The Global Oscillation Network Group (GONG) Project will place a network of instruments around the world to observe solar oscillations as continuously as possible for three years. The Project has now chosen the six network sites based on analysis of survey data from fifteen sites around the world. The chosen sites are: Big Bear Solar Observatory, California; Mauna Loa Solar Observatory, Hawaii: Learmonth Solar Observatory, Australia; Udaipur Solar Observatory, India; Observatorio del Teide, Tenerife; and Cerro Tololo Interamerican Observatory, Chile.

A moderate-resolution spectroscopic survey of Fleming's sample of 54 X-ray selected M dwarfs with photometric distances less than 25 pc is presented. All the objects consist of one or two dMe stars, some being doubles or spectroscopic binaries. Radial and rotation velocities have been measured by fits to the Halpha profiles. Radial velocities have been measured by cross correlation. Artificial broadening of an observed spectrum has produced a relationship between Halpha FWHM and rotation speed, which we use to infer rotation speeds for the entire sample by measurement of the Halpha emission line. We find three ultrafast rotators ( UFRs, v sin i greater than or equal to 100 km s(-1)) and eight stars with 30 km s(-1) v sin i < 100 km s(-1). We find that the UFRs have quite variable emission and should be observed for photometric variability. Cross-correlation velocities measured for UFRs are shown to depend on rotation speed and the filtering used. The radial velocity dispersion of the sample is 17 km s(-1). A new double emission line spectroscopic binary with a period of 3.55 days has been discovered, RX J1547.4+4507, and another known one is in the sample, the Hyades member RX J0442.5+2027. Three other objects are suspected spectroscopic binaries, and at least six are visual doubles. The only star in the sample observed to have significant lithium happens to be a known TW Hya association member, TWA 8A. These results all show that there are a number of young (<10(8) yr) and very young (<10(7) yr) low-mass stars in the immediate solar neighborhood. The Hα activity strength does not depend on rotation speed. Our fast rotators are less luminous than similarly fast rotators in the Pleiades. They are either younger than the Pleiades or gained angular momentum in a different way.

Pressure-induced lattice collapse was discovered in tetragonal (T) phase of single crystal Fe1.05Te at room temperature through x-ray and neutron-diffraction measurements. A remarkable compression along the c axis (similar to 5%) was observed upon increasing pressure from the ambient condition to 4 GPa. Indexed results demonstrate that the crystallographic structure remains unchanged after the collapse, revealing that the collapse does not break symmetry of crystal structure. The Fe-spin state change was proposed to account for the lattice collapse. The equations of state for the T phase and pressure-induced collapsed T phase were determined from the diffraction measurements.

The hyper-velocity star S5-HVS1, ejected 5 Myr ago from the Galactic Centre at 1800 km s(-1), was most likely produced by tidal break-up of a tight binary by the supermassive black hole SgrA*. Taking a Monte Carlo approach, we show that the former companion of S5-HVS1 was likely a main-sequence star between 1.2 and 6 M-circle dot and was captured into a highly eccentric orbit with pericentre distance in the range of 1-10 au and semimajor axis about 10(3) au. We then explore the fate of the captured star. We find that the heat deposited by tidally excited stellar oscillation modes leads to runaway disruption if the pericentre distance is smaller than about 3 au. Over the past 5 Myr, its angular momentum has been significantly modified by orbital relaxation, which may stochastically drive the pericentre inwards below 3 au and cause tidal disruption. We find an overall survival probability in the range 5 per cent to 50 per cent, depending on the local relaxation time in the close environment of the captured star, and the initial pericentre at capture. The pericentre distance of the surviving star has migrated to 10-100 au, making it potentially the most extreme member of the S-star cluster. From the ejection rate of S5-HVS1-like stars, we estimate that there may currently be a few stars in such highly eccentric orbits. They should be detectable (typically K-s less than or similar to 18.5 mag) by the GRAVITY instrument and by future Extremely Large Telescopes and hence provide an extraordinary probe of the spin of SgrA*.

The hyper-velocity star S5-HVS1, ejected 5 Myr ago from the Galactic Center at 1800 km/s, was most likely produced by tidal break-up of a tight binary by the supermassive black hole SgrA*. Taking a Monte Carlo approach, we show that the former companion of S5-HVS1 was likely a main-sequence star between 1.2 and 6M⊙ and was captured into a highly eccentric orbit with pericenter distance in the range 1–10 AU and semimajor axis about 103 AU. We then explore the fate of the captured star. We find that the heat deposited by tidally excited stellar oscillation modes leads to runaway disruption if the pericenter distance is smaller than about 3 AU. Over the past 5 Myr, its angular momentum has been significantly modified by orbital relaxation, which may stochastically drive the pericenter inwards below 3 AU and cause tidal disruption. We find an overall survival probability in the range 5% to 50%, depending on the local relaxation time in the close environment of the captured star, and the initial pericenter at capture. The pericenter distance of the surviving star has migrated to 10–100 AU, making it potentially the most extreme member of the S-star cluster. From the ejection rate of S5-HVS1-like stars, we estimate that there may currently be a few stars in such highly eccentric orbits. They should be detectable (typically Ks ≲ 18.5 mag) by the GRAVITY instrument and by future Extremely Large Telescopes and hence provide an extraordinary probe of the spin of SgrA*.