We propose an alternative method to laser cooling. Our approach utilizes the extreme brightness of a supersonic atomic beam, and the adiabatic atomic coilgun to slow atoms in the beam or to bring them to rest. We show how internal-state optical pumpi
ng and stimulated optical transitions, combined with magnetic forces can be used to cool the translational motion of atoms. This approach does not rely on momentum transfer from photons to atoms, as in laser cooling. We predict that our method can surpass laser cooling in terms of flux of ultra-cold atoms and phase-space density, with lower required laser power and reduced complexity.
Magnetic Towers represent one of two fundamental forms of MHD outflows. Driven by magnetic pressure gradients, these flows have been less well studied than magneto-centrifugally launched jets even though magnetic towers may well be as common. Here we
present new results exploring the behavior and evolution of magnetic tower outflows and demonstrate their connection with pulsed power experimental studies and purely hydrodynamic jets which might represent the asymptotic propagation regimes of magneto-centrifugally launched jets. High-resolution AMR MHD simulations (using the AstroBEAR code) provide insights into the underlying physics of magnetic towers and help us constrain models of their propagation. Our simulations have been designed to explore the effects of thermal energy losses and rotation on both tower flows and their hydro counterparts. We find these parameters have significant effects on the stability of magnetic towers, but mild effects on the stability of hydro jets. Current-driven perturbations in the Poynting Flux Dominated (PDF) towers are shown to be amplified in both the cooling and rotating cases. Our studies of the long term evolution of the towers show that the formation of weakly magnetized central jets within the tower are broken up by these instabilities becoming a series of collimated clumps which magnetization properties vary over time. In addition to discussing these results in light of laboratory experiments, we address their relevance to astrophysical observations of young star jets and outflow from highly evolved solar type stars.
Modern theoretical models of astrophysical jets combine accretion, rotation, and magnetic fields to launch and collimate supersonic flows from a central source. Near the source, magnetic field strengths must be large enough to collimate the jet requi
ring that the Poynting flux exceeds the kinetic-energy flux. The extent to which the Poynting flux dominates kinetic energy flux at large distances from the engine distinguishes two classes of models. In magneto-centrifugal launch (MCL) models, magnetic fields dominate only at scales $lesssim 100$ engine radii, after which the jets become hydrodynamically dominated (HD). By contrast, in Poynting flux dominated (PFD) magnetic tower models, the field dominates even out to much larger scales. To compare the large distance propagation differences of these two paradigms, we perform 3-D ideal MHD AMR simulations of both HD and PFD stellar jets formed via the same energy flux. We also compare how thermal energy losses and rotation of the jet base affects the stability in these jets. For the conditions described, we show that PFD and HD exhibit observationally distinguishable features: PFD jets are lighter, slower, and less stable than HD jets. Unlike HD jets, PFD jets develop current-driven instabilities that are exacerbated as cooling and rotation increase, resulting in jets that are clumpier than those in the HD limit. Our PFD jet simulations also resemble the magnetic towers that have been recently created in laboratory astrophysical jet experiments.
The Fermi Large Area Telescope (LAT) consists of 16 towers, each incorporating a tracker made up of a stack of 18 pairs of orthogonal silicon strip detectors (SSDs), interspersed with tungsten converter foils. The strip numbers of the struck strips i
n each SSD plane are collected by two read controllers (RCs), one at each end, and nine RCs are connected by one of eight cables to a cable controller (CC). The tracker readout electronics limit the number of strips that can be read out. Although each RC can store up to 64 hits, a CC can store maximum of only 128 hits. To insure that the photon shower development and backsplash in the lower layers of the tracker dont compromise the readout of the upper layers, we artificially limit the number of strips read out into each RC to 14, so that no CC can ever can see more than 126 hit strips. In this contribution, we explore other configurations that will allow for a more complete readout of large events, and investigate some of the consequences of using these configurations.
We present 3D-MHD AMR simulations of Poynting flux dominated (PFD) jets formed by injection of magnetic energy. We compare their evolution with a hydrodynamic jet which is formed by injecting kinetic energy with the same energy flux than the PFD jets
. We predict characteristic emission distributions for each of these jets. Current-driven perturbations in PFD jets are amplified by both cooling and rotation for the regimes studied: Shocks and thermal pressure support are weakened by cooling, making the jets more susceptible to kinking. Rotation amplifies the toroidal magnetic field which also exacerbates the kink instability.
Numeric convergence studies demonstrate that the evolution of an adiabatic clump is well-captured by roughly 100 cells per clump radius. The presence of radiative cooling, however, imposes limits on the problem due to the removal of thermal energy. N
umerical studies which include radiative cooling typically adopt the 100--200 cells per clump radius resolution. In this paper we present the results of a convergence study for radiatively cooling clumps undertaken over a broad range of resolutions, from 12 to 1,536 cells per clump radius, employing adaptive mesh refinement (AMR) in a 2D axisymmetric geometry (2.5D). We also provide a fully 3D simulation, at 192 cells per clump radius, which supports our 2.5D results. We find no appreciable self-convergence at ~100 cells per clump radius as small-scale differences owing to increasingly resolving the cooling length have global effects. We therefore conclude that self-convergence is an insufficient criterion to apply on its own when addressing the question of sufficient resolution for radiatively cooled shocked clump simulations. We suggest the adoption of alternate criteria to support a statement of sufficient resolution, such as the demonstration of adequate resolution of the cooling layers behind shocks. We discuss an associated refinement criteria for AMR codes.
We present archival Spitzer IRS spectra of 19 luminous 8 micron selected sources in the Large Magellanic Cloud (LMC). The object classes derived from these spectra and from an additional 24 spectra in the literature are compared with classifications
based on 2MASS/MSX (J, H, K, and 8 micron) colors in order to test the JHK8 classification scheme (Kastner et al. 2008). The IRS spectra confirm the classifications of 22 of the 31 sources that can be classified under the JHK8 system. The spectroscopic classification of 12 objects that were unclassifiable in the JHK8 scheme allow us to characterize regions of the color-color diagrams that previously lacked spectroscopic verification, enabling refinements to the JHK8 classification system. The results of these new classifications are consistent with previous results concerning the identification of the most infrared-luminous objects in the LMC. In particular, while the IRS spectra reveal several new examples of asymptotic giant branch (AGB) stars with O-rich envelopes, such objects are still far outnumbered by carbon stars (C-rich AGB stars). We show that Spitzer IRAC/MIPS color-color diagrams provide improved discrimination between red supergiants and oxygen-rich and carbon-rich asymptotic giant branch stars relative to those based on 2MASS/MSX colors. These diagrams will enable the most luminous IR sources in Local Group galaxies to be classified with high confidence based on their Spitzer colors. Such characterizations of stellar populations will continue to be possible during Spitzers warm mission, through the use of IRAC [3.6]-[4.5] and 2MASS colors.
(Abridged) The repeated discovery of supermassive black holes (SMBHs) at the centers of galactic bulges, and the discovery of relations between the SMBH mass (M) and the properties of these bulges, has been fundamental in directing our understanding
of both galaxy and SMBH formation and evolution. However, there are still many questions surrounding the SMBH - galaxy relations. For example, are the scaling relations linear and constant throughout cosmic history, and do all SMBHs lie on the scaling relations? These questions can only be answered by further high quality direct M estimates from a wide range in redshift. In this paper we determine the observational requirements necessary to directly determine SMBH masses, across cosmological distances, using current M modeling techniques. We also discuss the SMBH detection abilities of future facilities. We find that if different M modeling techniques, using different spectral features, can be shown to be consistent, then both 30 m ground- and 16 m space-based telescopes will be able to sample M 1e9Msol across ~95% of cosmic history. However, we find that the abilities of ground-based telescopes critically depend on future advancements in adaptive optics systems; more limited AO systems will result in limited effective spatial resolutions, and forces observations towards the near-infrared where spectral features are weaker and more susceptible to sky features. Ground-based AO systems will always be constrained by relatively bright sky backgrounds and atmospheric transmission. The latter forces the use of multiple spectral features and dramatically impacts the SMBH detection efficiency. The most efficient way to advance our database of direct SMBH masses is therefore through the use of a large (16 m) space-based UVOIR telescope.
We report the results of a mm-wave molecular line survey of the nearby (D ~ 70 pc), 12 Myr-old system V4046 Sgr -- a tight (9 R_sun separation), short-period (2.42 day) binary with nearly equal component masses of ~0.9 M_sun -- conducted with the 30
m telescope of the Institut de Radio Astronomie Millimetrique (IRAM). We detected rotational transitions of 12CO 13CO, HCN, CN, and HCO+. The double-peaked CO line profiles of V4046 Sgr are well fit by a model invoking a Keplerian disk with outer radius of ~250 AU that is viewed at an inclination i = 35 degrees. We infer minimum disk gas and dust masses of ~13 and ~20 Earth masses from the V4046 Sgr CO line and submm continuum fluxes, respectively. The actual disk gas mass could be much larger if the gas-phase CO is highly depleted and/or 13CO is very optically thick. The overall similarity of the circumbinary disk of V4046 Sgr to the disk orbiting the single, ~8 Myr-old star TW Hya -- a star/disk system often regarded as representative of the early solar nebula -- indicates that gas giant planets are likely commonplace among close binary star systems. Given the relatively advanced age and proximity of V4046 Sgr, these results provide strong motivation for future high-resolution imaging designed to ascertain whether a planetary system now orbits its twin suns.
Many new physics models predict resonances with masses in the TeV range which decay into a pair of top quarks. With its large cross section, t-bar t production at the Large Hadron Collider (LHC) offers an excellent opportunity to search for such part
icles. We present a detailed study of the discovery potential of the CERN Large Hadron Collider for Kaluza-Klein (KK) excitations of the gluon in bulk Randall-Sundrum (RS) models in the t-bar t -> ell^+/- nu b-bar bq-bar q (ell=e, mu) final state. We utilize final states with one or two tagged b-quarks, and two, three or four jets (including b-jets). Our calculations take into account the finite resolution of detectors, the energy loss due to b-quark decays, the expected reduced b-tagging efficiency at large t-bar t invariant masses, and include the background originating from Wb-bar b+jets, (Wb+W-bar b)+jets, W+jets, and single top + jets production. We derive semi-realistic 5 sigma discovery limits for nine different KK gluon scenarios, and compare them with those for KK gravitons, and a Z_H boson in the Littlest Higgs model. We also analyze the capabilities of the LHC experiments to differentiate between individual KK gluon models and measure the couplings of KK gluons to quarks. We find that, for the parameters and models chosen, KK gluons with masses up to about 4 TeV can be discovered at the LHC. The ability of the LHC to discriminate between different bulk RS models, and to measure the couplings of the KK gluons is found to be highly model dependent.
