Beltrami-like fields created by baroclinic effect in two-fluid plasmas

A theory of two-dimensional plasma evolution with Beltrami-like flow and field due to baroclinic effect has been presented. Particular solution of the nonlinear two-fluid equations is obtained. This simple model can explain the generation of magnetic field without assuming the presence of a seed in the system. Coupled field and flow naturally grow together. The theory has been applied to estimate B-field in laser-induced plasmas and the result is in good agreement with experimental values.Comment: 3 page

The First Supernova Explosions in the Universe

We investigate the supernova explosions that end the lives of massive Population III stars in low-mass minihalos (M~10^6 M_sun) at redshifts z~20. Employing the smoothed particle hydrodynamics method, we carry out numerical simulations in a cosmological set-up of pair-instability supernovae with explosion energies of E_SN=10^51 and 10^53 ergs. We find that the more energetic explosion leads to the complete disruption of the gas in the minihalo, whereas the lower explosion energy leaves much of the halo intact. The higher energy supernova expels > 90% of the stellar metals into a region ~1 kpc across over a timescale of 3-5 Myr. Due to this burst-like initial star formation episode, a large fraction of the universe could have been endowed with a metallicity floor, Z_min>10^-4 Z_sun, already at z>15.Comment: Published in ApJ Letter

Simulation tools for future interferometers

For the design and commissioning of the LIGO interferometer, simulation tools have been used explicitly and implicitly. The requirement of the advanced LIGO interferometer is much more demanding than the first generation interferometer. Development of revised simulation tools for future interferometers are underway in the LIGO Laboratory. The outline of those simulation tools and applications are discussed

Rossby-Haurwitz waves of a slowly and differentially rotating fluid shell

Recent studies have raised doubts about the occurrence of r modes in Newtonian stars with a large degree of differential rotation. To assess the validity of this conjecture we have solved the eigenvalue problem for Rossby-Haurwitz waves (the analogues of r waves on a thin-shell) in the presence of differential rotation. The results obtained indicate that the eigenvalue problem is never singular and that, at least for the case of a thin-shell, the analogues of r modes can be found for arbitrarily large degrees of differential rotation. This work clarifies the puzzling results obtained in calculations of differentially rotating axi-symmetric Newtonian stars.Comment: 8pages, 3figures. Submitted to CQ

A search for x-ray counterparts of gamma-ray bursts with the ROSAT PSPC

We search for faint X-ray bursts with duration 10--300 seconds in the ROSAT PSPC pointed observations with a total exposure of 1.6e7 seconds. We do not detect any events shorter than ~100s, i.e. those that could be related to the classic gamma-ray bursts. At the same time, we detect a number of long flares with durations of several hundred seconds. Most, but not all, of the long flares are associated with stars. If even a small number of those long flares, that cannot identified with stars, are X-ray afterglows of GRB, the number of X-ray afterglows greatly exceeds the number of BATSE GRB. This would imply that the beaming factor of gamma-rays from the burst should be >100. The non-detection of any short bursts in our data constrains the GRB counts at the fluences 1--2.5 orders of magnitude below the BATSE limit. The constrained burst counts are consistent with the extrapolation of the BATSE log N - log S relation. Finally, our results do not confirm a reality of short X-ray flashes found in the Einstein IPC data by Gotthelf, Hamilton and Helfand.Comment: Accepted to ApJ Letters. 4 pages with 3 figures, LaTeX2

Dense Molecular Gas In A Young Cluster Around MWC 1080 -- Rule Of The Massive Star

We present CS $J = 2 \to 1$, $^{13}$CO $J = 1 \to 0$, and C$^{18}$O $J = 1 \to 0$, observations with the 10-element Berkeley Illinois Maryland Association (BIMA) Array toward the young cluster around the Be star MWC 1080. These observations reveal a biconical outflow cavity with size $\sim$ 0.3 and 0.05 pc for the semimajor and semiminor axis and $\sim$ 45\arcdeg position angle. These transitions trace the dense gas, which is likely the swept-up gas of the outflow cavity, rather than the remaining natal gas or the outflow gas. The gas is clumpy; thirty-two clumps are identified. The identified clumps are approximately gravitationally bound and consistent with a standard isothermal sphere density, which suggests that they are likely collapsing protostellar cores. The gas kinematics suggests that there exists velocity gradients implying effects from the inclination of the cavity and MWC 1080. The kinematics of dense gas has also been affected by either outflows or stellar winds from MWC 1080, and lower-mass clumps are possibly under stronger effects from MWC 1080 than higher-mass clumps. In addition, low-mass cluster members tend to be formed in the denser and more turbulent cores, compared to isolated low-mass star-forming cores. This results from contributions of nearby forming massive stars, such as outflows or stellar winds. Therefore, we conclude that in clusters like the MWC 1080 system, effects from massive stars dominate the star-forming environment in both the kinematics and dynamics of the natal cloud and the formation of low-mass cluster members. This study provides insights into the effects of MWC 1080 on its natal cloud, and suggests a different low-mass star forming environment in clusters compared to isolated star formation.Comment: 42 pages, 5 tables, and 13 figures, accepted for publication in Ap

Invariants of Collective Neutrino Oscillations

We consider the flavor evolution of a dense neutrino gas by taking into account both vacuum oscillations and self interactions of neutrinos. We examine the system from a many-body perspective as well as from the point of view of an effective one-body description formulated in terms of the neutrino polarization vectors. We show that, in the single angle approximation, both the many-body picture and the effective one-particle picture possess several constants of motion. We write down these constants of motion explicitly in terms of the neutrino isospin operators for the many-body case and in terms of the polarization vectors for the effective one-body case. The existence of these constants of motion is a direct consequence of the fact that the collective neutrino oscillation Hamiltonian belongs to the class of Gaudin Hamiltonians. This class of Hamiltonians also includes the (reduced) BCS pairing Hamiltonian describing superconductivity. We point out the similarity between the collective neutrino oscillation Hamiltonian and the BCS pairing Hamiltonian. The constants of motion manifest the exact solvability of the system. Borrowing the well established techniques of calculating the exact BCS spectrum, we present exact eigenstates and eigenvalues of both the many-body and the effective one-particle Hamiltonians describing the collective neutrino oscillations. For the effective one-body case, we show that spectral splits of neutrinos can be understood in terms of the adiabatic evolution of some quasi-particle degrees of freedom from a high density region where they coincide with flavor eigenstates to the vacuum where they coincide with mass eigenstates. We write down the most general consistency equations which should be satisfied by the effective one-body eigenstates and show that they reduce to the spectral split consistency equations for the appropriate initial conditions.Comment: 26 pages with one figure. Published versio

Relativistic r-modes in Slowly Rotating Neutron Stars: Numerical Analysis in the Cowling Approximation

We investigate the properties of relativistic $r$-modes of slowly rotating neutron stars by using a relativistic version of the Cowling approximation. In our formalism, we take into account the influence of the Coriolis like force on the stellar oscillations, but ignore the effects of the centrifugal like force. For three neutron star models, we calculated the fundamental $r$-modes with $l'=m=2$ and 3. We found that the oscillation frequency $\bar\sigma$ of the fundamental $r$-mode is in a good approximation given by $\bar\sigma\approx \kappa_0 \Omega$, where $\bar\sigma$ is defined in the corotating frame at the spatial infinity, and $\Omega$ is the angular frequency of rotation of the star. The proportional coefficient $\kappa_0$ is only weakly dependent on $\Omega$, but it strongly depends on the relativistic parameter $GM/c^2R$, where $M$ and $R$ are the mass and the radius of the star. All the fundamental $r$-modes with $l'=m$ computed in this study are discrete modes with distinct regular eigenfunctions, and they all fall in the continuous part of the frequency spectrum associated with Kojima's equation (Kojima 1998). These relativistic $r$-modes are obtained by including the effects of rotation higher than the first order of $\Omega$ so that the buoyant force plays a role, the situation of which is quite similar to that for the Newtonian $r$-modes.Comment: 22 pages, 8 figures, accepted for publication in Ap

Ultralong-Range Rydberg Molecules in a Divalent-Atomic System

We report the creation of ultralong-range Sr$_2$ molecules comprising one ground-state $5s^2$ $^1S_0$ atom and one atom in a $5sns$ $^3S_1$ Rydberg state for $n$ ranging from 29 to 36. Molecules are created in a trapped ultracold atomic gas using two-photon excitation near resonant with the $5s5p$ $^3P_1$ intermediate state, and their formation is detected through ground-state atom loss from the trap. The observed molecular binding energies are fit with the aid of first-order perturbation theory that utilizes a Fermi pseudopotential with effective $s$-wave and $p$-wave scattering lengths to describe the interaction between an excited Rydberg electron and a ground-state Sr atom.Comment: 5 pages, 2 figure

General Relativistic Rossby-Haurwitz waves of a slowly and differentially rotating fluid shell

We show that, at first order in the angular velocity, the general relativistic description of Rossby-Haurwitz waves (the analogues of r-waves on a thin shell) can be obtained from the corresponding Newtonian one after a coordinate transformation. As an application, we show that the results recently obtained by Rezzolla and Yoshida (2001) in the analysis of Newtonian Rossby-Haurwitz waves of a slowly and differentially rotating, fluid shell apply also in General Relativity, at first order in the angular velocity.Comment: 4 pages. Comment to Class. Quantum Grav. 18(2001)L8