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

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

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

Risk Aversion and CO2 Regulatory Uncertainty in Power Generation Investment: Policy and Modeling Implications

Our simulation considers producers in a competitive energy market. Risk averse producers face uncertainty about future carbon regulation. Investment decisions are a two-stage equilibrium problem. Initially, investment is made under regulatory uncertainty; then the regulatory state is revealed and producers realize returns. We consider taxes, grandfathered permits and auctioned permits and show that outcomes vary under risk aversion; some anticipated policies yield perverse investment incentives, in that investment in the dirty technology is encouraged. Beliefs about the policy instrument that will be used to price carbon may be as important as certainty that carbon will be priced. More generally, a failure to consider risk aversion may bias policy models of the power sector

Magnetically-controlled velocity selection in a cold atom sample using stimulated Raman transitions

We observe velocity-selective two-photon resonances in a cold atom cloud in the presence of a magnetic field. We use these resonances to demonstrate a simple magnetometer with sub-mG resolution. The technique is particularly useful for zeroing the magnetic field and does not require any additional laser frequencies than are already used for standard magneto-optical traps. We verify the effects using Faraday rotation spectroscopy.Comment: 5 pages, 6 figure

Search for a Radio Pulsar in the Remnant of Supernova 1987A

We have observed the remnant of supernova SN~1987A (SNR~1987A), located in the Large Magellanic Cloud (LMC), to search for periodic and/or transient radio emission with the Parkes 64\,m-diameter radio telescope. We found no evidence of a radio pulsar in our periodicity search and derived 8$\sigma$ upper bounds on the flux density of any such source of $31\,\mu$Jy at 1.4~GHz and $21\,\mu$Jy at 3~GHz. Four candidate transient events were detected with greater than $7\sigma$ significance, with dispersion measures (DMs) in the range 150 to 840\,cm$^{-3}\,$pc. For two of them, we found a second pulse at slightly lower significance. However, we cannot at present conclude that any of these are associated with a pulsar in SNR~1987A. As a check on the system, we also observed PSR~B0540$-$69, a young pulsar which also lies in the LMC. We found eight giant pulses at the DM of this pulsar. We discuss the implications of these results for models of the supernova remnant, neutron star formation and pulsar evolution.Comment: 7 pages, 3 figures, 2 tables. Accepted for publication in MNRA

A southern hemisphere survey of the 5780 and 6284 {\AA} diffuse interstellar bands: correlation with the extinction

We present a new database of 5780.5 and 6283.8 {\AA} DIB measurements and also study their correlation with the reddening. The database is based on high-resolution, high-quality spectra of early-type nearby stars located in the southern hemisphere at an average distance of 300 pc. Equivalent widths of the two DIBs were determined by means of a realistic continuum fitting and synthetic atmospheric transmissions. For all stars that possess a precise measurement of their color excess, we compare the DIBs and the extinction. We find average linear relationships of the DIBS and the color excess that agree well with those of a previous survey of northern hemisphere stars closer than 550 pc. This similarity shows that there is no significant spatial dependence of the average relationship in the solar neighborhood within $\simeq$ 600 pc. A noticeably different result is our higher degree of correlation of the two DIBs with the extinction. We demonstrate that it is simply due to the lower temperature and intrinsic luminosity of our targets. Using cooler target stars reduces the number of outliers, especially for nearby stars, confirming that the radiation field of UV bright stars has a significant influence on the DIB strength. We have used the cleanest data to compute updated DIB shapes.Comment: Astronomy & Astrophysics (in press

Oxygen in Open Cluster Dwarfs: Pleiades and M34

We analyze the high-excitation O I lambda7774 triplet in high-resolution, moderate signal-to-noise ratio spectra of 15 Pleiades and eight M34 open cluster dwarfs over the effective temperature range of 5048-6172 K. Relative O abundances have been derived using model atmospheres interpolated from four different sets of ATLAS9 grids. In contrast to existing non-LTE (NLTE) predictions, a dramatic increase in the O I triplet abundance with decreasing temperature is seen for both clusters, regardless of the atmospheric model. S I abundances of three Pleiades stars derived from the high-excitation lambda6053 feature mimic the O I abundance behavior. O abundances have also been derived from the [O I] lambda6300 feature in three Pleiades stars; the abundances exhibit a much lower mean value than do the cool dwarf triplet results. Inasmuch as the [O I] abundances are presumed to be free from NLTE effects, their mean values ([O/H]6300=+0.14) provide the current best estimate of the Pleiades O abundance. Spreads in [O/H]Trip at a given temperature are also seen in both clusters; no correlation is found between the spreads and the chromospheric emission measures

A hierarchical Bayesian approach for handling missing classification data

Ecologists use classifications of individuals in categories to understand composition of populations and communities. These categories might be defined by demo- graphics, functional traits, or species. Assignment of categories is often imperfect, but frequently treated as observations without error. When individuals are observed but not classified, these “partial” observations must be modified to include the missing data mechanism to avoid spurious inference. We developed two hierarchical Bayesian models to overcome the assumption of perfect assignment to mutually exclusive categories in the multinomial distribu- tion of categorical counts, when classifications are missing. These models incorporate auxiliary information to adjust the posterior distributions of the proportions of membership in categories. In one model, we use an empirical Bayes approach, where a subset of data from one year serves as a prior for the missing data the next. In the other approach, we use a small random sample of data within a year to inform the distribution of the missing data. We performed a simulation to show the bias that occurs when partial observations were ignored and demonstrated the altered inference for the estimation of demographic ratios. We applied our models to demographic classifications of elk (Cervus elaphus nelsoni) to demonstrate improved inference for the proportions of sex and stage classes. We developed multiple modeling approaches using a generalizable nested multi- nomial structure to account for partially observed data that were missing not at random for classification counts. Accounting for classification uncertainty is important to accurately understand the composition of populations and communities in ecological studies

Metaphoric coherence: Distinguishing verbal metaphor from `anomaly\u27

Theories and computational models of metaphor comprehension generally circumvent the question of metaphor versus “anomaly” in favor of a treatment of metaphor versus literal language. Making the distinction between metaphoric and “anomalous” expressions is subject to wide variation in judgment, yet humans agree that some potentially metaphoric expressions are much more comprehensible than others. In the context of a program which interprets simple isolated sentences that are potential instances of cross‐modal and other verbal metaphor, I consider some possible coherence criteria which must be satisfied for an expression to be “conceivable” metaphorically. Metaphoric constraints on object nominals are represented as abstracted or extended along with the invariant structural components of the verb meaning in a metaphor. This approach distinguishes what is preserved in metaphoric extension from that which is “violated”, thus referring to both “similarity” and “dissimilarity” views of metaphor. The role and potential limits of represented abstracted properties and constraints is discussed as they relate to the recognition of incoherent semantic combinations and the rejection or adjustment of metaphoric interpretations