes. Also the effects of stellar-cycle variations in low-mass main-sequence stars are addressed.
A scalar-tensor theory of gravity can be made not only to account for the current cosmic acceleration, but also to satisfy solar-system and laboratory constraints, by introducing a non-linear derivative interaction for the scalar field. Such an additional scalar degree of freedom is called "Galileon". The basic idea is inspired by the DGP braneworld, but one can construct a ghost-free model that admits a self-accelerating solution. We perform a fully relativistic analysis of linear perturbations in Galileon cosmology. Although the Galileon model can mimic the background evolution of standard $\Lambda$CDM cosmology, the behavior of perturbation is quite different. It is shown that there exists a super-horizon growing mode in the metric and Galileon perturbations at early times, suggesting that the background is unstable. A fine-tuning of the initial condition for the Galileon fluctuation is thus required in order to promote a desirable evolution of perturbations at early times. Assuming the safe initial condition, we then compute the late-time evolution of perturbations and discuss observational implications in Galileon cosmology. In particular, we find anticorrelations in the cross-correlation of the integrated Sachs-Wolfe effect and large scale structure, similarly to the normal branch of the DGP model.
The 2 cm VLBA Survey observed since 1994 a set of ~170 Quasars, BL Lac objects, and radio galaxies, selected to be representative of the compact AGN radio population. This effort was continued as the MOJAVE project, where a statistically complete set of radio sources being monitored was defined. A comparison of the gamma-detection rates between the members of both samples shows that the MOJAVE-I sources, hosting generally faster jets, have a much higher detection rate than the sources not belonging to this sample. BL Lac objects are more favourably detected than QSOs in gamma-rays, in the same rate for both samples.
The up to 150 day uninterrupted high-precision photometry of about 100000 stars - provided so far by the exoplanet channel of the CoRoT space telescope - gave a new perspective on the planet population of our galactic neighbourhood. The seven planets with very accurate parameters widen the range of known planet properties in almost any respect. Giant planets have been detected at low metallicity, rapidly rotating and active, spotted stars. CoRoT-3 populated the brown dwarf desert and closed the gap of measured physical properties between standard giant planets and very low mass stars. CoRoT extended the known range of planet masses down to 5 Earth masses and up to 21 Jupiter masses, the radii to less than 2 Earth radii and up to the most inflated hot Jupiter found so far, and the periods of planets discovered by transits to 9 days. Two CoRoT planets have host stars with the lowest content of heavy elements known to show a transit hinting towards a different planet-host-star-metallicity relation then the one found by radial-velocity search programs. Finally the properties of the CoRoT-7b prove that terrestrial planets with a density close to Earth exist outside the Solar System. The detection of the secondary transit of CoRoT-1 at the $10^{-5}$-level and the very clear detection of the 1.7 Earth radii of CoRoT-7b at $3.5 10^{-4}$ relative flux are promising evidence of CoRoT being able to detect even smaller, Earth sized planets.
We have observed 8 faint cataclysmic variable stars photometrically. The nova-like Car2 was extensively sampled but showed little variability. V1040 Cen was observed near the end of a dwarf nova outburst and possessed dwarf nova and quasi-periodic oscillations. Ha 075648 has strong large amplitude flickering and a possible orbital modulation at 3.49 h. The correct identification for the nova remnant IL Nor (Nova Nor 1893) has been established. HS Pup (Nova Pup 1963) has a possible orbital period of 3.244 h. SDSS J2048-06 is a low mass transfer dwarf nova that in quiescence shows slow variations at 7.67 h (though poorly sampled with our observations) and an orbital modulation at 87.26 min. The dwarf nova CSS 081419-005022 has an orbital period of 1.796 h and the eclipsing dwarf nova CSS 112634-100210 has an orbital period of 1.8581 h.
We investigate non-Gaussianities in self-interacting curvaton models treating both renormalizable and non-renormalizable polynomial interactions. We scan the parameter space systematically and compute numerically the non-linearity parameters f_NL and g_NL. We find that even in the interaction dominated regime there are large regions consistent with current observable bounds. Whenever the interactions dominate, we discover significant deviations from the relations f_NL ~ 1/r_decay and g_NL ~ 1/r_decay valid for quadratic curvaton potentials, where r_decay measures the curvaton contribution to the total energy density at the time of its decay. Even if r_decay << 1, there always exists regions with f_NL ~ 0 since the sign of f_NL oscillates as a function of the parameters. While g_NL can also change sign, typically g_NL is non-zero in the low-f_NL regions. Hence, for some parameters the non-Gaussian statistics is dominated by g_NL rather than by f_NL. Due to self-interactions, both the relative signs of f_NL and g_NL and the functional relation between them is typically modified from the quadratic case, offering a possible experimental test of the curvaton interactions.
Diffusion of atoms can be important during quiescent phases of stellar evolution. Particularly in the very thin inert envelopes of subdwarf B stars, diffusive movements will considerably change the envelope structure and the surface abundances on a short timescale. Also, the subdwarfs will inherit the effects of diffusion in their direct progenitors, namely giants near the tip of the red giant branch. This will influence the global evolution and the pulsational properties of subdwarf B stars. We investigate the impact of gravitational settling, thermal diffusion and concentration diffusion on the evolution and pulsations of subdwarf B stars. Our diffusive stellar models are compared with models evolved without diffusion. We constructed subdwarf B models with a mass of 0.465 Msun from a 1 and 3 Msun ZAMS progenitor. The low mass star ignited helium in an energetic flash, while the intermediate mass star started helium fusion gently. For each progenitor type we computed series with and without atomic diffusion. Atomic diffusion in red giants causes the helium core mass at the onset of helium ignition to be larger. We find an increase of 0.0015 Msun for the 1 Msun model and 0.0036 Msun for the 3 Msun model. The effects on the red giant surface abundances are small after the first dredge up. The evolutionary tracks of the diffusive subdwarf B models are shifted to lower surface gravities and effective temperatures due to outward diffusion of hydrogen. This affects both the frequencies of the excited modes and the overall frequency spectrum. Especially the structure and pulsations of the post-non-degenerate sdB star are drastically altered, proving that atomic diffusion cannot be ignored in these stars.
We study the substructure statistics of a representative sample of galaxy clusters by means of two currently popular substructure characterisation methods, power ratios and centroid shifts. We use the 31 clusters from the REXCESS sample, compiled from the southern ROSAT All-Sky cluster survey REFLEX with a morphologically unbiased selection in X-ray luminosity and redshift, all of which have been reobserved with XMM-Newton. We investigate the uncertainties of the substructure parameters and examine the dependence of the results on projection effects, finding that the uncertainties of the parameters can be quite substantial. Thus while the quantification of the dynamical state of individual clusters with these parameters should be treated with extreme caution, these substructure measures provide powerful statistical tools to characterise trends of properties in large cluster samples. The centre shift parameter, w, is found to be more sensitive in general. For the REXCESS sample neither the occurence of substructure nor the presence of cool cores depends on cluster mass. There is a significant anti-correlation between the existence of substantial substructure and cool cores. The simulated clusters show on average larger substructure parameters than the observed clusters, a trend that is traced to the fact that cool regions are more pronounced in the simulated clusters, leading to stronger substructure measures in merging clusters and clusters with offset cores. Moreover, the frequency of cool regions is higher in the simulations than in the observations, implying that the description of the physical processes shaping cluster formation in the simulations requires further improvement.
The combined information from cosmic ray air showers that trigger both the surface and underground parts of the IceCube Neutrino Observatory allows the reconstruction of both the energy and mass of the primary particle through the knee region of the energy spectrum and above. The properties of high-energy muon bundles, created early in the formation of extensive air showers and capable of penetrating deep into the ice, are related to the primary energy and composition. New methods for reconstructing the direction and composition-sensitive properties of muon bundles are shown. Based on a likelihood minimization procedure using IceCube signals, and accounting for photon propagation, ice properties, and the energy loss processes of muons in ice, the muon bundle energy loss is reconstructed. The results of the high-energy muon bundle reconstruction in the deep ice and the reconstruction of the lateral distribution of low energy particles in the surface detector can be combined to study primary composition and energy. The performance and composition sensitivity for both simulated and experimental data are discussed.
We investigate the possible nonlinear variability properties of the black hole X-ray nova 4U1543-47 to complement the temporal studies based on linear techniques, and to search for signs of nonlinearity in Galactic black hole (GBH) light curves. First, we apply the weighted scaling index method (WSIM) to characterize the X-ray variability properties of 4U1543-47 in different spectral states during the 2002 outburst. Second, we use surrogate data to investigate whether the variability is nonlinear in any of the different spectral states. The main findings can be summarized as follows. The mean weighted scaling index appears to be able to parametrize uniquely the temporal variability properties of this GBH: the 3 different spectral states of the 2002 outburst of 4U1543-47 are characterized by different and well constrained values. The search for nonlinearity reveals that the variability is linear in all light curves with the notable exception of the very high state. Our results imply that we can use the WSIM to assign a single number, namely the mean weighted scaling index, to a light curve, and in this way discriminate among the different spectral states of a source. The detection of nonlinearity in the VHS, that is characterized by the presence of most prominent QPOs, suggests that intrinsically linear models which have been proposed to account for the low frequency QPOs in GBHs may be ruled out (abridged).
High resolution observations with the NIR adaptive optics integral field spectrograph SINFONI at the VLT proved the existence of massive and young nuclear star clusters in the centres of a sample of Seyfert galaxies. With the help of three-dimensional high resolution hydrodynamical simulations with the Pluto code, we follow the evolution of such clusters, focusing on stellar mass loss. This leads to clumpy or filamentary inflow of gas on large scales (tens of parsec), whereas a turbulent and very dense disc builds up on the parsec scale. In order to capture the relevant physics in the inner region, we treat this disc separately by viscously evolving the radial surface density distribution. This enables us to link the tens of parsec scale region (accessible via SINFONI observations) to the (sub-)parsec scale region (observable with the MIDI instrument and via water maser emission). In this work, we concentrate on the effects of a parametrised turbulent viscosity to generate angular momentum and mass transfer in the disc and additionally take star formation into account. Input parameters are constrained by observations of the nearby Seyfert 2 galaxy NGC 1068. At the current age of its nuclear starburst of 250 Myr, our simulations yield disc sizes of the order of 0.8 to 0.9 pc, gas masses of 1.0e6 solar masses and mass transfer rates of 0.025 solar masses per year through the inner rim of the disc. This shows that our large scale torus model is able to approximately account for the disc size as inferred from interferometric observations in the mid-infrared and compares well to the extent and mass of a rotating disc structure as inferred from water maser observations. Several other observational constraints are discussed as well.
We study the dynamical evolution of globular clusters containing primordial binaries, including full single and binary stellar evolution using our Monte Carlo cluster evolution code updated with an adaptation of the single and binary stellar evolution codes SSE/BSE from Hurley et. al (2000, 2002). We describe the modifications we have made to the code. We present several test calculations and comparisons with existing studies to illustrate the validity of the code. We show that our code finds very good agreement with direct N-body simulations including primordial binaries and stellar evolution. We find significant differences in the evolution of the global properties of the simulated clusters using stellar evolution compared to simulations without any stellar evolution. In particular, we find that the mass loss from stellar evolution acts as a significant energy production channel simply by reducing the total gravitational binding energy and can significantly prolong the initial core contraction phase before reaching the binary-burning quasi steady state of the cluster evolution as noticed in Paper IV. We simulate a large grid of clusters varying the initial cluster mass, binary fraction, and concentration and compare properties of the simulated clusters with those of the observed Galactic globular clusters (GGCs). We find that our simulated cluster properties agree well with the observed GGC properties. We explore in some detail qualitatively different clusters in different phases of their evolution, and construct synthetic Hertzprung-Russell diagrams for these clusters.
We report discovery of a young L dwarf binary, SDSS J2249+0044AB, found as the result of a Keck laser guide star adaptive optics imaging survey of young field brown dwarfs. Weak KI, NaI, and FeH features as well as strong VO absorption in the integrated-light J-band spectrum indicate a low surface gravity and hence young age for the system. From spatially resolved K-band spectra we determine spectral types of L3+-0.5 and L5+-1 for components A and B, respectively. SDSS J2249+0044A is spectrally very similar to G196-3B, an L3 companion to a young M2.5 field dwarf, thus we adopt 20-300 Myr (the age range of the G196-3 system) as the age of SDSS J2249+0044AB. By comparing our photometry to the absolute magnitudes of G196-3B we estimate a distance to SDSS J2249+0044AB of 54+-16 pc. Comparison of the luminosities to evolutionary models at an age of 100 Myr yields masses of 0.029+-0.006 and 0.022 +0.006-0.009 M_sun for SDSS J2249+0044A and B, respectively. Evolutionary models predict that either component could be burning deuterium, which could result in a mass ratio as low as 0.4, or alternatively, a reversal in the luminosities of the binary. The space motion of SDSS J2249+0044AB shows no obvious coincidence with known young moving groups, though radial velocity and parallax measurements are necessary to refine our analysis. The unusually red near-IR colors, young age, and low masses of the binary make it an important template for studying planetary-mass objects found by direct imaging surveys.
We obtain renormalized sets of right and left eigenvectors of the flux vector Jacobians of the relativistic MHD equations, which are regular and span a complete basis in any physical state including degenerate ones. The renormalization procedure relies on the characterization of the degeneracy types in terms of the normal and tangential components of the magnetic field to the wavefront in the fluid rest frame. Proper expressions of the renormalized eigenvectors in conserved variables are obtained through the corresponding matrix transformations. Our work completes previous analysis that present different sets of right eigenvectors for non-degenerate and degenerate states, and can be seen as a relativistic generalization of earlier work performed in classical MHD. Based on the full wave decomposition (FWD) provided by the the renormalized set of eigenvectors in conserved variables, we have also developed a linearized (Roe-type) Riemann solver. Extensive testing against one- and two-dimensional standard numerical problems allows us to conclude that our solver is very robust. When compared with a family of simpler solvers that avoid the knowledge of the full characteristic structure of the equations in the computation of the numerical fluxes, our solver turns out to be less diffusive than HLL and HLLC, and comparable in accuracy to the HLLD solver. The amount of operations needed by the FWD solver makes it less efficient computationally than those of the HLL family in one-dimensional problems. However its relative efficiency increases in multidimensional simulations.
We present a new approach to study the properties of the sun. We consider small variations of the physical and chemical properties of the sun with respect to Standard Solar Model predictions and we linearize the structure equations to relate them to the properties of the solar plasma. By assuming that the (variation of) the present solar composition can be estimated from the (variation of) the nuclear reaction rates and elemental diffusion efficiency in the present sun, we obtain a linear system of ordinary differential equations which can be used to calculate the response of the sun to an arbitrary modification of the input parameters (opacity, cross sections, etc.). This new approach is intended to be a complement to the traditional methods for solar model calculation and allows to investigate in a more efficient and transparent way the role of parameters and assumptions in solar model construction. We verify that these Linear Solar Models recover the predictions of the traditional solar models with an high level of accuracy.
We report on the radio-emission characteristics of 222 interplanetary (IP) shocks. A surprisingly large fraction of the IP shocks (~34%) is radio quiet (i.e., the shocks lacked type II radio bursts). The CMEs associated with the RQ shocks are generally slow (average speed ~535 km/s) and only ~40% of the CMEs were halos. The corresponding numbers for CMEs associated with radio loud (RL) shocks are 1237 km/s and 72%, respectively. The RQ shocks are also accompanied by lower peak soft X-ray flux. CMEs associated with RQ (RL) shocks are generally accelerating (decelerating). The kinematics of CMEs associated with the km type II bursts is similar to those of RQ shocks, except that the former are slightly more energetic. Comparison of the shock The RQ shocks seem to be mostly subcritical and quasi-perpendicular. The radio-quietness is predominant in the rise phase and decreases through the maximum and declining phases of solar cycle 23. The solar sources of the shock-driving CMEs follow the sunspot butterfly diagram, consistent with the higher-energy requirement for driving shocks.
In a logamediate inflationary universe model we introduce the curvaton field in order to bring this inflationary model to an end. In this approach we determine the reheating temperature. We also outline some interesting constraints on the parameters that describe our models. Thus, we give the parameter space in this scenario.
The very high energy (VHE; E > 100 GeV) gamma-ray blazar Markarian 501 has a history of extreme spectral variability and is an excellent laboratory for studying the physical processes within the jets of active galactic nuclei. A short term multi-wavelength study of Markarian 501 was coordinated in March 2009 using the Suzaku X-ray satellite as well as the VERITAS and MAGIC experiments to cover the critical X-ray and VHE gamma-ray bands. The results of the quiescent-state observations with VERITAS and Suzaku are combined with public data from the Fermi Gamma-ray Space Telescope and compared to historical observations of the source during an extreme outburst, to examine the spectral variability, particularly how the spectral energy distribution varies with flux.
The cosmological singularities of the Bianchi I universe are analyzed in the setting of loop geometry underlying the loop quantum cosmology. We solve the Hamiltonian constraint of the theory and find the Lie algebra of elementary observables. Physical compound observables are defined in terms of elementary ones. Modification of classical theory by holonomy around a loop removes the singularities. However, our model has a free parameter that cannot be determined within our method. Testing the model by the data of observational cosmology may be possible after quantization of our modified classical theory.
The stability of isotropic cosmological solutions for two-field models in the Bianchi I metric is considered. We proved that the conditions sufficient for the Lyapunov stability in the Friedmann-Robertson-Walker metric provide the stability with respect to anisotropic perturbations in the Bianchi I metric and with respect to the cold dark matter energy density fluctuations. Sufficient conditions for the Lyapunov stability of the isotropic fixed points of the system of the Einstein equations are found. The standard way to construct cosmological models with exact solutions in the Friedmann-Robertson-Walker metric is the superpotential method. We showed how this method can be applied to construct stable kink-type solutions and obtained conditions on superpotential, which are sufficient conditions for the Lyapunov stability. This result is applied to quintom models inspired by string field theory and the stability of kink-type isotropic solutions in these models is analysed.
We study the quintessential properties of the Black Hole solutions in a scalar--tensor theory of gravity with Higgs potential in view of the static and spherically symmetric line element. In view of our earlier results, Reissner--Nordstr\"om-like and Schwarzschild Black Hole solutions are derived with the introduction of a series-expansion method to solve the field equations without and with Higgs field mass. The physical consequences of the Black Hole solutions and the solutions obtained in the weak field limit are discussed in detail by the virtue of the equation-of-state parameter, the scalar-field excitations and the geodesic motion. The appearance of naked singularities is also discussed together with the dependence of Black Hole horizons on the field excitations, which are themselves dependent on pressure terms which effectively screen the mass terms. A close connection to flat rotation curves following the interaction with the scalar field is also presented in the weak field limit of gravity, together with a discussion of dynamical effects of scalar fields and pressure terms on mass.
A model of induced gravity with a Higgs potential is investigated in detail in view of the consequences of pressure components related to scalar-field excitations in terms of the constraints parting from energy density, solar-relativistic effects and galactic dynamics and dark-matter halos.
We determine the scalar potential for a D3-brane in a warped conifold background subject to general ultraviolet perturbations. Incorporating the effects of imaginary anti-self-dual (IASD) fluxes and four-dimensional curvature at the nonlinear level, we compute the leading terms in the D3-brane potential. We then provide strong cross-checks of our results by reproducing them in the dual gauge theory. Finally, we observe that the D3-brane potential induced by nonperturbative effects on D7-branes can be represented by a ten-dimensional supergravity solution containing suitable IASD fluxes. Our method allows for the systematic inclusion of compactification effects and serves to constrain the D3-brane effective action in a large class of stabilized compactifications.
The solar contribution to global mean air surface temperature change is analyzed by using an empirical bi-scale climate model characterized by both fast and slow characteristic time responses to solar forcing: $\tau_1 =0.4 \pm 0.1$ yr, and $\tau_2= 8 \pm 2$ yr or $\tau_2=12 \pm 3$ yr. Since 1980 the solar contribution to climate change is uncertain because of the severe uncertainty of the total solar irradiance satellite composites. The sun may have caused from a slight cooling, if PMOD TSI composite is used, to a significant warming (up to 65% of the total observed warming) if ACRIM, or other TSI composites are used. The model is calibrated only on the empirical 11-year solar cycle signature on the instrumental global surface temperature since 1980. The model reconstructs the major temperature patterns covering 400 years of solar induced temperature changes, as shown in recent paleoclimate global temperature records.
We take the recent result from the CDMS collaboration as a hint that the dark matter has an elastic scattering cross section with the nucleon in the vicinity of 10^-7 pb. By crossing symmetry such a cross section implies annihilation of dark matter into hadrons inside the halo, resulting in an anti-proton flux that could be constrained by data from the PAMELA collaboration if one includes a large boost factor necessary to explain the PAMELA excess in the positron fraction. As an illustration, we present a model-independent analysis for a fermionic dark matter and study the upper bound on the boost factor using the PAMELA anti-proton flux.
The Cryogenic Dark Matter Search recently announced the observation of two signal events with a 77% confidence level. Although statistically inconclusive, it is nevertheless suggestive. In this work we present a model-independent analysis on the implication of a positive signal in dark matter scattering off nuclei. Assuming the interaction between (scalar, fermion or vector) dark matter and the standard model induced by unknown new physics at the scale $\Lambda$, we examine various dimension-6 tree-level induced operators and constrain them using the current experimental data, e.g. the WMAP data of the relic abundance, CDMS II direct detection of the spin-independent scattering, and indirect detection data (Fermi LAT cosmic gamma-ray), etc. Finally, the LHC reach is also explored.
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This is the second paper of a series reporting the results from the PopStar evolutionary synthesis models. Here we present synthetic emission line spectra of H{\sc ii} regions photoionized by young star clusters, for seven values of cluster masses and for ages between 0.1 and 5.2 Myr. The ionizing Spectral Energy Distributions (SEDs) are those obtained by the PopStar code \citep*{mgb09} for six different metallicities, with a very low metallicity set, Z=0.0001, not included in previous similar works. We assume that the radius of the H{\sc ii} region is the distance at which the ionized gas is deposited by the action of the mechanical energy of the winds and supernovae from the central ionizing young cluster. In this way the ionization parameter is eliminated as free argument, since now its value is obtained from the cluster physical properties (mass, age and metallicity) and from the gaseous medium characteristics (density and abundances). We discuss our results and compare them with those from previous models and also with a large and data set of giant H{\sc ii} regions for which abundances have been derived in a homogeneous manner. The values of the [OIII] lines (at $\lambda\lambda$ 4363, 4959, 5007\AA) in the lowest metallicity nebulae are found to be very weak and similar to those coming from very high metallicity regions (solar or over-solar). Thus, the sole use of the oxygen lines is not enough to distinguish between very low and very high metallicity regions. In these cases we emphasize the need of the additional support of alternative metallicity tracers, like the [SIII] lines in the near-\textit{IR}.
Current cosmological models indicate that the Milky Way's stellar halo was assembled from many smaller systems. Based on the apparent absence of the most metal-poor stars in present-day dwarf galaxies, recent studies claimed that the true Galactic building blocks must have been vastly different from the surviving dwarfs. The discovery of an extremely iron-poor star (S1020549) in the Sculptor dwarf galaxy based on a medium-resolution spectrum cast some doubt on this conclusion. However, verification of the iron-deficiency and measurements of additional elements, such as the alpha-element Mg, are mandatory for demonstrating that the same type of stars produced the metals found in dwarf galaxies and the Galactic halo. Only then can dwarf galaxy stars be conclusively linked to early stellar halo assembly. Here we report high-resolution spectroscopic abundances for 11 elements in S1020549, confirming the iron abundance of less than 1/4000th that of the Sun, and showing that the overall abundance pattern mirrors that seen in low-metallicity halo stars, including the alpha-elements. Such chemical similarity indicates that the systems destroyed to form the halo billions of years ago were not fundamentally different from the progenitors of present-day dwarfs, and suggests that the early chemical enrichment of all galaxies may be nearly identical.
We present a near-infrared extinction study of nine dense cores at evolutionary stages between starless to Class I. Our results show that the density structure of all but one observed cores can be modeled with a single power law rho \propto r^p between ~ 0.2R-R of the cores. The starless cores in our sample show two different types of density structures, one follows p ~ -1.0 and the other follows p ~ -2.5, while the protostellar cores all have p ~ -2.5. The similarity between the prestellar cores with p ~ -2.5 and protostellar cores implies that those prestellar cores could be evolving towards the protostellar stage. The slope of p ~ -2.5 is steeper than that of an singular isothermal sphere, which may be interpreted with the evolutionary model of cores with finite mass.
General relativistic corrections to the expansion rate of the universe arise when the Einstein equations are averaged over a spatial volume in a locally inhomogeneous cosmology. It has been suggested that they may contribute to the observed cosmic acceleration. In this paper, we propose a new scheme that utilizes numerical simulations to make a realistic estimate of the magnitude of these corrections for general inhomogeneities in (3+1) spacetime. We then quantitatively calculate the volume averaged expansion rate using N-body large scale structure simulations and compare it with the expansion rate in a standard FRW cosmology. We find that in the weak gravitational field limit, the corrections are slightly larger than the previous claimed 10^{-5} level, but not large enough to drive the current cosmic acceleration. Nevertheless, the question of whether the cumulative effect can significantly change the expansion history of the universe needs to be further investigated with the strong field relativity.
A quick guide on how to use the FXCOR task in IRAF to cross-correlate a galaxy spectrum to a template star, in order to extract the galaxy's velocity dispersion.
To realize the accelerations in the early and late periods of our universe, we need to specify potentials for the dominant fields. In this paper, by using the Noether symmetry approach, we try to find suitable potentials in the "cosmic triad" vector field scenario. Because the equation of state parameter has been constrained in the range of $-1.21\leq \omega\leq -0.89$ by observations, we derive the Noether conditions for the vector field in quintessence, phantom and quintom models, respectively. In the first two cases, constant potential solutions have been obtained. What is more, a fast decaying point solution with power-law potential is also found for the vector field in quintessence model. For the quintom case, we find an interesting constraint $\tilde{C}V_{p}'=-CV_{q}'$ on the field potentials, where $C$ and $\tilde{C}$ are constants related to the Noether symmetry.
We present a study of the centroid frequencies and phase lags of the quasi-periodic oscillations (QPOs) as functions of photon energy for GRS 1915+105. It is found that the centroid frequencies of the 0.5-10 Hz QPOs and their phase lags are both energy dependent, and there exists an anti-correlation between the QPO frequency and phase lag. These new results challenge the popular QPO models, because none of them can fully explain the observed properties. We suggest that the observed QPO phase lags are partially due to the variation of the QPO frequency with energy, especially for those with frequency higher than 3.5 Hz.
The high mass X-ray binary 4U 1901+03 was reported to have the pulse profile evolving with the X-ray luminosity and energy during its outburst in February-July 2003: the pulse peak changed from double to single along with the decreasing luminosity. We have carried out a detailed analysis on the contemporary phase-resolved energy spectrum of 4U 1901+03 as observed by Rossi X-ray Timing Explorer (RXTE). We find that, both the continuum and the pulse spectra are phase dependent. The optical depth derived from the pulse spectrum is in general larger than that from the continuum. Fe Ka emission line is only detected in the spectrum of the continuum and is missing in the pulse spectrum. This suggests an origin of Fe emission from the accretion disk but not the surface of the neutron star.
On the basis of the Gerlach-Sengupta theory of gauge-invariant perturbations, a formula of the integrated Sachs-Wolfe effect for a central observer is derived on general spherically symmetric spacetimes. It will be useful for comparative studies of theoretical and observational aspects of the integrated Sachs-Wolfe effect in the Lemaitre-Tolman-Bondi cosmological models which have been noticed by explaining the apparent acceleration without cosmological constant.
We apply epicyclic resonances to the magnetic connection (MC) of a black hole (BH) with a relativistic accretion disc, interpreting the high frequency quasi-periodic oscillations (HFQPOs) with 3:2 pairs observed in three BH X-ray binaries. It turns out that the 3:2 HFQPO pairs are associated with the steep power-law states, and the severe damping can be overcome by transferring energy and angular momentum from a spinning BH to the inner disc in the MC process.
Numeric convergence studies demonstrate that the evolution of an adiabatic clump is well-captured by roughly 100 cells per clump radius. The presence of radiative cooling, however, imposes limits on the problem due to the removal of thermal energy. Numerical studies which include radiative cooling typically adopt the 100--200 cells per clump radius resolution. In this paper we present the results of a convergence study for radiatively cooling clumps undertaken over a broad range of resolutions, from 12 to 1,536 cells per clump radius, employing adaptive mesh refinement (AMR) in a 2D axisymmetric geometry ("2.5D"). We also provide a fully 3D simulation, at 192 cells per clump radius, which supports our 2.5D results. We find no appreciable self-convergence at ~100 cells per clump radius as small-scale differences owing to increasingly resolving the "cooling length" have global effects. We therefore conclude that self-convergence is an insufficient criterion to apply on its own when addressing the question of sufficient resolution for radiatively cooled shocked clump simulations. We suggest the adoption of alternate criteria to support a statement of sufficient resolution, such as the demonstration of adequate resolution of the cooling layers behind shocks. We discuss an associated refinement criteria for AMR codes.
The population of binary systems known to emit in the GeV and TeV bands consists of only a few firmly identified Galactic sources. These rare objects constitute extreme particle accelerators operating under varying, but regularly repeating, conditions. As such, they provide access to a unique laboratory in which to study particle acceleration, and the nature of gamma-ray production, emission and absorption processes near compact objects. Here we review the current observational status of the field, and discuss some of the recent interpretations of the results.
Several Cardassian universe models including the original, modified polytropic and exponential Cardassian models are constrained by the latest Constitution Type Ia supernova data, the position of the first acoustic peak of CMB from the five years WMAP data and the size of baryonic acoustic oscillation peak from the SDSS data. Both the spatial flat and curved universe are studied, and we also take account of the possible bulk viscosity of the matter fluid in the flat universe case.
The Hayabusa Spacecraft Asteroid Multiband Imaging Camera (AMICA) has acquired more than 1400 multispectral and high-resolution images of its target asteroid, 25143 Itokawa, since late August 2005. In this paper, we summarize the design and performance of AMICA. In addition, we describe the calibration methods, assumptions, and models, based on measurements. Major calibration steps include corrections for linearity and modeling and subtraction of bias, dark current, read-out smear, and pixel-to-pixel responsivity variations. AMICA v-band data were calibrated to radiance using in-flight stellar observations. The other band data were calibrated to reflectance by comparing them to ground-based observations to avoid the uncertainty of the solar irradiation in those bands. We found that the AMICA signal was linear with respect to the input signal to an accuracy of << 1% when the signal level was < 3800 DN. We verified that the absolute radiance calibration of the AMICA v-band (0.55 micron) was accurate to 4% or less, the accuracy of the disk-integrated spectra with respect to the AMICA v-band was about 1%, and the pixel-to-pixel responsivity (flatfield) variation was 3% or less. The uncertainty in background zero-level was 5 DN. From wide-band observations of star clusters, we found that the AMICA optics have an effective focal length of 120.80 \pm 0.03 mm, yielding a field-of-view (FOV) of 5.83 deg x 5.69 deg. The resulting geometric distortion model was accurate to within a third of a pixel. We demonstrated an image-restoration technique using the point-spread functions of stars, and confirmed that the technique functions well in all loss-less images. An artifact not corrected by this calibration is scattered light associated with bright disks in the FOV.
We present the improved distance moduli of 30 galaxies in the Canes Venatici I Cloud using advanced Tip of Red Giant Branch (TRGB) method (Makarov et.al. 2006). The method was determined for accurate estimation of the distances even if TRGB situated near photometric limit. The data were taken from the Archive of the Hubble Space Telescope (HST). Based on ACS and WFPC2 images of the HST we construct the color-magnitude diagrams of the resolved stellar population of the galaxies using Dolphot and HSTPhot packages. New refined method of the distance determination allows us to clarify the 3D structure of the Canes Venatici I Cloud. It consists of the central group of galaxies around M94 and the outskirt which is situated in gravitational field of the "core". The mass and mass-to-light ratio of the CVn have been estimated.
The onset of GRB afterglow is characterized by a smooth bump in the early afterglow lightcurve. We make an extensive search for such a feature. Twenty optically selected GRBs and 12 X-ray selected GRBs are found, among which 17 optically selected GRBs and 2 X-ray-selected GRBs have redshift measurements. We fit the lightcurves with a smooth broken power-law and measure the temporal characteristic timescales of the bumps at FWHM. Strong mutual correlations among these timescales are found, and a dimmer and broader bump tends to peak at a later peak time. The ratio of rising to decaying timescales is almost universal among bursts, but the ratio of the rising time to the peak time varies from 0.3~1. The E_iso is tightly correlated with the peak luminosity and the peak time of the bump in the burst frame. Assuming that the bumps signal the deceleration of the GRB fireballs in a constant density medium, we calculate the initial Lorentz factor (Gamma_0) and the deceleration radius (R_dec) of the GRBs in the optical-selected sample. It is found that Gamma_0 are typically a few hundreds, and the typical deceleration radius is R_dec~10^{17} cm. More intriguingly, a tight correlation between the Gamma_0 and E_iso is found, namely Gamma_0 ~ 195 E_iso, 52}^{0.27} (satisfied for both the optical and X-ray z-known samples). It is helpful to understand GRB physics, and may serve as an indicator of Gamma_0. We find that the early bright X-rays are usually dominated by a different component from the external shock emission, but occasionally (for one case) an achromatic deceleration feature is observed. Components in X-rays would contribute to the diversity of the observed X-ray lightcurves (abridge).
Results of the experiments on daemon detection performed in St-Petersburg in March 2009 are presented. Adding the data obtained with the daemon-sensitive FEU-167-1 PM tubes to the data amassed in our previous measurements (starting from 2000) raises the confidence level of existence of the spring maximum in NEACHO (near-Earth almost circular heliocentric orbit) daemon flux to ~5Sigma. The first test experiments conducted with the "dark" electron multiplier tubes, - TEU-167 with a thick (~0.5 um) Al coating over all of the inner surface of the near-cathode multiplier section, including also its front screen, look encouraging. They provide supportive evidence for the existence of diurnal modulation of the daemon flux and offer ~3.4x10-7 cm-2s-1 for its lower limit in March, in good agreement with our earlier estimates and measurements.
The Saturnian coorbital satellites Janus and Epimetheus present a unique dynamical configuration in the Solar System, because of high-amplitude horseshoe orbits, due to a mass ratio of order unity. As a consequence, they swap their orbits every 4 years, while their orbital periods is about 0.695 days. Recently, Tiscareno et al.(2009) got observational informations on the shapes and the rotational states of these satellites. In particular, they detected an offset in the expected equilibrium position of Janus, and a large libration of Epimetheus. We here propose to give a 3-dimensional theory of the rotation of these satellites in using these observed data, and to compare it to the observed rotations. We consider the two satellites as triaxial rigid bodies, and we perform numerical integrations of the system in assuming the free librations as damped. The periods of the three free librations we get, associated with the 3 dimensions, are respectively 1.267, 2.179 and 2.098 days for Janus, and 0.747, 1.804 and 5.542 days for Epimetheus. The proximity of 0.747 days to the orbital period causes a high sensitivity of the librations of Epimetheus to the moments of inertia. Our theory explains the amplitude of the librations of Janus and the error bars of the librations of Epimetheus, but not an observed offset in the orientation of Janus.
We study the utility of wavelets for detecting the redshift evolution of the dark energy equation of state w(z) from the combination of supernovae, CMB and BAO data. We show that local features in w, such as bumps, can be detected efficiently using wavelets. To demonstrate, we first generate a mock supernovae (SNe) data sample for a SNAP-like survey with a bump feature in w(z) hidden in, then successfully discover it by performing a blind wavelet analysis. We also apply our method to analyze the recently released "Constitution" SNe data, combined with WMAP and BAO from SDSS, and find weak hints of dark energy dynamics. Namely, we find that models with w(z) < -1 for 0.2 < z < 0.5, and w(z)> -1 for 0.5 < z <1, are mildly favored at 95% confidence level. This is in good agreement with several recent studies using other methods, such as redshift binning with principal component analysis (PCA) (e.g. Zhao and Zhang, arXiv:0908.1568)
The overall properties of the Herbig-Haro objects such as centerline velocity, transversal profile of velocity, flow of mass and energy are explained adopting two models for the turbulent jet. The complex shapes of the Herbig-Haro objects, such as the arc in HH34 can be explained introducing the combination of different kinematic effects such as velocity behavior along the main direction of the jet and the velocity of the star in the interstellar medium. The behavior of the intensity or brightness of the line of emission is explored in three different cases : transversal 1D cut, longitudinal 1D cut and 2D map. An analytical explanation for the enhancement in intensity or brightness such as usually modeled by the bow shock is given by a careful analysis of the geometrical properties of the torus.
When it comes to identifying or to characterizing gamma-ray sources, X-ray observations are of paramount importance. Correlated X-and-gamma-ray flux variations are a powerful identification tool, if the gamma-ray source is unidentified, or an important diagnostic tool to understand the behaviour of an identified source. Moreover, X-ray observations of non-variable unidentified gamma-ray sources, both galactic and extragalactic, can unveil interesting candidate counterparts, narrowing down the search space and improving significantly the chances for a successful identification. Swift observations of Fermi gamma-ray-selected pulsar error boxes provide accurate positions of likely counterparts. This makes it possible both to confirm pulsations and to improve timing solution, opening up a new synergy between X and gamma ray observations.
We deduce on hourly basis the spatial gradient of the cosmic ray density in three dimensions from the directional anisotropy of high-energy (~50 GeV) galactic cosmic ray (GCR) intensity observed with a global network of muon detectors on the Earth's surface. By analyzing the average features of the gradient in the corotational interaction regions (CIRs) recorded in successive two solar activity minimum periods, we find that the observed latitudinal gradient (Gz) changes its sign from negative to positive on the Earth's heliospheric current sheet (HCS) crossing from the northern to the southern hemisphere in A<0 epoch, while it changes from positive to negative in A>0 epoch. This is in accordance with the drift prediction. We also find a negative enhancement in Gx after the HCS crossing in both A<0 and A>0 epochs, but not in Gy. This asymmetrical feature of Gx and Gy indicates significant contributions from the parallel and perpendicular diffusions to the the gradient in CIRs in addition to the contribution from the drift effect.
The rationale behind recent calibrations of the Cepheid PL relation using the Wesenheit formulation is reviewed and reanalyzed, and it is shown that recent conclusions regarding a possible change in slope of the PL relation for short-period and long-period Cepheids are tied to a pathological distribution of HST calibrators within the instability strip. A recalibration of the period-luminosity relation is obtained using Galactic Cepheids in open clusters and groups, the resulting relationship, described by log L/L_sun = 2.415(+-0.035) + 1.148(+-0.044)log P, exhibiting only the moderate scatter expected from color spread within the instability strip. The relationship is confirmed by Cepheids with HST parallaxes, although without the need for Lutz-Kelker corrections, and in general by Cepheids with revised Hipparcos parallaxes, albeit with concerns about the cited precisions of the latter. A Wesenheit formulation of Wv = -2.259(+-0.083) - 4.185(+-0.103)log P for Galactic Cepheids is tested successfully using Cepheids in the inner regions of the galaxy NGC 4258, confirming the independent geometrical distance established for the galaxy from OH masers. Differences between the extinction properties of interstellar and extragalactic dust may yet play an important role in the further calibration of the Cepheid PL relation and its application to the extragalactic distance scale.
The Gaia satellite, to be launched in 2012, will offer an unprecedented survey of the whole sky down to magnitude 20. The multi-epoch nature of the mission provides a unique opportunity to study variable sources with their astrometric, photometric, spectro-photometric and radial velocity measurements. Many tens of millions of classical variable objects are expected to be detected, mostly stars but also QSOs and asteroids. The high number of objects observed by Gaia will enable statistical studies of populations of variable sources and of their properties. But Gaia will also allow the study of individual objects to some depth depending on their variability types, and the identification of potentially interesting candidates that would benefit from further ground based observations by the scientific community. Within the Gaia Data Processing and Analysis Consortium (DPAC), which is subdivided into 9 Coordination Units (CU), one (CU7) is dedicated to the variability analysis. Its goal is to provide information on variable sources for the Gaia intermediate and final catalogue releases.
If a sizeable fraction of the energy of supernova remnant shocks is channeled into energetic particles (commonly identified with Galactic cosmic rays), then the morphological evolution of the remnants must be distinctly modified. Evidence of such modifications has been recently obtained with the Chandra and XMM-Newton X-ray satellites. To investigate these effects, we coupled a semi-analytical kinetic model of shock acceleration with a 3D hydrodynamic code (by means of an effective adiabatic index). This enables us to study the time-dependent compression of the region between the forward and reverse shocks due to the back reaction of accelerated particles, concomitantly with the development of the Rayleigh-Taylor hydrodynamic instability at the contact discontinuity. Density profiles depend critically on the injection level eta of particles: for eta up to about 10^-4 modifications are weak and progressive, for eta of the order of 10^-3 modifications are strong and immediate. Nevertheless, the extension of the Rayleigh-Taylor unstable region does not depend on the injection rate. A first comparison of our simulations with observations of Tycho's remnant strengthens the case for efficient acceleration of protons at the forward shock.
I argue that Einstein overlooked an important aspect of the relativity of time in never quite realizing his quest to embody Mach's principle in his theory of gravity. As a step towards that goal, I broaden the Strong Equivalence Principle to a new principle of physics, the Cosmological Equivalence Principle, to account for the role of the evolving average regional density of the universe in the synchronisation of clocks and the relative calibration of inertial frames. In a universe dominated by voids of the size observed in large-scale structure surveys, the density contrasts of expanding regions are strong enough that a relative deceleration of the background between voids and the environment of galaxies, typically of order 10^{-10} m/s^2, must be accounted for. As a result one finds a universe whose present age varies by billions of years according to the position of the observer: a timescape. This model universe is observationally viable: it passes three critical independent tests, and makes additional predictions. Dark energy is revealed as a mis-identification of gravitational energy gradients and the resulting variance in clock rates. Understanding the biggest mystery in cosmology therefore involves a paradigm shift, but in an unexpected direction: the conceptual understanding of time and energy in Einstein's own theory is incomplete.
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