Parallax and Kinematics of PSR B0919+06 from VLBA Astrometry and Interstellar Scintillometry

Results are presented from a long-term astrometry program on PSR B0919+06 using the NRAO Very Long Baseline Array. With ten observations (seven epochs) between 1994--2000, we measure a proper motion of 18.35 +/- 0.06 mas/yr in RA, 86.56 +/- 0.12 mas/yr in Dec, and a parallax of 0.83 +/- 0.13 mas (68% confidence intervals). This yields a pulsar distance of 1.21 +/- 0.19 kpc, making PSR B0919+06 the farthest pulsar for which a trigonometric parallax has been obtained, and the implied pulsar transverse speed is 505 +/- 80 km/s. Combining the distance estimate with interstellar scintillation data spanning 20 years, we infer the existence of a patchy or clumpy scattering screen along the line of sight in addition to the distributed electron density predicted by models for the Galaxy, and constrain the location of this scattering region to within about 250 parsecs of the Sun. Comparison with the lines of sight towards other pulsars in the same quadrant of the Galaxy permits refinement of our knowledge of the local interstellar matter in this direction.Comment: 12 pages, includes 4 figures and 3 tables, uses AASTeX 5 (included); ApJ submitte

The Backgrounds Data Center

The Strategic Defense Initiative Organization has created data centers for midcourse, plumes, and backgrounds phenomenologies. The Backgrounds Data Center (BDC) has been designated as the prime archive for data collected by SDIO programs. The BDC maintains a Summary Catalog that contains 'metadata,' that is, information about data, such as when the data were obtained, what the spectral range of the data is, and what region of the Earth or sky was observed. Queries to this catalog result in a listing of all data sets (from all experiments in the Summary Catalog) that satisfy the specified criteria. Thus, the user can identify different experiments that made similar observations and order them from the BDC for analysis. On-site users can use the Science Analysis Facility (SAFE for this purpose. For some programs, the BDC maintains a Program Catalog, which can classify data in as many ways as desired (rather than just by position, time, and spectral range as in the Summary Catalog). For example, data sets could be tagged with such diverse parameters as solar illumination angle, signal level, or the value of a particular spectral ratio, as long as these quantities can be read from the digital record or calculated from it by the ingest program. All unclassified catalogs and unclassified data will be remotely accessible

Parallax of PSR J1744-1134 and the Local Interstellar Medium

We present the annual trigonometric parallax of PSR J1744-1134 derived from an analysis of pulse times of arrival. The measured parallax, pi = 2.8+/-0.3 mas ranks among the most precisely determined distances to any pulsar. The parallax distance of 357+/-39 pc is over twice that derived from the dispersion measure using the Taylor & Cordes model for the Galactic electron distribution. The mean electron density in the path to the pulsar, n_e = (0.0088 +/- 0.0009) cm^{-3}, is the lowest for any disk pulsar. We have compared the n_e for PSR J1744-1134 with those for another 11 nearby pulsars with independent distance estimates. We conclude that there is a striking asymmetry in the distribution of electrons in the local interstellar medium. The electron column densities for pulsars in the third Galactic quadrant are found to be systematically higher than for those in the first. The former correlate with the position of the well known local HI cavity in quadrant three. The excess electrons within the cavity may be in the form of HII clouds marking a region of interaction between the local hot bubble and a nearby superbubble.Comment: revised version accepted for publication in ApJ Letters; reanalysis of uncertainty in parallax measure and changes to fig

X-Ray Observations of the supernova remnant G21.5-0.9

We present the analysis of archival X-ray observations of the supernova remnant (SNR) G21.5-0.9. Based on its morphology and spectral properties, G21.5-0.9 has been classified as a Crab-like SNR. In their early analysis of the CHANDRA calibration data, Slane et al. (2000) discovered a low-surface-brightness, extended emission. They interpreted this component as the blast wave formed in the supernova (SN) explosion. In this paper, we present the CHANDRA analysis using a total exposure of ~150 ksec. We also include ROSAT and ASCA observations. Our analysis indicates that the extended emission is non-thermal -- a result in agreement with XMM observations. The entire remnant of radius ~ 2'.5 is best fitted with a power law model with a photon index steepening away from the center. The total unabsorbed flux in the 0.5-10 keV is 1.1E-10 erg/cm2/s with an 85% contribution from the 40" radius inner core. Timing analysis of the High-Resolution Camera (HRC) data failed to detect any pulsations. We put a 16% upper limit on the pulsed fraction. We derive the physical parameters of the putative pulsar and compare them with those of other plerions (such as the Crab and 3C 58). G21.5-0.9 remains the only plerion whose size in X-rays is bigger than in the radio. Deep radio observations will address this puzzle.Comment: 23 pages including 11 figures and 3 tables; accepted by ApJ June 22, 2001; to appear in Oct 20, 2001 issue of Ap

{BOAO Photometric Survey of Galactic Open Clusters. II. Physical Parameters of 12 Open Clusters

We have initiated a long-term project, the BOAO photometric survey of open clusters, to enlarge our understanding of galactic structure using UBVI CCD photometry of open clusters which have been little studied before. This is the second paper of the project in which we present the photometry of 12 open clusters. We have determined the cluster parameters by fitting the Padova isochrones to the color-magnitude diagrams of the clusters. All the clusters except for Be 0 and NGC 1348 are found to be intermediate-age to old (0.2 - 4.0 Gyrs) open clusters with a mean metallicity of [Fe/H] = 0.0.Comment: 11 page

Waste Tank Safety Program. Annual status report for FY 1993, Task 3: Organic chemistry

This task supports the tank-vapor project, mainly by providing organic analytical support and by analyzing Tank 241-C-103 (Tank C-103) vapor-space samples, collected via SUMMA{trademark} canisters, by gas chromatography (GC) and GC/mass spectrometry (MS). In the absence of receiving tank-vapor samples, we have focused our efforts toward validating the normal paraffin hydrocarbon (NPH) sampling and analysis methods and preparing the SUMMA{trademark} laboratory. All required milestones were met, including a report on the update of phase I sampling and analysis on August 15, 1993. This update described the work involved in preparing to analyze phase I samples (Appendix A). This report describes the analytical support provided by Pacific Northwest Laboratory (PNL){sup (a)} to the Hanford Tank Safety Vapor Program

Ultraviolet Imaging Polarimetry of the Large Magellanic Cloud. II. Models

Motivated by new sounding-rocket wide-field polarimetric images of the Large Magellanic Cloud, we have used a three-dimensional Monte Carlo radiation transfer code to investigate the escape of near-ultraviolet photons from young stellar associations embedded within a disk of dusty material (i.e. a galaxy). As photons propagate through the disk, they may be scattered or absorbed by dust. Scattered photons are polarized and tracked until they escape to be observed; absorbed photons heat the dust, which radiates isotropically in the far-infrared, where the galaxy is optically thin. The code produces four output images: near- UV and far-IR flux, and near-UV images in the linear Stokes parameters Q and U. From these images we construct simulated UV polarization maps of the LMC. We use these maps to place constraints on the star + dust geometry of the LMC and the optical properties of its dust grains. By tuning the model input parameters to produce maps that match the observed polarization maps, we derive information about the inclination of the LMC disk to the plane of the sky, and about the scattering phase function g. We compute a grid of models with i = 28 deg., 36 deg., and 45 deg., and g = 0.64, 0.70, 0.77, 0.83, and 0.90. The model which best reproduces the observed polarization maps has i = 36 +2/-5 degrees and g ~0.7. Because of the low signal-to-noise in the data, we cannot place firm constraints on the value of g. The highly inclined models do not match the observed centro-symmetric polarization patterns around bright OB associations, or the distribution of polarization values. Our models approximately reproduce the observed ultraviolet photopolarimetry of the western side of the LMC; however, the output images depend on many input parameters and are nonunique.Comment: Accepted to AJ. 20 pages, 7 figure

Driving-Induced Symmetry Breaking in the Spin-Boson System

A symmetric dissipative two-state system is asymptotically completely delocalized independent of the initial state. We show that driving-induced localization at long times can take place when both the bias and tunneling coupling energy are harmonically modulated. Dynamical symmetry breaking on average occurs when the driving frequencies are odd multiples of some reference frequency. This effect is universal, as it is independent of the dissipative mechanism. Possible candidates for an experimental observation are flux tunneling in the variable barrier rf SQUID and magnetization tunneling in magnetic molecular clusters.Comment: 4 pages, 4 figures, to be published in PR

Pharmaceutical cognitive enhancement in Greek university students: differences between users and non-users in social cognitive variables, burnout and engagement

Pharmaceutical cognitive enhancement (PCE) represents the non-medical use of prescribed medication for the improvement of cognitive functioning and academic performance. Although there are some studies about PCE prevalence, it is less clear how users and non-users of PCE substances differ with respect to their positive and negative student experiences (e.g., academic burnout, engagement with studies) and in social cognitive variables that relate to decision-making and self-regulation of PCE use. The present study assessed whether students with different experiences of PCE substance use displayed differences in academic burnout, study engagement and social cognitive variables relevant to PCE use. Three hundred and forty seven University students (M age = 22.15, SD = 1.69; 54% females) completed a battery of anonymous questionnaires on academic burnout, engagement with studies, social cognitive variables relevant to PCE use, and self-reported use of PCE substances and non-prescribed nutritional supplements. Three user groups emerged, namely, non-users (51.9%, n = 180), single users of non-prescribed dietary supplements (25.4%, n = 88), and dual users of both non-prescribed dietary supplements and PCE (22.8%, n = 79). Multivariate analysis of variance indicated significant differences among the three user groups in intentions, attitudes, social norms, and anticipated regret towards PCE use. No significant differences were observed with respect to academic burnout and work engagement. The findings show that University students may engage in PCE use independently of their student experiences. Rather, a chemically-assisted performance enhancement mindset seems to differentiate users from non-users of PCE substances

Star Formation in Space and Time: Taurus-Auriga

To understand the formation of stellar groups, one must first document carefully the birth pattern within real clusters and associations. In this study of Taurus-Auriga, we combine pre-main-sequence ages from our own evolutionary tracks with stellar positions from observational surveys. Aided by the extensive, millimeter data on the molecular clouds, we develop a picture of the region's history. Star formation began, at a relatively low level and in a spatially diffuse manner, at least 10 Myr in the past. Within the last few million years, new stars have been produced at an accelerating rate, almost exclusively within a confined group of striated cloud filaments. The gas both inside and around the filaments appears to be in force balance. Thus, the appearance of the filaments is due to global, quasi-static contraction of the parent cloud material. Gravity drives this contraction and shock dissipation mediates it, but the internal motion of the gas does not appear to be turbulent. The accelerating nature of recent star formation means that the condensation of cloud cores is a threshold phenomenon, requiring a minimum background density. Other, nearby cloud regions, including Lupus and Chamaeleon, contain some locales that have attained this density, and others that have not. In the latter, we find extensive and sometimes massive molecular gas that is still devoid of young stars.Comment: 19 pages, 7 figures, to be published in ApJ - December 20, 200