Optical observations of the AMPTE artificial comet and magnetotail barium releases

The first AMPTE artificial comet was observed with a low light level television camera operated aboard the NASA CV990 flying out of Moffett Field, California. The comet head, neutral cloud, and comet tail were all observed for four minutes with an unifiltered camera. Brief observations at T + 4 minutes through a 4554A Ba(+) filter confirmed the identification of the structures. The ion cloud expanded along with the neutral cloud at a rate of 2.3 km/sec (diameter) until it reached a final diameter of approx. 170 km at approx. T + 90 s. It also drifted with the neutral cloud until approx. 165 s. By T + 190 s it had reached a steady state velocity of 5.4 km/sec southward. A barium release in the magnetotail was observed from the CV990 in California, Eagle, Alaska, and Fairbanks, Alaska. Over a twenty-five minute period, the center of the barium streak drifted southward (approx. 500 m/sec), upward (24 km/sec) and eastward (approx 1 km/sec) in a nonrotating reference frame. An all-sky TV at Eagle showed a single auroral arc in the far North during this period

AMPS definition study on Optical Band Imager and Photometer System (OBIPS)

A study was conducted to define the characteristics of a modular optical diagnostic system (OBIPS) for AMPS, to provide input to Phase B studies, and to give information useful for experiment planning and design of other instrumentation. The system described consists of visual and UV-band imagers and visual and UV-band photometers; of these the imagers are most important because of their ability to measure intensity as a function of two spatial dimensions and time with high resolution. The various subsystems of OBIPS are in themselves modular with modules having a high degree of interchangeability for versatility, economy, and redundancy

Radio Counterparts of Compact Binary Mergers detectable in Gravitational Waves: A Simulation for an Optimized Survey

Mergers of binary neutron stars and black hole-neutron star binaries produce gravitational-wave (GW) emission and outflows with significant kinetic energies. These outflows result in radio emissions through synchrotron radiation. We explore the detectability of these synchrotron generated radio signals by follow-up observations of GW merger events lacking a detection of electromagnetic counterparts in other wavelengths. We model radio light curves arising from (i) sub-relativistic merger ejecta and (ii) ultra-relativistic jets. The former produces radio remnants on timescales of a few years and the latter produces $\gamma$-ray bursts in the direction of the jet and orphan-radio afterglows extending over wider angles on timescales of weeks. Based on the derived light curves, we suggest an optimized survey at $1.4$ GHz with five epochs separated by a logarithmic time interval. We estimate the detectability of the radio counterparts of simulated GW-merger events to be detected by advanced LIGO and Virgo by current and future radio facilities. The detectable distances for these GW merger events could be as high as 1 Gpc. $20$--$60\%$ of the long-lasting radio remnants will be detectable in the case of the moderate kinetic energy of $3\cdot 10^{50}$ erg and a circum-merger density of $0.1 {\rm cm^{-3}}$ or larger, while $5$--$20\%$ of the orphan radio afterglows with kinetic energy of $10^{48}$ erg will be detectable. The detection likelihood increases if one focuses on the well-localizable GW events. We discuss the background noise due to radio fluxes of host galaxies and false positives arising from extragalactic radio transients and variable Active Galactic Nuclei and we show that the quiet radio transient sky is of great advantage when searching for the radio counterparts.Comment: 23 pages, 10 figures, accepted for publication in Ap

School Sector, School Poverty, and the Catholic School Advantage

Equality of educational opportunity is threatened by long-standing gaps in student achievement by race, gender, and student poverty, as well as by school sector and school poverty. The true magnitude of these gaps cannot be understood, however, unless these factors are considered simultaneously. While accounting for the effects of demographic characteristics, this article focuses on the effects of school sector and school poverty on gains in academic achievement. Analyses from a longitudinal study of public and Catholic middle school students in and around the city of Chicago show that neither the public nor Catholic sector has a consistent advantage in increasing student achievement in sixth and eighth grade reading and mathematics. School poverty has a deleterious effect on student achievement, although this effect is considerably mitigated for students in Catholic schools

Ability Grouping in Catholic and Public Schools

Researchers have found that students who attend Catholic high schools tend to outperform public high school students on standardized tests of achievement. Although many aspects of this finding have been examined in subsequent research, little attention has been paid to the issue of how ability grouping affects achievement across school sectors. A nearly universal practice in middle and secondary schools, ability grouping works to channel learning opportunities to students. The authors trace the history of ability grouping and review the findings regarding ability group effects, the assignment process, and mobility across groups in each school sector. Their analyses suggest that the way ability grouping is implemented in Catholic schools contributes to the Catholic school advantage in achievement

Magnetospheric Radio Emissions from Exoplanets with the SKA

Planetary-scale magnetic fields are a window to a planet’s interior and provide shielding of the planet’s atmosphere and surface for life. The Earth, Mercury, Ganymede, and the giant planets of the solar system all contain internal dynamo currents that generate planetary-scale magnetic fields. When coupled to energetic (keV) electrons, such as those produced by solar wind-magnetosphere interaction (compression or magnetic reconnection), magnetosphere-ionosphere or magnetosphere-satellite coupling, the polar regions of a planetary magnetic field are the place of intense, coherent, circularly polarized cyclotron radio emissions. These emissions – that may be as intense as solar ones – are produced by all magnetized planets in the solar system in the MHz range, and up to 40 MHz at Jupiter. Detection of similar emissions from exoplanets will provide constraints on the thermal state, composition, and dynamics of their interior – very difficult to determine by other means – as well as an improved understanding of the planetary dynamo process and of the physics of star-planet plasma interactions. Detailed knowledge of magnetospheric emissions from solar system planets and the discovery of exoplanets motivated both theoretical and observational work on magnetospheric emissions from exoplanets. Scaling laws and theoretical frameworks were built and extrapolated to obtain order-of-magnitude predictions of frequencies and flux densities of exoplanetary radio emissions. The present stage of the theory suggests that radio detection of exoplanets will develop the new field of comparative exo-magnetospheric physics, but also permit to measure exoplanetary parameters such as rotation or orbit inclination. Observational searches started even before the confirmed discovery of the first exoplanet. We review the scientific return of the detection of exoplanetary radio emissions, the current status of observational searches, and discuss the future promise in the context of SKA, especially SKA1-LOW. To the extent that Jupiter’s magnetic field is not exceptionally strong, the current lower frequency limit of 50 MHz implies that SKA1-LOW will likely detect Jovian-mass planets. With the currently planned sensitivity of SKA1-LOW, we estimate that a Jupiter-like planet could be detected to about 10 pc. Within this volume there are ∼200 known stars and ∼35 currently known exoplanets, and this number should increase substantially with coming space missions dedicated to transits and powerful ground-based instruments. The accessible volume will be much increased if scaling laws derived in our solar system can be reliably extrapolated to exoplanetary systems, permitting to measure lower mass planets’ dynamos and magnetospheres

Periodic Radio and H-alpha Emission from the L Dwarf Binary 2MASSW J0746425+200032: Exploring the Magnetic Field Topology and Radius of an L Dwarf

[Abridged] We present an 8.5-hour simultaneous radio, X-ray, UV, and optical observation of the L dwarf binary 2MASSW J0746+20. We detect strong radio emission, dominated by short-duration periodic pulses at 4.86 GHz with P=124.32+/-0.11 min. The stability of the pulse profiles and arrival times demonstrates that they are due to the rotational modulation of a B~1.7 kG magnetic field. A quiescent non-variable component is also detected, likely due to emission from a uniform large-scale field. The H-alpha emission exhibits identical periodicity, but unlike the radio pulses it varies sinusoidally and is offset by exactly 1/4 of a phase. The sinusoidal variations require chromospheric emission from a large-scale field structure, with the radio pulses likely emanating from the magnetic poles. While both light curves can be explained by a rotating mis-aligned magnetic field, the 1/4 phase lag rules out a symmetric dipole topology since it would result in a phase lag of 1/2 (poloidal field) or zero (toroidal field). We therefore conclude that either (i) the field is dominated by a quadrupole configuration, which can naturally explain the 1/4 phase lag; or (ii) the H-alpha and/or radio emission regions are not trivially aligned with the field. Regardless of the field topology, we use the measured period along with the known rotation velocity (vsini=27 km/s), and the binary orbital inclination (i=142 deg), to derive a radius for the primary star of 0.078+/-0.010 R_sun. This is the first measurement of the radius of an L dwarf, and along with a mass of 0.085+/-0.010 M_sun it provides a constraint on the mass-radius relation below 0.1 M_sun. We find that the radius is about 30% smaller than expected from theoretical models, even for an age of a few Gyr.Comment: Submitted to Ap

Periodic Optical Variability of Radio Detected Ultracool Dwarfs

A fraction of very low mass stars and brown dwarfs are known to be radio active, in some cases producing periodic pulses. Extensive studies of two such objects have also revealed optical periodic variability and the nature of this variability remains unclear. Here we report on multi-epoch optical photometric monitoring of six radio detected dwarfs, spanning the $\sim$M8 - L3.5 spectral range, conducted to investigate the ubiquity of periodic optical variability in radio detected ultracool dwarfs. This survey is the most sensitive ground-based study carried out to date in search of periodic optical variability from late-type dwarfs, where we obtained 250 hours of monitoring, delivering photometric precision as low as $\sim$0.15%. Five of the six targets exhibit clear periodicity, in all cases likely associated with the rotation period of the dwarf, with a marginal detection found for the sixth. Our data points to a likely association between radio and optical periodic variability in late-M/early-L dwarfs, although the underlying physical cause of this correlation remains unclear. In one case, we have multiple epochs of monitoring of the archetype of pulsing radio dwarfs, the M9 TVLM 513-46546, spanning a period of 5 years, which is sufficiently stable in phase to allow us to establish a period of 1.95958 $\pm$ 0.00005 hours. This phase stability may be associated with a large-scale stable magnetic field, further strengthening the correlation between radio activity and periodic optical variability. Finally, we find a tentative spin-orbit alignment of one component of the very low mass binary LP 349-25.Comment: Accepted to The Astrophysical Journal; 22 pages; 12 figure

Attenuated Total Reflectance Mode for Transport through Membranes

This chapter is an introductory tutorial to attenuated total reflectance (ATR) mode of Fourier-transform infrared spectroscopy and how it can be used to measure transport through polymer membranes. In addition to covering the experimental set-up and time-resolved data processing, it will present the fundamental equations for analyzing the data in order to obtain diffusion coefficients. The chapter will present several example systems in which FTIR-ATR has been used to determine transport, including water diffusion through polyelectrolytes for fuel cells and block copolymers for water purification as well as ion transport through polymer electrolytes for lithium batteries. Perspectives on future applications in which the technique could provide fundamental understanding will also be covered