Detection of H-alpha emission from the Magellanic Stream: evidence for an extended gaseous Galactic halo

We have detected faint, diffuse H$\alpha emission from several points along the Magellanic Stream, using the Rutgers Fabry--Perot Interferometer at the CTIO 1.5-m telescope. At points on the leading edges of the H I clouds MS II, MS III, and MS IV, we detect H$\alpha emission of surface brightness $0.37 \pm 0.02$ Rayleighs, $0.21 \pm 0.04$ R, and $0.20 \pm 0.02$ R respectively, corresponding to emission measures of 1.0 to 0.5 \cmsixpc. We have observed several positions near the MS IV concentration, and find that the strongest emission is on the sharp leading-edge density gradient. There is less emission at points away from the gradient, and halfway between MS III and MS IV the H$\alpha surface brightness is$< 0.04$R. We attribute the H$\alpha emission at cloud leading edges to heating of the Stream clouds by ram pressure from ionized gas in the halo of the Galaxy. These observations suggest that ram pressure from halo gas plays a large role in stripping the Stream out of the Magellanic Clouds. They also suggest the presence of a relatively large density of gas, $n_{\rm H} \sim 10^{-4} cm^{-3}$, in the Galactic halo at $\sim 50$ kpc radius, and far above the Galactic plane, $b \sim -80\deg$. This implies that the Galaxy has a very large baryonic, gaseous extent, and supports models of Lyman-$\alpha and metal-line QSO absorption lines in which the absorption systems reside in extended galactic halos.Comment: 15 pages, aaspp latex, + 1 table & 3 figures. Accepted in A.J. Also available from http://www.physics.rutgers.edu/~bweiner/astro/papers

A Supersymmetric Twin Higgs

We present a supersymmetric realization of the twin Higgs mechanism, which cancels off all contributions to the Higgs mass generated above a scale f. Radiative corrections induced by the top quark sector lead to a breaking of the twin sector electroweak symmetry at a scale f ~ TeV. In our sector, below the scale f, these radiative corrections from the top quark are present but greatly weakened, naturally allowing a Z boson mass an order of magnitude below f, even with a top squark mass of order 1 TeV and a messenger scale near the Planck mass. A sufficient quartic interaction for our Higgs boson arises from the usual gauge contribution together with a radiative contribution from a heavy top squark. The mechanism requires the presence of an SU(2)-adjoint superfield, and can be simply unified. Naturalness in these theories is usually associated with light winos and sleptons, and is largely independent of the scale of the colored particles. The assumption of unification naturally predicts the existence of many exotic fields. The theory often has particles which may be stable on collider timescales, including an additional color octet superfield. In the limit that m_SUSY >> f, the mechanism yields a UV completion of the non-supersymmetric twin Higgs, but with the notable improvement of a tree-level quartic for the standard model Higgs. In this framework, a successful UV completion requires the existence of new charged fields well below the scale f.Comment: 20 page

Study of high voltage solar array configurations with integrated power control electronics

Solar array electrical configurations for voltage regulatio

Controlling Condensate Collapse and Expansion with an Optical Feshbach Resonance

We demonstrate control of the collapse and expansion of an 88Sr Bose-Einstein condensate using an optical Feshbach resonance (OFR) near the 1S0-3P1 intercombination transition at 689 nm. Significant changes in dynamics are caused by modifications of scattering length by up to +- ?10a_bg, where the background scattering length of 88Sr is a_bg = -2a0 (1a0 = 0.053 nm). Changes in scattering length are monitored through changes in the size of the condensate after a time-of-flight measurement. Because the background scattering length is close to zero, blue detuning of the OFR laser with respect to a photoassociative resonance leads to increased interaction energy and a faster condensate expansion, whereas red detuning triggers a collapse of the condensate. The results are modeled with the time-dependent nonlinear Gross-Pitaevskii equation.Comment: 5 pages, 3 figure

The Bose-Einstein correlation function C2(Q)C_2(Q) from a Quantum Field Theory point of view

We show that a recently proposed derivation of Bose-Einstein correlations (BEC) by means of a specific version of thermal Quantum Field Theory (QFT), supplemented by operator-field evolution of the Langevin type, allows for a deeper understanding of the possible coherent behaviour of the emitting source and a clear identification of the origin of the observed shape of the BEC function $C_2(Q)$. Previous conjectures in this matter obtained by other approaches are confirmed and have received complementary explanation.Comment: Some misprints corrected. To be publishe in Phys. Rev.

Second order equation of motion for electromagnetic radiation back-reaction

We take the viewpoint that the physically acceptable solutions of the Lorentz--Dirac equation for radiation back-reaction are actually determined by a second order equation of motion, the self-force being given as a function of spacetime location and velocity. We propose three different methods to obtain this self-force function. For two example systems, we determine the second order equation of motion exactly in the nonrelativistic regime via each of these three methods, the three methods leading to the same result. We reveal that, for both systems considered, back-reaction induces a damping proportional to velocity and, in addition, it decreases the effect of the external force.Comment: 13 page

The molecular and dusty composition of Betelgeuse's inner circumstellar environment

The study of the atmosphere of red supergiant stars in general and of Betelgeuse (alpha Orionis) in particular is of prime importance to understand dust formation and how mass is lost to the interstellar medium in evolved massive stars. A molecular shell, the MOLsphere (Tsuji, 2000a), in the atmosphere of Betelgeuse has been proposed to account for the near- and mid-infrared spectroscopic observations of Betelgeuse. The goal is to further test this hypothesis and to identify some of the molecules in this MOLsphere. We report on measurements taken with the mid-infrared two-telescope beam combiner of the VLTI, MIDI, operated between 7.5 and 13.5 $\mu$m. The data are compared to a simple geometric model of a photosphere surrounded by a warm absorbing and emitting shell. Physical characteristics of the shell are derived: size, temperature and optical depth. The chemical constituents are determined with an analysis consistent with available infrared spectra and interferometric data. We are able to account for the measured optical depth of the shell in the N band, the ISO-SWS spectrum and K and L band interferometric data with a shell whose inner and outer radii are given by the above range and with the following species: H2O, SiO and Al2O3. These results confirm the MOLsphere model. We bring evidence for more constituents and for the presence of species participating in the formation of dust grains in the atmosphere of the star, i.e. well below the distance at which the dust shell is detected. We believe these results bring key elements to the understanding of mass loss in Betelgeuse and red supergiants in general and bring support to the dust-driven scenario.Comment: 11 pages, 10 figures, accepted for publication in A&