Expansion of an invasive coral species over Abrolhos Bank,Southwestern Atlantic

Invasive coral species of the genus Tubastraea have been increasingly recorded in Southwestern Atlantic waters since the 1980s. Their invasion and infestation are mainly related to port and oil exploration activities. For the first time the presence of Tubastraea tagusensis colonies is reported in Espírito Santo State, colonizing a port shore area, and incrusting oil/gas platform structures situated in the southern Abrolhos Bank, which is part of the most important coral reef system of the South Atlantic Ocean. Tubastraea colonies exhibit fast growth and high recruitment rates, and colonized 40% of the analyzed structures in just four years. The projection of port and oil/gas industry growth for the Espírito Santo State (more than 300%) highlights an alert to the dispersal of this alien species to natural areas.     

Fully 3-dimensional calculations of dust mantle formation for a model of Comet 67P/Churyumov-Gerasimenko

A fully 3-dimensional implicit numerical model for comet nucleus evolution is presented, emphasizing dust mantle formation. A spherical configuration is considered with an initial composition of amorphous H₂O ice and dust, taking into account a discrete dust-grain size distribution. The model is applied to Comet 67P/Churyumov-Gerasimenko, adopting its orbital elements, rotation period and rotation axis inclination. We find that the dust mantle thickness varies over the surface from 1 cm to about 10 cm (thus lower and higher than the diurnal skin-depth, respectively). The size distribution of ejected grains varies along the orbit and is steeper than the initial one adopted for the nucleus. The crystallization front advances inward in spurts, and its depth varies between 1 and several meters. We test the effect of the thermal conductivity on the surface temperature distribution and depths of the dust mantle and crystallization front.     

Specific angular momentum of disc merger remnants and the λR-parameter

We use two-dimensional kinematic maps of simulated binary disc mergers to investigate the  λ_R  -parameter, which is a luminosity-weighted measure of projected angular momentum per unit mass. This parameter was introduced to subdivide the SAURON sample of early-type galaxies in so-called fast  λ_R > 0.1  and slow rotators  λ_R < 0.1  . Tests on merger remnants reveal that  λ_R  is a robust indicator of the true angular momentum content in elliptical galaxies. We find the same range of  λ_R  values in our merger remnants as in the SAURON galaxies. The merger mass ratio is decisive in transforming fast rotators into slow rotators in a single binary merger, the latter being created mostly in an equal-mass merger. Slow rotators have a  λ_R  which does not vary with projection. The confusion rate with face-on fast rotators is very small. Mergers with a gas component form slow rotators with smaller ellipticities than collisionless merger remnants have, and are in much better agreement with the SAURON slow rotators. Remergers of merger remnants are slow rotators, but tend to have too high ellipticities. Fast rotators maintain the angular momentum content from the progenitor disc galaxy if merger mass ratio is high. Some SAURON galaxies have values of  λ _R   as high as our progenitor disc galaxies.     

Pre-main-sequence variability across the radiative–convective gap

We use I -band imaging to perform a variability survey of the 13-Myr-old cluster h Per. We find a significant fraction of the cluster members to be variable. Most importantly, we find that variable members lie almost entirely on the convective side of the gap in the cluster sequence between fully convective stars and those which have a radiative core. This result is consistent with a scenario in which the magnetic field changes topology when the star changes from being fully convective to one containing a radiative core. When the star is convective, the magnetic field appears dominated by large-scale structures, resulting in global-size spots that drive the observed variability. For those stars with radiative cores, we observe a marked absence of variability due to spots, which suggests a switch to a magnetic field dominated by smaller-scale structures, resulting in many smaller spots and thus less apparent variability. This implies that wide field variability surveys may only be sensitive to fully convective stars. On the one hand, this reduces the chances of picking out young groups (since the convective stars are the lower mass and therefore fainter objects), but conversely the absolute magnitude of the head of the convective sequence provides a straightforward measure of age for those groups which are discovered.     

Bulge–disc decompositions and structural bimodality of Ursa Major cluster spiral galaxies

We present bulge and disc (B/D) decompositions of existing   K '  surface brightness profiles for 65 Ursa Major (UMa) cluster spiral galaxies. This improves upon the disc-only fits of Tully et al. The 1996 disc fits were used by Tully & Verheijen for their discovery of the bimodality of structural parameters in the UMa cluster galaxies. It is shown that our new one-dimensional B/D decompositions yield disc structural parameters that differ only slightly from the basic fits of Tully et al. and evidence for structural bimodality of UMa galaxies is maintained. Our B/D software for the decomposition of one-dimensional surface brightness profiles of galaxies uses a non-linear minimization scheme to recover the best-fitting Sérsic bulge and the exponential disc while accounting for the possible presence of a compact nucleus and spiral arms and for the effects of seeing and disc truncations. In agreement with Tully & Verheijen, we find that the distribution of near-infrared disc central surface brightnesses is bimodal with an F-test confidence of 80 per cent. There is also strong evidence for a local minimum in the luminosity function at     . A connection between the brightness bimodality and a dynamical bimodality, based on new H  i linewidths, is identified. The B/D parameters are presented in Table 1 .  

  Table 1.  B/D parameters.     

950.

The SAURON Project – XIV. No escape from V_esc: a global and local parameter in early-type galaxy evolution     

Nicholas Scott  Michele Cappellari  Roger L. Davies  R. Bacon  P. T. de Zeeuw  Eric Emsellem  Jésus Falcón-Barroso  Davor Krajnovi&#;  Harald Kuntschner  Richard M. McDermid  Reynier F. Peletier  Antonio Pipino  Marc Sarzi  Remco C. E. van den Bosch  Glenn van de Ven †  Eveline van Scherpenzeel 《Monthly notices of the Royal Astronomical Society》2009,398(4):1835-1857

     

[首页] « 上一页 [90] [91] [92] [93] [94] 95 [96] [97] [98] [99] [100] 下一页 » 末  页»