Chemistry and kinematics in the solar neighborhood: implications for stellar populations and for galaxy evolution

The immediate Solar neighborhood should be a fair sample of the local Galaxy. However, the chemical abundance distribution of long-lived disk stars very near the Sun contains a factor of five to ten more metal-poor stars, -1 \simlt {\rm [Fe/H]} \simlt -0.4 dex, than is consistent with modern star-count models of larger scale Galactic structure. The metallicity distribution of complete samples of long-lived stars has long been recognised as providing unique constraints on the early stages of chemical evolution of the Galaxy, so that one would like to resolve this anomaly. We present a new derivation of the local G-dwarf metallicity distribution, based on the Third Gliese catalog combined with Olsen's (1983) Str\"omgren photometry. Kinematic data for these same stars, as well as for a high-precision sample studied by Edvardsson {\sl et al.} (1993), provide clear evidence that the abundance distribution below [Fe/H]\sim -0.4 contains two over-lapping distributions, the thick disk and the thin disk. We achieve a reliable deconvolution of the relative numbers in each population by comparing the local metallicity distribution with a recent determination (Gilmore, Wyse \& Jones 1995) of the metallicity distribution of F/G stars {\sl in situ} some 1500pc from the Sun. The gravitational sieve of the Galactic potential acts on this second sample to segregate the low velocity dispersion, thin-disk, component of the local sample, leaving predominantly the second, higher velocity dispersion component. The combination of these two datasets allows us to determine the source of the local paradox: there is a substantial tail of the thin disk (defined kinematically) metallicity distribution, which extends below {\rm [Fe/H] \approx -0.4}dex. This is a robust conclusion, being consistent with the sum of star count, stellar spatia

Scaling Laws for Incipient Cavitation Noise

The noise produced by the motion or a body through a liquid differs from that produced by the motion of a body through a gas because of the possibility or cavitation in the liquid case. An adequate theory or cavitation and cavitation noise is not yet available, but the application or dimensional analysis together with the theoretical information so far obtained can yield scaling laws for this flow situation. In section II, a brief dissussion will be given or the scaling laws for hydrodynamic noise in some cases of non-cavitating flow; this discussion is included tor oompleteness. In section III, a summary or the present information on the scaling law. for incipient cavitation noise will be presented

Generalized coherent states are unique Bell states of quantum systems with Lie group symmetries

We consider quantum systems, whose dynamical symmetry groups are semisimple Lie groups, which can be split or decay into two subsystems of the same symmetry. We prove that the only states of such a system that factorize upon splitting are the generalized coherent states. Since Bell's inequality is never violated by the direct product state, when the system prepared in the generalized coherent state is split, no quantum correlations are created. Therefore, the generalized coherent states are the unique Bell states, i.e., the pure quantum states preserving the fundamental classical property of satisfying Bell's inequality upon splitting.Comment: 4 pages, REVTeX, amssymb style. More information on http://www.technion.ac.il/~brif/science.htm

Advanced propellant management system for spacecraft propulsion systems. Phase 1 - Survey study and evaluation

Apollo spacecraft propulsion system propellant managemen

Outer structure of the Galactic warp and flare: explaining the Canis Major over-density

(Abridged) We derive the structure of the Galactic stellar Warp and Flare using 2MASS RC and RGB stars, selected at mean heliocentric distances of 3, 7 and 17 kpc. Our results are: (i) a clear stellar warp signature is derived for the 3 selected rings; (ii) the derived stellar warp is consistent (both in amplitude and phase-angle) with that for the Galactic interstellar dust and HI gas; (iii) the Sun seems not to fall on the line of nodes. The stellar warp phase-angle orientation (+15 degrees) is close to the orientation angle of the Galactic bar and this produces an asymmetric warp for the inner rings; (iv) a Northern/Southern warp symmetry is observed only for the ring at 17 kpc; (v) treating a mixture of thin and thick disk populations we trace the disk flaring and derive a constant scale-height (~0.65 kpc) within R(GC)~15 kpc. Further out, the disk flaring increase gradually reaching a mean scale-height of ~1.5 kpc at R(GC)~23 kpc; and (vi) these results provide further robust evidence that there is no disk radial truncation at R(GC)~14 kpc. In the particular case of the Canis Major over-density we confirm its coincidence with the Southern stellar maximum warp occurring near l=240. We present evidence to conclude that all observed parameters (e.g. number density, radial velocities, proper motion etc) of CMa are consistent with it being a normal Milky Way outer-disk population, thereby leaving no justification for a more complex interpretations of its origin. The present analysis does not provide a conclusive test of the structure or origin of the Monoceros Ring. Nevertheless, we show that a warped flared Milky Way contributes significantly at the locations of the Monoceros Ring.Comment: 25 pages, 22 figures, accepted for publication in A&A. A higher resolution pdf file is available at http://wwwuser.oat.ts.astro.it/zaggia/public_html/warp

The merging history of the Milky Way

The age distribution, and chemical elemental abundances, of stars in the halo of the Milky Way provide constraints on theories of galaxy formation. As one specific example, the accretion of satellite galaxies similar to the present retinue of dwarf spheroidals (dSphs) would provide an observable metal-poor, intermediate-age population. This paper presents a quantitative assessment of any contribution made by such stars to the stellar halo. The bulk of the stellar populations in the halo show a well-defined turn-off, at B-V ~ 0.4, implying that the vast majority of the stars are old. The fraction of stars which lie blueward of this well-defined turn-off, with metallicities similar to that of the present dSphs, is used in this paper to place limits on the importance of the recent accretion of such systems. Very few (~ -1.5 dex). Direct comparison of this statistic with the colour distribution of the turnoff stars in the Carina dwarf allows us to derive an upper limit on the number of mergers of such satellite galaxies into the halo of the Milky Way. This upper limit is ~ 40 Carina-like galaxies. The higher metallicity data constrain satellite galaxies like the Fornax dwarf; only <~ 5 of these could have been accreted within the last < ~ 10 Gyr. We note that the low star-formation rates inferred for dSphs predict distinctive elemental abundance signatures; future data for field halo stars, including candidate younger stars, will provide a further robust test of accretion models

The 300km/s stellar stream near Segue 1: Insights From high-resolution spectroscopy of its brightest star

We present a chemical abundance analysis of 300S-1, the brightest likely member star of the 300 km/s stream near the faint satellite galaxy Segue 1. From a high-resolution Magellan/MIKE spectrum we determine a metallicity of [Fe/H] = -1.46 +- 0.05 +- 0.23 (random and systematic uncertainties) for star 300S-1, and find an abundance pattern similar to typical halo stars at this metallicity. Comparing our stellar parameters to theoretical isochrones, we estimate a distance of 18 +- 7 kpc. Both the metallicity and distance estimates are in good agreement with what can be inferred from comparing the SDSS photometric data of the stream stars to globular cluster sequences. While several other structures overlap with the stream in this part of the sky, the combination of kinematic, chemical and distance information makes it unlikely that these stars are associated with either the Segue 1 galaxy, the Sagittarius stream or the Orphan stream. Streams with halo-like abundance signatures, such as the 300 km/s stream, present another observational piece for understanding the accretion history of the Galactic halo.Comment: 13 pages, emulateapj, accepted for publication in Ap

Topological phase for entangled two-qubit states and the representation of the SO(3)group

We discuss the representation of the $SO(3)$ group by two-qubit maximally entangled states (MES). We analyze the correspondence between $SO(3)$ and the set of two-qubit MES which are experimentally realizable. As a result, we offer a new interpretation of some recently proposed experiments based on MES. Employing the tools of quantum optics we treat in terms of two-qubit MES some classical experiments in neutron interferometry, which showed the $\pi$-phase accrued by a spin-$1/2$ particle precessing in a magnetic field. By so doing, we can analyze the extent to which the recently proposed experiments - and future ones of the same sort - would involve essentially new physical aspects as compared with those performed in the past. We argue that the proposed experiments do extend the possibilities for displaying the double connectedness of $SO(3)$, although for that to be the case it results necessary to map elements of $SU(2)$ onto physical operations acting on two-level systems.Comment: 25 pages, 9 figure