The most compact bright radio-loud AGN—I. A new target sample selected for the space VLBI

We investigated the archival ground-based VLBI images of the extragalactic radio sources included in both the Wilkinson Microwave Anisotropy Probe (WMAP) and the Planck catalogues, and selected 49 bright and compact sources as potential targets for space Very Long Baseline Interferometry (VLBI) observations at mm wavelengths. These sources have a flat radio continuum spectrum between 33 and 94 GHz. They are identified as core-dominated active galactic nuclei (AGN), located at declinations above ?40^°, and have never been observed with ground-based VLBI at 86 GHz. The radio properties of the 49 new sources are presented. We compare this new sample with similar samples of compact AGN available from earlier studies. The new candidates, together with the existing bright compact AGN sample identified from 86-GHz ground-based VLBI imaging surveys, form a catalogue of more than 160 AGN. These could be primary targets for mm-VLBI observations on the ground, as well as for future mm-wavelength space VLBI missions such as the project with two satellites currently under study in China.     

Excess B‐modes extracted from the Planck polarization maps

One of the main obstacles for extracting the Cosmic Microwave Background (CMB) from mm/submm observations is the pollution from the main Galactic components: synchrotron, free‐free and thermal dust emission. The feasibility of using simple neural networks to extract CMB has been demonstrated on both temperature and polarization data obtained by the WMAP satellite. The main goal of this paper is to demonstrate the feasibility of neural networks for extracting the CMB signal from the Planck polarization data with high precision. Both auto‐correlation and cross‐correlation power spectra within a mask covering about 63 % of the sky have been used together with a “high pass filter” in order to minimize the influence of the remaining systematic errors in the Planck Q and U maps. Using the Planck 2015 released polarization maps, a BB power spectrum have been extracted by Multilayer Perceptron neural networks. This spectrum contains a bright feature with signal to noise ratios 4.5 within 200 ≪ l ≪ 250. The spectrum is significantly brighter than the BICEP2 2015 spectrum, with a spectral behaviour quite different from the “canonical” models (weak lensing plus B‐modes spectra with different tensor to scalar ratios). The feasibility of the neural network to remove the residual systematics from the available Planck polarization data to a high level has been demonstrated. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A fast method for finding bound systems in numerical simulations: Results from the formation of asteroid binaries

We present a new code (companion) that identifies bound systems of particles in O(NlogN) time. Simple binaries consisting of pairs of mutually bound particles and complex hierarchies consisting of collections of mutually bound particles are identifiable with this code. In comparison, brute force binary search methods scale as O(N²) while full hierarchy searches can be as expensive as O(N³), making analysis highly inefficient for multiple data sets with N?¹⁰³. A simple test case is provided to illustrate the method. Timing tests demonstrating O(NlogN) scaling with the new code on real data are presented. We apply our method to data from asteroid satellite simulations [Durda et al., 2004. Icarus 167, 382-396; Erratum: Icarus 170, 242; reprinted article: Icarus 170, 243-257] and note interesting multi-particle configurations. The code is available at http://www.astro.umd.edu/zoe/companion/ and is distributed under the terms and conditions of the GNU Public License.     

Hunting for overlooked eccentric eclipsing binaries from ASAS-3 survey

We present the results of searching for new candidates of eclipsing binaries with eccentric orbits in the ASAS Catalog of Variable Stars (ACVS) using publicly available data from the All Sky Automated Survey (ASAS) and the Transiting Exoplanet Survey Satellite (TESS). Unsupervised machine learning techniques were applied to find anomalies among the light curves of eclipsing binaries. The light curves modeling were performed using JKTEBOP code. The pulsation analysis was done with FAMIAS. We identified 19 new eclipsing binary candidates with non-zero eccentricities in the ACVS, including 10 candidates with eccentricities e ≥ 0.1. Estimates of eccentricities are given. We also report on possible presence of the small-amplitude stellar pulsations at least in two of the reported systems.     

A tool to estimate the Fermi Large Area Telescope background for short-duration observations

The proper estimation of the background is a crucial component of data analyses in astrophysics, such as source detection, temporal studies, spectroscopy, and localization. For the case of the Large Area Telescope (LAT) on board the Fermi spacecraft, approaches to estimate the background for short (≲1000 s duration) observations fail if they ignore the strong dependence of the LAT background on the continuously changing observational conditions. We present a (to be) publicly available background-estimation tool created and used by the LAT Collaboration in several analyses of Gamma Ray Bursts. This tool can accurately estimate the expected LAT background for any observational conditions, including, for example, observations with rapid variations of the Fermi spacecraft’s orientation occurring during automatic repointings.     

Galaxy properties derived with spectral energy distribution fitting in the Hawaii-Hubble Deep Field-North

We compile multi-wavelength data from ultraviolet to infrared(IR) bands as well as redshift and source-type information, for a large sample of 178 341 sources in the Hawaii-Hubble Deep Field-North field. A total of 145 635 sources among the full sample are classified/treated as galaxies and have redshift information available. We derive physical properties for these sources utilizing the spectral energy distribution fitting code CIGALE that is based on Bayesian analysis. Through various consistency and robustness checks, we find that our stellar-mass and star-formation rate(SFR) estimates are reliable, which is mainly due to two facts. Firstly, we adopt the most up-to-date and accurate redshifts and point spread functionmatched photometry; and secondly, we make sensible parameter choices with the CIGALE code and take into account the influences of mid-IR/far-IR data, star-formation history models, and AGN contribution. We release our catalog of galaxy properties publicly(including, e.g., redshift, stellar mass, SFR, age, metallicity, dust attenuation). It is the largest of its kind in this field and should facilitate future relevant studies on the formation and evolution of galaxies.     

Asteroid detection at millimetric wavelengths with the PLANCK survey

The PLANCK mission, originally devised for cosmological studies, offers the opportunity to observe Solar System objects at millimetric and submillimetric wavelengths. In this paper we concentrate on the asteroids of the Main Belt, a large class of minor bodies in the Solar System. At present, more that 40 000 of these asteroids have been discovered and their detection rate is rapidly increasing. We intend to estimate the number of asteroids that can be detected during the mission and to evaluate the strength of their signal. We have rescaled the instrument sensitivities, calculated by the LFI and HFI teams for sources fixed in the sky, introducing some degradation factors to properly account for moving objects. In this way a detection threshold is derived for asteroidal detection that is related to the diameter of the asteroid and its geocentric distance. We have developed a numerical code that models the detection of asteroids in the LFI and HFI channels during the mission. This code performs a detailed integration of the orbits of the asteroids in the timespan of the mission and identifies those bodies that fall in the beams of PLANCK and their signal strength. According to our simulations, a total of 397 objects will be observed by PLANCK and an asteroidal body will be detected in some beam in 30% of the total sky scan-circles. A significant fraction (in the range from 50 to 100 objects) of the 397 asteroids will be observed with a high S/N ratio. Flux measurements of a large sample of asteroids in the submillimeter and millimeter range are relevant since they allow to analyze the thermal emission and its relation to the surface and regolith properties. Furthermore, it will be possible to check on a wider base, the two standard thermal models, based on a nonrotating or rapidly rotating sphere. Our method can also be used to separate Solar System sources from cosmological sources in the survey. This work is based on PLANCK LFI activities.     

Comparative Analysis of a Transition Region Bright Point with a Blinker and Coronal Bright Point Using Multiple EIS Emission Lines

Since their discovery 20 year ago, transition region bright points have never been observed spectroscopically. Bright point properties have not been compared with similar transition region and coronal structures. In this work we have investigated three transient quiet Sun brightenings including a transition region bright point (TR BP), a coronal bright point (CBP) and a blinker. We use time-series observations of the extreme-ultraviolet emission lines of a wide range of temperature T (logT=5.3?–?6.4) from the EUV Imaging Spectrometer (EIS) onboard the Hinode satellite. We present the EIS temperature maps and Doppler maps, which are compared with magnetograms from the Michelson Doppler Imager (MDI) onboard the SOHO satellite. Doppler velocities of the TR BP and blinker are ≤?25 km?s^?1, which is typical of transient TR phenomena. The Doppler velocities of the CBP were found to be ≤?20 km?s^?1 with exception of those measured at logT=6.2 where a distinct bi-directional jet is observed. From an EM loci analysis we find evidence of single and double isothermal components in the TR BP and CBP, respectively. TR BP and CBP loci curves are characterized by broad distributions suggesting the existence of unresolved structure. By comparing and contrasting the physical characteristics of the events we find that the BP phenomena are an indication of multi-scaled self-similarity, given the similarities in both their underlying magnetic field configuration and evolution in relation to EUV flux changes. In contrast, the blinker phenomena and the TR BP are sufficiently dissimilar in their observed properties as to constitute different event classes. Our work is an indication that the measurement of similar characteristics across multiple event types holds class-predictive power, and is a significant step towards automated solar atmospheric multi-class classification of unresolved transient EUV sources. Finally, the analysis performed here establishes a connection between solar quiet region CBPs and jets.     

Observations of Bright Comets in CARA Archives I: Years 2002–2006

We have launched the Cometary Archives for Amateur Astronomers, CARA, aiming at coordinated collection of homogeneous, long-time based, continuous data set of bright comet observations. The project is based on a collaboration between professional and amateur astronomers. The archived quantity is a set of the photometric Afρ, measured in I, R or red continuum 647/10 nm filters. To derive coma profiles, Afρ is measured in at least different radii selected from a set of 50,000, 25,000, 12,500, 6,000 and 3,000 km. The data are free to download for registered users, special requests are available upon personal contact. We also provide aspecific code with a tutorial for the aperture photrometry of comets. The purpose of this paper is to introduce the observing methods, tools, software supports and web resources of project CARA.     

On the Transits of Solar System Objects in the Forthcoming Planck Mission: Data Flagging and Coeval Multi-Frequency Observations

In the context of current and future microwave surveys mainly dedicated to the accurate mapping of Cosmic Microwave Background (CMB), mm and sub-mm emissions from Solar System will represent a potential source of contamination as well as an opportunity for new Solar System studies. In particular, the forthcoming ESA Planck mission will be able to observe the point-like thermal emission from planets and some large asteroids as well as the diffused Zodiacal Light Emission (ZLE). After a brief introduction to the field, we focus on the identification of Solar System discrete objects in the Planck time ordered data.     

The STAROX stellar evolution code

This paper describes the STAROX stellar evolution code for the calculation of the evolution of a model of a spherical star. The code calculates a model at time t _k , that is the run of pressure, density, temperature, radius, energy flux and related variables on a mesh in mass M _i , given the distribution of chemical elements X _j (i) at t _k and the model at the previous time step t _k?1. It then advances the chemical composition to the next time step t _k+1 and calculates a new model at time t _k+1. This process is iterated to convergence. The model equations are solved by Newton–Raphson relaxation; the chemical equations are solved by an iterative procedure, each element being advanced in turn, and the process repeated to convergence. Convection is modelled by a mixing length model and convective mixing is treated as a diffusive process; chemical overshooting can be incorporated in parametric form. The equation of state is taken from OPAL tables and the opacity from a blend of OPAL and Alexander tables. Nuclear reaction rates are from NACRE but only cover the p–p chain and CNO cycle. The atmospheric layers are incorporated in the model by applying the surface boundary condition at small optical depth (τ≈0.001). The mesh in mass M _i is usually taken as fixed except that there is a moveable mesh point at the boundary of a convective core. Results are given for models of mass 0.9 and 5.0M _⊙ with initial composition X=0.7,Z=0.02 evolved to a state where the central hydrogen abundance is X _c =0.35, and for a model of mass 2.0M _⊙ with initial X=0.72,Z=0.02, evolved to X _c =0.01 and with core overshooting. In this latter case we compute two models one with and one without a moveable mesh point at the boundary of the convective core to illustrate the importance of having such a moveable mesh point for the determination of the Brunt–Väisälä frequency in the layers outside the core.     

Relativistic positioning: four-dimensional numerical approach in Minkowski space-time

We simulate the satellite constellations of two Global Navigation Satellite Systems: Galileo (EU) and GPS (USA). Satellite motions are described in the Schwarzschild space-time produced by an idealized spherically symmetric non rotating Earth. The trajectories are then circumferences centered at the same point as Earth. Photon motions are described in Minkowski space-time, where there is a well known relation, (Coll et al. in Class. Quantum Gravit. 27:065013, 2010a), between the emission and inertial coordinates of any event. Here, this relation is implemented in a numerical code, which is tested and applied. The first application is a detailed numerical four-dimensional analysis of the so-called emission coordinate region and co-region. In a second application, a GPS (Galileo) satellite is considered as the receiver and its emission coordinates are given by four Galileo (GPS) satellites. The bifurcation problem (double localization) in the positioning of the receiver satellite is then pointed out and discussed in detail.     

Ion temperature troughs in the equatorial topside ionosphere

The Retarding Potential Analyzer aboard OGO-6 sometimes recorded marked depressions of ion temperature as the satellite crossed the equatorial region. These “T_i troughs” occur at heights between about 700 km and the satellite apogee at 1100 km. At the centre of a trough, close to the dip equator, T_i is frequently 500–1000 K below its value at the northern and southern edges, which are usually 15°–20° in latitude from the centre of the trough. At a given season and local time, the occurrence, symmetry, depth and position of the troughs often vary markedly with longitude. The troughs have no particular association with equatorial troughs of ion concentration N_i.As suggested by Hanson, Nagy and Moffett, the T_i troughs appear to be caused by transequatorial winds that drive F region plasma along geomagnetic field lines. The plasma is adiabatically cooled as it is driven upwards on the “upwind” side of the dip equator, and heated as it descends on the “downwind” side. The available data on the occurrence of troughs at different longitudes, local times and seasons are reasonably consistent with wind directions deduced from Jacchia's model and the OGO-6 thermospheric model of Hedin et al., and with the north-south asymmetries of the tropical 630 nm airglow observed by OGO-4 and OGO-6. Factors determining the latitudinal extent of the troughs are discussed and some questions for further study are listed.     

On the loss of telemetry data in full-sky surveys from space

In this paper we discuss the issue of loosing telemetry (TM) data due to different reasons (e.g. spacecraft–ground transmissions) while performing a full-sky survey with space-borne instrumentation. This is a particularly important issue considering the current and future space missions (like Planck from ESA and MAP from NASA) operating from an orbit far from Earth with short periods of visibility from ground stations. We consider, as a working case, the Low Frequency Instrument (LFI) on-board the Planck satellite albeit the approach developed here can be easily applied to any kind of experiment that makes use of an observing (scanning) strategy which assumes repeated pointings of the same region of the sky on different time scales. The issue is addressed by means of a Monte Carlo approach. Our analysis clearly shows that, under quite general conditions, it is better to cover the sky more times with a lower fraction of TM retained than less times with a higher guaranteed TM fraction. In the case of Planck, an extension of mission time to allow a third sky coverage with 95% of the total TM guaranteed provides a significant reduction of the probability to loose scientific information with respect to an increase of the total guaranteed TM to 98% with the two nominal sky coverages.     

A VLBI and MERLIN Survey of faint,compact radio sources

We present preliminary results from a VLBI survey at λ=6 cm of a sample of 35 sources with flux densities of 2–100 mJy. These sources were selected from the VLA FIRST survey at λ=20 cm, in a 3 degree field around the bright calibrator 1156+295, simply by imposing S₂₀>10 mJy and θ<5 arcsec. MERLIN observations at λ6 cm detected 70/127 of these sources with a threshold of 2 mJy at 50 mas resolution and the closest 35 of these to the calibrator were observed with the VLBA+EVN in snapshot mode at λ6 cm. These sources are a mixture of flat and steep-spectrum sources and include: weak flat-spectrum nuclei of large radio galaxies, low power AGN in nearby galaxies and radio quiet quasars. With these short observations, the sensitivity is limited and most appear as either core-jets or simple point sources on the milliarcsec scale. Nonetheless, it is encouraging that with only 10 minutes observation per source, at least 35% of all sources with S₂₀>10 mJy can be detected and imaged with global 6 cm VLBI.     

The 6300 Å O1D airglow and dissociative recombination

Measurements of night-time 6300 Å airglow intensities at the Arecibo Observatory have been compared with dissociative recombination calculations based on electron densities derived from simultaneous incoherent backscatter measurements. The agreement indicates that the nightglow can be fully accounted for by dissociative recombination. Thecomparisons are examined to determine the importance of quenching, heavy ions, ionization above the F-layer peak, and the temperature parameter of the model atmosphere. Comparable fits between the observed and calculated intensities are found for several available model atmos- pheres (e.g. CIRA, Jacchia). The least-squares fitting process, used to make the comparisons, produces comparable fits over a wide range of combinations of neutral densities and of reaction constants. Yet, the fitting places constraints upon the possible combinations: these constraints indicate that the latest laboratory chemical constants and densities extrapolated to a base altitude are mutually consistent. However, by imposing an additional constraint, an aero- nomically derived preference is given for about one O(^1D) per combination. A preference is also given for the lower base densities of O₂ derived from rockets rather than from models. Altitude profiles for the 6300 Å and 5577 Å emissions are deduced. In the early evening, there are no large discrepancies in the fits that might indicate an effect from elicited states of O₊, vibrational excitation of O₂, or both. The technique of comparing observed and cal- culated 6300 Å intensities has considerable potential as an aeronomical tool for examination of other possible sources of emission and for determination of relative changes in the neutral atmosphere.