BIMA Array Observations of the Highly Unusual SiO Maser Source with a Bipolar Nebulosity, IRAS 19312+1950

We report the results of mapping observations of the bipolar nebula with SiO maser emission, IRAS 19312+1950, in the CO (J=1-0 and J=2-1), 13CO (J=1-0 and J=2-1), C18O (J=1-0), CS (J=2-1), SO (J_K=3_2-2_1) and HCO+ (J=3-2) lines with the Berkeley-Illinois-Maryland Association array. Evolutional status of this source has been evoking a controversy since its discovery, though SiO maser sources are usually identified as late-type stars with active mass loss. In line profiles, two kinematical components are found as reported in previous single-dish observations: a broad pedestal component and a narrow component. Spatio-kinetic properties of a broad component region traced by 12CO lines are roughly explained by a simple spherical outflow model with a typical expanding velocity of an AGB star, though some properties of the broad component region still conflict with properties of a typical AGB spherical outflow. A narrow component region apparently exhibits a bipolar flow. The angular size of the narrow component region is spatially larger than that of a broad component region. Intensity distribution of the CS emission avoids the central region of the source, and that of an SO broad component emission exhibits a small feature peaked exactly at the mapping center. According to the present results, if a broad component really originates in a spherical outflow, an oxygen-rich evolved stellar object seems to be a natural interpretation for the central star of IRAS 19312+1950.Comment: 27 pages, 11 figures; accepted for publication in Ap

Nuclear radiation problems, unmanned thermionic reactor ion propulsion spacecraft

A nuclear thermionic reactor as the electric power source for an electric propulsion spacecraft introduces a nuclear radiation environment that affects the spacecraft configuration, the use and location of electrical insulators and the science experiments. The spacecraft is conceptually configured to minimize the nuclear shield weight by: (1) a large length to diameter spacecraft; (2) eliminating piping penetrations through the shield; and (3) using the mercury propellant as gamma shield. Since the alumina material is damaged by the high nuclear radiation environment in the reactor it is desirable to locate the alumina insulator outside the reflector or develop a more radiation resistant insulator

Disk-Like Structure in the Semi-Regular Pulsating Star, X Her

The author reports a result of an interferometric observation of the semiragular pulsating star with an unusual narrow molecular line profile, X Her, in the CO J=1-0 line with the Berkeley-Illinois-Maryland array. In the CO spectrum, a double-component profile (including narrow and broad components) is seen as reported by previous observations. The narrow component consists of two spiky peaks. The spatial structure of the board component shows bipolar shape, and that of the narrow component shows an elliptical/spherical shape. The two peaks in the narrow component show a systematic difference in the integrated intensity map. The kinematical and geometrical properties of the narrow component are reminiscent of a Keplerian rotating disk with the central mass of 0.9 M_sun, though an interpretation by an expansion disk seems to be more natural. A secondary bipolar flow instead of the disk cannot be fully excluded as an interpretation of the narrow line.Comment: 12 pages, 4 figues, accepted for publication in Ap

Correlation between Infrared Colors and Intensity Ratios of SiO Maser Lines

We present the results of SiO millimeter-line observations of a sample of known SiO maser sources covering a wide dust-temperature range. A cold part of the sample was selected from the SiO maser sources found in our recent SiO maser survey of cold dusty objects. The aim of the present research is to investigate the causes of the correlation between infrared colors and SiO maser intensity ratios among different transition lines. In particular, the correlation between infrared colors and SiO maser intensity ratio among the J=1-0 v=1, 2, and 3 lines are mainly concerned in this paper. We observed in total 75 SiO maser sources with the Nobeyama 45m telescope quasi-simultaneously in the SiO J=1-0 v=0, 1, 2, 3, 4 and J=2-1 v=1, 2 lines. We also observed the sample in the 29SiO J=1-0 v=0 and J=2-1 v=0, and 30SiO J=1-0 v=0 lines, and the H2O 6(1,6)-5(2,3) line. As reported in previous papers, we confirmed that the intensity ratios of the SiO J=1-0 v=2 to v=1 lines clearly correlate with infrared colors. In addition, we found possible correlation between infrared colors and the intensity ratios of the SiO J=1-0 v=3 to v=1&2 lines. Two overlap lines of H2O (i.e., 11(6,6) nu_2=1 -> 12(7,5) nu_2=0 and 5(0,5) nu_2=2 -> 6(3,4) nu_2=1) might explain these correlation if these overlap lines become stronger with increase of infrared colors, although the phenomena also might be explained by more fundamental ways if we take into account the variation of opacity from object to object.Comment: 49 pages, 7 figures, 3 tables, accepted for publication in ApJ. Full resolution version available at http://www.asiaa.sinica.edu.tw/~junichi/paper

Prolific pair production with high-power lasers

Prolific electron-positron pair production is possible at laser intensities approaching 10^{24} W/cm^2 at a wavelength of 1 micron. An analysis of electron trajectories and interactions at the nodes (B=0) of two counter-propagating, circularly polarised laser beams shows that a cascade of gamma-rays and pairs develops. The geometry is generalised qualitatively to linear polarisation and laser beams incident on a solid target.Comment: 4 pages, 1 figure, minor revisions, accepted for publication in Physical Review Letter

The effect of facial expression and gaze direction on memory for unfamiliar faces

We report data from an experiment that investigated the influence of gaze direction and facial expression on face memory. Participants were shown a set of unfamiliar faces with either happy or angry facial expressions, which were either gazing straight ahead or had their gaze averted to one side. Memory for faces that were initially shown with angry expressions was found to be poorer when these faces had averted as opposed to direct gaze, whereas memory for individuals shown with happy faces was unaffected by gaze direction. We suggest that memory for another individual's face partly depends on an evaluation of the behavioural intention of that individual