The high-excitation planetary nebulae: NGC 3918 and IC 2448

International Ultraviolet Exploration observations of NGC 3918 and IC 2448 are presented. Combining these observations with data in the optical range and computed model structure, the chemical composition for these objects is derived. For NGC 3918 log C = -3.02, log N = -3.61 and log 0 = -3.22; while for IC 2448 log C = -3.44, log N = -81 and log 0 = 3.54

Decaying Sterile Neutrinos as a Heating Source in the Milky Way Center

Recent Chandra and Newton observations indicate that there are two-temperature components ($T \sim$ 8 keV, 0.8 keV) of the diffuse x-rays emitted from deep inside the center of Milky Way. We show that this can be explained by the existence of sterile neutrinos, which decay to emit photons that can be bound-free absorbed by the isothermal hot gas particles in the center of Milky Way. This model can account for the two-temperature components naturally as well as the energy needed to maintain the $\sim$ 8 keV temperature in the hot gas. The predicted sterile neutrino mass is between 16-18 keV.Comment: Accepted by MNRAS with minor correction

XMM-Newton observations of the nitrogen-rich Wolf-Rayet star WR 1

We present XMM-Newton results for the X-ray spectrum from the N-richWolf-Rayet (WR) star WR1. The EPIC instrument was used to obtain a medium-resolution spectrum. The following features characterize this spectrum: ( a) significant emission "bumps" appear that are coincident with the wavelengths of typical strong lines, such as MgXI, SiXIII, and SXV; (b) little emission is detected above 4 keV, in contrast to recent reports of a hard component in the stars WR 6 and WR 110 which are of similar subtype; and ( c) evidence for sulfur K-edge absorption at about 2.6 keV, which could only arise from absorption of X- rays by the ambient stellar wind. The lack of hard emission in our dataset is suggestive that WR 1 may truly be a single star, thus representing the first detailed X-ray spectrum that isolates the WR wind alone ( in contrast to colliding wind zones). Although the properties of the S-edge are not well- constrained by our data, it does appear to be real, and its detection indicates that at least some of the hot gas in WR 1 must reside interior to the radius of optical depth unity for the total absorptive opacity at the energy of the edge

Recombination spectrum and reddening in NGC 1068

Measurements of the emission-line intensities of NGC 1068 have been made over the wavelength range extending from λ_(rest) = 1216 Å to 1.875 μm. The data, plus other available emission-line data, can be explained in terms of a simple model where the emission lines are formed in an H II region, and the line ratios are consistent with those predicted by standard radiative recombination theory and reddening corresponding to E_(B-v) = 0.4 mag. The continuum flux is seen to consist of a galaxy component plus a nonstellar component which dominates the observed flux in the ultraviolet. The observed ultraviolet continuum does not show an absorption dip caused by the interstellar 2200 A feature nor does it contain enough energy to power the observed infrared flux

Spatially extended absorption around the z=2.63 radio galaxy MRC 2025-218: outflow or infall?

We present an investigation into the absorber in front of the z=2.63 radio galaxy MRC 2025-218, using integral field spectroscopy obtained at the Very Large Telescope, and long slit spectroscopy obtained at the Keck II telescope. The properties of MRC 2025-218 are particularly conducive to study the nature of the absorbing gas, i.e., this galaxy shows bright and spatially extended Ly-alpha emission, along with bright continuum emission from the active nucleus. Ly-alpha absorption is detected across ~40x30 kpc^2, has a covering factor of ~1, and shows remarkably little variation in its properties across its entire spatial extent. This absorber is kinematically detached from the extended emission line region (EELR). Its properties suggest that the absorber is outside of the EELR. We derive lower limits to the HI, HII and H column densities for this absorber of 3x10^16, 7x10^17 and 2x10^18 cm^-2, respectively. Moreover, the relatively bright emission from the active nucleus has allowed us to measure a number of metal absorption lines: CI, CII, CIV, NV, OI, SiII, SiIV, AlII and AlIII. The column density ratios are most naturally explained using photoionization by a hard continuum, with an ionization parameter U~0.0005-0.005. Shocks or photoionization by young stars cannot reproduce satisfactorily the measured column ratios. Using the ratio between the SiII* and SiII column densities, we derive a lower limit of >10 cm^-3 for the electron density of the absorber. The data do not allow useful constraints to be placed on the metallicity of the absorber. We consider two possibilities for the nature of this absorber: the cosmological infall of gas, and an outflow driven by supernovae or the radio-jets.Comment: Accepted for publication in MNRA

Are anthropogenic factors affecting nesting habitat of sea turtles? The case of Kanzul beach, Riviera Maya-Tulum (Mexico)

Marine coast modification and human pressure affects many species, including sea turtles. In order to study nine anthropogenic impacts that might affect nesting selection of females, incubation and hatching survival of loggerhead (Caretta caretta) and green turtle (Chelonia mydas), building structures were identified along a 5.2 km beach in Kanzul (Mexico). A high number of hotels and houses (88; 818 rooms), with an average density of 16.6 buildings per kilometer were found. These buildings form a barrier which prevents reaching the beach from inland, resulting in habitat fragmentation. Main pressures were detected during nesting selection (14.19% of turtle nesting attempts interrupted), and low impact were found during incubation (0.77%) and hatching (4.7%). There were three impacts defined as high: beach furniture that blocks out the movement of hatchlings or females, direct pressure by tourists, and artificial beachfront lighting that can potentially mislead hatchlings or females. High impacted areas showed lowest values in nesting selection and hatching success. Based on our results, we suggest management strategies to need to be implemented to reduce human pressure and to avoid nesting habitat loss of loggerhead and green turtle in Kanzul, Mexico

DESARROLLO DE UNA TÉCNICA DE PCR PARA DETECTAR VIRUS MAEDI-VISNA (VMV) LIBRE E INTEGRADO EN CÉLULAS Y APLICACIÓN AL ESTUDIO DE LA INFECCIÓN CALOSTRAL EN CORDEROS

A PCR test was developed to detect cell-free and cell-integrated maedi-visna virus (MVV), its degree of agreement with an LTR-PCR and an antibody ELISA of proven efficacy was analysed in colostrum samples and all three tests were employed to investigate colostral MVV infection in lambs. Primers were designed from gag gene sequences homologous in the six MVV sequences presently in GenBank, and amplify a 744bp frag- ment. 856 assays were carried out including 283 with the new gag-PCR and a good correlation was observed between the presence of cell-free and -integrated MVV. This is novel and questions the relative role of the two viral forms in MVV infection. Instead, the correlation between PCR and ELISA results was only moderate and provided further evidence that MVV detection may fail in infected animals. The PCRs detected MVV in colostrum ingested by most lambs that later tested seropositive at 10 months-old and additionally, the gag-PCR and to a lesser extent the LTR-PCR, detected MVV in colostrum taken by lambs seronegative at 10 months-old most likely because they ingested less colostrum. As well as providing further evidence of the positive association between MVV infection and volume of MVV-containing colostrum ingested, this result suggest that the gag-PCR developed is more sensitive than the LTR-PCR used in this study.Se desarrolló una técnica de PCR para detectar virus maedi-visna (VMV) libre e integrado en células, se estudio su concordancia con una PCR-LTR y un ELISA de anticuerpos de probada eficacia en muestras de calostro de ovejas infectadas y se emplearon los tres ensayos para investigar la infección calostral por VMV en corderos. Los cebadores se diseñaron en una región conservada en las seis secuencias de VMV disponibles en GenBank y amplifican un producto de 744 pares de bases (pb). Se realizaron 856 ensayos incluidos 283 con la gag, e independientemente de la PCR empleada se observó una buena correlación entre la presencia de virus libre e integrado y esto es novedoso y plantea la importancia relativa de ambas formas víricas en la infección por VMV. En cambio, la concordancia entre las PCRs y el ELISA fue solo moderada y se corroboró que a menudo no se detecta VMV en animales seropositivos. Las PCRs detectaron VMV en la mayoría de calostros ingeridos por corderos que posteriormente a los 10 meses de edad fueron seropositivos y además la gag y en menor medida la LTR, también en algunos calostros de corderos que fueron seronegativos, probablemente porque tomaron menos cantidad de calostro que los seropositivos. Además de aportar mas evidencia de la asociación positiva entre la infección por VMV y el volumen de calostro con VMV ingerido, este resultado sugiere que la gag es más sensible que la LTR en esta matriz