The High-Resolution Coronal Imager (Hi-C)

The High-Resolution Coronal Imager (Hi-C) was flown on a NASA sounding rocket on 11 July 2012. The goal of the Hi-C mission was to obtain high-resolution (≈?0.3?–?0.4′′), high-cadence (≈?5 seconds) images of a solar active region to investigate the dynamics of solar coronal structures at small spatial scales. The instrument consists of a normal-incidence telescope with the optics coated with multilayers to reflect a narrow wavelength range around 19.3 nm (including the Fe xii 19.5-nm spectral line) and a 4096×4096 camera with a plate scale of 0.1′′?pixel^?1. The target of the Hi-C rocket flight was Active Region 11520. Hi-C obtained 37 full-frame images and 86 partial-frame images during the rocket flight. Analysis of the Hi-C data indicates the corona is structured on scales smaller than currently resolved by existing satellite missions.     

Planetary theories with the aid of the expansions of elliptic functions

For coplanar circular orbits, the mutual perturbations between two bodies can be expressed in term of the argument of Jacobian elliptic functions instead of the difference of the mean longitudes. For a given pair of planets, such a change of time variable improves the convergence of the developments. At the first order of planetary masses an integration of Lagrange's equations for the osculating elements is performed. When compared to classical developments the results are reduced by an important factor. The method is then extended to the mutual perturbations of Jupiter and Saturn, at any order of planetary masses, either with Fourier series with two arguments, or with one argument solely, taking advantage of the close commensurability of the mean motions.     

The dynamics of eccentric accretion discs in superhump systems

We have applied an eccentric accretion disc theory in simplified form to the case of an accretion disc in a binary system, where the disc contains the 3:1 Lindblad resonance. This is relevant to the case of superhumps in SU Ursae Majoris cataclysmic variables and other systems, where it is thought that this resonance leads to growth of eccentricity and a modulation in the light curve due to the interaction of a precessing eccentric disc with tidal stresses. A single differential equation is formulated which describes the propagation, resonant excitation and viscous damping of eccentricity. The theory is first worked out in the simple case of a narrow ring and leads to the conclusion that the eccentricity distribution is locally suppressed by the presence of the resonance, creating a dip in the eccentricity at the resonant radius. Application of this theory to the superhump case confirms this conclusion and produces a more accurate expression for the precession rate of the disc than has been previously accomplished with simple dynamical estimates.     

Supergranule and Mesogranule Evolution

The MDI instrument on the SOHO satellite obtained a nearly continuous 45.5-hr run in high-resolution mode on 17–18 January 1997, collecting continuum, Dopplergram, and magnetogram images once per minute. This is one of the longest data sets yet obtained in this mode and shows significant evolution of the supergranulation pattern. After allowing for solar rotation within the fixed field of view, an area spanning 17° in latitude and 11° in longitude was extracted that covers the same area of the solar surface for the entire run. From the de-rotated continuum images, we computed flow maps of photospheric motions using local correlation techniques (LCT). Horizontal divergence maps constructed from the flow maps show local maxima of the size of mesogranules (5–10). We interpret these as mesogranules although the LCT flow map resolution (4.8 FWHM) may not completely resolve smaller mesogranules. Movies made from the divergence maps clearly show the outward convection (advection) of these mesogranules within each supergranule, and narrow boundaries of negative divergence outlining the supergranules. Several new supergranules are observed forming. These appear as areas of strong divergence that pop up between pre-existing supergranules and grow, pushing their neighbors apart. Others seem to perish between growing neighbors. We also computed the vertical component of vorticity from the flow maps. Movies of this vorticity do not show any obvious patterns.     

Nanometer‐scale anatomy of entire Stardust tracks

Abstract– We have developed new sample preparation and analytical techniques tailored for entire aerogel tracks of Wild 2 sample analyses both on “carrot” and “bulbous” tracks. We have successfully ultramicrotomed an entire track along its axis while preserving its original shape. This innovation allowed us to examine the distribution of fragments along the entire track from the entrance hole all the way to the terminal particle. The crystalline silicates we measured have Mg‐rich compositions and O isotopic compositions in the range of meteoritic materials, implying that they originated in the inner solar system. The terminal particle of the carrot track is a ¹⁶O‐rich forsteritic grain that may have formed in a similar environment as Ca‐, Al‐rich inclusions and amoeboid olivine aggregates in primitive carbonaceous chondrites. The track also contains submicron‐sized diamond grains likely formed in the solar system. Complex aromatic hydrocarbons distributed along aerogel tracks and in terminal particles. These organics are likely cometary but affected by shock heating.     

The Monitor project: rotation of low-mass stars in the open cluster NGC 2547

We report on the results of an I -band time-series photometric survey of NGC 2547 using the MPG/ESO 2.2-m telescope with Wide Field Imager, achieving better than 1 per cent photometric precision per data point over  14 ≲ I ≲ 18  . Candidate cluster members were selected from a V versus V − I colour–magnitude diagram over  12.5 < V < 24  (covering masses from  0.9 M_⊙  down to below the brown dwarf limit), finding 800 candidates, of which we expect ∼330 to be real cluster members, taking into account contamination from the field (which is most severe at the extremes of our mass range). Searching for periodic variations in these gave 176 detections over the mass range  0.1 ≲ M /M_⊙≲ 0.9  . The rotation period distributions were found to show a clear mass-dependent morphology, qualitatively intermediate between the distributions obtained from similar surveys in NGC 2362 and 2516, as would be expected from the age of this cluster. Models of the rotational evolution were investigated, finding that the evolution from NGC 2362 to 2547 was qualitatively reproduced (given the uncertainty in the age of NGC 2547) by solid body and core-envelope decoupled models from our earlier NGC 2516 study without need for significant modification.     

The dependence of galaxy formation on cosmological parameters: can we distinguish between the WMAP1 and WMAP3 parameter sets?

We combine N -body simulations of structure growth with physical modelling of galaxy evolution to investigate whether the shift in cosmological parameters between the first- and third-year results from the Wilkinson Microwave Anisotropy Probe ( WMAP ) affects predictions for the galaxy population. Structure formation is significantly delayed in the WMAP3 cosmology, because the initial matter fluctuation amplitude is lower on the relevant scales. The decrease in dark matter clustering strength is, however, almost entirely offset by an increase in halo bias, so predictions for galaxy clustering are barely altered. In both cosmologies, several combinations of physical parameters can reproduce observed, low-redshift galaxy properties; the star formation, supernova feedback and active galactic nucleus feedback efficiencies can be played off against each other to give similar results. Models which fit observed luminosity functions predict projected two-point correlation functions which scatter by about 10–20 per cent on large scale and by larger factors on small scale, depending both on cosmology and on details of galaxy formation. Measurements of the pairwise velocity distribution prefer the WMAP1 cosmology, but careful treatment of the systematics is needed. Given present modelling uncertainties, it is not easy to distinguish between the WMAP1 and WMAP3 cosmologies on the basis of low-redshift galaxy properties. Model predictions diverge more dramatically at high redshift. Better observational data at   z > 2  will better constrain galaxy formation and perhaps also cosmological parameters.     

Multifrequency integrated profiles of pulsars

We have observed a total of 67 pulsars at five frequencies ranging from 243 to 3100 MHz. Observations at the lower frequencies were made at the Giant Metre-Wave Telescope in India and those at higher frequencies at the Parkes Telescope in Australia. We present profiles from 34 of the sample with the best signal-to-noise ratio and the least scattering. The general 'rules' of pulsar profiles are seen in the data; profiles get narrower, the polarization fraction declines and outer components become more prominent as the frequency increases. Many counterexamples to these rules are also observed, and pulsars with complex profiles are especially prone to rule breaking. We hypothesize that the location of pulsar emission within the magnetosphere evolves with time as the pulsar spins down. In highly energetic pulsars, the emission comes from a confined range of high altitudes, in the middle range of spin down energies the emission occurs over a wide range of altitudes whereas in pulsars with low spin-down energies it is confined to low down in the magnetosphere.     

The population of pulsars with interpulses and the implications for beam evolution

The observed fraction of pulsars with interpulses, their period distribution and the observed pulse width versus pulse period correlation are shown to be inconsistent with a model in which the angle α between the magnetic axis and the rotation axis is random. This conclusion appears to be unavoidable, even when non-circular beams are considered. Allowing the magnetic axis to align from a random distribution at birth with a time-scale of  ∼7 × 10⁷ yr  can, however, explain those observations well. The time-scale derived is consistent with that obtained via independent methods. The probability that a pulsar beam intersects the line of sight is a function of the angle α and therefore beam evolution has important consequences for evolutionary models and for estimations of the total number of neutron stars. The validity of the standard formula for the spin-down rate, which is independent of α, appears to be questionable.     

Halo masses for optically selected and for radio-loud AGN from clustering and galaxy–galaxy lensing

We compute two-point correlation functions and measure the shear signal due to galaxy–galaxy lensing for 80 000 optically identified and 5700 radio-loud active galactic nuclei (AGN) from Data Release 4 of the Sloan Digital Sky Survey. Halo occupation models are used to estimate halo masses and satellite fractions for these two types of AGN. The large sample size allows us to separate AGN according to the stellar mass of their host galaxies. We study how the halo masses of optical and radio AGN differ from those of the parent population at fixed   M _*  . Halo masses deduced from clustering and from lensing agree satisfactorily. Radio AGN are found in more massive haloes than optical AGN: in our samples, their mean halo masses are  1.6 × 10¹³  and  8 × 10¹¹  h ⁻¹ M_⊙  , respectively. Optical AGN follow the same relation between stellar mass and halo mass as galaxies selected without regard to nuclear properties, but radio-loud AGN deviate significantly from this relation. The dark matter haloes of radio-loud AGN are about twice as massive as those of control galaxies of the same stellar mass. This boost is independent of radio luminosity, and persists even when our analysis is restricted to field galaxies. The large-scale gaseous environment of the galaxy clearly plays a crucial role in producing observable radio emission. The dark matter halo masses that we derive for the AGN in our two samples are in good agreement with recent models in which feedback from radio AGN becomes dominant in haloes where gas cools quasi-statically.