Searching for a kinematic signature of the moderately metal-poor stars in the Milky Way bulge using N-body simulations

Although there is consensus that metal-rich stars in the Milky Way bulge are formed via secular evolution of the thin disc, the origin of their metal-poor counterparts is still under debate. Two different origins have been invoked for metal-poor stars: they might be classical bulge stars or stars formed via internal evolution of a massive thick disc. We use N-body simulations to calculate the kinematic signature given by the difference in the mean Galactocentric radial velocity (ΔVGC) between metal-rich stars ([Fe/H] ≥ 0) and moderately metal-poor stars (–1.0 ≤ [Fe/H] < 0) in two models, one containing a thin disc and a small classical bulge (B/D = 0.1), and the other containing a thin disc and a massive centrally concentrated thick disc. We reasonably assume that thin-disk stars in each model may be considered as a proxy of metal-rich stars. Similarly, bulge stars and thick-disc stars may be considered as a proxy of metal-poor stars. We calculate ΔVGC at different latitudes (b = 0°, − 2°, − 4°, − 6°, − 8° and − 10°) and longitudes (l = 0°, ± 5°, ± 10° and ± 15°) and show that the ΔVGC trends predicted by the two models are different. We compare the predicted results with ARGOS data and APOGEE DR13 data and show that moderately metal-poor stars are well reproduced with the co-spatial stellar discs model, which has a massive thick disc. Our results give more evidence against the scenario that most of the metal-poor stars are classical bulge stars. If classical bulge stars exists, most of them probably have metallicities [Fe/H] < –1 dex, and their contribution to the mass of the bulge should be a small percentage of the total bulge mass.

Solar Power for Autonomous Floats

Advances in low-power instrumentation and communications now often make energy storage the limiting factor for long-term autonomous oceanographic measurements. Recent advances in photovoltaic cells, with efficiencies now close to 30%, make solar power potentially viable even for vehicles such as floats that only surface intermittently. A simple application, the development of a solar-powered Argos recovery beacon, is described here to illustrate the technology. The 65-cm2 solar array, submersible to at least 750 dbar, powers an Argos beacon. Tests indicate that with minor improvements the beacon will run indefinitely at any latitude equatorward of about 50°. Scaling up this design to current operational profiling floats, each profile could easily be powered by a few hours of solar charging, a shorter time than is currently being used for Argos data communications.