Adaptive Optics Imaging of IRAS 18276-1431: a bipolar pre-planetary nebula with circumstellar "searchlight beams" and "arcs"

We present high-angular resolution images of the post-AGB nebula IRAS18276-1431 (also known as OH17.7-2.0) obtained with the Keck II Adaptive Optics (AO) system in its Natural Guide Star (NGS) mode in the Kp, Lp, and Ms near-infrared bands. We also present supporting optical F606W and F814W HST images as well as interferometric observations of the 12CO(J=1-0), 13CO(J=1-0), and 2.6mm continuum emission with OVRO. The envelope of IRAS18276-1431 displays a clear bipolar morphology in our optical and NIR images with two lobes separated by a dark waist and surrounded by a faint 4.5"x3.4" halo. Our Kp-band image reveals two pairs of radial ``searchlight beams'' emerging from the nebula center and several intersecting, arc-like features. From our CO data we derive a mass of M>0.38[D/3kpc]^2 Msun and an expansion velocity v_exp=17km/s for the molecular envelope. The density in the halo follows a radial power-law proportional to r^-3, which is consistent with a mass-loss rate increasing with time. Analysis of the NIR colors indicates the presence of a compact central source of ~300-500K dust illuminating the nebula in addition to the central star. Modeling of the thermal IR suggests a two-shell structure in the dust envelope: 1) an outer shell with inner and outer radius R_in~1.6E16cm and R_out>~1.25E17cm, dust temperature T_d~105-50K, and a mean mass-loss rate of Mdot~1E-3Msun/yr; and 2) an inner shell with R_in~6.3E14cm, T_dust~500-105K, and Mdot~3E-5Msun/yr. An additional population of big dust grains (radius a>~0.4mm) with T_dust=150-20K and mass M_dust=(0.16-1.6)E-3 [D/3kpc]^2 Msun can account for the observed sub-mm and mm flux excess. The mass of the envelope enclosed within R_out=1.25E17cm derived from SED modeling is ~1[D/3kpc]^2 Msun.Comment: 46 pages, 14 figures, 3 tables, accepted for publication in ApJ. Figures 12 & 13 in low resolution. Full resolution versions are available upon request to the first autho

An?lisis de las pr?cticas pedag?gicas y su relaci?n con la calidad acad?mica de la educaci?n media en Nicanor Vel?squez Ortiz del municipio de Ambalema Tolima

79 p. Recurso Electr?nicoDebido a que las pr?cticas pedag?gicas son de suma importancia a nivel nacional e internacional en relaci?n con la calidad acad?mica y lo que respeta con las pruebas generales como son las pruebas pisa, las pruebas saber once en la educaci?n. Surge la importancia de esta investigaci?n despu?s de analizar la calidad acad?mica, en el cual el objetivo principal de esta investigaci?n es relacionar la influencia de las pr?cticas pedag?gicas en la calidad acad?mica de la instituci?n Nicanor Vel?squez Ortiz, adem?s identificar los factores que influye en el nivel acad?mico de educaci?n media de dicha instituci?n. La presente investigaci?n est? basada en un estudio de caso, teniendo en cuenta unas categor?as de investigaci?n (pertinencia, sistemas de evaluaci?n, pr?cticas pedagog?as, calidad acad?mica). Las t?cnicas para la recolecci?n de la informaci?n que se aplicaron son: entrevista a docentes de educaci?n media, testimonio focalizado a docentes y grupo focal con estudiantes de educaci?n media; los instrumentos para estas t?cnicas de recolecci?n de datos son cuestionarios. La poblaci?n de investigaci?n es la instituci?n educativa Nicanor Vel?squez Ortiz de Ambalema Tolima y la muestra es la educaci?n media de dicha instituci?n, con 85 participantes entre los 14 y 19 a?os y 6 docentes de entre 40 y 56 a?os .Como resultados, se observa que la calidad acad?mica en educaci?n media en esta instituci?n es baja debido a distintos factores como : algunos docentes no aplican sus pr?cticas pedag?gicas de acuerdo al enfoque de la instituci?n, falta de pertinencia por parte de los educandos debido a que no cuentan con h?bitos de estudio estructurados, falta de acompa?amiento por parte de los padres, la infraestructura no es la m?s adecuada ya que se presentan altas temperaturas en el municipio, no se cuenta con ventiladores adecuados, se presenta hacinamiento en las aulas de clase. En el caso de esta investigaci?n es evidente que la problem?tica en torno a la calidad acad?mica podr?a cambiar si lo docentes se comprometen de manera responsable a indagar en busca de la apropiaci?n del enfoque pedag?gico de la instituci?n y as? direccionar las pr?cticas pedag?gicas a dicho enfoque, en vista de que siempre ha existido este nivel en la instituci?n, con respecto a las pruebas saber once presentadas hace varios donde estas vienen presentado niveles desfavorables para el proceso educativo que lleva a cabo la instituci?n.Because teaching practices are vital to national and international level in relation to the academic quality and respecting the general tests such as PISA tests are the tests to know eleven education. It arises the importance of this research math teacher of the institution after analyzing the academic quality in which the main objective of this research is to investigate the influence of pedagogical practices in the academic quality of the institution Nicanor Velasquez Ortiz also identify factors influencing the academic level of secondary education in that institution. This research is based on a case study, considering a research categories (relevance, evaluation systems, practical teaching methods, academic quality). The techniques for gathering information were applied are: interview to middle school teachers, teachers and testimony focused focus group with high school students; instruments for these techniques of data collection are questionnaires. The research population is the educational institution Ambalema Nicanor Velasquez Ortiz of Tolima, the sample is the average education of the institution, with 85 participants between 14 and 19 years and 6 teachers aged between 40 and 56 years .As results, it appears that academic quality in secondary education at this institution is low due to several factors: some teachers do not apply their teaching according to the approach of the institution, irrelevance by the students because they do not have study habits structured, lack of support from parents, the infrastructure is not adequate since high temperatures in the city are presented, do not have adequate fans, overcrowding occurs in classrooms and natural resources are often lacking. In the case of this research it is evident that there is academic quality if managed to break the barrier that has always existed in the institution with respect to the evidence presented to know eleven years ago and has been presented this low academic level. Teachers It is recommended to investigate the pedagogical approach of the institution and thus address the pedagogical approach to such practices. Key Works: Academic quality, pedagogical practices, conceptions

The chemistry of compact planetary nebulae

We report high-sensitivity millimetre observations of several molecular species (13CO, HCN, HNC, CN, HCO+ and N2H+) in a sample of compact planetary nebulae. Some species such as HCO+ and CN are particularly abundant compared to envelopes around AGB stars or even interstellar clouds. We have estimated the following average values for the column densities ratios: CN/HCN~2.6, HCO+/HCN~0.5, and HNC/HCN~0.4. Thus, the chemical composition of the molecular envelopes in these compact PNe appears somewhat intermediate between the composition of proto-PNe (such as CRL 2688 or CRL 618) and well evolved PNe (such as the Ring, M4--9, or the Helix). From observations of the CO isotopomers, we have estimated that the 12C/13C ratio is in the range 10 ~< 12C/13C ~< 40. These values are below those expected from standard asymptotic giant branch models and suggest non-standard mixing processes. The observed molecular abundances are compared to very recent modelling work, and we conclude that the observations are well explained, in general terms, by time-dependent gas-phase chemical models in which the ionization rate is enhanced by several orders of magnitude with respect to the average interstellar value. Thus, our observations confirm that the chemistry in the neutral shells of PNe is essentially governed by the high energy radiation from the hot central stars. The complexity of the chemical processes is increased by numerous factors linked to the properties of the central star and the geometry and degree of clumpiness of the envelope. Several aspects of the PN chemistry that remains to be understood are discussed within the frame of the available chemical models.Comment: 9 pages, 3 figures. "In press" in Astronomy and Astrophysic

The Illumination and Growth of CRL 2688: An Analysis of New & Archival HST Observations

We present four-color images of CRL 2688 obtained in 2009 using the Wide-Field Camera 3 on HST. The F606W image is compared with archival images in very similar filters to monitor the proper motions of nebular structure. We find that the bright N-S lobes have expanded uniformly by 2.5% and that the ensemble of rings has translated radially by 0.07 in 6.65 y. The rings were ejected every 100y for ~4 millennia until the lobes formed 250y ago. Starlight scattered from the edges of the dark E-W dust lane is coincident with extant H2 images and leading tips of eight pairs of CO outflows. We interpret this as evidence that fingers lie within geometrically opposite cones of opening angles {\approx} 30{\circ} like those in CRL618. By combining our results of the rings with 12CO absorption from the extended AGB wind we ascertain that the rings were ejected at ~18 km s-1 with very little variation and that the distance to CRL2688, v_{exp}$/${\dot\theta}_exp$, is 300 - 350 pc. Our 2009 imaging program included filters that span 0.6 to 1.6{\mu}m. We constructed a two-dimensional dust scattering model of stellar radiation through CRL2688 that successfully reproduces the details of the nebular geometry, its integrated spectral energy distribution, and nearly all of its color variations. The model implies that the optical opacity of the lobes >~ 1, the dust particle density in the rings decreases as radius^{-3} and that the mass and momentum of the AGB winds and their rings have increased over time.Comment: (51 pages, 6 figures; accepted by ApJ

Linear sigma model and chiral symmetry at finite temperature

The chiral phase transition is investigated within the framework of the linear sigma model at finite temperature. We concentrate on the meson sector of the model and calculate the finite temperature effective potential in the Hartree approximation by using the Cornwall-Jackiw-Tomboulis formalism of composite operators. The effective potential is calculated for N=4 involving the usual sigma and three pions and in the large N approximation involving N-1 pion fields. In the N=4 case we have examined the theory both in the chiral limit and with the presence of a symmetry breaking term which generates the pion masses. In both cases we have solved the system of the resulting gap equations for the thermal effective masses of the particles numerically and we have investigated the evolution of the effective potential. In the N=4 case there is indication of a first order phase transition and the Goldstone theorem is not satisfied. The situation is different in the general case using the large $N$ approximation, the Goldstone theorem is satisfied and the phase transition is of the second order. For this analysis we have ignored quantum effects and we used the imaginary time formalism for calculations.Comment: 14 pages, 5 eps figures, RevTex, axodraw.st

Kinematics and H_2 morphology of the multipolar Post-AGB star IRAS 16594-4656

context: The spectrum of IRAS 16594-4656 shows shock excited H_2 emission and collisionally excited emission lines such as[O I],[C I],and [Fe II]. aim: The goal is to determine the location of the H_2 and [Fe II] shock emission, to determine the shock velocities,and constrain the physical properties in the shock. methods: High resolution spectra of the H_2 1-0 S(1),H_2 2-1 S(1), [Fe II], and Pa$\beta$ emission lines were obtained with the near infrared spectrograph Phoenix on Gemini South. results: The position-velocity diagrams of H_2 1-0 S(1), H_2 2-1 S(1), and [Fe II] are presented. The H_2 and [Fe II] emission is spatially extended. The collisionally excited [O I] and [C I] optical emission lines have a similar double peaked profile compared to the extracted H_2 profile and appear to be produced in the same shock. They all indicate an expansion velocity of ~8 km/s and the presence of a neutral, very high density region with $n_{\rm e}$ about 3 x 10^6 to 5 x10^7 cm$^{-3}$. The [Fe II] emission however is single peaked. It has a gaussian FWHM of 30 km/s and a total width of 62 km/s at 1% of the peak. The Pa$\beta$ profile is even wider with a gaussian FWHM of 48 km/s and a total width of 75 km/s at 1% of the peak. conclusions: The H$_2$ emission is excited in a slow 5 to 20 km/s shock into dense material at the edge of the lobes, caused by the interaction of the AGB ejecta and the post-AGB wind. The 3D representation of the H_2 data shows a hollow structure with less H_2 emission in the equatorial region. The [Fe II] emission is not present in the lobes, but originates close to the central star in fast shocks in the post-AGB wind or in a disk. The Pa$\beta$ emission also appears to originate close to the star.Comment: 11 pages and 8 figures; A&A in press; the paper includig high resolution figures can be downloaded from http://homepage.oma.be/gsteene/publications.htm

Water level fluctuations in a coastal lagoon: El Yali Ramsar wetland, Chile

El Yali coastal reserve is the most important wetland complex in Mediterranean climate central Chile, especially due to the native and foreign bird fauna which arrives here periodically. The coastal lagoon, part of a microtidal estuary (1.2m tidal range), is a shallow (< 1m depth) dynamic system and unique site of coexistence of northern halophyte and southern palustrian riparian vegetation. This study identifies and quantifies the effect of forcing variables in the lagoon water level over 1 year of data collection. Transects of piezometers with level sensors were installed between the coastal lagoon and the sea. Monthly water quality data were collected. During the winter rainy season, the lagoon connects with the sea via an ephemeral tidal inlet, producing noticeable daily variations in the water level, up to 80-cm depending on the tides. In contrast, during the season when bar closure of the inlet disconnects the lagoon from the sea, the lagoon level is very stable and only decreases very slowly due to evaporation, which also makes the system hypersaline. During the connection phase, analyses using general pattern, spectral and Fourier analysis of the sea-vs. lagoon-level signals show that two temporal scale hierarchies are relevant: monthly (due to moon cycles) and daily (due to tidal cycles every 12.5 and 24.2-h). A simple diffusion numerical model simulated the water table trends well for the sand bar between the lagoon and the sea, supporting the main effect of the sea level on the lagoon water levels

Across-arc geochemical variations in the Southern Volcanic Zone, Chile (34.5- 38.0°S): Constraints on Mantle Wedge and Input Compositions

Crustal assimilation (e.g. Hildreth and Moorbath, 1988) and/or subduction erosion (e.g. Stern, 1991; Kay et al., 2005) are believed to control the geochemical variations along the northern portion of the Chilean Southern Volcanic Zone. In order to evaluate these hypotheses, we present a comprehensive geochemical data set (major and trace elements and O-Sr-Nd-Hf-Pb isotopes) from Holocene primarily olivine-bearing volcanic rocks across the arc between 34.5-38.0°S, including volcanic front centers from Tinguiririca to Callaqui, the rear arc centers of Infernillo Volcanic Field, Laguna del Maule and Copahue, and extending 300 km into the backarc. We also present an equivalent data set for Chile Trench sediments outboard of this profile. The volcanic arc (including volcanic front and rear arc) samples primarily range from basalt to andesite/trachyandesite, whereas the backarc rocks are low-silica alkali basalts and trachybasalts. All samples show some characteristic subduction zone trace element enrichments and depletions, but the backarc samples show the least. Backarc basalts have higher Ce/Pb, Nb/U, Nb/Zr, and Ta/Hf, and lower Ba/Nb and Ba/La, consistent with less of a slab-derived component in the backarc and, consequently, lower degrees of mantle melting. The mantle-like δ18O in olivine and plagioclase phenocrysts (volcanic arc = 4.9-5.6 and backarc = 5.0-5.4 per mil) and lack of correlation between δ18O and indices of differentiation and other isotope ratios, argue against significant crustal assimilation. Volcanic arc and backarc samples almost completely overlap in Sr and Nd isotopic composition. High precision (double-spike) Pb isotope ratios are tightly correlated, precluding significant assimilation of older sialic crust but indicating mixing between a South Atlantic Mid Ocean-Ridge Basalt (MORB) source and a slab component derived from subducted sediments and altered oceanic crust. Hf-Nd isotope ratios define separate linear arrays for the volcanic arc and backarc, neither of which trend toward subducting sediment, possibly reflecting a primarily asthenospheric mantle array for the volcanic arc and involvement of enriched Proterozoic lithospheric mantle in the backarc. We propose a quantitative mixing model between a mixed-source, slab-derived melt and a heterogeneous mantle beneath the volcanic arc. The model is consistent with local geodynamic parameters, assuming water-saturated conditions within the slab

Young Exoplanet Transit Initiative (YETI)

We present the Young Exoplanet Transit Initiative (YETI), in which we use several 0.2 to 2.6m telescopes around the world to monitor continuously young (< 100 Myr), nearby (< 1 kpc) stellar clusters mainly to detect young transiting planets (and to study other variability phenomena on time-scales from minutes to years). The telescope network enables us to observe the targets continuously for several days in order not to miss any transit. The runs are typically one to two weeks long, about three runs per year per cluster in two or three subsequent years for about ten clusters. There are thousands of stars detectable in each field with several hundred known cluster members, e.g. in the first cluster observed, Tr-37, a typical cluster for the YETI survey, there are at least 469 known young stars detected in YETI data down to R=16.5 mag with sufficient precision of 50 milli-mag rms (5 mmag rms down to R=14.5 mag) to detect transits, so that we can expect at least about one young transiting object in this cluster. If we observe 10 similar clusters, we can expect to detect approximately 10 young transiting planets with radius determinations. The precision given above is for a typical telescope of the YETI network, namely the 60/90-cm Jena telescope (similar brightness limit, namely within +/-1 mag, for the others) so that planetary transits can be detected. For planets with mass and radius determinations, we can calculate the mean density and probe the internal structure. We aim to constrain planet formation models and their time-scales by discovering planets younger than 100 Myr and determining not only their orbital parameters, but also measuring their true masses and radii, which is possible so far only by the transit method. Here, we present an overview and first results. (Abstract shortened)Comment: 15 pages, 10 figures, AN accepted 2011 June 1