Bubble Chambers provided the dominant particle detection technology in accelerator experiments for several decades, eventually falling into disuse with the advent of other techniques. We report here on the first period of operation of an ultra-clean, room-temperature bubble chamber containing 1.5 kg of superheated CF$_{3}$I, a target maximally sensitive to spin-dependent and -independent Weakly Interacting Massive Particle (WIMP) couplings. An exposure in excess of 250 kg-days is obtained, with a live-time fraction reaching 80%. This illustrates the ability to employ bubble chambers in a new realm, the search for dark matter particles. Improved limits on the spin-dependent WIMP-proton scattering cross section are extracted from this first period. An extreme intrinsic insensitivity to the backgrounds commonly limiting these experiments (a rejection factor for photon-induced electrons of $\sim10^{-10}$) has been measured in operating conditions leading to the detection of low-energy nuclear recoils such as those expected from WIMPs.
In various astrophysical contexts, we analyze self-similar behaviours of magnetohydrodynamic (MHD) evolution of a quasi-spherical polytropic magnetized gas under self-gravity with the specific entropy conserved along streamlines. In particular, this MHD model analysis frees the scaling parameter $n$ in the conventional polytropic self-similar transformation from the constraint of $n+\gamma=2$ with $\gamma$ being the polytropic index and therefore substantially generalizes earlier analysis results on polytropic gas dynamics that has a constant specific entropy everywhere in space at all time. On the basis of the self-similar nonlinear MHD ordinary differential equations, we examine behaviours of the magnetosonic critical curves, the MHD shock conditions, and various asymptotic solutions. We then construct global semi-complete self-similar MHD solutions using a combination of analytical and numerical means and indicate plausible astrophysical applications of these magnetized flow solutions with or without MHD shocks.
A comparison between published field galaxy stellar mass functions (GSMFs) shows that the cosmic stellar mass density is in the range 4--8 per cent of the baryon density (assuming Omega_b = 0.045). There remain significant sources of uncertainty for the dust correction and underlying stellar mass-to-light ratio even assuming a reasonable universal stellar initial mass function. We determine the z < 0.05 GSMF using the New York University - Value-Added Galaxy Catalog sample of 49968 galaxies derived from the Sloan Digital Sky Survey and various estimates of stellar mass. The GSMF shows clear evidence for a low-mass upturn and is fitted with a double Schechter function that has alpha_2 =~ -1.6. At masses below ~ 10^8.5 Msun, the GSMF may be significantly incomplete because of missing low surface-brightness galaxies. One interpretation of the stellar mass-metallicity relation is that it is primarily caused by a lower fraction of available baryons converted to stars in low-mass galaxies. Using this principal, we determine a simple relationship between baryonic mass and stellar mass and present an `implied baryonic mass function'. This function has a faint-end slope, alpha_2 =~ -1.9. Thus, we find evidence that the slope of the low-mass end of the galaxy mass function could plausibly be as steep as the halo mass function. We illustrate the relationship between halo baryonic mass function --> galaxy baryonic mass function --> GSMF. This demonstrates the requirement for peak galaxy formation efficiency at baryonic masses ~ 10^11 Msun corresponding to a minimum in feedback effects. The baryonic-infall efficiency may have levelled off at lower masses.
Flares overlaid on the smooth power-law decay of Swift X-ray afterglows are rather common, appearing in roughly half the observed light curves. They are a manifestation of the late time activity of the inner engine, since their temporal evolution is too fast to be linked to activity taking place in the external shock blastwave. In this paper we show that the energy emitted in the form of flares decreases with time as a power-law. We discuss several possibilities in which the flares can be powered and the source of the observed variability. We show that late time accretion from a disk can provide the necessary energy input in both classes of short duration and long duration gamma-ray bursts.
In LambdaCDM, massive satellites are dragged into the disk-plane by dynamical friction where they dissolve into a stellar thick disk and a more massive dark matter disk. The distinctive kinematics of the dark disk matches the stars that also entered in the satellites. The lower velocities of the dark disk with respect to the Earth enhances detection rates at low recoil energy. For WIMP masses > 50 GeV/c^2, the detection rate increases by up to a factor of 3 in the 5 - 20 keV recoil energy range. Comparing this with rates at higher energy will improve constraints on the WIMP mass, particularly for masses > 100 GeV/c^2. The annual modulation signal of the dark disk is significantly boosted and its modulation phase is shifted by ~3 weeks relative to the dark halo. The variation of the observed phase with recoil energy can also be used to determine the WIMP mass once the dark disk properties are fixed by future astronomical surveys. The constraints on the WIMP interaction cross section from current experiments improve by factors of 1.4 to 3.5 when a typical contribution from the dark disk is included.
The non-Gaussian cold spot found in the WMAP data has created controversy about its origin. Here we calculate the Bayesian posterior probability ratios for three different models that could explain the cold spot. A recent work claimed that the Spot could be caused by a cosmic texture, while other papers suggest that it could be due to the gravitational effect produced by an anomalously large void. Also the Sunyaev-Zeldovich effect caused by a cluster is taken into account as a possible origin. We perform a template fitting on a 20 degrees radius patch centered at Galactic coordinates (b = -57circ, l = 209) and calculate the posterior probability ratios for the void and Sunyaev-Zeldovich models, comparing the results to those obtained with textures. Taking realistic priors for the parameters, the texture interpretation is favored, while the void and Sunyaev-Zeldovich hypotheses are discarded. The temperature decrement produced by voids or clusters is negligible considering realistic values for the parameters.
The NEMO (NEutrino Mediterranean Observatory) Collaboration installed, 25 km E offshore the port of Catania (Sicily) at 2000 m depth, an underwater laboratory to perform long-term tests of prototypes and new technologies for an underwater high energy neutrino km$^3$-scale detector in the Mediterranean Sea. In this framework the collaboration deployed and successfully operated for about two years, starting form January 2005, an experimental apparatus for on-line monitoring of deep-sea noise. The station was equipped with 4 hydrophones and it is operational in the range 30 Hz - 43 kHz. This interval of frequencies matches the range suitable for the proposed acoustic detection technique of high energy neutrinos. Hydrophone signals were digitized underwater at 96 kHz sampling frequency and 24 bits resolution. A custom software was developed to record data on high resolution 4-channels digital audio file. This paper deals with the data analysis procedure and first results on the determination of sea noise sound pressure density curves. The stored data library, consisting of more than 2000 hours of recordings, is a unique tool to model underwater acoustic noise at large depth, to characterise its variations as a function of environmental parameters, biological sources and human activities (ship traffic, ...), and to determine the presence of cetaceans in the area.
Planets form inside protostellar disks in a dead zone where the electrical resistivity of the gas is too high for magnetic forces to drive turbulence. We show that much of the dead zone nevertheless is active and flows toward the star while smooth, large-scale magnetic fields transfer the orbital angular momentum radially outward. Stellar X-ray and radionuclide ionization sustain a weak coupling of the dead zone gas to the magnetic fields, despite the rapid recombination of free charges on dust grains. Net radial magnetic fields are generated in the magneto-rotational turbulence in the electrically conducting top and bottom surface layers of the disk, and reach the midplane by Ohmic diffusion. A toroidal component to the fields is produced near the midplane by the orbital shear. The process is similar to the magnetization of the Solar tachocline. The result is a laminar, magnetically-driven accretion flow in the region where the planets form.
The self-accelerating braneworld model (DGP) seems to provide a simple alternative to the the standard $\Lambda$CDM cosmology to explain the current cosmic acceleration, which is strongly indicated by measurements of Type Ia supernovae, as well as other concordant observations. In this work, we investigate observational constraints on this scenario from gravitational lensing statistics using the Cosmic Lens All-Sky Survey (CLASS) lensing sample. We show that a large parameter space of the DGP model is in good agreement with this radio source gravitational lensing sample. In the flat case, $\Omega_\mathrm{K}=0$, the likelihood is maximized, ${\cal L}={\cal L_\mathrm{max}}$, for $\1 = 0.30_{-0.11}^{+0.19}$. If we relax the prior on $\Omega_\mathrm{K}$, the likelihood peaks at $\{\1,\2 \} \simeq \{0.29, 0.12\}$, just slightly in the region of open models. However the confidence contours are pretty elongated so that we can not discard either close or flat or open models
String cosmology models predict a relic background of gravitational wave produced during the dilaton-driven inflation. It's spectrum is most likely to be detected by ground gravitational wave laser interferometers (IFOs), like LIGO, Virgo, GEO, as the energy density grows rapidly with frequency. We show the certain ranges of the parameters that underlying string cosmology model using two approaches, associated with 5% false alarm and 95% detection rate. The result presents that the approach of combining multiple pairs of IFOs is better than the approach of directly combining the outputs of multiple IFOs for LIGOH, LIGOL, Virgo and GEO.
Spitzer images resolve the debris disk around \gamma Ophiuchi at both 24 and 70 um. The resolved images suggest a disk radius of ~520 AU at 70 um and >=260 AU at 24 um. The images, along with a consistent fit to the spectral energy distribution of the disk from 20 to 350 um, show that the primary disk structure is inclined by ~50 degree from the plane of the sky at a position angle of 55+/-2 degree. Among a group of twelve debris disks that have similar host star spectral types, ages and infrared fractional luminosities, the observed sizes in the infrared and color temperatures indicate that evolution of the debris disks is influenced by multiple parameters in addition to the proto-planetary disk initial mass.
In this paper, the holographic dark energy model is considered in Brans-Dicke theory where the holographic dark energy density $\rho_{\Lambda} =3c^2 M^{2}_{pl} L^{-2}$ is replaced with $\rho_{h}=3c^2 \Phi(t)L^{-2}$. Here $\Phi(t)=\frac{1}{8\pi G}$ is a time variable Newton constant. With this replacement, it is found that no accelerated expansion universe will be achieved when the Hubble horizon is taken as the role of IR cut-off. When the event horizon is adopted as the IR cut-off, an accelerated expansion universe is obtained. In this case, the equation of state of holographic dark energy $w_h$ takes a modified form $w_h = -{1/3}(1+\alpha+(2/c)\sqrt{\Omega_h})$. In the limit $\alpha\to 0$, the 'standard' holographic dark energy is recovered.
We use a mock galaxy catalogue based upon the Millennium Run simulation to investigate the intrinsic spatial properties of compact groups of galaxies. We find that approximately 30% of galaxy associations identified in our mock catalogue are physically dense systems of four or more galaxies with no interlopers, approximately half are close associations of 2, 3 or 4 galaxies with one or more interlopers, and the remainder are not physically dense. Genuine compact groups are preferentially brighter and more isolated than those with interlopers; by increasing the required minimum surface brightness of a group from the canonical value of 26mags/arcsec^2 to 22mags/arcsec^2, we can increase the proportion of genuinely compact systems identified with no interlopers from 29% to 75%. Of the genuine compact groups identified, more than half consist of a single dark matter halo with all the member galaxies deeply embedded within it. In some cases, there are other galaxies which share the same halo (typically with mass ~ 10^13 h^{-1} M_\odot) but which are not identified as being members of the compact group. This implies that compact groups are associated with group environments, some or all members of which are in the compact group. For those compact groups where all galaxies are in the same halo, the three-dimensional velocity dispersion of the compact group correlates broadly with the virial velocity of the dark matter halo. However, the scale-size of the group - and hence the fraction of the halo mass which the group samples - is completely uncorrelated with the properties of the dark matter halo. This means that masses derived under the simple assumption of virial equilibrium using the observed velocity dispersions and sizes of compact groups give incorrect estimates of the true mass of the underlying dark matter.
We have made a Monte Carlo simulation of the intergalactic absorption in order to model the Lyman continuum absorption, which is required to estimate the escape fraction of the Lyman continuum from distant galaxies. To input into the simulation, we derive an empirical distribution function of the intergalactic absorbers which reproduces recent observational statistics of the Lyman $\alpha$ forest, Lyman limit systems (LLSs), and damped Lyman $\alpha$ systems (DLAs) simultaneously. In particular, we assume a common functional form of the number evolution along the redshift for all types of absorbers. The Lyman series transmissions in our simulation reproduce the observed redshift evolution of the transmissions excellently, and the Lyman continuum transmission also agrees with an observed estimation which is still quite rare in the literature. The probability distribution of the Lyman $\alpha$ opacity in our simulation is log-normal with a tail towards a large opacity. This tail is produced by DLAs. The probability distribution of the Lyman continuum opacity in our simulation also show a broad tail towards a large opacity. This tail is produced by LLSs. Because of the rarity of LLSs, we have a chance to have a clean line of sight in the Lyman continuum even for $z\sim4$ with a probability of about 20%. Our simulation expects a good correlation between the Lyman continuum opacity and the Lyman $\alpha$ opacity, which may be useful to estimate the former from the latter for an individual line of sight.
Stars with planets at intermediate metallicities ([-0.7,-0.2] dex) exhibit properties that differ from the general field stars. Thirteen stars with planets reported in this metallicity range belong to the thick disc, while only one planet have been detected among stars of the thin disc. Although this statistics is weak, it contradicts the known correlation between the presence of planet and metallicity. We relate this finding to the specific property of the thin disc in this metallicity range, where stars are shown to rotate around the Galaxy faster than the Sun. Their orbital parameters are conveniently explained if they are contaminants coming from the outer Galactic disc, as a result of radial mixing. This must be considered together with the fact that metal-rich stars ([Fe/H]>+0.1 dex) found in the solar neighbourhood, which are the hosts of most of the detected planets, are suspected of being wanderers from the inner Galactic disc. It is then questionned why stars that originate in the inner and outer thin disc show respectively the highest and lowest rate of detected planets. It is suggested that the presence of giant planets might be primarily a function of a parameter linked to galactocentric radius, but not metallicity. Combined with the existing radial metallicity gradient, then radial mixing explains the correlation at high metallicity observed locally, but also the peculiarity found at low metallicity, which cannot be accounted for by a simple correlation between metallicity and planet probability.
In this paper, we initiate a new study of steady funnel-flow accretion onto strongly magnetized neutron stars, including a full treatment of shock generation. As a first step, we adopt a simplified model considering the flow within Newtonian theory and neglecting radiative pressure and cooling. The flow is taken to start from an accretion disc and then to follow magnetic field lines, forming a transonic funnel flow onto the magnetic poles. A standing shock occurs at a certain point in the flow and beyond this material accretes subsonically onto the star with high pressure and density. We calculate the location of the standing shock and all other features of the flow within the assumptions of our model. Applications to observed X-ray pulsars are discussed.
In this paper we set bounds on the radiation content of the Universe and neutrino properties by using the WMAP-5 year CMB measurements complemented with most of the existing CMB and LSS data (WMAP5+All),imposing also self-consistent BBN constraints on the primordial helium abundance. We consider lepton asymmetric cosmological models parametrized by the neutrino degeneracy parameter and the variation of the relativistic degrees of freedom, due to possible other physical processes occurred between BBN and structure formation epochs. We find that WMAP5+All data provides strong bounds on helium mass fraction and neutrino degeneracy parameter that rivals the similar bounds obtained from the conservative analysis of the present data on helium abundance. We also find a strong correlation between the matter energy density and the redshift of matter-radiation equality, z_re, showing that we observe non-zero equivalent number of relativistic neutrinos mainly via the change of the of z_re, rather than via neutrino anisotropic stress claimed by the WMAP team. We forecast that the CMB temperature and polarization measurements observed with high angular resolutions and sensitivities by the future Planck satellite will reduce the errors on these parameters down to values fully consistent with the BBN bounds.
We present deep and wide V, I CCD photometry of Ursa Major I (UMa I) dwarf spheroidal galaxy (dSph) in Local Group. The images of the galaxy were taken by Subaru/Suprime-Cam wide field camera, covering a field of 34\arcmin $\times$ 27\arcmin located at the centre of the galaxy. Colour-magnitude diagram (CMD) of the UMa I dSph shows a steep and narrow red giant branch (RGB), blue and red horizontal branch (HB), and main sequence (MS) stars. A well-defined main sequence turn-off (MSTO) is found to be located at V$_{0,MSTO}\sim$23.5 mag. The distance modulus is derived as $(m-M)_0=19.93\pm0.1$ (corresponding to a distance D$=96.8\pm4$ kpc) from the V-band magnitude of the horizontal branch (V$_{0,HB}=20.45\pm0.02$). The mean metallicity of the RGB stars is estimated by the V$-$I colour to [Fe/H]$\sim-2.0$. The turn-off age estimated by overlaying the theoretical isochrones reveals that most of stars in the UMa I dSph are formed at very early epoch ($\sim12$Gyrs ago). The isopleth map of stellar number density of the UMa I dSph, based upon the resolved star counts of MS, RGB, HB stars as well as blue stragglers (BS), shows that the morphology of the UMa I dSph is quite irregular and distorted, suggesting that the galaxy is in a process of disruption. The very old and metal-poor nature of the stellar population implies that the star formation history of this newly discoverd faint dSph may have been different from other well-known `classical' dSphs, which show significant stellar population of intermediate age. The stellar population of the UMa I dSph closely resembles that of Galactic old metal-poor globular cluster, but its size is typical of Galactic dSphs (r$_{e}$=188 [pc], r$_{1/2}$=300 [pc]), and the shape of its spatial density contours suggests that it is undergoing tidal disruption.
Alfven waves and ion-cyclotron absorption of high-frequency waves are frequently brought into models devoted to coronal heating and fast solar-wind acceleration. Signatures of ion-cyclotron resonance have already been observed in situ in the solar wind (HELIOS spacecrafts) and, recently, in the upper corona (UVCS/SOHO remote-sensing results). We propose a method to constrain both the Alfven wave amplitude and the preferential heating induced by ion-cyclotron resonance, above a partially developed polar coronal hole observed with the SUMER/SOHO spectrometer. The instrumental stray light contribution is first substracted from the spectra. By supposing that the non-thermal velocity is related to the Alfven wave amplitude, it is constrained through a density diagnostic and the gradient of the width of the Mg X 625 A line. The temperatures of several coronal ions, as functions of the distance above the limb, are then determined by substracting the non-thermal component to the observed line widths. The effect of stray light explains the apparent decrease with height in the width of several spectral lines, this decrease usually starting about 0.1-0.2 Rs above the limb. This result rules out any direct evidence of damping of the Alfven waves, often suggested by other authors. We also find that the ions with the smallest charge-to-mass ratios are the hottest ones at a fixed altitude and that they are subject to a stronger heating, as compared to the others, between 57" and 102" above the limb. This constitutes a serious clue to ion-cyclotron preferential heating.
In addition to buoyancy- and magnetic tension-driven instabilities, magnetic flux rings are also susceptible to an instability induced by the hydrodynamic drag force. We investigate the influence of the toroidal shape and equilibrium condition on the thresholds of the friction-induced instability and on their relevance for emerging magnetic flux in solar-like stars. Analytical instability criteria are derived for axial symmetric perturbations and for flux rings in the equatorial plane by analysing the sequence of principal minors of the coefficient matrices of dispersion polynomials. The general case of non-equatorial flux rings is investigated numerically by considering flux tubes in the solar overshoot region. The friction-induced instability occurs when an eigenmode reverses its direction of propagation due to advection, typically from the retrograde to the prograde direction. Since the reversal requires a certain relative velocity difference between plasma inside the flux tube and the environment, the instability criterion depends on the location and field strength of the flux ring. The friction-induced instability sets in at lower field strengths than buoyancy- and tension-driven instabilities. Its threshold is independent of the strength of friction, but the growth rates depend on the strength of the frictional coupling between flux tube and environment. The friction-induced instability lowers the critical magnetic field strength beyond which flux tubes are subject to growing perturbations. Whereas buoyancy- and tension-driven instabilities depend on the magnetic field strength alone, the dependence of hydrodynamic drag on the tube diameter gives rise to an additional dependence of growth times on the magnetic flux.
Centaurus A, the cosmic ray accelerator a few Mpc away from us is one of the nearest sources of extremely high energy cosmic rays. It would be interesting to see whether the gamma ray data currently available from Centaurus A in the GeV-TeV energy band can be explained with only proton proton interactions. We show that to be consistent with the gamma ray luminosity observed in the GeV-TeV energy range and the correlated extreme energy cosmic ray events observed by the Pierre Auger experiment, mechanisms of $\gamma$-ray production other than proton proton interactions are needed inside this radio-galaxy.
We report on H-band ground-based observations of a transit of the hot Neptune GJ 436b. Once combined to achieve an equivalent sampling as archived observations taken with Spitzer, our measurements reach comparable precision levels. We analyze both sets of observations in a consistent way, and measure the rate of orbital inclination change to be of 0.02+/-0.04 degrees in the time span between the two observations (253.8 d, corresponding to 0.03+/-0.05 degrees/yr if extrapolated). By performing simulations of planetary systems including a second planet GJ 436c which has been recently suggested (Ribas et al. 2008), this rate allows to put limits to the relative inclination between the two planets. The allowed inclinations for a 5 M_E super-Earth GJ 436c in a 5.2 d orbit are within ~7 degrees of the one of GJ 436b; for larger differences the observed inclination change can be reproduced only during short sections (<50%) of the orbital evolution of the system. The measured times of three transit centers of the system do not show any departure from linear ephemeris, a result that is only reproduced in <1% of the simulated orbits. Put together, these results argue against the proposed planet candidate GJ 436c.
The initial-final mass relationship connects the mass of a white dwarf with the mass of its progenitor in the main-sequence. Although this function is of fundamental importance to several fields in modern astrophysics, it is not well constrained either from the theoretical or the observational points of view. In this work we revise the present semi-empirical initial-final mass relationship by re-evaluating the available data. The distribution obtained from grouping all our results presents a considerable dispersion, which is larger than the uncertainties. We have carried out a weighted least-squares linear fit of these data and a careful analysis to give some clues on the dependence of this relationship on some parameters such as metallicity or rotation. The semi-empirical initial-final mass relationship arising from our study covers the range of initial masses from 1.0 to 6.5 M_sun, including in this way the low-mass domain, poorly studied until recently. Finally, we have also performed a test of the initial-final mass relationship by studying its effect on the luminosity function and on the mass distribution of white dwarfs. This was done by using different initial-final mass relationships from the literature, including the expression derived in this work, and comparing the results obtained with the observational data from the Palomar Green Survey and the Sloan Digital Sky Survey (SDSS). We find that the semi-empirical initial-final mass relationship derived here gives results in good agreement with the observational data, especially in the case of the white dwarf mass distribution.
Thanks to the recent availability of large surveys, there has been renewed interest in third-order correlation statistics. Measures of third-order clustering are sensitive to the structure of filaments and voids in the universe and are useful for studying large-scale structure. Thus, statistics of these third-order measures can be used to test and constrain parameters in cosmological models. Third-order measures such as the three-point correlation function are now commonly estimated for galaxy surveys. Studies of third-order clustering of absorption systems will complement these analyses. We define a statistic, which we denote K, that measures third-order clustering of a data set of point observations and focus on estimating this statistic for an absorber catalog. The statistic K can be considered a third-order version of the second-order Ripley K-function and allows one to study the abundance of various configurations of point triplets. In particular, configurations consisting of point triplets that lie close to a straight line can be examined. Studying third-order clustering of absorbers requires consideration of the absorbers as a three-dimensional process, observed on QSO lines of sight that extend radially in three-dimensional space from Earth. Since most of this three-dimensional space is not probed by the lines of sight, edge corrections become important. We use an analytical form of edge correction weights and construct an estimator of the statistic K for use with an absorber catalog. We show that with these weights, ratio-unbiased estimates of K can be obtained. Results from a simulation study also verify unbiasedness and provide information on the decrease of standard errors with increasing number of lines of sight.
In preparation for lively debate at the May 2008 SPD/AGU Meeting in Fort Lauderdale, this document attempts to briefly lay out my own view of the evolving controversy over how the solar wind is accelerated. It is still unknown to what extent the solar wind is fed by flux tubes that remain open (and are energized by footpoint-driven wavelike fluctuations), and to what extent much of the mass and energy is input more intermittently from closed loops into the open-field regions. It may turn out that a combination of the two ideas is needed to explain the full range of observed solar wind phenomena.
General relativistic quantum interference effects in the slowly rotating NUT space-time as the Sagnac effect and the phase shift effect of interfering particle in neutron interferometer are considered. It was found that in the case of the Sagnac effect the influence of NUT parameter is becoming important due to the fact that the angular velocity of the locally non rotating observer must be larger than one in the Kerr space-time. In the case of neutron interferometry it is found that due to the presence of NUT-parameter an additional term in the phase shift of interfering particle emerges. This term can be, in principle, detected by sensitive interferometer and derived results can be further used in experiments to detect the gravitomagnetic charge. Finally, as an example, we apply the obtained results to the calculation of the UCN (ultra-cold neutrons) energy level modification in the slowly rotating NUT space-time.
Links to: arXiv, form interface, find, astro-ph, recent, 0804, contact, help (Access key information)
We present the time evolution of the stellar metallicity for SDSS galaxies, a sample that spans five orders of magnitude in stellar mass (10^7 - 10^{12} Msun). Assuming the BC03 stellar population models, we find that more massive galaxies are more metal-rich than less massive ones at all redshifts; the mass-metallicity relation is imprinted in galaxies from the epoch of formation. For galaxies with present stellar masses > 10^{10} Msun, the time evolution of stellar metallicity is very weak, with at most 0.2-0.3 dex over a Hubble time- for this reason the mass-metallicity relation evolves little with redshift. However, for galaxies with present stellar masses < 10^{10} Msun, the evolution is significant, with metallicity increasing by more than a decade from redshift 3 to the present. By being able to recover the metallicity history, we have managed to identify the origin of a recent discrepancy between the metallicity recovered from nebular lines and absorption lines. As expected, we show that the young population dominates the former while the old population the latter. We have investigated the dependence on the stellar models used and find that older stellar population synthesis codes do not produce a clear result. Finally, we have explored the relationship between cluster environment and metallicity, and find a strong correlation in the sense that galaxies in high density regions have high metallicity.
Measurements of deuterium in the local interstellar medium have revealed large variations in D/H along different lines of sight. Moreover, recent Far Ultraviolet Spectroscopic Explorer (FUSE) measurements find D/H to be positively correlated with oxygen, suggesting that interstellar deuterium suffers significant depletion onto dust grains. This in turn implies that the total deuterium abundance in the local Galactic disk could be as high as ~84% of the primordial D abundance.Because deuterium is destroyed in stars D_{ISM}/D_{p} is also the fraction of material which has never been processed through stellar environments, which implies that most present-day interstellar baryons are unprocessed. It was proposed that the infall/accretion of pristine gas is needed to explain such a high deuterium abundance. However, we point out that the infall needed to maintain a high present-day D/H is in strong tension with observations that gas represents only some ~20% of Galactic baryons, with the balance in stars. This small gas fraction implies that, integrated over Galactic history, most baryons have been sequestered into stars and stellar remnants. We study this tension in the context of a wide class of Galactic evolution models for baryonic processing through stars, which show that deuterium destruction is strongly and cleanly correlated with the drop in the gas fraction. We find that FUSE deuterium observations and Galactic gas fraction estimates can be reconciled in some models; these demand a significant infall rate of pristine material that almost completely balances the rate of star formation. These successful models also demand a relatively low average fraction $R < 0.32$ of gas be returned by dying stars. Cosmological implications of dust depletion of D in high-redshift systems are discussed.
The magnetic theory for the production of jets by accreting objects is reviewed with emphasis on outstanding problem areas. An effort is made to show the connections behind the somewhat diverging nomenclature in the literature, to contrast the different points of view about basic mechanisms, and to provide handles to interpret the results of numerical simulations. The role of dissipation of magnetic energy in accelerating the flow is discussed, and its importance for explaining high Lorentz factors. The collimation of jets to the observed narrow angles is discussed with some critical remarks on the role of `hoop stress'. The transition between disk and outflow is one of the least understood parts of the magnetic theory; its role in setting the mass flux in the wind, in possible modulations of the mass flux, and the uncertainties in treating it realistically are discussed. Current views on most of these problems are still strongly biased by the restriction to 2 dimensions (axisymmetry) in previous analytical and numerical work; 3-D effects likely to be important are reviewed. An interesting problem area is the nature and origin of the strong, preferably highly ordered magnetic fields known to work best for jet production. The observational evidence for such fields and their behavior in numerical simulations is discussed. I argue that the presence or absence of such fields may well be the `second parameter' governing not only the presence of jets but also the X-ray spectra and timing behavior of X-ray binaries.
There is a growing body of evidence that the plasma loops seen with current instrumentation (SOHO, TRACE and Hinode) may consist of many sub-resolution elements or strands. Thus, the overall plasma evolution we observe in these features could be the cumulative result of numerous individual strands undergoing sporadic heating. This paper presents a short (10^9 cm ~ 10 Mm) ``global loop'' as 125 individual strands where each strand is modelled independently by a one-dimensional hydrodynamic simulation. The energy release mechanism across the strands consists of localised, discrete heating events (nano-flares). The strands are ``coupled'' together through the frequency distribution of the total energy input to the loop which follows a power law distribution with index alpha. The location and lifetime of each energy event occurring is random. Although a typical strand can go through a series of well-defined heating/cooling cycles, when the strands are combined, the overall quasi-static emission measure weighted thermal profile for the global loop reproduces a hot apex/cool base structure. Localised cool plasma blobs are seen to travel along individual strands which could cause the loop to `disappear' from coronal emission and appear in transition or chromospheric ones. As alpha increases (from 0 to 2.29 to 3.29), more weight is given to the smallest heating episodes. Consequently, the overall global loop apex temperature increases while the variation of the temperature around that value decreases. Any further increase in alpha saturates the loop apex temperature variations at the current simulation resolution. The effect of increasing the number of strands and the loop length as well as the implications of these results upon possible future observing campaigns for TRACE and Hinode are discussed.
The High-Energy Stereoscopic System (HESS) has detected intense diffuse TeV emission correlated with the distribution of molecular gas along the galactic ridge at the centre of our Galaxy. Earlier HESS observations of this region had already revealed the presence of several point sources at these energies, one of them (HESS J1745-290) coincident with the supermassive black hole Sagittarius A*. It is still not entirely clear what the origin of the TeV emission is, nor even whether it is due to hadronic or leptonic interactions. It is reasonable to suppose, however, that at least for the diffuse emission, the tight correlation of the intensity distribution with the molecular gas indicates a pionic-decay process involving relativistic protons. In this paper, we explore the possible source(s) of energetic hadrons at the galactic centre, and their propagation through a turbulent medium. We conclude that though Sagittarius A* itself may be the source of cosmic rays producing the emission in HESS J1745-290, it cannot be responsible for the diffuse emission farther out. A distribution of point sources, such as pulsar wind nebulae dispersed along the galactic plane, similarly do not produce a TeV emission profile consistent with the HESS map. We conclude that only a relativistic proton distribution accelerated throughout the inter-cloud medium can account for the TeV emission profile measured with HESS.
We have mapped the eta Chamaeleontis young stellar association in the far-infrared with the Multiband Imaging Photometer for Spitzer (MIPS) on the Spitzer Space Telescope. All sixteen members within the map region were detected at 24 um, along with five members at 70 um and two at 160 um. Ten stars show far-infrared excess emission indicating the presence of circumstellar disks; six of these have central clearings as evidenced by the onset of excess emission at >5 um. No new infrared excess sources are identified among the 113 2MASS field stars with 24 um photometry but not seen as X-ray sources, indicating that membership lists derived from X-ray surveys are reasonably complete. Circumstellar disks in the eta Cha association span the range from 1e-1 to 1e-4 in their fractional infrared luminosity, with a median Ldust /Lstar of 0.04. The presence of optically thick, optically thin, and intermediate optical depth disks within the same stellar group, in combination with the large fraction of disks with inner holes, indicates that the Cha association represents a crucial stage in circumstellar disk evolution.
A short observing run with the spectrometer Harps at the ESO 3.6-m telescope was conducted in order to continue exploring the asteroseismic properties of F type stars. In fact, Doppler observations of F type on the main sequence are demanding and remain currently limited to a single case (HD 49933). Comparison with photometric results obtained with the CoRoT mission on similar stars will be possible with an enhanced set of observations. We selected the 4th magnitude F8V star HD 203608, in order to investigate the oscillating properties of a low-metallicity star of the old galactic disk. A 5-night asteroseismic observation program has been conducted in August 2006 with Harps. Spectra were reduced with the on-line data reduction software provided by the instrument. A new statistical approach has been developed for extracting the significant peaks in the Fourier domain. The oscillation spectrum shows a significant excess power in the frequency range [1.5, 3.0 mHz]. It exhibits a large spacing about 120.4 $\mu$Hz at 2.5 mHz. Variations of the large spacing with frequency are clearly identified, which require an adapted asymptotic development. The modes identification is based on the unambiguous signature of 15 modes with $\ell = 0$ and 1. This observation shows the potential diagnostic of asteroseismic constraints. Including them in the stellar modeling enhances significantly the precision on the physical parameters of \cible, resulting in a much more precise position in the HR diagram. The age of the star is now determined in the range $7.25\pm0.07$ Gyr.
Motivated by recent Pierre Auger result on the correlation of the highest-energy cosmic rays with the nearby active galactic nuclei, we explore possible ultrahigh energy cosmic ray (UHECR) source distributions and their effects on GZK horizons. Effects on GZK horizons by local over-density of UHECR sources are examined carefully with constraints on the degree of local over-density inferred from the measured UHECR spectrum. We include the energy calibration effect on the Pierre Auger data in our studies. We propose possible local over-densities of UHECR sources which are testable in the future cosmic ray astronomy.
We show that the proportionately spaced emission bands in the dynamic spectrum of the Crab pulsar (Hankins T. H. & Eilek J. A., 2007, ApJ, 670, 693) fit the oscillations of the square of a Bessel function whose argument exceeds its order. This function has already been encountered in the analysis of the emission from a polarization current with a superluminal distribution pattern: a current whose distribution pattern rotates (with an angular frequency $\omega$) and oscillates (with a frequency $\Omega>\omega$ differing from an integral multiple of $\omega$) at the same time (Ardavan H., Ardavan A. & Singleton J., 2003, J Opt Soc Am A, 20, 2137). Using the results of our earlier analysis, we find that the dependence on frequency of the spacing and width of the observed emission bands can be quantitatively accounted for by an appropriate choice of the value of the single free parameter $\Omega/\omega$. In addition, the value of this parameter, thus implied by Hankins & Eilek's data, places the last peak in the amplitude of the oscillating Bessel function in question at a frequency ($\sim\Omega^3/\omega^2$) that agrees with the position of the observed ultraviolet peak in the spectrum of the Crab pulsar. We also show how the suppression of the emission bands by the interference of the contributions from differring polarizations can account for the differences in the time and frequency signatures of the interpulse and the main pulse in the Crab pulsar. Finally, we put the emission bands in the context of the observed continuum spectrum of the Crab pulsar by fitting this broadband spectrum (over 16 orders of magnitude of frequency) with that generated by an electric current with a superluminally rotating distribution pattern.
We report time-resolved optical CCD photometry on newly discovered SU UMa-type dwarf novae, FL TrA and CTCV J0549-4921. During the 2006 August outburst, we detected superhumps with a period of 0.59897(11) days for FL TrA, clarifying the SU UMa nature of the system. On the first night of our observations on FL TrA, the object showed no superhumps. This implies that it takes a few days for full development of superhumps. The superhump period variation diagram of FL TrA was similar to that observed in some WZ Sge stars and short period SU UMa-type stars. This indicates that the system is closely related to WZ Sge stars and SU UMa stars having short orbital periods. For CTCV J0549-4921, the candidates of the mean superhump period are 0.083249(10) days and 0.084257(8) days, respectively. Due to a lack of the observations, we cannot determine the true superhump period, but the latter period is favorable. Using the ASAS-3 archive, it turned out that the system shows only four outbursts over the past 6 years. The outburst amplitude of CTCV J0549-4921 was relatively small, with about 4.5 mag. One possibility is that mass evaporation may play a role during quiescence.
We use the observational $H(z)$ (OHD), distant type Ia supernovae
(SNe Ia), the Baryonic Acoustic Oscillation (BAO) peak and the Cosmic
Microwave Background (CMB) shift parameter data to constrain cosmological
parameters of $\Lambda$CDM cosmology and examine the role of OHD and SNe Ia
data in cosmological constraints. We marginalize the likelihood functions over
$h$ by integrating the probability density $P\propto^{-\chi^2/2}$ to obtain the
best fitting results and the confidence regions in the $\Omega_{\rm
m}$-$\Omega_{\Lambda}$ plane. Considering a prior of $h=0.73\pm0.03$ can
greatly improve the constraint on parameters. With such a prior, we show that
the OHD constraints in the direction roughly parallel to the dash straight line
that represents a flat universe are almost as restrictive as that from SNe Ia.
However, in the direction approximately orthogonal to this line, the OHD
constraint is weaker than that using SNe Ia data. For the combination analysis,
we find that the confidence regions of 68.3%, 95.4% and 99.7% levels using
OHD+BAO+CMB data are in good agreement with that of SNe Ia+BAO+CMB data. With a
large amount of OHD data in the future, we can probably constraint cosmological
parameters using OHD data instead of SNe Ia data.
The full set of published radial velocity data (52 measurements from Keck + 58 ones from ELODIE + 17 ones from CORALIE) for the star HD37124 is analysed. Two families of dynamically stable high-eccentricity orbital solutions for the planetary system were found. In the first one, the outer planets c and d are trapped in the 2/1 mean-motion resonance. The second family of solutions corresponds to the 5/2 mean-motion resonance between these planets. In both families, the two outer planets in the system are locked in (or close to) an apsidal corotation resonance. In the case of the 2/1 MMR, it is an asymmetric apsidal corotation (with the difference between the longitudes of periastra about $60^\circ$), whereas in the case of the 5/2 MMR it is a symmetric antialigned one (the difference between the longitudes of periastra is $180^\circ$).
We present and interpret new spectropolarimetric observations of the magnetic white dwarf WD 1953-011. Circular polarization and intensity spectra of the H$\alpha$ spectral line demonstrate the presence of two-component magnetic field in the photosphere of this star. The geometry consists of a weak, large scale component, and a strong, localized component. Analyzing the rotationally modulated low-field component, we establish a rotation period $P_{rot} = 1.4480 \pm 0.0001$ days. Modeling the measured magnetic observables, we find that the low-field component can be described by the superposition of a dipole and quadrupole. According to the best-fit model, the inclination of the stellar rotation axis with respect to the line of sight is $i \approx 20^\circ$, and the angle between the rotation axis and the dipolar axis is $\beta \approx 10^\circ$. The dipole strength at the pole is about 180 kG, and the quadrupolar strength is about 230 kG. These data suggest a fossil origin of the low-field component. In contrast, the strong-field component exhibits a peculiar, localized structure (``magnetic spot'') that confirms the conclusions of Maxted and co-workers. The mean field modulus of the spot ($|B_{spot}| = 520 \pm 7$ kG) together with its variable longitudinal magnetic field having a maximum of about +400 kG make it difficult to describe it naturally as a high-order component of the star's global poloidal field. Instead, we suggest that the observed strong-field region has a geometry similar to a magnetic flux tube.
Primordial gas in protogalactic dark matter (DM) halos with virial temperatures Tvir > 10^4K begins to cool and condense via atomic hydrogen. Provided this gas is irradiated by a strong ultraviolet (UV) flux and remains free of H2 and other molecules, it has been proposed that it may avoid fragmentation, and lead to the rapid formation of a supermassive black hole (SMBH) as massive as M~10^5-10^6 Msun. This ``head-start'' would help explain the presence of SMBHs with inferred masses of several x 10^9 Msun, powering the bright quasars discovered in the Sloan Digital Sky Survey at redshift z> 6. However, high-redshift DM halos with Tvir > 10^4K are likely already enriched with at least trace amounts of metals and dust produced by prior star-formation in their progenitors. Here we study the thermal and chemical evolution of low-metallicity gas exposed to extremely strong UV radiation fields. Our results, obtained in one-zone models, suggest that gas fragmentation is inevitable above a critical metallicity, whose value is between Zcr = 3x10^{-4} Zsun (in the absence of dust) and as low as Zcr = 5x10^{-6} Zsun (with a dust-to-gas mass ratio of about 0.01 Z/Zsun). We propose that when the metallicity exceeds these critical values, dense clusters of low-mass stars may form at the halo nucleus. The stars in such a cluster can then rapidly coalesce into a single massive star, which may produce an intermediate--mass BH remnant with a mass up to M < 10^2-10^3 Msun.
Based on the Thomas-Fermi approach, we describe and distinguish the electron distributions around extended nuclear cores: (i) in the case that cores are neutral for electrons bound by protons inside cores and proton and electron numbers are the same; (ii) in the case that super charged cores are bare, electrons (positrons) produced by vacuum polarization are bound by (fly into) cores (infinity).
Observations reveal that mature spiral galaxies consist of stars, gases and plasma approximately distributed in a thin disk of circular shape, usually with a central bulge. The rotation velocities quickly increase from the galactic center and then achieve a constant velocity from the core to the periphery. The basic dynamic behavior of a mature spiral galaxy, such as the Milky Way, is well described by simple models balancing Newtonian gravitational forces against the centrifugal forces associated with a rotating thin axisymmetric disk. In this research, we investigate the effects of adding central bulges to thin disk gravitational models. Even with the addition of substantial central bulges, all the critical essential features of our thin disk gravitational models are preserved. (1) Balancing Newtonian gravitational and centrifugal forces at every point within the disk yields computed radial mass distributions that describe the measured rotation velocity profiles of mature spiral galaxies successfully. (2) There is no need for gravity deviations or ``massive peripheral spherical halos of mysterious Dark Matter''. (3) The calculated total galactic masses are in good agreement with star count data. (4) The addition of central bulges increases the calculated total galactic masses, possibly more consistent with the presence of galactic gases, dust, grains, lumps, planets and plasma in addition to stars. (5) Compared with the light distribution, our mass distributions within the disk are larger out toward the galactic periphery which is cooler with lower opactiy/emissivity (and thus darker). This is apparent from edge-on views of galaxies which display a dark disk-line against a much brighter galactic halo.
A variety of events such as gamma-ray bursts may expose the Earth to an increased flux of high-energy cosmic rays, with potentially important effects on the biosphere. An atmospheric code, the NASA-Goddard Space Flight Center two-dimensional (latitude, altitude) time-dependent atmospheric model (NGSFC), can be used to study atmospheric chemistry changes. The effect on atmospheric chemistry from astrophysically created high energy cosmic rays can now be studied using the NGSFC code. A table has been created that, with the use of the NGSFC code can be used to simulate the effects of high energy cosmic rays (10 GeV to 1 PeV) ionizing the atmosphere. We discuss the table, its use, weaknesses, and strengths.
The aromatic features in M101 were studied spectroscopically and photometrically using observations from all three instruments on the Spitzer Space Telescope. The global SED of M101 shows strong aromatic feature (commonly called PAH feature) emission. The spatially resolved spectral and photometric measurements of the aromatic feature emission show strong variations with significantly weaker emission at larger radii. We compare these variations with changes in the ionization index (as measured by [NeIII]/[NeII] and [SIV/SIII], which we probe over the ranges 0.03-20 and 0.044-15 respectively) and metallicity (expressed as log(O/H)+12, which ranges from 8.1 to 8.8). Over these ranges, the spectroscopic equivalent widths of the aromatic features from 7 HII regions and the nucleus were found to correlate better with ionization index than with metallicity. This implies that the weakening of the aromatic emission in massive star forming regions is due primarily to processing of the dust grains in these environments, not to differences in how they form (although formation could still be important on a secondary basis). The behavior of the correlation between the aromatic feature equivalent widths and ionization index can be described as a constant equivalent width until a threshold in ionization index is reached ([NeIII]/[NeII] ~ 1), above which the equivalent widths decrease with a power law dependence. This behavior for M101 HII regions is also seen for the sample of starburst galaxies presented in the companion study of Engelbracht et al. (2008) which expands the range of [NeIII]/[NeII] ratios to 0.03-25 and log(O/H)+12 values to 7.1-8.8. The form of the correlation explains seemingly contradictory results present in the literature. [abridged]
We derive an expression for the entropy of a dark matter halo described by a Navarro-Frenk-White model with a core. The comparison of this entropy with the one of dark matter at the freeze-out era allows us to constraint the parameter space in mSUGRA models. Moreover, joining these constraints with the ones obtained from the usual abundance criteria and demanding both criteria to be consistent with the 2$\sigma$ bounds for the abundance of dark matter: $0.112\leq\Omega_{DM}h^2\leq0.122$, we are able to clearly discriminate validity regions among the values of $\tan \beta$, one of the parameters of the mSUGRA model. We found that for the explored regions of the parameter space, small values of tan$\beta$ are not favored; only for tan$\beta\simeq50$ are both criteria significantly consistent. In the region where both criteria are consistent we also found a lower bound for the neutralino mass, $m_{\chi}\geq 141$ GeV.
In this paper we study specific classes of radiating shocks which are widely spread in astrophysical environments. We present more general solutions of their structure and proceed to the analytical determination of physical quantities.
Supernovae of Type II is a phenomenon that occurs at the end of evolution of massive stars when the iron core of the star exceeds a mass limit. After collapse of the core under gravity the shock wave alone does not succeed in expelling the mass of the star and in this sense the role of neutrinos is the most important mechanism to do so. During the emission of neutrinos flavor conversion is possible, related the phenomenon of oscillations, which however depends directly on the particular density profile of the medium. In this paper we present results of numerical simulations of neutrino flavor conversion in protoneutron stars and after collapse. The probabilities of survival for a given flavor in a complete three-flavors framework is estimated through an algorithm which conserves unitarity to a high degree of accuracy. The sensitivity of the results to the different adopted models for the protoneutron star structure is examined in detail demonstrating how the neutrino signal could be used to check the validity of models.
On-orbit performance of the Solar Optical Telescope (SOT) aboard Hinode is described with some attentions on its unpredicted aspects. In general, SOT revealed an excellent performance and has been providing outstanding data. Some unexpected features exist, however, in behaviors of the focus position, throughput and structural stability. Most of them are recovered by the daily operation i.e., frequent focus adjustment, careful heater setting and corrections in data analysis. The tunable filter contains air bubbles which degrade the data quality significantly. Schemes for tuning the filter without disturbing the bubbles have been developed and tested, and some useful procedures to obtain Dopplergram and magnetogram are now available. October and March when the orbit of satellite becomes nearly perpendicular to the direction towards the sun provide a favorable condition for continuous runs of the narrow-band filter imager.
The spectrum of the gravitational wave background originating from quantum fluctuations during inflation is calculated numerically for various inflation models over a wide range of frequencies. We take into account three ingredients : the scalar field dynamics during inflation making no use of the slow-roll approximation, the fermionic decay of the scalar field with a small coupling constant during the reheating process, and the change of the effective number of degree of freedom g_* in the radiation-dominated era. By numerically solving for the evolution of gravitational waves during and after inflation up to the present, all of these effects can be examined comprehensively over a broad spectrum, even at very high frequencies. We find that the spectrum shows (i) a large deviation from the slow-roll approximation, (ii) a characteristic frequency dependence due to the reheating effect, and (iii) a damping due to the g_* changes. The slow-roll approximation overestimates the amplitude of the spectrum at frequencies beyond 10^{-5}Hz even if the change of g_* is taken into account.
Aims: From observations of the K4III star Beta UMi we attempt to determine
whether oscillations or any other form of variability is present.
Methods: A high-quality photometric time series of approximately 1000 days in
length obtained from the SMEI instrument on the Coriolis satellite is analysed.
Various statistical tests were performed to determine the significance of
features seen in the power density spectrum of the light curve.
Results: Two oscillations with frequencies 2.44 and 2.92 microhertz have been
identified. We interpret these oscillations as consecutive overtones of an
acoustic spectrum, implying a large frequency spacing of 0.48 microhertz. Using
derived asteroseismic parameters in combination with known astrophysical
parameters, we estimate the mass of Beta UMi to be 1.3 +/- 0.3 solar masses.
Peaks of the oscillations in the power density spectrum show width, implying
that modes are stochastically excited and damped by convection. The mode
lifetime is estimated at 18 +/- 9 days.
Recently, De Pontieu et al. (2007b) discovered a class of spicules that evolves more rapidly than previously known spicules, with rapid apparent motions of 50--150 km s${}^{-1}$, thickness of a few 100 km, and lifetimes of order 10--60 seconds. These so-called type II spicules have been difficult to study because of limited spatio-temporal and thermal resolution. Here we use the IBIS instrument to search for the high velocities in the disk counterpart of type II spicules. We have detected rapidly evolving events, with lifetimes that are less than a minute and often equal to the cadence of the instrument (19 secs). These events are characterized by a Doppler shift that only appears in the blue wing of the Ca II IR line. Furthermore the spatial extent, lifetime, and location near network, all suggest a link to type II spicules. However, the magnitude of the measured Doppler velocity is significantly lower than the apparent motions seen at the limb. We use Monte Carlo simulations to show that this discrepancy can be explained by a forward model in which the visibility on the disk of the high-velocity flows in these events is limited by a combination of line-of-sight projection and reduced opacity in upward propelled plasma, especially in reconnection driven jets that are powered by a roughly constant energy supply.
We give a concise, self-contained introduction to perturbation theory in cosmology at linear and second order, striking a balance between mathematical rigour and usability. In particular we discuss gauge issues and the active and passive approach to calculating gauge transformations. We also construct gauge-invariant variables, including the second order tensor perturbation on uniform curvature hypersurfaces.
We investigate the generation of gravitational waves in power-law inflationary models. The energy spectrum of the gravitational waves is calculated using the method of continuous Bogoliubov coefficients. We show that, by looking at the interval of frequencies between 10^(-5) and 10^5 Hz and also at the GHz range, important information can be obtained, both about the inflationary period itself and about the thermalization regime between the end of inflation and the beginning of the radiation-dominated era. We thus deem the development of gravitational wave detectors, covering the MHz/GHz range of frequencies, to be an important task for the future.
For the first time high-resolution optical spectroscopy of the variable star V2324Cyg associated with the IR-source IRAS20572+4919 is made. More than 200 absorption features (mostly FeII, TiII, CrII, YII, BaII, and YII) are identified within the wavelength interval 4549-7880AA. The spectral type and rotation velocity of the star are found to be F0III and Vsini=69km/s, respectively. HI and NaID lines have complex PCyg-type profiles with an emission component. Neither systematic trend of radial velocity Vr with line depth Ro nor temporal variability of Vr have been found. We determined the average heliocentric radial velocity Vr=-16.8\pm 0.6km/s. The radial velocities inferred from the cores of the absorption components of the H$\beta$ and NaI wind lines vary from -140 to -225km/s (and the expansion velocities of the corresponding layers, from about 120 to 210km/s). The maximum expansion velocity is found for the blue component of the split H$\alpha$ absorption: 450km/s for December 12, 1995. The model atmospheres method is used to determine the star's parameters: Teff=7500K, log g=2.0, $\xi_t$=6.0km/s, and metallicity, which is equal to the solar value. The main peculiarity of the chemical abundances pattern is the overabundance of lithium and sodium. The results cast some doubt on the classification of V2324Cyg as a post-AGB star.
Explanations to the accelerated expansion of the Universe are usually sought either in modifications of Einstein gravity or in new forms of energy density. An example of modified gravity is the braneworld Dvali-Gabadadze-Porrati (DGP) model which is characterized by a length scale which marks the cross-over between physics occurring in our four-dimensional brane and in a five-dimensional bulk space. An example of dark energy is Chaplygin gas which has similar asymptotic properties at early and late cosmic times. Since Chaplygin gas gives too much acceleration we combine it with the self-decelerating branch of the DGP model, taking the cross-over scales to be proportional. This 3-parameter model fits supernovae data with a goodness-of-fit equalling that of the LambdaCDM model. In contrast to generalized DGP models and Chaplygin gas models, this model is unique in the sense that it does not reduce to LambdaCDM for any choice of parameters.
The high energy resolution and low background, particularly in the hard X-ray band, of the X-ray Imaging Spectrometer onboard Suzaku provide excellent spectra of the Galactic center diffuse X-rays (GCDX). This paper reports on the results of spatially resolved spectroscopy of GCDX. The most pronounced features of GCDX are the K-shell transition lines from neutral (FeI) and He-like (FeXXV) irons at energies of 6.4keV and 6.7keV, respectively. The fluxes of these lines are non-uniformly and asymmetrically distributed with respect to Sgr A*. The 6.4keV lines are particularly bright on the positive side of the Galactic longitude (east-side) with clumpy structures. A bright clump near the GC exhibits a time variability over a timescale of a few years. Neither the 6.4keV nor 6.7keV line flux shows close proportionality to the continuum flux (5--10keV band); the 6.4keV line shows excess on the high flux side, and vice versa for the 6.7keV line. On the other hand, the sum of the 6.4keV plus 6.7keV line fluxes with a ratio of 1:2 shows good proportionality to the continuum flux, and hence we phenomenologically decomposed the continuum flux of the GCDX into the 6.4keV- and 6.7keV-associated continuums with a flux ratio of 1:2. Based on these facts, we have tried to estimate the contribution of diffuse and integrated flux of point sources to the GCDX.
The recurrent nova RS Oph undergoes nova eruptions every ~ 10-20years as a result of thermonuclear runaway on the surface of a white dwarf close to the Chandrasekhar limit. Both the progress of the eruption, and its aftermath, depend on the (poorly known) composition of the red giant in the RS Oph system. Our aim is to understand better the effect of the giant secondary on the recurrent nova eruption. Synthetic spectra were computed for a grid of M-giant model atmospheres having a range of effective temperatures 3200 < Teff < 4400 K, gravities 0 < log g < 1 and abundances -4 <[Fe/H] < 0.5, and fit to infrared spectra of RS Oph as it returned to quiescence after its 2006 eruption. We have modelled the infrared spectrum in the range 1.4-2.5 micron to determine metallicity and effective temperature of the red giant. We find Teff = 4100 +/- 100 K, log g = 0.0 +/- 0.5, [Fe/H] = 0.0 +/- 0.5, [C/H] = -0.8 +/- 0.2, [N/H] = +0.6 +/- 0.3 in the atmosphere of the secondary, and demonstrate that that inclusion of some dust `veiling' in the spectra cannot improve our fits.
We present a novel technique to measure $\sigma_8$, by measuring the dependence of the second-order bias of a density field on $\sigma_8$ using two separate techniques. Each technique employs area-averaged angular correlation functions ($\bar{\omega}_N$), one relying on the shape of $\bar{\omega}_2$, the other relying on the amplitude of $s_3$ ($s_3 =\bar{\omega}_3/\bar{\omega}_2^2$). We confirm the validity of the method by testing it on a mock catalog drawn from Millennium Simulation data and finding $\sigma_8^{measured}- \sigma_8^{true} = -0.002 \pm 0.062$. We create a catalog of photometrically selected LRGs from SDSS DR5 and separate it into three distinct data sets by photometric redshift, with median redshifts of 0.47, 0.53, and 0.61. Measurements of $c_2$, and $\sigma_8$ are made for each data set, assuming flat geometry and WMAP3 best-fit priors on $\Omega_m$, $h$, and $\Gamma$. We find, with increasing redshfit, $c_2 = 0.09 \pm 0.04$, $0.09 \pm 0.05$, and $0.09 \pm 0.03$ and $\sigma_8 = 0.78 \pm 0.08$, $0.80 \pm 0.09$, and $0.80 \pm 0.09$. We combine these three consistent $\sigma_8$ measurements to produce the result $\sigma_8 = 0.79 \pm 0.05$. Allowing the parameters $\Omega_m$, $h$, and $\Gamma$ to vary within their WMAP3 1$\sigma$ error, we find that the best-fit $\sigma_8$ does not change by more than 8% and we are thus confident our measurement is accurate to within 10%. We anticipate that future surveys, such as Pan-STARRS, DES, and LSST, will be able to employ this method to measure $\sigma_8$ to great precision, and will serve as an important check, complementary, on the values determined via more established methods.
We have obtained deep infrared $J$ and $K$ band observations of five fields located in the Large Magellanic Cloud (LMC) bar with the ESO New Technology Telescope equipped with the SOFI infrared camera. In our fields, 65 RR Lyrae stars catalogued by the OGLE collaboration were identified. Using different theoretical and empirical calibrations of the period-luminosity-metallicity relation, we find consistent LMC distance moduli values. Since the observed fields are situated very close to the center of the LMC, the correction for the tilt of the LMC bar with respect to the line of sight is negligible. Our adopted best true distance modulus to the LMC of $18.58 \pm 0.03$ (statistical) $\pm$ 0.11 (systematic) mag agrees very well with most independent determinations to this galaxy.
In a previous paper we suggested that, for a given p mode, the excitation function is the same as the component of the solar background noise that has an identical surface spherical harmonic projection (over the corresponding range of temporal frequency). An important consequence of this surmise is that the excitation of overtones of a given angular degree and azimuthal order will be correlated in time. In this note, we introduce the basic principles and a mathematical description of correlated mode excitation. We use simple, illustrative examples, involving two modes. Our treatment suggests that in the real observations, any signatures of the correlation would not appear as a correlation of the output amplitudes of overtones, but rather as subtle modifications to the power spectral density at frequencies between the central frequencies of the overtones. These modifications give a contribution to the observed peak asymmetries.
We consider the effect of a supernova (SN) explosion in a very massive binary that is expected to form in a portion of Population III stars with the mass higher than 100$M_\odot$. In a Population III binary system, a more massive star can result in the formation of a BH and a surrounding accretion disc. Such BH accretion could be a significant source of the cosmic reionization in the early universe. However, a less massive companion star evolves belatedly and eventually undergoes a SN explosion, so that the accretion disc around a BH might be blown off in a lifetime of companion star. In this paper, we explore the dynamical impact of a SN explosion on an accretion disc around a massive BH, and elucidate whether the BH accretion disc is totally demolished or not. For the purpose, we perform three-dimensional hydrodynamic simulations of a very massive binary system, where we assume a BH of $10^3 M_{\odot}$ that results from a direct collapse of a very massive star and a companion star of $100 M_{\odot}$ that undergoes a SN explosion. We calculate the remaining mass of a BH accretion disc as a function of time. As a result, it is found that a significant portion of gas disc can survive through three-dimensional geometrical effects even after the SN explosion of a companion star. Even if the SN explosion energy is higher by two orders of magnitude than the binding energy of gas disc, about a half of disc can be left over. The results imply that the Population III BH accretion disc can be a long-lived luminous source, and therefore could be an important ionizing source in the early universe.
Recent results from the Planetary Nebula Spectrograph (PN.S) survey have revealed a rapidly falling velocity dispersion profile in the nearby elliptical galaxy NGC 3379, casting doubts on whether this intermediate-luminosity galaxy has the kind of dark matter halo expected in LambdaCDM cosmology. We present a detailed dynamical study of this galaxy, combining long-slit spectroscopy, SAURON integral-field data, and PN.S velocities, reaching to more than seven effective radii (R_e). We construct spherical and axisymmetric dynamical models for these data with the flexible made-to-measure NMAGIC code, in a sequence of gravitational potentials with varying dark halo mass. We find that the data are consistent both with near-isotropic spherical systems dominated by the stellar mass, and with models in massive halos with strongly radially anisotropic outer parts (beta >~ 0.8 at 7R_e). Formal likelihood limits would exclude (at 1 sigma) the model with stars only, as well as halo models with v_circ(7R_e) >~ 250 km/s. A sequence of more realistic axisymmetric models of different inclinations and a small number of triaxial tests confirm the spherical results. All valid models fitting all the data are dynamically stable over Gyrs, including the most anisotropic ones. NGC 3379 may well have a dark matter halo as predicted by recent merger models within LambdaCDM cosmology, provided its outer envelope is strongly radially anisotropic. (abridged)
We present elemental abundances of 118 stars (28 of which are known extrasolar planetary host stars) observed as part of the Anglo-Australian Planet Search. Abundances of O, Mg, Cr, Y, Zr, Ba, Nd and Eu (along with previously published abundances for C and Si) are presented. This study is one of the first to specifically examine planetary host stars for the heavy elements produced by neutron capture reactions. We find that the host stars are chemically different to both the standard solar abundance and non-host stars in all elements studied, with enrichments over non-host stars ranging from 0.06 dex (for O) to 0.11 dex (for Cr and Y). Such abundance trends are in agreement with other previous studies of field stars and lead us to conclude that the chemical anomalies observed in planetary host stars are the result of normal galactic chemical evolution processes. Based on this observation, we conclude that the observed chemical traits of planetary host stars are primordial in origin, coming from the original nebula and not from a ``pollution'' process occurring during or after formation and that planet formation occurs naturally with the evolution of stellar material.
We present detailed numerical simulations of NGC 1433, an intermediate-type barred spiral showing strong morphological features including a secondary bar, nuclear ring, inner ring, outer pseudoring, and two striking, detached spiral arcs known as ``plumes.'' This galaxy is an ideal candidate for recreating the observed morphology through dynamical models and determining the pattern speed. We derived a gravitational potential from an $H$-band image of the galaxy and simulated the behavior of a two-dimensional disk of 100,000 inelastically colliding gas particles. We find that the closest matching morphology between a $B$-band image and a simulation occurs with a pattern speed of 0.89 km s$^{-1}$ arcsec$^{-1}$ $\pm$ 5-10%. We also determine that the ratio of corotation radius to the average published bar radius is 1.7 $\pm$ 0.3, with the ambiguity in the bar radius being the largest contributor to the error.
We have observed a small sample of powerful double radio sources (radio galaxies and quasars) at frequencies around 90 GHz with the BIMA millimetre array, with the intention of constraining the resolved high-frequency spectra of radio galaxies. When combined with other sources we have previously observed and with data from the BIMA archive, these observations allow us for the first time to make general statements about the high-frequency behaviour of compact components of radio galaxies -- cores, jets and hotspots. We find that cores in our sample remain flat-spectrum up to 90 GHz; jets in some of our targets are detected at 90 GHz for the first time in our new observations; and hotspots are found to be almost universal, but show a wide range of spectral properties. Emission from the extended lobes of radio galaxies is detected in a few cases and shows rough consistency with the expectations from standard spectral ageing models, though our ability to probe this in detail is limited by the sensitivity of BIMA. We briefly discuss the prospects for radio-galaxy astrophysics with ALMA.
Using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, we have obtained deep far-ultraviolet images of the compact elliptical galaxy M32. When combined with earlier near-ultraviolet images of the same field, these data enable the construction of an ultraviolet color-magnitude diagram of the hot horizontal branch (HB) population and other hot stars in late phases of stellar evolution. We find few post-asymptotic giant branch (PAGB) stars in the galaxy, implying that these stars either cross the HR diagram more rapidly than expected, and/or that they spend a significant fraction of their time enshrouded in circumstellar material. The predicted luminosity gap between the hot HB and its AGB-Manque (AGBM) progeny is less pronounced than expected, especially when compared to evolutionary tracks with enhanced helium abundances, implying that the presence of hot HB stars in this metal-rich population is not due to (Delta Y)/(Delta Z) > 4. Only a small fraction (~2%) of the HB population is hot enough to produce significant UV emission, yet most of the UV emission in this galaxy comes from the hot HB and AGBM stars, implying that PAGB stars are not a significant source of UV emission even in those elliptical galaxies with a weak UV excess.
The detection of significant concentrations of crystalline silicates in comets indicates an extensive radial mixing in the primordial solar nebula. In studying the radial transport of matter within protoplanetary disks by numerical model calculations it is essential to resolve the vertical disk structure since matter is mixed radially inward and outward by a complex 2-dimensional flow pattern that is superposed on the global inward directed accretion flow. A numerical model calculation for a protoplanetary accretion disks with radial and vertical mixing is performed in the 1+1-dimensional approximation. The global 2D velocity field of the disk is calculated from an analytical solution for the meridional flow pattern, that exhibits an inward drift in the upper layers and an outward drift in the midplane in most parts of the disk. The disk model is based on the $\beta$-prescription of viscosity and considers vertical self-gravitation of the disk. The mixing processes are studied for the following species: amorphous silicate grains (forsterite, enstatite) that crystallise by annealing, and carbonaceous grains that are destroyed by surface reactions with OH molecules at elevated temperatures. Considerable fractions of crystallised silicates and methane (formed as a by-product of carbon combustion) are transported to the site of comet formation far from the protosun within a period of 10$^6$ yrs. The 2-dimensional transport of tracers in the solar nebula offers a natural explanation for the presence of crystalline silicates in comets and the significant portions of crystalline silicates observed in accretion disks around young stellar objects.
We describe a new method to estimate the mass of black holes in Ultraluminous X-ray Sources (ULXs). The method is based on the recently discovered ``variability plane'', populated by Galactic stellar-mass black-hole candidates (BHCs) and supermassive active galactic nuclei (AGNs), in the parameter space defined by the black-hole mass, accretion rate and characteristic frequency. We apply this method to the two ULXs from which low-frequency quasi-periodic oscillations have been discovered, M82 X-1 and NGC 5408 X-1. For both sources we obtain a black-hole mass in the range 100~1300 Msun, thus providing evidence for these two sources to host an intermediate-mass black hole.
Nonlinear ideal magnetohydrodynamic (MHD) simulations of the propagation and expansion of a magnetic "bubble" plasma into a lower density, weakly-magnetized background plasma are presented. These simulations mimic the geometry and parameters of the Plasma Bubble Expansion Experiment (PBEX) [A. G. Lynn, Y. Zhang, S. C. Hsu, H. Li, W. Liu, M. Gilmore, and C. Watts, Bull. Amer. Phys. Soc. {\bf 52}, 53 (2007)], which is studying magnetic bubble expansion as a model for extra-galactic radio lobes. The simulations predict several key features of the bubble evolution. First, the direction of bubble expansion depends on the ratio of the bubble toroidal to poloidal magnetic field, with a higher ratio leading to expansion predominantly in the direction of propagation and a lower ratio leading to expansion predominantly normal to the direction of propagation. Second, an MHD shock and a trailing slow-mode compressible MHD wavefront are formed ahead of the bubble as it propagates into the background plasma. Third, the bubble expansion and propagation develop asymmetries about its propagation axis due to reconnection facilitated by numerical resistivity and to inhomogeneous angular momentum transport mainly due to the background magnetic field. These results will help guide the initial experiments and diagnostic measurements on PBEX.
The high- and low-frequency descriptions of the pre-decoupling plasma are deduced from the Vlasov-Landau treatment generalized to curved space-times and in the presence of the relativistic fluctuations of the geometry. It is demonstrated that the interplay between one-fluid and two-fluid treatments is mandatory for a complete and reliable calculation of the polarization observables. The Einstein-Boltzmann hierarchy is generalized to handle the dispersive propagation of the electromagnetic disturbances in the pre-decoupling plasma. Given the improved physical and numerical framework, the polarization observables are computed within the magnetized $\Lambda$CDM paradigm (m$\Lambda$CDM). In particular, the Faraday-induced B-mode is consistently estimated by taking into account the effects of the magnetic fields on the initial conditions of the Boltzmann hierarchy, on the dynamical equations and on the dispersion relations. The complete calculations of the angular power spectra constitutes the first step for the derivation of magnetized maps of the CMB temperature and polarization which are here obtained for the first time and within the minimal m$\Lambda$CDM model. The obtained results set the ground for direct experimental scrutiny of large-scale magnetism via the low and high frequency instruments of the Planck explorer satellite.
We present self-consistent models of gas in optically-thick dusty disks and calculate its thermal, density and chemical structure. The models focus on an accurate treatment of the upper layers where line emission originates, and at radii $\gtrsim 0.7$ AU. We present results of disks around $\sim 1{\rm M}_{\odot}$ stars where we have varied dust properties, X-ray luminosities and UV luminosities. We separately treat gas and dust thermal balance, and calculate line luminosities at infrared and sub-millimeter wavelengths from all transitions originating in the predominantly neutral gas that lies below the ionized surface of the disk. We find that the [ArII] 7$\mu$m, [NeII] 12.8$\mu$m, [FeI] 24$\mu$m, [SI] 25$\mu$m, [FeII] 26$\mu$m, [SiII] 35 $\mu$m, [OI] 63$\mu$m and pure rotational lines of H$_2$, H$_2$O and CO can be quite strong and are good indicators of the presence and distribution of gas in disks. We apply our models to the disk around the nearby young star, TW Hya, and find good agreement between our model calculations and observations. We also predict strong emission lines from the TW Hya disk that are likely to be detected by future facilities. A comparison of CO observations with our models suggests that the gas disk around TW Hya may be truncated to $\sim 120 $ AU, compared to its dust disk of 174 AU. We speculate that photoevaporation due to the strong stellar FUV field from TW Hya is responsible for the gas disk truncation.
We present the results of detailed spatial and spectral analysis of the pulsar wind nebula (PWN) in supernova remnant Kes 75 (G29.7-0.3) using a deep exposure with Chandra X-ray observatory. The PWN shows a complex morphology with clear axisymmetric structure. We identified a one-sided jet and two bright clumps aligned with the overall nebular elongation, and an arc-like feature perpendicular to the jet direction. Further spatial modeling with a torus and jet model indicates a position angle $207\arcdeg\pm8 \arcdeg$ for the PWN symmetry axis. We interpret the arc as an equatorial torus or wisp and the clumps could be shock interaction between the jets and the surrounding medium. The lack of any observable counter jet implies a flow velocity larger than 0.4c. Comparing to an archival observation 6 years earlier, some small-scale features in the PWN demonstrate strong variability: the flux of the inner jet doubles and the peak of the northern clump broadens and shifts 2" outward. In addition, the pulsar flux increases by 6 times, showing substantial spectral softening from $\Gamma$=1.1 to 1.9 and an emerging thermal component which was not observed in the first epoch. The changes in the pulsar spectrum are likely related to the magnetar-like bursts of the pulsar that occurred 7 days before the Chandra observation, as recently reported from RXTE observations.
We perform a general analysis on the possibility of obtaining metastable vacua with spontaneously broken N=1 supersymmetry and non-negative cosmological constant in the moduli sector of string models. More specifically, we study the condition under which the scalar partners of the Goldstino are non-tachyonic, which depends only on the Kahler potential. This condition is not only necessary but also sufficient, in the sense that all of the other scalar fields can be given arbitrarily large positive square masses if the superpotential is suitably tuned. We consider both heterotic and orientifold string compactifications in the large-volume limit and show that the no-scale property shared by these models severely restricts the allowed values for the `sGoldstino' masses in the superpotential parameter space. We find that a positive mass term may be achieved only for certain types of compactifications and specific Goldstino directions. Additionally, we show how subleading corrections to the Kahler potential which break the no-scale property may allow to lift these masses.
We study the full history of the universe in the presence of inflaton, matter, radiation, and holographic dark energy. The time evolution of the scale factor is obtained by solving the Friedmann equation of the universe without artificial ansatz. We discuss that the second law of thermodynamics dictates the accelerating expansion of the dark energy dominant phase to the universe. In addition, we show that a dimensionless combination of three scale factors at the equipartition times of matter-radiation, radiation-dark energy, and matter-dark energy provides a universal constant which depends only on the dark energy constant $d$.
For a uniform population of neutron stars whose spin-down is dominated by the emission of gravitational radiation, an argument by Blandford states that the expected gravitational wave amplitude of the nearest source is independent of the deformation and rotation frequency of the objects. Recent work has improved and extended this argument to set upper limits on the expected amplitude from neutron stars which also emit electromagnetic radiation. We restate these argments in a more general framework, and simulate the evolution of such a population of stars in the gravitational potential of our Galaxy. The simulations allow us to test the assumptions of Blandford's argument on a realistic model of our Galaxy. We show that the two key assumptions of the argument (two-dimensionality of the spatial distribution and a steady-state frequency distribution) are in general not fulfilled. The effective scaling dimension of the spatial distribution of neutron stars is significantly larger than two, and for frequencies detectable by terrestrial instruments the frequency distribution is not in a steady state unless the ellipticity is unrealistically large. Thus, in the cases of most interest, the maximum expected gravitational wave amplitude does have a strong dependence on the deformation and rotation frequency of the population. The results strengthen the previous upper limits on the expected gravitational wave amplitude from neutron stars.
Links to: arXiv, form interface, find, astro-ph, recent, 0804, contact, help (Access key information)
In this work we explore the effect of choosing flat priors on different parameterizations on the estimation of the tensor-to-scalar ratio and other parameters describing inflation. We show that a flat prior on the scale of inflation does not correspond to a flat prior on the tensor-to-scalar ratio, and that current data is not strong enough to render parameter estimation parameterization independent. Most importantly, we show that a flat prior on the scale of inflation raises the predicted tensor contribution, leading to a mild, yet non-zero 68 % c.l. lower bound on tensor perturbations from existing data. Which prior to choose remains for the moment a matter of taste. However this work provides more reason for optimism with respect to the possibility of future detection of primordial gravitational waves.
We present the results of a survey for trans-neptunian objects (TNOs) based on Subaru archival images, originally collected by Sheppard et al. (2005) as part of a search for irregular satellites of Uranus. The survey region covers 2.8 deg^2, centered on Uranus and observed near opposition on two adjacent nights. Our survey reaches half its maximum detection efficiency at R=25.69$\pm$0.01. The objects detected correspond to 82 TNOs, five Centaurs, and five irregular satellites. We model the cumulative number of TNOs brighter than a given apparent magnitude with both a single and double power law. The best fit single power law, with one object per square degree at magnitude $R_0 =22.6_{-0.4}^{+0.3}$ and a slope of $\alpha = 0.51_{-0.6}^{+0.5}$, is inconsistent with the results of similar searches with shallower limiting magnitudes. The best fit double power law, with a bright-end slope $\alpha_1 = 0.7_{-0.1}^{+0.2}$, a faint-end slope $\alpha_2=0.3_{-0.2}^{+0.2}$, a differential number density at R=23, $\sigma_{23} = 2.0_{-0.5}^{+0.5}$ and a magnitude break in the slope at $R_{eq} = 24.3_{-0.1}^{+0.8}$, is more likely than the single power law by a Bayes factor of ~26. This is the first survey with sufficient depth and areal coverage to identify the magnitude at which the break occurs without relying on the results of other surveys. ...
We study the cosmological evolution of the fine structure constant, $\alpha$, and the proton-to-electron mass ratio, $\mu=m_p/m_e$, in the context of a generic class of models where the gauge kinetic function is a linear function of a quintessence-type real scalar field, $\phi$, described by a Lagrangian with a standard kinetic term and a scalar field potential, $V(\phi)$. We further assume that the scalar field potential is a monotonic function of $\phi$ and that the scalar field is always rolling down the potential. We show that, for this class of models, low-redshift constrains on the evolution of $\alpha$ and $\mu$ can provide very stringent limits on the corresponding variations at high-redshift. We also demonstrate that these limits may be relaxed by considering more general models for the dynamics of $\alpha$ and $\mu$. However, in this case, the ability to reconstruct the evolution of the dark energy equation of state using varying couplings could be seriously compromised.
We present a summary of the conference "The Cosmic Agitator: Magnetic Fields in the Galaxy" held in Lexington KY in 2008 Mar 26-29. The presentation draws primarily from material in the slides prepared for the Conference Summary by one of us (Carl Heiles). Interested readers may navigate to the conference web site given in the paper to view the posted presentations in detail.
To investigate further the comparison between AGN and black hole X-ray binaries, we have studied the main X-ray variability properties of the Seyfert 1 Galaxy Markarian 335. We put particular emphasis on the X-ray time lags, which is a potentially important diagnostic of physical models. From a 100 ksec observation by XMM-Newton we show that the power spectrum of this source is well fitted by a bending power law model, and the bend time-scale Tb is precisely at the value predicted by the Tb vs Hbeta line-width relation of McHardy et al. Variations in different energy bands show time-scale dependent time lags, where higher energy bands lag lower ones. The lag, tau, varies as a function of the Fourier frequency, f, of the variability component in the light curves as tau propto 1/f at low frequencies, but there is a sharp cut-off in the lags at a frequency close to the bend frequency in the power spectrum. Similar behaviour is seen in black hole X-ray binary systems. The length of the time lags increases continuously with energy separation, in an almost log-linear relation. We show that the lag spectra can be produced by fluctuations propagating through the accretion flow as long as the energy spectrum of the X-ray emitting region hardens towards the centre.
Here, we present near-infrared spectroscopic observations of 15 helium atmosphere, metal-rich white dwarfs obtained at the NASA Infrared Telescope Facility. While a connection has been demonstrated between the most highly polluted, hydrogen atmosphere white dwarfs and the presence of warm circumstellar dust and gas, their frequency at the helium atmosphere variety is poorly constrained. None of our targets show excess near-infrared radiation consistent with warm orbiting material. Adding these near-infrared constraints to previous near- and mid-infrared observations, the frequency of warm circumstellar material at metal-bearing white dwarfs is at least 20% for hydrogen-dominated photospheres, but could be less than 5% for those effectively composed of helium alone. The lower occurrence of dust disks around helium atmosphere white dwarfs is consistent with Myr timescales for photospheric metals in massive convection zones. Analyzing the mass distribution of 10 white dwarfs with warm circumstellar material, we search for similar trends between the frequency of disks and the predicted frequency of massive planets around intermediate mass stars, but find the probability that disk-bearing white dwarfs are more massive than average is not significant.
I consider the physics of gravitational instabilities in the presence of dynamically important radiation pressure and gray radiative diffusion, governed by a constant opacity, kappa. For any non-zero radiation diffusion rate on an optically-thick scale, the medium is unstable unless the classical gas-only isothermal Jeans criterion is satisfied. When diffusion is "slow," although the dynamical Jeans instability is stabilized by radiation pressure on scales smaller than the adiabatic Jeans length, on these same spatial scales the medium is unstable to a diffusive mode. In this regime, neglecting gas pressure, the characteristic timescale for growth is independent of spatial scale and given by (3 kappa c_s^2)/(4 pi G c), where c_s is the adiabatic sound speed. This timescale is that required for a fluid parcel to radiate away its thermal energy content at the Eddington limit, the Kelvin-Helmholz timescale for a radiation pressure supported self-gravitating object. In the limit of "rapid" diffusion, radiation does nothing to suppress the Jeans instability and the medium is dynamically unstable unless the gas-only Jeans criterion is satisfied. I connect with treatments of Silk damping in the early universe. I discuss several applications, including photons diffusing in regions of extreme star formation (starburst galaxies & pc-scale AGN disks), and the diffusion of cosmic rays in normal galaxies and galaxy clusters. The former (particularly, starbursts) are "rapidly" diffusing and thus cannot be supported against dynamical instability in the linear regime by radiation pressure alone. The latter are more nearly "slowly" diffusing. I speculate that the turbulence in starbursts may be driven by the dynamical coupling between the radiation field and the self-gravitating gas, perhaps mediated by magnetic fields. (Abridged)
We investigate the crystallization rate of a one-component plasma (OCP) in the context of classical nucleation theory. From our derivation of the free energy of an arbitrary distribution of solid clusters embedded in a liquid phase, we derive the steady-state nucleation rate of an OCP as a function of the Coulomb coupling parameter. Our result for the rate is in accord with recent molecular dynamics simulations, but it is greater than that of previous analytical estimates by many orders of magnitude. Further molecular dynamics simulations of the nucleation rate of a supercooled liquid OCP for several values of the coupling parameter would clarify the physics of this process.
Using the ISOPHOT Serendipity Survey (ISOSS) at 170um a sample of galactic star-forming regions exhibiting very cold dust temperatures (< 20 K) and high masses (> 100 M_sun) has been established. We characterise the star-forming content of five regions that were selected as potential sites for early stage high-mass star formation using SCUBA (JCMT) and Spitzer observations. In every region we identify one to four submillimeter clumps with projected sizes between 0.1 and 0.4 pc. The dust temperatures range from 11.6 to 21.3 K and the estimated clump masses are 2 to 166 M_sun. Towards the majority of submillimeter peaks we find point sources in the near- to mid-infrared. Most are interpreted as low-mass young stellar objects but we also detect very red sources. They probably represent very young and deeply embedded protostars that continue to accrete clump material and may reach higher masses. Several candidate intermediate-mass proto- or pre-main-sequence stars embedded in the clumps are identified. A subset of four clumps may be massive enough (> 100 M_sun) to form high-mass stars and accompanying clusters. The absence of stellar precursors with current masses in the high-mass regime leave the type of star formation occuring in the clumps unsettled. We confirm the presence of large fractions of cold material as derived from large-scale far-infrared measurements which dominates the emission of most clumps and suggests that the star-forming process will continue.
We apply machine learning in the form of a nearest neighbor instance-based algorithm (NN) to generate full photometric redshift probability density functions (PDFs) for objects in the Fifth Data Release of the Sloan Digital Sky Survey (SDSS DR5). We use a conceptually simple but novel application of NN to generate the PDFs - perturbing the object colors by their measurement error - and using the resulting instances of nearest neighbor distributions to generate numerous individual redshifts. When the redshifts are compared to existing SDSS spectroscopic data, we find that the mean value of each PDF has a dispersion between the photometric and spectroscopic redshift consistent with other machine learning techniques, being sigma = 0.0207 +/- 0.0001 for main sample galaxies to r < 17.77 mag, sigma = 0.0243 +/- 0.0002 for luminous red galaxies to r < ~19.2 mag, and sigma = 0.343 +/- 0.005 for quasars to i < 20.3 mag. The PDFs allow the selection of subsets with improved statistics. For quasars, the improvement is dramatic: for those with a single peak in their probability distribution, the dispersion is reduced from 0.343 to sigma = 0.117 +/- 0.010, and the photometric redshift is within 0.3 of the spectroscopic redshift for 99.3 +/- 0.1% of the objects. Thus, for this optical quasar sample, we can virtually eliminate 'catastrophic' photometric redshift estimates. In addition to the SDSS sample, we incorporate ultraviolet photometry from the Third Data Release of the Galaxy Evolution Explorer All-Sky Imaging Survey (GALEX AIS GR3) to create PDFs for objects seen in both surveys. For quasars, the increased coverage of the observed frame UV of the SED results in significant improvement over the full SDSS sample, with sigma = 0.234 +/- 0.010. We demonstrate that this improvement is genuine. [Abridged]
We present recent results from the LCDM (Laboratory for Cosmological Data Mining; this http URL) collaboration between UIUC Astronomy and NCSA to deploy supercomputing cluster resources and machine learning algorithms for the mining of terascale astronomical datasets. This is a novel application in the field of astronomy, because we are using such resources for data mining, and not just performing simulations. Via a modified implementation of the NCSA cyberenvironment Data-to-Knowledge, we are able to provide improved classifications for over 100 million stars and galaxies in the Sloan Digital Sky Survey, improved distance measures, and a full exploitation of the simple but powerful k-nearest neighbor algorithm. A driving principle of this work is that our methods should be extensible from current terascale datasets to upcoming petascale datasets and beyond. We discuss issues encountered to-date, and further issues for the transition to petascale. In particular, disk I/O will become a major limiting factor unless the necessary infrastructure is implemented.
Context: We investigate the possible theoretical properties of the putative pulsar associated with the pulsar wind nebula IGR J18135-1751/HESS J1813-178 based upon recent gamma-ray observations and archival multi-wavelength observations. Aims: We show that when using the standard equations for magnetic dipole radiation with recent soft gamma-ray observations leads to deriving an extreme set of parameters (magnetic field, period and spin down rate) for the putative pulsar. Alternative scenarios that generate more typical parameter values are explored. Methods: The properties of the putative pulsar are calculated assuming that the 20-100 keV luminosity corresponds to 1% of Edot, that the source is 4.5 kpc away, and that the pulsar age is 300 yrs. This gives P = 0.55 s, Pdot = 3E-11 s/s, and B = 1.28E14 G. This is a very extreme set compared to the population of known pulsars in PWN systems. Using the equations for magnetic dipole losses makes it possible to adjust the initial assumptions to see what is required for a more reasonable set of pulsar parameters. Results: The current measured properties for IGR J18135-1751/HESS J1813-178 (i.e. luminosity, distance, and age) result in extreme properties of the unseen pulsar within the PWN. The simplest method for achieving more reasonable properties for the pulsar is to decouple the spin-down age of the pulsar from the actual age for the system.
In this letter, we briefly describe the evolution of a variety of self-gravitating protoplanetary disk models that contain annular grooves (e.g. gaps) in their surface density. These grooves are inspired by the density gaps that are presumed to open in response to the formation of a giant planet. Our work provides an extension of the previously studied groove modes that are known in the context of stellar disks. The emergence of spiral gravitational instabilities (GI) is predicted via a generalized eigenvalue code that performs a linear analysis, and confirmed with hydrodynamical simulations. We find the presence of a groove drives a fast-growing two-armed mode in moderately massive disks, and extends the importance of self-gravitating instabilities down to lower disk masses than for which they would otherwise occur. We discuss the potential importance of this instability in the context of planet formation, e.g. the modification of the torques driving Type II migration.
We have performed a timing and spectral analysis of the X-ray pulsar SWIFT J1626.6-5156 during a major X-ray outburst in order to unveil its nature and investigate its flaring activity. Epoch- and pulse-folding techniques were used to derive the spin period. Time-average and pulse-phase spectroscopy were employed to study the spectral variability in the flare and out-of-flare states and energy variations with pulse phase. Power spectra were obtained to investigate the periodic and aperiodic variability. Two large flares, with a duration of ~450 seconds were observed on 24 and 25 December 2005. During the flares, the X-ray intensity increased by a factor of 3.5, while the peak-to-peak pulsed amplitude increased from 45% to 70%. A third, smaller flare of duration ~180 s was observed on 27 December 2005. The flares seen in SWIFT J1626.6-5156 constitute the shortest events of this kind ever reported in a high-mass X-ray binary. In addition to the flaring activity, strong X-ray pulsations with Pspin=15.3714+-0.0003 s characterise the X-ray emission in SWIFT J1626.6-5156. After the major outburst, the light curve exhibits strong long-term variations modulated with a 45-day period. We relate this modulation to the orbital period of the system or to a harmonic. Power density spectra show, in addition to the harmonic components of the pulsation, strong band-limited noise with an integrated 0.01-100 Hz fractional rms of around 40% that increased to 64% during the flares. A weak QPO (fractional rms 4.7%) with characteristic frequency of 1 Hz was detected in the non-flare emission. The timing (short X-ray pulsations, long orbital period) and spectral (power-law with cut off energy and neutral iron line) properties of SWIFT J1626.6-5156 are characteristic of Be/X-ray binaries.
We investigate the sky distribution of z ~ 6 Lyman break galaxies selected as i'-dropouts having i' - z' > 1.45 down to z' < 26.5 in the Subaru Deep Field (SDF). We discover 37 i'-dropouts clustered in a projected comoving 21.6 x 21.6 Mpc^2 region at z = 6, showing a local density excess. Carrying out follow-up spectroscopy, we identify four of them as Lyman-alpha emitters at z = 5.92, 6.01, 6.03 and 6.03 (spread over a distance of 46.6 Mpc). The number density of the cluster itself in SDF is ~ 2.2 x 10^{-7} Mpc^{-3}, smaller than those of protoclusters (i.e., forming galaxy clusters) at z ~ 2-5.7. Also, the structure shows ~4-21 times larger galaxy number density than those of z ~ 6 galaxies in a general field. It has a mass of M ~ 1.5^{+1.8}_{-0.5} x 10^{15}M_sun, comparable to those of z ~ 0-5 protoclusters. Since the contamination of our sample by interlopers is estimated to be quite low, 5.9%, most of the other unconfirmed i'-dropouts in the overdense region can be also z ~ 6 galaxies. Hence, it could be a candidate forming cluster at z ~ 6, representing a progenitor of galaxy clusters seen in the recent-day Universe.
We present the number counts of Ks-band selected high redshift galaxy populations such as extremely red objects (EROs), B, z & K -band selected galaxies (BzKs) and distant red galaxies (DRGs) in the AKARI NEP field. The final catalogue contains 308 EROs (Ks<19.0 ; 54 percent are dusty star-forming EROs and the rest are passive old EROs), 137 star-forming BzKs and 38 passive old BzKs (Ks<19.0) and 64 DRGs (Ks<18.6). We also produce individual component source counts for both the dusty star-forming and passive populations. We compare the observed number counts of the high redshift passively evolving galaxy population with a backward pure luminosity evolution (PLE) model allowing different degrees of number density evolution. We find that the PLE model without density evolution fails to explain the observed counts at faint magnitudes, while the model incorporating negative density evolution is consistent with the observed counts of the passively evolving population. We also compare our observed counts of dusty star-forming EROs with a phenomenological evolutionary model postulating that the near-infrared EROs can be explained by the source densities of the far-infrared - submillimetre populations. Our model predicts that the dusty ERO source counts can be explained assuming a 25 percent contribution of submillimetre star-forming galaxies with the majority of brighter Ks -band detected dusty EROs having luminous (rather than HR10 type ultra-luminous) submillimetre counterparts. We propose that the fainter Ks>19.5 population is dominated by the sub-millijansky submillimetre population. We also predict a turnover in in dusty ERO counts around 19<Ks<20.
We report variability of the X-ray source, X-7, in NGC 6946, during a 60 ksec Chandra observation when the count rate decreased by a factor of ~1.5 in ~5000 secs. Spectral fitting of the high and low count rate segments of the light curve reveal that the simplest and most probable interpretation is that the X-ray spectra are due to disk black body emission with an absorbing hydrogen column density equal to the Galactic value of 2.1 X 10^{21} cm^{-2}. During the variation, the inner disk temperature decreased from ~0.29 to ~0.26 keV while the inner disk radius remained constant at ~6 X 10^8 cm. This translates into a luminosity variation from 3.8 to 2.8 X 10^{39} ergs cm^{-2} sec^{-1} and a black hole mass of ~400 solar masses. More complicated models like assuming intrinsic absorption and/or the addition of a power-law component imply a higher luminosity and a larger black hole mass. Even if the emission is beamed by a factor of ~5, the size of the emitting region would be > 2.7 X 10^8 cm implying a black hole mass > 180 solar masses. Thus, these spectral results provide strong evidence that the mass of the black hole in this source is definitely > 100 solar masses and more probably ~400 solar masses.
Context: Be stars are massive dwarf or subgiant stars that present temporary emission lines in their spectrum, and particularly in the Halpha line. The mechanism triggering these Be episodes is currently unknown, but binarity could play an important role. Aims: Previous observations with the VLT/VISIR instrument (Kervella & Domiciano de Souza 2007) revealed a faint companion to Achernar, the brightest Be star in the sky. The present observations are intended to characterize the physical nature of this object. Methods: We obtained near-IR images and an H-band spectrum of Achernar B using the VLT/NACO adaptive optics systems. Results: Our images clearly show the displacement of Achernar B over a portion of its orbit around Achernar A. Although these data are insuficient to derive the orbital parameters, they indicate a period of the order of 15 yr. The projected angular separation of the two objects in December 2007 was smaller than 0.15 arcsec, or 6.7 AU at the distance of Achernar. Conclusions: From its flux distribution in the near- and thermal-IR, Achernar B is most likely an A1V-A3V star. Its orbital period appears similar to the observed pseudo-periodicity of the Be phenomenon of Achernar. This indicates that an interaction between A and B at periastron could be the trigger of the Be episodes.
We present a novel method for generation of sets of the Cosmic Microwave
Background (CMB) anisotropy maps, which reproduces the $\Delta \l=2$
correlations associated with Alfv\'en turbulence. The method is based on the
non-linear transformation of the CMB maps, which is obtained from the Monte
Carlo simulation of the statistically isotropic Gaussian signal. Our method is
computationally fast and efficient.
We have applied two estimators (the cross-correlation estimator in multipole
domain for $\l+1,m$ and $\l-1,m$ modes and circular phase moments) to test the
statistical properties of derived maps. Both of these statistics confirm the
effectiveness of our generation method. We believe that our method can be
useful for fast generation of the non-Gaussian maps in the presence of the
primordial magnetic field, and be a valuable tool for the non-Gaussianity
investigation of the CMB in the framework of the future PLANCK data analysis.
The distribution of luminous radio galaxies in galaxy clusters has been observed to be concentrated in the inner region. We consider the role of dynamical friction of massive galaxies ($M\sim 10^{12.5}$ M$_{\odot}$), assuming them to be hosts of luminous radio galaxies, and show that beginning with a Navarro-Frenk-White density profile of a cluster of mass $M_{cl}\sim 10^{15}$ M$_{\odot}$ of concentration $c\sim 5$ and collapsing at $z\sim 1$, the density profile of radio galaxies evolve to a profile of concentration $c \sim 25$, as observed, in a time scale of $t\sim 3\hbox{--}5$ Gyr.
We show a text-book potential for single-field inflation, namely, the Coleman-Weinberg model can induce double inflation and formation of primordial black holes (PBHs), because fluctuations that leave the horizon near the end of first inflation are anomalously enhanced at the onset of second inflation when the time-dependent mode turns to a growing mode rather than a decaying mode. The mass of PBHs produced in this mechanism lies in several discrete ranges depending on the model parameters. We also calculate the effects of non-Gaussian statistics due to higher-order interactions on the abundance of PBHs, which turns out to be small.
We present the most accurate measurement to date of cosmological evolution of the near-infrared galaxy luminosity function, from the local Universe out to z~4. The analysis is based on a large and highly complete sample of galaxies selected from the first data release of the UKIDSS Ultra Deep Survey. Exploiting a master catalogue of K- and z-band selected galaxies over an area of 0.7 square degrees, we analyse a sample of ~50,000 galaxies, all with reliable photometry in 16-bands from the far-ultraviolet to the mid-infrared. The unique combination of large area and depth provided by the Ultra Deep Survey allows us to trace the evolution of the K-band luminosity function with unprecedented accuracy. In particular, via a maximum likelihood analysis we obtain a simple parameterization for the luminosity function and its cosmological evolution, including both luminosity and density evolution, which provides an excellent description of the data from z =0 up to z~4. We find differential evolution for galaxies dependent on galaxy luminosity, revealing once again the ``down-sizing behaviour'' of galaxy formation. Finally, we compare our results with the predictions of the latest theoretical models of galaxy formation, based both on semi-analytical prescriptions, and on full hydrodynamical simulations.
We consider sputtering of dust grains, believed to be formed in cooling supernovae ejecta, under the influence of reverse shocks. In the regime of self-similar evolution of reverse shocks, we can follow the evolution of ejecta density and temperature analytically as a function of time in different parts of the ejecta, and calculate the sputtering rate of graphite and silicate grains embedded in the ejecta as they encounter the reverse shock. Through analytic (1D) calculations, we find that a fraction of dust mass ($ 1\hbox{--}20$% for silicates and %$\le 5$% for graphites) can be sputtered by reverse shocks, the fraction varying with the grain size distribution and the steepness of the density profile of the ejecta mass. It is expected that many more grains will get sputtered in the region between the forward and reverse shocks, so that our analytical results provide a lower limit to the destroyed fraction of dust mass.
We study the implications of primordial magnetic fields for the thermal and ionization history of the post-recombination era. In particular we compute the effects of dissipation of primordial magnetic fields owing to ambipolar diffusion and decaying turbulence in the intergalactic medium (IGM) and the collapsing halos and compute the effects of the altered thermal and ionization history on the formation of molecular hydrogen. We show that, for magnetic field strengths in the range $2 \times 10^{-10} {\rm G} \la B_0 \la 2 \times 10^{-9} {\rm G}$, the molecular hydrogen fraction in IGM and collapsing halo can increase by a factor 5 to 1000 over the case with no magnetic fields. We discuss the implication of the increased molecular hydrogen fraction on the radiative transfer of UV photons and the formation of first structures in the universe.
We present deep colour-magnitude diagrams for three rich intermediate-age star clusters in the Large Magellanic Cloud, constructed from archival ACS F435W and F814W imaging. All three clusters exhibit clear evidence for peculiar main-sequence turn-offs. NGC 1846 and 1806 each possess two distinct turn-off branches, while the turn-off for NGC 1783 shows a much larger spread in colour than can be explained by the photometric uncertainties. We demonstrate that although all three clusters contain significant populations of unresolved binary stars, these cannot be the underlying cause of the observed turn-off morphologies. The simplest explanation is that each cluster is composed of at least two different stellar populations with very similar metal abundances but ages separated by up to ~300 Myr. The origin of these unusual properties remains unidentified; however, the fact that at least three massive clusters containing multiple stellar populations are now known in the LMC suggests a potentially significant formation channel.
Our aim is to investigate the intensity oscillations in coronal X-ray Bright Points (XBPs). We analysed a 7-hours long time sequence of the soft X-ray images obtained on April 14, 2007 with 2-min cadence using X-Ray Telescope (XRT) on-board the Hinode mission. We use SSW in IDL to derive the time series of 14 XBPs and 2 background regions. For the first time, we have tried to use power spectrum analysis on XBPs data to determine the periods of intensity oscillations. coronal X-ray Bright Points (XBPs). The power spectra of XBPs show several significant peaks at different frequencies corresponding to a wide variety of time scales which range from a few minutes to hours. The light curves of all the XBPs give the impression that the XBPs can be grouped into three classes depending on emission levels: (i) weak XBPs; (ii) bright XBPs; and (iii) very strong XBPs. The periods of intensity oscillation are consistent in all the XBPs and are independent of their brightness level, suggesting that the heating mechanisms in all the three groups of XBPs are similar. The different classes of XBPs may be related to the different strengths of the magnetic field with which they have been associated.
We present a study of the circumstellar environment of IRAS 04158+2805 based on multi-wavelength observations and models. Images in the optical and near-infrared, a polarisation map in the optical, and mid-infrared spectra were obtained with VLT-FORS1, CFHT-IR, and Spitzer-IRS. Additionally we used an X-ray spectrum observed with Chandra. We interpret the observations in terms of a central star surrounded by an axisymmetric circumstellar disc, but without an envelope, to test the validity of this simple geometry. We estimate the structural properties of the disc and its gas and dust content. We modelled the dust disc with a 3D continuum radiative transfer code, MCFOST, based on a Monte-Carlo method that provides synthetic scattered light images and polarisation maps, as well as spectral energy distributions. We find that the disc images and spectral energy distribution narrowly constrain many of the disc model parameters, such as a total dust mass of 1.0-1.75x10^-4 sollar masses and an inclination of 62-63 degrees. The maximum grain size required to fit all available data is of the order of 1.6-2.8 microns although the upper end of this range is loosely constrained. The observed optical polarisation map is reproduced well by the same disc model, suggesting that the geometry we find is adequate and the optical properties are representative of the visible dust content. We compare the inferred dust column density to the gas column density derived from the X-ray spectrum and find a gas-to-dust ratio along the line of sight that is consistent with the ISM value. To our knowledge, this measurement is the first to directly compare dust and gas column densities in a protoplanetary disc.
A power law cosmology is defined by the cosmological scale factor evolving as $t^{\alpha}$. In this work, we put bounds on $\alpha$ by using the joint test of the SNe Ia data from Supernova Legacy Survey (SNLS) and H(z) data with curvature constant $ k = 0, \pm 1$. We observe that the combined analysis with SNLS and H(z) data favours the open power cosmology with $\alpha = 1.31^{+0.06}_{-0.05}. It is also interesting to note that an Einstein - de Sitter model $(\alpha = 2/3)$ is ruled out at $2\sigma$ level.
Our aim is to search for atmospheric g-mode oscillations in UV network, UV bright points and Uv background regions. We have analysed a 6-hours of time sequence of ultraviolet (uv) images obtained on May 24, 2003 in 1600A continuum under high spatial and temporal resolution from Transition Region and Coronal Explorer (TRACE). We have selected an isolated 15 uv bright points, 15 uv network elements and 15 uv background regions in a quiet region from the images for the detailed analysis. We derived the cumulative intensity values of these features. The light curves of all the features have been derived for the total duration of observations and done the power spectrum analysis using the time series data. We found that the uv bright points, the uv network and uv background regions will exhibit a longer period of intensity oscillations namely, 5.5 hours, 4.6 hours and 3.4 hours respectively, in addition to the more familiar small scale intensity fluctuations. We suggest that the longer periods of oscillation may be related to solar atmospheric g-modes.
Our aim is to identify and trace the X-ray Bright Points (XBPs) over the disk and use them as tracers to determine the coronal rotation. This investigation will help to clarify and understand several issues: whether (i) the corona rotates differentially; (ii) the rotation depends on the sizes of the XBPs; and (iii) dependence on phases of the solar magnetic cycle. We analysed the daily full-disk soft X-ray images observed with (i) X-Ray Telescope (XRT) on-board the Hinode mission during January, March and April, 2007 and (ii) Soft X-ray Telescope (SXT) on-board the Yohkoh from 1992 to 2001 using SSW in IDL. We have used the tracer method to trace the passage of XBPs over the solar disk with the help of overlaying grids and derived the sidereal angular rotation velocity and the coordinates (latitude and longitude) of the XBPs. We have determined the position of a large number of XBPs both in Hinode/XRT and Yohkoh/SXT images and followed them over the solar disk as a function of time. We derived the coronal sidereal angular rotation velocity and compared it with heliocentric latitude and as a function of solar activity cycle. In addition, we measured the sizes of all the XBPs and related them with the coronal rotation. The important results derived from these investigations are: (i) the solar corona rotates differentially like the photosphere and chromosphere; (ii) the sidereal angular rotation velocity is independent of the sizes of the XBPs; (iii) the sidereal angular rotation velocity does not depend on phases of the solar magnetic cycle; and (iv) the differential rotation of the corona is present throughout the solar magnetic cycle.
Observations of very-high-energy (VHE, E > 250 GeV) gamma-ray emission from several blazars at z > 0.1 have placed stringent constraints on the elusive spectrum and intensity of the intergalactic infrared background radiation (IIBR). Correcting their observed VHE spectrum for gamma-gamma absorption even by the lowest plausible level of the IIBR provided evidence for a very hard (photon spectral index Gamma_{ph} < 2) intrinsic source spectrum out to TeV energies. Such a hard VHE gamma-ray spectrum poses a serious challenge to the conventional synchrotron-self-Compton interpretation of the VHE emission of TeV blazars and suggests the emergence of a separate emission component beyond a few hundred GeV. Here we propose that such a very hard, slowly variable VHE emission component in TeV blazars may be produced via Compton upscattering of Cosmic Microwave Background (CMB) photons by shock-accelerated electrons in an extended jet. For the case of 1ES 1101-232, this component could dominate the bolometric luminosity of the extended jet if the magnetic fields are of the order of typical intergalactic magnetic fields B ~ 10 micro-Gauss and electrons are still being accelerated out to TeV energies gamma > 4 X 10^6) on kiloparsec scales along the jet.
A model of dark matter and dark energy based on the concept of gravitational polarization is investigated. We propose an action in standard general relativity for describing, at some effective or phenomenological level, the dynamics of a dipolar medium, i.e. one endowed with a dipole moment vector, and polarizable in a gravitational field. Using first-order cosmological perturbations, we show that the dipolar fluid is undistinguishable from standard dark energy (a cosmological constant Lambda) plus standard dark matter (a pressureless perfect fluid), and therefore benefits from the successes of the Lambda-CDM scenario at cosmological scales. Invoking an argument of "weak clusterisation" of the mass distribution of dipole moments, we find that the dipolar dark matter reproduces the phenomenology of the modified Newtonian dynamics (MOND) at galactic scales. The dipolar medium action naturally contains a cosmological constant, and we show that if the model is to come from some fundamental underlying physics, the cosmological constant Lambda should be of the order of a0^2/c^4, where a0 denotes the MOND constant acceleration scale, in good agreement with observations.
NGC 4441 is a candidate for a merger between a spiral and an elliptical galaxy (S+E merger), because it shows typical tidal structures such as an optical tail and two shells. With a far-infrared luminosity of $\sim 5\cdot 10^9 L_{\odot}$ this galaxy belongs to the class of moderate luminosity mergers, in which the merging process induces (if at all) only a moderate starburst. The study of the atomic gas content allows us to investigate the merger history and the impact on the star formation. In particular, it is not clear from simulations whether an S+E merger leads to a gas concentration in the nucleus, resulting in a starburst, or whether the gas is spread out and therefore too diffuse for new star forming regions. We used the Westerbork Radio Synthesis Telescope to observe the properties of the HI. By using this interferometer, we are able to study the large-scale HI distribution and kinematics with high spatial and velocity resolution. We found two HI tails extending out to more than 40 kpc. In a central disc, the gas shows a fairly regular rotation pattern indicating that the gas started to settle after the merger. The total HI mass adds up to $1.5 \cdot 10^9 M_{\odot}$. By comparing the high resolution HI maps with deep optical images, differences between the stellar and gaseous tidal features are apparent, which indicates an S+E merger origin.
We outline a scenario which traces a direct path from freely-floating nebula particles to the first 10-100km-sized bodies in the terrestrial planet region, producing planetesimals which have properties matching those of primitive meteorite parent bodies. We call this "primary accretion". The scenario draws on elements of previous work, and introduces a new critical threshold for planetesimal formation. We presume the nebula to be weakly turbulent, which leads to dense concentrations of aerodynamically size-sorted particles having properties like those observed in chondrites. The fractional volume of the nebula occupied by these dense zones or clumps obeys a probability distribution as a function of their density, and the densest concentrations have particle mass density 100 times that of the gas. However, even these densest clumps are prevented by gas pressure from undergoing gravitational instability in the traditional sense (on a dynamical timescale). While in this state of arrested development, they are susceptible to disruption by the ram pressure of the differentially orbiting nebula gas. However, self-gravity can preserve sufficiently large and dense clumps from ram pressure disruption, allowing their entrained particles to sediment gently but inexorably towards their centers, producing 10-100 km "sandpile" planetesimals. Localized radial pressure fluctuations in the nebula, and interactions between differentially moving dense clumps, will also play a role that must be allowed for in future studies. The scenario is readily extended from meteorite parent bodies to primary accretion throughout the solar system.
This technical paper describes a software package that was designed to produce initial conditions for large cosmological simulations in the context of the Horizon collaboration. These tools generalize E. Bertschinger's Grafic1 software to distributed parallel architectures and offer a flexible alternative to the Grafic2 software for ``zoom'' initial conditions, at the price of large cumulated cpu and memory usage. The codes have been validated up to resolutions of 4096^3 and were used to generate the initial conditions of large hydrodynamical and dark matter simulations. They also provide means to generate constrained realisations for the purpose of generating initial conditions compatible with, e.g. the local group, or the SDSS catalog.
Context. Detecting regular dips in the light curve of a star is an easy way to detect the presence of an orbiting planet. COROT is a Franco-European mission launched at the end of 2006, and one of its main objectives is to detect planetary systems using the transit method. Aims. In this paper, we present a new method for transit detection and determine the smallest detected planetary radius, assuming a parent star like the Sun. Methods. We simulated light curves with Poisson noise and stellar variability, for which data from the VIRGO/PMO6 instrument on board SoHO were used. Transits were simulated using the UTM software. Light curves were denoised by the mean of a low-pass and a high-pass filter. The detection of periodic transits works on light curves folded at several trial periods with the particularity that no rebinning is performed after the folding. The best fit was obtain when all transits are overlayed, i.e when the data are folded at the right period. Results. Assuming a single data set lasting 150d, transits from a planet with a radius down to 2 Rearth can be detected. The efficiency depends neither on the transit duration nor on the number of transits observed. Furthermore we simulated transits with periods close to 150d in data sets containing three observations of 150d, separated by regular gaps with the same length. Again, planets with a radius down to 2 Rearth can be detected. Conclusions. Within the given range of parameters, the detection efficiency depends slightly on the apparent magnitude of the star but neither on the transit duration nor the number of transits. Furthermore, multiple observations might represent a solution for the COROT mission for detecting small planets when the orbital period is much longer than the duration of a single observation.
We present a detailed computation of the expected rate for Geomagnetic Conversion of Solar Axions to X-rays (GECOSAX) along the orbit of an x-ray satellite. We use realistic satellite orbits and propagation in time. A realistic model for the Earth's magnetic field, which properly accounts for its spatial non-uniformity, is used. We also account for the effect of the Earth's atmosphere on the propagation of x-rays in our calculation of axion-photon conversion probability. To estimate possible sensitivities to the axion-photon coupling g_{a\gamma}, we use an actual measurement of the expected backgrounds by the SUZAKU satellite. Assuming a detector area of 10^3 cm^2 and about 10^6 s of data, we show that a 2 \sigma limit of g_{a\gamma} < (4.7-6.6) times 10^{-11} GeV^{-1} from GECOSAX is achievable, for axion masses m_a<10^{-4} eV. This significantly exceeds current laboratory sensitivities to g_{a\gamma}.
We present a study of the relationship between the deficiency of neutral hydrogen and the local three-dimensional number density of spiral galaxies in the Arecibo catalog of global HI measurements (Springob et al. 2005). We find that the dependence on density of the HI content is weak at low densities, but increases sharply at high densities where interactions between galaxies and the intra-cluster medium become important. This behavior is reminiscent of the morphology-density relation (Dressler 1980) in that the effect manifests itself only at cluster-type densities, and indeed when we plot both the HI deficiency-density and morphology-density relations, we see that the densities at which they "turn up" are similar. This suggests that the physical mechanisms responsible for the increase in early types in clusters are also responsible for the decrease in HI content.
We report on the optical identification of the companion to the eclipsing millisecond pulsar PSR J1701$-$3006B in the globular cluster NGC 6266. A relatively bright star with an anomalous red colour and an optical variability ($\sim$ 0.2 mag) that nicely correlates with the orbital period of the pulsar ($\sim$ 0.144 days) has been found nearly coincident with the pulsar nominal position. This star is also found to lie within the error box position of an X-ray source detected by Chandra observations, thus supporting the hypothesis that some interaction is occurring between the pulsar wind and the gas streaming off the companion. Although the shape of the optical light curve is suggestive of a tidally deformed star which has nearly completely filled its Roche lobe, the luminosity ($\sim 1.9 L_\odot$) and the surface temperature ($\sim 6000$ K) of the star, deduced from the observed magnitude and colours, would imply a stellar radius significantly larger than the Roche lobe radius. Possible explanations for this apparent inconsistency are discussed.
Several mechanisms have been proposed to generate primordial magnetic fields and it is often assumed that magnetic fields are not affected by a sharp drop in ionization rate due to the cosmic recombination. We investigate the validity of the assumption by studying the behavior of magnetic fields and fluid motion around recombination. Fluid equations including the effect of recombination are considered for protons, electrons and neutral hydrogens separately, combining Maxwell equations. We find that the residual ionization rate required for the conservation of magnetic field at cosmological scales is about $10^{-10}$, which is much smaller than the standard value $\sim 10^{-4}$. Further we will show the acceleration of protons and electrons in the process of recombination which conpensates the decrease in the carrier of electric current in order to preserve electric current and then magnetic fields.
We present the results of high resolution absorption-line spectroscopy of 3 face-on galaxies, NGC 98, NGC 600, and NGC 1703 with the aim of searching for box/peanut (B/P)-shaped bulges. These observations test and confirm, for the first, time the prediction that face-on B/P-shaped bulges can be recognized by two minima in the profile along the bar's major axis of the fourth Gauss-Hermite moment h_4 of the line-of-sight velocity distribution (LOSVD). In NGC 98, a clear double minimum in h_4 is present along the major axis of the bar and before the end of the bar, as predicted. In contrast, in NGC 600, which is also a barred galaxy but lacks a substantial bulge, we do not find any significant kinematic signature for a B/P-shaped bulge. In NGC 1703, which is an unbarred control galaxy, we found no evidence of a B/P bulge. We also show directly that the LOSVD is broader at the location of the h_4 minimum in NGC 98 than elsewhere. This more direct method avoids possible artifacts associated with the degeneracy between the measurement of line-of-sight velocity dispersion and h_4.
Unlike in the Schwarzschild black hole background, gravitational perturbations in a Kerr black hole background can not be decomposed into simple tensor harmonics in the time domain. Here, we make mode decompositions only in the azimuthal direction. As a first step, we discuss the resulting (2+1)-dimensional Klein-Gordon differential equation for scalar perturbations with a two dimensional Dirac's $\delta$-function as a source representing a point particle orbiting a much larger black hole. To make this equation amenable for numerical integrations we explicitly remove analytically the singular behavior of the source and compute a global, well bahaved, effective source for the corresponding waveform.
The staid subject of exact static spherically symmetric perfect fluid solutions of Einstein's equations has been reinvigorated in the last decade. We now have several solution generating techniques which give rise to new exact solutions. Here the Einstein static Universe is transformed into a physically acceptable solution the properties of which are examined in detail. The emphasis here is on the importance of the integration constants that these generating techniques introduce.
It is shown that an electron-neutrino beam, propagating in a background plasma, can be decomposed into orbital momentum (OAM) states, similar to the OAM photon states. Coupling between different OAM neutrino states, in the presence of a plasma vortex, is considered. We show that plasma vorticity can be transfered to the neutrino beam, which is relevant to the understanding of the neutrino sources in astrophysics. Observation of neutrino OAM states could eventually become possible.
We study modulated inflation from kinetic term. Using the Mukhanov-Sasaki variable, it is possible to determine how mixing induced by the kinetic term feeds the curvature perturbation with the isocurvature perturbation. We show explicitly that the analytic result obtained from the evolution of the Mukhanov-Sasaki variable is consistent with the $\delta N$-formula. From our results, we find analytic conditions for the modulated fluctuation and the non-Gaussianity parameter.
Links to: arXiv, form interface, find, astro-ph, recent, 0804, contact, help (Access key information)
We present a technique that applies spectral synthesis to medium resolution
spectroscopy (MRS, R ~ 6000) in the red (6300 A < lambda < 9100 A) to measure
[Fe/H] and [alpha/Fe] of individual red giant stars over a wide metallicity
range. With the advent of highly multiplexed state-of-the-art spectrometers on
6-10 m telescopes, such spectra are available for several thousand stars in the
Local Group at distances of a few hundred kpc to ~1 Mpc. Stars at these
distances are typically too faint for high resolution abundance analysis. We
apply our technique to 284 red giant stars in seven Galactic globular clusters
and demonstrate that it reproduces the metallicities and alpha enhancements
derived from high resolution spectroscopy (HRS). The MRS technique excludes the
three Ca II triplet lines and instead relies on a plethora of weaker lines.
Unlike empirical metallicity estimators, such as the equivalent width of the Ca
II triplet, the synthetic method presented here is applicable over an
arbitrarily wide metallicity range and is independent of assumptions about the
alpha enhancement.
Estimates of cluster mean [Fe/H] from different HRS studies show typical
scatter of ~0.1 dex but can be larger than 0.2 dex for metal-rich clusters. The
scatter in HRS abundance estimates among individual stars in a given cluster is
also comparable to 0.1 dex. By comparison, the scatter among MRS [Fe/H]
estimates of individual stars in a given cluster is ~0.1 dex for most clusters
but 0.22 dex for the most metal-rich cluster, M71 (<[Fe/H]> = -0.7). A
star-by-star comparison of HRS vs. MRS [alpha/Fe] estimates indicates that the
precision in [alpha/Fe]_MRS is 0.05 dex.
We present the analysis of 4.5 years of nearly continuous observations of the classical Cepheid Polaris, which comprise the most precise data available for this star. We have made spectroscopic measurements from ground and photometric measurements from the WIRE star tracker and the SMEI instrument on the Coriolis satellite. Measurements of the amplitude of the dominant oscillation (P = 4 days), that go back more than a century, show a decrease from 120 mmag to 30 mmag (V magnitude) around the turn of the millennium. It has been speculated that the reason for the decrease in amplitude is the evolution of Polaris towards the edge of the instability strip. However, our new data reveal an increase in the amplitude by about 30% from 2003-2006. It now appears that the amplitude change is cyclic rather than monotonic, and most likely the result of a pulsation phenomenon. In addition, previous radial velocity campaigns have claimed the detection of long-period variation in Polaris (P > 40 days). Our radial velocity data are more precise than previous datasets, and we find no evidence for additional variation for periods in the range 3-50 days with an upper limit of 100 m/s. However, in the WIRE data we find evidence of variation on time-scales of 2-6 days, which we interpret as being due to granulation.
We present multiepoch spectra of 13 high-redshift Type Ia supernovae (SNe Ia) drawn from the literature, the ESSENCE and SNLS projects, and our own separate dedicated program on the ESO Very Large Telescope. We use the Supernova Identification (SNID) code of Blondin & Tonry to determine the spectral ages in the supernova rest frame. Comparison with the observed elapsed time yields an apparent aging rate consistent with the 1/(1+z) factor (where z is the redshift) expected in a homogeneous, isotropic, expanding universe. These measurements thus confirm the expansion hypothesis, while unambiguously excluding models that predict no time dilation, such as Zwicky's "tired light" hypothesis. We also test for power-law dependencies of the aging rate on redshift. The best-fit exponent for these models is consistent with the expected 1/(1+z) factor.
Observations of massive stars within the central parsec of the Galaxy show that, while most stars orbit within a well-defined disc, a significant fraction have large eccentricities and / or inclinations with respect to the disc plane. Here, we investigate whether this dynamically hot component could have arisen via scattering from an initially cold disc -- the expected initial condition if the stars formed from the fragmentation of an accretion disc. Using N-body methods, we evolve a variety of flat, cold, stellar systems, and study the effects of initial disc eccentricity, primordial binaries, very massive stars and intermediate mass black holes. We find, consistent with previous results, that a circular disc does not become eccentric enough unless there is a significant population of undetected 100--1000 Msun objects. However, since fragmentation of an eccentric disc can readily yield eccentric stellar orbits, the strongest constraints come from inclinations. We show that_none_ of our initial conditions yield the observed large inclinations, regardless of the initial disc eccentricity or the presence of massive objects. These results imply that the orbits of the young massive stars in the Galactic Centre are largely primordial, and that the stars are unlikely to have formed as a dynamically cold disc.
We report on new VLT optical spectroscopic and multi-wavelength archival observations of SN1996cr, a previously identified ULX known as Circinus Galaxy X-2. Our optical spectrum confirms SN1996cr as a bona fide type IIn SN, while archival imaging isolates its explosion date to between 1995-02-28 and 1996-03-16. SN1996cr is one of the closest SNe (~3.8 Mpc) in the last several decades and in terms of flux ranks among the brightest radio and X-ray SNe ever detected. The wealth of optical, X-ray, and radio observations that exist for this source provide relatively detailed constraints on its post-explosion expansion and progenitor history, including an preliminary angular size constaint from VLBI. The archival X-ray and radio data imply that the progenitor of SN1996cr evacuated a large cavity just prior to exploding: the blast wave likely expanded for ~1-2 yrs before eventually striking the dense circumstellar material which surrounds SN1996cr. The X-ray and radio emission, which trace the progenitor mass-loss rate, have respectively risen by a factor of ~2 and remained roughly constant over the past 7 yr. This behavior is reminiscent of the late rise of SN1987A, but 1000 times more luminous and much more rapid to onset. Complex Oxygen line emission in the optical spectrum further hints at a possible concentric shell or ring-like structure. The discovery of SN1996cr suggests that a substantial fraction of the closest SNe observed in the last several decades have occurred in wind-blown bubbles. Finally, cross-correlation with the BATSE GRB catalog yields a ~3sigma match with 4B 960202, marking perhaps the fourth GRB to be marginally associated with a type II SN. If correct, it would be the least luminous GRB detected to date. [Abridged]
As diversity in amphibian species declines, the search for causes has intensified. Work in this area has shown that amphibians are especially susceptible to the combination of heightened UVB radiation and increased nitrate concentrations. Various astrophysical events have been suggested as sources of ionizing radiation that could pose a threat to life on Earth, through destruction of the ozone layer and subsequent increase in UVB, followed by deposition of nitrate. In this study, we investigate whether the nitrate deposition following an ionizing event is sufficiently large to cause an additional stress beyond that of the heightened UVB previously considered. We have converted predicted nitrate depositions to concentration values, utilizing data from the New York State Department of Environmental Conservation Acid Rain Monitoring Network web site. Our results show that the increase in nitrate concentration in bodies of water following the most intense ionization event likely in the last billion years would not be sufficient to cause a serious additional stress on amphibian populations.
We present a detailed study of the X-ray properties of the galaxy cluster Abell 548b (z=0.04), using XMM-Newton data, and discuss the connection between the thermal properties and the presence of two extended relic radio sources located at the cluster periphery. We wish to analyze the dynamical state of the cluster and confirm the presence of a major merger. We will discuss the merger effects on the extended nonthermal emission. From the analysis of the temperature distribution and of the surface brightness profiles, we find evidence of a shock in the northern cluster region, just before the location of the two extended peripheral relics. From the optical analysis, we find that the cluster galaxies show a large $\sigma_V$, and two components are needed to fit their velocity distribution. Observational results were compared with a cluster simulation. The maps of gas temperature and density distribution from the simulation agree with the observational data in the case of a cluster merger nearly perpendicular to the plane of the sky and in the state after the maximum core collapse. We conclude that we are observing a galaxy cluster in a major merger phase, just after the maximum core collapse. The mass ratio is about 1:2, and the merger collision is nearly perpendicular to the plane of the sky. A shock is present in the northern cluster region, and it is very likely responsible for the electron reacceleration and the magnetic field amplification that will give cause the cluster relics. The relative position of the shock and the relics is strongly affected by projection effects.
This paper reports the first discovery of possible inverse Compoton (IC) X-ray emission below 10 keV in the typical high-energy peaked BL Lac object (HBL) PKS 2155--304. Two XMM-Newton observations performed in 2006 reveal that the 0.6--10 keV X-ray spectra of the source harden ($\Delta\Gamma \sim$ 0.1--0.3) at break energies of about 4 keV. The concave X-ray spectra of the source could be easily interpretated by a mixture of a steep component (i.e., the high energy tail of the synchrotron emission) and a flat one (i.e., the low energy side of the IC emission). However, the steep spectra ($\Gamma \sim$ 2.3) in the hard X-rays indicate that the synchrotron emission still domiantes over the IC one, while the latter is effectively present and perceived as flattening the synchrotron spectrum in this energy range. The quasi-simultaneous optical-UV-X-ray spectral energy distributions (SEDs) obtained with XMM-Newton suggest that the concave X-ray spectra of the source could be the result of down-ward shift of the synchrotron peak frequency to the optical band, incuring the IC emisssion to become more important in the hard ($\sim 4$--10 keV) X-ray band with respective to other cases in which the synchrotron emission peaks in the UV-soft-X-ray range. This discovery provides a new clue for a smooth transition between HBLs and the low-energy peaked BL Lac objects (LBLs).
Spitzer IRAC observations of two fields in the XUV-disk of M83 have been recently obtained,3R_{HII} away from the center of the galaxy (R_{HII)=6.6 kpc).GALEX UV images have shown the two fields to host in-situ recent star formation.The IRAC images are used in conjunction with GALEX data and new HI imaging from THINGS to constrain stellar masses and ages of the UV clumps in the fields,and to relate the local recent star formation to the reservoir of available gas. multi wavelength photometry in the UV and mid-IR bands of 136 UV clumps(spatial resolution >220pc) identified in the two target fields, together with model fitting of the stellar UV-MIR SED,suggest that the clumps cover a range of ages between a few Myr and >1Gyr with a median value around <100Myr,and have masses in the range 10^3-3*10^6M, with a peak ~10^4.7M.The range of observed ages,for which only a small fraction of the mass in stars appears to have formed in the past ~10Myr, agrees with the dearth of Ha emission observed in these outer fiel ds. At the location of our IRAC fields, the HI map shows localized enhancement and clumping of atomic gas. A comparison of the observed star formation with the gas reservoir shows that the UV clumps follow the Schmidt--Kennicutt scaling law of star formation,and that star formation is occurring in regions with gas dens ities at approximately (within a factor of a few) the critical density value de -rived according to the Toomre Q gravitational stability criterion. The signifi cant 8 micron excess in several of the clumps (16% of the total by number accou nting for ~67% of the 8 micron flux)) provides evidence for the existence of dust in these remote fields, in agreement with results for other galaxies. Furt hermore, we observe a relatively small excess of emission at 4.5 micron in the clumps...
The White Mountain Polarimeter (WMPol) is a dedicated ground-based microwave telescope and receiver system for observing polarization of the Cosmic Microwave Background. WMPol is located at an altitude of 3880 meters on a plateau in the White Mountains of Eastern California, USA, at the Barcroft Facility of the University of California White Mountain Research Station. Presented here is a description of the instrument and the data collected during April through October 2004. We set an upper limit on $E$-mode polarization of 14 $\mu\mathrm{K}$ (95% confidence limit) in the multipole range $170<\ell<240$. This result was obtained with 422 hours of observations of a 3 $\mathrm{deg}^2$ sky area about the North Celestial Pole, using a 42 GHz polarimeter. This upper limit is consistent with $EE$ polarization predicted from a standard $\Lambda$-CDM concordance model.
We have analyzed a time series of spectra in the hydrogen Lyman lines and the Lyman continuum obtained by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the SOlar Heliospheric Observatory (SOHO). The time series of about 2 hours and 22 minutes was obtained on 1999 March 9 in a quiet region near the center of the solar disk. For our analysis, we have selected a Lyman continuum window around 907 A, and the five Lyman lines: Ly5 (937.8 A), Ly7 (926.2 A), Ly9 (920.9 A), Ly11 (918.1 A), and Ly15 (915.3 A). A Fast Fourier analysis has been performed in the spatial domain, all along the slit length used, for all the spectra and for the total duration of the observations. We have detected a significant periodic spatial variations with Fourier transform power peaks around 9-10 arcsec and at 4 arcsec. They correspond to the scale of the mesogranulation structure and the width of the supergranular boundary, respectively. For the first time, this provides evidence for the existence of a meso-scale in the upper chromosphere, of the same size as observed in the photosphere and lower chromosphere by earlier studies. We find from the analysis that there seems to be no signature of any temporal evolution associated with the mesogranules, at least not during our observing period. This result suggests that the life time of mesogranules will be several hours or more, which confirms the earlier findings. In addition, we notice that the size (9-10 arcsec) of the mesocells appears to be the same in all Lyman lines and in the continuum, which are formed at different depths in the chromosphere.
Recent interferometric observations of the young stellar object(YSO) HH 30 have revealed a low velocity outflow in the $^{12}$CO J=1-2 molecule line (Pety et al. 2006). We present here two models of the low velocity disc winds with the aim of investigating an origin of this molecular outflow. Following Andlada et al. (2006) we treated HH 30 as a binary system. Two cases have been considered: i) the orbital period $P$ = 53 yrs and ii) $P \le$ 1 yr. Calculations showed that in the first case the outflow cone had a spiral-like structure due to summing the velocities of the orbital motion and the disc wind. Such a structure contradicts the observations. In the second case, the outflow cone demonstrates a symmetry relatively to the system axis and agrees well with the observations.
We present the results of quantitative spectral analysis of sdOs from the SDSS database. Fitting the Balmer, HeI and HeII lines to non-LTE model spectra, we derived their effective temperatures, surface gravities and helium abundances. We find the helium-enriched sdO stars to rally in a small intervall of Teff = 40,000K to 50,000K and log(g) = 5.5 to 6.0. We conclude, that the sdB stars are linked with the helium-deficient sdO stars, i.e. the sdBs are predecessors for the helium-deficient sdOs. To explain the helium-enriched sdO stars in their entirety, we regard two scenarios as most promising: The merging of two helium-core white dwarfs and the late hot flashers.
The Hubble parameter H0 is still not very well measured. Although the Hubble Key Project, Chandra and WMAP gave good estimates, the uncertainties remain quite large. In this brief report, we suggest an original and independent method to derive a lower limit on H0 using the absorption of very high energy gamma-rays by the cosmic infrared background. With conservative hypothesis, we obtain H0>74 km/s/Mpc at the 68% confidence level, which favors the upper end of the intervals allowed by dedicated experiments.
We show three-dimensional magnetohydrodynamical simulations of core collapse supernova in which the progenitor has magnetic fields inclined to the rotation axis. The simulations employed a simple empirical equation of state in which the pressure of degenerate gas is approximated by piecewise polytropes for simplicity. Neither energy loss due to neutrino is taken into account for simplicity. The simulations start from the stage of dynamical collapse of an iron core. The dynamical collapse halts at $ t $ = 189 ms by the pressure of high density gas and a proto-neutron star (PNS) forms. The evolution of PNS was followed about 40 milli-seconds in typical models. When the initial rotation is mildly fast and the initial magnetic fields are mildly strong, bipolar jets are launched from an upper atmosphere ($ r \sim 60 {\rm km} $) of the PNS. The jets are accelerated to $ \sim 3 \times 10 ^4 $ km s$^{-1}$, which is comparable to the escape velocity at the foot point. The jets are parallel to the initial rotation axis. Before the launch of the jets, magnetic fields are twisted by rotation of the PNS. The twisted magnetic fields form torus-shape multi-layers in which the azimuthal component changes alternately. The formation of magnetic multi-layers is due to the initial condition in which the magnetic fields are inclined with respect to the rotation axis. The energy of the jet depends only weakly on the initial magnetic field assumed. When the initial magnetic fields are weaker, the time lag is longer between the PNS formation and jet ejection. It is also shown that the time lag is related to the Alfv\'en transit time. Although the nearly spherical prompt shock propagates outward in our simulations, it is ...
The Alpha Centauri binary system, owing to its binarity, proximity and brightness, is a fundamental calibrating object for the theory of stellar structure and evolution. This role, however, is hindered by a considerable disagreement in the published analyses of its atmospheric parameters and abundances. We report a detailed spectroscopic analysis of both components of the Alpha Centauri binary system, differentially with respect to the Sun, based on high quality spectra (R = 35 000, S/N > 1000). The atmospheric parameters of the system are found to be Teff = 5820 K, [Fe/H] = +0.24, log g = 4.34 and xi = 1.46 km/s, for Alpha Cen A, and Teff = 5240 K, [Fe/H] = +0.25, log g = 4.44 and xi = 1.28 km/s for Alpha Cen B. The parameters were derived from the simultaneous excitation & ionization equilibria of the equivalent widths of Fe I and Fe II lines, by fitting theoretical profiles to the Halpha line and from photometric calibrations, good agreement being reached between the criteria for both stars. We derived the abundances of Na, Mg, Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Y and Ba, concluding that the abundance pattern of the system is solar but for significant Na, Mn and Ni excesses, and a deficit of Ba. An analysis of the position of the two stars in up-to-date theoretical evolutionary diagrams yields masses and ages in good agreement with the dynamical and seismological data. Its abundance pattern can be deemed normal in the context of recent data of metal-rich stars.
This paper reviews methods which can be used to detect binaries involving low- and intermediate-mass stars, with special emphasis on evolved systems. Besides the traditional methods involving radial-velocity or photometric monitoring, the paper discusses as well less known methods involving astrometry or maser (non-)detection. An extensive list of internet resources (mostly catalogues/databases of orbits and individual measurements) for the study of binary stars is provided at the end of the paper.
We study the problem of gravitational lensing by binary galaxies, idealized as two isothermal spheres. In a wide binary, each galaxy possesses individual tangential, nearly astroidal, caustics and roundish radial caustics. As the separation of the binary is made smaller, the caustics undergo a sequence of metamorphoses. The first metamorphosis occurs when the tangential caustics merge to form a single six-cusped caustic, lying interior to the radial caustics. At still smaller separations, the six-cusped caustic undergoes the second metamorphosis and splits into a four-cusped caustic and two three-cusped caustics, which shrink to zero size (an elliptic umbilic catastrophe) before they enlarge again and move away from the origin perpendicular to the binary axis. Finally, a third metamorphosis occurs as the three-cusp caustics join the radial caustics, leaving an inner distorted astroid caustic enclosed by two outer caustics. The maximum number of images possible is 7. Classifying the multiple imaging according to critical isochrones, there are only 8 possibilities: 2 three-image cases, 3 five-image cases, and 3 seven-image cases. When the isothermal spheres are singular, the core images vanish into the central singularity. The number of images may then be 1, 2, 3, 4 or 5, depending on the source location, and the separation and masses of the pair of lensing galaxies. The locations of metamorphoses, and the onset of threefold and fivefold multiple imaging, can be worked out analytically in this case.
A number of recent surveys for gravitational lenses have found examples of double Einstein rings. Here, we investigate analytically the occurrence of multiple Einstein rings. We prove, under very general assumptions, that at most one Einstein ring can arise from a mass distribution in a single plane lensing a single background source. Two or more Einstein rings can therefore only occur in multi-plane lensing. Surprisingly, we show that it is possible for a single source to produce more than one Einstein ring. If two point masses (or two isothermal spheres) in different planes are aligned with observer and source on the optical axis, we show that there are up to three Einstein rings. We also discuss the image morphologies for these two models if axisymmetry is broken, and give the first instances of magnification invariants in the case of two lens planes.
A recent paper (arXiv:0804.3463) claims that the presence of a soft X-ray
component in an X-ray source in NGC 6946 provides strong evidence that its
black hole mass is definitely $>100\msun$, and more probably $\sim 400\msun$,
even if the source is beamed.
I show that the data are instead very compatible with a black hole mass of
only $5\msun$, radiating isotropically (i.e. no beaming) and a mass transfer
rate about 60 times the Eddington value, i.e. $1.25 \times 10^{-5} \msun {\rm
yr}^{-1}$. Such a system is very similar to the probable descendant of the
Galactic X-ray binary Cygnus X--1 once the supergiant companion evolves to fill
its Roche lobe.
We describe an SPH model for chemical enrichment and radiative cooling in cosmological simulations of structure formation. This model includes: i) the delayed gas restitution from stars by means of a probabilistic approach designed to reduce the statistical noise and, hence, to allow for the study of the inner chemical structure of objects with moderately high numbers of particles; ii) the full dependence of metal production on the detailed chemical composition of stellar particles by using, for the first time in SPH codes, the Qij matrix formalism that relates each nucleosynthetic product to its sources; and iii) the full dependence of radiative cooling on the detailed chemical composition of gas particles, achieved through a fast algorithm using a new metallicity parameter zeta(T) that gives the weight of each element on the total cooling function. The resolution effects and the results obtained from this SPH chemical model have been tested by comparing its predictions in different problems with known theoretical solutions. We also present some preliminary results on the chemical properties of elliptical galaxies found in self-consistent cosmological simulations. Such simulations show that the above zeta-cooling method is important to prevent an overestimation of the metallicity-dependent cooling rate, whereas the Qij formalism is important to prevent a significant underestimation of the [alpha/Fe] ratio in simulated galaxy-like objects.
Many stormy events in astrophysics occur due to the sudden magnetic energy release. This is possible if a magnetic configuration abruptly changes its topology, an event usually referred to as magnetic reconnection. It is known that pure Ohmic decay is inefficient, occurring during cosmological times (due to the huge characteristic scales $L$). It is recognized that the presence of current sheets speeds up the process, but still insufficiently$^{1,2,3,4,5}$. We show that, in highly compressible and substantially gravitational media, the reconnection is fast enough to account for stormy events. Thus, highly compressible situations offer exiting opportunities in explanations of violent events, although full-scale compressible and gravitational simulations proved to be quite challenging.
We consider static spherically symmetric solutions of a general scalar field theory with non-standard kinetic energy coupled to gravity with a view to explain dark matter halos as a coherent state of the scalar field. Consistent solutions are found with a smooth scalar profile which can describe observed rotation curves. Some of the solutions have negative scalar energy density near the origin though the total energy is positive definite. The solutions with positive energy density everywhere have a steeper rotation curve near the origin than those that don't. We also reconsider the no scalar hair theorems for black holes with emphasis on asymptotic boundary conditions and super-luminal propagation. Some modifications and extensions of previous analyses are discussed.
The Noether symmetry of a generic $f(R)$ cosmological model is investigated by utilizing the behavior of the corresponding Lagrangian under the infinitesimal generators of the desired symmetry. We explicitly calculate the form of $f(R)$ for which such symmetries exist. It is shown that the resulting form of $f(R)$ yields a power law expansion for the cosmological scale factor. We also obtain the effective equation of state parameter for the corresponding cosmology and show that our model can provide a gravitational alternative to the quintessence.
We study the future evolution of quintessence/phantom dominated epoch in modified $F(R)$-gravity which unifies the early-time inflation with late-time acceleration and which is consistent with observational tests. Using the reconstruction technique it is demonstrated that there are models where any known (Big Rip, II, III or IV Type) singularity may classically occur. From another side, in Einstein frame (scalar-tensor description) only IV Type singularity occurs. Near the singularity the classical description breaks up, it is demonstrated that quantum effects act against the singularity and may prevent its appearance. The realistic $F(R)$-gravity which is future singularity free is proposed. We point out that additional modification of any $F(R)$-gravity by the terms relevant at the early universe is possible, in such a way that future singularity does not occur even classically.
We consider the dynamics of the open string tachyon condensation in a framework of the cubic fermionic String Field Theory including a non-minimal coupling with closed string massless modes, the graviton and the dilaton. Coupling of the open string tachyon and the dilaton is motivated by the open String Field Theory in a linear dilaton background and the flat space-time. We note that the dilaton gravity provides several restrictions on the tachyon condensation and show explicitly that the influence of the dilaton on the tachyon condensation is essential and provides a significant effect: oscillations of the Hubble parameter and the state parameter become of a cosmological scale. We give an estimation for the period of these oscillations (0.1-1) Gyr and note a good agreement of this period with the observed oscillations with a period (0.15-0.65) Gyr in a distribution of quasar spectra.
The ultimate goal of studying isospin physics via heavy-ion reactions with neutron-rich, stable and/or radioactive nuclei is to explore the isospin dependence of in-medium nuclear effective interactions and the equation of state of neutron-rich nuclear matter, particularly the isospin-dependent term in the equation of state, i.e., the density dependence of the symmetry energy. Because of its great importance for understanding many phenomena in both nuclear physics and astrophysics, the study of the density dependence of the nuclear symmetry energy has been the main focus of the intermediate-energy heavy-ion physics community during the last decade, and significant progress has been achieved both experimentally and theoretically. In particular, a number of phenomena or observables have been identified as sensitive probes to the density dependence of the nuclear symmetry energy. Experimental studies have confirmed some of these interesting isospin-dependent effects and allowed us to constrain relatively stringently the symmetry energy at sub-saturation densities. The impacts of this constrained density dependence of the symmetry energy on the properties of neutron stars have also been studied, and they were found to be very useful for the astrophysical community. With new opportunities provided by the various radioactive beam facilities being constructed around the world, the study of isospin physics is expected to remain one of the forefront research areas in nuclear physics. In this report, we review the major progress achieved during the last decade in isospin physics with heavy ion reactions and discuss future challenges to the most important issues in this field.
The Misner and Sharp approach to the study of gravitational collapse is extended to the viscous dissipative case in, both, the streaming out and the diffusion approximations. The dynamical equation is then coupled to causal transport equations for the heat flux, the shear and the bulk viscosity, in the context of Israel--Stewart theory, without excluding the thermodynamics viscous/heat coupling coefficients. The result is compared with previous works where these later coefficients were neglected and viscosity variables were not assumed to satisfy causal transport equations. Prospective applications of this result to some astrophysical scenarios are discussed.
Links to: arXiv, form interface, find, astro-ph, recent, 0804, contact, help (Access key information)
We use cosmological simulations in order to study the effects of supernova (SN) feedback on the formation of a Milky Way-type galaxy of virial mass ~10^12 M_sun/h. We analyse a set of simulations run with the code described by Scannapieco et al. (2005, 2006), where we have tested our star formation and feedback prescription using isolated galaxy models. Here we extend this work by simulating the formation of a galaxy in its proper cosmological framework, focusing on the ability of the model to form a disk-like structure in rotational support. We find that SN feedback plays a fundamental role in the evolution of the simulated galaxy, efficiently regulating the star formation activity, pressurizing the gas and generating mass-loaded galactic winds. These processes affect several galactic properties such as final stellar mass, morphology, angular momentum, chemical properties, and final gas and baryon fractions. In particular, we find that our model is able to reproduce extended disk components with high specific angular momentum and a significant fraction of young stars. The galaxies are also found to have significant spheroids composed almost entirely of stars formed at early times. We find that most combinations of the input parameters yield disk-like components, although with different sizes and thicknesses, indicating that the code can form disks without fine-tuning the implemented physics. We also show how our model scales to smaller systems. By analysing simulations of virial masses 10^9 M_sun/h and 10^10 M_sun/h, we find that the smaller the galaxy, the stronger the SN feedback effects.
To better understand the mechanism or mechanisms that lead to AGN activity today, we measure the X-ray AGN fraction in a new sample of nearby clusters and examine how it varies with galaxy properties, projected cluster-centric radius, and cluster velocity dispersion. We present new wide-field Chandra X-ray Observatory observations of Abell 85, Abell 754 and the background cluster Abell 89B out to their virial radii. Out of seventeen X-ray sources associated with galaxies in these clusters, we classify seven as X-ray AGN with L_{X,B} > 10^{41} erg/s. Only two of these would be classified as AGN based on their optical spectra. We combine these observations with archival data to create a sample of X-ray AGN from six z < 0.08 clusters and find that 3.4+1.1/-0.8% of M_R < -20 galaxies host X-ray AGN with L_{X,B} > 10^{41} erg/s. We find that more X-ray AGN are detected in more luminous galaxies and attribute this to larger spheriods in more luminous galaxies and increased sensitivity to lower Eddington-rate accretion from black holes in those spheroids. At a given X-ray luminosity limit, more massive black holes can be accreting less efficiently, yet still be detected. If interactions between galaxies are the principal drivers of AGN activity, then the AGN fraction should be higher in lower velocity dispersion clusters and the outskirts of clusters. However, the tendency of the most massive and early-type galaxies to lie in the centers of the richest clusters could dilute such trends. While we find no variation in the AGN fraction with projected cluster-centric radius, we do find that the AGN fraction increases significantly from 2.6+1.0/-0.8% in rich clusters to 10.0+6.2/-4.3% in those with lower velocity dispersions.
The physical properties and kinematics of the partially ionized interstellar material near the Sun are typical of warm diffuse clouds in the solar vicinity. The interstellar magnetic field at the heliosphere and the kinematics of nearby clouds are naturally explained in terms of the S1 superbubble shell. The interstellar radiation field at the Sun appears to be harder than the field ionizing ambient diffuse gas, which may be a consequence of the low opacity of the tiny cloud surrounding the heliosphere. The spatial context of the Local Bubble is consistent with our location in the Orion spur.
We discuss the implications for gravity wave detectors of a class of modified gravity theories which dispense with the need for dark matter. These models, which are known as Dark Matter Emulators, have the property that weak gravitational waves couple to the metric that would follow from general relativity without dark matter whereas ordinary particles couple to a combination of the metric and other fields which reproduces the result of general relativity with dark matter. We show that there is an appreciable difference in the Shapiro delays of gravitational waves and photons or neutrinos from the same source, with the gravity waves always arriving first. We compute the expected time lags for GRB 070201, for SN 1987a, and for Sco-X1. We estimate the probable error by taking account of the uncertainty in position, and by using three different dark matter profiles.
The Balmer line profiles of nonradiative supernova remnant shocks provide the means to measure the post-shock proton velocity distribution. While most analyses assume a Maxwellian velocity distribution, this is unlikely to be correct. In particular, neutral atoms that pass through the shock and become ionized downstream form a nonthermal distribution similar to that of pickup ions in the solar wind. We predict the H alpha line profiles from the combination of pickup protons and the ordinary shocked protons, and we consider the extent to which this distribution could affect the shock parameters derived from H alpha profiles. The Maxwellian assumption could lead to an underestimate of shock speed by up to about 15%. The isotropization of the pickup ion population generates wave energy, and we find that for the most favorable parameters this energy could significantly heat the thermal particles. Sufficiently accurate profiles could constrain the strength and direction of the magnetic field in the shocked plasma, and we discuss the distortions from a Gaussian profile to be expected in Tycho's supernova remnant.
We identify seven new ultracool white dwarfs discovered in the Sloan Digital Sky Survey (SDSS). The SDSS photometry, spectra, and proper motions are presented, and additional BVRI data are given for these and other previously discovered ultracool white dwarfs. The observed colors span a remarkably wide range, qualitatively similar to colors predicted by models for very cool white dwarfs. One of the new stars (SDSS J1251+44) exhibits strong collision-induced absorption (CIA) in its spectra, while the spectra and colors of the other six are consistent with mild CIA. Another of the new discoveries (SDSS J2239+00A) is part of a binary system -- its companion is also a cool white dwarf, and other data indicate that the companion exhibits an infrared flux deficiency, making this the first binary system composed of two CIA white dwarfs. A third discovery (SDSS J0310-00) has weak Balmer emission lines. The proper motions of all seven stars are consistent with membership in the disk or thick disk.
We take the line of sight velocity dispersions as functions of radius for 8 Milky Way dwarf spheroidal galaxies and use Jeans analysis to calculate the mass-to-light ratios (M/L) in Modified Newtonian Dynamics (MOND). Using the latest structural parameters, distances and variable velocity anisotropy, we find 6/8 dwarfs have sensible M/L using only the stellar populations. Sextans and Draco, however, have M/L=9.2_{-3.0}^{+5.3} and 43.9_{-19.3}^{+29.0} respectively, which poses a problem. Apart from the need for Sextans' integrated magnitude to be reviewed, we propose tidal effects intrinsic to MOND, testable with numerical simulations, but fully orbit dependant, which are disrupting Draco. The creation of the Magellanic Stream is also re-addressed in MOND, the scenario being the stream is ram pressure stripped from the SMC as it crosses the LMC.
(Abridged). We present new high spatial resolution narrowband imaging observations of extraplanar diffuse ionized gas (eDIG) in four late-type, actively star forming edge-on spirals, obtained with ACS on-board HST. Our F658N (H-alpha) observations reveal a multitude of structures on both small and large scales. Whereas all four galaxies have been studied with ground-based telescopes before, here the small scale structure of the extended emission line gas is presented for the first time at a spatial resolution of 0.05", corresponding to 5.0 pc at the mean distance to the target galaxies. The eDIG morphology is very different for all four targets, probably as a result of their different levels of star formation activity. We find that the morphology of the eDIG, in particular the break-up of diffuse emission into filaments in galaxy halos, shows a strong dependence on the level of star formation activity per unit area, and eDIG can be arranged into a morphological sequence. NGC4634 and NGC5775 have the highest SF rate per unit area in our sample and the observed morphology suggests that the break-up of the smooth eDIG layer into individual resolved filaments occurs only above a certain threshold of SF activity per unit area. Combined with ground-based data for samples that span a larger range of galaxy mass our results indicate that the gravitational potential also plays an important role in the eDIG morphology. In low-mass galaxies the gas can be expelled due to shallow gravitational potentials more easily and couple with strong star formation driven outflows on a local scale. This is in contrast to the more massive galaxies, which show smooth eDIG layers, unless they are powered by a superwind, as in the case of nucleated starburst galaxies.
We investigate a series of steady-state models of galaxy clusters, in which the hot intracluster gas is efficiently heated by active galactic nucleus (AGN) feedback and thermal conduction, and in which the mass accretion rates are highly reduced compared to those predicted by the standard cooling flow models. We perform a global Lagrangian stability analysis. We show for the first time that the global radial instability in cool core clusters can be suppressed by the AGN feedback mechanism, provided that the feedback efficiency exceeds a critical lower limit. Furthermore, our analysis naturally shows that the clusters can exist in two distinct forms. Globally stable clusters are expected to have either: 1) cool cores stabilized by both AGN feedback and conduction, or 2) non-cool cores stabilized primarily by conduction. Intermediate central temperatures typically lead to globally unstable solutions. This bimodality is consistent with the recently observed anticorrelation between the flatness of the temperature profiles and the AGN activity (Dunn & Fabian 2008) and the observation by Rafferty et al. (2008) that the shorter central cooling times tend to correspond to significantly younger AGN X-ray cavities.
In this paper, we revisit the parameterizations of the equation of state of dark energy and point out that comparing merely the $\chi^2$ of different fittings may not be optimal for choosing the "best" parametrization. Another figure of merit for evaluating different parametrizations based on the area of the $w(z) - z$ band is proposed. In light of the analysis of some two-parameter parameterizations and models based on available SNIa data, the area of $w(z)-z$ band seems to be a good figure of merit, especially in the situation that the value of $\chi^2_{\rm min}$ for different parametrizations are very close. Therefore, we argue that both the area of the $w(z)-z$ band and $\chi^2_{\rm min}$ should be synthetically considered for choosing a better parametrization of dark energy in the future experiments.
We have observed a total of 67 pulsars at five frequencies ranging from 243 to 3100 MHz. Observations at the lower frequencies were made at the Giant Metre Wave Telescope in India and those at higher frequencies at the Parkes Telescope in Australia. We present profiles from 34 of the sample with the best signal to noise ratio and the least scattering. The general `rules' of pulsar profiles are seen in the data; profiles get narrower, the polarization fraction declines and outer components become more prominent as the frequency increases. Many counterexamples to these rules are also observed, and pulsars with complex profiles are especially prone to rule breaking. We hypothesise that the location of pulsar emission within the magnetosphere evolves with time as the the pulsar spins down. In highly energetic pulsars, the emission comes from a confined range of high altitudes, in the middle range of spin down energies the emission occurs over a wide range of altitudes whereas in pulsars with low spin-down energies it is confined to low down in the magnetosphere.
Using effective temperature and metallicity derived from SDSS spectra for ~60,000 F and G type main sequence stars (0.2<g-r<0.6), we develop polynomial models for estimating these parameters from the SDSS u-g and g-r colors. We apply this method to SDSS photometric data for about 2 million F/G stars and measure the unbiased metallicity distribution for a complete volume-limited sample of stars at distances between 500 pc and 8 kpc. The metallicity distribution can be exquisitely modeled using two components with a spatially varying number ratio, that correspond to disk and halo. The two components also possess the kinematics expected for disk and halo stars. The metallicity of the halo component is spatially invariant, while the median disk metallicity smoothly decreases with distance from the Galactic plane from -0.6 at 500 pc to -0.8 beyond several kpc. The absence of a correlation between metallicity and kinematics for disk stars is in a conflict with the traditional decomposition in terms of thin and thick disks. We detect coherent substructures in the kinematics--metallicity space, such as the Monoceros stream, which rotates faster than the LSR, and has a median metallicity of [Fe/H]=-0.96, with an rms scatter of only ~0.15 dex. We extrapolate our results to the performance expected from the Large Synoptic Survey Telescope (LSST) and estimate that the LSST will obtain metallicity measurements accurate to 0.2 dex or better, with proper motion measurements accurate to ~0.2 mas/yr, for about 200 million F/G dwarf stars within a distance limit of ~100 kpc (g<23.5). [abridged]
The space astrometry mission GAIA will construct a dense optical QSO-based celestial reference frame. For consistency between optical and radio positions, it will be important to align the GAIA frame and the International Celestial Reference Frame (ICRF) with the highest accuracy. Currently, it is found that only 10% of the ICRF sources are suitable to establish this link, either because they are not bright enough at optical wavelengths or because they have significant extended radio emission which precludes reaching the highest astrometric accuracy. In order to improve the situation, we have initiated a VLBI survey dedicated to finding additional suitable radio sources for aligning the two frames. The sample consists of about 450 sources, typically 20 times weaker than the current ICRF sources (down to the 20 mJy flux level), which have been selected by cross-correlating optical and radio catalogues. This paper presents the observing strategy to detect, image, and measure accurate positions for these sources. It will also provide results about the VLBI detectability of the sources, as derived from initial observations with the European VLBI Network in June and October 2007. Based on these observations, an excellent detection rate of 89% is found, which is very promising for the continuation of this project.
I calculate a hybrid cross-power spectrum estimator from the WMAP 5-year CMB temperature maps, discuss the goodness of fit, and then constrain cosmological parameters. The spectrum and results are generally consistent with previous results, though the power spectrum error bars are slightly smaller and there are small shifts at high ell. The small improvement in error bars is obtained at very low numerical cost but does not significantly improve parameter constraints. I discuss the accuracy of the likelihood model and how constraints on the optical depth translate into constraints on the reionization history allowing for helium reionization. In the appendices I propose a simple reionization parameterization that determines the history in terms of a mid-point reionization redshift, and suggest a new likelihood approximation for chi-squared-like distributions with varying skewness.
We present the results of a study of a sample of 375 Extremely Red Galaxies (ERGs) in the Phoenix Deep Survey, 273 of which constitute a subsample which is 80% complete to K_s = 18.5 over an area of 1160 arcmin^2. The angular correlation function for ERGs is estimated, and the association of ERGs with faint radio sources explored. We find tentative evidence that ERGs and faint radio sources are associated at z > 0.5. A new overdensity-mapping algorithm has been used to characterize the ERG distribution, and identify a number of cluster candidates, including a likely cluster containing ERGs at 0.5 < z < 1. Our algorithm is also used in an attempt to probe the environments in which faint radio sources and ERGs are associated. We find limited evidence that the I - K_s > 4 criterion is more efficient than R - K_s > 5 at selecting dusty star-forming galaxies, rather than passively evolving ERGs.
Three Algol-type binaries in Cygnus constellation were selected for an analysis from a huge database of observations made by the INTEGRAL/OMC camera. These data were processed and analyzed, resulting in a first light-curve study of these neglected eclipsing binaries. The temperatures of the primary components range from 9500 K to 10500 K and the inclinations are circa 73deg (for PV Cyg and V1011 Cyg), while almost 90deg for V822 Cyg. All of them seem to be main-sequence stars, well within their critical Roche lobes. Nevertheless, further detailed analyses are still needed.
We present an analytic approximate seismic inversion scheme for damped transverse coronal loop oscillations based on the thin tube and thin boundary approximation for computing the period and the damping time. Asymptotic expressions for the period and damping rate are used to illustrate the process of seismological inversion in a simple and easy to follow manner. The inversion procedure is formulated in terms of two simple functions, which are given by simple closed expressions. The analytic seismic inversion shows that an infinite amount of 1-dimensional equilibrium models can reproduce the observed periods and damping times. It predicts a specific range of allowable values for the Alfven travel time and lower bounds for the density contrast and the inhomogeneity length scale. When the results of the present analytic seismic inversion are compared with those of a previous numerical inversion, excellent agreement is found up to the point that the analytic seismic inversion emerges as a tool for validating results of numerical inversions. Actually it helped us to identify and correct inaccuracies in a previous numerical investigation.
Gamma ray astronomy is now at the leading edge for studies related both to fundamental physics and astrophysics. The sensitivity of gamma detectors is limited by the huge amount of background, constituted by hadronic cosmic rays (typically two to three orders of magnitude more than the signal) and by the accidental background in the detectors. By using the information on the temporal evolution of the Cherenkov light, the background can be reduced. We will present here the results obtained within the MAGIC experiment using a new technique for the reduction of the background. Particle showers produced by gamma rays show a different temporal distribution with respect to showers produced by hadrons; the background due to accidental counts shows no dependence on time. Such novel strategy can increase the sensitivity of present instruments.
We analyze stationary accretion of selfgravitating gas onto a compact center within general-relativistic radiation hydrodynamics. Spherical symmetry and thin gas approximation are assumed. Numerical investigation shows that supersonic flows exist for small redshifts and they cease to exist for high redshifts and high luminosities. There exist two branches of flows (subsonic or supersonic) that originate at a bifurcation point and that embrace the set of subsonic solutions. The morphology of the set of subsonic solutions is essentially independent of redshifts and flows that belong to their boundary provide estimates of the gas abundance of subsonic solutions. It appears that prescribed boundary data guarantee uniqueness only of the bifurcation point, and that the latter has maximal luminosity.
We show that the mass-radius $(M-R)$ relation corresponding to the stiffest
equation of state (EOS) does not provide the necessary and sufficient condition
of dynamical stability for the equilibrium configurations, since such
configurations can not satisfy the `compatibility criterion'. In this
connection, we construct sequences composed of core-envelope models such that,
like the stiffest EOS, each member of these sequences satisfy the extreme case
of causality condition, $v = c = 1$, at the centre. We, thereafter, show that
the $M-R$ relation corresponding to the said core-envelope model sequences can
provide the necessary and sufficient condition of dynamical stability only when
the `compatibility criterion' for these sequences is `appropriately' satisfied.
However, the fulfillment of `compatibility criterion' can remain satisfied even
when the $M-R$ relation does not provide the necessary and sufficient condition
of dynamical stability for the equilibrium configurations.
In continuation to the results of previous study, these results explicitly
show that the `compatibility criterion' {\em independently} provides, in
general, the {\em necessary} and {\em sufficient} condition of hydrostatic
equilibrium for any regular sequence. Beside its fundamental feature, this
study can also explain simultaneously, both (the higher as well as lower)
values of the glitch healing parameter observed for the Crab and the Vela-like
pulsars respectively, on the basis of starquake model of glitch generation.
We present results from new low frequency observations of two extrasolar planetary systems (Epsilon Eridani and HD128311) taken at 150 MHz with the Giant Metrewave Radio Telescope (GMRT). We do not detect either system, but are able to place tight upper limits on their low frequency radio emission.
Aims: We explore the relation between charge state of polycyclic aromatic hydrocarbons (PAHs) and extinction curve morphology. Methods: We fit extinction curves with a dust model including core-mantle spherical particles of mixed chemical composition (silicate core, sp^2 and sp^3 carbonaceous layers), and an additional molecular component. We use exact methods to calculate the extinction due to classical particles and accurate computed absorption spectra of PAHs in different charge states, for the contribution due to the molecular component. Eesults: A combination of classical dust particles and mixtures of real PAHs satisfactorily matches the observed interstellar extinction curves. Variations in the charge state of PAHs produce changes consistent with the varying relative strengths of the bump and non-linear far-UV rise.
We report the serendipituous discovery of the new eclipsing polar 2XMMp J131223.4+173659. Its striking X-ray light curve attracted immediate interest when we were visually inspecting the source products of the 2XMMp catalogue. This light curve revealed its likely nature as a magnetic cataclysmic variable of AM Herculis (or polar) type with an orbital period of ~92 min, which was confirmed by follow-up optical spectroscopy and photometry. 2XMMp J131223.4+173659 probably has a one-pole accretion geometry. It joins the group of now nine objects that show no evidence of a soft component in their X-ray spectra despite being in a high accretion state, thus escaping ROSAT/EUVE detection. We discuss the likely accretion scenario, the system parameters, and the spectral energy distribution.
We present kinematic measurements of thin and thick disk components in a sample of nine edge-on galaxies. We extract stellar and ionized gas rotation curves at and above the galaxies' midplanes using the Ca II triplet absorption features and H-alpha emission lines measured with the GMOS spectrographs on Gemini North and South. For the higher mass galaxies in the sample, we fail to detect differences between the thin and thick disk kinematics. In the lower mass galaxies, there is a wide range of thick disk behavior including thick disks with substantial lag and one counter-rotating thick disk. We compare our rotation curves with expectations from thick disk formation models and conclude that the wide variety of thick disk kinematics favors a formation scenario where thick disk stars are accreted or formed during merger events as opposed to models that form thick disks through gradual thin disk heating.
We show the preliminary results of the application of our "fireshell" model to GRB060124. This source is very peculiar because it is the first event for which both the prompt and the afterglow emission were observed simultaneously by the three Swift instruments: BAT (15-350 keV), XRT (0.2-10 keV) and UVOT (170-650 nm), due to the presence of a precursor ~ 570 s before the main burst. We analyze GRB060124 within our "canonical" GRB scenario, identifying the precursor with the P-GRB and the prompt emission with the afterglow peak emission. In this way we reproduce correctly the energetics of both these two components. We reproduce also the observed time delay between the precursor (P-GRB) and the main burst. The effect of such a time delay in our model will be discussed.
Internal dynamical evolution can drive stellar systems into states of high central density. For many star clusters and galactic nuclei, the time scale on which this occurs is significantly less than the age of the universe. As a result, such systems are expected to be sites of frequent interactions among stars, binary systems, and stellar remnants, making them efficient factories for the production of compact binaries, intermediate-mass black holes, and other interesting and eminently observable astrophysical exotica. We describe some elements of the competition among stellar dynamics, stellar evolution, and other mechanisms to control the dynamics of stellar systems, and discuss briefly the techniques by which these systems are modeled and studied. Particular emphasis is placed on pathways leading to massive black holes in present-day globular clusters and other potentially detectable sources of gravitational radiation.
Bald patches are magnetic topologies in which the magnetic field is concave up over part of a photospheric polarity inversion line. A bald patch topology is believed to be the essential ingredient for filament channels and is often found in extrapolations of the observed photospheric field. Using an analytic source-surface model to calculate the magnetic topology of a small bipolar region embedded in a global magnetic dipole field, we demonstrate that although common in closed-field regions close to the solar equator, bald patches are unlikely to occur in the open-field topology of a coronal hole. Our results give rise to the following question: What happens to a bald patch topology when the surrounding field lines open up? This would be the case when a bald patch moves into a coronal hole, or when a coronal hole forms in an area that encompasses a bald patch. Our magnetostatic models show that, in this case, the bald patch topology almost invariably transforms into a null point topology with a spine and a fan. We argue that the time-dependent evolution of this scenario will be very dynamic since the change from a bald patch to null point topology cannot occur via a simple ideal evolution in the corona. We discuss the implications of these findings for recent Hinode XRT observations of coronal hole jets and give an outline of planned time-dependent 3D MHD simulations to fully assess this scenario.
In the present letter we find that Starobinsky's inflationary solution is also valid in the Dvali-Gabadadze-Porrati (DGP) model where a 3-brane is embedded in 5-dimensional Minkowski bulk. We show that such a solution is typically not supported by the Self-Accelerated branch of the model, giving therefore a natural selection of the conventional branch of solutions. In the absence of brane induced Einstein-Hilbert term the SA branch is always selected out. We then study the linearized modes around all such de Sitter brane solutions finding perturbative stability for a range of parameters of the brane QFT.
We investigate the Affleck-Dine mechanism when multiple flat directions have large values simultaneously. We consider in detail the case when both $LH_u$ and $H_uH_d$ flat directions are operative with a non-renormalizable superpotential. In case Hubble induced A-terms are present for these two flat directions, their initial values are determined completely by the potential and there are no ambiguities how they are mixed. Moreover, CP is violated even when the Hubble parameter is large due to the Hubble induced A-term and cross coupling in F-term, so that the lepton asymmetry is generated just after the end of inflation. As a result, compared with the case of single flat direction, the resultant lepton-to-entropy ratio is enhanced by a factor of $H_{osc}/m_{3/2}$, where $H_{osc}$ is the Hubble parameter at the onset of oscillation and $m_{3/2}$ is the gravitino mass. However, when Hubble induced A-terms do not exist, there remains indefiniteness of initial phases and CP is violated spontaneously by the phase difference between initial phase and potential minima of the hidden-sector induced A-terms. Therefore, CP-violation is not effective until the onset of the oscillation of scalar fields around the origin and there is suppression factor from thermal effect as is the case of single flat direction. In this case, the amplitude of baryon isocurvature perturbation imposes constraints on the model parameters.
A calculation of the current-quark-mass-dependence of nucleon static electromagnetic properties is necessary in order to use observational data as a means to place constraints on the variation of Nature's fundamental parameters. A Poincare' covariant Faddeev equation, which describes baryons as composites of confined-quarks and -nonpointlike-diquarks, is used to calculate this dependence The results indicate that, like observables dependent on the nucleons' magnetic moments, quantities sensitive to their magnetic and charge radii, such as the energy levels and transition frequencies in Hydrogen and Deuterium, might also provide a tool with which to place limits on the allowed variation in Nature's constants.
Provided ultrahigh-energy cosmic neutrinos are produced from the decays of charged pions arising from proton-proton and (or) proton-gamma collisions, their flavor ratios at a neutrino telescope will be \phi^T_e : \phi^T_\mu : \phi^T_\tau \approx 1 : 1 : 1. We show that the exact flavor democracy can occur if the unitary neutrino mixing matrix satisfies either \theta_13 = 0 and \theta_{23} = \pi/4 (CP invariance) or \delta= \pm \pi/2 and \theta_{23} = \pi/4 (CP violation) in the standard parametrization. Allowing for slight deviations from either condition, we calculate the corresponding neutrino flavor distribution at neutrino telescopes. If the neutrino mixing matrix is non-unitary, as expected in a class of seesaw models with TeV-scale Majorana neutrinos, we demonstrate that the effect of unitarity violation on the flavor democracy of cosmic neutrinos at neutrino telescopes can be as large as several percent.
It has been suggested that energetic photons propagating in vacuo should experience a non-trivial refractive index due to the foamy structure of space-time induced by quantum-gravitational fluctuations. The sensitivity of recent astrophysical observations, particularly of AGN Mk501 by the MAGIC Collaboration, approaches the Planck scale for a refractive index depending linearly on the photon energy. We present here a new derivation of this quantum-gravitational vacuum refraction index, based on a stringy analogue of the interaction of a photon with internal degrees of freedom in a conventional medium. We model the space-time foam as a gas of D-particles in the bulk space-time of a higher-dimensional cosmology where the observable Universe is a D3-brane. The interaction of an open string representing a photon with a D-particle stretches and excites the string, which subsequently decays and re-emits the photon with a time delay that increases linearly with the photon energy and is related to stringy uncertainty principles. We relate this derivation to other descriptions of the quantum-gravitational refractive index in vacuo.
Motivated by the fact that neutrinos are massive, we study the effect of neutrino Yukawa couplings on neutralino dark matter observables within the framework of a supersymmetric seesaw. We find that neutrino couplings significantly affect the neutralino relic density in regions of parameter space where soft SUSY-breaking slepton masses and/or trilinear couplings are large. Depending on the size of the couplings, the neutralino relic density spans over an order of magnitude in the A-funnel, focus point and stop-coannihilation regions of mSUGRA. We also show that dark matter detection rates can be modified by several orders of magnitude in these regions.
If light hidden sector photons exist, they could be produced through kinetic mixing with solar photons in the eV energy range. We propose to search for this hypothetical hidden photon flux with the Super-Kamiokande and/or upgraded CAST detectors. The proposed experiments are sensitive to mixing strengths as small as 10^-9 for hidden photon masses in the sub eV region and, in the case of non-observation, would improve limits recently obtained from photon regeneration laser experiments in this mass region.
We derive big-bang nucleosynthesis (BBN) constraints on both unstable and stable gravitino taking account of recent progresses in theoretical study of the BBN processes as well as observations of primordial light-element abundances. In the case of unstable gravitino, we set the upper limit on the reheating temperature assuming that the primordial gravitinos are mainly produced by the scattering processes of thermal particles. For stable gravitino, we consider Bino, stau and sneutrino as the next-to-the-lightest supersymmetric particle and obtain constraints on their properties. Compared with the previous works, we improved the following points: (i) we use the most recent observational data, (ii) for gravitino production, we include contribution of the longitudinal component, and (iii) for the case with unstable long-lived stau, we estimate the bound-state effect of stau accurately by solving the Boltzmann equation.
A cosmological model of dark energy interacting with dark matter and another general component of the universe is investigated. We found general constraints on these models imposing an accelerated expansion. The same is also studied in the case for holographic dark energy.
We present a new numerical scheme to solve the initial value problem for black hole-neutron star binaries. This method takes advantage of the flexibility and fast convergence of a multidomain spectral representation of the initial data to construct high-accuracy solutions at a relatively low computational cost. We provide convergence tests of the method for both isolated neutron stars and irrotational binaries. In the second case, we show that we can resolve the small inconsistencies that are part of the quasi-equilibrium formulation, and that these inconsistencies are significantly smaller than observed in previous works. The possibility of generating a wide variety of initial data is also demonstrated through two new configurations inspired by results from binary black holes. First, we show that choosing a modified Kerr-Schild conformal metric instead of a flat conformal metric allows for the construction of quasi-equilibrium binaries with a spinning black hole. Second, we construct binaries in low-eccentricity orbits, which are a better approximation to astrophysical binaries than quasi-equilibrium systems.
Links to: arXiv, form interface, find, astro-ph, recent, 0804, contact, help (Access key information)