The spectrum of HM Sagittae: A planetary nebula excited by a Wolf-Rayet star

A total of image tube spectrograms of HM Sagittae were obtained. More than 70 emission lines, including several broad emission features, were identified. An analysis of the spectra indicates that HM Sagittae is a planetary nebula excited by a Wolf-Rayet star. The most conspicuous Wolf-Rayet feature is that attributed to a blend of C III at 4650 A and He II at 4686 A

Cygnus A at 99 GHz: Observations of the three principal components and interpretation of the central source

The three principal emission components of Cygnus A were observed at 99 GHz, the highest frequency at which radio measurements of this source have been accomplished. The observations show no definite indication of a high-frequency cutoff in the spectrum of the compact central component, which perhaps may be attributed to an optically thin synchrotron source that peaks at a frequency of several hundred GHz

Límites a la variación natural: implicaciones para el manejo o gestión sistémica

Collectively, the tenets and principles of management emphasize the importance of recognizing and understanding limits. These tenets require the demonstration, measurement and practical use of information about limits to natural variation. It is important to identify limits so as not to incur the risks and loss of integrity when limits are exceeded. Thus, by managing within natural limits, humans (managers) simultaneously can achieve sustainability and minimize risk, as well as account for complexity. This is at the heart of systemic management. Systemic management embodies the basic tenets of anagement. One tenet requires that management ensure that nothing exceed the limits observed in its natural variation. This tenet is based on the principle that variation is constrained by a variety of limiting factors, many of which involve risks. Another tenet of management requires that such factors be considered simultaneously, exhaustively, and in proportion to their relative importance. These factors, in combination, make up the complexity that managers are required to consider in applying the basic principles of management. This combination of elements is reflected in observed limits to natural variation that account for each factor and its relative importance. This paper summarizes conclusions from the literature that has addressed the concept of limits to natural variation, especially in regard to management. It describes: 1. How such limits are inherent to complex systems; 2. How limits have been recognized to be important to the process of management; 3. How they can be used in management. The inherent limits include both those set by the context in which systems occur (extrinsic factors) as well as those set by the components and processes within systems (intrinsic factors). This paper shows that information about limits is of utility in guiding human action to fit humans within the normal range of natural variation. This is part of systemic management: finding an integral and sustainable place for humans in systems such as ecosystems and the biosphere. Another part of sustainability, however, involves action to promote systems capable of sustainably supporting humans and human activities, not only as individuals, but also as a species. It is important to distinguish what can and what can not be done in this regard.En conjunto, los dogmas y principios del manejo enfatizan la importancia del reconocimiento y la comprensión de los límites. Estos principios requieren la demostración, medida y uso práctico de la información sobre los límites de la variación natural. Es importante identificar los límites para no incurrir en riesgos y pérdida de integridad cuando dichos límites se sobrepasan. Con el manejo dentro de unos límites naturales, el hombre (el responsable del manejo) puede conseguir simultáneamente sostenibilidad y minimización de riesgos, así como explicar la complejidad. Ésto está en el núcleo central del manejo sistémico. El manejo sistémico engloba los principios básicos de cualquier tipo de manejo. Uno de los principios requiere que el manejo asegure que nada exceda los límites observados en la variación natural. Este principio se basa en que la variación está condicionada por varios factores limitantes, muchos de los cuales conllevan riesgos. Otro principio del manejo requiere que estos factores sean considerados simultáneamente, exhaustivamente y en proporción a su importancia relativa. Dichos factores, en combinación, constituyen la complejidad que los responsables del manejo deben considerar al aplicar los principios básicos de su función controladora. Esta combinación de elementos se refleja en los límites observados en la variación natural referentes a cada factor natural y su importancia relativa. El presente artículo resume conclusiones extraídas de la literatura científica respecto el concepto de variación natural, especialmente en el ámbito del manejo describe: 1. En qué medida estos límites son inherentes a los sistemas complejos; 2. Cómo se ha reconocido la importancia de estos límites para el proceso de manejo; y 3. Cómo pueden utilizarse para el manejo. Los límites inherentes incluyen tanto los establecidos por el contexto donde los sistemas se desarrollan (factores extrínsecos) como los establecidos por los componentes y procesos internos de los sistemas (factores intrínsecos). La información sobre los límites es útil como guía de la acción humana para acomodar los seres humanos al espectro normal de la variación natural. Esto forma parte del manejo sistémico: encontrar un lugar integral y sostenible para el hombre en sistemas tales como los ecosistemas y la biosfera. Otra parte de la sostenibilidad, sin embargo, implica acciones destinadas a promover sistemas capaces de proporcionar apoyo sostenible al hombre y a sus actividades, no sólo como individuo sino también como especie. Es importante distinguir qué puede y que no puede hacerse a este respeto

OH Emission in the Direction of TV Gem and BI Cyg

OH maser main-line emission at 1665 MHz has been detected in the direction of two late-type supergiants, TV Gem (Mllab) and BI Cyg (M3Iab), with the 43-m telescope and 18-cm receiver at NRAO-Green Bank. Detection of two new OH maser sources here is particularly interesting in view of the relatively small number of late-type supergiants that are known as molecular radio sources or associated in close proximity with OH emission clouds. The infrared, ultraviolet, and radio properties of these stars are discussed briefly

Cygnus A at 99 GHz: Observations of the Three Principal Components and the Interpretation of the Central Source

The three principal emission components of Cygnus A have been observed at 99 GHz, the highest frequency at which radio measurements of this source have been accomplished. The observations show no definite indication of a high-frequency cutoff in the spectrum of the compact central component, which perhaps may be attributed to an optically thin synchrotron source that peaks at a frequency of several hundred GHz

150 GHz Observations of Three Radio Galaxies

Radio galaxies were observed for the first time at 150 GHz. The central sources in Cyg A and 3C Ill were detected, as were the two radio lobes of Cyg A. No emission was found from the central source in 3C 236. Each of these three central sources has been previously discussed as the site of the energy supply for the associated distant components. The millimeter-wavelength emission from the central sources in Cyg A and 3C 111 is probably due in each case to a compact component that is optically thin to synchrotron radiation above about 35 GHz. These components are similar, although the compact component in 3C 111 is more luminous at both radio and X-ray wavelengths than the one in Cyg A. The 3C 111 central source was much weaker than anticipated on the basis of prior observations at 90 GHz, perhaps due to variability. Even at 150 GHz, there is no evidence of a high-frequency cutoff in the spectrum of the central source in Cyg A, and variability of this source also is expected. The flux densities of the Cyg A lobes are consistent with the power laws derived at lower frequencies, indicating that no steepening occurs in their spectra out to at least 150 GHz. There is no evidence for a compact, optically thick component in 3C 236

Gravitational wave detection using pulsars: status of the Parkes Pulsar Timing Array project

The first direct detection of gravitational waves may be made through observations of pulsars. The principal aim of pulsar timing array projects being carried out worldwide is to detect ultra-low frequency gravitational waves (f ~ 10^-9 to 10^-8 Hz). Such waves are expected to be caused by coalescing supermassive binary black holes in the cores of merged galaxies. It is also possible that a detectable signal could have been produced in the inflationary era or by cosmic strings. In this paper we review the current status of the Parkes Pulsar Timing Array project (the only such project in the Southern hemisphere) and compare the pulsar timing technique with other forms of gravitational-wave detection such as ground- and space-based interferometer systems.Comment: Accepted for publication in PAS

An improved solar wind electron-density model for pulsar timing

Variations in the solar wind density introduce variable delays into pulsar timing observations. Current pulsar timing analysis programs only implement simple models of the solar wind, which not only limit the timing accuracy, but can also affect measurements of pulsar rotational, astrometric and orbital parameters. We describe a new model of the solar wind electron density content which uses observations from the Wilcox Solar Observatory of the solar magnetic field. We have implemented this model into the tempo2 pulsar timing package. We show that this model is more accurate than previous models and that these corrections are necessary for high precision pulsar timing applications.Comment: Accepted by ApJ, 13 pages, 4 figure

The Sensitivity of the Parkes Pulsar Timing Array to Individual Sources of Gravitational Waves

We present the sensitivity of the Parkes Pulsar Timing Array to gravitational waves emitted by individual super-massive black-hole binary systems in the early phases of coalescing at the cores of merged galaxies. Our analysis includes a detailed study of the effects of fitting a pulsar timing model to non-white timing residuals. Pulsar timing is sensitive at nanoHertz frequencies and hence complementary to LIGO and LISA. We place a sky-averaged constraint on the merger rate of nearby ($z < 0.6$) black-hole binaries in the early phases of coalescence with a chirp mass of 10^{10}\,\rmn{M}_\odot of less than one merger every seven years. The prospects for future gravitational-wave astronomy of this type with the proposed Square Kilometre Array telescope are discussed.Comment: fixed error in equation (4). [13 pages, 6 figures, 1 table, published in MNRAS