Deep-ocean piezometer probe technology for geotechnical investigations

Two single-sensor piezometer probes, 8 mm in diameter, were developed for deep-ocean geotechnical investigations. These probes were tested in a hyperbaric chamber pressurized to 55 MPa (8000 psi). Testing was performed for a period of five weeks under high hydrostatic pressure with the probes inserted in reconstituted illitic marine sediment. Small differential pore-water pressures were generated in response to both mechanically and thermally generated forcing functions. During deep-ocean simulated pressure tests, the sensors exhibited excellent sensitivity and stability. These developments in piezometer-probe technology provide a quantitative means of assessing important geotechnical parameters of fine-grained seabed deposits.     

Lamprothamnium prosperity in permannetly hypersaline water

The leuco-halophytic charophyte,Lamprothamnium papulosum, readily germinates, grows and reproduces in C1 Pond of ICI's solar saltworks near Port Alma, a permanently hypersaline waterbody in Queensland, Australia. Its morphology very much resembles that ofChara corallina, although the two central cells of the axial node are subdivided, a feature found inLamprothamnium but not inChara. Some of the characteristics of the Port Alma population, like the occurrence of a considerable proportion of pedicellate gametangia among the normal sessile ones, or the deviation in the sizes of some plant parts from the ranges that have been reported previously, are unusual, even for this highly variable species. Florida Agricultural Experiment Station Journal Series No. 6876     

Photometric Evolution of the Orbital Light Curves of the Slow Nova V723 Cas

UBVRI photoelectric and CCD photometry of the slow nova V723 Cas obtained in the years 1995–2003 is presented. The evolution of light curves in 1-year intervals, folded with the orbital period 0.69326 days, shows an increase of the amplitude of the wave-like variations from 0.07 to 1.3 mag during the years 1997–2003. The fact that the shape and amplitude of the orbital light curves does not depend on wavelength is most probably related to the geometry of eclipses combined with the distribution of circumstellar matter in the system.     

Nova Sagittarii 1998 (V4633 Sgr): a permanent superhump system or an asynchronous polar?

We report the results of observations of V4633 Sgr (Nova Sagittarii 1998) during     . Two photometric periodicities were present in the light curve during the three years of observations: a stable one at     , which is probably the orbital period of the underlying binary system; and a second one of lower coherence, approximately 2.5 per cent longer than the former. The latter periodicity may be a permanent superhump, or, alternatively, the spin period of the white dwarf in a nearly synchronous magnetic system. A third period, at     , corresponding to the beat between the two periods was probably present in 1999. Our results suggest that a process of mass transfer has taken place in the binary system since no later than two-and-a-half months after the nova eruption. We derive an interstellar reddening of     from our spectroscopic measurements and published photometric data, and estimate a distance of     to this nova.     

Preliminary results of the multisite time-series campaign on the sdB pulsator PG 1325+101

I present a model for the formation and evolution of a massive disk galaxy, within a growing dark halo whose mass evolves according to cosmological simulations of structure formation. The galactic evolution is simulated with a new 3D chemo-dynamical code, including dark matter, stars and a multi-phase ISM. We follow the evolution from redshift z = 4.85 until the present epoch. The energy release by massive stars and supernovae prevents a rapid collapse of the baryonic matter and delays the maximum star formation until redshift z ≈ 1. The galaxy forms radially from inside-out and vertically from top-to-bottom. The feedback of stars leads to turbulent motions and large-scale flows in the ISM. As one result the galactic disk is significantly enriched by chemical elements synthesized in bulge stars.     

Variability and multiperiodic oscillations in the X-ray light curve of the classical nova V4743 Sgr

The classical nova V4743 Sgr was observed with XMM–Newton for about 10 h on 2003 April 4, 6.5 months after optical maximum. At this time, this nova had become the brightest supersoft X-ray source ever observed. In this paper, we present the results of a time-series analysis performed on the X-ray light curve (LC) obtained in this observation, and in a previous shorter observation done with Chandra 16 d earlier. Intense variability, with amplitude as large as 40 per cent of the total flux, was observed both times. Similarities can be found between the two observations in the structure of the variations. Most of the variability is well represented as a combination of oscillations at a set of discrete frequencies lower than 1.7 mHz. At least five frequencies are constant over the 16 d time interval between the two observations. We suggest that a period in the power spectrum of both LCs at the frequency of 0.75 mHz and its first harmonic are related to the spin period of the white dwarf (WD) in the system, and that other observed frequencies are signatures of non-radial WD pulsations. A possible signal with a 24 000 s period is also found in the XMM–Newton LC: a cycle and a half are clearly identified. This period is consistent with the 24 278 s periodicity discovered in the optical LC of the source and thought to be the orbital period of the nova binary stellar system.     

In situ vane system for seafloor strength investigations

The In Situ Vane (ISV) system has been developed to determine the strength profile within the upper 1.5 m of deep sea clays. The system is designed to operate in 6000-m water depth after one-year dormancy on the bottom and consists of four integrated packages; controller and data acquisition system, mechanical system, volume compensator, and power supply. This paper describes development of a prototype which was used under a pressure of 550 bars after a 30-day dormancy and of the full system which was successfully used in a deep water (5800 m) test. In the first full application of the system the ISV will be used to measure changes in sediment strength caused by high temperature (300degC) as part of the U.S. Subseabed Disposal Program.     

V4633 Sgr – a probable second asynchronous polar classical nova

Photometric observations of V4633 Sgr (Nova Sagittarii 1998) during 1998–2005 reveal the presence of a stable photometric periodicity at   P ₁= 180.8 min  which is probably the orbital period of the underlying binary system. A second period was present in the light curve of the object for 6 yr. Shortly after the nova eruption it was measured as   P ₂= 185.6 min  . It has decreased monotonically in the following few years reaching the value   P ₂= 183.9 min  in 2003. In 2004 it was no longer detectable. We suggest that the second periodicity is the spin of the magnetic white dwarf of this system that rotates nearly synchronously with the orbital revolution. According to our interpretation, the post-eruption evolution of Nova V4633 Sgr follows a track similar to the one taken by V1500 Cyg (Nova Cygni 1975) after that nova eruption, on a somewhat longer time-scale. The asynchronism is probably the result of the nova outburst that led to a considerable expansion of the white dwarf's photosphere. The increase in the moment of inertia of the star was associated with a corresponding decrease in its spin rate. Our observations have followed the spinning-up of the white dwarf resulting from the contraction of its outer envelope as the star is slowly returning to its pre-outburst state. It is thus the second known asynchronous polar classical nova.     

Massive stars exploding in a He-rich circumstellar medium – I. Type Ibn (SN 2006jc-like) events

We present new spectroscopic and photometric data of the Type Ibn supernovae 2006jc, 2000er and 2002ao. We discuss the general properties of this recently proposed supernova family, which also includes SN 1999cq. The early-time monitoring of SN 2000er traces the evolution of this class of objects during the first few days after the shock breakout. An overall similarity in the photometric and spectroscopic evolution is found among the members of this group, which would be unexpected if the energy in these core-collapse events was dominated by the interaction between supernova ejecta and circumstellar medium. Type Ibn supernovae appear to be rather normal Type Ib/c supernova explosions which occur within a He-rich circumstellar environment. SNe Ibn are therefore likely produced by the explosion of Wolf–Rayet progenitors still embedded in the He-rich material lost by the star in recent mass-loss episodes, which resemble known luminous blue variable eruptions. The evolved Wolf–Rayet star could either result from the evolution of a very massive star or be the more evolved member of a massive binary system. We also suggest that there are a number of arguments in favour of a Type Ibn classification for the historical SN 1885A (S-Andromedae), previously considered as an anomalous Type Ia event with some resemblance to SN 1991bg.