The discovery of cosmic acceleration has presented a unique challenge for cosmologists. As observational cosmology forges ahead, theorists have struggled to make sense of a standard model that requires extreme fine tuning. This challenge is known as the cosmological constant problem. The theory of gravitational aether is an alternative to general relativity that does not suffer from this fine-tuning problem, as it decouples the quantum field theory vacuum from geometry, while remaining consistent with other tests of gravity. In this paper, we study static black hole solutions in this theory and show that it manifests a UV-IR coupling: Aether couples the spacetime metric close to the black hole horizon, to metric at infinity. We then show that using the Trans-Planckian ansatz (as a quantum gravity effect) close to the black hole horizon, leads to an accelerating cosmological solution, far from the horizon. Interestingly, this acceleration matches current observations for stellar mass black holes. Based on our current understanding of the black hole accretion history in the Universe, we then make a prediction for how the effective dark energy density should evolve with redshift, which can be tested with future dark energy probes.
Aims. To study at multiple frequencies the radio emission arising from the massive galaxy cluster MACS J0717.5+3745 (z=0.55). Known to be an extremely complex cluster merger, the system is uniquely suited for an investigation of the phenomena at work in the intra-cluster medium (ICM) during cluster collisions. Methods. We use multi-frequency and multi-resolution data obtained with the Very Large Array radio telescope, and X-ray features revealed by Chandra, to probe the non-thermal and thermal components of the ICM, their relations and interactions. Results. The cluster shows highly complex radio emission. A bright, giant radio halo is detected at frequencies as high as 4.8 GHz. MACS J0717.5+3745 is the most distant cluster currently known to host a radio halo. This radio halo is also the most powerful ever observed, and the second case for which polarized radio emission has been detected, indicating that the magnetic field is ordered on large scales.
Galaxy formation models typically assume that the size and rotation speed of galaxy disks are largely dictated by the mass, concentration, and spin of their surrounding dark matter haloes. Equally important, however, are the fraction of baryons in the halo that collect into the central galaxy, as well as the net angular momentum that they are able to retain during its assembly process. We explore the latter using a set of four large cosmological N-body/gasdynamical simulations drawn from the OWLS (OverWhelmingly Large Simulations) project. These runs differ only in their implementation of feedback from supernovae. We find that, when expressed as fractions of their virial values, galaxy mass and net angular momentum are tightly correlated. Galaxy mass fractions, m_d=M_gal/M_vir, depend strongly on feedback, but only weakly on halo mass or spin over the halo mass range explored here (M_vir>1e11 h^{-1}M_sun). The angular momentum of a galaxy, j_d=J_gal/J_vir, correlates with m_d in a manner that is insensitive to feedback and that deviates strongly from the simple j_d = m_d assumption often adopted in semi-analytic models of galaxy formation. The m_d-j_d correlation implies that, in a given halo, galaxy disk size is maximal when the central galaxy makes up a substantial fraction (~20%-30%) of all baryons within the virial radius. At z=2, such systems may host gaseous disks with radial scale lengths as large as those reported for star-forming disks by the SINS survey, even in moderately massive haloes of average spin. Extended disks at z=2 may thus signal the presence of systems where galaxy formation has been particularly efficient, rather than the existence of haloes with unusually high spin parameter.
We use the OWLS (OverWhelmingly Large Simulations) set of cosmological Nbody/gasdynamical simulations to study the properties of simulated galaxies at z=2. We focus on the effect of supernova feedback from evolving stars on the baryonic mass and angular momentum content of galaxies that assemble at the center of 1e11-3e12 h^{-1}M_\odot halos. Our main finding is that the mass and angular momentum of such galaxies are strongly coupled, in a way that is approximately independent of feedback: varying the feedback implementation leads, in a given halo, to large variations in galaxy mass but leaves the galaxy mass-angular momentum correlation largely unaltered. In particular, the ratio between the angular momentum of a galaxy and that of its surrounding halo (j_d=J_gal/J_vir) correlates closely with the galaxy mass (expressed in units of the virial mass of the halo; m_d=M_gal/M_vir). This correlation differs substantially from the m_d=j_d assumption commonly adopted in semianalytic models of galaxy formation. We use these results to infer the sizes of disk galaxies at z=2 expected in the LCDM scenario and to interpret recent observations of extended disks at z~2 by the SINS collaboration
We present a harmonic expansion of the observed line-of-sight velocity field as a method to recover and investigate spiral structures in the nuclear regions of galaxies. Application to the emission-line velocity field within the circumnuclear starforming ring of NGC1097, obtained with the GMOS-IFU spectrograph, reveals a three-arm spiral in the non-circular motions, which agrees with a two-arm dust spiral in the surface brightness. This nuclear spiral is consistent with a weak perturbation in the gravitational potential due to a two-arm logarithmic spiral, with a pitch angle of 52+/-4 degrees derived directly from the harmonic expansion of the velocity field. Next, we use a simple spiral perturbation model to constrain the fraction of the measured non-circular motions that is due to radial inflow. We combine the resulting inflow velocity with the gas density in the spiral arms, inferred from emission line ratios, to estimate the mass inflow rate as a function of radius, which reaches about 0.011 Msun/yr at a distance of 70 pc from the center. This corresponds to a fraction of about 4.2 x 10^{-3} of the Eddington mass accretion rate onto the central black hole in NGC1097, and is fully consistent with previous mass accretion models fitted to the observed spectral energy distribution in the nucleus of this LINER/Seyfert1 galaxy. We conclude that the line-of-sight velocity not only can provide a cleaner view of nuclear spirals than the associated dust, but that the presented method also allows the quantitative study of these possibly important links in fueling the centers of galaxies, including providing a handle on the mass inflow rate as a function of radius.
Massive stars drive powerful, supersonic winds via the radiative momentum associated with the thermal UV emission from their photospheres. Shock phenomena are ubiquitous in these winds, heating them to millions, and sometimes tens of millions, of degrees. The emission line spectra from the shock-heated plasma provide powerful diagnostics of the winds' physical conditions, which in turn provide constraints on models of wind shock heating. Here I show how x-ray line transfer is affected by photoelectric absorption in the partially ionized component of the wind and how it can be modeled to determine the astrophysically important mass-loss rates of these stellar winds. I also discuss how photoexcitation out of metastable excited levels of helium-like ions can provide critical information about the location of the hot plasma in magnetically channeled massive star winds.
We investigate the cosmological-scale influence of outflows driven by AGNs on metal enrichment of the intergalactic medium. AGNs are located in dense cosmological structures which tend to be anisotropic. We designed a semi-analytical model for anisotropic AGN outflows which expand away along the direction of least resistance. This model was implemented into a cosmological numerical simulation algorithm for simulating the growth of large-scale structure in the universe. Using this modified algorithm, we perform a series of 9 simulations inside cosmological volumes of size $(128 h^{-1}{\rm Mpc})^3$, in a concordance $\Lambda$CDM universe, varying the opening angle of the outflows, the lifetimes of the AGNs, their kinetic fractions, and their level of clustering. For each simulation, we compute the volume fraction of the IGM enriched in metals by the outflows. The resulting enriched volume fractions are relatively small at $z \gtrsim 2.5$, and then grow rapidly afterward up to $z = 0$. We find that AGN outflows enrich from 65% to 100% of the entire universe at the present epoch, for different values of the model parameters. The enriched volume fraction depends weakly on the opening angle of the outflows. However, increasingly anisotropic outflows preferentially enrich underdense regions, a trend found more prominent at higher redshifts and decreasing at lower redshifts. The enriched volume fraction increases with increasing kinetic fraction and decreasing AGN lifetime and level of clustering.
We investigate the dependence of stellar properties on the initial kinematic structure of the gas in star-forming molecular clouds. We compare the results from two large-scale hydrodynamical simulations of star cluster formation that resolve the fragmentation process down to the opacity limit, the first of which was reported by Bate, Bonnell and Bromm. The initial conditions of the two calculations are identical, but in the new simulation the power spectrum of the velocity field imposed on the cloud initially and allowed to decay is biased in favour of large-scale motions. Whereas the calculation of Bate et al. began with a power spectrum P(k) ~ k^{-4} to match the Larson scaling relations for the turbulent motions observed in molecular clouds, the new calculation begins with a power spectrum P(k) ~ k^{-6}. Despite this change to the initial motions in the cloud and the resulting density structure of the molecular cloud, the resulting stellar properties resulting from the two calculations are indistinguishable. This demonstrates that the results of such hydrodynamical calculations of star cluster formation are relatively insensitive to the initial conditions. It is also consistent with the fact that the statistical properties of stars and brown dwarfs (e.g. the stellar initial mass function) are observed to be relatively invariant within our Galaxy and do not appear to depend on environment.
The radio-quiet quasar SDSS J1536+0441 shows two broad-line emission systems that Boroson & Lauer interpret as a candidate binary black-hole system with a separation of 0.1 pc (0.02 mas). From new VLA imaging at 8.5 GHz, two faint sources, separated by 0.97 arcsec (5.1 kpc), have been discovered within the quasar's optical localization region. Each radio source is unresolved, with a diameter of less than 0.37 arcsec (1.9 kpc). A double radio structure is seen in some other radio-quiet quasars, and the double may be energized here by the candidate 0.1-pc binary black-hole system. Alternatively, the radio emission may arise from a binary system of quasars with a projected separation of 5.1 kpc, and the two quasars may produce the two observed broad-line emission systems. Binary active galactic nuclei with a kpc scale separation are known from radio and X-ray observations, and a few such system are expected in the Boroson & Lauer sample based on the observed clustering of quasars down to the 10 kpc scale. Future observations designed to distinguish between the 0.1 pc and 5 kpc scales for the binary system are suggested.
We report a large spin-up glitch in PSR J1846-0258 which coincided with the onset of magnetar-like behavior on 2006 May 31. We show that the pulsar experienced an unusually large glitch recovery, with a recovery fraction of Q=5.9+/-0.3, resulting in a net decrease of the pulse frequency. Such a glitch recovery has never before been observed in a rotation-powered pulsar, however, similar but smaller glitch over-recovery has been recently reported in the magnetar AXP 4U 0142+61 and may have occurred in the SGR 1900+14. We discuss the implications of the unusual timing behavior in PSR J1846-0258 on its status as the first identified magnetically active rotation-powered pulsar.
The Method of Light Curve Simulations is a tool that has been applied to X-ray monitoring observations of Active Galactic Nuclei (AGN) for the characterization of the Power Density Spectrum (PDS) of temporal variability and measurement of associated break frequencies (which appear to be an important diagnostic for the mass of the black hole in these systems as well as their accretion state). It relies on a model for the PDS that is fit to the observed data. The determination of confidence regions on the fitted model parameters is of particular importance, and we show how the Neyman construction based on distributions of estimates may be implemented in the context of light curve simulations. We believe that this procedure offers advantages over the method used in earlier reports on PDS model fits, not least with respect to the correspondence between the size of the confidence region and the precision with which the data constrain the values of the model parameters. We plan to apply the new procedure to existing RXTE and XMM observations of Seyfert I galaxies as well as RXTE observations of the Seyfert II galaxy NGC 4945.
A fundamental assumption inherent in the standard Lambda+CDM Hot Big Bang (HBB) model is that photons lose energy as they are redshifted due to the expansion of the universe. We show that for the Quasi-Static Universe (QSU) model, in which photon energy is an invariant in the cosmological reference frame, the photon number density in the universe today is a factor of approximately 1600 less than in the standard model. We examine some of the consequences for a number of processes that occur during the thermal history of the early universe, including primordial nucleosynthesis, the formation of neutral hydrogen (recombination), and the evolution of the Cosmic Microwave Background (CMB) radiation. We show that the QSU model predicts that the measured CMB photon noise level will be a factor of 40 higher than the level that would be observed assuming the standard HBB model. The CMB data that will be collected by the recently launched Planck satellite mission provides an ideal opportunity to test the validity of this prediction.
We present an upper limit of galactic diffuse gamma-ray flux, measured with the GAMMA experiment at energy about 175 TeV. The results were obtained using selection of muon poor extensive air showers at mountain level (700 g/cm^2, Mt. Aragats, Armenia) for 5 GeV muon energy threshold. An upper limit for the differential flux at energy E=175+/-25 TeV is equal to (5.8-7.0)x10^-12 [erg m^2 s sr]^-1 for 95% confidence level.
We present a Differential Emission Measure (DEM) analysis of the quiet solar corona on disk using data obtained by the Extreme-ultraviolet Imaging Spectrometer (EIS) on Hinode. We show that the expected quiet Sun DEM distribution can be recovered from judiciously selected lines, and that their average intensities can be reproduced to within 30%. We present a subset of these selected lines spanning the temperature range log T = 5.6 to 6.4 K that can be used to derive the DEM distribution reliably, including a subset of Iron lines that can be used to derive the DEM distribution free of the possibility of uncertainties in the elemental abundances. The subset can be used without the need for extensive measurements and the observed intensities can be reproduced to within the estimated uncertainty in the pre-launch calibration of EIS. Furthermore, using this subset, we also demonstrate that the quiet coronal DEM distribution can be recovered on size scales down to the spatial resolution of the instrument (1" pixels). The subset will therefore be useful for studies of small-scale spatial inhomogeneities in the coronal temperature structure, for example, in addition to studies requiring multiple DEM derivations in space or time. We apply the subset to 45 quiet Sun datasets taken in the period 2007 January to April, and show that although the absolute magnitude of the coronal DEM may scale with the amount of released energy, the shape of the distribution is very similar up to at least log T $\sim$ 6.2 K in all cases. This result is further evidence that the {\it shape} of the quiet Sun DEM is mainly a function of the radiating and conducting properties of the plasma and is fairly insensitive to the location and rate of energy deposition.
The estimate of the energy deposition rate (EDR) for neutrino pair annihilation has been carried out. The EDR for the neutrinos coming from the equatorial plane of a rotating neutron star is calculated along the rotation axis using the Cook-Shapiro-Teukolsky (CST) metric. The neutrino trajectories and hence the neutrino emitted from the disk is affected by the redshift due to disk rotation and gravitation. The EDR is very sensitive to the value of the temperature and its variation along the disk. The rotation of the star has a negative effect on the EDR, it decreases with increase in rotational velocity.
The Sixth Data Release (DR6) in the Sloan Digital Sky Survey (SDSS) provides more photometric regions, new features and more accurate data around globular cluster Palomar 5. A new method, Back Propagation Neural Network (BPNN), is used to estimate the probability of cluster member to detect its tidal tails. Cluster and field stars, used for training the networks, are extracted over a $40\times20$ deg$^2$ field by color-magnitude diagrams (CMDs). The best BPNNs with two hidden layers and Levenberg-Marquardt (LM) training algorithm are determined by the chosen cluster and field samples. The membership probabilities of stars in the whole field are obtained with the BPNNs, and contour maps of the probability distribution show that a tail extends $5.42\dg$ to the north of the cluster and a tail extends $3.77\dg$ to the south. The whole tails are similar to those detected by \citet{od03}, but no longer debris of the cluster is found to the northeast of the sky. The radial density profiles are investigated both along the tails and near the cluster center. Quite a few substructures are discovered in the tails. The number density profile of the cluster is fitted with the King model and the tidal radius is determined as $14.28'$. However, the King model cannot fit the observed profile at the outer regions ($R > 8'$) because of the tidal tails generated by the tidal force. Luminosity functions of the cluster and the tidal tails are calculated, which confirm that the tails originate from Palomar 5.
We present a summary of our previous investigations of the physical and chemical structure of the Horsehead nebula, and discuss how these studies led to advances on the understanding of the impact of FUV radiation on the structure of dense interstellar clouds. Specific molecular tracers can be used to isolate different environments, that are more sensitive to changes in the FUV radiation or density than the classical tracers of molecular gas : the CO isotopologues or the dust (sub)millimeter continuum emission. They include the HCO or CCH radicals for the FUV illuminated interfaces, or the molecular ions H$^{13}$CO$^+$, DCO$^+$ and other deuterated species (DNC, DCN) for the cold dense core. We discuss future prospects in the context of Herschel and ALMA.
We report the results of spectroscopic observations, obtained with the Gemini North Multi-Object Spectrograph, of 9 planetary nebulae (PNe) and 15 \hii\ regions located in the 5.5\arcmin $\times$5.5\arcmin inner region of the nearby starburst galaxy IC10. Twelve new candidate PNe have been discovered during our pre-imaging phase. Nine of them have been spectroscopically confirmed. The direct availability of the electron temperature diagnostics in several nebulae allowed an accurate determination of the metallicity map of IC10 at two epochs: the present-time from \hii regions and the old/intermediate-age from PNe. We found a non-homogeneous distribution of metals at both epochs, but similar average abundances were found for the two populations. The derived age-metallicity relation shows a little global enrichment interpreted as the loss of metals by SN winds and to differential gas outflows. Finally, we analyzed the production of oxygen --through the third dredge-up-- in the chemical abundance patterns of the PN populations belonging to several dwarf irregular galaxies. We found that the third dredge-up of oxygen is a metallicity dependent phenomenon occurring mainly for 12+$\log$(O/H)$\leq$7.7 and substantially absent in IC10 PNe.
CoRoT-2a is a young (about 0.5 Gyr) G7V star accompanied by a transiting hot-Jupiter, discovered by the CoRoT satellite (Alonso et al. 2008; Bouchy et al. 2008). An analysis of its photospheric activity, based on spot modelling techniques previously developed by our group for the analysis of the Sun as a star, shows that the active regions on CoRoT-2a arised within two active longitudes separated by about 180 degrees and rotating with periods of 4.5221 and 4.5543 days, respectively, at epoch of CoRoT observations (112 continous days centered at 2007.6). We show that the total spotted area oscillates with a period of about about 8.9 days, a value close to 10 times the synodic period of the planet with respect to the active longitude pattern rotating in 4.5221 days. Moreover, the variance of the stellar flux is modulated in phase with the planet orbital period. This suggests a possible star-planet magnetic interaction, a phenomenon already seen in other extrasolar planetary systems hosting hot-Jupiters.
We present evidence for Milky-Way-like, low-excitation molecular gas reservoirs in near-IR selected massive galaxies at z~1.5, based on IRAM Plateau de Bure Interferometer CO[3-2] and NRAO Very Large Array CO[1-0] line observations for two galaxies that had been previously detected in CO[2-1] emission. The CO[3-2] flux of BzK-21000 at z=1.522 is comparable within the errors to its CO[2-1] flux, implying that the CO[3-2] transition is significantly sub-thermally excited. The combined CO[1-0] observations of the two sources result in a detection at the 3 sigma level that is consistent with a higher CO[1-0] luminosity than that of CO[2-1]. Contrary to what is observed in submillimeter galaxies and QSOs, in which the CO transitions are thermally excited up to J>=3, these galaxies have low-excitation molecular gas, similar to that in the Milky Way and local spirals. This is the first time that such conditions have been observed at high redshift. A Large Velocity Gradient analysis suggests that molecular clouds with density and kinetic temperature comparable to local spirals can reproduce our observations. The similarity in the CO excitation properties suggests that a high, Milky-Way-like, CO to H_2 conversion factor could be appropriate for these systems. If such low-excitation properties are representative of ordinary galaxies at high redshift, centimeter telescopes such as the Expanded Very Large Array and the longest wavelength Atacama Large Millimeter Array bands will be the best tools for studying the molecular gas content in these systems through the observations of CO emission lines.
In order to understand the cosmic ray propagation mechanism in galaxies, and its correlation with the sites of star formation, we compare the spatially resolved radio spectral index of three spiral galaxies with their IR distribution. We present new low-frequency radio continuum observations of the galaxies NGC 0628, NGC 3627, and NGC 7331, taken at 327 MHz with the Very Large Array. We complemented our data set with sensitive archival observations at 1.4 GHz and we studied the variations of the radio spectral index within the disks of these spiral galaxies. We also compared the spectral index distribution and the IR distribution, using 70 $\mu$m Spitzer observations. We found that in these galaxies the non-thermal spectral index is anticorrelated with the radio brightness. Bright regions, like the bar in NGC 3627 or the circumnuclear region in NGC 7331, are characterized by a flatter spectrum with respect to the underlying disk. Therefore, a systematic steepening of the spectral index with the increasing distance from the center of these galaxies is observed. Furthermore, by comparing the radio images with the 70 $\mu$m images of the Spitzer satellite we found that a similar anticorrelation exists between the radio spectral index and the infrared brightness, as expected on the basis of the local correlation between the radio continuum and the infrared emission. Our results support the idea that in regions of intense star formation the electron diffusion must be efficient. The observed anticorrelation between radio brightness and spectral index, may imply that the cosmic ray density and the magnetic field strength are significantly higher in these regions than in their surroundings.
Hierarchical models of structure formation predict that galaxy clusters grow via mergers of smaller clusters and galaxy groups, as well as through continuous accretion of gas. MACS J0717.5+3745 is an X-ray luminous and complex merging cluster, located at a redshift of 0.55. Here we present Giant Metrewave Radio Telescope (GMRT) radio observations at 610 MHz of this cluster. The main aim of the observations is to search for diffuse radio emission within the galaxy cluster MACS J0717.5+3745 related to the ongoing merger. These GMRT observations are complemented by Very Large Array (VLA) archival observations at 1.4, 4.9 and 8.5 GHz. We have discovered a radio halo in the cluster MACS J0717.5+3745 with a size of about 1.2 Mpc. The radio power P_1.4 GHz is 5 x 10^25 W/Hz, which makes it the most powerful radio halo known till date. A 700 kpc radio structure, which we classify as a radio relic, is located in between the merging substructures of the system. The location of this relic roughly coincides with regions of the intra-cluster medium (ICM) that have a significant enhancement in temperature as shown by Chandra. The major axis of the relic is also roughly perpendicular to the merger axis. This shows that the relic might be the result of a merger-related shock wave, where particles are accelerated via the diffuse shock acceleration (DSA) mechanism. Alternatively, the relic might trace an accretion shock of a large-scale galaxy filament to the south-west. The global spectral index of radio emission within the cluster is found to be -1.24 +/-0.05 between 4.9 GHz and 610 MHz. We derive a value of 1.1 microGauss for the equipartition magnetic field strength at the location of the radio halo. [abridged].
We used the multiplex capabilities of the AAOmega spectrograph at the Anglo-Australian Telescope to create a half-square-degree map of the neutral and low-ionized ISM in front of the nearby (~5 kpc), most massive Galactic globular cluster, omega Centauri. Its redshifted, metal-poor and hot horizontal branch stars probe the medium-strong Ca II K and Na I D2 line absorption, and weak absorption in the lambda5780 and lambda5797 Diffuse Interstellar Bands (DIBs), on scales around a parsec. The kinematical and thermodynamical picture emerging from these data is that we predominantly probe the warm neutral medium and weakly-ionized medium of the Galactic Disc-Halo interface, ~0.3-1 kpc above the mid-plane. A comparison with Spitzer Space Telescope 24-micron and DIRBE/IRAS maps of the warm and cold dust emission confirms that both Na I and Ca II trace the overall column density of the warm neutral and weakly-ionized medium. Clear signatures are seen of the depletion of calcium atoms from the gas phase into dust grains. Curiously, the coarse DIRBE/IRAS map is a more reliable representation of the relative reddening between sightlines than the Na I and Ca II absorption-line measurements, most likely because the latter are sensitive to fluctuations in the local ionization conditions. The behaviour of the DIBs is consistent with the lambda5780 band being stronger than the lambda5797 band in regions where the ultraviolet radiation level is relatively high, as in the Disc-Halo interface. This region corresponds to a sigma-type cloud. In all, our maps and simple analytical model calculations show in unprecedented detail that small-scale density and/or ionization structures exist in the extra-planar gas of a spiral galaxy. (abridged)
In this short paper we show that making turbulence two- rather than three-dimensional may increase effective turbulent viscosity by about 40%. Dimensionless hydrodynamical viscosity parameter up to \alpha\_{max} = 0.25 M_t^2 may be obtained in this approach, that is in better agreement with the observational data on non-stationary accretion than the values obtained in numerical simulations. However, the \alpha-parameter values known from observations are still several times higher.
The BH masses and the Eddington ratios for a sample of 65 young radio
galaxies [27 GPS and 38 CSS sources] are estimated by various methods. We find
that the average BH mass of these young radio galaxies is <log M_bh>=8.3, which
is less than that of radio loud QSOs and low redshift radio galaxies(<log
M_bh>=9.0). The CSS/GPS sources have relatively high Eddington ratios with
average ratio <log L_bol/L_Edd>=-0.56, which are similar to those of narrow
line Seyfert 1 galaxies (NLS1s). It suggests that the CSS/GPS sources may not
only be in the early stage of radio activities, but also in the early stage of
their accretion activities.
We find that the young radio galaxies as a class deviate systematically from
the M_bh-\sigma_* relation defined by nearby inactive galaxies, when using
\sigma_[O III] as a surrogate for the stellar velocity dispersion \sigma_*.
There is no significant correlation between the deviation of the [O III]
emission line width, $\Delta\sigma$=\sigma_[O III]-\sigma_[pred], and the
jet/accretion power, where \sigma_[pred] are calculated from the Tremaine et
al. relation using the estimated BH masses. However, we find that the deviation
$\Delta\sigma$ in young radio galaxies is well correlated with the Eddington
ratio, and this correlation is found to be similar to that of radio quiet AGN
(QSOs/NLS1s) where the radio jet is absent or weak. We suggest that the
accretion activities may still play an important role in shaping the kinematics
of [O III] narrow line in these young radio galaxies.
We present new evolutionary synthesis models for Simple Stellar Populations for a wide range of ages and metallicities. The models are based on the Padova isochrones. The core of the spectral library is provided by the medium resolution Lejeune et al. atmosphere models. These spectra are complemented by NLTE atmosphere models for hot stars that have an important impact in the stellar cluster's ionizing spectra: O, B and WR stellar spectra at the early ages, and spectra of post-AGB stars and planetary nebulae, at intermediate and old ages. At young ages, our models compare well with other existing models but we find that, the inclusion of the nebular continuum, not considered in several other models, reddens significantly the integrated colours of very young stellar populations. This is consistent with the results of spectral synthesis codes particularly devised for the study of starburst galaxies. At intermediate and old ages, the agreement with literature model is good and, in particular, we reproduce well the observed colours of star clusters in LMC. Given the ability to produce good integrated spectra from the far-UV to the infrared at any age, we consider that our models are particularly suited for the study of high redshift galaxies. These models are available on the web site {this http URL} and also through the Virtual Observatory Tools on the PopStar server.
Dark Matter detectors with directional sensitivity have the potential of yielding an unambiguous positive observation of WIMPs as well as discriminating between galactic Dark Matter halo models. In this article, we introduce the motivation for directional detectors, discuss the experimental techniques that make directional detection possible, and review the status of the experimental effort in this field.
We present projected rotational velocity values for 97 Galactic, 55 SMC, and 106 LMC O-B type stars from archival FUSE observations. The evolved and unevolved samples from each environment are compared through the Kolmogorov-Smirnov test to determine if the distribution of equatorial rotational velocities is metallicity dependent for these massive objects. Stellar interior models predict that massive stars with SMC metallicity will have significantly reduced angular momentum loss on the main sequence compared to their Galactic counterparts. Our results find some support for this prediction but also show that even at Galactic metallicity, evolved and unevolved massive stars have fairly similar fractions of stars with large V sin i values. Macroturbulent broadening that is present in the spectral features of Galactic evolved massive stars is lower in the LMC and SMC samples. This suggests the processes that lead to macroturbulence are dependent upon metallicity.
We have performed a simulation of a next generation sky survey's (Pan-STARRS 1) efficiency for detecting Earth-impacting asteroids. The steady-state sky-plane distribution of the impactors long before impact is concentrated towards small solar elongations (Chesley and Spahr, 2004) but we find that there is interesting and potentially exploitable behavior in the sky-plane distribution in the months leading up to impact. The next generation surveys will find most of the dangerous impactors (>140m diameter) during their decade-long survey missions though there is the potential to miss difficult objects with long synodic periods appearing in the direction of the Sun, as well as objects with long orbital periods that spend much of their time far from the Sun and Earth. A space-based platform that can observe close to the Sun may be needed to identify many of the potential impactors that spend much of their time interior to the Earth's orbit. The next generation surveys have a good chance of imaging a bolide like 2008TC3 before it enters the atmosphere but the difficulty will lie in obtaining enough images in advance of impact to allow an accurate pre-impact orbit to be computed.
We present the results of a Doppler tomographic reconstruction of the UV spectra of the double-lined, O binary HD 100213 based on observations made with the International Ultraviolet Explorer (IUE). We used cross-correlation methods to obtain radial velocities, confirm the orbital elements, estimate the UV flux ratio, and determine projected rotational velocities. The individual component spectra are classified as O7 V + O8 V using UV criteria defined by Penny, Gies, & Bagnuolo. We present a model fit of the eclipsing light curve from observations from the Hipparcos satellite and published observations of Andersen & Gronbech. We derive an orbital inclination, i=77.7deg+/-1.0deg. This analysis indicates that both stars are currently experiencing Roche lobe overflow (RLOF), which confirms earlier results that this is one of only a few massive contact binaries. Our derived masses, Mp/Msolar=16.7+/-0.4 and Ms/Msolar=10.4+/-0.4, are significantly lower than those computed from the Doppler shifts of lines in the optical spectrum. We suggest that the difference occurs because mutual irradiation decreases the upper atmospheric temperature gradient in the inward-facing hemispheres of both stars, which makes lower excitation lines appear weaker there and shifts their center of light away from the center of mass. We compare the current state of HD 100213 with predicted outcomes of massive close binary evolutionary models, and suggest that the system is currently in a very slow case AA mass transfer stage.
Context. We use Hubble Space Telescope photometry of six rich, compact star
clusters in the Large Magellanic Cloud (LMC), with ages ranging from 0.01 to
1.0 Gyr, to derive the clusters' stellar mass functions (MFs) at their
half-mass radii.
Aims. The LMC is an ideal environment to study stellar MFs, because it
contains a large population of compact clusters at different evolutionary
stages. We aim to obtain constraints on the initial MFs (IMFs) of our sample
clusters on the basis of their present-day MFs, combined with our understanding
of their dynamical and photometric evolution.
Methods. We derive the clusters' present-day MFs below 1.0 Msun using deep
observations with the Space Telescope Imaging Spectrograph and updated stellar
population synthesis models.
Results. Since the relaxation timescales of low-mass stars are very long,
dynamical evolution will not have affected the MFs below 1.0 Msun
significantly, so that - within the uncertainties - the derived MFs are
consistent with the solar-neighbourhood IMF, at least for the younger clusters.
Conclusions. The IMF in the low-density, low-metallicity environment of the
LMC disk is not significantly different from that in the solar neighbourhood.
A revised catalogue of 274 Galactic supernova remnants (SNRs) is presented, along with some simple statistics of their parameters. It is shown that the remnants that have recently been identified are generally faint, as is expected from the selection effects that apply to the identification of remnants.
We apply the needlet formalism to the Wilkinson Microwave Anisotropy Probe 5-year data, looking for evidence of non-Gaussianity in the bispectrum of the needlet amplitudes. We confirm earlier findings of an asymmetry in the non-Gaussianity between the northern and southern galactic hemispheres. We attempt to isolate which scales and geometrical configurations are most anomalous, and find the bispectrum is most significant on large scales and in the more co-linear configurations, and also in the `squeezed' configurations. However, these anomalies do not appear to affect the estimate of the non-linear parameter $\fnl$, and we see no significant difference between its value measured in the two hemispheres.
We briefly discuss the history of X-ray polarimetry for astronomical applications including a guide to the appropriate statistics. We also provide an introduction to some of the new techniques discussed in more detail elsewhere in these proceedings. We conclude our discussion with our concerns over adequate ground calibration, especially with respect to unpolarized beams, and at the system level.
Context. Mathematical optimization can be used as a computational tool to obtain the optimal solution to a given problem in a systematic and efficient way. For example, in twice-differentiable functions and problems with no constraints, the optimization consists of finding the points where the gradient of the objective function is zero and using the Hessian matrix to classify the type of each point. Sometimes, however it is impossible to compute these derivatives and other type of techniques must be employed such as the steepest descent/ascent method and more sophisticated methods such as those based on the evolutionary algorithms. Aims. We present a simple algorithm based on the idea of genetic algorithms (GA) for optimization. We refer to this algorithm as AGA (Asexual Genetic Algorithm) and apply it to two kinds of problems: the maximization of a function where classical methods fail and model fitting in astronomy. For the latter case, we minimize the chi-square function to estimate the parameters in two examples: the orbits of exoplanets by taking a set of radial velocity data, and the spectral energy distribution (SED) observed towards a YSO (Young Stellar Object). Methods. The algorithm AGA may also be called genetic, although it differs from standard genetic algorithms in two main aspects: a) the initial population is not encoded, and b) the new generations are constructed by asexual reproduction. Results. Applying our algorithm in optimizing some complicated functions, we find the global maxima within a few iterations. For model fitting to the orbits of exoplanets and the SED of a YSO, we estimate the parameters and their associated errors.
Hydrodynamic simulations of granular convection predict the existence of supersonic flows covering ~3-4% of the solar surface at any time, but these flows have not been detected unambigously as yet. Using data from the spectropolarimeter aboard the Hinode satellite, I present direct evidence of fast horizontal plasma motions in quiet Sun granules. Their visibility increases toward the limb due to more favorable viewing conditions. At the resolution of Hinode, the horizontal flows give rise to asymmetric intensity profiles with very inclined blue wings and even line satellites located blueward of the main absorption feature. Doppler shifts of up to 9 km/s are observed at the edges of bright granules, demonstrating that the flows reach supersonic speeds. The strongest velocities occur in patches of 0.5 arcsec or less. They tend to be associated with enhanced continuum intensities, line widths, and equivalent widths, but large values of these parameters do not necessarily imply the existence of supersonic flows. Time series of spectropolarimetric measurements in regions away from disk center show the transient nature of the strong horizontal motions, which last only for a fraction of the granule lifetime. Supersonic flows are expected to produce shocks at the boundaries between granules and intergranular lanes, and may also play a role in the emergence of small-scale magnetic fields in quiet Sun internetwork regions.
We study the optimal use of third order statistics in the analysis of weak lensing by large-scale structure. These higher order statistics have long been advocated as a powerful tool to break measured degeneracies between cosmological parameters. Using ray-tracing simulations, incorporating important survey features such as a realistic depth-dependent redshift distribution, we find that a joint two- and three-point correlation function analysis is a much stronger probe of cosmology than the skewness statistic. We compare different observing strategies, showing that for a limited survey time there is an optimal depth for the measurement of third-order statistics, which balances statistical noise and cosmic variance against signal amplitude. We find that the chosen CFHTLS observing strategy was optimal and forecast that a joint two- and three-point analysis of the completed CFHTLS-Wide will constrain the amplitude of the matter power spectrum $\sigma_8$ to 10\% and the matter density parameter $\Omega_m$ to 17\%, a factor of ~2.5 improvement on the two-point analysis alone. Our error analysis includes all non-Gaussian terms, finding that the coupling between cosmic variance and shot noise is a non-negligible contribution which should be included in any future analytical error calculations.
In an anisotropic universe, observers not positioned at a point of special symmetry should observe cosmic parallax - the relative angular motion of test galaxies over cosmic time. It was recently argued that the non-observance of this effect in upcoming precision astrometry missions such as Gaia may be used to place strong bounds on the position of off-center observers in a void-model universe described by the Lemaitre-Tolman-Bondi metric. We consider the analogous effect in anisotropic cosmological models described by an axisymmetric homogeneous Bianchi type I metric and discuss whether any observation of cosmic parallax would distinguish between different anisotropic evolutions.
A star that wanders too close to a massive black hole (BH) is shredded by the BH's tidal gravity. Stellar gas falls back to the BH, releasing a flare of energy. In anticipation of upcoming transient surveys, we predict the light curves and spectra of tidal flares as a function of time, highlighting the unique signatures of tidal flares in the optical and near-IR. Some of the gas initially bound to the BH is likely blown away when the fallback rate is super-Eddington at early times. This outflow produces an optical luminosity comparable to that of a supernova; such events have durations of ~10 days and may have been missed in supernova searches that exclude the nuclear regions of galaxies. When the fallback rate subsides below Eddington, the gas accretes onto the BH via a thin disk whose emission peaks in the UV to soft X-rays. Some of this emission is reprocessed by the unbound stellar debris, producing a spectrum of very broad emission lines (with no corresponding narrow forbidden lines). These lines are strongest for BHs with MBH ~ 10^5 - 10^6 Msun and thus optical surveys are particularly sensitive to the lowest mass BHs in galactic nuclei. Calibrating our models to ROSAT and GALEX observations, we predict detection rates for Pan-STARRS, PTF, and LSST and highlight observational challenges in the optical. Pan-STARRS should detect at least tens of events per year--many more if current theoretical models of super-Eddington outflows are correct. These surveys will significantly improve our knowledge of stellar dynamics in galactic nuclei, the physics of super-Eddington accretion, the demography of intermediate mass BHs, and the role of tidal disruption in the growth of massive BHs.
The ACS Nearby Galaxy Survey Treasury (ANGST) is a systematic survey to establish a legacy of uniform multi-color photometry of resolved stars for a volume-limited sample of nearby galaxies (D<4 Mpc). The survey volume encompasses 69 galaxies in diverse environments, including close pairs, small & large groups, filaments, and truly isolated regions. The galaxies include a nearly complete range of morphological types spanning a factor of ~10^4 in luminosity and star formation rate. The survey data consists of images taken with ACS on HST, supplemented with archival data and new WFPC2 imaging taken after the failure of ACS. Survey images include wide field tilings covering the full radial extent of each galaxy, and single deep pointings in uncrowded regions of the most massive galaxies in the volume. The new wide field imaging in ANGST reaches median 50% completenesses of m_F475W=28.0 mag, m_F606W=27.3 mag, and m_F814W=27.3 mag, several magnitudes below the tip of the red giant branch (TRGB). The deep fields reach magnitudes sufficient to fully resolve the structure in the red clump. The resulting photometric catalogs are publicly accessible and contain over 34 million photometric measurements of >14 million stars. In this paper we present the details of the sample selection, imaging, data reduction, and the resulting photometric catalogs, along with an analysis of the photometric uncertainties (systematic and random), for both the ACS and WFPC2 imaging. We also present uniformly derived relative distances measured from the apparent magnitude of the TRGB.
We study the steady state motion of bubble walls in cosmological phase transitions. Taking into account the boundary and continuity conditions for the fluid variables, we calculate numerically the wall velocity as a function of the nucleation temperature, the latent heat, and a friction parameter. We determine regions in the space of these parameters in which detonations and/or deflagrations are allowed. In order to apply the results to a physical case, we calculate these quantities in a specific model, which consists of an extension of the Standard Model with singlet scalar fields. We also obtain analytic approximations for the wall velocity, both in the case of deflagrations and of detonations.
Neutrino telescopes with cubic kilometer volume have the potential to discover new particles. Among them are next to lightest supersymmetric (NLSPs) and next to lightest Kaluza-Klein (NLKPs) particles. Two NLSPs or NLKPs will transverse the detector simultaneously producing parallel charged tracks. The track separation inside the detector can be a few hundred meters. As these particles might propagate a few thousand kilometers before reaching the detector, multiple scattering could enhance the pair separation at the detector. We find that the multiple scattering will alter the separation distribution enough to increase the number of NLKP pairs separated by more than 100 meters (a reasonable experimental cut) by up to 46% depending on the NLKP mass. Vertical upcoming NLSPs will have their separation increased by 24% due to multiple scattering.
We formulate Horava-Lifshitz cosmology with an additional scalar field that leads to an effective dark energy sector. We find that, due to the inherited features from the gravitational background, Horava-Lifshitz dark energy naturally presents very interesting behaviors, possessing a varying equation-of-state parameter, exhibiting phantom behavior and allowing for a realization of the phantom divide crossing. In addition, Horava-Lifshitz dark energy guarantees for a bounce at small scale factors and it may trigger the turnaround at large scale factors, leading naturally to cyclic cosmology.
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We study the final architecture of planetary systems that evolve under the combined effects of planet-planet and planetesimal scattering. Using N-body simulations we investigate the dynamics of marginally unstable systems of gas and ice giants both in isolation and when the planets form interior to a planetesimal belt. The unstable isolated systems evolve under planet-planet scattering to yield an eccentricity distribution that matches that observed for extrasolar planets. When planetesimals are included the outcome depends upon the total mass of the planets. For system masses exceeding about one Jupiter mass the final eccentricity distribution remains broad, whereas for lower mass planetary systems a combination of divergent orbital evolution and recircularization of scattered planets results in a preponderance of nearly circular final orbits. We also study the fate of marginally stable multiple planet systems in the presence of planetesimal disks, and find that for high planet masses the majority of such systems evolve into resonance. A significant fraction lead to resonant chains that are planetary analogs of Jupiter's Galilean satellites. We predict that a transition from eccentric to near-circular orbits will be observed once extrasolar planet surveys detect sub-Jovian mass planets at orbital radii of 5-10 AU.
[Abridged] To simulate the kinds of observations that will eventually be obtained for exoplanets, the Deep Impact spacecraft obtained light curves of Earth at seven wavebands spanning 300-1000 nm as part of the EPOXI mission of opportunity. In this paper we analyze disc-integrated light curves, treating Earth as if it were an exoplanet, to determine if we can detect the presence of oceans and continents. We present two observations each spanning one day, taken at gibbous phases. The rotation of the planet leads to diurnal albedo variations of 15-30%, with the largest relative changes occuring at the reddest wavelengths. To characterize these variations in an unbiased manner we carry out a principal component analysis of the multi-band light curves; this analysis reveals that 98% of the diurnal color changes of Earth are due to only 2 dominant eigencolors. We use the time-variations of these two eigencolors to construct longitudinal maps of the Earth, treating it as a non-uniform Lambert sphere. We find that the spectral and spatial distributions of the eigencolors correspond to cloud-free continents and oceans; this despite the fact that our observations were taken on days with typical cloud cover. We also find that the near-infrared wavebands are particularly useful in distinguishing between land and water. Based on this experiment we conclude that it should be possible to infer the existence of water oceans on exoplanets with time-resolved broadband observations taken by a large space-based coronagraphic telescope.
We perform an extensive test of theoretical stellar models for main-sequence stars in ugriz, using cluster fiducial sequences obtained in the previous paper of this series. We generate a set of isochrones using the Yale Rotating Evolutionary Code (YREC) with updated input physics, and derive magnitudes and colors in ugriz from MARCS model atmospheres. These models match cluster main sequences over a wide range of metallicity within the errors of the adopted cluster parameters. However, we find a large discrepancy of model colors at the lower main sequence (Teff < ~4500 K) for clusters at and above solar metallicity. We also reach similar conclusions using the theoretical isochrones of Girardi et al. and Dotter et al., but our new models are generally in better agreement with the data. Using our theoretical isochrones, we also derive main-sequence fitting distances and turn-off ages for five key globular clusters, and demonstrate the ability to derive these quantities from photometric data in the Sloan Digital Sky Survey. In particular, we exploit multiple color indices (g - r, g - i, and g - z) in the parameter estimation, which allows us to evaluate internal systematic errors. Our distance estimates, with an error of sigma(m - M) = 0.03-0.11 mag for individual clusters, are consistent with Hipparcos-based subdwarf fitting distances derived in the Johnson-Cousins or Stromgren photometric systems.
The conversion of the globular cluster luminosity function (GCLF, dN/dlogL) to the globular cluster mass function (GCMF, dN/dlogM) is addressed. Dissolving globular clusters (GCs) become preferentially depleted in low-mass stars, which have a high mass-to-light ratio. This has been shown to result in a mass-to-light ratio (M/L) that increases with GC luminosity or mass, because more massive GCs have lost a smaller fraction of their stars than low-mass GCs. Using GC models, we study the influence of the luminosity dependency of M/L on the inferred GCMF. The observed GCLF is consistent with a powerlaw or Schechter type GC initial mass function in combination with a cluster mass-dependent mass loss rate. Below the peak, the logarithmic slope of the GCMF is shallower than that of the GCLF (0.7 versus 1.0), whereas the peak mass is 0.1-0.3 dex lower when accounting for the variability of M/L than in the case where a constant M/L is adopted.
We present analyses of variability in the red giant stars in the metal-poor globular cluster NGC6397, based on data obtained with the Hubble Space Telescope. We use an non-standard data reduction approach to turn a 23-day observing run originally aimed at imaging the white dwarf population, into time-series photometry of the cluster's highly saturated red giant stars. With this technique we obtain noise levels in the final power spectra down to 50 parts per million, which allows us to search for low amplitude solar-like oscillations. We compare the observed excess power seen in the power spectra with estimates of the typical frequency range, frequency spacing and amplitude from scaling the solar oscillations. We see evidence that the detected variability is consistent with solar-like oscillations in at least one and perhaps up to four stars. With metallicities two orders of magnitude lower than of the Sun, these stars present so far the best evidence of solar-like oscillations in such a low metallicity environment.
Using the recently developed effective field theory of inflation, we argue that the size and the shape of the non-Gaussianities generated by single-field inflation are generically well described by two parameters: f_NL^equil, which characterizes the size of the signal that is peaked on equilateral configurations, and f_NL^orthog, which instead characterizes the size of the signal which is peaked both on equilateral configurations and flat-triangle configurations (with opposite signs). The shape of non-Gaussianities associated with f_NL^orthog is orthogonal to the one associated to f_NL^equil, and former analysis have been mostly blind to it. We perform the optimal analysis of the WMAP 5-year data for both of these parameters. We find no evidence of non-Gaussianity, and we have the following constraints: -125 < f_NL^equil < 435, -369 < f_NL^orthog < 71 at 95% CL. We show that both of these constraints can be translated into limits on parameters of the Lagrangian of single-field inflation. For one of them, the speed of sound of the inflaton fluctuations, we find that it is either bounded to be c_s > 0.011 at 95% CL. or alternatively to be so small that the higher-derivative kinetic term dominate at horizon crossing. We are able to put similar constraints on the other operators of the inflaton Lagrangian.
The state of the hot gas in clusters of galaxies is investigated with a set of model clusters, created by assuming a polytropic equation of state (Gamma=1.2) and hydrostatic equilibrium inside gravitational potential wells drawn from a dark matter simulation. Star formation, energy input, and nonthermal pressure support are included. To match the gas fractions seen in non-radiative hydrodynamical simulations, roughly 5% of the binding energy of the dark matter must be transferred to the gas during cluster formation; the presence of nonthermal pressure support increases this value. In order to match X-ray observations, scale-free behavior must be broken. This can be due to either variation of the efficiency of star formation with cluster mass M_500, or the input of additional energy proportional to the formed stellar mass M_F. These two processes have similar effects on X-ray scalings. If 9% of the gas is converted into stars, independent of cluster mass, then feedback energy input of 1.2e-5*M_Fc^2 (or ~1.0 keV per particle) is required to match observed clusters. Alternatively, if the stellar mass fraction varies as M_500^-0.26 then a lower feedback of 4e-6*M_Fc^2 is needed, and if the stellar fraction varies as steeply as M_500^-0.49 then no additional feedback is necessary. The model clusters reproduce the observed trends of gas temperature and gas mass fraction with cluster mass, as well as observed entropy and pressure profiles; thus they provide a calibrated basis with which to interpret upcoming SZ surveys. One consequence of the increased gas energy is that the baryon fraction inside the virial radius is less than roughly 90% of the cosmic mean, even for the most massive clusters.
To date, no accretion model has succeeded in reproducing all observed constraints in the inner Solar System. These constraints include 1) the orbits, in particular the small eccentricities, and 2) the masses of the terrestrial planets -- Mars' relatively small mass in particular has not been adequately reproduced in previous simulations; 3) the formation timescales of Earth and Mars, as interpreted from Hf/W isotopes; 4) the bulk structure of the asteroid belt, in particular the lack of an imprint of planetary embryo-sized objects; and 5) Earth's relatively large water content, assuming that it was delivered in the form of water-rich primitive asteroidal material. Here we present results of 40 high-resolution (N=1000-2000) dynamical simulations of late-stage planetary accretion with the goal of reproducing these constraints, although neglecting the planet Mercury. We assume that Jupiter and Saturn are fully-formed at the start of each simulation, and test orbital configurations that are both consistent with and contrary to the "Nice model." We find that a configuration with Jupiter and Saturn on circular orbits forms low-eccentricity terrestrial planets and a water-rich Earth on the correct timescale, but Mars' mass is too large by a factor of 5-10 and embryos are often stranded in the asteroid belt. A configuration with Jupiter and Saturn in their current locations but with slightly higher initial eccentricities (e = 0.07-0.1) produces a small Mars, an embryo-free asteroid belt, and a reasonable Earth analog but rarely allows water delivery to Earth. None of the configurations we tested reproduced all the observed constraints. (abridged)
Axion-Like Particles (ALPs) are the focus of intense current research. We analyze photon-ALP conversion in the context of relativistic jet models of Active Galactic Nuclei (AGN) for more than 100 sources. Contrary to previous claims, we find that this process cannot occur above 100 GeV regardless of the actual AGN model and the values of ALP parameters. This result rules out a proposed strategy to bypass the cosmic opacity above 100 GeV, as apparently required by observations. We also show that for some AGN an observable effect can show up in the X and soft gamma-ray bands.
Progenitors of Type Ia supernovae (SNe) have been predicted to modify their ambient circumstellar (CSM) and interstellar environments through the action of their powerful winds. While there is X-ray and optical evidence for circumstellar interaction in several remnants of Type Ia SNe, widespread evidence for such interaction in Type Ia SNe themselves has been lacking. We consider prospects for detection of CSM shells that have been predicted to be common around Type Ia SNe. Such shells are most easily detected in Na I absorption lines. Variable (declining) absorption is expected to occur soon after the explosion, primarily during the SN rise time, for shells located within 1 - 10 pc of a SN. The distance of the shell from the SN can be determined by measuring the time scale for line variability.
We revisit echelle spectra (spectral resolution R ~ 40000) of 8 Gamma-Ray Burst afterglows to obtain the incidence (dN/dz) of weak intervening Mg II systems at a mean redshift of <z> = 1.5. We show that dN/dz of systems having restframe equivalent widths 0.07 A < W_r(MgII) < 1 A toward GRBs is statistically consistent with the incidence toward QSOs. Our result is in contrast to the results for Mg II systems having W_r > 1 A, where dN/dz toward GRBs has been found to be larger than toward QSOs by a factor of ~ 4. We confirm the overdensity albeit at a factor of ~ 3 only. This suggests that any explanation for the GRB/QSO discrepancy, be it intrinsic to the absorbers or a selection effect, should be inherent only to the galaxies that host strong absorbers in the line-of-sight to GRBs. We argue that, of all scenarios that have been proposed, lensing amplification is the one that could explain the strong Mg II enhancement while allowing for no significant enhancement in the weak absorbers.
We present an analysis of several high-resolution Chandra grating observations of the X-ray binary pulsar Her X-1. With a total exposure of 170 ks, the observations are separated by years and cover three combinations of orbital and super-orbital phases. Our goal is to determine distinct properties of the photoionized emission and its dependence on phase-dependent variations of the continuum. We find that the continua can be described by a partial covering model which above 2 keV is consistent with recent results from \rxte studies and at low energies is consistent with recent \xmm and \sax studies. Besides a powerlaw with fixed index, an additional thermal blackbody of 114 eV is required to fit wavelengths above 12 \AA ($\sim$ 1 keV). We find that likely all the variability is caused by highly variable absorption columns in the range (1 -- 3)$\times 10^{23}$ cm$^{-2}$. Strong Fe K line fluorescence in almost all observations reveals that dense, cool material is present not only in the outer regions of the disk but interspersed throughout the disk. Most spectra show strong line emission stemming from a photoionized accretion disk corona. We model the line emission with generic thermal plasma models as well as with the photoionization code XSTAR and investigate changes of the ionization balance with orbital and superorbital phases. Most accretion disk coronal properties such as disk radii, temperatures, and plasma densities are consistent with previous findings for the low state. We find that these properties change negligibly with respect to orbital and super-orbital phases. A couple of the higher energy lines exhibit emissivities that are significantly in excess of expectations from a static accretion disk corona.
We investigate a k-essence field localized on the brane evolving linearly with the cosmological time for arbitrary kinetic functions and consider the atypical k-essence model for linear and nonlinear k-fields in Friedmann-Robertson-Walker (FRW) cosmology. In the former case the k-field is driven by an inverse quadratic polynomial potential and the solutions exhibit several different behaviors which include expanding, contracting and bouncing universes as well as a model with a finite time span, some of them ending in a big crunch or a big rip. In the latter case we find the potential and show that the atypical k-essence model is dynamically uncomplete. Particularly, by selecting the extended tachyonic kinetic functions we analyze the high and low energy limits of our model, obtaining the nearly power law solution. We introduce a tachyon field with negative energy density and show that the universe evolves between two singularities.
We present new far-infrared (FIR) images of the edge-on starburst galaxy NGC253 obtained with the Far-Infrared Surveyor (FIS) onboard AKARI at wavelengths of 90 um and 140 um. We have clearly detected FIR dust emission extended in the halo of the galaxy; there are two filamentary emission structures extending from the galactic disk up to 9 kpc in the northern and 6 kpc in the northwestern direction. From its spatial coincidence with the X-ray plasma outflow, the extended FIR emission is very likely to represent outflowing dust entrained by superwinds. The ratios of surface brightness at 90 um to that at 140 um suggest that the temperatures of the dust in the halo are getting higher in the regions far from the disk, implying that there exist extra dust heating sources in the halo of the galaxy.
Due to close encounters with the inner planets, Near-Earth-Asteroids (NEAs) can have very chaotic orbits. Because of this chaoticity, a statistical treatment of the dynamical properties of NEAs becomes difficult or even impossible. We propose a new way to classify NEAs by using methods from Fuzzy Logic. We demonstrate how a fuzzy characterization of NEAs can be obtained and how a subsequent analysis can deliver valid and quantitative results concerning the long-term dynamics of NEAs.
We try to understand the thermal X-ray emission and reproduce the cooling behavior of isolated pulsars in a solid quark star regime. We focus on the population with common properties of manifesting considerable thermal emission, owning ordinary magnetic fields $\sim10^{11-13}$ G, comparatively young ages $10^{3-6}$ yrs, and spins of a few tens of milliseconds to a few seconds. The sample thus includes 14 active cooling pulsar candidates, 6 central compact objects (CCOs) and the Magnificent Seven, or 7 X-ray dim isolated neutron stars (XDINs); other 11 sources with identification of the upper limits on their thermal luminosity are also considered. The release rate of residual inner energy of solid quark stars, evaluated by Debye elastic medium theory, is found to be negligible comparing with the observational X-ray bolometric luminosity, and hence, for solid quark stars, the thermal emission could predominantly originate from stellar heating processes. For pulsars with magnetospheric activities, the heating could spin-down powered; a statistical study is thus carried out and presents that a 1/2-law or a linear-law between the bolometric luminosity and the spin energy loss rate could exist, i.e. $L_{\rm bol}\propto\dot{E}^{1/2}$ or $L_{\rm bol}\propto\dot{E}$, basing on which the thermal radiative processes are reproduced. For 6 CCOs and 7 XDINs, or inactive pulsar candidates, the stellar heating may be of accretion origin, either to the interstellar medium or to the fallback disks in the associated supernova remnants. Individual or general properties of these pulsars could be the implications on their propeller states, the linkages and thus the evolutions; such topics are also involved.
(Abridged) Stellar mass black hole X-ray binaries exhibit X-ray spectral states which also have distinct and characteristic temporal properties. These states are believed to correspond to different accretion disk geometries. We present analysis of two long XMM-Newton observations of the Ultra-Luminous X-ray source (ULX) NGC 1313 X-1, which reveal that the system was in two different spectral/temporal states. With a count rate of 1.5 counts/s and a fractional variability amplitude of ~15%, the ULX was in a high flux and strongly variable state in March 2006. In October 2006, the count rate of the ULX had reduced by a factor of ~2 and the spectral shape was distinctly different with the presence of a soft component. No strong variability was detected during this low flux state with an upper limit on the amplitude < 3%. Moreover, the spectral properties of the two states implies that the accretion disk geometry was different for them. The low flux state is consistent with a model where a standard accretion disk is truncated at a radius of ~17 Schwarzschild radius around a ~200 Msun black hole. The inner hot region Comptonizes photons from the outer disk to give the primary spectral component. The spectrum of the high flux state is not compatible with such a geometry. Instead, it is consistent with a model where a hot corona covers a cold accretion disk and Comptonizes the disk photons. The variability as a function of energy is also shown to be consistent with the corona model. Despite these broad analogies with Galactic black hole systems, the spectral nature of the ULX is distinct in having a colder Comptonizing temperature (~2 keV) and higher optical depth (~15) than what is observed for the Galactic ones.
This work aims to the study of the Sh 2-307 HII region and related stellar population. Near-infrared imaging and spectroscopic observations in the direction of Sh 2-307 were performed using OSIRIS at SOAR Telescope. From J-, H- and K-band spectra of the brightest source in the cluster, we conclude that it has a near-infrared spectra compatible with that taken for O9v-O9.5v stars. Using the derived spectral type and the respective J, H and K-band photometry, we compute a heliocentric distance of 3.2(0.5) kpc, which for R0 = 8 kpc, puts this cluster at more than 10 kpc from the Galactic centre. From the Brg, H2, and continuum narrow-band images we were able to detect both the NIR counterpart of the associated HII region, as well as, the interface between the ionised and the cool molecular gas. Using the 5 Ghz continuum flux density taken from the PMN catalogue and the Brg narrow band image we estimate that the HII region has a mean diameter of 0.94(0.15) pc, mean electron density of 550 cm-3 and an estimated dynamical age of 1.6 Myears years. The large fraction of sources presenting excess emission at 2micron suggests that the stellar population is very young, with many sources still in the pre-main sequence accreting phase. By the use of theoretical pre-main sequence tracks we derived a cluster mean age of about 2.5 Myears, and from the analyses of the fraction of excess emission sources as a function of their spatial distribution we found evidence for an age spread for the embedded pre-main sequence stellar population. Finally, from the study of the spatial distribution of the low-mass sources relative to the main-cluster source and associated photo-dissociation zones, we conclude that the O-type star probably has been triggering the star formation process in the region.
We present a consistent self-contained and pedagogical review of the CMB Gibbs sampler, focusing on computational methods and code design. We provide an easy-to-use CMB Gibbs sampler named SLAVE developed in C++ using object-oriented design. While discussing why the need for a Gibbs sampler is evident and what the Gibbs sampler can be used for in a cosmological context, we review in detail the analytical expressions for the conditional probability densities and discuss the problems of galactic foreground removal and anisotropic noise. Having demonstrated that SLAVE is a working, usable CMB Gibbs sampler, we present the algorithm for white noise level estimation. We then give a short guide on operating SLAVE before introducing the post-processing utilities for obtaining the best-fit power spectrum using the Blackwell-Rao estimator.
The magnetic field of the solar corona has a large-scale dipole character, which maps into the bipolar field in the solar wind. Using standard representations of the coronal field, we show that high-energy ions can be trapped stably in these large-scale closed fields. The drift shells that describe the conservation of the third adiabatic invariant may have complicated geometries. Particles trapped in these zones would resemble the Van Allen Belts and could have detectable consequences. We discuss potential sources of trapped particles.
Differential K-band luminosity functions (LFs) are presented for a complete sample of 1613 nearby bright galaxies segregated by visible morphology. The LF for late-type spirals follows a power law that rises towards low luminosities whereas the LFs for ellipticals, lenticulars and bulge-dominated spirals are peaked and decline toward both higher and lower luminosities. Each morphological type (E, S0, S0/a-Sab, Sb-Sbc, Sc-Scd) contributes approximately equally to the overall K-band luminosity density of galaxies in the local universe. Type averaged bulge/disk ratios are used to subtract the disk component leading to the prediction that the K-band LF for bulges is bimodal with ellipticals dominating the high luminosity peak, comprising 60% of the bulge luminosity density in the local universe with the remaining 40% contributed by lenticulars and the bulges of spirals. Overall, bulges contribute 30% of the galaxy luminosity density at K in the local universe with spiral disks making up the remainder. If bulge luminosities indicate central black hole masses, then our results predict that the black hole mass function is also bimodal.
We present a mid-infrared coronagraph to target the direct observation of extrasolar planets, for Space Infrared telescope for Cosmology and Astrophysics (SPICA). We have commenced studies for a coronagraph for SPICA, in which this coronagraph is currently regarded as a option of the focal plane instruments. The primary target of the SPICA coronagraph is the direct observation of Jovian exo-planets. A strategy of the baseline survey and the specifications for the coronagraph instrument for the survey are introduced together. The main wavelengths and the contrast required for the observations are 3.5--27$\mu$m, and 10$^{-6}$, respectively. Laboratory experiments were performed with a visible laser to demonstrate the principles of the coronagraphs. We also present recent progress of technology to realize an infrared coronagraph for SPICA. Considering SPICA to be an essential platform for coronagraphs and the progress of key technologies, we propose to develop a mid-infrared coronagraph instrument for SPICA and to perform the direct observation of exo-planets by using it.
We use the cosmology-independent gamma-ray burst (GRB) distances of Y. Wang (2008) to constrain dark energy cosmological model parameters. Current GRB data alone can not tightly constrain cosmological parameters and allow for a wide range of dark energy models. When used jointly with current Type Ia supernovae data and baryon acoustic peak measurements, the GRB data favor slightly lower values of nonrelativistic matter energy density. We show that with a future factor of 2 reduction in the GRB distance errors, GRBs can give very tight constraints on cosmological parameters.
We analyze the effect of plasma screening on nuclear reaction rates in dense matter composed of atomic nuclei of one or two types. We perform semiclassical calculations of the Coulomb barrier penetrability taking into account a radial mean field potential of plasma ions. The mean field potential is extracted from the results of extensive Monte Carlo calculations of radial pair distribution functions of ions in binary ionic mixtures. We calculate the reaction rates in a wide range of plasma parameters and approximate these rates by an analytical expression that is expected to be applicable for multicomponent ions mixtures. Also, we analyze Gamow-peak energies of reacting ions in various nuclear burning regimes. For illustration, we study nuclear burning in C-O mixtures.
We present an approach for analysing the morphology and physical properties of Hi features near giant OB asso- ciations in M33, in the context of a model whereby the Hi excess arises from photodissociation of the molecular gas in remnants of the parent Giant Molecular Clouds (GMCs). Examples are presented here in the environs of NGC604 and CPSDPZ204, two prominent Hii regions in M33. These are the first results of a detailed analysis of the environs of a large number of OB associations in that galaxy. We present evidence for "diffusion" of the far-UV radiation from the OB association through a clumpy remnant GMC, and show further that enhanced CO(1-0) emission appears preferentially associated with GMCs of higher volume density.
In this short note, we are going to classify the cosmological evolutions in the recently proposed, nonrelativistic gravitational theory, the Ho\v{r}ava-Lifshitz (HL) theory. We consider the original HL theory (theory I), and the modified version obtained by an analytic continuation of parameters (theory II). We discuss the possiblilities of cosmological evolutions with arbitrary matter.
The Sloan Digital Sky Survey (SDSS) source J102347.6+003841 is a binary star with a 4.75 hr orbital period. A recent radio pulsar survey showed that its primary is a millisecond pulsar (MSP). Here we analyze the SDSS spectrum of the source in detail. The spectrum was taken on 2001 February 1, when the source was in a bright state and showed broad, double-peaked hydrogen and helium lines -- dramatically different from the G-type absorption spectrum seen from 2003 onward. The lines are consistent with emission from a disk around the compact primary. We derive properties of the disk by fitting the SDSS continuum with a simple disk model, and find a temperature range of 2000--34000 K from the outer to inner edge of the disk. The disk inner and outer radii were approximately 10^9 and 5.7x10^10 cm, respectively. These results further emphasize the unique feature of the source: it is evidently a system at the beginning of its life as a recycled radio pulsar. The disk mass is estimated to have been ~10^23 g, most of which would have been lost due to the pulsar wind ablation (or due to the propeller effect if the disk had extended inside the light cylinder of the pulsar) before the final disk disruption event. The system could undergo repeated episodes of disk formation. Close monitoring of the source is needed to catch the system in its bright state again, so that this unusual example of a pulsar-disk interaction can be studied in much detail.
We present the results of HI observations of five groups of galaxies spanning a range of velocity dispersion and spiral fraction (brightest optical group member in parenthesis): NGC 7582 (NGC 7552), USGC U207 (NGC 2759), USGC U070 (NGC 664), USGC U412 (NGC 3822), USGC U451 (NGC 4065). Neutral intragroup gas is detected in three of the five groups. We present the discovery of a previously uncataloged galaxy in the USGC U070 group at RA(2000)= 01h45m27s, Dec(2000) = +04d36'19" which we are designating FSW J014526.92+043619.1. We compile an HI mass function for the group environment and find that the faint-end slope is consistent with being flat.
The paper provides a review of A.M. Mathai's applications of the theory of special functions, particularly generalized hypergeometric functions, to problems in stellar physics and formation of structure in the Universe and to questions related to reaction, diffusion, and reaction-diffusion models. The essay also highlights Mathai's recent work on entropic, distributional, and differential pathways to basic concepts in statistical mechanics, making use of his earlier research results in information and statistical distribution theory. The results presented in the essay cover a period of time in Mathai's research from 1982 to 2008 and are all related to the thematic area of the gravitationally stabilized solar fusion reactor and fractional reaction-diffusion, taking into account concepts of non-extensive statistical mechanics. The time period referred to above coincides also with Mathai's exceptional contributions to the establishment and operation of the Centre for Mathematical Sciences, India, as well as the holding of the United Nations (UN)/European Space Agency (ESA)/National Aeronautics and Space Administration (NASA) of the United States/ Japanese Aerospace Exploration Agency (JAXA) Workshops on basic space science and the International Heliophysical Year 2007, around the world. Professor Mathai's contributions to the latter, since 1991, are a testimony for his social conscience applied to international scientific activity.
Numerous studies over the past 30 years have suggested there is a causal connection between the motion of the Sun through the Galaxy and terrestrial mass extinctions or climate change. Proposed mechanisms include comet impacts (via perturbation of the Oort cloud), cosmic rays and supernovae, the effects of which are modulated by the passage of the Sun through the Galactic midplane or spiral arms. Supposed periodicities in the fossil record, impact cratering dates or climate proxies over the Phanerozoic (past 545 Myr) are frequently cited as evidence in support of these hypotheses. This remains a controversial subject, with many refutations and replies having been published. Here I review both the mechanisms and the evidence for and against the relevance of astronomical phenomena to climate change and evolution. This necessarily includes a critical assessment of time series analysis techniques and hypothesis testing. Some of the studies have suffered from flaws in methodology, in particular drawing incorrect conclusions based on ruling out a null hypothesis. I conclude that there is little evidence for intrinsic periodicities in biodiversity, impact cratering or climate on timescales of tens to hundreds of Myr. Furthermore, Galactic midplane and spiral arm crossings seem to have little or no impact on biological or climate variation above background level. (truncated)
We study how axisymmetric magnetohydrodynamical (MHD) accretion flows depend on gamma adiabatic index in the polytropic equation of state. This work is an extension of Moscibrodzka & Proga (2008), where we investigated the gamma dependence of 2-D Bondi-like accretion flows in the hydrodynamical (HD) limit. Our main goal is to study if simulations for various gamma can give us insights into to the problem of various modes of accretion observed in several types of accretion systems such as black hole binaries (BHB), active galactic nuclei (AGN), and gamma-ray bursts (GRBs). We find that for gamma >~ 4/3, the fast rotating flow forms a thick torus that is supported by rotation and gas pressure. As shown before for gamma=5/3, such a torus produces a strong, persistent bipolar outflow that can significantly reduce the polar funnel accretion of a slowly rotating flow. For low gamma, close to 1, the torus is thin and is supported by rotation. The thin torus produces an unsteady outflow which is too weak to propagate throughout the polar funnel inflow. Compared to their HD counterparts, the MHD simulations show that the magnetized torus can produce an outflow and does not exhibit regular oscillations. Generally, our simulations demonstrate how the torus thickness affects the outflow production. They also support the notion that the geometrical thickness of the torus correlates with the power of the torus outflow. Our results, applied to observations, suggest that the torus ability to radiatively cool and become thin can correspond to a suppression of a jet as observed in the BHB during a transition from a hard/low to soft/high spectral state and a transition from a quiescent to hard/low state in AGN.
We present a detailed spectral study (photoionization modelling and variability) of the "Big Dipper" 4U 1624-490 based on a \chandra-High Energy Transmission Gratings Spectrometer (HETGS) observation over the $\sim76$ ks binary orbit of 4U 1624-490. While the continuum spectrum can be modeled using a blackbody plus power-law, a slightly better fit is obtained using a single $\Gamma=2.25$ power-law partially (71%) covered by a local absorber of column density $N_{\rm H, Local}=8.1_{-0.6}^{+0.7}\times 10^{22} \rm cm^{-2}$. The data show a possible quasi-sinusoidal modulation with period $43_{-9}^{+13}$ ks that might be due to changes in local obscuration. Photoionization modeling with the {\sc xstar} code and variability studies of the observed strong \ion{Fe}{25} and \ion{Fe}{26} absorption lines point to a two-temperature plasma for their origin: a highly ionized component of ionization parameter $\xi_{\rm hot} \approx 10^{4.3} {\rm ergs cm s^{-1}}$ ($T\sim 3.0\times 10^{6}$ K) associated with an extended accretion disk corona of radius $R \sim3\times10^{10}$ cm, and a less ionized more variable component of $\xi \approx 10^{3.4} {\rm ergs cm s^{-1}}$ ($T\sim 1.0\times 10^{6}$ K) and $\rm \xi \approx 10^{3.1} ergs cm s^{-1}$ ($T\sim 0.9\times 10^{6}$ K) coincident with the accretion disk rim. We use this, with the observed \ion{Fe}{25} and \ion{Fe}{26} absorption line variations (in wavelength, strength, and width) to construct a viewing geometry that is mapped to changes in plasma conditions over the 4U 1624-490 orbital period.
By analyzing the gas temperature maps created from the Chandra archive data, we reveal the prevailing existence of temperature substructures on ~100 kpc scales in the central regions of nine intermediate-redshift (z~0.1) galaxy clusters, which resemble those found in the Virgo and Coma Clusters. Each substructure contains a clump of hot plasma whose temperature is about 2-3 keV higher than the environment, corresponding to an excess thermal energy of ~1E58-1E60 erg per clump. Since if there were no significant non-gravitational heating sources, these substructures would have perished in 1E8-1E9 yrs due to thermal conduction and turbulent flows, whose velocity is found to range from about 200 to 400 km/s, we conclude that the substructures cannot be created and sustained by inhomogeneous radiative cooling. We also eliminate the possibilities that the temperature substructures are caused by supernova explosions, or by the non-thermal X-ray emission due to the inverse-Comptonization of the CMB photons. By calculating the rising time of AGN-induced buoyant bubbles, we speculate that the intermittent AGN outbursts (~ 1E60 erg per burst) may have played a crucial role in the forming of the high temperature substructures. Our results are supported by recent study of McNamara & Nulsen (2007), posing a tight observational constraint on future theoretical and numerical studies.
We consider a thin accretion disc warped due to the Bardeen-Petterson effect, presenting both analytical and numerical solutions for the situation that the two viscosity coefficients vary with radius as power law, with the two power law indices not necessarily equal. The analytical solutions are compared with numerical ones, showing that our new analytical solution is more accurate than previous one, which overestimates the inclination changing in the outer disc. Our new analytical solution is appropriate for moderately warped discs, while for extremely misaligned disc, only numerical solution is appropriate.
We present $u'g'R$ optical images taken with the MMT/Megacam and the Subaru/Suprime of the Extended Groth Strip survey. The total survey covers an area of about $\sim 1$ degree$^2$, including four sub-fields and is optimized for the study of galaxies at $z\sim3$. Our methods for photometric calibration in AB magnitudes, the limiting magnitude and the galaxy number count are described. A sample of 1642 photometrically selected candidate LBGs to an apparent $R_{AB}$ magnitude limit of 25.0 is present. The average sky surface density of our LBGs sample is $\sim$ 1.0 arcmin$^{-2}$, slightly higher than the previous finding.
Society's view of astronomers has changed over time and from culture to culture. This review discusses some of the many ways that astronomers have been perceived by their societies and suggests ways that astronomers can influence public perception of ourselves and our profession in the future.
The scope of this paper is to perform a detailed spectroscopic study of the northern O-type supergiant HD 195592. We use a large sample of high quality spectra in order to investigate its multiplicity, and to probe the line profile variability. Our analysis reveals a clear spectroscopic binary signature in the profile of the He {\sc i} $\lambda$ 6678 line, pointing to a probable O + B system. We report on low amplitude radial velocity variations in every strong absorption line in the blue spectrum of HD 195592. These variations are ruled by two time-scales respectively of 5.063 and about 20 days. The former is firmly established, whilst the latter is poorly constrained. We report also on a very significant line profile variability of the H $\beta$ line, with time scales strongly related to those of the radial velocities. Our results provide significant evidence that HD 195592 is a binary system, with a period that might be the variability time-scale of about 5 days. The second time scale may be the signature of an additional star moving along a wider orbit provided its mass is low enough, even though direct evidence for the presence of a third star is still lacking. Alternatively, the second time-scale may be the signature of a variability intrinsic to the stellar wind of the primary, potentially related to the stellar rotation.
We investigate the relation between the star-formation activity in galaxies and environment at z=1.2 in the COSMOS field, using the fraction of [OII] emitters and the local galaxy density. The fraction of [OII] emitters appears to be almost constant over the surface density of galaxies between 0.2 and 10 Mpc^-2. This trend is different from that seen in the local universe where the star-formation activity is weaker in higher density regions. To understand this difference between z~1 and z~0, we study the fraction of non-isolated galaxies as a function of local galaxy density. We find that the fraction of non-isolated galaxies increases with increasing density. Our results suggest that the star formation in galaxies at z~1 is triggered by galaxy interaction and/or mergers.
Context: Stellar evolution theory suggests that the relationship between number ratios of supernova (SN) types and metallicity holds important clues as to the nature of the progenitor stars (mass, metallicity, rotation, binarity, etc). Aims: We investigate the metallicity dependence of number ratios of various SN types, using a large sample of SN along with information on their radial position in, and magnitude of, their host galaxy. Methods: We derive typical galaxian metallicities (using the well known metallicity-luminosity relation) and local metallicities, i.e. at the position of the SN; in the latter case, we use the empirical fact that the metallicity gradients in disk galaxies are ~ constant when expressed in dex/R25. Results: We confirm a dependence of the N(Ibc)/N(II) ratio on metallicity; recent single star models with rotation and binary star models with no rotation appear to reproduce equally well that metallicity dependence. The size of our sample does not allow significant conclusions on the N(Ic)/N(Ib) ratio. Finally, we find an unexpected metallicity dependence of the ratio of thermonuclear to core collapse supernovae, which we interpret in terms of the star formation properties of the host galaxies.
The BL Lac object H1426+428 ($z\equiv 0.129$) is an established source of TeV $\gamma$-rays and detections of these photons from this object also have important implications for estimating the Extragalactic Background Light (EBL) in addition to the understanding of the particle acceleration and $\gamma$-ray production mechanisms in the AGN jets. We have observed this source for about 244h in 2004, 2006 and 2007 with the TACTIC $\gamma$-ray telescope located at Mt. Abu, India. Detailed analysis of these data do not indicate the presence of any statistically significant TeV $\gamma$-ray signal from the source direction. Accordingly, we have placed an upper limit of $\leq1.18\times10^{-12}$ $photons$ $cm^{-2}$ $s^{-1}$ on the integrated $\gamma$-ray flux at 3$\sigma$ significance level.
A sample of large northern Spitzer Infrared Nearby Galaxies Survey (SINGS) galaxies has recently been observed with the Westerbork Synthesis Radio Telescope (WSRT). We present observations of the linearly polarized radio continuum emission in this WSRT-SINGS galaxy sample. Of the 28 galaxies treated in this paper, 21 are detected in polarized radio continuum at 18- and 22-cm wavelengths. We utilize the rotation measure synthesis (RM-Synthesis) method, as implemented by Brentjens & de Bruyn, to coherently detect polarized emission from a large fractional bandwidth, while simultaneously assessing the degree of Faraday rotation experienced by the radiation along each line-of-sight. This represents the first time that the polarized emission and its Faraday rotation have been systematically probed down to ~10 microJy/beam RMS for a large sample of galaxies. Non-zero Faraday rotation is found to be ubiquitous in all of the target fields, from both the Galactic foreground and the target galaxies themselves. In this paper, we present an overview of the polarized emission detected in each of the WSRT-SINGS galaxies. The most prominent trend is a systematic modulation of the polarized intensity with galactic azimuth, such that a global minimum in the polarized intensity is seen toward the kinematically receding major axis. The implied large-scale magnetic field geometry is discussed in a companion paper. A second novel result is the detection of multiple nuclear Faraday depth components that are offset to both positive and negative RM by 100-200 rad/m^2 in all targets that host polarized (circum-)nuclear emission.
We present models representing the scattering of quasar radiation off free electrons and dust grains in geometries that approximate the structure of quasar host galaxies. We show that, for reasonable assumptions, scattering alone can easily produce ratios of nuclear (point source) to extended fluxes comparable to those determined in studies of quasar hosts. This result suggests that scattered quasar light, as well as stellar emission from the host galaxy, contributes significantly to the detected extended flux, leading to uncertainty in the inferred properties of quasar host. A significant contribution from scattered quasar light will lead to overestimates of the luminosity and hence mass of the host galaxy, and may also distort its morphology. Scattering of quasar light within the host galaxy may provide alternative explanations for the apparent peak in host luminosity at z = 2-3; possibly the overall average higher luminosity of radio-loud host galaxies relative to those of radio-quiet quasars (RQQs), and the apparent preference of high-luminosity RQQs for spheroidal rather than disk galaxies.
We investigate the radial color gradients of galactic disks using a sample of about 20,000 face-on spiral galaxies selected from the fourth data release of the Sloan Digital Sky Survey (SDSS-DR4). We combine galaxies with similar concentration, size and luminosity to construct composite galaxies, and then measure their color profiles by stacking the azimuthally averaged radial color profiles of all the member galaxies. Except for the smallest galaxies (R_{50}<3 kpc), almost all galaxies show negative disk color gradients with mean g-r gradient G_{gr}=-0.006 mag kpc^{-1} and r-z gradient G_{rz}=-0.018 mag kpc^{-1}. The disk color gradients are independent of the morphological types of galaxies and strongly dependent on the disk surface brightness \mu_{d}, with lower surface brightness galactic disks having steeper color gradients. We quantify the intrinsic correlation between color gradients and surface brightness as G_{gr}=-0.011\mu_{d}+0.233 and G_{rz}=-0.015\mu_{d}+0.324. These quantified correlations provide tight observational constraints on the formation and evolution models of spiral galaxies.
We report a possible change in the orbit parameters of the TrES-2 exoplanet. With a period of 2.470621 days, the TrES-2 exoplanet exhibits almost "grazing" transits 110.4 minutes duration as measured in 2006 by Holman and collaborators. We observed two transits of TrES-2 in 2008 using the 1.2m Oskar-Luhning telescope (OLT) of Hamburg observatory employing CCD photometry in an i-band and a near to R-band filter. A careful light curve analysis including a re-analysis of the 2006 observations shows that the current transit duration has shortened since 2006 by ~ 3.16 minutes. Although the new observations were taken in a different filter we argue that the observed change in transit duration time cannot be attributed to the treatment of limb darkening. If we assume the stellar and planetary radii to be constant, a change in orbit inclination is the most likely cause of this change in transit duration.
The correlation between Ca and Halpha chromospheric emission, known to be positive in the solar case, has been found to vary between -1 and 1 for other stars. Our objective is to understand the factors influencing this correlation in the solar case, and then to extrapolate our interpretation to other stars. We characterize the correlation between both types of emission in the solar case for different time scales. Then we determine the filling factors due to plages and filaments, and reconstruct the Ca and Halpha emission to test different physical conditions in terms of plage and filament contrasts. We have been able to precisely determine the correlation in the solar case as a function of the cycle phase. We interpret the results as reflecting the balance between the emission in plages and the absorption in filaments. We found that correlations close to zero or slightly negative can be obtained when considering the same spatio-temporal distribution of plages and filaments than on the sun but with greater contrast. However, with that assumption, correlations close to -1 cannot be obtained for example. Stars with a very low Halpha contrast in plages and filaments well correlated with plages could produce a correlation close to -1. This study opens new ways to study stellar activity, and provides a new diagnosis that will ultimately help to understand the magnetic configuration of stars other than the sun.
We calculate the evolution of molecular line profiles of HCO$^+$ and C$^{18}$O toward a dense core thatis forming inside a magnetized turbulent molecular cloud. Features of the profiles can be affected more significantly by coupled velocity and abundance structures in the outer region than those in the inner dense part of the core. The velocity structure at large radii is dominated by a turbulent flow nearby and accretion shocks onto the core, which resulting in the variation between inward and outward motions during the evolution of the core. The chemical abundance structure is significantly affected by the depletion of molecules in the central region with high density and low temperature. During the evolution of the core, the asymmetry of line profiles easily changes from blue to red, and vice versa. According to our study, the observed reversed (red) asymmetry toward some starless cores could be interpreted as an intrinsic result of outward motion in the outer region of a dense core, which is embedded in a turbulent environment and still grows in density at the center.
A generalized parameterization $w_\beta(z)$ for the dark energy equation of state (EoS) is proposed and some of its cosmological consequences are investigated. We show that in the limit of the characteristic dimensionless parameter $\beta \to +1, 0$ and -1 some well-known EoS parameterizations are fully recovered whereas for other values of $\beta$ the proposed parameterization admits a wider and new range of cosmological solutions. We also discuss possible constraints on the $w_\beta(z)$ parameters from current observational data.
We refute recent claims in the literature that stars with relativistically deep potentials cannot exist in $f(R)$ gravity. Numerical examples of stable stars, including relativistic ($GM_\star/r_\star \sim 0.1$), constant density stars, are studied. As a star is made larger, non-linear "chameleon" effects screen much of the star's mass, stabilizing gravity at the stellar center. Furthermore, we show that the onset of this chameleon screening is unrelated to strong gravity. At large central pressures $P>\rho/3$, $f(R)$ gravity, like general relativity, does have a maximum gravitational potential, but at a slightly smaller value: $GM_\star/r_\star = 0.345 < 4/9$ for constant density and one choice of parameters. This difference is associated with negative central curvature $R$ under general relativity not being accessed in the $f(R)$ model, but does not apply to any known astrophysical object.
AIMS. In this paper we present the chemical abundance analysis from high resolution UVES spectra of seventeen bright giant stars of the Globular Cluster M~22. RESULTS. We obtained an average iron abundance of [Fe/H]=-1.76\pm0.02 (internal errors only) and an \alpha enhancement of 0.36\pm0.04 (internal errors only). Na and O, and Al and O follow the well known anti-correlation found in many other GCs. We identified two groups of stars with significantly different abundances of the s-process elements Y, Zr and Ba. The relative numbers of the two group members are very similar to the ratio of the stars in the two SGBs of M22 recently found by Piotto (2009). Y and Ba abundances do not correlate with Na, O and Al. The s-element rich stars are also richer in iron and have higher Ca abundances. The results from high resolution spectra have been further confirmed by lower resolution GIRAFFE spectra of fourteen additional M22 stars. GIRAFFE spectra show also that the Eu -- a pure r-process element -- abundance is not related to the iron content. We discuss the chemical abundance pattern of M22 stars in the context of the multiple stellar populations in GC scenario.
Though a black hole can theoretically possess very big charge ($Q/(\sqrt{G}
M) \simeq 1$), the charge of the real astrophysical black holes is usually
considered to be negligible. This supposition is based on the fact that an
astrophysical black hole is always surrounded by some plasma, which is a very
good conductor. However, it disregards that the black holes have usually some
angular momentum, which can be interpreted as its rotation of a sort. If in the
plasma surrounding the hole there is some magnetic field, it led to the
electric field creation and, consequently, to the charge separation.
In this article we estimate the upper limit of the electric charge of stellar
mass astrophysical black holes. We have considered a new black hole formation
process and shown that the charge of a new-born black hole can be significant
($\sim 10^{13}$ {Coulombs}). Though the obtained charge of an astrophysical
black hole is big, the charge to mass ratio is small $Q/(\sqrt{G} M) \sim
10^{-7}$, and it is not enough to effect significantly neither on the
gravitational field of the star nor on the dynamics of its collapse.
In this paper we very preliminarily investigate the possibility of measuring the post-Newtonian general relativistic gravitoelectric and gravitomagnetic components of the acceleration of gravity on the Earth, in continuous regime, with two absolute measurements at the equator and the south pole with superconducting gravimeters. The magnitudes of such relativistic effects are 10^-10 m s^-2 and 10^-11 m s^-2, respectively. Unfortunately, the present-day uncertainties in the Earth's geodetic parameters which enter the classical Newtonian terms induce systematic errors 1-2 orders of magnitude larger than the relativistic ones. Moreover, a \sim 1 ngal sensitivity can be reached by the currently available superconducting gravimeters, but only for relative measurements.
We discuss a novel explanation of the dark energy as a manifestation of macroscopic non-locality coming from quantum gravity, as proposed by Markopoulou. It has been previously suggested that in a transition from an early quantum geometric phase of the universe to a low temperature phase characterized by an emergent spacetime metric, locality might have been "disordered". This means that there is a mismatch of micro-locality, as determined by the microscopic quantum dynamics and macro-locality as determined by the classical metric that governs the emergent low energy physics. In this paper we discuss the consequences for cosmology by studying a simple extension of the standard cosmological models with disordered locality. We show that the consequences can include a naturally small vacuum energy.
In the non-relativistic theory of gravitation recently proposed by Horava, the Hamiltonian constraint is not a local equation satisfied at each spatial point but an equation integrated over a whole space. The global Hamiltonian constraint is less restrictive than its local version, and allows a richer set of solutions than in general relativity. We show that a component which behaves like pressureless dust emerges as an "integration constant" of dynamical equations. Consequently, classical solutions to the infrared limit of Horava-Lifshitz gravity can mimic general relativity plus cold dark matter.
For the universe I use dimensionless entropy $S/k = \ln \Omega$ for which the most convenient unit is the googol ($10^{100}$) and take all dark matter as black holes whereupon the present entropy is about a thousand googols independently of whether dark energy possesses entropy. While the energy of the universe has been established to be about 0.04 baryons, 0.24 dark matter and 0.72 dark energy, the cosmological entropy is almost entirely, about $(1 - 10^{-15})$, from black holes and only $10^{-15}$ from everything else. This identification of all dark matter as black holes is natural in statistical mechanics.
We compute the tree-level connected four-point function of the primordial curvature perturbation for a fairly general minimally coupled single field inflationary model, where the inflaton's Lagrangian is a general function of the scalar field and its first derivatives. This model includes K-inflation and DBI-inflation as particular cases. We show that, at the leading order in the slow-roll expansion and in the small sound speed limit, there are two important tree-level diagrams for the trispectrum. One is a diagram where a scalar mode is exchanged and the other is a diagram where the interaction occurs at a point, i.e. a contact interaction diagram. The scalar exchange contribution is comparable to the contact interaction contribution. For the DBI-inflation model, in the so-called equilateral configuration, the scalar exchange trispectrum is maximized when the angles between the four momentum vectors are equal and in this case the amplitude of the trispectrum from the scalar exchange is one order of magnitude higher than the contact interaction trispectrum.
The purpose of this reanalysis of the WMAP uncalibrated time ordered data (TOD) was two fold. The first was to assess the reliability of the algorithm used to reconstruct the official WMAP sky maps of the CMB from the TOD. In particular, to investigate the possibility that some part of the reported anisotropies might be an artefact of the image reconstruction used. The second was to evaluate a proposed criterion for ensuring reliable detection of a signal of interest. The criterion is that, for the reliable detection of a signal of interest, it must be demonstrated that all images consistent with the data have the signal of interest. The criterion was implemented by testing the null hypothesis that the TOD was consistent with no anisotropies when WMAP's hourly calibration parameters were allowed to vary. It was shown independently for all 20 WMAP channels that sky maps with no anisotropies outside the galactic band, other than the dipole, where a better fit to the uncalibrated TOD than those from the official analysis. Thus the official WMAP analysis does not satisfy the proposed criterion raising the possibility that the reported anisotropies are artefacts of the image reconstruction. The recently launched Planck satellite, because of is use of repetitive circular scans, will be the first instrument able to detect the reported anisotropies without the use of image reconstruction. Thus Planck will provide an independent check of both the image reconstruction used in the WMAP official analysis and the proposed criterion. Assuming the proposed criterion is correct, the results of this reanalysis suggest that any anisotropies detected by Planck will be many times smaller than those reported by WMAP.
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A novel technique is employed for estimating attenuation curves in galaxies where only photometry and spectroscopic redshifts are available. This technique provides a powerful measure of particular extinction features such as the UV bump at 2175\A, which has been observed in environments ranging from the Milky Way to high-redshift star-forming galaxies. Knowledge of the typical strength of the UV bump is crucial for converting restframe UV flux into star formation rates, and yet there are surprisingly few observational constraints on this feature. The UV bump will impart a unique signature as it moves through various filters due to redshifting; its presence can therefore be disentangled from other stellar population effects. The utility of this technique is demonstrated with a large sample of galaxies drawn from the DEEP2 Galaxy Redshift Survey. The observed B-R color of star-forming galaxies at 0.6<z<1.4 disfavors the presence of a UV bump, and instead favors restframe UV (1800\A<lambda<3000\A) attenuation curves similar to the Milky Way without a UV bump or a power--law with index delta=-0.7.
In the cold dark matter scenario, dark matter halos are assembled hierarchically from smaller subunits. Some of these subunits are disrupted during the merging process, whereas others survive temporarily in the form of subhalos. A long-standing problem with this picture is that the number of subhalos predicted by simulations exceeds the number of luminous dwarf galaxies seen in the the vicinity of large galaxies like the Milky Way. Many of the subhalos must therefore have remained dark or very faint. If cold dark matter subhalos are as common as predicted, gravitational lensing may in principle offer a promising route to detection. In this review, we describe the many ways through which lensing by subhalos can manifest itself, and summarize the results from current efforts to constrain the properties of cold dark matter subhalos using such effects.
(Abridged) We revisit the question of the nature of ULXs through a detailed investigation of their spectral shape, using the highest quality X-ray data available in the XMM-Newton public archives. We confirm that simple spectral models commonly used for the analysis and interpretation of ULXs (power-law continuum and multi-colour disc blackbody models) are inadequate in the face of such high quality data. Instead we find two near ubiquitous features in the spectrum: a soft excess and a roll-over in the spectrum at energies above 3keV. We investigate a range of more physical models to describe these data. We find that disc plus Comptonised corona models fit the data well, but the derived corona is cool, and optically thick (tau ~ 5-30). We argue that these observed disc temperatures are not a good indicator of the black hole mass as the powerful, optically thick corona drains energy from the inner disc, and obscures it. We estimate the intrinsic (corona-less) disc temperature, and demonstrate that in most cases it lies in the regime of stellar mass black holes. These objects have spectra which range from those similar to the highest mass accretion rate states in Galactic binaries, to those which clearly have two peaks, one at energies below 1 keV (from the outer, unComptonised disc) and one above 3 keV (from the Comptonised, inner disc). However, a few ULXs have a significantly cooler corrected disc temperature; we suggest that these are the most extreme stellar mass black hole accretors, in which a massive wind completely envelopes the inner disc regions, creating a cool photosphere. We conclude that ULXs provide us with an observational template for the transition between Eddington and super-Eddington accretion flows, with the latter occupying a new ultraluminous accretion state.
Expanding upon the work of Way & Srivastava 2006 we demonstrate how the use
of training sets of comparable size continue to make Gaussian Process
Regression a competitive and in many ways a superior approach to that of Neural
Networks and other least-squares fitting methods. This is possible via new
matrix inversion techniques developed for Gaussian Processes that do not
require that the kernel matrix be sparse. This development, combined with a
neural-network kernel function appears to give superior results for this
problem.
We demonstrate that there appears to be a minimum number of training set
galaxies needed to obtain the optimal fit when using our Gaussian Process
Regression rank-reduction methods. We also find that morphological information
included with many photometric surveys appears, for the most part, to make the
photometric redshift evaluation slightly worse rather than better. This would
indicate that morphological information simply adds noise from the Gaussian
Process point of view.
In addition we show that cross-match catalog results involving 2MASS and SDSS
or GALEX have to be evaluated in the context of the resulting cross-match
magnitude and redshift distribution. Otherwise one may be misled into overly
optimistic conclusions.
New CCD photometric observations of the eclipsing system AR Boo were obtained from February 2006 to April 2008. The star's photometric properties are derived from detailed studies of the period variability and of all available light curves. We find that over about 56 years the orbital period of the system has varied due to a combination of an upward parabola and a sinusoid rather than in a monotonic fashion. Mass transfer from the less massive primary to the more massive secondary component is likely responsible for at least a significant part of the secular period change. The cyclical variation with a period of 7.57 yrs and a semi-amplitude of 0.0015 d can be produced either by a light-travel-time effect due to an unseen companion with a scaled mass of $M_3 \sin i_3$=0.081 $M_\odot$ or by a magnetic period modulation in the secondary star. Historical light curves of AR Boo, as well as our own, display season-to-season light variability, which are best modeled by including both a cool spot and a hot one on the secondary star. We think that the spots express magnetic dynamo-related activity and offer limited support for preferring the magnetic interpretation of the 7.57-year cycle over the third-body understanding. Our solutions confirm that AR Boo belongs to the W-subtype contact binary class, consisting of a hotter, less massive primary star with a spectral type of G9 and a companion of spectral type K1.
The sample of 137 low-redshift type Ia supernovae with 0.05 < z < 0.3 obtained from the SDSS-II Supernova Survey for the southern equatorial stripe of 300 square degrees is used to derive the luminosity functions of type Ia supernovae and of their host galaxies in the gri passbands. We show that the luminosity function of type Ia supernova host galaxies matches well with that of galaxies in the general field, suggesting that the occurrence of type Ia supernovae does not favour a particular type of galaxies but is predominantly proportional to the luminosity of galaxies. The only evidence that points to possible correlation between the supernova rate and star formation activity is that the supernova rate in late-type galaxies is higher than that in early-type galaxies by 31+/-35%. The sample contains 8 type Ia supernovae whose host galaxies were not identified, but it is shown that their occurrence is consistent with them occurred in low luminous galaxies beyond the survey. The luminosity function of type Ia supernovae is approximately Gaussian with the full-width half maximum being a factor of 1.4 in luminosity. The Gaussian distribution becomes tighter if the ratio of extinction to reddening, R_V, is lower than the characteristic value for the Milky Way and if luminosity is corrected for the light curve shape. The colour excess is ~0.07 mag which is significantly smaller than reddening expected for field galaxies. This colour excess does not vary with the distance of the supernovae from the centre of the host galaxy to 15 kpc. This suggests that the major part of the colour excess appears to be either intrinsic or reddening that arises in the immediate environment of supernova, rather than interstellar reddening in host galaxies.
We present the discovery of six new quasars at z~6 selected from the Sloan Digital Sky Survey (SDSS) southern survey, a deep imaging survey obtained by repeatedly scanning a stripe along the celestial equator. The six quasars are about two magnitudes fainter than the luminous z~6 quasars found in the SDSS main survey and one magnitude fainter than the quasars reported in Paper I (Jiang et al. 2008). Four of them comprise a complete flux-limited sample at 21<z_AB<21.8 over an effective area of 195 deg^2. The other two quasars are fainter than z_AB=22 and are not part of the complete sample. The quasar luminosity function at z~6 is well described as a single power law \Phi(L_{1450}) \propto L_{1450}^{\beta} over the luminosity range -28<M_{1450}<-25. The best-fitting slope \beta varies from -2.6 to -3.1, depending on the quasar samples used, with a statistical error of 0.3-0.4. About 40% of the quasars discovered in the SDSS southern survey have very narrow Lya emission lines, which may indicate small black hole masses and high Eddington luminosity ratios, and therefore short black hole growth time scales for these faint quasars at early epochs.
Superluminal preons (superbradyons) with a critical speed in vacuum much larger than the speed of light would, if they exist, play a fundamental role as constituents of the physical vacuum. If they are present as free particles in our Universe, they would spontaneously decay by emitting standard particles until they reach a speed equal or close to that of light. They would then form a cosmological sea where the relation between inertial and gravitational masses would differ from conventional Physics. Superbradyons may be at the origin of cosmological and astrophysical phenomena usually associated to dark matter and dark energy. Then, superbradyon spontaneous decays and similar interactions would be candidates to explain data on electron and positron abundances (PAMELA, ATIC, Fermi LAT, HESS, PPB-BETS) considered as possible dark matter signatures.
The Antarctic plateau contains the best sites on earth for many forms of astronomy, but none of the existing bases were selected with astronomy as the primary motivation. In this paper, we try to systematically compare the merits of potential observatory sites. We include South Pole, Domes A, C and F, and also Ridge B (running NE from Dome A), and what we call 'Ridge A' (running SW from Dome A). Our analysis combines satellite data, published results and atmospheric models, to compare the boundary layer, weather, free atmosphere, sky brightness, precipitable water vapour, and surface temperature at each site. We find that all Antarctic sites are likely compromised for optical work by airglow and aurorae. Of the sites with existing bases, Dome A is the best overall; but we find that Ridge A offers an even better site. We also find that Dome F is a remarkably good site. Dome C is less good as a thermal infrared or terahertz site, but would be able to take advantage of a predicted 'OH hole' over Antarctica during Spring.
Recent observations as well as theoretical studies of YSO jets suggest the presence of two steady components: a disk wind type outflow needed to explain the observed high mass loss rates and a stellar wind type outflow probably accounting for the observed stellar spin down. In this framework, we construct numerical two-component jet models by properly mixing an analytical disk wind solution with a complementary analytically derived stellar outflow. Their combination is controlled by both spatial and temporal parameters, in order to address different physical conditions and time variable features. We study the temporal evolution and the interaction of the two jet components on both small and large scales. The simulations reach steady state configurations close to the initial solutions. Although time variability is not found to considerably affect the dynamics, flow fluctuations generate condensations, whose large scale structures have a strong resemblance to observed YSO jet knots.
In this paper, the holographic dark energy in Brans-Dicke theory is confronted by cosmic observations from SN Ia, BAO and CMB shift parameter. The best fit parameters are found in $1\sigma$ region: $\Omega_{h0}=0.683^{+0.035}_{-0.038}$, $c=0.605^{+0.138}_{-0.107}$ and $\alpha=0.00662^{+0.00477}_{-0.00467}$ (equivalently $\omega=905.690^{+637.906}_{-651.471}$ which is less the solar system bound and consistent with other constraint results). With these best fit values of the parameters, it is found the universe is undergoing accelerated expansion, and the current value of equation of state of holographic dark energy $w_{h0}=-1.246^{+0.191}_{-0.144}$ which is phantom like in Brans-Dicke theory. The evolution of effective Newton's constant is also explored.
We study second-order perturbations for a general non-canonical scalar field, minimally coupled to gravity, on the unperturbed FRW background, where metric fluctuations are neglected a priori. By employing different approaches to cosmological perturbation theory, we show that, even in this simplified set-up, there arise ambiguities in the expressions of physically relevant quantities, such as the effective speed of the perturbations, and the stress tensor and energy density display a potential instability which is not present at linear order. We also discuss the significance of our analysis in light of the possible linearization instability of these fields about the FRW background.
We study the metallicities and abundance ratios of early-type galaxies in cosmological semi-analytic models (SAMs) within the hierarchical galaxy formation paradigm. To achieve this we implemented a detailed galactic chemical evolution (GCE) model and can now predict abundances of individual elements for the galaxies in the semi-analytic simulations. This is the first time that detailed GCE has been coupled to a SAM that includes feedback from Active Galactic Nuclei (AGN). We find that the new models are able to reproduce the observed mass-metallicity (M*-[Z/H]) relation and, for the first time in a SAM, we reproduce the observed positive slope of the mass-abundance ratio (M*-[$\alpha$/Fe]) relation. Our results indicate that in order to simultaneously match these observations of early-type galaxies, the use of both a very mildly top-heavy IMF (i.e., with a slope of x=1.1 as opposed to a standard x=1.3), and a lower fraction of binaries that explode as Type Ia supernovae appears to be required. We also examine the rate of supernova explosions in the simulated galaxies. In early-type (non-star forming) galaxies, our predictions are also consistent with the observed SNe rates. However, in star-forming galaxies, a higher fraction of SN Ia binaries than in our preferred model is required to match the data, perhaps indicating the need for a population of SN Ia with very short delay times.
We detect radio emission in an additional two epochs of the ultracool dwarf binary LP 349- 25, finding that the observed emission is broadband and steady on timescales between 10s and 10.7 hours, as well as on timescales of 0.6 and 1.6 years. This system is unusual for ultracool dwarfs with detectable radio emission, in exhibiting a lack of any large scale variability, particularly the bursting (periodic or aperiodic) behavior exhibited by the other objects with detectable levels of radio emission. We explore the constraints that the lack of variability on long and short timescales, and flat spectral index, imply about the radio-emitting structures and mechanism. The temporal constraints argue for a high latitude emitting region with a large inclination so that it is always in view, and survives for at least 0.6 year. Temporal constraints also limit the plasma conditions, implying that the electron density be n_e <4x10^5 cm-3 and B < 130 G in order not to see time variations due to collisional or radiative losses from high energy particles. The observations and constraints provided by them are most compatible with a nonthermal radio emission mechanism, likely gyrosynchrotron emission from a spatially homogeneous or inhomogeneous source. This indicates that, similar to behaviors noted for chromospheric, transition region, and coronal plasmas in ultracool dwarfs, the magnetic activity patterns observed in active higher mass stars can survive to the substellar boundary. We also present new epochs of multi-frequency radio observations for the the ultracool dwarfs 2MASS 05233822-140322 and 2MASS14563831-2809473(=LHS 3003); each has been detected in at least one previous epoch but are not detected in the epochs reported here.
The spectrum from the black hole X-ray transient GRO J1655-40. obtained using the $Chandra$ High Energy Transmission Grating (HETG) in 2005 is notable as a laboratory for the study of warm absorbers, and for the presence of many lines from odd-$Z$ elements between Na and Co (and Ti and Cr) not previously observed in X-rays. We present synthetic spectral models which can be used to constrain these element abundances and other parameters describing the outflow from the warm absorber in this object. We present results of fitting to the spectrum using various tools and techniques, including automated line fitting, phenomenological models, and photoionization modeling. We show that the behavior of the curves of growth of lines from H-like and Li-like ions indicate that the lines are either saturated or affected by filling-in from scattered or a partially covered continuum source. We confirm the conclusion of previous work by \cite{Mill06} and \cite{Mill08} which shows that the ionization conditions are not consistent with wind driving due to thermal expansion. The spectrum provides the opportunity to measure abundances for several elements not typically observable in the X-ray band. These show a pattern of enhancement for iron peak elements, and solar or sub-solar values for elements lighter than calcium. Models show that this is consistent with enrichment by a core-collapse supernova. We discuss the implications these values for the evolutionary history of this system.
Before the age of modern photographic and CCD observations alpha Cassiopeiae was labelled as a variable star, though this variability has not been seen with modern instrumentation. We present an analysis of 3 years of high precision space-based photometric measurements of the suspected variable star alpha Cassiopeiae, obtained by the broad band Solar Mass Ejection Imager (SMEI) instrument on board the Coriolis satellite. Over the 3 years of observations the star appears to not show any significant variability. Also, data from the Hipparcos epoch photometry annex shows no significant variability.
Within the framework of linearized Einstein field equations we compute the gravi tomagnetic effects on a test particle orbiting around a slow rotating, spherical body with a bulging ring fixed to the equatorial plane. Our results show that t he effect of the precesion is increased by the presence of the ring.
The dark matter content of early,- type galaxies (ETGs) is a hotly debated topic with contrasting results arguing in favour or against the presence of significant dark mass within the effective radius and the change with luminosity and mass. In order to address this question, we investigate here the global mass - to - light ratio $\Upsilon(r) = M(r)/L(r)$ of a sample of 21 lenses observed within the Sloan Lens ACS (SLACS) survey. We follow the usual approach of modeling the galaxy as a two component systems, but we use a phenomenological ansatz for $\Upsilon(r)$, proposed by some of us in Tortora et al. (2007), able to smoothly interpolate between constant $M/L$ models and a wide class of dark matter haloes. The resulting galaxy model is then fitted to the data on the Einstein radius and velocity dispersion. Our phenomenological model turns out to be in well agreement with the data suggesting the presence of massive dark matter haloes in order to explain the lensing and dynamics properties of the SLACS lenses. According to the values of the dark matter mass fraction, we argue that the halo may play a significant role in the inner regions probed by the data, but such a conclusion strongly depends on the adopted initial mass function of the stellar population. Finally, we find that the dark matter mass fraction within $R_{eff}$ scales with both the total luminosity and stellar mass in such a way that more luminous (and hence more massive) galaxies have a larger dark matter content.
The acceleration of the universe is described as a dynamical effect of the extrinsic curvature of space-time. By extending previous results, the extrinsic curvature is regarded as an independent spin-2 field, determined by a set of non-linear equations similar to Einstein's equations. In this framework, we investigate some cosmological consequences of this class of scenarios and test its observational viability by performing a statistical analysis with current type Ia Supernova data.
In colliding-wind binaries, shocks accelerate a fraction of the electrons up to relativistic speeds. These electrons then emit synchrotron radiation at radio wavelengths. Whether or not we detect this radiation depends on the size of the free-free absorption region in the stellar winds of both components. One expects long-period binaries to be detectable, but not the short-period ones. It was therefore surprising to find that Cyg OB2 No. 8A (P = 21.9 d) does show variability locked with orbital phase. To investigate this, we developed a model for the relativistic electron generation (including cooling and advection) and the radiative transfer of the synchrotron emission through the stellar wind. Using this model, we show that the synchrotron emitting region in Cyg OB2 No. 8A does extend far enough beyond the free-free absorption region to generate orbit-locked variability in the radio flux. This model can also be applied to other non-thermal emitters and will prove useful in interpreting observations from future surveys, such as COBRaS - the Cyg OB2 Radio Survey.
In this paper we investigate if the phantom-like regime in the LDGP model can be enlarged by the inclusion of a Gauss-Bonnet (GB) term into the bulk. However, we show that the opposite occurs: the GB effect seems instead to induce a breakdown of the phantom-like behaviour at an even smaller redshift.
An updated Science Vision for the SOFIA project is presented, including an overview of the characteristics and capabilities of the observatory and first generation instruments. A primary focus is placed on four science themes: 'The Formation of Stars and Planets', 'The Interstellar Medium of the Milky Way', 'Galaxies and the Galactic Center' and 'Planetary Science'.
Using the Infrared Spectrograph on board the Spitzer Space Telescope, we present low-resolution (64 < lambda / dlambda < 124), mid-infrared (20-38 micron) spectra of 23 high-redshift ULIRGs detected in the Bootes field of the NOAO Deep Wide-Field Survey. All of the sources were selected to have 1) fnu(24 micron) > 0.5 mJy; 2) R-[24] > 14 Vega mag; and 3) a prominent rest-frame 1.6 micron stellar photospheric feature redshifted into Spitzer's 3-8 micron IRAC bands. Of these, 20 show emission from polycyclic aromatic hydrocarbons (PAHs), usually interpreted as signatures of star formation. The PAH features indicate redshifts in the range 1.5 < z < 3.0, with a mean of <z>=1.96 and a dispersion of 0.30. Based on local templates, these sources have extremely large infrared luminosities, comparable to that of submillimeter galaxies. Our results confirm previous indications that the rest-frame 1.6 micron stellar bump can be efficiently used to select highly obscured starforming galaxies at z~2, and that the fraction of starburst-dominated ULIRGs increases to faint 24 micron flux densities. Using local templates, we find that the observed narrow redshift distribution is due to the fact that the 24 micron detectability of PAH-rich sources peaks sharply at z = 1.9. We can analogously explain the broader redshift distribution of Spitzer-detected AGN-dominated ULIRGs based on the shapes of their SEDs. Finally, we conclude that z~2 sources with a detectable 1.6 micron stellar opacity feature lack sufficient AGN emission to veil the 7.7 micron PAH band.
We have searched for variable stars in deep V-band images of a field towards the Galactic plane in Carina. The images were taken with VIMOS instrument at ESO VLT during 4 contiguous nights in April 2005. We detected 348 variables among 50897 stars in the magnitude range between V=15.4 and V=24.5 mag. Upon detection, we classified the variables by direct eye inspection of their light curves. All variable objects but 9 OGLE transits in the field are new discoveries. We provide a complete catalog of all variables which includes eclipsing/ellipsoidal binaries, miscellaneous pulsators (mostly delta Scuti-type variables), stars with flares and other (irregular and likely long-period) variables. Only two of the stars in our sample are known to host planets. Our result give some implications for future large variability surveys.
Cosmic filaments play a role of bridges along which matter and gas accrete onto galaxies to trigger star formation and feed central black holes. Here we explore the correlations between the intrinsic properties of void galaxies and the linearity $R_L$ of void filaments (degree of filament's straightness). We focus on void regions since the bridge effect of filaments should be most conspicuous in the pristine underdense regions like voids. Analyzing the Millennium-Run semi-analytic galaxy catalogue, we identify void filaments consisting of more than four galaxies (three edges) and calculate the means of central black hole mass, star formation rate, and stellar mass as a function of R_L. It is shown that the void galaxies constituting more straight filaments tend to have higher luminosity, more massive central black holes and higher star formation rate. Among the three properties, the central black hole mass is most strongly correlated with R_L. It is also shown that the dark halos constituting straight filaments tend to have similar masses. Our results suggest that the fuel-supply for central black holes and star formation of void galaxies occurs most efficiently along straight void filaments whose potential wells are generated by similar-mass dark halos.
We introduce a large class of scalar-tensor theories where gravity becomes stronger at large distances via the exchange of a scalar that mixes with the graviton. At small distances, i.e. large curvature, the scalar is screened via an analog of the Vainshtein mechanism of massive gravity. The crossover distance between the two regimes can be made cosmological by an appropriate choice of the parameters.
In this paper we have recalled the semiclassical metric obtained from a classical analysis of the loop quantum black hole (LQBH). We show that the regular Reissner-Nordstrom-like metric is self-dual in the sense of T-duality: the form of the metric obtained in Loop quantum Gravity (LQG) is invariant under the exchange "r <-> a0/r" where "a0" is proportional to the minimum area in LQG and "r" is the standard Schwarzschild radial coordinate at asymptotic infinity. Of particular interest, the symmetry imposes that if an observer at "r" close to infinity sees a black hole of mass "m" an observer in the other asymptotic infinity beyond the horizon (at "r" close to "0") sees a dual mass "mp/m" ("mp" is the Planck mass). We then show that small LQBH are stable and could be a component of dark matter. Ultra-light LQBHs created shortly after the Big Bang would now have a mass of approximately "10^(-5) mp" and emit radiation with a typical energy of about 10^(13) - 10^(14) eV but they would also emit cosmic rays of much higher energies, albeit few of them. If these small LQBHs form a majority of the dark matter of the Milky Way's Halo, the production rate of ultra-high-energy-cosmic-rays (UHECR) by these ultra light black holes would be compatible with the observed rate of the Auger detector.
By extending the lepton sector of standard model to include one sterile neutrino and two sets of new Higgs doublets and right-handed neutrinos, denoted by $(\eta_1, N_1, N_3)$ and $(\eta_2, N_2, N_4)$, with two $Z_2$ symmetries, the puzzles of neutrino masses, matter-antimatter asymmetry and cosmic-ray excess observed by Fermi-LAT and PAMELA can be resolved simultaneously. The characters of the model are: (a) neutrino masses arise from type-I and radiative seesaw mechanisms; (b) leptogenesis leading to baryon asymmetry at the energy scale of $O(1- 10\rm TeV)$ could be realized through soft $Z_2$ symmetry breaking effects; and (c) the conditions of small couplings for a long-lived dark matter could be achieved naturally through loop corrections due to the same soft symmetry breaking effects. The candidate for dark matter in leptophilic decays could fit the Fermi-LAT and PAMELA data well.
Cosmologically long-lived, composite states arise as natural dark matter candidates in theories with a strongly interacting hidden sector at a scale of 10 - 100 TeV. Light axion-like states, with masses in the 1 MeV - 10 GeV range, are also generic, and can decay via Higgs couplings to light standard model particles. Such a scenario is well motivated in the context of very low energy supersymmetry breaking, where ubiquitous cosmological problems associated with the gravitino are avoided. We investigate the astrophysical and collider signatures of this scenario, assuming that dark matter decays into the axion-like states via dimension six operators, and we present an illustrative model exhibiting these features. We conclude that the recent data from PAMELA, FERMI, and H.E.S.S. points to this setup as a compelling paradigm for dark matter. This has important implications for future diffuse gamma ray measurements and collider searches.
We study cosmological perturbations in Ho\v{r}ava-Lifshitz Gravity. We consider scalar metric fluctuations about a homogeneous and isotropic space-time. Starting from the most general metric, we work out the complete second order action for the perturbations. We then make use of the residual gauge invariance and of the constraint equations to reduce the number of dynamical degrees of freedom. After introducing the Sasaki-Mukhanov variable, the combination of spatial metric fluctuation and matter inhomogeneity for which the action in General Relativity has canonical form, we find that this variable has the standard time derivative term in the second order action, and that the extra degree of freedom is non-dynamical. The limit $\lambda \to 1$ is well-behaved, unlike what is obtained when performing incomplete analyses of cosmological fluctuations. Thus, there is no strong coupling problem for Ho\v{r}ava-Lifshitz gravity when considering cosmological solutions. We also compute the spectrum of cosmological perturbations. If the potential in the action is taken to be of "detailed balance" form, we find a cancelation of the highest derivative terms in the action for the curvature fluctuations. As a consequence, the initial spectrum of perturbations will not be scale-invariant in a general spacetime background. As an application, we consider fluctuations in an inflationary background and draw connections with the "trans-Planckian problem" for cosmological perturbations. In the special case in which the potential term in the action is of detailed balance form and in which $\lambda = 1$, the equation of motion for cosmological perturbations in the far UV takes the same form as in GR. However, in general the equation of motion is characterized by a modified dispersion relation.
Supersymmetry implies that stable non-topological solitons, Q-balls, could form in the early universe and could make up all or part of dark matter. We show that the relic Q-balls passing through Earth can produce a detectable neutrino flux. The peculiar zenith angle dependence and a small annual modulation of this flux can be used as signatures of dark-matter Q-balls.
The Tensor-Vector-Scalar theory of gravity, which was designed as a relativistic implementation to the modified dynamics paradigm, has fared quite well as an alternative to dark matter, on both galactic and cosmological scales. However, its performance in the solar system, as embodied in the post-Newtonian formalism, has not yet been fully investigated. Tamaki has recently attempted to calculate the preferred frame parameters for TeVeS, but ignored the cosmological value of the scalar field, thus concluding that the Newtonian potential must be static in order to be consistent with the vector equation. We show that when the cosmological value of the scalar field is taken into account, there is no constraint on the Newtonian potential; however, the cosmological value of the scalar field is tightly linked to the vector field coupling constant K, preventing the former from evolving as predicted by its equation of motion. We then proceed to investigate the post-Newtonian limit of a generalized version of TeVeS, with {\AE}ther type vector action, and show that its \beta,\gamma and \xi parameters are as in GR, while solar system constraints on the preferred frame parameters \alpha_1 and \alpha_2 can be satisfied within a modest range of small values of the scalar and vector fields coupling parameters, and for values of the cosmological scalar field consistent with evolution within the framework of existing models.
We discuss the reconstruction of neutrino flavor ratios at astrophysical sources from future neutrino-telescope measurements, given the knowledge of neutrino mixing angles obtained from terrestrial experiments. With a statistical analysis, we demonstrated that the pion source and the muon damped source can be distinguished from each other at the $3 \sigma$ level provided the accuracies in the measurement of $R\equiv\phi (\nu_{\mu})/(\phi (\nu_{e})+\phi (\nu_{\tau}))$ and $S\equiv\phi (\nu_e)/\phi (\nu_{\tau})$ can both reach about 10%. On the other hand, the above two sources are very difficult to distinguish by merely measuring $R$ alone. We also discuss the effect of leptonic CP phase on such a flavor-ratio reconstruction.
A survey of the worldwide litterature reveals that the question Are We Alone in the Universe ? has been formulated only in the western litterature. Here I try to understand why it is so. To investigate this problem it is first necessary to clarify what western culture means.
Links to: arXiv, form interface, find, astro-ph, recent, 0905, contact, help (Access key information)
The CRESST experiment monitors 300g CaWO_4 crystals as targets for particle interactions in an ultra low background environment. In this paper, we analyze the background spectra that are recorded by three detectors over many weeks of data taking. Understanding these spectra is mandatory if one wants to further reduce the background level, and allows us to cross-check the calibration of the detectors. We identify a variety of sources, such as intrinsic contaminations due to primordial radioisotopes and cosmogenic activation of the target material. In particular, we detect a 3.6keV X-ray line from the decay of 41-Ca with an activity of (26\pm4)\mu Bq, corresponding to a ratio 41-Ca/40-Ca=(2.2\pm0.3)\times10^{-16}.
We study the dynamics of the Magellanic Clouds in a model for the Local Group whose mass is constrained using the timing argument/two-body limit of the action principle. The goal is to evaluate the role of M31 in generating the high angular momentum orbit of the Clouds, a puzzle that has only been exacerbated by the latest $HST$ proper motion measurements. We study the effects of varying the total Local Group mass, the relative mass of the Milky Way and M31, the proper motion of M31, and the proper motion of the LMC on this problem. Over a large part of this parameter-space we find that tides from M31 are insignificant. For a range of LMC proper motions approximately $3\sigma$ higher than the mean and total Local Group mass $> 3.5\times 10^{12} M_\odot$, M31 can provide a significant torque to the LMC orbit. However, if the LMC is bound to the MW, then M31 is found to have negligible effect on its motion and the origin of the high angular momentum of the system remains a puzzle. Finally, we use the timing argument to calculate the total mass of the MW-LMC system based on the assumption that they are encountering each other for the first time, their previous perigalacticon being a Hubble time ago, obtaining $M_{\rm MW} + M_{\rm LMC} = (8.7 \pm 0.8) \times 10^{11} M_\odot$.
By using high-resolution 1D hydrodynamical simulations, we investigate the effects of purely mechanical feedback from super massive black holes (SMBHs) in the evolution of elliptical galaxies for a broad range of feedback efficiencies and compare the results to four major observational constraints. In particular, we focus on 1) the central black hole to stellar mass ratio of the host galaxy, 2) the lifetime of the luminous quasar phase, 3) the mass of stars formed in the host galaxy within the last Gyr, and 4) the X-ray luminosity of the hot diffuse gas. As a result, we try to pin down the most successful range of mechanical feedback efficiencies. We find that while low feedback efficiencies result in too much growth of the SMBH, high efficiencies totally blow out the hot interstellar gas, and the models are characterized by very low thermal X-ray luminosity well below the observed range. The net lifetime of the quasar phase is strongly coupled to the mass ratio between SMBH and its host galaxy, while the X-ray luminosity is generally correlated to the recent star formation within the last Gyr. When considering the popularly adopted model of the constant feedback efficiency, the feedback energy deposited into the ambient medium should be more than 0.01% of the SMBH accretion energy to be consistent with the SMBH mass to stellar mass ratio in the local universe. Yet, the X-ray luminosity of the hot gas favors about 0.005% of the accretion energy as the mechanical AGN feedback energy. We conclude that the purely mechanical feedback mode is unlikely to be simultaneously compatible with all four observable tests, even allowing a broad range of feedback efficiencies, and that including both radiative and mechanical feedback together may be a solution to comply the observational constraints. [abridged]
Using the data obtained with the Spitzer Space telescope as part of the Surveying the Agents of a Galaxy's Evolution (SAGE) legacy survey, we have studied the variations of the dust composition and abundance across the Large Magellanic Cloud (LMC). Such variations are expected, as the explosive events which have lead to the formation of the many HI shells observed should have affected the dust properties. Using a model and comparing with a reference spectral energy distribution from our Galaxy, we deduce the relative abundance variations of small dust grains across the LMC. We examined the infrared color ratios as well as the relative abundances of very small grains (VSGs) and polycyclic aromatic hydrocarbons (PAHs) relative to the big grain (BG) abundance. Results show that each dust component could have different origins or evolution in the interstellar medium (ISM). The VSG abundance traces the star formation activity and could result from shattering of larger grains, whereas the PAH abundance increases around molecular clouds as well as in the stellar bar, where they could have been injected into the ISM during mass loss from old stars.
[Abridged] We have carried out a deep X-ray and optical survey with Chandra and HST of low-extinction regions in the Galactic bulge. Here we present the results of a search for low-luminosity (L_X <~ 1e34 ergs/s) accreting binaries in the region closest to the Galactic Center, at an angular offset of 1.4deg, that we have named the Limiting Window. Based on their blue optical colors, excess Halpha fluxes, and high X-ray--to--optical flux ratios, we identify three likely cataclysmic variables (CVs). Distance estimates put these systems farther than >~2 kpc. Based on their Halpha-excess fluxes and/or high X-ray--to--optical flux ratios, we find 22 candidate accreting binaries; however, the properties of some can also be explained if they are dMe stars or active galaxies. We investigate the CV number density towards the bulge and find that the number of observed candidate CVs is consistent with or lower than the number expected for a constant CV-to-star ratio that is fixed to the local value. The X-ray properties of two likely CVs are similar to those of the faint, hard X-ray sources in the Galactic-Center region that have been explained by (mainly) magnetic CVs. If our candidates belong to the same population, they would be the first members to be optically identified; optical or infrared identification of their Galactic-Center analogs would be impossible due to the higher obscuration. We speculate that all Galactic hard X-ray sources in our field can be explained by magnetic CVs.
Analysis of high spatial resolution VLA images shows that the free-free emission from NGC7538 IRS1 is dominated by a collimated ionized wind. We have re-analyzed high angular resolution VLA archive data from 6 cm to 7 mm, and measured separately the flux density from the compact bipolar core and the extended (1.5" - 3") lobes. We find that the flux density of the core is proportional to the frequency to the power of alpha, with alpha being about 0.7. The frequency dependence of the total flux density is slightly steeper with alpha = 0.8. A massive optically thick hypercompact core with a steep density gradient can explain this frequency dependence, but it cannot explain the extremely broad recombination line velocities observed in this source. Neither can it explain why the core is bipolar rather than spherical, nor the observed decrease of 4% in the flux density in less than 10 years. An ionized wind modulated by accretion is expected to vary, because the accretion flow from the surrounding cloud will vary over time. BIMA and CARMA continuum observations at 3 mm show that the free-free emission still dominates at 3 mm. HCO+ J = 1 - 0 observations combined with FCRAO single dish data show a clear inverse P Cygni profile towards IRS1. These observations confirm that IRS1 is heavily accreting with an accretion rate of about 2 times 10(-4) solar masses per year.
We use Minkowski Functionals (MF) to constrain a primordial non-Gaussian contribution to the CMB intensity field as observed in the 150 GHz and 145 GHz BOOMERanG maps from the 1998 and 2003 flights, respectively, performing for the first time a joint analysis of the two datasets. A perturbative expansion of the MF formulae in the limit of a weakly non-Gaussian field yields analytical formulae, derived by Hikage et al. (2006), which can be used to constrain the coupling parameter f_NL without the need for non-Gaussian simulations. We find -1020<f_NL<390 at 95% CL, significantly improving the previous constraints by De Troia et al. (2007) on the BOOMERanG 2003 dataset. These are the best f_NL limits to date for suborbital probes.
We revisit the flare on 1992 January 13, which is now universally termed the ``Masuda flare''. Our work is motivated by the remarkable improvement of Yohkoh hard X-ray imaging, which was only achieved after the intensive investigations on this famous event. With the calibrated Hard X-ray Telescope (HXT) data, we find that the hard X-ray coronal source is indeed a loop-top source, located slightly above the soft X-ray loop but within the 10% brightness contour of the HXT L-band thermal loop, rather than distinctly above the loop top as in the original HXT images. This critical change relieves the longstanding difficulties of understanding the original Masuda flare, viz., the lack of L-band emission of the coronal source, and the low density at the coronal source location. Despite the generally accepted belief that the coronal emission in the Masuda flare was nonthermal, we find its spectrum can be explained either by thermal bremsstrahlung of a superhot plasma (80 MK), or by nonthermal bremsstrahlung at a thick-thin target, with the injecting electron index derived from the coronal emission approximately equal to that from the footpoints. We propose a simplified picture, featuring the field line shrinkage effect and the resultant increase of the loss-cone angle at the coronal trap, to qualitatively explain that as time progresses the hard X-ray coronal source diminishes in brightness relative to the footpoints, that its centroid position moves to higher altitudes, and that the footpoint spectrum is successively hardening, with the coronal spectrum softening simultaneously.
We use two independent methods to forecast the dark energy measurements achievable by combining future galaxy redshift surveys based on the radio HI emission line with Cosmic Microwave Background (CMB) data from the {\sl Planck} satellite. In the first method we focus on the `standard ruler' provided by the baryon acoustic oscillation (BAO) length scale. In the second method we utilize additional information encoded in the galaxy power spectrum including galaxy bias from velocity-space distortions and the growth of cosmic structure. We find that a radio synthesis array with about 10 per cent of the collecting area of the Square Kilometre Array (SKA), equipped with a wide ($10-100 ~ {\rm deg}^2$) field-of-view, would have the capacity to perform a $20{,}000 ~ {\rm deg}^2$ redshift survey to a maximum redshift $z_{\rm max} \sim 0.8$ and thereby produce dark energy measurements that are competitive with surveys likely to be undertaken by optical telescopes around 2015. There would then be powerful arguments for adding collecting area to such a `Phase-1' SKA because of the square-law scaling of survey speed with telescope sensitivity for HI surveys, compared to the linear scaling for optical redshift surveys. The full SKA telescope should, by performing a $20{,}000 ~ {\rm deg}^2$ HI redshift survey to $z_{\rm max} \sim 2$ around 2020, yield an accurate measurement of cosmological parameters independent of CMB datasets. Combining CMB ({\sl Planck}) and galaxy power spectrum (SKA) measurements will drive errors in the dark energy equation-of-state parameter $w$ well below the 1 per cent level. The major systematic uncertainty in these forecasts is the lack of direct information about the mass function of high-redshift HI-emitting galaxies.
This paper discusses the thermodynamics of a black hole with respect to Hawking radiation and the entropy. We look at a unified picture of black hole entropy and curvature and how this can lead to the usual black hole luminosity due to Hawking radiation. It is also shown how the volume inside the horizon, apart from surface area, can play a role in understanding the Hawking flux. In addition holography also implies a phase space associated with the interior volume and this happens to be just a quantum of phase space, filled with just one photon. Generalised uncertainty principle can be incorporated in this analysis. These results hold for all black hole masses in any dimensions.
We report the results of a time-series CCD photometric survey of variable stars in the field of the open cluster NGC 2126. In about one square degree field covering the cluster, a total number of 21 variable candidates are detected during this survey, of which 16 are newly found. The periods, classifications and spectral types of 14 newly discovered variables are discussed, which consist of six eclipsing binaries systems, three pulsating variable stars, three long period variables, one RS CVn star, and one W UMa or $\delta$ Scuti star. In addition, there are two variable candidates, the properties of which cannot be determined in this paper. By a method based on fitting spectral energy distributions(SEDs) of stars with theoretical ones, the membership probabilities and the fundamental parameters of this cluster are determined. As a result, five variables are probably members of NGC 2126. The fundamental parameters of the this cluster are determined as: the metallicity to be 0.008 $Z_\odot$, the age $\log(t)$= 8.95, the distance modulus $(m-M)_{0}$= 10.34 and the reddening value $E(B-V)$=0.55 mag.
We analyse the spectral energy distribution of the evolved carbon giant DY Per with a spectral synthesis technique. The red giant shows the photometric features of R CrB type stars. We derive the atmospheric parameters of DY Per using three variants of molecular line lists. We estimate Teff to be in the range 2900 < Teff < 3300 K. We adopted log g = 0. The star may be metal deficient and hydrogen deficient. The maximum possible carbon abundance in the star, [C]=0.94, provides the following atmospheric parameters: Tef=3100 K, [Fe/H] = 0, log(C/O)=0.6, [N/Fe] = 0, [H/He] = 0, with Jorgensen's line lists for the molecules C2 and CN.
So far, six mechanisms have been proposed to account for the Galactic disk heating. Of these, the most important appear to be a combination of scattering of stars by molecular clouds and by spiral arms. We study a further mechanism, namely, the repeated disk impact of the original Galactic Globular Cluster population up to the present. We find that Globular Clusters could have contributed at most a small fraction of the current vertical energy of the disk, as they could heat the whole disk to {$\sigma $}$_{z}$ = 5.5kms$^{{\rm -} {\rm 1}}$ (c.f. the observed 18 and 39 kms$^{{\rm -} {\rm 1}}$ for the thick and thin disks respectively). We find that the rate of rise of disk heat ($\alpha$=0.22 in \textit{$\sigma $}$_{z}$ $\sim t^{\alpha}$ with \textit t being time), is close to that found for scattering by molecular clouds.
Aims. A global O-Na abundance anti-correlation is observed in globular
clusters, which is not present in the Galactic field population. Open clusters
are thought to be chemically homogeneous internally. We aim to explore the O
and Na abundance pattern among the open cluster population of the Galactic
disk.
Methods. We combine open cluster abundance ratios of O and Na from
high-resolution spectroscopic studies in the literature and normalize them to a
common solar scale. We compare the open cluster abundances against the globular
clusters and disk field.
Results. We find that the different environments show different abundance
patterns. The open clusters do not show the O-Na anti-correlation at the
extreme O-depletion / Na-enhancement as observed in globular clusters.
Furthermore, the high Na abundances in open clusters do not match the disk
field stars. If real, it may be suggesting that the dissolution of present-day
open clusters is not a significant contribution to building the Galactic disk.
Large-scale homogeneous studies of clusters and field will further confirm the
reality of the Na enhancement.
We carried out two-dimensional magnetohydrodynamic simulations of the Galactic gas disk to show that the dense loop-like structures discovered by the Galactic center molecular cloud survey by NANTEN 4 m telescope can be formed by the buoyant rise of magnetic loops due to the Parker instability. At the initial state, we assumed a gravitationally stratified disk consisting of the cool layer ($T \sim 10^3$ K), warm layer ($T \sim 10^4$ K), and hot layer ($T \sim 10^5$ K). Simulation box is a local part of the disk containing the equatorial plane. The gravitational field is approximated by that of a point mass at the galactic center. The self-gravity, and the effects of the galactic rotation are ignored. Numerical results indicate that the length of the magnetic loops emerging from the disk is determined by the scale height of the hot layer ($\sim$ 100 pc at 1 kpc from the Galactic center). The loop length, velocity gradient along the loops and large velocity dispersions at their foot points are consistent with the NANTEN observations. We also show that the loops become top-heavy when the curvature of the loop is sufficiently small, so that the rising loop accumulates the overlying gas faster than sliding it down along the loop. This mechanism is similar to that of the formation of solar chromospheric arch filaments. The molecular loops emerge from the low temperature layer just like the dark filaments observed in the H$\alpha$ image of the emerging flux region of the sun.
We present detailed clustering analysis of a large K-band selected local galaxy sample, which is constructed from the 2MASS and the SDSS and consists of $82,486$ galaxies with $10 < K < 13.5$ and $0.01 < z < 0.1$. The two-point correlation function of the magnitude-limited sample in real space at small scales is well described by a power law $\xi(r)=(r/6.44\pm0.23)^{-1.81\pm0.02}$. The pairwise velocity dispersion is derived from the anisotropic two-point correlation function and find the dispersion $\sigma_{12}=685\pm 17\kms$ if its scale invariance is assumed, which is larger than values measured in optical bands selected galaxy samples. We further investigate the dependence of the two-point correlation function and the $\sigma_{12}$ on the $g-r$ color and the $K$-band luminosity, obtain similar results to previous works in optical bands. Comparing a mock galaxy sample with our real data indicates that the semi-analytical model can not mimic the $\sigma_{12}$ in observation albeit it can approximate the two-point correlation function within measurement uncertainties.
We apply the statistical measure of complexity introduced by Lopez-Ruiz, Mancini and Calbet to neutron stars structure. Neutron stars is a classical example where the gravitational field and quantum behavior are combined and produce a macroscopic dense object. Actually, we continue the recent application of Sanudo and Pacheco to white dwarfs structure. We concentrate our study on the connection between complexity and neutron star properties, like maximum mass and the corresponding radius, applying a specific set of realistic equation of states. Moreover, the effect of the strength of the gravitational field on the neutron star structure and consequently on the complexity measure is also investigated. It is seen that neutron stars, consistent with astronomical observations so far, are ordered systems (low complexity), which cannot grow in complexity as their mass increases. This is a result of the interplay of gravity, the short-range nuclear force and the very short-range weak interaction.
We present computations of nucleosynthesis in red giants and asymptotic giant branch stars of Population I experiencing extended mixing. The assumed physical cause for mass transport is the buoyancy of magnetized structures, according to recent suggestions. The peculiar property of such a mechanism is to allow for both fast and slow mixing phenomena, as required for reproducing the spread in Li abundances displayed by red giants and as discussed in an accompanying paper. We explore here the effects of this kind of mass transport on CNO and intermediatemass nuclei and compare the results with the available evidence from evolved red giants and from the isotopic composition of presolar grains of AGB origin. It is found that a good general accord exists between predictions and measurements; in this framework we also show which type of observational data best constrains the various parameters. We conclude that magnetic buoyancy, allowing for mixing at rather different speeds, can be an interesting scenario to explore for explaining together the abundances of CNO nuclei and of Li.
The Suzaku X-ray satellite observed the nearby spiral galaxy NGC 4258 for a total good exposure time of 100 ks. We present an analysis of the Suzaku XIS data, in which we confirm that the 0.5--2 keV spectra of the interstellar medium (ISM) are well-represented by a two-temperature model. The cool and hot ISM temperatures are 0.23+-0.02 and 0.59 +-0.01 keV, respectively. Suzaku's excellent spectral sensitivity enables us to measure the metal abundances of O, Ne, Mg, Si and Fe of the ISM for the first time. The resultant abundance pattern of O, Mg, Si, and Fe is consistent with that of the new solar abundance table of Lodders (2003), rather than Anders & Grevesse (1989). This suggests that the metal enrichment processes of NGC 4258 and of our Galaxy are similar.
Since the discovery of the first broad iron-K line in 1995 from the Seyfert Galaxy MCG--6-30-15, broad iron-K lines have been found in several other Seyfert galaxies, from accreting stellar mass black holes and even from accreting neutron stars. The iron-K line is prominent in the reflection spectrum created by the hard X-ray continuum irradiating dense accreting matter. Relativistic distortion of the line makes it sensitive to the strong gravity and spin of the black hole. The accompanying iron-L line emission should be detectable when the iron abundance is high. Here we report the first discovery of both iron-K and L emission, using XMM-Newton observations of the Narrow-Line Seyfert 1 Galaxy 1H0707-495. The bright Fe-L emission has enabled us, for the first time, to detect a reverberation lag of 30 s between the direct X-ray continuum and its reflection from matter falling into the hole. The observed reverberation timescale is comparable to the light-crossing time of the innermost radii around a supermassive black hole. The combination of spectral and timing data on 1H0707-495 provides strong evidence that we are witnessing emission from matter within a gravitational radius, or a fraction of a light-minute, from the event horizon of a rapidly-spinning, massive black hole.
We have combined the CLASX Chandra survey in Lockman with the Spitzer SWIRE
survey data to study the X-ray-infrared connection for AGN. The sample consists
of 401 X-ray-sources, of which 306 are detected by Spitzer, and a further 257
AGN candidates detected through their dust torus, but not by Chandra. For X-ray
sources the X-ray hardness ratio has been modelled in terms of a power-law with
absorption N(H). The optical and infrared data have been modelled in terms of
our well-established optical galaxy and QSO templates, and infrared templates
based on radiative transfer models.
Our estimate of the N(H) distribution is consistent with other studies, but
we do find a higher proportion of low absorption objects at z < 0.5 than at z >
0.5. While we find only one X-ray AGN with N(H) > 10^{24} cm^{-2}, we argue
that 10 objects with torus luminosity apparently exceeding the bolometric X-ray
to 3 \mu m luminosity are strong candidates for being heavily absorbed in
X-rays. We also estimate that at least half of the infrared-detected AGN dust
tori which are undetected in X-rays are likely to be Compton thick. Our
estimate of the total number of Compton-thick objects corresponds to > 20%$ of
the combined SWIRE-CLASX sample (and with an upper limit of 39 %).
The range of dust covering factors is 1-100 %, with a mean of 40 %, ie a Type
2 fraction of 40 %. Measured by the ratio of dust torus luminosity to X-ray or
(for Type 1 objects) optical luminosity, the covering factor appears to
decrease towards intermediate AGN luminosity, in contradiction to estimates
based on ratios of narrow-line and broad-line spectra, but may increase again
at low AGN luminosity.
We report the detection of pulsed gamma-rays from the young, spin-powered radio pulsar PSR J2021+3651 using data acquired with the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (formerly GLAST). The light curve consists of two narrow peaks of similar amplitude separated by 0.468 +/- 0.002 in phase. The first peak lags the maximum of the 2 GHz radio pulse by 0.162 +/- 0.004 +/- 0.01 in phase. The integral gamma-ray photon flux above 100 MeV is (56 +/- 3 +/- 11) x 10^{-8} /cm2/s. The photon spectrum is well-described by an exponentially cut-off power law of the form dF/dE = kE^{-\Gamma} e^(-E/E_c) where the energy E is expressed in GeV. The photon index is \Gamma = 1.5 +/- 0.1 +/- 0.1 and the exponential cut-off is E_c = 2.4 +/- 0.3 +/- 0.5 GeV. The first uncertainty is statistical and the second is systematic. The integral photon flux of the bridge is approximately 10% of the pulsed emission, and the upper limit on off-pulse gamma-ray emission from a putative pulsar wind nebula is <10% of the pulsed emission at the 95% confidence level. Radio polarization measurements yield a rotation measure of RM = 524 +/- 4 rad/m^2 but a poorly constrained magnetic geometry. Re-analysis of Chandra data enhanced the significance of the weak X-ray pulsations, and the first peak is roughly phase-aligned with the first gamma-ray peak. We discuss the emission region and beaming geometry based on the shape and spectrum of the gamma-ray light curve combined with radio and X-ray measurements, and the implications for the pulsar distance. Gamma-ray emission from the polar cap region seems unlikely for this pulsar.
Instabilities of the dust layer in a protoplanetary disk are investigated. It
is known that the streaming instability develops and dust density concentration
occurs in a situation where the initial dust density is uniform. This work
considers the effect of initial dust density gradient vertical to the midplane.
Dust and gas are treated as different fluids. Pressure of dust fluid is assumed
to be zero. The gas friction time is assumed to be constant. Axisymmetric
two-dimensional numerical simulation was performed using the spectral method.
We found that an instability develops with a growth rate on the order of the
Keplerian angular velocity even if the gas friction time multiplied by the
Keplerian angular velocity is as small as 0.001.
This instability is powered by two sources: (1) the vertical shear of the
azimuthal velocity, and (2) the relative motion of dust and gas coupled with
the dust density fluctuation due to advection. This instability diffuses dust
by turbulent advection and the maximum dust density decreases. This means that
the dust concentration by the streaming instability which is seen in the case
of a uniform initial dust density becomes ineffective as dust density gradient
increases by the dust settling toward the midplane.
We use the data of Wisconsin H$\alpha$ Mapper (WHAM) to test the hypothesis of whether the amplitudes and spectrum of density fluctuations measured by WHAM may be matched to the data obtained for interstellar scintillations and scattering. To do this, first of all, adjusted the mean level of signal in the adjacent patches of the data. Then, assuming that the spectrum is Kolmogorov, we successfully matched the amplitudes of turbulence obtained from the WHAM data and the interstellar density fluctuations reported in the existing literature. As a result, we conclude that the existing data is consistent with the a Kolmogorov cascade which spans from $10^6$ to $10^{17}$ $m$.
We study the spectroscopic and photometric properties of carbon stars. In the first paper of this series we focus on objects that can be described by hydrostatic models neglecting dynamical phenomena like pulsation and mass loss. As a consequence, the reddening due to circumstellar dust is not included. Our results are collected in a database, which can be used in conjunction with stellar evolution and population synthesis calculations involving the AGB. We have computed a grid of 746 spherically symmetric COMARCS atmospheres covering effective temperatures between 2400 and 4000K, surface gravities from log(g) = 0.0 to -1.0, metallicities ranging from the solar value down to one tenth of it and C/O ratios in the interval between 1.05 and 5.0. Subsequently, we used these models to create synthetic low resolution spectra and photometric data for a large number of filter systems. The tables including the results are electronically available. We have selected some of the most commonly used colours in order to discuss their behaviour as a function of the stellar parameters. A comparison with measured data shows that down to 2800K the agreement between predictions and observations of carbon stars is good. Below this limit the synthetic colours are much too blue. The obvious reason for these problems is the neglect of circumstellar reddening and structural changes due to pulsation and mass loss.
We detail an innovative new technique for measuring the 2-D velocity moments
(rotation velocity, velocity dispersion and Gauss-Hermite coefficients h$_3$
and h$_4$) of the stellar populations of galaxy halos using spectra from Keck
DEIMOS multi-object spectroscopic observations. The data are used to
reconstruct 2-D rotation velocity maps.
Here we present data for five nearby early-type galaxies to ~3 effective
radii. We provide significant insights into the global kinematic structure of
these galaxies, and challenge the accepted morphological classification in
several cases. We show that between 1-3 effective radii the velocity dispersion
declines very slowly, if at all, in all five galaxies. For the two galaxies
with velocity dispersion profiles available from planetary nebulae data we find
very good agreement with our stellar profiles. We find a variety of rotation
profiles beyond 1 effective radius, i.e rotation speed remaining constant,
decreasing \emph{and} increasing with radius. These results are of particular
importance to studies which attempt to classify galaxies by their kinematic
structure within one effective radius, such as the recent definition of fast-
and slow- rotator classes by the SAURON project. Our data suggests that the
rotator class may change when larger galacto-centric radii are probed. This has
important implications for dynamical modeling of early-type galaxies. The data
from this study are available on-line.
We imaged the position of the Naked-Eye Burst, GRB080319B, before, during and after its gamma-ray activity with sub-second temporal resolution and discovered the fast variability of its prompt optical emission. Its characteristics and similarity with properties of gamma emission temporal structure suggest that it reflects the behaviour of internal engine -- supposedly, a hyperaccreting solar-mass black hole formed in the collapse of a massive stellar core.
PILOT (the Pathfinder for an International Large Optical Telescope) is a proposed 2.5 m optical/infrared telescope to be located at Dome C on the Antarctic plateau. Conditions at Dome C are known to be exceptional for astronomy. The seeing (above ~30 m height), coherence time, and isoplanatic angle are all twice s good as at typical mid-latitude sites, while the water-vapour column, and the atmosphere and telescope thermal emission are all an order of magnitude better. These conditions enable a unique scientific capability for PILOT, which is addressed in this series of papers. The current paper presents an overview of the optical and instrumentation suite for PILO and its expected performance, a summary of the key science goals and observational approach for the facility, a discussion of the synergies between the science goals for PILOT and other telescopes, and a discussion of the future of Antarctic astronomy. Paper II and Paper III present details of the science projects divided, respectively, between the distant Universe (i.e., studies of first light, and the assembly and evolution of structure) and the nearby Universe (i.e., studies of Local Group galaxies, the Milky Way, and the Solar System).
There have been recent claims that a significant fraction of type 2 AGN accrete close or even above the Eddington limit. In type 2 AGN the bolometric luminosity (L_b) is generally inferred from the [OIII] emission line luminosity (L_OIII). The key issue, in order to estimate the bolometric luminosity in these AGN, is therefore to know the bolometric correction to be applied to L_OIII. A complication arises from the fact that the observed L_OIII is affected by extinction, likely due to dust within the narrow line region. The extinction-corrected [OIII] luminosity (L^c_OIII) is a better estimator of the nuclear luminosity than L_OIII. However, so far only the bolometric correction to be applied to the uncorrected L_OIII has been evaluated. This paper is devoted to estimate the bolometric correction C_OIII=L_b/L^c_OIII in order to derive the Eddington ratios for the type 2 AGN in a sample of SDSS objects. We have collected from the literature 61 sources with reliable estimate of both L^c_OIII and X-ray luminosities (L_X). To estimate C_OIII, we combined the observed correlation between L^c_OIII and L_X with the X-ray bolometric correction. We found, contrary to previous studies, a linear correlation between L^c_OIII and L_X. We estimated C_OIII using the luminosity-dependent X-ray bolometric correction of Marconi et al. (2004), and we found a mean value of C_OIII in the luminosity ranges log L_OIII=38-40, 40-42, and 42-44 of 87, 142 and 454 respectively. We used it to calculate the Eddington ratio distribution of type 2 SDSS AGN at 0.3<z<0.4 and we found that these sources are not accreting near their Eddington limit, contrary to previous claims.
We present numerical simulations of the axisymmetric accretion of a massive
magnetized plasma torus on a rotating black hole. We use a realistic equation
of state, which takes into account neutrino cooling and energy loss due to
nucleus dissociations. We simulated various magnetic field configurations and
torus models, both optically thick and thin for neutrinos. It is shown that the
neutrino cooling does not significantly change either the structure of the
accretion flow or the total energy release of the system. The calculations
evidence heating of the wind surrounding the collapsar by the shock waves
generated at the jet-wind border. This mechanism can give rise to a hot corona
around the binary system like SS433.
Angular momentum of the accreting matter defines the time scale of the
accretion. Due to the absence of the magnetic dynamo in our calculations, the
initial strength and topology of the magnetic field determines magnetization of
the black hole, jet formation properties and the total energy yield. We
estimated the total energy transformed to jets as $1.3\times 10^{52}$ {ergs}
which was sufficient to explain hypernova explosions like GRB 980425 or GRB
030329.
A temporal analysis of the noise is performed, and non linearities are taken into account. We then extend the correlation method to groups of several pixels to derive the interpixel capacitance of a detector, found to be x = -0.0263 +/- 0.0020 (stat) +/- 0.0040 (syst). All measurements are consistent to a sub-percent accuracy.
We present an analysis of Li abundances in low mass stars (LMS) during the Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) stages, based on a new determination of their luminosities and evolutionary status. By applying recently suggested models for extra-mixing, induced by magnetic buoyancy, we show that both Li-rich and Li-poor stars can be accounted for. The simplest scenario implies the development of fast instabilities on the RGB, where Li is produced. When the fields increase in strength, buoyancy slows down and Li is destroyed. 3He is consumed, at variable rates. The process continues on the AGB, where however moderate mass circulation rates have little effect on Li due to the short time available. O-rich and C-rich stars show different histories of Li production/destruction, possibly indicative of different masses. More complex transport schemes are allowed by magnetic buoyancy, with larger effects on Li, but most normal LMS seem to show only the range of Li variation discussed here.
We present the results of a systematic search for large-scale spectroscopic
variability in apparently single Wolf-Rayet stars brighter than ~12.5. In this
first paper we characterize the various forms of variability detected and
distinguish several separate groups. For each star in our sample, we obtained
4-5 high-resolution spectra with a signal-to-noise ratio ~100. Our ultimate
goal is to identify new candidates presenting variability that potentially
comes from Co-rotating Interaction Regions (CIR).
Out of a sample of 25 stars, 10 were found to display large-scale changes of
which 4 are of CIR-type (WR1, WR115, WR120 and WR134). The star WR134 was
already known to show such changes from previous studies. Three WN8 stars
present a different type of large-scale variability and we believe deserve a
group of their own. Also, all three WC9d stars in our sample present
large-scale variability, but it remains to be checked if these are binaries, as
many dust-making WR stars are double. Finally, of the remaining stars, 10 were
found to show small-amplitude spectral changes which we attribute to normal
line-profile variability due to inhomogeneities in the wind, and 5 were found
to show no spectral variability, as far as can be concluded from the data in
hand.
Follow-up studies are required to identify potential periods for our
candidates showing CIR-type changes and eventually estimate a rotation rate for
these WR stars.
Diffusive shock acceleration is invoked to explain non-thermal particle acceleration in Supernova Remnants, Active Galactic Nuclei (AGN) Jets, Gamma ray Bursts (GRBs) and various large scale cosmic structures. The importance of achieving the highest observed particle energies by such a mechanism in a given astrophysical situation is a recurring theme. In this work, shock acceleration in relativistic shocks is discussed, mostly focusing on a numerical study concerning proton acceleration efficiency by subluminal and superluminal shocks, emphasising on the dependence of the scattering model, bulk Lorentz factor and the angle between the magnetic field and the shock flow. We developed a diffuse cosmic ray model based on the study of different shock boost factors, which shows that spectra from AGN fit current observations of ultra high energy cosmic rays, above 5.7 x 10^10 GeV, much better than GRBs, indicating that AGN are the primary candidates to explain the UHECR flux. Recent Fermi observations of GRB090816c indicate very flat spectra which are expected within our model predictions and support evidence that GRB particle spectra can be flat, when the shock Lorentz factor is of order ~1000.
We have combined the results from our recent observations of Damped and sub-Damped Lyman-alpha systems with the MIKE and UVES spectrographs on the Magellan Clay and VLT Kueyen telescopes with ones from the literature to determine the N(HI)-weighted mean metallicity of these systems based both on Fe, a depleted element in QSO absorbers and the local ISM, and Zn a relatively undepleted element. In each case, the N(HI)-weighted mean metallicity is higher and shows faster evolution in sub-DLAs than the classical DLA systems. Large grids of photoionisation models over the sub-DLA \nhI range with CLOUDY show that the ionisation corrections to the abundances are in general small, however the fraction of ionized H can be up to ~90 per cent. The individual spectra have been shifted to the rest frame of the absorber and averaged together to determine the average properties of these systems at z<1.5. We find that the average abundance pattern of the Sub-DLA systems is similar to the gas in the halo of the Milky Way, with an offset of ~0.3 dex in the overall metallicity. Both DLAs and Sub-DLAs show similar characteristics in their relative abundances patterns, although the DLAs have smaller <[Mn/Zn]> as well as higher <[Ti/Zn]> and <[Cr/Zn]>. We calculate the contribution of sub-DLAs to the metal budget of the Universe, and find that the sub-DLA systems at z<1.5 contain a comoving density of metals Omega_met (3.5-15.8)x10^{5} M_sun Mpc^{-3}, at least twice the comoving density of metals in the DLA systems. The sub-DLAs do however track global chemical evolution models much more closely than do the DLAs, perhaps indicating that they are a less dust biased metallicity indicator of galaxies at high redshifts than the DLA systems.
Hydrogen and/or helium accreted by a neutron star from a binary companion may undergo thermonuclear fusion. At different mass accretion rates different burning regimes are discerned. Theoretical models predict helium fusion to proceed as a thermonuclear runaway for accretion rates below the Eddington limit and as stable burning above this limit. Observations, however, place the boundary close to 10% of the Eddington limit. We study the effect of rotationally induced transport processes on the stability of helium burning. For the first time detailed calculations of thin helium shell burning on neutron stars are performed using a hydrodynamic stellar evolution code including rotation and rotationally induced magnetic fields. We find that in most cases the instabilities from the magnetic field provide the dominant contribution to the chemical mixing, while Eddington-Sweet circulations become important at high rotation rates. As helium is diffused to greater depths, the stability of the burning is increased, such that the critical accretion rate for stable helium burning is found to be lower. Combined with a higher heat flux from the crust, as suggested by recent studies, turbulent mixing could explain the observed critical accretion rate. Furthermore, close to this boundary we find oscillatory burning, which previous studies have linked to mHz QPOs. In models where we continuously lower the heat flux from the crust, the period of the oscillations increases by up to several tens of percents, similar to the observed frequency drift, suggesting that this drift could be caused by the cooling of deeper layers.
We present and analyse new R-band frames of the gravitationally lensed double quasar FBQ 0951+2635. These images were obtained with the 1.5m AZT-22 Telescope at Maidanak (Uzbekistan) in the 2001-2006 period. Previous results in the R band (1999-2001 period) and the new data allow us to discuss the dominant kind of microlensing variability in FBQ 0951+2635. The time evolution of the flux ratio A/B does not favour the continuous production of short-timescale (months) flares in the faintest quasar component B (crossing the central region of the lensing galaxy). Instead of a rapid variability scenario, the observations are consistent with the existence of a long-timescale fluctuation. The flux ratio shows a bump in the 2003-2004 period and a quasi-flat trend in more recent epochs. Apart from the global behaviour of A/B, we study the intra-year variability over the first semester of 2004, which is reasonably well sampled. Short-timescale microlensing is not detected in that period. Additional data in the i band (from new i-band images taken in 2007 with the 2m Liverpool Robotic Telescope at La Palma, Canary Islands) also indicate the absence of short-timescale events in 2007.
The two-point angular correlation function is a traditional method used to search for deviations from expectations of isotropy. In this paper we develop and explore a statistically descriptive three-point method with the intended application being the search for deviations from isotropy in the highest energy cosmic rays. We compare the sensitivity of a two-point method and a "shape-strength" method for a variety of Monte-Carlo simulated anisotropic signals. Studies are done with anisotropic source signals diluted by an isotropic background. Type I and II errors for rejecting the hypothesis of isotropic cosmic ray arrival directions are evaluated for four different event sample sizes: 27, 40, 60 and 80 events, consistent with near term data expectations from the Pierre Auger Observatory. In all cases the ability to reject the isotropic hypothesis improves with event size and with the fraction of anisotropic signal. While ~40 event data sets should be sufficient for reliable identification of anisotropy in cases of rather extreme (highly anisotropic) data, much larger data sets are suggested for reliable identification of more subtle anisotropies. The shape-strength method consistently performs better than the two point method and can be easily adapted to an arbitrary experimental exposure on the celestial sphere.
We have undertaken a systematic search for candidate supernovae from high-redshift Population III stars in a field that has been observed with repeated imaging on a cadence of 2-3 weeks over a 2.2 year baseline, the Spitzer/IRAC Dark Field. The individual epochs reach a typical 5-sigma depth of 1 uJy in IRAC Channel 1 (3.6 um). Requiring a minimum of four epochs coverage, the total effective area searched is 214 sq arcminutes. The unprecedented depth and multi-epochal nature of these data make it ideal for a first foray to detect transient objects which may be candidate luminous Pair Instability Supernovae from the primordial-metallicity first stars. The search was conducted over a broad range of timescales, allowing for different durations of the putative candidates' light curve plateau phases. All candidates were vetted by inspection of the Spitzer imaging data, as well as deep HST/ACS F814W imaging available over the full field. While many resolved-source objects were found with Spitzer variability, no transient objects could plausibly be identified as high-redshift supernovae candidates. The resulting 95% confidence level upper limit is 23/sq deg/yr, for sources with plateau timescales under 400/(1+z) days and brightnesses above ~1 uJy.
General relativity postulates the Minkowski space-time to be the standard
flat geometry against which we compare all curved space-times and the
gravitational ground state where particles, quantum fields and their vacuum
states are primarily conceived. On the other hand, experimental evidences show
that there exists a non-zero cosmological constant, which implies in a deSitter
space-time, not compatible with the assumed Minkowski structure. Such
inconsistency is shown to be a consequence of the lack of a application
independent curvature standard in Riemann's geometry, leading eventually to the
cosmological constant problem in general relativity.
We show how the curvature standard in Riemann's geometry can be fixed by
Nash's theorem on locally embedded Riemannian geometries, which imply in the
existence of extra dimensions. The resulting gravitational theory is more
general than general relativity, similar to brane-world gravity, but where the
propagation of the gravitational field along the extra dimensions is a
mathematical necessity, rather than being a a postulate. After a brief
introduction to Nash's theorem, we show that the vacuum energy density must
remain confined to four-dimensional space-times, but the cosmological constant
resulting from the contracted Bianchi identity is a gravitational contribution
which propagates in the extra dimensions. Therefore, the comparison between the
vacuum energy and the cosmological constant in general relativity ceases to be.
Instead, the geometrical fix provided by Nash's theorem suggests that the
vacuum energy density contributes to the perturbations of the gravitational
field.
We study nonrelativistic gravity using the Hamiltonian formalism. For the dynamics of general relativity (relativistic gravity) the formalism is well known and called the ADM formalism. We show that if the lapse function is constrained correctly, then nonrelativistic gravity is described by a consistent Hamiltonian system. Surprisingly, nonrelativistic gravity can have solutions identical to relativistic gravity ones. In particular, (A)dS black holes of Einstein gravity and IR limit of Horava gravity are locally identical.
We explore the dark matter detection prospects in the Minimal Supersymmetric Standard Model in the scenario where the scalar partners of the fermions and the Higgs particles (except for the Standard-Model-like one) are assumed to be very heavy and are removed from the low-energy spectrum. We analyse the neutralino LSP ($\chi_1^0$) in scenarios where the gaugino mass parameters are universal at the GUT scale and also the case where they are non-universal. This analysis is carried out in the framework of a Xenon-like 100 kg experiment. In general, an important fraction of the parameter space giving rise to the dark matter relic density measured by WMAP can be probed and excluded in the case of not detecting any WIMP. In the opposite case, once a WIMP signal has been found, we show that for a light $\chi_1^0$ which is a higgsino-gaugino mixture it is possible to reconstruct efficiently the mass and the scattering cross-section of the neutralino LSP. Moreover, we show that it is also feasible to put strong constraints over some of the parameters of the Lagrangian, e.g. the higgsino and the gaugino mass parameters.
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The nature of galaxies selected at submillimeter wavelengths (SMGs, S_850 > 3 mJy), some of the bolometrically most luminous objects at high redshifts, is still elusive. In particular their star formation histories and source of emission are not accurately constrained. In this paper we present the first spectral energy distribution fits of 76 SMGs with spectroscopic redshifts using all photometric datapoints from ultraviolet to radio simultaneously. We find that they are highly star-forming (median star formation rate 659 Msol yr^{-1}), hosting significant stellar populations (median stellar mass 3.5x10^{11} Msol) of which only a minor part (7%) has been formed in the ongoing starburst episode. This implies that in the past, SMGs experienced either another starburst episode or merger with several galaxies. The properties of SMGs suggest that they are progenitors of present-day elliptical galaxies. We find that these bright SMGs contribute significantly to the cosmic star formation rate density (8%) and stellar mass density (9-17%) at redshifts 4-2. Using number counts at low fluxes we find that as much as one third of the cosmic star formation at these redshifts took place in SMGs brighter than 0.1 mJy. We find evidence that the local linear far-infrared-radio correlation holds up to redshift of 3.6. This also suggests that the major source of infrared emission in SMGs is star formation not active galactic nuclei (AGNs).
We examine the long-standing cooling flow problem in galaxy clusters with 3D MHD simulations of isolated clusters including radiative cooling and anisotropic thermal conduction along magnetic field lines. The central regions of the intracluster medium (ICM) can have cooling timescales of ~200 Myr or shorter--in order to prevent a cooling catastrophe the ICM must be heated by some mechanism such as AGN feedback or thermal conduction from the thermal reservoir at large radii. The cores of galaxy clusters are linearly unstable to the heat-flux-driven buoyancy instability (HBI), which significantly changes the thermodynamics of the cluster core. The HBI is a convective, buoyancy-driven instability that rearranges the magnetic field to be preferentially perpendicular to the temperature gradient. For a wide range of parameters, our simulations demonstrate that in the presence of the HBI, the effective radial thermal conductivity is reduced to less than 10% of the full Spitzer conductivity. With this suppression of conductive heating, the cooling catastrophe occurs on a timescale comparable to the central cooling time of the cluster. Thermal conduction alone is thus unlikely to stabilize clusters with low central entropies and short central cooling timescales. High central entropy clusters have sufficiently long cooling times that conduction can help stave off the cooling catastrophe for cosmologically interesting timescales.
High resolution (~1 arcminute) astronomical imaging at low frequency (below 150 MHz) has only recently become practical with the development of new calibration algorithms for removing ionospheric distortions. In addition to opening a new window in observational astronomy, the process of calibrating the ionospheric distortions also probes ionospheric structure in an unprecedented way. Here we explore one aspect of this new type of ionospheric measurement, the differential refraction of celestial source pairs as a function of their angular separation. This measurement probes variations in the spatial gradient of the line-of-sight total electron content (TEC) to 0.001 TECU/km accuracy over spatial scales of under 10 km to over 100 km. We use data from the VLA Low-frequency Sky Survey (VLSS; Cohen et al. 2007, AJ 134, 1245), a nearly complete 74 MHz survey of the entire sky visible to the Very Large Array (VLA) telescope in Socorro, New Mexico. These data comprise over 500 hours of observations, all calibrated in a standard way. While ionospheric spatial structure varies greatly from one observation to the next, when analyzed over hundreds of hours, statistical patterns become apparent. We present a detailed characterization of how the median differential refraction depends on source pair separation, elevation and time of day. We find that elevation effects are large, but geometrically predictable and can be "removed" analytically using a "thin-shell" model of the ionosphere. We find significantly greater ionospheric spatial variations during the day than at night. These diurnal variations appear to affect the larger angular scales to a greater degree indicating that they come from disturbances on relatively larger spatial scales (100s of km, rather than 10s of km).
We show that the Sagittarius dwarf tidal stream can be traced with very red K/M-giant stars selected from SDSS photometry. A subset of these stars are spectroscopically confirmed with SEGUE and SDSS spectra, and the distance scale of 2MASS and SDSS M giants is calibrated to the RR Lyrae distance scale. The absolute g band magnitude of the K/M-giant stars at the tip of the giant branch is M_g=-1.0. The line-of-sight velocities of the M giant and BHB stars that are spatially coincident with the Sgr dwarf tidal stream are consistent with those of previous authors, reinforcing the need for new models that can explain all of the Sgr tidal debris stream observations. We estimate stellar densities along the tidal tails that can be used to help constrain future models. The K/M-giant, BHB, and F-turnoff stars in the lower surface brightness tidal stream that is adjacent to the main leading Sgr dwarf tidal tail have velocities and metallicities that are similar to those of the stars in the leading tidal tail. The ratio of K/M giants to BHBs and BHBs to F-turnoff stars are also similar for both branches of the leading tidal tail. We show that there is an additional low-metallicity tidal stream near the Sgr trailing tidal tail.
We present the rest-frame optical luminosity function (LF) of red sequence galaxies in 16 clusters at 0.4<z<0.8 drawn from the ESO Distant Cluster Survey (EDisCS). We compare our clusters to an analogous sample from the Sloan Digital Sky Survey (SDSS) and match the EDisCS clusters to their most likely descendants. We measure all LFs down to M M* + (2.5 - 3.5). At z<0.8, the bright end of the LF is consistent with passive evolution but there is a significant build-up of the faint end of the red sequence towards lower redshift. There is a weak dependence of the LF on cluster velocity dispersion for EDisCS but no such dependence for the SDSS clusters. We find tentative evidence that red sequence galaxies brighter than a threshold magnitude are already in place, and that this threshold evolves to fainter magnitudes toward lower redshifts. We compare the EDisCS LFs with the LF of co-eval red sequence galaxies in the field and find that the bright end of the LFs agree. However, relative to the number of bright red galaxies, the field has more faint red galaxies than clusters at 0.6<z<0.8 but fewer at 0.4<z<0.6, implying differential evolution. We compare the total light in the EDisCS cluster red sequences to the total red sequence light in our SDSS cluster sample. Clusters at 0.4<z<0.8 must increase their luminosity on the red sequence (and therefore stellar mass in red galaxies) by a factor of 1-3 by z=0. The necessary processes that add mass to the red sequence in clusters predict local clusters that are over-luminous as compared to those observed in the SDSS. The predicted cluster luminosities can be reconciled with observed local cluster luminosities by combining multiple previously known effects.
While the average metallicity of the intergalactic medium rises above Z~10^{-3} Zsun by the end of the reionization, pockets of metal-free gas can still exist at later times. We quantify the presence of a long tail in the formation rate of metal-free halos during late stages of reionization (redshift z~6), which might offer the best window to detect Population III stars. Using cosmological simulations for the growth of dark matter halos, coupled with analytical recipes for the metal enrichment of their interstellar medium, we show that pockets of metal-free gas exist at z~6 even under the assumption of high efficiency in metal pollution via winds. A comoving metal-free halo formation rate d^2n/dtdV > 10^{-9} Mpc^{-3}yr^{-1} is expected at z=6 for halos with virial temperature T_{vir}~10^4 K (mass ~10^8 Msun), sufficient to initiate cooling even with strong negative radiative feedback. Under the assumption of a single Population III supernova formed per metal-free halo, we expect an observed supernova rate of 2.6x10^{-3} deg^{-2}yr^{-1} in the same redshift range. These metal-free stars and their supernovae will be isolated and outside galaxies (at distances >150 h^{-1} kpc) and thus significantly less biased than the general population of ~10^8 Msun halos at z~6. Supernova searches for metal-free explosions must thus rely on large area surveys. If metal-free stars produce very luminous supernovae, like SN2006gy, then a multi-epoch survey reaching m_AB =27 at 1 micron is sufficient for detecting them at z=6. While the Large Synoptic Survey Telescope will not reach this depth in the z band, it will be able to detect several tens of Population III supernovae in the i and r bands at z <5.5, when their observed rate is down to 3-8x10^{-4} deg^{-2} yr^{-1}.
Cosmological simulations of Population III star formation suggest an initial mass function (IMF) biased toward very massive stars (M>100Msun) formed in minihalos at redshift z>20, when the cooling is driven by molecular hydrogen. However, this result conflicts with observations of extremely-metal poor (EMP) stars in the Milky Way halo, whose r-process elemental abundances appear to be incompatible with those expected from very massive Population III progenitors. We propose that the IMF of second-generation stars formed at z>10, before reionization, is deficient in sub-solar mass stars, owing to the high cosmic microwave background temperature floor. The observed EMP stars are formed preferentially at z<10 in pockets of gas enriched to metallicity Z>10^{-3.5} Zsun by winds from Population II stars. Our cosmological simulations of structure formation show that current samples of EMP stars can only constrain the IMF of late-time Population III stars, formed at z<13 in halos with virial temperature Tvir 10^4 K. This suggests that pair instability supernovae were not produced primarily by this population. To begin probing the IMF of Population III stars formed at higher redshift will require a large survey, with at least 500 and probably several thousand EMP stars of metallicities Z~10^{-3.5} Zsun.
We perform a suite of simulations of cooling cores in clusters of galaxies in order to investigate the effect of the recently discovered heat flux buoyancy instability (HBI) on the evolution of cores. Our models follow the 3-dimensional magnetohydrodynamics (MHD) of cooling cluster cores and capture the effects of anisotropic heat conduction along the lines of magnetic field, but do not account for the cosmological setting of clusters or the presence of AGN. Our model clusters can be divided into three groups according to their final thermodynamical state: catastrophically collapsing cores, isothermal cores, and an intermediate group whose final state is determined by the initial configuration of magnetic field. Modeled cores that are reminiscent of real cluster cores show evolution towards thermal collapse on a time scale which is prolonged by a factor of ~2-10 compared with the zero-conduction cases. The principal effect of the HBI is to re-orient field lines to be perpendicular to the temperature gradient. Once the field has been wrapped up onto spherical surfaces surrounding the core, the core is insulated from further conductive heating (with the effective thermal conduction suppressed to less than 1/100th of the Spitzer value) and proceeds to collapse. We speculate that, in real clusters, the central AGN and possibly mergers play the role of "stirrers," periodically disrupting the azimuthal field structure and allowing thermal conduction to sporadically heat the core.
We study the short- and long-term effects of an intermediate mass black hole (IMBH) on the orbits of stars bound to the supermassive black hole (SMBH) at the center of the Milky Way. A regularized N-body code including post-Newtonian terms is used to carry out direct integrations of 19 stars in the S-star cluster for 10 Myr. The mass of the IMBH is assigned one of four values from 400 Msun to 4000 Msun, and its initial semi-major axis with respect to the SMBH is varied from 0.3-30 mpc, bracketing the radii at which inspiral of the IMBH is expected to stall. We consider two values for the eccentricity of the IMBH/SMBH binary, e=(0,0.7), and 12 values for the orientation of the binary's plane. Changes at the level of 1% in the orbital elements of the S-stars could occur in just a few years if the IMBH is sufficiently massive. On time scales of 1 Myr or longer, the IMBH efficiently randomizes the eccentricities and orbital inclinations of the S-stars. Kozai oscillations are observed when the IMBH lies well outside the orbits of the stars. Perturbations from the IMBH can eject stars from the cluster, producing hypervelocity stars, and can also scatter stars into the SMBH; stars with high initial eccentricities are most likely to be affected in both cases. The distribution of S-star orbital elements is significantly altered from its currently-observed form by IMBHs with masses greater than 1000 Msun if the IMBH/SMBH semi-major axis lies in the range 3-10 mpc. We use these results to further constrain the allowed parameters of an IMBH/SMBH binary at the Galactic center.
The gas-phase chemistry of water in protoplanetary disks is analyzed with a model based on X-ray heating and ionization of the disk atmosphere. Several uncertain processes appear to play critical roles in generating the column densities of warm water that are detected from disks at infrared wavelengths. The dominant factors are the reactions that form molecular hydrogen, including formation on warm grains, and the ionization and heating of the atmosphere. All of these can work together to produce a region of high water abundances in the molecular transition layer of the inner disk atmosphere, where atoms are transformed into molecules, the temperature drops from thousands to hundreds of Kelvins, and the ionization begins to be dominated by the heavy elements. Grain formation of molecular hydrogen and mechanical heating of the atmosphere can play important roles in this region and directly affect the amount of warm water in protoplanetary disk atmospheres. Thus it may be possible to account for the existing measurements of water emission from Tauri disks without invoking transport of water from cooler to warmer regions. The hydroxyl radical OH is under-abundant in this model of disk atmospheres and requires consideration of additional production and excitation processes.
We investigate the effect of dry merging on the color-magnitude relation (CMR) of galaxies and find that the amount of merging predicted by a hierarchical model results in a red sequence that compares well with the observed low-redshift relation. A sample of 29,000 early-type galaxies selected from the Sloan Digital Sky Survey Data Release 6 shows that the bright end of the CMR has a shallower slope and smaller scatter than the faint end. This magnitude dependence is predicted by a simple toy model in which gas-rich mergers move galaxies onto a "creation red sequence" (CRS) by quenching their star formation, and subsequent mergers between red, gas-poor galaxies (so-called "dry" mergers) move galaxies along the relation. We use galaxy merger trees from a semianalytic model of galaxy formation to test the amplitude of this effect and find a change in slope at the bright end that brackets the observations, using gas fraction thresholds of 10-30% to separate wet and dry mergers. A more realistic model that includes scatter in the CRS shows that dry merging decreases the scatter at the bright end. Contrary to previous claims, the small scatter in the observed CMR thus cannot be used to constrain the amount of dry merging.
We calibrate the Baryonic Tully-Fisher (BTF) Relation using a sample of gas dominated galaxies. These determine the absolute scale of the baryonic mass--rotation speed relation independent of the choice of stellar mass estimator. We find a BTF slope of $3.94\pm0.07$ (random) $\pm 0.08$ (systematic) and a zero point of $1.79\pm0.26$ (random) $\pm 0.25$ (systematic). We apply this relation to estimate the stellar masses of star dominated galaxies. This procedure reproduces the trend of mass-to-light ratio with color predicted by population synthesis models. The normalization is also correct, consistent with empirical estimates of the IMF used in such models.
A simple mid-infrared-to-optical color criterion of R-[24]>14 Vega mag results in a robust selection of approximately half of the redshift 2 ultraluminous infrared galaxy (ULIRG) population. These `Dust-Obscured Galaxies', or DOGs, have many properties that suggest that they are good candidates for systems in a transition phase between gas-rich mergers and QSOs.
The cross correlation method (hereafter CC) is widely used to derive the radial velocity curve of Cepheids when the signal to noise of the spectra is low. However, if it is used with the wrong projection factor, it might introduce some biases in the Baade-Wesselink (hereafter BW) methods of determining the distance of Cepheids. In addition, it might affect the average value of the radial velocity curve (or gamma-velocity) important for Galactic structure studies. We aim to derive a period-projection factor relation (hereafter Pp) appropriate to be used together with the CC method. Moreover, we investigate whether the CC method can explain the misunderstood previous calculation of the K-term of Cepheids. We observed eight galactic Cepheids with the HARPS spectrograph. For each star, we derive an interpolated CC radial velocity curve using the HARPS pipeline. The amplitudes of these curves are used to determine the correction to be applied to the semi-theoretical projection factor derived in Nardetto et al. (2007). Their average value (or gamma-velocity) are also compared to the center-of-mass velocities derived in Nardetto et al. (2008). The correction in amplitudes allows us to derive a new Pp relation: p = [-0.08+-0.05] log P +[1.31+-0.06]. We also find a negligible wavelength dependence (over the optical range) of the Pp relation. We finally show that the gamma-velocity derived from the CC method is systematically blue-shifted by about 1.0 +- 0.2km/s compared to the center-of-mass velocity of the star. An additional blue-shift of 1.0km/s is thus needed to totally explain the previous calculation of the K-term of Cepheids (around 2km/s). The new Pp relation we derived is a solid tool for the distance scale calibration (abridged).
In this article we explore the aspect of the F ring with respect to the
anti-alignment configuration between the ring and Prometheus. We focus our
attention on the shape of the F ring's azimuthal channels which were first
reported by Porco et al. (2005) and numerically explored by Murray et al.
(2005), who found excellent agreement between Cassini's ISS reprojected images
and their numerical model via a direct comparison. We find that for
anti-alignment the channels are wider and go deeper inside the ring material.
From our numerical model we find a new feature, an island in the middle of
the channel. This island is made up of the particles that have been perturbed
the most by Prometheus and only appears when this satellite is close to
apoapsis. In addition, plots of the anti-alignment configuration for different
orbital stages of Prometheus are obtained and discussed here.
In this paper, linear first order expansion of deceleration parameter $q(z)=q_0+q_1(1-a)$ ($M_1$), constant jerk $j=j_0$ ($M_2$) and third order expansion of luminosity distance ($M_3$) are confronted with cosmic observations: SCP 307 SN Ia, BAO and observational Hubble data (OHD). Likelihood is implemented to find the best fit model parameters. All these models give the same prediction of the evolution of the universe which is undergoing accelerated expansion currently and experiences a transition from decelerated expansion to accelerated expansion. But, the transition redshift depends on the concrete parameterized form of the model assumed. $M_1$ and $M_2$ give value of transition redshift about $z_t\sim 0.6$. $M_3$ gives a larger one, say $z_t\sim 1$. The $\chi^2/dof$ implies almost the same goodness of the models. But, for its badness of evolution of deceleration parameter at high redshift $z>1$, $M_3$ can not be reliable. $M_1$ and $M_2$ are compatible with $\Lambda$CDM model at the $2\sigma$ and $1\sigma$ confidence levels respectively. $M_3$ is not compatible with $\Lambda$CDM model at $2\sigma$ confidence level. From $M_1$ and $M_2$ models, one can conclude that the cosmic data favor a cosmological model having $j_0<-1$.
We report the discovery by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope of high-energy gamma-ray emission from the peculiar quasar PMN J0948+0022 (z=0.5846). The optical spectrum of this object exhibits rather narrow Hbeta (FWHM(Hbeta) ~ 1500 km s^-1), weak forbidden lines and is therefore classified as a narrow-line type I quasar. This class of objects is thought to have relatively small black hole mass and to accrete at high Eddington ratio. The radio loudness and variability of the compact radio core indicates the presence of a relativistic jet. Quasi simultaneous radio-optical-X-ray and gamma-ray observations are presented. Both radio and gamma-ray emission (observed over 5-months) are strongly variable. The simultaneous optical and X-ray data from Swift show a blue continuum attributed to the accretion disk and a hard X-ray spectrum attributed to the jet. The resulting broad band spectral energy distribution (SED) and, in particular, the gamma-ray spectrum measured by Fermi are similar to those of more powerful FSRQ. A comparison of the radio and gamma-ray characteristics of PMN J0948+0022 with the other blazars detected by LAT shows that this source has a relatively low radio and gamma-ray power, with respect to other FSRQ. The physical parameters obtained from modelling the SED also fall at the low power end of the FSRQ parameter region discussed in Celotti & Ghisellini (2008). We suggest that the similarity of the SED of PMN J0948+0022 to that of more massive and more powerful quasars can be understood in a scenario in which the SED properties depend on the Eddington ratio rather than on the absolute power.
There are two families of luminous elliptical galaxies: cusp galaxies, with steep central surface-brightness profiles, and core galaxies, whose surface-brightness profiles have flat central cores. Thermal evaporation of accreted cold gas by the hot interstellar medium may be at the origin of this cusp-core dichotomy: in less massive (hot-gas poor) galaxies central cores are likely to be refilled by central starbursts following cold gas infall, while in more massive (hot-gas rich) galaxies most cold gas is eliminated and central cores survive. This scenario is consistent with the observation that cusp and core galaxies differ systematically in terms of optical luminosity, X-ray gas content, age of the central stellar population, and properties of the active galactic nucleus.
We present VLT eclipse photometry for the giant planet CoRoT-1b. We observed a transit in the R-band filter and an occultation in a narrow filter centered on 2.09 microns. Our analysis of this new photometry and published radial velocities, in combination with stellar-evolutionary modeling, leads to a planetary mass and radius of 1.07 (+0.13,-0.18) M_Jup and 1.45 (+0.07,-0.13) R_Jup, confirming the very low density previously deduced from CoRoT photometry. The large occultation depth that we measure at 2.09 microns (0.278 (+0.043,-0.066) %) is consistent with thermal emission and is better reproduced by an atmospheric model with no redistribution of the absorbed stellar flux to the night side of the planet.
Context: We use the first XMM serendipitous source catalogue (1XMM) to
compile a sample of normal X-ray galaxies
Aims: We seek to expand the database of X-ray selected normal galaxies at
intermediate redshifts and examine the relation between X-ray emission and star
formation for late-type systems
Methods: The candidates are selected based on their X-ray (soft spectra),
X-ray to optical [log(fx/fo)<-2] and optical (extended sources) properties. 44
candidates are found and 35 are spectroscopically observed with the Australian
National University's 2.3m telescope to examine their nature.
Results: Of the 35 sources observed, 2 are AGN, 11 emission line galaxies, 12
absorption line galaxies, 6 have featureless spectra while 4 are associated
with Galactic stars. We combine our emission line sample with earlier works
forming the most comprehensive X-ray selected galaxy sample for the study of
the X-ray luminosity to the Halpha luminosity - a well-calibrated
star-formation indicator - relation.
Conclusions: We find that the X-ray luminosity strongly correlates with the
Halpha luminosity, suggesting that the X-rays efficiently trace the
star-formation.
Low-mass star formation is described by gravitational collapse of dense cores of gas and dust. At some point during the collapse, a disk is formed around the protostar and the disk will spin up and grow in size as the core contracts because of angular momentum conservation. The question is how early the disk formation process occurs. In this paper we aim to characterize the kinematical state of a deeply embedded, Class 0 young stellar object, NGC1333-IRAS2A, based on high angular resolution (< 1$''$ $\approx$ 200 AU) interferometric observations of HCN and H$^{13}$CN J = 4-3 from the Submillimeter Array, and test whether a circumstellar disk can be detected based on gas kinematic features. We adopt a physical model which has been shown to describe the object well and obtain a fit of a parameterized model of the velocity field, using a two-dimensional axis-symmetric radiation transfer code. The parameterization and fit to the high angular resolution data characterize the central dynamical mass and the ratio of infall velocity to rotation velocity. We find a large amount of infall and very little rotation on all scales. The central object has a relatively low mass of 0.25 M$_\odot$ . As an object with a low stellar mass compared to the envelope mass, we conclude that NGC1333-IRAS2A is consistent with the suggestion that, as a Class 0 object, it represents the earliest stages of star formation. The large amount of infall relative to rotation also suggests that this is a young object. We do however find the need of a central compact component on scales of a few hundred AU based on the continuum data, which suggests that disk formation happens shortly after the initial gravitational collapse. The data do not reveal a distinct velocity field for this 0.1 M$_\odot$ component.
In a recent paper (Vigoureux et al. Int. J. Theor. Phys. 47:928, 2007) it has been suggested that the velocity of light and the expansion of the universe are two aspects of one single concept connecting space and time in the expanding universe. It has then be shown that solving Friedmann's equations with that interpretation (and keeping c = constant) can explain number of unnatural features of the standard cosmology (for example: the flatness problem, the problem of the observed uniformity in term of temperature and density of the cosmological background radiation, the small-scale inhomogeneity problem...) and leads to reconsider the Hubble diagram of distance moduli and redshifts as obtained from recent observations of type Ia supernovae without having to need an accelerating universe. In the present work we examine the problem of the cosmological constant. We show that our model can exactly generate $\Lambda$ (equation of state $P_\varphi = - \rho_\varphi c^2$ with $\Lambda \propto R^{-2}$) contrarily to the standard model which cannot generate it exactly. We also show how it can solve the so-called cosmic coincidence problem.
We analyse a high-resolution, fully cosmological, hydrodynamical disc galaxy simulation, to study the source of the double-exponential light profiles seen in many stellar discs, and the effects of stellar radial migration upon the spatio-temporal evolution of both the disc age and metallicity distributions. We find a "break" in the pure exponential stellar surface brightness profile, and trace its origin to a sharp decrease in the star formation per unit surface area, itself produced by a decrease in the gas volume density due to a warping of the gas disc. Star formation in the disc continues well beyond the break. We find that the break is more pronounced in bluer wavebands. By contrast, we find little or no break in the mass density profile. This is, in part, due to the net radial migration of stars towards the external parts of the disc. Beyond the break radius, we find that ~60% of the resident stars migrated from the inner disc, while ~25% formed in situ. Our simulated galaxy also has a minimum in the age profile at the break radius but, in disagreement with some previous studies, migration is not the main mechanism producing this shape. In our simulation, the disc metallicity gradient flattens with time, consistent with an "inside-out" formation scenario. We do not find any difference in the intensity or the position of the break with inclination, suggesting that perhaps the differences found in empirical studies are driven by dust extinction.
Motivated by the PAMELA anomaly in the fluxes of cosmic-ray electron and positron, we study the cosmic gamma-ray induced by the inverse Compton (IC) scattering process in unstable dark matter scenario assuming that the anomaly is due to the electron and positron emission by the decay of dark matter. We calculate the fluxes of IC-induced gamma-ray produced in our Galaxy and that from cosmological distance, and show that both of them are significant. If the gamma-ray flux is precisely determined by Fermi Gamma-ray Space Telescope for various line-of-sight directions, it will provide an important test of the decaying dark matter scenario.
PILOT (the Pathfinder for an International Large Optical Telescope) is a proposed 2.5 m optical/infrared telescope to be located at Dome C on the Antarctic plateau. The atmospheric conditions at Dome C deliver a high sensitivity, high photometric precision, wide-field, high spatial resolution, and high-cadence imaging capability to the PILOT telescope. These capabilities enable a unique scientific potential for PILOT, which is addressed in this series of papers. The current paper presents a series of projects dealing with the distant (redshift >) Universe, that have been identified as key science drivers for the PILOT facility. The potential for PILOT to detect the first populations of stars to form in the early Universe, via infrared projects searching for pair-instability supernovae and gamma-ray burst afterglows, is investigated. Two projects are proposed to examine the assembly and evolution of structure in the Universe: an infrared survey searching for the first evolved galaxies at high redshift, and an optical survey aimed at characterising moderate-redshift galaxy clusters. Finally, a large-area weak-lensing survey and a program to obtain supernovae infrared light-curves are proposed to examine the nature and evolution of dark energy and dark matter.
We study the relation between nitrogen and oxygen abundances as a function of metallicity for a sample of emission-line objects for which a direct measurement of the metallicity has been possible. This sample is representative of the very different conditions in ionization and chemical enrichement that we can find in the Universe. We first construct the N/O vs. O/H diagram and we discuss its large dispersion at all metallicity regimes. Using the same sample and a large grid of photoionization models covering very different values of the N/O ratio, we then study the most widely used strong-line calibrators of metallicity based on [NII] emission lines, such as N2 and O3N2. We demonstrate that these parameters underestimate the metallicity at low N/O ratios and viceversa. We investigate also the effect of the N/O ratio on different diagnostic diagrams used to discriminate narrow-line AGNs from star forming regions, such as the [OIII]/Hbeta vs. [NII}]/Halpha, and we show that a large fraction of the galaxies catalogued as composite in this diagram can be, in fact, star forming galaxies with a high value of the N/O ratio. Finally, using strong-line methods sensitive to the N/O abundance ratio, like N2O2 and N2S2, we investigate the relation between this ratio and the stellar mass for the galaxies of the SDSS. We find, as in the case of the mass-metallicity relation, a correlation between these two quantities and a flattening of the relation for the most massive galaxies, which could be a consequence of the enhancement of the dispersion of N/O in the high metallicity regime.
We present near-infrared (1 - 2.5 micron) spectroscopic and photometric results of Nova V2615 Ophiuchi which was discovered in outburst in 2007 March. Our observations span a period of ~ 80 days starting from 2007 March 28 when the nova was at its maximum light. The evolution of the spectra are shown from the initial P-Cygni phase to an emission-line phase and finally to a dust formation stage. The characteristics of the JHK spectra are very similar to those observed in a nova outburst occurring on a carbon-oxygen white dwarf. We analyse an observed line at 2.088 micron and suggest it could be due to FeII excited by Lyman alpha fluorescence. The highlight of the observations is the detection of the first overtone bands of carbon monoxide (CO) in the 2.29 - 2.40 micron region. The CO bands are modeled to estimate the temperature and mass of the emitting CO gas and also to place limits on the 12C/13C ratio. The CO bands are recorded over several epochs thereby allowing a rare opportunity to study its evolution from a phase of constant strength through a stage when the CO is destroyed fairly rapidly. We compare the observed timescales involved in the evolution of the CO emission and find a good agreement with model predictions that investigate the chemistry in a nova outflow during the early stages.
We present a detailed kinematical analysis of the young compact hourglass-shaped planetary nebula Hb 12. We performed optical imaging and longslit spectroscopy of Hb 12 using the Manchester echelle spectrometer with the 2.1m San Pedro Martir telescope. We reveal, for the first time, the presence of end caps (or knots) aligned with the bipolar lobes of the planetary nebula shell in a deep [NII]6584 image of Hb 12. We measured from our spectroscopy radial velocities of 120 km/s for these knots. We have derived the inclination angle of the hourglass shaped nebular shell to be 65 degrees to the line of sight. It has been suggested that Hb 12's central star system is an eclipsing binary (Hsia et al. 2006) which would imply a binary inclination of at least 80 degrees. However, if the central binary has been the major shaping influence on the nebula then both nebula and binary would be expected to share a common inclination angle. Finally, we report the discovery of high-velocity knots with Hubble-type velocities, close to the core of Hb 12, observed in Halpha and oriented in the same direction as the end caps. Very different velocities and kinematical ages were calculated for the outer and inner knots showing that they may originate from different outburst events.
PILOT (the Pathfinder for an International Large Optical Telescope is a proposed 2.5 m optical/infrared telescope to be located at DomeC on the Antarctic plateau. The atmospheric conditions at Dome C deliver a high sensitivity, high photometric precision, wide-field, high spatial resolution, and high-cadence imaging capability to the PILOT telescope. These capabilities enable a unique scientific potential for PILOT, which is addressed in this series of papers. The current paper presents a series of projects dealing with the nearby Universe that have been identified as key science drivers for the PILOT facility. Several projects are proposed that examine stellar populations in nearby galaxies and stellar clusters in order to gain insight into the formation and evolution processes of galaxies and stars. A series of projects will investigate the molecular phase of the Galaxy and explore the ecology of star formation, and investigate the formation processes of stellar and planetary systems. Three projects in the field of exoplanet science are proposed: a search for free-floating low-mass planets and dwarfs, a program of follow-up observations of gravitational microlensing events, and a study of infrared light-curves for previously discovered exoplanets. Three projects are also proposed in the field of planetary and space science: optical and near-infrared studies aimed at characterising planetary atmospheres, a study of coronal mass ejections from the Sun, and a monitoring program searching for small-scale Low Earth Orbit satellite debris items.
The MIMAC project is a multi-chamber detector for Dark Matter search, aiming at measuring both track and ionization with a matrix of micromegas micro-TPC filled with He3 and CF4. Recent experimental results on the first measurements of the Helium quenching factor at low energy (1 keV recoil) are presented, together with the first simulation of the track reconstruction. Recontruction of track of alpha from Radon impurities is shown as a first proof of concept.
We point out a natural mechanism for quenching of star formation in early-type galaxies. It automatically links the color of a galaxy with its morphology and does not require gas consumption, removal or termination of gas supply. Given that star formation takes place in gravitationally unstable gas disks, it can be quenched when a disk becomes stable against fragmentation to bound clumps. This can result from the growth of a stellar spheroid, for instance by mergers. We present the concept of morphological quenching (MQ) using standard disk instability analysis, and demonstrate its natural occurrence in a cosmological simulation using an efficient zoom-in technique. We show that the transition from a stellar disk to a spheroid can be sufficient to stabilize the gas disk, quench star formation, and turn an early-type galaxy red and dead while gas accretion continues. The turbulence necessary for disk stability can be stirred up by sheared perturbations within the disk in the absence of bound star-forming clumps. While gas stripping processes are limited to dense groups and clusters, and other quenching mechanisms like AGN feedback, virial shock heating and gravitational heating, are limited to halos more massive than 10^12 Mo, the MQ can explain the appearance of red ellipticals even in less massive halos and in the field. The dense gas disks observed in some of today's red ellipticals may be the relics of this mechanism, whereas red galaxies with quenched gas disks are expected to be more frequent at high redshift.
We present nine newly observed transits of TrES-3, taken as part of a transit timing program using the RISE instrument on the Liverpool Telescope. A Markov-Chain Monte-Carlo analysis was used to determine the planet-star radius ratio and inclination of the system, which were found to be Rp/Rstar=0.1664^{+0.0011}_{-0.0018} and i = 81.73^{+0.13}_{-0.04} respectively, consistent with previous results. The central transit times and uncertainties were also calculated, using a residual-permutation algorithm as an independent check on the errors. A re-analysis of eight previously published TrES-3 light curves was conducted to determine the transit times and uncertainties using consistent techniques. Whilst the transit times were not found to be in agreement with a linear ephemeris, giving chi^2 = 35.07 for 15 degrees of freedom, we interpret this to be the result of systematics in the light curves rather than a real transit timing variation. This is because the light curves that show the largest deviation from a constant period either have relatively little out-of-transit coverage, or have clear systematics. A new ephemeris was calculated using the transit times, and was found to be T_c(0) = 2454632.62610 +- 0.00006 HJD and P = 1.3061864 +- 0.0000005 days. The transit times were then used to place upper mass limits as a function of the period ratio of a potential perturbing planet, showing that our data are sufficiently sensitive to have probed for sub-Earth mass planets in both interior and exterior 2:1 resonances, assuming the additional planet is in an initially circular orbit.
To further our knowledge of the complex physical process of galaxy formation, it is essential that we characterize the formation and evolution of large databases of galaxies. The spectral synthesis STARLIGHT code of Cid Fernandes et al. (2004) was designed for this purpose. Results of STARLIGHT are highly dependent on the choice of input basis of simple stellar population (SSP) spectra. Speed of the code, which uses random walks through the parameter space, scales as the square of the number of basis spectra, making it computationally necessary to choose a small number of SSPs that are coarsely sampled in age and metallicity. In this paper, we develop methods based on diffusion map (Lafon & Lee, 2006) that, for the first time, choose appropriate bases of prototype SSP spectra from a large set of SSP spectra designed to approximate the continuous grid of age and metallicity of SSPs of which galaxies are truly composed. We show that our techniques achieve better accuracy of physical parameter estimation for simulated galaxies. Specifically, we show that our methods significantly decrease the age-metallicity degeneracy that is common in galaxy population synthesis methods. We analyze a sample of 3046 galaxies in SDSS DR6 and compare the parameter estimates obtained from different basis choices.
The acceleration of protons and electrons in a reconnecting current sheet (RCS) is simulated with a particle-in-cell (PIC) 2D3V code for the proton-to-electron mass ratio of 100. The electro-magnetic configuration forming the RCS incorporates all three components of the magnetic field (including the guiding field) and a drifted electric field. PIC simulations reveal that there is a polarisation electric field that appears during acceleration owing to a separation of electrons from protons towards the midplane of the RCS. If the plasma density is low, the polarisation field is weak and the particle trajectories in the PIC simulations are similar to those in the test particle (TP) approach. For the higher plasma density the polarisation field is stronger and it affects the trajectories of protons by increasing their orbits during acceleration. This field also leads to a less asymmetrical abundances of ejected protons towards the midplane in comparison with the TP approach. For a given magnetic topology electrons in PIC simulations are ejected to the same semispace as protons, contrary to the TP results. This happens because the polarisation field extends far beyond the thickness of a current sheet. This field decelerates the electrons, which are initially ejected into the semispace opposite to the protons, returns them back to the RCS, and, eventually, leads to the electron ejection into the same semispace as protons. Energy distribution of the ejected electrons is rather wide and single-peak, contrary to the two-peak narrow-energy distribution obtained in the TP approach. In the case of a strong guiding field, the mean energy of the ejected electrons is found to be smaller than it is predicted analytically and by the TP simulations.
HR8799 is a nearby A-type star with a debris disk and three planetary candidates recently imaged directly. We undertake a coherent analysis of various portions of observational data on all known components of the system. The goal is to elucidate the architecture and evolutionary status of the system. We try to further constrain the age and orientation of the system, orbits and masses of the companions, as well as the location of dust. From the high luminosity of debris dust and dynamical constraints, we argue for a rather young system's age of <50Myr. The system must be seen nearly, but not exactly, pole-on. Our analysis of the stellar rotational velocity yields an inclination of 13-30deg, whereas i>20deg is needed for the system to be dynamically stable, which suggests a probable inclination range of 20-30deg. The spectral energy distribution is naturally reproduced with two dust rings associated with two planetesimal belts. The inner "asteroid belt" is located at ~10AU inside the orbit of the innermost companion and a "Kuiper belt" at >100AU is just exterior to the orbit of the outermost companion. The dust masses in the inner and outer ring are estimated to be ~1E-05 and 4E-02 M_earth, respectively. We show that all three planetary candidates may be stable in the mass range suggested in the discovery paper by Marois et al. 2008 (between 5 and 13 Jupiter masses), but only for some of all possible orientations. Stable orbits imply a double (4:2:1) mean-motion resonance between all three companions. We finally show that in the cases where the companions themselves are orbitally stable, the dust-producing planetesimal belts are also stable against planetary perturbations.
The MIMAC project is multi-chamber detector for Dark Matter search, aiming at measuring both track and ionization with a matrix of micromegas micro-TPC filled with He3 and CF4. Recent experimental results on the first measurements of the Helium quenching factor at low energy (1 keV recoil) are presented.
IceCube is a km^3 scale neutrino detector being constructed deep in the Antarctic ice. When complete, IceCube will consist of 4800 optical modules deployed on 80 strings between 1450 and 2450 m of depth. During the 2007-2008 data taking season, 22 strings were operational. This configuration is already much larger than previous neutrino telescopes and provides better sensitivity to point sources of high energy (>1 TeV) neutrino emission. Such astrophysical objects are leading candidates for the acceleration of cosmic rays. We describe the IceCube detector and present the methods and results of several recent searches for steady (e.g. AGN) and transient (GRB) point sources.
The clustering amplitude of galaxies depends on their intrinsic luminosity. We compare the properties of publicly available galaxy formation models with clustering measurements from the two-degree field galaxy redshift survey. The model predictions show the same qualitative behaviour as the data but fail to match the observations at the level of accuracy at which current measurements can be made. We demonstrate that this is due to the model producing too many satellite galaxies in massive haloes. We implement simple models to describe two new processes, satellite-satellite mergers and the tidal dissolution of satellites to investigate their impact on the predicted clustering. We find that both processes need to be included in order to produce a model which matches the observations.
Neutrino with magnetic moment can experience a chirality flip while
scattering off charged particles. This effect may lead to important
consequences for the dynamics and the neutrino signal of the core-collapse
supernova. It is known that if neutrino is a Dirac fermion, then nu_L->nu_R
transition induced by the chirality flip leads to the emission of sterile
right-handed neutrinos. The typical energies of these neutrinos are rather
high, E ~ (100-200)MeV. Neutrino spin precession in the magnetic field either
inside the collapsing star or in the interstellar space may lead to the
backward transition, nu_R->nu_L. Both possibilities are known to be
interesting. In the former case high-energy neutrinos can deliver additional
energy to the supernova envelope, which can help the supernova to explode. In
the latter case high-energy neutrinos may be detected simultaneously with the
"normal" supernova neutrino signal, which would be a smoking gun for the Dirac
neutrino magnetic moment. We report the results of the calculation of the
supernova right-handed neutrino luminosity up to 250 ms after bounce. They
allow to refine the estimates of the energy emitted in right-handed neutrinos.
Also the sensitivity of water Cherenkov detectors to the Dirac neutrino
magnetic moment is estimated. For mu_Dirac=10^{-13}mu_B Super-Kamiokande is
expected to detect few high-energy events from a galactic supernova explosion.
Also we briefly discuss the case of Majorana neutrino magnetic moment. It is
pointed out that spin flips may quickly equilibrate electron neutrinos with
non-electron antineutrinos if mu_Majorana~10^{-12}mu_B. This may lead to
various consequences for supernova physics.
We study thermodynamics of cosmological models in the Horava-Lifshitz theory of gravity, and systematically investigate the evolution of the universe filled with a perfect fluid that has the equation of state $p=w\rho$, where $p$ and $\rho$ denote, respectively, the pressure and energy density of the fluid, and $w$ is an arbitrary real constant. Depending on specific values of the free parameters involved in the models, we classify all of them into various cases. In each case the main properties of the evolution are studied in detail, including the periods of deceleration and/or acceleration, and the existence of big bang, big crunch, and big rip singularities. We pay particular attention on models that may give rise to a bouncing universe.
The properties of the quantum universe on extremely small spacetime scales are studied in the semi-classical approach to the well-defined quantum model. It is shown that near the initial cosmological singularity point quantum gravity effects ~ h exhibit themselves in the form of additional matter source with the negative pressure and the equation of state as for ultrastiff matter. The analytical solution of the equations of theory of gravity, in which matter is represented by the radiation and additional matter source of quantum nature, is found. It is shown that in the stage of the evolution of the universe, when quantum corrections ~ h dominate over the radiation, the geometry of the universe is described by the metric which is conformal to a metric of a unit four-sphere in a five-dimensional Euclidean flat space. In the radiation dominated era the metric is found to be conformal to a unit hyperboloid embedded in a five-dimensional Lorentz-signatured flat space. The origin of the universe can be interpreted as a quantum transition of the system from the region in a phase space with a trajectory in imaginary time into the region, where the equations of motion have the solution in real time. Near the boundary between two regions the universe undergoes almost an exponential expansion which passes smoothly into the expansion under the action of radiation dominating over matter. As a result of such a quantum transition the geometry of the universe changes. This agrees with the hypothesis about the possible change of geometry after the nucleation of expanding universe from `nothing'.
The dynamical property of the Tsallis distribution is studied from a Fokker-Planck equation. For the dynamical system with an arbitrary potential function, Markovian friction and Gaussian white noise, we show that no possible non-equilibrium dynamics can use the Tsallis distribution for the statistical description. The Tsallis distribution stands for a simple isothermal situation with no friction and no noise.
A new scenario of hybrid-like inflation is considered for sneutrino and MSSM fields. Contrary to the usual hybrid inflation model, the direct coupling between a trigger field and the sneutrino/MSSM inflaton field is not necessary for the scenario. The dissipation and the radiation from the sneutrino/MSSM inflaton can be written explicitly by using the Yukawa couplings. Remote inflation does not require the shift symmetry or cancellation in solving the eta-problem.
We calculate the ground state energy of cold and dense spin polarized quark matter with corrections due to correlation energy $(E_{corr})$. Expressions for $E_{corr}$ both in the non-relativistic and ultra-relativistic regimes have been derived and compared with the exchange and kinetic term present in the perturbation series. It is observed that the inclusion of correlation energy does not rule out the possibility of the ferromagnetic phase transition at low density within the model proposed by Tatsumi\cite{tatsumi00}. We also derive the spin stiffness constant in the high density limit of such a spin polarized matter.
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