The Distribution of Dark Matter in a Ringed Galaxy

Outer rings are located at the greatest distance from the galaxy center of any feature resonant with a bar. Because of their large scale, their morphology is sensitive to the distribution of the dark matter in the galaxy. We introduce here how study of these rings can constrain the mass-to-light ratio of the bar, and so the percentage of dark matter in the center of these galaxies. We compare periodic orbits integrated in the ringed galaxy NGC 6782 near the outer Lindblad resonance to the shape of the outer ring. The non-axisymmetric component of the potential resulting from the bar is derived from a near-infrared image of the galaxy. The axisymmetric component is derived assuming a flat rotation curve. We find that the pinched non-self-intersecting periodic orbits are more elongated for higher bar mass-to-light ratios and faster bars. The inferred mass-to-light ratio of the bar depends on the assumed inclination of the galaxy. With an assumed galaxy inclination of i=41 degrees, for the orbits to be consistent with the observed ring morphology the mass-to-light ratio of the bar must be high, greater than 70% of a maximal disk value. For i=45 degrees, the mass-to-light ratio of the bar is $75\pm 15$ of the maximal disk value. Since the velocity field of these rings can be used to constrain the galaxy inclination as well as which periodic orbit is represented in the ring, further study will yield tighter constraints on the mass-to-light ratio of the bar. If a near maximal disk value for the bar is required, then either there would be little dark matter within the bar, or the dark matter contained in the disk of the galaxy would be non-axisymmetric and would rotate with the bar.Comment: AAS Latex + jpg Figures, Accepted for publication in Ap

A Bose-Einstein condensate interferometer with macroscopic arm separation

A Michelson interferometer using Bose-Einstein condensates is demonstrated with coherence times of up to 44 ms and arm separations up to 0.18 mm. This arm separation is larger than that observed for any previous atom interferometer. The device uses atoms weakly confined in a magnetic guide and the atomic motion is controlled using Bragg interactions with an off-resonant standing wave laser beam.Comment: 4 pages, 3 figure

Searching for Machos (and other Dark Matter Candidates) in a Simulated Galaxy

We conduct gravitational microlensing experiments in a galaxy taken from a cosmological N-body simulation. Hypothetical observers measure the optical depth and event rate toward hypothetical LMCs and compare their results with model predictions. Since we control the accuracy and sophistication of the model, we can determine how good it has to be for statistical errors to dominate over systematic ones. Several thousand independent microlensing experiments are performed. When the ``best-fit'' triaxial model for the mass distribution of the halo is used, the agreement between the measured and predicted optical depths is quite good: by and large the discrepancies are consistent with statistical fluctuations. If, on the other hand, a spherical model is used, systematic errors dominate. Even with our ``best-fit'' model, there are a few rare experiments where the deviation between the measured and predicted optical depths cannot be understood in terms of statistical fluctuations. In these experiments there is typically a clump of particles crossing the line of sight to the hypothetical LMC. These clumps can be either gravitationally bound systems or transient phenomena in a galaxy that is still undergoing phase mixing. Substructure of this type, if present in the Galactic distribution of Machos, can lead to large systematic errors in the analysis of microlensing experiments. We also describe how hypothetical WIMP and axion detection experiments might be conducted in a simulated N-body galaxy.Comment: 18 pages of text (LaTeX, AASTeX) with 12 figures. submitted to the Astrophysical Journa

A Neutral Hydrogen Survey of Polar-Ring Galaxies: I. Green Bank Observations of the Northern Sample

We present the results of a neutral hydrogen survey conducted with the Green Bank 140-foot radio telescope of 47 northern objects in the polar-ring galaxy atlas of Whitmore \etal\ (1990). We detected 39 of these above our detection limit of 1.7 \hbox{Jy\CDOT\KMS}; the average measured flux of 21 Jy\CDOT\KMS\ corresponds to an average neutral hydrogen mass of $\rm 5.3 \times 10^9$ \MSUN for a Hubble constant of $\rm H_0 = 75$ \KMS \ Mpc$^{-1}$. For the polar-ring galaxies in our sample that have also been observed with radio arrays, we find that the 21\AMIN\ (FWHM) Green Bank beam often includes much more flux than found by the synthesis instruments for the polar rings alone; some of these galaxies are known to have gas-rich companions. We compare the neutral hydrogen content of the sample to the blue luminosity and IRAS fluxes. The \HI-to-blue- light ratios of the confirmed and probable polar rings are around unity in solar units, indicating that polar ring galaxies (or their environments) are as gas-rich as typical irregular galaxies. For their blue luminosity, the confirmed polar rings are underluminous in the far-infrared, as compared with the rest of the sample. They are also FIR-underluminous for their \HI\ masses, which suggests that most of the gas in the ring may be in stable orbits, rather than flowing inward to trigger star formation in the central galaxy. The more disordered class of `related objects,' which includes a number of obvious mergers, is highly luminous in the far-infrared.Comment: 34 pages, LaTeX file, Institute for Advanced Study number AST 93/4

Stabilizing an Attractive Bose-Einstein Condensate by Driving a Surface Collective Mode

Bose-Einstein condensates of $^7$Li have been limited in number due to attractive interatomic interactions. Beyond this number, the condensate undergoes collective collapse. We study theoretically the effect of driving low-lying collective modes of the condensate by a weak asymmetric sinusoidally time-dependent field. We find that driving the radial breathing mode further destabilizes the condensate, while excitation of the quadrupolar surface mode causes the condensate to become more stable by imparting quasi-angular momentum to it. We show that a significantly larger number of atoms may occupy the condensate, which can then be sustained almost indefinitely. All effects are predicted to be clearly visible in experiments and efforts are under way for their experimental realization.Comment: 4 ReVTeX pages + 2 postscript figure

Probing Dark Matter

Recent novel observations have probed the baryonic fraction of the galactic dark matter that has eluded astronomers for decades. Late in 1993, the MACHO and EROS collaborations announced in this journal the detection of transient and achromatic brightenings of a handful of stars in the Large Magellanic Cloud that are best interpreted as gravitational microlensing by low-mass foreground objects (MACHOS). This tantalized astronomers, for it implied that the population of cool, compact objects these lenses represent could be the elusive dark matter of our galactic halo. A year later in 1994, Sackett et al. reported the discovery of a red halo in the galaxy NGC 5907 that seems to follow the inferred radial distribution of its dark matter. This suggested that dwarf stars could constitute its missing component. Since NGC 5907 is similar to the Milky Way in type and radius, some surmised that the solution of the galactic dark matter problem was an abundance of ordinary low-mass stars. Now Bahcall et al., using the Wide-Field Camera of the recently repaired Hubble Space Telescope, have dashed this hope.Comment: 3 pages, Plain TeX, no figures, published as a News and Views in Nature 373, 191 (1995

Proceedings of the 3rd International Conference on Manufacturng Research ICMR2005: Advances in Manufacturing Technology and Management

The International Conference on Manufacturing Research (ICMR) is an annual event, normally held in the early part of September. For many years, it was an UK National Conference that had successfully brought academics and industrialists together to share their knowledge and experiences. Now the conference has developed as a major international event with a growing number of international delegates participating to exchange their research findings with UK researchers and practitioners. The next conference (ICMR2005) will be held at Cranfield University, a distinctive postgraduate university focusing on engineering, management and applied science

Intermittent implosion and pattern formation of trapped Bose-Einstein condensates with attractive interaction

The collapsing dynamics of a trapped Bose-Einstein condensate (BEC) with attractive interaction are revealed to exhibit two previously unknown phenomena. During the collapse, BEC undergoes a series of rapid implosions that occur {\it intermittently} within a very small region. When the sign of the interaction is suddenly switched from repulsive to attractive, e.g., by the Feshbach resonance, density fluctuations grow to form various patterns such as a shell structure.Comment: 5 pages, 2 figures, RevTeX, epsf.sty, corrected loss rate

Lupus-TR-3b: A Low-Mass Transiting Hot Jupiter in the Galactic Plane?

We present a strong case for a transiting Hot Jupiter planet identified during a single-field transit survey towards the Lupus Galactic plane. The object, Lupus-TR-3b, transits a V=17.4 K1V host star every 3.91405d. Spectroscopy and stellar colors indicate a host star with effective temperature 5000 +/- 150K, with a stellar mass and radius of 0.87 +/- 0.04M_sun and 0.82 +/- 0.05R_sun, respectively. Limb-darkened transit fitting yields a companion radius of 0.89 +/- 0.07R_J and an orbital inclination of 88.3 +1.3/-0.8 deg. Magellan 6.5m MIKE radial velocity measurements reveal a 2.4 sigma K=114 +/- 25m/s sinusoidal variation in phase with the transit ephemeris. The resulting mass is 0.81 +/- 0.18M_J and density 1.4 +/- 0.4g/cm^3. Y-band PANIC image deconvolution reveal a V>=21 red neighbor 0.4'' away which, although highly unlikely, we cannot conclusively rule out as a blended binary with current data. However, blend simulations show that only the most unusual binary system can reproduce our observations. This object is very likely a planet, detected from a highly efficient observational strategy. Lupus-TR-3b constitutes the faintest ground-based detection to date, and one of the lowest mass Hot Jupiters known.Comment: 4 pages, 4 figures, accepted for publication in ApJ