We re-assess the XMM-Newton and Swift observations of HLX1, to examine the evidence for its identification as an intermediate-mass black hole. We show that the X-ray spectral and timing properties are equally consistent with an intermediate-mass black hole in a high state, or with a foreground neutron star with a luminosity of about a few times 10^{32} erg/s ~ 10^{-6} L_{Edd}, located at a distance of about 1.5 to 3 kpc. Contrary to previously published results, we find that the X-ray spectral change between the two XMM-Newton observations of 2004 and 2008 (going from power-law dominated to thermal dominated) is not associated with a change in the X-ray luminosity. The thermal component becomes more dominant (and hotter) during the 2009 outburst seen by Swift, but in a way that is consistent with either scenario.
GRB 090423 is the most distant spectroscopically-confirmed source observed in the universe. Using observations at 37.5 GHz, we place constraints on molecular gas emission in the CO(3-2) line from its host galaxy and immediate environs. The source was not detected either in line emission or in the rest-frame 850 micron continuum, yielding an upper limit of S_{8mm}=9.3 milli-Jy and M(H_2)<4.3x10^9 M_sun (3 sigma), applying standard conversions. This implies that the host galaxy of GRB 090423 did not possess a large reservoir of warm molecular gas but was rather modest either in star formation rate or in mass. It suggests that this was not an extreme starburst, and hence that gamma ray bursts at high redshift trace relatively modest star formation rates, in keeping with the behaviour seen at lower redshifts. We do, however, identify a millimetre emission line source in the field of GRB 090423. Plausible interpretations include a CO(1-0) emitting galaxy at z=2.1, CO(2-1) at z=5.2 and CO(3-2) at z=8.3. Efforts to identify a counterpart for the molecular line emitter and to further characterise this source are continuing.
Variability is a property shared by practically all AGN. This makes variability selection a possible technique for identifying AGN. Given that variability selection makes no prior assumption about spectral properties, it is a powerful technique for detecting both low-luminosity AGN in which the host galaxy emission is dominating and AGN with unusual spectral properties. In this paper, we will discuss and test different statistical methods for the detection of variability in sparsely sampled data that allow full control over the false positive rates. We will apply these methods to the GOODS North and South fields and present a catalog of variable sources in the z band in both GOODS fields. Out of 11931 objects checked, we find 155 variable sources at a significance level of 99.9%, corresponding to about 1.3% of all objects. After rejection of stars and supernovae, 139 variability selected AGN remain. Their magnitudes reach down as faint as 25.5 mag in z. Spectroscopic redshifts are available for 22 of the variability selected AGN, ranging from 0.046 to 3.7. The absolute magnitudes in the rest-frame z-band range from ~ -18 to -24, reaching substantially fainter than the typical luminosities probed by traditional X-ray and spectroscopic AGN selection in these fields. Therefore, this is a powerful technique for future exploration of the evolution of the faint end of the AGN luminosity function up to high redshifts.
Massive member galaxies of galaxy groups at redshift z=0 are mostly quenched systems with either a disk or an elliptical morphology. Observations indicate that, to a large extent, this results from environmental forcing over the past eight billion years since redshift z~1. Many physical processes may be responsible for making elliptical morphologies and quenching star formation, but the mainly responsible mechanisms, and the epochs and timescales at/on which they operate, however, have not been yet identified. The challenge is to connect the large-scale, cosmological formation of the group, which affects the global evolution of group members, to the galactic sub-kpc scale, where star formation and stellar feedback dominate the physics of the gas and the galaxy morphology. Here we report a simulation of the formation of a group of galaxies with sufficient resolution to track the evolution of gas and stars of about a dozen galaxy group members over cosmic history. Ellipticals form, as suspected, through galaxy mergers. In contrast with what has often been speculated, however, these mergers occur at z>1, before the merging progenitors enter the virial radius of the group and before the group is fully assembled. Quenching of star formation in the still star-forming elliptical galaxies lags behind their morphological transformation, but, once started, is taking less than a billion years to complete. As long envisaged the quenching happens as the galaxies precipitate into the finally assembled group and are stripped of their gas - both hot and cold, in a temporal sequence. A similar sort is followed by unmerged, disk galaxies, which, as they join the group, are turned into the red-and-dead disks that abound in these environments.
We investigate the physical properties and structure of the outer rings of SN 1987A to understand the formation and evolution of the rings of SN 1987A. We used low resolution spectroscopy from VLT/FORS1 and high resolution spectra from UVES to estimate the physical conditions in the outer rings using nebular analysis for emission lines such as [O II], [O III], [N II] and [S II]. We also measured the velocity at two positions of the outer rings to test a geometrical model for the rings. Additionally, we used data from the HST science archives to check the evolution of the outer rings of SN 1987A for a period that covers almost 11 years. We measured the flux in four different regions, two for each outer ring. We chose regions away from the two bright neighbouring stars and as far as possible from the inner ring, and we created light curves for the emission lines of [O III], H{\alpha}, and [N II]. The profiles of the lightcurves display a declining behaviour, which is consistent with that the initial supernova flash powered the outer rings. The electron density of the emitting gas in the outer rings, as estimated through nebular analysis in forbidden [O II] and [S II] lines, <= 3*10^3 cm^-3, has not changed over the last ~ 15 years, and also the [N II] temperature remains fairly constant at ~ 1.2*10^4 K. We find no obvious difference in density and temperature for the two outer rings. For an assumed distance of 50 kpc to the supernova, the distance between the supernova and the closest parts of the outer rings could be as short as ~ 1.7*10^18 cm. Interaction between the supernova ejecta and the outer rings could therefore start in less than ~ 20 years. We do not expect the outer rings to show the same optical display as the equatorial ring when this happens. Instead soft X-rays should provide a better way of observing the ejecta-outer rings interaction.
We report the discovery of four relatively massive (2-7MJ) transiting extrasolar planets. HAT-P-20b orbits a V=11.339 K3 dwarf star with a period P=2.875317+/-0.000004d. The host star has a mass of 0.760+/-0.03 Msun, radius of 0.690+/-0.02 Rsun, Teff=4595+/-80 K, and metallicity [Fe/H]=+0.35+/-0.08. HAT-P-20b has a mass of 7.246+/-0.187 MJ, and radius of 0.867+/-0.033 RJ yielding a mean density of 13.78+/-1.50 gcm^-3 , which is the second highest value among all known exoplanets. HAT-P-21b orbits a V=11.685 G3 dwarf on an eccentric (e=0.2280+/-0.016) orbit, with a period of P=4.1244810+/-000007d. The host star has a mass of 0.95+/-0.04Msun, radius of 1.10+/-0.08Rsun, Teff=5588+/-80K, and [Fe/H]=+0.01+/-0.08. HAT-P-21b has a mass of 4.063+/-0.161MJ, and radius of 1.024+/-0.092RJ. HAT-P-22b orbits the V=9.732 G5 dwarf HD233731, with P=3.2122200+/-0.000009d. The host star has a mass of 0.92+/-0.03Msun, radius of 1.04+/-0.04Rsun, Teff=5302+/-80K, and metallicity of +0.24+/-0.08. The planet has a mass of 2.147+/-0.061 MJ, and compact radius of 1.080+/-0.058RJ. The host star also harbors an M-dwarf companion at a wide separation. Finally, HAT-P-23b orbits a V=12.432 G0 dwarf star, with a period P=1.212884+/-0.000002d. The host star has a mass of 1.13+/-0.04sun, radius of 1.20+/-0.07Rsun, Teff=5905+/-80K, and [Fe/H]=+0.15+/-0.04. The planetary companion has a mass of 2.090+/-0.111MJ, and radius of 1.368+/-0.090RJ (abridged).
We report the discovery of HAT-P-24b, a transiting extrasolar planet orbiting the moderately bright V=11.818 F8 dwarf star GSC 0774-01441, with a period P = 3.3552464 +/- 0.0000071 d, transit epoch Tc = 2455216.97669 +/- 0.00024 (BJD_UTC), and transit duration 3.653 +/- 0.025 hours. The host star has a mass of 1.186 +/- 0.042 Msun , radius of 1.294 +/- 0.071 Rsun , effective temperature 6373 +/- 80 K, and a low metallicity of [Fe/H] = -0.16 +/- 0.08. The planetary companion has a mass of 0.681 +/- 0.031 MJ , and radius of 1.243 +/- 0.072 RJ yielding a mean density of 0.439 +/- 0.069 g cm-3 . By repeating our global fits with different parameter sets, we have performed a critical investigation of the fitting techniques used for previous HAT planetary discoveries. We find that the system properties are robust against the choice of priors. The effects of fixed versus fitted limb darkening are also examined. HAT-P-24b probably maintains a small eccentricity of e = 0.052 +0.022 -0.017, which is accepted over the circular orbit model with false alarm probability 5.8%. In the absence of eccentricity pumping, this result suggests HAT-P-24b experiences less tidal dissipation than Jupiter. Due to relatively rapid stellar rotation, we estimate that HAT-P-24b should exhibit one of the largest known Rossiter-McLaughlin effect amplitudes for an exoplanet (deltaVRM ~ 95 m/s) and thus a precise measurement of the sky-projected spin-orbit alignment should be possible.
In this work we simulate the $50-200$ MHz radio sky that is constrained in the field of view ($5^{\circ}$ radius) of the 21 Centimeter Array (21CMA), by carrying out Monte-Carlo simulations to model redshifted cosmological reionization signals and strong contaminating foregrounds, including emissions from our Galaxy, galaxy clusters, and extragalactic point sources. As an improvement of previous works, we consider in detail not only random variations of morphological and spectroscopic parameters within the ranges allowed by multi-band observations, but also evolution of radio halos in galaxy clusters, assuming that relativistic electrons are re-accelerated in the ICM in merger events and lose energy via both synchrotron emission and inverse Compton scattering with CMB photons. By introducing a new approach designed on the basis of independent component analysis (ICA) and wavelet detection algorithm, we prove that, with a cumulative observation of one month with the 21CMA array, about $80\%$ of galaxy clusters with central brightness temperatures of $> 10~{\rm K}$ at 65 MHz can be safely identified and separated from the overwhelmingly bright foreground. We find that the morphological and spectroscopic distortions are extremely small as compared to the input simulated clusters, and the reduced $\chi^2$ of brightness temperature profiles and spectra are controlled to be $\lesssim 0.5$ and $\lesssim 1.3$, respectively. These results robustly indicate that in the near future a sample of dozens of bright galaxy clusters will be disentangled from the foreground in 21CMA observations, the study of which will greatly improve our knowledge about cluster merger rates, electron acceleration mechanisms in cluster radio halos, and magnetic field in the ICM.
A wide range of models describing modifications to General Relativity have been proposed, but no fundamental parameter set exists to describe them. Similarly, no fundamental theory exists for dark energy to parameterize its potential deviation from a cosmological constant. This motivates a model-independent search for deviations from the concordance GR+LambdaCDM cosmological model in large galaxy redshift surveys. We describe two model-independent tests of the growth of cosmological structure, in the form of quantities that must equal one if GR+LambdaCDM is correct. The first, epsilon, was introduced previously as a scale-independent consistency check between the expansion history and structure growth. The second, upsilon, is introduced here as a test of scale-dependence in the linear evolution of matter density perturbations. We show that the ongoing and near-future galaxy redshift surveys WiggleZ, BOSS, and HETDEX will constrain these quantities at the 5-10% level, representing a stringent test of concordance cosmology at different redshifts. When redshift space distortions are used to probe the growth of cosmological structure, galaxies at higher redshift with lower bias are found to be most powerful in detecting deviations from the GR+LambdaCDM model.
The Energetic X-ray Imaging Survey Telescope (EXIST) is designed to i) use the birth of stellar mass black holes, as revealed by cosmic Gamma-Ray Bursts (GRBs), as probes of the very first stars and galaxies to exist in the Universe. Both their extreme luminosity (~104 times larger than the most luminous quasars) and their hard X-ray detectability over the full sky with wide-field imaging make them ideal "back-lights" to measure cosmic structure with X-ray, optical and near-IR (nIR) spectra over many sight lines to high redshift. The full-sky imaging detection and rapid followup narrow-field imaging and spectroscopy allow two additional primary science objectives: ii) novel surveys of supermassive black holes (SMBHs) accreting as very luminous but rare quasars, which can trace the birth and growth of the first SMBHs as well as quiescent SMBHs (non-accreting) which reveal their presence by X-ray flares from the tidal disruption of passing field stars; and iii) a multiwavelength Time Domain Astrophysics (TDA) survey to measure the temporal variability and physics of a wide range of objects, from birth to death of stars and from the thermal to non-thermal Universe. These science objectives are achieved with the telescopes and mission as proposed for EXIST described here.
In a recent paper by C. Gao, M. Kunz, A. Liddle and D. Parkinson [arXiv:0912.0949], the unification of dark matter and dark energy was explored within a theory containing a scalar field of non-Lagrangian type. This scalar field, different from the classic quintessence, can be obtained from the scalar field representation of an interacting two-fluid mixture described in the paper by L.P. Chimento and M. Forte
We study the kinematically narrow, low-ionization line emission from a bright, starburst galaxy at z = 0.69 using slit spectroscopy obtained with Keck/LRIS. The spectrum reveals strong absorption in MgII and FeII resonance transitions with Doppler shifts of -200 to -300 km/s, indicating a cool gas outflow. Emission in MgII near and redward of systemic velocity, in concert with the observed absorption, yields a P Cygni-like line profile similar to those observed in the Ly alpha transition in Lyman Break Galaxies. Further, the MgII emission is spatially resolved, and extends significantly beyond the emission from stars and HII regions within the galaxy. Assuming the emission has a simple, symmetric surface brightness profile, we find that the gas extends to distances > ~7 kpc. We also detect several narrow FeII* fine-structure lines in emission near the systemic velocity, arising from energy levels which are radiatively excited directly from the ground state. We suggest that the MgII and FeII* emission is generated by photon scattering in the observed outflow, and emphasize that this emission is a generic prediction of outflows. These observations provide the first direct constraints on the minimum spatial extent and morphology of the wind from a distant galaxy. Estimates of these parameters are crucial for understanding the impact of outflows in driving galaxy evolution.
We present observations of wavelength-dependent flux ratios for 4 gravitational lens systems (SDSS~J1650+4251, HE~0435$-$1223, FBQ 0951+2635, and Q~0142$-$100) obtained with the Nordic Optical telescope (NOT). The use of narrow band photometry, as well as the excellent seeing conditions during the observations, allow us to set good baselines to study their chromatic behavior. For SDSS~J1650+4251 we determine the extinction curve of the dust in the $z_L=0.58$ lens galaxy, and find that the 2175 \AA \ feature is absent. In the case of HE~0435$-$1223 we clearly detect chromatic microlensing. This allows us to estimate the wavelength dependent size of the accretion disk. We found an R-band disk size of $r^{R}_s=13\pm5$ light days for a linear prior on $r^{R}_s$ and of $r^{R}_s=7\pm6$ light days for a logarithmic prior. For a power law size-wavelength scaling of $r_s\propto\lambda^{p}$, we were able to constrain the value of the exponent to $p=1.3\pm0.3$ for both $r^{R}_s$ priors, which is in agreement with the temperature profiles of simple thin disk models.
We investigate the effect of a new triple-alpha reaction rate from Ogata et al. (2009) on helium ignition conditions on accreting neutron stars and on the properties of the subsequent type I X-ray burst. We find that the new rate leads to significantly lower ignition column density for accreting neutron stars at low accretion rates. We compare the results of our ignition models for a pure helium accretor to observations of bursts in ultra-compact X-ray binary (UCXBs), which are believed to have nearly pure helium donors. For mdot > 0.001 mdot_Edd, the new triple-alpha reaction rate from Ogata et al. (2009) predicts a maximum helium ignition column of ~ 3 x 10^9 g cm^{-2}, corresponding to a burst energy of ~ 4 x 10^{40} ergs. For mdot ~ 0.01 mdot_Edd at which intermediate long bursts occur, the predicted burst energies are at least a factor of 10 too low to explain the observed energies of such bursts in UCXBs. This finding adds to the doubts cast on the triple-alpha reaction rate of Ogata et al. (2009) by the low-mass stellar evolution results of Dotter & Paxton (2009).
If an orbit is fitted from combined RV and astrometric data, the orbit should be physically consistent with both data sets. The Keplerian orbit of a planet is a highly nonlinear function of seven parameters. The astrometric orbit problem can be partially linearized via transformation to four linear parameters (related four Thiele-Innes constants) plus three nonlinear parameters: eccentricity, period and periastron time. The RV orbit problem can be partially linearized via transformation to two additional linear parameters plus the same three nonlinear parameters. Unfortunately, the two linear parameters from RV are not linearly related to the four linear parameters from astrometry. Because of this difficulty, currently available algorithms for fitting combined RV and astrometric data to multiple-planet systems employ at least five nonlinear parameters per planet. We have developed a new algorithm for fitting orbits of multiple planet systems from combined data sets of radial velocity and astrometric measurements. The new algorithm satisfies the RV-astrometry consistency requirement, while using three nonlinear parameters per planet. We expect the reduction in nonlinearity to give the algorithm a significant advantage in computation speed over existing algorithms. In this work, we describe the algorithm, which has been validated in the context of a recent double-blind planet detection simulation study.
We present a technique to synthesise telluric absorption and emission features both for in-situ wavelength calibration and for their removal from astronomical spectra. While the presented technique is applicable for a wide variety of optical and infrared spectra, we concentrate in this paper on selected high-resolution near-infrared spectra obtained with the CRIRES spectrograph to demonstrate its performance and limitation. We find that synthetic spectra reproduce telluric absorption features to about 2%, even close to saturated line cores. Thus, synthetic telluric spectra could be used to replace the observation of telluric standard stars, saving valuable observing time. This technique also provides a precise in-situ wavelength calibration, especially useful for high-resolution near-infrared spectra in the absence of other calibration sources.
Inhomogeneous cosmological models are able to fit cosmological observations without dark energy under the assumption that we live close to the "center" of a very large-scale under--dense region. Most studies fitting observations by means of inhomogeneities also assume spherical symmetry, and thus being at (or very near) the center may imply being located at a very special and unlikely observation point. We argue that such spherical voids should be treated only as a gross first approximation to configurations that follow from a suitable smoothing out of the non--spherical part of the inhomogeneities on angular scales. In this Letter we present a non-spherical inhomogeneous and anisotropic model that supports the above statement and, at the same time, addresses the limitations of spherical inhomogeneities. By using a thin-shell approximation to the quasi--spherical Szekeres solution, we construct a model of evolving cosmic structures, containing several elongated supercluster-like structures with underdense regions between them, which altogether provides a reasonable coarse-grained description of realistic structures. While this configuration is not spherically symmetric, its proper volume average yields a spherical void profile of 250 Mpc that roughly agrees with observations. Also, by considering a non-spherical inhomogeneity, the definition of a "center" location becomes more nuanced, and thus the constraints placed by fitting observations on our position with respect to this location become less restrictive.
We present new radial velocities from AAOmega on the Anglo-Australian Telescope for 307 galaxies (b_J < 19.5) in the region of the rich cluster Abell 1386. Consistent with other studies of galaxy clusters that constitute sub-units of superstructures, we find that the velocity distribution of A1386 is very broad (21,000--42,000 kms^-1, or z=0.08--0.14) and complex. The mean redshift of the cluster that Abell designated as number 1386 is found to be ~0.104. However, we find that it consists of various superpositions of line-of-sight components. We investigate the reality of each component by testing for substructure and searching for giant elliptical galaxies in each and show that A1386 is made up of at least four significant clusters or groups along the line of sight whose global parameters we detail. Peculiar velocities of brightest galaxies for each of the groups are computed and found to be different from previous works, largely due to the complexity of the sky area and the depth of analysis performed in the present work. We also analyse A1386 in the context of its parent superclusters: Leo A, and especially the Sloan Great Wall. Although the new clusters may be moving toward mass concentrations in the Sloan Great Wall or beyond, many are most likely not yet physically bound to it.
We present high-resolution L'-band imaging of the inner scattered light structure of Class 0 protostar L1527 IRS (IRAS 04368+2557) taken with the Gemini North telescope. The central point-source like feature seen in Spitzer Space Telescope IRAC images is resolved in the Gemini image into a compact bipolar structure with a narrow dark lane in the center. Two scattered light lobes are extended ~1.8" (200 AU) perpendicular to the direction of the outflow and ~2.5" (350 AU) along the outflow axis; the narrow dark lane between the scattered light lobes is ~0.45" (60 AU) thick. The observations are consistent with our initial modeling of a bright inner cavity separated by a dark lane due to extinction along the line of sight of the central protostar by the disk (Tobin et al. 2008). The bright, compact scattered light might be due to complex inner structure generated by the outflow, as suggested in our first paper, or it may more likely be the upper layers of the disk forming from infalling matter.
Extinction maps at 8 micron from the Spitzer Space Telescope show that many Class 0 protostars exhibit complex, irregular, and on-axisymmetric structure within the densest regions of their dusty envelopes. Many of the systems have highly irregular and on-axisymmetric morphologies on scales $\sim$1000 AU, with a quarter of the sample exhibiting filamentary or flattened dense structures. Complex envelope structure is observed in regions spatially distinct from outflow cavities, and the densest structures often show no systematic alignment perpendicular to the cavities. We suggest that the observed envelope complexity is the result of collapse from protostellar cores with initially non-equilibrium structures. The striking non-axisymmetry in many envelopes could provide favorable conditions for the formation of binary systems. We then show that the kinematics around L1165 as probed with N2H+ are indicative of asymmetric infall; the velocity gradient is not perpendicular to the outflow.
The August 2010 edition of the AAO newsletter has been newly updated and renamed the AAO Observer as we become the Australian Astronomical Observatory. This edition contains articles on the Galaxy And Mass Assembly survey, a bipolar Type I planetary nebula an open cluster as well as PCA sky subtraction for AAOmega; an OH spectrograph named GNOSIS and an overview of our recent conference "Celebrating the AAO: past, present, and future".
We examine the effectiveness of the weak gravity conjecture in constraining the dark energy by comparing with observations. For general dark energy models with plausible phenomenological interactions between dark sectors, we find that although the weak gravity conjecture can constrain the dark energy, the constraint is looser than that from the observations.
The Sunrise balloon-borne solar observatory consists of a 1m aperture Gregory telescope, a UV filter imager, an imaging vector polarimeter, an image stabilization system and further infrastructure. The first science flight of Sunrise yielded high-quality data that reveal the structure, dynamics and evolution of solar convection, oscillations and magnetic fields at a resolution of around 100 km in the quiet Sun. After a brief description of instruments and data, first qualitative results are presented. In contrast to earlier observations, we clearly see granulation at 214 nm. Images in Ca II H display narrow, short-lived dark intergranular lanes between the bright edges of granules. The very small-scale, mixed-polarity internetwork fields are found to be highly dynamic. A significant increase in detectable magnetic flux is found after phase-diversity-related reconstruction of polarization maps, indicating that the polarities are mixed right down to the spatial resolution limit, and probably beyond.
The tidal stirring model envisions the formation of dwarf spheroidal (dSph) galaxies in the Local Group via the tidal interaction of disky dwarf systems with a larger host galaxy like the Milky Way. These progenitor disks are embedded in extended dark halos and during the evolution both components suffer strong mass loss. In addition, the disks undergo the morphological transformation into spheroids and the transition from ordered to random motion of their stars. Using collisionless N-body simulations we construct a model for the nearby and highly elongated Sagittarius (Sgr) dSph galaxy within the framework of the tidal stirring scenario. Constrained by the present known orbit of the dwarf, the model suggests that in order to produce the majority of tidal debris observed as the Sgr stream, but not yet transform the core of the dwarf into a spherical shape, Sgr must have just passed the second pericenter of its current orbit around the Milky Way. In the model, the stellar component of Sgr is still very elongated after the second pericenter and morphologically intermediate between the strong bar formed at the first pericenter and the almost spherical shape existing after the third pericenter. This is thus the first model of the evolution of the Sgr dwarf that accounts for its observed very elliptical shape. At the present time there is very little intrinsic rotation left and the velocity gradient detected along the major axis is almost entirely of tidal origin. We model the recently measured velocity dispersion profile for Sgr assuming that mass traces light and estimate its current total mass within 5 kpc to be 5.2 x 10^8 M_sun. To have this mass at present, the model requires that the initial virial mass of Sgr must have been as high as 1.6 x 10^10 M_sun, comparable to that of the Large Magellanic Cloud, which may serve as a suitable analog for the pre-interaction, Sgr progenitor.
In this contribution I summarize some recent successes, and focus on remaining challenges, in understanding the formation and evolution of planetary systems in the context of the Blue Dots initiative. Because our understanding is incomplete, we cannot yet articulate a "design reference mission" engineering matrix suitable for an exploration mission where success is defined as obtaining a spectrum of a potentially habitable world around a nearby star. However, as progress accelerates, we can identify observational programs that would address fundamental scientific questions through hypothesis testing such that the null result is interesting.
Metallicity is one of four free parameters typically considered when fitting isochrones to the cluster sequence. Unfortunately, this parameter is often ignored or assumed to be solar in most papers. Hence an unknown bias is introduced in the estimation of the other three cluster parameters (age, reddening and distance). Furthermore, studying the metallicity of open clusters allows us not only to derive the Galactic abundance gradient on a global scale, but also to trace the local solar environment in more detail. In a series of three papers, we investigate the current status of published metallicities for open clusters from widely different photometric and spectroscopic methods. A detailed comparison of the results allows us to establish more reliable photometric calibrations and corrections for isochrone fitting techniques. Well established databases such as WEBDA help us to perform a homogeneous analysis of available measurements for a significant number of open clusters. The literature was searched for [Fe/H] estimates on the basis of photometric calibrations in any available filter system. On the basis of results published by Tadross, we demonstrate the caveats of the calibration choice and its possible impact. In total, we find 406 individual metallicity values for 188 open clusters within 64 publications. The values were, finally, unweightedly averaged. Our final sample includes [Fe/H] values for 188 open clusters. Tracing the solar environment within 4000x4000 pc**2 we identify a patchy metallicity distribution as an extension to the Local Bubble that significantly influences the estimation of the Galactic metallicity gradient, even on a global scale. In addition, further investigations of more distant open clusters are clearly needed to obtain a more profound picture at Galactocentric distances beyond 10 000 pc.
Cosmological hydrodynamical simulations of primordial star formation suggest that the gas within the first star-forming halos is turbulent. This has strong implications on the subsequent evolution, in particular on the generation of magnetic fields. Using high-resolution numerical simulations, we show that in the presence of turbulence, weak seed magnetic fields are exponentially amplified by the small-scale dynamo during the formation of the first stars. We conclude that strong magnetic fields are generated during the birth of the first stars in the universe, potentially modifying the mass distribution of these stars and influencing the subsequent cosmic evolution. We find that the presence of the small-scale turbulent dynamo can only be identified in numerical simulations in which the turbulent motions in the central core are resolved with at least 32 grid cells.
Correlations between the intrinsic shapes of galaxies and the large-scale galaxy density field provide an important tool to investigate galaxy intrinsic alignments, which constitute a major astrophysical systematic in cosmological weak lensing (cosmic shear) surveys, but also yield insight into the formation and evolution of galaxies. We measure galaxy position-shape correlations in the MegaZ-LRG sample for more than 800,000 luminous red galaxies, making the first such measurement with a photometric redshift sample. In combination with a re-analysis of several spectroscopic SDSS samples, we constrain an intrinsic alignment model for early-type galaxies over long baselines in redshift (z ~ 0.7) and luminosity (4mag). We develop and test the formalism to incorporate photometric redshift scatter in the modelling. For r_p > 6 Mpc/h, the fits to galaxy position-shape correlation functions are consistent with the scaling with r_p and redshift of a revised, nonlinear version of the linear alignment model for all samples. An extra redshift dependence proportional to (1+z)^n is constrained to n=-0.3+/-0.8 (1sigma). To obtain consistent amplitudes for all data, an additional dependence on galaxy luminosity proportional to L^b with b=1.1+0.3-0.2 is required. The normalisation of the intrinsic alignment power spectrum is found to be (0.077 +/- 0.008)/rho_{cr} for galaxies at redshift 0.3 and r band magnitude of -22 (k- and evolution-corrected to z=0). Assuming zero intrinsic alignments for blue galaxies, we assess the bias on cosmological parameters for a tomographic CFHTLS-like lensing survey. Both the resulting mean bias and its uncertainty are smaller than the 1sigma statistical errors when using the constraints from all samples combined. The addition of MegaZ-LRG data reduces the uncertainty in intrinsic alignment bias on cosmological parameters by factors of three to seven. (abridged)
Using the width of emission lines in XMM-Newton Reflection Grating Spectrometer spectra, we place direct constraints on the turbulent velocities of X-ray emitting medium in the cores of 62 galaxy clusters, groups and elliptical galaxies. We find five objects where we can place an upper limit on the line-of-sight broadening of 500 km/s (90 per cent confidence level), using a single thermal component model. Two other objects are lower than this limit when two thermal components are used. Half of the objects examined have an upper limit on the velocity broadening of less than 700 km/s. To look for objects which have significant turbulent broadening, we use Chandra spectral maps to compute the expected broadening caused by the spatial extent of the source. Comparing these with our observed results, we find that Klemola 44 has extra broadening at the level of 1500 km/s. RX J1347.5-1145 shows weak evidence for turbulent velocities at 800 km/s. In addition we obtain limits on turbulence for Zw3146, Abell 496, Abell 1795, Abell 2204 and HCG 62 of less than 200 km/s. After subtraction of the spatial contribution and including a 50 km/s systematic uncertainty, we find at least 15 sources with less than 20 per cent of the thermal energy density in turbulence.
In this paper we present a novel class of compact orthomode transducers which use digital calibration to synthesize the desired polarization vectors while maintaining high isolation and minimizing mass and volume. These digital orthomode transducers consist of an arbitrary number of planar probes in a circular waveguide, each of which is connected to an independent receiver chain designed for stability of complex gain. The outputs of each receiver chain are then digitized and combined numerically with calibrated, complex coefficients. Measurements on two prototype digital orthomode transducers, one with three probes and one with four, show better than 50 dB polarization isolation over a 10 C temperature range with a single calibration.
A design methodology and synthesis equations are described for lumped-element filter prototypes having low-pass, high-pass, band-pass, or band-stop characteristics with theoretically perfect input- and output-match at all frequencies. Such filters are a useful building block in a wide variety of systems in which the highly reactive out-of-band termination presented by a conventional filter is undesirable. The filter topology is first derived from basic principles. Then the relative merits of several implementations and tunings are compared via simulation. Finally, measured data on low-pass and band-pass filter examples are presented which illustrate the practical advantages as well as showing excellent agreement between measurement and theory.
We develop a purely mathematical tool to recover some of the information lost in the non-linear collapse of large-scale structure. From a set of 141 simulations of dark matter density fields, we construct a non-linear Weiner filter in order to separate Gaussian and non-Gaussian structure in wavelet space. We find that the non-Gaussian power is dominant at smaller scales, as expected from the theory of structure formation, while the Gaussian counterpart is damped by an order of magnitude on small scales. We find that it is possible to increase the Fisher information by a factor of three before reaching the translinear plateau, an effect comparable to other techniques like the linear reconstruction of the density field.
This is the first in a series of papers that introduces a new paradigm for understanding the jet in M87: a collimated relativistic flow in which strong magnetic fields play a dominant dynamical role. Here wefocus on the flow downstream of HST-1 - an essentially stationary flaring feature that ejects trails of superluminal components. We propose that these components are quad relativistic magnetohydrodynamic shock fronts (forward/reverse fast and slow modes) in a narrow jet with a helically twisted magnetic structure. And we demonstrate the properties of such shocks with simple one-dimensional numerical simulations. Quasi-periodic ejections of similar component trails may be responsible for the M87 jet substructures observed further downstream on 100 - 1,000 pc scales. This new paradigm requires the assimilation of some new concepts into the astrophysical jet community, particularly the behavior of slow/fast-mode waves/shocks and of current-driven helical kink instabilities. However, the prospects of these ideas applying to a large number of other jet systems may make this worth the effort.
The interplanetary magnetic fluctuation spectrum obeys a Kolmogorovian power law at scales above the proton inertial length and gyroradius which is well regarded as an inertial range. Below these scales a power law index around $-2.5$ is often measured and associated to nonlinear dispersive processes. Recent observations reveal a third region at scales below the electron inertial length. This region is characterized by a steeper spectrum that some refer to it as the dissipation range. We investigate this range of scales in the electron magnetohydrodynamic approximation and derive an exact and universal law for a third-order structure function. This law can predict a magnetic fluctuation spectrum with an index of $-11/3$ which is in agreement with the observed spectrum at the smallest scales. We conclude on the possible existence of a third turbulence regime in the solar wind instead of a dissipation range as recently postulated.
Exact nonlinear diffusion equations of spectral transfer are derived for anisotropic magnetohydrodynamics in the regime of wave turbulence. The background of the analysis is the asymptotic Alfv\'en wave turbulence equations from which a differential limit is taken. The result is a universal diffusion-type equation in ${\bf k}$-space which describes in a simple way and without free parameter the energy transport perpendicular to the external magnetic field ${\bf B_0}$ for transverse and parallel fluctuations. These exact equations are compatible with both the thermodynamic equilibrium and the finite flux spectra derived by Galtier et al. (2000); it improves therefore the model built heuristically by Litwick \& Goldreich (2003) for which only the second solution was recovered. This new system offers a powerful description of a wide class of astrophysical plasmas with non-zero cross-helicity.
Data from the operation of a bubble chamber filled with $3.5$ kg of CF$_{3}$I in a shallow underground site are reported. An analysis of ultrasound signals accompanying bubble nucleations confirms that alpha decays generate a significantly louder acoustic emission than single nuclear recoils, leading to an efficient background discrimination. Three dark matter candidate events were observed during an effective exposure of $28.1$ kg-day, consistent with a neutron background. This observation provides the strongest direct detection constraint to date on WIMP-proton spin-dependent scattering for WIMP masses $>20$ GeV/c$^{2}$.
The dynamics of the two-dimensional (2D) state in driven tridimensional (3D) incompressible magnetohydrodynamic turbulence is investigated through high-resolution direct numerical simulations and in the presence of an external magnetic field at various intensities. For such a flow the 2D state (or slow mode) and the 3D modes correspond respectively to spectral fluctuations in the plan $k_\parallel=0$ and in the area $k_\parallel>0$. It is shown that if initially the 2D state is set to zero it becomes non negligible in few turnover times particularly when the external magnetic field is strong. The maintenance of a large scale driving leads to a break for the energy spectra of 3D modes; when the driving is stopped the previous break is removed and a decay phase emerges with alfv\'enic fluctuations. For a strong external magnetic field the energy at large perpendicular scales lies mainly in the 2D state and in all situations a pinning effect is observed at small scales.
Globular clusters are useful to test the validity of Newtonian dynamics in
the low acceleration regime typical of galaxies, without the complications of
non-baryonic dark matter. Specifically, in absence of disturbing effects, e.g.
tidal heating, their velocity dispersion is expected to vanish at large radii.
If such behaviour is not observed, and in particular if, as observed in
elliptical galaxies, the dispersion is found constant at large radii below a
certain threshold acceleration, this might indicate a break down of Newtonian
dynamics.
To minimise the effects of tidal heating in this paper we study the velocity
dispersion profile of two distant globular clusters, NGC 1851 and NGC 1904.
The velocity dispersion profile is derived from accurate radial velocities
measurements, obtained at the ESO 8m VLT telescope. Reliable data for 184 and
146 bona fide cluster star members, respectively for NGC 1851 and NGC 1904,
were obtained.
These data allow to trace the velocity dispersion profile up to ~2r0, where
r0 is the radius at which the cluster internal acceleration of gravity is a0 =
10e-8 cm/s/s. It is found that in both clusters the velocity dispersion becomes
constant beyond ~r0. These new results are fully in agreement with those found
for other five globular clusters previously investigated as part of this
project. Taken all together, these 7 clusters support the claim that the
velocity dispersion is constant beyond r0, irrespectively of the specific
physical properties of the clusters: mass, size, dynamical history, and
distance from the Milky Way. The strong similarly with the constant velocity
dispersion observed in elliptical galaxies beyond r0 is suggestive of a common
origin for this phenomenon in the two class of objects, and might indicate a
breakdown of Newtonian dynamics below a0.
We aim to unveil their 3-dimensional geometry of Abell 2255 through WSRT observations at 18, 21, 25, 85, and 200 cm. The polarization images of the cluster were processed through rotation measure (RM) synthesis, producing three final RM cubes. The radio galaxies and the filaments at the edges of the halo are detected in the high-frequency RM cube, obtained by combining the data at 18, 21, and 25 cm. Their Faraday spectra show different levels of complexity. The radio galaxies lying near by the cluster center have Faraday spectra with multiple peaks, while those at large distances show only one peak, as do the filaments. Similar RM distributions are observed for the external radio galaxies and for the filaments, with much lower average RM values and RM variance than those found in previous works for the central radio galaxies. The 85 cm RM cube is dominated by the Galactic foreground emission, but it also shows features associated with the cluster. At 2 m, no polarized emission from A2255 nor our Galaxy is detected. The radial trend observed in the RM distributions of the radio galaxies and in the complexity of their Faraday spectra favors the interpretation that the external Faraday screen for all the sources in A2255 is the ICM. Its differential contribution depends on the amount of medium that the radio signal crosses along the line of sight. The filaments should therefore be located at the periphery of the cluster, and their apparent central location comes from projection effects. Their high fractional polarization and morphology suggest that they are relics rather than part of a genuine radio halo. Their inferred large distance from the cluster center and their geometry could argue for an association with large-scale structure (LSS) shocks.
This work presents a homogeneous derivation of atmospheric parameters and iron abundances for a sample of giant and subgiant stars which host giant planets, as well as a control sample of subgiant stars not known to host giant planets. The analysis is done using the same technique as for our previous analysis of a large sample of planet-hosting and control sample dwarf stars. A comparison between the distributions of [Fe/H] in planet-hosting main-sequence stars, subgiants, and giants within these samples finds that the main-sequence stars and subgiants have the same mean metallicity of <[Fe/H]> =~ +0.11 dex, while the giant sample is typically more metal poor, having an average metallicity of <[Fe/H]> = -0.06 dex. The fact that the subgiants have the same average metallicities as the dwarfs indicates that significant accretion of solid metal-rich material onto the planet-hosting stars has not taken place, as such material would be diluted in the evolution from dwarf to subgiant. The lower metallicity found for the planet-hosting giant stars in comparison with the planet-hosting dwarfs and subgiants is interpreted as being related to the underlying stellar mass, with giants having larger masses and thus, on average larger-mass protoplanetary disks. In core accretion models of planet formation, larger disk masses can contain the critical amount of metals necessary to form giant planets even at lower metallicities.
Current theory regarding heavy element nucleosynthesis in metal-poor environments states that the r-process would be dominant. The star HD140283 has been the subject of debate after it appeared in some studies to be dominated by the s-process. We provide an independent measure of the Ba isotope mixture in HD140283 using an extremely high quality spectrum and an extensive chi^2 analysis. We exploit hyperfine splitting of the BaII 4554 \AA\ and 4934 \AA\ resonance lines in an effort to constrain the isotope ratio in 1D LTE. Using the code ATLAS in conjunction with KURUCZ06 model atmospheres we analyse 93 Fe lines to determine the star's macroturbulence. With this information we construct a grid of Ba synthetic spectra and, using a \chi^2 code, fit these to our observed data to determine the isotopic ratio, fodd, which represents the ratio of odd to even isotopes. We also analyse the Eu lines. We set a new upper limit of the rotation of HD140283 at vsin{i}\leq3.9\kms, a new upper limit on [Eu/H] < -2.80 and abundances [Fe/H] = -2.59\pm0.09, [Ba/H] = -3.46\pm0.11. This leads to a new lower limit on [Ba/Eu] > -0.66. We find that, in the framework of a 1D LTE analysis, the isotopic ratios of Ba in HD140283 indicate fodd=0.02\pm0.06, a purely s-process signature. This implies that observations and analysis do not validate currently accepted theory. We speculate that a 1D code, due to simplifying assumptions, is not adequate when dealing with observations with high levels of resolution and S/N because of the turbulent motions associated with a 3D stellar atmosphere. New approaches to analysing isotopic ratios, in particular 3D hydrodynamics, need to be considered when dealing with the levels of detail required to properly determine them. However published 3D results exacerbate the disagreement between theory and observation.
10 to 10^5 solar mass black holes with dark matter spikes that formed in early minihalos and still exist in our Milky Way Galaxy today are examined in light of recent data from the Fermi Gamma-Ray Space Telescope (FGST). The dark matter spikes surrounding black holes in our Galaxy are sites of significant dark matter annihilation. We examine the signatures of annihilations into gamma-rays, electrons and positrons, and neutrinos. We find that some significant fraction of the point sources detected by FGST might be due to dark matter annihilation near black holes in our Galaxy. We obtain limits on the properties of dark matter annihilations in the spikes using the information in the FGST First Source Catalog as well as the diffuse gamma-ray flux measured by FGST. We determine the maximum fraction of high redshift minihalos that could have hosted the formation of the first generation of stars and, subsequently, their black hole remnants. The strength of the limits depends on the choice of annihilation channel and black hole mass; limits are strongest for the heaviest black holes and annhilation to $b \bar{b}$ and $W^+W^-$ final states. The larger black holes considered in this paper may arise as the remnants of Dark Stars after the dark matter fuel is exhausted and thermonuclear burning runs its course; thus FGST observations may be used to constrain the properties of Dark Stars. Additionally, we comment on the excess positron flux found by PAMELA and its possible interpretation in terms of dark matter annihilation around these black hole spikes.
We report about stability conditions for static, spherically symmetric objects that share the essential features of mass varying neutrinos in cosmological scenarios. Compact structures of particles with variable mass are held together preponderantly by an attractive force mediated by a background scalar field. Their corresponding conditions for equilibrium and stability are given in terms of the ratio between the total mass-energy and the spherical lump radius, $M/R$. We show that the mass varying mechanism leading to lump formation can modify the cosmological predictions for the cosmological neutrino mass limits. Our study comprises Tolman-Oppenheimer-Volkoff solutions of relativistic objects with non-uniform energy densities. The results leave open some questions concerning stable regular solutions that, to an external observer, very closely reproduce the preliminary conditions to form Schwarzschild black holes.
We explore the viability of a bulk viscous matter-dominated Universe to explain the present accelerated expansion of the Universe. The model is composed by a pressureless fluid with bulk viscosity of the form \zeta = \zeta_0 + \zeta_1 * H where \zeta_0 and \zeta_1 are constants and H is the Hubble parameter. The pressureless fluid characterizes both the baryon and dark matter components. We study the behavior of the Universe according to this model analyzing the scale factor as well as some curvature scalars and the matter density. On the other hand, we compute the best estimated values of \zeta_0 and \zeta_1 using the type Ia Supernovae (SNe Ia) probe. We find that from all the possible scenarios for the Universe, the preferred one by the best estimated values of (\zeta_0, \zeta_1) is that of an expanding Universe beginning with a Big- Bang, followed by a decelerated expansion at early times, and with a smooth transition in recent times to an accelerated expansion epoch that is going to continue forever. The predicted age of the Universe is a little smaller than the mean value of the observational constraint coming from the oldest globular clusters but it is still inside of the confidence interval of this constraint. A drawback of the model is the violation of the local second law of thermodynamics in redshifts z >= 1. However, when we assume \zeta_1 = 0, the simple model \zeta = \zeta_0 evaluated at the best estimated value for \zeta_0 satisfies the local second law of thermodynamics, the age of the Universe is in perfect agreement with the constraint of globular clusters, and it also has a Big-Bang, followed by a decelerated expansion with the smooth transition to an accelerated expansion epoch in late times, that is going to continue forever.
In this paper, we explore the parameter space of hilltop supernatural inflation model and show the regime within which there is no gravitino problem even if we consider both thermal and nonthermal production mechanisms. We make plots for the allowed reheating temperature as a function of gravitino mass by constraints from big-bang nucleosynthesis. We also plot the constraint when gravitino is assumed to be stable and plays the role of dark matter.
We consider a possibility of capture of a heavy charged massive particle $\chi^-$ by the nucleus leading to appearance of a bound state. A simple analytic formula allowing to calculate binding energies of the $N\chi^-$ bound state for different nuclei is derived. If the binding energy is sufficiently large the particle $\chi^-$ is stable inside the nucleus. The probabilities of the nuclear fissions for such states are calculated. It is shown that the bound states are more stable to a possible fission in comparison to the bare nucleus. This makes an observation of this hypothetical charged massive particle and the superheavy nuclei more probable.
We investigate the Hamiltonian structure of linearized extended Ho\v{r}ava- Lifshitz gravity in a flat cosmological background following the Faddeev-Jackiw's Hamiltonian reduction formalism. The Hamiltonian structure of extended Ho\v{r}ava-Lifshitz gravity is similar to that of the projectable version of original Ho\v{r}ava-Lifshitz gravity, in which there is one primary constraint and so there are two physical degrees of freedom. We also find that extra scalar graviton mode in an inflationary background can be decoupled from the matter field in the infrared (IR) limit, but it is coupled to the matter field in a general cosmological background. But it is necessary to go beyond linear order in order to draw any conclusion of the strong coupling problem.
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[NIRSS is one of three concepts that contributed to the Wide-Field Infrared Survey Telescope (WFIRST) mission advocated by the Decadal Survey.] Operating beyond the reaches of the Earth's atmosphere, free of its limiting absorption and thermal background, the Near-Infrared Sky Surveyor (NIRSS) will deeply map the entire sky at near-infrared wavelengths, thereby enabling new and fundamental discoveries ranging from the identification of extrasolar planets to probing the reionization epoch by identifying thousands of quasars at z>10. NIRSS will directly address the NASA scientific objective of studying cosmic origins by using a 1.5-meter telescope to reach full-sky 0.2 uJy (25.6 mag AB) sensitivities in four passbands from 1 to 4 microns in a 4-yr mission. At the three shorter passbands (1 - 2.5 microns), the proposed depth is comparable to the deepest pencil-beam surveys done to date and is 3000 times more sensitive than the only previous all-sky near-infrared survey, 2MASS. At the longest passband (3.5 micron), which is not feasible from the ground, NIRSS will be 500 times more sensitive than WISE. NIRSS fills a pivotal gap in our knowledge of the celestial sphere, is a natural complement to WISE, and is well matched to the next generation of deep (0.1 uJy), wide-area (>2 pi ster), ground-based optical surveys (LSST and Pan-Starrs). With the high thermal backgrounds of ground-based infrared observations, a near-infrared full sky survey at sub-uJy sensitivity is only feasible from space.
We report the discovery of HAT-P-25b, a transiting extrasolar planet orbiting the V = 13.19 G5 dwarf star GSC 1788-01237, with a period P = 3.652836 +/- 0.000019 days, transit epoch Tc = 2455176.85173 +/- 0.00047 (BJD), and transit duration 0.1174 +/- 0.0017 days. The host star has mass of 1.01 +/- 0.03 M(Sun), radius of 0.96 +(0.05)-(0.04) R(Sun), effective temperature 5500 +/- 80 K, and metallicity [Fe/H] = +0.31 +/- 0.08. The planetary companion has a mass of 0.567 +/- 0.022 M(Jup), and radius of 1.190 +(0.081)-(0.056) R(Jup) yielding a mean density of 0.42 +/- 0.07 g cm-3. Comparing these observations with recent theoretical models, we find that HAT-P-25b is consistent with a hydrogen-helium dominated gas giant planet with negligible core mass and age 3.2 +/- 2.3 Gyr. The properties of HAT-P-25b support several previously observed correlations for planets in the mass range 0.4 < M < 0.7 M(Jup), including those of core mass vs. metallicity, planet radius vs. equilibrium temperature, and orbital period vs. planet mass. We also note that HAT-P-25b orbits the faintest star found by HATNet to have a transiting planet to date, and is one of only a very few number of planets discovered from the ground orbiting a star fainter than V = 13.0.
We report on two XMM-Newton observations of the planetary host star HD189733. The system has a close in planet and it can potentially affect the coronal structure via interactions with the magnetosphere. We have obtained X-ray spectra and light curves from EPIC and RGS on board XMM-Newton which we have analyzed and interpreted. We reduced X-ray data from primary transit and secondary eclipse occurred in April 17th 2007 and May 18th 2009, respectively. In the April 2007 observation only variability due to weak flares is recognized. In 2009 HD189733 exhibited a X-ray flux always larger than in the 2007 observation. The average flux in 2009 was higher than in 2007 observation by a factor of 45%. During the 2009 secondary eclipse we observed a softening of the X-ray spectrum significant at level of ~3 sigma. Further, we observed the most intense flare recorded at either epochs. This flare occurred 3 ks after the end of the eclipse.The flare decay shows several minor ignitions perhaps linked to the main event and hinting for secondary loops that emit triggered by the main loop. Magneto-Hydro-Dynamical (MHD) simulations show that the magnetic interaction between planet and star enhances the density and the magnetic field in a region comprised between the planet and the star because of their relative orbital/rotation motion. X-ray observations and model predictions are globally found in agreement, despite the quite simple MHD model and the lack of precise estimate of parameters including the alignment and the intensity of stellar and planetary magnetic fields. Future observations should confirm or disprove this hypothesis, by determining whether flares are systematically recurring in the light curve at the same planetary phase.
We perform state-of-the-art, 3D, time-dependent simulations of magnetized disk winds, carried out to simulation scales of 60 Astronomical Units, in order to confront optical HST observations of protostellar jets. We ``observe'' the optical forbidden line emission produced by shocks within our simulated jets and compare these with actual observations. Our simulations reproduce the rich structure of time varying jets, including jet rotation far from the source, an inner (up to 400 km/s) and outer (less than 100 km/s) component of the jet, and jet widths of up to 20 Astronomical Units in agreement with observed jets. These simulations when compared with the data are able to constrain disk wind models. In particular, models featuring a disk magnetic field with a modest radial spatial variation across the disk are favored.
We obtained Spitzer/IRAC 3.6-8 micron images of the nearby spiral galaxy NGC 4258 to study possible interactions between dust and the radio jet. In our analysis we also included high-resolution radio continuum, H-alpha, CO, and X-ray data. Our data reveal that the 8 micron emission, believed to originate largely from PAH molecules and hot dust, is an excellent tracer of the normal spiral structure in NGC 4258, and hence it originates from the galactic plane. We investigated the possibility of dust destruction by the radio jet by calculating correlation coefficients between the 8 micron and radio continuum emissions along the jet in two independent ways, namely (i) from wavelet-transformed maps of the original images at different spatial scales, and (ii) from one-dimensional intensity cuts perpendicular to the projected path of the radio jet on the sky. No definitive sign of a correlation (or anticorrelation) was detected on relevant spatial scales with either approach, implying that any dust destruction must take place at spatial scales that are not resolved by our observations.
We have conducted a 4030-square-deg near-infrared proper motion survey using multi-epoch data from the Two Micron All-Sky Survey (2MASS). We find 2778 proper motion candidates, 647 of which are not listed in SIMBAD. After comparison to DSS images, we find that 107 of our proper motion candidates lack counterparts at B-, R-, and I-bands and are thus 2MASS-only detections. We present results of spectroscopic follow-up of 188 targets that include the infrared-only sources along with selected optical-counterpart sources with faint reduced proper motions or interesting colors. We also establish a set of near-infrared spectroscopic standards with which to anchor near-infrared classifications for our objects. Among the discoveries are six young field brown dwarfs, five "red L" dwarfs, three L-type subdwarfs, twelve M-type subdwarfs, eight "blue L" dwarfs, and several T dwarfs. We further refine the definitions of these exotic classes to aid future identification of similar objects. We examine their kinematics and find that both the "blue L" and "red L" dwarfs appear to be drawn from a relatively old population. This survey provides a glimpse of the kinds of research that will be possible through time-domain infrared projects such as the UKIDSS Large Area Survey, various VISTA surveys, and WISE, and also through z- or y-band enabled, multi-epoch surveys such as Pan-STARRS and LSST.
The magnetic chemically peculiar star CU Virginis is a unique astrophysical laboratory for stellar magnetospheres and coherent emission processes. It is the only known main sequence star to emit a radio pulse every rotation period. Here we report on new observations of the CU Virginis pulse profile in the 13 and 20\,cm radio bands. The profile is known to be characterised by two peaks of 100$\%$ circularly polarised emission that are thought to arise in an electron-cyclotron maser mechanism. We find that the trailing peak is stable at both 13 and 20\,cm, whereas the leading peak is intermittent at 13\,cm. Our measured pulse arrival times confirm the discrepancy previously reported between the putative stellar rotation rates measured with optical data and with radio observations. We suggest that this period discrepancy might be caused by an unknown companion or by instabilities in the emission region. Regular long-term pulse timing and simultaneous multi-wavelength observations are essential to clarify the behaviour of this emerging class of transient radio source.
High-precision pulsar timing relies on a solar-system ephemeris in order to convert times of arrival (TOAs) of pulses measured at an observatory to the solar system barycenter. Any error in the conversion to the barycentric TOAs leads to a systematic variation in the observed timing residuals; specifically, an incorrect planetary mass leads to a predominantly sinusoidal variation having a period and phase associated with the planet's orbital motion about the Sun. By using an array of pulsars (PSRs J0437-4715, J1744-1134, J1857+0943, J1909-3744), the masses of the planetary systems from Mercury to Saturn have been determined. These masses are consistent with the best-known masses determined by spacecraft observations, with the mass of the Jovian system, 9.547921(2)E-4 Msun, being significantly more accurate than the mass determined from the Pioneer and Voyager spacecraft, and consistent with but less accurate than the value from the Galileo spacecraft. While spacecraft are likely to produce the most accurate measurements for individual solar system bodies, the pulsar technique is sensitive to planetary system masses and has the potential to provide the most accurate values of these masses for some planets.
We report on the first detection of ionospheric disturbances caused by short repeated gamma-ray bursts from the magnetar SGR J1550-5418. Very low frequency (VLF) radio wave data obtained in South America clearly show sudden amplitude and phase changes at the corresponding times of eight SGR bursts. Maximum amplitude and phase changes of the VLF signals appear to be correlated with the gamma-ray fluence. On the other hand, VLF recovery timescales do not show any significant correlation with the fluence, possibly suggesting that the bursts' spectra are not similar to each other. In summary, the Earth's ionosphere can be used as a very large gamma-ray detector and the VLF observations provide us with a new method to monitor high energy astrophysical phenomena without interruption such as Earth Occultation.
Significant progress has been made recently in our understanding of the structure of stellar magnetic fields, thanks to advances in detection methods such as Zeeman-Doppler Imaging. The extrapolation of this surface magnetic field into the corona has provided 3D models of the coronal magnetic field and plasma. This method is sensitive mainly to the magnetic field in the bright regions of the stellar surface. The dark (spotted) regions are censored because the Zeeman signature there is suppressed. By modelling the magnetic field that might have been contained in these spots, we have studied the effect that this loss of information might have on our understanding of the coronal structure. As examples, we have chosen two stars (V374 peg and AB Dor) that have very different magnetograms and patterns of spot coverage. We find that the effect of the spot field depends not only on the relative amount of flux in the spots, but also its distribution across the stellar surface. For a star such as AB Dor with a high spot coverage and a large polar spot, at its greatest effect the spot field may almost double the fraction of the flux that is open (hence decreasing the spindown time) while at the same time increasing the X-ray emission measure by two orders of magnitude and significantly affecting the X-ray rotational modulation.
We present ultraviolet (UV) color-magnitude relations (CMRs) of early-type dwarf galaxies in the Virgo cluster, based on Galaxy Evolution Explorer (GALEX) UV and Sloan Digital Sky Survey (SDSS) optical imaging data. We find that dwarf lenticular galaxies (dS0s), including peculiar dwarf elliptical galaxies (dEs) with disk substructures and blue centers, show a surprisingly distinct and tight locus separated from that of ordinary dEs, which is not clearly seen in previous CMRs. The dS0s in UV CMRs follow a steeper sequence than dEs and show bluer UV-optical color at a given magnitude. We also find that the UV CMRs of dEs in the outer cluster region are slightly steeper than that of their counterparts in the inner region, due to the existence of faint, blue dEs in the outer region. We explore the observed CMRs with population models of a luminosity-dependent delayed exponential star formation history. We confirm that the feature of delayed star formation of early-type dwarf galaxies in Virgo cluster is strongly correlated with their morphology and environment. The observed CMR of dS0s is well matched by models with relatively long delayed star formation. Our results suggest that dS0s are most likely transitional objects at the stage of subsequent transformation of late-type progenitors to ordinary red dEs in the cluster environment. In any case, UV photometry provides a powerful tool to disentangle the diverse subpopulations of early-type dwarf galaxies and uncover their evolutionary histories.
The frequently observed association between giant radio halos and merging galaxy clusters has driven present theoretical models of non-thermal emission from galaxy clusters, which are based on the idea that the energy dissipated during cluster-cluster mergers could power the formation of radio halos. To quantitatively test the merger-halo connection we present the first statistical study based on deep radio data and X-ray observations of a complete X-ray selected sample of galaxy clusters with X-ray luminosity > 5x 10^44 erg/s and redshift 0.2<z< 0.32. Using several methods to characterize cluster substructures, namely the power ratios, centroid shift and X-ray brightness concentration parameter, we show that clusters with and without radio halo can be quantitatively differentiated in terms of their dynamical properties. In particular, we confirm that radio halos are associated to dynamically disturbed clusters and cluster without radio halo are more ``relaxed'', with only a couple of exceptions where a disturbed cluster does not exhibit a halo.
We present evidence for Quasi Periodic Oscillations (QPOs) in the recurrent outburst activity from SGR 1806-20 using Rossi X-ray Timing Explorer (RXTE) observations during November 1996. Searching for QPOs in a sample of 30 bursts at similar frequencies to those previously reported in the December 27, 2004 giant flare, we find evidence for a QPO in a burst at 648 Hz at 5.17{\sigma} confidence level, lying within 3.75% from the 625 Hz QPO discovered in the giant flare. Two additional features are also detected around 84 and 103 Hz in two other bursts at 4.2{\sigma} and 4.8{\sigma} confidence level, respectively, which lie within 8.85% and 11.83% respectively from the QPO at 92.5 Hz also detected in the giant flare. Accounting for the number of bursts analyzed the confidence levels for the 84, 103 and 648 Hz becomes 3{\sigma}, 3.6{\sigma} and 3.4{\sigma} respectively. Extending our search to other frequency ranges, we find candidates at 1096, 1230, 2785 and 3690 Hz in 3 different bursts with confidence levels lying between 4.14{\sigma}-4.46{\sigma}, which is reduced to 2.3{\sigma}-3{\sigma} after accounting for a certain confirmation bias in each case. The fact that we can find evidence for QPOs in the recurrent bursts at frequencies relatively close to those found in the giant flare is intriguing. We examine the candidate QPOs in relation with those found in the giant flare and discuss their possible physical origin.
GALPROP is a numerical code for calculating the galactic propagation of relativistic charged particles and the diffuse emissions produced during their propagation. The code incorporates as much realistic astrophysical input as possible together with latest theoretical developments and has become a de facto standard in astrophysics of cosmic rays. We present GALPROP WebRun, a service to the scientific community enabling easy use of the freely available GALPROP code via web browsers. In addition, we introduce the latest GALPROP version 54, available through this service.
The channeling of the ion recoiling after a collision with a WIMP changes the ionization signal in direct detection experiments, producing a larger signal than otherwise expected. We give estimates of the fraction of channeled recoiling ions in Si and Ge crystals using analytic models produced since the 1960's and 70's to describe channeling and blocking effects. We used data obtained to avoid channeling in the implantation of dopants in Si crystals to test our models.
Here I will review the high time resolution radio sky, focusing on millisecond scales. This is primarily occupied by neutron stars, the well-known radio pulsars and the recently identified group of transient sources known as Rotating RAdio Transients (RRATs). The RRATs appear to be abundant in the Galaxy, which at first glance may be difficult to reconcile with the observed supernova rate. However, as I will discuss, it seems that the RRATs can be explained as pulsars which are either extreme nullers, highly variable or weak/distant. I will re-cap some recent results including a re-analysis of the Parkes Multi-beam Pulsar Survey, which has identified several new sources, as well as the unusual timing behaviour of RRAT J1819-1458. This leads to an examination of where RRATs fit within the evolution of neutron stars post-supernova.
Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV to 10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA.
In this paper we numerically calculate the spherical rotating MHD flows driven by an imposed Lorentz force in respect of both axisymmetric flow and instabilities. We test various rotation rates and field strengths as well as the two magnetic boundary conditions.
An unexpected feature of Titan's atmosphere is the strong depletion in primordial noble gases revealed by the Gas Chromatograph Mass Spectrometer aboard the Huygens probe during its descent on 2005 January 14. Although several plausible explanations have already been formulated, no definitive response to this issue has been yet found. Here, we investigate the possible sequestration of these noble gases in the liquid contained in lakes and wet terrains on Titan and the consequences for their atmospheric abundances. Considering the atmosphere and the liquid existing on the soil as a whole system, we compute the abundance of each noble gas relative to nitrogen. To do so, we make the assumption of thermodynamic equilibrium between the liquid and the atmosphere, the abundances of the different constituents being determined via {\bf } regular solution theory. We find that xenon's atmospheric depletion can be explained by its dissolution at ambient temperature in the liquid presumably present on Titan's soil. In the cases of argon and krypton, we find that the fractions incorporated in the liquid are negligible, implying that an alternative mechanism must be invoked to explain their atmospheric depletion.
A key result of hydrogravitational dynamics cosmology relevant to astrobiology is the early formation of vast numbers of hot primordial-gas planets in million-solar-mass clumps as the dark matter of galaxies and the hosts of first life. Photon viscous forces in the expanding universe of the turbulent big bang prevent fragmentations of the plasma for mass scales smaller than protogalaxies. At the plasma to gas transition 300,000 years after the big bang, the 10^7 decrease in kinematic viscosity {\nu} explains why ~3x10^7 planets are observed to exist per star in typical galaxies like the Milky Way, not eight or nine. Stars form by a binary accretional cascade from Earth-mass primordial planets to progressively larger masses that collect and recycle the stardust chemicals of life produced when stars overeat and explode. The astonishing complexity of molecular biology observed on Earth is possible to explain only if enormous numbers of primordial planets and their fragments have hosted the formation and wide scattering of the seeds of life virtually from the beginning of time. Geochemical and biological evidence suggests that life on Earth appears at the earliest moment it can survive, in highly evolved forms with complexity requiring a time scale in excess of the age of the galaxy. This is quite impossible within standard cold-dark-matter cosmology where planets are relatively recent, rare and cold, completely lacking mechanisms for intergalactic transport of life forms.
Matos, Guzman and Nunez proposed a model of galactic halo based on an exponential-potential scalar field that could induce a rotation curve that is constant for all radii. We demonstrate that with suitable boundary conditions, such scalar field dark matter (SDM) can not only produce the observed constant rotation curve at large radius but also give rise to the correct power-law scaling near the galactic core region. This solves the existing cusp-core problem faced by the conventional cold dark matter (CDM) model.
We present the results of a dedicated search for extremely metal-poor stars in the Fornax, Sculptor and Sextans dSphs. Five stars were selected from two earlier VLT/Giraffe and HET/HRS surveys and subsequently followed up at high spectroscopic resolution with VLT/UVES. All of them turned out to have [Fe/H] <= -3 and three stars are below [Fe/H]~-3.5. This constitutes the first evidence that the classical dSphs Fornax and Sextans join Sculptor in containing extremely metal-poor stars and suggests that all of the classical dSphs contain extremely metal-poor stars. One giant in Sculptor at [Fe/H]=-3.96 +- 0.10 is the most metal-poor star ever observed in an external galaxy. We carried out a detailed analysis of the chemical abundances of the alpha, iron peak, and the heavy elements, and we performed a comparison with the Milky Way halo and the ultra faint dwarf stellar populations. Carbon, barium and strontium show distinct features characterized by the early stages of galaxy formation and can constrain the origin of their nucleosynthesis.
[abridged] We describe the first results from the NOAO Outer Limits Survey. The survey consists of deep images of 55 0.6x0.6 degree fields at distances up to 20 degrees from the LMC/SMC, and 10 controls. The fields probe the outer structure of the Clouds, the Magellanic Stream, the Leading Arm, and the wake of the new LMC orbit. Images were taken in 5 filters on the CTIO Blanco 4-m and Mosaic2 camera, with calibration at the CTIO 0.9-m. The CRI images reach depths below the oldest LMC/SMC main sequence (MS) turnoffs, yielding probes of structure combined with ability to measure stellar ages and metallicities. M and DDO51 images allow for discrimination of LMC and SMC giant stars from foreground dwarfs, allowing us to use giants as additional probes. From photometry of 8 fields at radii of 7-19 degrees N of the LMC bar, we find MS stars associated with the LMC to 16 degrees from the LMC center, while the much rarer giants can only be convincingly detected out to 11 degrees. In one control field, we see the signature of the Milky Way globular cluster NGC 1851. The CMDs show that while at 7-degree radius LMC populations as young as 500 Myr are present, at radii more than 11 degrees only the underlying old metal-poor population remains, demonstrating the existence of a population gradient. Even at extreme distances, the dominant age is much less than "globular Cluster age." MS star counts follow an exponential decline with a scale length of 1.15 kpc, essentially the same scale length as gleaned for the inner LMC disk from prior studies. While we cannot rule out tidal structure elsewhere, detection of ordered structure to 12 disk scale lengths is unprecedented, and adds to the puzzle of the LMC's interaction history. Our results do not rule out the possible existence of an LMC stellar halo, which may only dominate the disk at yet larger radii.
We report on a variable high-velocity narrow absorption line outflow in the redshift 2.3 quasar J2123-0050. Five distinct outflow systems are detected with velocity shifts from -9710 to -14,050 km/s and CIV 1548,1551 line widths of FWHM = 62-164 km/s. These data require five distinct outflow structures with similar kinematics, physical conditions and characteristic sizes of order 0.01-0.02 pc. The most likely location is ~5 pc from the quasar. The coordinated line variations in <0.63 yr (rest) are best explained by global changes in the outflow ionization caused by changes in the quasar's ionizing flux. The absence of strong X-ray absorption shows that radiative shielding is not needed to maintain the moderate ionizations and therefore, apparently, it is not needed to facilitate the radiative acceleration to high speeds. The kinetic energy yield of this flow is at least two orders of magnitude too low to be important for feedback to the host galaxy's evolution.
Near-infrared medium-resolution spectra of seven bright brown dwarfs are
presented. The spectra were obtained with the Infrared Camera (IRC) on board
the infrared astronomical satellite AKARI, covering 2.5--5.0 um with a spectral
resolution of approximately 120. The spectral types of the objects range from
L5 to T8, and enable us to study the spectral evolution of brown dwarfs. The
observed spectra are in general consistent with the predictions from the
previous observations and photospheric models. We find that the CO fundamental
band around 4.6 um is clearly seen even in the T8 dwarf 2MASS J041519-0935,
confirming the presence of non-equilibrium chemical state in the atmosphere. We
also identify the CO_2 fundamental stretching-mode band at 4.2 um for the first
time in the spectra of late-L and T-type brown dwarfs.
We analyze the observed spectra by comparing with the predicted ones based on
the Unified Cloudy Model (UCM). Although overall spectral energy distributions
(SEDs) can be reasonably fitted with the UCM, observed CO and CO_2 bands in
late-L and T-dwarfs are unexpectedly stronger than the model predictions
assuming local thermodynamical equilibrium (LTE). We examine the vertical
mixing model and find that this model explains the CO band at least partly in
the T-dwarfs 2MASS J041519-0935 and 2MASS J055919-1404. The CO fundamental band
also shows excess absorption against the predicted one in the L9 dwarf SDSS
J083008+4828. Since CO is already highly abundant in the upper photospheres of
late-L dwarfs, the extra CO by vertical mixing has little effect on the CO band
strengths, and the vertical mixing model cannot be applied to this L-dwarf. A
more serious problem is that the significant enhancement of the CO_2 4.2 um
band in both the late-L and T dwarfs cannot be explained at all by the vertical
mixing model. The enhancement of the CO_2 band remains puzzling.
The LASCO coronagraphs, in continuous operation since 1995, have observed the evolution of the solar corona and coronal mass ejections (CMEs) over a full solar cycle with high quality images and regular cadence. This is the first time that such a dataset becomes available and constitutes a unique resource for the study of CMEs. In this paper, we present a comprehensive investigation of the solar cycle dependence on the CME mass and energy over a full solar cycle (1996-2009) including the first in-depth discussion of the mass and energy analysis methods and their associated errors. Our analysis provides several results worthy of further studies. It demonstrates the possible existence of two event classes; 'normal' CMEs reaching constant mass for $>10$ R$_{\sun}$ and 'pseudo' CMEs which disappear in the C3 FOV. It shows that the mass and energy properties of CME reach constant levels, and therefore should be measured, only above $\sim 10 R_\sun$. The mass density ($g/R_\sun^2$) of CMEs varies relatively little ($<$ order of magnitude) suggesting that the majority of the mass originates from a small range in coronal heights. We find a sudden reduction in the CME mass in mid-2003 which may be related to a change in the electron content of the large scale corona and we uncover the presence of a six-month periodicity in the ejected mass from 2003 onwards.
We investigate medium effects due to density-dependent magnetic moments of baryons on neutron stars under strong magnetic fields. If we allow the variation of anomalous magnetic moments (AMMs) of baryons in dense matter under strong magnetic fields, AMMs of nucleons are enhanced to be larger than those of hyperons. The enhancement naturally affects the chemical potentials of baryons to be large and leads to the increase of a proton fraction. Consequently, it causes the suppression of hyperons, resulting in the stiffness of the equation of state. Under the presumed strong magnetic fields, we evaluate relevant particles' population, the equation of state and the maximum masses of neutron stars by including density-dependent AMMs and compare them with those obtained from AMMs in free space.
We present high spatial resolution optical imaging and polarization observations of the PSR B0540-69.3 and its highly dynamical pulsar wind nebula (PWN) performed with HST, and compare them with X-ray data obtained with the Chandra X-ray Observatory. We have studied the bright region southwest of the pulsar where a bright "blob" is seen in 1999. We show that it may be a result of local energy deposition around 1999, and that the emission from this then faded away. Polarization data from 2007 show that the polarization properties show dramatic spatial variations at the 1999 blob position arguing for a local process. Several other positions along the pulsar-"blob" orientation show similar changes in polarization, indicating previous recent local energy depositions. In X-rays, the spectrum steepens away from the "blob" position, faster orthogonal to the pulsar-"blob" direction than along this axis of orientation. This could indicate that the pulsar-"blob" orientation is an axis along where energy in the PWN is mainly injected, and that this is then mediated to the filaments in the PWN by shocks. We highlight this by constructing an [S II]-to-[O III]-ratio map. We argue, through modeling, that the high [S II]/[O III] ratio is not due to time-dependent photoionization caused by possible rapid Xray emission variations in the "blob" region. We have also created a multiwavelength energy spectrum for the "blob" position showing that one can, to within 2sigma, connect the optical and X-ray emission by a single power law. We obtain best power-law fits for the X-ray spectrum if we include "extra" oxygen, in addition to the oxygen column density in the interstellar gas of the Large Magellanic Cloud and the Milky Way. This oxygen is most naturally explained by the oxygen-rich ejecta of the supernova remnant. The oxygen needed likely places the progenitor mass in the 20 - 25 Msun range.
In the paper Pulsar Electrodynamics, published in 1969, Goldreich and Julian propose some basic properties of pulsars, such as the oft-cited Goldreich-Julian density, light cylinder, open and closed magnetic field lines, corotation and so on. However, inspection of their mathematics reveals three mistakes: first, the relative velocity is irrelevantly replaced by the corotation velocity; second, a hypothesis in their theory is contradictory to Maxwell's equations; and third, their theory neglected a special solution of the frozen-in field equation which is of particular importance for pulsar research. We additionally describe the results of a series of magnetohydrodynamic experiments that may be beneficial to the understanding of pulsar electrodynamics.
Although the influence of magnetic fields is regarded as vital in the star formation process, only a few magnetohydrodynamics (MHD) simulations have been performed on this subject within the smoothed particle hydrodynamics (SPH) method. This is largely due to the unsatisfactory treatment of non-vanishing divergence of the magnetic field. Recently smoothed particle magnetohydrodynamics (SPMHD) simulations based on Euler potentials have proven to be successful in treating MHD collapse and fragmentation problems, however these methods are known to have some intrinsical difficulties. We have performed SPMHD simulations based on a traditional approach evolving the magnetic field itself using the induction equation. To account for the numerical divergence, we have chosen an approach that subtracts the effects of numerical divergence from the force equation, and additionally we employ artificial magnetic dissipation as a regularization scheme. We apply this realization of SPMHD to a widely known setup, a variation of the 'Boss \& Bodenheimer standard isothermal test case', to study the impact of the magnetic fields on collapse and fragmentation. In our simulations, we concentrate on setups, where the initial magnetic field is parallel to the rotation axis. We examine different field strengths and compare our results to other findings reported in the literature. We are able to confirm specific results found elsewhere, namely the delayed onset of star formation for strong fields, accompanied by the the tendency to form only single stars. We also find, contrary to other authors, a speed-up of the onset of star formation at intermediate field strengths, and the formation of triple systems. The latter is attributed to magnetic tension forces that aid fragmentation in these cases.
Using a model of force balance in Saturn's disk-like magnetosphere, we show that variations in hot plasma pressure can change the magnetic field configuration. This effect changes (i) the location of the magnetopause, even at fixed solar wind dynamic pressure, and (ii) the magnetic mapping between ionosphere and disk. The model uses equatorial observations as a boundary condition-we test its predictions over a wide latitude range by comparison with a Cassini high-inclination orbit of magnetic field and hot plasma pressure data. We find reasonable agreement over time scales larger than the period of Saturn kilometric radiation (also known as the camshaft period).
The dark cloud Lynds 723 (L723) is a low-mass star-forming region where one of the few known cases of a quadrupolar CO outflow has been reported. Two recent works have found that the radio continuum source VLA 2, towards the centre of the CO outflow, is actually a multiple system of young stellar objects (YSOs). Several line-emission nebulae that lie projected on the east-west CO outflow were detected in narrow-band Halpha and [SII] images. The spectra of the knots are characteristic of shock-excited gas (Herbig-Haro spectra), with supersonic blueshifted velocities, which suggests an optical outflow also powered by the VLA 2 YSO system of L723. We imaged a field of ~5' X 5' centred on HH 223, which includes the whole region of the quadrupolar CO outflow with nir narrow-band filters . The H2 line-emission structures appear distributed over a region of 5.5' (0.5 pc for a distance of 300 pc) at both sides of the VLA 2 YSO system, with an S-shape morphology, and are projected onto the east-west CO outflow. Most of them were resolved in smaller knotty substructures. The [FeII] emission only appears associated with HH 223. An additional nebular emission from the continuum in Hc and Kc appears associated with HH 223-K1, the structure closest to the VLA 2 YSO system, and could be tracing the cavity walls. We propose that the H2 structures form part of a large-scale near-infrared outflow, which is also associated with the VLA 2 YSO system. The current data do not allow us to discern which of the YSOs of VLA 2 is powering this large scale optical/near-infrared outflow.
We report photometric and radial velocity observations of the XO-4 transiting planetary system, conducted with the FLWO 1.2m telescope and the 8.2m Subaru Telescope. Based on the new light curves, the refined transit ephemeris of XO-4b is $P = 4.1250828 \pm 0.0000040$ days and $T_c [BJD_TDB] = 2454485.93323 \pm 0.00039$. We measured the Rossiter-McLaughlin effect of XO-4b and estimated the sky-projected angle between the stellar spin axis and the planetary orbital axis to be $\lambda = -46.7^{\circ} ^{+8.1^{\circ}}_{-6.1^{\circ}}$. This measurement of $\lambda$ is less robust than in some other cases because the impact parameter of the transit is small, causing a strong degeneracy between $\lambda$ and the projected stellar rotational velocity. Nevertheless, our finding of a spin-orbit misalignment suggests that the migration process for XO-4b involved few-body dynamics rather than interaction with a gaseous disk. In addition, our result conforms with the pattern reported by Winn et al. (2010, ApJL, 718, L145) that high obliquities are preferentially found for stars with effective temperatures hotter than 6250~K.
Radio synchrotron emission, its polarization and its Faraday rotation are powerful tools to study the strength and structure of interstellar magnetic fields. In the Milky Way, Faraday rotation of the polarized emission from pulsars and background sources indicate that the regular field follows the spiral arms and has one reversal inside the solar radius, but the overall field structure in our Galaxy is still unclear. In nearby galaxies, ordered fields with spiral structure exist in grand-design, barred and flocculent galaxies. The strongest ordered fields (10-15 \muG) are found in interarm regions. Faraday rotation of the diffuse polarized radio emission from the disks of spiral galaxies sometimes reveals large-scale patterns, which are signatures of regular fields generated by a mean-field dynamo. - The SKA and its precursor telescopes will open a new era in the observation of cosmic magnetic fields and help to understand their origin. All-sky surveys of Faraday rotation measures (RM) towards a dense grid of polarized background sources with the ASKAP (POSSUM), MeerKAT and the SKA are dedicated to measure fields in intervening galaxies and will be used to model the overall structure and strength of the magnetic fields in the Milky Way and beyond. Examples for joint polarimetric observations between the SKA and the E-ELT are given.
Triggered by the study of Carquillat & Prieur (2007, MNRAS, 380, 1064) of Am binaries, I reanalyse their sample of 60 orbits to derive the mass ratio distribution (MRD), assuming as they did a priori functional forms, i.e. a power law or a Gaussian. The sample is then extended using orbits published by several groups and a full analysis of the MRD is made, without any assumption on the functional form. I derive the MRD using a Richardson-Lucy inversion method, assuming a fixed mass of the Am primary and randomly distributed orbital inclinations. Using the large sub-sample of double-lined spectroscopic binaries, I show that this methodology is indeed perfectly adequate. Using the inversion method, applied to my extended sample of 162 systems, I find that the final MRD can be approximated by a uniform distribution.
The formation mechanism of the barium stars is thought to be well understood. Barium-rich material, lost in a stellar wind from a thermally-pulsing asymptotic-giant branch star in a binary system, is accreted by its companion main-sequence star. Now, many millions of years later, the primary is an unseen white dwarf and the secondary has itself evolved into a giant which displays absorption lines of barium in its spectrum and is what we call a barium star. A similar wind-accretion mechanism is also thought to form the low-metallicity CH and carbon-enhanced metal-poor stars. Qualitatively the picture seems clear but quantitatively it is decidedly murky: several key outstanding problems remain which challenge our basic understanding of binary-star physics. Barium stars with orbital periods less than about 4,000 days should -- according to theory -- be in circular orbits because of tidal dissipation, yet they are often observed to be eccentric. Only one barium-star period longer than 10^4 days has been published although such stars are predicted to exist in large numbers. In this paper we attempt to shed light on these problems. First, we consider the impact of kicking the white dwarf at its birth, a notion which is supported by independent evidence from studies of globular clusters. Second, we increase the amount of orbital angular momentum loss during wind mass transfer, which shrinks barium-star binaries to the required period range. We conclude with a discussion of possible physical mechanisms and implications of a kick, such as the break up of wide barium-star binaries and the limits imposed on our models by observations.
We assembled a catalogue of bright, hot subdwarf and white dwarf stars extracted from a joint ultraviolet, optical, and infrared source list. The selection is secured using colour criteria that correlate well with effective temperatures T_eff ~> 12,000 K. We built a N_UV-V versus V-J diagram for more than 60,000 bright sources using the Galaxy Evolution Explorer (GALEX) N_UV magnitude (N_UV<14), and the associated Guide Star Catalog (GSC2.3.2) photographic quick-V magnitude and the Two Micron All Sky Survey (2MASS) J and H magnitudes. This distillation process delivered a catalogue of approximately 700 sources with N_UV-V<0.5 comprising ~160 known hot subdwarf stars and another ~60 known white dwarf stars. A reduced proper-motion diagram built using the proper-motion measurements extracted from the Naval Observatory Merged Astrometric Dataset allowed us to identify an additional ~120 new hot subdwarf candidates and ~10 hot white dwarf candidates. We present a spectroscopic study of a subset of 52 subdwarfs, 48 of them analysed here for the first time, and with nine objects brighter than V ~ 12. Our sample of spectroscopically confirmed hot subdwarfs comprises ten sdO stars and 42 sdB stars suitable for pulsation and binary studies. We also present a study of 50 known white dwarfs selected in the GALEX survey and six new white dwarfs from our catalogue of subluminous candidates. Ultraviolet, optical, and infrared synthetic magnitudes employed in the selection and analysis of white dwarf stars are listed in appendix.
Theories of thick disk formation can be differentiated by measurements of stellar elemental abundances. We have undertaken a study of metal-poor stars selected from the RAVE spectroscopic survey of bright stars to establish whether or not there is a significant population of metal-poor thick-disk stars ([Fe/H] <~ -1.0) and to measure their elemental abundances. In this paper, we present abundances of four alpha-elements (Mg, Si, Ca, Ti) and iron for a subsample of 212 RGB and 31 RC/HB stars from this study. We find that the [alpha/Fe] ratios are enhanced implying that enrichment proceeded by purely core-collapse supernovae. This requires that star formation in each star forming region had a short duration. The relative lack of scatter in the [alpha/Fe] ratios implies good mixing in the ISM prior to star formation. In addition, the ratios resemble that of the halo, indicating that the halo and thick disk share a similar massive star IMF. We conclude that the alpha enhancement of the metal-poor thick disk implies that direct accretion of stars from dwarf galaxies similar to surviving dwarf galaxies today did not play a major role in the formation of the thick disk.
[Abridged] Several large scale photometric and spectroscopic surveys are being undertaken to provide a more detailed picture of the Milky Way. Given the necessity of generalisation in the determination of, e.g., stellar parameters when tens and hundred of thousands of stars are considered it remains important to provide independent, detailed studies to verify the methods used in the surveys. We evaluate available calibrations for deriving [M/H] from Stromgren photometry and develop the standard sequences for dwarf stars to reflect their metallicity dependence and test how well metallicities derived from ugriz photometry reproduce metallicities derived from the well-tested system of Stromgren photometry. We use a catalogue of dwarf stars with both Stromgren uvby photometry and spectroscopically determined iron abundances (in total 451 dwarf stars with 0.3<(b-y)_0<1.0). We also evaluate available calibrations that determine log g. A larger catalogue, in which metallicity is determined directly from uvby photometry, is used to trace metallicity-dependent standard sequences for dwarf stars. We derive new standard sequences in the c_1,0 versus (b-y)_0 plane and in the c_1,0 versus (v-y)_0 plane for dwarf stars with 0.40 < (b-y)_0 < 0.95 and 1.10 < (v-y)_0 < 2.38. We recommend the calibrations by Ramirez & Me'endez (2005) for deriving metallicities from Stromgren photometry and find that intermediate band photometry, such as Stromgren photometry, more accurately than broad band photometry reproduces spectroscopically determined [Fe/H]. Stromgren photometry is also better at differentiating between dwarf and giant stars. We conclude that additional investigations of the differences between metallicities derived from ugriz photometry and intermediate-band photometry, such as Stromgren photometry, are required.
CoRoT-7 is an 11th magnitude K-star whose light curve shows transits with
depth of 0.3 mmag and a period of 0.854 d, superimposed on variability at the
precent level, due to the modulation of evolving active regions with the star's
23 d rotation period. In this paper, we revisit the published HARPS radial
velocity measurements of the object, which were previously used to estimate the
companion mass, but have been the subject of ongoing debate.
We build a realistic model of the star's activity during the HARPS
observations, by fitting simultaneously the line width (as measured by the
width of the cross-correlation function) and the line bisector, and use it to
evaluate the contribution of activity to the RV variations. The data show clear
evidence of errors above the level of the formal uncertainties, which are
accounted for neither by activity, nor by any plausible planet model, and
increase rapidly with decreasing signal-to-noise of the spectra. Allowing for
these, we re-evaluate the semi-amplitude of the CoRoT-7b signal, finding
K_b=1.6 +-1.3m/s, a tentative detection with a much reduced significance
compared to previous estimates. We also argue that the combined presence of
activity and additional errors preclude a meaningful search for additional
low-mass companions, despite previous claims to the contrary.
Taken at face value, our analysis points to a lower density for CoRoT-7b, the
1-sigma mass range spanning 1-4 M_Earth, and allowing for a wide range of bulk
compositions. In particular, an ice-rich composition is compatible with the RV
constraints. More generally, this study highlights the importance of a
realistic treatment of both activity and uncertainties, particularly in the
medium signal-to-noise ratio regime, which applies to most small planet
candidates from CoRoT and Kepler.
Three decades ago the first convincing evidence of microbial fossils in carbonaceous chondrites was discovered and reported by Hans Dieter Pflug and his collaborators. In addition to morphology, other data, notably laser mass spectroscopy, confirmed the identification of such structures as putative bacterial fossils. Balloon-borne cryosampling of the stratosphere enables recovery of fragile cometary dust aggregates with their structure and carbonaceous matter largely intact. Scanning electron microscope studies of texture and morphology of particles in the Cardiff collection, together with Energy Dispersive X-ray identifications, show two main types of putative bio-fossils - firstly organic-walled hollow spheres around 10 microns across, secondly siliceous diatom skeletons similar to those found in carbonaceous chondrites and terrestrial sedimentary rocks and termed "acritarchs". Since carbonaceous chondrites (particularly Type 1 chondrites) are thought to be extinct comets the data reviewed in this article provide strong support for theories of cometary panspermia.
Glint, the specular reflection of sunlight off Earth's oceans, may reveal the presence of oceans on an extrasolar planet. As an Earth-like planet nears crescent phases, the size of the ocean glint spot increases relative to the fraction of illuminated disk, while the reflectivity of this spot increases. Both effects change the planet's visible reflectivity as a function of phase. However, strong forward scattering of radiation by clouds can also produce increases in a planet's reflectivity as it approaches crescent phases, and surface glint can be obscured by Rayleigh scattering and atmospheric absorption. Here we explore the detectability of glint in the presence of an atmosphere and realistic phase-dependent scattering from oceans and clouds. We use the NASA Astrobiology Institute's Virtual Planetary Laboratory 3-D line-by-line, multiple-scattering spectral Earth model to simulate Earth's broadband visible brightness and reflectivity over an orbit. Our validated simulations successfully reproduce phase-dependent Earthshine observations. We find that the glinting Earth can be as much as 100% brighter at crescent phases than simulations that do not include glint, and that the effect is dependent on both orbital inclination and wavelength, where the latter dependence is caused by Rayleigh scattering limiting sensitivity to the surface. We show that this phenomenon may be observable using the James Webb Space Telescope (JWST) paired with an external occulter.
We present evidence for Quasi-Periodic Oscillations (QPOs) in the recurrent outburst emission from the soft gamma repeater SGR 1806-20 using NASA's Rossi X-ray Timing Explorer (RXTE) observations. By searching a sample of 30 bursts for timing signals at the frequencies of the QPOs discovered in the 2004 December 27 giant flare from the source, we find three QPOs at 84, 103, and 648 Hz in three different bursts. The first two QPOs lie within $\sim$ 1$\: \sigma$ from the 92 Hz QPO detected in the giant flare. The third QPO lie within $\sim$ 9$\: \sigma$ from the 625 Hz QPO also detected in the same flare. The detected QPOs are found in bursts with different durations, morphologies, and brightness, and are vindicated by Monte Carlo simulations, which set a lower limit confidence interval $\geq 4.3 \sigma$. We also find evidence for candidate QPOs at higher frequencies in other bursts with lower statistical significance. The fact that we can find evidence for QPOs in the recurrent bursts at frequencies relatively close to those found in the giant flare is intriguing and can offer insight about the origin of the oscillations. We confront our finding against the available theoretical models and discuss the connection between the QPOs we report and those detected in the giant flares. The implications to the neutron star properties are also discussed.
We report the results of an infrared Doppler survey designed to detect brown dwarf and giant planetary companions to a magnitude-limited sample of ultracool dwarfs. Using the NIRSPEC spectrograph on the Keck II telescope, we obtained approximately 600 radial velocity measurements over a period of six years for a sample of 59 late-M and L dwarfs spanning spectral types M8/L0 to L6. A subsample of 46 of our targets have been observed on three or more epochs. We rely on telluric CH4 absorption features in the Earth's atmosphere as a simultaneous wavelength reference and exploit the rich set of CO absorption features found in the K-band spectra of cool stars and brown dwarfs to measure radial velocities and projected rotational velocities. For a bright, slowly rotating M dwarf standard we demonstrate a radial velocity precision of 50 m/s, and for slowly rotating L dwarfs we achieve a typical radial velocity precision of approximately 200 m/s. This precision is sufficient for the detection of close-in giant planetary companions to mid-L dwarfs as well as more equal mass spectroscopic binary systems with small separations (a<2 AU). We present an orbital solution for the subdwarf binary LSR1610-0040 as well as an improved solution for the M/T binary 2M0320-04. We also combine our radial velocity measurements with distance estimates and proper motions from the literature to estimate the dispersion of the space velocities of the objects in our sample. Using a kinematic age estimate we conclude that our UCDs have an age of 5.0+0.7-0.6 Gyr, similar to that of nearby sun-like stars. We simulate the efficiency with which we detect spectroscopic binaries and find that the rate of tight (a<1 AU) binaries in our sample is 2.5+8.6-1.6%, consistent with recent estimates in the literature of a tight binary fraction of 3-4%. (abridged)
The presence of dust strongly affects the way we see galaxies and also the chemical abundances we measure in gas. It is therefore important to study he chemical evolution of galaxies by taking into account dust evolution. We aim at performing a detailed study of abundance ratios of high redshift objects and their dust properties. We focus on Lyman-Break galaxies (LBGs) and Quasar (QSO) hosts and likely progenitors of low- and high-mass present-day elliptical galaxies, respectively. We have adopted a chemical evolution model for elliptical galaxies taking account the dust production from low and intermediate mass stars, supernovae Ia, supernovae II, QSOs and both dust destruction and accretion processes. By means of such a model we have followed the chemical evolution of ellipticals of different baryonic masses. Our model complies with chemical downsizing. We made predictions for the abundance ratios versus metallicity trends for models of differing masses that can be used to constrain the star formation rate, initial mass function and dust mass in observed galaxies. We predict the existence of a high redshift dust mass-stellar mass relationship. We have found a good agreement with the properties of LBGs if we assume that they formed at redshift z=2-4. In particular, a non-negligible amount of dust is needed to explain the observed abundance pattern. We studied the QSO SDSS J114816, one of the most distant QSO ever observed (z=6.4), and we have been able to reproduce the amount of dust measured in this object. The dust is clearly due to the production from supernovae and the most massive AGB stars as well as from the grain growth in the interstellar medium. The QSO dust is likely to dominate only in the very central regions of the galaxies and during the early development of the galactic wind.
We use results from long-time core-collapse supernovae simulations to investigate the impact of the late time evolution of the ejecta and of the nuclear physics input on the calculated r-process abundances. Based on the latest hydrodynamical simulations, heavy r-process elements cannot be synthesized in the neutrino-driven winds that follow the supernova explosion. However, by artificially increasing the wind entropy, elements up to A=195 can be made. In this way one can reproduce the typical behavior of high-entropy ejecta where the r-process is expected to occur. We identify which nuclear physics input is more important depending on the dynamical evolution of the ejecta. When the evolution proceeds at high temperatures, an (ng, gn) equilibrium is reached and nuclear masses have a big impact on the abundances, while at low temperature there is a competition between neutron captures and beta decays. After neutrons are almost exhausted, matter decays to stability and our results show that in both cases neutron captures are key for determining the final abundances, the position of the peaks, and the formation of the rare-earth peak.
We present a new analysis of kinematic data of the young planetary nebula BD+30 3639. The data include spectroscopic long-slit and internal proper motion measurements. In this paper we also introduce a new type of mapping of kinematic proper motion data that we name "criss-cross" mapping. It basically consists of finding all points where extended proper motion vectors cross converge. From the crossing points a map is generated which helps to interpret the kinematic data. From the criss-cross mapping of BD+30 3639, we conclude that the kinematic center is approximately 0.5 arcsec offset to the South-East from the central star. The mapping does also show evidence for a non-homologous expansion of the nebula that is consistent with a disturbance aligned with the bipolar molecular bullets.
We report the discovery of HAT-P-17b,c, a multi-planet system with an inner transiting planet in a short-period, eccentric orbit and an outer planet in a 4.8 yr, nearly circular orbit. The inner planet, HAT-P-17b, transits the bright V = 10.54 early K dwarf star GSC 2717-00417, with an orbital period P = 10.338523 +/- 0.000009 d, orbital eccentricity e = 0.346 +/- 0.007, transit epoch T_c = 2454801.16945 +/- 0.00020, and transit duration 0.1691 +/- 0.0009 d. HAT-P-17b has a mass of 0.530 +/- 0.018 M_J and radius of 1.010 +/- 0.029 R_J yielding a mean density of 0.64 +/- 0.05 g cm^-3. This planet has a relatively low equilibrium temperature in the range 780-927 K, making it an attractive target for follow-up spectroscopic studies. The outer planet, HAT-P-17c, has a significantly longer orbital period P_2 = 1797^+58_-89 d and a minimum mass m_2 sin i_2 = 1.4^+1.1_-0.4 M_J. The orbital inclination of HAT-P-17c is unknown as transits have not been observed and may not be present. The host star has a mass of 0.86 +/- 0.04 M_Sun, radius of 0.84 +/- 0.02, effective temperature 5246 +/- 80 K, and metallicity [Fe/H] = 0.00 +/- 0.08. HAT-P-17 is the second multi-planet system detected from ground-based transit surveys.
One of the most attractive events in the pre-main sequence evolution is the FU Orionis (FUor) outburst. Because only a small number of FUor stars have been detected to date, photometric and spectral studies of every new object are of great interest. Recently, a new FUor candidate was discovered by Anton Khruslov - V582 Aur. To confirm the FUors nature of this object we started regular photometric observations with the telescopes of the National Astronomical Observatory Rozhen (Bulgaria). A high-resolution spectrum of V582 Aur was obtained with the 1.93 m telescope in Haute-Provence Observatory (France).
We build five-dimensional spherically symmetric wormholes within the DGP theory. We calculate the energy localized on the shell, and we find that the wormholes could be supported by matter not violating the energy conditions. We also show that solitonic shells characterized by zero pressure and zero energy can exist; thereafter we make some observations regarding their dynamic on the phase plane. In addition, we concentrate on the mechanical stability of wormholes under radial perturbation preserving the original spherical symmetry. In order to do that, we consider linearized perturbations around static solutions. We obtain that for certain values of the mass $\mu$ and crossover scale $r_{c}$ stable wormholes exist with very small values of squared speed sound. Unlike the case of Einstein's gravity, this type of wormholes fulfills the energy conditions. Finally, we show that the gravitational field associated with these wormhole configurations is attractive for $\mu>0$.
We study longstanding problem of cosmological clock in the context of Brans--Dicke theory of gravitation. We present the Hamiltonian formulation of the theory for a class of spatially homogenous cosmological models. Then, we show that formulation of the Brans--Dicke theory in the Einstein frame allows how an identification of an appropriate cosmological time variable, as a function of the scalar field in the theory, can be emerged in quantum cosmology. The classical and quantum results are applied to the Friedmann--Robertson--Walker cosmological models.
We compute a novel type of large non-Gaussianity due to small periodic features in general single field inflationary models. We show that the non-Bunch-Davies vacuum component generated by features, although has a very small amplitude, can have significant impact on the non-Gaussianity. Three mechanisms are turned on simultaneously in such models, namely the resonant effect, non-Bunch-Davies vacuum and higher derivative kinetic terms, resulting in a bispectrum with distinctive shapes and running. The size can be equal to or larger than that previously found in each single mechanism.
We study linear cosmological perturbations in the ``healthy extension'' of Horava-Lifshitz gravity which has recently been analyzed \cite{BPS2}. We find that there are two degrees of freedom for scalar metric fluctuations, but that one of them decouples in the infrared limit. Also, for appropriate choices of the parameters defining the Lagrangian, the extra mode can be made well-behaved even in the ultraviolet.
The violation of local ${\cal P}$ and ${\cal CP}$ invariance in QCD, as it is observed at RHIC, has been a subject of intense discussions for the last couple of years.Separately, a new thermalization scenario for heavy ion collisions through the event horizon as a manifestation of the Unruh effect, has been also suggested. In this paper we argue that these two, naively unrelated phenomena, are actually two sides of the same coin as they are deeply rooted into the same fundamental physics related to some very nontrivial topological features of QCD. We formulate the universality conjecture for ${\cal P}$ and ${\cal CP}$ odd effects in heavy ion collisions analogous to the universal thermal behaviour observed in all other high energy interactions.
The lowest order constrained variational (LOCV) technique has been used to
investigate some of the thermodynamic properties of spin polarized hot
asymmetric nuclear matter, such as the free energy, symmetry energy,
susceptibility and equation of state. We have shown that the symmetry energy of
the nuclear matter is substantially sensitive to the value of spin
polarization.
Our calculations show that the equation of state of the polarized hot
asymmetric nuclear matter is stiffer for the higher values of the polarization
as well as the isospin asymmetry parameter. Our results for the free energy and
susceptibility show that the spontaneous ferromagnetic phase transition cannot
occur for hot asymmetric matter.
We study cosmic-rays in decaying dark matter scenario, assuming that the dark matter is the lightest superparticle and it decays through a R-parity violating operator. We calculate the fluxes of cosmic-rays from the decay of the dark matter and those from the standard astrophysical phenomena in the same propagation model using the GALPROP package. We reevaluate the preferred parameters characterizing standard astrophysical cosmic-ray sources with taking account of the effects of dark matter decay. We show that, if energetic leptons are produced by the decay of the dark matter, the fluxes of cosmic-ray positron and electron can be in good agreements with both PAMELA and Fermi-LAT data in wide parameter region. It is also discussed that, in the case where sizable number of hadrons are also produced by the decay of the dark matter, the mass of the dark matter is constrained to be less than 200-300 GeV in order to avoid the overproduction of anti-proton. We also show that the cosmic gamma-ray flux can be consistent with the results of Fermi-LAT observation if the mass of the dark matter is smaller than nearly 4 TeV.
We study cosmological vector and tensor perturbations in Horava-Lifshitz gravity, adopting the most general Sotiriou-Visser-Weinfurtner generalization without the detailed balance but with projectability condition. After deriving the general formulas in a flat FRW background, we find that the vector perturbations are identical to those given in general relativity. This is true also in the non-flat cases. For the tensor perturbations, high order derivatives of the curvatures produce effectively an anisotropic stress, which could have significant efforts on the high-frequency modes of gravitational waves, while for the low-frenquency modes, the efforts are negligible. The power spectrum is scale-invariant in the UV regime, because of the particular dispersion relations. But, due to lower-order corrections, it will eventually reduce to that given in GR in the IR limit. Applying the general formulas to the de Sitter and power-law backgrounds, we calculate the power spectrum and index, using the uniform approximations, and obtain their analytical expressions in both cases.
We suggest the possibility of creation in the early Universe of stable domains of radius a few kilometers wide, formed by coherently excited states of $\pi$-mesons. Such domains appear dark to an external observer, since the decay rate of the said coherent pionic states into photons is vanishingly small. The related thermal insulation of the domains from the outer world could have allowed them to survive till present days. The estimated maximum radius and the period of rotation of such objects turn out to be compatible with those of certain pulsars.
In this paper, we propose two new models in $f(T)$ gravity to realize the crossing of the phantom divide line for the effective equation of state, and we then study the observational constraints on the model parameters. The best fit results suggest that the observations favor a crossing of the phantom divide line.
In order to extend the experimental database relevant for the astrophysical gamma-process towards the unexplored heavier mass region, the cross sections of the 151Eu(alpha,gamma)155Tb and 151Eu(alpha,n)154Tb reactions have been measured at low energies between 12 and 17 MeV using the activation technique. The results are compared with the predictions of statistical model calculations and it is found that the calculations overestimate the cross sections by about a factor of two. A sensitivity analysis shows that this discrepancy is caused by the inadequate description of the alpha+nucleus channel. A factor of two reduction of the reaction rate of 151Eu(alpha,gamma)155Tb in gamma-process network calculations with respect to theoretical rates using the optical potential by McFadden and Satchler (1966) is recommended.
We first comment on the search for a deviation from the linear photon dispersion relation, in particular based on cosmic photons from Gamma Ray Bursts. Then we consider the non-commutative space as a theoretical concept that could lead to such a deviation, which would be a manifestation of Lorentz Invariance Violation. In particular we review a numerical study of pure U(1) gauge theory in a 4d non-commutative space. Starting from a finite lattice, we explore the phase diagram and the extrapolation to the continuum and infinite volume. These simultaneous limits - taken at fixed non-commutativity - lead to a phase of broken Poincare symmetry, where the photon appears to be IR stable, despite a negative IR divergence to one loop.
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Our team is carrying out a multi-year observing program to directly image and characterize young extrasolar planets using the Near-Infrared Coronagraphic Imager (NICI) on the Gemini-South 8.1-meter telescope. NICI is the first instrument on a large telescope designed from the outset for high-contrast imaging, comprising a high-performance curvature adaptive optics system with a simultaneous dual-channel coronagraphic imager. Combined with state-of-the-art observing methods and data processing, NICI typically achieves ~2 magnitudes better contrast compared to previous ground-based or space-based programs, at separations inside of ~2 arcsec. In preparation for the Campaign, we carried out efforts to identify previously unrecognized young stars, to rigorously construct our observing strategy, and to optimize the combination of angular and spectral differential imaging. The Planet-Finding Campaign is in its second year, with first-epoch imaging of 174 stars already obtained out of a total sample of 300 stars. We describe the Campaign's goals, design, implementation, performance, and preliminary results. The NICI Campaign represents the largest and most sensitive imaging survey to date for massive (~1 Mjup) planets around other stars. Upon completion, the Campaign will establish the best measurements to date on the properties of young gas-giant planets at ~5-10 AU separations. Finally, Campaign discoveries will be well-suited to long-term orbital monitoring and detailed spectrophotometric followup with next-generation planet-finding instruments.
We derive stellar masses from SED fitting for ~400 Lyman Break Galaxies at z~4, 5, 6, and 7 from Hubble-WFC3/IR and Spitzer IRAC observations of the ERS field. Stellar Mass Functions (MFs) are determined from our new stellar mass M - UV luminosity relation and recent, deep UV Luminosity Functions (LFs). For the 299 z~4 galaxies we find that the M-Luv relation is a log-linear relation with a slope of -1.7 +/- 0.2, which results in luminosity-dependent M/Luv ratios, and large intrinsic scatter of ~0.5 dex. There is no evidence for M/L evolution from z~7 to z~4, suggesting that the specific SFR at a given mass does not evolve rapidly. Combining the observed M-Luv relation with the UV LFs results in steep MFs with slopes alpha_M ~-1.4 to -1.6 at low masses. This slope, however, is flatter than the MFs obtained from recent hydrodynamical simulations. We use these MFs to estimate the Stellar Mass Density (SMD) to a fixed Muv < -18 as a function of redshift and find a SMD growth proportional to (1+z)^(-3.4 +/- 0.8) from z~7 to z~4. We also compare the SMD growth to that from the observed SFR density, accounting for the LF evolution by using an evolving limit of 0.2L*(z). The resulting SMD growth proportional to (1+z)^(-2.8 +/- 0.9) shows a similar increasing trend to the integral of the SFR density proportional to (1+z)^(-6.3 +/- 0.6), but significant differences remain. These could result from too large dust corrections to the SFR at later times, stellar masses being overestimated at early times, or from non-monotonic star formation histories.
According to the no-hair theorem, astrophysical black holes are uniquely described by their mass and spin. In this paper, we review a new framework for testing the no-hair hypothesis with observations in the electromagnetic spectrum. The approach is formulated in terms of a Kerr-like spacetime containing a quadrupole moment that is independent of both mass and spin. If the no-hair theorem is correct, then any deviation from the Kerr metric quadrupole has to be zero. We show how upcoming VLBI imaging observations of Sgr A* as well as spectroscopic observations of iron lines from accreting black holes with IXO may lead to the first astrophysical test of the no-hair theorem.
We report a discovery of the circularly polarized CH $A^2\Delta-X^2\Pi$ and $B^2\Sigma^- -X^2\Pi$ molecular bands in the spectrum of the DQ white dwarf GJ 841B. This is only the second such object since the discovery of G99-37 in the 1970s. GJ 841B is also the first WD to unambiguously show polarization in the C_2 Swan bands. By modeling the intensity and circular polarization in the CH bands we determine the longitudinal magnetic field strength of 1.3 +- 0.5 MG and the temperature of 6100 +- 200 K in the absorbing region. We also present new observations of G99-37 and obtain estimates of the magnetic field strength 7.3 +- 0.3 MG and temperature 6200 +- 200 K, in good agreement with previous results.
The phenomenon of double-periodic Cepheid pulsation is still poorly understood. Recently we rediscussed the problem of modelling the double-periodic pulsation with non-linear hydrocodes. We showed that the published non-resonant double-mode models are incorrect, because they exclude the negative buoyancy effects. Aims. We continue our efforts to verify whether the Kuhfuss one-equation convection model with negative buoyancy included can reproduce the double-periodic Cepheid pulsation. Methods. Using the direct time integration hydrocode, which implements the Kuhfuss convection model, we search for stable double-periodic Cepheid models. We search for models pulsating in both fundamental and first overtone modes (F+1O), as well as in the two lowest order overtones (1O+2O). In the latter case, we focus on reproducing double-overtone Cepheids of the Large Magellanic Cloud (LMC). Results. We have found full amplitude non-linear beat Cepheid models of both types, F+1O and 1O+2O. In the case of F+1O models, the beat pulsation is most likely caused by the three-mode resonance, 2omega_1=omega_0+omega_2, while in the double-overtone models the underlying mechanism (resonant or non-resonant) cannot be identified beyond doubt. Double-periodic models found in our survey exist, however, only in narrow period ranges and cannot explain the majority of the observed double-periodic objects. Conclusions. With only little doubt left, we conclude that current one dimensional one-equation convection models are incapable of reproducing the majority of the observed beat Cepheids. Among the shortcomings of current pulsation hydrocodes, the simple treatment of convection seems to be the most severe one. Growing evidence for the presence of non-radial modes in Cepheids suggests that the interaction between radial and non-radial modes should also be investigated.
We previously reported observations of quasar spectra from the Keck telescope suggesting a smaller value of the fine structure constant, alpha, at high redshift. A new sample of 153 measurements from the ESO Very Large Telescope (VLT), probing a different direction in the universe, also depends on redshift, but in the opposite sense, that is, alpha appears on average to be larger in the past. The combined dataset is well represented by a spatial dipole, significant at the 4.1 sigma level, in the direction right ascension 17.3 +/- 0.6 hours, declination -61 +/- 9 degrees. A detailed analysis for systematics, using observations duplicated at both telescopes, reveals none which are likely to emulate this result.
Novae are thermonuclear explosions on a white dwarf surface fueled by mass accreted from a companion star. Current physical models posit that shocked expanding gas from the nova shell can produce X-ray emission but emission at higher energies has not been widely expected. Here, we report the Fermi Large Area Telescope detection of variable gamma-ray (0.1-10 GeV) emission from the recently-detected optical nova of the symbiotic star V407 Cygni. We propose that the material of the nova shell interacts with the dense ambient medium of the red giant primary, and that particles can be accelerated effectively to produce pi0 decay gamma-rays from proton-proton interactions. Emission involving inverse Compton scattering of the red giant radiation is also considered and is not ruled out.
When making use of tabulations of empirical bolometric corrections for stars (BC_V), a commonly overlooked fact is that while the zero point is arbitrary, the bolometric magnitude of the Sun (Mbol_Sun) that is used in combination with such tables cannot be chosen arbitrarily. It must be consistent with the zero point of BC_V so that the apparent brightness of the Sun is reproduced. The latter is a measured quantity, for which we adopt the value V_Sun = -26.76 +/- 0.03. Inconsistent values of Mbol_Sun are listed in many of the most popular sources of BC_V. We quantify errors that are introduced by not paying attention to this detail. We also take the opportunity to reprint the BC_V coefficients of the often used polynomial fits by Flower (1996), which were misprinted in the original publication.
A novel method to characterize the topology of the early-universe intergalactic medium during the epoch of cosmic reionization is presented. The 21-cm radiation background from high redshift is analyzed through calculation of the 2-dimensional (2D) genus. The radiative transfer of hydrogen-ionizing photons and ionization-rate equations are calculated in a suite of numerical simulations under various input parameters. The 2D genus is calculated from the mock 21-cm images of high-redshift universe. We construct the 2D genus curve by varying the threshold differential brightness temperature, and compare this to the 2D genus curve of the underlying density field. We find that (1) the 2D genus curve reflects the evolutionary track of cosmic reionization and (2) the 2D genus curve can discriminate between certain reionization scenarios and thus indirectly probe the properties of radiation-sources. Choosing the right beam shape of a radio antenna is found crucial for this analysis. Square Kilometer Array (SKA) is found to be a suitable apparatus for this analysis in terms of sensitivity, even though some deterioration of the data for this purpose is unavoidable under the planned size of the antenna core.
The Atacama B-mode Search (ABS) experiment is a 145 GHz polarimeter designed to measure the B-mode polarization of the Cosmic Microwave Background (CMB) at large angular scales. The ABS instrument will ship to the Atacama Desert of Chile fully tested and ready to observe in 2010. ABS will image large-angular-scale CMB polarization anisotropies onto a focal plane of 240 feedhorn-coupled, transition-edge sensor (TES) polarimeters, using a cryogenic crossed-Dragone design. The ABS detectors, which are fabricated at NIST, use orthomode transducers to couple orthogonal polarizations of incoming radiation onto separate TES bolometers. The incoming radiation is modulated by an ambient-temperature half-wave plate in front of the vacuum window at an aperture stop. Preliminary detector characterization indicates that the ABS detectors can achieve a sensitivity of 300 $\mu K \sqrt{s}$ in the field. This paper describes the ABS optical design and detector readout scheme, including feedhorn design and performance, magnetic shielding, focal plane architecture, and cryogenic electronics.
We present IRAC/MIPS Spitzer Space Telescope observations of the solar type and the low mass stellar population of the young (~5 Myr) Lambda Orionis cluster. Combining optical and 2MASS photometry, we identify 436 stars as probable members of the cluster. Given the distance (450 pc) and the age of the cluster, our sample ranges in mass from 2 solar mass to objects below the substellar limit. With the addition of the Spitzer mid-infrared data, we have identified 49 stars bearing disks in the stellar cluster. Using spectral energy distribution (SED) slopes, we place objects in several classes: non-excess stars (diskless), stars with optically thick disks, stars with ``evolved disks''( with smaller excesses than optically thick disk systems), and ``transitional disks'' candidates (in which the inner disk is partially or fully cleared). The disk fraction depends on the stellar mass, ranging from ~6% for K type stars (Rc-J<2) to ~27% for stars with spectral type M5 or later (Rc-J>4). We confirm the dependence of disk fraction on stellar mass in this age range found in other studies. Regarding clustering levels, the overall fraction of disks in the Lambda Orionis cluster is similar to those reported in other stellar groups with ages normally quoted as ~5 Myr.
We present an analysis of highly magnetized neutron stars "magnetars", in search for high frequency oscillations in the recurrent emission from the soft gamma repeater SGR 1806-20, and we discuss the physical interpretation of these oscillations and its implications on the neutron star properties and structure. We present evidence for Quasi-Periodic Oscillations (QPOs) in the recurrent outburst activity from SGR 1806-20 using RXTE observations. By searching for timing signals at the frequencies of the QPOs discovered in the 2004 December 27 giant flare from the source, we find three QPOs at 84, 103, and 648 Hz in three different bursts. The first two QPOs lie within 8.85% and 11.83%, respectively, from the 92 Hz QPO detected in the giant flare. The third QPO lie within 3.75% from the 625 Hz QPO also detected in the same flare. The detected QPOs are found in bursts with different durations, morphologies, and brightness, and are vindicated by Monte Carlo simulations. We also find evidence for candidate QPOs at higher frequencies in other bursts with lower statistical significance. The fact that we can find evidence for QPOs in the recurrent bursts at frequencies relatively close to those found in the giant flare is intriguing and can offer insight about the origin of the oscillations. We confront our findings against the available theoretical models and discuss the physical interpretation of these QPOs. The leading interpretation for the origin of magnetar QPOs suggests that these toroidal seismic oscillatory modes are most likely to be excited by a crustquake of the neutron star crust. Other models have been proposed to explain the magnetar QPO phenomena including magnetospheric oscillations, magnetic flux tubes and modes of a passive debris disk. Theoretical modeling and observation of QPOs will be very useful in putting stringent constraints on neutron star equation of state.
In this work we investigate higher order statistics for the $\lcdm$ and ReBEL scalar-interacting dark matter models by analyzing $180\hmpc$ dark matter N-body simulation ensembles. The N-point correlation functions and the related hierarchical amplitudes, such as skewness and kurtosis, are computed using the Count-In-Cells method. Our studies demonstrate that the hierarchical amplitudes $S_n$ of the scalar-interacting dark matter model significantly deviate from the values in the $\lcdm$ cosmology on scales comparable and smaller then the screening length $r_s$ of a given scalar-interacting model. The corresponding additional forces that enhance the total attractive force exerted on dark matter particles at galaxy scales lowers the values of the hierarchical amplitudes $S_n$. We conclude that hypothetical additional exotic interactions in the dark matter sector should leave detectable markers in the higher-order correlation statistics of the density field. We focussed in detail on the redshift evolution of the dark matter field's skewness and kurtosis. From this investigation we find that the deviations from the canonical $\lcdm$ model introduced by the presence of the ``fifth'' force attain a maximum value at redshifts $0.5<z<2$. We therefore conclude that moderate redshift data are better suited for setting observational constraints on the investigated ReBEL models.
We assess the detection prospects of a gravitational wave background associated with sub-luminous gamma-ray bursts (SL-GRBs). We assume that the central engines of a significant proportion of these bursts are provided by newly born magnetars and consider two plausible GW emission mechanisms. Firstly, the deformation-induced triaxial GW emission from a newly born magnetar. Secondly, the onset of a secular bar-mode instability, associated with the long lived plateau observed in the X-ray afterglows of many gamma-ray bursts (Corsi & Meszaros 2009a). With regards to detectability, we find that the onset of a secular instability is the most optimistic scenario: under the hypothesis that SL-GRBs associated with secularly unstable magnetars occur at a rate of (48; 80)Gpc^{-3}yr^{-1} or greater, cross-correlation of data from two Einstein Telescopes (ETs) could detect the GW background associated to this signal with a signal-to-noise ratio of 3 or greater after 1 year of observation. Assuming neutron star spindown results purely from triaxial GW emissions, we find that rates of around (130;350)Gpc^{-3}yr^{-1} will be required by ET to detect the resulting GW background. We show that a background signal from secular instabilities could potentially mask a primordial GW background signal in the frequency range where ET is most sen- sitive. Finally, we show how accounting for cosmic metallicity evolution can increase the predicted signal-to-noise ratio for background signals associated with SL-GRBs.
Much of our understanding of modern astrophysics rest on the notion that the Initial Mass Function (IMF) is universal. Our observations of a sample of HI-selected galaxies in the light of H-alpha and the far-ultraviolet (FUV) challenge this result. The flux ratio H-alpha/FUV from these star formation tracers shows strong correlations with surface-brightness in H-alpha and the R band: Low Surface Brightness galaxies have lower H-alpha/FUV ratios compared to High Surface Brightness galaxies as well as compared to expectations from equilibrium models of constant star formation rate using commonly favored IMF parameters. I argue against recent claims in the literature that attribute these results to errors in the dust corrections, the micro-history of star formation, sample issues or escaping ionizing photons. Instead, the most plausible explanation for the correlations is the systematic variations of the upper mass limit and/or the slope of the IMF. I present a plausible physical scenario for producing the IMF variations, and suggest future research directions.
We present the numerical simulations of winds from evolved giant stars using a fully non-linear, time dependent 2.5-dimensional magnetohydrodynamic (MHD) code. This study extends our previous fully non-linear MHD wind simulations to include a broadband frequency spectrum of Alfv\'en waves that drive winds from red giant stars. We calculated four Alfv\'en wind models that cover the whole range of Alfv\'en wave frequency spectrum to characterize the role of freely propagated and reflected Alfv\'en waves in the gravitationally stratified atmosphere of a late-type giant star. Our simulations demonstrate that, unlike linear Alfv\'en wave-driven wind models, a stellar wind model based on plasma acceleration due to broadband non-linear Alfv\'en waves, can consistently reproduce the wide range of observed radial velocity profiles of the winds, their terminal velocities and the observed mass loss rates. Comparison of the calculated mass loss rates with the empirically determined mass loss rate for alpha Tau suggests an anisotropic and time-dependent nature of stellar winds from evolved giants.
In the past years a wealth of observations has unraveled the structural properties of dark and luminous mass distribution in galaxies, a benchmark for understanding dark matter and the process of galaxy formation. The study of the kinematics of over thousand spirals has evidenced a dark-luminous matter coupling and the presence of a series of scaling laws, pictured by the Universal Rotation Curve paradigm, an intriguing observational scenario not easily explained by present theories of galaxy formation.
The 88 constellations as defined by the IAU segment the sky into regions, separated by an intricate set of boundaries. A binary tree decomposition of this landscape is given which tessellates the celestial sphere into rectangles. This allows a fast determination of the constellation membership of any given sky coordinate.
The Large Area Telescope on the Fermi gamma-ray Space Telescope (FGST, ex-GLAST) provides unprecedented sensitivity for all-sky monitoring of gamma-ray activity. It is an adequate telescope to detect transient sources, since the observatory scans the entire sky every three hours and allows a general search for flaring activity on daily timescale. This search is conducted automatically as part of the ground processing of the data and allows a fast response -less than a day- to transient events. Follow-up observations in X-rays, optical, and radio are then performed to attempt to identify the origin of the emission and probe the possible existence of new transient gamma-ray sources in the Galaxy. Since its launch on 11th June 2008, Fermi-LAT has detected nearly 1500 gamma-ray sources, nearly half of them being extragalactic. After a brief census of detected celestial objects, we report here on the LAT results focusing on Galactic transient binary systems. The Fermi-LAT has detected 2 gamma-ray binaries, a microquasar and an unexpected new type of gamma-ray source: a symbiotic nova.
DSPSR is a high-performance, open-source, object-oriented, digital signal processing software library and application suite for use in radio pulsar astronomy. Written primarily in C++, the library implements an extensive range of modular algorithms that can optionally exploit both multiple-core processors and general-purpose graphics processing units. After over a decade of research and development, DSPSR is now stable and in widespread use in the community. This paper presents a detailed description of its functionality, justification of major design decisions, analysis of phase-coherent dispersion removal algorithms, and demonstration of performance on some contemporary microprocessor architectures.
Small-scale transient phenomena in the quiet Sun are believed to play an important role in coronal heating and solar wind generation. One of them named as "X-ray jet" is the subject of our study. We indent to investigate the dynamics, evolution and physical properties of this phenomenon. We combine spatially and temporally multi-instrument observations obtained simultaneously with the SUMER spectrometer onboard SoHO, EIS and XRT onboard Hinode, and EUVI/SECCHI onboard the Ahead and Behind STEREO spacecrafts. We derive plasma parameters such as temperatures and densities as well as dynamics by using spectral lines formed in the temperature range from 10 000 K to 12 MK. We also use image difference technique to investigate the evolution of the complex structure of the studied phenomenon. With the available unique combination of data we were able to establish that the formation of a jet-like event is triggered by not one but several energy depositions which are most probably originating from magnetic reconnection. Each energy deposition is followed by the expulsion of pre-existing or new reconnected loops and/or collimated flow along open magnetic field lines. We derived in great detail the dynamic process of X-ray jet formation and evolution. We also found for the first time spectroscopically in the quiet Sun a temperature of 12~MK and density of 4 10^10~cm^-3 in a reconnection site. We raise an issue concerning an uncertainty in using the SUMER Mg X 624.9 A line for coronal diagnostics. We clearly identified two types of up-flow: one collimated up-flow along open magnetic field lines and a plasma cloud formed from the expelled BP loops. We also report a cooler down-flow along closed magnetic field lines. A comparison is made with a model developed by Moreno-Insertis \etal\ (2008).
We investigate protostellar collapse of molecular cloud cores by numerical simulations, taking into account turbulence and magnetic fields. By using the adaptive mesh refinement technique, the collapse is followed over a wide dynamic range from the scale of a turbulent cloud core to that of the first core. The cloud core is lumpy in the low density region owing to the turbulence, while it has a smooth density distribution in the dense region produced by the collapse. The shape of the dense region depends mainly on the mass of the cloud core; a massive cloud core tends to be prolate while a less massive cloud core tends to be oblate. In both cases, anisotropy of the dense region increases during the isothermal collapse. The minor axis of the dense region is always oriented parallel to the local magnetic field. All the models eventually yield spherical first cores supported mainly by the thermal pressure. Most of turbulent cloud cores exhibit protostellar outflows around the first cores. These outflows are classified into two types, bipolar and spiral flows, according to the morphology of the associated magnetic field. Bipolar flow often appears in the less massive cloud core. The rotation axis of the first core is oriented parallel to the local magnetic field for bipolar flow, while the orientation of the rotation axis from the global magnetic field depends on the magnetic field strength. In spiral flow, the rotation axis is not aligned with the local magnetic field.
We report two spectropolarimetric observations of SN 2005hk, which is a close copy of the "very peculiar" SN 2002cx, showing low peak luminosity, slow decline, high ionization near peak and an unusually low expansion velocity of only about 7,000 km s^-1. Further to the data presented by Chornock et al., (2006), at -4 days before maximum, we present data of this object taken on 9 November 2005 (near maximum) and 23 November (+ two weeks) that show the continuum and most of the spectral lines to be polarized at levels of about 0.2-0.3%. At both epochs the data corresponds to the Spectropolarimetric Type D1. The general low level of line polarization suggests that the line forming regions for most species observed in the spectrum have a similar shape to that of the photosphere, which deviates from a spherical symmetry by <10%. In comparison with spectropolarimetry of Type Ia and Core-collapse SNe at similar epochs, we find that the properties of SN 2005hk are most similar to those of Type Ia SNe. In particular, we find the low levels of continuum and line polarization to indicate that the explosion mechanism is approximately spherical, with homogeneous ejecta (unlike the chemically segregated ejecta of CCSNe). We discuss the possibility that SN 2005hk was the result of the pure deflagration of a white dwarf and note the issues concerning this interpretation.
We report the discovery of an active galactic nucleus (AGN) pair in the interacting galaxy system IRAS 20210+1121 at z = 0.056. An XMM-Newton observation reveals the presence of an obscured (Nh ~ 5 x 10^{23} cm^-2), Seyfert-like (L_{2-10 keV} = 4.7 x 10^{42} erg/s) nucleus in the northern galaxy, which lacks unambiguous optical AGN signatures. Our spectral analysis also provides strong evidence that the IR-luminous southern galaxy hosts a Type 2 quasar embedded in a bright starburst emission. In particular, the X-ray primary continuum from the nucleus appears totally depressed in the XMM-Newton band as expected in case of a Compton-Thick absorber, and only the emission produced by Compton scattering ('reflection') of the continuum from circumnuclear matter is seen. As such, IRAS 20210+1121 seems to provide an excellent opportunity to witness a key, early phase in the quasar evolution predicted by the theoretical models of quasar activation by galaxy collisions.
We present a study of shape, spectra and polarization properties of giant
pulses (GPs) from the Crab pulsar at the very high frequencies of 8.5 and 15.1
GHz. Studies at 15.1 GHz were performed for the first time. Observations were
conducted with the 100-m radio telescope in Effelsberg in Oct-Nov 2007 at the
frequencies of 8.5 and 15.1 GHz as part of an extensive campaign of
multi-station multi-frequency observations of the Crab pulsar. A selection of
the strongest pulses was recorded with a new data acquisition system, based on
a fast digital oscilloscope, providing nanosecond time resolution in two
polarizations in a bandwidth of about 500 MHz. We analyzed the pulse shapes,
polarisation and dynamic spectra of GPs as well as the cross-correlations
between their LHC and RHC signals. No events were detected outside main pulse
and interpulse windows. GP properties were found to be very different for GPs
emitted at longitudes of the main pulse and the interpulse. Cross-correlations
of the LHC and RHC signals show regular patterns in the frequency domain for
the main pulse, but these are missing for the interpulse GPs. We consider
consequences of application of the rotating vector model to explain the
apparent smooth variation in the position angle of linear polarization for main
pulse GPs.
We also introduce a new scenario of GP generation as a direct consequence of
the polar cap discharge. We find further evidence for strong nano-shot
discharges in the magnetosphere of the Crab pulsar. The repetitive frequency
spectrum seen in GPs at the main pulse phase is interpreted as a diffraction
pattern of regular structures in the emission region. The interpulse GPs
however have a spectrum that resembles that of amplitude modulated noise.
Propagation effects may be the cause of the differences.
We present the results of our analysis of cosmic-ray electrons using about 8 million electron candidates detected in the first 12 months on-orbit by the Fermi Large Area Telescope. This work extends our previously-published cosmic-ray electron spectrum down to 7 GeV, giving a spectral range of approximately 2.5 decades up to 1 TeV. We describe in detail the analysis and its validation using beam-test and on-orbit data. In addition, we describe the spectrum measured via a subset of events selected for the best energy resolution as a cross-check on the measurement using the full event sample. Our electron spectrum can be described with a power law $\propto {\rm E}^{-3.08 \pm 0.05}$ with no prominent spectral features within systematic uncertainties. Within the limits of our uncertainties, we can accommodate a slight spectral hardening at around 100 GeV and a slight softening above 500 GeV.
We analyze the propagation of waves in sunspots from the photosphere to the chromosphere using time series of co-spatial Ca II H intensity spectra (including its line blends) and polarimetric spectra of Si I 10827 and the He I 10830 multiplet. From the Doppler shifts of these lines we retrieve the variation of the velocity along the line-of-sight at several heights. Phase spectra are used to obtain the relation between the oscillatory signals. Our analysis reveals standing waves at frequencies lower than 4 mHz and a continuous propagation of waves at higher frequencies, which steepen into shocks in the chromosphere when approaching the formation height of the Ca II H core. The observed non-linearities are weaker in Ca II H than in He I lines. Our analysis suggests that the Ca II H core forms at a lower height than the He I 10830 line: a time delay of about 20 s is measured between the Doppler signal detected at both wavelengths. We fit a model of linear slow magnetoacoustic wave propagation in a stratified atmosphere with radiative losses according to Newton's cooling law to the phase spectra and derive the difference in the formation height of the spectral lines. We show that the linear model describes well the wave propagation up to the formation height of Ca II H, where non-linearities start to become very important.
Context: we study the convection-pulsation coupling that occurs in cold
Cepheids close to the red edge of the classical instability strip. In these
stars, the surface convective zone is supposed to stabilise the radial
oscillations excited by the kappa-mechanism.
Aims: we study the influence of the convective motions onto the amplitude and
the nonlinear saturation of acoustic modes excited by kappa-mechanism. We are
interested in determining the physical conditions needed to lead to a quenching
of oscillations by convection.
Methods: we compute two-dimensional nonlinear simulations (DNS) of the
convection-pulsation coupling, in which the oscillations are sustained by a
continuous physical process: the kappa-mechanism. Thanks to both a frequential
analysis and a projection of the physical fields onto an acoustic subspace, we
study how the convective motions affect the unstable radial oscillations.
Results: depending on the initial physical conditions, two main behaviours
are obtained: (i) either the unstable fundamental acoustic mode has a large
amplitude, carries the bulk of the kinetic energy and shows a nonlinear
saturation similar to the purely radiative case; (ii) or the convective motions
affect significantly the mode amplitude that remains very weak. In this second
case, convection is quenching the acoustic oscillations. We interpret these
discrepancies in terms of the difference in density contrast: larger
stratification leads to smaller convective plumes that do not affect much the
purely radial modes, while large-scale vortices may quench the oscillations.
One of the principal scientific reasons for wanting to resume in situ exploration of the lunar surface is to gain access to the record it contains of early Solar System history. Part of this record will pertain to the galactic environment of the Solar System, including variations in the cosmic ray flux, energetic galactic events (e.g, supernovae and/or gamma-ray bursts), and passages of the Solar System through dense interstellar clouds. Much of this record is of astrobiological interest as these processes may have affected the evolution of life on Earth, and perhaps other Solar System bodies. We argue that this galactic record, as for that of more local Solar System processes also of astrobiological interest, will be best preserved in ancient, buried regolith ('palaeoregolith') deposits in the lunar near sub-surface. Locating and sampling such deposits will be an important objective of future lunar exploration activities.
We have previously shown that a very small amount of Lorentz invariance violation (LIV), which suppresses photomeson interactions of ultrahigh energy cosmic rays (UHECRs) with cosmic background radiation (CBR) photons, can produce a spectrum of cosmic rays that is consistent with that currently observed by the Pierre Auger Observatory (PAO) and HiRes experiments. Here, we calculate the corresponding flux of high energy neutrinos generated by the propagation of UHECR protons through the CBR in the presence of LIV. We find that LIV produces a reduction in the flux of the highest energy neutrinos and a reduction in the energy of the peak of the neutrino energy flux spectrum, both depending on the strength of the LIV. Thus, observations of the UHE neutrino spectrum provide a clear test for the existence and amount of LIV at the highest energies. We further discuss the ability of current and future proposed detectors make such observations.
We show that in the exponential $f(T)$ model studied by E. Linder [arXiv:1005.3039, Phys.Rev.D 81, 127301 (2010)], it is impossible to have the crossing of the phantom divide line $w_{\mathrm{DE}}=-1$.
Beamforming is central to the processing function of all phased arrays and becomes particularly challenging with a large number of antenna element (e.g. >100,000). The ability to beamform efficiently with reasonable power requirements is discussed in this paper. Whilst the most appropriate beamforming technology will change over time due to semiconductor and processing developments, we present a hierarchical structure which is technology agnostic and describe both Radio-Frequency (RF) and digital hierarchical beamforming approaches. We present implementations of both RF and digital beamforming systems on two antenna array demonstrators, namely the Electronic Multi Beam Radio Astronomy ConcEpt (EMBRACE) and the dualpolarisation all-digital array (2-PAD). This paper will compare and contrast both digital and analogue implementations without considering the deep system design of these arrays.
In this paper, we consider the problem of optimum multi-domain real-time beamforming and high-precision beam pattern positioning in application to very large wideband array antennas, particularly to the Square Kilometre Array (SKA) aperture array antenna. We present a new structure for wideband space-frequency beamforming and beamsteering that maximizes detectability of cosmic signals over the array operational frequency range.
We have made the first map of CO(J=3-2) emission covering the disk of the
edge-on galaxy, NGC~4631, which is known for its spectacular gaseous halo. The
strongest emission, which we model with a Gaussian ring,occurs within a radius
of 5 kpc. Weaker disk emission is detected out to radii of 12 kpc, the most
extensive molecular component yet seen in this galaxy. From comparisons with
infrared data, we find that CO(J=3-2) emission more closely follows the hot
dust component, rather than the cold dust,consistent with it being a good
tracer of star formation. The first maps of $R_{3-2/1-0}$, H$_2$ mass surface
density and SFE have been made for the inner 2.4 kpc radius region. Only 20\%
of the SF occurs in this region and excitation conditions are typical of galaxy
disks, rather than of central starbursts. The SFE suggests long gas consumption
timescales ($>$ $10^9$ yr).
The velocity field is dominated by a steeply rising rotation curve in the
region of the central molecular ring followed by a flatter curve in the disk. A
very steep gradient in the rotation curve is observed at the nucleus, providing
the first evidence for a central concentration of mass:
M$_{dyn}\,=\,5\,\times\,10^7$ M$_\odot$ within a radius of 282 pc. The velocity
field shows anomalous features indicating the presence of molecular outflows;
one of them is associated with a previously observed CO(J=1-0) expanding shell.
Consistent with these outflows is the presence of a thick ($z$ up to $1.4$ kpc)
CO(J=3-2) disk. We suggest that the interaction between NGC~4631 and its
companion(s) has agitated the disk and also initiated star formation which was
likely higher in the past than it is now. These may be necessary conditions for
seeing prominent halos.
The C-Band All-Sky Survey (C-BASS) aims to produce sensitive, all-sky maps of diffuse Galactic emission at 5 GHz in total intensity and linear polarization. These maps will be used (with other surveys) to separate the several astrophysical components contributing to microwave emission, and in particular will allow an accurate map of synchrotron emission to be produced for the subtraction of foregrounds from measurements of the polarized Cosmic Microwave Background. We describe the design of the analog instrument, the optics of our 6.1 m dish at the Owens Valley Radio Observatory, the status of observations, and first-look data.
We performed a visual and numeric analysis of the deviation of the microwave background temperature on WMAP maps. We proved that the microwave background inhomogeneities possess the property of the central symmetry resulting from the two kinds of central symmetry of the opposite signs. After the computer modeling we have established the relation between the coefficient of the central symmetry and the values of the symmetrical and antisymmetrical components of the deviation of the temperature. The obtained distribution of the symmetry coefficient on the map of the celestial sphere in Mollweide projection testifies on a contribution of both kinds of central symmetry which is approximately equal on the average in absolute magnitude but opposite by sign and where one kind of the central symmetry prevails on some sections of the celestial sphere and another kind - on the others. The average resulting value of the symmetry coefficient on the sections with angular measures less than 15-200 varies within the range from -50% to +50% with some prevalence of the antisymmetry - the average coefficient of the central symmetry for the whole celestial sphere is -4 +/- 1%. (antisymmetry 4%). Small scale structure of the distribution indicates that it is the result of the combined action of the mechanisms of the central symmetry and central antisymmetry, close to 100%.
SGR~0501+4516 was discovered with the Swift satellite on 2008 August 22, after it emitted a series of very energetic bursts. Since then, the source was extensively monitored with Swift, the Rossi X-ray Timing Explorer (RXTE) and observed with Chandra and XMM-Newton, providing a wealth of information about its outburst behavior and burst induced changes of its persistent X-ray emission. Here we report the most accurate location of SGR~0501+4516 (with an accuracy of 0.11'') derived with Chandra. Using the combined RXTE, Swift/X-ray Telescope, Chandra and XMM-Newton observations we construct a phase connected timing solution with the longest time baseline (~240 days) to date for the source. We find that the pulse profile of the source is energy dependent and exhibits remarkable variations associated with the SGR~0501+4516 bursting activity. We also find significant spectral evolution (hardening) of the source persistent emission associated with bursts. Finally, we discuss the consequences of the SGR~0501+4516 proximity to the supernova remnant, SNR G160.9+2.6 (HB9).
FU Orionis is the prototype of a class of eruptive young stars (``FUors'') characterized by strong optical outbursts. We recently completed an exploratory survey of FUors using XMM-Newton to determine their X-ray properties, about which little was previously known. The prototype FU Ori and V1735 Cyg were detected. The X-ray spectrum of FU Ori was found to be unusual, consisting of a cool moderately-absorbed component plus a hotter component viewed through an absorption column density that is an order of magnitude higher. We present here a sensitive (99 ks) follow-up X-ray observation of FU Ori obtained at higher angular resolution with Chandra ACIS-S. The unusual multi-component spectrum is confirmed. The hot component is centered on FU Ori and dominates the emission above 2 keV. It is variable (a signature of magnetic activity) and is probably coronal emission originating close to FU Ori's surface viewed through cool gas in FU Ori's strong wind or accretion stream. In contrast, the X-ray centroid of the soft emission below 2 keV is offset 0.20 arcsec to the southeast of FU Ori, toward the near-IR companion (FU Ori S). This offset amounts to slightly less than half the separation between the two stars. The most likely explanation for the offset is that the companion contributes significantly to the softer X-ray emission below 2 keV (and weakly above 2 keV). The superimposed X-ray contributions from FU Ori and the companion resolve the paradox posed by XMM-Newton of an apparently single X-ray source viewed through two different absorption columns.
We show that the popular ILC approach is unstable in respect to the division of the sample of map pixels to the set of ``homogeneous'' subsamples. For suitable choice of such subsamples we can obtain the restored CMB signal with amplitudes ranged from zero to the amplitudes of the observed signal. We propose approach which allows us to obtain reasonable estimates of $C_\ell$ at $\ell\leq 30$ and similar to WMAP $C_\ell$ for larger $\ell$. With this approach we reduce some anomalies of the WMAP results. In particular, our estimate of the quadrupole is well consistent to theoretical one, the effect of the ``axis of evil'' is suppressed and the symmetry of the north and south galactic hemispheres increases. This results can change estimates of quadrupole polarization and the redshift of reionization of the Universe. We propose also new simple approach which can improve WMAP estimates of high $\ell$ power spectrum.
The majority of atomic hydrogen Br{\gamma} emission detected in the spectra of young stellar objects (YSOs) is believed to arise from the recombination regions associated with the magnetospheric accretion of circumstellar disk material onto the forming star. In this paper, we present the results of a K-band IFU spectroscopic study of Br{\gamma} emission in eight young protostars: CW Tau, DG Tau, Haro 6-10, HL Tau, HV Tau C, RW Aur, T Tau and XZ Tau. We spatially resolve Br{\gamma} emission structures in half of these young stars and find that most of the extended emission is consistent with the location and velocities of the known Herbig-Haro flows associated with these systems. At some velocities through the Br{\gamma} line profile, the spatially extended emission comprises 20% or more of the integrated flux in that spectral channel. However, the total spatially extended Br{\gamma} is typically less than ~10% of the flux integrated over the full emission profile. For DG Tau and Haro 6-10 S, we estimate the mass outflow rate using simple assumptions about the hydrogen emission region, and compare this to the derived mass accretion rate. We detect extended Br{\gamma} in the vicinity of the more obscured targets in our sample and conclude that spatially extended Br{\gamma} emission may exist toward other stars, but unattenuated photospheric flux probably limits its detectability.
The balance of evidence indicates that individual galaxies and groups or clusters of galaxies are embedded in enormous distributions of cold, weakly interacting dark matter. These dark matter 'halos' provide the scaffolding for all luminous structure in the universe, and their properties comprise an essential part of the current cosmological model. I review the internal properties of dark matter halos, focussing on the simple, universal trends predicted by numerical simulations of structure formation. Simulations indicate that halos should all have roughly the same spherically-averaged density profile and kinematic structure, and predict simple distributions of shape, formation history and substructure in density and kinematics, over an enormous range of halo mass and for all common variants of the concordance cosmology. I describe observational progress towards testing these predictions by measuring masses, shapes, profiles and substructure in real halos, using baryonic tracers or gravitational lensing. An important property of simulated halos (possibly the most important property) is their dynamical 'age', or degree of internal relaxation. The age of a halo may have almost as much effect as its mass in determining the state of its baryonic contents, so halo ages are also worth trying to measure observationally. I review recent gravitational lensing studies of galaxy clusters which should measure substructure and relaxation in a large sample of individual cluster halos, producing quantitative measures of age that are well-matched to theoretical predictions. The age distributions inferred from these studies will lead to second-generation tests of the cosmological model, as well as an improved understanding of cluster assembly and the evolution of galaxies within clusters.
We present the 'simage' software suite for the simulation of artificial extragalactic images, based empirically around real observations of the Hubble Ultra Deep Field (UDF). The simulations reproduce galaxies with realistic and complex morphologies via the modeling of UDF galaxies as shapelets. Images can be created in the B, V, i and z bands for both space- and ground-based telescopes and instruments. The simulated images can be produced for any required field size, exposure time, Point Spread Function (PSF), telescope mirror size, pixel resolution, field star density, and a variety of detector noise sources. It has the capability to create images with both a pre-determined number of galaxies or one calibrated to the number counts of pre-existing data sets such as the HST COSMOS survey. In addition, simple options are included to add a known weak gravitational lensing (both shear and flexion) to the simulated images. The software is available in Interactive Data Language (IDL) and can be freely downloaded for scientific, developmental and teaching purposes.
The remarkable detection of a spatial variation in the fine-structure constant, alpha, from quasar absorption systems must be independently confirmed by complementary searches. In this letter, we discuss how terrestrial measurements of time-variation of the fundamental constants in the laboratory, meteorite data, and analysis of the Oklo nuclear reactor can be used to corroborate the spatial variation seen by astronomers. Furthermore, we show that spatial variation of the fundamental constants may be observable as spatial anisotropy in the cosmic microwave background, the accelerated expansion (dark energy), and large-scale structure of the Universe.
We propose a survey of a rocky region in the north-east part of Sudan, using the satellite imagery from Google Maps. In particular we analyse the region which lies to the north of Nakasib Suture. Images reveal craters and ring complexes. To enhance their features, images are processed with a method based on fractional calculus. Two of these structures are proposed as possible impact craters.
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In this Letter we report a spectroscopic confirmation of the association of HLX-1, the brightest ultra-luminous X-ray source, with the galaxy ESO 243-49. At the host galaxy distance of 95 Mpc, the maximum observed 0.2 - 10 keV luminosity is 1.2E42 erg/s. This luminosity is ~400 times above the Eddington limit for a 20 Msun black hole, and has been interpreted as implying an accreting intermediate mass black hole with a mass in excess of 500 Msun (assuming the luminosity is a factor of 10 above the Eddington value). However, a number of other ultra-luminous X-ray sources have been later identified as background active galaxies or foreground sources. It has recently been claimed that HLX-1 could be a quiescent neutron star X-ray binary at a Galactic distance of only 2.5 kpc, so a definitive association with the host galaxy is crucial in order to confirm the nature of the object. Here we report the detection of the Halpha emission line for the recently identified optical counterpart at a redshift consistent with that of ESO 243-49. This finding definitively places HLX-1 inside ESO 243-49, confirming the extreme maximum luminosity and strengthening the case for it containing an accreting intermediate mass black hole of more than 500 Msun.
We present photometric and spectroscopic observations of the Type Ia supernova SN 2009nr in UGC 8255 (z=0.0122). Following the discovery announcement at what turned out to be ten days after peak, we detected it at V ~15.7 mag in data collected by the All Sky Automated Survey (ASAS) North telescope 2 weeks prior to the peak, and then followed it up with telescopes ranging in aperture from 10-cm to 6.5-m. Using early photometric data available only from ASAS, we find that the SN is similar to the over-luminous Type Ia SN 1991T, with a peak at Mv=-19.6 mag, and a slow decline rate of Dm_15(B)=0.95 mag. The early post-maximum spectra closely resemble those of SN 1991T, while the late time spectra are more similar to those of normal Type Ia SNe. Interestingly, SN 2009nr has a projected distance of 13.0 kpc (~4.3 disk scale lengths) from the nucleus of the small star-forming host galaxy UGC 8255. This indicates that the progenitor of SN 2009nr is not associated with a young stellar population, calling into question the conventional association of luminous SNe Ia with the ``prompt'' component directly correlated with current star formation. The early time discovery of SN 2009nr using ASAS demonstrates the science utility of high cadence all sky surveys conducted using small telescopes for the discovery of nearby (d=<50 Mpc) supernovae.
We present a detailed analysis of the structure and resolved stellar populations of simulated merger remnants, and compare them to observations of compact quiescent galaxies at z ~ 2. We find that major merging is a viable mechanism to produce systems of ~ 10^11 Msun and ~ 1 kpc size, provided the gas fraction at the time of final coalescence is high (~ 40%), and provided that the progenitors are compact star-forming galaxies, as expected at high redshift. Their integrated spectral energy distributions and velocity dispersions are in good agreement with the observations, and their position in the (v_{maj}/sigma, ellipticity) diagram traces the upper envelope of the distribution of lower redshift early-type galaxies. The simulated merger remnants show time- and sightline-dependent M/L ratio gradients that result from a superposition of radially dependent stellar age, stellar metallicity, and extinction. The median ratio of effective radius in rest-frame V-band light to that in mass surface density is ~ 2 during the quiescent remnant phase. This is typically expressed by a negative color gradient (i.e., red core), which we expect to correlate with the integrated color of the system. Finally, the simulations differ from the observations in their surface brightness profile shape. The simulated remnants are typically best fit by high (n >> 4) Sersic indices, whereas observed quiescent galaxies at z ~ 2 tend to be less cuspy (median n ~ 2.3). Limiting early star formation in the progenitors may be required to prevent the simulated merger remnants from having extended wings.
We present ground-based optical observations of the September 2009 and January 2010 transits of HD 80606b. Based on 3 partial light curves of the September 2009 event, we derive a midtransit time of T_c [HJD] = 2455099.196 +- 0.026, which is about 1 sigma away from the previously predicted time. We observed the January 2010 event from 9 different locations, with most phases of the transit being observed by at least 3 different teams. We determine a midtransit time of T_c [HJD] = 2455210.6502 +- 0.0064, which is within 1.3 sigma of the time derived from a Spitzer observation of the same event.
During the tidal disruption of a star by a massive black hole (BH) of mass MBH <~ 10^7 Msun, stellar debris falls back to the BH at a rate well above the Eddington rate. A fraction of this gas is subsequently blown away from the BH, producing an optically bright flare of radiation. We predict the spectra and spectral evolution of tidal disruption events, focusing on the photoionized gas outside this outflow's photosphere. The spectrum will show absorption lines that are strongly blueshifted relative to the host galaxy, very broad (0.01-0.1c), and strongest at UV wavelengths (e.g., C IV, Ly alpha, O VI), lasting ~ 1 month for a 10^6 Msun BH. Meanwhile, supernovae in galactic nuclei are a significant source of confusion in optical surveys for tidal disruption events: we estimate that nuclear Type Ia supernovae are two orders of magnitude more common than tidal disruption events at z ~ 0.1 for ground-based surveys. Nuclear Type II supernovae occur at a comparable rate but can be excluded by pre-selecting red galaxies. Supernova contamination can be reduced to a manageable level using high-resolution follow-up imaging with adaptive optics or the Hubble Space Telescope. Our predictions should help optical transient surveys capitalize on their potential for discovering tidal disruption events.
We estimate the He II to H I column density ratio, \eta = N(He II)/N(H I), in the intergalactic medium towards the high redshift (z_{em} = 2.885) bright quasar QSO HE 2347-4342 using Voigt-profile fitting of the H I transitions in the Lyman series and the He II Lyman-$\alpha$ transition as observed by the FUSE satellite. In agreement with previous studies, we find that $\eta > 50$ in most of the Lyman-$\alpha$ forest except in four regions where it is much smaller ($\eta \sim 10-20$) and therefore inconsistent with photo-ionization by the UV background flux. We detect O VI and C IV absorption lines associated with two of these regions ($z_{\rm abs}$ = 2.6346 and 2.6498). We show that if we constrain the fit of the H I and/or He II absorption profiles with the presence of metal components, we can accommodate $\eta$ values in the range 15-100 in these systems assuming broadening is intermediate between pure thermal and pure turbulent. While simple photo-ionization models reproduce the observed N(O VI)/N(C IV) ratio, they fail to produce low $\eta$ values contrary to models with high temperature (i.e T $\ge 10^5$ K). The Doppler parameters measured for different species suggest a multiphase nature of the absorbing regions. Therefore, if low $\eta$ values were to be confirmed, we would favor a multi-phase model in which most of the gas is at high temperature ($>$ 10$^5$ K) but the metals and in particular C IV are due to lower temperature ($\sim$ few $10^4$ K) photo-ionized gas.
Stars in galaxies form in giant molecular clouds that coalesce when the atomic hydrogen is converted into molecules. There are currently two dominant models for what property of the galactic disk determines its molecular fraction: either hydrostatic pressure driven by the gravity of gas and stars, or a combination of gas column density and metallicity. To assess the validity of these models, we compare theoretical predictions to the observed atomic gas content of low-metallicity dwarf galaxies with high stellar densities. The extreme conditions found in these systems are optimal to distinguish the two models, otherwise degenerate in nearby spirals. Locally, on scales <100 pc, we find that the state of the interstellar medium is mostly sensitive to the gas column density and metallicity rather than hydrostatic pressure. On larger scales where the average stellar density is considerably lower, both pressure and shielding models reproduce the observations, even at low metallicity. We conclude that models based on gas and dust shielding more closely describe the process of molecular formation, especially at the high resolution that can be achieved in modern galaxy simulations or with future radio/millimeter arrays.
Theory suggests that a star making a close passage by a supermassive black hole at the center of a galaxy can under most circumstances be expected to emit a giant flare of radiation as it is disrupted and a portion of the resulting stream of shock-heated stellar debris falls back onto the black hole itself. We examine the first results of an ongoing archival survey of galaxy clusters using Chandra and XMM-selected data, and report a likely tidal disruption flare from SDSS J131122.15-012345.6 in Abell 1689. The flare is observed to vary by a factor of >30 over at least 2 years, to have maximum L_X(0.3-3.0 keV)> 5 x 10^{42} erg s^{-1} and to emit as a blackbody with kT~0.12 keV. From the galaxy population as determined by existing studies of the cluster, we estimate a tidal disruption rate of 1.2 x 10^{-4} galaxy^{-1} year^{-1} if we assume a contribution to the observable rate from galaxies whose range of luminosities corresponds to a central black hole mass (M_bh) between 10^6 and 10^8 M_sun.
We report the discovery of a brown dwarf that transits one member of the M+M binary system LHS6343AB every 12.71 days. The transits were discovered using photometric data from the Kelper public data release. The LHS6343 stellar system was previously identified as a single high-proper-motion M dwarf. We use high-contrast imaging to resolve the system into two low-mass stars with masses 0.45 Msun and 0.36 Msun, respectively, with a projected separation of 55 arcsec. High-resolution spectroscopy shows that the more massive component undergoes Doppler variations consistent with Keplerian motion, with a period equal to the photometric transit period and an amplitude consistent with a companion mass of M_C = 61.6 +/- 2.2 Mjup. Based on an analysis of the Kepler light curve we estimate the radius of the companion to be R_C = 1.217 +/- 0.028 Rjup. Given the age of the system (> 1 Gyr), the radius of LHS6343C is much larger than predicted by interior structure models of brown dwarfs.
Standard maximum-likelihood estimators for binary-star and exoplanet eccentricities are biased high, in the sense that the estimated eccentricity tends to be larger than the true eccentricity. As with most non-trivial observables, a simple histogram of estimated eccentricities is not a good estimate of the true eccentricity distribution. Here we develop and test a hierarchical probabilistic method for performing the relevant meta-analysis, that is, inferring the true eccentricity distribution, taking as input the likelihood functions for the individual-star eccentricities, or samplings of the posterior probability distributions for the eccentricities (under a given, uninformative prior). The method is a simple implementation of a hierarchical Bayesian model; it can also be seen as a kind of heteroscedastic deconvolution. It can be applied to any quantity measured with finite precision--other orbital parameters, or indeed any astronomical measurements of any kind, including magnitudes, parallaxes, or photometric redshifts--so long as the measurements have been communicated as a likelihood function or a posterior sampling.
Supermassive black holes are probably present in the centre of the majority
of the galaxies. There is a consensus that these exotic objects are formed by
the growth of seeds either by accreting mass from a circumnuclear disk and/or
by coalescences during merger episodes.
The mass fraction of the disk captured by the central object and the related
timescale are still open questions, as well as how these quantities depend on
parameters like the initial mass of the disk or the seed or on the angular
momentum transport mechanism. This paper is addressed to these particular
aspects of the accretion disk evolution and of the growth of seeds.
The time-dependent hydrodynamic equations were solved numerically for an
axi-symmetric disk in which the gravitational potential includes contributions
both from the central object and from the disk itself. The numerical code is
based on a Eulerian formalism, using a finite difference method of
second-order, according to the Van Leer upwind algorithm on a staggered mesh.
The present simulations indicate that seeds capture about a half of the
initial disk mass, a result weakly dependent on model parameters. The
timescales required for accreting 50% of the disk mass are in the range 130-540
Myr, depending on the adopted parameters. These timescales permit to explain
the presence of bright quasars at z ~ 6.5. Moreover, at the end of the disk
evolution, a ``torus-like" geometry develops, offering a natural explanation
for the presence of these structures in the central regions of AGNs,
representing an additional support to the unified model.
We investigate potential biases in the measurements of exoplanet orbital parameters obtained from radial velocity observations for single-planet systems. We create a mock catalog of radial velocity data, choosing input planet masses, periods, and observing patterns from actual radial velocity surveys and varying input eccentricities. We apply Markov Chain Monte Carlo (MCMC) simulations and compare the resulting orbital parameters to the input values. We find that a combination of the effective signal-to-noise ratio of the data, the maximal gap in phase coverage, and the total number of periods covered by observations is a good predictor of the quality of derived orbit parameters. As eccentricity is positive definite, we find that eccentricities of planets on nearly circular orbits are preferentially overestimated, with typical bias of 1-2 times the median eccentricity uncertainty in a survey (e.g., 0.04 in the Butler et al. 2006 catalog). When performing population analysis, we recommend using the mode of the marginalized posterior eccentricity distribution to minimize potential biases. While the Butler et al. (2006) catalog reports eccentricities below 0.05 for just 17% of single-planet systems, we estimate that the true fraction of e < 0.05 orbits is about f(0.05)=38\pm 9%. For planets with P > 10 days, we find f(0.05)=28\pm 8% versus 10% from Butler et al. (2006). These planets either never acquired a large eccentricity or were circularized following any significant eccentricity excitation.
We report the new spectroscopic observations of the gravitational lens RXJ 021+4529 with the multi-mode focal reducer SCORPIO of the SAO RAS 6-m telescope. The new spectral observations were compared with the previously observed spectra of components A and B of RXJ 0921+4529, i.e. the same components observed in different epochs. We found a significant difference in the spectrum between the components that cannot be explained with microlensing and/or spectral variation. We conclude that RXJ 0921+4529 is a binary quasar system, where redshifts of quasars A and B are 1.6535 +/- 0.0005 and 1.6625 +/- 0.0015, respectively.
The GalICS (Galaxies in Cosmological Simulations) semi-analytical model of hierar- chical galaxy formation is used to investigate the effects of different galactic properties, including star formation rate (SFR) and outflows, on the shape of the mass metallic- ity relation and to predict the relation for galaxies at redshift z=2.27 and z=3.54. Our version of GalICS has the chemical evolution implemented in great detail and is less heavily reliant on approximations such as instantaneous recycling. We vary the model parameters controlling both the efficiency and redshift dependence of the SFR as well as the efficiency of supernova feedback. We find that the factors controlling the SFR influence the relation significantly at all redshifts and require a strong redshift dependence, proportional to 1+z, in order to reproduce the observed relation at the low mass end. Indeed, at any redshift, the predicted relation flattens out at the high mass end resulting in a poorer agreement with observations in this regime. We also find that variation of the parameters associated with outflows has a minimal effect on the relation at high redshift but does serve to alter its shape in the more recent past. We thus conclude that the relation is one between SFR and mass and that outflows are only important in shaping the relation at late times. When the relation is stratified by SFR it is apparent that the predicted galaxies with increasing stellar masses have higher SFRs, supporting the view that galaxy downsizing is the origin of the relation. Attempting to reproduce the observed relation, we vary the parameters controlling the efficiency of star formation and its redshift dependence and compare the predicted relations with Erb et al. (2006) at z=2.27 and Maiolino et al. (2008) at z=3.54 in order to find the best-fitting parameters. (Abridged)
Submillimetre continuum radiation allows us to probe cold objects, particularly the earliest, dusty phases of star formation, high-redshift galaxies and circumstellar disks. The submillimetre window gives a unique view of the physical and dynamical conditions in the neutral and molecular interstellar medium. In the next decade a combination of wide-field surveys with single-dish telescopes and targeted follow-up with ALMA and other facilities should enable rapid progress in answering questions about the origins of planetary systems, stars and galaxies.
The aim of this paper is to present a new fast-convergent numerically stable space-time adaptive processing (STAP) algorithm derived using a novel technique of feedback orthogonalization. The main advantages of this approach lie in its perfected stability to computational errors and faults which makes its real-time implementation on substantially faster and cheaper regular fixed-point processors possible.
We have performed a comprehensive chemical abundance analysis of the extremely metal-poor ([Ar/H]<-2) halo planetary nebula (PN) BoBn 1 based on IUE archive data, Subaru/HDS spectra, VLT/UVES archive data, and Spitzer/IRS spectra. We have detected over 600 lines in total and calculated ionic and elemental abundances of 13 elements using detected optical recombination lines (ORLs) and collisionally excited lines (CELs). The estimations of C, N, O, and Ne abundances from the ORLs and Kr, Xe, and Ba from the CELs are done the first for this nebula, empirically and theoretically. The C, N, O, and Ne abundances from ORLs are systematically larger than those from CELs. The abundance discrepancies apart from O could be explained by a temperature fluctuation model, and that of O might be by a hydrogen deficient cold component model. We have detected 5 fluorine and several s-process elements. The amounts of [F/H], [Kr/H], and [Xe/H] suggest that BoBn 1 is the most F-rich among F detected PNe and is a heavy s-process element rich PN. We have confirmed dust in the nebula that is composed of amorphous carbon and PAHs with a total mass of 5.8 x 10^-6 Msun. The photo-ionization models built with non-LTE theoretical stellar atmospheres indicate that the progenitor was a 1-1.5 Msun star that would evolve into a white dwarf with an ~0.62 Msun core mass and ~0.09 Msun ionized nebula. The derived elemental abundances have been reviewed from the standpoint of theoretical nucleosynthesis models. It is likely that the elemental abundances except N could be explained either by a 1.5 Msun single star model or by a binary model composed of 0.75 Msun + 1.5 Msun stars. Careful examination implies that BoBn 1 has evolved from a 0.75 Msun + 1.5 Msun binary and experienced coalescence during the evolution to become a visible PN, similar to the other extremely metal-poor halo PN, K 648 in M 15.
NGC 7009 is a fascinating example of a high excitation, elliptical planetary nebula (PN) containing circum-nebular rings, and FLIERs and jets along the major axis. We present visual spectroscopy along multiple position angles through the nucleus, taken with the Observatorio Astronomico Nacional (Mexico); mid-infrared (MIR) spectroscopy and imaging acquired using the Infrared Space Observatory (ISO) and Spitzer Space Telescope (SST), and narrow band imaging obtained using the Hubble Space Telescope (HST). The data show that the mid-infrared (MIR) continuum is dominated by a broad ~ 100K continuum, and a strong excess attributable to crystalline silicate emission. The primary peaks in this excess are similar to those observed in Forsterite and clino- and ortho-enstatite. We use the ground-based spectroscopy, and ratioing of HST images to investigate the presence of shocks in the ansae and interior envelope. It is concluded that line ratios in the ansae may be partially consistent with shock excitation, although these features are primarily dominated by photo-ionisation. We also note evidence for shock excitation at the limits of the interior elliptical shell, and for multiple bow-shock structures centered upon the ansae.
The supernova remnant (SNR) G357.7+0.3 appears to have caused considerable shredding of the local interstellar medium (ISM), leading to the formation of multiple cloud fragments having bright rims and cometary structures. We investigate five of these regions using mid-infrared (MIR) imaging and photometry deriving from the Spitzer Space Telescope (SST), as well as photometry deriving from the 2MASS near-infrared all sky survey, the Mid-Course Science Experiment (MSX), and the Multiband Imaging Photometer for Spitzer (MIPSGAL) survey of the Galactic plane. It is noted that two of the rims show evidence for emission by shock excited H2 transitions, whilst the centres of the clouds also show evidence for dark extinction cores, observed in silhouette against the bright emission rims. Levels of extinction for these cores are determined to be of order AV ~ 17-26 mag, whilst densities n(HI) are of order ~ 10^4 cm^(-3), and masses in the region of ~40-100 Msun. It is shown that the wavelength dependence of extinction is probably similar to that of Cardelli et al. and Martin & Whittet, but differs from the MIR extinction trends of Indebetouw et al. The distributions of Class I young stellar objects (YSOs) implies that many of them are physically associated with the clouds, and were likely formed as a result of interaction between the clouds and SN winds. A determination of the spectral energy distributions (SEDs) of these stars, together with 2-D radiative transfer modelling of their continua is used to place constraints upon their properties.
Variable ultraluminous X-ray sources (ULXs), which are considered to be black hole binaries (BHBs), are known to show state transitions similarly to Galactic BHBs. However, the relation between the ULX states and the Galactic BHB states is still unclear primarily due to less well-understood behaviors of ULXs in contrast to the Galactic BHBs. Here, we report a statistical X-ray spectral study of 34 energy spectra from seven bright ULXs in the interacting galaxy systems M51 and NGC4490/85, using archive data from multiple Chandra and XMM-Newton observations spanning for a few years. In order to compare with Galactic BHB states, we applied representative spectral models of BHBs; a power-law (PL), a multi-color disk black body (MCD), and a slim disk model to all the ULX spectra. We found a hint of a bimodal structure in the luminosity distribution of the samples, suggesting that ULXs have two states with typical luminosities of 3-6*10^{39} and 1.5-3*10^{39} ergs/s. Most spectra in the brighter state are explained by the MCD or the slim disk model, whereas those in the fainter state are explained by the PL model. In particular, the slim disk model successfully explains the observed spectral variations of NGC4490/85 ULX-6 and ULX-8 by changes of the mass accretion rate to a black hole of an estimated mass of <40 Msun. From the best-fit model parameters of each state, we speculate that the brighter state in these two ULXs corresponds to the brightest state of Galactic BHBs, which is often called the ``apparently standard state''. The fainter state of the ULXs has a PL shaped spectrum, but the photon index range is much wider than that seen in any single state of Galactic BHBs. We thus speculate that it is a state unique to ULXs. Some sources show much fainter and steeper spectra than the faint state, which we identified as another state.
We present an analysis of the gamma-ray data obtained with the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the direction of SNR W49B (G43.3-0.2). A bright unresolved gamma-ray source detected at a significance of 38 sigma is found to coincide with SNR W49B. The energy spectrum in the 0.2-200 GeV range gradually steepens toward high energies. The luminosity is estimated to be 1.5x10^{36} (D/8 kpc)^2 erg s^-1 in this energy range. There is no indication that the gamma-ray emission comes from a pulsar. Assuming that the SNR shell is the site of gamma-ray production, the observed spectrum can be explained either by the decay of neutral pi mesons produced through the proton-proton collisions or by electron bremsstrahlung. The calculated energy density of relativistic particles responsible for the LAT flux is estimated to be remarkably large, U_{e,p}>10^4 eV cm^-3, for either gamma-ray production mechanism.
We analyze the three-dimensional kinematics of about 82000 Tycho-2 stars belonging to the red giant clump (RGC). First, based on all of the currently available data, we have determined new, most probable components of the residual rotation vector of the optical realization of the ICRS/HIPPARCOS system relative to an inertial frame of reference, \omega_x,\omega_y,\omega_z)= (-0.11,0.24,-0.52)+/-(0.14,0.10,0.16) mas/yr. The stellar proper motions in RA have then be corrected by applying the correction \omega_z = -0.52 mas/yr. We show that, apart from their involvement in the general Galactic rotation described by the Oort constants A= 15.82+/-0.21 km/s/kpc and B=-10.87+/-0.15 km/s/kpc, the RGC stars have kinematic peculiarities in the Galactic yz plane related to the kinematics of the warped stellar-gaseous Galactic disk. We show that the parameters of the linear Ogorodnikov-Milne model that describe the kinematics of RGC stars in the zx plane do not differ significantly from zero. The situation in the yz plane is different. For example, the component of the solid-body rotation vector of the local solar neighborhood around the Galactic x axis is M_32- = -2.6+/-0.2 km/s/kpc. Two parameters of the deformation tensor in this plane, namely M_23^+ = 1.0+/-0.2 km/s/kpc and (M_33-M_22)= -1.3+/-0.4 km/s/kpc, also differ significantly from zero. On the whole, the kinematics of the warped stellar-gaseous Galactic disk in the local solar neighborhood can be described as a rotation around the Galactic X axis (close to the line of nodes of this structure) with an angular velocity (-3.1+/-0.5) < \Omega_W < (-4.4+/-0.5) km/s/kpc.
We present a current best estimate of the integrated near-infrared (NIR) extragalactic background light (EBL) attributable to resolved galaxies in J, H, and Ks. Our results in units of nW m-2 sr-1 are 11.7+5.6 -2.6 in J, 11.5+4.5 -1.5 in H and 10.0+2.8 -0.8 in Ks. We derive these new limits by combining our deep wide-field NIR photometry from five widely separated fields with other studies from the literature to create a galaxy counts sample that is highly complete and has good counting statistics out to JHKs ~ 27-28. As part of this effort we present new ultradeep Ks-band galaxy counts from 22 hours of observations with the Multi Object Infrared Camera and Spectrograph (MOIRCS) instrument on the Subaru Telescope. We use this MOIRCS Ks-band mosaic to estimate the total missing flux from sources beyond our detection limits. Our new limits to the NIR EBL are in basic agreement with, but 10 - 20% higher than previous estimates, bringing them into better agreement with estimates of the total NIR EBL (resolved + unresolved sources) obtained from TeV gamma-ray opacity measurements and recent direct measurements of the total NIR EBL. We examine field to field variations in our photometry to show that the integrated light from galaxies is isotropic to within uncertainties, consistent with the expected large-scale isotropy of the EBL. Our data also allow for a robust estimate of the NIR light from Galactic stars, which we find to be 14.7 +/- 2.4 in J, 10.1 +/- 1.9 in H and 7.6 +/- 1.8 in Ks in units of nW m-2 sr-1.
While doing optical study in an instrument similar to the interferometers dedicated to the Very Large Telescope (VLT), we have to take care of the pupil and focus conjugations. Modules with artificial sources are designed to simulate the stellar beams, in terms of collimation and pupil location. They constitute alignment and calibration tools. In this paper, we present such a module in which the pupil mask is not located in a collimated beam thus introducing Fresnel diffraction. We study the instrumental contrast taking into account the spatial coherence of the source, and the pupil diffraction. The considered example is MATISSE, but this study can apply to any other instrument concerned with Fresnel diffraction.
Observations of distant sources of high-energy (HE) gamma-rays are affected by attenuation resulting from the interaction of the gamma-rays with low energy photons from the diffuse meta-galactic radiation fields at ultraviolet (UV) to infrared (IR) wavelengths (Extragalactic Background Light; EBL). Recently, a large data-set of HE observations from the 1st year survey of the Large Area Telescope (LAT) instrument on-board of the Fermi satellite became available, covering an energy range from 100 MeV up to 100 GeV. In this paper, the potential of such large HE data-sets to probe the density of the EBL - especially in the UV to optical - is explored. The data from the catalog is investigated for an attenuation signature in the energy range 10-100 GeV and the results are compared with the predictions from EBL model calculations. No clear signature is found. The statistics are still limited by (1) the sensitivity of Fermi/LAT to detect sources above 10 GeV, (2) the number of firmly identified sources with known redshift, both which will improve over the coming years.
We study the ability of magnetic helicity expulsion to alleviate catastrophic $\alpha$-quenching in mean field dynamos in two--dimensional spherical wedge domains. Motivated by the physical state of the outer regions of the Sun, we consider $\alpha^2\Omega$ mean field models with a dynamical $\alpha$ quenching. We include two mechanisms which have the potential to facilitate helicity expulsion, namely advection by a mean flow (``solar wind'') and meridional circulation. We find that a wind alone can prevent catastrophic quenching, with the field saturating at finite amplitude. In certain parameter ranges, the presence of a large-scale meridional circulation can reinforce this alleviation. However, the saturated field strengths are typically below the equipartition field strength. We discuss possible mechanisms that might increase the saturated field.
The kinematics of damped Lyman alpha absorbers (DLAs) are difficult to reproduce in hierarchical galaxy formation models, particularly the preponderance of wide systems. We investigate DLA kinematics at z=3 using high-resolution cosmological hydrodynamical simulations that include a heuristic model for galactic outflows. Without outflows, our simulations fail to yield enough wide DLAs, as in previous studies. With outflows, predicted DLA kinematics are in much better agreement with observations. Comparing two outflow models, we find that a model based on momentum-driven wind scalings provides the best match to the observed DLA kinematic statistics of Prochaska & Wolfe. In this model, DLAs typically arise a few kpc away from galaxies that would be identified in emission. Narrow DLAs can arise from any halo and galaxy mass, but wide ones only arise in halos with mass >10^11 Mo, from either large central or small satellite galaxies. This implies that the success of this outflow model originates from being most efficient at pushing gas out from small satellite galaxies living in larger halos. This increases the cross-section for large halos relative to smaller ones, thereby yielding wider kinematics. Our simulations do not include radiative transfer effects or detailed metal tracking, and outflows are modeled heuristically, but they strongly suggest that galactic outflows are central to understanding DLA kinematics. An interesting consequence is that DLA kinematics may place constraints on the nature and efficiency of gas ejection from high-z galaxies.
Larson (1981) first noted a scaling relation between masses and sizes in molecular clouds that implies that these objects have approximately constant column densities. This original claim, based upon millimeter observations of carbon monoxide lines, has been challenged by many theorists, arguing that the apparent constant column density observed is merely the result of the limited dynamic range of observations, and that in reality clouds have column density variations over two orders of magnitudes. In this letter we investigate a set of nearby molecular clouds with near-infrared excess methods, which guarantee very large dynamic ranges and robust column density measurements, to test the validity of Larson's third law. We verify that different clouds have almost identical average column densities above a given extinction threshold; this holds regardless of the extinction threshold, but the actual average surface mass density is a function of the specific threshold used. We show that a second version of Larson's third law, involving the mass-radius relation for single clouds and cores, does not hold in our sample, indicating that individual clouds are not objects that can be described by constant column density. Our results instead indicate that molecular clouds are characterized by a universal structure. Finally we point out that this universal structure can be linked to the log-normal nature of cloud column density distributions.
This paper introduces the idea that the general mixing inequality obeyed by evolving stellar phase densities may place useful constraints on the possible history of the over-all galaxy population. We construct simple models for the full stellar phase space distributions of galaxies' disk and spheroidal components, and reproduce the well-known result that the maximum phase density of an elliptical galaxy is too high to be produced collisionlessly from a disk system, although we also show that the inclusion of a bulge component in the disk removes this evolutionary impediment. In order to draw more general conclusions about the evolution of the galaxy population, we use the Millennium Galaxy Catalogue to construct a model of the entire phase density distribution of stars in a representative sample of the local Universe. In such a composite population, we show that the mixing inequality rules out some evolutionary paths that are not prohibited by consideration of the maximum phase density alone, and thus show that the massive ellipticals in this population could not have formed purely from collisionless mergers of a low mass galaxy population like that found in the local Universe. Although the violation of the mixing inequality is in this case quite minor, and hence avoidable with a modest amount of non-collisionless star formation in the merger process, it does confirm the potential of this approach. The future measurement of stellar phase densities at higher redshift will allow this potential to be fully exploited, offering a new way to look at the possible pathways for galaxy evolution, and to learn about the environment of star formation through the way that this phase space becomes populated over time.
Very luminous extragalactic water masers, the megamasers, are associated with active galactic nuclei (AGN) in galaxies characterized by accretion disks, radio jets, and nuclear outflows. Weaker masers, the kilomasers, seem to be mostly related to star formation activity, although the possibility exists that some of these sources may belong to the weak tail of the AGN maser distribution. It is of particular importance to accurately locate the water maser emission to reveal its origin and shed light onto extragalactic star forming activity or to elucidate the highly obscured central regions of galaxies. We performed interferometric observations of three galaxies, NGC3556, Arp299, and NGC4151, where water emission was found. Statistical tools have been used to study the relation between OH and water maser emission in galaxies. The maser in NGC3556 is associated with a compact radio continuum source that is most likely a supernova remnant or radio supernova. In Arp299, the luminous water maser has been decomposed in three main emitting regions associated with the nuclear regions of the two main galaxies of the system, NGC3690 and IC694, and the region of overlap. In NGC4151, only one of the two previously observed maser components has been tentatively detected. This feature, if real, is associated with the galaxy's central region. The only galaxy, so far, where luminous maser emission from two maser species, OH and H2O has been confidently detected is Arp299. Weaker masers from these two species do instead coexist in a number of objects. A larger number of objects searched for both maser species are, however, necessary to better assess these last two results.
Context. The first magnetic fields in O- and B-type stars that do not belong to the Bp-star class, have been discovered. The cyclic UV wind-line variability, which has been observed in a significant fraction of early-type stars, is likely to be related to such magnetic fields. Aims. We attempt to improve our understanding of massive-star magnetic fields, and observe twenty-five carefully-selected, OB-type stars. Methods. Of these stars we obtain 136 magnetic field strength measurements. We present the UV wind-line variability of all selected targets and summarise spectropolarimetric observations acquired using the MUSICOS spectropolarimeter, mounted at the TBL, Pic du Midi, between December 1998 and November 2004. From the average Stokes I and V line profiles, derived using the LSD method, we measure the magnetic field strengths, radial velocities, and first moment of the line profiles. Results. No significant magnetic field is detected in any OB-type star that we observed. Typical 1{\sigma} errors are between 15 and 200 G. A possible magnetic-field detection for the O9V star 10 Lac remains uncertain, because the field measurements depend critically on the fringe- effect correction in the Stokes V spectra. We find excess emission in UV-wind lines, centred about the rest wavelength, to be a new indirect indicator of the presence of a magnetic field in early B-type stars. The most promising candidates to host magnetic fields are the B-type stars {\delta} Cet and 6 Cep, and a number of O stars. Conclusions. Although some O and B stars have strong dipolar field, which cause periodic variability in the UV wind-lines, such strong fields are not widespread. If the variability observed in the UV wind-lines of OB stars is generally caused by surface magnetic fields, these fields are either weak (<~few hundred G) or localised.
The collapse of dense cores with different metallicities is studied by hydrodynamical calculations coupled with detailed chemical and radiative processes. For this purpose, we construct a simple chemical network with non-equilibrium reactions among 15 chemical species, which reproduces the abundance of important molecular coolants by more detailed network very well. The evolution is followed until the formation of a hydrostatic protostar at the center. In a lower-metallicity gas cloud, the temperature during the collapse remains high owing to less efficient cooling. Using the temperature evolution at the center as a function the density, we discuss the possibility of fragmentation during the dust-cooling phase. The critical metallicity for the fragmentation is 10^{-5}Z_sun assuming moderate elongation of the cloud cores at the onset of this phase. From the density and velocity distributions at the time of protostar formation, we evaluate the mass accretion rate in the subsequent accretion phase. Using these accretion rates, we also calculate the evolution of the protostars under the assumption of stationary accretion flow. Finally, we discuss possible suppression of fragmentation by heating of the ambient gas by protostellar radiation, which is considered important in the contemporary star formation. We argue that it is negligible for <10^{-2}Zsun.
In a few years, the second generation instruments of the Very Large Telescope Interferometer (VLTI) will routinely provide observations with 4 to 6 telescopes simultaneously. To reach their ultimate performance, they will need a fringe sensor capable to measure in real time the randomly varying optical paths differences. A collaboration between LAOG (PI institute), IAGL, OCA and GIPSA-Lab has proposed the Planar Optics Phase Sensor concept to ESO for the 2nd Generation Fringe Tracker. This concept is based on the integrated optics technologies, enabling the conception of extremely compact interferometric instruments naturally providing single-mode spatial filtering. It allows operations with 4 and 6 telescopes by measuring the fringes position thanks to a spectrally dispersed ABCD method. We present here the main analysis which led to the current concept as well as the expected on-sky performance and the proposed design.
Following up our recent analysis devoted to the impact of non steady accretion on the location of young low-mass stars or brown dwarfs in the Herzsprung-Russell diagram, we perform a detailed analysis devoted to the effect of burst accretion on the internal structure of low-mass and solar type stars. We find that episodic accretion can produce objects with significantly higher central temperatures than the ones of the non accreting counterparts of same mass and age. As a consequence, lithium depletion can be severely enhanced in these objects. This provides a natural explanation for the unexpected level of lithium depletion observed in young objects for the inferred age of their parent cluster. These results confirm the limited reliability of lithium abundance as a criterion for assessing or rejecting cluster membership. They also show that lithium is not a reliable age indicator, because its fate strongly depends on the past accretion history of the star. Under the assumption that giant planets primarily form in massive disks prone to gravitational instability and thus to accretion burst episodes, the same analysis also explains the higher Li depletion observed in planet hosting stars. At last, we show that, depending on the burst rate and intensity, accretion outbursts can produce solar mass stars with lower convective envelope masses, at ages less than a few tens of Myr, than predicted by standard (non or slowly accreting) pre-main sequence models. This result has interesting, although speculative, implications for the recently discovered depletion of refractory elements in the Sun.
LOFAR is a new and innovative effort to build a radio-telescope operating at the multi-meter wavelength spectral window. One of the most exciting applications of LOFAR will be the search for redshifted 21-cm line emission from the Epoch of Reionization (EoR). It is currently believed that the Dark Ages, the period after recombination when the Universe turned neutral, lasted until around the Universe was 400,000 years old. During the EoR, objects started to form in the early universe and they were energetic enough to ionize neutral hydrogen. The precision and accuracy required to achieve this scientific goal, can be essentially translated into accumulating large amounts of data. The data model describing the response of the LOFAR telescope to the intensity distribution of the sky is characterized by the non-linearity of the parameters and the large level of noise compared to the desired cosmological signal. In this poster, we present the implementation of a statistically optimal map-making process and its properties. The basic assumptions of this method are that the noise is Gaussian and independent between the stations and frequency channels and that the dynamic range of the data can been enhanced significantly during the off-line LOFAR processing. These assumptions match our expectations for the LOFAR Epoch of Reionization Experiment.
We have developed a high resolution combined physical and chemical model of a protoplanetary disk surrounding a typical T Tauri star. Our aims were to use our model to calculate the chemical structure of disks on small scales (sub-milli-arcsecond in the inner disk for objects at the distance of Taurus, ~ 140 pc) to investigate the various chemical processes thought to be important in disks and to determine potential molecular tracers of each process. Our gas-phase network was extracted from the UMIST Database for Astrochemistry to which we added gas-grain interactions including freeze out and thermal and non-thermal desorption (cosmic-ray induced desorption, photodesorption and X-ray desorption) and a grain-surface network. We find that cosmic-ray induced desorption has the least effect on our disk chemical structure while photodesorption has a significant effect, enhancing the abundances of most gas-phase molecules throughout the disk and affecting the abundances and distribution of HCN, CN and CS, in particular. In the outer disk, we also see enhancements in the abundances of H2O and CO2. X-ray desorption is a potentially powerful mechanism in disks, acting to homogenise the fractional abundances of gas-phase species across the depth and increasing the column densities of most molecules although there remain significant uncertainties in the rates adopted for this process. The addition of grain-surface chemistry enhances the fractional abundances of several small complex organic molecules including CH3OH, HCOOCH3 and CH3OCH3 to potentially observable values (i.e. a fractional abundance of >~ 1.0E-11).
We announce the discovery of a new low-mass, pre-main sequence eclipsing binary, MML 53. Previous observations of MML 53 found it to be a pre-main sequence spectroscopic multiple associated with the 15-22 Myr Upper Centaurus Lupus cluster. We identify the object as an eclipsing binary for the first time through the analysis of multiple seasons of time series photometry from the SuperWASP transiting planet survey. Re-analysis of a single archive spectrum shows MML 53 to be a spatially unresolved triple system of young stars which all exhibit significant lithium absorption. Two of the components comprise an eclipsing binary with period, P = 2.097891(6) +- 0.000005 and mass ratio, q~0.8. Here, we present the analysis of the discovery data.
In this paper, we report a detailed investigation of the multiwavelength properties of a newly detected gamma-ray pulsar, PSR J2021+4026, in both observational and theoretical aspects. We firstly identify an X-ray source in the XMM-Newton serendipitous source catalogue, 2XMM J202131.0+402645, located within the 95% confidence circle of PSR J2021+4026. With an archival Chandra observation, this identification provides an X-ray position with arcsecond accuracy which is helpful in facilitating further investigations. Searching for the pulsed radio emission at the position of 2XMM J202131.0+402645 with a 25-m telescope at Urumqi Astronomical Observatory resulted in null detection and places an upper-limit of 0.1~mJy for any pulsed signal at 18~cm. Together with the emission properties in X-ray and gamma-ray, the radio quietness suggests PSR J2021+4026 to be another member of Geminga-like pulsars. In the radio sky survey data, extended emission features have been identified in the gamma-ray error circle of PSR J2021+4026. We have also re-analyzed the gamma-ray data collected by FERMI's Large Area Telescope. We found that the X-ray position of 2XMM J202131.0+402645 is consistent with that of the optimal gamma-ray timing solution. We have further modeled the results in the context of outer gap model which provides us with constraints for the pulsar emission geometry such as magnetic inclination angle and the viewing angle. We have also discussed the possibility of whether PSR J2021+4026 has any physical association with the supernova remnant G78.2+2.1 (gamma-Cygni).
We present an analysis of the X-ray spectral properties observed from black hole candidate (BHC) binary SS~433. We have analyzed RXTE data from this source, coordinated with Green Bank Interferometer/RATAN-600. We show that SS~433 undergoes a X-ray spectral transition from the low hard state (LHS) to the intermediate state (IS). We show that the X-ray broad-band energy spectra during all spectral states are well fit by a sum of so called ``Bulk Motion Comptonization (BMC) component'' and by two (broad and narrow) Gaussians for the continuum and line emissions respectively. In addition to these spectral model components we also find a strong feature that we identify as a "blackbody-like (BB)" component which color temperature is in the range of 4-5 keV in 24 IS spectra during the radio outburst decay in SS~433. Our observational results on the "high temperature BB" bump leads us to suggest the presence of gravitationally redshifted annihilation line emission in this source. I\ We have also established the photon index saturation at about 2.3 in index vs mass accretion correlation. This index-mass accretion correlation allows us to evaluate the low limit of black hole (BH) mass of compact object in SS~433, M_{bh}> 2 solar masses, using the scaling method using BHC GX 339-4 as a reference source. Our estimate of the BH mass in SS 433 is consistent with recent BH mass measurement using the radial-velocity measurements of the binary system by Hillwig & Gies who find that M_{x}=(4.3+/-0.8 solar masses. This is the smallest BH mass found up to now among all BH sources. Moreover, the index saturation effect versus mass accretion rate revealed in SS~433, like in a number of other BH candidates, is the strong observational evidence for the presence of a BH in SS~433.
We use the GALPROP code for cosmic-ray (CR) propagation to calculate the broad-band luminosity spectrum of the Milky Way related to CR propagation and interactions in the interstellar medium. This includes gamma-ray emission from the production and subsequent decay of neutral pions, bremsstrahlung, and inverse Compton scattering, and synchrotron radiation. The Galaxy is found to be nearly a CR electron calorimeter, but {\it only} if gamma ray emitting processes are taken into account. Synchrotron radiation alone accounts for only one third of the total electron energy losses with ~10-20% of the total synchrotron emission from secondary CR electrons and positrons. The relationship between far-infrared and radio luminosity that we find from our models is consistent with that found for galaxies in general. The results will be useful for understanding the connection between diffuse emissions from radio through gamma rays in ``normal'' (non-AGN dominated) galaxies, as well as for estimating the broad-band extragalactic diffuse background from these kinds of galaxies.
The ASTrometric and phase-Referenced Astronomy (ASTRA) project will provide phase referencing and astrometric observations at the Keck Interferometer, leading to enhanced sensitivity and the ability to monitor orbits at an accuracy level of 30-100 microarcseconds. Here we discuss recent scientific results from ASTRA, and describe new scientific programs that will begin in 2010-2011. We begin with results from the "self phase referencing" (SPR) mode of ASTRA, which uses continuum light to correct atmospheric phase variations and produce a phase-stabilized channel for spectroscopy. We have observed a number of protoplanetary disks using SPR and a grism providing a spectral dispersion of ~2000. In our data we spatially resolve emission from dust as well as gas. Hydrogen line emission is spectrally resolved, allowing differential phase measurements across the emission line that constrain the relative centroids of different velocity components at the 10 microarcsecond level. In the upcoming year, we will begin dual-field phase referencing (DFPR) measurements of the Galactic Center and a number of exoplanet systems. These observations will, in part, serve as precursors to astrometric monitoring of stellar orbits in the Galactic Center and stellar wobbles of exoplanet host stars. We describe the design of several scientific investigations capitalizing on the upcoming phase-referencing and astrometric capabilities of ASTRA.
We report the discovery of TWA 30B, a wide (~3400 AU), co-moving M dwarf companion to the nearby (~42 pc) young star TWA 30. Companionship is confirmed from their statistically consistent proper motions and radial velocities, as well as a chance alignment probability of only 0.08%. Like TWA 30A, the spectrum of TWA 30B shows signatures of an actively accreting disk (H I and alkali line emission) and forbidden emission lines tracing outflowing material ([O I], [O II], [O III], [S II], and [N II]). We have also detected [C I] emission in the optical data, marking the first such detection of this line in a pre-main sequence star. Negligible radial velocity shifts in the emission lines relative to the stellar frame of rest (Delta V < 30 km/s) indicate that the outflows are viewed in the plane of the sky and that the corresponding circumstellar disk is viewed edge-on. Indeed, TWA 30B appears to be heavily obscured by its disk, given that it is 5 magnitudes fainter than TWA 30A at K-band despite having a slightly earlier spectral type (M4 versus M5). The near-infrared spectrum of TWA 30B also evinces an excess that varies on day timescales, with colors that follow classical T Tauri tracks as opposed to variable reddening (as is the case for TWA 30A). Multi-epoch data show this excess to be well-modeled by a blackbody component with temperatures ranging from 630 to 880 K and emitting areas that scale inversely with the temperature. The variable excess may arise from disk structure such as a rim or a warp at the inner disk edge located at a radial distance of ~3-5 R_sun. As the second and third closest actively accreting and outflowing stars to the Sun (after TWA 3), TWA 30AB presents an ideal system for detailed study of star and planetary formation processes at the low-mass end of the hydrogen-burning spectrum.
A decade of X-ray stellar observations with Chandra and XMM-Newton has led to significant advances in our understanding of the physical processes at work in hot (magnetized) plasmas in stars and their immediate environment, providing new perspectives and challenges, and in turn the need for improved models. The wealth of high-quality stellar spectra has allowed us to investigate, in detail, the characteristics of the X-ray emission across the HR diagram. Progress has been made in addressing issues ranging from classical stellar activity in stars with solar-like dynamos (such as flares, activity cycles, spatial and thermal structuring of the X-ray emitting plasma, evolution of X-ray activity with age), to X-ray generating processes (e.g. accretion, jets, magnetically confined winds) that were poorly understood in the pre-Chandra/XMM-Newton era. I discuss the progress made in the study of high energy stellar physics and its impact in a wider astrophysical context, focusing on the role of spectral diagnostics now accessible.
In this paper I report the highlights of the talk: "Universal properties in galaxies and cored Dark Matter profiles", given at: Colloquium Lectures, Ecole Internationale d'Astrophysique Daniel Chalonge. The 14th Paris Cosmology Colloquium 2010 "The Standard Model of the Universe: Theory and Observations".
We describe a variability study of the moderately old open cluster NGC 6819. We have detected 4 new detached eclipsing binaries near the cluster turnoff (one of which may be in a triple system). Several of these systems should be able to provide mass and radius information, and can therefore constrain the age of the cluster. We have also newly detected one possible detached binary member about 3.5 magnitudes below the turnoff. One EW-type binary (probably not a cluster member) shows unusually strong night-to-night light curve variations in sets of observations separated by 8 years. According to the best current information, the three brightest variables we detected (2 of them new) are cluster members, making them blue stragglers. One is a delta Scu pulsating variable, one is a close but detached binary, and the third contains a detached short period binary that shows total eclipses. In each case, however, there is evidence hinting that the system may have been produced through the interaction of more than two stars.
The radionuclide 22Na is a potential astronomical observable that is expected to be produced in classical novae in quantities that depend on the thermonuclear rate of the 22Na(p,g)23Mg reaction. We have measured the strengths of low-energy 22Na(p,g)23Mg resonances directly and absolutely using a radioactive 22Na target. We find the strengths of resonances at E_p = 213, 288, 454, and 610 keV to be higher than previous measurements by factors of 2.4 to 3.2, and we exclude important contributions to the rate from proposed resonances at E_p = 198, 209, and 232 keV. The 22Na abundances expected in the ejecta of classical novae are reduced by a factor of ~ 2.
We study the cosmology of a generalized Galileon field $\phi$ with five covariant Lagrangians in which $\phi$ is replaced by general scalar functions $f_i(\phi)$ ($i=1, \cdots, 5$). For these theories, the equations of motion remain at second-order in time derivatives. We restrict the functional forms of $f_i (\phi)$ from the demand to obtain de Sitter solutions responsible for dark energy. There are two possible choices for power-law functions $f_i(\phi)$, depending on whether the coupling $F(\phi)$ with the Ricci scalar $R$ is independent of $\phi$ or depends on $\phi$. The former corresponds to the covariant Galileon theory that respects the Galilean symmetry in the Minkowski space-time. For generalized Galileon theories we derive the conditions for the avoidance of ghosts and Laplacian instabilities associated with scalar and tensor perturbations as well as the condition for the stability of de Sitter solutions. We also carry out detailed analytic and numerical study for the cosmological dynamics of the covariant Galileon theory.
The review of basic cosmological properties of four-dimensional F(R)-gravity, including FRW equations of motion and its accelerating solutions, generalized fluid and scalar-tensor representation of the theory is done. Cosmological reconstruction equation is written and conditions for stability of cosmological solution are discussed. The overview of realistic F(R)-models unifying inflation with dark energy epoch is made. The avoidance of finite-time future singularities in such theories via the introduction of R^2-term is studied. New realistic non-singular F(R)-gravity unifying early-time inflation with late-time acceleration is presented. The exit from inflationary era in such model may be caused by the gravitational scenario. It is demonstrated that five-dimensional F(R)-gravity considered as non-perturbative stringy effective action leads to universal relation for viscous bound ratio.
We consider higher derivative gravity lagrangians in 3 and 4 dimensions including upto six derivative curvature invariants. Following a suggestion by Myers, these lagrangians are constructed such that the fluctuations around (anti) de Sitter spaces have second order equations of motion. We show that these lagrangians admit $c$-theorems both in the context of AdS/CFT and cosmology. In the context of cosmology, the monotonic function is the entropy defined on the cosmological horizon through Wald's formula. Exact black hole solutions which are asymptotically (anti) de Sitter are presented. An interesting lower bound for entropy is found in de Sitter space. Some aspects of cosmology in both $D=3$ and $D=4$ are discussed.
The evolution of the mass of a black hole embedded in a universe filled with dark energy and cold dark matter is calculated in a closed form within a test fluid model in a Schwarzschild metric, taking into account the cosmological evolution of both fluids. The result describes exactly how accretion asymptotically switches from the matter-dominated to the Lambda-dominated regime. For early epochs, the black hole mass increases due to dark matter accretion, and on later epochs the increase in mass stops as dark energy accretion takes over. Thus, the unphysical behaviour of previous analyses is improved in this simple exact model.
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Here we report the detection of a 626 s periodic modulation from the X-ray source 2XMM J174016.0-290337 located in the direction of the Galactic center. We present temporal and spectral analyses of archival XMM-Newton data and photometry of archived near-infrared data in order to investigate the nature of this source. We find that the X-ray light curve shows a strong modulation at 626 +/- 2 s with a confidence level > 99.9% and a pulsed fraction of 54%. Spectral fitting demonstrates that the spectrum is consistent with an absorbed power law. No significant spectral variability was observed over the 626 s period. We have investigated the possibility that the 626 s period is orbital in nature (either that of an ultra-compact X-ray binary or an AM CVn) or related to the spin of a compact object (either an accretion powered pulsar or an intermediate polar). The X-ray properties of the source and the photometry of the candidate near-infrared counterparts are consistent with an accreting neutron star X-ray binary on the near-side of the Galactic bulge, where the 626 s period is most likely indicative of the pulsar spin period. However, we cannot rule out an ultra-compact X-ray binary or an intermediate polar with the data at hand. In the former case, if the 626 s modulation is the orbital period of an X-ray binary, it would be the shortest period system known. In the latter case, the modulation would be the spin period of a magnetic white dwarf. However, we find no evidence for absorption dips over the 626 s period, a low temperature black body spectral component, or Fe Kalpha emission lines. These features are commonly observed in intermediate polars, making 2XMM J174016.0-290337 a rather unusual member of this class if confirmed. We instead suggest that 2XMM J174016.0-290337 could be a new addition to the emerging class of symbiotic X-ray binaries.
SN2009ku, discovered by Pan-STARRS-1, is a Type Ia supernova (SNIa), and a member of the distinct SN2002cx-like class of SNeIa. Its light curves are similar to the prototypical SN2002cx, but are slightly broader and have a later rise to maximum in g. SN2009ku is brighter (~0.6 mag) than other SN2002cx-like objects, peaking at M_V = -18.4 mag - which is still significantly fainter than typical SNeIa. SN2009ku, which had an ejecta velocity of ~2000 kms^-1 at 18 days after maximum brightness is spectroscopically most similar to SN2008ha, which also had extremely low-velocity ejecta. However, SN2008ha had an exceedingly low luminosity, peaking at M_V = -14.2 mag, ~4 mag fainter than SN2009ku. The contrast of high luminosity and low ejecta velocity for SN2009ku is contrary to an emerging trend seen for the SN2002cx class. SN2009ku is a counter-example of a previously held belief that the class was more homogeneous than typical SNeIa, indicating that the class has a diverse progenitor population and/or complicated explosion physics. As the first example of a member of this class of objects from the new generation of transient surveys, SN2009ku is an indication of the potential for these surveys to find rare and interesting objects.
There are several planned and ongoing experiments designed to explore the Epoch of Reionization (EoR), the pivotal period during which the gas in the intergalactic medium went from being entirely neutral to almost entirely ionized. These experiments will probe the EoR, through the redshifted 21 cm line from neutral hydrogen, using radio arrays: e.g. Low Frequency Array (LOFAR) and Murchinson Widefield Array (MWA). Unfortunately however, the cosmological 21 cm signal is highly contaminated by astrophysical foregrounds and by non-astrophysical and instrumental effects. Therefore, to reliably detect the cosmological signal, it is essential to understand very well all data components, their influence on the desired signal and explore additional complementary or corroborating probes of the EoR. These proceedings give an overview of observational constrains of the foregrounds, present theoretical efforts to model the foregrounds, and discuss a problem of the foreground removal. The major results are presented for the LOFAR-EoR experiment.
Stellar population synthesis (SPS) models are a key ingredient of many galaxy evolution studies. Unfortunately, the models are still poorly calibrated for certain stellar evolution stages. Of particular concern is the treatment of the thermally-pulsing asymptotic giant branch (TP-AGB) phase, as different implementations lead to systematic differences in derived galaxy properties. Post-starburst galaxies are a promising calibration sample, as TP-AGB stars are thought to be most prominently visible during this phase. Here, we use post-starburst galaxies in the NEWFIRM medium-band survey (NMBS) to assess different SPS models. The available photometry allows the selection of a homogeneous and well-defined sample of 62 post-starburst galaxies at 0.7<z<2.0, from which we construct a well-sampled composite spectral energy distribution (SED) over the range 1200-40 000 Angstrom. The SED is well-fit by the Bruzual & Charlot (2003) SPS models, while the Maraston (2005) models do not reproduce the rest-frame optical and near-infrared parts of the SED simultaneously. When the fitting is restricted to lambda < 6000 Angstrom, the Maraston (2005) models over-predict the near-infrared luminosity, implying that these models give too much weight to TP-AGB stars. Using the flexible SPS models by Conroy et al. (2009), and assuming solar metallicity, we find that the contribution of TP-AGB stars to the integrated SED is a factor of ~3 lower than predicted by the latest Padova TP-AGB models. Whether this is due to lower bolometric luminosities, shorter lifetimes, and/or heavy dust obscuration of TP-AGB stars remains to be addressed. Altogether, our data demand a low contribution from TP-AGB stars to the SED of post-starburst galaxies.
I present first results of LOFAR observations with international baselines. An important cornerstone was the detection of the first long-baseline fringes. Their analysis turns out to be extremely useful to investigate and solve a number of technical issues of the instrument. Crude maps of the sky are created from single-baseline delay/fringe-rate spectra and compared with a short-baseline synthesis map. First long-baseline LBA images are shown of the source 3C196, a bright quasar whose sub-components can only be resolved with the long baselines. The corresponding sub-arcsec HBA image does not show the same amount of details yet, but HBA results are expected to improve significantly very soon. The LBA long-baseline image of 3C196 comprises the highest-resolution radio map ever produced at this low frequency.
We present measurements of the average flux densities of massive ($M_{*} \approx 2\times 10^{11}~\rm M_{\odot}$) galaxies at redshifts $1.7 < z < 2.9$, obtained by stacking positions of known objects taken from the GOODS NICMOS Survey (GNS) catalog, on maps at 870\rmicron\ (LABOCA); 250, 350, 500\rmicron\ (BLAST); and 24\rmicron\ (\emph{Spitzer}). A modified black body dust spectrum fit to the stacked flux densities indicates a median [interquartile] star-formation rate of $\rm SFR=148~[110, 189]~\rm M_{\odot}~yr^{-1}$. Galaxies are grouped according to their S\'{e}rsic indices, $n$, dividing the population into disk-like and spheroid-like galaxies. We find evidence that most of the star formation is occurring in $n \le 2$ (disk-like) galaxies, with median [interquartile] $\rm SFR=231~[188, 288]~\rm M_{\odot}~yr^{-1}$, while the $n > 2$ (spheroid-like) population is forming stars with median [interquartile] $\rm SFR=57~[36, 83]~\rm M_{\odot}~yr^{-1}$. Thus, while the star formation signal in this sample is clearly dominated by disk-like galaxies, on average the compact, spheroid-like population appear to be red but not dead, and that localized, dust obscured star formation is a likely mechanism for size evolution in this population, consistent with several models of galaxy growth.
The low-mass end of the stellar Initial Mass Function (IMF) is constrained by focusing on the baryon-dominated central regions of strong lensing galaxies. We study in this letter the Einstein Cross (Q2237+0305), a z=0.04 barred galaxy whose bulge acts as lens on a background quasar. The positions of the four quasar images constrain the surface mass density on the lens plane, whereas the surface brightness (H-band NICMOS/HST imaging) along with deep spectroscopy of the lens (VLT/FORS1) allow us to constrain the stellar mass content, for a range of IMFs. We find that a classical single power law (Salpeter IMF) predicts more stellar mass than the observed lensing estimates. This result is confirmed at the 99% confidence level, and is robust to systematic effects due to the choice of population synthesis models, the presence of dust, or the complex disk/bulge population mix. Our non-parametric methodology is more robust than kinematic estimates, as we do not need to make any assumptions about the dynamical state of the galaxy or its decomposition into bulge and disk. Over a range of low-mass power law slopes (with Salpeter being Gamma=+1.35) we find that at a 90% confidence level, slopes with Gamma>0 are ruled out.
We present a numerical simulation of a gamma-ray burst jet from a long-lasting engine in the core of a 16 solar mass Wolf-Rayet star. The engine is active for 6000 s with a luminosity that decays in time as a power-law with index -5/3. Even though there is no short time-scale variability in the engine luminosity, we find that the jet's kinetic luminosity outside the progenitor star is characterized by fluctuations with relatively short time scale. We analyze the temporal characteristics of those fluctuations and we find that they are consistent with the properties of observed flares in the X-ray afterglows. The peak to continuum flux ratio of the flares in the simulation is consistent with some, but not all, the observed flares. We propose that propagation instabilities, rather than variability in the engine luminosity, may be responsible for the X-ray flares with moderate contrast. Strong flares such as the one detected in GRB 050502B, instead, cannot be reproduced in this model and require strong variability in the engine activity.
Supernova remnants are thought to be the dominant source of Galactic cosmic
rays. This requires that at least 5% of the available energy is transferred to
cosmic rays, implying a high cosmic-ray pressure downstream of supernova
remnant shocks. Recently, it has been shown that the downstream temperature in
some remnants is low compared to the measured shock velocities, implying that
additional pressure support by accelerated particles is present.
Here we use a two-fluid thermodynamic approach to derive the relation between
post-shock fractional cosmic-ray pressure and post-shock temperature, assuming
no additional heating beyond adiabatic heating in the shock precursor and with
all non-adiabatic heating occurring at the subshock. The derived relations show
that a high fractional cosmic-ray pressure is only possible, if a substantial
fraction of the incoming energy flux escapes from the system. Recently a shock
velocity and a downstream proton temperature was measured for a shock in the
supernova remnant RCW 86. We apply the two-fluid solutions to these
measurements and find that the the downstream fractional cosmic-ray pressure is
at least 50% with a cosmic-ray energy flux escape of at least 20%. In general,
in order to have 5% of the supernova energy go into accelerating cosmic rays,
on average the post-shock cosmic-ray pressure needs to be 30% for an effective
cosmic-ray adiabatic index of 4/3.
I provide a pedagogic review of adaptive mesh refinement (AMR) radiation hydrodynamics (RHD) methods and codes used in simulations of star formation, at a level suitable for researchers who are not computational experts. I begin with a brief overview of the types of RHD processes that are most important to star formation, and then I formally introduce the equations of RHD and the approximations one uses to render them computationally tractable. I discuss strategies for solving these approximate equations on adaptive grids, with particular emphasis on identifying the main advantages and disadvantages of various approximations and numerical approaches. Finally, I conclude by discussing areas ripe for improvement.
We present chemical abundance analysis of a sample of 15 red giant branch (RGB) stars of the Globular Cluster NGC~1851 distributed along the two RGBs of the (v, v-y) CMD. We determined abundances for C+N+O, Na, $\alpha$, iron-peak, and s-elements. We found that the two RGB populations significantly differ in their light (N,O,Na) and s-element content. On the other hand, they do not show any significant difference in their $\alpha$ and iron-peak element content. More importantly, the two RGB populations do not show any significant difference in their total C+N+O content. Our results do not support previous hypotheses suggesting that the origin of the two RGBs and the two subgiant branches of the cluster is related to a different content of either $\alpha$ (including Ca) or iron-peak elements, or C+N+O abundance, due to a second generation polluted by SNeII.
Using archival VLBI data for 3114 radio-luminous active galactic nuclei, we searched for binary supermassive black holes using a radio spectral index mapping technique which targets spatially resolved, double radio-emitting nuclei. Only one source was detected as a double nucleus. This result is compared with a cosmological merger rate model and interpreted in terms of (1) implications for post-merger timescales for centralisation of the two black holes, (2) implications for the possibility of "stalled" systems, and (3) the relationship of radio activity in nuclei to mergers. Our analysis suggests that the binary evolution of paired supermassive black holes (both of masses >= 1e8 Msun) spends less than 500 Myr in progression from the merging of galactic stellar cores to within the purported stalling radius for supermassive black hole pairs. The data show no evidence for an excess of stalled binary systems at small separations. We see circumstantial evidence that the relative state of radio emission between paired supermassive black holes is correlated within orbital separations of 2.5 kpc.
We show that the motions of supergranules are consistent with a model in which they are simply advected by the axisymmetric flows in the Sun's surface shear layer. We produce a 10-day series of simulated Doppler images at a 15-minute cadence that reproduces most spatial and temporal characteristics seen in the SOHO/MDI Doppler data. Our simulated data have a spectrum of cellular flows with just two components -- a granule component that peaks at spherical wavenumbers of about 4000 and a supergranule component that peaks at wavenumbers of about 110. We include the advection of these cellular components by the axisymmetric flows -- differential rotation and meridional flow -- whose variations with latitude and depth (wavenumber) are consistent with observations. We mimic the evolution of the cellular pattern by introducing random variations to the phases of the spectral components at rates that reproduce the levels of cross-correlation as functions of time and latitude. Our simulated data do not include any wave-like characteristics for the supergranules yet can reproduce the rotation characteristics previously attributed to wave-like behavior. We find rotation rates which appear faster than the actual rotation rates and attribute this to the projection effects. We find that the measured meridional flow does accurately represent the actual flow and that the observations indicate poleward flow to $65\degr-70\degr$ latitude with equatorward counter cells in the polar regions.
Like the solar corona, the external magnetic field of magnetars is twisted by surface motions of the star. The twist energy is dissipated over time. We discuss the theory of this activity and its observational status. (1) Theory predicts that the magnetosphere tends to untwist in a peculiar way: a bundle of electric currents (the "j-bundle") is formed with a sharp boundary, which shrinks toward the magnetic dipole axis. Recent observations of shrinking hot spots on magnetars are consistent with this behavior. (2) Continual discharge fills the j-bundle with electron-positron plasma, maintaining a nonthermal corona around the neutron star. The corona outside a few stellar radii strongly interacts with the stellar radiation and forms a "radiatively locked" outflow with a high e+- multiplicity. The locked plasma annihilates near the apexes of the closed magnetic field lines. (3) New radiative-transfer simulations suggest a simple mechanism that shapes the observed X-ray spectrum from 0.1 keV to 1 MeV: part of the thermal X-rays emitted by the neutron star are reflected from the outer corona and then upscattered by the inner relativistic outflow in the j-bundle, producing a beam of hard X-rays.
The high-precision light curves from the Kepler mission contain valuable information on the nature of the phenomena producing the transit-like signals. To assist in exploring the possibility that they are the result of an astrophysical false positive, we describe a procedure we refer to as BLENDER to model the photometry not in terms of a planet orbiting a star, but instead as a "blend". A blend may consist of a background or foreground eclipsing binary (or star-planet pair) whose eclipses are attenuated by the light of the candidate and possibly other stars within the photometric aperture. We apply the technique to the case of KOI-377, a particularly interesting Kepler target harboring two previously confirmed Saturn-size planets (Kepler-9 b and Kepler-9 c) showing transit timing variations, and an additional shallower signal with a 1.6-day period that would correspond to a super-Earth with a radius of 1.4 R(Earth), the smallest yet discovered. Using BLENDER together with constraints from high-resolution imaging, spectroscopy, and astrometry (centroid motions), we are able to rule out all blends for the two deeper signals and provide independent validation of their planetary nature. For the shallower signal we rule out a large fraction of the false positive scenarios that might mimic these transit-like events. The false alarm rate (FAR) for remaining blends depends in part (and inversely) on the unknown frequency of small-size planets. Our most conservative (smallest) estimates of this frequency lead to a FAR of 0.0059, implying a high likelihood that the signal is due to a super-Earth-size planet rather than a false positive.
The 11-year activity cycle of the Sun is a consequence of a dynamo process occurring beneath its surface. We analyzed photometric data obtained by the CoRoT space mission, showing solar-like oscillations in the star HD49933, for signatures of stellar magnetic activity. Asteroseismic measurements of global changes in the oscillation frequencies and mode amplitudes reveal a modulation of at least 120 days, with the minimum frequency shift corresponding to maximum amplitude as in the Sun. These observations are evidence of a stellar magnetic activity cycle taking place beneath the surface of HD49933 and provide constraints for stellar dynamo models under conditions different from those of the Sun.
We study reconstruction of the lensing potential power spectrum from CMB temperature data, with an eye to the Planck experiment. We work with the optimal quadratic estimator of Okamoto and Hu, which we characterize thoroughly in application to reconstruction of the lensing power spectrum. We find that at multipoles L<250 our current understanding of this estimator is biased at the 15% level by beyond-gradient terms in the Taylor expansion of lensing effects. We present the full lensed trispectrum to fourth order in the lensing potential to explain this effect. We show that the low-L bias, as well as a previously known bias at high-L, is relevant to the determination of cosmology and must be corrected for in order to avoid significant parameter errors. We also investigate the covariance of the reconstructed power, finding broad correlations of ~0.1%. Finally, we discuss several small improvements which may be made to the optimal estimator to mitigate these problems.
We propose two efficient numerical methods of evaluating the luminosity distance in the spatially flat LCDM universe. The first method is based on the Carlson symmetric form of elliptic integrals, which is highly accurate and can replace numerical quadratures. The second method, using a modified version of Hermite interpolation, is less accurate but involves only basic numerical operations and can be easily implemented. We compare our methods with other numerical approximation schemes and explore their respective features and limitations. Possible extensions of these methods to other cosmological models are also discussed.
Recently, type Ia supernovae data appear to support a dark energy whose equation of state $w$ crosses $-1$, which is a much more amazing problem than the acceleration of the universe. We show that it is possible for the equation of state to cross the phantom divide by only a single scalar field in the gravity with an additional inverse power-law term of Ricci scalar in the Lagrangian. The necessary and sufficient condition for a universe in which the dark energy can cross the phantom divide is obtained. Some analytical solutions with $w<-1$ or $w>-1$ are obtained. A minimal coupled scalar with different potentials, including quadratic, cubic, quantic, exponential and logarithmic potentials are investigated via numerical methods, respectively. All these potentials lead to the crossing behavior. We show that it is a general geometric result which is independent on the concrete form of the potential of the scalar.
The recently commissioned Compact Array Broadband Backend (CABB) on the Australia Telescope Compact Array (ATCA) provides 2 GHz bandwidth in each frequency and polarisation, significantly increasing the sensitivity of the Array. This increased sensitivity allows for larger samples of sources to be targeted whilst also probing fainter radio luminosities. Using CABB, we have observed a large sample of objects at 20 GHz to investigate the high-frequency radio luminosity distribution of X-ray selected QSOs at redshifts less than 1. Observing at high frequencies allows us to focus on the core emission of the AGN, hence recording the most recent activity.
We present the result of our investigation on the impact of the low Solar abundance of Asplund and collaborators (2004) on the derived ages for the oldest star clusters based on isochrone fittings. We have constructed new stellar models and corresponding isochrones using this new solar mixture with a proper Solar calibration. We have found that the use of the Asplund et al. (2004) metallicity causes the typical ages for old globular clusters in the Milky Way to be increased roughly by 10\%. Although this may appear small, it has a significant impact on the interpretation for the formation epoch of Milky Way globular clusters. The Asplund et al. (2004) abundance may not necessarily threaten the current concordance cosmology but would suggest that Milky Way globular clusters formed before the reionization and before the main galaxy body starts to build up. This is in contrast to the current understanding on the galaxy formation.
The study concerns the streamer belt observed at high spectral resolution during the minimum of solar cycle 22 with the Ultraviolet Coronagraph Spectrometer (UVCS) onboard SOHO. On the basis of a spectroscopic analysis of the O VI doublet, the solar wind plasma parameters are inferred in the extended corona. The analysis accounts for the coronal magnetic topology, extrapolated through a 3D magneto-hydrodynamic model, in order to define the streamer boundary and to analyse the edges of coronal holes. The results of the analysis allow an accurate identification of the source regions of the slow coronal wind that are confirmed to be along the streamer boundary in the open magnetic field region.
We investigate the observational constraints on the oscillating scalar field model using data from type Ia supernovae, cosmic microwave background anisotropies, and baryon acoustic oscillations. According to a Fourier analysis, the galaxy number count $N$ from redshift $z$ data indicates that galaxies have preferred periodic redshift spacings. We fix the mass of the scalar field as $m_\phi=3.2\times 10^{-31}h$ ${\rm eV}$ such that the scalar field model can account for the redshift spacings, and we constrain the other basic parameters by comparing the model with accurate observational data. We obtain the following constraints: $\Omega_{m,0}=0.28\pm 0.03$ (95\% C.L.), $\Omega_{\phi,0} < 0.035$ (95\% C.L.), $\xi > -158$ (95\% C.L.) (in the range $\xi \le 0$). The best fit values of the energy density parameter of the scalar field and the coupling constant are $\Omega_{\phi,0}= 0.01$ and $\xi= -25$, respectively. The value of $\Omega_{\phi,0}$ is close to but not equal to $0$. Hence, in the scalar field model, the amplitude of the galaxy number count cannot be large. However, because the best fit values of $\Omega_{\phi,0}$ and $\xi$ are not $0$, the scalar field model has the possibility of accounting for the periodic structure in the $N$--$z$ relation of galaxies. The variation of the effective gravitational constant in the scalar field model is not inconsistent with the bound from observation.
We carry out hydrodynamical simulations of galaxy formation that simultaneously follow radiative transfer of hydrogen-ionising photons, based on the optically-thin variable Eddinton tensor approximation as implemented in the {\small GADGET} code. We consider only star-forming galaxies as sources and examine to what extent they can yield a reasonable reionisation history and thermal state of the intergalactic medium at redshifts around $z\sim 3$. This serves as an important benchmark for our self-consistent methodology to simulate galaxy formation and reionisation, and for future improvements through accounting of other sources and other wavelength ranges. We find that star formation alone is sufficient for reionising the Universe by redshift $z\sim6$. For a suitable choice of the escape fraction and the heating efficiency, our models are approximately able to account at the same time for the one-point function and the power spectrum of the Lyman-$\alpha$ forest. The radiation field has an important impact on the star formation rate density in our simulations and significantly lowers the gaseous and stellar fractions in low-mass dark matter halos. Our results thus directly demonstrate the importance of radiative feedback for galaxy formation. The spatial and temporal importance of this effect can be studied accurately with the modelling technique explored here, allowing more faithful simulations of galaxy formation.
Context: The dusty nuclear regions of luminous infra-red galaxies (LIRGs) are heated by either an intense burst of massive star formation, an active galactic nucleus (AGN), or a combination of both. Disentangling the contribution of each of those putative dust-heating agents is a challenging task, and direct imaging of the innermost few pc can only be accomplished at radio wavelengths, using very high-angular resolution observations. Aims: We observed the nucleus A of the interacting starburst galaxy Arp 299, using very long baseline interferometry (VLBI) radio observations at 1.7 and 5.0 GHz. Our aim was to characterize the compact sources in the innermost few pc region of Arp 299-A, as well as to detect recently exploded core-collapse supernovae. Methods: We used the European VLBI Network (EVN) to image the 1.7 and 5.0 GHz compact radio emission of the parsec-scale structure in the nucleus of Arp 299-A with milliarcsecond resolution. Results: Our EVN observations show that one of the compact VLBI sources, A1, previously detected at 5.0 GHz, has a flat spectrum between 1.7 and 5.0 GHz and is the brightest source at both frequencies. Our 1.7 GHz EVN image shows also diffuse, low-surface brightness emission extending westwards from A1 and displays a prominent core-jet structure. Conclusions: The morphology, radio luminosity, spectral index and ratio of radio-to-X-ray emission of the A1-A5 region is consistent with a low-luminosity AGN (LLAGN), and rules out the possibility that it is a chain of young radio supernovae (RSNe) and supernova remnants (SNRs). We therefore conclude that A1-A5 is the long-sought AGN in Arp 299-A. This finding may suggest that both starburst and AGN are frequently associated phenomena in mergers.
In order to investigate the origin of the excess of strong MgII systems towards GRB afterglows as compared to QSO sightlines, we have measured the incidence of MgII absorbers towards a third class of objects: the Blazars. This class includes the BL Lac object population for which a tentative excess of MgII systems had already been reported. We observed with FORS1 at the ESO-VLT 42 Blazars with an emission redshift 0.8<z_em<1.9, to which we added the three high z northern objects belonging to the 1Jy BL Lac sample. We detect 32 MgII absorbers in the redshift range 0.35-1.45, leading to an excess in the incidence of MgII absorbers compared to that measured towards QSOs by a factor ~2, detected at 3 sigma. The amplitude of the effect is similar to that found along GRB sightlines. Our analysis provides a new piece of evidence that the observed incidence of MgII absorbers might depend on the type of background source. In front of Blazars, the excess is apparent for both 'strong' (w_ r(2796) > 1.0 A) and weaker (0.3 < w_r(2796) < 1.0 A) MgII systems. The dependence on velocity separation with respect to the background Blazars indicates, at the ~1.5 sigma level, a potential excess for beta = v/c ~0.1. We show that biases involving dust extinction or gravitational amplification are not likely to notably affect the incidence of MgII systems towards Blazars. Finally we discuss the physical conditions required for these absorbers to be gas entrained by the powerful Blazar jets. More realistic numerical modelling of jet-ambient gas interaction is required to reach any firm conclusions as well as repeat observations at high spectral resolution of strong MgII absorbers towards Blazars in both high and low states.
We submit recent claims of a semi-significant detection of primordial tensor perturbations in the WMAP data to a closer scrutiny. Our conclusion is in brief that no such mode is present at a detectable level once the analysis is done more carefully. These claims have their root in a brief debate in the late 1990s about the standard calculation of the scalar and tensor spectra in standard inflationary theory, where Grishchuk and collaborators claimed that their amplitudes should be roughly equal. We give a brief summary of the debate and our own reasons for why the standard calculation is correct.
LINC-NIRVANA will realize the interferometric imaging focal station of the Large Binocular Telescope. A double Layer Oriented multi-conjugate adaptive optics system assists the two arms of the interferometer, supplying high order wave-front correction. In order to counterbalance the field rotation, mechanical derotation for the two ground wave-front sensors, and optical derotators for the mid-high layers sensors fix the positions of the focal planes with respect to the pyramids aboard the wave-front sensors. The derotation introduces pupil images rotation on the wavefront sensors: the projection of the deformable mirrors on the sensor consequently change. The proper adjustment of the control matrix will be applied in real-time through numerical computation of the new matrix. In this paper we investigate the temporal and computational aspects related to the pupils rotation, explicitly computing the wave-front errors that may be generated.
Black holes are fascinating objects. As a class of solutions to the Einstein equations they have been studied a great deal, yielding a wealth of theoretical results. But do they really exist? What do astronomers really mean when they claim to have observational evidence of their existence? To answer these questions, I will focus on a particular range of black-hole masses, approximately from 100 to 10000 solar masses. Black holes of this size are named Intermediate Mass Black Holes (IMBHs) and their existence is still heavily disputed, so they will be perfect for illustrating the observational challenges faced by a black hole hunter
We present an accurate analysis of the peculiar Horizontal Branch (HB) of the massive Galactic globular cluster NGC 2808, based on high-resolution far-UV and optical images of the central region of the cluster obtained with HST. We confirm the multimodal distribution of stars along the HB: 4 sub-populations separated by gaps are distinguishable. The detailed comparison with suitable theoretical models showed that (i) it is not possible to reproduce the luminosity of the entire HB with a single helium abundance, while an appropriate modeling is possible for three HB groups by assuming different helium abundances in the range 0.24 < Y < 0.4 that are consistent with the multiple populations observed in the Main Sequence; (ii) canonical HB models are not able to properly match the observational properties of the stars populating the hottest end of the observed HB distribution, the so called "blue-hook region". These objects are probably "hot-flashers" , stars that peel off the red giant branch before reaching the tip and ignite helium at high effective temperatures. Both of these conclusions are based on the luminosity of the HB in the optical and UV bands and do not depend on specific assumptions about mass loss.
The observable quantities in optical interferometry, which are the modulus
and the phase of the complex visibility, may be corrupted by parasitic fringes
superimposed on the genuine fringe pattern. These fringes are due to an
interference phenomenon occurring from straylight effects inside an
interferometric instrument. We developed an analytical approach to better
understand this phenomenon when straylight causes crosstalk between beams.
We deduced that the parasitic interference significantly affects the
interferometric phase and thus the associated observables including the
differential phase and the closure phase. The amount of parasitic flux coupled
to the piston between beams appears to be very influential in this degradation.
For instance, considering a point-like source and a piston ranging from
$\lambda/500$ to $\lambda/5$ in L band ($\lambda=3.5\:\mu$m), a parasitic flux
of about 1\% of the total flux produces a parasitic phase reaching at most one
third of the intrinsic phase. The piston, which can have different origins
(instrumental stability, atmospheric perturbations, ...), thus amplifies the
effect of parasitic interference.
According to specifications of piston correction in space or at ground level
(respectively $\lambda/500\approx 2$nm and $\lambda/30\approx 100$nm), the
detection of hot Jupiter-like planets, one of the most challenging aims for
current ground-based interferometers, limits parasitic radiation to about 5\%
of the incident intensity. This was evaluated by considering different types of
hot Jupiter synthetic spectra.
Otherwise, if no fringe tracking is used, the detection of a typical hot
Jupiter-like system with a solar-like star would admit a maximum level of
parasitic intensity of 0.01\% for piston errors equal to $\lambda$/15. If the
fringe tracking specifications are not precisely observed, it thus appears that
the allowed level of parasitic intensity dramatically decreases and may prevent
the detection. In parallel, the calibration of the parasitic phase by a
reference star, at this accuracy level, seems very difficult. Moreover, since
parasitic phase is an object-dependent quantity, the use of a hypothetical
phase abacus, directly giving the parasitic phase from a given parasitic flux
level, is also impossible. Some instrumental solutions, implemented at the
instrument design stage for limiting or preventing this parasitic interference,
appears to be crucial and are presented in this paper.
Modified teleparallel gravity theory with the torsion scalar have recently gained a lot of attention as a possible explanation of dark energy. We perform a thorough reconstruction analysis on the so-called $F(T)$ models, where $F(T)$ is some general function of the torsion term, and derive conditions for the equivalence between of $F(T)$ models with purely kinetic k-essence. We present a new class models of $F(T)$ - gravity and k-essence.
A complex event observed in the radio pulses from the Crab pulsar in 1997 included echoes, a dispersive delay, and large changes in intensity. It is shown that these phenomena were due to refraction at the edge of a plasma cloud in the outer region of the Crab Nebula. Several similar events have been observed, although in less detail. It is suggested that the plasma cloud is in the form of filaments with diameter around 3 x 10^11m and electron density of order 10^4 cm-3
Aims: We study the formation of substellar objects (exoplanets and brown dwarfs) as companions to young nearby stars. Methods: With high contrast AO imaging obtained with NACO at ESO's VLT we search for faint companion-candidates around our targets, whose companionship can be confirmed with astrometry. Results: In the course of our imaging campaign we found a faint substellar companion of the nearby pre-main sequence star PZ Tel, a member of the beta Pic moving group. The companion is 5-6 mag fainter than its host star in JHK and is located at a separation of only 0.3 arcsec (or 15 AU of projected separation) north-east of PZ Tel. Within three NACO observing epochs we could confirm common proper motion (>39 sigma) and detected orbital motion of PZ Tel B around its primary (>37 sigma). The photometry of the newly found companion is consistent with a brown dwarf with a mass of 24 to 40 MJup, at the distance (50 pc) and age (8-20 Myr) of PZ Tel. The effective temperature of the companion, derived from its photometry, ranges between 2500 and 2700 K, which corresponds to a spectral type between M6 and M8. After beta Pic b, PZ Tel B is the second closest substellar companion imaged directly around a young star.
We present radiation hydrodynamics simulations of the collapse of massive pre-stellar cores. We treat frequency dependent radiative feedback from stellar evolution and accretion luminosity at a numerical resolution down to 1.27 AU. In the 2D approximation of axially symmetric simulations, it is possible for the first time to simulate the whole accretion phase (up to the end of the accretion disk epoch) for the forming massive star and to perform a broad scan of the parameter space. Our simulation series show evidently the necessity to incorporate the dust sublimation front to preserve the high shielding property of massive accretion disks. While confirming the upper mass limit of spherically symmetric accretion, our disk accretion models show a persistent high anisotropy of the corresponding thermal radiation field. This yields to the growth of the highest-mass stars ever formed in multi-dimensional radiation hydrodynamics simulations, far beyond the upper mass limit of spherical accretion. Non-axially symmetric effects are not necessary to sustain accretion. The radiation pressure launches a stable bipolar outflow, which grows in angle with time as presumed from observations. For an initial mass of the pre-stellar host core of 60, 120, 240, and 480 Msun the masses of the final stars formed in our simulations add up to 28.2, 56.5, 92.6, and at least 137.2 Msun respectively.
Using simultaneous observations in X-rays and optical, we have performed a homogeneous analysis of the cross-correlation behaviours of four X-ray binaries: SWIFT J1753.5-0127, GX 339-4, Sco X-1, and Cyg X-2. With high time-resolution observations using ULTRACAM and RXTE, we concentrate on the short time-scale, dt<20 s, variability in these sources. Here we present our database of observations, with three simultaneous energy bands in both the optical and the X-ray, and multiple epochs of observation for each source, all with ~second or better time resolution. For the first time, we include a dynamical cross-correlation analysis, i.e., an investigation of how the cross-correlation function changes within an observation. We describe a number of trends which emerge. We include the full dataset of results, and pick a few striking relationships from among them for further discussion. We find, that the surprising form of X-ray/optical cross-correlation functions, a positive correlation signal preceded by an anti-correlation signal, is seen in all the sources at least some of the time. Such behaviour suggests a mechanism other than reprocessing as being the dominant driver of the short-term variability in the optical emission. This behaviour appears more pronounced when the X-ray spectrum is hard. Furthermore, we find that the cross-correlation relationships themselves are not stable in time, but vary significantly in strength and form. This all hints at dynamic interactions between the emitting components which could be modelled through non-linear or differential relationships.
The continuum high-energy gamma-ray emission between 1 GeV and 100 TeV from the Crab Nebula has been measured for the first time in overlapping energy bands by the Fermi large-area telescope (Fermi/LAT) below ~ 100 GeV and by ground-based imaging air Cherenkov telescopes (IACTs) above ~ 60 GeV. To follow up on the phenomenological approach suggested by Hillas et al. (1998), the broad band spectral and spatial measurement (from radio to low-energy gamma-rays < 1 GeV) is used to extract the shape of the electron spectrum. While this model per construction provides an excellent description of the data at energies < 1 GeV, the predicted inverse Compton component matches the combined Fermi/LAT and IACT measurements remarkably well after including all relevant seed photon fields and fitting the average magnetic field to B = (124 +/- 6 (stat.) +15 / -6 (sys.) ) {\mu}G. The close match of the resulting broad band inverse Compton component with the combined Fermi/LAT and IACTs data is used to derive instrument specific energy-calibration factors. These factors can be used to combine data from Fermi/LAT and IACTs without suffering from systematic uncertainties on the common energy scale. As a first application of the cross calibration, we derive an upper limit to the diffuse gamma-ray emission between 250 GeV and 1 TeV based upon the combined measurements of Fermi/LAT and the H.E.S.S. ground-based Cherenkov telescopes. Finally, the predictions of the magneto-hydrodynamic flow model of Kennel & Coroniti (1984) are compared to the measured SED.
We utilize the extensive datasets available for the Perseus molecular cloud to analyze the relationship between the kinematics of small-scale dense cores and the larger structures in which they are embedded. The kinematic measures presented here can be used in conjunction with those discussed in our previous work as strong observational constraints that numerical simulations (or analytic models) of star formation should match. We find that dense cores have small motions with respect to the 13CO gas, about one third of the 13CO velocity dispersion along the same line of sight. Within each extinction region, the core-to-core velocity dispersion is about half of the total (13CO) velocity dispersion seen in the region. Large-scale velocity gradients account for roughly half of the total velocity dispersion in each region, similar to what is predicted from large-scale turbulent modes following a power spectrum of P(k) ~ k^{-4}.
We present methodology and results of numerical modeling of the interaction of GRB prompt emission with the circumburst medium using a modified version of the multi-group radiation hydrocode STELLA. The modification includes the nonstationary photoionization, the photoionization heating and the Compton heating along with the hydrodynamics and radiation transfer. The lightcurves and spectra of the outcoming gamma-ray, X-ray and optical emission are calculated for a set of models (shells) of the circumburst environment, which differ in dimensions, density, density profile, composition, temperature. In some cases total bolometric and optical luminosities can reach 10^47 and 10^43 erg/s respectively. These effects can be responsible for irregularities which are seen on lightcurves of some GRB's X-ray and optical afterglows.
The DQ white dwarfs are stars whose atmosphere is enriched with carbon, which for cool stars ($T_{\rm eff}<8000\rm \, K$) is indicated by the Swan bands of $\rm C_2$ in the optical part of their spectra. With decreasing effective temperature these molecular bands undergo a significant blueshift ($\sim 100-300 \AA$). The origin of this phenomenon has been disputed over the last two decades and has remained unknown. We attempt to address this problem by investigating the impact of dense helium on the spectroscopic properties of molecular carbon under the physical conditions encountered inside helium-rich, fluid-like atmospheres of cool DQ white dwarfs. We found that the electronic transition energy $T_e$ increases monotonically with the helium density ($\Delta T_{\rm e}\rm\, (eV)\sim1.6 \, \it \rho \rm \, (g/cm^3)$). This causes the Swan absorption to occur at shorter wavelengths compared with unperturbed $\rm C_2$. On the other hand the pressure-induced increase in the vibrational frequency is insufficient to account for the observed Swan bands shifts. This is consistent with the observations and indicates that the observed Swan-like molecular bands are most likely the pressure-shifted bands of $\rm C_2$.
(abridged) We have measured the absolute proper motions of nine low-latitude,
inner Galaxy globular clusters, namely NGC 6273 (M 19), NGC 6284, NGC 6287, NGC
6293, NGC 6333 (M 9), NGC 6342, NGC 6356, NGC 6388 and NGC 6441. These are the
first determinations ever made for these clusters. The proper motions are on
the ICRS via Hipparcos. The proper-motion errors range between 0.4 and 0.9
mas/yr, and are dominated by the number of measurable cluster members in these
regions which are very crowded by the bulge/bar and the thick disk. This samle
contains five metal poor ([Fe/H < -1.0) and four metal rich clusters; seven
clusters are located within 4 kpc from the Galactic center, while the remaining
two, namely NGC 6356 and NGC 6284 are in the background of the bulge at 7.5 kpc
from the Galactic center. By combining proper motions with radial velocities
and distances from the literature we derive 3D velocities. In a number of
cases, distance uncertainties make the kinematical classification ambiguous.
The two metal rich clusters NGC 6388 and NGC 6441 have velocities
incompatibile with membership in the thick disk or the bar of the Milky Way.
They can be though of as members of a kinematically hot system in the inner
Galaxy. Curiously, both clusters have similar velocity components. Together
with their similar Galactic location and peculiar but similar
stellar-population characteristics, these two clusters may share a common
origin. Their velocities are also very low indicating that the two clusters are
now at/near apocenter, and they will not leave the inner ~4 kpc of the Galaxy.
In support of the EPOXI mission, we have compiled the secular light curve (SLC) of comet 103P/Hartley 2, the next target of EPOXI. a) Of the order of 30 photometric parameters are measured, over 20 of them new. The turn on point of activity is -4.2 +/- 0.1 AU from the Sun, which corresponds to -400 +/- 40 d before perihelion. The total active time is TACTIVE= 1484 +/- 43 d. b) 103P is a young dwarf comet, young because it has a photometric age P-AGE(1,1) = 15 +/- 2 cy (comet years), and dwarf because its diameter is DEFFE = 1.14 +/- 0.16 km. c) The nucleus is very active, and the amplitude of the SLC is ASEC= 10.8 +/- 0.1 mag in 1997. This comet is as active as 1P/Halley, but much smaller. d) After remaining active up to aphelion, the comet spills-over its activity into the next orbit. e) Two linear laws change slope at a break point located at RBP = -1.20 +/- 0.1 AU before perihelion, and magnitude mBP = 9.4 +/- 0.1. Sublimation is not controlled by water ice. The controlling substance may be CO or CO2 ice. CO2 has been detected spectroscopically. f) The water budget of this comet is calculated. The comet expends 1.88 10^10 kg of water per apparition. A new water-budget age is defined and it is found that WB-AGE = 19 cy vs WB-AGE = 0.65 cy for 1P/Halley and 28 cy for 9P. g) The values of Af{\rho} are calculated on two dates and we find dust production rates of 106 and 37 kg/s. h) The thickness of the layer lost per apparition is calculated, and we find {\Delta}r = 39 m where r is the radius. Since the radius of this comet is r = 570 m, it is found that at the present rate the comet may disappear in only 17 revolutions (~109 y). i) All comets visited by spacecraft are young objects. 103P follows the same trend. It is expected that the surface morphology that will be found in future EPOXI images should be very similar to that of previous comets.
The IfA Deep survey uncovered ~130 thermonuclear supernovae (TNSNe, i.e. Type Ia) candidates at redshifts from z=0.1 out to beyond z=1. The TNSN explosion rates derived from these data have been controversial, conflicting with evidence emerging from other surveys. This work revisits the IfA Deep survey to re-evaluate the photometric evidence. Applying the SOFT program to the light curves of all SN candidates, we derive new classification grades and redshift estimates. We find a volumetric rate for z~0.5 that is substantially smaller than the originally published values, bringing the revised IfA Deep rate into good agreement with other surveys. With our improved photometric analysis techniques, we are able to confidently extend the rate measurements to higher redshifts, and we find a steadily increasing TNSN rate, with no indication of a peak out to z=1.05.
We present a sample of 968 K5-M6 dwarfs detected in the AKARI-IRC Point Source Catalog. The vast majority of these low-mass stars have brightnesses in the AKARI broad 9-micron (S9W) filter that match expectations of model photospheres. Mismatched double stars have been excluded. Hot (200-600K) debris disks can produce excesses in this mid-infrared filter. We discuss five M dwarfs which have excesses that may be significant but require independent confirmation. We also discuss 50 detections with the L18W filter, and support the claimed Spitzer detection of a warm debris disk around AT Mic. We also report a previously unrecognized disk around a T Tauri star.
With the use of N-body calculations the amount and properties of escaping stars from low-N (N = 100 and 1000) young embedded star clusters prior to gas expulsion are studied over the first 5 Myr of their existence. Besides the number of stars also different initial radii and binary populations are examined as well as virialised and collapsing clusters. It is found that these clusters can loose substantial amounts (up to 20%) of stars within 5 Myr with considerable velocities up to more than 100 km/s. Even with their mean velocities between 2 and 8 km/s these stars will still be travelling between 2 and 30 pc during the 5 Myr. Therefore can large amounts of distributed stars in star-forming regions not necessarily be counted as evidence for the isolated formation of stars.
In the minimal formulation of gravity with Lifshitz-type anisotropic scaling, the gauge symmetries of the system are foliation-preserving diffeomorphisms of spacetime. Consequently, compared to general relativity, the spectrum contains an extra scalar graviton polarization. Here we investigate the possibility of extending the gauge group by a local U(1) symmetry to "nonrelativistic general covariance." This extended gauge symmetry eliminates the scalar graviton, and forces the coupling constant $\lambda$ in the kinetic term of the minimal formulation to take its relativistic value, $\lambda=1$. The resulting theory exhibits anisotropic scaling at short distances, and reproduces many features of general relativity at long distances.
We describe in detail full numerical and perturbative techniques to compute the gravitational radiation from intermediate mass ratio (IMR) black-hole-binary (BHB) inspirals and mergers. We perform a series of full numerical simulations of nonspinning black holes with mass ratios q=1/10 and q=1/15 from different initial separations and for different finite difference resolutions. The highest resolution runs reach phase accuracies with errors <0.05 radians when the gravitational wave frequency is 0.2/M. In order to perform those full numerical runs, we adapted the gauge of the moving punctures approach with a variable damping term for the shift. We also derive an extrapolation (to infinite radius) formula for the waveform extracted at finite radius. For the perturbative evolutions we use the full numerical tracks, transformed into the Schwarzschild gauge, in the source terms of the Regge-Wheller-Zerilli Schwarzschild perturbations formalism. We then extend this perturbative formalism to take into account small intrinsic spins of the large black hole, and validate it by computing the quasinormal mode (QNM) frequencies, where we find good agreement for spins |a/M|<0.3. Including the final spins improves the overlap functions when comparing full numerical and perturbative waveforms, reaching 99.5% for the leading (l,m)=(2,2) and (3,3) modes, and 98.3% for the nonleading (2,1) mode in the q=1/10 case, which includes 8 orbits before merger. For the q=1/15 case, we obtain overlaps near 99.7% for all three modes. We discuss the modeling of the full inspiral and merger based on a combined matching of Post-Newtonian, Full Numerical, and Geodesic trajectories.
We propose a possible new way to resolve the long standing problem of strong supersymmetry breaking coexisting with a small cosmological constant. We consider a scalar component of a minimally coupled N=1 supermultiplet in a general Friedmann-Robertson-Walker (FRW) expanding universe. We argue that a tiny term, proportional to H^2 ~ 10^(-122) in Plank's units, appearing in the field equations due to this expansion will provide both, the small vacuum energy and the heavy mass of the scalar supersymmetric partner. We present a non-perturbative solution for the scalar field with an unusual dual-frequency behavior. This solution has two characteristic mass scales related to the Hubble parameter as H^(1/4) and H^(1/2) measured in Plank's units.
We use four years of introductory astronomy scores to analyze the ability of
the current population to perform college level work and measure the amount of
grade inflation across various majors. Using an objective grading scale, one
that is independent of grading curves, we find that 29% of intro astronomy
students fail to meet minimal standards for college level work. Of the
remaining students, 41% achieve satisfactory work, 30% achieve mastery of the
topics.
Intro astronomy scores correlate with SAT and college GPA. Sequential mapping
of the objective grade scheme onto GPA finds that college grades are inflated
by 0.2 for natural sciences majors, 0.3 for social sciences, professional
schools and undeclared majors), 0.5 for humanities majors. It is unclear from
the data whether grade inflation is due to easier grading curves or depression
of course material. Experiments with student motivation tools indicates that
poor student performance is due to deficiency in student abilities rather than
social factors (such as study time or decreased interest in academics), i.e.,
more stringent admission standards would resolve grade inflation.
We construct a chaotic inflation model in which the Higgs fields play the role of the inflaton in the singlet extension of the supersymmetric standard model. The key idea is to impose a shift symmetry on the D-flat direction Hu Hd in the Kahler potential. The model is a realization of the recently proposed running kinetic inflation, in which the coefficient of the kinetic term grows as the inflaton field. The inflaton potential depends on the structure of the Higgs sector. For instance, the inflaton potential is proportional to phi^{2/3} during inflation in the NMSSM.
The relativistic quantum interference effects in the spacetime of slowly rotating object in the Ho\v{r}ava-Lifshitz gravity as the Sagnac effect and phase shift of interfering particle in neutron interferometer are derived. We consider the extension of Kehagias-Sfetsos (KS) solution~\cite{ks09} in the Ho\v{r}ava-Lifshitz gravity for the slowly rotating gravitating object. Using the covariant Klein-Gordon equation in the nonrelativistic approximation, it is shown that the phase shift in the interference of particles includes the gravitational potential term with the KS parameter $\omega$. It is found that in the case of the Sagnac effect, the influence of the KS parameter $\omega$ is becoming important due to the fact that the angular velocity of the locally non rotating observer is increased in Ho\v{r}ava gravity. From the results of the recent experiments~\cite{holgeretal} we have obtained lower limit for the coupling KS constant as $\omega \simeq 1.25 \cdot 10^{-25} \rm{cm}^{2}$. Finally, as an example, we apply the obtained results to the calculation of the UCN (ultra-cold neutrons) energy level modification in the gravitational field of slowly rotating gravitating object in the Ho\v{r}ava-Lifshitz gravity.
We calculate the rate for thermal production of axions via scattering of quarks and gluons in the primordial quark-gluon plasma. To obtain a finite result in a gauge-invariant way that is consistent to leading order in the strong gauge coupling, we use systematic field theoretical methods such as hard thermal loop resummation and the Braaten-Yuan prescription. The thermally produced yield, the decoupling temperature, and the density parameter are computed for axions with a mass below 10 meV. In this regime, with a Peccei-Quinn scale above 6x10^8 GeV, the associated axion population can still be relativistic today and can coexist with the axion cold dark matter condensate.
We update our estimates of charged and neutral current neutrino total cross sections on isoscalar nucleons at ultrahigh energies using a global (x, Q^2) fit, motivated by the Froissart bound, to the F_2 (electron-proton) structure function utilizing the most recent analysis of the complete ZEUS and H1 data sets from HERA I. Using the large Q^2, small Bjorken-x limits of the "wee" parton model, we connect the ultrahigh energy neutrino cross sections directly to the large Q^2, small-x extrapolation of our new fit, which we assume saturates the Froissart bound. We compare both to our previous work, which utilized only the smaller ZEUS data set, as well as to recent results of a calculation using the ZEUS-S based global perturbative QCD parton distributions using the combined HERA I results as input. Our new results substantiate our previous conclusions, again predicting significantly smaller cross sections than those predicted by extrapolating pQCD calculations to neutrino energies above 10^9 GeV.
In inflationary models, the predicted amplitude of primordial density perturbations Q is much larger than the observed value (~10^{-5}) for natural choices of parameters. To explain the requisite exponential fine-tuning, anthropic selection is often invoked, especially in cases where microphysics is expected to produce a complex energy landscape. By contrast, we find examples of ekpyrotic models based on heterotic M-theory for which dynamical selection naturally favors the observed value of Q.
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