An updated catalog of OH-maser-emitting planetary nebulae

Aims. We studied the characteristics of planetary nebulae (PNe) that show both OH maser and radio continuum emission (hereafter OHPNe). These have been proposed to be very young PNe, and therefore, they could be key objects for understanding the formation and evolution of PNe. Methods. We consulted the literature searching for interferometric observations of radio continuum and OH masers toward evolved stars, including the information from several surveys. We also processed radio continuum and OH maser observations toward PNe in the Very Large Array data archive. The high positional accuracy provided by interferometric observations allow us to confirm or reject the association between OH maser and radio continuum emission. Results. We found a total of six PNe that present both OH maser and radio continuum emissions, as confirmed with radio interferometric observations. These are bona fide OHPNe. The confirmed OHPNe present a bipolar morphology in resolved images of their ionized emission at different wavelengths, suggesting that the OH maser emission in PNe is related to nonspherical mass-loss phenomena. The OH maser spectra in PNe present a clear asymmetry, tending to show blueshifted emission with respect to the systemic velocity. Their infrared colors suggest that most of these objects are very young PNe. OHPNe do not form a homogeneous group, and seem to represent a variety of different evolutionary stages. We suggest that OH masers pumped in the AGB phase may disappear during the post-AGB phase, but reappear once the source becomes a PN and its radio continuum emission is amplified by the OH molecules. Therefore, OH maser emission could last significantly longer than the previously assumed 1000 yr after the end of the AGB phase. This maser lifetime may be longer in PNe with more massive central stars, which ionize a larger amount of gas in the envelope.Comment: 16 pages, 5 figures, 4 tables. Accepted for publication by Astronomy & Astrophysic

Position-Velocity Diagrams for the Maser Emission coming from a Keplerian Ring

We have studied the maser emission from a thin, planar, gaseous ring in Keplerian rotation around a central mass observed edge-on. The absorption coefficient within the ring is assumed to follow a power law dependence with the distance from the central mass as, k=k0r^{-q}. We have calculated position-velocity diagrams for the most intense maser features, for different values of the exponent q. We have found that, depending on the value of q, these diagrams can be qualitatively different. The most intense maser emission at a given velocity can either come mainly from regions close to the inner or outer edges of the amplifying ring or from the line perpendicular to the line of sight and passing through the central mass (as is commonly assumed). Particularly, when q>1 the position-velocity diagram is qualitatively similar to the one observed for the water maser emission in the nucleus of the galaxy NGC 4258. In the context of this simple model, we conclude that in this object the absorption coefficient depends on the radius of the amplifying ring as a decreasing function, in order to have significant emission coming from the inner edge of the ring.Comment: 13 pages, 7 figures, to appear in the 2007 July 20 issue of The Astrophysical Journa

Training as A Growth Strategy for Trade SMEs in The Veracruz-Boca Del Río Conurbated Area

This research shows, based on the statistics, that the main entities that generate employment are small and medium-sized enterprises; the survey of the National Institute of Statistics and Geography (INEGI) serves as sustenance added to those generated by the National Micro-business Survey (ENAMIN ). In the context of training, the results of this study reflect that training for workers is not a priority. Consequently, they do not have it, even though it is regulated as a worker's right by the Ley Federal del Trabajo and an obligation for the business sector. The result shows the companies' conformity with the duality of the benefit of training since this fundamental part that could allow them to achieve greater competitiveness in the market is not found in their planning

Las diligencias diplomáticas de Miura Yoshiaki como último ministro de Japón en México en el umbral de la Guerra del Pacífico

El ministro Miura Yoshiaki fue el último representante diplomático de Japón en México en el inicio de la Guerra del Pacífico. El objetivo del presente artículo es analizar las condiciones y acciones realizadas por Miura antes y después del rompimiento de las relaciones diplomáticas el 8 de diciembre de 1941 como resultado del inicio de la guerra del Pacífico. Dentro de la creciente tensión entre Tokio y Washington, Miura desplegó una diplomacia ofensiva para contener el cerco económico que Estados Unidos estaba armando contra Japón buscando que México no se alineara a esas acciones. Es un hecho que los esfuerzos para refrendar los lazos de amistad entre las dos naciones cada vez se veían más difíciles de mantener por las condiciones de acercamiento del gobierno de Manuel Ávila Camacho a las directivas marcadas por la Casa Blanca contra las potencias del Eje

Statistical Analysis of Water Masers in Star-Forming Regions: Cepheus A and W75 N

We have done a statistical analysis of Very Long Baseline Array (VLBA) data of water masers in the star-forming regions (SFRs) Cepheus A and W75 N, using correlation functions to study the spatial clustering and Doppler-velocity distribution of these masers. Two-point spatial correlation functions show a characteristic scale size for clusters of water maser spots < or ~1 AU, similar to the values found in other SFRs. This suggests that the scale for water maser excitation tends to be < or ~1 AU. Velocity correlation functions show power-law dependences with indices that can be explained by regular velocity fields, such as expansion and/or rotation. These velocity fields are similar to those indicated by the water maser proper-motion measurements; therefore, the velocity correlation functions appear to reveal the organized motion of water maser spots on scales larger than 1 AU.Comment: 16 pages, 8 figures, and 3 tables. Accepted by The Astrophysical Journa

Las diligencias diplomáticas de Miura Yoshiaki como último ministro de Japón en México en el umbral de la Guerra del Pacífico

Minister Miura Yoshiaki was the last diplomatic representative of Japan in Mexico at the beginning of the War of the Pacific. The objective of this article is to analyze the conditions and actions carried out by Miura before and after the severance of diplomatic relations on December 8, 1941 as a result of the start of the Pacific War. Within the growing tension between Tokyo and Washington, Miura deployed offensive diplomacy to contain the economic siege that the United States was arming against Japan, seeking to prevent Mexico from aligning itself with those actions. It is a fact that the efforts to endorse the ties of friendship between the two nations were increasingly difficult to maintain due to the conditions of rapprochement of the government of Manuel Ávila Camacho to the directives set by the White House against the Axis powers.El ministro Miura Yoshiaki fue el último representante diplomático de Japón en México en el inicio de la Guerra del Pacífico. El objetivo del presente artículo es analizar las condiciones y acciones realizadas por Miura antes y después del rompimiento de las relaciones diplomáticas el 8 de diciembre de 1941 como resultado del inicio de la guerra del Pacífico. Dentro de la creciente tensión entre Tokio y Washington, Miura desplegó una diplomacia ofensiva para contener el cerco económico que Estados Unidos estaba armando contra Japón buscando que México no se alineara a esas acciones. Es un hecho que los esfuerzos para refrendar los lazos de amistad entre las dos naciones cada vez se veían más difíciles de mantener por las condiciones de acercamiento del gobierno de Manuel Ávila Camacho a las directivas marcadas por la Casa Blanca contra las potencias del Eje