Discovery of 28 pulsars using new techniques for sorting pulsar candidates

Modern pulsar surveys produce many millions of candidate pulsars, far more than can be individually inspected. Traditional methods for filtering these candidates, based upon the signal-to-noise ratio of the detection, cannot easily distinguish between interference signals and pulsars. We have developed a new method of scoring candidates using a series of heuristics which test for pulsar-like properties of the signal. This significantly increases the sensitivity to weak pulsars and pulsars with periods close to interference signals. By applying this and other techniques for ranking candidates from a previous processing of the Parkes Multi-beam Pulsar Survey, 28 previously unknown pulsars have been discovered. These include an eccentric binary system and a young pulsar which is spatially coincident with a known supernova remnant.Comment: To be published in Monthly Notices of the Royal Astronomical Society. 11 pages, 9 figure

IUE observations of a luminous M supergiant that exhibits intense continuum in the far ultraviolet

Observations of the late type M supergiant TV Gem (M1Iab) reveal strong UV continuum between 1200 A and 3200 A. The continuum is essentially featureless with the exception of a number of broad absorption features in the short wavelength spectra range. An absorption feature centered around 1400 A could be due to Si IV absorption found typically in spectra of middle B type stars. UV emission from this star is unexpected because earlier ground-based observations give no indication of a possible association with an early companion or circumstellar ionized nebulosity. A B9 or A1 III - IV type star approximately 2to 3 magnitudes fainter than the M star could explain the level of UV continuum observed, but a fully self consistent explanation that includes the B-V color index of TV Gem is not as yet possible. The continuum flux dependence with wavelength in the UV spectral range could be attributed to a high energy source such as an accretion disc. It is suggested TV Gem is a good candidate for HEAO-2 (Einstein) satellite observations because a high energy object in close proximity to the M star would likely be a source of soft X-ray emission

IUE observations and interpretation of the symbiotic star RW Hya

The IUE observations of the high excitation symbiotic star RW Hya (gM2 + pec) are discussed. Analysis of the intense UV continuum observed between 1100 A to 2000 A suggests this star is a binary system in which the secondary is identified as a hot subdwarf with T sub eff being approximately 100,000 K. A distance to the system of 1000 pc is deduced. The UV spectrum consists of mainly semiforbidden and allowed transition lines of which the CIV (1548 A, 1550 A) emission lines are particularly strong, and UV continuum at both shorter and longer wavelengths. Strong forbidden lines seem to be absent suggesting the presence of a nebula of high densities. Tidal interaction between the red giant primary and the hot subdwarf is suggested as a likely means to form the observed nebula. RW Hya is suggested as a possible source of soft X-ray emission from material accreting onto the surface of the hot subdwarf. Detection of such emission with HEAO-B would give information if this accretion is taking place via Roche lobe overlow or via capture from a stellar wind emitted by the primary. A general discussion of elemental and ionic abundances in the nebula is also presented

Li I and K I Scatter in Cool Pleiades Dwarfs

We utilize high-resolution (R~60,000), high S/N (~100) spectroscopy of 17 cool Pleiades dwarfs to examine the confounding star-to-star scatter in the 6707 Li I line strengths in this young cluster. Our Pleiads, selected for their small projected rotational velocity and modest chromospheric emission, evince substantial scatter in the linestrengths of 6707 Li I feature that is absent in the 7699 K I resonance line. The Li I scatter is not correlated with that in the high-excitation 7774 O I feature, and the magnitude of the former is greater than the latter despite the larger temperature sensitivity of the O I feature. These results suggest that systematic errors in linestrength measurements due to blending, color (or color-based T_eff) errors, or line formation effects related to an overlying chromosphere are not the principal source of Li I scatter in our stars. There do exist analytic spot models that can produce the observed Li scatter without introducing scatter in the K I line strengths or the color-magnitude diagram. However, these models predict factor of >3 differences in abundances derived from the subordinate 6104 and resonance 6707 Li I features; we find no difference in the abundances determined from these two features. These analytic spot models also predict CN line strengths significantly larger than we observe in our spectra. The simplest explanation of the Li, K, CN, and photometric data is that there must be a real abundance component to the Pleiades Li dispersion. We suggest that this real abundance component is the manifestation of relic differences in erstwhile pre-main-sequence Li burning caused by effects of surface activity on stellar structure. We discuss observational predictions of these effects.Comment: 35 pages, 7 figures; accepted by Ap

IUE observations of two late-type stars Bx Mon (M + pec) and TV Gem (M1 Iab)

The IUE observations of two late type stars BX Mon and TV Gem that reveal the emission properties in the ultraviolet of subluminous companions are discussed. Analysis of the continuum emission observed from BX Mon suggests the companion, is a middle A III star. High excitation emission lines observed between 1200 A and 2000 A that generally do not typify emission observed in either late M type variables or A type stars are also detected. It is suggested that these strong high excitation lines arise in a large volume of gas heated by nonradiation processes that could be the result of tidal interaction and mass exchange in the binary system. In contrast to stars such as BX Mon, the luminous M1 supergiant TV Gem shows unexpected intense UV continuum throughout the sensitivity range of IUE. The UV spectrum of TV Gem is characterized by intense continuum with broad absorption features detected in the short wavelength range. The analysis shows that the companion could be a B9 or A1 III-IV star. Alternate suggestions are presented for explaining the UV continuum in terms of an accretion disk in association with TV Gem

Alternative model for the administration and analysis of research-based assessments

Research-based assessments represent a valuable tool for both instructors and researchers interested in improving undergraduate physics education. However, the historical model for disseminating and propagating conceptual and attitudinal assessments developed by the physics education research (PER) community has not resulted in widespread adoption of these assessments within the broader community of physics instructors. Within this historical model, assessment developers create high quality, validated assessments, make them available for a wide range of instructors to use, and provide minimal (if any) support to assist with administration or analysis of the results. Here, we present and discuss an alternative model for assessment dissemination, which is characterized by centralized data collection and analysis. This model provides a greater degree of support for both researchers and instructors in order to more explicitly support adoption of research-based assessments. Specifically, we describe our experiences developing a centralized, automated system for an attitudinal assessment we previously created to examine students' epistemologies and expectations about experimental physics. This system provides a proof-of-concept that we use to discuss the advantages associated with centralized administration and data collection for research-based assessments in PER. We also discuss the challenges that we encountered while developing, maintaining, and automating this system. Ultimately, we argue that centralized administration and data collection for standardized assessments is a viable and potentially advantageous alternative to the default model characterized by decentralized administration and analysis. Moreover, with the help of online administration and automation, this model can support the long-term sustainability of centralized assessment systems.Comment: 7 pages, 1 figure, accepted in Phys. Rev. PE

Space missions to comets

The broad impact of a cometary mission is assessed with particular emphasis on scientific interest in a fly-by mission to Halley's comet and a rendezvous with Tempel 2. Scientific results, speculations, and future plans are discussed