Dynamical detection of three triple stellar systems in open clusters

We present a kinematic analysis of three triple stellar systems belonging to two open clusters: CPD-60{\deg}961 and HD66137 in NGC2516, and HD315031 in NGC6530. All three systems are hierarchical triples with a close binary bound to a third body in a wider orbit, whose presence is detected through velocity variations of the close binary barycentre. Orbital parameters are derived from radial velocity curves. Absolute parameters for all stars are estimated assuming cluster membership. Some dynamical and evolutionary aspects of these systems are discussed, particularly the possible influence of Kozai cycles. The two systems of NGC2516 have similar orbital configurations with inner periods of 11.23 d and 8.70 d and outer periods of 9.79 yr and 9.24 yr. We report also radial velocity measurements of the components of the visual binary CPD-60{\deg}944 in NGC2516. Including results from previous works, this cluster would harbor 5 hierarchical triples. The young system HD315031 has an inner binary with a period of 1.37 d and a very eccentric (e=0.85) outer orbit with a period of 483 d. Possible dynamical evolutionary scenarios are discussed. Long-term radial velocity monitoring is highlighted as strategy for the detection of subsystems with intermediate separations, which are hard to cover with normal spectroscopic studies or visual techniques.Comment: 9 pages, 5 figures. Accepted by Monthly Notices of the Royal Astronomical Societ

Program Notes for Graduate Recital

The purpose of this research paper is to provide scholarly program notes to accompany the Graduate Recital of Season Cowley, which took place on May 9, 2015. Program notes for John Adams’ Gnarly Buttons (1996), Eric P. Mandat’s Tricolor Capers (1980), Krzysztof Penderecki’s Quartet for Clarinet and String Trio (1993), and Derek Bermel’s Theme and Absurdities (1993) are included

The effect of small streamwise velocity distortion on the boundary layer flow over a thin flat plate with application to boundary layer stability theory

Researchers show how an initially linear spanwise disturbance in the free stream velocity field is amplified by leading edge bluntness effects and ultimately leads to a small amplitude but linear spanwise motion far downstream from the edge. This spanwise motion is imposed on the boundary layer flow and ultimately causes an order-one change in its profile shape. The modified profiles are highly unstable and can support Tollmein-Schlichting wave growth well upstream of the theoretical lower branch of the neutral stability curve for a Blasius boundary layer

LOW-MASS X-RAY BINARIES AND THEIR RELATION TO THE NON-X-RAY SOURCES

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73252/1/j.1749-6632.1977.tb37032.x.pd

Dependence of the open-closed field line boundary in Saturn's ionosphere on both the IMF and solar wind dynamic pressure:comparison with the UV auroral oval observed by the HST

We model the open magnetic field region in Saturn's southern polar ionosphere during two compression regions observed by the Cassini spacecraft upstream of Saturn in January 2004, and compare these with the auroral ovals observed simultaneously in ultraviolet images obtained by the Hubble Space Telescope. The modelling employs the paraboloid model of Saturn's magnetospheric magnetic field, whose parameters are varied according to the observed values of both the solar wind dynamic pressure and the interplanetary magnetic field (IMF) vector. It is shown that the open field area responds strongly to the IMF vector for both expanded and compressed magnetic models, corresponding to low and high dynamic pressure, respectively. It is also shown that the computed open field region agrees with the poleward boundary of the auroras as well as or better than those derived previously from a model in which only the variation of the IMF vector was taken into account. The results again support the hypothesis that the auroral oval at Saturn is associated with the open-closed field line boundary and hence with the solar wind interaction

The interaction between transpolar arcs and cusp spots

Transpolar arcs and cusp spots are both auroral phenomena which occur when the interplanetary magnetic field is northward. Transpolar arcs are associated with magnetic reconnection in the magnetotail, which closes magnetic flux and results in a "wedge" of closed flux which remains trapped, embedded in the magnetotail lobe. The cusp spot is an indicator of lobe reconnection at the high-latitude magnetopause; in its simplest case, lobe reconnection redistributes open flux without resulting in any net change in the open flux content of the magnetosphere. We present observations of the two phenomena interacting--i.e., a transpolar arc intersecting a cusp spot during part of its lifetime. The significance of this observation is that lobe reconnection can have the effect of opening closed magnetotail flux. We argue that such events should not be rare

A revised comparison of distant and nearby solar twins

Properties of solar twins reported by Lehmann et al. (2023) at kiloparsec distances from the local standard of rest (LSR) are compared to solar twins within 100 pc of the Sun. These have velocity distributions closely similar to those of the nearby twins in addition to closely matching $T_{\rm eff}$, $\log{(g)}$ and $[Fe/H]$. The new twins are at slightly higher galactic latitudes, and are somewhat closer to the Galactic center. Additionally, they may be significantly older than nearby solar twins.Comment: Revised and updated version of 2023 RNAAS 7, 8

The relation of metal-poor stars to nearby solar analogues

Sun-like dwarf stars in the solar neighborhood reflect ages, an ``average'' chemical evolution, and departures from that average. We show the chemical, and kinematic properties of four groups of Sunlike dwarfs form a continuum related to age. We plot [Fe/H] vs. age, as well as kinematical values for the four groups. The vertical (negative) scatter in [Fe/H] increases with age in a systematic way: as the age increases, [Fe/H] decreases. The sets of Solar and metal-poor stars in the solar neighborhood are related by distributions in [Fe/H] vs. age, as well as in Galactic position (XYZ) and velocity space (UVW). Among the samples there are no clusters of points that set one sample apart from the others. The distributions vary slowly from one set to the next, suggesting a mixture of stellar populations. A plot in Energy vs angular momentum phase space, with coordinate origin moved to the Galactic center, highlights different aspects of the kinematics of the four groups of stars. We finally compare the kinematic properties of these four groups with those of two sets of ultra metal-poor stars.Comment: 8 pages, 6 figure

Turbulent transport in tokamak plasmas with rotational shear

Nonlinear gyrokinetic simulations have been conducted to investigate turbulent transport in tokamak plasmas with rotational shear. At sufficiently large flow shears, linear instabilities are suppressed, but transiently growing modes drive subcritical turbulence whose amplitude increases with flow shear. This leads to a local minimum in the heat flux, indicating an optimal E x B shear value for plasma confinement. Local maxima in the momentum fluxes are also observed, allowing for the possibility of bifurcations in the E x B shear. The sensitive dependence of heat flux on temperature gradient is relaxed for large flow shear values, with the critical temperature gradient increasing at lower flow shear values. The turbulent Prandtl number is found to be largely independent of temperature and flow gradients, with a value close to unity.Comment: 4 pages, 5 figures, submitted to PR