9286 Stars: An Agglomeration of Stellar Polarization Catalogs

This is a revision. The revisions are minor. The new version of the catalog should be used in preference to the old. The most serious error in the older version was that $\theta_diff$ was incorrect, being sometimes far too large, for Reiz and Franco entries; the correct values are all zero for that reference. We present an agglomeration of stellar polarization catalogs with results for 9286 stars. We have endeavored to eliminate errors, provide accurate (arcsecond) positions, sensibly weight multiple observations of the same star, and provide reasonable distances. This catalog is included as an ASCII file (catalog.txt) in the source of this submission.Comment: The most serious error in the older version was that $\theta_diff$ was incorrect, being sometimes far too large, for Reiz and Franco entries; the correct values are all zero for that reference. 11 pages, no figures. Accepted for Astronomical Journal. Catalog also available as an ASCII file by anonymous FTP from ftp://vermi.berkeley.edu/pub/polcat/p14.ou

The Effect of the Random Magnetic Field Component on the Parker Instability

The Parker instability is considered to play important roles in the evolution of the interstellar medium. Most studies on the development of the instability so far have been based on an initial equilibrium system with a uniform magnetic field. However, the Galactic magnetic field possesses a random component in addition to the mean uniform component, with comparable strength of the two components. Parker and Jokipii have recently suggested that the random component can suppress the growth of small wavelength perturbations. Here, we extend their analysis by including gas pressure which was ignored in their work, and study the stabilizing effect of the random component in the interstellar gas with finite pressure. Following Parker and Jokipii, the magnetic field is modeled as a mean azimuthal component, $B(z)$, plus a random radial component, $\epsilon(z) B(z)$, where $\epsilon(z)$ is a random function of height from the equatorial plane. We show that for the observationally suggested values of $^{1/2}$, the tension due to the random component becomes important, so that the growth of the instability is either significantly reduced or completely suppressed. When the instability still works, the radial wavenumber of the most unstable mode is found to be zero. That is, the instability is reduced to be effectively two-dimensional. We discuss briefly the implications of our finding.Comment: 10 pages including 2 figures, to appear in The Astrophysical Journal Letter

Line-of-Sight Reddening Predictions: Zero Points, Accuracies, the Interstellar Medium, and the Stellar Populations of Elliptical Galaxies

Revised (B-V)_0-Mg_2 data for 402 elliptical galaxies are given to test reddening predictions which can also tell us both what the intrinsic errors are in this relationship among gE galaxy stellar populations, as well as details of nearby structure in the interstellar medium (ISM) of our Galaxy and of the intrinsic errors in reddening predictions. Using least-squares fits, the explicit 1-sigma errors in the Burstein-Heiles (BH) and the Schlegel et al. (IR) predicted reddenings are calculated, as well as the 1-sigma observational error in the (B-V)_0-Mg_2 for gE galaxies. It is found that, in directions with E(B-V)<0.100 mag (where most of these galaxies lie), 1-sigma errors in the IR reddening predictions are 0.006 to 0.009 in E(B-V) mag, those for BH reddening prediction are 0.011 mag, and the 1-sigma agreement between the two reddening predictions is 0.007 mag. IR predictions have an accuracy of 0.010-0.011 mag in directions with E(B-V)>= 0.100 mag, significantly better than those of the BH predictions (0.024-0.025). Gas-to-dust variations that vary by a factor of 3, both high and low, exist along many lines-of-sight in our Galaxy. The approx 0.02 higher reddening zero point in E(B-V) previously determined by Schlegel et al. is confirmed, primarily at the Galactic poles. Despite this, both methods also predict many directions with E(B-V)<0.015 mag. Independent evidence of reddening at the North Galactic pole is reviewed, with the conclusion that there still exists directions at the NGP that have E(B-V)<<0.01. Two lines of evidence suggest that IR reddenings are overpredicted in directions with high gas-to-dust ratios. As high gas-to-dust directions in the ISM also include the Galactic poles, this overprediction is the likely cause of the E(B-V) = 0.02 mag larger IR reddening zero point.Comment: 5 figure

Mechanism of Ambipolar Field-Effect Carrier Injections in One-Dimensional Mott Insulators

To clarify the mechanism of recently reported, ambipolar carrier injections into quasi-one-dimensional Mott insulators on which field-effect transistors are fabricated, we employ the one-dimensional Hubbard model attached to a tight-binding model for source and drain electrodes. To take account of the formation of Schottky barriers, we add scalar and vector potentials, which satisfy the Poisson equation with boundary values depending on the drain voltage, the gate bias, and the work-function difference. The current-voltage characteristics are obtained by solving the time-dependent Schr\"odinger equation in the unrestricted Hartree-Fock approximation. Its validity is discussed with the help of the Lanczos method applied to small systems. We find generally ambipolar carrier injections in Mott insulators even if the work function of the crystal is quite different from that of the electrodes. They result from balancing the correlation effect with the barrier effect. For the gate-bias polarity with higher Schottky barriers, the correlation effect is weakened accordingly, owing to collective transport in the one-dimensional correlated electron systems.Comment: 21 pages, 10 figures, to appear in J. Phys. Soc. Jp

A Comparative Study of the Parker Instability under Three Models of the Galactic Gravity

To examine how non-uniform nature of the Galactic gravity might affect length and time scales of the Parker instability, we took three models of gravity, uniform, linear and realistic ones. To make comparisons of the three gravity models on a common basis, we first fixed the ratio of magnetic pressure to gas pressure at $\alpha$ = 0.25, that of cosmic-ray pressure at $\beta$ = 0.4, and the rms velocity of interstellar clouds at $a_s$ = 6.4 km s$^{-1}$, and then adjusted parameters of the gravity models in such a way that the resulting density scale heights for the three models may all have the same value of 160 pc. Performing linear stability analyses onto equilibrium states under the three models with the typical ISM conditions, we calculate the maximum growth rate and corresponding length scale for each of the gravity models. Under the uniform gravity the Parker instability has the growth time of 1.2$\times10^{8}$ years and the length scale of 1.6 kpc for symmetric mode. Under the realistic gravity it grows in 1.8$\times10^{7}$ years for both symmetric and antisymmetric modes, and develops density condensations at intervals of 400 pc for the symmetric mode and 200 pc for the antisymmetric one. A simple change of the gravity model has thus reduced the growth time by almost an order of magnitude and its length scale by factors of four to eight. These results suggest that an onset of the Parker instability in the ISM may not necessarily be confined to the regions of high $\alpha$ and $\beta$.Comment: Accepted for publication in ApJ, using aaspp4.sty, 18 text pages with 9 figure

Spherical collapse of supermassive stars: neutrino emission and gamma-ray bursts

We present the results of numerical simulations of the spherically symmetric gravitational collapse of supermassive stars (SMS). The collapse is studied using a general relativistic hydrodynamics code. The coupled system of Einstein and fluid equations is solved employing observer time coordinates, by foliating the spacetime by means of outgoing null hypersurfaces. The code contains an equation of state which includes effects due to radiation, electrons and baryons, and detailed microphysics to account for electron-positron pairs. In addition energy losses by thermal neutrino emission are included. We are able to follow the collapse of SMS from the onset of instability up to the point of black hole formation. Several SMS with masses in the range $5\times 10^5 M_{\odot}- 10^9 M_{\odot}$ are simulated. In all models an apparent horizon forms initially, enclosing the innermost 25% of the stellar mass. From the computed neutrino luminosities, estimates of the energy deposition by $\nu\bar{\nu}$-annihilation are obtained. Only a small fraction of this energy is deposited near the surface of the star, where, as proposed recently by Fuller & Shi (1998), it could cause the ultrarelativistic flow believed to be responsible for $\gamma$-ray bursts. Our simulations show that for collapsing SMS with masses larger than $5\times 10^5 M_{\odot}$ the energy deposition is at least two orders of magnitude too small to explain the energetics of observed long-duration bursts at cosmological redshifts. In addition, in the absence of rotational effects the energy is deposited in a region containing most of the stellar mass. Therefore relativistic ejection of matter is impossible.Comment: 13 pages, 11 figures, submitted to A&

Detecting z > 2 Type IIn Supernovae

Type IIn supernovae (SNe IIn) dominate the brightest supernova events in observed FUV flux (~1200-2000A). We show that multi-band, multi-epoch optical surveys complete to m_r = 27 can detect the FUV emission of ~25 z > 2 SNe IIn deg^-2 yr^-1 rest-frame (~10 SNe IIn deg^-2 yr^-1 observed-frame) to 4 sigma using a technique monitoring color-selected galaxies. Moreover, the strength and evolution of the bright emission lines observed in low redshift SNe IIn imply that the Ly-a emission features in ~70% of z > 2 SNe IIn are above 8m-class telescope spectroscopic thresholds for ~2 yr rest-frame. As a result, existing facilities have the capability to both photometrically detect and spectroscopically confirm z > 2 SNe IIn and pave the way for efficient searches by future 8m-class survey and 30m-class telescopes. The method presented here uses the sensitivities and wide-field capabilities of current optical instruments and exploits (1) the efficiency of z > 2 galaxy color-selection techniques, (2) the intrinsic brightness distribution ( = -19.0 +/-0.9) and blue profile of SNe IIn continua, (3) the presence of extremely bright, long-lived emission features, and (4) the potential to detect blueshifted SNe Ly-a emission shortward of host galaxy Ly-a features.Comment: 26 pages (pre-print), 6 figures, accepted Ap

A Fully Tunable Single-Walled Carbon Nanotube Diode

We demonstrate a fully tunable diode structure utilizing a fully suspended single-walled carbon nanotube (SWNT). The diode's turn-on voltage under forward bias can be continuously tuned up to 4.3 V by controlling gate voltages, which is ~6 times the nanotube bandgap energy. Furthermore, the same device design can be configured into a backward diode by tuning the band-to-band tunneling current with gate voltages. A nanotube backward diode is demonstrated for the first time with nonlinearity exceeding the ideal diode. These results suggest that a tunable nanotube diode can be a unique building block for developing next generation programmable nanoelectronic logic and integrated circuits.Comment: 14 pages, 4 figure

Statistical Properties of Galactic Starlight Polarization

We present a statistical analysis of Galactic interstellar polarization from the largest compilation available of starlight data. The data comprises ~ 9300 stars of which we have selected ~ 5500 for our analysis. We find a nearly linear growth of mean polarization degree with extinction. The amplitude of this correlation shows that interstellar grains are not fully aligned with the Galactic magnetic field, which can be interpreted as the effect of a large random component of the field. In agreement with earlier studies of more limited scope, we estimate the ratio of the uniform to the random plane-of-the-sky components of the magnetic field to be B_u/B_r = 0.8. Moreover, a clear correlation exists between polarization degree and polarization angle what provides evidence that the magnetic field geometry follows Galactic structures on large-scales. The angular power spectrum C_l of the starlight polarization degree for Galactic plane data (|b| < 10 deg) is consistent with a power-law, C_l ~ l^{-1.5} (where l ~ 180 deg/\theta is the multipole order), for all angular scales \theta > 10 arcmin. An investigation of sparse and inhomogeneous sampling of the data shows that the starlight data analyzed traces an underlying polarized continuum that has the same power spectrum slope, C_l ~ l^{-1.5}. Our findings suggest that starlight data can be safely used for the modeling of Galactic polarized continuum emission at other wavelengths.Comment: 31 pages, 11 figures. Minor corrections and some clarifications included. Matches version accepted for publication by the Astrophysical Journa