We report the discovery of water vapour toward the carbon star V Cygni. We have used Herschel's HIFI instrument, in dual beam switch mode, to observe the 1(11) - 0(00) para-water transition at 1113.3430 GHz in the upper sideband of the Band 4b receiver. The observed spectral line profile is nearly parabolic, but with a slight asymmetry associated with blueshifted absorption, and the integrated antenna temperature is 1.69 \pm 0.17 K km/s. This detection of thermal water vapour emission, carried out as part of a small survey of water in carbon-rich stars, is only the second such detection toward a carbon-rich AGB star, the first having been obtained by the Submillimeter Wave Astronomy Satellite toward IRC+10216. For an assumed ortho-to-para ratio of 3 for water, the observed line intensity implies a water outflow rate ~ (3 - 6) E-5 Earth masses per year and a water abundance relative to H2 of ~ (2-5) E-6. This value is a factor of at least 1E+4 larger than the expected photospheric abundance in a carbon-rich environment, and - as in IRC+10216 - raises the intriguing possibility that the observed water is produced by the vapourisation of orbiting comets or dwarf planets. However, observations of the single line observed to date do not permit us to place strong constraints upon the spatial distribution or origin of the observed water, but future observations of additional transitions will allow us to determine the inner radius of the H2O-emitting zone, and the H2O ortho-to-para ratio, and thereby to place important constraints upon the origin of the observed water emission.
Context. For accurately measuring intensities and determining magnetic field strengths of small-scale solar (magnetic) structure, knowledge of and compensation for the point spread function is crucial. For images recorded with the Swedish 1-meter Solar Telescope, restoration with Multi-Frame Blind Deconvolution and Joint Phase Diverse Speckle methods lead to remarkable improvements in image quality but granulation contrasts that are too low, indicating additional stray light. Aims. We propose a method to compensate for stray light from high-order atmospheric aberrations not included in MFBD and JPDS processing. Methods. To compensate for uncorrected aberrations, a reformulation of the image restoration process is proposed that allows the average effect of hundreds of high-order modes to be compensated for by relying on Kolmogorov statistics for these modes. The applicability of the method requires simultaneous measurements of Fried's parameter r0. The method is tested with simulations as well as real data and extended to include compensation for conventional stray light. Results. We find that only part of the reduction of granulation contrast in SST images is due to uncompensated high-order aberrations. The remainder is still unaccounted for and attributed to stray light from the atmosphere, the telescope with its re-imaging system and to various high-altitude seeing effects. Conclusions. We conclude that statistical compensation of high-order modes is a viable method to reduce the loss of contrast occurring when a limited number of aberrations is explicitly compensated for with MFBD and JPDS processing. We show that good such compensation is possible with only 10 recorded frames. The main limitation of the method is that already MFBD and JPDS processing introduces high-order compensation that, if not taken into account, can lead to over-compensation.
We report on the multi-wavelength observations of PKS 1510-089 (a flat spectrum radio quasar at z=0.361) during its high activity period between 2008 September and 2009 June. During this 11 months period, the source was characterized by a complex variability at optical, UV and gamma-ray bands, on time scales down to 6-12 hours. The brightest gamma-ray isotropic luminosity, recorded on 2009 March 26, was ~ 2x10^48erg s^-1. The spectrum in the Fermi-LAT energy range shows a mild curvature well described by a log-parabolic law, and can be understood as due to the Klein-Nishina effect. The gamma-ray flux has a complex correlation with the other wavelengths. There is no correlation at all with the X-ray band, a weak correlation with the UV, and a significant correlation with the optical flux. The gamma-ray flux seems to lead the optical one by about 13 days. From the UV photometry we estimated a black hole mass of ~ 5.4x10^8 solar masses, and an accretion rate of ~ 0.5 solar masses/year. Although the power in the thermal and non-thermal outputs is smaller compared to the very luminous and distant flat spectrum radio quasars, PKS 1510-089 exhibits a quite large Compton dominance and a prominent big blue bump (BBB) as observed in the most powerful gamma-ray quasars. The BBB was still prominent during the historical maximum optical state in 2009 May, but the optical/UV spectral index was softer than in the quiescent state. This seems to indicate that the BBB was not completely dominated by the synchrotron emission during the highest optical state. We model the broadband spectrum assuming a leptonic scenario in which the inverse Compton emission is dominated by the scattering of soft photons produced externally to the jet. The resulting model-dependent jet energetic content is compatible with the accretion disk powering the jet, with a total efficiency within the Kerr black hole limit.
Integral Field Spectroscopy obtained with PPak and the 3.5m telescope at the Calar Alto Observatory has been used to study an outer HII region complex in the well studied galaxy NGC 6946. This technique provides detailed maps of the region in different emission lines yielding spatially resolved information about the physical properties of the gas. The configuration was chosen to cover the whole spectrum from 3600 up to 10000 A. We selected four luminous knots, to perform a detailed integrated spectroscopic analysis of these structures and of the whole PPak field-of-view (FOV). For all the knots the electron density has been found to be very similar and below 100 cm^-3. The [OIII] electron temperature was measured in knots A, B, C and in the integrated PPak-field, and was found to be around 8000 K. The temperatures of [OII] and [SIII] were estimated in the four cases. The elemental abundances computed from the "direct method" are typical of high metallicity disk HII regions, with a mean value of 12+log(O/H)= 8.65, comparable to what has been found in this galaxy by other authors for regions at similar galactocentric distance. Therefore, a remarkable abundance uniformity is found despite the different excitations found throughout the nebula. Wolf-Rayet features have been detected in three of the knots, leading to a derived total number of WR stars of 125, 22 and 5, for knots A, C and B, respectively. The integrated spectrum of the whole PPak FOV shows high excitation and a relatively evolved age which does not correspond to the individual knot evolutionary stages. Some effects associated to the loss of spatial resolution could also be evidenced by the higher ionising temperature that is deduced from the eta' parameter measured in the integrated PPak spectrum with respect to that of the individual knots.
I present a review of Smoothed Particle Hydrodynamics (SPH), with the aim of providing a mathematically rigorous, clear derivation of the algorithms from first principles. The method of discretising a continuous field into particles using a smoothing kernel is considered, and also the errors associated with this approach. A fully conservative form of SPH is then derived from the Lagrangian, demonstrating the explicit conservation of mass, linear and angular momenta and energy/entropy. The method is then extended to self-consistently include spatially varying smoothing lengths, (self) gravity and various forms of artificial viscosity, required for the correct treatment of shocks. Finally two common methods of time integration are discussed, the Runge-Kutta-Fehlberg and leapfrog integrators, along with an overview of time-stepping criteria.
Neutrino astronomy beyond the Sun was first imagined in the late 1950s; by
the 1970s, it was realized that kilometer-scale neutrino detectors were
required. The first such instrument, IceCube, is near completion and taking
data. The IceCube project transforms a cubic kilometer of deep and
ultra-transparent Antarctic ice into a particle detector. A total of 5,160
optical sensors are embedded into a gigaton of Antarctic ice to detect the
Cherenkov light emitted by secondary particles produced when neutrinos interact
with nuclei in the ice. Each optical sensor is a complete data acquisition
system, including a phototube, digitization electronics, control and trigger
systems and LEDs for calibration. The light patterns reveal the type (flavor)
of neutrino interaction and the energy and direction of the neutrino, making
neutrino astronomy possible. The scientific missions of IceCube include such
varied tasks as the search for sources of cosmic rays, the observation of
Galactic supernova explosions, the search for dark matter, and the study of the
neutrinos themselves. These reach energies well beyond those produced with
accelerator beams.
The outline of this review is as follows:
Neutrino Astronomy and Kilometer-Scale Detectors. High-Energy Neutrino
Telescopes: Methodologies of Neutrino Detection. IceCube Hardware. High-Energy
Neutrino Telescopes: Beyond Astronomy. Future Projects
SWAS and Odin provided stringent upper limits on the gas phase water abundance of dark clouds (x(H2O) < 7x10^-9). We investigate the chemistry of water vapor in starless cores beyond the previous upper limits using the highly improved angular resolution and sensitivity of Herschel and measure the abundance of water vapor during evolutionary stages just preceding star formation. High spectral resolution observations of the fundamental ortho water (o-H2O) transition (557 GHz) were carried out with Herschel HIFI toward two starless cores: B68, a Bok globule, and L1544, a prestellar core embedded in the Taurus molecular cloud complex. The rms in the brightness temperature measured for the B68 and L1544 spectra is 2.0 and 2.2 mK, respectively, in a velocity bin of 0.59 km s^-1. The continuum level is 3.5+/-0.2 mK in B68 and 11.4+/-0.4 mK in L1544. No significant feature is detected in B68 and the 3 sigma upper limit is consistent with a column density of o-H2O N(o-H2O) < 2.5x10^13 cm^-2, or a fractional abundance x(o-H2O) < 1.3x10^-9, more than an order of magnitude lower than the SWAS upper limit on this source. The L1544 spectrum shows an absorption feature at a 5 sigma level from which we obtain the first value of the o-H2O column density ever measured in dark clouds: N(o-H2O) = (8+/-4)x10^12 cm^-2. The corresponding fractional abundance is x(o-H2O) ~ 5x10^-9 at radii > 7000 AU and ~2x10^-10 toward the center. The radiative transfer analysis shows that this is consistent with a x(o-H2O) profile peaking at ~10^-8, 0.1 pc away from the core center, where both freeze-out and photodissociation are negligible. Herschel has provided the first measurement of water vapor in dark regions. Prestellar cores such as L1544 (with their high central densities, strong continuum, and large envelopes) are very promising tools to finally shed light on the solid/vapor balance of water in molecular clouds.
Recent mid-infrared observations of young stellar objects have found significant variations possibly indicative of changes in the structure of the circumstellar disk. Previous models of this variability have been restricted to axisymmetric perturbations in the disk. We consider simple models of a non-axisymmetric variation in the inner disk, such as a warp or a spiral wave. We find that the precession of these non-axisymmetric structures produce negligible flux variations but a change in the height of these structures can lead to significant changes in the mid-infrared flux. Applying these models to observations of the young stellar object LRLL 31 suggests that the observed variability could be explained by a warped inner disk with variable scale height. This suggests that some of the variability observed in young stellar objects could be explained by non-axisymmetric disturbances in the inner disk and this variability would be easily observable in future studies.
We present 7.5-14.2um low-resolution spectroscopy, obtained with the Spitzer Infrared Spectrograph, of the T8.5 dwarf Wolf 940 B, which is a companion to an M4 dwarf with a projected separation of 400 AU. We combine these data with previously published near-infrared spectroscopy and mid-infrared photometry, to produce the spectral energy distribution for the very low-temperature T dwarf. We use atmospheric models to derive the bolometric correction and obtain a luminosity of log L/Lsun = -6.01 +/- 0.05. Evolutionary models are used with the luminosity to constrain the values of effective temperature (T_eff) and surface gravity, and hence mass and age for the T dwarf. We further restrict the allowed range of T_eff and gravity using age constraints implied by the M dwarf primary, and refine the physical properties of the T dwarf by comparison of the observed and modelled spectroscopy and photometry. This comparison indicates that Wolf 940 B has a metallicity within 0.2 dex of solar, as more extreme values give poor fits to the data - lower metallicity produces a poor fit at lambda > 2um while higher metallicity produces a poor fit at lambda < 2um. This is consistent with the independently derived value of [m/H] = +0.24 +/- 0.09 for the primary star, using the Johnson & Apps (2008) M_K:V-K relationship. We find that the T dwarf atmosphere is undergoing vigorous mixing, with an eddy diffusion coefficient K_zz of 10^4 to 10^6 cm^2 s^-1. We derive an effective temperature of 585 K to 625 K, and surface gravity log g = 4.83 to 5.22 (cm s^-2), for an age range of 3 Gyr to 10 Gyr, as implied by the kinematic and H alpha properties of the M dwarf primary. The lower gravity corresponds to the lower temperature and younger age for the system, and the higher value to the higher temperature and older age. The mass of the T dwarf is 24 M_Jupiter to 45 M_Jupiter for the younger to older age limit.
Answering well-known fundamental questions is usually regarded as the major goal of science. Discovery of other unknown and fundamental questions is, however, even more important. Recognition that "we didn't know anything" is the basic scientific driver for the next generation. Cosmology indeed enjoys such an exciting epoch. What is the composition of our universe? This is one of the well-known fundamental questions that philosophers, astronomers and physicists have tried to answer for centuries. Around the end of the last century, cosmologists finally recognized that "We didn't know anything". Except for atoms that comprise slightly less than 5% of the universe, our universe is apparently dominated by unknown components; 23% is the known unknown (dark matter), and 72% is the unknown unknown (dark energy). In the course of answering a known fundamental question, we have discovered an unknown, even more fundamental, question: "What is dark matter? What is dark energy?" There are a variety of realistic particle physics models for dark matter, and its experimental detection may be within reach. On the other hand, it is fair to say that there is no widely accepted theoretical framework to describe the nature of dark energy. This is exactly why astronomical observations will play a key role in unveiling its nature. I will review our current understanding of the "dark sky", and then present on-going Japanese project, SuMIRe, to discover even more unexpected questions.
The turbulent magnetic diffusivity in the solar convection zone is one of the most poorly constrained ingredients of mean-field dynamo models. This lack of constraint has previously led to controversy regarding the most appropriate set of parameters, as different assumptions on the value of turbulent diffusivity lead to radically different solar cycle predictions. Typically, the dynamo community uses double step diffusivity profiles characterized by low values of diffusivity in the bulk of the convection zone. However, these low diffusivity values are not consistent with theoretical estimates based on mixing-length theory -- which suggest much higher values for turbulent diffusivity. To make matters worse, kinematic dynamo simulations cannot yield sustainable magnetic cycles using these theoretical estimates. In this work we show that magnetic cycles become viable if we combine the theoretically estimated diffusivity profile with magnetic quenching of the diffusivity. Furthermore, we find that the main features of this solution can be reproduced by a dynamo simulation using a prescribed (kinematic) diffusivity profile that is based on the spatiotemporal geometric-average of the dynamically quenched diffusivity. Here, we provide an analytic fit to the dynamically quenched diffusivity profile, which can be used in kinematic dynamo simulations. Having successfully reconciled the mixing-length theory estimated diffusivity profile with kinematic dynamo models, we argue that they remain a viable tool for understanding the solar magnetic cycle.
We present first comparisons between Light Element Primary Process (LEPP) abundances observed in ultra metal poor (UMP) stars and nucleosynthesis calculations based on long-time hydrodynamical simulations of core-collapse supernovae and their neutrino-driven wind. Observations indicate that r-process elements have at least two components: heavy r-process nuclei (A > 130) that are synthesized by rapid neutron capture in a yet unknown site and LEPP elements (mainly Sr, Y, Zr). We show that our neutrino-driven wind simulations can explain the observed LEPP pattern. We explore in detail the sensitivity of the calculated abundances to the electron fraction, which is a key nucleosynthesis parameter but poorly known due to uncertainties in neutrino interactions and transport. Our results show that the observed LEPP pattern can also be realized in proton-rich winds, which are obtained in the most recent supernova simulations. However, a small amount of neutron-rich matter from supernovae is necessary to account for the expected LEPP contribution to the solar system.
We derive a simple analytical expression for the two-body force in a sub-class of MOND-like theories and make testable predictions in the modification to the two-body orbital period, shape, and precession rate, and escape speed etc. We demonstrate the applications of the modified Kepler's law in the timing of satellite orbits around the Milky Way, and checking the feasibility of MOND in the orbit of Large Magellanic Cloud, the M31 galaxy, and the merging Bullet Clusters. MOND appears to be consistent with satellite orbits although with a tight margin. Our results on two-bodies are also generalized to restricted three-body, many-body problems, rings and shells.
We examine the question as to whether the f(R) gravity theories, in both metric and in Palatini formalisms, permit space-times in which the causality is violated. We show that the field equations of these f(R) gravity theories admit solutions with violation of causality for a physically well-motivated perfect-fluid matter content.
The precise radial-velocity measurements of 4 G-type giants, 11Com, $\zeta$ Hya, $\epsilon$ Tau, and $\eta$ Her were carried out. The short-term variations with amplitudes, 1-7m/s and periods, 3-10 hours were detected. A period analysis shows that the individual power distribution is in a Gaussian shape and their peak frequencies ($\nu_{max}$) are in a good agreement with the prediction by the scaling law. With using a pre-whitening procedure, significant frequency peaks more than 3 $\sigma$ are extracted for these giants. From these peaks, we determined the large frequency separation by constructing highest peak distribution of collapsed power spectrum, which is also in good agreement with what the scaling law for the large separation predicts. Echelle diagrams of oscillation frequency were created based on the extracted large separations, which is very useful to clarify the properties of oscillation modes. In these echelle diagrams, odd-even mode sequences are clearly seen. Therefore, it is certain that in these G-type giants, non-radial modes are detected in addition to radial mode. As a consequence, these properties of oscillation modes are shown to follow what Dzymbowski et al.(2001) and Dupret et al.(2009) theoretically predicted. Damping times for these giants were estimated with the same method as that developed by Stello et al.(2004). The relation of Q value (ratio of damping time to period) to the period was discussed by adding the data of the other stars ranging from dwarfs to giants.
We calculate light curves produced by a hot spot of a rapidly rotating neutron star, assuming that the spot is perturbed by a core $r$-mode, which is destabilized by emitting gravitational waves. To calculate light curves, we take account of relativistic effects such as the Doppler boost due to the rapid rotation and light bending assuming the Schwarzschild metric around the neutron star. We assume that the core $r$-modes penetrate to the surface fluid ocean to have sufficiently large amplitudes to disturb the spot. For a $l'=m$ core $r$-mode, the oscillation frequency $\omega\approx2m\Omega/[l'(l'+1)]$ defined in the co-rotating frame of the star will be detected by a distant observer, where $l'$ and $m$ are respectively the spherical harmonic degree and the azimuthal wave number of the mode, and $\Omega$ is the spin frequency of the star. In a linear theory of oscillation, using a parameter $A$ we parametrize the mode amplitudes such that ${\rm max}\left(|\xi_\theta|,|\xi_\phi|\right)/R=A$ at the surface, where $\xi_\theta$ and $\xi_\phi$ are the $\theta$ and $\phi$ components of the displacement vector of the mode and $R$ is the radius of the star. For the $l'=m=2$ $r$-mode with $\omega=2\Omega/3$, we find that the fractional Fourier amplitudes at $\omega=2\Omega/3$ in light curves depend on the angular distance $\theta_s$ of the spot centre measured from the rotation axis and become comparable to or even larger than $A\sim0.001$ for small values of $\theta_s$.
We report on the initial analysis of Herschel/HIFI carbon monoxide observations of the martian atmosphere performed between 11 and 16 April 2010. We selected the (7-6) rotational transitions of the isotopes ^{13}CO and C^{18}O at 771 and 768 GHz respectively in order to retrieve the mean vertical profile of temperature and the mean volume mixing ratio of carbon monoxide. The derived temperature profile agrees within less than 5 K with general circulation model predictions up to an altitude of 45 km, however show about 12-15 K lower values at 60 km. The carbon monoxide mixing ratio was determined to be 980 \pm 150 ppm, in agreement with the 900 ppm derived from Herschel/SPIRE observations in November 2009.
We report on the initial analysis of Herschel/HIFI observations of hydrogen chloride (HCl), hydrogen peroxide (H_2O_2) and molecular oxygen (O_2) in the martian atmosphere performed on 13 and 16 April 2010 (L_s ~ 77{\deg}). We derived a constant volume mixing ratio of 1400 +/- 120 ppm for O_2 and determined upper limits of 200 ppt for HCl and 2 ppb for H_2O_2. Radiative transfer model calculations indicate that the vertical profile of O_2 may not be constant. Photochemical models find lowest values for H_2O_2 around L_s ~ 75{\deg} but overestimate the volume mixing ratio compared to our measurements.
Although recent measurements of the shower profiles of ultra-high energy cosmic rays suggest that they are largely initiated by heavy nuclei, such conclusions rely on hadronic interaction models which have large uncertainties. We investigate an alternative test of cosmic ray composition which is based on the observation of ultra-high energy photons produced through cosmic ray interactions with diffuse low energy photon backgrounds during intergalactic propagation. We show that if the ultra-high energy cosmic rays are dominated by heavy nuclei, the flux of these photons is suppressed by approximately an order of magnitude relative to the proton-dominated case. Future observations by the Pierre Auger Observatory may be able to use this observable to constrain the composition of the primaries, thus providing an important cross-check of hadronic interaction models.
We have investigated the impact of the $^{14}N(p,\gamma)^{15}O$ reaction rate recently redetermined by the LUNA experiment, on the shell H-burning and core He-burning phases of low-mass, metal poor stellar models. The new reaction rate has small but noticeable effects, the largest one being a $\sim$7-8\% reduction of the red giant branch lifetimes. To different degrees, the lifetimes and luminosities of horizontal branch models, the mass of the stellar models evolving within the RR Lyrae instability strip, the luminosity of the red giant branch luminosity function bump, the theoretical calibrations of the R-parameter and tip of the red giant branch luminosity are also affected. Predictions for the tip of the red giant branch luminosity, in particular, are in very good agreement with the currently available empirical constraints.
We investigate the jet morphology and kinematics of a statistically complete radio-loud AGN sample in terms of the gamma-ray properties of the sources. Gamma-ray detected AGN dominate the high end of the jet apparent speed distribution of the total sample. Gamma-variable sources show stronger evolution in their jet morphology. A 5.1% of the sources show large (> 15 degrees) swings in their jet ejection angle.
We present new more sensitive high-resolution radio observations of a compact broad absorption line (BAL) quasar, 1045+352, made with the EVN+MERLIN at 5 GHz. They allowed us to trace the connection between the arcsecond structure and the radio core of the quasar. The radio morphology of 1045+352 is dominated by a knotty jet showing several bends. We discuss possible scenarios that could explain such a complex morphology: galaxy merger, accretion disk instability, precession of the jet and jet-cloud interactions. It is possible that we are witnessing an ongoing jet precession in this source due to internal instabilities within the jet flow, however, a dense environment detected in the submillimeter band and an outflowing material suggested by the X-ray absorption could strongly interact with the jet. It is difficult to establish the orientation between the jet axis and the observer in 1045+352 because of the complex structure. Nevertheless taking into account the most recent inner radio structure we conclude that the radio jet is oriented close to the line of sight which can mean that the opening angle of the accretion disk wind can be large in this source. We also suggest that there is no direct correlation between the jet-observer orientation and the possibility of observing BALs.
We report on the first detection of $^{13}$C enhancement in two B[e] supergiants in the Large Magellanic Cloud. Stellar evolution models predict the surface abundance in $^{13}$C to strongly increase during main-sequence and post-main sequence evolution of massive stars. However, direct identification of chemically processed material on the surface of B[e] supergiants is hampered by their dense, disk-forming winds, hiding the stars. Recent theoretical computations predict the detectability of enhanced $^{13}$C via the molecular emission in $^{13}$CO arising in the circumstellar disks of B[e] supergiants. To test this potential method and to unambiguously identify a post-main sequence B[e]SG by its $^{13}$CO emission, we have obtained high-quality $K$-band spectra of two known B[e] supergiants in the Large Magellanic Cloud, using the Very Large Telescope's Spectrograph for INtegral Field Observation in the Near-Infrared (VLT/SINFONI). Both stars clearly show the $^{13}$CO band emission, whose strength implies a strong enhancement of $^{13}$C, in agreement with theoretical predictions. This first ever direct confirmation of the evolved nature of B[e] supergiants thus paves the way to the first identification of a Galactic B[e] supergiant.
The Fermi Large Area Telescope, in collaboration with several groups from the radio community, have had marvellous success at uncovering new gamma-ray millisecond pulsars (MSPs). In fact, MSPs now make up a sizable fraction of the total number of known gamma-ray pulsars. The MSP population is characterized by a variety of pulse profile shapes, peak separations, and radio-to-gamma phase lags, with some members exhibiting nearly phase-aligned radio and gamma-ray light curves (LCs). The MSPs' short spin periods underline the importance of including special relativistic effects in LC calculations, even for emission originating from near the stellar surface. We present results on modelling and classification of MSP LCs using standard pulsar model geometries.
The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLAST-Pol) is a suborbital mapping experiment designed to study the role played by magnetic fields in the star formation process. BLAST-Pol is the reconstructed BLAST telescope, with the addition of linear polarization capability. Using a 1.8 m Cassegrain telescope, BLAST-Pol images the sky onto a focal plane that consists of 280 bolometric detectors in three arrays, observing simultaneously at 250, 350, and 500 um. The diffraction-limited optical system provides a resolution of 30'' at 250 um. The polarimeter consists of photolithographic polarizing grids mounted in front of each bolometer/detector array. A rotating 4 K achromatic half-wave plate provides additional polarization modulation. With its unprecedented mapping speed and resolution, BLAST-Pol will produce three-color polarization maps for a large number of molecular clouds. The instrument provides a much needed bridge in spatial coverage between larger-scale, coarse resolution surveys and narrow field of view, and high resolution observations of substructure within molecular cloud cores. The first science flight will be from McMurdo Station, Antarctica in December 2010.
We consider models of gas flow in spiral galaxies in which the spiral structure has been excited by various possible mechanisms: a global steady density wave, self-gravity of the stellar disc and an external tidal interaction, as well as the case of a galaxy with a central rotating bar. In each model we estimate in a simple manner the likely current positions of star clusters of a variety of ages, ranging from ~ 2 Myr to around 130 Myr, depending on the model. We find that the spatial distribution of cluster of different ages varies markedly depending on the model, and propose that observations of the locations of age-dated stellar clusters is a possible discriminant between excitation mechanisms for spiral structure in an individual galaxy.
Weak gravitational lensing changes the angular power spectra of the cosmic microwave background (CMB) temperature and polarization in a characteristic way containing valuable information for cosmological parameter estimation and weak lensing reconstructions. So far, analytical expressions for the lensed CMB power spectra assume the probability density function (PDF) of the lensing excursion angle to be Gaussian. However, coherent light deflection by nonlinear structures at low redshifts causes deviations from a pure Gaussian PDF. Working in the flat-sky limit we develop a method for computing the lensed CMB power spectra which takes these non-Gaussian features into account. Our method does not assume any specific PDF but uses instead an expansion of the characteristic function of the lensing excursion angle into its moments. Measuring these in the CMB lensing deflection field obtained from the Millennium Simulation we show that the change in the lensed power spectra is only at the 0.1% - 0.4% level on very small scales (below 4 arcmin) and demonstrate that the assumption of a Gaussian lensing excursion angle PDF is well applicable.
The sightline to the brighter member of the gravitationally lensed quasar
pair UM 673A,B intersects a damped Lyman-alpha system (DLA) at z = 1.62650
which, because of its low redshift, has not been recognised before. Our high
quality echelle spectra of the pair, obtained with HIRES on the Keck I
telescope, show a drop in neutral hydrogen column density N(H I) by a factor of
at least 400 between UM 673A and B, indicating that the DLA's extent in this
direction is much less than the 2.7 kpc separation between the two sightlines
at z = 1.62650. By reassessing this new case together with published data on
other QSO pairs, we conclude that the typical size (radius) of DLAs at these
redshifts is R ~ (5 +/- 3) kpc, smaller than previously realised. Highly
ionized gas associated with the DLA is more extended, as we find only small
differences in the C IV absorption profiles between the two sightlines.
Coincident with UM 673B, we detect a weak and narrow Ly-alpha emission line
which we attribute to star formation activity at a rate SFR >~ 0.2 M_solar/yr.
From consideration of lensing models, we conclude that the transverse distance
of the Ly-alpha emitting region from the DLA is likely to be ~11 kpc.
The DLA in UM 673A is metal-poor, with an overall metallicity Z_DLA ~ 1/30
Z_solar, and has a very low internal velocity dispersion. It exhibits some
apparent peculiarities in its detailed chemical composition, with the elements
Ti, Ni, and Zn being deficient relative to Fe by factors of 2-3. The [Zn/Fe]
ratio is lower than those measured in any other DLA or Galactic halo star,
presumably reflecting somewhat unusual previous enrichment by stellar
nucleosynthesis. We discuss the implications of these results for the nature of
the galaxy hosting the DLA.
Circumstellar envelopes (CSEs) of a variety of evolved stars have been found to contain ammonia (NH3) in amounts that exceed predictions from conventional chemical models by many orders of magnitude. The observations reported here were performed in order to better constrain the NH3 abundance in the CSEs of four, quite diverse, oxygen-rich stars using the NH3 ortho J_K = 1_0 - 0_0 ground-state line. We used the Heterodyne Instrument for the Far Infrared aboard Herschel to observe the NH3 J_K = 1_0 - 0_0 transition near 572.5 GHz, simultaneously with the ortho-H2O J_Ka,Kc = 1_1,0 -1_0,1 transition, toward VY CMa, OH 26.5+0.6, IRC+10420, and IK Tau. We conducted non-LTE radiative transfer modeling with the goal to derive the NH3 abundance in these objects' CSEs. For the latter two stars, Very Large Array imaging of NH3 radio-wavelength inversion lines were used to provide further constraints, particularly on the spatial extent of the NH3-emitting regions. Results. We find remarkably strong NH3 emission in all of our objects with the NH3 line intensities rivaling those obtained for the ground state H2O line. The NH3 abundances relative to H2 are very high and range from 2 x 10-7 to 3 x 10-6 for the objects we have studied. Our observations confirm and even deepen the circumstellar NH3 enigma. While our radiative transfer modeling does not yield satisfactory fits to the observed line profiles, it leads to abundance estimates that confirm the very high values found in earlier studies. New ways to tackle this mystery will include further Herschel observations of more NH3 lines and imaging with the Expanded Very Large Array.
The planet formation process and subsequent planet migration may lead to configurations resulting in strong dynamical interactions among the various planets. Well-studied possible outcomes include collisions between planets, scattering events that eject one or more of the planets, and a collision of one or more of the planets with the parent star. In this work we consider one other possibility that has seemingly been overlooked in the various scattering calculations presented in the literature: the tidal capture of two planets which leads to the formation of a binary planet (or binary brown dwarf) in orbit about the parent star. We carry out extensive numerical simulations of such dynamical and tidal interactions to explore the parameter space for the formation of such binary planets. We show that tidal formation of binary planets is possible for typical planet masses and distances from the host star. The detection (or lack thereof) of planet-planet binaries can thus be used to constrain the properties of planetary systems, including their mutual spacing during formation, and the fraction of close planets in very eccentric orbits which are believed to form by a closely related process.
We report the first detection of the ground-state rotational transition of the methylidyne cation CH+ towards the massive star-forming region DR21 with the HIFI instrument onboard the Herschel satellite. The line profile exhibits a broad emission line, in addition to two deep and broad absorption features associated with the DR21 molecular ridge and foreground gas. These observations allow us to determine a CH+ J=1-0 line frequency of 835137 +/- 3 MHz, in good agreement with a recent experimental determination. We estimate the CH+ column density to be a few 1e13 cm^-2 in the gas seen in emission, and > 1e14 cm^-2 in the components responsible for the absorption, which is indicative of a high line of sight average abundance [CH+]/[H] > 1.2x10^-8. We show that the CH+ column densities agree well with the predictions of state-of-the-art C-shock models in dense UV-illuminated gas for the emission line, and with those of turbulent dissipation models in diffuse gas for the absorption lines.
The energy release due to neutralino WIMP self-annihilation in the thermalization volume inside a compact object is shown to be comparable to the energy needed to create a long-lived lump of strange quark matter, or strangelet, for WIMP masses above a few GeV. Since strange matter is the most stable state of matter, accretion of self-annihilating dark matter onto neutron stars provides a mechanism to seed compact objects with lumps of strange quark matter and this effect may trigger a conversion of most of the star into a strange star. Using an energy estimate based on the Fermi gas model combined with the MIT bag model for the long-lived strangelet, a new limit on the possible values of the WIMP mass can be set that is competitive with those from direct searches. Our limit is especially important for subdominant species of massive neutralinos.
We study the colour-magnitude relation (CMR) for a sample of 172 morphologically-classified E/S0 cluster galaxies from the ESO Distant Cluster Survey (EDisCS) at 0.4<z<0.8. The intrinsic colour scatter about the CMR is very small (0.076) in rest-frame U-V. Only 7% of the galaxies are significantly bluer than the CMR. The scarcity of blue S0s indicates that, if they are the descendants of spirals, these were already red when they became S0s. We observe no dependence of the CMR scatter with redshift or cluster velocity dispersion. This implies that by the time cluster E/S0s achieve their morphology, the vast majority have already joined the red sequence. We estimate the galaxy formation redshift z_F for each cluster and find that it does not depend on the cluster velocity dispersion. However, z_F increases weakly with cluster redshift. This trend becomes clearer when including higher-z clusters from the literature, suggesting that, at any given z, in order to have a population of fully-formed E and S0s they needed to have formed most of their stars 2-4 Gyr prior to observation. In other words, the galaxies that already have early-type (ET) morphologies also have reasonably-old stellar populations. This is partly a manifestation of the "progenitor bias", but also a consequence of the fact that the vast majority of the ETs in clusters (in particular the massive ones) were already red by the time they achieved their morphology. E and S0 galaxies exhibit very similar colour scatter, implying similar stellar population ages. We also find that fainter ETs finished forming their stars later, consistent with the cluster red sequence being built over time and the brightest galaxies reaching the red sequence earlier than fainter ones. Finally, we find that the ET cluster galaxies must have had their star formation truncated over an extended period of at least 1 Gyr. [abridged]
The coupling (R A^2)/6 of a vector field to gravity was proposed as a mechanism for generating a primordial magnetic field, and more recently as a mechanism for generating a statistically anisotropic contribution to the primordial curvature perturbation. In either case, the vector field's perturbation has both a transverse and a longitudinal component, and the latter has some unusual features which call into question the health of the theory. We calculate for the first time the energy density generated by the longitudinal field perturbations, and go on to argue that the theory may well be healthy in at least some versions.
We present a grid of LTE atmospheric models and synthetic spectra that cover the spectral class range from mid-G to mid-K, and luminosity classes from V to III, that is dense in Teff sampling (Delta Teff=62.5 K), for stars of solar metallicity and moderately metal poor scaled solar abundance ([A/H]=0.0 and -0.5). All models have been computed with two choices of atomic line list: a) the "big" line lists of Kurucz (1992) that best reproduce the broad-band solar blue and near UV flux level, and b) the "small" lists of Kurucz & Peytremann (1975) that provide the best fit to the high resolution solar blue and near-UV spectrum. We compare our model SEDs to a sample of stars carefully selected from the large catalog of uniformly re-calibrated spectrophotometry of Burnashev (1985) with the goal of determining how the quality of fit varies with stellar parameters, especially in the historically troublesome blue and near-UV bands. We confirm that our models computed with the "big" line list recover the derived Teff values of the PHOENIX NextGen grid, but find that the models computed with the "small" line list provide greater internal self-consistency among different spectral bands, and closer agreement with the empirical Teff scale of Ramirez & Melendez (2005), but not to the interferometrically derived Teff values of Baines et al. (2010). We find no evidence that the near UV band discrepancy between models and observations for Arcturus (alpha Boo) reported by Short & Hauschildt (2003 and 2009) is pervasive, and that Arcturus may be peculiar in this regard.
X-ray observations of EXO~0748-676 during thermonuclear bursts revealed a set of narrow (\Delta \lambda /\lambda = 0.018) absorption lines that potentially originate from the stellar photosphere. The identification of these lines with particular atomic transitions led to the measurement of the surface gravitational redshift of the neutron star and to constraints on its mass and radius. However, the recent detection of 552 Hz oscillations at 15% rms amplitude revealed the spin frequency of the neutron star and brought into question the consistency of such a rapid spin with the narrow width of the absorption lines. Here, we calculate the amplitudes of burst oscillations and the width of absorption lines emerging from the surface of a rapidly rotating neutron star for a wide range of model parameters. We show that no combination of neutron-star and geometric parameters can simultaneously reproduce the narrowness of the absorption lines, the high amplitude of the oscillations, and the observed flux at the time the oscillations were detected. We, therefore, conclude that the observed absorption lines are unlikely to originate from the surface of this neutron star.
Using effective field theory techniques we calculate the source multipole moments needed to obtain the spin contributions to the power radiated in gravitational waves from inspiralling compact binaries to third Post-Newtonian order (3PN). The multipoles depend linearly and quadratically on the spins and include both spin(1)spin(2) and spin(1)spin(1) components. The results in this paper provide the last missing ingredient required to determine the phase evolution to 3PN including all spin effects which we will report in a separate paper.
We present a class of spherically symmetric vacuum solutions to an asymptotically safe theory of gravity containing high-derivative terms. We find quantum corrected Schwarzschild-(anti)-de Sitter solutions with running gravitational coupling parameters. The evolution of the couplings is determined by their corresponding renormalization group flow equations. These black holes exhibit properties of a classical Schwarzschild solution at large length scales. At the center, the metric factor remains smooth but the curvature singularity, while softened by the quantum corrections, persists. The solutions have an outer event horizon and an inner Cauchy horizon which equate when the physical mass decreases to a critical value. Super-extremal solutions with masses below the critical value correspond to naked singularities. The Hawking temperature of the black hole vanishes when the physical mass reaches the critical value. Hence, the black holes in the asymptotically safe gravitational theory never completely evaporate. For appropriate values of the parameters such stable black hole remnants make excellent dark matter candidates.
Inflationary cosmology attempts to provide a natural explanation for the flatness and homogeneity of the observable universe. In the context of reversible (unitary) evolution, this goal is difficult to satisfy, as Liouville's theorem implies that no dynamical process can evolve a large number of initial states into a small number of final states. We use the invariant measure on solutions to Einstein's equation to quantify the problems of cosmological fine-tuning. The most natural interpretation of the measure is the flatness problem does not exist; almost all Robertson-Walker cosmologies are spatially flat. The homogeneity of the early universe, however, does represent a substantial fine-tuning; the horizon problem is real. When perturbations are taken into account, inflation only occurs in a negligibly small fraction of cosmological histories, less than $10^{-6.6\times 10^7}$. We argue that while inflation does not affect the number of initial conditions that evolve into a late universe like our own, it nevertheless provides an appealing target for true theories of initial conditions, by allowing for small patches of space with sub-Planckian curvature to grow into reasonable universes.
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I introduce a new code for fast calculation of the Lomb-Scargle periodogram, that leverages the computing power of graphics processing units (GPUs). After establishing a background to the newly emergent field of GPU computing, I discuss the code design and narrate the key parts of the source. Benchmarking calculations indicate no significant differences in accuracy compared to an equivalent CPU-based code; however, the code is up to 200 times faster than the CPU equivalent. Possible applications include spectral analysis of long photometric time series obtained by ongoing satellite missions; and Monte-Carlo simulation of periodogram statistical properties.
We find that X-ray sources in the Extended Chandra Deep Field South are strongly spatially correlated with LABOCA 870 micron sources. We investigate the dependence of this correlation on X-ray flux, hardness ratio and column density, finding that specifically faint and absorbed X-ray sources are significant sub-mm emitters. In the X-ray source redshift subsample we confirm the previous result that higher luminosity sources (L_X>10^44 ergs/s) have greater 870um fluxes but we also find that this subsample selects against absorbed sources, faint in X-ray flux. Overall, we find that X-ray sources contribute 1.5 \pm 0.1 Jy/deg^2 to the sub-mm background, ~3% of the total, in agreement with the prediction of an obscured AGN model which also gives a reasonable fit to the bright sub-mm source counts. This non-unified model also suggests that when Compton-thick, X-ray-undetected sources are included, then the fractional AGN contribution to the sub-mm background would rise from ~3% to a total of 25-40%, although in a unified model the AGN contribution would only reach ~13%, because the sub-mm flux of the X-ray sources is then more representative of the whole AGN population. Measurements of the dependence of sub-mm flux on X-ray flux, luminosity and column density all agree well with the predictions of the non-unified AGN model. Heavily absorbed, X-ray-undetected AGN could explain the further cross-correlation we find between sub-mm sources and z > 0.5 red galaxies. We conclude that sub-mm galaxies may contain the long-sought absorbed AGN population needed to explain the X-ray background.
Astronomy depends on ever increasing computing power. Processor clock-rates have plateaued, and increased performance is now appearing in the form of additional processor cores on a single chip. This poses significant challenges to the astronomy software community. Graphics Processing Units (GPUs), now capable of general-purpose computation, exemplify both the difficult learning-curve and the significant speedups exhibited by massively-parallel hardware architectures. We present a generalised approach to tackling this paradigm shift, based on the analysis of algorithms. We describe a small collection of foundation algorithms relevant to astronomy and explain how they may be used to ease the transition to massively-parallel computing architectures. We demonstrate the effectiveness of our approach by applying it to four well-known astronomy problems: Hogbom CLEAN, inverse ray-shooting for gravitational lensing, pulsar dedispersion and volume rendering. Algorithms with well-defined memory access patterns and high arithmetic intensity stand to receive the greatest performance boost from massively-parallel architectures, while those that involve a significant amount of decision-making may struggle to take advantage of the available processing power.
Microlensing perturbations to the flux ratios of gravitationally lensed quasar images can vary with wavelength because of the chromatic dependence of the accretion disk's apparent size. Multiwavelength observations of microlensed quasars can thus constrain the temperature profiles of their accretion disks, a fundamental test of an important astrophysical process which is not possible using any other method. We present single-epoch broadband photometry of 12 quadruply lensed quasars in 8 bands ranging from 0.36 to 2.2 microns, and Chandra 0.5--8keV flux ratios for five of them. We combine the optical/IR and X-ray ratios, together with X-ray ratios from the literature, using a Bayesian approach to constrain the half-light radii of the quasars in each filter. Comparing the overall disk sizes and wavelength slopes to those predicted by the standard thin accretion disk model, we find that on average the disks are larger than predicted by nearly an order of magnitude, with sizes that grow more slowly with wavelength than predicted. Though the error bars on the slope are large for individual quasars, the large sample size lends weight to the result. Our results present severe difficulties for a standard thin accretion disk as the main source of UV/optical radiation from quasars.
Many observational studies have revealed the presence of multiple stellar generations in Galactic globular clusters. These studies suggest that second-generation stars make up a significant fraction of the current mass of globular clusters, with the second-generation mass fraction ranging from ~50 to 80 per cent in individual clusters. In this Letter we carry out hydrodynamical simulations to explore the dependence of the mass of second-generation stars on the initial mass and structural parameters and stellar initial mass function (IMF) of the parent cluster. We then use the results of these simulations to estimate the fraction, f_{SG,H}, of the mass of the Galactic stellar halo composed of second-generation stars that originated in globular clusters. We study the dependence of f_{SG,H} on the parameters of the initial mass function of the Galactic globular cluster system. For a broad range of initial conditions, we find that the fraction of mass of the Galactic stellar halo in second-generation stars is always small, f_{SG,H}<4-6 per cent for a Kroupa-1993 IMF and f_{SG,H}<7-9 per cent for a Kroupa-2001 IMF.
The Two Micron All-Sky Survey (2MASS) has provided a uniform photometric catalog to search for previously unknown red AGN and QSOs. We have extended the search to the southern equatorial sky by obtaining spectra for 1182 AGN candidates using the 6dF multifibre spectrograph on the UK Schmidt Telescope. These were scheduled as auxiliary targets for the 6dF Galaxy Redshift Survey. The candidates were selected using a single color cut of J - Ks > 2 to Ks ~ 15.5 and a galactic latitude of |b|>30 deg. 432 spectra were of sufficient quality to enable a reliable classification. 116 sources (or ~27%) were securely classified as type 1 AGN, 20 as probable type 1s, and 57 as probable type 2 AGN. Most of them span the redshift range 0.05<z<0.5 and only 8 (or ~6%) were previously identified as AGN or QSOs. Our selection leads to a significantly higher AGN identification rate amongst local galaxies (>20%) than in any previous galaxy survey. A small fraction of the type 1 AGN could have their optical colors reddened by optically thin dust with A_V<2 mag relative to optically selected QSOs. A handful show evidence for excess far-IR emission. The equivalent width (EW) and color distributions of the type 1 and 2 AGN are consistent with AGN unified models. In particular, the EW of the [OIII] emission line weakly correlates with optical--near-IR color in each class of AGN, suggesting anisotropic obscuration of the AGN continuum. Overall, the optical properties of the 2MASS red AGN are not dramatically different from those of optically-selected QSOs. Our near-IR selection appears to detect the most near-IR luminous QSOs in the local universe to z~0.6 and provides incentive to extend the search to deeper near-IR surveys.
Ellesmere Island, at the most northerly tip of Canada, possesses the highest mountain peaks within 10 degrees of the pole. The highest is 2616 m, with many summits over 1000 m, high enough to place them above a stable low-elevation thermal inversion that persists through winter darkness. Our group has studied four mountains along the northwestern coast which have the additional benefit of smooth onshore airflow from the ice-locked Arctic Ocean. We deployed small robotic site testing stations at three sites, the highest of which is over 1600 m and within 8 degrees of the pole. Basic weather and sky clarity data for over three years beginning in 2006 are presented here, and compared with available nearby sea-level data and one manned mid-elevation site. Our results point to coastal mountain sites experiencing good weather: low median wind speed, high clear-sky fraction and the expectation of excellent seeing. Some practical aspects of access to these remote locations and operation and maintenance of equipment there are also discussed.
Gauss-Hermite and Gauss-Laguerre ("shapelet") decompositions of images have become important tools in galaxy modeling, particularly for the purpose of extracting ellipticity and morphological information from astronomical data. However, the standard shapelet basis functions cannot compactly represent galaxies with high ellipticity or large Sersic index, and the resulting underfitting bias has been shown to present a serious challenge for weak-lensing methods based on shapelets. We present here a new convolution relation and a compound "multi-scale" shapelet basis to address these problems, and provide a proof-of-concept demonstration using a small sample of nearby galaxies.
A sunspot penumbra is observationally examined to reveal properties of small-scale flow structures and how they are related to the filamentary magnetic structures and the Evershed flow. We also study how the photospheric dynamics is related to chromospheric activities. The study is based on data analysis of spectro-polarimetric observations of photospheric Fe I lines with the Solar Optical Telescope aboard Hinode in a sunspot penumbra at different heliocentric angles. Vector magnetic fields and velocities are derived using the spectro-polarimetric data and a Stokes inversion technique. An observation with a Ca II H filtergram co-spatial and co-temporal with the spectro-polarimetric one is also used to study possible chromospheric responses. We find small patches with downflows at photospheric layers. The downflow patches have a size of 0.5" or smaller and have a geometrical configuration different from that of the Evershed flow. The downflow velocity is about 1 km/s at lower photspheric layers, and is almost zero in the upper layers. Some of the downflow patches are associated with brightenings seen in Ca II H images. The downflows are possible observational signatures of downward flows driven by magnetic reconnection in the interlaced magnetic field configuration, where upward flows make brightenings in the chromosphere. Another possibility is that they are concentrated downward flows of overturning magnetoconvection.
Helioseismology has provided very detailed information about the solar interior, and extensive data on a large number of stars, although at less detail, are promised by the ongoing and upcoming asteroseismic projects. In the solar case there remain serious challenges in understanding the inferred solar structure, particularly in the light of the revised determinations of the solar surface composition. Also, a secure understanding of the origins of solar rotation as inferred from helioseismology, both in the radiative interior and in the convection zone, is still missing. In the stellar case challenges are certain to appear as the data allow more detailed inferences of the properties of stellar cores. Large remaining uncertainties in modelling concerns the properties of convective cores and other processes that may cause mixing. As a result of developing asteroseismic signatures addressing these and other issues, we can look forward to a highly challenging, and hence exciting, era of stellar astrophysics.
4U 1822-37 is a Low Mass X-ray Binary (LMXB) system with an Accretion Disk Corona. We have obtained 16 new mid-eclipse time measurements of this source during the last 13 years using X- ray observations made with the RXTE-PCA, RXTE-ASM, Swift-XRT, XMM-Newton and Chandra observatories. These, along with the earlier known mid-eclipse times have been used to accurately determine the timescale for a change in the orbital period of 4U 1822-37. We have derived an orbital period Porb = 0.23210887(15) d, which is changing at the rate of \cdot Porb = 1.3(3) x 10-10 d d-1 (at T0 = MJD 45614). The timescale for a change in the orbital period is Porb/ \cdot Porb of 4.9(1.1) x 106 yr. We also report the detection of 0.59290132(11) s (at T0 = MJD 51975) X-ray pulsations from the source with a long term average \cdot Pspin of -2.481(4) x 10-12 s s-1, i.e., a spin-up time scale (Pspin/ \cdot Pspin) of 7578(13) yr. In view of these results, we have discussed various mechanisms that could be responsible for the orbital evolution in this system. Assuming the extreme case of conservative mass transfer, we have found that the measured \cdot Porb requires a large mass transfer rate of (4.2 - 5.2) x 10-8 M\odot yr-1 which together with the spin up rate implies a magnetic field strength in the range of (1-3) x 108 G. Using the long term RXTE-ASM light curve, we have found that the X-ray intensity of the source has decreased over the last 13 years by ? 40% and there are long term fluctuations at time scales of about a year. In addition to the long term intensity variation, we have also observed significant variation in the intensity during the eclipse.
The distributions of frequencies of the maximum oscillation power ($\nu_{max}$) and the large frequency separation ($\Delta\nu$) of red giant stars observed by CoRoT have a dominant peak. Miglio et al. (2009) identify that the stars are red-clump stars. Using stellar population synthesis method, we studied the effects of Reimers mass loss, binary interactions, star formation rate and the mixing-length parameter on the distributions of $\nu_{max}$ and $\Delta\nu$ of red-clump stars. The Reimers mass loss can result in an increase in the $\nu_{max}$ and $\Delta\nu$ of old population which lost a considerable amount of mass, but lead to a small decrease in those of middle-age population which lost a little bit of mass. A high mass-loss rate impedes the low-mass and low-metal stars evolving into core-helium burning stage. Both Reimers mass loss and star formation rate mainly affect the number of CHeB stars with $\nu_{max}$ and $\Delta\nu$, but have almost no effect on the peak locations of the $\nu_{max}$ and $\Delta\nu$. Binary interactions also can lead to that the $\nu_{max}$ and $\Delta\nu$ of some stars increase or decrease. But the fraction of CHeB stars undergoing binary interactions is very small in our simulations. Thus the peak locations are also not affected by binary interactions. The nonuniform distributions of the $\nu_{max}$ and $\Delta\nu$ are mainly caused by the most of red-clump stars having an approximate radius rather than mass. However, the radius of red-clump stars decreases with increasing the mixing-length parameter. Thus the peak locations of the $\nu_{max}$ and $\Delta\nu$ can be affected by the mixing-length parameter.
Sgr A* exhibits flaring in the infrared several times each day, occasionally accompanied by flaring in X-rays. The infrared flares are believed to arise through synchrotron emission from a transient population of accelerated electrons. The X-ray flaring has been interpreted as self-synchrotron-compton, inverse compton, or synchrotron emission associated with the transient electrons. Here I consider the upscattering of infrared flare photons by relativistic thermal electrons in the accretion flow around Sgr A*. Typical profiles of electron density and temperature in the accretion flow are adopted and the X-ray light curves produced by upscattering of infrared flare photons by the accretion flow are computed. Peak X-ray luminosities between 1e33 and 1e34 erg/s are attained for a 10 mJy near-infrared flare, compatible with observed coincident infrared/X-ray flares from Sgr A*. Even if this process is not responsible for the observed flares it still presents a serious constraint on accretion flow models, which must avoid over-producing X-rays and also predicting observable time lags between flaring in infrared and in X-rays. Future high-resolution infrared instrumentation will be able to place the location of the infrared flare and in coordination with the X-ray would severely constrain the disc geometry and the radial profiles of electron density and temperature in the accretion flow.
Interferometric measurements of optical path length differences of stars over large baselines can deliver extremely accurate astrometric data. The interferometer GRAVITY will simultaneously measure two objects in the field of view of the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory (ESO) and determine their angular separation to a precision of 10 micro arcseconds in only 5 minutes. To perform the astrometric measurement with such a high accuracy, the differential path length through the VLTI and the instrument has to be measured (and tracked since Earth's rotation will permanently change it) by a laser metrology to an even higher level of accuracy (corresponding to 1 nm in 3 minutes). Usually, heterodyne differential path techniques are used for nanometer precision measurements, but with these methods it is difficult to track the full beam size and to follow the light path up to the primary mirror of the telescope. Here, we present the preliminary design of a differential path metrology system, developed within the GRAVITY project. It measures the instrumental differential path over the full pupil size and up to the entrance pupil location. The differential phase is measured by detecting the laser fringe pattern both on the telescopes' secondary mirrors as well as after reflection at the primary mirror. Based on our proposed design we evaluate the phase measurement accuracy based on a full budget of possible statistical and systematic errors. We show that this metrology design fulfills the high precision requirement of GRAVITY.
The ANTARES high energy neutrino telescope is a three-dimensional array of about 900 photomultipliers distributed over 12 mooring lines installed in the Mediterranean Sea. Between February and November 2007 it acquired data in a 5-line configuration. The zenith angular distribution of the atmospheric muon flux and the associated depth-intensity relation are measured and compared with previous measurements and Monte Carlo expectations. An evaluation of the systematic effects due to uncertainties on environmental and detector parameters is presented.
Context. Light elements and nitrogen surface abundances together can constrain the mixing efficiencies in massive stars on the main sequence, because moderate mixing at the surface leads to a depletion of light elements but only later to an enrichment in nitrogen. Aims. We want to test the rotational mixing prescriptions included in the Geneva stellar evolution code (GENEC) by following the evolution of surface abundances of light isotopes in massive stars. Methods. The GENEC is a 1D code containing sophisticated prescriptions for rotational mixing. We implemented an extended reaction network into this code including the light elements Li, Be and B, which allowed us to perform calculations testing the rotation induced mixing. Results. We followed 9, 12 and 15 solar mass models with rotation from the zero age main sequence up to the end of He burning. The calculations show the expected behaviour with faster depletion of light isotopes for faster rotating stars and more massive stars. Conclusions. We find that the mixing prescriptions used in the present rotating models for massive single stars can account for most of the observations. However the uncertainties are quite large making it hard to draw a firm conclusion on the mixing scenario.
As a result of applying the original optical variability search method on publicly available data, we have found eight new cataclysmic variables and two possible Optically Violent Variable quasars among the previously unidentified X-ray sources in the ROSAT catalog. We describe the search method and present the characteristics of the newly identified variable stars. The obtained results demonstrate the large potential of the concept of Virtual Observatory for identifying new objects of astrophysical interest.
We present a concept, developed at the National Astronomy and Ionosphere Center (NAIC) at Arecibo, Puerto Rico, for active suppression of Global Positioning System (GPS) signals in the 305 m dish radio receiver path prior to backend processing. The subsystem does not require an auxiliary antenna and is intended for easy integration with radio telescope systems with a goal of being a turnkey addition to virtually any facility. Working with actual sampled signal data, we have focused on the detection and cancellation of the GPS L3 signal at 1381.05 MHz which, during periodic test modes and particularly during system-wide tests, interfere with observations of objects in a range of redshifts that includes the Coma supercluster, for example. This signal can dynamically change modulation modes and our scheme is capable of detecting these changes and applying cancellation or sending a blanking signal, as appropriate. The subsystem can also be adapted to GPS L1 (1575.42 MHz), L2C (1227.6 MHz), and others. A follow-up is underway to develop a prototype to deploy and evaluate at NAIC.
My Ph.D. Thesis is devoted to the study of groups and clusters of galaxies in the X-ray band. This field has been very active in the last ten years, thanks to the data gathered from the Chandra and XMM satellites. Clusters of galaxies are prominent X-ray sources thanks to thermal bremsstrahlung emission from the diffuse ICM heated to 10^7-10^8 K, which provides about 15% of their total mass. The analysis of the X-ray emission from groups and clusters allows to study the large scale structure of the Universe, to constrain the cosmological parameters, and to investigate the interaction between the ICM and the cluster galaxies. My scientific work is mainly focused on the realization of a new X-ray survey of galaxy clusters, the SXCS, obtained from the previously unexplored archive of the X-Ray Telescope (XRT) on board of the Swift satellite. The goal is not only to build a new catalogue, but also to characterize the thermodynamical and chemical properties of the brightest groups and clusters in the survey catalogue. Moreover, given the overall characteristics of the survey, I also expect to detect some clusters at redshift z>1, which will have a strong impact in the study of the large scale structure of the Universe and the cosmological parameters. During my work I also contributed substantially to the image simulator code of a new proposed X-ray mission submitted to the NASA Astro 2010 Decadal Survey: the Wide Field X-ray Telescope (WFXT). This work represents an important part of the scientific case of WFXT, since, for first time in the simulations I included realistic populations of all the source types contributing to the extragalactic X-ray sky, namely groups and clusters of galaxies, active galactic nuclei, and star-forming galaxies. Thanks to this work, the scientific cases of WFXT can now be tested on solid ground.
Resonant absorption and mode conversion are both extensively studied mechanisms for wave "absorption" in solar magnetohydrodynamics (MHD). But are they really distinct? We re-examine a well-known simple resonant absorption model in a cold MHD plasma that places the resonance inside an evanescent region. The normal mode solutions display the standard singular resonant features. However, these same normal modes may be used to construct a ray bundle which very clearly undergoes mode conversion to an Alfv\'en wave with no singularities. We therefore conclude that resonant absorption and mode conversion are in fact the same thing, at least for this model problem. The prime distinguishing characteristic that determines which of the two descriptions is most natural in a given circumstance is whether the converted wave can provide a net escape of energy from the conversion/absorption region of physical space. If it cannot, it is forced to run away in wavenumber space instead, thereby generating the arbitrarily small scales in situ that we recognize as fundamental to resonant absorption and phase mixing. On the other hand, if the converted wave takes net energy way, singularities do not develop, though phase mixing may still develop with distance as the wave recedes.
Kepler is a NASA mission designed to detect exoplanets and characterize the properties of exoplanetary systems. Kepler also includes an asteroseismic programme which is being conducted through the Kepler Asteroseismic Science Consortium (KASC), whose 400 members are organized into 13 working groups by type of variable star. So far data have been available from the first 7 month of the mission containing a total of 2937 targets observed at a 1-min. cadence for periods between 10 days and 7 months. The goals of the asteroseismic part of the Kepler project is to perform detailed studies of stellar interiors. The first results of the asteroseismic analysis are orders of magnitude better than seen before, and this bodes well for how the future analysis of Kepler data for many types of stars will impact our general understanding of stellar structure and evolution.
We analyze the effect of foregrounds on the observed alignment of CMBR quadrupole and octopole. The alignment between these multipoles is studied by using a symmetry based approach which assigns a principal eigenvector (PEV) or an axis with each multipole. We determine the significance of alignment between these multipoles by using the Internal Linear Combination (ILC) 5 and 7 year map s and also the maps obtained by using the Internal Power Spectrum Estimation (IPSE) procedure. The effect of foreground cleaning is studied in detail within the framework of the IPSE method both analytically and numerically. By using simulated CMBR data, we study how the PEVs of the pure simulated CMB map differ from those of the final cleaned map. We find that, in general, the shift in the PEVs is relatively small and in random directions. Due to the random nature of the shift we conclude that it can only lead to misalignment rather than alignment of multipoles. We also directly estimate the significance of alignment by using simulated cleaned maps. We find that the results in this case are identical to those obtained by simple analytic estimate or by using simulated pure CMB maps.
To investigate whether distinctions exist between low and high-luminosity Class II 6.7-GHz methanol masers, we have undertaken multi-line mapping observations of various molecular lines, including the NH3(1,1), (2,2), (3,3), (4,4) and 12CO(1-0) transitions, towards a sample of 9 low-luminosity 6.7-GHz masers, and 12CO (1-0) observations towards a sample of 8 high-luminosity 6.7-GHz masers, for which we already had NH3 spectral line data. Emission in the NH3 (1,1), (2,2) and (3,3) transitions was detected in 8 out of 9 low-luminosity maser sources, in which 14 cores were identified. We derive densities, column densities, temperatures, core sizes and masses of both low and high-luminosity maser regions. Comparative analysis of the physical quantities reveals marked distinctions between the low-luminosity and high-luminosity groups: in general, cores associated with high-luminosity 6.7-GHz masers are larger and more massive than those traced by low-luminosity 6.7-GHz masers; regions traced by the high-luminosity masers have larger column densities but lower densities than those of the low-luminosity maser regions. Further, strong correlations between 6.7-GHz maser luminosity and NH3(1,1) and (2,2) line widths are found, indicating that internal motions in high-luminosity maser regions are more energetic than those in low-luminosity maser regions. A 12CO (1-0) outflow analysis also shows distinctions in that outflows associated with high-luminosity masers have wider line wings and larger sizes than those associated with low-luminosity masers.
The reliability of infrared (IR) and ultraviolet (UV) emissions to measure star formation rates in galaxies is investigated for a large sample of galaxies observed with the SPIRE and PACS instruments on Herschel as part of the HerMES project. We build flux-limited 250 micron samples of sources at redshift z<1, cross-matched with the Spitzer/MIPS and GALEX catalogues. About 60 % of the Herschel sources are detected in UV. The total IR luminosities, L_IR, of the sources are estimated using a SED-fitting code that fits to fluxes between 24 and 500 micron. Dust attenuation is discussed on the basis of commonly-used diagnostics: the L_IR/L_UV ratio and the slope, beta, of the UV continuum. A mean dust attenuation A_UV of ~ 3 mag is measured in the samples. L_IR/L_UV is found to correlate with L_IR. Galaxies with L_IR > 10 ^{11} L_sun and 0.5< z<1 exhibit a mean dust attenuation A_UV about 0.7 mag lower than that found for their local counterparts, although with a large dispersion. Our galaxy samples span a large range of beta and L_IR/L_UV values which, for the most part, are distributed between the ranges defined by the relations found locally for starburst and normal star-forming galaxies. As a consequence the recipe commonly applied to local starbursts is found to overestimate the dust attenuation correction in our galaxy sample by a factor ~2-3 .
Aims. We study the statistical properties of the gravitational field generated by galaxy distribution from the Sloan Digital Sky Survey (DR7). We characterize the probability density function (PDF) of gravitational force fluctuations and we relate its limiting behaviors to the correlation properties of the underlying density field. In addition, we study whether the PDF converges to an asymptotic shape within sample volumes. Methods. We consider several volume limited samples of the Sloan Digital Sky Survey and we compute the gravitational force PDF. The gravitational force is computed in spheres of varying radius, and so its PDF. Results. We find that (i) the PDF of the force displays features that can be understood in terms of galaxy two-point correlations and that (ii) density fluctuations at the largest scales probed, i.e. r \approx 100 Mpc/h, still significantly contribute to the amplitude of the gravitational force. Conclusions. Our main conclusion is that fluctuations in the gravitational force field generated by galaxy structures are relevant also at scales ~ 100 Mpc/h. By assuming that the gravitational fluctuations in the galaxy distribution reflect those in the whole matter distribution, and that peculiar velocities and accelerations are simply correlated, we may conclude that large-scale fluctuations in the galaxy density field can be the source of the large scale flows recently observed.
We have observed CH absorption lines ($J=3/2, N=1 \leftarrow J=1/2, N=1$) against the continuum source Sgr~B2(M) using the \textit{Herschel}/HIFI instrument. With the high spectral resolution and wide velocity coverage provided by HIFI, 31 CH absorption features with different radial velocities and line widths are detected and identified. The narrower line width and lower column density clouds show `spiral arm' cloud characteristics, while the absorption component with the broadest line width and highest column density corresponds to the gas from the Sgr~B2 envelope. The observations show that each `spiral arm' harbors multiple velocity components, indicating that the clouds are not uniform and that they have internal structure. This line-of-sight through almost the entire Galaxy offers unique possibilities to study the basic chemistry of simple molecules in diffuse clouds, as a variety of different cloud classes are sampled simultaneously. We find that the linear relationship between CH and H$_2$ column densities found at lower $A_V$ by UV observations does not continue into the range of higher visual extinction. There, the curve flattens, which probably means that CH is depleted in the denser cores of these clouds.
Almost all sources of high energy particles and photons are associated with jet phenomena. Prominent sources of such highly relativistic outflows are pulsar winds and Active Galactic Nuclei. The current understanding of these jets assumes diluted plasmas which are best described as kinetic phenomena. In this kinetic description particle acceleration to ultra-relativistic speeds can occur in completely unmagnetized and neutral plasmas through insetting effects of instabilities. Even though the morphology and nature of particle spectra are understood to a certain extent, the composition of the jets is not known yet. While Poynting-flux dominated jets are certainly composed of electron-positron plasmas, the understanding of the governing physics in AGN jets is mostly unclear. In this article we investigate how the constituting elements of an electron-positron-proton plasma behave differently under the variation of the fundamental mass-ratio m_p/m_e. We studied initially unmagnetized counterstreaming plasmas using fully relativistic three-dimensional particle-in-cell simulations to investigate the influence of the mass-ratio on particle acceleration and magnetic field generation in electron-positron-proton plasmas. We covered a range of mass-ratios m_p/m_e between 1 and 100 with a particle number composition of n_{p^+}/n_{e^+} of 1 in one stream, only protons are injected in the other, whereas electrons are present in both to guarantee charge neutrality in the simulation box. We find that with increasing proton mass the instability takes longer to develop and for mass-ratios > 20 the particles seem to be accelerated in two phases which can be accounted to the individual instabilities of the different species. This means that for high mass ratios the coupling between electrons/positrons and the heavier protons, which occurs in low mass-ratios, disappears.
Supernovae of Type IIb contain large fractions of helium and traces of
hydrogen, which can be observed in the early and late spectra. Estimates of the
hydrogen and helium mass and distribution are mainly based on early-time
spectroscopy and are uncertain since the respective lines are usually observed
in absorption. Constraining the mass and distribution of H and He is important
to gain insight into the progenitor systems of these SNe.
We implement a NLTE treatment of hydrogen and helium in a three-dimensional
nebular code. Ionisation, recombination, (non-)thermal electron excitation and
H$\alpha$ line scattering are taken into account to compute the formation of
H$\alpha$, which is by far the strongest H line observed in the nebular spectra
of SNe IIb. Other lines of H and He are also computed but are rarely identified
in the nebular phase. Nebular models are computed for the Type IIb SNe 1993J,
2001ig, 2003bg and 2008ax as well as for SN 2007Y, which shows H$\alpha$
absorption features at early times and strong H$\alpha$ emission in its late
phase, but has been classified as a SN Ib. We suggest to classify SN 2007Y as a
SN IIb. Optical spectra exist for all SNe of our sample, and there is one IR
nebular observation of SN 2008ax, which allows an exploration of its helium
mass and distribution.
We develop a three-dimensional model for SN 2008ax. We obtain estimates for
the total mass and kinetic energy in good agreement with the results from
light-curve modelling found in the literature. We further derive abundances of
He, C, O, Ca and $^{56}$Ni. We demonstrate that H$\alpha$ absorption is
probably responsible for the double-peaked profile of the [O {\sc i}]
$\lambda\lambda$ 6300, 6363 doublet in several SNe IIb and present a mechanism
alternative to shock interaction for generating late-time H$\alpha$ emission of
SNe IIb.
We present a search for Herschel-PACS counterparts of dust-obscured, high-redshift objects previously selected at submillimeter and millimeter wavelengths in the Great Observatories Origins Deep Survey North field. We detect 22 of 56 submillimeter galaxies (39%) with a SNR of >=3 at 100 micron down to 3.0 mJy, and/or at 160 micron down to 5.7 mJy. The fraction of SMGs seen at 160 micron is higher than that at 100 micron. About 50% of radio-identified SMGs are associated with PACS sources. We find a trend between the SCUBA/PACS flux ratio and redshift, suggesting that these flux ratios could be used as a coarse redshift indicator. PACS undetected submm/mm selected sources tend to lie at higher redshifts than the PACS detected ones. A total of 12 sources (21% of our SMG sample) remain unidentified and the fact that they are blank fields at Herschel-PACS and VLA 20 cm wavelength may imply higher redshifts for them than for the average SMG population (e.g., z>3-4). The Herschel-PACS imaging of these dust-obscured starbursts at high-redshifts suggests that their far-infrared spectral energy distributions have significantly different shapes than template libraries of local infrared galaxies.
Excursion set theory, where density perturbations evolve stochastically with the smoothing scale, provides a method for computing the mass function of cosmological structures like dark matter halos, sheets and filaments. The computation of these mass functions is mapped into the so-called first-passage time problem in the presence of a moving barrier. In this paper we use the path integral formulation of the excursion set theory developed recently to analytically solve the first-passage time problem in the presence of a generic moving barrier, in particular the barrier corresponding to ellipsoidal collapse. We perform the computation for both Gaussian and non-Gaussian initial conditions. The expression of the halo mass function for the ellipsoidal collapse barrier and with non-Gaussianity is therefore obtained in a fully consistent way and it does not require the introduction of any form factor artificially derived from the Press-Schechter formalism based on the spherical collapse and usually adopted in the literature.
We present the results from 1.5D diffusion simulations of the Kippenhahn-Schlueter prominence model magnetic field evolution under the influence of the ambipolar terms of Cowling resistivity. We show that initially the evolution is determined by the ratio of the horizontal and vertical magnetic fields, which gives current sheet thinning (thickening) when this ratio is large (small) and a marginal case where a new characteristic current sheet length scale is formed. After a timespan greater than the Cowling resistivity time, the current sheet thickens as a power law of $t$ independent of the ratio of the field strengths. These results imply that when Cowling resistivity is included in the model, the tearing instability time scale is reduced by more than one order of magnitude when the ratio of the horizontal field to the vertical field is 20\% or less. These results imply that, over the course of its lifetime, the structure of the prominence can be significantly altered by Cowling resistivity, and in some cases will allow the tearing instability to occur.
We present the compilation and properties of a Meta-Catalogue of X-ray detected Clusters of galaxies, the MCXC. This very large catalogue is based on publicly available ROSAT All Sky Survey-based (NORAS, REFLEX, BCS, SGP, NEP, MACS, and CIZA) and serendipitous (160SD, 400SD, SHARC, WARPS, and EMSS) cluster catalogues. Data have been systematically homogenised to an overdensity of 500, and duplicate entries originating from overlaps between the survey areas of the individual input catalogues are carefully handled. The MCXC comprises 1743 clusters with virtually no duplicate entries. For each cluster the MCXC provides: three identifiers, a redshift, coordinates, membership of original catalogue, and standardised 0.1-2.4 keV band luminosity L_500, total mass M_500, and radius R_500. The meta-catalogue additionally furnishes information on overlaps between the input catalogues and the luminosity ratios when measurements from different surveys are available, and also gives notes on individual objects. The MCXC is available in electronic format for maximum usefulness in X-ray, SZ, and multi-wavelength studies.
The unique properties of dark matter are revealed during collisions between
clusters of galaxies, like the bullet cluster (1E 0657-56) and baby bullet
(MACSJ0025-12). These systems provide evidence for an additional, invisible
mass in the separation between the distribution of their total mass, measured
via gravitational lensing, and their ordinary 'baryonic' matter, measured via
its X-ray emission. Unfortunately, the information available from these systems
is limited by their rarity. Constraints on the properties of dark matter, such
as its interaction cross-section, are therefore restricted by uncertainties in
the individual systems' impact velocity, impact parameter and orientation with
respect to the line of sight.
Here we develop a complementary, statistical measurement in which every piece
of substructure falling into every massive cluster is treated as a bullet. We
define 'bulleticity' as the mean separation between dark matter and ordinary
matter, and we measure a positive signal in hydrodynamical simulations. The
phase space of substructure orbits also exhibits symmetries that provide a
statistical null test. A real detection of bulleticity would provide evidence
for a difference in the interaction cross-sections of baryonic and dark matter,
and may rule out hypotheses of non-particulate dark matter that are otherwise
able to model individual systems.
We describe a semi-analytical approach to non-linear diffusive shock acceleration in the case in which nuclei other than protons are also accelerated. The structure of the shock is determined by the complex interplay of all nuclei, and in turn this shock structure determines the spectra of all components. The magnetic field amplification upstream is described as due to streaming instability of all nuclear species. The amplified magnetic field is then taken into account for its dynamical feedback on the shock structure as well as in terms of the induced modification of the velocity of the scattering centers that enters the particle transport equation. The spectra of accelerated particles are steep enough to be compared with observed cosmic ray spectra only if the magnetic field is sufficiently amplified and the scattering centers have high speed in the frame of the background plasma. We discuss the implications of this generalized approach on the structure of the knee in the all-particle cosmic ray spectrum, which we interpret as due to an increasingly heavier chemical composition above $10^{15}$eV. The effects of a non trivial chemical composition at the sources on the gamma ray emission from a supernova remnant when gamma rays are of hadronic origin are also discussed.
We investigate the effects of the environment on star-formation in a sample of massive luminous and ultra-luminous infrared galaxies (LIRGs and ULIRGs) with S(24 micron)>80 uJy and i+<24 in the COSMOS field. We exploit the accurate photometric redshifts in COSMOS to characterize the galaxy environment and study the evolution of the fraction of LIRGs and ULIRGs in different environments in the redshift range z=0.3-1.2 and in bins of stellar mass. We find that the environment plays a role in the star formation processes and evolution of LIRGs and ULIRGs. We find an overall increase of the ULIRG+LIRG fraction in an optically-selected sample with increasing redshift, as expected from the evolution of the star formation rate density. We find that the ULIRG+LIRG fraction decreases with increasing density up to z~1, and that the dependence on density flattens with increasing redshift. We do not observe the reversal of the star-formation rate density relation up to z=1 in massive LIRGs and ULIRGs, suggesting that such reversal might occur at higher redshift in this infrared luminosity range.
We present a single pulse study of pulsar B1944+17, whose non-random nulls dominate nearly 70% of its pulses and usually occur at mode boundaries. When not in the null state, this pulsar displays four bright modes of emission, three of which exhibit drifting subpulses. B1944+17 displays a weak interpulse whose position relative to the main pulse we find to be frequency independent. Its emission is nearly 100% polarized, its polarization-angle traverse is very shallow and opposite in direction to that of the main pulse, and it nulls approximately two-thirds of the time. Geometric modeling indicates that this pulsar is a nearly aligned rotator whose alpha value is hardly 2 degrees--i.e., its magnetic axis is so closely aligned with its rotation axis that its sightline orbit remains within its conal beam. The star's nulls appear to be of two distinct types: those with lengths less than about 8 rotation periods appear to be pseudonulls--that is, produced by "empty" sightline traverses through the conal beam system; whereas the longer nulls appear to represent actual cessations of the pulsar's emission engine.
Damped transverse oscillations of solar prominence fine structures are frequently reported and have been interpreted as kink magnetohydrodynamic (MHD) modes. Here, we investigate standing kink MHD oscillations in a prominence fine structure. Our model is composed of a magnetic tube only partially filled with the prominence material, while the coronal plasma occupies both the rest of the tube and the external medium. Ion-neutral collisions and resonant absorption are the considered damping mechanisms. Approximate analytical expressions of the period, the damping time, and the ratio of the damping time to the period are derived for the fundamental kink mode. A parametric study is performed by numerically solving the full dispersion relation. We find that the dominant damping mechanism is resonant absorption, which provides realistic damping ratios, whereas ion-neutral collisions are irrelevant for the damping. The values of the damping ratio are independent of both the prominence thread length and its position within the magnetic tube, and coincide with the values for a tube fully filled with the prominence plasma. The implications of our results in the context of the MHD seismology technique are discussed, pointing out that the reported short-period (2 -- 10 min) and short-wavelength (700 -- 8,000 km) thread oscillations may not be consistent with a standing mode interpretation and could be related to propagating waves. Finally, we show that the inversion of some prominence physical parameters, e.g., Alfv\'en speed, magnetic field strength, transverse inhomogeneity length-scale, etc., is possible using observationally determined values of the period and damping time of the oscillations along with the analytical approximations of these quantities.
Reply to Flambaum and Porsev comment arXiv:1004.2540 on "21 cm radiation - a new probe of variation in the fine structure constant" arXiv:astro-ph/0701752
The present article is about the statistical mechanics of non-trivial field configurations. The non-trivial fields arise from the negative sign of the commutators and the anticommutators of the bosonic and fermionic field excitations. These kinds of fields were previously studied by Pauli and Lee and Wick. The thermal distribution function of the above mentioned fields are calculated in the article and using the thermal distribution functions the energy density, pressure and entropy density of the non-trivial field configurations are found out. The results match exactly with a previous calculation done by Fornal et. al. for higher derivative Lee-Wick theories showing a deeper similarity with the earlier work. It is assumed that such kinds of non-trivial fields may have existed in the early universe and may have some cosmological relevance.
We present further analysis of an anisotropic, non-singular early universe model that leads to the viable cosmology presented in Dechant et al (arXiv:0809.4335). Although this model (the DLH model) contains scalar field matter, it is reminiscent of the Taub-NUT vacuum solution in that it has biaxial Bianchi IX geometry and its evolution exhibits a dimensionality reduction at a quasi-regular singularity that one can identify with the big-bang. We show that the DLH and Taub-NUT metrics are related by a coordinate transformation, in which the DLH time coordinate plays the role of conformal time for Taub-NUT. Since both models continue through the big-bang, the coordinate transformation can become multivalued. In particular, in mapping from DLH to Taub-NUT, the Taub-NUT time can take only positive values. We present explicit maps between the DLH and Taub-NUT models, with and without a scalar field. In the vacuum DLH model, we find a periodic solution expressible in terms of elliptic integrals. Mapping the vacuum solution over to Taub-NUT coordinates, recovers the standard (non-periodic) Taub-NUT solution in the Taub region, where Taub-NUT time takes positive values, but does not exhibit the two NUT regions known in the standard Taub-NUT solution. Conversely, mapping the complete Taub-NUT solution to the DLH case reveals that the NUT regions correspond to imaginary time and space in DLH coordinates. We show that many of the well-known `pathologies' of the Taub-NUT solution arise because the traditional coordinates are connected by a multivalued transformation to the physically more meaningful DLH coordinates. In particular, the `open-to-closed-to-open' transition and the Taub and NUT regions of the (Lorentzian) Taub-NUT model are replaced by a closed pancaking universe with spacelike homogeneous sections at all times.
We present a successful inflation model based on $\lambda \phi^4$ potential in which a Standard Model (SM) singlet inflaton $\phi$, with mass of around a TeV or less, also plays the role of a weakly interacting scalar dark matter particle (WIMP). The WIMP relic abundance generated after inflation is in accord with the current observations. The spectral index $n_s$ lies within the WMAP 1-$\sigma$ bounds, while the Planck satellite may observe the tensor-to-scalar ratio, a canonical measure of gravity waves, which we estimate lies between 0.003 and 0.007.An unbroken $Z_2$ parity ensures that the scalar WIMP is absolutely stable.
An effect generated by the nonexponential behavior of the survival amplitude of an unstable state in the long time region is considered. We find that the instantaneous energy of the unstable state for a large class of models of unstable states tends to the minimal energy of the system ${\cal E}_{min}$ as $t\rightarrow\infty$ which is much smaller than the energy of this state for $t$ of the order of the lifetime of the considered state. Analyzing the transition time region between exponential and non-exponential form of the survival amplitude we find that the instantaneous energy of the considered unstable state can take large values, much larger than the energy of this state for $t$ from the exponential time region. Taking into account results obtained for a model considered, it is hypothesized that this purely quantum mechanical effect may be responsible for the properties of broad resonances such as $\sigma$ meson as well as having astrophysical and cosmological consequences.
We present the first quantitative comparison of two independent general-relativistic hydrodynamics codes, the Whisky code and the SACRA code. We compare the output of simulations starting from the same initial data and carried out with the configuration (numerical methods, grid setup, resolution, gauges) which for each code has been found to give consistent and sufficiently accurate results, in particular in terms of cleanness of gravitational waveforms. We focus on the quantities that should be conserved during the evolution (rest mass, total mass energy, and total angular momentum) and on the gravitational-wave amplitude and frequency. We find that the results produced by the two codes agree at a reasonable level, with variations in the different quantities but always at better than about 10%.
Dynamo action is shown to be induced from homogeneous non-minimal photon-torsion axial coupling in the quantum electrodynamics (QED) framework in Riemann flat spacetime contortion decays. The geometrical optics in Riemann-Cartan spacetime is considering and a plane wave expansion of the electromagnetic vector potential is considered leading to a set of the equations for the ray congruence. Since we are interested mainly on the torsion effects in this first report we just consider the Riemann-flat case composed of the Minkowskian spacetime with torsion. It is also shown that in torsionic de Sitter background the vacuum polarisation does alter the propagation of individual photons, an effect which is absent in Riemannian spaces. It is shown that the cosmological torsion background inhomogeneities induce Lorentz violation and massive photon modes in this QED. Magnetic dynamos in this torsioned spacetime electrodynamics are simpler obtained in Fourier space than the cosmic ones, previously obtained by Bassett et al Phys Rev D, in Friedmann universe. By deriving plasma dispersion for linear electrodynamics in Riemann Cartan spacetime, dynamo action seems to be possible for plasma frequencies in some polarizations. The important cosmic magnetic field problem of breaking conformal flatness is naturally solved here since the photon torsion coupling breaks conformal flatness.
In this note we briefly summarize the main future targets and strategies for axion and general low energy particle physics identified in the "3rd axion strategy meeting" held during the AXIONS 2010 workshop. This summary follows a wide discussion with contributions from many of the workshop attendees.
Using Crumeyrolle's hypercomplex theory in the case of symmetric connection, we show that the description of the space-time of general relativity as a diagonal four dimensional submanifold immersed in an eight dimensional hypercomplex manifold leads to a geometrical origin of the cosmological constant and dark energy. The cosmological constant appears naturally in the new filed equations and its expression is given as the norm of an undetermined four-vector $U$, i.e., $\Lambda=6g_{\mu\nu}U^{\mu}U^{\nu}$. Consequently, the cosmological constant is space-time dependent, a Lorentz invariant scalar, and may be positive, negative or null. A new energy momentum tensor of the dark energy is obtained which depends on the cosmological constant and its first derivative with respect to the metric. As an application, we obtain the spherical solution for the field equations. In cosmology, the modified Friedmann equations are proposed and a condition on $\Lambda$ for an accelerating universe is deduced.
We present new atomic data (radiative transitions rates and collision strengths) from large scale calculations and a non-LTE spectral model for Fe III. This model is in very good agreement with observed astronomical emission spectra, in contrast with previous models that yield large discrepancies with observations. The present atomic computations employ a combination of atomic physics methods, e.g. relativistic Hatree-Fock, the Thomas-Fermi-Dirac potential, and Dirac-Fock computation of A-values and R-matrix with intermediate coupling frame transformation and Dirac R-matrix. We study the advantages and shortcomings of each method. It is found that the Dirac R-matrix collision strengths yield excellent agreement with observations, much improved over previously available models. By contrast, the transformation of LS-coupling R-matrix fails to yield accurate effective collision strengths at around 10^4 K, despite using very large configuration expansions, due to the limited treatment of spin-orbit effects in the near threshold resonances of the collision strengths. The present work demonstrates that accurate atomic data for low ionization iron-peak species is now within reach.
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We use data drawn from the DEEP2 Galaxy Redshift Survey to investigate the relationship between local galaxy density, stellar mass, and rest-frame galaxy color. At z ~ 0.9, we find that the shape of the stellar mass function at the high-mass (log (M*/Msun) > 10.1) end depends on the local environment, with high-density regions favoring more massive systems. Accounting for this stellar mass-environment relation (i.e., working at fixed stellar mass), we find a significant color-density relation for galaxies with 10.6 < log(M*/Msun) < 11.1 and 0.75 < z < 0.95. This result is shown to be robust to variations in the sample selection and to extend to even lower masses (down to log(M*/Msun) ~ 10.4). We conclude by discussing our results in comparison to recent works in the literature, which report no significant correlation between galaxy properties and environment at fixed stellar mass for the same redshift and stellar mass domain. The non-detection of environmental dependence found in other data sets is largely attributable to their smaller samples size and lower sampling density, as well as systematic effects such as inaccurate redshifts and biased analysis techniques. Ultimately, our results based on DEEP2 data illustrate that the evolutionary state of a galaxy at z ~ 1 is not exclusively determined by the stellar mass of the galaxy. Instead, we show that local environment appears to play a distinct role in the transformation of galaxy properties at z > 1.
We present an analysis of the constraints on the amplitude of primordial non-Gaussianity of local type described by the dimensionless parameter $f_{\rm NL}$. These constraints are set by the auto-correlation functions (ACFs) of two large scale structure probes, the radio sources from NRAO VLA Sky Survey (NVSS) and the quasar catalogue of Sloan Digital Sky Survey Release Six (SDSS DR6 QSOs), as well as by their cross-correlation functions (CCFs) with the cosmic microwave background (CMB) temperature map (Integrated Sachs-Wolfe effect). Several systematic effects that may affect the observational estimates of the ACFs and of the CCFs are investigated and conservatively accounted for. Our approach exploits the large-scale scale-dependence of the non-Gaussian halo bias. The derived constraints on {$f_{\rm NL}$} coming from the NVSS CCF and from the QSO ACF and CCF are weaker than those previously obtained from the NVSS ACF, but still consistent with them. Finally, we obtain the constraints on $f_{\rm NL}=53\pm25$ ($1\,\sigma$) and $f_{\rm NL}=47\pm21$ ($1\,\sigma$) from NVSS data and SDSS DR6 QSO data, respectively.
HESS J1632-478 is an extended and still unidentified TeV source in the galactic plane. In order to identify the source of the very high energy emission and to constrain its spectral energy distribution, we used a deep observation of the field obtained with XMM-Newton together with data from Molonglo, Spitzer and Fermi to detect counterparts at other wavelengths. The flux density emitted by HESS J1632-478 peaks at very high energies and is more than 20 times weaker at all other wavelengths probed. The source spectrum features two large prominent bumps with the synchrotron emission peaking in the ultraviolet and the external inverse Compton emission peaking in the TeV. HESS J1632-478 is an energetic pulsar wind nebula with an age of the order of 10^4 years. Its bolometric (mostly GeV-TeV) luminosity reaches 10% of the current pulsar spin down power. The synchrotron nebula has a size of 1 pc and contains an unresolved point-like X-ray source, probably the pulsar with its wind termination shock.
We present an overview of the design of IRIS, an infrared (0.85 - 2.5 micron) integral field spectrograph and imaging camera for the Thirty Meter Telescope (TMT). With extremely low wavefront error (<30 nm) and on-board wavefront sensors, IRIS will take advantage of the high angular resolution of the narrow field infrared adaptive optics system (NFIRAOS) to dissect the sky at the diffraction limit of the 30-meter aperture. With a primary spectral resolution of 4000 and spatial sampling starting at 4 milliarcseconds, the instrument will create an unparalleled ability to explore high redshift galaxies, the Galactic center, star forming regions and virtually any astrophysical object. This paper summarizes the entire design and basic capabilities. Among the design innovations is the combination of lenslet and slicer integral field units, new 4Kx4k detectors, extremely precise atmospheric dispersion correction, infrared wavefront sensors, and a very large vacuum cryogenic system.
We present a study of strong cool core, highly-luminous (most with L_x > 10^(45) erg/s), clusters of galaxies in which the mean central active galactic nucleus jet power must be very high yet no central point X-ray source is detected. Using the unique spatial resolution of Chandra, a sample of 13 clusters is analysed, including A1835, A2204, and one of the most massive cool core clusters, RXCJ1504.1-0248. All of the central galaxies host a radio source, indicating an active nucleus, and no obvious X-ray point source. For all clusters in the sample, the nucleus has an X-ray bolometric luminosity below 2 per cent of that of the entire cluster. Most have a nucleus 2-10 keV X-ray luminosity less than about 10^(42) erg/s . We investigate how these clusters can have such strong X-ray luminosities, short radiative cooling-times of the inner intracluster gas requiring strong energy feedback to counterbalance that cooling, and yet have such radiatively-inefficient cores. Our study focuses on deriving the nucleus X-ray properties of the clusters as defined in the above question, while briefly addressing possible solutions.
We present sensitivity estimates for point and resolved astronomical sources for the current design of the InfraRed Imaging Spectrograph (IRIS) on the future Thirty Meter Telescope (TMT). IRIS, with TMT's adaptive optics system, will achieve unprecedented point source sensitivities in the near-infrared (0.84 - 2.45 {\mu}m) when compared to systems on current 8-10m ground based telescopes. The IRIS imager, in 5 hours of total integration, will be able to perform a few percent photometry on 26 - 29 magnitude (AB) point sources in the near-infrared broadband filters (Z, Y, J, H, K). The integral field spectrograph, with a range of scales and filters, will achieve good signal-to-noise on 22 - 26 magnitude (AB) point sources with a spectral resolution of R=4,000 in 5 hours of total integration time. We also present simulated 3D IRIS data of resolved high-redshift star forming galaxies (1 < z < 5), illustrating the extraordinary potential of this instrument to probe the dynamics, assembly, and chemical abundances of galaxies in the early universe. With its finest spatial scales, IRIS will be able to study luminous, massive, high-redshift star forming galaxies (star formation rates ~ 10 - 100 M yr-1) at ~100 pc resolution. Utilizing the coarsest spatial scales, IRIS will be able to observe fainter, less massive high-redshift galaxies, with integrated star formation rates less than 1 M yr-1, yielding a factor of 3 to 10 gain in sensitivity compared to current integral field spectrographs. The combination of both fine and coarse spatial scales with the diffraction-limit of the TMT will significantly advance our understanding of early galaxy formation processes and their subsequent evolution into presentday galaxies.
The InfraRed Imaging Spectrograph (IRIS) is a first-light instrument being designed for the Thirty Meter Telescope (TMT). IRIS is a combination of an imager that will cover a 16.4" field of view at the diffraction limit of TMT (4 mas sampling), and an integral field unit spectrograph that will sample objects at 4-50 mas scales. IRIS will open up new areas of observational parameter space, allowing major progress in diverse fields of astronomy. We present the science case and resulting requirements for the performance of IRIS. Ultimately, the spectrograph will enable very well-resolved and sensitive studies of the kinematics and internal chemical abundances of high-redshift galaxies, shedding light on many scenarios for the evolution of galaxies at early times. With unprecedented imaging and spectroscopy of exoplanets, IRIS will allow detailed exploration of a range of planetary systems that are inaccessible with current technology. By revealing details about resolved stellar populations in nearby galaxies, it will directly probe the formation of systems like our own Milky Way. Because it will be possible to directly characterize the stellar initial mass function in many environments and in galaxies outside of the the Milky Way, IRIS will enable a greater understanding of whether stars form differently in diverse conditions. IRIS will reveal detailed kinematics in the centers of low-mass galaxies, allowing a test of black hole formation scenarios. Finally, it will revolutionize the characterization of reionization and the first galaxies to form in the universe.
We present a conceptual design for the atmospheric dispersion corrector (ADC) for TMT's Infrared Imaging Spectrograph (IRIS). The severe requirements of this ADC are reviewed, as are limitations to observing caused by uncorrectable atmospheric effects. The requirement of residual dispersion less than 1 milliarcsecond can be met with certain glass combinations. The design decisions are discussed and the performance of the design ADC is described. Alternative options and their performance tradeoffs are also presented.
The Infra-Red Imaging Spectrograph (IRIS) is one of the three first light instruments for the Thirty Meter Telescope (TMT) and is the only one to directly sample the diffraction limit. The instrument consists of a parallel imager and off-axis Integral Field Spectrograph (IFS) for optimum use of the near infrared (0.84um-2.4um) Adaptive Optics corrected focal surface. We present an overview of the IRIS spectrograph that is designed to probe a range of scientific targets from the dynamics and morphology of high-z galaxies to studying the atmospheres and surfaces of solar system objects, the latter requiring a narrow field and high Strehl performance. The IRIS spectrograph is a hybrid system consisting of two state of the art IFS technologies providing four plate scales (4mas, 9mas, 25mas, 50mas spaxel sizes). We present the design of the unique hybrid system that combines the power of a lenslet spectrograph and image slicer spectrograph in a configuration where major hardware is shared. The result is a powerful yet economical solution to what would otherwise require two separate 30m-class instruments.
Observations of clusters of galaxies suggest that they contain significantly fewer baryons (gas plus stars) than the cosmic baryon fraction. This `missing baryon' puzzle is especially surprising for the most massive clusters which are expected to be representative of the cosmic matter content of the universe (baryons and dark matter). Here we show that the baryons may not actually be missing from clusters, but rather are extended to larger radii than typically observed. The baryon deficiency is typically observed in the central regions of clusters (~0.5 the virial radius). However, the observed gas-density profile is significantly shallower than the mass-density profile, implying that the gas is more extended than the mass and that the gas fraction increases with radius. We use the observed density profiles of gas and mass in clusters to extrapolate the measured baryon fraction as a function of radius and as a function of cluster mass. We find that the baryon fraction reaches the cosmic value near the virial radius for all groups and clusters above 5e13 solar masses. This suggests that the baryons are not missing, they are simply located in cluster outskirts. Heating processes (shock-heating of the intracluster gas, plus supernovae and AGN feedback) that cause the gas to expand are likely explanations for these results. Upcoming observations should be able to detect these baryons.
We extend our analysis of the observed disturbances on the outskirts of the HI disk of the Milky Way. We employ the additional constraints of the phase of the modes of the observed HI image and asymmetry in the radial velocity field to derive the azimuth of the perturber inferred to be responsible for the disturbances in the HI disk. We carry out a modal analysis of the phase of the disturbances in the HI image and in SPH simulations of a Milky Way-like galaxy tidally interacting with dark perturbers, the relative offset of which we utilize to derive the perturber azimuth. To make a direct connection with observations, we express our results in sun-centered coordinates, predicting that the perturber responsible for the observed disturbances is between $-50 \la l \la -10$. We show explicitly that the phase of the disturbances in the outskirts of simulated galaxies at the time that best fits the Fourier amplitudes, our primary metric for the azimuth determination, is relatively insensitive to the equation of state. Our calculations here represent our continuing efforts to develop the "Tidal Analysis" method of Chakrabarti \& Blitz (2009; CB09). CB09 employed SPH simulations to examine tidal interactions between perturbing dark sub-halos and the Milky Way. They found that the amplitudes of the Fourier modes of the observed planar disturbances are best-fit by a perturbing dark sub-halo with mass one-hundredth that of the Milky Way, and a pericentric approach distance of $\sim 5-10~\rm kpc$. The overarching goal of this work is to attempt to outline an alternate procedure to optical studies for characterizing and potentially discovering dwarf galaxies -- whereby one can approximately infer the azimuthal location of a perturber, its mass and pericentric distance (CB09) from analysis of its tidal gravitational imprints on the HI disk of the primary galaxy.
We investigate how the shape of the galaxy two-point correlation function as measured in the zCOSMOS survey depends on local environment, quantified in terms of the density contrast on scales of 5 Mpc/h. We show that the flat shape previously observed at redshifts between z=0.6 and z=1 can be explained by this volume being simply 10% over-abundant in high-density environments, with respect to a Universal density probability distribution function. When galaxies corresponding to the top 10% tail of the distribution are excluded, the measured w_p(r_p) steepens and becomes indistinguishable from LCDM predictions on all scales. This is the same effect recognised by Abbas & Sheth in the SDSS data at z~0 and explained as a natural consequence of halo-environment correlations in a hierarchical scenario. Galaxies living in high-density regions trace dark matter halos with typically higher masses, which are more correlated. If the density probability distribution function of the sample is particularly rich in high-density regions because of the variance introduced by its finite size, this produces a distorted two-point correlation function. We argue that this is the dominant effect responsible for the observed "peculiar" clustering in the COSMOS field.
Samples returned from comet 81P/Wild 2 by Stardust confirm that substantial quantities of crystalline silicates were incorporated into the comet at formation. We investigate the constraints that this observation places upon protoplanetary disk physics, assuming that outward transport of particles processed at high temperatures occurs via advection and turbulent diffusion in an evolving disk. We also look for constraints on particle formation locations. Our results are based upon 1D disk models that evolve with time under the action of viscosity and photoevaporation, and track solid transport using an ensemble of individual particle trajectories. We find that two classes of disk model are consistent with the Stardust findings. One class features a high particle diffusivity (a Schmidt number Sc < 1), which suffices to diffuse particles up to 20 microns in size outward against the mean gas flow. For Sc > 1, such models are unlikely to be viable, and significant outward transport requires that the particles of interest settle into a midplane layer that experiences an outward gas flow. In either class of models, the mass of inner disk material that reaches the outer disk is a strong function of the disk's initial compactness. Hence, models of grain transport within steady-state disks underestimate the efficiency of outward transport. Neither model results in sustained outward transport of very large particles exceeding a mm in size. We show that the transport efficiency generally falls off rapidly with time. Hence, high-temperature material must be rapidly incorporated into icy bodies to avoid fallback, and significant radial transport may only occur during the initial phase of rapid disk evolution. It may also vary substantially between disks depending upon their initial mass distributions. We discuss implications for Spitzer observations of crystalline silicates in T Tauri disks.
We use standard polynomial expansion technique to show the existence of a relation between polytropic model and the description of gas spheres at finite temperature. A numerical analysis is made concerning the obtained perturbative parameters. It is shown that there is a correspondence between polytropic and gas sphere thermal models for fermions and bosons. For instance, the polytropic index $n$ displays evident correlation with temperature and chemical potential.
The InfraRed Imaging Spectrograph (IRIS) is a first light client science instrument for the TMT observatory that operates as a client of the NFIRAOS facility multi-conjugate adaptive optics system. This paper reports on the concept study and baseline concept design of the On-Instrument WaveFront Sensors (OIWFS) and NFIRAOS interface subsystems of the IRIS science instrument, a collaborative effort by NRC-HIA, Caltech, and TMT AO and Instrument teams. This includes work on system engineering, structural and thermal design, sky coverage modeling, patrol geometry, probe optics and mechanics design, camera design, and controls design.
We discuss the nature and origin of a rich complex of narrow absorption lines in the quasar J102325.31+514251.0 at redshift 3.447. We measure nine C IV(\lambda1548,1551) absorption line systems with velocities from -1400 to -6200 km/s, and full widths at half minimum ranging from 16 to 350 km/s. We also detect other absorption lines in these systems, including H I, C III, N V, O VI, and Si IV. Lower ionisation lines are not present, indicating a generally high degree of ionisation in all nine systems. The total hydrogen column densities range from <=10^{17.2} to 10^{19.1}cm^{-2}. We examine several diagnostics to estimate more directly the location and origin of each absorber. Four of the systems can be attributed to a quasar-driven outflow based on line profiles that are smooth and broad compared to thermal line widths. Several systems also have other indicators of a quasar outflow origin, including partial covering. Altogether there is direct evidence for 6 of the 9 systems forming in a quasar outflow. Consistent with a near-quasar origin, eight of the systems have metallicity values or lower limits in the range Z >= 1-8 Z_{sun}. The lowest velocity system, which has an ambiguous location, also has the lowest metallicity, Z <= 0.3 Z_{sun}, and might form in a non-outflow environment farther from the quasar. Overall, however, this complex of narrow absorption lines can be identified with a highly structured, multi-component outflow from the quasar. The high metallicities are similar to those derived for other quasars at similar redshifts and luminosities, and are consistent with evolution scenarios wherein quasars appear after the main episodes of star formation and metal enrichment in the host galaxies.
We compute the infrared (IR) emission from high-redshift galaxies in cosmological smoothed particle hydrodynamics simulations by coupling the output of the simulation with the population synthesis code `GRASIL' by Silva et al. Based on the stellar mass, metallicity and formation time of each star particle, we estimate the full spectral energy distribution of each star particle from ultraviolet to IR, and compute the luminosity function of simulated galaxies in the Spitzer broadband filters for direct comparison with the available Spitzer observations.
We have performed a comprehensive ground-based observational program aimed at characterizing the circumstellar material orbiting three single white dwarf stars previously known to possess gaseous disks. Near-infrared imaging unambiguously detects excess infrared emission towards Ton 345 and allows us to refine models for the circumstellar dust around all three white dwarf stars. We find that each white dwarf hosts gaseous and dusty disks that are roughly spatially coincident, a result that is consistent with a scenario in which dusty and gaseous material has its origin in remnant parent bodies of the white dwarfs' planetary systems. We briefly describe a new model for the gas disk heating mechanism in which the gaseous material behaves like a "Z II" region. In this Z II region, gas primarily composed of metals is photoionized by ultraviolet light and cools through optically thick allowed Ca II-line emission.
Ambipolar diffusion is important in redistributing magnetic flux and in damping Alfven waves in molecular clouds. The importance of ambipolar diffusion on a length scale $\ell$ is governed by the ambipolar diffusion Reynolds number, $\rad=\ell/\lad$, where $\lad$ is the characteristic length scale for ambipolar diffusion. The logarithmic mean of the AD Reynolds number in a sample of 15 molecular clumps with measured magnetic fields (Crutcher 1999) is 17, comparable to the theoretically expected value. We identify several regimes of ambipolar diffusion in a turbulent medium, depending on the ratio of the flow time to collision times between ions and neutrals; the clumps observed by Crutcher (1999) are all in the standard regime of ambipolar diffusion, in which the neutrals and ions are coupled over a flow time. We have carried out two-fluid simulations of ambipolar diffusion in isothermal, turbulent boxes for a range of values of $\rad$. The mean Mach numbers were fixed at $\calm=3$ and $\ma=0.67$; self-gravity was not included. We study the properties of overdensities--i.e., clumps--in the simulation and show that the slope of the higher-mass portion of the clump mass spectrum increases as $\rad$ decreases, which is qualitatively consistent with Padoan et al. (2007)'s finding that the mass spectrum in hydrodynamic turbulence is significantly steeper than in ideal MHD turbulence. For a value of $\rad$ similar to the observed value, we find a slope that is consistent with that of the high-mass end of the Initial Mass Function for stars. However, the value we find for the spectral index in our ideal MHD simulation differs from theirs, presumably because our simulations have different initial conditions. This suggests that the mass spectrum of the clumps in the Padoan et al. (2007) turbulent fragmentation model for the IMF depends on the environment, which would conflict with evidence ...
The results of an observational campaign on the new $\delta$ Scuti pulsator \astrobj{HD~207331} are reported. The star was observed photometrically from August 26 to September 2, 2009 from the Observatorio San Pedro M\'artir (0.84-m telescope, Mexico) and the Observatorio del Teide (0.80-m telescope, Spain). An overall run of 53.8 h of useful data was collected from the two sites. Four oscillation frequencies for \astrobj{HD~207331} have been found above a 99\% confidence level. These results confirm the multiperiodic pulsation nature of the star suggested in previous observations with sparse data. Spectroscopic observations carried out in 2009 allowed us to derive its spectral type and luminosity class as well as to estimate its rotation rate. A simple comparison with models is performed.
We study the dependence of satellite galaxy properties on the distance to the host galaxy and the orbital motion using the SDSS data. From SDSS DR7 we find 3515 isolated satellite systems of galaxies at z<0.03 that contain 8904 satellite galaxies. Using this sample we construct a catalog of 635 satellites associated with 215 host galaxies whose spin directions are determined by our inspection of the SDSS color images and/or by spectroscopic observations in the literature. We divide satellite galaxies into prograde and retrograde orbit subsamples depending on their orbital motion respect to the spin direction of the host. We find that the number of galaxies in prograde orbit is nearly equal to that of retrograde orbit galaxies: the fraction of satellites in prograde orbit is 50+/-2%. The velocity distribution of satellites with respect to their hosts is found almost symmetric: the median bulk rotation of satellites is -1+/- 8 km/s. It is found that the radial distribution of early-type satellites in prograde orbit is strongly concentrated toward the host while that of retrograde ones shows much less concentration. We also find the orbital speed of late-type satellites in prograde orbit increases as the projected distance to the host (R) decreases while the speed decreases for those in retrograde orbit. At R less than 0.1 times the host virial radius the orbital speed decreases in both prograde and retrograde orbit cases. Prograde satellites are on average fainter than retrograde satellites for both early and late morphological types. The u-r color becomes redder as R decreases for both prograde and retrograde orbit late-type satellites. The differences between prograde and retrograde orbit satellites may be attributed to their different origin or the different strength of physical processes that they have experienced through hydrodynamic interactions with their host galaxies.
(abridged) We present a study of stellar population of LAEs at z=4.86 in GOODS-N and its flanking field. With the publicly available IRAC data in GOODS-N and further IRAC observations in the flanking fields, we select five LAEs which are not contaminated by neighboring objects in IRAC images and construct their observed SEDs with I_c, z', IRAC 3.6micron, and 4.5micron band photometry. The SEDs cover the rest-frame UV to optical wavelengths. We derive stellar masses, ages, color excesses, and star formation rates of five LAEs using SED fitting method. Assuming the constant star formation history, we find that the stellar masses range from 10^8 to $10^{10} Msun with the median value of 2.5x10^9 Msun. The derived ages range from very young ages (7.4 Myr) to 437 Myr with a median age of 25 Myr. The color excess E(B-V) are between 0.1-0.4 mag. Star formation rates are 55-209 Msun/yr. A comparison of the stellar populations is made between three LAEs and 88 LBGs selected at the same redshift, in the same observed field, and down to the same limit of the rest-frame UV luminosity. These three LAEs are the brightest and reddest samples among the whole LAE samples at z=4.86. The LAEs distribute at the relatively faint part of UV-luminosity distribution of LBGs. Deriving the stellar properties of the LBGs by fitting their SEDs with the same model ensures that model difference does not affect the comparison. It is found that the stellar properties of the LAEs lie on distributions of those of LBGs. On average, the LAEs show less dust extinction, and lower star formation rates than LBGs, while the stellar mass of LAEs nearly lies in the middle part of the mass distribution of LBGs. However, the stellar properties of LAEs and LBGs are similar at the fixed UV or optical luminosity. We also examine the relations between the output properties from the SED fitting and the rest-frame Lya equivalent width.
We present an analysis of deep WSRT observations of the HI in 33 nearby early-type galaxies selected from a sample studied earlier at optical wavelengths with the SAURON integral-field spectrograph. The sample covers both field environments and the Virgo cluster. Our analysis shows that gas accretion plays a role in the evolution of field early-type galaxies, but less so for those in clusters. For detection limits of a few times 10^6 Msun, HI is detected in about 2/3 of the field galaxies, while <10% of the Virgo objects are detected. In about half of the detections, the HI forms a regularly rotating disc or ring. All HI discs have counterparts of ionised gas and inner HI discs are also detected in molecular gas. The cold ISM is dominated by molecular gas (M_H2/M_HI ~ 10). We conclude that accretion of HI is common for field early-type galaxies, but the amount of material involved is usually small. Cluster galaxies appear not to accrete HI. The few galaxies with a significant young sub-population all have inner gas discs, but for the remaining galaxies there is no trend between stellar population and HI. Some early-type galaxies are very gas rich, but only have an old population. The stellar populations of field galaxies are typically younger than those in Virgo. This is likely related to differences in accretion history. In about 50% of the galaxies we detect a central continuum source. In many objects this emission is from a low-luminosity AGN, in some it is consistent with the observed star formation. Galaxies with HI in the central regions are more likely detected in continuum. This is due to a higher probability for star formation to occur in such galaxies and not to HI-related AGN fuelling. (Abridged)
We report on atomic gas (HI) and molecular gas (as traced by CO(2-1)) redshifted absorption features toward the nuclear regions of the closest powerful radio galaxy, Centaurus A (NGC 5128). Our HI observations using the Very Long Baseline Array allow us to discern with unprecedented sub-parsec resolution HI absorption profiles toward different positions along the 21 cm continuum jet emission in the inner 0."3 (or 5.4 pc). In addition, our CO(2-1) data obtained with the Submillimeter Array probe the bulk of the absorbing molecular gas with little contamination by emission, not possible with previous CO single-dish observations. We shed light with these data on the physical properties of the gas in the line of sight, emphasizing the still open debate about the nature of the gas that produces the broad absorption line (~55 km/s). First, the broad H I line is more prominent toward the central and brightest 21 cm continuum component than toward a region along the jet at a distance ~ 20 mas (or 0.4 pc) further from it. This suggests that the broad absorption line arises from gas located close to the nucleus, rather than from diffuse and more distant gas. Second, the different velocity components detected in the CO(2-1) absorption spectrum match well other molecular lines, such as those of HCO+(1-0), except the broad absorption line that is detected in HCO+(1-0) (and most likely related to that of the H I). Dissociation of molecular hydrogen due to the AGN seems to be efficient at distances <= 10 pc, which might contribute to the depth of the broad H I and molecular lines.
Cygnus X-3 is an accreting high-mass X-ray binary composed of a Wolf-Rayet star and an unknown compact object, possibly a black hole. The gamma-ray space telescope Fermi found definitive evidence that high-energy emission is produced in this system. We propose a scenario to explain the GeV gamma-ray emission in Cygnus X-3. In this model, energetic electron-positron pairs are accelerated at a specific location in the relativistic jet, possibly related to a recollimation shock, and upscatter the stellar photons to high energies. The comparison with Fermi observations shows that the jet should be inclined close to the line of sight and pairs should not be located within the system. Energetically speaking, a massive compact object is favored. We report also on our investigations of the gamma-ray absorption of GeV photons with the radiation emitted by a standard accretion disk in Cygnus X-3. This study shows that the gamma-ray source should not lie too close to the compact object.
C18O spectral line observations, NIR spectrosopy, narrow and broad band NIR imaging and stellar J,H,Ks photometry are used to analyse the structure of the archetype cometary globule 1 (CG 1) head and the extinction of stars in its direction. A young stellar object (YSO) associated with a bright NIR nebulosity and a molecular hydrogen object (a probable obscured HH-object), were discovered in the globule. Molecular hydrogen and Br_gamma line emission is seen in the direction of the YSO. The observed maximum optical extinction in the globule head is 9.2 magnitudes. The peak N(H2) column density and the total mass derived from the extinction are 9.0 10^21 cm-2 and and 16.7 Msun (d/300pc)^2. C18O emission in the globule head is detected in a 4' by 1'5 area with a sharp maximum SW of the YSO. Three regions (C18O_SE, C18O_max and C18O_NW) can be discerned in C18O line velocity and excitation temperature. C18O_SE coincides with a strong NIR surface brightness below the bright HAeBe star NX Pup and C18O_NW with the optical extinction maximum. Because of variations in the C18O excitation temperature the integrated line emission does not follow the optical extinction. It is argued that the C18O excitation temperatures in C18O_SE and C18O_max is higher than in C18O_NW because of radiative heating by NX Pup (C18O_SE) and interaction of the YSO with the parent cloud (C18O_max). No indication other than the molecular hydrogen emission {and the molecular hydrogen object of a strong molecular outflow from the YSO is evident. The IRAS point source 07178-4429 located in the CG 1 head resolves into two sources in the HIRES enhanced IRAS images. The 12 and 25 micron emission originates mainly in the star NX Puppis and the 60 and 100 micron emission in the YSO. The IRAS FIR luminosity of the YSO is 3.1 Lsun.
Radio astronomy is entering a new era with new and future radio observatories such as the Low Frequency Array and the Square Kilometer Array. We describe in detail an automated flagging pipeline and evaluate its performance. With only a fraction of the computational cost of correlation and its use of the previously introduced SumThreshold method, it is found to be both fast and unrivalled in its high accuracy. The LOFAR radio environment is analysed with the help of this pipeline. The high time and spectral resolution of LOFAR have resulted in an observatory where only a few percent of the data is lost due to RFI.
BA-type supergiants are amongst the most optically-bright stars. They are observable in extragalactic environments, hence potential accurate distance indicators. Emission activity in the Halpha line of the BA supergiants Rigel (B8Ia) and Deneb (A2Ia) is indicative of presence of localized time-dependent mass ejections. Here, we employ optical interferometry to study the Halpha line-formation region in these stellar environments. High spatial- (0.001 arcsec) and spectral- (R=30 000) resolution observations of Halpha were obtained with the visible recombiner VEGA installed on the CHARA interferometer, using the S1S2 array-baseline (34m). Six independent observations were done on Deneb over the years 2008 and 2009, and two on Rigel in 2009. We analyze this dataset with the 1D non-LTE radiative-transfer code CMFGEN, and assess the impact of the wind on the visible and near-IR interferometric signatures, using both Balmer-line and continuum photons. We observe a visibility decrease in Halpha for both Rigel and Deneb, suggesting that the line-formation region is extended (1.5-1.75 R*). We observe a significant visibility decrease for Deneb in the SiII6371 line. We witness time variations in the differential phase for Deneb, implying an inhomogeneous and unsteady circumstellar environment, while no such variability is seen in differential visibilities. Radiative-transfer modeling of Deneb, with allowance for stellar-wind mass loss, accounts fairly well for the observed decrease in the Halpha visibility. Based on the observed differential visibilities, we estimate that the mass-loss rate of Deneb has changed by less than 5%.
In this last Paper III additional evidences that the solar high energetic particles radiation with energies higher as 100 MeV (the solar cosmic rays SCR) is an very important component for the "Sun- climate" relationship are given (see also Paper I and II). The total solar irradiance (TSI) and the galactic cosmic rays (GCR) variations given an integral climate effect of cooling in sunspot minima and warming in the sunspot maxima. Unlike the both ones the powerful solar corpuscular events plays a cooling climate role during the epochs of their heigh levels. By this one subcenturial global and regional temperature quasi- cyclic changes by duration of approximately 60 years could be track during the last 150 years of instrumental climate observations . It has been also evided in the paper that this subcenturial oscilation is very important in the Group sunspot number (GSN) data series since the Maunder minimum up to the end of 20th century. Thus the solar erruptive activity effect make the total "Sun -climate" relationship essentially more complicated as it could be follow when only the TSI and GCR variations are taken into account. In this light the climate warming tendency after AD 1975 is rather by a natural as by an antropogenic origin. Most probably the last one is very close related to the general downward tendency of erruptive solar events which is superimposed over the high long term TSI levels during the last three decades (AD 1975-2007). It is evided, that the efficiency of the solar corpuscular activuty over the climate is strongly depended by the "north-south" asymmetry of the solar activity centers (as a proxy the sunspots area north-south asymmetry index A is used there). The climate cooling effect in the Northern hemisphere is most powerful during the epochs of positive values of A.
We present new images and photometry of the massive star forming complex Cygnus X obtained with IRAC and MIPS on the Spitzer Space Telescope. A combination of IRAC, MIPS, UKIDSS, and 2MASS data are used to identify and classify young stellar objects. Of the 8,231 sources detected exhibiting infrared excess in Cygnus X North, 670 are classified as Class I and 7,249 are classified as Class II. Using spectra from the FAST spectrograph at the Fred L. Whipple Observatory and Hectospec on the MMT, we spectrally typed 536 sources in the Cygnus X complex to identify the massive stars. We find that YSOs tend to be grouped in the neighborhoods of massive B stars (spectral types B0 to B9). We present a minimal spanning tree analysis of clusters in two regions in Cygnus X North. The fraction of infrared excess sources that belong to clusters with >10 members is found to be 50--70%. Most Class II objects lie in dense clusters within blown out HII regions, while Class I sources tend to reside in more filamentary structures along the bright-rimmed clouds, indicating possible triggered star formation.
We performed a sensitive search for the ground-state emission lines of ortho- and para-water vapor in the DM Tau protoplanetary disk using the Herschel/HIFI instrument. No strong lines are detected down to 3sigma levels in 0.5 km/s channels of 4.2 mK for the 1_{10}--1_{01} line and 12.6 mK for the 1_{11}--0_{00} line. We report a very tentative detection, however, of the 1_{10}--1_{01} line in the Wide Band Spectrometer, with a strength of T_{mb}=2.7 mK, a width of 5.6 km/s and an integrated intensity of 16.0 mK km/s. The latter constitutes a 6sigma detection. Regardless of the reality of this tentative detection, model calculations indicate that our sensitive limits on the line strengths preclude efficient desorption of water in the UV illuminated regions of the disk. We hypothesize that more than 95-99% of the water ice is locked up in coagulated grains that have settled to the midplane.
Imaging microwave observations of an eruptive, partially occulted solar flare on 18 April 2001 suggest that the global structure of the event can be described by the helical kink instability of a twisted magnetic flux rope. This model is suggested by the inverse gamma shape of the source exhibiting crossing legs of a rising flux loop and by evidence that the legs interact at or near the crossing point. The interaction is reflected by the location of peak brightness near the crossing point and by the formation of superimposed compact nonthermal sources most likely at or near the crossing point. These sources propagate upward along both legs, merge into a single, bright source at the top of the structure, and continue to rise at a velocity $>\!1000$~km\,s$^{-1}$. The compact sources trap accelerated electrons which radiate in the radio and hard X-ray ranges. This suggests that they are plasmoids, although their internal structure is not revealed by the data. They exhibit variations of the radio brightness temperature at a characteristic time scale of $\sim\!40$~s, anti-correlated to their area, which also support their interpretation as plasmoids. Their propagation path differs from the standard scenario of plasmoid formation and propagation in the flare current sheet, suggesting the helical current sheet formed by the instability instead.
Numerical simulations of the helical ($m\!=\!1$) kink instability of an arched, line-tied flux rope demonstrate that the helical deformation enforces reconnection between the legs of the rope if modes with two helical turns are dominant as a result of high initial twist in the range $\Phi\gtrsim6\pi$. Such reconnection is complex, involving also the ambient field. In addition to breaking up the original rope, it can form a new, low-lying, less twisted flux rope. The new flux rope is pushed downward by the reconnection outflow, which typically forces it to break as well by reconnecting with the ambient field. The top part of the original rope, largely rooted in the sources of the ambient flux after the break-up, can fully erupt or be halted at low heights, producing a "failed eruption." The helical current sheet associated with the instability is squeezed between the approaching legs, temporarily forming a double current sheet. The leg-leg reconnection proceeds at a high rate, producing sufficiently strong electric fields that it would be able to accelerate particles. It may also form plasmoids, or plasmoid-like structures, which trap energetic particles and propagate out of the reconnection region up to the top of the erupting flux rope along the helical current sheet. The kinking of a highly twisted flux rope involving leg-leg reconnection can explain key features of an eruptive but partially occulted solar flare on 18 April 2001, which ejected a relatively compact hard X-ray and microwave source and was associated with a fast coronal mass ejection.
We discuss the detection of absorption by interstellar hydrogen fluoride (HF) along the sight line to the submillimeter continuum sources W49N and W51. We have used Herschel's HIFI instrument in dual beam switch mode to observe the 1232.4762 GHz J = 1 - 0 HF transition in the upper sideband of the band 5a receiver. We detected foreground absorption by HF toward both sources over a wide range of velocities. Optically thin absorption components were detected on both sight lines, allowing us to measure - as opposed to obtain a lower limit on - the column density of HF for the first time. As in previous observations of HF toward the source G10.6-0.4, the derived HF column density is typically comparable to that of water vapor, even though the elemental abundance of oxygen is greater than that of fluorine by four orders of magnitude. We used the rather uncertain N(CH)-N(H2) relationship derived previously toward diffuse molecular clouds to infer the molecular hydrogen column density in the clouds exhibiting HF absorption. Within the uncertainties, we find that the abundance of HF with respect to H2 is consistent with the theoretical prediction that HF is the main reservoir of gas-phase fluorine for these clouds. Thus, hydrogen fluoride has the potential to become an excellent tracer of molecular hydrogen, and provides a sensitive probe of clouds of small H2 column density. Indeed, the observations of hydrogen fluoride reported here reveal the presence of a low column density diffuse molecular cloud along the W51 sight line, at an LSR velocity of ~ 24kms-1, that had not been identified in molecular absorption line studies prior to the launch of Herschel.
We report a detection of the fundamental rotational transition of hydrogen fluoride in absorption towards Orion KL using Herschel/HIFI. After the removal of contaminating features associated with common molecules ("weeds"), the HF spectrum shows a P-Cygni profile, with weak redshifted emission and strong blue-shifted absorption, associated with the low-velocity molecular outflow. We derive an estimate of 2.9 x 10^13 cm^-2 for the HF column density responsible for the broad absorption component. Using our best estimate of the H2 column density within the low-velocity molecular outflow, we obtain a lower limit of ~1.6 x 10^-10 for the HF abundance relative to hydrogen nuclei, corresponding to 0.6% of the solar abundance of fluorine. This value is close to that inferred from previous ISO observations of HF J=2--1 absorption towards Sgr B2, but is in sharp contrast to the lower limit of 6 x 10^-9 derived by Neufeld et al. (2010) for cold, foreground clouds on the line of sight towards G10.6-0.4.
A multi-epoch H$\alpha$ survey of the early-type spiral galaxy M94 (NGC 4736) has been completed as part of a program to establish the galaxy's nova rate. A total of 4 nova candidates were discovered in 7 epochs of observation during the period from 2005 to 2007. After making corrections for temporal coverage and spatial completeness, a global nova rate of 5.0$^{+1.8}_{-1.4}$ yr$^{-1}$ was determined. This rate corresponds to a specific-luminosity nova rate of 1.4 $\pm$ 0.5 novae per year per 10$^{10} L_{\odot,K}$ when the K luminosity is determined from the B - K color, or 1.5 $\pm$ 0.4 novae per year per 10$^{10} L_{\odot,K}$ when the K luminosity is derived from the Two Micron All Sky Survey. These values are slightly lower than that of other galaxies with measured nova rates, which typically lie in the range of 2-3 novae per year per 10$^{10} L_{\odot}$ in the K band.
The determination of the Ba abundance in globular cluster (GC) stars is a very powerful test to address several issues in the framework of multiple population scenarios. We measured the Ba content for a sample of more than 1200 stars in 15 Galactic GCs, using high-resolution FLAMES/Giraffe spectra. We found no variation in [Ba/Fe] ratios for different stellar populations within each cluster; this means that low-mass asymptotic giant branch (AGB) stars do not significantly contribute to the intra-cluster pollution.\\ Very interestingly, we obtained that the fraction of Ba-stars in first generation (FG) stars is close to the values derived for field stars ($\sim$2\%); on the other hand, second generation (SG) stars present a significant lower fraction. An independent and successful test, based on radial velocity variations among giant stars in NGC~6121, confirms our finding: the binary fraction among FG stars is about $\sim$12\% to be compared with $\sim$1\% of SG stars. This is an evidence that SG stars formed in a denser environment, where infant mortality of binary systems was particularly efficient.
The CEA/LETI and CEA/SAp started the development of far-infrared filled bolometer arrays for space applications over a decade ago. The unique design of these detectors makes possible the assembling of large focal planes comprising thousands of bolometers running at 300 mK with very low power dissipation. Ten arrays of 16x16 pixels were thoroughly tested on the ground, and integrated in the Herschel/PACS instrument before launch in May 2009. These detectors have been successfully commissioned and are now operating in their nominal environment at the second Lagrangian point of the Earth-Sun system. In this paper we briefly explain the functioning of CEA bolometer arrays, and we present the properties of the detectors focusing on their noise characteristics, the effect of cosmic rays on the signal, the repeatability of the measurements, and the stability of the system.
In this paper we intend to provide an indirect method to detect Jovian planets by studying near infrared emission spectra originating in the protoplanetary disks around T Tauri stars. Our idea is to investigate whether a massive planet could induce any observable effect on the spectral lines emerging in the disks atmosphere. As a tracer molecule we propose CO, being excited in the ro-vibrational fundamental band in the disk atmosphere to a distance of ~2-3 AU (depending on the stellar mass) where terrestrial planets thought to form. The synthetic molecular spectral line profiles were calculated by an own developed semi-analytical double layer disk model. 2D gas dynamics were incorporated in the calculation of synthetic spectral lines. We demonstrate that a massive planet embedded in a protoplanetary disk strongly influences the originally circularly Keplerian gas dynamics. The perturbed motion of the gas can be detected by comparing the CO line profiles in emission emerging from planet-bearing to those of planet-free disk models. The planet signal has two major characteristics: a permanent line profile asymmetry, and short timescale variability correlated with the orbital phase of the giant planet. We have found that the strength of the asymmetry depends on the physical parameters of the star-planet-disk system, such as the disk inclination angle, the planetary and stellar masses, the orbital distance, and the size of the disk inner cavity. The permanent line profile asymmetry is caused by a disk being in an eccentric state in the gap opened by the giant planet. However, the variable component is a consequence of the local dynamical perturbation by the orbiting giant planet. We show that a forming giant planet, still embedded in the protoplanetary disk, can be detected using contemporary or future high-resolution near-IR spectrographs like VLT/CRIRES and ELT/METIS.
We present initial results from the Herschel GT key program: Herschel observations of EXtra-Ordinary Sources (HEXOS) and outline the promise and potential of spectral surveys with Herschel/HIFI. The HIFI instrument offers unprecedented sensitivity, as well as continuous spectral coverage across the gaps imposed by the atmosphere, opening up a largely unexplored wavelength regime to high-resolution spectroscopy. We show the spectrum of Orion KL between 480 and 560 GHz and from 1.06 to 1.115 THz. From these data, we confirm that HIFI separately measures the dust continuum and spectrally resolves emission lines in Orion KL. Based on this capability we demonstrate that the line contribution to the broad-band continuum in this molecule-rich source is ~20-40% below 1 THz and declines to a few percent at higher frequencies. We also tentatively identify multiple transitions of HD18O in the spectra. The first detection of this rare isotopologue in the interstellar medium suggests that HDO emission is optically thick in the Orion hot core with HDO/H2O ~ 0.02. We discuss the implications of this detection for the water D/H ratio in hot cores.
We study the spherical Mexican hat wavelet (SMHW) as a detector of primordial non-Gaussianity of the local type on the Cosmic Microwave Background (CMB) anisotropies. For this purpose we define third order statistics based on the wavelet coefficient maps and the original map. We find the dependence of these statistics in terms of the non-linear coupling parameter fnl and the bispectrum of this type of non-Gaussianity. We compare the analytical values for these statistics with the results obtained with non-Gaussian simulations for an ideal full-sky CMB experiment without noise. We study the power of this method to detect fnl, i. e. the variance of this parameter, and compare it with the variance obtained from the primary bispectrum for the same experiment. Finally we apply our wavelet based estimator on WMAP-like maps with incomplete sky and inhomogeneous noise and compare with the optimal bispectrum estimator. The results show that the wavelet cubic statistics are as efficient as the bispectrum as optimal detectors of this type of primordial non-Gaussianity.
We constrain the parameterized post-Einsteinian framework with binary pulsar observations of orbital period decay due to gravitational wave emission. This framework proposes to enhance the amplitude and phase of gravitational waveform templates through post-Einsteinian parameters to search for generic deviations from General Relativity in gravitational wave data. Such enhancements interpolate between General Relativity and alternative theory predictions, but their magnitude must be such as to satisfy all current experiments and observations. The data that currently constrains the parameterized post-Einsteinian framework the most is the orbital period decay of binary pulsars. We use such observations to place upper limits on the magnitude of post-Einsteinian parameters, which will be critical when gravitational waves are detected and this framework is implemented.
We study the inflationary dynamics in a model of slow-roll inflation in warped throat. Inflation is realized by the motion of a D-brane along the radial direction of the throat, and at later stages instabilities develop in the angular directions. We closely investigate both the single field potential relevant for the slow-roll phase, and the full multi-field one including the angular modes which becomes important at later stages. We study the main features of the instability process, discussing its possible consequences and identifying the vacua towards which the angular modes are driven.
We construct the gauge invariant free action for cosmological perturbations for the nonminimally coupled inflaton field in the Jordan frame. For this the phase space formalism is used, which keeps track of all the dynamical and constraint fields. We perform explicit conformal transformations to demonstrate the physical equivalence between the Jordan and Einstein frames at the level of quadratic perturbations. We show how to generalize the formalism to the case of a more complicated scalar sector with an internal symmetry, such as Higgs inflation. This work represents a first step in developing gauge invariant perturbation theory for nonminimally coupled inflationary models.
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The launch of the Fermi Gamma-ray Space Telescope has heralded a new era in the study of gamma-ray pulsars. The population of confirmed gamma-ray pulsars has gone from 6-7 to more than 60, and the superb sensitivity of the Large Area Telescope (LAT) on Fermi has allowed the detailed study of their spectra and light curves. Twenty-four of these pulsars were discovered in blind searches of the gamma-ray data, and twenty-one of these are, at present, radio quiet, despite deep radio follow-up observations. In addition, millisecond pulsars have been confirmed as a class of gamma-ray emitters, both individually and collectively in globular clusters. Recently, radio searches in the direction of LAT sources with no likely counterparts have been highly productive, leading to the discovery of a large number of new millisecond pulsars. Taken together, these discoveries promise a great improvement in the understanding of the gamma-ray emission properties and Galactic population of pulsars. We summarize some of the results stemming from these newly-detected pulsars and their timing and multi-wavelength follow-up observations.
The majority of short gamma-ray bursts (SGRBs) are thought to originate from the merger of compact binary systems collapsing directly to form a black hole. However, it has been proposed that both SGRBs and long gamma-ray bursts (LGRBs) may, on rare occasions, form an unstable millisecond pulsar (magnetar) prior to final collapse. GRB 090515, detected by the Swift satellite was extremely short, with a T_90 of 0.036 +/- 0.016 s, and had a very low fluence of 2 x 10^-8 erg cm^-2 and faint optical afterglow. Despite this, the 0.3 - 10 keV flux in the first 200 s was the highest observed for a SGRB by the Swift X-ray Telescope (XRT). The X-ray light curve showed an unusual plateau and steep decay, becoming undetectable after ~500 s. This behaviour is similar to that observed in some long bursts proposed to have magnetars contributing to their emission. In this paper, we present the Swift observations of GRB 090515 and compare it to other gamma-ray bursts (GRBs) in the Swift sample. Additionally, we present optical observations from Gemini, which detected an afterglow of magnitude 26.4 +/- 0.1 at T+ 1.7 hours after the burst. We discuss potential causes of the unusual 0.3 - 10 keV emission and suggest it might be energy injection from an unstable millisecond pulsar. Using the duration and flux of the plateau of GRB 090515, we place constraints on the millisecond pulsar spin period and magnetic field.
The characterization of dark energy is a central task of cosmology. To go beyond a cosmological constant, we need to introduce at least an equation of state and a sound speed and consider observational tests that involve perturbations. If dark energy is not completely homogeneous on observable scales then the Poisson equation is modified and dark matter clustering is directly affected. One can then search for observational effects of dark energy clustering using dark matter as a probe. In this paper we exploit an analytical approximate solution of the perturbation equations in a general dark energy cosmology to analyze the performance of next-decade large scale surveys in constraining equation of state and sound speed. We find that tomographic weak lensing and galaxy redshift surveys can constrain the sound speed of the dark energy only if the latter is small, of the order of $c_{s}\lesssim0.01$ (in units of $c$). For larger sound speeds the error grows to 100% and more. We conclude that large scale structure observations contain very little information about the perturbations in canonical scalar field models with a sound speed of unity. Nevertheless, they are able to detect the presence of "cold" dark energy, i.e. a dark energy with non-relativistic speed of sound.
GRS1915+105 is a very peculiar black hole binary that exhibits accretion-related states that are not observed in any other stellar-mass black hole system. One of these states, however -- referred to as the plateau state -- may be related to the canonical hard state of black hole X-ray binaries. Both the plateau and hard state are associated with steady, relatively lower X-ray emission and flat/inverted radio emission, that is sometimes resolved into compact, self-absorbed jets. However, while generally black hole binaries quench their jets when the luminosity becomes too high, GRS1915+105 seems to sustain them despite the fact that it accretes at near- or super-Eddington rates. In order to investigate the relationship between the plateau and the hard state, we fit two multi-wavelength observations using a steady-state outflow-dominated model, developed for hard state black hole binaries. The data sets consist of quasi-simultaneous observations in radio, near-infrared and X-ray bands. Interestingly, we find both significant differences between the two plateau states, as well as between the best-fit model parameters and those representative of the hard state. We discuss our interpretation of these results, and the possible implications for GRS 1915+105's relationship to canonical black hole candidates.
We have used moderate resolution, near-infrared spectra from the SpeX spectrograph on the NASA Infrared Telescope facility to characterize the stellar content of Barnard 59 (B59), the most active star-forming core in the Pipe Nebula. Measuring luminosity and temperature sensitive features in the spectra of 20 candidate YSOs, we identified likely background giant stars and measured each star's spectral type, extinction, and NIR continuum excess. We find that B59 is composed of late type (K4-M6) low-mass (0.9--0.1 M_sun) YSOs whose median stellar age is comparable to, if not slightly older than, that of YSOs within the Rho Oph, Taurus, and Chameleon star forming regions. Deriving absolute age estimates from pre-main sequence models computed by D'Antona et al., and accounting only for statistical uncertainties, we measure B59's median stellar age to be 2.6+/-0.8 Myrs. Including potential systematic effects increases the error budget for B59's median (DM98) stellar age to 2.6+4.1/-2.6 Myrs. We also find that the relative age orderings implied by pre-main sequence evolutionary tracks depend on the range of stellar masses sampled, as model isochrones possess significantly different mass dependencies. The maximum likelihood median stellar age we measure for B59, and the region's observed gas properties, suggest that the B59 dense core has been stable against global collapse for roughly 6 dynamical timescales, and is actively forming stars with a star formation efficiency per dynamical time of ~6%. This maximum likelihood value agrees well with recent star formation simulations that incorporate various forms of support against collapse, such as sub-critical magnetic fields, outflows, and radiative feedback from protostellar heating. [abridged]
When a satellite galaxy falls into a massive dark matter halo, it suffers the dynamical friction force which drag it into the halo center and finally it merger with the central galaxy. The time interval between entry and merger is called as the dynamical friction timescale (T_df). Many studies have been dedicated to derive T_df using analytical models or N-body simulations. These studies have obtained qualitative agreements on how T_df depends on the orbit parameters, and mass ratio between satellite and host halo. However, there are still disagreements on the accurate form of T_df . In this paper, we present a semi-analytical model to predict T_df and we focus on interpreting the discrepancies among different studies. We find that the treatment of mass loss from satellite by tidal stripping dominates the behavior of T_df . We also identify other model parameters which affect the predicted T_df.
We study the luminosity gap, dm12, between the first and second ranked galaxies in a sample of 59 massive galaxy clusters, using data from the Hale Telescope, HST, Chandra, and Spitzer. We find that the dm12 distribution, p(dm12), is a declining function of dm12, to which we fitted a straight line: p(dm12) propto -(0.13+/-0.02)dm12. The fraction of clusters with "large" luminosity gaps is p(dm12>=1)=0.37+/-0.08, which represents a 3sigma excess over that obtained from Monte Carlo simulations of a Schechter function that matches the mean cluster galaxy luminosity function. We also identify four clusters with "extreme" luminosity gaps, dm12>=2, giving a fraction of p(dm12>=2)=0.07+0.05-0.03. More generally, large luminosity gap clusters are relatively homogeneous, with elliptical/disky brightest cluster galaxies (BCGs), cuspy gas density profiles (i.e. strong cool cores), high concentrations, and low substructure fractions. In contrast, small luminosity gap clusters are heterogeneous, spanning the full range of boxy/elliptical/disky BCG morphologies, the full range of cool core strengths and dark matter concentrations, and have large substructure fractions. Taken together, these results imply that the amplitude of the luminosity gap is a function of both the formation epoch, and the recent infall history of the cluster. "BCG dominance" is therefore a phase that a cluster may evolve through, and is not an evolutionary "cul-de-sac". We also compare our results with semi-analytic model predictions based on the Millennium Simulation. None of the models are able to reproduce all of the observational results, underlining the inability of current models to match the empirical properties of BCGs. We identify the strength of AGN feedback and the efficiency with which cluster galaxies are replenished after they merge with the BCG in each model as possible causes of these discrepancies. [Abridged]
Water in Star-forming regions with Herschel (WISH) is a Herschel Key Program investigating the water chemistry in young stellar objects (YSOs) during protostellar evolution. Hydroxyl (OH) is one of the reactants in the chemical network most closely linked to the formation and destruction of H2O. High-temperature chemistry connects OH and H2O through the OH + H2 <-> H2O + H reactions. Formation of H2O from OH is efficient in the high-temperature regime found in shocks and the innermost part of protostellar envelopes. Moreover, in the presence of UV photons, OH can be produced from the photo-dissociation of H2O. High-resolution spectroscopy of the OH 163.12 micron triplet towards HH 46 and NGC 1333 IRAS 2A was carried out with the Heterodyne Instrument for the Far Infrared (HIFI) on board Herschel. The low- and intermediate-mass YSOs HH 46, TMR 1, IRAS 15398-3359, DK Cha, NGC 7129 FIRS 2, and NGC 1333 IRAS 2A were observed with the Photodetector Array Camera and Spectrometer (PACS) in four transitions of OH and two [OI] lines. The OH transitions at 79, 84, 119, and 163 micron and [OI] emission at 63 and 145 micron were detected with PACS towards the class I low-mass YSOs as well as the intermediate-mass and class I Herbig Ae sources. No OH emission was detected from the class 0 YSO NGC 1333 IRAS 2A, though the 119 micron was detected in absorption. With HIFI, the 163.12 micron was not detected from HH 46 and only tentatively detected from NGC 1333 IRAS 2A. The combination of the PACS and HIFI results for HH 46 constrains the line width (FWHM > 11 km/s) and indicates that the OH emission likely originates from shocked gas. This scenario is supported by trends of the OH flux increasing with the [OI] flux and the bolometric luminosity. Similar OH line ratios for most sources suggest that OH has comparable excitation temperatures despite the different physical properties of the sources.
Dense and cold clouds seem to populate the broad line region surrounding the central black hole in AGNs. These clouds could interact with the AGN jet base and this could have observational consequences. We want to study the gamma-ray emission produced by these jet-cloud interactions, and explore under which conditions this radiation would be detectable. We investigate the hydrodynamical properties of jet-cloud interactions and the resulting shocks, and develop a model to compute the spectral energy distribution of the emission generated by the particles accelerated in these shocks. We discuss our model in the context of radio-loud AGNs, with applications to two representative cases, the low-luminous Centaurus A, and the powerful 3C 273. Some fraction of the jet power can be channelled to gamma-rays, which would be likely dominated by synchrotron self-Compton radiation, and show typical variability timescales similar to the cloud lifetime within the jet, which is longer than several hours. Many clouds can interact with the jet simultaneously leading to fluxes significantly higher than in one interaction, but then variability will be smoothed out. Jet-cloud interactions may produce detectable gamma-rays in non-blazar AGNs, of transient nature in nearby low-luminous sources like Cen A, and steady in the case of powerful objects of FR II type.
In the late nineteenth century, Antoine Henri Becquerel discovered radioactivity and thus the physics of weak interactions, well before atomic and quantum physics was known. The different types of radioactive decay, alpha, beta, and gamma decay, all are different types of interactions causing the same, spontaneous, and time-independent decay of an unstable nucleus into another and more stable nucleus. Nuclear reactions in cosmic sites re-arrange the basic constituents of atomic nuclei (neutrons and protons) among the different configurations which are allowed by Nature, thus producing radioactive isotopes as a by-product. Throughout cosmic history, such reactions occur in different sites, and lead to rearrangements of the relative abundances of cosmic nuclei, a process called cosmic chemical evolution, which can be studied through the observations of radioactivity. The special role of radioactivity in such studies is contributed by the intrinsic decay of such material after it has been produced in cosmic sites. This brings in a new aspect, the clock of the radioactive decay. Observational studies of cosmic radioactivities intrinsically obtain isotopic information which are at the heart of cosmic nucleosynthesis. They are best performed by precision mass spectroscopy in terrestrial laboratories, which has been combined with sophisticated radiochemistry to extract meteoritic components originating from outside the solar system, and by spectroscopy of characteristic gamma-ray lines emitted upon radioactive decay in cosmic environments and measured with space-based telescopes. This book describes where and how specific astronomical messages from cosmic radioactivity help to complement the studies of cosmic nucleosynthesis sites anad of cosmic chemical evolution.
We studied both components of a slightly overlooked visual binary HR 1847 spectroscopically to determine its basic physical and orbital parameters. Basic stellar parameters were determined by comparing synthetic spectra to the observed echelle spectra, which cover both the optical and near-IR regions. New observations of this system used the Ond\v{r}ejov and Rozhen 2-m telescopes and their coud\'e spectrographs. Radial velocities from individual spectra were measured and then analysed with the code {\FOTEL} to determine orbital parameters. The spectroscopic orbit of HR 1847A is presented for the first time. It is a single-lined spectroscopic binary with a B-type primary, a period of 719.79 days, and a highly eccentric orbit with e=0.7. We confirmed that HR 1847B is a Be star. Its H\alpha emission significantly decreased from 2003 to 2008. Both components have a spectral type B7-8 and luminosity class IV-V.
Antarctica provides a unique environment for astronomy. The cold, dry and stable air found above the high plateau, as well as the pure ice below, offers new opportunities across the photon & particle spectrum. The summits of the plateau provide the best seeing conditions, the darkest skies and the most transparent atmosphere of any earth-based observing site. Astronomical activities are now underway at four plateau sites: the Amundsen-Scott South Pole Station, Concordia Station at Dome C, Kunlun Station at Dome A and Fuji Station at Dome F, in addition to long duration ballooning from the coastal station of McMurdo. Astronomy conducted includes optical, IR, THz & sub-mm, measurements of the CMBR, solar, as well as high energy astrophysics involving measurement of cosmic rays, gamma rays and neutrinos. Antarctica is also the richest source of meteorites on our planet. An extensive range of site testing measurements have been made over the high plateau. We summarise the facets of Antarctica that are driving developments in astronomy, and review the results of the site testing experiments undertaken to quantify those characteristics of the plateau relevant for it pursuit. We outline the historical development of the astronomy on the continent, and then review the principal scientific results to have emerged over the past three decades of activity in the discipline. We discuss how science is conducted in Antarctica, and in particular the difficulties, as well as the advantages, faced by astronomers seeking to bring their experiments there. We also review some of the political issues that will be encountered, both at national and international level. Finally, we discuss where Antarctic astronomy may be heading in the coming decade, in particular plans for IR & THz astronomy, including new facilities being considered for these wavebands at high plateau stations.
Photospheric (thermal) emission is inherent to the gamma-ray burst (GRB) "fireball" model. We show here, that inclusion of this component in the analysis of the GRB prompt emission phase naturally explains some of the prompt GRB spectra seen by the Fermi satellite over its entire energy band. The sub-MeV peak is explained as multi-color black body emission, and the high energy tail, extending up to the GeV band, results from roughly similar contributions of synchrotron emission, synchrotron self Compton (SSC) and Comptonization of the thermal photons by energetic electrons originating after dissipation of the kinetic energy above the photosphere. We show how this analysis method results in a complete, self consistent picture of the physical conditions at both emission sites of the thermal and non-thermal radiation. We study the connection between the thermal and non-thermal parts of the spectrum, and show how the values of the free model parameters are deduced from the data. We demonstrate our analysis method on GRB090902B: We deduce a Lorentz factor in the range 780 <= \eta <= 1000, photospheric radius r_{ph} ~ 6.1 - 7.8*10^{11} cm and dissipation radius r_\gamma >= 3.8 - 5.0*10^{15} cm. By comparison to afterglow data, we deduce that a large fraction, \epsilon_d ~ 85% - 95% of the kinetic energy is dissipated, and that large fraction, ~equipartition of this energy is carried by the electrons and the magnetic field. This high value of \epsilon_d questions the "internal shock" scenario as the main energy dissipation mechanism for this GRB.
We study the correlation of the velocity dispersion of the coexisting molecules H13CN and H13CO+ and the turbulent energy dissipation scale in the DR21(OH) star-forming region. The down-shift of the H13CO+ spectrum relative to H13CN is consistent with the presence of ambipolar diffusion at dissipation length scales that helps the process of turbulent energy dissipation, but at a different cut-off for ions compared to the neutrals. We use our observational data to calculate a turbulent ambipolar diffusion length scale L'\simeq17 mpc and a strength of B_{pos}\simeq1.7 mG for the plane of the sky component of the magnetic field in DR21(OH).
The interaction between interplanetary small-scale magnetic flux ropes and the magnetic field in the ambient solar wind is an important topic to understand- ing the evolution of magnetic structures in the heliosphere. Through a survey of 125 previously reported small flux ropes from 1995 to 2005, we find that 44 of them reveal clear signatures of Alfvenic fluctuations, and thus classify them into Alfven wave trains rather than flux ropes. Signatures of magnetic reconnection, generally including a plasma jet of ~30 km/s within a magnetic field rotational region, are clearly present at boundaries of about 42% of the flux ropes and 14% of the wave trains. The reconnection exhausts are often observed to show a local increase in the proton temperature, density and plasma beta. About 66% of the reconnection events at flux rope boundaries are associated with a magnetic field shear angle larger than 90 deg and 73% of them reveal a decrease by 20% or more in the magnetic field magnitude, suggesting a dominance of anti-parallel reconnec- tion at flux rope boundaries. The occurrence rate of magnetic reconnection at flux rope boundaries through the year of 1995 to 2005 is also investigated and we find that it is relatively low around solar maximum and much higher when ap- proaching solar minima. The average magnetic field depression and shear angle for reconnection events at flux rope boundaries also reveal a similar trend from 1995 to 2005. Our results demonstrate for the first time that boundaries of a substantial fraction of small-scale flux ropes have properties similar to those of magnetic clouds, in the sense that both of them exhibit signatures of magnetic reconnection. The observed reconnection signatures could be related either to the formation of small flux ropes, or to the interaction between flux ropes and the interplanetary magnetic fields.
Shortly after the first results of Chandra and XMM-Newton appeared, many researchers in the field abandoned the term "cooling flow clusters" in favor of the name "cool core clusters". This change, I argue, has been causing damage by promoting the view that there is no substantial cooling in these clusters. In this contribution I discuss the following points, with emphasize on the last one that deals with magnetic fields in cooling flow clusters. (1) Both AGN-feedback and hot-gas cooling to form stars occur during galaxy formation as well as in cooling flow clusters. Ignoring cooling of the intra-cluster medium, as implied by the term "cool core", does not encourage comparative study of AGN feedback in cooling flow clusters with that of galaxy formation. (2) The line of thought that there is no cooling might lead to wrong questions and research directions. (3) A key question in both cooling flow clusters and during galaxy formation is the mode of accretion by the super massive black hole (SMBH). When cooling is neglected only accretion from the hot phase remains. Accretion from the hot phase, such as the Bondi accretion, suffers from some severe problems. (4) When it is accepted that moderate quantities of gas are cooling, it becomes clear that global heat conduction must be substantially suppressed. This does not favor a globally ordered magnetic field. As well, it makes global heat conduction unattractive.
Infrared studies have revealed debris likely related to planet formation in orbit around ~30% of youthful, intermediate mass, main sequence stars. We present evidence, based on atmospheric pollution by various elements heavier than helium, that a comparable fraction of the white dwarf descendants of such main sequence stars are orbited by planetary systems. These systems have survived, at least in part, through all stages of stellar evolution that precede the white dwarf. During the time interval (~200 million years) that a typical polluted white dwarf in our sample has been cooling it has accreted from its planetary system the mass of one of the largest asteroids in our solar system (e.g., Vesta or Ceres). Usually, this accreted mass will be only a fraction of the total mass of rocky material that orbits these white dwarfs; for plausible planetary system configurations we estimate that this total mass is likely to be at least equal to that of the Sun's asteroid belt, and perhaps much larger. We report abundances of a suite of 8 elements detected in the little studied star G241-6 that we find to be among the most heavily polluted of all moderately bright white dwarfs.
We have used the Low Resolution Imaging Spectrograph (LRIS) on the W.M. Keck I telescope to obtain spatially resolved spectroscopy of a small sample of six post-starburst and three dusty-starburst galaxies in the rich cluster CL0016+16 at z=0.55. We use this to measure radial profiles of the Hdelta and OII3727 lines which are diagnostic probes of the mechanisms that give rise to the abrupt changes in star-formation rates in these galaxies. In the post-starburst sample we are unable to detect any radial gradients in the Hdelta line equivalent width - although one galaxy exhibits a gradient from one side of the galaxy to the other. The absence of Hdelta gradients in these galaxies is consistent with their production via interaction with the intra-cluster medium, however, our limited spatial sampling prevents us from drawing robust conclusions. All members of the sample have early type morphologies, typical of post-starburst galaxies in general, but lack the high incidence of tidal tails and disturbances seen in local field samples. This argues against a merger origin and adds weight to a scenario where truncation by the intra-cluster medium is at work. The post-starburst spectral signature is consistent over the radial extent probed with no evidence of OII3727 emission and strong Hdelta absorption at all radii i.e. the post-starburst classification is not an aperture effect. In contrast the dusty-starburst sample shows a tendency for a central concentration of OII3727 emission. This is most straightforwardly interpreted as the consequence of a central starburst. However, other possibilities exist such as a non-uniform dust distribution (which is expected in such galaxies) and/or a non-uniform starburst age distribution. The sample exhibit late type and irregular morphologies.
Bright point sources associated with extragalactic AGN and radio galaxies are an important foreground for low frequency radio experiments aimed at detecting the redshifted 21cm emission from neutral hydrogen during the epoch of reionization. The frequency dependence of the synthesized beam implies that the sidelobes of these sources will move across the field of view as a function of observing frequency, hence frustrating line-of-sight foreground subtraction techniques. We describe a method for subtracting these point sources from dirty maps produced by an instrument such as the MWA. This technique combines matched filters with an iterative centroiding scheme to locate and characterize point sources in the presence of a diffuse background. Simulations show that this technique can improve the dynamic range of EOR maps by 2-3 orders of magnitude.
We report on the analysis of Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) monitoring observations of the $\gamma$-ray binary system LS I +61 303, covering 35 full cycles of its orbital motion. This constitutes the largest continuous X-ray monitoring dataset analyzed to date for this source. Such an extended analysis allows us to report: a) the discovery of variability in the orbital profiles of the X- ray emission, b) the existence of a few (recent) short flares on top of the overall behavior typical of the source, which, given the PCA field-of-view, may or may not be associated with LS I +61 303, and c) the determination of the orbital periodicity using soft X-ray data alone.
The two main components of the closest star system, {\alpha}-Centauri AB(RA 14h39m, Dec-60o50', J2000.0) is indubitbaly one of the most studied visual double stars. This paper presents the results of our recalculation of orbital and physical parameters of the system using Thiele-van den Bos method, based on observational data from year 1900 to 2002. Despite some significant discrepancies, in general our results confirmed previous results of orbital parameter determinations using different method.
Since its first discovery, most extrasolar planets were detected using radial velocity (RV) method. However, the RV method does not provide all parameters required to characterize a planetary system. Recently, Charbonneau et al.(2000) and Brown et al(2001)have shown that the RV planet orbiting HD 209458 can be observed using transit method yielding some additional information. As pointed out by Castellano (2004), this method can be undertaken using small aperture telescopes and inexpensive CCDs. We report here new observations of planetary transit in HD 102195 and HD 209458 performed at the Bosscha Observatory since March 2006. Some preliminary results will be presented
The results of numerical simulations of the dynamics of galactic disks, which are submerged into nonaxisymmetric dark massive halo are discussed. Galaxy disks dynamics in the nonaxisymmetric (triaxial) dark halo were investigated in detail by the high resolution numerical hydrodynamical methods (TVD \& SPH) and N-body models. The long-lived two arms spiral structure generates for a wide range of parameters. The spiral structure is global and number of turns can be 2-3 in depends of model parameters. Morphology and kinematics of spiral structures were investigated in depends of the halo and the disk parameters. The spiral structure rotates slowly and the angular velocity varies is quasiperiodic.
A VI Wesenheit diagram featuring SX Phoenicis, delta Scuti, RR Lyrae, type II and classical Cepheid variables is calibrated by means of geometric-based distances inferred from HST, Hipparcos, and VLBA observations (n=30). The distance to a target population follows from the offset between the observed Wesenheit magnitudes and the calibrated template. The method is evaluated by ascertaining the distance moduli for the LMC (mu_0=18.43+-0.03 se) and the globular clusters Omega Cen, M54, M13, M3, and M15. The results agree with estimates cited in the literature, although a nearer distance to M13 is favored and observations of variables in M15 suffer from photometric contamination. A Wesenheit template of the LMC can be employed since that galaxy exhibits precise OGLE data for variables of differing classes, that includes recent observations for delta Scuti variables indicating the stars follow a steeper VI Wesenheit function than classical Cepheids pulsating in the fundamental mode. VI photometry for the calibrators is tabulated to facilitate further research, and includes new observations acquired via the AAVSO's robotic telescope network (e.g., VY Pyx: <V>=7.25 and <V>-<I>=6.58). The approach outlined here supersedes the lead author's prior first-order effort to unify variables of the instability strip in order to establish distances.
Abridged: We detail and benchmark two sophisticated chemical models developed by the Heidelberg and Bordeaux astrochemistry groups. The main goal of this study is to elaborate on a few well-described tests for state-of-the-art astrochemical codes covering a range of physical conditions and chemical processes, in particular those aimed at constraining current and future interferometric observations of protoplanetary disks. We consider three physical models: a cold molecular cloud core, a hot core, and an outer region of a T Tauri disk. Our chemical network (for both models) is based on the original gas-phase osu_03_2008 ratefile and includes gas-grain interactions and a set of surface reactions for the H-, O-, C-, S-, and N-bearing molecules. The benchmarking is performed with the increasing complexity of the considered processes: (1) the pure gas-phase chemistry, (2) the gas-phase chemistry with accretion and desorption, and (3) the full gas-grain model with surface reactions. Using atomic initial abundances with heavily depleted metals and hydrogen in its molecular form, the chemical evolution is modeled within 10^9 years. The time-dependent abundances calculated with the two chemical models are essentially the same for all considered physical cases and for all species, including the most complex polyatomic ions and organic molecules. This result however required a lot of efforts to make all necessary details consistent through the model runs, e.g. definition of the gas particle density, density of grain surface sites, the strength and shape of the UV radiation field, etc. The reference models and the benchmark setup, along with the two chemical codes and resulting time-dependent abundances are made publicly available in the Internet: this http URL
We present the results of radio observations of the black hole binaries GRO J1655-40 and XTE J1550-564 in quiescence, with the upgraded Australia Telescope Compact Array. Neither system was detected. Radio flux density upper limits (3 sigma) of 26 micro Jy (at 5.5 GHz), 47 micro Jy (at 9 GHz) for GRO J1655-40, and 1.4 mJy (at 1.75 GHz), 27 micro Jy (at 5.5 GHz), 47 micro Jy (at 9 GHz) for XTE J1550-564 were measured. In conjunction with quasi-simultaneous Chandra X-ray observations (in the case of GRO J1655-40) and Faulkes Telescope optical observations (XTE J1550-564) we find that these systems provide the first evidence of relatively `radio quiet' black hole binaries at low luminosities; indicating that the scatter observed in the hard state X-ray:radio correlation at higher luminosities may also extend towards quiescent levels.
The nature of the dark energy is still a mystery and several models have been proposed to explain it. Here we consider a phenomenological model for dark energy decay into photons and particles as proposed by Lima (J. Lima, Phys. Rev. D 54, 2571 (1996)). He studied the thermodynamic aspects of decaying dark energy models in particular in the case of a continuous photon creation and/or disruption. Following his approach, we derive a temperature redshift relation for the CMB which depends on the effective equation of state $w_{eff}$ and on the "adiabatic index" $\gamma$. Comparing our relation with the data on the CMB temperature as a function of the redshift obtained from Sunyaev-Zel'dovich observations and at higher redshift from quasar absorption line spectra, we find $w_{eff}=-0.97 \pm 0.034$, adopting for the adiabatic index $\gamma=4/3$, in good agreement with current estimates and still compatible with $w_{eff}=-1$, implying that the dark energy content being constant in time.
A new L-band 7 feed array at the 100-m telescope is used to perform an unbiased, fully sampled HI survey of the whole northern hemisphere - the Effelsberg-Bonn HI Survey (EBHIS). The use of state-of-the-art digital Fast Fourier Transform spectrometers based on FPGAs - superior in dynamic range and allowing fast dumping of spectra - makes it possible to apply sophisticated RFI mitigation schemes. Based on the current status of the survey we discuss the RFI situation at the 100-m telescope and present a fast algorithm to automatically identify RFI in the raw data output from the spectrometer. Using simulations we show that it is feasible to detect more than 95% of all RFI in excess of 1 sigma amplitude with less than 1% false positives.
Most globular clusters have half-mass radii of a few pc with no apparent correlation with their masses. This is different from elliptical galaxies, for which the Faber-Jackson relation suggests a strong positive correlation between mass and radius. Objects that are somewhat in between globular clusters and low-mass galaxies, such as ultra-compact dwarf galaxies, have a mass-radius relation consistent with the extension of the relation for bright ellipticals. Here we show that at an age of 10 Gyr a break in the mass-radius relation at ~10^6 Msun is established because objects below this mass, i.e. globular clusters, have undergone expansion driven by stellar evolution and hard binaries. From numerical simulations we find that the combined energy production of these two effects in the core comes into balance with the flux of energy that is conducted across the half-mass radius by relaxation. An important property of this `balanced' evolution is that the cluster half-mass radius is independent of its initial value and is a function of the number of bound stars and the age only. It is therefore not possible to infer the initial mass-radius relation of globular clusters and we can only conclude that the present day properties are consistent with the hypothesis that all hot stellar systems formed with the same mass-radius relation and that globular clusters have moved away from this relation because of a Hubble time of stellar and dynamical evolution.
We have used high resolution spectra obtained with the spectrograph FLAMES at the ESO Very Large Telescope to determine the kinematical properties and the abundance patterns of 20 blue straggler stars (BSSs) in the globular cluster M4. We found that ~ 40% of the measured BSSs are fast rotators (with rotational velocities > 50 km/s). This is the largest frequency of rapidly rotating BSSs ever detected in a globular cluster. In addition, at odds with what has been found in 47 Tucanae, no evidence of carbon and/or oxygen depletion has been revealed in the sample of 11 BSSs for which we were able to measure the abundances. This could be due either to low statistics, or to a different BSS formation process acting in M4.
Recently, a new model obtained from generalizing teleparallel gravity, named $f(T)$ theory, is proposed to explain the present cosmic accelerating expansion with no need of dark energy. In this paper, we analyze the dynamical property of this theory. For a concrete power law model, we obtain that the dynamical system has a stable de Sitter phase along with an unstable radiation dominated phase and an unstable matter dominated one. We show that the Universe can evolve from a radiation dominated era to a matter dominated one, and finally enter an exponential expansion phase.
Spacecraft observations in the inner heliosphere offer the first opportunity to measure 1-10 MeV solar neutrons. We discuss the physics of low-energy neutron production in solar flares and show that, even at interacting-particle energies of 2 MeV/nucleon, neutrons with energies >10 MeV are produced. On the other hand, a significant fraction of 1-10 MeV neutrons result from interactions of >10 MeV/nucleon ions in typical flare spectra. We calculate the escaping neutron spectra for mono-energetic and power-law particle spectra at the Sun for the location and observation angle of MESSENGER at the time of its reported detection of low-energy neutrons associated with the 2007 December 31 solar flare. We detail concerns about this questionable observation of solar neutrons: 1. the inferred number of accelerated protons at the Sun for this modest M2-class flare was 10X larger than any flare observed to date, 2. the onset and duration of the 'solar' neutron count rate was similar to that of the solar energetic particles (SEPs), and 3. the authors' argument that the SEPs were dominated by electrons and so could not have produced the neutron counts locally in the spacecraft. In contrast we argue that solar energetic protons and alpha particles, through local neutron production and accidental coincidences, were the source of most of the reported 'solar-neutron' counts.
Using the Chandra X-ray Observatory, we have pinpointed the location of a faint X-ray point source (CXOUJ182913.1-125113) and an associated diffuse nebula in the composite supernova remnant G18.95-1.1. These objects appear to be the long-sought pulsar and its wind nebula. The X-ray spectrum of the point source is best described by an absorbed powerlaw model with Gamma=1.6 and an N_H of ~1x10^(22) cm^(-2). This model predicts a relatively low unabsorbed X-ray luminosity of about L_X (0.5-8.0keV) = 4.1x10^(31)D_2^2 erg s^(-1), where D_2 is the distance in units of 2kpc. The best-fitted model of the diffuse nebula is a combination of thermal (kT = 0.48keV) and non-thermal (1.4 < Gamma < 1.9) emission. The unabsorbed X-ray luminosity of L_X = 5.4x10^(33)D_2^2 erg s^(-1) in the 0.5-8keV energy band seems to be largely dominated by the thermal component from the SNR, providing 87% of L_X in this band. No radio or X-ray pulsations have been reported for CXOUJ182913.1-125113. If we assume an age of ~5300yr for G18.95-1.1 and use the X-ray luminosity for the pulsar and the wind nebula together with the relationship between spin-down luminosity (via magnetic dipole radiation) and period, we estimate the pulsar's period to be P = 0.4s. Compared to other rotation-powered pulsars, a magnetic field of 2.2x10^(13)G is implied by its location in the P-Pdot diagram, a value which is close to that of the quantum critical field.
A sample of 129 unresolved radio sources with ultra-high linear polarisation (>30 per cent) has been selected from the NVSS (NRAO VLA Sky Survey). Such high average linear polarisation is unusual in extragalactic sources. Higher resolution ATCA (Australia Telescope Compact Array) and VLA (Very Large Array) observations confirm the high average polarisation but find that most of these sources are extended. SDSS (Sloan Digital Sky Survey) spectroscopy, where available, shows that the optical counterparts are elliptical galaxies with no detectable emission lines. The optical spectra, radio luminosity, linear size and spectral index of these sources are typical of radio-loud AGNs. Galaxy counts within a 1 Mpc radius of the radio sources show that these highly polarised sources are in environments similar to their low polarisation (<2 per cent) counterparts. Similarly the line-of-sight environments of the ultra-high polarisation sources are on average indistinguishable from those of the low polarisation sources. We conclude that the extraordinarily high average polarisation must be due to intrinsic properties of the sources, such as an extremely ordered source magnetic field, low internal thermal plasma density or the source magnetic field is preferentially oriented in the plane of the sky.
The physical processes that heat the solar corona and accelerate the solar wind remain unknown after many years of study. Some have suggested that the wind is driven by waves and turbulence in open magnetic flux tubes, and others have suggested that plasma is injected into the open tubes by magnetic reconnection with closed loops. In order to test the latter idea, we developed Monte Carlo simulations of the photospheric "magnetic carpet" and extrapolated the time-varying coronal field. These models were constructed for a range of different magnetic flux imbalance ratios. Completely balanced models represent quiet regions on the Sun and source regions of slow solar wind streams. Highly imbalanced models represent coronal holes and source regions of fast wind streams. The models agree with observed emergence rates, surface flux densities, and number distributions of magnetic elements. Despite having no imposed supergranular motions, a realistic network of magnetic "funnels" appeared spontaneously. We computed the rate at which closed field lines open up (i.e., recycling times for open flux), and we estimated the energy flux released in reconnection events involving the opening up of closed flux tubes. For quiet regions and mixed-polarity coronal holes, these energy fluxes were found to be much lower than required to accelerate the solar wind. For the most imbalanced coronal holes, the energy fluxes may be large enough to power the solar wind, but the recycling times are far longer than the time it takes the solar wind to accelerate into the low corona. Thus, it is unlikely that either the slow or fast solar wind is driven by reconnection and loop-opening processes in the magnetic carpet.
We investigate the observational signatures of three models of the early Universe in the $B$-mode polarization of the Cosmic Microwave Background (CMB) radiation. In addition to the standard single field inflationary model, we also consider the constraints obtainable on the loop quantum cosmology model (from Loop Quantum Gravity) and on cosmic strings, expected to be copiously produced during the latter stages of Brane inflation. We first examine the observational features of the three models, and then use current $B$-mode polarization data from the BICEP and QUaD experiments to constrain their parameters. We also examine the detectability of the primordial $B$-mode signal predicted by these models and forecast the parameter constraints achievable with future CMB polarization experiments. We find that: (a) since $B$-mode polarization measurements are mostly unaffected by parameter degeneracies, they provide the cleanest probe of these early Universe models; (b) using the BICEP and QUaD data we obtain the following parameter constraints: $r=0.02^{+0.31}_{-0.26}$ ($1\sigma$ for the tensor-to-scalar ratio in the single field inflationary model); $m < 1.36\times 10^{-8} \text{M}_{\text{pl}}$ and $k_{*} < 2.43 \times 10^{-4} \text{Mpc}^{-1}$ ($1\sigma$ for the mass and scale parameters in the loop quantum cosmology model); and $G\mu < 5.77 \times 10^{-7}$ ($1\sigma$ for the cosmic string tension); (c) although it is not statistically significant, there is weak evidence for both the pre-inflationary bounce of the loop quantum cosmology model and for a non-zero cosmic string tension; (d) future CMB observations (both satellite missions and forthcoming sub-orbital experiments) will provide much more rigorous tests of these early Universe models.
We report the results of the first deep, wide-field, near-infrared methane imaging survey of the Rho Ophiuchi cloud core to search for T dwarfs. Among the 6587 objects detected, 22 were identified as T dwarf candidates. Brown dwarf models indicate that at the age and distance of the Rho Ophiuchi cloud, these T dwarf candidates have masses between 1 and 2 Jupiter masses. If confirmed as genuine T dwarfs, these objects would be the youngest, lowest mass, and lowest gravity free-floating objects ever directly observed. The existence of these candidates suggests that the initial mass function of the Rho Ophiuchi cloud extends well into the regime of planetary mass objects. A large fraction (59% +/- 16%) of our T dwarf candidates appear to be surrounded by circumstellar disks, and thus represent the lowest mass objects yet found to harbor circumstellar disks.
We show that microscopic calculations based on chiral effective field theory interactions constrain the properties of dense matter below nuclear densities to a much higher degree than is reflected in current neutron star modeling. Combined with observed neutron star masses, our results lead to a radius R = 11.8 +- 2.1 km for a M = 1.4 M_{solar} neutron star, where the theoretical error is due, in about equal amounts, to uncertainties in many-body forces and to the extrapolation to high densities.
We investigate the cosmological evolution of the tachyon and phantom-tachyon scalar field by considering the potential parameter $\Gamma$($=\frac{V V"}{V'^2}$) as a function of another potential parameter $\lambda$($=\frac{V'}{\kappa V^{3/2}}$), which correspondingly extends the analysis of the evolution of our universe from two-dimensional autonomous dynamical system to the three-dimension. It allows us to investigate the more general situation where the potential is not restricted to inverse square potential and .One result is that, apart from the inverse square potential, there are a large number of potentials which can give the scaling and dominant solution when the function $\Gamma(\lambda)$ equals $3/2$ for one or some values of $\lambda_{*}$ as well as the parameter $\lambda_{*}$ satisfies condition Eq.(18) or Eq.(19). We also find that for a class of different potentials the dynamics evolution of the universe are actually the same and therefore undistinguishable.
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We use stellar dynamics, strong lensing, stellar population synthesis models, and weak lensing shear measurements to constrain the dark matter (DM) profile and stellar mass in a sample of 53 massive early-type galaxies. We explore three DM halo models (unperturbed Navarro Frenk & White [NFW] halos and the adiabatic contraction models of Blumenthal and Gnedin) and impose a model for the relationship between the stellar and virial mass (i.e., a relationship for the star-formation efficiency as a function of halo mass). We show that, given our model assumptions, the data clearly prefer a Salpeter-like initial mass function (IMF) over a lighter IMF (e.g., Chabrier or Kroupa), irrespective of the choice of DM halo. In addition, we find that the data prefer at most a moderate amount of adiabatic contraction (Blumenthal adiabatic contraction is strongly disfavored) and are only consistent with no adiabatic contraction (i.e., a NFW halo) if a mass-dependent IMF is assumed, in the sense of a more massive normalization of the IMF for more massive halos.
The CIAS Chalonge Workshop `Dark Matter in the Universe and Universal Properties of Galaxies: Theory and Observations', was held at the Meudon Ch^ateau of Observatoire de Paris on 8-11 June 2010. The Workshop approached DM in a fourfold way: astronomical observations of DM structures (galaxy properties, halos, rotation curves and density profiles), DM numerical simulations (with and without baryons), theoretical astrophysics and cosmology (kinetic theory, Boltzmann-Vlasov evolution), astroparticle physics. Peter Biermann, Alfonso Cavaliere, Hector J. de Vega, Gianfranco Gentile, Chandra Jog, Andrea Lapi, Paolo Salucci, Norma G. Sanchez, Pasquale Serpico, Rainer Stiele, Janine van Eymeren and Markus Weber present here their highlights of the Workshop. The summary and conclusions by H. J. de Vega and N. G. Sanchez stress among other points the growing evidence that DM particles have a mass in the keV scale and that those keV scale particles naturally produce the small scale structures observed in galaxies. Wimps (DM particles heavier than 1 GeV) are strongly disfavoured combining theory with galaxy astronomical observations. Peter Biermann presents his live minutes of the Workshop and concludes that a right-handed sterile neutrino of mass of a few keV is the most interesting DM candidate. Photos of the Workshop are included.
The three-point correlation function (3PCF) provides an important view into the clustering of galaxies that is not available to its lower order cousin, the two-point correlation function (2PCF). Higher order statistics, such as the 3PCF, are necessary to probe the non-Gaussian structure and shape information expected in these distributions. We measure the clustering of spectroscopic galaxies in the Main Galaxy Sample of the Sloan Digital Sky Survey (SDSS), focusing on the shape or configuration dependence of the reduced 3PCF in both redshift and projected space. This work constitutes the largest number of galaxies ever used to investigate the reduced 3PCF, using over 220,000 galaxies in three volume-limited samples. We find significant configuration dependence of the reduced 3PCF at 3-27 Mpc/h, in agreement with LCDM predictions and in disagreement with the hierarchical ansatz. Below 6 Mpc/h, the redshift space reduced 3PCF shows a smaller amplitude and weak configuration dependence in comparison with projected measurements suggesting that redshift distortions, and not galaxy bias, can make the reduced 3PCF appear consistent with the hierarchical ansatz. The reduced 3PCF shows a weaker dependence on luminosity than the 2PCF, with no significant dependence on scales above 9 Mpc/h. On scales less than 9 Mpc/h, the reduced 3PCF appears more affected by galaxy color than luminosty. We demonstrate the extreme sensitivity of the 3PCF to systematic effects such as sky completeness and binning scheme, along with the difficulty of resolving the errors. Some comparable analyses make assumptions that do not consistently account for these effects.
This paper reports the spectral and timing analyses of the quiescent low-mass X-ray binary U24 observed during five archived Chandra-ACIS exposures of the nearby globular cluster NGC 6397, for a total of 350 ksec. We find that the X-ray flux and the parameters of the hydrogen atmosphere spectral model are consistent with those previously published. Following the timing analysis, we find no evidence of short or long-term intensity variability. We also report the improved neutron star physical radius measurements, with statistical accuracy of the order of ~10%: R_ns = 8.9(+0.9)(-0.6) km for M_ns = 1.4 Msun. Alternatively, we provide the best-fit projected radius R_infinity= 11.9(+2.2)(-2.5)km, as seen by an observer at infinity. The best-fit effective temperature, kTeff = 80(+4)(-5) eV, is used to estimate the neutron star core temperature which falls in the range T_core = (3.0 - 9.8) x10 7 K, depending on the atmosphere model considered. This makes U24 the fourth most precisely measured neutron star radius among qLMXBs, after those in OmCen, in M13 and the qLMXB 47Tuc X7.
The formation of planetesimals via gravitational instability of the dust layer in a protoplanetary disks demands that there be local patches where dust is concentrated by a factor of $\sim$ a few $\times 10^3$ over the background value. Vortices in protoplanetary disks may concentrate dust to these values allowing them to be the nurseries of planetesimals. The concentration of dust in the cores of vortices increases the dust-gas ratio of the core compared to the background disk, creating a "heavy vortex." In this work, we show that these vortices are subject to an instability which we have called the heavy-core instability. Using Floquet theory, we show that this instability occurs in elliptical protoplanetary vortices when the gas-dust density of the core of the vortex is heavier than the ambient gas-dust density by a few tens of percent. The heavy-core instability grows very rapidly, with a growth timescale of a few vortex rotation periods. While the nonlinear evolution of this instability remains unknown, it will likely increase the velocity dispersion of the dust layer in the vortex because instability sets in well before sufficient dust can gather to form a protoplanetary seed. This instability may thus preclude vortices from being sites of planetesimal formation.
We use the high angular resolution in the near-infrared of the WFC3 on HST to identify and characterize 1.5 < z < 3.5 galaxies in the HUDF09 and ERS fields. Specifically, (i) we construct H-band selected catalogs of galaxies complete down to AB=27(25) mag in the HUDF09(ERS) fields, and publish these source catalogs; (ii) present optimized color-selection criteria for identifying galaxies at 1.5 < z < 3.5 - i.e., a YHVz criterion, which offers a selection rate within the target redshift interval of 96%(92%) down to H < 27(25) mag in the HUDF09(ERS), with contamination from interlopers at lower or higher redshifts of only ~15%; and (iii) compare the WFC3/IR rest-frame optical morphologies of these galaxies with their ACS-based rest-frame UV morphologies. The WFC3 NIR images reveal galaxies at these redshifts that were undetected in the rest-frame UV HUDF/GOODS images, as well as true centers and regular disks in galaxies classified as highly irregular in rest-frame UV light. Across the entire 1.5 < z < 3.5 redshift range, galaxies in which regular disks are unveiled in the WFC3 images tend to be quite massive, i.e., >10^10.5 Msun. In contrast, less massive galaxies maintain an irregular morphology in the rest-frame optical light, indicating that, at these epochs, low-mass galaxies are not dynamically settled. At the highest masses, >10^11 Msun, galaxies at 2.25 < z < 3.5 show the whole variety of morphologies, from irregular to disk to spheroid, in roughly similar proportions. Strikingly, however, galaxies of similar high masses at 1.5 < z < 2.25 are virtually all elliptical-like spheroids. In our small sample, the fraction of star-forming galaxies at these mass scales decreases from ~60% to zero. If confirmed, this indicates that z ~ 2 is the epoch of both the morphological transformations and quenching of star-formation that results in the massive elliptical population.
Context. High resolution X-ray observations of classical T Tauri stars (CTTSs) show a soft X-ray excess due to high density plasma (n_e=10^11-10^13 cm^-3). This emission has been attributed to shock-heated accreting material impacting onto the stellar surface. Aims. We investigate the observability of the shock-heated accreting material in the X-ray band as a function of the accretion stream properties (velocity, density, and metal abundance) in the case of plasma-beta<<1 in the post-shock zone. Methods. We use a 1-D hydrodynamic model describing the impact of an accretion stream onto the chromosphere, including the effects of radiative cooling, gravity and thermal conduction. We explore the space of relevant parameters and synthesize from the model results the X-ray emission in the [0.5-8.0] keV band and in the resonance lines of O VII (21.60 Ang) and Ne IX (13.45 Ang), taking into account the absorption from the chromosphere. Results. The accretion stream properties influence the temperature and the stand-off height of the shocked slab and its sinking in the chromosphere, determining the observability of the shocked plasma. Our model predicts that X-ray observations preferentially detect emission from low density and high velocity shocked accretion streams due to the large absorption of dense post-shock plasma. In all the cases examined, the post-shock zone exhibits quasi-periodic oscillations due to thermal instabilities, but in the case of inhomogeneous streams and beta<<1, the shock oscillations are hardly detectable. Conclusions. We suggest that, if accretion streams are inhomogeneous, the selection effect introduced by the absorption on observable plasma components may explain the discrepancy between the accretion rate measured by optical and X-ray data as well as the different densities measured using different He-like triplets in the X-ray band.
We measure alignments on scales of 1 Mpc $h^{-1}_{71}$ for galaxies in Abell 1689 ($z=0.18$) from an existing Hubble Space Telescope mosaic. We find evidence of galaxy alignment in the inner 500 $h^{-1}_{71}$ kpc. The alignment appears to be stronger towards the centre and is mostly present among the fainter galaxies, while bright galaxies are unaligned. This is consistent with a model where alignments originate from tidal locking.
Since the last phase coherent timing solution of the nearby radio-quiet isolated neutron star RX J0720.4-3125 six new XMM-Newton and three Chandra observations were carried out. The phase coherent timing solutions from previous authors were performed without restricting to a fixed energy band. However, we recently showed that the phase residuals are energy dependent, and thus phase coherent solutions must be computed referring always to the same energy band. We updated the phase coherent timing solution for RX J0720.4-3125 by including the recent XMM-Newton EPIC-pn, MOS1, MOS2 and Chandra ACIS data in the energy range 400-1000~eV. Altogether these observations cover a time span of almost 10~yrs. A further timing solution was obtained including the ROSAT pointed data. In this case, observations cover a time span of $\approx$16~yrs. To illustrate the timing differences between the soft band (120-400~eV) and the hard band (400-1000~eV) a timing solution for the soft band is also presented and the results are verified using a $\mathrm{Z_{n}^{2}}$ test. In contrast to previous work, we obtain almost identical solutions whether or not we include the ROSAT or Chandra data. Thanks to the restriction to the hard band, the data points from EPIC-pn are in better agreement with those from MOS1, MOS2 and Chandra than in previous works. In general the phase residuals are still large and vary with time. In particular, the latest XMM-Newton and Chandra data show that the phase residuals have attained relatively large and negative values.
We present a grid of models of accreting brown dwarf systems with circumstellar discs. The calculations involve a self-consistent solution of both vertical hydrostatic and radiative equilibrium along with a sophisticated treatment of dust sublimation. We have simulated observations of the spectral energy distributions and several broadband photometric systems. Analysis of the disc structures and simulated observations reveal a natural dichotomy in accretion rates, with \logmdot $>-$9 and $\leq -$9 classed as extreme and typical accretors respectively. Derivation of ages and masses from our simulated photometry using isochrones is demonstrated to be unreliable even for typical accretors. Although current brown dwarf disc candidate selection criteria have been shown to be largely reliable when applied to our model grid we suggest improved selection criteria in several colour indices. We show that as accretion rates increase brown dwarf disc systems are less likely to be correctly identified. This suggests that, within our grid, systems with higher accretion rates would be preferentially lost during brown dwarf target selection. We suggest that observations used to assert a $\dot{M}\propto M_*^2$ relationship may contain an intrinsic selection bias.
We analyze EUV spectra of the full solar disk from the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS) spanning a period of two years. The observations were obtained via a fortuitous off-axis light path in the 140 -- 270 Angstrom passband. The general appearance of the spectra remained relatively stable over the two-year time period, but did show significant variations of up to 25% between two sets of Fe lines that show peak emission at 1 MK and 2 MK. The variations occur at a measured period of 27.2 days and are caused by regions of hotter and cooler plasma rotating into, and out of, the field of view. The CHIANTI spectral code is employed to determine plasma temperatures, densities, and emission measures. A set of five isothermal plasmas fit the full disk spectra well. A 1 -- 2 MK plasma of Fe contributes 85% of the total emission in the CHIPS passband. The standard Differential Emission Measures (DEMs) supplied with the CHIANTI package do not fit the CHIPS spectra well as they over-predict emission at temperatures below log(T) = 6.0 and above log(T) = 6.3. The results are important for cross-calibrating TIMED, SORCE, SOHO/EIT, and CDS/GIS, as well as the recently launched Solar Dynamics Observatory.
We present tomography of the circum-galactic metal distribution at redshift 1.7 to 4.5 derived from echellete spectroscopy of binary quasars. We find CIV systems at similar redshifts in paired sightlines more often than expected for sightline-independent redshifts. As the separation of the sightlines increases from 36 kpc to 907 kpc, the amplitude of this clustering decreases. At the largest separations, the CIV systems cluster similar to Lyman-break galaxies (Adelberger et al. 2005a). The CIV systems are significantly less correlated than these galaxies, however, at separations less than R_1 ~ 0.42 +/- 0.15 h-1 comoving Mpc. Measured in real space, i.e., transverse to the sightlines, this length scale is significantly smaller than the break scale estimated from the line-of-sight correlation function in redshift space (Scannapieco et al. 2006a). Using a simple model, we interpret the new real-space measurement as an indication of the typical physical size of enriched regions. We adopt this size for enriched regions and fit the redshift-space distortion in the line-of-sight correlation function. The fitted velocity kick is consistent with the peculiar velocity of galaxies as determined by the underlying mass distribution and places an upper limit on the outflow (or inflow) speed of metals. The implied time scale for dispersing metals is larger than the typical stellar ages of Lyman-break galaxies (Shapley et al. 2001), and we argue that enrichment by galaxies at z > 4.3 played a greater role in dispersing metals. To further constrain the growth of enriched regions, we discuss empirical constraints on the evolution of the CIV correlation function with cosmic time. This study demonstrates the potential of tomography for measuring the metal enrichment history of the circum-galactic medium.
We present the results of an on-sky point spread function reconstruction (PSF-R) experiment for the Gemini North telescope adaptive optics system, Altair, in the simplest mode, bright on-axis natural guise star. We demonstrate that our PSF-R method does work for system performance diagnostic but suffers from hidden telescope and system aberrations that are not accounted for in the model, making the reconstruction unsuccessful for Altair, for now. We discuss the probable origin of the discrepancy. In the last section, we propose alternative PSF-R methods for future multiple natural and laser guide stars systems.
Gravitational lensing induces significant errors in the measured distances to high-redshift standard candles and standard sirens such as type-Ia supernovae, gamma-ray bursts, and merging supermassive black hole binaries. There will therefore be a significant benefit from correcting for the lensing error by using independent and accurate estimates of the lensing magnification. We investigate how accurately the magnification can be inferred from convergence maps reconstructed from galaxy shear and flexion data. We employ ray-tracing through the Millennium Simulation to simulate lensing observations in large fields, and perform a weak-lensing reconstruction on these fields. We identify optimal ways to filter the reconstructed convergence maps and to convert them to magnification maps. We find that a shear survey with 100 galaxies/arcmin^2 can help to reduce the lensing-induced distance errors for standard candles/sirens at redshifts z=1.5 (z=5) on average by 20% (10%), whereas a futuristic survey with shear and flexion estimates from 500 galaxies/arcmin^2 yields much larger reductions of 50% (35%). For redshifts z>=3, a further improvement by 5% can be achieved, if the individual redshifts of the galaxies are used in the reconstruction. Moreover, the reconstruction allows one to identify regions for which the convergence is low, and in which an error reduction by up to 75% can be achieved.
The spatial-temporal distribution of absorption-line systems (ALSs) observed in QSO spectra within the cosmological redshift interval z = 0.0--4.3 is investigated on the base of our updated catalog of absorption systems. We consider so called metallic systems including basically lines of heavy elements. The sample of the data displays regular variations (with amplitudes ~ 15 -- 20%) in the z-distribution of ALSs as well as in the eta-distribution, where eta is a dimensionless line-of-sight comoving distance, relatively to smoother dependences. The eta-distribution reveals the periodicity with period Delta eta = 0.036 +/- 0.002, which corresponds to a spatial characteristic scale (108 +/- 6) h(-1) Mpc or (alternatively) a temporal interval (350 +/- 20) h(-1) Myr for the LambdaCDM cosmological model. We discuss a possibility of a spatial interpretation of the results treating the pattern obtained as a trace of an order imprinted on the galaxy clustering in the early Universe.
We investigate a sample of eleven Galactic X-ray sources recently discovered with INTEGRAL or RXTE with the goal of identifying their optical and/or near-infrared (NIR) counterpart. For this purpose new Chandra positions of nine objects are presented together with follow-up observations of all the targets in the optical and NIR. For the four sources IGR J16194-2810, IGRJ 16479-4514, IGR J16500-3307 and IGR J19308+530, the Chandra position confirms an existing association with an optical/NIR object, while for two sources (XTE J1716-389 and 18490-0000) it rules out previously proposed counterparts indicating new ones. In the case of IGR J17597-220, a counterpart is selected out of the several possibilities proposed in the literature and we present the first association with an optical/NIR source for J16293-4603 and XTE J1743-363. Moreover, optical/NIR observations are reported for XTE J1710-281 and IGR J17254-3257: we investigate the counterpart to the X-ray sources based on their XMM-Newton positions. We discuss the nature of each system considering its optical/NIR and X-ray properties.
We report the discovery by the CoRoT satellite of a new transiting giant planet in a 2.83 days orbit about a V=15.5 solar analog star (M_* = 1.08 +- 0.08 M_sun, R_* = 1.1 +- 0.1 R_sun, T_eff = 5675 +- 80 K). This new planet, CoRoT-12b, has a mass of 0.92 +- 0.07 M_Jup and a radius of 1.44 +- 0.13 R_Jup. Its low density can be explained by standard models for irradiated planets.
We implemented sink particles in the Adaptive Mesh Refinement (AMR) code FLASH to model the gravitational collapse and accretion in turbulent molecular clouds and cores. Sink particles are frequently used to measure properties of star formation in numerical simulations, such as the star formation rate and efficiency, and the mass distribution of stars. We show that a sole density threshold for sink particle creation is insufficient in case of supersonic flows, because the density can exceed the threshold in strong shocks that do not necessarily lead to local collapse. Additional physical collapse indicators have to be considered. We apply our AMR sink particle module to the formation of a star cluster, and compare it to a Smoothed Particle Hydrodynamics (SPH) code with sink particles. Our comparison shows encouraging agreement of gas and sink particle properties.
The accuracy of Milne-Eddington (ME) inversions, used to retrieve the magnetic field vector, depends upon the signal-to-noise ratio (SNR) of the spectro-polarimetric observations. The SNR in real observations varies from pixel to pixel, therefore the accuracy of the field vector also varies over the map. The aim of this work is to study the effect of polarimetric noise on the inference of magnetic field vector and the magnetic non-potentiality of a real sunspot. To this end, we use Hinode SOT/SP vector magnetogram of a real sunspot NOAA 10933 as an input to generate synthetic Stokes profiles under ME model assumptions. We then add normally-distributed polarimetric noise of the level 0.5\% of continuum intensity to these synthetic profiles and invert them again using ME code. This process is repeated 100 times with different realizations of noise. It is found that within most of the sunspot area (> 90% area) the spread in the (i) field strength is less than 8 Gauss, (ii) field inclination is less than 1 degree, and (iii) field azimuth is less than 5 degrees. Further, we determine the uncertainty in the magnetic non-potentiality of a sunspot as determined by the force-free parameter alpha_g and Spatially Averaged Signed Shear Angle (SASSA). It is found that for the sunspot studied here these parameters are alpha_g = -3.5 +/- 0.37 (x 10^{-9} m^{-1}) and SASSA = -1.68 +/- 0.014 degrees. This suggests that the SASSA is a less dispersion non-potentiality parameter as compared to alpha_g. Further, we examine the effect of increasing noise levels viz. 0.01, 0.1, 0.5 and 1% of continuum intensity and find that SASSA is less vulnerable to noise as compared to alpha_g parameter.
High cadence, multiwavelength, optical observations of solar magnetic bright points, captured at disk center using the ROSA and IBIS imaging systems on the Dunn Solar Telescope, are presented. Magnetic bright points manifesting in the Na I D1 core are found to preferentially exist in regions containing strong downflows, in addition to co-spatial underlying photospheric magnetic field concentrations. Downdrafts within Na I D1 bright points exhibit speeds of up to 7km/s, with preferred structural symmetry in intensity, magnetic field and velocity profiles about the bright point center. Excess intensities associated with G-band and Ca II K observations of magnetic bright points reveal a power-law trend when plotted as a function of magnetic flux density. However, Na I D1 observations of the same magnetic features indicate an intensity plateau at weak magnetic field strengths below ~150G, suggesting the presence of a two-component heating process; one which is primarily acoustic, the other predominantly magnetic. We suggest that this finding is related to the physical expansion of magnetic flux tubes, with weak field strengths (~50G) expanding by ~76%, compared to a ~44% expansion when higher field strengths (~150G) are present. These observations provide the first experimental evidence of rapid downdrafts in Na I D1 magnetic bright points, and reveal the nature of a previously unresolved intensity plateau associated with these structures.
Recent observations have revealed that red, optically--passive spiral galaxies with little or no optical emission lines, harbour significant amounts of dust-obscured star formation. We propose that these observational results can be explained if the spatial distributions of the cold gas and star-forming regions in these spiral galaxies are significantly more compact than those in blue star-forming spirals. Our numerical simulations show that if the sizes of star-forming regions in spiral galaxies with disk sizes of R_d are ~ 0.3R_d, such galaxies appear to have lower star formation rates as well as higher degrees of dust extinction. This is mainly because star formation in these spirals occurs only in the inner regions where both the gas densities and metallicities are higher, and hence the dust extinction is also significantly higher. We discuss whether star formation occurring preferentially in the inner regions of spirals is closely associated with the stripping of halo and disk gas via some sort of environmental effect. We suggest that the "outside-in truncation of star formation" is the key to a better understanding of apparently optically--passive spirals with dusty star-forming regions.
We investigate the main physical properties of low-metallicity Asymptotic Giant Branch stars, with the aim of quantifying the uncertainties that presently affect the predicted chemical yields of these stars, associated to mass loss and description of molecular opacities. We find that above a threshold mass, M ~ 3.5Msun for Z=0.001, the results are little dependent on the opacity treatment, as long as hot-bottom burning prevents the surface C/O ratio from exceeding unity; the yields of these massive AGB stars are expected to be mostly determined by the efficiency of convection, with a relatively mild dependence on the mass-loss description. A much higher degree of uncertainty is associated to the yields of less massive models, which critically depend on the adopted molecular opacities. An interval of masses exists, say 2.0-3.0Msun, (the exact range depends on mass loss), in which HBB may be even extinguished following the cooling produced by the opacity of C-bearing molecules. The yields of these stars are the most uncertain, the variation range being the largest (up to ~ 2dex) for the nitrogen and sodium yields. For very low-mass models, not experiencing hot-bottom burning (M< 1.5Msun),the description of mass loss and the treatment of the convective boundaries are crucial for the occurrence of the third dredge-up, with sizable consequences on the CNO yields.
Rotation curves constrain a galaxy's underlying mass density profile, under the assumption that the observed rotation produces a centripetal force that exactly balances the inward force of gravity. However, most rotation curves are measured using emission lines from gas, which can experience additional forces due to pressure. In realistic galaxy disks, the gas pressure declines with radius, providing additional radial support to the disk. The measured tangential rotation speed will therefore tend to lag the true circular velocity of a test particle. The gas pressure is dominated by turbulence, and we evaluate its likely amplitude from recent estimates of the gas velocity dispersion and surface density. We show that where the amplitude of the rotation curve is comparable to the characteristic velocities of the interstellar turbulence, pressure support may lead to underestimates of the mass density of the underlying dark matter halo and the inner slope of its density profile. These effects may be significant for galaxies with rotation speeds <75km/s, but are unlikely to be significant in higher mass galaxies. We find that pressure support can be sustained over long timescales, because any reduction in support due to the conversion of gas into stars is compensated for by an inward flow of gas. However, we point to many uncertainties in assessing the importance of pressure support in galaxies. Thus, while pressure support may alleviate possible tensions between rotation curve observations and LambdaCDM on kiloparsec scales, it should not be viewed as a definitive solution at this time.
We show that the fate of moons of a close-in giant planet is mainly determined by the migration history of the planet in the protoplanetary disk. As the planet migrates in the disk from beyond the snow line towards a multi-day period orbit, the formed and forming moons become unstable as the planet's sphere of influence shrinks. Disk-driven migration is faster than the moons' tidal orbital evolution. Moons are eventually ejected from around close-in exoplanets or forced into collision with them before tides from the star affect their orbits. If moons are detected around close-in exoplanets, they are unlikely to have been formed in situ, instead they were captured from the protoplanetary disk on retrograde orbits around the planets.
Xi UrsaMajoris ({\xi} Uma) historically is one of the most important double star inconstellation Ursa Major, found by Sir William Herschel on May, 2, 1780 and the first binary successfully determined by using the principle of two body problem in 1828 by Savary. This star consists of two pair wide binary ADS8119 AB; in this case HD 98231(ADS8119 A) as primary and HD98230 (ADS 8119 B) as secondary. We have collected the observational data consist of separation angular ({\rho}) and position angle ({\theta}) fromthe observations in 1780 up to 2005 taken from Bosscha Observatory and other Observatories in the world. This paper presents the recent status of orbit binary system ADS 8119. By using Thiele Van den Bos method and empirical formula Strand's Mass-Luminosity relation we have determined the orbit and mass of ADS 8119AB. The result is; Orbital and Physical Element of ADS 8119 AB. Dynamical Elements, Orbit Orientation, Masses-Parallax; P = 60 years, e = 0.426, T = 1935.8, i = 110o9, {\Omega} = 104o.7, {\omega} = 117o5, M1 = 1.4Mo, M2 = 1.2Mo, p = 0".122
We present a short review of the impact regime experienced by the terrestrial planets within our own Solar system, describing the three populations of potentially hazardous objects which move on orbits that take them through the inner Solar system. Of these populations, the origins of two (the Near-Earth Asteroids and the Long-Period Comets) are well understood, with members originating in the Asteroid belt and Oort cloud, respectively. By contrast, the source of the third population, the Short-Period Comets, is still under debate. The proximate source of these objects is the Centaurs, a population of dynamically unstable objects that pass perihelion between the orbits of Jupiter and Neptune. However, a variety of different origins have been suggested for the Centaur population. Here, we present evidence that at least a significant fraction of the Centaur population can be sourced from the planetary Trojan clouds, stable reservoirs of objects moving in 1:1 mean-motion resonance with the giant planets (primarily Jupiter and Neptune). Focusing on simulations of the Neptunian Trojan population, we show that an ongoing flux of objects should be leaving that region to move on orbits within the Centaur population. With conservative estimates of the flux from the Neptunian Trojan clouds, we show that their contribution to that population could be of order ~3%, while more realistic estimates suggest that the Neptune Trojans could even be the main source of fresh Centaurs. We suggest that further observational work is needed to constrain the contribution made by the Neptune Trojans to the ongoing flux of material to the inner Solar system, and believe that future studies of the habitability of exoplanetary systems should take care not to neglect the contribution of resonant objects (such as planetary Trojans) to the impact flux that could be experienced by potentially habitable worlds.
The solar meridional flow is an important ingredient in Babcock-Leighton type models of the solar dynamo. Global variations of this flow have been suggested to explain the variations in the amplitudes and lengths of the activity cycles. Recently, cycle-related variations in the amplitude of the $P_2^1$ term in the Legendre decomposition of the observed meridional flow have been reported. The result is often interpreted in terms of an overall variation in the flow amplitude during the activity cycle. Using a semi-empirical model based upon the observed distribution of magnetic flux on the solar surface, we show that the reported variations of the $P_2^1$ term can be explained by the observed localized inflows into the active region belts. No variation of the overall meridional flow amplitude is required.
ANTARES is a high-energy neutrino telescope installed in the Mediterranean Sea at a depth of 2475 m. It consists of a three-dimensional array of optical modules, each containing a large photomultiplier tube. A total of 2700 front-end ASICs named Analogue Ring Samplers (ARS) process the phototube signals, measure their arrival time, amplitude and shape as well as perform monitoring and calibration tasks. The ARS chip processes the analogue signals from the optical modules and converts information into digital data. All the information is transmitted to shore through further multiplexing electronics and an optical link. This paper describes the performance of the ARS chip; results from the functionality and characterization tests in the laboratory are summarized and the long-term performance in the apparatus is illustrated.
The HIFI instrument on board the Herschel Space Observatory has been used to observe interstellar nitrogen hydrides along the sight-line towards G10.6-0.4 in order to improve our understanding of the interstellar chemistry of nitrogen. We report observations of absorption in NH N=1-0, J=2-1 and ortho-NH2 1_1,1-0_0,0. We also observed ortho-NH3 1_0-0_0, and 2_0-1_0, para-NH3 2_1-1_1, and searched unsuccessfully for NH+. All detections show emission and absorption associated directly with the hot-core source itself as well as absorption by foreground material over a wide range of velocities. All spectra show similar, non-saturated, absorption features, which we attribute to diffuse molecular gas. Total column densities over the velocity range 11-54 km/s are estimated. The similar profiles suggest fairly uniform abundances relative to hydrogen, approximately 6*10^-9, 3*10^-9, and 3*10^-9 for NH, NH2, and NH3, respectively. These abundances are discussed with reference to models of gas-phase and surface chemistry.
We have performed a complete re-calibration and re-analysis of all the available Very-Long-Baseline-Interferometry (VLBI) observations of supernova SN1993J, following an homogeneous and well-defined methodology. VLBI observations of SN1993J at 69 epochs, spanning 13 years, were performed by two teams, which used different strategies and analysis tools. The results obtained by each group are similar, but their conclusions on the supernova expansion and the shape and evolution of the emitting region differ significantly. From our analysis of the combined set of observations, we have obtained an expansion curve with unprecedented time resolution and coverage. We find that the data from both teams are compatible when analyzed with the same methodology. One expansion index ($m_3 = 0.87 \pm 0.02$) is enough to model the expansion observed at 1.7\,GHz, while two expansion indices ($m_1 = 0.925\pm0.016$ and $m_2 = 0.808\pm0.004$), separated by a break time, $t_{br} = 390\pm40$ days, are needed to model the data at the higher frequencies up to day $\sim4000$ after explosion. We thus confirm the wavelength dependence of the size of the emitting region reported by one of the groups. We also find that all sizes measured at epochs later than day $\sim 4000$ after explosion are systematically smaller than our model predictions (i.e., an additional expansion index might be needed to properly model these data). We also estimate the fractional shell width ($0.31 \pm 0.02$, average of all epochs and frequencies) and the level of opacity to the radio emission by the ejecta. Finally, we study the distribution and evolution of the azimuthal anisotropies (hot spots) found around the radio shell during the expansion. These anisotropies have intensities of $\sim 20$\% of the mean flux density of the shell, and appear to systematically evolve during the expansion.
Theories of gravity for which gravitons can be treated as massive particles have presently been studied as realistic modifications of General Relativity, and can be tested with cosmological observations. In this work, we study the ability of a recently proposed theory with massive gravitons, the so-called Visser theory, to explain the measurements of luminosity distance from the Union2 compilation, the most recent Type-Ia Supernovae (SNe Ia) dataset, adopting the current ratio of the total density of non-relativistic matter to the critical density ($\Omega_m$) as a free parameter. We also combine the SNe Ia data with constraints from Baryon Acoustic Oscillations (BAO) and CMB measurements. We find that, for the allowed interval of values for $\Omega_m$, a model based on Visser's theory can produce an accelerated expansion period without any dark energy component, but the combined analysis (SNe Ia + BAO + CMB) shows that the model is disfavored when compared with $\Lambda$CDM model.
The goal of the paper is to present new results on light echoes from young stellar objects. Broad band CCD images were obtained over three months at one-to-two week intervals for the field of NGC 6726, using the large field-of-view remotely-operated telescope on top of Cerro Burek. We detected scattered light echoes around two young, low-amplitude, irregular variable stars. Observations revealed not just one, but multiple light echoes from brightness pulses of the T Tauri star S CrA and the Herbig Ae/Be star R CrA. Analysis of S CrA's recurring echoes suggests that the star is located 138 +/- 16 pc from Earth, making these the closest echoes ever detected. The environment that scatters the stellar light from S CrA is compatible with an incomplete dust shell or an inclined torus some 10,000 AU in radius and containing $\sim$ $2 \times 10^{-3}$ $M_{\sun}$ of dust. The cause of such concentration at $\sim$ 10,000AU from the star is unknown. It could be the remnant of the envelope from which the star formed, but the distance of the cloud is remarkably similar to the nominal distance of the Oort cloud to the Sun, leading us to also speculate that the dust (or ice) seen around S CrA might have the same origin as the Solar System Oort cloud.
In the past ten years of regular operations, a new generation of Cherenkov telescopes have established binary systems as a new class of Very High Energy gamma-ray (VHE) emitters. Particle acceleration in these systems may occur either in an accretion-powered jet (microquasar) or in the shock between a pulsar wind and a stellar wind (wind-wind). This paper describes the phenomenology of the three VHE binaries PSR~B1259-63, LS 5039 and LS I +61 303. Two other objects may belong to this new class: HESS J0632+057 is a point-like variable VHE source whose multiwavelength behaviour resembles that of the other binaries, whereas Cyg X-1 is a well-known accreting system which may have been detected in VHE during a flaring episode. The paper concludes with a review of the latest searches for other binaries with Cherenkov telescopes, with special emphasis on Cyg X-3.
We study the properties of ISM substructure and turbulence in hydrodynamic (AMR) galaxy simulations with resolutions up to 0.8 pc and 5x10^3 Msun. We analyse the power spectrum of the density distribution, and various components of the velocity field. We show that the disk thickness is about the average Jeans scale length, and is mainly regulated by gravitational instabilities. From this scale of energy injection, a turbulence cascade towards small-scale is observed, with almost isotropic small-scale motions. On scales larger than the disk thickness, density waves are observed, but there is also a full range of substructures with chaotic and strongly non-isotropic gas velocity dispersions. The power spectrum of vorticity in an LMC-sized model suggests that an inverse cascade of turbulence might be present, although energy input over a wide range of scales in the coupled gaseous+stellar fluid could also explain this quasi-2D regime on scales larger than the disk scale height. Similar regimes of gas turbulence are also found in massive high-redshift disks with high gas fractions. Disk properties and ISM turbulence appear to be mainly regulated by gravitational processes, both on large scales and inside dense clouds. Star formation feedback is however essential to maintain the ISM in a steady state by balancing a systematic gas dissipation into dense and small clumps. Our galaxy simulations employ a thermal model based on a barotropic Equation of State (EoS) aimed at modelling the equilibrium of gas between various heating and cooling processes. Denser gas is typically colder in this approach, which is shown to correctly reproduce the density structures of a star-forming, turbulent, unstable and cloudy ISM down to scales of a few parsecs.
We examine the effects of a hydrodynamical wind on advection dominated accretion flows with thermal conduction in the presence of a toroidal magnetic field under a self-similar treatment. The disk gas is assumed to be isothermal. For a steady state structure of such accretion flows a set of self similar solutions are presented. The mass-accretion rate $\dot{M}$ decreases with radius $r$ as $\dot{M}\propto r^{s+\frac{1}{2}}$, where $s$ is an arbitrary constant. We show that existence of wind will lead to enhance the accretion velocity. Cooling effects of outflows or winds are noticeable and should be taken into account for calculating luminosity and effective temperature of optically thin and thick ADAFs. Increasing the effect of wind, decreases the disk's temperature, because of energy flux which is taken away by winds. We will see that for a given set of input parameters, the solution reaches to a non-rotating limit at a specific value of $\phi_s$. The values of this limitation on $\phi_s$ will increase by adding $s$, wind parameter. In fact, the higher values of $s$ will allow the disk to have physical rotating solution for larger $\phi_s$.
In this paper, we investigate the perturbations in matter bounce induced from Lee-Wick lagrangian with the involvement of non-minimal coupling to the Einstein Gravity. We find that this extra non-minimal coupling term can cause a red-tilt on the primordial metric perturbation at extremely large scales. It can also lead to large enhancement of reheating of the normal field particles compared to the usual minimal coupling models.
M-type asteroids, as defined in the Tholen taxonomy (Tholen, 1984), are medium albedo bodies supposed to have a metallic composition and to be the progenitors both of differentiated iron-nickel meteorites and enstatite chondrites. We carried out a spectroscopic survey in the visible and near infrared wavelength range (0.4-2.5 micron) of 30 asteroids chosen from the population of asteroids initially classified as Tholen M -types, aiming to investigate their surface composition. The data were obtained during several observing runs during the years 2004-2007 at the TNG, NTT, and IRTF telescopes. We computed the spectral slopes in several wavelength ranges for each observed asteroid, and we searched for diagnostic spectral features. We confirm a large variety of spectral behaviors for these objects as their spectra are extended into the near-infrared, including the identification of weak absorption bands, mainly of the 0.9 micron band tentatively attributed to orthopyroxene, and of the 0.43 micron band that may be associated to chlorites and Mg-rich serpentines or pyroxene minerals such us pigeonite or augite. A comparison with previously published data indicates that the surfaces of several asteroids belonging to the M-class may vary significantly. We attempt to constrain the asteroid surface compositions of our sample by looking for meteorite spectral analogues in the RELAB database and by modelling with geographical mixtures of selected meteorites/minerals. We confirm that iron meteorites, pallasites, and enstatite chondrites are the best matches to most objects in our sample, as suggested for M-type asteroids. The presence of subtle absorption features on several asteroids confirms that not all objects defined by the Tholen M-class have a pure metallic composition.
I present mass functions of actively accreting black holes detected in different quasar surveys which in concert cover a wide range of cosmic history. I briefly address what we learn from these mass functions. I summarize the motivation for such a study and the methods by which we determine black hole masses.
(Abridged) Lunar occultations (LO) are a very efficient and powerful technique, that achieves the best combination of high angular resolution and sensitivity possible today at near-infrared wavelengths. Given that the events are fixed in time, that the sources are occulted randomly, and that the telescope use is minimal, the technique is very well suited for service mode observations. We have established a program of routine LO observations at the VLT observatory, especially designed to take advantage of short breaks available in-between other programs. We have used the ISAAC instrument in burst mode, capable of producing continuous read-outs at millisecond rates on a suitable subwindow. Given the random nature of the source selection, our aim has been primarily the investigation of a large number of stellar sources at the highest angular resolution in order to detect new binaries. Serendipitous results such as resolved sources and detection of circumstellar components were also anticipated. We have recorded the signal from background stars for a few seconds, around the predicted time of occultation by the Moon's dark limb. At millisecond time resolution, a characteristic diffraction pattern can be observed. Patterns for two or more sources superimpose linearly, and this property is used for the detection of binary stars. The detailed analysis of the diffraction fringes can be used to measure specific properties such as the stellar angular size and the presence of extended light sources such as a circumstellar shell. We present a list of 191 stars for which LO data could be recorded and analyzed. Results include the detection of 16 binary and 2 triple stars, all but one of which were previously unknown. The projected angular separations are as small as 4 milliarcseconds and magnitude differences as high as ?K=5.8 mag...
The IceCube Observatory is a kilometer-cube neutrino telescope under construction at the South Pole and planned to be completed in early 2011. When completed it will consist of 5,160 Digital Optical Modules (DOMs) which detect Cherenkov radiation from the charged particles produced in neutrino interactions and by cosmic ray initiated atmospheric showers. IceCube construction is currently 90% complete. A selection of the most recent scientific results are shown here. The measurement of the anisotropy in arrival direction of galactic cosmic rays will also be presented and discussed.
We perform a linear stability analysis of dynamical Chern-Simons modified gravity in the geometric optics approximation and find that it is linearly stable on the backgrounds considered. Our analysis also reveals that gravitational waves in the modified theory travel at the speed of light in Minkowski spacetime. However, on a Schwarzschild background the characteristic speed of propagation along a given direction splits into two modes, one subluminal and one superluminal. The width of the splitting depends on the azimuthal components of the propagation vector, is linearly proportional to the mass of the black hole, and decreases with the third inverse power of the distance from the black hole. Radial propagation is unaffected, implying that as probed by gravitational waves the location of the event horizon of the spacetime is unaltered. The analysis further reveals that when a high frequency, pure gravitational wave is scattered from a black hole, a scalar wave of comparable amplitude is excited, and vice-versa.
We investigate effects of noncommutativity of phase space generated by two scalar fields conformally coupled to curvature in FRW cosmology. We restrict deformation of minisuperspace to noncommutativity between scalar fields and between their canonical conjugate momenta. The investigation is carried out by means of comparative analysis of mathematical properties of time evolution of variables in classical model and wave function of universe in quantum level. We find that impose of noncommutativity causes more ability in tuning time solutions of scalar fields and hence, has important implications in evolution of universe. We get that noncommutative parameter in momenta sector is the only responsible parameter for noncommutative effects in flat universes. A distinguishing feature of noncommutative solutions of scalar fields is that they can be simulated with well known harmonic oscillators, depend on values of spatial curvature. Namely, free, forced and damped harmonic oscillators corresponding to flat, closed and open universes. In this respect, we call them cosmical oscillators. In closed universes, when noncommutative parameters are small, cosmical oscillators have analogous effect with familiar beating effect in sound phenomenon. The existence of non-zero constant potential does not change solutions of scalar fields, but modifies scale factor. An interesting feature of well behaved solutions of wave functions is that functional form of its radial part is the same as commutative ones provided that given replacement of constants, caused by noncommutative parameters, is performed. Further, Noether theorem have been employed to explore effects of noncommutativity on underlying symmetries in commutative frame. Two of six Noether symmetries of flat universes, in general, are retained in noncommutative case, and one out of three ones in non flat universes.
According to theoretical physics the cosmological constant (CC) is expected to be much larger in magnitude than other energy densities in the universe, which is in stark contrast to the observed Big Bang evolution. We address this old CC problem not by introducing an extremely fine-tuned counterterm, but in the context of modified gravity in the Palatini formalism. In our model the large CC term is filtered out, and it does not prevent a standard cosmological evolution. We discuss the filter effect in the epochs of radiation and matter domination as well as in the asymptotic de Sitter future. The final expansion rate can be much lower than inferred from the large CC without using a fine-tuned counterterm. Finally, we show that the CC filter works also in the Kottler (Schwarzschild-de Sitter) metric describing a black hole environment with a CC compatible to the future de Sitter cosmos.
We consider a Lorentz-violating theory of inflation consisting of Einstein-aether theory with a scalar inflaton coupled bilinearly to the expansion of the aether. We determine the conditions for linearized stability, positive energy and vanishing of preferred-frame post-Newtonian parameters, and find that all these conditions can be met. In homogeneous and isotropic cosmology, the inflaton-aether expansion coupling leads to a driving force on the inflaton that is proportional to the Hubble parameter. This force affects the slow-roll dynamics, but still allows for a natural end to inflation.
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