Star formation in the starburst cluster in NGC 3603

We have used new, deep, visible and near infrared observations of the compact starburst cluster in the giant HII region NGC 3603 and its surroundings with the WFC3 on HST and HAWK-I on the VLT to study in detail the physical properties of its intermediate mass (∼1–3 M_⊙) stellar population. We show that after correction for differential extinction and actively accreting stars, and the study of field star contamination, strong evidence remains for a continuous spread in the ages of pre-main sequence stars in the range ∼2 to ∼30 Myr within the temporal resolution available. Existing differences among presently available theoretical models account for the largest possible variation in shape of the measured age histograms within these limits. We also find that this isochronal age spread in the near infrared and visible Colour-Magnitude Diagrams cannot be reproduced by any other presently known source of astrophysical or instrumental scatter that could mimic the luminosity spread seen in our observations except, possibly, episodic accretion. The measured age spread and the stellar spatial distribution in the cluster are consistent with the hypothesis that star formation started at least 20–30 Myrs ago progressing slowly but continuously up to at least a few million years ago. All the stars in the considered mass range are distributed in a flattened oblate spheroidal pattern with the major axis oriented in an approximate South-East–North-West direction, and with the length of the equatorial axis decreasing with increasing age. This asymmetry is most likely due to the fact that star formation occurred along a filament of gas and dust in the natal molecular cloud oriented locally in this direction.     

Waves generated by a moving point-source within a finite-depth ocean

We consider a flat ocean of finite depth h consisting of an inviscid, incompressible fluid with no surface tension. A source of constant strength moves uniformly in a horizontal direction at a constant depth. We study the wake generated by this moving disturbance.Using the Fourier transform approach, we determine the unique velocity potential for this irrotational, steady motion, subject to the bottom and free-surface boundary conditions and to its vanishing at infinity.     

Thermoluminescence dating of the Kamil impact crater (Egypt)

Thermoluminescence (TL) dating has been used to determine the age of the meteorite impact crater at Gebel Kamil (Egyptian Sahara). Previous studies suggested that the 45 m diameter structure was produced by a fall in recent times (less than 5000 years ago) of an iron meteorite impactor into quartz‐arenites and siltstones belonging to the Lower Cretaceous Gilf Kebir Formation. The impact caused the complete fragmentation of the impactor, and the formation of a variety of impactites (e.g., partially vitrified dark and light materials) present as ejecta within the crater and in the surrounding area. After a series of tests to evaluate the TL properties of different materials including shocked intra‐crater target rocks and different types of ejecta, we selected a suite of light‐colored ejecta that showed evidence of strong thermal shock effects (e.g., partial vitrification and the presence of high‐temperature and ‐pressure silica phases). The abundance of quartz in the target rocks, including the vitrified impactites, allowed TL dating to be undertaken. The variability of radioactivity of the intracrateric target rocks and the lack of direct in situ dosimetric evaluations prevented precise dating; it was, however, possible to constrain the impact in the 2000 BC–500 AD range. If, as we believe, the radioactivity measured in the fallback deposits is a reliable estimate of the mean radioactivity of the site, the narrower range 1600–400 BC (at the 2σ confidence level) can be realistically proposed.     

Planet formation process as a phase transition

We discuss the condensation of ring-shaped nebular matter into a protoplanet such as an isothermal phase transition. Within an elementary model for this process, we analyze the effect of the relevant physical parameters (mass and temperature of the nebular matter) on the critical width of the ring which allows the transition.     

The mass distribution in the innermost regions of spiral galaxies

We use high-spatial resolution (100 pc) rotation curves of 83 spiral galaxies to investigate the mass distribution of their innermost kpc. We show that, in this region, the luminous matter completely accounts for the gravitational potential and no dark component is required. The derived I-band disk mass-to-light ratios agree well with those obtained from population synthesis models and correlate with color in a similar way. We find strict upper limits of 10⁷ M for the masses of compact bodies at the center of spirals, ruling out that these systems host the remnants of the quasar activity.     

Solar radio pulsating structures during September 9, 2001 at meter wavelength

Pulsating structures recorded at 237 MHz that are associated to decimetric continuum enhancement during the September 9, 2001 solar radio burst are described. We analyzed the radiopolarimetric data recorded at the Trieste Solar Radio System (INAF—Trieste Astronomical Observatory—Basovizza Observing Station) with very high time resolution (1 ms) at metric frequencies. Two different types of pulsations that occur in about 4 minutes at the same frequency are described. The possible mechanisms are analyzed and some parameters of the associated magnetic structure are estimated.     

An experimental comparison of silica gel and quartz sand grains as sediment media for growing vegetation at the laboratory scale

In this technical note we compare silica gel grains and quartz sand as sediment media for vegetation root growth in laboratory experiments for ecohydrology and ecohydraulics. Silica gel grains become quite transparent when saturated with water. This would be useful in order to non-invasively observe the rate of growth of plant roots and plan parallel laboratory experiments made in more typical sand sediments. In this work, we compare the results of preliminary tests conducted using quartz sand with the same grain size distribution of silica gel grains. We show that the complex microstructure of silica gel grains seems to influence the evaporation and, in turn, plant growth dynamics. The potential and limitations of the use of silica grains are accordingly discussed in light of more detailed experiments.     

Geochemical study of graywackes as a possible starting material of para-amphibolites

The possibility of para-amphibolites originating from the metamorphic transformation of graywackes is investigated. A series of 35 samples of Vosges graywackes has been studied and the geochemical trends for major and trace elements have been determined to this end. The strong similarity of the geochemical characteristics of this group of graywackes to those of a series of para-amphibolites of the Western Alps conforms to the present hypothesis. By comparing sedimentary geochemical trends with igneous trends one is able to distinguish ortho- from para-derivatives.